Steel and tin cans

A steel can, tin can, tin (especially in British English, Australian English, Canadian English and South African English), steel packaging, or can is a container for the distribution or storage of goods, made of thin metal. Many cans require opening by cutting the "end" open; others have removable covers. They can store a broad variety of contents: food, beverages, oil, chemicals, etc. Steel cans are made of tinplate (tin-coated steel) or of tin-free steel. In some dialects, even aluminium cans are called "tin cans".
Steel cans are highly recyclable, with around 65% of steel cans being recycled.
History.
The tin canning process was conceived by the Frenchman Philippe de Girard, who had British merchant Peter Durand patent the idea in 1810. The canning concept was based on experimental food preservation work in glass containers the year before by the French inventor Nicholas Appert. Durand did not pursue food canning, but, in 1812, sold his patent to two Englishmen, Bryan Donkin and John Hall, who refined the process and product, and set up the world's first commercial canning factory on Southwark Park Road, London. By 1813 they were producing their first tin canned goods for the Royal Navy. By 1820, tin canisters or cans were being used for gunpowder, seeds, and turpentine.
Early tin cans were sealed by soldering with a tin–lead alloy, which could lead to lead poisoning.
In 1901 in the United States, the American Can Company was founded, at the time producing 90% of the tin cans in the United States.
Canned food in tin cans was already quite popular in various countries when technological advancements in the 1920s lowered the cost of the cans even further. In 1935, the first beer in metal cans was sold; it was an instant sales success.
Description.
Most cans are right circular cylinders with identical and parallel round tops and bottoms with vertical sides. However, cans for small volumes or particularly-shaped contents, the top and bottom may be rounded-corner rectangles or ovals. Other contents may suit a can that is somewhat conical in shape.
Fabrication of most cans results in at least one "rim"—a narrow ring slightly larger than the outside diameter of the rest of the can. The flat surfaces of rimmed cans are recessed from the edge of any rim (toward the middle of the can) by about the width of the rim; the inside diameter of a rim, adjacent to this recessed surface, is slightly smaller than the inside diameter of the rest of the can.
Three-piece can construction results in top and bottom rims. In two-piece construction, one piece is a flat top and the other a deep-drawn cup-shaped piece that combines the (at least roughly) cylindrical wall and the round base. Transition between wall and base is usually gradual. Such cans have a single rim at the top. Some cans have a separate cover that slides onto the top or is hinged.
Two piece steel cans can be made by "drawing" to form the bottom and sides and adding an "end" at the top: these do not have side seams. Cans can be fabricated with separate slip-on, or friction fit covers and with covers attached by hinges. Various easy opening methods are available.
In the mid-20th century, a few milk products were packaged in nearly rimless cans, reflecting different construction; in this case, one flat surface had a hole (for filling the nearly complete can) that was sealed after filling with a quickly solidifying drop of molten solder. Concern arose that the milk contained unsafe levels of lead leached from this solder plug.
Advantages of steel cans.
A number of factors make steel cans ideal containers for beverages. Steel cans are stronger than cartons or plastic, and less fragile than glass, protecting the product in transit and preventing leakage or spillage, while also reducing the need for secondary packaging.
Steel and aluminium packaging offer 100% barrier protection against light, water and air, and metal cans without resealable closures are among the most tamper-evident of all packaging materials. Steel cans preserve and protect the product from damage by light, oxidation, extremes of temperature and contamination, safeguarding flavour, appearance and quality from factory to final consumer. Food and drink packed in steel cans has equivalent vitamin content to freshly prepared, without needing preserving agents. Steel cans also extend the product's shelf-life, allowing longer sell-by and use-by dates and reducing waste.
As an ambient packaging medium, steel cans do not require cooling in the supply chain, simplifying logistics and storage, and saving energy and cost. At the same time, steel's relatively high thermal conductivity means canned drinks chill much more rapidly and easily than those in glass or plastic bottles.
A World Steel Association initiative, Choose Steel, is encouraging the use of steel for beverage cans.
Materials.
No cans currently in wide use are composed primarily or wholly of tin; that term rather reflects the nearly exclusive use in cans, until the second half of the 20th century, of tinplate steel, which combined the physical strength and relatively low price of steel with the corrosion resistance of tin. Depending on contents and available coatings, some canneries still use tin-free steel.
In some local dialects, any metal can, even aluminium, might be called a "tin can". Use of aluminium in cans began in 1957. Aluminium is less costly than tin-plated steel but offers the same resistance to corrosion in addition to greater malleability, resulting in ease of manufacture; this gave rise to the two-piece can, where all but the top of the can is simply stamped out of a single piece of aluminium, rather than laboriously constructed from three pieces of steel.
A can traditionally has a printed paper or plastic label glued to the outside of the curved surface, indicating its contents. Some labels contain additional information, such as recipes, on the reverse side. More recently labels are sometimes printed directly onto the metal before or after the metal sheet is formed into the individual cans.
In November 1991, US can manufacturers voluntarily eliminated lead seams in food cans. However, imported food cans continued to include lead soldered seams. In 1995, the US FDA issued a rule prohibiting lead soldered food cans, including both domestic and imported food cans.
In modern times, the majority of food cans in the UK have been lined with a plastic coating containing bisphenol A (BPA). The coating prevents acids and other substances from corroding the tin or aluminium of the can, but leaching of BPA into the can's contents was investigated as a potential health hazard.
Standard sizes.
Cans come in a variety of shapes and sizes. Walls are often stiffened with rib bulges, especially on larger cans, to help the can resist dents that can cause seams to split.
Can sizes in the United States have an assortment of designations and sizes. For example, size 7/8 contains one serving of half a cup with an estimated weight of 4 ounces; size 1 "picnic" has two or three servings totalling one and a quarter cups with an estimated weight of 10 ounces; size 303 has four servings totalling 2 cups weighing 15 ounces; and size 10 cans, most widely used by food services selling to cafeterias and restaurants, have twenty-five servings totalling 13 cups with an estimated weight of 103 ounces (size of a roughly 3 pound coffee can). These are U.S. customary cups, not British Imperial standard.
In the United States, cook books sometimes reference cans by size. The Can Manufacturers Institute defines these sizes, expressing them in three-digit numbers, as measured in whole and sixteenths of an inch for the container's nominal outside dimensions: a 307 × 512 would thus measure 3 and 7/16" in diameter by 5 and 3/4" (12/16") in height. Older can numbers are often expressed as single digits, their contents being calculated for room-temperature water as approximately eleven ounces (#1 "picnic" can), twenty ounces (#2), thirty-two ounces (#3), fifty-eight ounces (#5), and one-hundred-ten ounces (#10 "coffee" can).
In parts of the world using the metric system, tins are made in 250, 500, 750 ml (millilitre) and 1 L (litre) sizes (250 ml is approximately 1 cup or 8 ounces). Cans imported from the US often have odd sizes such as 3.8 L (1 US gallon), 1.9 L (1/2 US gallon), and 946 ml (2 US pints / 1 quart).
In the UK and Australia, cans are usually measured by net weight. A standard size tin can holds roughly 400 g; though the weight can vary between 385 g and 425 g depending on the density of the contents. The smaller half sized can holds roughly 200 g, typically varying between 170 g and 225 g.
Fabrication of cans.
Rimmed three-piece can construction involves several stages;
Double seam rims are crucial to the joining of the wall to a top or bottom surface. An extremely tight fit between the pieces must be accomplished to prevent leakage; the process of accomplishing this radically deforms the rims of the parts. Part of the tube that forms the wall is bent, almost at its end, turning outward through 90 degrees, and then bent further, toward the middle of the tube, until it is parallel to the rest of the tube, a total bend of 180 degrees.
The outer edge of the flat piece is bent against this toward the middle of the tubular wall, until parallel with the wall, turning inward through 90 degrees. The edge of bent portion is bent further through another 90 degrees, inward now toward the axis of the tube and parallel to the main portion of the flat piece, making a total bend of 180 degrees. It is bent far enough inward that its circular edge is now slightly "smaller" in diameter than the edge of the tube. Bending it yet further, until it is parallel with the tube's axis, gives it a total bend of 270 degrees. It now envelops the outward rim of the tube.
Looking outward from the axis of the tube, the first surface is the unbent portion of the tube. Slightly further out is a narrow portion of the top, including its edge. The outward-bent portion of the tube, including its edge, is still slightly further out. Furthest out is the 90-degree-bent portion of the flat surface.
The combined interacting forces, as the portion of the flat surface adjacent to the interior of the tube is indented toward the middle of the tube and then outward "forward" the axis of the tube, and the other bent portions of the flat piece and the tube are all forced "toward" the axis of the tube, drives these five thicknesses of metal against each other from inside and out, forming a "dry" joint so tight that welding or solder is not needed to strengthen or seal it. Illustrations of this process can be found on pages 20–22 of the FAO Fisheries Technical Paper 285 "Manual on fish canning" located here.
Design and manufacture.
Steel for can making.
The majority of steel used in packaging is tinplate, which is steel that has been coated with a thin layer of tin, whose functionality is required for the production process. The tin layer is usually applied by electroplating.
Two-piece steel can design.
Most steel beverage cans are two-piece designs, made from 1) a disc re-formed into a cylinder with an integral end, double-seamed after filling and 2) a loose end to close it. Steel cans are made in many different diameters and volumes, with opening mechanisms that vary from ring pulls and tab openers, to wide open mouths. Modern can making lines may produce up to 1000 cans per minute.
Drawn-and-ironed (DWI) steel cans.
The process of re-forming sheet metal without changing its thickness is known as 'drawing'. Thinning the walls of a two-piece can by passing it through circular dies is called 'ironing'. Steel beverage cans are therefore generally referred to as drawn-and-ironed, or DWI, cans (sometimes D&I). The DWI process is used for making cans where the height is greater than the diameter, and is particularly suited to making large volumes of cans of the same basic specification.
Steel can wall thicknesses are now 30% thinner and weigh 40% less than 30 years ago, reducing the amounts of raw materials and energy required to make them. They are also up to 40% thinner than aluminium.
Magnetic properties.
Steel is a ferrous metal and is therefore magnetic. For beverage packaging this is unique. This allows the use of magnetic conveyor systems to transfer empty cans through the filling and packing processes, increasing accuracy and reducing potential spillage and waste. In recycling facilities, steel cans may be readily separated from other waste using magnetic equipment including cross-belt separators, also known as overband magnets, and drum magnets.
Opening cans.
The first cans were heavy-weight containers that required ingenuity to open, with implements such as knives. Not until several years later, after can manufacturers started using thinner metal sheets, were any dedicated can openers developed.
While beverage cans or cans of fluid such as broth can merely be punctured to remove the product, solid or semisolid contents require removing one end of the can. This can be accomplished with a heavy knife or other sharp tool—but can openers are much more convenient.
Some cans, such as those used for sardines, have a specially scored lid so that the user can break out the metal by the leverage of winding it around a slotted twist-key or church key. Until the mid-20th century, some sardine tins had solder-attached lids, and the twist-key or church key worked by forcing the solder joint apart.
The advent of pull tabs in beverage cans spread to the canning of various food products, such as pet food or nuts (and non-food products such as motor oil and tennis balls). The ends are known as "easy open" lids because they open without any tools or implements. An additional innovation developed for specifically for food cans uses a tab that is bent slightly upwards, creating a larger surface area for easier finger access.
Cans can be made with easy open features. Some cans have screw caps for pouring liquids and resealing. Some have hinged covers or slip-on covers for easy access. Paint cans often have a removable plug on the top for access and for reclosing.
Recycling and re-use.
Steel from cans and other sources is the most recycled packaging material. Around 65% of steel cans are recycled. In the United States, 63% of steel cans are recycled, compared to 52% of aluminium cans. In Europe, the recycling rate in 2016 is 79.5%.
Most can recycling occurs at the smelters, but individual consumers also directly reuse cans in various ways. For instance some people use two tin cans to form a camp or survival stove to cook small meals.
Sustainability and recycling of steel beverage cans.
Steel recycling.
From an ecological perspective, steel may be regarded as a closed-loop material: post-consumer waste can be collected, recycled and used to make new cans or other products. Each tonne of scrap steel recycled saves 1.5 tonnes of CO2, 1.4 tonnes of iron ore and 740 kg of coal. Steel is the world's most recycled material, with more than 85% of all the world's steel products being recycled at the end of their life: an estimated 630 million tonnes of steel scrap were recycled in 2017, saving 945 million tonnes of CO2.
Steel can recycling.
A steel can can be recycled again and again without loss of quality; however, for the food grade steel it's required to remove tin from the scrap metal, which is done by way of electrochemistry: the tin is leached from a high pH solution at low negative voltage.
Recycling a single can saves the equivalent power for one laundry load, 1 hour of TV or 24 hours of lighting (10W LED bulb).
Steel beverage cans are recycled by being melted down in an electric arc furnace or basic oxygen furnace.
Most steel cans also carry some form of recycling identification such as the Metal Recycles Forever Mark Recyclable Steel and the Choose Steel campaign logo. There is also a campaign in Europe called Every Can Counts, encouraging can recycling in the workplace
Smaller carbon footprint.
All beverage packaging creates CO2 emissions at every stage in the production process, from raw material extraction, processing and manufacture through to recycling. However, steel cans are an ecological top performer, as cans can always be recycled. The steel industry needs the used cans and will use them in the production of new steel product. By recycling the cans and closing the loop, CO2 emissions are dramatically reduced. There is also the potential for higher global steel recycling rates as consumers become more aware of the benefits.
Health issues.
Dissolution of tin into the food.
Tin is corrosion resistant, but acidic food like fruits and vegetables can corrode the tin layer. Nausea, vomiting, and diarrhea have been reported after ingesting canned food containing 200 mg/kg of tin. A 2002 study showed that 99.5% of 1200 tested cans contained below the UK regulatory limit of 200 mg/kg of tin, an improvement over most previous studies largely attributed to the increased use of fully lacquered cans for acidic foods, and concluded that the results do not raise any long term food safety concerns for consumers. The two non-compliant products were voluntarily recalled.
Evidence of tin impurities can be indicated by color, as in the case of pears, but lack of color change does not guarantee that a food is not tainted with tin.
Bisphenol-A.
Bisphenol-A (BPA) is a controversial chemical compound present in commercially available tin can plastic linings and transferred to canned food. The inside of the can is coated with an epoxy coating, in an attempt to prevent food or beverage from coming into contact with the metal. The longer food is in a can, and the warmer and more acidic it is, the more BPA leaches into it. In September 2010, Canada became the first country to declare BPA a toxic substance. In the European Union and Canada, BPA use is banned in baby bottles.
The FDA does not regulate BPA (see BPA controversy#Public health regulatory history in the United States). Several companies, like Campbell's Soup, announced plans to eliminate BPA from the linings of their cans, but have not said which chemical they plan to replace it with. (See BPA controversy#Chemical manufacturers reactions to bans.)


