As in the production of steel or aluminum castings, molding mixtures for bronze casting have requirements for resistance to high temperatures and strength. It is especially important to take them into account when making large castings. Therefore, to increase resistance to thermochemical influences, the molds are dried, which also increases their mechanical strength. However, this operation significantly increases the duration of the technological cycle, which is why mixtures that harden quickly are increasingly used.
Typical molding compound compositions for bronze casting
Liquid glass-based materials have become widely used in the manufacture of bronze castings. Molds made from such mixtures are used for both small and large products and are able to withstand significant temperatures.
Mixtures based on technical lingosulphanate are widely used. Despite their wide distribution, chromomagnesite masses based on liquid glass are increasingly used, due to slightly lower ductility. They include pre-processed chromomagnesite bricks. However, the disadvantages include a low gas permeability, which affects the thickness of the facing layer.
Often, the composition of the molding mixture for casting bronze may include chromium iron ore. Such compositions contain up to forty percent of the fine fraction, and to increase strength, the addition of no more than 3% lignosulfonate is allowed.
Sand-clay mixtures with a base of liquid glass are also widely used in bronze casting. Such a molding mixture for bronze allows you to significantly reduce the duration of the technological process, increases productivity and reduces the number of scrap. At the same time, the use of recycled materials is complicated.
In exceptional cases, zirconium mixtures are used. As in the case of aluminum casting, they allow for high-quality castings, but due to the high cost of the materials, they have not found widespread use.
However, when manufacturing products from non-ferrous metals, it is necessary to achieve high indicators of surface cleanliness. For these purposes, a composition based on fine sand is used. It may also include a small percentage of regenerated materials. In addition, special non-stick coatings or materials based on fuel oil and the like are used.
The influence of molding composition on product quality
In order to ensure high quality castings, it is necessary to constantly monitor the composition of the molding compound. This is done by conducting laboratory tests and making necessary adjustments. Stabilizing the composition reduces the number of scrap and maintains product quality at the required level.
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