In order to ensure the quality of castings, the core used inis generally dry core. The clay core and oil core sand are divided into several kinds of binder according to the resin core.
Clay sand core
A simple core made of clay sand.
Oil sand core
The core made by sand casting core sand with dry oil or semi dry oil as binder is widely used. The viscosity of oil is low, the fluidity of mixed sand casting core sand is good, and it is easy to compact when making core. However, the strength of the newly made core is very low. Generally, it should be carried out with a profiling core support plate, and then dried in an oven at 200 ~ 300 ℃ for several hours. The oil is oxidized by air to harden it. The disadvantages of this core making method are: the core is easy to deform in the process of demoulding, handling and baking, resulting in the reduction of dimensional accuracy of sand castings; Long baking time and high energy consumption.
Resin sand core
Various cores made of resin sand. The core is taken out after hardening in the core box, which can ensure the tolerance of the shape and size of the core. According to different hardening methods, the manufacturing of resin sand core is generally divided into three methods: hot core box core making, shell core making and cold core box core making. ① Hot box coremaking: it appeared in the late 1950s. Furan resin is usually used as core sand binder, and latent hardener (such as ammonium chloride) is also added. When making the core, keep the core box at 200 ~ 300 ℃, after the sand casting core sand is injected into the core box, ammonium chloride reacts with free formaldehyde in the resin at a higher temperature to form acid, so as to harden the core quickly. It takes about 10 ~ 100 seconds to establish the demoulding strength. Using hot core box to make core, the dimensional accuracy of core is relatively high, but the process device is complex and expensive, the energy consumption is much, the irritant gas is discharged, and the working conditions of workers are also very poor. ② The shell core is made by covering mold sand thermal method, and the sand core cast by sand mold has high strength and good quality; ③ Cold box coremaking: appeared in the late 1960s. Urethane resin is used as core sand binder. When this method is used, the core box is not heated, and the core can be hardened by blowing amine steam into it for a few seconds. This method is superior to the hot core box method in energy, environment and production efficiency. In the mid-1970s, the furan resin cold core box method hardened by blowing sulfur dioxide appeared again. 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.
Sodium silicate sand core
Sand cores made with glass as binder can be divided into the following types: water glass CO2 method, ester hardened water glass self hardening method and water glass methyl formate cold core box method.