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Common failure modes for plastic molds
The plastic mold is a mold for plastic processing and is made of plastic steel such as 45 steel, P20 and 718. Analysis of the failure of plastic molds can better guide the development of mold steel. The failure modes of plastic molds are:
1. Wear and corrosion of the cavity surface
1) The plastic melt flows in the cavity with a certain pressure, and the solidified plastic parts are released from the mold, causing friction on the molding surface of the mold and causing wear.
2) The reinforced resin filler in the plastic will cause erosion, abrasion and corrosion on the surface of the mold cavity.
3) At the same time, chlorine, fluorine and other components in the plastic processing are thermally decomposed to corrode gases HCl and HF.
These cross-overs can cause damage to the coating or protective layer on the surface of the cavity, causing wear and corrosion.
2. Plastic deformation failure
1) The surface of the plastic model cavity is pressed and heated to cause plastic deformation failure, especially when the small mold is working on large tonnage equipment, it is more likely to cause overload plastic deformation.
2) The material used in the plastic mold has insufficient material strength and toughness, and the deformation resistance is low.
3) The hardened layer on the surface of the plastic mold cavity is too thin, the deformation resistance is insufficient or the working temperature is higher than the tempering temperature to cause phase change softening.
These can cause damage to the surface of the mold, such as depressions, wrinkles, pitting, corner collapse, and the like.
3, the break of the plastic mold
1) The shape of the plastic mold is complicated. There are many corners, thin walls, etc., and local stress concentration at these parts will cause cracking.
2) Structural stress, thermal stress caused by temperature difference or insufficient tempering, at the use temperature, the retained austenite transforms into martensite, causing local volume expansion, resulting in tissue stress inside the mold.
Due to the above reasons, the domestic mold life is only 1/3-1/5 of foreign countries. The material developer of the mold should be considered based on the above aspects in order to develop a better carbon, alloy, and composite plastic mold steel.