How to solve the problem of porosity in lost foam casting 2

3. Improve the breathability of the paint

The particle size of the refractory aggregate should be suitable. The 70-100 mesh sand-like substance in the aggregate should contain 10-15%. The composite suspension agent binder is used. The prepared coating has high and low temperature strength, wear resistance, and easy to brush. No cracking, large exhaust capacity, good air permeability, uniform sintering, easy to peel off and peel off when unpacking, no wetting and chemical reaction with alloy, generally castings are painted twice, coating thickness is 1-1.2mm.

The quality management of lost foam paint is critical. During mass production, periodically check the air permeability of the slag coating and adjust the particle size of the aggregate in time. Since the binder and suspending agent of the paint contain organic substances, special attention should be paid to the fermentation enzyme change of the paint in the summer and autumn seasons. Qualified castings are inseparable from the paint. Controlling the quality of the paint cannot be taken lightly.

4. The pouring temperature should be suitable

Due to the exothermic gasification foam during the filling process of the lost foam, it is recommended that the pouring temperature of the ferrous alloy is 30-50℃ higher than that of the sand casting. The thermal effect of the liquid metal and foam is restricted by the pouring temperature. The pouring temperature is suitable for sufficient pyrolysis. The pyrolysis products of the pattern are mainly in the form of small molecule gas. It is easy to exit the cavity under the action of the negative pressure field. When the pouring temperature is low, the pattern Insufficient pyrolysis, liquid phase residue will block the coating layer, the pyrolysis gas discharge is hindered, back pressure is formed in the cavity, the filling fluidity is reduced, coupled with the fast solidification speed, the gas slag in the alloy is too late to float Collected in the riser, the probability of generating stomata increases. The pouring temperature should be matched with the smelted alloy to avoid other casting defects due to high temperature.

5. Final deoxidation of molten steel and sedation in the bag

Lost foam follows the principle of high temperature and low temperature rapid pouring. High temperature discharge is to leave a suitable time for sedation in the ladle. The final deoxidation and slag removal of molten steel is a prerequisite for reducing three-hole defects. Sampling is observed before the furnace to observe the shrinkage of the molten steel. The stove should be kept clean and hygienic.

6. Reasonable pouring position

The casting position of the casting is to obtain good gasification conditions and exhaust conditions during filling, which is convenient for gasification and slag removal. Choose vertical or oblique pouring, that is, follow the principle of side surface area. The casting system should have slag blocking gas collection and Packing function.