Influence of gating and other processing parameters on mold filling the LFC process

摘要

Two separate sets of experiments were conducted to better understand the principles of gating in the lost foam casting (LFC) process. First, tests to find the critical gate size that controls the metal velocity and fill time were performed forboth 319 aluminum and gray cast iron. For aluminum using a low-permeability coating, the gate never served as the system choke-the recession rate of the foam or the rate of transport of foam decomposition products through the coating controlled the rateof fill until the gate size was extremely small. For aluminum with a high-permeability coating, or for gray iron with any coating, the gate could be made small enough to serve as the choke; however, the critical gate size was so small that the patterncould not be effectively secured to the cluster.Second, two statistically designed experiments were used to compare the effects of gate size, number of gates and top versus bottom gating to other typical casting parameters, including foam density, type of refractory coating and pouring temperature, inproducing aluminum lost foam castings. The key factor in both experiments was the refractory coating: a high-permeability coating provided rapid transport of foam decomposition products, leading to high metal velocities during filling. The high metalvelocities, in turn, led to a high probability of forming internal porosity in the casting. The gating design-size of gates, number of gates and placement of gates-was not statistically significant.