Technical Article


An Investment Casting Foundry Experience in Improving Degassing and Grain Refining in Molten Aluminum Alloys


by Robert Zebick, Atlantic Casting & Engineering; & Brian Began, Foseco Foundry Division, Vesuvius PLC T


he requirements to degas, flux and grain refine molten aluminum alloys for investment casting are


well established. The evolution of casting buyer requirements; now requiring larger castings or more complicated geometries than the previous generation, continually require better and more consistent melt treatments for the molten aluminum. Fortunately, several recent


technological advancements


have allowed degassing, flux and grain refining to be higher performing and more environmentally-friendly than were historically achievable. This article reports on the efforts of Atlantic Casting & Engineering (ACE) in Clifton, NJ to implement an improved aluminum alloy treatment process to keep up with the demands of industry. Moreover, the article will document the rationale and evaluation process for implementing the process improvements and discuss the economic, technical and environmental benefits achieved upon complete implementation of the new treatment process. ACE is privately-owned and has business


been in manufacturing


for over 80 years high-precision


and


geometrically complex cast parts, primarily for the aerospace market, but also serving the military, electronics, transportation, medical and various other marketplaces. ACE melts and pours an array of


aluminum alloys including 201, A203, A205, C355, A356 and F357. These melts are melted and prepared in one of six electric-resistant crucible furnaces ranging in size from 1200 lbs. to 250 lbs.


26 ❘ May 2020 ®


Figure 1: Picture of the RPT Apparatus Used to Assess Degassing Efficiency


in capacity with all elemental additions made directly into the furnace. The historical method for treating aluminum entailed adding metallic-form TiBor (5%Ti, 1%B) pucks into the melt at a rate of .25% the weight of aluminum to be treated. The additions were made prior to the degassing process, which utilized an iron-cross or gear shaped rotary impellor connected to a simple pneumatic drive degassing unit that is raised, lowered and transported via an overhead hoist. High purity argon was the purge gas used during the 30-minute rotary degassing cycles.


In addition to rotary degassing, hexachloroethane degassing pills were


Alloy 201


A203 A205 C355 A356 F357


Specific Gravity Specification Min.


2.70 2.80 2.83 2.65 2.65 2.65


Table 1: Alloys and Specific Gravity Threshold Minimums


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