Tandem rolling mill

A tandem rolling mill is a rolling mill with two or more close-coupled stands, where the reduction is achieved by the inter-stand tension(s) and the compressive force between the work rolls.
For mills rolling thinner strip, bridles may be added either at the entry and/or the exit to increase the strip tension near the adjacent stands further increasing their reduction capability.
Introduction.
The first mention of a tandem rolling mill is Richard Ford's 1766 English patent for the hot rolling of wire.
In 1798 he received another patent, this time for the hot rolling of plates and sheets using a tandem mill.
The main advantages of a tandem mill are:
One disadvantage of a tandem mill is the high capital cost compared to that of a single stand reversing mill.
The need for tandem rolling mills, and rolling mills in general, is being reduced by the use of continuous casters.
The development of transfer bar casting, also called thin slab casting meant that slab roughing mills were no-longer required.
Thin strip casting with a thickness of 2 mm has bypassed the tandem hot mill; and further reduction in the casting thickness to produce strip steel the same as annealed cold rolled strip will bypass the tandem cold mill and the annealing process.
Each stand of a tandem mill is set up for rolling using the mill-stand's spring curve and the compressive curve of the metal so that both the rolling force and the exit thickness of each stand are determined.
This article describes the characteristics of a mill stand, the properties of a metal (especially steel), and the control of a tandem mill using both equations and diagrams.
Mill stand characteristics.
The mill stand spring curve is obtained by pressing the work rolls together with increasing force. This causes the work rolls to bend, the screw-downs to compress and the mill housings to stretch.
To reduce work roll bending, a much larger roll is positioned above the top work roll and another is placed below the bottom work roll. This arrangement is called a 4-high mill, as shown in sketch 1.
The red line in graph 1 is the linear approximation
or conversely, the screw-down position
where is called the mill modulus and is the slope of the spring curve in the area of the datum point . For most mills is approximately 4 MN/mm. Larger values would require much thicker mill housings and screw-downs.
A datum is performed by lowering the screws below face until the measured force equals the required datum force , at which point the screw-down position is set so that it equals the datum screw position . At BlueScope Steel's No. 2 temper mill the datum point was 5 mm at a force of 7 MN.
Wood and Ivacheff
analysed the information obtained when measuring the mill modulus by pressing the work rolls together until a typical rolling force was reached, and then they continued to measure the force and screw-down position as the rolls were lifted. The shape of the plotted figures (overlaid, looped, or a figure eight) was found to give good indication of the mill stand's condition.
The datum point is chosen so that the screw-down position is never negative. This was necessary with the control computers of the 1960s, such as the GE/PAC 4020 installed at the then Australian Iron & Steel (now BlueScope) Port Kembla plate mill, which used an assembler language that did not like negative numbers.
Also, a datum point is used rather than trying to measure the point at which the force just becomes zero.
The exact equation used to calculate the required screw-down setting for a required force is:
where: is the value to best suit the measured values and is an adapter which corrects for the thermal expansion of the mill housing and rolls as they warm up during rolling. It is set to zero after a work roll change, when the datum is performed with the new rolls at room temperature.
Using the measured values of and during the rolling of one piece of metal, allows the adaptor to be calculated for use at the start of the next piece.
Roll force measurement.
Load cells are used to measure the force exerted onto the work rolls by the product.
To obtain the true roll force acting on the work rolls the position of the load cells is important; are they with the filler plates under the bottom backup-roll bearings, or on top of the top backup-roll bearings. Both positions are shown in sketch 2.
Another thing that must be considered (if they are present) is the roll balance cylinders.
The roll balance cylinders act to separate the work rolls (no force between them) when the screw-downs are raised; that is, the force of the balance cylinders is just greater than the weight of the top roll set, .
The above roll weights and are only nominal values; the actual values will vary a little depending on how many times the rolls have been ground down between campaigns.
Since the roll weights are only nominal values, any residual error is slowly zeroed out whenever the roll balance is on and the screws are raised sufficiently.
Steel characteristics.
A useful formula for the compression curve of steel is:
where
 moves the curve vertically, i.e. it sets the initial yield stress;
 changes the slope, i.e. the metal's work hardening rate.
The initial steep section in graph 2 is elastic compression. The effective height of this is reduced by the entry and exit tensions when present, as in a tandem mill. Notice that the curve becomes steeper as the thickness approaches zero, i.e. it would take infinite force to make the steel infinitely thin.
The slope of the plastic region around the operating point is normally represented by the letter .
Mathematical modelling.
For a rolling mill to operate, the work roll gap is set prior to the product entering the mill. Originally this setting was empirical; that is, set by the operators according to their experiences of that product's initial dimensions and the required finished thickness.
With a reversing mill, the profile of intermediate thicknesses was also empirical. To obtain greater consistency, attempts were made to characterize the rolling process. In 1948, Bland and Ford
 were one of the first to publish such a mathematical model.
Essentially such mathematical models represent the mill (its spring curve) and the compressive behavior of the product to calculate the mill's "setup".
Mill setup calculation.
The term "setup" is used for the calculation of the actuator settings required by each mill stand to roll the product. These settings include the initial screw-down position, the main drive speed, and the entry and exit tension references where applicable.
This setup calculation is normally performed either in a lower-level computer or a PLC that controls a rolling mill stand(s).
A graphical representation of a mill model can be obtained by plotting the mill stand spring curve and the compression curve for the strip against the same distance axes; then the intersection point gives the solution of expected rolling force , and final Strip Thickness , and also the required initial screw-down position . See graph 3.
In its simplest form
This equation is known as the BISRA equation. It is also known as the gaugemeter equation because measurements of and can be used to calculate the exit thickness as measured by an instrument called a thickness gauge.
If the work rolls are initially pressed together by the screw-downs, then there will be a force acting between the top and bottom work rolls before the strip is present. In this situation, the Mill is said to be set "below face", as shown in graph 3. This is often the case with thin strip.
However, if there is an actual gap before the metal enters the mill, then will be zero, and (from equation 1) must be greater than
The calculation is repeated for the following stands with the exit thickness of the one stand becoming the entry thickness of the next stand. Note that the compression curve has a greater or lesser elastic region depending on the entry and exit tension stresses of that next stand.
Interstand tensions.
One could say the steel is compressed by the force of the work rolls, equivalent to forging; however, if there are tensions present, then it could be said that the steel is stretched by the tension pulling it through the rotating work rolls, as in extruding through a die. See sketch 3.
The tensions reduce the effective elasticity of the product by an amount equal to the induced tension strain. This tension effect is represented in graphs 2 and 3 by drawing the steel compression curve with the elastic region reduced accordingly.
The relationship of the rolling force to the entry and exit strip tensions is important in determining the finished strip flatness. Too much force produces strip with edge wave (often called "pressure wave"). Too much tension, that is too little force, can cause center buckle (depending on the crown of the rolls).
The tension stress is 30% to 50% of the yield stress for cold mills and often higher in hot mills (which can result in heavy necking and even strip breaks).
In sketch 4, observe that the force is offset from the work roll centers because the strip is thicker at the entry than at the exit; this is one component of the torque that the main drives must supply. The other component is the difference in the tension forces. If the exit tension force is much greater than the entry tension force, then the tension torque may be larger than the torque due to the rolling-force and the main drives will generate power.
The neutral point, or no-slip point is the point within the roll bite where the work rolls and the strip are doing the same speed.
The position of the neutral point is influenced by the entry and exit tensions.
Shudder occurs when the neutral point is at an edge of the roll bite; that is the work rolls are alternately grabbing the strip and letting it slip.
Forward slip is the ratio of the exit strip speed to the work rolls peripheral speed. Backward slip is the ratio of the entry strip speed to the work rolls peripheral speed.
Roll wear.
As the strip slides through the work rolls it polishes them and the strip. This changes the friction coefficient of the strip-to-roll surface. So, to predict the forces and the power required to drive the work rolls, the mill modelling estimates this roll wear based on the length of strip rolled.
To reduce the friction in the roll bite, a warm oil-water emulsion is sprayed at the entry side of the roll bite in cold rolling mills.
The work rolls of all the stands in a tandem mill are normally changed at the same time. The new work rolls will have been ground to restore their desired crown and roughness. When this is done, the roll wear is reset to zero in the modelling.
The heat generated in the roll bite of a cold mill warms both the strip and the rolls. Since the cold mill rolls have no coolant applied, just a small amount of warm oil-water emulsion, the work rolls in a cold mill become hotter than those in a hot mill, where copious amounts of cold water are sprayed at the exit side of the roll bite.
Back-up roll bearings speed effect.
The back-up roll bearings are usually white-metal bearings which rely on a film of oil between the shaft and the white-metal to reduce the friction; as seen in sketch 5.
As the speed increases more oil is dragged into the active region of the bearing and this increases the thickness of the oil film in this region. This pushes the top work roll down and the bottom work roll up, which reduces the roll gap in the same manner as running the screws down. To compensate for this, most screw-down control loops include a feed-forward parameter derived from either; an equation of rolling speed, or a value extracted from a lookup table using linear interpolation.
To ensure an oil film exists even at zero speed; pumps are often used to force oil through very tiny holes into the bearing's active region; this is referred to as hydrostatics.
In Chart 1, the scale for the screw-downs position (mauve trace) was 0.2mm per division; this was too coarse. Consequently Chart 2 was created from a similar coil, but with a screw-down position scale of 0.06mm per division; that is, from 5.8mm to 6.4mm.
In the chart recordings, notice that the force (light green trace) has been held constant by the automatic control, which has raised the screw-downs (mauve trace) as the speed (red trace) has increased. This increase in screw position is a measure of the white metal bearing speed effect.
For a more accurate measurement, the force of each mill stand is measured as it is run through its speed range without strip present.
The values measured from Chart 2 were plotted in an Excel spreadsheet. The equation that was used to match the measured points was .
Note that the use of oil hydrostatics can hold the oil film nearly constant up to about 20% of full speed; hence no screw-down movement would be required in that low speed range (this is shown as the red line in the graph of the measured points).
Now recall the gaugemeter equation in its simplest form:
This equation is modified to include the backup roll bearing speed effect especially when rolling product which has a thickness similar to the speed effect (~400 μm at some temper mills). Thus,
Discontinuity in the stress verses strain of annealed steel.
The discontinuity in the stress/strain of annealed steel makes it impossible to create round tinned steel-cans. Wherever the steel bends first is where most of the bending will occur, rather than uniformly.
The discontinuity is shown within the red circle in graph 4. It is the reason the strip is given a light reduction (~1.3%) normally referred to as an elongation or extension.
Since it is referred to as an elongation and not a reduction, this strip is said to have been reduced only once (at the cold mill prior to annealing); hence the term single reduced (SR).
After the elongation, the discontinuity is no longer present.
Alternatively; after annealing, the steel strip can be reduced a second time (by up to 30%) to make it both thinner and work hardened. When this is done, the strip is said to have been reduced twice; that is, doubled reduced (DR).
Grade adaption.
While a tandem mill is rolling, the "setup" computer collects the following information:
It also has available the coil's schedule information:
The actual rolling forces are compared with the forces predicted by the mill model given the information obtained. Any differences adjust the calculated forces by trimming the force adaptors, . Thus equation 5 becomes
Recall that equation 3 gave the compressive strength of steel at BlueScope steel's 5 stand cold mill
The average value of the force adaptors trimmed the value of for the actual grade being rolled.
Also the slope of the force adaptors corrected the work hardening rate, for the same grade of steel. The value of for super-strapping was approximately twice that for normal tin-plate.
This made switching between grades from coil-to-coil much smoother.
Threading.
A few difficulties arise when threading any tandem cold mill.
One way to minimize these problems is to use "open-gap" threading.
With open-gap threading, the next stand to be threaded has a roll gap greater than the thickness of the strip. Once threaded, the top work roll is lowered onto the strip and then the strip moves on. Open-gap threading ensures that the head-end does not mark the work rolls as it enters the roll-gap. And having the strip stopped as the screw-downs are lowered avoids skidding as the work roll just touch the strip.
For "closed-gap" threading of a tandem mill, it is important that the head-end of the strip remains flat so that it enters the next stand easily. Immediately the strip enters a stand, there is no tension on either side of it; this means that the force would be greater than during rolling, so the roll gap (screw-downs) initially needs to be increased a little with respect to that required during rolling in order to prevent excessive edge-wave.
The closed-gap screw-down setting is calculated using the mill model for thread speed and with no tensions.
Another issue with closed-gap threading is the speed of the stand being threaded.
It needs to be faster than the proceeding stand, so that the strip doesn't build up between the stands; but not so fast that it pulls the strip taught too quickly and breaks the strip.
In all cases, the strip's head-end will remain thicker because of the lack of tensions as it is threaded; consequently there will be a sizeable amount of head-end off-gauge strip that must be scrapped later.
Notice in the gif simulation, that the head-end speed remained constant when moving.
This was the practice at BlueScope Steel's 5 stand cold mill.
Control issues.
The control of a tandem rolling mill is multi-layered.
Two examples are shown for BlueScope Steel's No.2 temper mill with the exit stand configured for strip shape (flatness).
At the lowest level is the current/voltage control of the DC electrical drive motors.
