Frequent problems with die casting
1. Pouring system, overflow system
(1) Requirements for the mold sprue on the cold chamber horizontal die casting
①The size of the inner diameter of the pressure chamber should be selected according to the required specific pressure and the degree of fullness of the pressure chamber. At the same time, the deviation of the inner diameter of the sprue sleeve should be appropriately enlarged by a few wires compared with the deviation of the inner diameter of the pressure chamber, so as to avoid the difference between the sprue sleeve and the pressure chamber. Indoor diameters are not coaxial, causing the punch to be stuck or worn out, and the wall thickness of the sprue sleeve should not be too thin. The length of the sprue sleeve should generally be less than the delivery lead of the injection punch, so that the paint can come out of the pressure chamber.
②The inner hole of the pressure chamber and the sprue sleeve should be finely ground after heat treatment, and then ground along the axis direction, and the surface roughness should be ≤Ra0.2μm.
③ The shunt and the cavity forming the paint, the depth of the concave is equal to the depth of the runner, its diameter matches the inner diameter of the sprue sleeve, and has a 5° slope along the demolding direction. When the coating introduction type sprue is used, the fullness of the pressure chamber can be improved because the volume of the effective length of the pressure chamber is shortened.
(2) Requirements for Beilun die-casting mold runner
①The entrance of the runner of the cold horizontal mold should generally be located at more than 2/3 of the inner diameter of the upper part of the pressure chamber, so as to prevent the molten metal in the pressure chamber from entering the runner prematurely under the action of gravity and starting to solidify in advance.
②The cross-sectional area of the runner should gradually decrease from the sprue to the inner gate. If the cross-section is enlarged, negative pressure will appear when the molten metal flows through, and it is easy to inhale the gas on the parting surface and increase the flow of the molten metal. The vortex in the air is wrapped in air. Generally, the section at the outlet is 10-30% smaller than that at the inlet.
③The runner should have a certain length and depth. The purpose of maintaining a certain length is to stabilize the flow and guide. If the depth is not enough, the molten metal will cool down quickly, and if the depth is too deep, the condensation will be too slow, which will not only affect the productivity but also increase the amount of return material.
④ The cross-sectional area of the runner should be larger than the cross-sectional area of the inner gate to ensure the speed of the molten metal entering the mold. The cross-sectional area of the main runner should be larger than that of each branch runner.
⑤ Both sides of the bottom of the runner should be rounded to avoid early cracks, and the two sides can be made with a slope of about 5°. The surface roughness of the runner part is less than or equal to Ra0.4μm.