How to improve the performance of cast binders

Casting organic binders and inorganic binders are two important types of sand-type (core) binder systems. The source of technology was developed in European and American countries from the 1950s to the 1960s. CO2 gas hard water glass sand also appeared earlier. The search for the hardening mechanism of the new binder system and the improvement of the performance of the existing products have not stopped. In particular, whether the inorganic binder can have the performance of the organic binder on the sand, and the breakthrough of the inorganic binder becomes Eternal expectations. Combining the experience of the author in the past 30 years in the research of modeling materials, the following describes some of the simple and obvious understanding of the advantages and disadvantages of the two organic/inorganic binder systems and share them with colleagues in the industry.

I. Advantages and disadvantages of organic/inorganic binders

1. Advantages of organic binders In chemistry, the structure determines the properties of a substance. Organic binders contain one element, carbon, which can be linked together to form a polymer. The organic binder gives a lot of sand/core advantages in casting: good sand type (core) strength; high production efficiency; good surface quality and dimensional accuracy of castings; excellent sand-drop performance; .
Disadvantages Of course, due to the fact that the material itself is organic, there are also some disadvantages: raw materials originate from petroleum products or agricultural chemicals; the product price is high and continues to rise; the VOC value is high when styling and making the core, which endangers the operator's health; In the process, a large amount of harmful gases are generated and pollute the environment.

2. Inorganic binder

The inorganic binder constituents are sodium, potassium, magnesium, calcium, aluminum, silicon and phosphorus, and the compounds are generally silicates, phosphates and aluminates. Inorganic binders often bond sand cores together by dehydration, but this depends on the rate of evaporation of moisture. Due to its characteristics, it has the following advantages: The inorganic binder has a wide range of sources and the raw materials are inexpensive; the inorganic binder has no problem of solvent volatilization; and the inorganic binder does not produce harmful gases when the casting is poured.

Water-based inorganic binders generally cure slowly and are related to the rate of moisture migration. Inorganic binders react with silica sand to form low melting points. All these make the inorganic binder show the following insufficiency on the sand: the hardening speed is slow and the strength of the sand is low; the performance and the environment are very sensitive to the moisture and humidity; the sand-breaking property is poor; the reuse rate of the old sand is low.

Second, the application of organic / inorganic binder in China

The choice of binder for casting determines the production process of the casting. The choice of binder type is very important. It not only determines the amount of investment in fixed assets such as the scale of production workshops, tooling moulds, modelling core making equipment, used sand recycling equipment, and cleaning equipment. Also determined the production process, production costs, management methods, worker proficiency and product market position and many other factors. The choice of binder type is closely related to the type of castings, past habits and experiences, local raw material prices and sources. The choice of adhesive type will also generally focus on the feasibility of this adhesive in the future, its economic feasibility, the feasibility of environmental protection and the feasibility of energy saving, consumption reduction and reuse.

At present, China can produce various types of binder for self-hardening sand, with high technical level and all localization. It is an indisputable fact that the production of single-piece and small-batch cast iron pieces using furan resin sand is an ideal process. Although the price of furan resin has risen in recent years, the furan resin sand is still the lowest compared with other types of self-hardened resin sands. Therefore, furan resin in our country is still the first choice for cast iron resin sand process for a long time in the future. In the production of steel castings, the use of alkaline phenolic resins, nitrogen-free furan resins, especially heat-resistant cracked furan resins, and ester-hardened water glass sand have become the consensus of the foundry industry. The research and development of alkaline phenolic resin and ester hardened water glass with high regeneration rate of old sand and regeneration equipment are the key to break through the application of self-hardening sand for casting steel.

Of course, we must not forget that the use of CO2 hardened water glass in steel castings has improved. In the production of sand-type (core) cast colored castings, there is no satisfactory binder system. At present, most of the materials are organic resins, which are only derived from the use of binders for cast iron to reduce their high-temperature strength and other indicators. High-nitrofuran resin, alkaline phenolic resin, PEP-SET, etc. can be selected as the sand core binder. In recent years, hot-air-cured hot-core box (or warm-box) inorganic binder products have been introduced by German companies. The amount of binder added is only about 2.0%, and the strength of the sand core is sufficient for manufacturing automotive aluminum castings. Grade I and II sand cores. This undoubtedly sparked new hope for the development of inorganic binders. However, at present, the binder is an in-mold heat-hardening, and sand cores for single-piece and small-quantity castings are not yet available for operation. For the comparison of organic and inorganic binders, the properties of the self-hardening sands are shown in the attached table.

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