Research On Side Extruding Formation Of Equal-Section Cores

A new process was brought forward, which forming continuously fine equal-section cores for investment casting with side extrusion process. The forming tooling and core materials were designed and optimized. This process will realize a continuous and high efficiency technique, which can overcome the disadvantages of conventional core making process such as thermal extrusion in large batch production of small equal-section cores.The investment casting cores were formed by side extrusion. These cores consist of zircon and alumina powders, which are suitable for most cast alloys. Having been fired under different temperature, the strength value of cores was regarded as the main objective parameter and formability as referential index. Taking the addition amount of starch, phosphoric acid, glycerol, polyethylene glycol (PEG) as influencing factors, orthogonal experiments have been done to search for the optimized formula of core materials.The strength value rises suddenly as exposed to a very high temperature or for a long time. If the cores are fired for a long time and at a high temperature, they will be sintered severely. Strength and hardness are so high that it is hard to clean up from the casting.The experiment result shows that phosphoric acid bonded cores are strongerthan silica-sol bonded ones for zircon based system. The strength of alumina based core is not sensitive with the changes of phosphoric acid amount and the temperature.Improving on granularity distribution of core materials will reduce the degree of sintering, as a result reduce the strength after high temperature heating. So that it is easier to clean up residual core from the casting.Starch and glycerol are added to the core base materials as plasticizer and modifier, which affect the strength of casting core slightly. Starch can improve the flowability and formability of materials. The addition of glycerol has the advantage of keeping the core materials wet in a certain extent.The fact shows that this forming technics is feasible and easy to operate. Further more, it is able to form thin and equal-section cores continuously and efficiently. The side-extrusion formed cores have been used to produce precision casting. Good internal surface quality has been obtained, proving the core possesses good high-temperature properties and can endure the impact of molten steel without break. Furthermore, comparing the two kinds of cores, the alumina-based is easier to clean up than the zirconia-based ones.