- January 01, 1996, Mykytiuk, Andrew
Brakes and clutches for tension control are available in many configurations for virtually every converting application. Like all parts of the industry, this one is rapidly evolving.
In 1970 when the Montalvo Corp., Portland, ME, developed the dual-disc, multiple-range brake, the converting industry finally had a brake system designed specifically for its own applications. With this system, instead of having one disc that either caliper was pressing on from both sides or an axial cylinder pressing up against one side, the brake had two discs with the actuating cylinders pushing out against the discs from the inside for greatly improved braking. Both discs had ribbed surfaces on the outside, tripling the outside surface area for greatly improved cooling. This brake offered the capacity to cool down much larger applications, so much so that it started to replace water-cooled brakes. This revolutionary design, which is the basis of many of the tension control braking systems available today, was the critical development that allowed converters to run their equipment faster than ever.
After this point, the development of brakes and clutches specifically for converting applications began in earnest. The hydraulically actuated brake was rapidly replaced by pneumatic systems. Brakes with more than one cylinder were developed, so that, depending on the application, the brake's torque rating could be adjusted by turning individual cylinders on or off. Horton, Minneapolis, MN, offers a diaphragm-operated unit called the STC 600 Tension Control Clutch, which incorporates pistons in three different sizes within the same unit. These pistons can be actuated singly or in any combination, and air pressure can be varied from piston to piston as well."
About 10 to 12 years ago all electro-pneumatic controllers used strain gauge transducers (transducers sense web tension and send a signal back to the control panel, which then compares it to a setpoint and either increases or decreases the air pressure going to the brake). Computers control tension today and have revolutionized that aspect of the business.
There are braking systems available that have eliminated the need for dry friction components altogether. They have almost nothing in common with conventional mechanical systems. Magnetic Power Systems, Fenton, MO, uses an electromagnetic field to couple drive components. Merobel USA, Merrillville, IN, utilizes magnetic particle technology. "The air gap between the two rotors is filled with magnetic powder," says Jean Baptiste Barruel, technical engineer for Merobel. He says that the advantage of this technology is torque proportional to electrical current, and torque is independent of variations in speed.
Another major impact occurred when the government outlawed asbestos as a component of brake pads. Today's high-performance pads, instead of being as much as 80% asbestos, are a proprietary mix of binders and phenolic resins crosslinked with polyamids.
According to Wissenback, the air-cooled disc system is the most effective as far as heat dissipation goes, it is the most cost-effective and easiest to work on, and, if you size it right, it will last forever. But the drive to improve even the most effective systems cannot be stopped. There is movement away from cast iron - an ongoing effort to make a low-inertia brake. Until now this has been done by making the disc less massive, while still maintaining the heat capacity of the disc.
Twin Fin, Austinburg, OH, offers a composite brake made from a patented silicon carbide homogeneous metal matrix aluminum material. Twin Fin president Mike Farinacci reports that the material has the same strength as cast iron but the thermal characteristics of aluminum. "The weight is one-third that of cast iron. This translates into low inertia, drastically reducing overhung weight, shaft load, and sizing and reducing tension control feedback response time."
"The market is moving heavily toward electrically controlled machines," says Montalvo president Ed Montalvo. He predicts growth in DC regenerative braking, AC variable-speed braking, and AC servo braking. "Do I think they will ever replace the friction device in the smaller applications? They could, but I don't see it happening for a long time."