Sand casting is suitable for casting large precision castings

Nowadays, processing plants in China use raw sand from Inner Mongolia, Hebei Province, Liaoning Province and other places, with good quality and no problems. The problem lies in the supervision and usage of the sand. Precision casting, also known as lost wax casting, produces products that are precise, complex, and close to the final shape of the parts. They can be used directly without or with minimal processing, and are an advanced process that forms near net shapes. Precision casting refers to the general term for the process of obtaining precise dimensional castings. Compared to traditional sand casting processes, precision casting produces castings with more precise dimensions and better surface smoothness. It includes investment casting, ceramic mold casting, metal mold casting, pressure casting, and lost foam casting.         

When the molding sand and high-temperature molten iron come into contact, the sand particles lose their crystal water and form a thoroughly dried hard sand layer. Even if the sand particles in the hard sand layer maintain their shape, they are more likely to break and transform into micro powders with a little pressure. Precision casting refers to the general term for the process of obtaining precise dimensional castings. Compared to traditional sand casting processes, precision casting produces castings with more precise dimensions and better surface smoothness. It includes investment casting, ceramic mold casting, metal mold casting, pressure casting, and lost foam casting. If there are too many micro powders in the molding sand that have lost their crystalline water, the permeability of the molding sand will decrease, making clay, bentonite and other molding sand binders ineffective. Moreover, micro powders are prone to absorbing moisture, resulting in their low temperature resistance and melting into glass like material upon contact with high-temperature molten iron, causing sand sticking. The sand sticking that appears on the inner side of castings in precision casting factories is all caused by micro powder, and the amount of micro powder (ZW) with a mesh size of 200 or more in the molding sand should be less than 1%. 

The common precision casting method for castings in large and medium-sized precision casting factories is sand casting, followed by special precision casting methods such as metal mold casting, investment casting (using molds for casting), chemical formula: CaSO4 · 2H2O type precision casting, etc. Sand casting can be divided into clay sand molds, organic binder sand molds, resin self hardening sand molds, lost foam molds, and so on. The precision casting methods for castings in large and medium-sized precision casting factories usually use lost foam casting technology, resin sand casting, solid precision casting, high-grade precision casting, etc. For example, the bed, columns, beams, slide tables, etc. of large and medium-sized cast iron platforms on CNC lathes are all designed using these types of casting processes. The material for castings in large and medium-sized precision casting factories is HT200-350, which can undertake castings of about 60 tons of loose parts for precision casting factories. The advantages of using resin sand casting for casting parts in large and medium-sized precision casting factories: Lost foam casting has significant advantages for producing loose parts or mass-produced car covers, CNC lathe bed bodies, and other large and medium-sized precision casting factory castings, such as good surface quality. The principle for determining the precision casting method: sand casting is preferred for castings in large and medium-sized precision casting factories, and the precision casting method should be matched with the production and manufacturing batch. Precision casting methods such as low-pressure casting, die-casting molds (known as the mother of industry) (essentially a method of casting liquid forging), centrifugal casting, etc. are only suitable for large-scale production due to the high prices of machinery and die-casting molds. Large and medium-sized precision casting factories can produce castings in bulk or in large quantities. In order to improve the appearance of the surface of castings in precision casting factories, it is necessary to improve the molding sand. When the construction equipment is used to extract the precision casting parts from the sand box, the dried sand adjacent to the precision casting parts is scooped off with a shovel and thrown outside the processing plant, and new sand is filled inside the plant. Mix clay, bentonite, and sand using a roller type sand mixer. At this point, with a ratio of 70% old sand and 30% new sand in the processing plant, if it continues for three months, the overall quality of the molding sand in the processing plant will be improved.