SAND CASTING EQUIPMENT.

3、exploding sticky sand can sometimes be seen on the upper surface of the casting pouring position sticky sand defects, and usually sticky sand appears on the lower surface of the pouring position. This is caused by the explosion when pouring molten iron surface adjacent to the upper surface of the cavity. At the beginning of pouring, the water of the sand evaporates and coalesces on the upper surface of the cavity where the temperature is low, and when the metal surface rises and the upper surface of the cavity begins to contact, the water suddenly evaporates and the explosion occurs. When the sand moisture content and coal dust content is high, sand ventilation conditions are poor and pouring speed is too fast, more likely to occur when the explosion of sticky sand.
The amount of coal dust in the sand wet cast iron parts to prevent sticky sand and improve the surface finish of the most important sand additive is coal dust. The following will discuss the quality of coal dust, the effective coal dust content, coal dust substitutes and the new situation of application.
3.1 The quality of pulverized coal better pulverized coal should meet the following performance indicators.
3.11 ash content is not more than 10% (the lower the better, foreign general commercial coal dust is not more than 7%). Ash content of pulverized coal is measured to check the amount of residual gangue in pulverized coal. Foundry plant using too much ash in the coal dust, not only can not prevent the castings sticky sand, and will produce a large number of sand holes, porosity defects.
3.12 volatile fraction between 30 ~ 38% (preferably 32 ~ 37%), volatile fraction determination purpose is to determine the coal powder of the raw material bituminous coal species. If the volatile fraction is lower than 30%, indicating that the coal is not pure. If higher than 38%, it may contain gas coal.
3.13 Coke slag characteristics 5 to 6 levels (3 to 4 levels are still available). Measurement of volatile fraction after observing the residue in the crucible can be derived from the coke characteristics, according to the national standard coke characteristics are divided into 8 levels, which reflects the amount and duration of the gas-solid-liquid three-phase colloid generated by pulverized coal in the process of heating and dry distillation. Coke slag characteristics 5 to 6 levels of coal powder anti-sticky sand performance is the best, such coal powder in the pouring can plug the surface of the pores between the sand particles, and do not make the sand particles form a bonded together coarse particles.
3.14 Bright carbon generation amount 10～18% (preferably above 12%). Bright carbon is the volatiles of coal dust in a reducing atmosphere at high temperatures for gas-phase pyrolysis and precipitation of microscopic crystals, it covers the surface of the cavity sand grains, so that the sand is not wetted by iron, thus preventing sticky sand defects.
3.15 effective coal dust content and the need to know whether the sand can play a role in the effective coal dust is sufficient, how much residual coal dust in the old sand, in order to decide how much coal dust should be added when mixing sand. The method used abroad is to determine the volatile fraction of the sand and the old sand, burning reduction, the amount of full carbon, etc. to indirectly estimate the effective content of coal dust. These tests are more tedious and time-consuming, and can not get the specific figures of the effective pulverized coal. In our country, the method of measuring the amount of gas generation is less time consuming, and the effective pulverized coal content can be measured and calculated in a few minutes. The principle is based on the effective state of pulverized coal in the heat of the amount of gas generated. Usually, the amount of gas generated by the sand of high-density molding can be in the range of 16~22mL/g. The amount of gas generated by the sand of ordinary machine molding can be in the range of 20～26mL/g.
3.16 coal powder substitutes plant resin, oil-containing bentonite and starch materials can be used to replace coal powder. Among them, the starch material anti-sticky sand effect and high-quality coal dust is basically equivalent. But only suitable for the production of gray iron castings, such as for the production of ductile iron parts are likely to produce subcutaneous porosity defects, because it can not produce sufficient reducing atmosphere. There are also commodities are mainly coal dust, mixed with a small amount of other materials, may also have anti-sticky sand effect. But there are also some "coal powder substitute" goods, the specific formula is not known, and the lack of quality evaluation and testing standards. Users should choose carefully and rely on the casting test to judge. Small sand mixer can be used, adding the same raw sand and bentonite, respectively, adding different anti-cohesive sand materials, mixed sand should try to maintain the same or close to the same air permeability, the same molding hardness, the same pouring temperature.

3.2 Compare the surface finish of the casting, and then you can make a decision on the selection. There are two main types of goods for producing anti-sticky sand.
3.21 High-efficiency coal dust: Add 20 to 40% of high softening point petroleum asphalt in coal dust, so that its bright carbon content increased to 12-20%, anti-sticky sand ability is greatly improved.
3.22 Mixed additive: It is a mixture of high quality bentonite and high quality coal dust. If there is a special need, you can also add starch, wood flour and other materials again. Large foundry plant in a production line in the product characteristics close, bentonite and coal dust ratio does not need to change frequently. The use of mixing additions is easy to control and manage, and the equipment is simplified. The recipe is developed jointly by engineers from both supply and demand sides according to the specific casting production conditions. It is delivered to the workshop by bulk tanker and pneumatically conveyed into the material tank.
3.23 The amount of coal dust additive for single sand mixing depends on the quality of coal dust itself, and is also influenced by sand/iron ratio, casting thickness, pouring temperature, cooling time, cleaning method, specific requirements for casting surface finish, etc. xinyuanzhuGroup uses high efficiency coal dust and concludes that the general amount of coal dust additive for single sand of wet cast iron parts is 0.15 ~ 0.3%, individual thick large pieces of 0.5%. Even though the price of high-efficiency pulverized coal is slightly higher (less than twice that of ordinary pulverized coal), the consumption is only a fraction of that of ordinary pulverized coal. The use of high-quality high-efficiency pulverized coal not only reduces production costs significantly, but also saves storage and transportation costs. Moreover, the mud content and water content in the sand are greatly reduced, and the toughness, air permeability and moldability are improved. Not only the surface of the casting is smooth, but also the defects such as porosity and sand holes are inevitably reduced.

Xinyuanzhu Group specializes in the production of Ductile iron castings, Pig iron gray iron casting, Steel casting, Brass Casting, Malleable Iron Casting, and undertakes batch casting processing of castings. Welcome guests to cooperate with pictures or samples.