The box body is an important part of the gear box. It bears the reaction force from the transmission of the gear. It must have enough rigidity to bear the force and torque, prevent deformation and ensure the transmission quality. The design of the box is carried out according to the layout arrangement of the power transmission, processing and assembling conditions, convenient for inspection and maintenance. The reaction force and relative value of bearing and seat supports in different directions, appropriate supporting structure and wall thickness are selected, and necessary reinforcing bars are added. The position of the reinforcement should be consistent with the direction of the force causing the deformation of the box.

The stress situation of the box body is very complicated and the distribution is not uniform. Only by using modern calculation methods, such as finite element method and fracture mechanics, can the stress distribution condition be calculated accurately. The result is very close to the actual stress.

The case cover shall also be provided with air permeable cover, oil gauge or oil level indicator. The oil injector and oil drain hole are provided at the corresponding position. There should be enough space around the oil drain hole. The gear box adopts forced lubrication and cooling, and the installation position of oil inlet and outlet and related hydraulic parts is set at the appropriate part of the box body.