How to solve air and gas blow holes in the Aluminum Gravity Die Castings? A shop floor experience and 4 case studies

摘要

Part1: Many aluminum castings are being produce using static gravity die casting process. Air & Gas blow holes are the two major problems encountered in the castings in general. (1)Air blow holes are due to flow characteristics such as 'Vortex formation & gaining' more speeds th; exceeds Renold's number 3500, which leads to turbulencein the metal flow. Air mix up starts in the molten metal if is pouredthroughthe top risers of the casting without any controls usinghand ladles.In the dies with "controlled running system, it can happen in the pouring basin itself, down sprue& while entering in to the die cavity with high speed. It also happens some times inside the die cavity due to internal complex shapes. (2)Gasblowholes occur due to 1)Excess resin Content in the sand, 2) lack of permeability in the Sand dueto the use of very fine grain sand, 3) If the core is made 'solid ' instead of "hollow", the gases penetrate in to the casting .4) Lack of venting in the die cavity. In this paper, the design aspects, which are to be taken care of while designing the die, to avoid / reduce the above two defects, are explained. Theblow holes are "Globule" in shape with the "Grayish" bottomsurface. Whereas the Resin blow holes are also in "Globule" shape, but with Shiny" bottom surface or brownish in the case of tiny holes. The shop floor foundry men should be able to diagnose them. For this, a practical method is explained. A Matrix diagram is given for analyzing & finding the root causes This is derived from the 'Cause and Effect 'Diagram of Prof. Ishikawa san of Japan (7QC Tools). At first tentatively fix some probable causes, then conduct experiments & find the root Causes . Part 2 :- Four case studies are presented to Illustrate the effectiveness of the Matrix diagram.