What is chemical adhesive sand

Among the chemical adhesives, sand is the filler, which is often needed in the bonding process.

According to the chemical composition, the molding sand adhesive can be divided into two categories: inorganic binders and organic binders. The main inorganic binders are clay and water glass.

and cement, phosphate.

etc., among which clay and water glass are more used. Organic binders mainly include vegetable oil, syrup, dextrin, and carboxymethyl cellulose.

Rosin, grease, vacuum residue, noisy asphalt, pulp waste liquid, synthetic resin, etc., vegetable oil and synthetic resin are more used.

The most widely used and largest amount of molding sand binder. Clay is mainly composed of fine crystalline clay minerals, such as kaolinite and montmorillonite. Clay is mainly divided into two categories: ordinary clay and bentonite according to the types of clay minerals and the properties of the dust.

Ordinary clay, also known as white clay, is composed of kaolin clay minerals, which contain more Al2O3 and have higher refractory properties. Ordinary clay is mostly used for dry sand molding. Bentonite is mainly composed of montmorillonite minerals, which can be divided into calcium bentonite and sodium bentonite according to the adsorbed cations.

The cations adsorbed by calcium-bentonite are mainly Ca. The positive dissociation difference yards adsorbed by sodium bentonite are mainly Na. Bentonite has a higher wet adhesion than ordinary clay and is generally used for green sand molding.

After the binder and sand are mixed with the sand rolling grains, the sand particles are coated to form a sticky mumu knotting agent film, so that the sand particles are bonded to each other (see figure), so as to endow the sand preparation slow mold and core with sufficient strength, so that it will not be deformed and broken during the handling, assembly and pouring process.

Commonly used are phenolic resin, furan resin, isocyanate, urinary resin, etc. When synthetic resin is used as a binder, an appropriate hardener should be added in combination with the hardening method. There are 3 commonly used hardening methods.

Heat hardening: using phenolic resin as the binder, using the heated metal pattern or core box to manufacture the thin shell sand mold or core, or using furan resin as the binder to manufacture the core in the heated core box, the hardening speed is fast, the production efficiency is high, the shape and dimensional accuracy of the casting and the surface quality are very good. It is widely used in mass-produced automobiles, tractors and other industries.

Aerosol hardening: isocyanate, ureabolite resin and phenolic resin are used as binders to blow amine aerosols; Or furan resin is used as a binder, peroxide is added when mixing sand, and SO2 gas is blown in. With this hardening method, the core can be hardened quickly in a few seconds to 30 seconds.

The high production speed of cores, the high accuracy of casting shapes and dimensions, and the energy savings are increasingly used in the automotive, tractor and other industries that produce castings in batches. Self-hardening at room temperature: furan resin, alpha phenolic resin or isocyanate and hydroxyl resin are used as binders, and liquid hardener is added to the molding sand at the same time, and the sand mold mold and core made can gradually harden themselves at room temperature.

Because the sand mold and core do not need to be heated and dried, the strength after hardening is high, the collapse performance after pouring is good, and the surface of the casting is excellent, which can manufacture small, medium and large sand molds and cores, which are used more in industrial production such as machine tools, mining machinery, power machinery, metallurgical machinery, etc.

The basic material of the clay mold used in ancient Chinese casting (known as Tao Fan in ancient times) was clay with strong bonding energy. With the development of technology, a large number of sand particles are sandwiched in the mud mold, and sand is gradually used as the main material, and the clay becomes a binder. Clay is still widely used today.

Later, various inorganic and organic binders appeared, such as vegetable oil, rosin, dextrin, water glass and synthetic resin. 1943 German JCronin invented the use of phenolic resin as a binder to make thin-shell sand molds.

1947 Czechoslovakia LPetergera uses water glass as a sand binder, blows CO2 gas to harden it, and makes sand molds and cores. The application of these two binders opens up new avenues for the chemical hardening of sand molds and cores.

Chemical hardening is to add a small amount of hard ruler to some organic or inorganic adhesive orange knotting agent, and through the chemical and physical interaction between them, the purpose of hardening the sand mold and core in a short time is achieved. The dimensional accuracy, surface finish and productivity of castings poured by chemically hardened sand molds have been greatly improved, and they are soon widely used. Since the late 50s, furan resin binders have been used in various countries, and the core can be hardened after 1 2 minutes of core making in a heated core box.