Common Questionsand Misconceptions

Misconception: While there is a growing emphasis put on the use of blanks, there remains confusion in regards to the actual definition of a Cut‑To‑Length Line as opposed to a Blanking Line, and a blank as opposed to a sheet.

Clarification: A blank is generally thought of as a relatively close tolerance part. Typically, it is already cut to a specific size. As a result, a blank normally goes directly into the next manufacturing process without being resheared.

A sheet on the other hand is cut to a standard size which is later resheared before use.

Cut‑To‑Length Lines are generally thought of as systems that produce sheets while Blanking Lines, utilizing close tolerance Feed Systems in conjunction with Edge Trimmers or In‑Line Slitters, have the ability to produce sheets as well as close tolerance blanks.

Summary: Typically, the two systems are quite similar, the main difference being the Measuring System they incorporate.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: Aluminum normally takes less force to cut than steel. Consequently, it is common belief that it is easier to level as well.

Clarification: In order to induce permanent set into a particular type of material, the material must be stretched beyond its yield. If yield is not exceeded, the material will spring back to its original shape.

All steels have the same elasticity regardless of tensile or yield strength; that is, until the yield point is reached, they all stretch the same amount under a given load.

As compared to steel, aluminum is more elastic; that is, it will stretch more under the same load. As a result, aluminum with the same yield strength as steel requires more elongation to induce a permanent set.

The work rolls must be entered deeper resulting in increased machine loading, deflection, and power requirements. Likewise, an exotic material such as titanium which is even more elastic is exceedingly more difficult to level.

Summary: Because aluminum is soft, it requires less tonnage to cut. The leveling process however has a direct relationship to the material’s elasticity. The more elastic a given type of material, the more difficult it is to level.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: In some applications, looping type CTL/Blanking Lines can reintroduce set back into the strip after it has already been leveled. While this is a true statement, it is often perceived as an inherent problem associated with this particular type of line.

Clarification: A looping type line operates with an accumulation loop located between the Leveler and Feed. The loop allows the material to be leveled continuously while the Feed stops it momentarily for shearing.

Because the material is leveled prior to entering the loop, a radius of sufficient size must be maintained as the material passes through the loop in order to prevent the reintroduction of set back into the strip.

If this bend radius were too small, the material would be stretched beyond its yield point resulting in the reintroduction of set.

Because of its low yield, soft steel typically requires much larger radii while very elastic material such as aluminum requires somewhat less.

Normally, the distance between the two ramp radii used to assist the material in and out of the loop are spaced apart twice this radius. As the material passes through the loop, it sags between the ramps creating a half circle. This half circle is referred to as a full loop.

Summary: Looping Lines will reintroduce set into the strip if the appropriate radius is not used. The size of the radius is strictly a function of the gage, yield, and type of material to be processed.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: Although distinctly different, these specifications are often misinterpreted as having the same meaning.

Clarification: Repeatability refers to the ability to repeat or duplicate a given set of conditions or circumstances within a specific range or tolerance. “Machine” repeatability refers to the ability of a particular machine to mechanically repeat a motion or action.

As an example, in the case of a roll Feed, if the Feed reportedly has a machine repeatability of ±.005″ (0.127 mm) the machine would supposedly mechanically repeat within ±.005″ (0.127 mm).

“Part” repeatability refers to the dimensional deviation between the parts produced during a particular process. If a system has a stated part length repeatability of ±.005″ (0.127 mm), hypothetically the length of the parts produced during this process will not deviate more than ±.005″ (0.127 mm) from one piece to another.

Summary: While machine repeatability directly relates to the part tolerances, a machine can potentially produce, it refers to only the machines mechanical ability to repeat.

Although machine and part repeatability can be theoretically the same, because of other influences, the two are generally different. Part repeatability refers to the finished product; as a result, it is the most meaningful of the two statistics.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: It is sometimes suggested that pull‑off type Uncoilers will stretch thin and/or soft material during continuous line operation. Consequently, a powered payoff type Uncoiler should be used in these applications. Is there a factual basis to substantiate this claim?

Clarification: Uncoiler are used in two basic modes of operation. A powered type Uncoiler is driven in order to produce a slack loop of uncoiled material between the Uncoiler and Leveler. This slack loop provides loose material to feed into side guides allowing the strip to be aligned prior to entering the Leveler.

A pull‑off type Uncoiler is typically powered for threading purposes; however, once in operation, it becomes a pull‑off where the material is simply pulled from the coil.

To prevent jerking and ensure smooth payoff, the unit incorporates a drag brake in order to maintain constant tension on the material between the Uncoiler and Leveler.