Digital printing

Digital printing is a method of printing from a digital-based image directly to a variety of media. It usually refers to professional printing where small-run jobs from desktop publishing and other digital sources are printed using large-format and/or high-volume laser or inkjet printers.
Digital printing has a higher cost per page than more traditional offset printing methods, but this price is usually offset by avoiding the cost of all the technical steps required to make printing plates. It also allows for on-demand printing, short turnaround time, and even a modification of the image (variable data) used for each impression. The savings in labor and the ever-increasing capability of digital presses means that digital printing is reaching the point where it can match or supersede offset printing technology's ability to produce larger print runs of several thousand sheets at a low price.
Process.
The greatest difference between digital printing and analog methods, such as lithography, flexography, gravure, and letterpress, is that in digital printing (introduced in the 1980s) there is no need to replace the printing plate, whereas in analog printing the plates are repeatedly replaced. This results in quicker turnaround time and lower cost in digital printing, but typically a loss of detail in most commercial digital printing processes. The most popular methods include inkjet and laser printers, which deposit pigment and toner, respectively, onto substrates, such as paper, canvas, glass, metal, and marble.
In many of the processes, the ink or toner does not permeate the substrate, as does conventional ink, but forms a thin layer on the surface that may be additionally adhered to the substrate by a fuser fluid with thermal (toner) or ultraviolet curing (ink).
Digital printing methods of note.
Fine art inkjet printing.
Fine art digital inkjet printing is printing from a computer image file directly to an inkjet printer as a final output. It evolved from digital proofing technology from Kodak, 3M, and other major manufacturers, with artists and other printers trying to adapt these dedicated prepress proofing machines to fine-art printing. There was experimentation with many of these types of printers, the most notable being the IRIS printer, initially adapted to fine-art printing by programmer David Coons, and adopted for fine-art work by Graham Nash at his Nash Editions printing company in 1991. Initially, these printers were limited to glossy papers, but the IRIS Graphics printer allowed the use of a variety of papers that included traditional and non-traditional media. The IRIS printer was the standard for fine art digital printmaking for many years, and is still in use today, but has been superseded by large-format printers from other manufacturers such as Epson and HP that use fade-resistant, archival inks (pigment-based, as well as newer solvent-based inks), and archival substrates specifically designed for fine-art printing.
Substrates in fine art inkjet printmaking include traditional fine-art papers such as Rives BFK, Arches watercolor paper, treated and untreated canvas, experimental substrates (such as metal and plastic), and fabric.
For artists making reproductions of their original work, inkjet printing is more expensive on a per-print basis than the traditional four-color offset lithography, but with inkjet printing the artist does not have to pay for the expensive printing-plate setup or the marketing and storage needed for large four-color offset print runs. Inkjet reproductions can be printed and sold individually in accordance with demand. Inkjet printing has the added advantage of allowing artists to take total control of the production of their images, including the final color correction and the substrates being used, with some artists owning and operating their own printers.
Digital inkjet printing also allows for the output of digital art of all types as finished pieces or as an element in a further art piece. Experimental artists often add texture or other media to the surface of a final print, or use it as part of a mixed-media work. Many terms for the process have been used over the years, including "digigraph" and "giclée". Thousands of print shops and digital printmakers now offer services to painters, photographers, and digital artists around the world.
Notable digital laser exposure.
Digital images are exposed onto true, light sensitive photographic paper with lasers and processed in photographic developers and fixers. These prints are true photographs and have continuous tone in the image detail. The archival quality of the print is as high as the manufacturer's rating for any given photo paper used. In large format prints, the greatest advantage is that, since no lens is used, there is no vignetting or detail distortion in the corners of the image.
Digital printing technology has grown significantly over the past few years with substantial developments in quality and sheet sizes.
Digital cylinder printing.
Digital cylinder printing is when a machine directly lays ink onto a curved surface that usually is the wall of an object that has a circular cross section, and a constant, tapered, or variable diameter. Digital cylinder printing is a method of reproducing black-and-white or full-color images and text onto cylindrical objects, typically promotional products, through use of digital imaging systems.
The digital process is by definition faster than conventional screen printing, because it requires fewer production steps and less set-up time for multiple colors and more complex jobs. This in turn enables reduced run lengths.
The ability of digital cylinder printing machines to print full color in one pass, including primers, varnishes and specialty inks, enables multiple design techniques, which include:
Full-wrap cylindrical printing also benefits from seamless borders with no visual overlap. For ease of print file preparation, original design artwork should be able to be imaged on cylinders and tapered items without the need for manipulation or distortion; i.e., flat images will print to scale on a curved surface, with software automatically making the adjustment. The more advanced systems available on the market can handle these requirements.
The digital cylindrical printing process involves inserting a cylinder-shaped item, or part, into a fixture, which securely holds it in place. The part then travels under a print head mechanism in which tiny droplets of CMYK (cyan, magenta, yellow, and black) inks are released in a specific pattern to form an image. Typically, one part is printed at a time and can require from 8 to 45 seconds to complete, depending on artwork complexity and quality. It is then finished with a UV coating to add a glossy finish and protect it from abrasion.
There are three different imaging techniques used by digital cylinder printing machines: multi-pass, single pass, and helical printing.
Multi-Pass: Multi-pass printing is when the print heads or printed object move axially in steps down the part, like a flatbed printer. The move time is inefficient and can lead to stitching artifacts between moves.
Single Pass: Single pass involves using an array of print heads to print the full image length with a single revolution of the printed object. Different colors are usually printed at different stations, leading to higher cost, increased complexity, and sensitivity to print nozzle drop-outs.
Helical Printing: Helical printing is a hybrid method between the single-pass and multi-pass approaches. Image data is mapped to allow continuous imaging in a helical pattern with a limited number of print heads. Users can optimize the print resolution, speed, and curing controls to optimize image quality or choose higher speed if quality isn’t critical. Tapers can be imaged at high speed and curved vessels can be managed through the range of controls offered.
Items that can be printed using digital cylindrical processes include cups, tumblers, thermos bottles, bottles, makeup containers, machine parts, carrier tubes, pens, tubes, jars and others.
Applications.
Digital printing has many advantages over traditional methods. Some applications of note include:
personalization of printed materials