At this level the bridles and reels are in open-loop tension mode; this means they run with a voltage which is related to the strip speed and a current controlled according to the tension required in the nearby strip. The tension reel has a motoring current to pull the strip taught, and the payoff reel generates to pull back against the strip. To keep these tensions constant during acceleration/deceleration of the mill, an additional current must be applied to the reels and bridles to produce the extra torque required to accelerate/decelerate them, especially when there is a large part of a coil on a reel. This is referred to as “inertia compensation”.
Above the direct motor controls, is the last stand's force control which sets the strip flatness. The rolls heat up slowly while processing a coil, and this would close the roll gap and increase the rolling force; however, to prevent this increase, the force control raises the screw-downs occasionally, as required.
Also at this level is the inter-stand tension control. It can act into either of the adjacent stands, but as in the diagrams shown, it acted into both stands in the proportions shown.
The thickness/elongation controls and speed profile sit above all of the other control loops.
The speed profile is determined in the mathematic modelling according to the desired reduction. It is multiplied by the master ramp's speed as set by the operator using his/her inputs, which are: thread (go to thread speed); run (accelerate to top speed); hold (stop acceleration/deceleration); stop (steady deceleration to zero speed); and emergency stop (uses maximum deceleration possible).
Back-up roll eccentricity.
With hot rolled slabs and plates, the thickness varies mainly due to the changes in the temperature along the length. The colder sections are a result of the supports in the re-heat furnace.
When cold rolling, virtually all of the strip thickness variation is the result of the eccentricity and out-of-roundness of the back-up rolls from about stand three of the hot strip mill through to the finished product.
The back-up roll eccentricity can be up to 100 μm in magnitude per stack. The eccentricity can be measured off-line by plotting the force variation against time with the mill on creep, no strip present, and the mill stand below face.
A modified fourier analysis was employed by the five stand cold mill at Bluescope Steel, Port Kembla from 1986 until that cold mill ceased production in 2009. Within each coil, the exit thickness deviation times 10 for every meter of strip was stored in a file. This file was analyzed separately for each frequency/wavelength from 5m to 60m in steps of 0.1m. To improve the accuracy, care was taken to use a full multiple of each wavelength (100*). The calculate amplitudes were plotted against the wavelength, so that the spikes could be compared to the expected wavelengths created by the backup rolls of each stand.
If a mill stand is fitted with hydraulic pistons in series with, or instead of the electrically driven mechanical screws, then it is possible to eliminate the effect of that stands back-up roll eccentricity. While rolling, the eccentricity of each back-up roll is determined by sampling the roll force and assigning it to the corresponding portion of each back-up roll's rotational position. These recordings are then used to operate the hydraulic piston so as to neutralize the eccentricities.
Sensitivities and their uses.
In a tandem rolling mill, the gearing of the screw-downs is normally large enough that the work rolls can be moved during rolling. With such a ratio the worm gear is said to be self-locking; that is, the rolling force is unable to push through the worm drive and rotate the electrical drive motor. This means that no brake is attached to the electrical motor.
If during rolling, it is necessary to move the screw-downs to correct either the rolling force or the exit strip thickness, then consider the triangle, shown circled in the graph 5 and enlarged in sketch 6, created when the screw-downs are moved down from the purple line to the green line.
The strip becomes thinner and the rolling force increases.
 with , but the slope , and the slope
Therefore,
Which gives
This term is used to ensure that the control of the rolling force using the screws is independent of the metal being rolled.
Using gives
This factor is used to guarantee that the control of the exit thickness by the screws is independent of the metal being rolled.
The process sensitivities are highly product dependent, so to obtain reasonable values they are calculated off-line in the setup computer, and then incorporated in the real-time control systems.
Mass flow.
A rolling mill does not create nor destroy steel during normal steady state rolling. That is, the same mass of steel leaves the mill as entered it.
And so; expressing the entry volume as , and the exit volume
The density is unaffected by the rolling process and can be cancelled out.
The width may change, but it does so by an insignificant amount (only a fraction of the strip thickness), and so the change may be ignored when rolling thin (<1mm) strip. The roll force tends to widen the strip, while the entry and exit tensions (when present) tend to make the strip narrower.
So, cancelling the density , the width , and the time , gives
This can be used in a rolling mill to calculate the exit thickness that the X-ray gauge will measure when the corresponding portion of the strip finally reaches the gauge.
By assuming all of the cold mill head-end off-gauge has been completely removed by the previous continuous annealing line; the scheduled entry thickness can be substituted in place of the actual entry thickness, .
Then the entry bridle and exit bridle speeds can be used as the measurements of entry speed, and exit speed, respectively.
The resulting calculated thickness deviation can be seen as the light blue trace in chart recording 3. Notice that the thickness control was working at thread speed (red trace). In the block diagram, the calculated gauge (thickness) is q62 and the thickness error is q66. Note the use of the sensitivity factor dS/dh as q2. There are two other interesting factors with this control:
A bumpless PI control.
Initially the control appears to be a PD control with q18 containing a P term equal to q16 times the gain q4, plus a D term being the constant q10 times the change in q16. However, since q20 is effectively added to itself, this summation converts the P term into an integral, and the D term becomes a proportional term. This arrangement has the advantage that the gains q4 and q10 can be changed while the control loop is active without causing a step in the output q20; that is, it's a bumpless control. The overall maximum/minimum limit is designed to prevent the equivalent of integral windup.
An NIC trim into the inter-stand tension control.
Normally moving the screw-downs to correct the strip thickness would perturb the inter-stand tension; its control would then need to trim the speed of the appropriate stand to restore the tension. So, what is required, is a compensating trim applied to the tension control at the same time as the thickness trim goes to the screw-downs. This is referred to as a non-interactive control;
that is, the thickness correction no-longer disturbs the tension. In the block diagram, the screw trim q20 is converted into a compensating IS tension trim using the sensitivity factor dT/dS (the value of this was measured by applying a small step change to the thickness reference and looking for any change in the IS tension).
For the coil in chart recording 1 above, the cold mill Head-end off-gauge was not fully removed at the CA line; this can be seen as the difference between the X-ray deviation (green trace) and the calculated thickness deviation (light blue trace).
Bridle rolls.
Bridle rolls are used to increase or decrease the strip tension in a processing line or rolling mill.
The bridle rolls normally come in a set of two, three, or four rolls of equal diameter, with each roll individually powered by an electric motor/generator. The drives of the entry bridle generate power as they pull back and increase the strip tension after them. This power is partly provided by the exit bridle which pulls on the strip before it, and so decreases the strip tension after it.
To assist with threading there are normally guides and even a pinch roll or rolls, as shown for the two roll bridle in sketch 7.
To determine the size of the electrical drives, it is necessary to calculate the values of the intermediate tension or tensions.
The maximum tension difference across a single bridle roll is determined by the wrap angle (in radians) of the strip around that roll, and the roll-to-strip sliding friction , i.e.
The power required to drive such a bridle is , i.e.
The electrical power required by the drive motor = volts ⋅ amps. The voltage can be regulated according to the strip speed, leaving the current to be proportional to the required tension change.
To prevent slippage, the bridle rolls within a set are operated at only a fraction of the maximum tension difference, so the actual tension difference across each bridle roll will be . That is, a lower value of friction is used in the calculations.
Consider the simplest case:
A two roll bridle set with both rolls having the same wrap angle . Then , and .
Therefore which gives,
And so
Now consider an example:
And so, the second bridle requires just over 40% more motor power compared to the first.
If one wishes to reduce the number of spares; then it is desirable to have motors of the same power.
To do that, the wrap angle on the first bridle must be increased so that the tension difference across both bridles is the same;
. That is,
Let the wrap angle of bridle roll 1 be , where is the wrap angle of bridle roll 2.
That is
Taking logarithms of both sides gives
For bridle roll 2:
Again, taking logarithms gives
From equations B4 and B5:
Now consider a four roll bridle with tensions . Normally in such a bridle set, all of the rolls have the same strip wrap angle, as shown in sketch 7.
The wrap angle from to is the same as that from to .
Therefore, using equation B2
Similarly,
So if we let then which gives
And finally
Inter-stand tension control.
Consider a violin string:
Now consider the strip between the stands of a multi-stand mill:
The overall transfer function from speed-difference to tension is:
Therefore, the control loop divides the tension error by the strip width and the strip thickness in order to have a consistent response.
In chart recording 4, the two components necessary to change the tension (brown trace) can be seen in the speed trim (light blue trace). There is the extra speed difference necessary to stretch the strip already in the inter-stand gap (large trim); and the slight increase in speed difference to maintain the new level of tension.
Strip shape.
Strip shape is one of the important quality factors of a finished strip, along with the thickness and the mechanical properties.
Poor shape is revealed when the strip fails to lie flat when placed unrestrained on a flat surface. To perform this test, a sample of strip is taken at least 3 wraps in from the end of the finished coil; this is called a "run-out".
Shape errors occur when the strip has not been rolled uniformly across its width.
The problem is, that strip shape cannot be seen while the strip is being rolled because it is under tension; hence the need to do a run-out.
The main shape defects are:
An error in shape is quoted in I-units. If part of 100m of strip is rolled 1mm longer than the rest, then it is in error by one I-unit.
There are a few ways in which the shape can be influenced:
Coil collapse.
If a coil of thin strip is wound with low tension,
then it may not have the strength to support itself and may collapse, especially if roughly handled, see figure 1(a).
A solution is to provide chocks to support the coils more appropriately.
If a large coil is wound with a high tension,
then the tension stress builds up on the inner wraps and can cause them to kink, as seen in figure 1(b).
An early solution was to place a steel sleeve onto the tension reel mandrel before the coil started.
However, loading the sleeve slowed production, and the handling of the sleeves back from the following production lines added an extra cost.
Figure 1(c) shows a coil with a sleeve sitting on chocks.
Industrial Automation Services devised a solution.
The early wraps are wound with a high tension to create a pseudo sleeve,
then the body of the coil is wound with a moderate tension supported by that pseudo sleeve; as shown in figure 1(d).
Computers and HMI.
In the 1980's it became possible for digital displays to replace hard-wired headboard-mimics and operator control/display panels.
The descriptions below are based on the upgrade of BlueScope Steel's 5 stand cold mill in 1985.
There are normally three levels of computers directly associated with a tandem rolling mill, as shown in sketch 11.
Level 1 real-time control.
At the lowest level is a Programable Logic Controller, PLC or minicomputer.
The PLC or minicomputer contains the control loops that run the rolling mill. It receives inputs into these dynamic controls directly from the hard-wired desk
and gets the targets for the exit thickness, the tensions and the screw-down positions from the setup computer.
The desk controls include the speed requests (the thread, run and stop push buttons), any screw-down movements
(each joystick has raise, lower, tilt left, and tilt right), and the tension trims (increase / decrease toggle switches).
Level 2 batch processing.
At level 2 is a keyboard and screen having a menu-based interface into the setup computer's mill model.
This operator interface is normally described as the Human Machine Interface, HMI. Through this interface
the operator trims the setup for the next coil. He/she can trim the individual stand reductions, the inter-stand tensions, and the top speed as required.
When the last stand has force control, then the rolling force can also be trimmed.
At this level there are a few TV monitors. At BlueScope Steel's cold mill these monitors included:
Actually these displays can be connected to either level 1 or level 2; for example, after the more recent (in 1997) BlueScope Steel upgrade of their 6 stand hot strip mill,
the operator displays are driven by the level 1 PLC's.
Level 3 supervision.
The setup computer gets each coil's primary data from a scheduling computer.
This scheduling computer usually receives the product's data from the previous production unit
and will pass on the results of this mill's rolling to the next unit.
The primary data sent by the scheduling computer consists of the nominal entry thickness and width, the aim thickness, and if rolling a plate the aim width.
The scheduler assembles the coils or plates to be processed within each campaign using his/her Human Computer Interface, HCI terminal.
A campaign begins with a scheduled roll change; that is, when all of the work rolls of the tandem mill are changed together.
For a cold tandem mill, the campaign has a coffin-shaped width profile. The first few coils are about 3/4 of the full width.
Gradually the coils become wider until the maximum product width is reached. This allows the thermal camber of the rolls to develop before rolling the full-width product.
From then on the product becomes narrower, to avoid the excessive work roll wear corresponding to the strip edges.
Rolling mill definitions.
These definition only apply to the rolling of slabs, plates and strip in a rolling mill.
Reduction.
Reduction, is defined as the per-unit change in thickness with respect to the entry thickness , and so formula_1 formula_1where is the exit thickness.
As the material is reduced, its length becomes proportionately longer; this can be seen in the attached GIF movie.
There are many other definitions of the word reduction; such as in chemistry, medicine, surgery, safety, investment, and in a more general sense, such as in cooking and waste reduction, etc.
Elongation.
When the reduction is small (<2%), it is normally referred to as an elongation or an extension.
Elongation, is defined as the per-unit increase in length due to a decrease in area with respect to the entry, regardless of shape.
Given an entry length , then formula_1 formula_1where is the final length.
If the width is unaffected (as is the case when rolling thin strip <2mm, see sketch 12), then the mass flow concept, gives formula_1
When the elongation is large it is normally measured as reduction, which is defined as the per-unit change in thickness with respect to the entry thickness ; and so if is the exit thickness,
Note that the thickness difference is divided by the exit thickness for elongation and by the entry thickness with reduction; so they are not identical.
An elongation of typically 1.3% is performed to eliminate the discontinuity (seen at the yield point in graph 6) in the stress verses strain reaction of thin steel strip before it is tinned ready for making cans intended for containing preserved foods.
There are many other definitions of the word elongation; such as in astronomy, plasma physics, genetics, and in a more general sense, such as referring to the lengthening of an elastic band.


