Raw and auxiliary materials for coated sand

　　 Coated sand is sand or core sand with solid resin film covering the surface before moulding. There are two kinds of film sand process, cold method and hot method: in the cold method, dissolve the ethanol resin, add utropin in the sand mixing process, so that the two are coated on the surface of the sand, ethanol volatilisation, filling of the film sand; the sand is heated to a certain temperature, add the resin to make the sand melting, stirring coated with the resin on the surface of the sand, add the aqueous utropin and the lubricants, cooling, crushing, sieving the film sand. Used for cast steel and cast iron.

　　 The original sand is the main body of the cladding sand. Requirements for the original sand is: high refractoriness, low volatile matter, particles for high strength, you can generally choose natural silica sand, mainly because of the abundant reserves, the price is relatively inexpensive, to meet their own casting technology requirements. Specialised sand (such as zircon sand, chromite sand, ceramic sand, magnetite sand, etc.) is only used for castings with special requirements.

　　 Cast iron and non-ferrous metal casting sand requirements in more than 90%, cast steel model requirements in more than 98%. More acidic sand is better than more alkaline sand. Mud content and LT;0.3%. Particle size distribution:It is desirable to use sieve concentration, sieve dispersion. Particles for shape:As far as possible can choose the roundness of good silica sand, angle analysis coefficient as a general should be less than 1.3.Usually silica sand through the second scrub can meet the requirements, but in order to improve the performance of the coating sand, silica sand can be acid washing or high temperature active treatment.

　　 Bonding performance on the quality management of the coated sand has a very important impact, people have been conducting research enterprises how to improve the performance of phenolic resin through the development of foreign countries have been able to develop their own different performance of special resins, such as high-strength and low-gas resins, easy to disperse resins, etc., have been used in place of phenolic resins modified polyester resins, but did not get popularity, modified phenolic resins are still widely used. In recent years, China has been developing rapidly in the research and development of phenolic resin for laminated sand.

　　 Curing agent, lubricant and additives, the conventional curing agent for resin sand is Utropin, the amount of which is added to 5% to 20% of the resin. In order to meet some special requirements (such as anti-flaking, fast aggregation speed, etc.), some companies have developed a special curing agent. The role of the lubricant is to prevent agglomeration, and to improve the fluidity and release of the coated sand, mainly calcium stearate, ammonium stearate. The lubricant should try to be able to choose products with high melting point, in order to prevent the coated sand in the use of de-filming phenomenon.

　　 The main role of additives is to improve the performance of coated sand. Widely researched and applied additives mainly include additives with high temperature resistance and additives, folding function additives, strengthening toughening additives, anti-sticking sand additives and wet additives. Many laminating sand factories have unique additive formulations, the performance of additives for the production of speciality laminating sand plays a vital role, is one of the core competitiveness of the laminating sand market.