Rivet

A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the "tail". On installation, the rivet is placed in a punched or drilled hole, and the tail is "upset" or "bucked" (i.e., deformed), so that it expands to about 1.5 times the original shaft diameter, holding the rivet in place. In other words, the pounding or pulling creates a new "head" on the tail end by smashing the "tail" material flatter, resulting in a rivet that is roughly a dumbbell shape. To distinguish between the two ends of the rivet, the original head is called the "factory head" and the deformed end is called the "shop head" or buck-tail.
Because there is effectively a head on each end of an installed rivet, it can support tension loads. However, it is much more capable of supporting shear loads (loads perpendicular to the axis of the shaft).
Fastenings used in traditional wooden boat building, such as copper nails and clinch bolts, work on the same principle as the rivet but were in use long before the term "rivet" was introduced and, where they are remembered, are usually classified among nails and bolts respectively.
History.
Rivet holes have been found in Egyptian spearheads dating back to the Naqada culture of between 4400 and 3000 B.C. Archeologists have also uncovered many Bronze Age swords and daggers with rivet holes where the handles would have been. The rivets themselves were essentially short rods of metal, which metalworkers hammered into a pre-drilled hole on one side and deformed on the other to hold them in place.
Types.
There are several types of rivets, designed to meet different cost, accessibility, and strength requirements:
Solid/round head rivets.
Solid rivets are one of the oldest and most reliable types of fasteners, having been found in archaeological findings dating back to the Bronze Age. Solid rivets consist simply of a shaft and head that are deformed with a hammer or rivet gun. A rivet compression or crimping tool can also deform this type of rivet. This tool is mainly used on rivets close to the edge of the fastened material since the tool is limited by the depth of its frame. A rivet compression tool does not require two people and is generally the most foolproof way to install solid rivets.
Solid rivets are used in applications where reliability and safety count. A typical application for solid rivets can be found within the structural parts of aircraft. Hundreds of thousands of solid rivets are used to assemble the frame of a modern aircraft. Such rivets come with rounded (universal) or 100° countersunk heads. Typical materials for aircraft rivets are aluminium alloys (2017, 2024, 2117, 7050, 5056, 55000, V-65), titanium, and nickel-based alloys (e.g., Monel). Some aluminium alloy rivets are too hard to buck and must be softened by solution treating (precipitation hardening) prior to being bucked. "Ice box" aluminium alloy rivets harden with age, and must likewise be annealed and then kept at sub-freezing temperatures (hence the name "ice box") to slow the age-hardening process. Steel rivets can be found in static structures such as bridges, cranes, and building frames.
The setting of these fasteners requires access to both sides of a structure. Solid rivets are driven using a hydraulically, pneumatically, or electromagnetically actuated squeezing tool or even a handheld hammer. Applications where only one side is accessible require "blind" rivets.
Solid rivets are also used by some artisans in the construction of modern reproduction of medieval armour, jewellery and metal couture.
High-strength structural steel rivets.
Until relatively recently, structural steel connections were either welded or riveted. High-strength bolts have largely replaced structural steel rivets. Indeed, the latest steel construction specifications published by AISC (the 14th Edition) no longer cover their installation. The reason for the change is primarily due to the expense of skilled workers required to install high-strength structural steel rivets. Whereas two relatively unskilled workers can install and tighten high-strength bolts, it normally takes four skilled workers to install rivets (warmer, catcher, holder, basher).
At a central location near the areas being riveted, a furnace was set up. Rivets were placed in the furnace and heated to approximately 900 °C or "cherry red". The rivet warmer or "cook" used tongs to remove individual rivets and throw them to a catcher stationed near the joints to be riveted. The "catcher" (usually) caught the rivet in a leather or wooden bucket with an ash-lined bottom. The catcher inserted the rivet into the hole to be riveted, then quickly turned to catch the next rivet. The "holder up" or "holder on" would hold a heavy "bucking bar" or dolly or another (larger) pneumatic jack against the round "shop head" of the rivet, while the riveter (sometimes two riveters) applied a hammer or pneumatic rivet hammer With a "rivet set" to the tail of the rivet, making it mushroom against the joint forming the "field head" into its final domed shape. Alternatively, the buck is hammered more or less flush with the structure in a counter-sunk hole. Before the use of pneumatic hammers, e.g. in the construction of RMS "Titanic", the man who hammered the rivet was known as the "basher". As the hot rivet was well above its service temperature when the field head was forged, it was unable to create significant tension. However, upon cooling, the rivet contracted axially exerting the clamping force on the joint.
The last commonly used high-strength structural steel rivets were designated ASTM A502 Grade 1 rivets.
Such riveted structures may be insufficient to resist seismic loading from earthquakes if the structure was not engineered for such forces, a common problem of older steel bridges. This is because a hot rivet cannot be properly heat treated to add strength and hardness. In the seismic retrofit of such structures, it is common practice to remove critical rivets with an oxygen torch, precision ream the hole, then insert a machined and heat-treated bolt.
Semi-tubular rivets.
Semi-tubular rivets (also known as tubular rivets) are similar to solid rivets, except they have a partial hole (opposite the head) at the tip. The purpose of this hole is to reduce the amount of force needed for application by rolling the tubular portion outward. The force needed to apply a semi-tubular rivet is about 1/4 of the amount needed to apply a solid rivet. Tubular rivets are sometimes preferred for pivot points (a joint where movement is desired) since the swelling of the rivet is only at the tail. The type of equipment used to apply semi-tubular rivets ranges from prototyping tools to fully automated systems. Typical installation tools (from lowest to highest price) are hand set, manual squeezer, pneumatic squeezer, kick press, impact riveter, and finally PLC-controlled robotics. The most common machine is the impact riveter and the most common use of semi-tubular rivets is in lighting, brakes, ladders, binders, HVAC duct-work, mechanical products, and electronics. They are offered from 1/16-inch (1.6 mm) to 3/8-inch (9.5 mm) in diameter (other sizes are considered highly special) and can be up to 8 inches (203 mm) long. A wide variety of materials and platings are available, most common base metals are steel, brass, copper, stainless, aluminum and the most common platings are zinc, nickel, brass, tin. Tubular rivets are normally waxed to facilitate proper assembly. An installed tubular rivet has a head on one side, with a rolled-over and exposed shallow blind hole on the other.
Blind rivets.
Blind rivets, commonly referred to as "pop" rivets (POP is the brand name of the original manufacturer, now owned by Stanley Engineered Fastening, a division of Stanley Black & Decker) are tubular and are supplied with a nail-like mandrel through the center which has a "necked" or weakened area near the head. The rivet assembly is inserted into a hole drilled through the parts to be joined and a specially designed tool is used to draw the mandrel through the rivet. The compression force between the head of the mandrel and the tool expands the diameter of the tube throughout its length, locking the sheets being fastened if the hole was the correct size. The head of the mandrel also expands the blind end of the rivet to a diameter greater than that of the drilled hole, compressing the fastened sheets between the head of the rivet and the head of the mandrel. At a predetermined tension, the mandrel breaks at the necked location. With open tubular rivets, the head of the mandrel may or may not remain embedded in the expanded portion of the rivet, and can come loose at a later time. More expensive closed-end tubular rivets are formed around the mandrel so the head of the mandrel is always retained inside the blind end after installation. "Pop" rivets can be fully installed with access to only one side of a part or structure.
Prior to the invention of blind rivets, installation of a rivet typically required access to both sides of the assembly: a rivet hammer on one side and a bucking bar on the other side. In 1916, Royal Navy reservist and engineer Hamilton Neil Wylie filed a patent for an "improved means of closing tubular rivets" (granted May 1917). In 1922 Wylie joined the British aircraft manufacturer Armstrong-Whitworth Ltd to advise on metal construction techniques; here he continued to develop his rivet design with a further 1927 patent that incorporated the pull-through mandrel and allowed the rivet to be used "blind". By 1928, the George Tucker Eyelet Company, of Birmingham, England, produced a "cup" rivet based on the design. It required a separate GKN mandrel and the rivet body to be hand-assembled prior to use for the building of the Siskin III aircraft. Together with Armstrong-Whitworth, the Geo. Tucker Co. further modified the rivet design to produce a one-piece unit incorporating a mandrel and rivet. This product was later developed in aluminium and trademarked as the "POP" rivet. The United Shoe Machinery Co. produced the design in the U.S. as inventors such as Carl Cherry and Lou Huck experimented with other techniques for expanding solid rivets.
They are available in flat head, countersunk head, and modified flush head with standard diameters of 1/8, 5/32, and 3/16 inch. Blind rivets are made from soft aluminum alloy, steel (including stainless steel), copper, and Monel.
There are also "", which are designed to take shear and tensile loads.
The rivet body is normally manufactured using one of three methods:
There is a vast array of specialty blind rivets that are suited for high strength or plastic applications. Typical types include:
Internally and externally locked structural blind rivets can be used in aircraft applications because, unlike other types of blind rivets, the locked mandrels cannot fall out and are watertight. Since the mandrel is locked into place, they have the same or greater shear-load-carrying capacity as solid rivets and may be used to replace solid rivets on all but the most critical stressed aircraft structures.
The typical assembly process requires the operator to install the rivet in the nose of the tool by hand and then actuate the tool. However, in recent years automated riveting systems have become popular in an effort to reduce assembly costs and repetitive disorders. The cost of such tools ranges from US$1,500 for auto-feed pneumatics to US$50,000 for fully robotic systems.
While structural blind rivets using a locked mandrel are common, there are also aircraft applications using "non-structural" blind rivets where the reduced, but still predictable, strength of the rivet without the mandrel is used as the design strength. A method popularized by Chris Heintz of Zenith Aircraft uses a common flat-head (countersunk) rivet which is drawn into a specially machined nosepiece that forms it into a round-head rivet, taking up much of the variation inherent in hole size found in amateur aircraft construction. Aircraft designed with these rivets use rivet strength figures measured with the mandrel removed.
Oscar rivets.
