(1) Sand casting
Sand casting is a process which uses sand mold to produce castings. Because of its low cost, short manufacturing time and wide applicability, it is still used as the main process of wear-resistant plate production. At present,has made great progress. There are many production lines of VRH sodium silicate sand and resin sand at home and abroad. Clay sand and sodium silicate sand are the most widely used in domestic production. Advanced resin sand has brought good results to some wear-resistant plate mold production enterprises. Some of them also select resin sand and sodium silicate sand in layers and then use C2 overall hardening, which improves the surface energy of castings and gets a low production cost way of resin sand. But even so, the fundamental disadvantage of sand casting still exists, the production efficiency is reduced because the mold can not be reused, the dimensional accuracy of the product is poor because of the poor rigidity of the mold, and the surface quality of the workpiece is seriously affected by the phenomena of sand flushing and sand inclusion. Solidification under gravity limits the improvement of mechanical properties of castings, and the service life of the final workpiece is short due to casting defects, which restrains the development of wear-resistant parts industry.
(2) Lost foam casting
Lost foam casting is a kind of. It is a foam or wax model that combines the bond into a model family and has the same shape of the workpiece and is painted with fire-resistant paint and dried. After embedding the sand into the thousand quartz sand, the model is vaporized under negative pressure pouring, and the metal liquid is filled with the model position and solidified to form the workpieces.
Lost foam casting has no flash, burr, draft angle, parting surface and sand core. It has the advantages of accurate molding, simple procedure and no need to take mold, so it reduces the size error and improves the precision of wear-resistant plate. In addition, EPC does not use chemical binder to aid molding. Foam plastics are basically harmless to the environment at low temperatures, and the recovery rate of molding sand can reach more than 95%, so it can be said to be a green casting method. However, there are some limitations in the EPC process. When pouring the molten metal, the gasification process of the model will absorb a lot of heat, resulting in the temperature drop of the front molten metal, the poor flow performance, and the formation of casting defects such as pores and cold shuts. For wear-resistant plate parts, these defects will undoubtedly reduce the service life. In addition, the basic research on foam model materials inin China is progressed slowly, which limits the application of wear resistant plate parts in EPC.
(3) Bimetal composite process
Bimetallic composite process is a kind of molding method which selects many kinds of metals according to the needs of different parts of the casting. After composite, the workpiece can give full play to various excellent properties of different alloys, effectively make up for their own shortcomings, so as to achieve better service performance. According to bimetal composite method, it can be divided into three categories: solid-liquid, liquid-liquid and solid-solid composite.
1) Solid liquid recombination
The solid-liquid composite casting technology is a kind of technology that the cladding metal liquid is poured on the prefabricated matrix, or the surface treated matrix is sunk in the cladding metal, and the continuous diffusion area between metals is formed through the diffusion reaction between different metals, so as to form the composite material. This method has high requirements for the compatibility of material heat treatment process. If the thermal physical properties of different materials cannot match each other, cracks will appear on the composite interface in the production process or subsequent heat treatment process. Therefore, the development of this process is slow and it is not suitable for the production of large wear-resistant plate parts.
2) Liquid liquid recombination
The liquid-liquid complex process is a process that more than two kinds of metal liquid are poured into the mold cavity in turn, and metallurgical bonding occurs between different metal interfaces. The earliest application of this technology is the production of roll pipe fittings. In recent years, some manufacturers have used this method to manufacture wear-resistant plate moulds and produced jaw plates of cast steel high chromium cast iron bimetallic crusher and lining plates of ball mill. However, in the process of compounding, defects such as mixing, shrinkage cavity and inclusion are easy to appear, and the technology is complex, the cost is high, and it is not suitable to realize.
3) Welding compound method
In the solid-solid composite, welding composite method is mostly used, among which explosive welding and surfacing are the most widely used methods. Explosive welding is a new technology of high-strength welding, which is driven by the high-strength impact produced by explosion to drive the composite plate to collide with the substrate at a high speed. On the exposed metal surface, a thin layer of welding transition zone with melting, diffusion, plastic deformation and waveform characteristics is formed by the instantaneous high pressure generated by the impact point, thus realizing high-strength welding. The explosive welding products have excellent performance and are suitable for the production of single, thick and large area composite slab and multi-layer composite plate. However, they have poor working conditions, low mechanization degree and certain danger. The bimetal materials prepared have large deformation and unevenness, which are rarely used in the production of plate wear-resistant parts.
Hardfacing is the stacking of materials with special properties on the surface of parts by welding, which can improve the wear resistance of workpieces and reduce the production cost. However, the residual stress of other alloys on the surface of iron and steel parts is large, and the shrinkage ratio of the alloy is not the same in the process of surfacing, so it is easy to crack. In order to reduce the dilution of the base material to the wear-resistant layer alloy, multi-layer surfacing is often needed, which is difficult to ensure the overall wear-resistant performance.
4) Direct rolling
Direct rolling method is also a kind of solid solid recovery method, which is mainly divided into hot rolling composite, cold rolling composite and vacuum composite. Hot emulsion compounding is a method of combining two metals by overlapping and welding their edges. The interface of the two metals is similar to viscous fluid, forming stable thermal diffusion under high temperature conditions, which can be used to produce large wear-resistant plate parts. However, the hot rolling process is complex, the processing cycle is long, the interface is easy to oxidize and the quality is worrying. The cold rolling compounding process can be described as Surface treatment, cold rolling combination and diffusion annealing can produce atom combination between different metals by compression and strengthen them by diffusion annealing. It is difficult to control the plate shape during cold rolling and lamination, and the rolling piece is easy to edge crack, and the alloy will deform unsteadily and transversely break when the deformation resistance is large, so it is not suitable for the production of large wear-resistant plate. Vacuum lamination is the same as hot rolling and lamination, the difference is that there is no oxidizing atmosphere under vacuum, which reduces the blocking effect of oxide film and adsorbing layer on the metal interface combination, The cost is high, the control of gas atmosphere is difficult, so far there is no production conditions for large parts.