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Low-pressure sand mold components.
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The V-Process Boosts Product Quality for Domite Wear Technology

June 23, 2020
A vacuum molding technology emphasizes accuracy and consistency, and a new installation is having quality and cost benefits for one ferrous foundry.

Domite Wear Technology, a ferrous foundry in Paris, Ont., has adopted a new option in molding technology, and initial reports from the process developer indicate positive results for product quality and productivity. The V-Process developed by HWS Sinto is based on a vacuum molding machine, which Domite Wear Technology has introduced along with a turntable and shake-table station, to cast wear plates and wear liners for mining equipment and aggregate-processing machinery.  

HWS Sinto is developer and builder of machinery for metal casting, metal finishing, and shot-blasting, and a wholly owned subsidiary of Sintokogio Ltd. Sinto America Inc. worked with its affiliate company and Domite to install the new molding line during Q3 2019. 

The V-Process uses clean and dry, binder-free sand to form dimensionally accurate molds, with no need for sand mullers or mixers, or reclamation and reconditioning equipment. A vacuum is generated when a thermo-plastic film (0.002- or .005-in thick) is deep-drawn over a prepared pattern to form the mold shape, which is maintained through the pouring, cooling, and emptying stages. The pattern (with vent holes in the film) is placed on hollow carrier plate, and a heater softens the plastic film. Then, softened film is draped over the pattern with 200 to 400 mm Hg vacuum through the pattern vents to draw it tightly around the pattern.

Next, the flask is placed on the film-coated pattern, and filled with dry sand. Slight vibration compacts sand to its maximum bulk density.

A sprue cup is formed and the mold surface is leveled, and then the back of the mold is covered with unheated plastic film. A vacuum is applied to the flask, and atmospheric pressure hardens the sand. When the vacuum is released on the pattern carrier plate, the mold is released easily.

The cope and drag assembly forms a plastic-lined cavity, and during pouring, molds are kept under vacuum.

After the mold has cooled the vacuum is released and free-flowing sand drops away, leaving a clean casting, with no sand lumps. The cooled sand is collected and re-used.

According to Sinto, advantages of V-Process molding include:
  Elevated molding and pouring heights that allow for automatic sand collection and easy clean-up;
  Excellent dimensional accuracy thanks to a sand forming technique that is entirely sealed in plastic film and hardened by vacuum suction;
  Highly consistent and repeatable mold accuracy;
  No pattern wear and no need for draft;•  No movement of the mold wall due to high mold hardness; and,
  No mold deformation due to volatile sand additives.

In addition, the foundry operators can manage the cooling process by switching the vacuum on and/or off, to reduce internal stresses within the casting. Plain, uncoated sand can be used, with no requirement for sand preparation, or reclamation for recycled sand.

Also, the V-Process operates without cores and requires no shakeout process for cooled castings.

The Domite Wear Technology vacuum molding machine has a flask size of 1,270×1,270×250/250 mm, producing two to four molds per hour.

Previously, castings produced on the foundry’s no-bake line required manual cleaning and grinding, and the results still exhibited a rough surface quality.  Castings produced by the V-Process are more dimensionally accurate, according to Domite Wear Technology, requiring less grinding, and have a very smooth surface. “We have been able to lower the previously intensive labor and finishing costs by 75%,” according to foundry president Andrew Guiducci, “and the end product is a beautiful casting.”

Since last fall, when Sinto America completed installing the V-Process equipment, Domite has been operating the line at its full capability, producing about 10,000 lbs. of wear plates during March 2020.