Injection mold should have the performance characteristics
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Injection moulds are more complex than metal moulds. According to the working conditions, injection moulds often need to improve some special properties.
1. Easy to unmold
The surface disturbance of the die and its parts is the main factor which leads to the demolding, especially for the steel die with low surface hardness. The surface disturbance is due to the properties of the mold material itself (such as porosity), or the damage to the properties of the mold after a long period of use (the effect of the resin).
2. Good abrasion resistance, corrosion resistance and oxidation resistance
For plastic mould due to the plastic molding processing was conducted in a certain temperature, the working temperature of mould and generally under 250 ℃, and because some plastic (PE, PP and PB, such as polyolefin derlin POM;Polyamide PA;Linear polyester PC, PBT and PET;PPE, PEEK, PAEK/PPS, PSU and PES (polysulfone/polysulfone) will decompose hydrogen chloride or hydrogen fluoride gas when heated during molding, which will cause corrosion on the surface of the plastic mold.At the same time, most of the plastics are added with a certain amount of filler, such as glass fiber, powder filler will cause wear on the surface of the plastic mold, after the corrosion of the mold surface roughness increase will aggravate the mold wear lead to failure.Therefore, to improve the service life of plastic mold is to improve its surface wear resistance, corrosion resistance, thermal adhesion by taking necessary technical means.
3. High hardness and stability
These properties are ideal for injection moulds with textured surfaces and moulds for the processing of engineering plastics, including polyamide and polyaromatic sulfone/polysulfone.
These problems encountered by the injection mold can be solved by PVD coating, which makes the injection mold have the following properties:
(1) higher wear resistance, greatly extend the life of the mold;
(2) the rubber material can flow for a longer time, better filling effect;
(3) improve the surface quality of plastic products and reduce the defect rate;
(4) demoulding is easier and even the use of demoulding agent can be avoided;
(5) effectively prevent corrosive materials from eroding the mold matrix;
(6) the mold is easy to clean and the cleaning cycle is longer.
In addition, plastic molds are generally tempered at low temperatures, so PVD coatings that are generally treated at high temperatures are not suitable. In this case, the low temperature PVD coating process should be used to ensure that the mold substrate coating is not annealed.
Based on the obvious advantages of PVD coating, many scientists have adopted this process in the injection mold. Unbalanced magnetron sputtering method (PVO), will Cr12MoV steel production of PVC plastic injection molding, the conventional heat treatment after deposition of TiN film, make its wear resistance increase, and because of the improvement of the performance of the resistance to salt fog corrosion, make the mould surface caused by pitting corrosion will not occur when stripping the sticky mold, plastic parts surface is smooth, good quality and service life is 2 ~ 4 times higher than the original, improved the production efficiency.Some researchers used PVD method to coat TIN on the plastic mold, which improved the life of the mold.For the leadscrews used in the manufacture of jet forming, the multiple arc method and the multiple arcs HCD method in the PVD method are used together to reduce the rejection rate to almost zero.The screw treated by PVD method has good performance of resin film removal and reduces the burn-out of resin at the same time.In addition, TIN was coated on die core by PVD method, and the number of shot peening was 3 times higher than that without treatment.