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THE FABRICATOR®
Flatness in coil processing operations: New turns in the leveling process
By Eric Theis, Contributing Writer
August 16, 2001
Most flat-rolled coil processing operations use some sort of roller leveling technology. Operations people understand what these machines can do to improve the quality of the product they produce. In the competitive marketplace, customers demand and get more that just flat sheets or slit coils.


Figure 1:
The different colors shown here indicate how much force or stretching is involved in bending metal over a roll without strip tension.
Precision Roller Leveling With Tension
Some coil processing lines now add tension to the leveling process. This process extends the lower capacity range of the precision roller leveler, produces greater stability in the metal, and may even make the metal flatter.
In a roller leveler, the material is alternately bent up and down, stretching the outside and comressing the inside of each bend. On the first bend, the bottom is stretched and the top is compressed; on the second bend, the bottom is compressed and the top is stretched, and so on. The neutral area in the middle is neither elongated nor compressed past the yield point. Permanent change in the metal is strictly on the surfaces.
A computer analysis of tension and compression forces is shown in Figure 1. The different colors indicate how much force or stretching is involved in bending the metal over that particular roll diameter. The stresses or force, and therefore the strain or stretching, are symmetrical about the center of the cross section.
The yellow, green, and purple areas are completely symmetrical about the neutral fiber (the center part that is neither compressed nor stretched). The yield point is exceeded in the red areas. Where it is yellow, the material is right at yield point. In the blue and green areas, the material is in the elastic range, and no permanent change has been made.


Figure 2:
The computer analysis shown here indicates the level of force or stretching that is found when tension is applied to the strip.
Putting the material under tension as it goes through the flattener or leveler moves the neutral fiber toward the inside of the bend. The strip tension adds to the bending tension on the outside of the bend. It subtracts from the bending compression on the inside of the bend. There is less compression on the inside and more tension on the outside. Therefore, less elongation occurs on the inside of the bend, while more occurs on the outside of the bend. The neutral fiber moves toward the inside radius of the bend.
Figure 2 shows the computer analysis again, this time with tension on the strip. This time the stress pattern is not symmetrical. With the material under tension, the neutral fiber moves toward the inside of each bend, first toward the top surface, then toward the bottom surface in the next bend, then toward the top surface again, and so forth. The process is reversed again and again as the material progresses through the flattener or leveler. By the time the metal exits the machine, it has exceeded its yield point on more or possibly all of the cross section, not just the top and bottom surfaces.


