Mold deposits are materials that are deposited in the gaps between the inserts of molds for plastic injection molding or in the corners of the cavity. When the deposits accumulate, defects occur such as short shot of the molded item, or the shape is not accurately transferred to the molded article.

The causes of deposits can be the deposition of chemical constituent in the plastic or can be due to the effect of the chemicals or oil traces on the surface of the mold. The moisture in air can get adhered to the gap between the inserts and can cause the generation of rust, deposits get accumulated on such rusted parts, and the accumulation of deposits grows.

Although it is difficult for the "soot component" or the gas component in the volatile gases generated from the plastic to get adhered when the mold temperature is high due to molding operation, if the mold is removed from the molding machine and the mold temperature decreases, the gas components, etc. become solidified and become deposits.

The mold will last long if the deposits are removed periodically by dismantling and cleaning the mold. At the time of designing the mold, it is important to consider the optimum periodicity at which to dismantle and clean the mold.

In addition, it is also effective to adopt a mold structure which makes it difficult for deposits to get accumulated. For example, methods such as providing a gas vent surrounding the core pin and providing a groove surrounding the ejector pin and the runner lock pin for gas to escape are used in practice. It is also effective to use rust resistant steel such as stainless steel for the material of the mold components, or to provide hard chromium plating or a PVD film coating.

There are also some cases in which the gaseous components are forcibly exhausted using a vacuum suction device, but this makes the structure of the mold complicated.

During maintenance of the mold, the adhered matter is removed carefully by ultrasonic cleaning or using organic solvents to degrease the mold.