Low plastic water bottle

A low plastic water bottle is one that uses less plastic than a regular water bottle, typically by having the same internal volume but being made from thinner plastic. Some such bottles have less than half the plastic of a regular water bottle.
The low plastic water bottle has seen an increase in production over the last few years. This is mainly because making low plastic bottles is more efficient, cost-effective, and more environmentally friendly than producing regular bottles. A large number of water companies now exclusively use a low plastic design for their 16.9 oz bottles.
Recycling.
Companies have also taken recycling into consideration. Previously when water bottles were bought in packs of 24, there was a plastic wrap around the bottles and there was a cardboard base. This packaging was not recyclable, but now some water companies have made the packaging fully recyclable, and also have eliminated the cardboard base. Eliminating the cardboard base saves 20 million pounds of corrugated material annually. The plastic reduction in the bottles themselves saves 75 million pounds of plastic.
Thinner plastic bottles are harder to recycle. The average yield of PET bottle recycling in Europe dropped from 73% to 63% between 2011 and 2017, with low-plastic bottles being blamed for a higher moisture content in recycling bales, and for producing thinner plastic flakes which are more likely to be discarded during the recycling process.
Replacements for plastics.
At least one other commercial attempt has been made toward the creation of cheap, non-plastic containers for water. In 2009, Ecologic Brands, Inc. released a water bottle which was created using a combination of recyclable, sustainable sheet stock such as bamboo or palm leaves. The design was entered into INNOVIC's Next Big Thing Award for 2009. The company has since gone on to create a paper jug which can be used as a holder for a recyclable plastic bag for liquids such as milk and detergent.