Oscar rivets are similar to blind rivets in appearance and installation but have splits (typically three) along the hollow shaft. These splits cause the shaft to fold and flare out (similar to the wings on a toggle bolt's nut) as the mandrel is drawn into the rivet. This flare (or flange) provides a wide bearing surface that reduces the chance of rivet pull-out. This design is ideal for high-vibration applications where the back surface is inaccessible.
A version of the Oscar rivet is the Olympic rivet which uses an aluminum mandrel that is drawn into the rivet head. After installation, the head and mandrel are shaved off flush resulting in an appearance closely resembling a brazier head-driven rivet. They are used in the repair of Airstream trailers to replicate the look of the original rivets.
Drive rivet.
A drive rivet is a form of blind rivet that has a short mandrel protruding from the head that is driven in with a hammer to flare out the end inserted in the hole. This is commonly used to rivet wood panels into place since the hole does not need to be drilled all the way through the panel, producing an aesthetically pleasing appearance. They can also be used with plastic, metal, and other materials and require no special setting tool other than a hammer and possibly a backing block (steel or some other dense material) placed behind the location of the rivet while hammering it into place. Drive rivets have less clamping force than most other rivets. Drive screws, possibly another name for drive rivets, are commonly used to hold nameplates into blind holes. They typically have spiral threads that grip the side of the hole.
Flush rivet.
A flush rivet is used primarily on external metal surfaces where good appearance and the elimination of unnecessary aerodynamic drag are important. A flush rivet takes advantage of a countersunk or dimpled hole; they are also commonly referred to as countersunk rivets. Countersunk or flush rivets are used extensively on the exterior of aircraft for aerodynamic reasons such as reduced drag and turbulence. Additional post-installation machining may be performed to perfect the airflow.
Flush riveting was invented in America in the 1930s by Vladimir Pavlecka and his team at Douglas Aircraft. The technology was used by Howard Hughes in the design and production of his H-1 plane, the Hughes H-1 Racer.
Friction-lock rivet.
These resemble an expanding bolt except the shaft snaps below the surface when the tension is sufficient. The blind end may be either countersunk ('flush') or dome-shaped.
One early form of blind rivet that was the first to be widely used for aircraft construction and repair was the Cherry friction-lock rivet. Originally, Cherry friction locks were available in two styles, hollow shank pull-through and self-plugging types. The pull-through type is no longer common; however, the self-plugging Cherry friction-lock rivet is still used for repairing light aircraft.
Cherry friction-lock rivets are available in two head styles, universal and 100-degree countersunk. Furthermore, they are usually supplied in three standard diameters, 1/8, 5/32 and 3/16 inch.
A friction-lock rivet cannot replace a solid shank rivet, size for size. When a friction lock is used to replace a solid shank rivet, it must be at least one size larger in diameter because the friction-lock rivet loses considerable strength if its center stem falls out due to vibrations or damage.
Self-piercing rivets.
Self-pierce riveting (SPR) is a process of joining two or more materials using an engineered rivet. Unlike solid, blind and semi-tubular rivets, self-pierce rivets do not require a drilled or punched hole.
SPRs are cold-forged to a semi-tubular shape and contain a partial hole to the opposite end of the head. The end geometry of the rivet has a chamfered poke that helps the rivet pierce the materials being joined. A hydraulic or electric servo rivet setter drives the rivet into the material, and an upsetting die provides a cavity for the displaced bottom sheet material to flow. The SPR process is described in here SPR process.
The self-pierce rivet fully pierces the top sheet material(s) but only partially pierces the bottom sheet. As the tail end of the rivet does not break through the bottom sheet it provides a water or gas-tight joint. With the influence of the upsetting die, the tail end of the rivet flares and interlocks into the bottom sheet forming a low profile button.
Rivets need to be harder than the materials being joined. they are heat treated to various levels of hardness depending on the material's ductility and hardness. Rivets come in a range of diameters and lengths depending on the materials being joined; head styles are either flush countersunk or pan heads.
Depending on the rivet setter configuration, i.e. hydraulic, servo, stroke, nose-to-die gap, feed system etc., cycle times can be as quick as one second. Rivets are typically fed to the rivet setter nose from tape and come in cassette or spool form for continuous production.
Riveting systems can be manual or automated depending on the application requirements; all systems are very flexible in terms of product design and ease of integration into a manufacturing process.
SPR joins a range of dissimilar materials such as steel, aluminum, plastics, composites and pre-coated or pre-painted materials. Benefits include low energy demands, no heat, fumes, sparks or waste and very repeatable quality.
Compression rivets.
Compression rivets are commonly used for functional or decorative purposes on clothing, accessories, and other items. They have male and female halves that press together, through a hole in the material. "Double cap rivets" have aesthetic caps on both sides. "Single cap rivets" have caps on just one side; the other side is low profile with a visible hole. "Cutlery rivets" are commonly used to attach handles to knife blades and other utensils.
Sizes.
Rivets come in both inch series and metric series:
The main official standards relate more to technical parameters such as ultimate tensile strength and surface finishing than physical length and diameter. They are:
Imperial.
Rivet diameters are commonly measured in -inch increments and their lengths in -inch increments, expressed as "dash numbers" at the end of the rivet identification number. A "dash 3 dash 4" (XXXXXX-3-4) designation indicates a -inch diameter and -inch (or -inch) length. Some rivets lengths are also available in "half sizes", and have a dash number such as –3.5 ( inch) to indicate they are half-size. The letters and digits in a rivet's identification number that precede its dash numbers indicate the specification under which the rivet was manufactured and the head style. On many rivets, a size in 32nds may be stamped on the rivet head. Other makings on the rivet head, such as small raised or depressed dimples or small raised bars indicate the rivet's alloy.
To become a proper fastener, a rivet should be placed in a hole ideally 4–6 thousandths of an inch larger in diameter. This allows the rivet to be easily and fully inserted, then setting allows the rivet to expand, tightly filling the gap and maximizing strength.
Metric.
Rivet diameters and lengths are measured in millimeters. Conveniently, the rivet diameter relates to the drill required to make a hole to accept the rivet, rather than the actual diameter of the rivet, which is slightly smaller. This facilitates the use of a simple drill-gauge to check both rivet and drill are compatible. For general use, diameters between 2 mm – 20 mm and lengths from 5 mm – 50 mm are common. The design type, material and any finish is usually expressed in plain language (often English).
Applications.
Before welding techniques and bolted joints were developed, metal-framed buildings and structures such as the Eiffel Tower, Shukhov Tower and the Sydney Harbour Bridge were generally held together by riveting, as were automobile chassis. Riveting is still widely used in applications where light weight and high strength are critical, such as in an aircraft. Many sheet-metal alloys are preferably not welded as deformation and modification of material properties can occur.
A large number of countries used rivets in the construction of armored tanks during World War II, including the M3 Lee (General Grant) manufactured in the United States. However, many countries soon learned that rivets were a large weakness in tank design since if a tank was hit by a large projectile it would dislocate the rivets and they would fly around the inside of the tank and injure or kill the crew, even if the projectile did not penetrate the armor. Some countries such as Italy, Japan, and Britain used rivets in some or all of their tank designs throughout the war for various reasons, such as lack of welding equipment or inability to weld very thick plates of armor effectively.
Blind rivets are used almost universally in the construction of plywood road cases.
Common but more exotic uses of rivets are to reinforce jeans and to produce the distinctive sound of a sizzle cymbal.
Joint analysis.
The stress and shear in a rivet are analyzed like a bolted joint. However, it is not wise to combine rivets with bolts and screws in the same joint. Rivets fill the hole where they are installed to establish a very tight fit (often called an interference fit). It is difficult or impossible to obtain such a tight fit with other fasteners. The result is that rivets in the same joint with loose fasteners carry more of the load—they are effectively stiffer. The rivet can then fail before it can redistribute load to the other loose-fit fasteners like bolts and screws. This often causes catastrophic failure of the joint when the fasteners "unzip". In general, a joint composed of similar fasteners is the most efficient because all fasteners reach capacity simultaneously.
Installation.
Solid and semi-tubular rivets.
There are several methods for installing solid rivets.
Rivets small enough and soft enough are often "bucked". In this process, the installer places a rivet gun against the factory head and holds a bucking bar against the tail or a hard working surface. The bucking bar is a specially shaped solid block of metal. The rivet gun provides a series of high-impulse forces that upsets and work hardens the tail of the rivet between the work and the inertia of the bucking bar. Rivets that are large or hard may be more easily installed by squeezing instead. In this process, a tool in contact with each end of the rivet clinches to deform the rivet.
Rivets may also be upset by hand, using a ball-peen hammer. The head is placed in a special hole made to accommodate it, known as a rivet-set. The hammer is applied to the buck-tail of the rivet, rolling an edge so that it is flush against the material.
Testing.
Solid rivets for construction.
A hammer is also used to "ring" an installed rivet, as a non-destructive test for tightness and imperfections. The inspector taps the head (usually the factory head) of the rivet with the hammer while touching the rivet and base plate lightly with the other hand and judges the quality of the audibly returned sound and the feel of the sound traveling through the metal to the operator's fingers. A rivet tightly set in its hole returns a clean and clear ring, while a loose rivet produces a recognizably different sound.
Testing of blind rivets.
A blind rivet has strength properties that can be measured in terms of shear and tensile strength. Occasionally rivets also undergo performance testing for other critical features, such as pushout force, break load and salt spray resistance. A standardized destructive test according to the Inch Fastener Standards is widely accepted.
The shear test involves installing a rivet into two plates at specified hardness and thickness and measuring the force necessary to shear the plates. The tensile test is basically the same, except that it measures the pullout strength. Per the IFI-135 standard, all blind rivets produced must meet this standard. These tests determine the strength of the rivet, and not the strength of the assembly. To determine the strength of the assembly a user must consult an engineering guide or the Machinery's Handbook.


