Analytical precision casting technology
From:Tongling sanyuan special casting co. LTDAddtime:2018-07-09
Precision casting is a casting method compared with traditional casting technology. It can obtain relatively accurate shape and high casting precision. The common practice is to first make the electrode of the required blank (the residual amount is very small or the residual amount is not left) and then use the electrode corrosion mode to form the cavity. The original wax model was obtained by casting wax. Coat the wax mould with high temperature resistant liquid sand. After enough thickness is obtained, it is dried and heated to melt the internal wax mould, and the cavity is consistent with the required blank. Cast iron water in the mold cavity, and after solidification, peel off the shell, you can get the precision products.
Waxless casting, now known as investment casting, is a casting process with little or no cutting. It is not only applicable to the various types, various kinds of alloy casting, and produce the casting dimension accuracy and surface quality is higher than other casting method, even other casting method is difficult to cast the complex, high temperature resistant, not easy machining castings, all can use revestment precision casting wrought.
The precision casting of molten mould is developed on the basis of ancient wax mould casting. As ancient civilizations, China is the use of this technology is one of the early, long centuries BC, the ancient Chinese working people created this kind of lost wax casting technology, used for casting tripod with a variety of fine decorative pattern and text and household utensils and other products, such as the tomb when the spring and autumn period and the statue of plate, etc. Tomb statue of plate base for multiple mutually intertwined dragons, they end to end, staggered up and down, form the middle hollow out layers of moire pattern, these designs using ordinary casting process are hard to make out, and with the method of lost wax casting process, can make use of the characteristics of paraffin wax no strength, easy to carve, carved with ordinary tools can and want to get the tomb of paraffin wax material arts and crafts of the plates, then additional gating system, coating, dewaxing, pouring, beautiful tomb statue of plate can be calculated out.
The modern investment casting method was applied in industrial production in the 1940s. At that time, the development of aero-jet engines required the manufacture of complex shape, size **** and heat-resistant alloy parts with smooth surface, such as blade, impeller and nozzle. Due to heat resistant alloy materials difficult to machining, complex shape parts, so that can't or difficult to use other methods, therefore, need to find a new precision forming technology, then draw lessons from the ancient tradition of lost wax casting, after improvement of materials and technology, modern investment casting method on the basis of ancient technology for the development of the important. Therefore, the development of aviation industry has promoted the application of investment casting, and the continuous improvement of investment casting has created favorable conditions for the aviation industry to further improve its performance.
China began to apply investment casting to industrial production in the 1950s and 1960s. Within this advanced casting process with the development of the huge, successively in the aviation, automobile, machine tools, ships, internal combustion engines, gas turbines, telecommunications equipment, weapons, medical equipment and tool widely used in manufacturing industry, also used for manufacturing arts and crafts. So-called investment casting process, simply be with fusible materials (such as wax material or plastic) into the meltability model (referred to as "investment pattern or model), on which the coated with several layers of tailor-made refractory coating, after drying and hardening type to form a whole shell, reoccupy steam or hot water from the melt in the shell model, and then put type shells in the sand, dry sand by filling in all round its modelling, * * after the high-temperature roasting cast into the furnace (such as high strength shell, can need not modelling and will release the shell directly after roasting), cast type or shell after roasting, and are casting in pouring molten metal.
Size precision investment castings, general of CT4-6 (sand casting is CT10 ~ 13, die-casting is CT5 ~ 7), of course, due to the complexity of investment casting process, factors influencing the dimension accuracy of castings is more, such as mold material shrinkage and deformation of casting, shell in the process of heating and cooling line quantity change, alloy of shrinkage and deformation of castings in the solidification process, so the average size although higher precision investment castings, but still need to improve the consistency (in medium and high temperature of the wax casting size consistency to improve a lot). When pressing the mold, the pressure type with high finish of the cavity surface is adopted. In addition, the shell is made of special high temperature resistant binder and refractory refractory refractory coating, which is applied to the melting mould. Therefore, the surface smoothness of the investment casting is higher than that of the general casting parts. Generally speaking, it can reach ra.1.6 ~ 3.2m.
The advantages of investment casting is due to the investment castings with high dimensional accuracy and surface finish, so can reduce machining work, only in parts a little higher requirements on the parts machining allowance, and even some castings for grinding, polishing allowance, only can be used without machining. It can be seen that the method of investment casting can save a lot of machine equipment and processing time, and greatly save metal raw materials.
Another advantage of the investment casting method is that it can cast complex castings of various alloys, especially high temperature alloy castings. For example, the blade of jet engine, its streamlined outer profile and inner cavity for cooling, can hardly be formed by mechanical processing. The casting process can not only be produced in batch, but also avoid the stress concentration of residual blade after machining.