Let’s talk chatter. Not just because it’s cold outside, but because it is a common defect in the coating industry.

What is chatter? For those who have not dealt with this issue, chatter is a variation in coating that looks like a solid crossweb line at regular intervals down the web.

The reason I want to talk chatter is because it is a common defect that people want to blame on the coating head. However, it typically aligns with another piece of equipment.

But if I see the fluid coming out of the coating head, and the defect starts right at the application of the fluid to the web, why can’t I blame the coating station? Because the underlying reason for chatter is one of two things, and you can’t see either of them.

Mechanical variations can occur from rolls that are not in compliance, vibrations in the structure or framework, or drives that run the upstream equipment. The rolls that are not “true” will match up with the frequency of the defect, so it is good to know the diameters of the rolls in the process.

The vibrations can be monitored with a vibration analyzer, and the drives can be matched for frequency.

Well, the mechanical problems should have mechanical solutions (i.e., replace the bad rollers, drives, etc.). Likewise, the pumps should be replaced with non-pulsating alternatives.

However, if there is still some chatter after these adjustments have been made, you can consider a piece of stabilizing equipment. One option is a vacuum chamber at the site where the fluid interacts with the substrate. A vacuum box can stabilize the substrate/fluid interface and reduce variation.

But be careful, a vacuum box also can cause chatter! You need to make sure the box is sealed and operating properly.

The reason a vacuum box may help reduce the defect of chatter is simply that the fluid likes itself more than it likes the substrate. This interface problem also may be improved by encouraging the fluid to adhere to the substrate by pre-treating the substrate chemically or with an energy source.

I hope this has provided an example of how coating is an interactive process. For the coating defect of chatter, even though the fluid meets the substrate at the coating head, the main issue is not the coating station itself but the peripheral equipment.

So remember to keep your thoughts open and look outside of the coating station when analyzing defects. The root cause may not be obvious to the observer.