Figure 3:
A pair of large driven pinch rolls provides tension immediately following the leveler.
Leveling with tension assist can go up to 1/2-inch or even 5/8-inch thickness capacity, which would be difficult with a tension leveler. The depth into the cross section at which the yield point is exceeded depends on the amount of tension. In the installation shown in Figure 3, a pair of large, driven pinch rolls provides tension immediately following the leveler. An on-the-fly cut-to-length shear follows the pinch rolls.
On-the-fly shearing eliminates the need to stop the line for the cut. For example, it may not be practical to loop heavy plate coil, but if the line is stopped for cutting, whether under tension or not, a set mark could be made on the material surface. Also, tension in the leveler would be loosened, resulting in leveling discontinuity. This can be avoided by using on-the-fly, nonstop shearing. The line in the lead-in photo completes a 5,000-pound sheet lift in less than 30 seconds.
Leveling in the Slitting Process
What about leveling in slitting lines? If a coil that has a typical crown or thick center is slit, the center mults on the recoiler will have a larger diameter than the outer mults. That makes the center mults wind quicker, while the outer mults wind slowly and more loosely, with the apparent excess hanging down into a loop.
Years ago, paper would be stuffed into these loose outer mults so that they would act as though they were the same diameter as the center cuts, winding tightly in the process. Today, the American National Standards Institute (ANSI) B11.14 standards for slitting safety, applying to line owners and operators alike, prohibit paper stuffing unless the line is stopped or the operator is protected. Stuffing paper or cardboard is no longer necessary because slitting technology has eliminated the need to do it.
Thirty years ago, friction drag devices were developed to put tension on all the strands or mults going onto the rewind mandrel.
The apparent excess strand on the outer, looser mults was allowed to hang down into a looping pit between the slitter and drag device. That solved the differential strand rewind issue but introduced new problems. Aside from having to dig, clean out, and walk around the pit, any dirt or grit in the friction drag devices could scratch or imprint the coil surface.
In addition, coil shape and straightness could not be better than the master coil, and was often worse. Leveling individual narrow mults after slitting was neither mechanically nor financially feasible.
Slitter-induced cross bow is another problem. It will not occur in a perfect setup: the male and female stripper rings are exactly right, the slitter knives are sharp and set up correctly, and the slitter arbors do not deflect. Of course, most setups are not perfect.
An imperfect slitter setup puts alternating up/down cross bow into each piece. The first cut pushes from the male down into the female. The second cut pushes from the male up into the female, then down, up, etc. The result is individual mults with alternating edges up and edges down. This is a problem for critical stamping applications, roll forming, and tube making because the up-bow mults do not run parts quite the same as the down-bow mults do.
Stampers, tube makers, and roll formers sometimes ask the slitter to rotate every other slit mult 180 degrees so all the burrs and cross bows are in the same direction, in hopes that this will solve the problem, at least on narrow strands. What actually happens is that the master coil comes from the mill with cross bow, and that cross bow adds to the cross bow from the slitter on the first cut, subtracts from it on the second cut, adds to it on the third cut, etc. The result is one mult that is bowed, one that is flat, one bowed, one flat, and so on. Rotating or twisting alternate slit mults 180 degrees will not eliminate this problem, but it will put all the slitter burrs in the same direction.


Figure 4
Leveling with tension assist of each strand immediately after sliting and before recoiling can help contrpl many of the problems associated with cross bow.
A Nonconventional Slitting Process
Leveling with tension assist of each strand immediately after slitting and before recoiling can help eliminate these problems. That is what Strand ExtensionerTM, a proprietary slitting process developed by the author's company, does. This particular slitting line configuration was originally developed to elongate the thicker center strands that would otherwise recoil faster and tighter. When this process is used, all strands rewind tightly without dangerous paper stuffing or a friction drag device and looping pit. Most of these lines sit on a flat floor.
With this process, the line operator stands at the main control panel, away from the dangerous recoiler nip, and changes the amount of elongation in the tight mults by flipping a control lever. Just as with a roller leveler, the operator can elongate some parts of the coil relative to other parts by adjusting the backup roller flites to deliberately vary the sink or penetration of the upper and lower work rolls (see Figure 4) at different points along the face of the machine.
On a conventional slitter, splitting a coil with a thick or crowned center results in two cambered strips curving toward each other on the recoiler. They squeal as they bind against the overarm separator on a pull-through line. Sometimes, a scrap center cut can prevent this problem. The slit mults can be steered onto the recoiler with a drag and pit line, but there are still two cambered halves. With this proprietary process, the center can be stretched, steering the two halves on the recoiler, without the help of a separator at the recoiler and without making a scrap center cut.


Figure 5:
In tension leveling, the coil is put under significant tension between pull and drag bridles placed before and after the roller-leveling device.
Tension Leveling
In tension leveling, the coil is put under significant tension between pull and drag bridles placed before and after the roller leveling device (see Figure 5). With tension leveling, all parts of the metal are pulled past the yield point, top to bottom and edge to edge. All the previous history of trapped stress should be deleted. The material should be perfectly flat and relatively free of internal stresses.
Tension leveling usually is restricted to the gauge thickness of metal. Because of the massive equipment and horsepowers involved, full tension leveling usually is not practical for thicker hot-rolled plate coils. However, more and more tension leveling lines are being found processing cold-rolled steel and aluminum products in toll processors and service centers.