Pallet jack

A pallet jack, also known as a pallet truck, pallet pump, pump truck, scooter, dog, or jigger is a tool used to lift and move pallets. Pallet jacks are the most basic form of a forklift and are intended to move pallets within a warehouse.
Operational principle.
The jack is steered by a tiller-like lever called a 'tow bar' that also acts on the pump piston for raising the forks. A small lever on the tow bar's steering handle releases the hydraulic fluid, causing the forks to lower. The steering wheels are located directly below the tow bar and support the jacking mechanism.
The front wheels inside the end of the forks are mounted on push rods attached to linkages that go to levers attached to the jack cylinder. As the hydraulic jack at the 'tiller' end is raised, the links force the wheels down, raising the forks vertically above the front wheels, raising the load upward until it clears the floor. The pallet is only lifted enough to clear the floor for subsequent travel. Oftentimes, pallet jacks are used to move and organize pallets inside a trailer, especially when there is no forklift truck access or availability.
History.
Manual pallet jacks have existed since at least 1918. Early types lifted the forks and load only by mechanical linkages. More modern type uses a hand pumped hydraulic jack to lift.
Types.
Manual pallet jack.
A manual pallet jack is a hand-powered jack most commonly seen in retail and personal warehousing operations. They are used predominantly for lifting, lowering and steering pallets from one place to another.
Powered pallet jack.
Powered pallet jacks, also known as electric pallet trucks, walkies, single or double pallet jacks, or power jack, are motorized to allow lifting and moving of heavier and stacked pallets. Some contain a platform for the user to stand while moving pallets. The powered pallet jack is generally moved by a throttle on the handle to move forward or in reverse and steered by swinging the handle in the intended direction. Some contain a type of dead man's switch rather than a brake to stop the machine should the user need to stop quickly or leave the machine while it is in use. Others use a system known as "plugging" wherein the driver turns the throttle from forward to reverse (or vice versa) to slow and stop the machine, as the dead man's switch is used in emergencies only.
Rough terrain pallet jack.
Rough terrain pallet jacks are designed specifically for use on uneven ground. They are made using heavy-duty frames and robust pneumatic tyres so that they can be manoeuvred over rough surfaces with ease. Many manufacturers opt for watertight wheel bearings, a hydraulic elevator or a built-in pump to ensure their rough terrain pallet jacks are easy and comfortable to use, even in the harshest conditions.
Operational risks.
Pallet jacks are classed as material-handling equipment (MHE). Under most health and safety law, training is required in their use (particularly for powered pallet jacks) and, as the loads carried are heavy, there is a substantial risk of accidents resulting in injuries.
Typical dimensions.
Industry seems to have 'standardized' pallet jacks in several ways:
In Eurasia the overall dimensions are similar, as modern container palletization has forced standardization in the dimensional domain globally.


Vapor polishing

Vapor polishing is a method of polishing plastics to reduce the surface roughness or improve clarity. Typically, a component is exposed to a chemical vapor causing the surface to flow thereby improving the surface finish. This method of polishing is frequently used to return clear materials to an optical quality finish after machining. Vapor polishing works well in the internal features of components.
Feature size changes of the plastic component generally do not occur. Post stress relieving is usually required as vapor polishing sets up surface stresses that can cause crazing.
Plastics that respond well to vapor polishing are polycarbonate, acrylic, polysulfone, PEI, and ABS.
The technique is also being used to improve the surface of objects created with 3D printing techniques. As the printer deposits layer upon layer of material to build the object, the surface is often not entirely smooth. The smoothness of the surface can be greatly increased by vapor polishing.


Rule based DFM analysis for deep drawing. Deep drawing is a widely used cold sheet metal forming process to draw the sheet metal in forming dye of desirable cross-section using mechanical force of the punch. DFM refers to design for manufacturability. DFA refers to design for assembly. DFMA stands for design for manufacture and assembly. It is a practice for designing the engineering components keeping manufacturing and assembly aspects in mind. DFMA tries to tackle the problems that may come during the manufacturing and assembly at the design stage itself. Changes in the parts design to remove these problems while keeping the functionality of the parts intact. This is done to reduce the cost of iterations thus making the manufacturing of components more efficient and economical.
In the deep drawing process, a blank of sheet metal (usually circular) is placed on the die. The die is fixed to the base. The metal blank is held in position on the die using blank holder. Mechanical force is applied on the part of the metal blank above the die cavity through a punch. As the punch force increases the metal flows from the flange region in to the die cavity.
Here is the Rule based DFM analysis for Deep drawing process. These rules can be incorporated at the design stage to improve the efficiency of the process:
Material of Sheet Metal.
As the deep drawing is a cold forming operation, the germane properties of the sheet metal are formability, ductility and yield strength. The material should have good formability and ductility so that it can be drawn into the desired shape without any cracks. The yield strength of the material should be low facilitating initiation of the flow of metal without tearing near the punch radius.
Clearance between Punch and Die.
Clearance between the punch and die guides the flow of the metal into the die. Clearance should be more than the metal thickness to avoid concentration of metal at the top of the die cavity. Clearance should not be as large so that the flow of metal into the die region becomes unrestricted leading to the wrinkling of wall.
Die corner radius.
Radius of curvature at the die where the metal enters from the flange region into the die region is an important geometrical parameter. If the die corner radius is small than wrinkling near the flange region becomes more prominent. Too small die corner radius results in cracks due to sharp change in the direction of metal flow. Generally it should be 5-10 times the sheet thickness.
Punch corner radius.
As the metal draws into the die the thickness of the sheet decreases near in the lower region of the punch. Maximum reduction happens near punch corner because the metal flow decreases significantly here. Too sharp corner results in cracks near the punch base. Corner radius of punch should be 4-10 times the sheet thickness.
Blank holding force.
The friction in the flange region is mainly affected by blank holding force. Blank holding force is required for checking the amount of the metal flow in to the die. The low value of blank holding force results in wrinkling in the flange region and too high value of holding force results in increase in the drawing force due to the increase in the friction between the flange region. The blank holding force should be just enough to restrict the flow of the metal.
Drawing Ratio.
Measurement of the amount of drawing performed on a sheet metal blank is quantified using drawing ratio. The higher the drawing ratio, the more extreme the amount of deep drawing. Due to the geometry, forces, metal flow and material properties of the work, there is a limit to the amount of deep drawing that can be performed on a sheet metal blank in a single operation. The drawing ratio is roughly calculated as,
DR = Db/Dp.
Db is the diameter of the blank and Dp is the diameter of the punch. For shapes that are noncircular the maximum diameter is sometimes used, or occasionally drawing ratio is calculated using surface areas. The limit to the drawing ratio for an operation is usually 2 or under


