The Real Coatings Delivery Problems

Q: I have been associated with the liquid industrial finishing market for over 40 years. I have been involved with many systems from basic hand spraying to complex computer controlled rotatory atomizers. I often sit back and listen to the application problems the end users have with their systems. Almost always, they say they have application problems, so fix the atomizer. But is this really the problem? Many times, it has nothing to do with the atomizer, but instead the paint delivery system to the atomizer.

A: The types of minor overlooked problems that a delivery system can have include lack of agitation, too much agitation, no coatings temperature control, and no coatings circulation.

Lack of agitation. I have seen a new container of coatings brought to the pumping system and not completely or not even agitated at all. A lot of the pigments and fillers in the coating settle to the bottom of the container. The siphon assembly picks up coating from the bottom of the container, so the first few gallons contain a lot of pigments/fillers. This leads to clogged filters and fluid tips. And because there is way too much pigment, the fluid pressures need to be turned down. After the first few gallons have been used, the remainder of the container has too low of volume solids, so full coating hide is dramatically reduced. At the same time, because of the reduced solids (pigments and fillers), more film build is required, but runs are often the result. So, a lack of agitation can and does result in two application problems, which are not application problems at all.

Too much agitation. This is a frequent problem with liquid systems. I visited a company that used 55-gallon open head drums for its paint delivery systems. To save dollars, it removed the drum covers and created a pie-shaped cutout for the agitator and siphon assembly. The agitators were the old-style direct drive air motors with 5-inch mixing blades. On the first day, we opened a fresh drum of black paint, mixed it, and then took the viscosity readings. The next day, after about 18 hours of agitation with the cutout drum cover, the viscosity had gone up 10 seconds. The open cover with the high-speed agitator had driven a lot of the solvents out of the coating. The paint was in the system for only two days. The coating applied well on the first day, but on the second day there were a lot of application problems.

The solution: full drum covers with built-in siphon assemblies and large-bladed slow agitation. When this simple change was made, the viscosity remained constant, even after a week of being online. Controlled slow large-bladed agitation results in a uniform blending of the coatings while keeping the solvents in the coating and not allowing them to be driven out of the coating.

Thermal viscosity control. The coating viscosity changes as the coating temperature fluctuates. An example of this was a system we installed in Florida. The system was sold with both inline heaters and secondary heat transfer systems (SHTS) to help maintain the coatings temperature. After the system was started and successfully ran for about a month, the plant manager visited the system with the operator. He thought because he is in Florida that he does not need all the heater application systems. He told the operator to turn off both the inline and SHTS systems. Within five minutes, the finish started to look bad with many voids in the coating. The fluid pressure and atomization air pressures (this was an Airmix system) all had to be increased but the finish still looked bad, and the overspray dramatically increased. So, even using more paint (increased fluid pressures), the finish still looked bad.

The two heat generation systems were turned back on, and within minutes, the fluid pressures were reduced to their previous levels while the atomization air was also reduced. This proved that maintaining the coatings at their thermal viscosity flat line temperatures, the application system was repeatable, which enabled system control.

No coatings circulation. Almost all coatings are thixotropic in nature, that is, when energy is input into the coatings, the viscosity will drop to a repeatable level. When coatings are agitated and circulated, energy is driven into the coatings. By maintaining uniform agitation and fluid circulation, the resulting viscosities are much more repeatable and easily controlled by the pumping systems. If either or both agitation and circulation are stopped, the viscosity will rise to a point which will affect the application system results.