A Traversing Base allows the Uncoiler to move laterally. The lateral movement is used to keep coils running on centerline. If the material walks off center, the Uncoiler automatically compensates by moving in the opposite direction until the strip is centered.

Summary: Although a pull‑off Uncoiler creates tension on the strip, minimal back tension is required for proper operation.

Because the amount of tension needed is directly related to the gage and width of the material i.e. the heavier the material the greater the tension, the material most susceptible to damage requires the least amount of tension.

As a result, the likelihood of the material being stretched during normal operation is extremely remote. To the contrary, because pull‑off Uncoiler align the strip by moving the entire coil laterally, edge guides are eliminated. Consequently, a pull‑off Uncoiler is particularly well suited for this application.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: While Edge Trimmers are often used to trim a strip to a specific width prior to being cut‑to‑length, the process is often perceived as having the ability to eliminate camber as well.

Clarification: Virtually all material has some degree of camber. There are two forms.

The most predominate is dubbed “sweep”. Sweep refers to a strip in which the curvature of the material continues in the same direction throughout the coil. This would be representative for most mill coils.

A second less frequent type of camber is termed “snake”. Snake refers to a strip where the curvature alternates from side to side. Both forms result from one edge of the strip being longer than the other. In order to actually remove camber, the short edge of the strip would have to be elongated by stretching it or the material would have to be physically sheared on all four edges on a sheet Shear.

Typically, as the material tracks through an Edge Trimmer, it duplicates the camber already present in the strip. The strip steers through the knives as a car would negotiate a curve. Without this steering action, the knives would eventually run off the strip.

Summary: Although Edge Trimmers can accurately trim a strip to a specific width, these units do not have the ability to remove camber.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: It is fairly common for some manufacturers to locate the Edge Trimmer before the Leveler while other manufacturers locate the unit directly after. Is there a reason for doing so?

Clarification: With any slitting/shearing process, there is stress induced into the material as it is cut. Typically, the heavier the material and the narrower the strip, the greater the potential stress. By locating the Edge Trimmer before the Leveler, the strip is leveled after being trimmed thereby reducing this stress.

The Leveler also has a tendency to knock down the burr which may have resulted from the slitting process. Although locating the Edge Trim before the Leveler has benefits, it also has potential limitations as well.

Because the strip is first trimmed and then leveled, shape irregularities in the strip can affect tolerances. In addition, the leveling process itself can cause infinitesimal dimensional changes to occur as well.

Edge Trimmers positioned behind the Leveler trim the material after it has been leveled. Consequently, shape irregularities are removed prior to trimming and optimum tolerances can be achieved.

Summary: Typically, either configuration will work equally well. While both approaches have theoretical reasons for doing so, the benefits of one over the other are minimal.

The stress induced into a strip, especially a wide strip which is normally the case when you are edge trimming, is inconsequential. The Leveler can cause dimensional changes to occur. However, these changes are insignificant as well.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: While Leveler designs may vary from manufacturer to manufacturer, there are basic fundamentals that ultimately determine a leveler’s configuration for a specific application.

Clarification: The most important consideration when selecting a leveler is work roll diameter and roll spacing. The diameter of these rolls will determine the gage range the machine can effectively level.

As an example, a 1.75″ (44 mm) diameter roll would typically have an effective range of .024″ (.610 mm) through .134″ (3.4 mm) mild steel, while a 2.187″ (56 mm) diameter roll would be limited to .036″ (.914 mm) through .164″ (4.17 mm) mild steel. Normally, these ranges will vary only slightly between manufacturers.

Levelers are often referred to as 4, 5, or 6 HI. A 4 HI machine consists of upper and lower work rolls and a group of upper and lower backups. A 5 HI unit refers to a machine that also incorporates a full width intermediate roll normally between the top work rolls and the adjustable backups.

A 6 HI machine utilizes intermediate rolls on the top and bottom. This extra set of rolls eliminates backup roll wear on the work rolls which might otherwise mark soft or surface critical material. Marks resulting from worn work rolls are often referred to as skunk or zebra strips.

Summary: When purchasing a new leveler, the manufacturers will select an appropriate unit based on your specifications. If you’re purchasing a unit on the used market, do not be mislead into purchasing a leveler with 3″ (76 mm) rolls if your primary application is .048″ (1.22 mm).

Consequently, although a 4 HI Leveler with reground work rolls can adequately level aluminum, marking will occur once the rolls wear slightly. For consistent long term results, a 6 HI machine should be employed.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: While virtually everyone in manufacturing has been exposed to the problems caused by camber, uncertainty remains regarding how camber is defined and to what degree it influences part tolerances.

