Coated sand is a kind of sand base which is made of high quality and selected natural sand, through resin coated system with special performance and the most ideal technology, according to the technical requirements of different users, it strives to combine the most perfect aspects of normal temperature performance, high temperature performance, collapsibility, fluidity and surface roughness of castings.Coated sand is widely used in automobile engine, diesel engine, hydraulic parts and other industries.
The technological process of the precoated sand casting is that the heating temperature is 200-300 DEG C, the solidification time is 30-150 s, and the sand injection pressure is 0.15-0.60 MPa.The sand core with simple shape and good fluidity can choose lower sand shooting pressure, the thin sand core can choose lower heating temperature, and the solidification time can be appropriately prolonged when the heating temperature is low.Resin used in coated sand is phenolic resin. The advantages of precoated sand coremaking process are: suitable strength performance; Good liquidity; Core surface quality is good (Ra = 6.3-12.5μm); Sand core has strong hygroscopicity resistance; Good collapsibility and easy cleaning.
1. Mold temperature
The mold temperature is one of the main factors affecting the shell thickness and strength, generally controlled at 220 ~ 260℃ and selected according to the following principles:
(1) enough heat to ensure the resin softening and curing on the resin coated sand;
(2) ensuring that the shell thickness required is formed and the shell mold (core) surface is not coked;
(3) To minimize the time of crusting and hardening so as to improve productivity.
2. Shooting pressure and time
Shooting time is generally controlled in 3 ~ 10s; If the time is too short, the sand mold (core) can not be formed. Shooting pressure is generally about 0.6 MPa; When the pressure is too low, it is easy to cause insufficient or loose phenomenon.
3. Hardening time
The length of hardening time mainly depends on the thickness of sand mold (core) and the temperature of mold, generally about 60-120 seconds. If the time is too short, the strength of the shell will be low if it is not fully solidified; If the time is too long, the surface layer of sand mold (core) is easy to burn, which will affect the quality of castings.