Two misunderstandings of technical personnel on thread standards

1) The principle of the tolerance zone for thread inspection: there is a tolerance zone diagram distributed along the thread profile and a table of tolerance values u200bu200bfor each diameter. The vast majority of technical personnel in China believe that the thread profile of a product qualified by the thread gauge inspection should fall within the tolerance range specified by the thread standard, and the thread quality should be no problem. When the thread quality of qualified products was found to be very poor, they were at a loss and did not know where the problem was. In fact, the thread is a complex geometry, it has many technical parameters. If you want to fully control the quality of the thread (using the principle of tolerance zone), you need to measure all the parameters of the thread, which will take a lot of time and high inspection costs. This is not feasible in actual production. Moreover, in different occasions, the functions and requirements of the various parameters of the thread are different, and some parameters can be guaranteed by the production process without separate inspection. At present, the thread pass and stop gauges used in our country are derived from the Taylor principle invented by the British in 1905. Its advantage is that it is economical and can guarantee assembly; its disadvantage is that the thread quality assurance level is low and there are many technical loopholes. China should earnestly study and learn from the American thread inspection system technology (standard) to improve the level of thread manufacturing in my country. (Guide: The size and weight of steel)

2) The relationship between the gauge inspection of the sealed thread and the sealing guarantee: the vast majority of Chinese technicians believe that the thread shape that is qualified by the thread gauge inspection should fall within the tolerance range specified by the thread standard. There should be no problem with the tightness. In fact, the thread inspection performed by the gauge has little to do with ensuring the tightness of the thread. The thread inspection only guarantees the assembly position relationship between the internal and external threads. In order to ensure the tightness of the thread, the company must take certain internal control measures. As Chinese technicians do not realize this, mechanical products often leak, and export products often return. These have severely affected the competitiveness of Chinese products in the international market. In the 21st century, ISO, Europe and North America have generally increased the number of testing gauges for sealed pipe threads. my country should keep up with the latest changes in the world and improve its sealing ability for sealed pipe threads.

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