Main quality problems of tractor axle housing by sand casting

At present, most companies adopt the process of sodium silicate sand casting and V-method casting for production. According to the characteristics of open production mode, ZHY casting adopts sodium silicate sand casting. This kind of casting method has many characteristics, which can be summarized as suitable for multi variety and small batch production, especially for bridge shell with complex structure and shape, with low production cost and high production efficiency. The main advantages of this kind of cast steel axle housing are good strength and toughness and high overall safety factor. However, due to the characteristics of gravity casting, as well as the complex design structure and strict quality requirements of the axle housing, the defective product rate is as high as 70%. Based on this, this subject selects a certain type of tractor split axle housing as a case, as shown in Figure 1, as the research object, in order to design and calculate the sand casting process scheme, formulate the corresponding process parameter settings, and put forward the best sand casting process solution on the basis of process scheme optimization, simulation and optimization.

The sand casting process of axle housing is relatively complex. Under the action of gravity, molten steel enters a specific mold cavity by heating and generates parts and components after cooling. General sand mold casting process includes mold making and inspection, including mold, modeling, melting, pouring, cleaning and other links. This leads to many factors affecting the product, poor product quality stability, high requirements for the internal and appearance quality of the axle housing, resulting in three sand casting defects such as shrinkage, lack of meat and unqualified air tightness in the process of processing and use. It is mainly reflected in the following aspects: at the critical wall thickness of the shrinkage cavity, due to insufficient feeding pressure, there is a volume deficit in the axle housing itself, resulting in irregular shape and rough internal hole defects; The organization is not compact (oil leakage) and the product is not well sealed. After assembly, there is oil leakage in the axle housing during driving.

For this kind of sand mold casting axle housing, the above sand mold casting defects are common faults, including both surface defects and internal defects. The main harm is that it can not be identified by visual inspection. The traditional detection equipment can directly and accurately detect the defect location, resulting in many product quality defects and high subsequent maintenance cost.

Through the observation of the oil leakage position, the inspection results show that the oil leakage parts are in the depression below the axle shaft oil seal seat in the axle housing, which is the wall thickness connection of the inter wheel differential, and other parts such as the axle housing connecting plate are well sealed without oil leakage. It is preliminarily judged that the oil leakage is caused by internal sand casting defects of the axle housing.

According to the comprehensive review and analysis, the oil leakage parts are all the depressions under the axle shaft oil seal seat in the axle housing, and the specific positions are shown in Fig. 2 and Fig. 3.

2)3D diagram of axle housing 3)2D diagram view of axle housing