During the pouring process, due to the excessive amount of gas released by the thermal decomposition of the gas mold and can not be eliminated in time, the air pressure in the casting cavity rises sharply, which is easy to cause fire spraying or metal liquid spraying, resulting in the scrapping of steel castings. Preventive measures include:
(1) The density of EPS pattern shall be controlled at 0.016 ~ 0.022 g / cm3. The pattern shall be dry and dried after coating to reduce the moisture content and gas generation.
(2) Select the coating with good air permeability and adjust the coating thickness (1.5 ~ 2.5mm is appropriate) so that the gas can escape in time after the pattern is cracked.
(3) Control the permeability and particle size of dry sand; The design of sand box should be scientific, reasonable and applicable. Control the negative pressure (suction by vacuum pump) to make the pattern gasify under the condition of vacuum and hypoxia, and rarely burn and reduce the gas generation.
(4) Control the pouring temperature and pouring speed to ensure the gasification of the pattern with the heat of liquid steel. At the same time, control the pouring speed when the pattern produces a large amount of gas, so as to avoid too fast pouring speed and promote the burst of pyrolysis gas.
(5) A reasonable gating system is designed to ensure that the molten metal filling is stable, balanced and quickly filled with the mold pattern, so as to ensure that the cracking gas of the pattern escapes out of the mold cavity and is sucked out.