Figure 6:
A temper mill and matched precision leveler can produce plates that are entirely flat and stay that way.
Trapped Stresses and Stability
A temper mill and matched precision leveler (see Figure 6) can produce plates that are entirely flat and stay that way. That is an important issue for working with heavy material.
Fabricators who use laser burning tables or turret punch presses want to ensure that their parts will stay flat. If trapped stresses are released by cutting or heating, the material will not stay flat. A temper mill in a cut-to-length line is primarily for surface effect, but used in conjunction with roller leveling, it can affect part stability and surface quality.
A temper mill can be used to flatten material, although not as effectively as a leveler. The temper mill primarily hardens the surface, raising its yield point without elongating it lengthwise, resulting in a better, smoother hot-rolled plate surface. It also increases the amount of elongation required to get beyond the elastic limit at the surface.
When plate is bent in a leveler, the surfaces are stretched or compressed in direct proportion to the distance from the neutral centerline. When the plate is unbent, that stretching and compression are reversed, also in direct proportion to the distance from the centerline. The problem with this reversal process is that where the metal surface has been forced past its yield point, it does not want to go back to zero, which means trapped internal stresses have been added. The random trapped stress in the received mill material may have been traded for a more consistent trapped stress, but it has not been eliminated.
The temper mill, on the other hand, raises the surface hardness of the metal, without lengthwise elongation, before the roller leveling process. Now, when the plate coil is bent over the leveling rolls, the extension required to exceed the yield point and permanently change the length of the surface relative to the core is higher than that required below the surface. Thus, the surfaces have no problem reverting to their original semiflat condition, and the remaining trapped stresses are minimized. The result is flat plate and stability.
The trapped stresses that come from the mill are variable and random. They are not consistent from one edge of the coil to the other, or from one end of the coil to the other.
A nonbacked-up flattener is used primarily for controlling coil set or longbow, an outer surface effect. Trapped stresses remain in the middle, so the metal is not stable. With a precision leveler, the yield point is exceeded about 80 percent of the way from the top and bottom surfaces toward the center. Only the 20 percent of the thickness in the middle has not exceeded the yield point, and thus it is much more stable. The addition of tension assist to the leveling process increases the depth of the yielding effect in the metal cross section. Adding a temper mill to a heavy cut-to-length line further reduces the remaining trapped stresses.


