Axle housing is one of the main components of engineering vehicles, which carries the strong force of transmission and load. The structure of axle housing is complex, and the wall thickness is uneven, and the difference is large. In view of the increasing requirements of users for the comfort and safety of heavy-duty engineering vehicles, only the axle housing with high strength, high toughness, high fatigue resistance and good weldability can meet the requirements of heavy-duty vehicles under bad road conditions in mines.
The production process of axle housing castings is mainlyand V-method casting. In recent years, due to the rapid development of process, many casting companies try to produce with lost foam . However, most lost foam casting steel axle housings can not meet the user’s standards. Even if some castings are installed on vehicles, the axle housing will have cracks and oil leakage during service. The reasons are as follows.
(1) the difference of the wall thickness of the carburized axle housing is quite large, resulting in the narrow combustion space of the foam. Even if the shell process is not easy to burn, the surface carbon content can not be controlled.
(2) Inclusion leakage the inner cavity of the axle housing is a relatively closed space, which is filled with lubricating oil. There shall be no leakage during service. High pressure leakage test shall be carried out before processing. Because the spiral case wall in the middle of the axle housing is thin, generally 12 mm ~ 16 mm, it is easy to precipitate inclusions during solidification of liquid steel under high negative pressure, increasing the probability of leakage.
(3) The volute wall in the middle of the cracked rear axle is thin, while the flange of the semi-circular opening of the volute has a thickness of 35 mm ~ 60 mm, and is connected with the thin cylinder shaft pipe at both ends, resulting in large internal stress during cooling shrinkage, and cracks are easy to occur at the transition and flange of the connection.
(4) The length of axle housing of deformed heavy engineering vehicles is mostly more than 1300 mm. The axle housing is a slender cylinder with an opening in the middle, and the wall thickness varies greatly. It is easy to deform in the following three processes: ① it begins to deform after the white mold is naturally dried; ② Coating, improper drying support and deformation during drying; ③ Deformation caused by shrinkage stress caused by uneven temperature after casting. After heat treatment, castings need to be reshaped by a press in order to achieve qualified dimensional tolerance. Based on the above four points, few casting companies have used lost foam casting process to mass produce heavy-duty vehicle cast steel axle housing. Requirements for compactness: the leakage test time of the whole casting under the pressure of 0.3 ~ 0.5 MPa shall be greater than 10 min. Magnetic particle flaw detection shall be conducted for the whole after heat treatment. The hardness shall be 190 ~ 240 Hb, and the oxide layer shall be removed by shot blasting.