What is coated sand? Detailed introduction of coated sand

What is coated sand? Detailed introduction of coated sand

Characteristics of coated sand

1、With suitable physical strength properties, it can be made into high-strength shell core coated sand, medium-strength hot core box coated sand, low-strength non-ferrous alloy coated sand.

2, the production of moulds (cores) good fluidity, clear contours, dense structure, can make complex sand core, such as cylinder head, cylinder water jacket core.

3, the sand core surface quality is good, little or no coating to obtain the surface quality of castings. The surface roughness can reach Ra=6.3~12.5μm, and the dimensional accuracy can reach CT7~CT9 level.

4、Good collapsibility and easy cleaning of castings.

5、Sand core has strong anti-hygroscopicity and long storage time, which is good for storage, transport and use.

6、The cost of coated sand is high and the energy consumption is relatively large. In the process of moulding, core making and pouring, it will produce irritating smell, and it may be caked in long term storage in high temperature and high humidity season.

Preparation process of coated sand

The preparation process of coated sand mainly includes cold coating, warm coating and hot coating, of which hot coating is commonly used, featuring low numerical dosage and high production efficiency.

1、Cold coating process. The raw sand and thermosetting powder phenolic resin are added to the sand mixer and stirred well, and then the appropriate amount of solvent is added to continue stirring until the powder resin melts and adheres to the surface of the sand grains, the flux evaporates, and the sand is crushed and sieved. Simply. This method of sand mixing time is long, solvent consumption, volatile solvent gas is easy to explode, so it is rarely used.

2, warm coating process. Mix the thermosetting liquid phenolic resin with raw sand at 60~80℃, mix for 2~3 minutes and then make sand, cool, crush and sieve.

3. Hot lamination process. The raw sand is first heated to a certain temperature, then mixed with resin and calcium stearate respectively, cooled, crushed and sieved. The mixing process is different due to the different equipments and ratios.

Laminating sand should be stored in well-sealed containers or bags for 0.5 to 1 year at room temperature (≤20℃) under dry conditions. If the coated sand is stored for too long, local caking may occur. If the agglomeration is not serious, it can be crushed and sieved for use.

Production process of coated sand core

Coated sand has a wide range of applications, and its process methods are not the same. Whether it is core making or moulding, the basic process requirements are (except for wet process): heating temperature 200~300℃, curing time 30~150s, sand injection pressure 0.15~0.6Mpa. The specific parameters should be adjusted according to the equipment model, weight and complexity of the type (core), and the type of coated sand. Sand injection pressure is low, fine, fine sand core to choose a lower heating temperature, heating temperature is low when the appropriate extension of maintenance time; and vice versa.

Main varieties of coated sand

1、Ordinary coated sand. It consists of quartz sand, thermoplastic phenolic resin, calcium stearate, no relevant additives. It is suitable for the production of general cast iron parts.

2、High-strength low-gas-producing coated sand. It is a newer product of ordinary coated sand. It is prepared by adding relevant additives and adopting new technology. Its strength is more than 30% higher than that of ordinary coated sand, and the amount of gas production is also significantly reduced. It is suitable for the production of complex precision cast iron parts.

3、High temperature type coated sand. It has the characteristics of high strength and long heat resistance under high temperature, and is suitable for the production of complex thin-walled cast iron parts such as automobile engine block, cylinder head and container corner.

4、Easy to collapse type coated sand. With good strength and excellent low-temperature collapse, suitable for the production of non-ferrous metal castings.

5、Other special requirements for the film-coated sand. In order to meet the needs of different products, developed a series of special film sand, such as: centrifugal casting film sand, cold hard film sand, wet film sand, anti-sticking sand, anti-veining, anti-orange peel film sand and so on.