Dip-and-Bake Systems (Electric Motors)

3.16.1
The dip-and-bake system is probably one of the most common conventional methods of applying varnish. In this process, the complete stator and coil assembly is submerged in a tank of varnish, either under normal atmosphere or under vacuum or pressure.
Various parts may be either preheated or at ambient temperature depending on the type of varnish being used. The size of the part and configuration of the windings will determine the amount of time it takes for the varnish to fill the voids in the slots and windings. Submerging the part for various time intervals, weighing the part, and electrically testing the part after baking will determine the proper dip time. One disadvantage of dipping parts in varnish is that removal of the varnish in unwanted areas is required after baking, thus adding to the cost of the finished assembly.
Conventional dip-and-bake systems using convection heat typically have dip times in the range of 5 to 30 min for larger parts and bake times of 2 to 4 h at 350°F (205°C). Times range from 30 s to 5 min for smaller parts. Parts coated with water-based varnishes will operate at lower temperatures.
Production lines processing over 200 parts per hour most often can justify and utilize a dip-and-bake system.
Dipping systems primarily use three different processing methods.
1. Indexing rack system. In the first method, a part is set on a rack or lowered by a hoist into the varnish. It is then removed from the varnish, allowed to drain, and set into a chain-type conveyor system. Once the rack is loaded onto the chains, it
is conveyed through the oven and allowed to cure for the recommended time. Transformers are often manufactured by this method.
2. Batch oven system. The second method of curing uses the same dipping system, but the coated rack of parts is placed into a tray oven or batch oven. Midsized stators are often processed by this method. Curing is normally completed all at one level. Stacking the racks with separators is required if multiple levels of parts are to be cured in the oven.
3. Continuous system. In the third method, the part is hung on an overhead conveyor which either is indexed on timed intervals or is continuously moving. The conveyor travels through a preheat zone, goes on through the dip tank into the bake oven, and returns back to the loading/unloading area. Quite often, cooling by forced ambient air or chilled air is incorporated into the system as the final step in the process. Parts are hung on the conveyor either by single wire hooks or on a multipart fixture. Multipart fixtures and drag-through dip systems are very common and can process the highest volume of parts per hour.