Rösle

Rösle is a kitchen accessory manufacturer based in the small Bavarian town of Marktoberdorf in Germany. Rösle developed the Open Kitchen concept. Originally started in 1888 by Karl Theodor Rösle as an industrial roofing manufacturer, Rösle expanded into kitchen utensils prior to World War II. The company saw rapid growth throughout the 1950s and onwards and in 1993 the Rösle brand became solely dedicated to kitchen tools. In 2012, RÖSLE started their own BBQ range.
Production changes.
In 2009 the company closed its factory in Germany and sub-contracted production to various firms in China. While insisting the quality would remain, consumer feedback has been poor, leading to a growing market for used, German-made Rösle products.
As of 2022, the Masterclass sub-brand of knives are made in Solingen, Germany.


Product engineering

Product engineering refer to the process of designing and developing a device, assembly, or system such that it be produced as an item for sale through some product manufacturing process. Product engineering usually entails activity dealing with issues of cost, producibility, quality, performance, reliability, serviceability, intended lifespan and user features. These product characteristics are generally all sought in the attempt to make the resulting product attractive to its intended market and a successful contributor to the business of the organization that intends to offer the product to that market. It includes design, development and transitioning to manufacturing of the product. The term encompasses developing the concept of the product and the design and development of its hardware and software components. After the initial design and development is done, transitioning the product to manufacture it in volumes is considered part of product engineering.
For example, the engineering of a digital camera would include defining the feature set, design of the optics, the physical, aesthetic and ergonomic design of the packaging, developing the various electrical and mechanical component for the capture, processing and storage of image and developing the software that allows the user to see the pictures, store them in memory and download them to a computer.
Product engineering is an engineering discipline that deals with both design and manufacturing aspects of a product.
Area of responsibility.
Product engineers are the technical interface between the component development team and the production side (Front End and Back End), especially after the development phase and qualifications when the high volume production is running.
Product engineers improve the product quality and secure the product reliability by balancing the cost of tests and tests coverage that could impact the production fall-off. They support failure analysis request from customers.
Knowledge and skills.
The job requires the product engineer to have a very good working knowledge of:
Tools.
A product engineer will use a wide range of tools and software, possibly including:
20/20, AutoCad, CATIA, PTC Creo, Solidworks, Unigraphics, Labview, JMP, DataConductor.


Automated optical inspection

Automated optical inspection (AOI) is an automated visual inspection of printed circuit board (PCB) (or LCD, transistor) manufacture where a camera autonomously scans the device under test for both catastrophic failure (e.g. missing component) and quality defects (e.g. fillet size or shape or component skew). It is commonly used in the manufacturing process because it is a non-contact test method. It is implemented at many stages through the manufacturing process including bare board inspection, solder paste inspection (SPI), pre-reflow and post-re-flow as well as other stages.
Historically, the primary place for AOI systems has been after solder re-flow or "post-production." Mainly because, post-re-flow AOI systems can inspect for most types of defects (component placement, solder shorts, missing solder, etc.) at one place in the line with one single system. In this way the faulty boards are reworked and the other boards are sent to the next process stage.
SMT inspection.
AOIs for a PCB board with components may inspect the following features:
AOI can be used in the following locations in the SMT lines: post paste, pre-reflow, post-reflow, or wave areas.
Bare PCB inspection.
AOI for a bare PCB board inspection may detect these features:
The triggering of a defects report may be either rule-based (e.g. no lines on the board should be smaller than 50μ) or CAD based in which the board is locally compared with the intended design.
This inspection is much more reliable and repeatable than manual visual inspection.
In many cases, smaller circuit board designs are driving up the demand for AOI vs in-circuit testing.
Related technologies.
The following are related technologies and are also used in electronic production to test for the correct operation of electronics printed circuit boards:
References.
4. Automated Optical Inspection (AOI) Equipment List


Bending (metalworking)

