Nowadays, the processing plants in my country use raw sand from Inner Mongolia, Hebei Province, Liaoning Province and other places. The quality is good and there is no problem. The problem is the supervision and usage of sand.
As soon as the molding sand and the high-temperature molten iron meet, the sand will lose the crystal water contained in it, and a hard sand layer will be formed. Converted to micropowder. If there are too many micropowders that have lost crystal water in the molding sand, the air permeability of the molding sand will be reduced, so that the molding sand binders such as clay and bentonite will not work, and the micropowder is easy to absorb water, so its own temperature resistance is not too high. When it comes into contact with high-temperature molten iron, it melts into glass, causing sticky sand. The sticky sand that appears on the inside of the castings in the precision foundry is all caused by micropowder, and the amount of micropowder (ZW (〖ZW) above 200 mesh) in the molding sand should be less than 1%.
The most common precision casting methods for castings in large and medium-sized precision foundries are sand casting, and then there are special casting methods, such as metal mold casting, investment casting, and gypsum casting. Sand casting can be divided into clay sand, organic binder sand, resin no-bake sand, lost foam and so on. The precision casting method of casting parts in large and medium-sized precision foundries usually uses lost foam casting technology, resin sand casting, solid type precision casting, high-grade precision casting, etc., such as the bed, column, beam, slide, etc. Taiwan, etc. are all designed with these types of casting processes. Casting materials for large and medium-sized precision foundries: HT200-350, which can contract about 60 tons of precision foundry castings.
Advantages of using resin sand to cast castings in large and medium-sized precision foundries: Lost foam casting has great advantages for the production of small and mass-produced car covers, CNC lathe beds and other large and medium-sized precision foundries. Good surface quality and other advantages. The principle for determining the precision casting method: sand casting is preferred for castings in large and medium-sized precision foundries, and the precision casting method should match the production batch. The price is relatively expensive, so it is only suitable for mass production. The castings of large and medium-sized precision foundries can be cast in bulk and can be produced in large quantities. In order to make the surface of the castings of the precision foundry beautiful, the molding sand must be improved. When the construction equipment knocks out the castings of the precision foundry from the sand box, shovel the dry-fired sand close to the castings of the precision foundry and throw it outside the processing plant, and fill the factory with new sand. Mix the clay, bentonite and sand with a roller sand mixer. At this time, with the ratio of 70% of the old sand and 30% of the new sand in the processing plant, if it lasts for three months, the molding sand of the processing plant will be improved on the whole.