Powder coating, a widely used alternative to liquid paints, is preferred in many applications because it does not require the use of a volatile solvent. The process uses fine, dry thermoplastic or thermoset powders that are electrostatically attracted to the object being coated and then thermally set and fused to form a tough, hard skin that typically is thicker and more durable than conventional paint.
A successful powder coating operation depends on consistent powder characteristics from batch to batch including purity, particle size, color, chemical composition and thermal properties. Naturally, powder production technologies are closely guarded trade secrets.
Powder problems
Major powder suppliers tend to be experienced paint manufacturers because the two technologies are so closely related. When one of the largest powder producers moved an East Coast operation into a new-to-them location in a 20-year-old industrial building, the producer immediately began to experience production and product quality issues.
The production issues centered around clogged spray nozzles used in the production process, chillers fouled with sediment and excessive wear on other production equipment. More importantly, customers were noticing a decrease in the quality of the powder they were supplied. They saw a higher-than-acceptable number of inclusions that produced defects in the finished surface of the customer’s products.
Both issues were quickly traced to the plant’s aging water supply system. The process lines in the plant use 600 gallons per minute (gpm) of water originally sourced from the municipal supply. The water is chilled to various temperatures used in the process and then recirculated through a cooling tower in a semi-closed loop that requires only makeup water from the municipal system.
Upon inspection it was discovered that the plant piping was heavily corroded and clogged with sediment. One section of 6-inch supply piping, for example, was more than 50 percent blocked with scale and sediment, robbing the downstream processes of adequate flow.
Plant managers initiated a program to replace the worst of the piping and performed an acid wash to free up accumulated scale in the system. Given the extent of the contamination, however, it simply was not economically feasible to replace all piping in the plant, and an alternative solution was required.
Upon inspection it was discovered that the plant piping was heavily corroded and clogged with sediment. One section of 6-inch supply piping, for example, was more than 50 percent blocked with scale and sediment, robbing the downstream processes of adequate flow.
Considering the options
At this point the facilities’ management team called in Engineering Sales Associates (ESA) of Charlotte, North Carolina, to explore the possibility of creating a filtration solution to eliminate the contamination at point of use. The task was assigned to ESA Solutions Manager Brandon Pue.
“The customer’s initial request was for point-of-use strainers at each critical device in the production system,” Pue said, “so that’s where we started.” He said they installed eight 2-inch strainers with 400 mesh elements to protect key equipment, but before long they found they needed a more comprehensive solution.
“The strainer installations included flowmeters and valving that allowed us to monitor each station independently,” Pue said. “What we found is that the amount of contamination still in the system quickly filled the strainers, which created a maintenance requirement, negatively impacting production. We needed an additional solution to clean up the whole system and not just the points of use.”
ESA’s analysis determined that the optimum solution was to continuously filter the entire 600 gpm flow to 25 microns. Achieving that result was complicated by the customer’s strong preference for a nonbackwashing filter system and the physical space limitations of the plant.
The first solutions they looked at — a bag filter and a self-cleaning filter — required more floor space than they had available. Working with engineers, they found the best solution was a pair of magnetically coupled self-cleaning strainers.
These self-cleaning strainers are mechanically cleaned by moving a disc over the surface of a cylindrical wire filter screen. In this model the cleaning disc is magnetically coupled to the actuating piston, which eliminates the need for shaft and external drive seals and greatly reduces system maintenance requirements. Process liquid is introduced in the center of the media and flows through it to be discharged on the outside.
Contaminants are collected on the inside surface of the media, and when the flow restriction reaches a predetermined value, the disc moves up and down to remove the contaminants and deposit them at the bottom of the filter housing where they can be purged. Very little process fluid is lost during the contaminant purge, and the entire process is accomplished while the filter is operating at full capacity with no interruption of liquid flow through the system.
