The Countergravity Process

Developed by Hitchiner's Technical Center in the 1970s, the Countergravity Low pressure Air melt, or CLA, has proven to be more efficient and yield a higher quality product that traditional ladle pouring casting procedures. 

In the CLA process, the mold is placed in a vacuum chamber with an open snout, or fill pipe, facing down. The chamber is sealed and lowered a precise distance into the melt. A vacuum is created, which draws the metal up into the sprue cavity, filling every section completely. After a brief hold time allowing the metal to partially solidify, the vacuum is released and the residual metal in the central sprue flows back into the melt. Only a short gating stub remains on the casting, which is later removed by a mass production gate grinding machine.

The driving force behind the development of this process was economics. Unlike gravity poured parts, which must be cut away from the central sprue, there is no need to leave room for the cut-off blade in the design of a CLA casting cluster. As a result, many more parts can be assembled on a CLA sprue, increasing output by two to three times conventional assemblies. Another advantage to using CLA is reducing waste. About 60% to 94% of the metal used will produce product, compared with 15% to 50% in gravity poured parts where much of the cast weight is in the sprue and gating.

A Superior Casting

The CLA process offers our customers more versatility in their designs and ultimately a higher-quality product. Because the sprue is filled in a non-turbulent fashion from clean metal beneath the surface of the melt, castings with far less slag and non-metallic inclusions are produced. Typically, countergravity cast metal contains only 15% of the inclusions of poured metal of the same analysis. This cleaner metal has been shown to reduce tool wear by 100% to 500% in comparative machining tests done under controlled conditions, and shows very few after-polish defects in highly polished parts. CLA also gives us the ability to cast sections for our customers as thin as .015 of an inch and allows us to control of grain size.

Innovations in Investment Castings

In the years since its development, CLA has been adapted for use in a number of specific applications. including:

CLV: The Countergravity Low pressure Vacuum process employed by Hitchiner's Gas Turbine Division, applies countergravity casting technology to reactive alloys that must be cast in an inert or vacuum atmosphere. Briefly, metal is melted in a vacuum in the lower chamber of the casting machine. The hot mold is introduced in a separate upper chamber and a vacuum is created there. Both chambers are back filled with Argon. A valve is opened and the melt is raised until the snout of the sprue enters the molten metal. Additional vacuum is applied to the upper chamber to draw the metal up. The vacuum is released after the parts and gates have solidified.

CLI: The Countergravity Low-pressure Inert gas process blankets the melt with an inert gas to cast reactive alloys quickly and efficiently.

C3: The C-cubed process uses centrifugal force to aid in mold fill-out in thin sections. View CLI-C3 Process video.

SSCLA: A version of CLA which supports the mold with sand. Hitchiner has deployed a high-volume, fully automated multi-station rotary SSCLA casting machine at its main production facility.

SLIC: SLIC (several layer investment casting) is the latest fuel-efficient, clean Hitchiner® countergravity casting process. SLIC reduces shell material usage by about 70%, floor space requirements by up to 70%, and mold-heating energy by 87.5% while eliminating the need for large burnout furnaces. The water-based process achieves these goals by significantly reducing the number of shell layers needed to make molds.

Metal Casting Technology, Inc. (MCT), a wholly-owned research and development subsidiary of Hitchiner Manufacturing Co., Inc. developed this environmentally friendly process. Canadian automotive manufacturer Wescast Industries licensed SLIC in 2007 and product development is ongoing at MCT and Hitchiner.