Extrusion is a plastic deformation process in which raw material (billet) is forced to flow by compression through the die opening of a smaller cross-section area. The extrusion process is divided in two basic types: direct extrusion and indirect extrusion. In direct extrusion the billet is pushed through the die with ram pressure, whereas in indirect extrusion a die moves relative to the container.
Rule based analysis of extrusion process would help to determine a set of rules essential for consideration while designing a product, or even during cost estimation of a product. Some rules are discussed below.
Material.
Material of the profile to be extruded plays an essential role in determining process parameters and potential limitations of a process. For example, minimum thickness of extruded carbon steel sheet is 3mm whereas same sheet of aluminium can be extruded into minimum sheet thicknesses of 1mm. A variety of materials such as Carbon steel, aluminium, titanium, magnesium, ABS and PVC etc. can be manufactured via extrusion processes.
Profile shape.
Extrusion processes can extrude sheets into a high variety of profile shapes, but it is essential to consider profile features, to ensure product feasibility and strength.
Wall thickness.
When deciding the wall thickness of any extrusion profile, strength and cost efficiency are two main factors. Though Uniform wall thicknesses are most easy to manufacture, wall thickness can easily be varied as necessary within a profile. If changes in the wall thickness are unavoidable, make them as gradual rather than abrupt variations. Thick with thin cross sections should be avoided, as material tends to flow faster where thicker sections occur, giving rise to more expected distortion in an extruded shape.
For an extrusion process wall thickness may vary from 1mm (aluminium) to 32mm (PVC).
Corner Radii.
Extrusion processes cannot achieve sharp corners without additional fabrication. Internal corners should be filleted with a minimum radius of 0.5-1mm, and sharp external edges should be rounded as those tips can easily become wavy and uneven.
Solid profiles if possible.
Solid Profiles can reduce die costs and are often easier to produce.
Fewer cavities in hollow profiles.
Varieties of hollow profiles are often very difficult to produce, but a hollow profile can be replaced by two telescoping profiles, to ease product manufacturing. In many cases reducing the number of cavities in a hollow profile makes it easier to extrude, which can also increases die stability.
Profiles with deep channels.
For profiles with pockets or channels, a basic rule is that the width to height ratio should be approximately 1:3. This ensures that the strength of the die is not jeopardised. When using larger radii at the opening of the channel, and a full radius at the bottom, width-to-height ratios could rise to 1:4.
Heat sinks.
Use of cooling fins on profiles greatly increases areas for heat dissipation. Surface area can be further increased by giving any fins a wavy surface. An undulating surface increases heat dissipation area of any fins. However, where there is forced air-cooling longitudinally along the profile, it can be better to leave fins smooth. This helps to avoid a problem of eddy formation.
Surface Finish.
During an extrusion process it is essential to consider the surface finish of exposed product surfaces. As a general rule, the narrower an exposed surface, the more uniform its finish becomes. Webs, flanges and abrupt changes in metal thickness may show up as marks on the opposite surface of an extrusion, particularly on thin sections. The marking of exposed surfaces can be minimized with design changes such as rounding transitions, to reduce the chance of opposite-side streaking.
Symmetry.
Symmetry provides for more balance forces and helps avoiding over stressing areas of the extruding die. Hollow areas within the cross section, in particular, should be balanced.
Length tolerances.
Some waste tolerances are often included in a required extrusion's length. It can be difficult and expensive to cut a perfect length during production, as metals or thermoplastics expand and contract at different temperatures. Greater accuracy is often possible if lengths are cut off-line. A typical length tolerance for UPVC might be +/- 1mm (0.2%) on a 500mm total length.
Extrusion ratio.
Extrusion Reduction ratio is the ratio of the cross sectional areas in the shape of the die opening to that of the container through which the billet is pushed. A large-diameter billet pushed through a very small die opening has a high reduction ratio, and it may sometimes not be possible to extrude such a part. Ratios of 75:1 are common, though difficult.
The solution, however, for a difficult ratio shape is to make the part on a press with a smaller container. Another option is to use a multihole die that lets a number of profiles extrude simultaneously. They also come in handy for small shapes that are too long to handle practically, with even the shortest billets a press can extrude.


DFM Guidelines for Hot Metal Extrusion Process

Extrusion is a metal forming process to form parts with constant cross-section along its length. This process uses a metal billet or ingot which is inserted in a chamber. One side of this contains a die to produce the desired cross section and the other side a hydraulic ram is present to push the metal billet or ingot. Metal flows around the profile of the die and after solidification takes the desired shape.
Extrusion process can be done with the material hot or cold, but most of the metals are heated before the process, if high surface finish and tight tolerances are required then the material is not heated.
DFM stands for design for manufacturing, so as the name suggest the design is manufacturing friendly, in simple terms design that can be manufactured easily and cheaply. DFM guidelines define a set of rules for a person designing a product to ease the manufacturing process, reduce cost and time. For example, if a hole is to be drilled, if the designer specifies a standard hole size then it reduces the cost because the drill bits of unusual sizes are not readily available they have to be custom made.
Material based guidelines.
Nowadays, quite a wide variety of metals are currently extruded commercially, the most common are (in order of decreasing extrudability): Aluminium, Magnesium and their alloys, Copper and Copper alloys, low-carbon and medium-carbon steels, low-alloy steels and stainless steels. So obviously as the extrudability decrease the cost of production increases


Rule-based DFM analysis for electric discharge machining

Electrical discharge machining (or EDM) is one of the most accurate manufacturing processes available for creating complex or simple shapes and geometries within parts and assemblies. A machining method typically used for hard metals, EDM makes it possible to work with metals for which traditional machining techniques are ineffective.
Design for manufacturability (also sometimes known as design for manufacturing or DFM) is the general engineering art of designing products in such a way that they are easy to manufacture. The concept exists in almost all engineering disciplines, but the implementation differs widely depending on the manufacturing technology. DFM describes the process of designing or engineering a product in order to facilitate the manufacturing process in order to reduce its manufacturing costs. DFM will allow potential problems to be fixed in the design phase which is the least expensive place to address them. Other factors may affect the manufacturability such as the type of raw material, the form of the raw material, dimensional tolerances, and secondary processing such as finishing.
Depending on various types of manufacturing processes there are set guidelines for DFM practices. These DFM guidelines help to precisely define various tolerances, rules and common manufacturing checks related to DFM. Rule based guidelines which can be referred to while designing parts are mentioned below. The parts are designed considering manufacturability with electrical discharge machining in mind.
Mechanical design considerations.
Minimum internal corner radius.
The minimum internal corner radius of the feature will dictate the maximum wire diameter that can be used. The wire diameter needs to be less than double the minimum internal corner radius for successful machining. However, the amount of final overcut and a small amount of maneuvering need to be taken into account for the corner to be generated. For small diameter wires, the following are recommended:
Surface finishing.
Surface finishing comprises the small local deviations of a surface from the perfectly flat ideal. It is one of the important factors that controls friction and transfer layer formation during sliding.
Many wire EDM machines have adopted the pulse generating circuit using low power for ignition and high power for machining. However, it is not suitable for finishing process since the energy generated by the high voltage sub-circuit is too high to obtain a desired fine surface. Relaxing the surface finish allows the manufacturer to produce the part with fewer passes, at a higher current level and a higher metal-removal rate, enabling lower production time and cost.
Material removal.
The removal of material in EDM is associated with the erosive effects produced when discrete and spatial discharge occurs between the tool and work-piece electrodes. Short duration sparks generated between these two electrodes. The generator releases electrical energy, which is responsible for melting a small quantity of material from both the electrodes. The part should be designed and prepared such that the amount of stock removed by EDM is relatively small. Traditional machining techniques, such as milling can be used to remove bulk of stock with the finishing operations performed by EDM.
Simultaneous machining.
EDM enhanced with CNC systems is a highly competitive model for making forging dies, casting tooling, plastic injection molds and tooling for powder metals. It enables the user to machine simultaneously multiple highly precise parts from a single clamping. Designs should be considered such that several parts can be stacked and machined simultaneously or a single part can have several EDM operations performed simultaneously.
Enlarging holes.
When existing holes are to be enlarged or reshaped by EDM, through holes are preferred to blind holes as they permit easier flow of dielectric fluid past the area being machined.
Sharp corners.
When cutting sharp corners, the wire dwells longer by the inside radius causing a slight overcut. On the outside radius, it speeds, leaving a slight undercut. Hence, sharp corners should be avoided while designing part.
Galvanic corrosion.
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact, in the presence of an electrolyte. In EDM, there will be some degree of material exchange between the wire or the probe and the base material. Electrodes and base material should be chosen to prevent galvanic corrosion as far as possible.


Rule based DFM analysis for metal spinning. Metal spinning is a lesser known metal forming and fabricating manufacturing process. It is more conventionally used for the manufacturing of axis-symmetric parts. Its ability to create parts that require high tolerance and high strength makes it an outstanding process to manufacture a wide range of parts for automobile, aerospace, defence and medical industries. Typical components produced by metal spinning are lamp bases, reflectors, hollowware (pitchers, tankards, vases, candlesticks, etc.), pots, bans bowls and components for electrical equipment. Design for manufacturability (also sometimes known as design for manufacturing or DFM) is the general engineering art of designing products in such a way that they are easy to manufacture. The concept exists in almost all engineering disciplines, but the implementation differs widely depending on the manufacturing technology. DFM describes the process of designing or engineering a product in order to facilitate the manufacturing process in order to reduce the manufacturing costs. DFM will allow potential problems to be fixed in the design phase which is the least expensive place to address them. Other factors may affect the manufacturability such as the type of raw material, the form of the raw material, dimensional tolerances, and secondary processing such as finishing.
Depending on various types of manufacturing processes that are set guidelines for Design for manufacturability (DFM) practices. These DFM guidelines help to precisely define various tolerances, rules and common manufacturing checks related to DFM. Below are certain rule based standard guidelines which can be referred to while designing parts for metal spinning considering manufacturability in mind.
Design Considerations.
The most common guidelines following design recommendations are not mandatory rules but rather suggestions for promoting ease of manufacture:
Metal Thickness.
The thickness of the metal to be spun can vary from about 0.1 mm (0.004 in) to 120 mm (4 or 5 in) on special machines and with hot material. The most common thickness, however, are 0.6 to 1.3 mm (0.024 to 0.050 in). Maximum thickness and size are limited only by the size of the equipment and the power available to make the metal flow.
Specifying material 25 or 30 percent thicker than the finished-part thickness is usually sufficient to allow for such reduction in wall thickness. However, material too thick for easy spinning should not be specified. Both extra-thick and extra-thin materials make spinning more difficult. For precision work, extra thick metal pieces may be spun and then machined to final dimensions.
Shape.
In spinning, the conical shape is the easiest to form and the most economical. The metal is not subjected to such severe strain when worked down to its extreme depth because the angle at which the chuck meets the metal is small and allows better control of the metal during the spinning operation. The hemispherical shape is more difficult to spin because the angle grows increasingly sharper as the metal is forced farther back on the chuck. In spinning a cylinder, the metal is exposed to greater strain because of the sharp angle. This operation requires more time and skill.
Radius at corners.
Blended radii and fillets are preferable to sharp corners for ease of spinning. Sharp corners tend to cause thinning of stock and, in the case of external corners, breakage of wood or masonite chucks. A desirable minimum is 6 mm (1/4 in), although 3 mm (1/8 in) usually causes no problems. In the spinning process, a metal is exposed to larger strains at sharp angles.
Spinning Ratio.
Spinning ratio is defined as depth to diameter ratio and serves as a critical metric for the spinning process. A rating of 100 indicates maximum suitability for the type of spinning indicated, while lower rating values indicate proportionally less ease of forming with spinning methods. It is preferred to use as shallow part as possible, i.e. avoid deep cylindrical designs, which require repeated operations and annealing. A spinning ratio of less than 1:4 is preferable. Spinning ratios are normally classified as follows: Shallow (less than 1:4), Moderate (1:4 to 3:4), Deep(3:4 to 5:4).
Tapering Angle.
If the part has cylindrical sides and a wood chuck is used, allow a taper of 2° or more, if possible, to facilitate removal of the part from the chuck. With steel chucks, less taper is required, as little as 1/4° will be satisfactory.
Feature Based Rules.
Internal flanges and other configurations of re-entrant shapes are more costly to produce because they require special, more complex chucks or spinning without backup support for the work. Also, it is preferred to dimension parts to surfaces adjacent to the chuck (usually inside dimension). This allows the chuck maker to apply these dimensions directly to the chuck, and it avoids variations in diameter or length caused by variations in material thickness.


