The fundamental focus of the method to solve the shrinkage defects of ship inspection castings is "heat balance". The method is:

(1) The rapid solidification is carried out at the thick and hot spots formed by the casting structure of the machine tool ship inspection, which artificially causes the basic balance of the temperature field of the machine tool casting. Internal and external cold iron shall be used, and zircon sand with large heat storage capacity, chromite ore sand or special coating shall be used locally.

(2) Reasonable process design. The ingate is located at the relatively thin wall of the machine tool casting, and it is scattered for several hours. Make the metal liquid entering the thick wall solidify first, and then solidify at the thin wall, so that all parts basically achieve balanced solidification. For machine tool castings with uniform wall thickness, multiple ingates and air outlets are used. There are many internal runners, which are dispersed and evenly distributed to make the overall heat balance. The air outlet holes are thin and many, which means that the exhaust is smooth and plays the role of heat dissipation.

(3) Change the position of the ingate

(4) It is very important to select molding materials with large heat storage capacity for the production of anti-wear products with EPC! Chromite sand replaces quartz sand and other sand types with small heat storage capacity, which will achieve good results and better micro vibration after pouring!

(5) Low temperature fast burning, open gating system. Make the molten metal fill the mold quickly, smoothly and evenly. This should be adjusted according to local conditions.

(6) The machine tool casting strength of nodular iron is high, the surface hardness is ≥ 90, and the sand box rigidity is large, which is beneficial to eliminating shrinkage porosity.

(7) When the riser is required, the hot riser shall be moved for the first time and leave the hot joint. If the riser is placed on the hot joint, the size of the riser will be increased to form "thermal heating". If it is not done well, it will not only be difficult to remove the shrinkage porosity, but also produce concentrated shrinkage holes, which will reduce the process yield.

(8) The inclined placement and alloying of the mold are beneficial. Eliminating shrinkage porosity of machine tool castings is a complex process of understanding and implementation. Based on the basic principle of "heat balance", scientific analysis shall be made on the shell casting, reasonable process scheme shall be formulated, appropriate molding materials, tooling and correct operation shall be relocated and standardized.

After the liquid metal is injected into the casting mold, the liquid metal first contacted with the mold wall will quickly solidify into fine grains because the temperature drops faster and there are a large number of solid particles on the mold wall to form crystal nuclei. With the increase of the distance from the mold wall, the influence of the mold wall is gradually weakened. The main axis of the crystal grows along the average direction of heat dissipation, that is, it grows into columnar crystals parallel to each other along the direction perpendicular to the mold wall.

In the center of the casting, there is no obvious directionality of heat dissipation, the cooling solidification is slow, and the crystal grows freely in all directions to form an equiaxed crystal region. Obviously, the structure of the casting is uneven. And generally, the grain size is relatively large. The crystallization of liquid metal is carried out in the form of dendritic growth, and the liquid metal between the branches will solidify, but it is difficult to completely fill the metal liquid between the branches, which results in the general non compactness of the casting.

In addition, the volume of liquid metal will shrink during cooling and solidification. If it is not supplemented timely and sufficiently, it may also form porosity or shrinkage cavity. The casting is formed by one-time casting, the shape is often complex and irregular, and the surface is often difficult to process.