Velocity Measurement and Verification with Modeling of Naturally Pressurized Gating Systems

Abstract

There has been reluctance from many iron foundries to adopt naturally pressurized gating systems due to the lack of knowledge on the application of the theories set out by Dr. John Campbell. The applications of naturally pressurized gating systems are still evolving and, in many cases, are counterintuitive to foundry engineers. This research tested proposed gating system behavior during filling, and from the resulting data, velocity losses (friction coefficients) through ceramic foam filters were measured. The verification of the velocity by modeling and simulation of these systems proved relatively accurate in most cases studied. The research concluded that a vertical vortex sprue system had the highest velocity reduction, reducing it by 37% (friction coefficient of 0.63), but had some initial air bubbles travel through the gate before steady-state flow occurred. The most effective gating system tested was a bottom gate and ceramic foam filter combination utilizing a bypass for the initial damaged metal and initial velocity reduction. The in-line gating using 10PPI and 20 PPI ceramic foam filters had a reduction in velocity of 16% and 28%, respectively, but caused major bubbles and jetting of the initial metal at the gate. When using filters in-line with the runner, the filter print and the bypass should be vented and the bypass have sufficient volume to counteract the initial high-velocity metal entering from the sprue. A bypass of sufficient size, reduced the initial velocity of metal through the gate, allowed priming of the filter, eliminated jetting, and reduced the chance of damaged metal from entering the mold.