Plastic products are widely used in industry and daily life, the plastic mold has to precision, large scale and multi cavity in the direction of development, performance requirements of plastic mold steel is more and more high, some developed countries independent plastic mold steel series. The performance of plastic mold steel plastic products should be based on the type, application, molding method and production quantity and size. General requirements of heat treatment heat treatment process is simple, small deformation or deformation, the cutting performance of pre hardened state, mirror polishing performance and etch properties, low surface roughness, long service life.
The cutting performance for large, complex and precise extrusion and injection mould, usually pre hardened to 28-35HRC, then cutting and grinding to the required size and accuracy, directly put into use, so as to avoid the deformation of heat treatment, oxidation and decarburization of defects. Join the cutting elements S, Co and rare earth, used to improve the performance of cutting hardened steel.
The surface of the mirror processing performance of laser disc and plastic lens plastic products such as roughness is high, mainly by the mold cavity roughness to ensure that the general mold cavity roughness than the plastic products of high level. The purity, microstructure and hardness and surface machining technology of die steel and steel mirror processing performance. High hardness, fine and uniform microstructure, non-metallic inclusions, are beneficial to the improvement of mirror polishing. Plastic mould steel high requirements of mirror polishing often adopts vacuum melting or vacuum degassing.
The surface of certain plastics the etch performance requirements present a clear and full pattern, and the leather industry in the large leather embossed version, are required to have good lithographic performance pattern of die steel, requirements for material performance pattern lithography and mirror polishing performance similar to that of the pure steel must be high, to dense, hardness to be high.
The corrosion resistance of chlorine and fluorine resin and adding anti burning agent in ABS resin, in the molding process will release corrosive gases. For this type of plastic mould to use corrosion resistant plastic die steel surface or with chrome or nickel phosphorus amorphous coating.
In addition to the requirements of the special performance, also plastic mold steel has good wear resistance and welding performance.
The types and characteristics of 2. new plastic die steel
At present, China has not yet formed a series of independent plastic mold steel, steel level is not high, using some traditional steel, commonly used are 45, 40Cr, T10A, 38CrMoA1, 5CrNiMo, 4Cr5MoV1Si, CrWMn and Cr12MoV etc.. In order to avoid deformation of the mold thermal annealing, had to use the normalized 45 steel 40Cr. or the mould of low hardness, poor abrasion resistance, surface roughness, affecting the appearance quality of the products, for the mold cavity is complex, high hardness, the alloy steel CrWMn, Cr12MoV manufacturing, the heat treatment deformation and not difficult to control to request. In recent years, our country has introduced some common plastic mold steel and abroad a lot of new plastic die steel is developed, its chemical composition table, according to the chemical composition and special properties, these steels can be divided into four types of pre hard type, pre hardened cutting type, age hardening and cold extrusion molding etc..
The pre hardened quenched and tempered steel belongs to this kind of P20, 718 (Sweden) and H13 steel. 718 steel can be regarded as a modified P20 steel, H13 steel is a typical hot die steel. The carbon content of steel is 0.30%-0.50%, belonging to Cr-Mo steel. By adding Ni, Mn, V and Si elements, to further improve the hardenability of steel and tempering stability, maintain the consistency of microstructure and properties in large cross sections. These are mostly in the steel mills fully forged into modules, after quenching and tempering to the required hardness of about 30HRC, making mould directly available to users without heat treatment, thus completely avoid the deformation of heat treatment, this kind of steel is widely used in the manufacture of large and medium An precision injection mold.
The pre hardened cutting shape steel belongs to this type of 5NiSCa, SM1 and 8Cr2S etc.. Compared with the pre hardened and tempered steel, improve the carbon content, and adding a certain amount of cutting elements S or S-Ca, to improve the cutting performance, single S steel, has good cutting performance in low and medium speed cutting conditions. Because the steel in MnS along the direction of deformation in elongation after hot deformation, increase the anisotropy of the steel, the transverse plasticity and toughness of steel decreased significantly.The S-Ca composite and spraying metallurgy technology, can improve the shape and distribution of MnS in steel, the steel to improve performance. Therefore, to improve the carbon content in steel and tempered hardness is 36-45HRC, the user does not need to reheat treatment, can directly make the mold smoothly cutting processing, and reduce the surface roughness of the die, improves the wear resistance, this kind of pre hardened easy cutting plastic die steel for the manufacture of large and medium-sized mold.
The age hardening type belongs to this kind of steel are 25CrNi3MoA1PMSSM2 and 06CrNi6MoVTiA1 steel. The PMS steel has excellent properties of mirror polishing. This kind of steel is low carbon, low nickel aging hardening. After high temperature solution treatment of austenitic low carbon martensite, its hardness is about 50HRC, in order to machining, after high temperature tempering, well tempered sorbite, the hardness decreased to 24HRC, processing the mold cavity, at 500-540 DEG C during the ageing treatment, the precipitation of NiA1 alloy phase, the deformation the matrix hardness rose to 40HRC. the aging treatment is very small, can be controlled below 5/10000, this kind of steel is suitable for the production of high precision plastic mold, but also in the softening treatment to low thickness, cold extrusion molding method for manufacturing complex mold cavity.
The cold extrusion molding type belongs to this kind of steel is only LJ 8416 and two steel. The latter is the introduction of Swedish steel.Steel carbon content is very low, Kunshan plastic mould steel This kind of steel with extrusion and heat treatment process of high performance cold. Add a small amount of alloy elements in steel to improve the hardenability of the steel and the solid solution strengthening effect. After annealing, the hardness is low, generally less than 130HBS, the steel has good performance of cold extrusion die. A mold made of high concentration after carburizing and quenching and tempering treatment, the surface layer of high hardness, wear resistance, but the heart still keep good toughness. This method is suitable for plastic mould in repetitive manufacturing cavity or shallow cavity, can reduce costs, improve productivity.