| It is kNown that there is an enormous market of wear-resistant parts industry,especially for the large-scale wear-resistant plate parts.For the current casting methods,the shortcomings such as shrinkage defect,coarse structure and short service life were encountered in the production of such large wear-resistant parts,and the performance of the products cannot be further improved,thus resulting in the enormous waste of resources.In this paper,the research on the production of large-scale wear-resistant plate parts was carried out by the advanced liquid die forging technology,and two representative types of workpieces with large difference in shape and structure were selected--the wear-resistant side guide plate for broadband conveyor line of hot-rolling mill(abbreviated as side guide plate)and the bimodal liner used in ?5.5m×8.5m overflow ball mill for gold mine(abbreviated as bimodal liner).The liquid die forging process design,mold design and related verification of the two products were implemented,and the simulation was carried out using the ProCAST software,respectively,then the feasibility of the method was verified.After that,the production of liquid die forging of large-scale wear-resistant plate parts was carried out,and the technical design of the equipment of the production line was conducted.Then the side guide plate products that meet the requirements were successfully obtained through the debugging of the process and equipment.Finally,the metallographic structure and mechanical properties of the side guide plate material(high chromium cast iron)prepared by the methods of sand mold casting,metal mold casting and liquid die forging were compared and studied by means of SEM,electric Brovey hardness tester,JB-50B impact testing machine as well as the other experimental equipment.The superiority of the liquid die forging process for the production of large wear-resistant plate parts was quantitatively revealed,and the effect of pressure on the microstructure and properties of workpieces was analyzed.Meanwhile,the fracture mechanism and wear mechanism of the side guide plate samples were also analyzed.The main conclusions of current study are as follows.(1)For the difficulties of liquid forging of wear-resistant sheet with large-scale,the following solutions can be used:?To divide the parts into two parts and adopt horizontal molding are given to avoid the die size being too large;?Combined with direct and indirect liquid forging,multi-point local direct compression scheme is adopted in order to solve the excessive tonnage of liquid forging machine caused by large projected area;?The pouring scheme of the Flip ladle+Spout+Pressure chamber can be adopted when the pouring quantity is too large,and the height of the mould can be reduced because the metal liquid can be stored by the cavity and pressure chamber together;? The cooling water cavity can be designed for key parts of die to solve the problem overheating of mold;?The way of unloading can be flexibly matched with the jacking rod and the press head.Through verification and simulation,the process parameters and die structure design are reasonable and meet the requirements of liquid forging.(2)In practical work,the key technology of liquid forging for wear-resistant sheet parts with large-scale is as follows:?The design of the clearance of the press head and chamber can be calculated with reference to the radial thermal expansion of the pipe.In order to prevent steel leakage,the thickNess of graphite coating can be adjusted to adapt to the change of clearance at different temperature under different die times;?Debugging the equipment,process and operation to reduce the initial pressure time and prevent excessive condensation in the chamber;?The study also considered pouring time,starting pressure time and combining computer simulation technology to determine pouring quantity;?The linear shrinkage rate is calculated by the difference between the upper and lower dimensions of the die cavity,properly tri mming and polishing,and the friction surface of demoulding can be lubricated by a better concessional coating to reduce the friction force and avoid cracking in the position without the release angle;?Besides these traditional liquid forging process parameters,the new parameters can be added according to the forming needs in the PLC program,such as the start-up shrinkage time;?In order to prevent the compression of the pressure head,the closed pump is chosen as the first step to keep the pressure.At the same time,the double signal condition is designed for each PLC operation.The preferred condition is according to the process action design,the second selection condition is the protection condition.(3)The microstructures and properties of side guide plate made by high chromium cast iron under metal mould casting(0 MPa)and liquid forging(148 MPa,212 MPa)were compared.The results show that the pressure can refine the microstructure significantly and improve the hardness,impact toughness and wear resistance of heat-treated samples.Under as-cast condition,the average length,width of primary austenite,and the diameter of eutectic cell at specific pressure of 212 MPa are reduced by 68%,32%and 64.3%respectively compared with that of metal casting.The hardness,impact toughness and wear resistance of 212 MPa are increased by 6%,23.6%and 29.4%respectively under heat treatment.(4)The wear resistance of side guide plate made by high chromium cast iron in liquid forging and sand casting were compared after heat treatment.The results show that the liquid forging process improved the wear resistance of products.When the liquid forging pressure is 212 MPa,the wear resistance were increased by 36.8%respectively.(5)Fracture mechanism and wear mechanism of side guide plate made by high chromium cast iron were analyzed by comparing impact fracture and wear surface of specimens.The impact fracture of metal specimens is cleavage fracture.The impact fracture of specimens under 148 MPa and 212 MPa hydroforging specific pressure is quasi cleavage fracture.The wear mechanism of the samples under the sand casting,metal casting and liquid forging processes is the same,which is the joint action of cutting wear mechanism,plastic wear mechanism,chipping wear mechanism and crack growth mechanism.In su mmary,liquid forging can be applied to large wear-resistant sheet metal parts(large steel parts).Compared with sand casting and metal casting,the properties of liquid forging products have been greatly improved. |
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