Above: A compact slitting line built by Burghardt + Schmidt features various components designed to handle light-gauge, sensitive material, including stainless steel, aluminum, copper and brass, in a way that avoids surface defects.

Vacuum tension stand provides worry-free handling of light-gauge, surface-critical strip

October 2017 - The environments in which metals are rolled, packaged, transported, uncoiled, threaded, sliced and re-rolled present many opportunities to damage the material itself, especially the surface. Yet, there are an increasing number of applications where the surface must have zero defects: No scratches, no dents, no smears, no dust, no debris, no oil or grease, no burrs.

Burghardt + Schmidt, a machinery builder based in Remchingen, Germany, has developed a vacuum tension stand for slitting lines. The stand works best on lines that process tinplate, soft copper, aluminum, stainless steel and most surface-critical materials between 0.001-inch and 0.12-inch thick.

The company, which also builds slitting, cut-to-length, stretch-bend leveling and packaging systems, has found eager adopters in Europe and is taking orders for the tension stand in North America as well, says Mike McGuire, the Wheaton, Illinois-based USA sales executive for Burghardt + Schmidt.

Applications for thin-gauge, surface-critical strip are appliances, connectors, modems and cosmetic uses.

“End users of light gauge, surface-critical material are demanding tighter tolerances on slit strip, with very little burr,” says McGuire. Burghardt + Schmidt has a burr measuring system to monitor that. End users also require that their material not be scratched or have any buildup on it. “Most tension stands use pressure between two surfaces and that may create drag marks. Felt pads can take in metal dust, tines or slivers and then mar the surfaces coming through it,” he says.

How it works

The vacuum drum roll rotates with the speed of the strip. It doesn’t matter if it’s a full-width coil or any number of slit mults. “We draw it into the vacuum drum and nothing touches the top of the material. Once the material passes the slitting head, nothing is touching the top all the way to the recoiler,” according to McGuire.

The roll is covered with a thin felt-type material. The drum is perforated so that air surrounding the coil and strips can be drawn into the vacuum roll. The electrical motor is the only part of the system outsourced; all other components are manufactured in house. “Our company deals in very tight tolerances and we want to control those tolerances,” McGuire explains.

The operator can set widths at the control panel so that air is drawn only where strips are running. “If you are only running 6 inches wide, you don’t have to have this on at 60 inches wide. It saves power,” he notes.

From the uncoiler, the system “controls all the tension of the strip as it enters the sitter head with a dancer roll, and ‘S’ bridle rolls. Then we have anti-flutter rolls. Mults drop into the pit after slitting. After the looping pit, separator disks control the placement of the strips onto the vacuum stand, then the strips are fed onto a bridle roll at the recoiler,” says McGuire.

Applications

Burghardt + Schmidt has built vacuum tension stands up to 64 inches wide. Along with tinplate, the system is a good fit for light-gauge copper and brass, aluminum and stainless steel, where finished surfaces must be flawless. Applications could be appliances, connectors, modems in computers, any cosmetic purpose and wherever a defect would prevent the conduction of electricity such as when slitting lamination material. “Only the vacuum stand eliminates any and all marking of the material,” says McGuire.

After the looping pit, separator disks control the placement of the strips onto the vacuum stand, then the strips are fed onto a bridle roll at the recoiler.

Engineering prowess

Burghardt + Schmidt employs 17 mechanical engineers focused on equipment design. “We also have electrical engineers designing how we want the system to operate and communicate,” McGuire says. “We design the power needed and the motors necessary and we design the ones inside the vacuum drum. But Siemens designs the ultimate complete line controls. They are outsourced because we want them dedicated to the controls, and we seek out the best, most up-to-date technology at the moment.”

In house, says McGuire, the company has developed “a machine that can measure burr. The system can measure burr prior to or after the tension stand and prior to being recoiled. We can measure the burr and provide a complete analysis.”

The reason this analysis is worthwhile is that “a heavy burr can cut rolls in the tension stand” or cause rejects from an end user. Burghardt + Schmidt slitting lines guarantee 0.000079 inch for runout and 0.00037 inch for parallelism.

They’ll also measure the depth of knife penetration and automatically change it as the material is being slit to be sure it is the correct penetration all along the full coil length.

“Our customers are making products that can have almost no burr. With this system, we can measure it. We have cameras that track it and provides the customer with a histogram,” says McGuire. Alternatively, a customer can set the desired burr tolerance, graph the burr and highlight where it may be out of the designated tolerance. “This allows an operator to see where the burr is during the rotation of the knife and check if the knives are dull or chipped, says McGuire, adding that no other machinery builder offers this type of system.

When using the measuring system, slitting line operators “won’t have to cut pieces out, take it off the line and measure it with a micrometer or other subjective tool,” he notes.

Extra benefits

Besides preventing surface flaws, the vacuum tension stand has additional benefits, according to McGuire. “We can grab coils after the slitter head and feed the strips into the vacuum stand automatically, move and place them into the proper position, then at the bridle stand measure the tension.”

As the coil OD builds up, the tension stand backs up so that the radius or the angle at which you are rewinding is consistent. With that function, you don’t need an overarm separator, he notes.

With a vacuum stand, slitters don’t have to slow down because nothing is touching the top of the strips, so productivity rises.

“The customers we visit may have to run their material very slowly in order to see defects. With a vacuum stand, they don’t have to slow down because nothing is touching the top of the strips. Productivity rises, and you don’t need to stop the line to clean or exchange the tension pads, or wipe down the tension rolls.”

Most slitters with rolls or drag tension stands may need to stop the coil and replace the felt when it becomes dirty and begins to mark the slit material. This does not happen with the vacuum roll.

When necessary, the vacuum roll can be cleaned with a vacuum at the end of a run or multiple runs, and eventually be replaced when it wears out.

Because the tension is controlled from the uncoiler and completely through the line to the recoiler  “we do not need an entry looping pit. That saves money in foundation work,” notes McGuire.

Almost every other manufacturer of slitting line equipment for thin and surface-sensitive material requires users to install two looping pits and change speeds when working on surface-critical material. However, “With the vacuum roll, you can run 1,000 feet per minute and be sure it’s smooth.” MM