Bending is a manufacturing process that produces a V-shape, U-shape, or channel shape along a straight axis in ductile materials, most commonly sheet metal. Commonly used equipment include box and pan brakes, brake presses, and other specialized machine presses. Typical products that are made like this are boxes such as electrical enclosures and rectangular ductwork.
Process.
In press brake forming, a work piece is positioned over the die block and the die block presses the sheet to form a shape. Usually bending has to overcome both tensile stresses and compressive stresses. When bending is done, the residual stresses cause the material to "" towards its original position, so the sheet must be over-bent to achieve the proper bend angle. The amount of spring back is dependent on the material, and the type of forming. When sheet metal is bent, it stretches in length. The "bend deduction" is the amount the sheet metal will stretch when bent as measured from the outside edges of the bend. The "bend radius" refers to the inside radius. The formed bend radius is dependent upon the dies used, the material properties, and the material thickness.
The U-punch forms a U-shape with a single punch.
Types.
There are three basic types of bending on a press brake, each is defined by the relationship of the end tool position to the thickness of the material. These three are Air Bending, Bottoming and Coining. The configuration of the tools for these three types of bending are nearly identical. A die with a long rail form tool with a radiused tip that locates the inside profile of the bend is called a punch. Punches are usually attached to the ram of the machine by clamps and move to produce the bending force. A die with a long rail form tool that has concave or V shaped lengthwise channel that locate the outside profile of the form is called a die. Dies are usually stationary and located under the material on the bed of the machine. Note that some locations do not differentiate between the two different kinds of dies (punches and dies). The other types of bending listed use specially designed tools or machines to perform the work.
Air bending.
This bending method forms material by pressing a punch (also called the upper or top die) into the material, forcing it into a bottom V-die, which is mounted on the press. The punch forms the bend so that the distance between the punch and the side wall of the V is greater than the material thickness (T).
Either a V-shaped or square opening may be used in the bottom die (dies are frequently referred to as tools or tooling). Because it requires less bend force, air bending tends to use smaller tools than other methods.
Some of the newer bottom tools are adjustable, so, by using a single set of top and bottom tools and varying press-stroke depth, different profiles and products can be produced. Different materials and thicknesses can be bent in varying bend angles, adding the advantage of flexibility to air bending. There are also fewer tool changes, thus, higher productivity.
A disadvantage of air bending is that, because the sheet does not stay in full contact with the dies, it is not as precise as some other methods, and stroke depth must be kept very accurate. Variations in the thickness of the material and wear on the tools can result in defects in parts produced. Thus, the use of adequate process models is important.
Air bending's angle accuracy is approximately ±0.5 deg. Angle accuracy is ensured by applying a value to the width of the V opening, ranging from 6 T (six times material thickness) for sheets to 3 mm thick to 12 T for sheets more than 10 mm thick. Springback depends on material properties, influencing the resulting bend angle.
Depending on material properties, the sheet may be overbent to compensate for springback.
Air bending does not require the bottom tool to have the same radius as the punch. Bend radius is determined by material elasticity rather than tool shape.
The flexibility and relatively low tonnage required by air bending are helping to make it a popular choice. Quality problems associated with this method are countered by angle-measuring systems, clamps and crowning systems adjustable along the x and y axes, and wear-resistant tools.
The K-factor approximations given below are more likely to be accurate for air bending than the other types of bending due to the lower forces involved in the forming process.
Bottoming.
In bottoming, the sheet is forced against the V opening in the bottom tool. U-shaped openings cannot be used. Space is left between the sheet and the bottom of the V opening. The optimum width of the V opening is 6 T (T stands for material thickness) for sheets about 3 mm thick, up to about 12 T for 12 mm thick sheets. The bending radius must be at least 0.8 T to 2 T for sheet steel. Larger bend radii require about the same force for bottoming as they do for air bending, however, smaller radii require greater force—up to five times as much—than air bending. Advantages of bottoming include greater accuracy and less springback. A disadvantage is that a different tool set is needed for each bend angle, sheet thickness, and material. In general, air bending is the preferred technique.
Coining.
In coining, the top tool forces the material into the bottom die with 5 to 30 times the force of air bending, causing permanent deformation through the sheet. There is little, if any, spring back. Coining can produce an inside radius as low as 0.4 T, with a 5 T width of the V opening. While coining can attain high precision, higher costs mean that it is not often used.
Three-point bending.
Three-point bending is a newer process that uses a die with an adjustable-height bottom tool, moved by a servo motor. The height can be set within 0.01 mm. Adjustments between the ram and the upper tool are made using a hydraulic cushion, which accommodates deviations in sheet thickness. Three-point bending can achieve bend angles with 0.25 deg. precision. While three-point bending permits high flexibility and precision, it also entails high costs and there are fewer tools readily available. It is being used mostly in high-value niche markets.
Folding.
In folding, clamping beams hold the longer side of the sheet. The beam rises and folds the sheet around a bend profile. The bend beam can move the sheet up or down, permitting the fabricating of parts with positive and negative bend angles. The resulting bend angle is influenced by the folding angle of the beam, tool geometry, and material properties. Large sheets can be handled in this process, making the operation easily automated. There is little risk of surface damage to the sheet.
Wiping.
In wiping, the longest end of the sheet is clamped, then the tool moves up and down, bending the sheet around the bend profile. Though faster than folding, wiping has a higher risk of producing scratches or otherwise damaging the sheet, because the tool is moving over the sheet surface. The risk increases if sharp angles are being produced.
This method will typically bottom or coin the material to set the edge to help overcome springback. In this bending method, the radius of the bottom die determines the final bending radius.
Rotary bending.
Rotary bending is similar to wiping but the top die is made of a freely rotating cylinder with the final formed shape cut into it and a matching bottom die. On contact with the sheet, the roll contacts on two points and it rotates as the forming process bends the sheet. This bending method is typically considered a "non-marking" forming process suitable to pre-painted or easily marred surfaces. This bending process can produce angles greater than 90° in a single hit on standard press brakes process.
Roll bending.
The roll bending process induces a curve into bar or plate workpieces.
There should be proper pre-punching allowance.
Elastomer bending.
In this method, the bottom V-die is replaced by a flat pad of urethane or rubber. As the punch forms the part, the urethane deflects and allows the material to form around the punch. This bending method has a number of advantages. The urethane will wrap the material around the punch and the end bend radius will be very close to the actual radius on the punch. It provides a non-marring bend and is suitable for pre-painted or sensitive materials. Using a special punch called a "radius ruler" with relieved areas on the urethane U-bends greater than 180° can be achieved in one hit, something that is not possible with conventional press tooling. Urethane tooling should be considered a consumable item and while they are not cheap, they are a fraction of the cost of dedicated steel. It also has some drawbacks, this method requires tonnage similar to bottoming and coining and does not do well on flanges that are irregular in shape, that is where the edge of the bent flange is not parallel to the bend and is short enough to engage the urethane pad.
Joggling.
Joggling, also known as joggle bending, is an offset bending process in which two opposite bends with equal angles are formed in a single action creating a small s-shape bend profile and an offset between the unbent face and the result flange that is typically less than 5 material thicknesses. Often the offset will be one material thickness, in order to allow a lap joint where the edge of one sheet of material is laid on top of the other.
Calculations.
Many variations of these formulas exist and are readily available online. These variations may often seem to be at odds with one another, but they are invariably the same formulas simplified or combined. What is presented here are the unsimplified formulas.
All formulas use the following keys:
The "neutral line" (also called the Neutral axis) is an imaginary profile that can be drawn through a cross-section of the workpiece that represents the locus where no tensile or compressive stress are present but shear stresses are at their maximum. In the bend region, the material between the neutral line and the "inside" radius will be under "compression" during the bend while the material between the neutral line and the "outside" radius will be under "tension" during the bend. Its location in the material is a function of the forces used to form the part and the material yield and tensile strengths. This theoretical definition also coincides with the geometric definition of the plane representing the unbent flat pattern shape within the cross-section of the bent part. Furthermore, the bend allowance (see below) in air bending depends primarily on the width of the opening of the bottom die. As a result, the bending process is more complicated than it appears to be at first sight.
Both bend deduction and bend allowance represent the difference between the neutral line or unbent "flat pattern" (the required length of the material prior to bending) and the formed bend. Subtracting them from the combined length of both flanges gives the flat pattern length. The question of which to use is determined by the dimensioning method used to define the flanges as shown in the two diagrams below. The flat pattern length is always shorter in length than the sum of all the flange length dimensions due to the geometric transformation. This gives rise to the common perspective that that material is stretching during bending and the bend deduction and bend allowance are the distance that each bend stretches. While a helpful way to look at it, a careful examination of the formulas and stresses involved show this to be false.
Most 3D Solid Modeling CAD software has sheet metal functions or add-ons that performs these calculations automatically.
Bend allowance.
The "bend allowance" (BA) is the length of the arc of the neutral line between the tangent points of a bend in any material. Adding the length of each flange as dimensioned by B in the diagram to the BA gives the Flat Pattern length. This bend allowance formula is used to determine the flat pattern length when a bend is dimensioned from 1) the center of the radius, 2) a tangent point of the radius (B) or 3) the outside tangent point of the radius on an acute angle bend (C). When dimensioned to the outside tangent, the material thickness and bend radius are subtracted from it to find the dimension to the tangent point of the radius before adding in the bend allowance.
The BA can be estimated using the following formula, which incorporates the empirical K-factor:
Bend deduction.
The bend deduction BD is defined as the difference between the sum of the flange lengths (from the edge to the apex) and the initial flat length.
The "outside set back" (OSSB) is the length from the tangent point of the radius to the apex of the outside of the bend. The "bend deduction" (BD) is twice the outside setback minus the bend allowance. BD is calculated using the following formula, where A is the angle in radians (=degrees*π/180):
For bends at 90 degrees this formula can be simplified to:
K-factor.
"K-factor" is a ratio of the location of the neutral line to the material thickness as defined by t/T where t = location of the neutral line and T = material thickness. The K-factor formula does not take the forming stresses into account but is simply a geometric calculation of the location of the neutral line after the forces are applied and is thus the roll-up of all the unknown (error) factors for a given setup. The K-factor depends on many variable including the material, the type of bending operation (coining, bottoming, air-bending, etc.) the tools, etc. and is typically between 0.3 and 0.5.
The following equation relates the K-factor to the bend allowance:
The following table is a "rule of thumb". Actual results may vary remarkably.
The following formula can be used in place of the table as a good "approximation" of the K-factor for air bending:
Advantages and disadvantages.
Bending is a cost-effective near net shape process when used for low to medium quantities. Parts usually are lightweight with good mechanical properties. A disadvantage is that some process variants are sensitive to variations in material properties. For instance, differences in spring-back have a direct influence on the resulting bend angle. To mitigate this, various methods for in-process control have been developed. Other approaches include combining brakeforming with incremental forming.
Broadly speaking, each bend corresponds with a set-up (although sometimes, multiple bends can be formed simultaneously). The relatively large number of set-ups and the geometrical changes during bending make it difficult to address tolerances and bending errors a priori during set-up planning, although some attempts have been made


