Last year we installed an expensive electric conveyor dryer to eliminate problems with parts rusting after mass finishing and/or washing operations. (We use, and prefer, water-based inhibitors.) The problem still exists, though it is greatly reduced. We can vary the time and temperature in the dryer, but have not found the ideal settings. Can you offer any suggestions? R.W.
You are not alone in frustration with this situation. While it is good to dry parts before packaging, it is possible to destroy some of the rust inhibitors with too much heat. The inhibitors should not be heated much beyond the boiling point of water. We generally recommend keeping the surface temperature of the parts below 250ºF and allowing enough time to dry at that temperature.
Additional Comment. This month’s questions about drying parts show that the single best answer may not be out there. If I were starting with a clean sheet of paper I would frequently favor a heated dip tank with a drag-out conveyor. Take care to minimize the time that parts remain in the high humidity area above the hot solution. The energy cost is probably lower than with other methods, and there is less chance of using more energy than necessary. This also helps rinse off the media residue from mass finishing – and clean parts are less prone to corrosion.
The temperature in the dip or hot wash only needs to be high enough for the parts to be reasonably dry before the next operation. If you want the parts to flash dry, you will need about 180ºF.
If you use a hot dip, or hot wash, it often works well to use the same compound that is used in the vibratory finisher. You can use the freshly prepared mixture in the dip tank, and pump from there to the finisher. This keeps the final wash cleaner, controls bacteria better and simplifies the operation. A float level and venturi type proportioner will keep the system full with the proper solution at all times.