The tubing thread cone is generally processed in two steps, i.e. rough turning with an external turning tool and fine turning with an tubing thread combing tool. In order to reduce the influence of taper error on the sealing performance of tubing thread connection, the following measures are formulated for the reason of large taper error during tubing thread processing:
During the processing of tubing thread parts, the taper angle error shall be controlled within the range of 1°47′24″, and the taper error shall be checked and corrected frequently. Because of the accuracy of the external cone measurement, the angle can be measured by sine gauge after the cone is turned out. The inner cone shall be colored by cone plug gauge of the same specification, and the contact area shall be greater than 60%.
The die support of the profiling lathe shall be overhauled every three months, and the accuracy of the profiling lathe and the CNC lathe shall be overhauled every six months.
After the internal and external cone of the tubing thread is rough turned, the single side comb amount is 0.3 ~ 0.5mm to ensure the integrity of the thread profile when combing the tubing thread. In order to ensure that the internal thread of the tubing has enough machining allowance, the diameter of the preformed blank hole of the coupling is specified, and the tolerance zone is h14.
The straightness of the thread centrum of the tubing shall be checked by light transmission with a flat ruler. When the plain line is in the middle concave state, it shall not be greater than 0.01mm. When the plain line is in the middle convex state, it shall not be greater than 0.03mm.