What is the use of bentonite for the foundry industry?
Bentonite for foundry is the largest user of bentonite, with an annual consumption of 1.1 million tons.
Bentonite is mainly used in clay bonding sand because it has the characteristics of strong cohesive force, high plasticity, good film removal, excellent gas permeability and stable physical and chemical properties under high temperature and wet conditions. Clay bonded sand is used as a modeling material to produce castings. This is a long-established process. In today's vigorous development of various chemical bonding sands, clay wet sand is still the most important modeling material, and its application range is wide. The big one is that no other modeling material can match it. Modern high-pressure molding, injection molding, gas-punching, static-pressure molding, and non-shock-pressure vacuum molding are all based on the premise of using clay wet sand. The ability of clay wet sand to adapt to molding conditions is extremely strong. . Bentonite for casting mainly consists of sodium bentonite and calcium sodium bentonite. Sodium bentonite is processed from natural sodium bentonite or artificial sodium bentonite. It is popular in the foundry industry for its good reusability and high wet compress strength. . Because of its good plasticity, it can restrain the phenomenon of casting sand, crusting, falling block, sand landslide, etc., combined with strong formability and high cavity strength, it is convenient for metal industry to cast wet or dry mold, which is the first choice for precision casting. Sand binder. Calcium sodium bentonite is processed from natural calcium sodium bentonite and is a sand binder commonly used in light castings. It is popular with users for its practicality and ease of sand cleaning. Compared with other adhesives, bentonite has an important feature, that is, it has a certain heat resistance. As long as the heating temperature is not too high, the bentonite which is freed of free water can still recover the viscosity as long as water is added. The bonding ability of bentonite can only be manifested after adding water. Bentonite loses its ability to bond and is also associated with its dehydration. So far, it is believed that there are three forms of water in bentonite: one type of water is free water, that is, water adsorbed by bentonite particles. When heated to above 100 °C, free water can be removed, bentonite free of free water, and bonding ability. Unaffected; the two kinds of water are firmly combined with water, heated at 110 ° C for a long time, bentonite can completely remove free water, but will not remove the strong bound water. Bentonite, which has been completely freed of water, will continue to lose weight at higher temperatures (eg, 200 ° C, 300 ° C), indicating that there is still water loss. After the bentonite is heated and dehydrated by this, as long as water is added, the binding ability can be completely restored; the three kinds of water are lattice water, and some people call it structural water. The lattice water can only be partially or completely removed at a relatively high temperature. After the lattice water of the swollen water is removed, the bonding ability is lost and it becomes a dead clay. Different bentonites have different temperatures at which they lose their bonding ability. It was proved by differential thermal analysis experiments that in general, the natural sodium bentonite has a failure temperature of 638 ° C and the calcium bentonite is 316 ° C. Artificially activated sodium bentonite has different failure temperatures due to different activation conditions, but is lower than natural sodium bentonite.