Technology of high temperature and high pressure valve casting

1. Casting process analysis

Before the casting of valve castings, relevant personnel need to know the valve structure and valve overview in detail, such as blank weight, shape, size, etc. In this type of high temperature and high pressure valve casting, its structure and shape are almost the same. By observing the appearance of the casting, it is found that it is composed of three circular pipes, so its shape is tee tubular. Relevant personnel shall check the centerline of the pipeline to see whether it is in the same plane.

All pipes with the same axial direction are provided with flanges, and the thickness of the inner wall of the other pipe orifice is large. The nozzles of these pipes are processed products. The internal and external diameter dimensions of the three pipes are the same, so the valve casting is relatively uniform as a whole. Annular pipe is the main object of casting process. During casting, relevant personnel need to make all annular pipes have the same concentricity, control the wall thickness of each pipe and make its tolerance within the allowable range. However, according to the current casting process, it is still difficult to achieve the purpose. In the design of casting process, relevant personnel should also consider the simultaneous feeding of three pipelines.

2. Casting process design

There are many problems to be solved in the casting process. Relevant personnel should focus on the following design.

One is the shrinkage of valve castings. Valve castings may shrink in application. Relevant personnel shall control the shrinkage within a certain range so that it will not affect the function of valve castings. Based on this, the shrinkage of valve castings shall be determined. When determining this parameter, we should also consider the material, valve casting structure and other factors. The final internal and external cavity scale parameters are 2% and 1.50% respectively.

Second, parting surface. Effectively select the parting surface to solve the problem of simultaneous feeding and shrinkage of annular pipeline. Take the parting surface as the collection position of all pipeline centerline. In the design, relevant personnel need to find the pipeline center, and the collection position of central extension line is the parting surface. Under the action of parting surface, the integral valve casting will be divided into two parts evenly. This plane has the largest cross-sectional area. Relevant personnel should also check the collection position of the axial centerline to see if there is only one plane. In valve casting, relevant personnel should control the use of sand core, which can avoid the occurrence of drape joint.

The third is the gating system. The pouring method is bottom pouring type, and the relevant system design shall also meet the requirements of bottom pouring type. It mainly designs the sprue and gate. In terms of sprue, it is necessary to ensure its corrosion resistance and stability, so that it can safely bear the impact of liquid metal and avoid various defects. The runner also plays the role of blocking metal slag. In the design, it should be avoided to block the gas discharge of the cavity. In order to ensure the filling effect of the gating system, it is also necessary to solve the influence of metal chromium, mainly to improve the cold shut and wrinkle phenomenon. Also deal with the oxide film produced by chromium. In addition, the pouring time, the mass flow rate of liquid steel and the diameter of wrapped hole should be designed and controlled to meet the quality requirements of steel castings. Among these parameters, the diameter of cladding hole and the mass flow rate of molten steel will affect each other. Relevant personnel will analyze the relationship between them through data and summarizing the law in several experiments. Finally, the cross-sectional area of components should be accurately calculated to make the size of gating system meet the requirements.

3. Determination of other process parameters

Effective control of other process parameters can avoid cracks in valve castings. These processes mainly refer to the process of chilled furan resin quartz sand except casting and smelting. This process mainly takes sand mold material as the molding material of valve casting. The sand separation layer in the valve casting pipeline under the action of this process mainly uses thick chrome ore, its thickness should be controlled to be ≥ 0.03 m but not > 0.05 M, and the sand content in the sand core is (0.08 ~ 0.10) M.