Sometimes it’s really the little things that make a difference.
About 10 years ago, I was conducting a training session for a variety of students, including a small manufacturer of kitchen cabinets, a semi-professional woodworker, a distributor of coatings products and about 10 other students of varied background and experience.
All of the students had some problem or complaint with regard to their previous or current finishing experience, as was to be expected. After all, that is why we were involved in the training. One student in particular, the cabinet shop owner with the most experience, also had the most problems to solve.
He also had the most excuses as to why he could not apply the solutions that were presented in the class.
Here’s the biggest hurdle he had to overcome. He was located very close to the water in an estuarial area on the East Coast. Average temperatures ranged from 38 to 89 degrees. It was always quite humid.
To avoid blushing, he had to add retarder and complained of the very slow dry-to-stack time. He also had problems days or weeks later with printing or blocking on stacked or packed parts.
The blushing was caused by the application of coating to substrate under such conditions that moisture present in the air immediately adjacent to the surface could precipitate on that surface while the coating was still wet. That happens when the temperature of the surface is at or below the dew point.
When the dew point and the actual (ambient) temperature are close together, the risk of blushing is high. For instance, at 85 degrees, when the humidity is at 61 percent, the dew point is 70 degrees. If the substrate and the coating are above 70 degrees and the coating can be applied with no drop in temperature, there should be no blushing. However, when there is a drop in pressure from a compressed air spray system, there is a loss of heat in the material being sprayed and the air accompanying the material as it travels from the gun to the work. While the coating is still wet, there is a further drop in the temperature of the film because of the evaporation of the fast evaporating solvents, such as acetone, alcohols, MEK and others.
The cumulative effect of this cooling can drop the temperatures of the coating below the dew point. Exacerbating the effect of the evaporation was the practice of having quite a bit of air movement through the finishing booth during the spray operation and the initial drying of the sprayed objects, especially in warmer weather. Some of the increased airflow was due to an effort to cool the employees; some was due to the belief that it would improve the drying by speeding up the release of solvents from the wet film.
While increased airflow will speed up the drying to some extent, it has the greatest effect at the surface of the film. If that surface is dried too much or too quickly, it tends to seal in the solvents lower down in the film. Those solvents will work their way to the surface eventually, and then into the atmosphere, but the end result may be that the complete drying of the film is slowed even more, so that the film might remain too soft for stacking or rubbing for many days.
Attempting a fix
While the shop owner knew that the shop’s humidity was high, he didn’t understand the exact relationship between the temperature and the relative humidity and the thresholds that were critical. He did not monitor either temperature or humidity in the shop, but paid some attention to The Weather Channel’s reporting on local conditions.
I repeatedly tried to lead him to understand that he could alter that environment in the area immediately surrounding the surface he was spraying and that it was not necessary for him to alter the environment in the whole shop. That is, he could heat the surface and the area immediately adjacent to that surface with an infrared or hybrid (infrared and convection) heating system. The equipment necessary could be purchased quite economically and could be moved into the spray booth prior to spraying to warm the object, moved out for spraying and back in for drying when the spraying operation was halted. Or it and the sprayed objects could be moved to a dedicated drying area as necessary.
We advised that the material storage be elevated off the concrete floor to prevent the excessive heat loss from the cool concrete and to allow better warm airflow around the containers. We also emphasized the practice of making sure that the coating material was sprayed at the proper temperature rather than over-thinning or adding retarders. A condensing/coalescing dryer was recommended to remove excess water from the air supply, which also served many air tools.
Supplied with a lot of information that he was having difficulty processing, but willing to continue to work on it, the shop owner left with a certificate of completion, a list of useful resources and some reference tables and graphs.
We finally got through
About four months later, we heard from the owner. First, he wanted to thank us for not giving up on him. He also wanted to share a success story. He had gradually put in place most of the suggestions we gave him, starting with keeping track of the actual temperature, relative humidity and air movement in the finishing area. One thing he discovered was that on large jobs requiring lots of late hours the humidity spiked when it began to cool off at the end of the day and blushing was more likely to occur. In that case, his finishers would add retarder to prevent the blush, which slowed down the drying of the film. As the air continued to cool, the further overnight drying was retarded even further by the combination of lowered temperature and slower solvent residing in the film. This delayed progress, causing a hurry-up attitude that resulted in more damage because of movement of the cabinets within the shop. I’m sure you can appreciate the cascade of events.
Some of the economies he had realized by improving spray technique encouraged him to invest in the infrared dryers, which along with picking the better times to spray almost eliminated blushing and blocking of poorly dried films, freeing some of his bottlenecks. His finishing costs continued to go down as more and more employees bought in to the changes.
He claimed that it took him about three months to decide to be serious about accepting the changes and another month for his employees to become believers.
The keys to the shop owner’s eventual success in solving his finishing problems were:
• Learning and accepting the principles governing the behavior of the finishing materials.
• Measuring and recording the environmental conditions present when the problems occurred.
• Accurately assessing the costs of continuing what he was doing vs. making changes in the environment under his control.
• Implementing new protocols to control the immediate environment in which the objects were sprayed and dried.
• Providing training to his spray technicians and other employees concerning applying those new protocols.
• Providing encouragement and incentives for changing their procedures and performance.
• Allowing time for the changes to become the norm.
Because he applied the changes incrementally, he and his employees were able to see the effect of each improvement and the resulting cost savings. That savings encouraged and financed the next step, so the investment was quickly rewarded.