As a traditional core making process, coated sand process still occupies an important position in casting production. Although furan core making process, cold core making process and other processes are constantly developing and applying, its core making process is still widely used in various casting industries due to its excellent fluidity, high strength and thermal stability, as well as long storage time. It is still difficult to replace in some industries such as hydraulic parts, turbine shells and other high-end casting industries.
Characteristics:
suitable strength performance; good fluidity, the sand molds and sand cores produced have clear contours and dense structure, and can produce complex sand cores; the surface quality of the sand mold (core) is good, the surface roughness can reach Ra=6.3~12.5μm, and the dimensional accuracy can reach CT7~CT9 level; good disintegration, and the castings are easy to clean.
Scope of application
It can be used to make both casting molds and sand cores. The molds or cores can be used in conjunction with each other or with other sand molds (cores); it can be used not only for metal gravity casting or low-pressure casting, but also for iron sand casting and hot centrifugal casting; it can be used not only for the production of cast iron and non-ferrous alloy castings, but also for the production of steel castings.
composition
Generally composed of refractory materials, binders, curing agents, lubricants and special additives.
(1) Refractory materials are the main components of it. The requirements for refractory materials are: high refractoriness, low volatiles, relatively round particles, solid, etc. Natural scrubbed silica sand is generally used. The requirements for silica sand are: high SiO2 content (cast iron and non-ferrous alloy castings require more than 90%, and cast steel parts require more than 97%); mud content is not more than 0.3% (for scrubbed sand)–[the mud content of washed sand is less than; the particle size ① is distributed on 3 to 5 adjacent sieve numbers; the particle shape is round, and the angular factor should not be greater than 1.3; the acid consumption value is not less than 5ml.
(2) Phenolic resin is generally used as the binder.
(3) Hexamethylenetetramine is usually used as the curing agent; calcium stearate is generally used as the lubricant, which is used to prevent from agglomerating and increase fluidity. The main function of the additive is to improve the performance of the coated sand.
(4) Basic ratio of Component Ratio (mass fraction, %) Explanation: Raw sand 100 Scrubbing sand, Phenolic resin 1.0-3.0 (weight of raw sand), Hexamethylenetetramine (aqueous solution 2) 10-15 (weight of resin), Calcium stearate 5-7 (weight of resin), Additives 0.1-0.5 (weight of raw sand). 1:2) 10-15 (weight of resin), Calcium stearate 5-7 (weight of resin), Additives 0.1-0.5 (weight of raw sand).
Production process
The preparation process mainly includes cold coating, warm coating and hot coating. At present, the production almost all adopts hot coating. The hot coating process is to heat the raw sand to a certain temperature, and then mix and stir with resin, urotropine aqueous solution and calcium stearate respectively, and then cool, crush and screen. Due to the difference in formula, the mixing process is different. At present, there are many types of production lines in China. There are about 2000~2300 semi-automatic production lines with manual feeding, and there are nearly 50 computer-controlled fully automatic production lines, which effectively improves production efficiency and product stability. For example, the automated visual production line of xx Casting Co., Ltd. has a feeding time control accuracy of 0.1 second, a heating temperature control accuracy of 1/10℃, and the sand mixing state can be observed at all times through video, with a production efficiency of 6 tons/hour.
Advantages of process
Excellent fluidity
It is coated with solid resin and appears as dry sand. Excellent fluidity is its biggest advantage, which is particularly suitable for complex and small sand cores.
Excellent surface quality of sand core
It is compacted by shot blasting, and the surface of the sand core is dense and smooth, which can effectively improve the surface finish of the casting.
Low cost of shell core making
It has a high melting point and can be used for shell core making, with less sand consumption, lower cost and better air permeability.
High strength and thermal stability
using thermoplastic phenolic resin, it has high strength and thermal stability, which gives it unique advantages in the application of some thick and large parts.
Long storage period of sand core
Alkaline phenolic resin used in coated sand is hydrophobic, the sand core has good moisture resistance, no special requirements for the storage environment, and no significant decrease in strength after long-term storage.
Wide range of application
Coated sand core is suitable for casting processes of all metal materials.
If you want to know more about shell mold casting process, pls feel free to contact lydia@welongchina.com.
Post time: Jun-13-2024
