What is the best method of cleaning electrocoat racks and hooks? J.I.
System design and type of parts being run are major considerations in answering this question. If electrocoat is the only coating applied, the cleaning frequency and type may be different from when the electrocoat is a primer with liquid or powder as a topcoat. Very large and/or heavy parts will establish ground much better and longer than very small or light parts, also changing the frequency and type of cleaning. A third major consideration in cleaning tooling (racks, hooks, hangers, etc.) is the design of the tooling. Some tooling design makes the ground points removable from the main rack and increases the density of the essential components to be cleaned and reduces costs. This cost reduction needs to be compared to the labor to disassemble and the increased tooling cost.
The most frequently used method for cleaning electrocoat tooling is burn-off with an afterburner to eliminate air pollution. Most burn-off equipment is gas-fired, batch-loaded, sealed with limited oxygen access and blowout panels. Typical cycle times are 4-6 hours depending on metal thickness. Cycle time is also increased if the electrocoat is a primer and several layers of topcoat are also burned off. Removal of the ash from the clean racks is usually a quality issue. The best method is to use a high-pressure wash after cleaning, but some operations just run them through the pretreatment washer.
Two similar cleaning systems are in-line burn-off on monorail lines that clean the racks each conveyor cycle or molten salt bath burn-off. Both of these require some type of air scrubber to eliminate air pollution. They both reduce time for cleaning but probably have a higher initial and/or operating cost.
Shot or grit blasting is probably the second most used cleaning method and is quite often preferred for very heavy tooling that would require excessive gas usage for burn-off and allows for "as needed" only areas to be cleaned. Disadvantages of blasting are the labor required and the removal of rack material along with the coating. This will also remove or round-off sharp contact points used for establishing ground.
Similar to the "as needed" only areas being cleaned by blasting is to file or grind the contact points on racks as "no-coat" and "light-coat" rejects increase. Again, labor is probably the determining cost factor.
The last "cleaning method" that I have seen is not actually cleaning. It consists of replacing and throwing away the contact points (usually hooks) on the rack crossbars. Again, cost needs to be considered along with rack design. This system is usually for very lightweight parts and/or where parts are powder coated after electrocoat.