In this process, castings with the physical properties of forgings are possible through the use of deeply anodized aluminum molds with a special pouring technique giving progressive freezing from the bottom up. It is applicable to all usual casting alloys based on steel, cast iron, magnesium and aluminum. With anodized aluminum molds, cooling time of the cast metal is shorter than is the case with sand casting, the prolonged cooling time of which produces relatively large quantities of gas which must be allowed to escape through the permeable sand mold. But with the anodized aluminum mold the mold surface tends to absorb and hold some atmospheric gases, hydrogen being the worst offender.
When the casting is poured, the occluded gases are released by the mold and are entrapped at the surface of the cooling casting, producing a minutely mottled effect. These gases can be released by heating the mold in a vacuum. Improvement in surface finish depends upon the degree of vacuum and duration of treatment.
The customer constructed the vacuum dehydrating oven which is also used as a vacuum furnace at temperatures to 950 ° F. The heat source is the Chromalox Electric strip heater. Fifty strip heaters totaling 37.5 kW were installed horizontally around the circumference of the vessel, and twelve segment heaters (which are shaped approximately like a slice of pie) in the door. The latter are curved slightly to fit the convex form of the door. Insulation is between three and four inches thick.
- It contributed to economical oven construction and operation.
- Its compactness is an advantage as the vessel is located in a crowded area.
- There is no gas exhaust problem.
- Temperatures needed are quickly attained and maintained.
- Control is exceptionally easy.
- It is a clean heat source.
- It is completely safe.
- Maintenance is zero.