In sand casting production, metal subsidies are often set to extend the feeding distance of the riser. In most cases, the subsidies need to be removed, resulting in the subsidy itself and the energy consumption when removing the subsidies, especially for sand castings made of dual phase steel with high alloy content, which is a great waste. Using efficient heating and insulation subsidy instead of metal subsidy can save this part of metal and reduce the loss of removing metal subsidy, so as to reduce the cost. The heating and thermal insulation subsidy is to use the heating material to replace the subsidized metal material. After pouring, the subsidized material burns and heats the metal liquid to keep the metal liquid at the subsidized position liquid for a certain time and play the role of forming a feeding channel. At present, there are few materials in the molding material market that meet the requirements of sand casting and can be used to make heating and thermal insulation subsidies. After screening, we determined to use Ex5 blend heating and thermal insulation material of a company for production test. Fig. 1 and Fig. 2 are the combustion and thermal insulation curves when the common heating material and Ex5 blend heating and thermal insulation material are made into risers with the same size. The horizontal axis in the figure is the time (min), and the vertical axis is the temperature of liquid steel in the riser (℃). It can be seen from figures 1 and 2 that the ordinary heating material can keep the metal material in the riser at 1147 ℃ for 2.25 min, while the Ex5 blend heating and insulation material can keep the metal material in the riser at 1147 ℃ for 5.70 min. it can be seen that the Ex5 blend heating and insulation material has better heating and insulation performance.
(1) The heating subsidy made of Ex5 blend heating insulation material can preliminarily determine its effect according to the simulation results through the simulation software; The radiographic inspection and visual inspection show that the designed heating subsidy can meet the internal quality and surface quality requirements of sand castings. Therefore, the subsidy of Ex5 blend high-efficiency heating and insulation material can replace the metal subsidy.
(2) In the production test, high-efficiency heat insulation materials with the same size of metal subsidies are used to replace metal subsidies, which significantly improves the process yield of sand castings from 51.4% to 55.1%, reduces metal consumption, energy consumption and other consumption when removing subsidies, and deducts the consumption cost of heat subsidy materials, It can still reduce the production cost to a great extent.
During the test, two sand castings were cast in the same furnace, one of which was subsidized by metal and the other by heating and thermal insulation materials. A gate valve body is selected as the production test object, and the outline dimension of the sand mold casting is 830 mm × 500 mm × 440 mm, the blank weight is 540 kg, and the material is Dual Phase Steel ASTM a890 5A.