The investment castings pouring and clean-up operation method

When considering the three aspects of the problem, the main basis is still the basic principles of general casting process, especially in the process scheme, process parameters ( Such as casting rounded corners, dial the die Angle, machining allowance, craft reinforcement, etc. ) , in addition to the specific data as a result of investment precision casting process characteristic is slightly different, and the design principles and sand mold casting is exactly the same. High dimensional 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 the casting during solidification, etc. , so ordinary size although higher precision investment castings, but still need to improve the consistency ( The medium and high temperature wax casting dimension consistency to improve a lot) 。 Suppress moudle, will use the cavity surface finish high pressure type, as a result, the casting surface finish. In addition, the shell consists of high temperature resistant special mixture of the binder and refractory refractory coating coated on the casting and made, direct contact with molten metal inside the cavity of high surface finish. So, the surface finish of investment castings is higher than the general casting, general of Ra. 1. 6 to 3. 2μm。 Investment casting the biggest advantage is due to the investment casting 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 only grinding, polishing allowance, don't need to machining can be used. Using investment casting method, therefore, can be a lot of saving machine tool equipment and processing time, greatly saving metal materials. The investment castings pouring investment casting pouring methods often used are: 1) There are several type thermal gravity casting method. This is one of the most widely used casting form, namely after the shell from the roaster, by pouring at high temperature. At this time in metal shell cooling slowly, can under the condition of the liquid filling mold, so the castings can replicate the shape of the cavity, improve the accuracy of the castings. But casting slow cooling in hot type can make coarse grains, which reduces the mechanical properties of castings. In the casting of the carbon steel casting, casting surface with a slower cooling also easy oxidation and decarburization, reducing the casting surface hardness, finish and dimensional accuracy. 2) Vacuum suction casting pouring shell on the vacuum box, through the shell of the small pore suck gas in the cavity, can make the liquid metal mold filling better, copy the shape of the cavity, improve casting accuracy, prevent the pores, the defects of misrun. The method has been applied to abroad. 3) Crystallization under pressure pouring shell on the pressure inside the tank, after, immediately closed pressure tank, the tank ventilation with high pressure air or inert gas, make the casting solidification under pressure, in order to increase the density of castings. The maximum pressure in a foreign country has reached 150 ATM. 4) Directional crystallization ( Directional solidification) Some such as turbine blades, such as magnetic steel investment castings, if their crystal structure is arranged in a certain direction of the columnar crystal, their performance will improve a lot, so the investment casting directional crystallization technology is rapidly developed. The clearing of investment castings clean up the content of the investment castings mainly for: ( 1) Removed from the casting shell; ( 2) Since the pouring down the castings at system; ( 3) Remove the casting on the adhesion of shell refractory; ( 4) Clean up the castings after heat treatment, such as scale, all sides and cutting gate residue, etc.