Water glass sand casting process

The application practice of resin sand casting technology for decades at home and abroad shows that although resin sand has the advantages of high dimensional accuracy of castings, smooth surface and high molding efficiency, it can manufacture castings with complex shapes and strict internal quality requirements, and it is easy to recycle and regenerate old sand. However, the production cost of resin sand is high and the environmental pollution is serious. Under the conditions that people have increasingly strict requirements for their own living conditions and the environment, due to the large investment in workshop labor protection and production environment sanitation, the application of resin sand is subject to certain restrictions. limit. The water glass is colorless, odorless and non-toxic, and there is no irritating or toxic gas overflow during the sand mixing molding, hardening and casting processes. Therefore, in recent years, many countries have paid more attention to water glass sand.

The hardening methods of water glass sand can be divided into three categories: hot hardening, air hardening and self-hardening, including many methods. However, there are two commonly used hardening methods:

1. Ordinary CO2 gas hard method
This method is the earliest rapid prototyping process in the field of water glass binder. Because of its simple equipment, convenient operation, flexible use and low cost, it has been widely used in the production of most steel castings at home and abroad.
The main advantages of CO2 gas hardened water glass sand are: fast hardening speed and high strength; after hardening, the mold is released, and the casting precision is high.
The disadvantages of ordinary CO2 gas-hardened water glass sand are: the strength of the mold (core) sand is low, and the amount of water glass added (mass fraction) is often as high as 7~8% or more; the water content is large, and it is easy to absorb moisture; Hard permeability is poor in winter; The collapsibility is poor, the old sand is difficult to regenerate, and a large amount of old sand is discarded, resulting in alkaline pollution of the environment.

2. Organic ester self-hardening method
This method uses liquid organic ester instead of CO2 gas as the hardener of water glass.
The advantages of this hardening process are: the mold (core) sand has high strength, and the amount of water glass added can be reduced to less than 3.5%; the hard penetration in winter is good, and the hardening speed can be changed according to production and environmental conditions. The type of curing agent is adjusted (5~150min); the mold (core) sand has good collapsibility, the casting sand is easy to clean, the old sand is easy to regenerate by dry method, and the recycling rate is ≥ 80%, which reduces the impact of water glass alkaline waste sand on the ecological environment. It saves the transportation and land occupation of waste sand, and saves high-quality silica sand resources; the molding sand has good thermoplasticity and low gas generation, which can overcome the defects such as cracks and pores that are prone to occur when furan resin sand produces steel castings; it can overcome CO2 water Glass sand has process problems such as poor sand mold surface stability and easy over-blowing. The quality and dimensional accuracy of castings are comparable to resin sand; the production cost is the lowest among all no-bake sand processes, and the labor conditions are good.

The main disadvantage of this hardening process is that the core sand has a slow hardening speed and poor fluidity.
At present, in the current casting production, composite hardening process is sometimes used, such as short-term CO2 blowing to achieve the drafting strength and then drafting, then blowing hot air, or drying, or using organic esters to harden, or natural dehydration and drying to obtain larger the final strength and improve the production efficiency.

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