March 11, 2004
Years ago it was customary for coil processors to have dedicated slitting lines for specific materials and gauges. Today's larger, stronger, and thinner-gauge coils, however, require service centers to be able to process many materials and gauges on the same machine.
Productivity is at the forefront for equipment builders today because their customers demand it, and processing margins for users of coil processing equipment haven't changed from years ago. For a company to be profitable, its equipment has to produce more. It's that simple.
To accommodate the ever-changing coil slitting industry, equipment manufacturers are building new features into their lines.
To minimize setup time, some lines have three- and four-head slitters that can be interchanged in less than a minute.
To minimize setup time, most lines incorporate two-head slitters and some have three- and even four-head slitters (see Figure 1) that can be interchanged in less than a minute. Powered slitter tooling lockups eliminate mechanical nuts. Uncoiler filler plates, separator tooling bars, tensioning devices, deflector rolls, and recoiler mandrels can be changed quickly as well.
In slitting, threading is paramount to productivity. A high passline configuration (see Figure 2) allows the uncoiler and recoiler to be close-coupled so the line threads quickly. With this configuration, material never is reverse-bent. Material is paid off the uncoiler and threaded through the line into the recoiler gripper slot hands-free.
A high passline configuration allows material to be threaded off the uncoiler, into the slitter, through the tension system, and into the recoiler gripper slot hands-free, which eliminates coil breaks because the material is never reverse-bent.
With the advent of larger, thinner-gauge coils, line speeds have had to increase to improve throughput. Some lines process material at 1,000, 1,500, or 2,000 feet per minute, depending on the minimum material thickness and coil size. The thinner the gauge and larger the coil, the faster the line should operate to reduce running time.
For thin-gauge processing, some coil processors drive the strip into a loop before the slitter so that it is slit under zero tension (see Figure 3). When the slitter pulls material off of the uncoiler under tension, the knives can slip, causing knife marks on the strip and premature knife wear. In addition, the post-slit loop is difficult to control if material slips in the slitter. Slitting material tension-free eliminates these problems, produces a good cut edge, and helps eliminate the inducement of camber into the strip.
For thin-gauge processing, some coil processors drive the strip into a loop before the slitter so that it is slit under zero tension.
It is increasingly common for large incoming master coils to be stored on saddles or turntables (see Figure 4) instead of turnstiles, because these storage devices are easier to load with a crane or forklift.
To handle the bigger coils, uncoilers and recoilers may be equipped with outboard bearing supports (see Figures 2 and 3). Coil loading cars are provided with more lift to handle a variety of coil outside diameters (ODs).
It is not uncommon for today's slitters to process coils measuring 20 to 30 inches inside diameter (ID); however, expanding mandrel uncoilers are designed to process sizes from 16 to 20 in. or 20 to 24 in.
To exceed that range, uncoilers can be equipped with quick-change steel plate quills that slide over the base mandrel to increase the ID. The quick-change quill is loaded onto the mandrel with the coil car and attached with two bolts. Changeover can be achieved in three minutes.
Four-position coil storage turntables are easy to load with a crane or forklift.
Entry crop shears often are used to remove the outside coil wrap. While the line is down, the shear cuts off the unwanted scrap material, and then it goes into a scrap collection car or onto a scrap conveyor that dumps it into a hopper.
A more productive option for removing the outside wrap is a turret uncoiler. While a master coil is running, the next coil in line can be loaded and sheared offline in an entry prep station. As soon as the master coil tails out of the line, the next coil is ready to go.
Depending on the thickness capacity of the line, scrap ballers, winders, or choppers are used to handle scrap.
Scrap ballers are most suitable for thin-gauge lines up to about 0.135 in. Edge trim is diverted into an accumulation area and wound offline. Because a scrap baller never tugs at the trim, it can handle narrower trim widths and thinner gauges.
Scrap winders are best-suited for intermediate- to heavy-gauge material. A scrap winder winds trim under tension as it comes out of the slitter.
Scrap choppers can process almost all gauges but are more commonly found on heavy-gauge lines because thick scrap is difficult to handle. The knives on the choppers must be sharpened as they wear. How often they must be sharpened depends on the material thickness, strength, and production requirements.
