Cinching, sometimes referred to as friction scratches or pickoff, is the result of the movement or slipping of painted-metal coil laps against each other. This phenomenon causes the removal of paint, creating small- or medium-sized scratches formed in the same direction of the slipping or movement of the coil laps.
The vast majority of cinching incidents are caused by improper brake pressure on an uncoiler spool, or by an expandable arbor brake. For portable rollformers, improper brake pressure on the uncoiler spool is by far the most common cause of cinching damage on coil. New machine operators who are not familiar with the use of the brake or have not been properly trained in use of the equipment often are responsible for most cinching problems.
To avoid cinching, the operator must ensure that there is proper tension on the metal coil. The idea is to allow it to uncoil without tightening the laps or loosening the coil so that it does not unravel. If either of these things happen, the laps will rub against each other and cause cinching.
On portable rollformers, the crude brake, which works by tightening a bolt on the shaft, is the only way to adjust tension on the coil. Because a spool suspends the coil on a portable rollformer, the operator must take into account the weight of the coil when brake pressure is applied. It is also important for them to know that when the machine starts, a tug will be observed.
There is a balance of brake tension that operators must find on their machines. If the brake is set too tight, the tug that happens when the machine starts will tighten the coil by moving the laps. As time goes on, the paint can no longer absorb the force of this abrasion and it will be removed in the direction of the tug or the force applied to it. Conversely, if the brake setting is too loose, the tug of the machine will cause the coil to unravel and scrape against the rollforming machine. If this scenario plays out, the laps of the coil will loosen to the point where they will rub against each other when the machine starts up, again causing cinching and damaging the coil.
It is important to remember that as the coil is used and grows smaller in size, the rollformer no longer has to pull as much weight and brake pressure needs to be adjusted, depending on how the coil is responding.
Coil Care
Cinching problems have been around for many years. As a result, a number of solutions and troubleshooting techniques have developed over time. For example, the expandable uncoiler for portable rollforming machines has been developed and put into use. An expandable uncoiler will support the coil as it is used, but proper brake pressure still is critical to avoid cinching.
While new advances have done a lot to reduce material waste and improve production, there still are contractors everywhere using machines with technology that is more than 20 years old. In those cases, good training and experience are the only ways to prevent operator-caused cinching.
The other commonly reported reason for cinching is the improper transport of a painted coil. The only sure way to avoid cinching while transporting coil on a rollforming machine is to keep it banded on skids in a way that those in the industry refer to as “eye to sky”. When the coil arrives at the jobsite, it must be tilted to a horizontal position using slings and then mounted on the rollforming machine. Moving the coil to a horizontal position on the ground or on a concrete or asphalt surface using levers or a tow motor may cause cinching in the coil before it even makes it to the machine.
If the contractor is going to transport a coil on a spool, the outer lap of the coil must be securely taped or banded. The coil must be absolutely secure or the vibration from transportation will cause it to unravel and cinching will begin. Finally, never transport a coil on a spool while it is still threaded into the rollforming machine. Whatever is left on the spool by the time it reaches its destination will be damaged and essentially will be junk.
There are some clear signs that cinching is the cause of short longitudinal scratches. Worn or broken pieces on the spools, idler rolls, and guides are signs of cinching. Gaps or air spaces between sections of the laps of the coil is another sign. And the ability to move the laps of coil with hand pressure alone indicates that the coil has unraveled.
Another simple way to identify whether cinching has occurred is to draw a straight vertical line with a marker on the laps of a coil from the inner diameter to the outer diameter. Then run 50 to 100 feet of coil. If the straight vertical line becomes a dotted line at an angle that becomes horizontal, the coil laps are slipping and cinching will occur.
If you are an experienced contractor who suddenly finds yourself having trouble with cinching, something has changed with the rollformer operation and coil handling protocol. It is possible that a new operator doesn’t understand proper procedure for running the rollformer or transporting the coil.
Gene Johnson has been the quality and environmental manager at Perth Amboy, N.J.–based Englert for the past 15 years. He is responsible for the integrity of a broad range of roofing, gutter, and environmental products, and has been in the coil-coating industry since 1968.