Technical requirements for impeller production
(1) The surface of the casting shall be smooth and free from defects such as pores and sand holes;
(2) Five blades should be evenly distributed;
(3) The unbalanced mass is less than or equal to 80g;
(4) The hardness of heat treatment is hrc40-45 [b];
(5) One coat of iron red perchloroethylene primer shall be applied to the non processed surface and large outer circle after processing;
(6) Remove the unbalanced mass from the front and rear cover plates and the outer circle of the blades.
At present, the production process of such impeller is shown in the figure, and two boxes of resin sand are used for molding. The sand core part is composed of one core and two cores. One core is composed of five cores which are respectively made on the core mould. After the completion of 1 × core combination, sand shall be filled in 2 × core positions to form a whole sand core. The riser diameter is Φ 230mm and the height is 400mm. The area of the sprue and the runner are respectively Σ a direct = 3846mm2, Σ a horizontal = 1912.5mm2 = 1912.5mm2, Σ a internal = 3500mm2. The advantage of this technology is that the filling speed is fast. In this way, the oxidation of alloy liquid metal and the insufficient cold isolated casting of blade are avoided. It is beneficial to the feeding of hot spot and avoids the defects such as shrinkage porosity and shrinkage at the hub and flange. Many batches of qualified castings have been successfully produced by this process.
But the disadvantage of this technology is that the modeling is very complicated, the technical requirements of workers are high, and the quality of static balance is difficult to guarantee. Because the working face and the back face of impeller blades are all space warped surfaces, it is impossible to obtain an ideal whole sand core by using the traditional sand molding technology. Therefore, the sand core can only be divided into several parts, fixed into a whole sand core with aluminum ring, and then lower the core. As shown in the figure:
The five sand cores of 1 core are made of wood mold and assembled manually. Therefore, the whole molding process has a high labor intensity and technology for workers. And the stability and accuracy of manual assembly are poor. At present, the static balance of this kind of impeller is 2200g without machining. The worst static equilibrium value is 5000g. However, the requirement of static balance experiment, unbalanced mass ≤ 80g, brings great difficulty to the follow-up machining. Therefore, it is imperative to improve the process.