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Casting process 3.1 Casting process characteristics Since all surfaces need to be machined, the shape and position accuracy of the blade casting must be ensured during the casting process. There are several difficulties in the casting process: Traditional casting blades have the following two requirements: ①. The customer needs to provide an expanded view of the section from near to far in the circumferential direction; ②. In the actual production process, make 3-5 graphite rings according to the circumferential radius of the profile development diagram provided by the customer. This parting method is more suitable for small size castings. The advantage of this parting method is that the model has less waste and high utilization rate, but it is not suitable for large castings.

The size of the blades cast in this paper is large. According to this method of casting, the utilization rate of graphite is less than 50%, and the model cannot be reused; due to the structural characteristics of the blade and the uneven thickness of the blade, the cooling speed of each part of the casting is caused. Different, the degree of shrinkage is different, the casting is deformed during solidification; the distance between the furthest part of the blade and the wheel is large, and the riser and the farthest end of the hub cannot form a good feeding channel; the customer only provides three-dimensional A picture, and in actual production and process design, you need to convert the three-dimensional picture into a two-dimensional picture. The structure of the blade surface of the blade is complicated, the measurement positions are many, the accuracy requirements are high, and the spatial position is difficult to determine, which brings great difficulty to the detection. 3.2. Casting process design Traditional casting blade castings are first divided into several circular sections according to the circumferential direction. Then, the cross-sectional view along the circumferential direction is made into a template, and the template is drawn on the graphite type according to the corresponding position, and finally the excess graphite is removed. This parting method is more suitable for the production of small-sized castings. This scheme is not suitable for large-scale blade casting. This blade has a large appearance and a large number of pieces. Considering factors such as cost and human labor intensity, designing a reusable model is the first problem to be solved in the design. After careful discussion and research, the original process was changed to the following method. The original casting process plan of Brass Bushing Sleeve Roller Bearing the impeller The current casting process plan of the impeller In the current process, the original ring-shaped group plan is changed to a combination of rectangular parallelepiped materials.

The size of each rectangular block material is 640mmx440mmx60mm. Rules, each piece of material is easy to choose without waste. Each material is divided into two pieces according to the chamfering and following edges, which realizes the reuse of the model. When making the model, the deformation of the blade during the solidification process was fully considered. During solidification and cooling of liquid alloys, during the solid shrinkage phase (shrinkage from the solidification termination temperature TS to room temperature), the volume shrinkage of the casting is linear with the temperature drop. This relationship determines the size of the "reduced scale" of the casting. See the curve of the volume of the casting with temperature. The liquid shrinkage bookmark1 solid shrinkage TSTL temperature. The curve of the volume of the casting with temperature.

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For alloys that are easily oxidized, such as aluminum, magnesium alloys and some copper alloys, it can avoid or reduce the formation of regenerated slag during the filling process of the molten metal. Side-injection pouring system: the pouring system that introduces metal from the side walls of the casting is called side-injection pouring system. Since the side injection type pouring system can be flexibly opened around the casting according to the condition of the mold parting surface, it is very convenient, so most of the castings in production are side injection type pouring systems. There are many types of side injection type pouring systems. According to the height and condition of the introduction of the molten metal, it can be divided into five types: top injection type, bottom injection type, middle injection type, stepped type and vertical gap type. Compound pouring system: For heavy and large castings, the use of a variety of gate forms, often unable to meet the requirements, according to the situation of castings, joint use of several gates. Pouring systems with different proportions of elemental sections can be divided into closed gating system, open gating system, semi-closed gating system, and closed-open gating system. The location of the pouring system has a great influence on the quality of castings, which is one of the key issues in the design of the pouring system. The location of the gate is mainly to study how to reasonably place the inner runner in the casting. This not only affects the filling of the cavity with the molten metal, but also affects the temperature and solidification process of the casting.

The solidification of castings can in principle be divided into two categories: sequential solidification and simultaneous solidification. The so-called sequential solidification means that the thin part and the lower part of the casting (farthest from the riser) solidify first, then the thick part and the upper part (closer to the riser) Solidification, and finally the riser solidification. Simultaneous solidification means the solidification of castings with different thicknesses or with uniform wall thickness. According to the principle of sequential solidification, the pouring system is set up, the shrinkage holes are concentrated in the riser, and a densely structured casting can be obtained, but the temperature difference is large, the stress is large, and the casting is easily deformed or even cracked. If the setting of the pouring system conforms to the principle of simultaneous solidification, the cooling of each part of the casting Bimetallic bushing company  is uniform and the stress is small, but it is unfavorable for the shrinkage, and shrinkage holes or shrinkage often occur in the central part or local thick part of the casting.

Therefore, the choice of solidification principle should be based on comprehensive consideration of the nature of the casting alloy, the structural characteristics of the casting and the working conditions. In general, alloys with large shrinkage (such as cast steel) and castings with uneven wall thickness or strict quality requirements are mostly solidified sequentially, while alloys with small shrinkage (such as gray cast iron) and castings with uniform wall thickness are mostly used at the same time. Solidification, top-injection and up-injection, and opening the sprue at the thick wall of the casting are conducive to sequential solidification; uniformly dispersing the sprue and opening the sprue at the thin wall of the casting are conducive to simultaneous solidification. How to achieve a certain solidification principle for a casting must be fully considered with the riser, cold iron and other technological measures. In addition to considering the principle of solidification, the following main rules should be observed when determining the specific location of the inner runner: the path for the molten metal to enter the casting mold and the flow of the molten metal in the cavity as short as possible. This can avoid excessive heat loss of the molten metal, reduce the temperature difference between the parts of the casting, and reduce metal consumption, such as a wedge runner. Do not open the gate in important parts of the casting. The overheated inner runner due to the flow of a large amount of molten metal will cause the casting grains to be coarse and may shrink. For castings like worm gears, it is not possible to open the in-runner on the side wall, and the horn gate or the bottom injection type are mostly used. The molten metal should be smoothly filled along the side wall of the cavity, and the front side is not allowed to impact the casting mold and the sand core, especially the protruding parts, so as not to cause defects such as sand flushing and sand holes. For round castings, the inner runner should be opened along the tangent direction. For some castings with even wall thickness and large area, such as cover, plate and cover castings, the size and number of inflow runners should be increased so that the molten metal is uniformly dispersed into the cavity to avoid cold insulation and deformation. In addition, the opening of the sprue should consider the smooth exhaust (for example, the mold of the rain gate is equipped with an air outlet, which is also necessary for the blanking gate). It should not hinder the shrinkage of castings, and should be easy to knock off and polish during cleaning.