Improvement measures for main casting defects of waste valve castings

According to the causes of valve casting defects, we have taken improvement measures mainly from the following aspects:

(1) Properly increase the carbon equivalent of molten iron and enhance the self feeding ability of the material by graphitization expansion.

(2) When pounding the box, ensure the compactness of molding sand, improve the strength of sand mold and promote the self feeding capacity of valve castings.

(3) Before mold closing, blow the loose sand in the mold cavity, and carefully check the mold cavity.

(4) After on-site pouring, the sand mold of valve body casting that is not poured shall be left, and its gate cup and air outlet shall be tightly covered to prevent the entry of loose sand.

(5) Clean the solid slag on the surface of molten iron before pouring; Increase the initial pouring temperature of molten iron and reduce the tendency of molten iron to produce secondary oxidation slag; The valve castings shall be poured at the initial stage after the furnace is opened as far as possible to reduce the large amount of thin slag generated by the lining after repeated use; For 610mm valve castings, for the lap joint of the runner, combined with other parameters during pouring, filter screens are installed at the inlet and outlet, and the multi piece lap fiber filter screen is improved to a single piece, so as to improve the slag retaining effect of the gating system.

(6) Carbon steel, ordinary gray cast iron or nodular cast iron shall be used as raw materials; Reduce the content of alloy elements in molten iron, such as Cr and Mn, and reduce the gas content of molten iron itself; All sand cores before core lowering shall be painted overhead and stored within a time limit to prevent moisture absorption of sand cores; In rainy days or seasons with high humidity, it is best to bake the mold cavity and the surface of the sand core with a blowtorch before lowering the core, so as to reduce the gas output of the sand mold; Small valve castings are poured at high temperature to facilitate the exhaust of molten iron and reduce the generation of casting slag of valve castings.

(7) When pouring 1067mm valve castings, it is required to pound the upper and lower molds on the same bottom plate in front of the fixed sand mixer, and there shall be no sundries on the bottom plate; It is not allowed to put it in other places to reduce the source of variation; It is forbidden to lift the sand mold and the bottom plate of the mold together to prevent the deformation of the bottom plate.

(0) when pouring 2.2mm valve body castings, put an appropriate amount of resin sand on the core head of the foot sand core and close the mold as soon as possible.