Contaminants that enter the oven will be carried rapidly to the parts by the recirculating blowers and can eventually be embedded into the finish before it completes the cure cycle. Total heating time is the sum of the time that it takes for the parts to reach the predetermined cure temperature plus the time that is required for the part to remain at that temperature to complete full cure. To accurately determine the total oven time it is helpful to send a temperature recorder into the oven with a probe attached to the parts surface and another that will measure the oven atmospheric temperature. Most powder sales representatives will be happy to help you run such a test. Once the total oven time is determined for the given mass, or part, some type of timing system must be implemented to insure that the parts are exposed to the necessary heat for the proper time.
Conveyorized ovens use line speeds to establish the total oven duration.
Batch finishers will use some sort of timer with a bell or flashing light to remind the coating applicators that the parts are to be removed from the oven. Housekeeping is one subject that I cannot write enough about and for good cause. If contamination is abundant on the shop floor of any plant that I visit, I will bet good money that the inside of the oven, spray booth, collector system, powder hopper, etc. will also contain the same contaminants. Shop air flow is constantly moving and changing. Lift trucks moving about, doors opening and closing, fan and air conditioners blowing, compressed air being used for part blow off and many more factors involving air movement will cause contaminants such as dirt, lint, hair, and trash to be introduced into the finishing system.