Figure 7: Recently, the I-unit of flatness designation, which takes into account both wave height and wave length, has been gaining more acceptance.
How Flat Is Flat?
Measuring, or even describing, flatness has been a tricky issue. In the past, ASTM flatness tolerances have described a maximum height of wave in 8 feet, without any mention of the number of waves in those 8 feet. In fabrication fit-up, it makes a lot of difference whether there is a 1/8-inch rise in 8 feet, or in every 8 inches. Recently, the I-unit of flatness designation (see Figure 7), which takes into account both wave height and wave length, has been gaining acceptance.
A cold mill can get less than 15 I-units of flatness. Coming off a temper mill, material may have less than 10 I-units. With a roller leveler, tension-assisted leveler, or tension leveler, the number may be 5 I-units, and possibly less than 1 I-unit. That is a big difference.
Leveler Maintenance Options
Keeping leveling equipment cleaned and well maintained is important. Options are available to help simplify maintenance work on these machines.
Most manufacturers offer optional work roll nest cassettes. These leveler cassettes can be pulled in and out of the leveler as a unit. More than one cassette may be used, sometimes with different roll diameters. Different cassettes can be put in, or they can be flipped open for cleaning, off-line. This option is recommended for production lines that will run continuously for three or four shifts. It is also recommended when leveling with tension assist of each strand after slitting because this method runs more coil in a given period of time. For a conventional service center cut-to-length line, this option may not be necessary. For a toll processor, it may be more attractive. Another option is a leveler with a roll-open top. The top frame opens like a book, either mechanically in the case of smaller machines or with hydraulic lifts. It is quick and exposes both the upper and lower roll banks for easy cleaning.
The simplest roll cleaning aid is an extra-high, wide-opening top frame. The upper leveler frame opens vertically to about a 4-inch gap so that cleaning equipment can work on the rolls.
Four-High, Five-High, and Six-High Levelers
The basic roller leveler is a four-high configuration. This is the most flexible from a shape control point of view. The back-up rollers will not wear grooves in the glass-hard work rolls under normal use, but they can burnish the surfaces of the work rolls. This burnish mark may leave an impression on the surface of soft, polished, or other flat-rolled materials. Although the impression is too small to measure, it is visible.
If such marking is a problem, a six-high leveler might be an appropriate choice. Full-length intermediate rolls support full-length work rolls, and they in turn are supported by flites of back-up rollers. A burnish mark on the intermediate roll does not transfer to the work roll. This configuration can be very stiff, and roll bend control may not be sufficient for optimum shape control.
On a five-high leveler, on which the back-up roller flite adjustment wedges usually are found, the intermediate rolls are eliminated but retained on top. On the bottom, the work rolls and their back-up roller flites give better roll bend flexibility for improved flatness control. On the top, the full-length intermediate rolls are retained between the work rolls and the back-up rollers to avoid striping. This means that the top surface of the coil will not be striped, but the bottom may be. Usually, however, only one side of a coil is critical.
Options on Levelers
Many of the newer levelers include operator's stations that hang from pendants or are mounted on swing-out hinges for easy control positioning at the machine exit. Other control features may include the following:
1. Automatic roll positioning "remembers" settings. It can remember specific coils if the operator wants to do re-books. The operator can ask the machine to go to 10-gauge cold-rolled steel, the coil from the second shift at a certain mill, and the control will remember the settings from the last time the operator ran that material and will go to that position automatically.
2. Automatic calibration simplifies recalibration after roll changes to adjust for changes in roll diameter. A properly designed leveler should not need recalibration between roll changes.
3. Computer fault finding diagnostics show on a screen what is wrong with a coil line. They generally indicate, on some items, what is going to go wrong before it does. For instance, if the oil level or pressure is low, the diagnostics will indicate that before lubrication runs out.
Summary
The addition of tension assist to the leveling process in cut-to-length or slitting lines can extend the capacity range and improve material stability. A temper mill paired with a leveler can also improve surface condition and hardness and further enhance stability. A number of options on newer equipment are designed to make operation, maintenance, and roll cleaning easier.

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该制造商®
平坦在线圈加工业务：新的转折的水准进程
由Eric泰斯，作出贡献的作家
2001年8月16日
大多数单位的冷轧线圈加工业务使用某种形式的轧辊技术水准。行动的人都明白，这些机器有什么可以做，以改善产品的质量，他们生产。在竞争激烈的市场，客户的需求，并获得更多刚刚单位表或狭缝线圈。


图1 ：
不同的颜色在这里显示表明，有多少武力或伸展是涉及在弯弯超过了唱名无带的紧张局势。
精密轧辊水准与张力
一些线圈加工流水线，现在新增的紧张局势，以平进程。这个过程中扩大了低容量范围的精密轧辊矫直机，产生更大的稳定性，在金属，甚至可能使金属奉承。
在一个轧辊矫直机，材料是交替一意孤行，向上和向下伸展外comressing内每个弯。关于第一弯，底部是伸展和顶端是压缩;关于第二个弯，底部是压缩和顶端是伸展，等等。中立地区，在中东既不是拉长，也没有压缩，过去屈服点。永久性的变化，在金属是严格对表面。
电脑分析的紧张局势和压缩势力，是如图1所示。不同的颜色显示，有多少武力或伸展是涉及在弯曲的金属，较特别是轧辊直径。该讲或武力，因此，应变或伸展，约是对称的中心截面。
黄色，绿色，紫色和地区是完全对称的关于中立的纤维（该中心的一部分，这是既不压缩也不紧张） 。产量超过一点是在红色地区。它是黄色，材料是正确的，在屈服点。在蓝色和绿色的地方，材料是在弹性范围内，并没有永久性的变化已经取得了。


