Intrusive pores are the key way to cause pores in lost foam stainless steel castings. The reasons for their occurrence are as follows.

(1) During the whole pouring process, the pouring time is too short and the filling is too fast. The foam pattern cannot be quickly vaporized. The cracked liquid material enters the metal material liquid. After the casting is condensed, the vapor cannot be discharged. And pores are generated in the casting.

(2) The air supply volume of the foam plastic shape increases greatly with the increase of the pouring temperature, as shown in the figure2In order to change the air pressure with the pouring time during pouring, it can be seen that the air pressure rises sharply at the moment of pouring, because the casting temperature of steel castings is relatively high, and the amount of air supplied at the moment of pouring is very large, and the steam is not It can be discharged in time, especially when the desolubilization is in the flow field, the vapor will be drawn into it, resulting in pores.

(3) The wrong operation of the adhesive used to bond the foam pattern is the key reason for the intrusive pores. In specific production, it is found that stainless steel castings usually cause a lot of pores at the adhesion of the foam pattern. If you use connectors or nails to connect the foam pattern, it is not easy to cause pores at this point. It is because more adhesive is applied at the junction, no matter what851Super glue orABGlue, its relative density is several times or even dozens of times that of foam plastic, its vaporization rate is much slower than foam plastic and its vaporization temperature is higher. When the glue has not vaporized, the metal material liquid rises and wraps the glue. The whole process of refrigeration continues to vaporize, which in turn creates pores in the casting.

(4) Moisture is also one of the factors that produce pores in stainless steel castings. The key sources of moisture during pouring are the following aspects: First, the coating is not completely air-dried, or because the water-based coating containsCMCOrganic chemical binders such as, polyvinyl alcohol, white glue, tapioca starch, etc., if the paint pattern can not be poured in time after air-drying, it will digest and absorb the moisture in the air. In addition, the suspending agent such as sodium bentonite of the coating mostly contains structural water and bound water, because the air-drying temperature of the pattern is generally only40At temperatures above ℃, the structural water and bound water generally still remain in the paint, and these water vaporize under the effect of high temperature desolventization; second, the foam shape is not sufficiently dry, and there is still a lot of water remaining in the foam beads Steam; the third is from the water in the sand.