Clarification: Camber is the deviation of a side edge of a strip from a straight edge. It is caused by one side of the strip being longer than the other.

Camber is measured by placing a straight edge on the concave side of the strip and measuring the distance between the straight edge and the sheet at the center most portion of the arc. When possible, this measurement should be taken over a span of 20’‑0″ (6096 mm). This increment serves as a good benchmark since this is the length mills refer to when referencing camber.

The standard mill specifications for camber is 1″ in 20’‑0″ (6096 mm). Most mills normally offer a quarter of this tolerance of .25″ (6.35 mm) in 20’‑0″ (6096 mm). However, the majority of commercial grade coil produced today generally has less than this amount. It is also important to be aware of the fact that because camber is a continuous curve or radius of the strip, if you have a given amount of camber in a specific distance, if you double this distance, the camber will increase by four times that amount.

As an example, a camber statistic of .0625″ (1.59 mm) in 6’‑0″ (1829 mm) appears to be relatively small when mathematically projected over 20’‑0″ (6096 mm). This figure is actually .6875″ (17.45 mm) which is considered excessive.

Summary: Camber is the most prominent factor influencing part tolerances. In order to produce close tolerance parts without reshearing, camber must be minimal. The tighter the tolerances required the less camber that can be tolerated.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: Because of their widespread use in Blanking Lines, the bow tie Shear is often perceived as being capable of producing better tolerances than standard rake Shears.

Clarification: A Shear’s design in regards to the type of blade used has no direct bearing on the tolerances a particular line is capable of producing. The tolerances achieved are primarily a function of the type of Measuring System the line incorporates and how the material is presented to the Shear.

A Shear can, however, influence the actual tolerances yielded if the strip is not held adequately while being sheared. If the material is allowed to shift, the finished part will be affected.

Normally straight rake Shears utilize a material hold down to hold the material in position during shearing. Some bow tie Shears rely solely on the action of the blade entering simultaneously from both sides and moving towards the center of the strip to maintain position while others incorporate a hold down as well.

Summary: In reference to tolerances, either type of Shear is suitable. However, a hold down is highly recommended to achieve optimum results.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: It is common belief that straight blade or standard rake Shears have a tendency to bend one corner of the sheet being cut. The use of a bow tie Shear has been associated with the solution to this problem.

Clarification: When used in certain applications, standard rake Shears have been known to bend down one edge of the strip as it is being cut, while in other applications it does not.

In order to understand what causes the problem, you must look beyond the Shear. Under close observation, you will find that it is not the type of Shear that actually causes the problem. It is the lack of support beneath the material while the strip is being cut.

Because a straight rake Shear cuts from one side of the strip to the other, if the material being cut is not supported as the Shear blades cut across the material, the side of the strip the blades first entered will sag causing the strip to twist.

The wider the strip and the further the blades enter, the greater the bending load on the remaining uncut portion of the strip.

As a result, before the full width of the material is severed, this twisting action causes the corner of the opposing edge to bend under the weight of the sheet. Normally, the slower the Shear the more pronounced the problem.

The bow tie Shear came into general use with the development of lines requiring Shears with high cycle speeds.

Bow tie blades with equal rake from both ends to the center of the blades shorten the stroke, cutting in half the overlapping of the blades at the bottom of the stroke. As a result, although the tonnage requirements are typically double those of standard rake Shears, their cycle speeds are much higher.

Summary: Under certain circumstances, a straight rake Shear can bend the edge of a sheet. However, this occurrence is due to the lack of material support and not the Shear itself. As a result, when properly applied, the standard rake Shear will produce satisfactory results. The use of a bow tie Shear is dependent on Shear cycle speed requirements.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: It was once common practice for manufacturers to locate the Leveler after the Shear. However, today most manufacturers position the Leveler before the Shear. What is the reason for doing so and how does Leveler location affect the finished parts?

Clarification: When Levelers first came into widespread use several decades ago, it was typically located after the Shear. While this position offers the simplest integration into the line, it also imposed certain limitations.

Because parts were measured and cut-to-length prior to being leveled, shape irregularities could affect part tolerances. The leveling process could also change the parts dimensionally.

As a result, as part tolerances became more critical, manufacturers began locating the Leveler before the Shear. This allowed the Leveler to operate continuously while permitting the strip to be leveled prior to being measured and cut‑to‑length.

Locating the Leveler before the Shear also eliminates the tendency of the entry Leveler rolls to mark the leading edge of each sheet.