Monopoly profit

Monopoly profit is an inflated level of profit due to the monopolistic practices of an enterprise.
Basic classical and neoclassical theory.
Traditional economics state that in a competitive market, no firm can command elevated premiums for the price of goods and services as a result of sufficient competition. In contrast, insufficient competition can provide a producer with disproportionate pricing power. Withholding production to drive prices higher produces additional profit, which is called "monopoly profits".
According to classical and neoclassical economic thought, firms in a perfectly competitive market are price takers because no firm can charge a price that is different from the equilibrium price set within the entire industry's perfectly competitive market. Since a competitive market has many competing firms, a customer can buy widgets from any of the competing firms. Because of this tight competition, competing firms in a market each have their own horizontal demand curve that is fixed at a single price established by market equilibrium for the entire industry as a whole. Each firm in a competitive market has buyers for its product as long as the firm charges "no more than" the single price. Since firms cannot control the activities of other firms that produce the same widget sold within the market, a firm that charges a price that is higher than the industry's market equilibrium price would lose business; customers would respond by buying their widgets from other competing firms that charge the lower market equilibrium price, which makes deviation from the market equilibrium price impossible.
Perfect competition is commonly characterized by an idealized situation in which all firms within the industry produce exact comparable goods that are perfect substitutes. With the exception of commodity markets, this idealized situation does not typically exist in many actual markets, but in many cases, there exist similar products that are easily interchangeable because they are close substitutes (for example, butter and margarine). A significant rise in a product's price tends to cause customers to switch from this good to a lower priced close substitute. In some cases, firms that produce differing but similar goods have similar production processes, which makes it relatively easy for one-good firms to switch their manufacturing processes to produce a different but similar good. This would be the case when the cost of changing the firm's manufacturing process to produce the similar good can be somewhat immaterial in relationship to the firm's overall profit and cost. Since consumers tend to replace goods whose prices are high with cheaper close substitutes, and the existence of close substitutes whose manufacturing processes are similar allows a firm producing a low-priced good to easily switch over to producing the other higher priced good, the competition model accurately explains why the existence of different similar goods form competitive forces that deny any single firm the ability to establish a monopoly in their product. This effect is observable in a high profit and production cost industry, such as the car industry, and other industries facing competition from imports.
By contrast, the lack of competition in a market ensures the firm (monopoly) has a downward sloping demand curve. Although raising prices causes the monopoly to lose some business, some sales can be made at higher prices. Although monopolists are constrained by consumer demand, they are not "price takers" because they can influence price through their production decisions. The monopolist can either have a "target level of output" that will ensure the monopoly price as the given consumer demand in the industry's market reacts to the fixed and limited market supply, or it can set a fixed monopoly price at the onset and adjust output until it can ensure no excess inventories occur at the final output level chosen. At each price, the firm must accept the level of output as determined by the market's consumer demand, and every output quantity is identified with a price that is determined by the market's consumer demand. The price and output are co-determined by consumer demand and the firm's production cost structure.
A firm with monopoly power sets a monopoly price that maximizes the monopoly profit. The most profitable price for the monopoly occurs when output level ensures the marginal cost (MC) equals the marginal revenue (MR) associated with the demand curve. Under normal market conditions for a monopolist, this monopoly price is higher than the marginal (economic) cost of producing the product, indicating that the price paid by the consumer, which is equal to their marginal benefit, is above the firm's MC.
Persistence.
Without barriers to entry and collusion in a market, the existence of a monopoly and monopoly profit cannot persist in the long run. Normally, when economic profit exists within an industry, economic agents form new firms in the industry to obtain at least a portion of the existing economic profit. As new firms enter the industry, they increase the supply of the product available in the market, and they are forced to charge a lower price to entice consumers to buy the additional supply they are supplying as competition. Since consumers flock toward the lowest price (in search of a bargain), older firms within the industry may lose their existing customers to the new firms entering the industry, and are forced to lower their prices to match the prices set by the new firms. New firms continue to enter the industry until the price of the product is lowered to the point that it is the same as the average economic cost of producing the product, and economic profit disappears. When this happens, economic agents outside of the industry find no advantage to entering the industry, supply of the product stops increasing, and the price charged for the product stabilizes.
Normally, a firm that introduces a brand new product can initially secure a monopoly for a short while. At this stage, the initial price the consumer must pay for the product is high, and the demand for, as well as the availability of the product in the market, will be limited. As time passes, when the profitability of the product is well established, the number of firms that produce this product will increase until the available product supply becomes relatively large, and the product's price shrinks down to the level of the average economic cost of producing the product. When this occurs, all monopoly associated with producing and selling the product disappears, and the initial monopoly turns into a (perfectly) competitive industry.
When consumers have complete information about the prices available in the market and the quality of the products sold by the various firms, there cannot be a persistent monopolistic situation in the absence of barriers to entry and collusion. Various barriers to entry include patent rights and the monopolization of a natural resource needed to produce a product. The American firm Alcoa Aluminum is a historical example of a monopoly due to natural resource control; its control of "practically every source of bauxite in the United States" was one key reason that "[it] was, for a long time, the sole producer of aluminum in the United States".
A barrier to entry can exist in a market situation that is characterized by a combination of high fixed costs in production and a relatively small demand within the firm's product market. Since a high fixed cost results in a higher product market unit costs at lower production levels, and lower unit costs at higher production levels, the combination of a small product market demand for the firm's product, and the high revenue levels the firm needs to cover the high fixed costs it faces, indicate the product market will be dominated by a single large firm that uses economies of scale to minimize both its unit cost and its product price. New firms would be reticent to enter a product market if an apparent slim economic profit can turn into an immediate economic loss for all firms upon a new entry. However, since the qualities of most economic markets make them contestable markets, there may be a greater magnitude of product differentiation within this overall market structure, making it similar to monopolistic competition.
Government intervention.
Competition laws were created to prevent powerful firms from using their economic power to artificially create the barriers to entry they need to protect their monopoly profits, including the use of predatory pricing toward smaller competitors. In the United States, Microsoft Corporation was initially convicted of breaking competition laws and engaging in anti-competitive behavior to form a barrier in "United States v. Microsoft Corporation"; after a successful appeal on technical grounds, Microsoft agreed to a settlement with the Department of Justice in which they were faced with stringent oversight procedures and explicit requirements designed to prevent the predatory behavior. The company was successfully convicted of similar anti-competitive behavior in the European Economic Community's second highest court, the Court of First Instance, in 2007. If firms in an industry collude they can also limit production to restrict supply, and ensure the price of the product remains high enough to ensure all of the firms in the industry achieve an economic profit.
If a government feels it is impractical to have a competitive market, it sometimes tries to regulate the monopoly by controlling the price the monopoly charges for its product. The old AT&T monopoly, which existed before the courts ordered its breakup and tried to force competition in the market, had to get government approval to raise its prices. The government examined the monopoly's costs and determined if the monopoly should be allowed to raise its price; if the government felt that the cost did not justify a higher price, it rejected the monopoly's application. Although a regulated monopoly will not have a monopoly profit that is high as it would be in an unregulated situation, it still can have an economic profit that is still above what a competitive firm has in a truly competitive market.


Co-fired ceramic

Co-fired ceramic devices are monolithic, ceramic microelectronic devices where the entire ceramic support structure and any conductive, resistive, and dielectric materials are fired in a kiln at the same time. Typical devices include capacitors, inductors, resistors, transformers, and hybrid circuits. The technology is also used for robust assembly and packaging of electronic components multi-layer packaging in the electronics industry, such as military electronics, MEMS, microprocessor and RF applications.
Co-fired ceramic devices are fabricated using a multilayer approach. The starting material is composite green tapes, consisting of ceramic particles mixed with polymer binders. The tapes are flexible and can be machined, for example, using cutting, milling, punching and embossing. Metal structures can be added to the layers, commonly using filling and screen printing. Individual tapes are then bonded together in a lamination procedure before the devices are fired in a kiln, where the polymer part of the tape is combusted and the ceramic particles sinter together, forming a hard and dense ceramic component.
Co-firing can be divided into low-temperature (LTCC) and high-temperature (HTCC) applications: low temperature means that the sintering temperature is below , while high temperature is around . The lower sintering temperature for LTCC materials is made possible through the addition of a glassy phase to the ceramic, which lowers its melting temperature.
Due to a multilayer approach based on glass-ceramics sheets, this technology offers the possibility to integrate into the LTCC body passive electrical components and conductor lines typically manufactured in thick-film technology. This differs from semiconductor device fabrication, where layers are processed serially, and each new layer is fabricated on top of previous layers.
History.
Co-fired ceramics were first developed in the late 1950s and early 1960s to make more robust capacitors. The technology was later expanded in the 1960s to include multilayer structures similar to printed circuit boards.
Components.
Hybrid circuits.
LTCC technology is especially beneficial for RF and high-frequency applications. In RF and wireless applications, LTCC technology is also used to produce multilayer hybrid integrated circuits, which can include resistors, inductors, capacitors, and active components in the same package. In detail, these applications comprise mobile telecommunication devices (0.8–2 GHz), wireless local networks such as Bluetooth (2.4 GHz) to in-car radars (50–140 GHz, and 76 GHz). LTCC hybrids have a smaller initial ("non recurring") cost as compared with ICs, making them an attractive alternative to ASICs for small scale integration devices.
Inductors.
Inductors are formed by printing conductor windings on ferrite ceramic tape. Depending on the desired inductance and current carrying capabilities a partial winding to several windings may be printed on each layer. Under certain circumstances, a non-ferrite ceramic may be used. This is most common for hybrid circuits where capacitors, inductors, and resistors will all be present and for high operating frequency applications where the hysteresis loop of the ferrite becomes an issue.
Resistors.
Resistors may be embedded components or added to the top layer post-firing. Using screen printing, a resistor paste is printed onto the LTCC surface, from which resistances needed in the circuit are generated. When fired, these resistors deviate from their design value (±25%) and therefore require adjustment to meet the final tolerance. With Laser trimming one can achieve these resistances with different cut forms to the exact resistance value (±1%) desired. With this procedure, the need for additional discrete resistors can be reduced, thereby allowing a further miniaturization of the printed circuit boards.
Transformers.
LTCC transformers are similar to LTCC inductors except transformers contain two or more windings. To improve coupling between windings transformers includes a low-permeability dielectric material printed over the windings on each layer. The monolithic nature of LTCC transformers leads to a lower height than traditional wire wound transformers. Also, the integrated core and windings mean these transformers are not prone to wire break failures in high mechanical stress environments.
Sensors.
Integration of thick-film passive components and 3D mechanical structures inside one module permitted the fabrication of sophisticated 3D LTCC sensors e.g. accelerometers.
Microsystems.
The possibility of the fabrication of many various passive thick-film components, sensors and 3D mechanical structures enabled the fabrication of multilayer LTCC microsystems.
Using HTCC technology, microsystems for harsh environments, such as working temperatures of 1000 °C, have been realized.
Applications.
LTCC substrates can be most beneficially used for the realization of miniaturized devices and robust substrates. LTCC technology allows the combination of individual layers with different functionalities such as high permittivity and low dielectric loss into a single multilayer laminated package and thereby to achieve multi-functionality in combination with a high integration and interconnection level. It also provides the possibility to fabricate three-dimensional, robust structures enabling in combination with thick film technology the integration of passive, electronic components, such as capacitors, resistors, and inductors into a single device.
Comparison.
Low-temperature co-firing technology presents advantages compared to other packaging technologies including high-temperature co-firing: the ceramic is generally fired below 1,000 °C due to a special composition of the material. This permits the co-firing with highly conductive materials (silver, copper, and gold). LTCC also features the ability to embed passive elements, such as resistors, capacitors and inductors into the ceramic package, minimising the size of the completed module.
HTCC components generally consist of multilayers of alumina or zirconia with platinum, tungsten and moly-manganese metalization. The advantages of HTCC in packaging technology includes mechanical rigidity and hermeticity, both of which are important in high-reliability and environmentally stressful applications. Another advantage is HTCC's thermal dissipation capability, which makes this a microprocessor packaging choice, especially for higher-performance processors.
Compared to LTCC, HTCC has higher-resistance conductive layers.


