SAND CASTING EQUIPMENT.

The fluidity and filling capacity of high chromium cast iron are close to that of gray cast iron. Therefore, when designing the casting system of high chromium cast iron, it is recommended to adopt semi-closed casting system. The semi-closed gating system has the largest broken area at the transverse gate and the flow resistance section at the inner gate. The molten iron can fill the gating system during the pouring process, so the filling is relatively stable and the scouring force on the casting mold is small. As the molten iron flow slows down at the gate, it has a certain slag holding capacity. The cross-section area of each part of the gating system can be selected according to the following proportion: the total area of the inner gate is less than the total area of the straight gate is less than the total area of the transverse gate
(1.1~1.2) (1.3~1.5) (medium and small castings)
1:1.2:1.4(large and medium thickness parts)

For some thick-walled castings, low temperature casting is required near the liquidus temperature, and for some high chromium cast iron with eutectic composition, due to the wide solidification temperature range, the appearance of paste solidification and the early stop of molten iron flow, closed casting system should be adopted for these two types of castings, so that the mold can be filled with higher flow rate and shorter casting time. The cross-sectional area of each part of the system can be selected according to the following proportion:
The total area of internal sprue is less than the total area of transverse sprue less than the broken area of straight sprue
1：（1.2~1.25）：（1.4~1.5）

Improper casting system design may limit or hinder casting shrinkage, especially in a casting system with multiple internal sprue on a large cross section. Restricting or hindering shrinkage may lead to internal stress, deformation or even fracture of the casting. The casting deformation and cracking defects caused by the casting system of high chromium cast iron are more common than the similar cases of cast steel and deserve people''s attention. In order to avoid this situation, the buffer gate with a small amount of expansion and contraction can be used. At the same time, the break area of the gate and the inner gate should be properly controlled so that the gate can shrink or break when the solid shrinkage occurs.

1.1 If the casting is thin (e.g., wall thickness is less than 15mm) and the wall thickness is uniform (e.g., board castings), it should promote the balanced solidification of the casting and improve the process yield. This kind of castings should be arranged with more internal spouts evenly distributed around the thin wall to avoid excessive heat concentration and local shrinkage. The inner spout can be properly thickened close to the casting (8~10mm away from the casting), so that the inner spout can play some role of shrinkage cavity and avoid shrinkage hole at the joint with the casting. For thin castings with uneven wall thickness, if riser is placed at the thick wall, the inner runner should be opened near the riser to facilitate sequential solidification of the castings.

1.2 For castings of medium thickness (e.g., 50~80mm) but with uniform wall thickness, the internal spout shall be opened near or enter the casting through the riser to form a temperature gradient within the casting. At the same time, the flow rate of molten iron was decreased, the casting time was increased, and the temperature gradient of casting was steepened, which was beneficial to improve the filling and shrinking efficiency of riser.

1.3 The internal gate size and layout shall be determined by reference to the composition of high chromium cast iron. In principle, the temperature distribution of sequential solidification should be created. The internal gate size of near eutectic component casting should be smaller than that of far eutectic component casting.

1.4 The internal gate should not be placed on the anti-wear surface. Because of this, the temperature of the part connecting the inner spout to the casting will be higher, the microstructure of the anti-wear surface will be larger, and the anti-wear ability of the casting will be affected. Empirical data on the total cross-sectional area of internal spout of high chromium cast iron castings, which have been used for a long time in production with good results.

2. Runner. The main function of the runner is to transfer molten iron from the straight gate to the inner gate through which it is introduced into the casting. In the process of conveying, it can remove slag and control the velocity of molten iron. Cast with horizontal parting, runner is generally placed on top box. The section is designed as a narrow and high trapezoid. It can be in the same box with the inner runner or put the inner runner in the lower box. The two can be connected at the parting surface. In the same case, the runner height should be 3~5 times of the runner height to prevent the suction action of molten iron flowing through the runner using the slag removed from the runner to flow into the casting. The broken area of the runner shall be selected according to the proportion of the casting system section mentioned above.

3. Straight runner. The straight runner connects the runner cup to the runner runner. The straight runner shall be high enough to allow the molten iron to enter the runner and the inner runner under a certain pressure head to ensure the perfect filling of the molten iron and to force out the gas that may exist in the molten iron. The broken area of the direct runner shall also be selected according to the proportion of the broken area of each part of the gating system mentioned above.

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