Design of plastic components

Injection molding has been one of the most popular ways for fabricating plastic parts for a very long time. They are used in automotive interior parts, electronic housings, housewares, medical equipment, compact discs, and even doghouses. Below are certain rule based standard guidelines which can be referred to while designing parts for injection molding considering manufacturability in mind.
Geometric considerations.
The most common guidelines refer to the specification of various relationships between geometric parameters which result in easier or better manufacturability. Some of these are as follows:
Wall Thickness.
Non-uniform wall sections can contribute to warpage and stresses in molded parts. Sections which are too thin have a higher chance of breakage in handling, may restrict the flow of material and may trap air causing a defective part. Too heavy a wall thickness, on the other hand, will slow the curing cycle and add to material cost and increase cycle time.
Generally, thinner walls are more feasible with small parts rather than with large ones. The limiting factor in wall thinness is the tendency for the plastic material in thin walls to cool and solidify before the mold is filled. The shorter the material flow, the thinner the wall can be. Walls also should be as uniform in thickness as possible to avoid warpage from uneven shrinkage. When changes in wall thickness are unavoidable, the transition should be gradual and not abrupt.
Some plastics are more sensitive to wall thickness than others, where acetal and ABS plastics max out at around 0.12 in. thick (3 mm), acrylic can go to 0.5 in. (12 mm), polyurethane to 0.75 in. (18 mm), and certain fiber-reinforced plastics to 1 in. (25 mm) or more. Even so, designers should recognize that very thick cross sections can increase the likelihood of cosmetic defects like sink.
Draft angles.
Draft angle design is an important factor when designing plastic parts. Because of shrinkage of plastic material, injection molded parts have a tendency to shrink onto a core. This creates higher contact pressure on the core surface and increases friction between the core and the part, thus making ejection of the part from the mold difficult. Hence, draft angles should be designed properly to assist in part ejection. This also reduces cycle time and improves productivity. Draft angles should be used on interior and exterior walls of the part along the pulling direction.
The minimum allowable draft angle is harder to quantify. Plastic material suppliers and molders are the authority on what is the lowest acceptable draft. In most instances, 1degree per side will be sufficient, but between 2 degree and 5 degree per side would be preferable. If the design is not compatible with 1 degree, then allow for 0.5 degree on each side. Even a small draft angle, such as 0.25 degree, is preferable to none at all.
Radius at corners.
Generously rounded corners provide a number of advantages. There is less stress concentration on the part and on the tool. Because of sharp corners, material flow is not smooth and tends to be difficult to fill, reduces tooling strength and causes stress concentration. Parts with radii and fillets are more economical and easier to produce, reduce chipping, simplify mold construction and add strength to molded part with good appearance.
Sharp Corners general design guidelines in injection molding suggest that corner radii should be at least one-half the wall thickness. It is recommended to avoid sharp corners and use generous fillets and radii whenever required. During injection molding, the molten plastic has to navigate turns or corners. Rounded corners will ease plastic flow, so engineers should generously radius the corners of all parts. In contrast, sharp inside corners result in molded-in stress particularly during the cooling process when the top of the part tries to shrink and the material pulls against the corners. Moreover, the first rule of plastic design i.e. uniform wall thickness will be obeyed. As the plastic goes around a well-proportioned corner, it will not be subjected to area increases and abrupt changes in direction. Cavity packing pressure stays consistent. This leads to a strong, dimensionally stable corner that will resist post-mold warpage.
Hole depth to diameter ratio.
Core pins are used to produce holes in plastic parts. Through holes are easier to produce than blind holes which don't go through the entire part. Blind holes are created by pins that are supported at only one end; hence such pins should not be long. Longer pins will deflect more and be pushed by the pressure of the molten plastic material during molding. It is recommended that hole depth-to-diameter ratio should not be more than 2.
Feature Based Rules.
Ribs.
Rib features help in strengthening the molded part without adding to wall thickness. In some cases, they can also act as decorative features. Ribs also provide alignment in mating parts or provide stopping surfaces for assemblies. However, projections like ribs can create cavity filling, venting, and ejection problems. These problems become more troublesome for taller ribs. Ribs need to be designed in correct proportion to avoid defects such as short shots and provide the required strength. Thick and deep ribs can cause sink marks and filling problems respectively. Deep ribs can also lead to ejection problems. If ribs are too long or too wide, supporting ribs may be required. It is better to use a number of smaller ribs instead of one large rib.
Boss.
Boss, a basic design element in plastics, is typically cylindrical and used as a mounting fixture, location point, reinforcement feature or spacer. Under service conditions, bosses are often subjected to loadings not encountered in other sections of a component.
Undercut detection.
Undercuts should be avoided for ease of manufacturing. Undercuts typically require additional mechanisms for manufacture adding to mold cost and complexity. In addition, the part must have room to flex and deform. Clever part design or minor design concessions often can eliminate complex mechanisms for undercuts. Undercuts may require additional time for unloading molds. It is recommended that undercuts on a part should be avoided to the extent possible.
Fillet.
Sharp corners increase concentrations, which are prone to air entrapments, air voids, and sink marks hence weakening the structural integrity of the plastic part. It must be eliminated using radii whenever is possible.
It is recommended that an inside radius be a minimum of one times the thickness.
At corners, the suggested inside radius is 0.5 times the material thickness and the outside radius is 1.5 times the material thickness. A bigger radius should be used if part design allows
Simulation.
The design of injection moulded components can be further improved and optimised by using injection moulding simulation software such as Autodesk Moldflow and SolidWorks Plastics. This software works with components designed in CAD to simulate how a polymer behaves when it enters a injection mould cavity. It can predict how the molten material flows and freezes, any part geometry that is too thin or too thick and if there are any weaknesses created in the plastic from defects such as weld lines.
When simulation is undertaken in the design phase of a project, in advance of the tool being manufactured, it can help to identify the problems discussed above and allow the designer to iteratively modify and re-simulate the design to make improvements. Use of simulation in the design phase can help to reduce problems with the physical mould and therefore reduce time to market, reduce the use of material and energy, prevent surface defects such as sink and flow marks, and reduce the time taken to inject, cool and eject the part, improving the injection moulding machine's output rate.


Machine Sazi Tabriz

Machine Sazi Tabriz Co. (Tabriz Machinery Manufacturing Co.) which is also called by its abbreviation MST, is a Machine tool manufacturing factory in Tabriz, Iran. The major products of the factory are machinery tools such as turning machines, milling machines, drilling machines, grinding machines. A large variety of MST's products are CNC controlled machines. The MST manufacturing complex established on 1969 with technological helps from east European countries. The MST serves as a nationwide base for design and manufacturing of machine tools. MST owns the Machine Sazi football club, since 1969 to now.