Duplex printing

Duplex printing is a feature of some computer printers and multi-function printers (MFPs) that allows the printing of a sheet of paper on both sides automatically. Print devices without this capability can only print on a single side of paper, sometimes called single-sided printing or simplex printing.
Consumer and low-to-medium volume office printers use a duplexing unit that reverses a piece of paper after the first side has been printed. Duplex multifunction printers that also support duplex scanning have a "reversing automatic document feeder" (RADF) for scanning both sides. Higher volume printers may effectively have two print engines in a single device, and are able to print both sides of the paper in a single pass.
Overview.
Duplex print devices, depending on options, software, and printer settings, can print single-sided page to single-sided page (1:1) or double-sided page to double-sided page (2:2). Many can also combine single-sided pages into a double-sided page format (1:2). Double-sided booklet formats (2:2 with a center fold) are also available, depending on optional outputs from the printer.
Printing Formats.
Duplexed documents can be printed to be bound on either the short edge or the long edge. This functionality is mostly available on printers that come with a duplexer. Long edge binding in portrait mode allows pages to be turned side-to-side like a book. Short-edge binding allows the pages to be oriented correctly if they are flipped vertically, as in a notepad. This second form of printing/binding is sometimes known as "tumble." If the printing is done in landscape mode, these concepts are transposed since the print direction is different.
Single-Sided Printing.
Single-sided printers can print on both sides of the paper via manual removal and turning over of a stack of sheets after one side is printed on; however, the user has to manually turn the (half-done) print job over and re-invoke the printing of the document, with care to ensure that the order and orientation is correct. Printing software frequently has an option to print only odd or even pages, simplifying this process.
'Perfecting' in Commercial Printing.
In commercial printing (books, magazines, newspapers, etc.), the term applied to imparting an image to both sides of the substrate at the same time is 'perfecting' and is commonly achieved—especially in lithography—by passing the substrate through a perfecting drum, thus turning the sheet over after the first side is printed. The turned sheet then continues its way through the press, being gripped at the opposite edge whilst the second side is printed. This in effect tumbles the job; therefore, accurate sheet sizing is necessary to ensure accurate backing up of the job.
Some printers only support duplexing if an optional attachment is fitted.


Planned obsolescence (disambiguation)

Planned obsolescence is the policy of deliberately manufacturing a product with a limited lifespan.
Planned obsolescence may also refer to:


Get it Made

Get It Made is a manufacturing company based in London, UK. The company identifies as an online subcontracting platform that connects its clients with manufacturers.
History.
Get It Made was founded in 2011 by director Luke Smoothy.
According to the founder, he started the company with less than one thousand British pounds of seed money.
Its customer base is predominantly UK and Ireland based, but it also has clients in Northern Europe, Eastern Europe, Australia, and New Zealand.
The organisation offers a £10,000 grant to manufacturing start-ups led by people under thirty years old.
Process.
The company does not have in-house machinery; it uses the manufacturing capability of other companies to fulfil orders. The company has a small supplier base in the UK, the Czech Republic, and China.
Its services offered include CNC machining, aluminium extrusions, aluminium die casting, lost wax casting, low-volume silicone moulding, high-volume injection moulding, stamping (pressing), fabricating, tube and wire manipulation, welding, laser cutting, and water-jet cutting.


Ultrasonic welding of thermoplastics

Ultrasonic welding is a method of joining thermoplastic components by heating and subsequent melting of surfaces in contact. Mechanical vibration with frequency between 10 and 70 kHz and amplitude of 10 to 250 μm is applied to joining parts. After ultrasonic energy is turned off, the parts remain in contact under pressure for some time while the melt layer cools down creating a weld.
Different join designs and process controls are used in ultrasonic welding. A sharp surface feature is typically introduced to one of the parts ensuring consistency of the welding process. Components of ultrasonic welding systems as well as the areas of application are described in the article Ultrasonic welding.
Advantages and disadvantages.
Following advantages are typically attributed to ultrasonic welding:
Following are the disadvantages of ultrasonic welding:
Process description.
Plunge and continuous welding are the welding modes of thermoplastics.
Plunge ultrasonic welding.
With plunge ultrasonic welding the parts are first secured in a fixture. Ultrasonic energy is then applied to create a weld. After the weld is cooled down, the parts are removed from the fixture.
At the start of the process, an actuator is moved to a part. This stage is called "downstroke." Ultrasonic energy can be applied during this phase depending on the size of a horn used. The larger the horn the harder it is to vibrate. Therefore, application of ultrasonic energy during the down stroke becomes necessary ("pre-triggering"). In other cases, the vibration is applied after the horn came in contact with the part and some pressure has been created. The force is then continues to increase linearly until some predefined value.
The power rises at the same time as ultrasonic energy is being applied in order to accommodate the stack vibration. After some period of time a steady-state process, which indicate sufficient melting at the interface, is reached. At this point, ultrasonic energy is turned off. In production, this often happens prior to reaching the steady-state process as desired strength of the weld joint for a particular application is typically reached at this point. The tooling continues to stay on the part for a period of time called "hold time." This allows for certain pressure ("hold force") to be applied to the part. Hold time typically lasts for one half of weld time allowing the weld to solidify.
The tooling is being removed from the part during a phase called “up-stroke.” This stage takes place at the completion of the hold time. Some amount of plastic substrate can remain on tooling surface after the welding process. To clean the surface, ultrasonic energy is applied when the tool is being retracted from the part ("post weld burst").
Continuous ultrasonic welding.
Continuous ultrasonic welding mode is used for joining thin layers of material and is often employed for manufacturing products for hospitals such as gowns and sterile garments, and in other applications.
Two layers of material are pulled through a space between a disk – rotary drum (anvil) – and a horn (image). Anvil's surface contains certain pattern. The weld is created at these asperities and the areas between the peaks remain unboned. Surface of the horn is typically round, which prevents undesirable seizing of material. Round horn also allows for proper force distribution at the contact interface.
More than two layers of material can be welded at once. The materials to be welded experience similar vibrations to those in plunge welding but shorter in time. Hold force to the newly welded region is provided by previously welded section that has come out of the tooling and cooled down.
Scan welding is a type of continuous ultrasonic welding in which case large plates or sheets can be welded. In scan welding, a part is secured on a stationary table and the horn moves across the part creating a weld joint. A combination of stationary horn and mobile table can also be employed. The horn has round edges as in case with continuous welding and the ultrasonic vibrations are similar to those in plunge welding. The horn can be used to provide the hold force.
Process control.
Different ultrasonic welding machines offer different process controls. Each application determines the level of process control. In case with ordinary spot welds, a hand-held welder would be sufficient. More sophisticated equipment with computerized controls and built-in statistical process control (SPC) software may be appropriate in medical devices industry and other applications requiring narrow tolerances and high quality welds.
Following modes of process control are used in ultrasonic welding:
Most of these modes require microprocessor based controller while a basic welding system would be enough for time mode. Welding parameters can be monitored in real time with microprocessor based controllers.
The majority of welding systems include "time mode" that allows the operator to specify the duration of welding process independent from other parameters. In "energy control mode", the vibration of the tool continues until a preset energy level is reached. Energy mode can be used in conjunction with time mode to improve the quality of welded parts. Certain time limits can be defined to reach the necessary energy level. Should the actual time for reaching the preset energy level deviate from those time limits, such an event would be indicative of a potential issue with the weld.
In "collapse mode", ultrasonic energy is applied until the parts have collapsed (moved relative to one another) to a certain height. In addition to microprocessor based controller, a linear encoder is used in systems with collapse control. In this mode, the final height of the weld joint can also be controlled by detecting the position of the horn. In "peak power mode", the vibration continues until predefined power level is reached. The final dimensions of the weld joint can also be controlled with "ground detect mode". In this case, ultrasonic energy is applied until the horn makes electrical contact with the fixture that is positioned at the desired height.
Various combinations of process control modes can be employed to define an operating window and aid in quality control.
Joint design.
As with other welding processes, join design is essential step in product development. Many factors should be considered in joint design such as materials to be welded, thickness of parts, operating conditions of the final product, aesthetics and others. Narrow contact area between joining parts is essential design attribute. It allows lower energy input for generating a surface layer of molten plastic. Parts fit-up should provide necessary alignment without interference with their surface features.
Energy directors.

