Research On Investment Casting Technique For K4169Volute

Cast superalloy is an indispensible structural material which has been extensively applied in the field of aviation and aerospace. The oxygen pump case-volute which is cast in K4169cast superalloy by investment casting, is one of the key components of the airspace flight engine. The volute with complicated structure is composed of three parts:inlet flange, outlet flange and volute runner, and the discrepancy of the wall thickness is great, the thickness of inlet flange is33.5mm, the volute runner only6mm, moreover, the section shape of the volute runner is complicated. These are very likely to cause cast defections during the solidification process, such as shrinkage cavity and deformation. In addition, this casting can only work in strict conditions with liquid oxygen-hydrogen and high pressure. So it is demanded that castings have high metallurgical quality, excellent comprehensive mechanical properties and dimensional accuracy. These factors all combine to make the volute difficult to cast. Taking the K4169volute casting as the object of study, this paper attempts at a systematic research on its precision-investment casting technology, so as to obtain qualfied superalloy casting in accordance with some specific technological requirements.In this paper, based on numerical simulation technology and drawing upon ProCAST, the filling and solidification process of volute casting is simulated, the porosity defection is predicated, and the optimized casting parameter is acquired. The results show that the top gating pouring system and the feeding system to feed the outlet flanges adopted at last can make volute castings fill cavity rapidly and smoothly, and then solidify progressively. As a result, there is less visible porosity in the key locations of the casting, and only a small amount of dispersive porosity appears around the ribs of volute runners. The castings have short solidification time and few cast defections by adopting the plan of pouring technology in which the shell temperature is850℃and the pouring temperature is1450℃.The research on investment casting technology of volute shows that through adopting the proposal in which soluble core with metal inner cores is shaped into volute rotary impressions and the secondary forming technology, the wax pattern used to manufacture volute castings which conforms to technological requirements can be produced. By using the silica sol ceramic shell technology, the face coating is smeared for two layers with silica sol and zircon powder, the corundum sand is used as its stucco, and the backup layer is brushed for five layers with silica sol and the coal gangue powder, the coal gangue sand is used as its stucco. Shells thus produced boast of high strength at high temperature, excellent surface quality. Combining with the numerical simulation and the structural features of volutes, the volute is cast by using filling sand modeling technology, hot shell and gravity pouring with vacuum technology. After hot isostatic processing:117℃/130MPa/4h, and the improved heat treatment:1095℃x2h/AC+955℃x2h, furnace cooling to700℃/AC+720×8h,50℃/h to620℃×8h/AC, the porosity defect of the casting is under better control and homogenization of its microstructure is improved. The castings have desirable metallurgical quality and entirely meet the requirements of the design and use.After analyzing the alloy quality of trial-produced volute castings, this paper reveals that K4169volute castings have high dimensional accuracy and high surface quality. Internal microporosity is low and in line with the simulation results. From macroscopic view, the microstructure of the whole casting is equiaxed grains, different sections all present dendritic crystal features, secondary dendrite arm spacing (SDAS) is measured, and the relationship between SDAS and cooling rate (T) of section which is precdicted is as follows: SDAS(d2)=218.68(T)-1/3-36.07. From microscopic view, more acicular8phases exist sections of inlet flange and outlet flange, in which interdendritic y" phases are large in size and number, however, at the dendrite arm y" phases are small in size and number. There are few8phases in section of volute runner, and y" phases in interdendritic region and dendritic arm are small in size, and their number don’t significantly differ. Meanwhile, the hardness of different sections is also different. All in all, these results are associated with the cooling speed of volutes sections in essence.