图2 ：
计算机分析表明，此处显示的水平武力或伸展是时发现的紧张局势，是适用于带。
把材料置于紧张，因为这是不言而喻通过flattener矫直机的动作或中性纤维走向内弯曲。该地带的紧张局势增加了弯曲的紧张局势，外面的弯曲。它减去从弯曲压缩就内弯曲。有少压缩对内部和更多的紧张局势，对外开放。因此，少伸长发生在内部的弯曲，而更多的发生在境外的弯曲。中性纤维走向内半径的弯道。
图2显示计算机分析，这与时间的紧张局势，带钢。这个时候的应力模式是不是对称。与物质的紧张局势下，中立的纤维走向内每个弯曲，首先对顶面，然后对底部的表面，在未来弯曲，然后对顶面再次，等等。进程是扭转一而再，再而作为材料的进展，通过flattener或矫直机。由时间的金属出口的机器，它已超出其屈服点或更多的可能，所有的截面，而不只是顶部和底部表面。


图3 ：
一对大驱动的夹卷规定的紧张局势后立即矫直机。
平与张力，协助可以去到2英寸，甚至5/8-inch厚度的能力，这将是困难与张力矫直机。深入到横截面在哪个屈服点是超过，就看数额的紧张局势。在安装如图3所示，一对大，夹送辊驱动提供了紧张之后立即矫直机。一对- -飞横切剪切如下压力辊。
关于- -飞剪无需停止线的削减。例如，它可能是不实际的循环中厚板线圈，但如果是停止线切割，无论是下紧张或没有，一套马克可以作出对材料表面。此外，紧张局势在矫直机会松脱，导致在水准间断。这可避免使用对- -飞，直飞剪切。该行中，铅在照片完成了5000磅的资产负债表电梯，不到30秒。
水准，在切分过程
什么水准约在纵剪线？如果一个线圈有一个典型的官方或厚的中心是狭缝，该中心mults就recoiler将有较大的直径比外mults 。这使得该中心mults风更快，而外层空间mults风慢慢和更松散的，明显超出吊下来成为一个循环。
几年前，文件将塞进这些松散的外mults ，使他们将作为虽然他们都是一样的直径为中心的削减，紧紧缠绕在这个过程中。今天，美国国家标准学会（ ANSI ） b11.14标准分条机，安全，适用于符合业主和经营者，都禁止文件馅，除非线是停止或经营者的保护。馅用纸张或纸板不再是必要的，因为切分技术，消除了需要做的。
三十年前，摩擦拖动装置被发达国家提出的紧张局势，所有strands或mults去上倒带芯棒。
明显超过钢绞线上外，宽松的mults被允许坑下跌成为一个缝盘坑之间的纵切并拖动装置。这解决了微分钢绞线倒带问题，而是介绍了新的问题。除了具有挖掘，清理，走动一事，任何污垢或沙砾在摩擦拖动装置，可以从无到有，或印记线圈的表面。
在此外，线圈的形状和直线不能优于主线圈，往往是更糟。找平个别狭隘的mults后，纵剪既不是机械，也没有在财政上是可行的。
分切机诱导两岸低头是另一个问题。它不会发生在一个完美的格局：男性和女性汽提塔戒指是完全正确的，纵切刀，是夏普和正确设置，及分切机乔木不偏离。当然，最设置还不完善。
一个不完善的分切机安装了交替向上/向下交叉低头到每一块。第一削减推动从男性为女性。第二削减推动从男性成女性，然后下降， ，等结果是个别mults与交流的优势和优势。这是一个问题的关键加盖印花申请，滚压成形，管决策，因为设立低头mults不运行的部分不尽相同，作为向下低头mults做的。
母碟，管制造商，和轧辊成型，有时要求分切机旋转，每其他狭缝多180度，使所有的毛刺和跨弓箭是在同一方向，在希望这将解决这个问题，至少在狭窄的strands 。究竟情况是，主线圈来自轧机与两岸低头，并表示，两岸低头，增加了两岸低头，从纵切关于第一削减，减去从它关于第二个削减，增加了它的关于第三次削减等。其结果是一多是低头，是一个单位，一鞠躬，一个单位，等等。旋转或扭候补委员，狭缝mults 180度将不会消除这个问题，但它将把所有的分切机毛刺在同一方向。