How to check for roll wear on a roll coater or adhesive spreader

Photo By Black Bros.

Roll coating machines allow for an even application of hot melt or cold glue application on many different substrates. Worn or damaged rolls on a roll coater can apply excessive, uneven, or insufficient amounts of adhesive or coating onto the substrate.  Excessive coating could cost thousands of dollars in material waste.  Insufficient coating can result in rejects of your product, costing you money in scrap.

You may be asking yourself, what is an easy way to check for roll wear on your roll coating machine? The following tips may prove useful in maintaining your machine and rolls at optimum performance. Because safety should always be of utmost priority, all actions below are to be done only while a machine is locked out and tagged out.

Coating rolls
The coating rolls, when worn or improperly ground or grooved, are the chief cause of material waste. So how do you check for roll wear?
Clean the rolls and leave the reservoir empty. 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 is even, you are halfway there. Start the machine, with all guards and covers in place and watch this strip of light. If it winks at you (light/no light) and you believe the bearings are good, the roll is not concentric and should be serviced.

Grooved rollers are similar to the tires on your car; when the grooving starts to wear, they don’t work as well and should be serviced. 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. As the diagram shows, when the grooved roll has lost 1/3 of its groove depth it has lost more than half its capacity to carry the glue. If you suspect your rolls may need to be checked, you should speak to an experienced roll manufacturer who can help you determine if the rolls need servicing and provide estimates for repair.

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

End seals
Proper alignment of your machine’s end seals to the roll flange make for a clean roll coating operation. However, improper alignment of the end seals to the roll flange can cause a loss of coating material due to leaking. Material that leaks past the end seal is wasted and may cause damage to mechanical components. If the end seals are worn or distorted, the flange 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.

Roll coating machines can be built to endure many decades when they are well maintained. 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, 800-252-2568, or visit

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