Quality control of foam in Lost Foam Casting for stainless steel valves

1.Selection and pretreatment of foam raw materials

EPMMA and STMMA foam are often used in stainless steel valve castings. The former has a large volume of gas and a carbon content of about 60%. The latter is produced by the ratio of EPS and EPM-MA at 30: 70.

In the test, EPM Ma with appropriate particle size and low carbon content can reduce the pouring temperature of stainless steel, improve the mold filling effect and reduce casting defects. The thinnest part of stainless steel valve casting is 5 mm, the thickest part is 18 mm, and the bead size is 0.5 mm 4~ 0. 6 mm, and the pre foaming density shall be controlled within the range of 25 ~ 28 g / L.

2.Foam pattern forming control

The foam pattern of stainless steel valve castings is made of steam cylinder. Before filling, clean all kinds of dirt and moisture on the mold cavity with compressed air, and fill after assembling the mold. The air pressure during packing shall be kept at 0.5 โ„ƒ 2~ 0. 3 MPa. After the filling is completed, preheat the steam in the steam cylinder. When the steam cylinder reaches a certain temperature, put the filled mold into the preheated steam cylinder, close the steam cylinder, and inject steam to make the beads in the mold cavity expand evenly, the surface of the pattern is smooth, and the pressure in the steam cylinder is controlled at 0 10~ 0. 15 MPa, pressure holding time of 100 ~ 120 s. After discharging the steam, take out the mold and soak it in water for cooling. In order to reduce the deformation degree of the pattern, during the mold opening sampling process, blow each position of the pattern with compressed air to make the pattern come out of the mold smoothly. The compressed air shall be blown in the direction perpendicular to the parting surface of the die, and the air pressure shall not be too high to avoid damaging the surface of the pattern.