How to improve the performance of casting binder

Casting organic binders and inorganic binders are two important types of sand mold (core) bonding systems. The technology sources were all developed in European and American countries in the 1950s and 1960s, and CO2 hard water glass sand appeared earlier. The exploration of the hardening mechanism of the new binder system and the improvement of the application performance of existing products have become an unstoppable work. In particular, whether the inorganic binder can have the performance of the organic binder on the molding sand, the breakthrough of the inorganic binder has become The eternal expectation. Combining the author’s experience in the process of researching modeling materials for the past 30 years, the following introduces some simple understandings of the advantages and disadvantages of the two major bonding systems of organic/inorganic binders, which are shared with colleagues in the industry.

1. The advantages and disadvantages of organic/inorganic binders

1. Organic binder
advantage In chemistry, structure determines the properties of substances. Organic binders all contain one element-carbon, which can be connected to each other to form a polymer. In casting, the organic binder gives the sand mold/core many advantages: good sand mold (core) strength; high production efficiency; good casting surface quality and dimensional accuracy; excellent falling sand performance; better old sand recycling ratio .
Disadvantage Of course, because the material itself is organic, there are some shortcomings as follows: raw materials are derived from petroleum products or agricultural chemicals; product prices are high and continue to rise; when modeling and core making, the VOC value is high, which endangers the health of operators; pouring During the process, a large amount of harmful gas is produced, which pollutes the environment.

2. Inorganic binder

The constituent elements of the inorganic binder are sodium, potassium, magnesium, calcium, aluminum, silicon and phosphorus, and its compounds are generally silicates, phosphates and aluminates. Inorganic binders usually bond sand cores together by dehydration, but this depends on the evaporation rate of water. Because of its characteristics, it has the following advantages: inorganic binder has a wide range of sources and cheap raw materials; inorganic binder has no solvent volatilization problem; inorganic binder does not produce harmful gases when castings.

Water-based inorganic binders generally have a slow curing speed, which is related to the speed of water migration. The inorganic binder can react with silica sand to form a low melting point substance. All these make the inorganic binder show the following deficiencies on the molding sand: slow hardening speed and low strength of the molding sand; the use performance and the environment are very sensitive to moisture and humidity; the sand breakability is poor; the old sand recycling rate is low.

2. The application status of organic/inorganic binders in China

The choice of casting binder determines the production process of castings. The choice of the type of binder is very important, it not only determines the scale of the production workshop, tooling, mold core equipment, old sand recycling equipment and cleaning equipment and other fixed assets investment. Many factors such as production technology, production costs, management methods, worker proficiency, and product market position have also been determined. The choice of binder type is closely related to the type of castings, past habits and experience, and local raw material prices and sources. The choice of binder type generally focuses on the technical feasibility, economic feasibility, environmental feasibility, energy saving, consumption reduction and reuse of this binder in the future.

At present, our country can produce various types of binders for self-setting sand, with high technical level, and all of them are made in China. It is an indisputable fact that the production of single-piece and small-batch iron castings using furan resin sand is an ideal process. Although the price of furan resin has risen in recent years, compared with other types of self-setting resin sand, the cost of furan resin sand is still the lowest. Therefore, furan resin in our country will still be the best in cast iron resin sand technology for a long period of time in the future. In the production of steel castings, the use of basic phenolic resins, nitrogen-free furan resins, especially heat-resistant furan resins, and ester-hardened sodium silicate sand have become the consensus of the foundry industry. The research and development of alkaline phenolic resin and ester hardened sodium silicate with high regeneration rate of used sand and regeneration equipment are the key to breaking through the application of self-hardening sand for cast steel.

Of course, we must not forget the application and improvement of CO2 hardened water glass in steel castings. In the production of sand mold (core) cast non-ferrous castings, there is no good binder system yet. 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 nitrogen furan resin, alkaline phenolic resin, PEP-SET, etc. can be selected as sand core binders. In recent years, the hot-air hardened hot core box (or warm core box) inorganic binder product proposed by the German company has been on the market. The binder content is only about 2.0%, and the sand core strength is sufficient to manufacture automotive aluminum castings. Grade I and Grade II sand cores. This undoubtedly ignited new hope for the development and progress of inorganic binders. However, at present, the adhesive is hardened by in-mold heating, and the production of sand cores for single-piece and small-batch castings does not yet have the possibility of being operable. The technical performance comparison of organic and inorganic binder self-hardening sand is shown in the attached table. Regeneration and equipment of ester-hardened sodium silicate used sand

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