Many lines have the capability to inspect material as it is being processed. Material is run into an inspection station (see Figure 3) that comprises fluorescent and adjustable-flash-rate strobe lights to illuminate the strip.
In more complex lines, an inspection tower may be provided. With a tower, material flows out of the trimmer or slitter in the horizontal position. Deflector rolls within the tower divert material upward, laterally, and then downward so that an inspector can walk around the strip while it's running to inspect both the top and bottom.
The disadvantage of inspecting in the slitting line is that material must run at considerably reduced speeds to allow viewing of defects.
The larger coils being processed today require deeper looping pits, yet sometimes it isn't possible to dig a pit as deep as it should be. In those cases, a loop doubler can be introduced into the line. The doubler forms two loops in the pit instead of one.
Pad tension stands are acceptable for noncriticial-surface materials, heavy-gauge, and hot-rolled products, but they can damage light-gauge coated and surface-sensitive materials. Pad tension stands squeeze the material between two felt-covered platens operated by hydraulic or pneumatic cylinders.
Roll tension stands (see Figures 1 and 3) are suitable for critical surfaces. Quick-change roll sets provide back tension for running a variety of materials. The roll sets can come with nonwoven rolls for oiled products and various polyurethane coverings for dry, coated, painted, and bright metals. The rolls can be interchanged without the use of an overhead crane.
The roll sets are coupled with pneumatic brakes or motor-driven drag generators.
An inline leveler in four-, five-, or six-high configurations removes shape defects such as edge wave, center buckle, and slitter-induced crossbow. It also rolls over the burr caused by an improper tooling setup.
Positioned between the tension stand and recoiler, the leveler works the strip to eliminate undesirable shape conditions. The work rolls are arranged on close centers and supported by adjustable multiflight backup bearings to permit roll bending, which is critical to providing shape correction.
The inline leveler is used in conjunction with a looping pit to attain close-tolerance precision slitting. With a clustered roll design, one machine can process material from 0.015 to 0.250 in. thick.
A drawing lubricant may need to be applied to strip that will be stamped. Lubricant is pumped from offline storage drums through a heater to attain the proper viscosity and then applied to the strip via programmable logic-controlled nozzles.
Nonwoven applicator rolls with an adjustable nip are used to control film thickness. An enclosure encapsulates the lube applicator so oil doesn't escape into the air or drip onto the adjacent equipment or floor.
With the exception of lighter-gauge coils that can be secured with adhesive tape, almost all slit coil mults need to be banded before being stripped off of the recoiler. Turret recoilers (see Figure 1) allow OD coil bands to be applied to the slit coil mults while another coil is running.
A turret recoiler consists of two mandrels mounted on a turret base with an outboard drive. As one recoiler is winding up a coil, the other is positioned offline so that coil mults can be banded. Overarm separator spindles and recoiler filler plates can be interchanged offline as well. When a master coil must be broken two, three, or four times, a turret recoiler can save a lot of time.
To handle large slits, coil unloading cars may be supplied with powered clamps to secure the slit coil mults as they are stripped off the recoiler.
With the increased strength of the material being processed on today's equipment, it's important to be able to secure the mults on the recoiler before OD banding. High-strength material can slip out of the overarm separator and injure the operator.
Tail hold-down clamps are incorporated into the overarm separator to secure the slit mults before banding. This ensures that all of the wraps wound on the recoiler are securely held in place so a band can be applied safely around the coil OD.
Bolt-on steel filler plates typically are used to change recoiler drum sizes but take a long time to install. Another method that reduces the time required to change recoiler drum sizes is a quick-change steel plate quill supported on a fixture and locked into place using one bolt. The assembly is loaded onto the mandrel with the coil car and can help reduce recoiler drum change time from 30 to three minutes.
To handle large slit coils, coil unloading cars may be supplied with powered clamps (see Figure 5) to secure the slit coil mults as they are stripped off the recoiler. A hydraulic cylinder-positioned hold-down device with adjustable clamps secures coils in place.
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