In order to ensure the quality of the casting, the core used in sand casting is generally a dry core. According to different binders used in the core, the core is divided into clay sand core, oil sand core and resin sand core.
Clay sand core
A simple core made of clay sand.
Oil sand core
The core made of core sand with dry oil or semi-drying oil as binder has a wide application. The viscosity of the oil is low, and the mixed core sand has good fluidity and is easy to compact when the core is made. However, the strength of the newly formed core is very low, and it is generally carried out by using a contoured core plate, and then baked in an oven at 200 to 300 Â° C for several hours, and the oil is oxidized by air to harden it. The disadvantage of this core making method is that 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 to ensure the correct shape and size of the core. Depending on the hardening method, the manufacture of resin sand cores is generally divided into two methods: hot core box core making and cold core box core making. 1 hot core box method core: appeared in the late 1950s. A furan resin is usually used as a core sand binder, and a latent hardener such as ammonium chloride is also added. When the core is made, the core box is kept at 200 to 300 Â° C, and after the core sand is injected into the core box, ammonium chloride reacts with free formaldehyde in the resin to form an acid at a relatively high temperature, so that the core is hardened quickly. It takes about 10 to 100 seconds to establish the release strength. The core is made by the hot core box method, and the core has a relatively high dimensional accuracy, but the process device is complicated and expensive, consumes a lot of energy, emits irritating gas, and the working conditions of the workers are also poor. 2 cold core box method core: appeared in the late 60s. A urethane resin was used as the core sand binder. When the core is formed by this method, the core box is not heated, and the core is blown into the amine vapor 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 of blowing sulfur dioxide hardened appeared. The hardening mechanism is completely different from the urethane cold box method, but the process characteristics, such as fast hardening and high core strength, are roughly the same as the urethane cold box method.
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