Shelf-ready packaging

Shelf-ready packaging (SRP) and retail-ready packaging (RRP) (also "prêt-à-vendre" (PAV)) refers to the packaging of a product so that it is delivered to a retailer in packaging which is optimized for efficient stocking and sale.
Background.
Retailers, particularly large big-box stores, superstores and warehouse clubs, sell large quantities of fast-moving consumer goods. These retailers often want to have items shipped from their distribution centers to the stores in unit loads and bulk boxes: these can be stocked without handling of the merchandise. The purpose of corrugated shipping containers is to put case goods directly onto shelves and stocking locations without individually handling the unit packs or primary packages. Many large retailers ask for items to remain on pallets rather than use shelves. Retailers often require products to come in retail-ready packaging to reduce stocking costs by saving labor expenses.
Ready-to-go display stands and end caps are put in the retail sales location by forklift trucks without assembly or manual handling of unit packs.
Requirements.
Retailers commonly specify all aspects of incoming logistics and packaging to their suppliers. This includes pallet size, bar code format and placement, RFID tags, strength of corrugated shipping containers etc. Boxes must be easy to open and prepare for stocking. Several designs are available. Box perforations, tear tape, etc. must be intuitive and easy. box cutters are often discouraged. Frequently, requirements for reusable packaging and sustainable packaging are also provided.
The principles of shelf-ready packaging are almost universal. Not all retailers have identical requirements. For example, Costcos "Structural Packaging Specifications", Target's "Shelf Ready and Transit Packaging Standards, Hardgoods", and Walmart's "RRP and PDQ Display Standard Style Guide" are similar but not identical.
Regional coordination in Europe has produced an agreement on common functional requirements for the design of SRP. The Efficient Consumer Response (ECR), Europe Working Group, has published "Shelf Ready Packaging" to help standardize programs.
Manufacturers and packagers need to be aware of the diverse requirements of retailers as they package and ship products. Sometimes consultants and contract packagers with experience in shelf-ready-packaging are useful.
Types.
Due to the fact that there are many different products which need to be packed in a SRP, products can be delivered by a variety of solutions.
Shelf tray.
SRP solutions which can be placed in the shelf are predominantly made of corrugated cardboard. In general, these consist of a tray (secondary packaging) and a cover (a lid which protects the product). The cover can be easily separated from the tray by a perforation. Sometimes the cover of a tray is a transparent film which protects the products from mechanical and climatic influences.
Re-usable plastic tray.
In addition to SRP made of corrugated cardboard, packaging can also be made of reusable materials such as plastic. Such plastic containers can be reused directly in the store. If reuse is not possible, the containers can be returned to the producer.
Merchandising unit.
Merchandising units represent another type of SRP solutions. They are used for secondary placement. Normally, promotional goods or fast-moving products are presented in a merchandising unit. An enormous number of products can be placed in a merchandising unit. Therefore, the merchandising unit serves as SRP. Secondary placements can trigger impulse purchases. Often, roll-up palettes, called dollies, are used as a base for merchandising units. Rolling pallets facilitate the handling of merchandising units and increase flexibility.
Importance of shelf-ready packaging.
Shelf-ready packaging continues to be growing in many market segments, including over-the-counter pharmaceuticals. SRP helps retail stores to achieve cost savings in labor and in packaging materials. It also makes packaged products easier to spot for customers, resulting in better sales. Significant efforts and investments are usually made in improving aisle efficiency for consumers, ensuring consistent demand for suitable retail-ready products from physical outlets.


Fast Radius

Fast Radius  is a company that provides manufacturing services in four main areas: application discovery, product design and testing, production-grade manufacturing, and global fulfillment. Its on-demand manufacturing capabilities include additive manufacturing, or 3D printing, CNC machining, injection molding, and urethane casting.
Fast Radius’ headquarters is located in Chicago, Illinois, with additional facilities located in Atlanta, Georgia; Louisville, Kentucky; and Singapore. Fast Radius operates a digital Cloud Manufacturing Platform that allows users to order parts and manage the product lifecycle from product development through fulfillment.
History and about.
Fast Radius, LLC was formed in 2014 by Rick Smith and Mitch Free, and in 2017, Fast Radius, LLC merged with Fast Radius, Inc. Fast Radius, Inc. was co-founded by Lou Rassey, Pat McCusker, Bill King, and John Nanry in a partnership with the shipping and logistics company UPS in an effort to leverage additive manufacturing as a supply chain solution. Since its founding, the company has grown to more than 240 full-time employees and has expanded from supply chain solutions to all manner of parts manufacturing.
Currently, Fast Radius specializes in manufacturing industrial-grade metal and plastic parts for applications including consumer goods, medical devices, automotive, aerospace, industrial equipment, and electronics, along with product development and design services and artificial phalluses.
Its Chicago headquarters, which has been in operation since 2018, is home to the largest public install base of Carbon DLS 3D printers in North America. It was named a Lighthouse Factory, a distinction honoring the best digital factories in the world, by the World Economic Forum.
In addition, Fast Radius’ has a large footprint of HP Multi Jet Fusion (MJF) equipment, Formlabs Stereolithography (SLA) printers, and the Desktop Metal Studio System. Fast Radius also has a robust presence of Stratasys FDM printers co-located at the UPS World Port facility in Louisville, Kentucky. The company is technology-agnostic, and works with a global network of manufacturers to provide CNC machining, injection molding, and urethane casting services.
Notable customers include Satair (an Airbus Services Company), Curtiss Motorcycles, Axial3D, Bastian Solutions (a Toyota Advanced Logistics Company), Rawlings, Yanfeng, Aptiv, Danfoss, and Steelcase.
In 2019, Fast Radius raised $48 million in a Series B funding round led by UPS and assisted by Drive Capital.
During the COVID-19 pandemic, Fast Radius designed a 3D-printed respirator mask in response to the nationwide PPE shortage. The company released the design files and instructions online as an open-source resource. Fast Radius also produced face shield kits for frontline healthcare workers. They also worked with the University of Illinois at Urbana-Champaign to design and patent a microfluidics chip for a point-of-care COVID-19 testing solution.
In 2022, the company became listed on Nasdaq through a merger with ECP Environmental Growth Opportunities Corp. As of August 29, 2022, the company remains insolvent and the stock's share price is down over 95% since its IPO.


Race (bearing)

The rolling-elements of a rolling-element bearing ride on races. The large race that goes into a bore is called the "outer race", and the small race that the shaft rides in is called the "inner race".
Design.
In the case of ball bearings, the bearing has inner and outer "races" and a set of balls. Each race is a ring with a groove where the balls rest. The groove is usually shaped so the ball is a slightly loose fit in the groove. Thus, in principle, the ball contacts each race at a single point. However, a load on an infinitely small point would cause infinitely high contact pressure. In practice, the ball deforms (flattens) slightly where it contacts each race, much as a tire flattens where it touches the road. The race also dents slightly where each ball presses on it. Thus, the contact between ball and race is of finite size and has finite pressure. The deformed ball and race do not roll entirely smoothly because different parts of the ball are moving at different speeds as it rolls. Thus, there are opposing forces and sliding motions at each ball/race contact. Overall, these cause bearing drag. "V" groove raceways distribute the load evenly over the balls as they travel on four points of contact, creating a straight line rolling effect and decreasing the amount of friction created by a full contact round groove design.
In some applications the two races may be arranged on plates parallel to the plane of the balls, rather than on inner and outer sleeves. In this case, the inner and outer sides of the grooves that form the race should have different angles with respect to this plane, with a steeper angle on the inside groove and a shallower angle on the outside groove, so that each ball can rotate properly without slipping.
Manufacture.
Centerless grinding.
The outer diameter (OD) of the races are often centerless ground using the throughfeed process. Centerless grinding can achieve a very high degree of accuracy, especially when done in stages. These stages are: rough, semi-finish and finish. Each grinding stage is designed to remove enough stock material from the casing so that the next stage does not encounter any problems such as burning or surface chatter, the finish stage achieves the final dimension. Each grinding wheel at all of the aforementioned stages has a varying degree of abrasive quality (finish being the finest grade) to achieve the appropriate stock removal for the next stage and final surface finish required.
Feeding.
Bearing casings are introduced to the grinding action via means of a transfer from the delivery system to a pair of infeed rollers, these infeed rollers are tapered to a certain angle so that the casings are driven forward until the regulating wheel and grinding wheel catch them and slow them to their grinding speed which can be altered by speed control of the regulating wheel. The casings are constantly rotating and are fed into the grinding area to prevent separation which can cause finish/size problems or even a "bump" that can potentially crack or destroy casings and will damage the grinding and regulating wheels.
Work rest blade.
Whilst grinding, the bearing cases run through the grinding stages in one long tube of casings that is showered with a cutting fluid.
The 'tube' rests on a hardened steel blade with an angled, highly ground surface held on a horizontal plane between the grinding wheel and regulating wheel, often named a Work Rest Blade, the tube causes wear on the working surface of the blade so it must be reground at regular intervals. The height of the work rest blade perfectly aligns the bearing casing with the horizontal centreline of the grinding wheel creating a flawless ground finish, the work rest blade height can be altered using packing bars placed underneath the blade, height adjustments must be made depending on the diameter of the casings being ground.
Inspection.
Each casing exits the grinding zone onto a high speed conveyor that delivers them to whatever storage and/or inspection arrangement a manufacturer may have, inspection is also carried out by the operator of the centreless line, by checking finish appearance, diameter, squareness and roundness by use of a dial test indicator in varying configurations, size allowances are permitted but are extremely tight depending on the customers requirements and can vary plus or minus within micrometres of finish diameter, Sizes can be adjusted on all grinding stages via a compensation button which can be pushed to remove extra material in varying micrometre units, the grinding wheel can move away at the same compensation to make the casings bigger if so required if the casing size moves from the operators target, and as the grinding wheel wears. Because a centerless grinding line has typically three grinding machines the operator must be in complete control and must prevent blockages in transfers, grinding exits and packing areas, also size and quality must constantly be checked, so the operator is always alert while operating the line and checking for problems and quality issues.
Safety.
Safety features include an emergency stop button which immediately moves the grinding wheel away from the ground rings on its revolutionary axis. Because of the wheel's momentum, it cannot be stopped but the power is cut and the wheel slows naturally, it cannot be reactivated until the emergency stop is reset. After the emergency stop is activated, the size of the workpiece must be re-established before the line can be reactivated into production mode.
Finishing.
The outer and inner bearing casings are then sent on for raceway grinding, superfinishing and final assembly.


Board-to-board connector

Board-to-board (BTB) connectors are used to connect printed circuit boards (PCB), electronic components that contain a conductive pattern printed on the surface of the insulating base in an accurate and repeatable manner. Each terminal on a BTB connector is connected to a PCB.
A BTB connector includes housing and a specific number of terminals. The terminal is made from a conductive material (mostly copper alloy), and plated to improve conductivity and antirust. Terminals transmit the current/signal between PCBs connected by BTB; the housing is made of insulating material (mostly plastic).
Classification.
BTB connectors are divided up into four mounting types:
BTB connectors are selected by considering the mounting method, pin pitch, number of the rows (aka number of the ways), pin length, stacker height etc.