1 Scheme for machining the inner surface of pneumatic ball valve shell The inner surface of shell parts can be machined by turning, milling, grinding and other methods. In order to process the shell of the pneumatic ball valve shown in Figure 1, the two inner surfaces of the ball were milled separately with a forming milling cutter before, but the machining accuracy failed to meet the requirements. Therefore, the processing of this part is listed as a scientific research topic in the university.)

Stability of non-metallic contraction joint and its manufacturing method
During the normal operation of non-metallic contraction joints, the gravity of the pipe system is required to be borne by various supports and hangers, so that the pipe system can freely shrink (contract); Tongjing often uses the pre deformation of the pipeline to reduce the thrust of the pipe support and strengthen its stability, which are particularly important in the process of installation, new construction and reconstruction.
During the normal operation of non-metallic contraction joints, the gravity of the pipe system is required to be borne by various pipe supports (hangers). The mass of the corresponding flue for this installation is 20t, which is borne by a constant force spring. In the process of transformation, the rigid fixation of the pipeline system was stopped, but the reset of the constant force spring was not stopped; Due to the particularity of the displacement of the constant force spring, when the external load is removed, it cannot return to the original state. Therefore, after re installation, the constant force spring is in a state of no force in practice; When the rigid fixation is removed, the mass of the flue is pressed down to form the downward movement of the pipeline.