Energy director is a triangular section molded on one of the joint parts. While the parts initially contact each other through this triangle, it carries the highest stress, and is therefore the first portion to melt under application of ultrasonic energy. The purpose of energy directors is to ensure that sufficient amount of material is melted as they fill out the gap between mating parts. Energy directors most commonly used with amorphous polymers, but can also be used with semi-crystalline polymers.
While flash is commonly produced with such joint design, it can be covered with a flash trap. This joint feature conceals the flash providing aesthetic appearance. Minimum recommended wall thickness in this case is 2.03 – 2.29 mm. Since the smaller surface area is used to create a weld with step joint design, it could have lower strength than butt joint design.
Following dimensions for energy directors are typically recommended:
Sharper apex angle provides greater weld strength and ensures tight seal. Such design also works well with polycarbonate and acrylic.
Butt joint is one of the most common weld configurations used with energy directors. Hermetic seal may not be easily achieved in semi-crystalline polymers as they crystallize faster when exposed to air atmosphere. However, hermetic seal can be obtained with amorphous polymers provided good alignment of mating parts with additional fixtures.
Tongue and groove joint design does not require additional fixtures for proper alignment. Molten plastic is fully enclosed in the groove providing aesthetic appearance. Minimum recommended wall thickness is 3.05 – 3.12 mm.
Shear joints.
Some applications require the plastic welds to be hermetically stable. To satisfy this requirement, shear joints are typically used instead of energy directors. To achieve proper sealing, small tolerances are necessary. Such a stipulation could be difficult to satisfy with larger parts.
When a shear joint is assembled, top part contacts the bottom one along a thin edge, which is the first section to melt. This molten material then flows along the side wall of the bottom part filling up the gap between the parts. While a shear joint provides alignment for mating parts, it often requires additional fixtures to support the top part of the joint from deflecting outwards as it experiences pressing force from the tool. To mitigate the risk of deflection, robust design of the top part ensuring sufficient stiffness is essential.
Shear joints can be used with all polymers. They are well-suited for cylindrical parts.


Blow fill seal

Blow-Fill-Seal, also spelled as Blow/Fill/Seal, in this article abbreviated as BFS, is an automated manufacturing process by which plastic containers, such as bottles or ampoules are, in a continuous operation, blow-formed, filled, and sealed. It takes place in a sterile, enclosed area inside a machine, without human intervention, and thus can be used to aseptically manufacture sterile pharmaceutical or non-pharamceutical liquid/semiliquid unit-dosage forms. BFS is an advanced aseptic processing technology that is typically used for filling and packaging of certain sterile liquid formulations like liquid ophthalmics, inhalational anesthetics, or lavaging agents, but can also be used for injectables, parenteral medicines, and several other liquid or semiliquid medications, with fill volumes ranging from 0.1...1000 cm³. Compared against traditional glass ampoules, BFS ampoules are inexpensive, lightweight, and shatterproof.
History.
BFS was developed in the early 1960s at Rommelag. In 1963, Gerhard Hansen applied for a patent on the BFS process. Originally, it was used for packaging of non-sterile products, such as non-sterile medical devices, food, and cosmetics. In the early 1970s, Rommelag's Bottelpack system was first used for packing large volume pharmaceutical solutions. By the late 1980s, BFS had been well-established in the packaging industry, especially for packaging pharmaceutical and healthcare products. During the 1980s and 1990s, BFS came into use for the now common small volume unit-dosage forms. Since the early 2000s, BFS has been emerging as the preferred packaging process for parenteral products.
BFS process.
The BFS process functions similarly to conventional extrusion blow molding, and takes place within a BFS machine. First, a plastic polymer resin is heated to >160 °C and compressed to 35 MPa, allowing it to be extruded in tubular form, and be taken over by an open two-part mold to form the container. Then, the mold closes which welds the bottom of the container. Simultaneously, the parison above the mold is cut, or the filling needles are placed in the parison head without the parison being cut (rotary BFS type). Next, a filling mandrel with blowing air function is placed in the neck area that seals the container. Sterile compressed air is then introduced through the filling mandrel to inflate and form the container. In the BFS process for smaller ampoules the compressed air system is avoided by using vacuum forming the container instead. After the BFS container has been formed, the desired liquid is filled into the container through the filling mandrel unit. Then, the filling mandrel unit is lifted off, and the head mold hermetically seals the container. Simultaneously, the head contour is formed by vacuum. In the last step, the mold opens and the finished container leaves the mold.
One process cycle takes a few seconds. The process speed and thus process output largely depends upon the BFS container size and the BFS machinery dimensioning. For instance, in the early 2000s, Rommelag's 3012, 305, and 4010 M machines had outputs of approximately 4000, 8000, or 20,000 containers per hour. These machines have been succeeded by the Rommelag 312, 321, 360, 364 and 460 machines with output ranges of up to 35,000 containers per hour.
Sterility requirements.
The BFS processes is an aseptic filling process, which produces sterile products and thus needs to be sterile. Aseptic BFS machines must be designed in a way that prevents extraneous contamination. Thus, rotary-type BFS machines are placed in classified areas same as shuttle-type BFS machines (open parison), which have a cleanroom shroud grade-A-compliant provided with sterilised air and kept under overpressure. Automatic SIP programs are used to sterilise the BFS equipment and this avoids human interventions. Due to automatic start up and filling processes BFS machines require no human interaction during the actual BFS process. However, certain adjustments or interventions need to be carried out by personnel. Both particle and microbiological contamination monitoring are required in a BFS machine environment, as well as routine CIP/SIP processes. BFS machines are typically fitted with several different sterilising air filtration systems for the buffer air, support parison air and air shroud grade A air (if needed for shuttle machines, e. g. open parison type ones). Typically, the air is sterilised by filtration systems that have automatic filter integrity testing installed (i. e. automatic water intrusion or particle testing). The air systems are typically integrated into the SIP cycle of the BFS machine.
BFS material.
The materials used in BFS packaging are usually polyolefins, mainly polyethylene (LDPE or HDPE), and polypropylene (PP). These materials are robust and inert to ensure sterility and tightness during the product's shelf life. Diffusion tendencies can be reduced by using virgin polymers, but diffusion cannot be prevented entirely. This is due to the nature of polyolefins and their additives, if present. Several polyethylene suppliers have developed special EP or USP grade resin for BFS containers. Permeation into BFS containers and water loss may be an issue with some BFS resin. Therefore, in some applications, secondary packaging methods (laminate pouches) are used.
Advantages.
BFS allows many different container designs, a consistent high process quality, a high process output, and is, compared against other packaging processes, inexpensive. In addition to that, BFS containers are lighter than glass containers, and shatterproof, which eases their transport. Due to the single-dose nature of BFS containers, they are more convenient to use for patients. BFS technology assures high levels of sterility, especially compared against conventional filling, which is mainly achieved by the absence of human contact/interventions – a major source of contamination.


Elmos Semiconductor

Elmos Semiconductor SE is a German manufacturer of semiconductor products headquartered in Dortmund, North Rhine-Westphalia, Germany.
Elmos supplies automotive application-specific integrated circuits (ASICs).
Silicon Microstructures.
Silicon Microstructures, Inc.(SMI) was founded in 1991 as a commercial source of high-performance silicon pressure sensors, including Microelectromechanical systems sensors, and accelerometers. Its first product was a silicon sensor for very low-pressure usage. SMI was acquired in March 2001 from OSI Systems.
SMI began production on higher performance, system level sensors and microstructures, wireless, RF and bus addressable microstructures.
In August 2002, SMI acquired the IC Sensors' wafer fabrication operations and wafer R&D group and relocated to Milpitas, California. The following year, Silicon Microstructures undertook a significant and complete wafer fabrication upgrade to expand the facility for full 6" wafer handling.
This facility processed primarily 6 inch wafers and has advanced technical capabilities including deep reactive ion etching (DRIE) and plasma enhanced fusion bonding.


Tetrapolar plug

A standard tetrapolar telephone plug in electronics and telecommunications, has four round metal pins and one plastic pin. The design is only used in Belgium for telephone wiring. It is similar to the tripolar telephone plug of Italy and also the Swedish telephone plug.
The plastic pin adds a presence function. When not inserted into a jack, the jack itself (mechanically) connects the incoming line to the next socket. The article on the Swedish telephone plug details its functional principles.


Bar puller

A bar puller is a tool for automatically drawing in material (round tubes or solid bars) on a CNC lathe. The machined part is cut off and new material has to be fed into the machine.
Function.
Bar pullers are used in CNC lathes to automatically draw in bars from the clamping chuck. In this case they serve as a substitute for a bar feeder on an NC/CNC lathe.
The clamping chuck is fitted directly into the turret of the lathe or into the bar holder. There are two different versions, depending on the design: Start on the X-axis (starting from the radius) or start on the Z-axis (direction of the spindle).
A bar feeder magazine and workpiece stop are not required when a bar puller is used.
Material.
The housing can be made of aluminium or steel, the top jaws are made of case-hardened steel, tempered steel and burnished.
History.
The history of the bar puller begins with the introduction of the NC/CNC lathes in around 1980. At this time lathes were changed to permit inexpensive and economical production of small or medium-sized batches.
The bar puller serves to draw bars into the lathe without operators having to feed the machine with material each time it is required. With the introduction of CNC (Computerized Numerical Control) for the lathes it was possible to ensure the reliability of the individual process operations (moving the turret to the material, opening the clamping chuck, drawing in the material, closing the clamping chuck, moving the turret away with the bar puller).