Sand Core Type
In order to ensure the quality of castings, the cores used in sand casting are generally dry cores. According to the different binders used in the core, the core is divided into clay sand core, oil sand core and resin sand core.
Clay Sand Core
Simple core made of clay sand.
Oil Sand Core
The core sand made of dry oil or semi-dry oil as the binder is widely used. The oil has low viscosity, the mixed core sand has good fluidity, and it is easy to compact when making the core. But the strength of the newly made core is very low, and it is generally accepted by a profiling core board, and then baked in an oven at 200-300°C for several hours, and the oil is oxidized by air to harden it. The shortcomings of this core making method are: the core is easily deformed during demolding, handling and baking, resulting in reduced dimensional accuracy of the casting; long baking time and high energy consumption.
Resin Sand Core
Various cores made of resin sand. After the core is hardened in the core box, it can be taken out, which can ensure the tolerance of the shape and size of the core. According to different hardening methods, the manufacture of resin sand cores is generally divided into three methods: hot core box core, shell core and cold core box core.
- The hot core box method for core production: Appeared in the late 1950s. Usually furan resin is used as the core sand binder, and a latent hardener (such as ammonium chloride) is also added. When making the core, keep the core box at 200-300°C. After the core sand is injected into the core box, the ammonium chloride reacts with the free formaldehyde in the resin to generate acid at a higher temperature, so that the core will harden quickly. It takes about 10-100 seconds to establish the release strength. The core is made by the hot core box method, and the dimensional accuracy of the core is relatively high, but the process equipment is complicated and expensive, energy consumption is high, irritating gas is discharged, and the working conditions of the workers are also very poor.
- The shell core is made by the thermal method of overmolded sand, which has high strength and good quality;
- The cold box method of core making: Appeared in the late 1960s. Use urethane resin as the core sand binder. When the core is made by this method, the core box is not heated, and amine steam is blown into it for a few seconds to harden the core. This method is superior to the hot box method in terms of energy, environment, and production efficiency. In the mid-1970s, the furan resin cold box method, which was hardened by blowing sulfur dioxide, appeared again. The hardening mechanism is completely different from the urethane cold core box method, but the process characteristics, such as fast hardening and high core strength, are roughly the same as the urethane cold core box method.
Water Glass Sand Core
Sand cores made of water glass as a binder can be divided into the following types: water glass CO2 method, ester hardening water glass self-hardening method, and water glass methyl formate cold box method.