How to measure the drying time of paint film?

Since the drying of Coating and the formation of film are a very slow and continuous process, in order to observe the whole change in the drying process and the time required for actual drying, an automatic drying time meter can be used. One is to use a motor to drive the gear through the speed box, and move in a straight line on the film at a slow speed of 3o mm/h, for a total of 24 hours. With the gradual drying of the film, the gear traces gradually change from deep to shallow until they all disappear. The other is to use a motor to drive the funnel containing fine sand, and move slowly on the film-coated sample, the sand will constantly fall on the film, forming linear sand traces to measure the time required for different stages of drying. Further, the needle tip is used to slowly draw a circle with a radius of 5 cm on the film, and it takes 24 hours to draw a circle, so that the drying degree of the film can be observed on a smaller test plate area, and the actual drying time required.