The fouling-resistant coating (applied to the left side of the plate) prevents scale buildup on a panel-type heat exchanger used in a zinc phosphate solution.

Downtime has always been costly, but in today’s economy, downtime makes an even greater impact on the bottom line. With this in mind, one Midwestern metal finishing shop worked closely with its heat transfer equipment supplier to eliminate its downtime problem.

The metal finisher uses Temp-Plate heating panels from the Heat Transfer Division of Paul Mueller Co., Springfield, Mo. The panel-type heat exchanger can be used as an immersion, clamp-on or integral heat transfer surface.

The Midwestern metal finishing shop uses the panel-type exchangers to heat its zinc phosphate solution. Every nine days, however, the finisher had to pull the panels out of the solution because they would lose their ability to transfer sufficient heat. This downtime was not related to the performance of the heating panels. Instead, it was a result of an extreme buildup of scale on the plates, which use steam to heat the zinc phosphate solution.

The process to remove the scale was time consuming and labor intensive, requiring the company to pull the plates, wait for the zinc phosphate to dry (a two- to three-hour process), and then remove the scale from the plates using chisels. In all, the operation experienced downtime about three days per month, with each delay lasting about three hours.

After an initial analysis, Mueller suggested a coating for the plates that prolonged the time between cleaning significantly in light phosphate. Over time, however, the scale buildup continued.

After a more in-depth examination of the process, the Mueller team then suggested that the finisher try a fouling-resistant coating called FoulFree 100. The metal finishing shop agreed, and the panels were coated with FoulFree 100 and reinstalled.

Nine days after reinstallation, the coils were inspected and the heat transfer performance was tested. The zinc phosphate operation was observed to be performing at its normal level and did not require cleaning. After 80 days of operation, the heating plates were re-inspected, and again, the unit did not require cleaning. At 162 days after installation, the heating equipment was once again removed for inspection. The special coating still looked good. Though a small amount of phosphate clung to the panel, most of it slid off the panel as it was lifted from the tank. The customer is so pleased with the fouling-resistant coating that it has placed an order for three additional panels.

For more information from the Heat Transfer Division of Paul Mueller Co., call (417) 575-9000 or visit