Summary: To simplify installation, the practice of installing the Leveler after the Shear is still used today occasionally when adding a Leveler to an existing line. However, because of the benefits, most new systems manufactured today place the Leveler before the Shear.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: It is relatively common to see some lines incorporating both a Straightener and a Leveler while other systems use only a Leveler. What’s the difference?

Clarification: The practice of using both a Straightener and a Leveler in the same line varies from manufacturer to manufacturer. Typically, if both machines are used, the manufacturer will contend that by using a Straightener to remove coil set prior to leveling, better flatness can be achieved.

Manufacturers that use only the Leveler maintain that when the strip is leveled, coil set is also removed as a consequence of the process and prior removal has negligible benefits.

Because the coil set in the material constantly changes throughout a coil, as with a Straightener, the first group of work rolls in a Leveler are actually used to induce reverse coil set into the strip.

This reverse set is constant, which the remaining rolls can flatten without constant roll adjustment. This basic principle of operation eliminates the necessity to precondition the strip.

Summary: In regards to effectiveness, either line configuration will produce satisfactory results. However, most equipment manufacturers that actually produce a Leveler state that prestraightening is not required.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: Although there has been widespread use of Straighteners and Levelers for decades, there remains a great deal of confusion regarding the proper application and capabilities of each machine.

Clarification: Conventional Straighteners, sometimes referred to as Flatteners, incorporate a series of large diameter work rolls. Typically, between five and eleven rolls are used.

As the material passes through the rolls, it is alternately bent from the tangent of one roll to the tangent of the next. As a result of this bending process, coil set and crossbow is removed.

However, because this bending motion is restricted to one axis, i.e. up and down in the same horizontal plane, Straighteners cannot correct side to side strip length variations.

A similar machine used to remove coil set is the precision Straightener. The precision Straightener incorporates a series of relatively small diameter work rolls. Backups are used to maintain parallelism between the top and bottom rolls.

Because of their similarities, a precision Straightener can be mistaken for a roller type corrective Leveler. However, unlike the Leveler, the Straightener’s backups are fixed. As a result, a precision Straightener is also limited to the removal of coil set and crossbow.

Similar to the precision Straightener, a corrective Leveler incorporates a series of closely spaced relatively small work rolls. Along each roll are backups. However, the Leveler’s backups can be adjusted to intentionally deflect a portion of the corresponding roll.

Thus, if the material contains an edge wave, the rolls are deflected at their centers and the opposing edge. This stretches the center and opposing edge of the strip while leaving the wavy edge its original length. This stretching equalizes the strip dimensionally resulting in flat material.

Summary: While there are similarities between machines, there are evident differences between Straighteners and Levelers. Although a precision Straightener can work material more than a conventional Straightener due to the size and number of work rolls, the benefits of a precision Straightener over a conventional unit are marginal.

Both machines are limited to removing coil set and crossbow. In applications where the removal of coil set and crossbow is sufficient, either configuration will work satisfactory. Application that necessitates optimum flatness requires a corrective Leveler.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.

Misconception: Line speed is a specification often used to help determine the production capability of a line. Line speed refers to the speed of the material during normal line operation. However, line speed is often misinterpreted as system output or yield which actually refers to the amount of material processed in a given minute.

Line speed and yield would be identical if you were evaluating a continuously operating processing line such as a Slitter. However, it is frequently misapplied to intermittently operating or variable speed Cut-To-Length Lines.

Clarification: In the case of a start/stop Cut-To-Length Line, line speed refers to the speed of the material while it is moving. However, because this type of system operates intermittently, the material is stopped momentarily while it is being sheared. As a result, yield differs from actual line speed.

A dual speed hump table Cut-To-Length Line operates with two speed modes, in one mode line speed is relatively high. However, while the strip is being sheared, the line is in a creep mode and the material is actually moving considerably slower.

Consequently the yield is an average between the two speeds and the duration of time spent in each mode.

The Feed System in a looping type line operates intermittently. An accumulation loop between the Feed and Leveler allows the material to be leveled continuously while the Feed stops the strip momentarily for shearing.

While feed speed may easily exceed 600 FPM, because the material is stopped for shearing, yield again varies from actual line speed.

To determine yield, you must again average the feed speed, dwell time, deceleration and acceleration rates.

Summary: Although line speed and yield can be identical, there is a distinct difference between the two.

The most meaningful statistic is true yield. The easiest way to determine yield on any Cut-To-Length Line is to simply count the number of parts produced in a given minute and multiply that number by the part length. This will be the yield for that particular part.

In addition to part length, it is also important to consider the circumstances under which this speed was achieved, i.e. what type of material was being processed, how wide, what gage, and the part tolerance being attained.

These variables will ultimately determine the true yield a system is capable of producing.

Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.