The difference between the gas porosity and shrinkage cavity in casting process (2)
1) when non-ferro alloy is melted, charge, solvent, tool and ladle should be preheated and dried fully, rust and oil should be removed, and the amount of charge should be properly limited.
(2) to prevent excessive oxidation and inhalation of molten metal during melting, to add deoxidation, degassing and slag removal, to cover the surface of molten metal pool in pouring ladle with solvent, to prevent the reoxidation of metals, gettering and harmful impurities from returning to molten pool. When using aluminum to deoxidize cast steel and cast iron, the residual aluminum content should be strictly controlled, and the deoxidization of molten steel with aluminum should be avoided as far as possible, in order to remove gas and harmful impurity in molten steel, desulphurization should be strengthened, the content of original soup should be reduced, the addition of nodulizer should be reduced as far as possible, the residual magnesium content of cast iron should be reduced, and the inoculation treatment should be strengthened.
(3) when pouring, the liquid metal should not be broken flow, and the filling speed should not be too high. The pouring position and the pouring system should be set to ensure the liquid metal filling the cavity smoothly, and to facilitate the smooth discharge of the gas in the cavity.
(4) when casting, should ensure the mold and core vent unobstructed, sand core to open the vent channel, closed to fill the core gap, so as to avoid drilling into the liquid metal plug vent channel.
(5) increase the sprue height to improve the filling metal hydrostatic pressure.
(6) to reduce the amount of resin and hardener in resin sand, to adopt low nitrogen or no nitrogen resin and raw sand and reclaimed sand with round shape, moderate particle size, low ignition loss and fine powder content, so as to reduce the gas emission of resin sand and improve the permeability of resin sand
The defects of shrink holes and the methods of prevention and control
And castings produce shrink holes, shrink, for many reasons, there are castings and pattern design reasons, there are sandbox design is not suitable reasons, there are reasons for the design of the sand vent, there are the reasons for the type of sand to avoid displacement, there are also reasons for the production aspects, there are improper mixing of metal chemical components, there is the improper operation of the melting link reasons, there are reasons for pouring.
Because of the many reasons for the casting shrink hole, it is often time-consuming to find the root cause. How to quickly determine the internal causes of casting shrink hole, which requires us to multi-contrast casting shrink defect cases, memorizing theoretical characteristics, strengthen learning, so as to improve the understanding of such defects and solution ability.