Roll coaters are used to apply hot melts or cold glues evenly onto a variety of substrates. If you notice excessive, uneven or insufficient amounts of adhesive or coatings applied, it can be due to worn or damaged rolls. Here’s how to check them.

Coating rolls: If worn or improperly ground or grooved, coating rolls are a chief cause of material waste. To check for roll wear, clean the rolls and leave the reservoir empty. Next, adjust the coating rolls to a gap of approximately 1/32 inch. You should be able to see a strip of light between the rolls.

If the rolls are touching on the ends but not the center, they are worn from substrates being run in the middle. If touching in the center but not the ends, they are swollen. Either way, it is time for servicing.

If the strip of light is even, start the machine with all guards and covers in place. Watch to see if the strip of light winks at you (light/no light) and you believe the bearings are good, the roll is not concentric and should be serviced.

Grooved rollers should be serviced when the grooving starts to wear. Sometimes there will be a noticeable change in the settings needed to obtain proper spread as the threads lose their ability to hold and carry coating. Other times it will be visibly noticeable that the grooved roll is almost ground smooth. When the grooved roll has lost 1/3 of its groove depth it has lost more than half its capacity to carry the glue.

In addition to worn rolls, there are other parts of a roll coating machine that may cause uneven or excessive application of coating: the elevator gear box, end seals, coating roll drive, and doctor roll drive should all be checked.

Elevator gearbox: Check the elevator screw, steel worm gear and bronze worm gear. Wear can cause sloppy vertical adjustment of the coating roll.

End seals: Improper alignment of the end seals to the roll flange can cause a loss of coating material due to leaking. If the end seals are worn or distorted, the flange is worn or misaligned, or the rolls were improperly installed, you can end up losing coating material.

Coating roll drive: Check for worn sprockets or chains. These could cause erratic coating and costly rejects.

Doctor roll drive: Gear and clutch wear can cause slippage and erratic spread.  If the clutch is too loose the coating roll will move at a 1:1 ratio with the coating roll, which would cause more coating to be applied.  If the clutch is too tight the rolls will chatter especially during clean-up when the adhesive or coating has been removed and only water remains.

Most types of adhesives and coatings should be cleaned from the machine and rolls regularly. Checking your roll coating system for wear and tear can help save you money, whether your machine requires a new set of rolls or your rolls are able to be reconditioned or regrooved and returned to your facility.

Source: Black Bros. Co. For information call 815-539-7451 or visit BlackBros.com.