Sealing technology

The inch seal pipe thread is a general purpose seal pipe thread. In use, a seal filler is added to the thread pair. Its characteristics are relatively economical and the processing accuracy is moderate. Without sealing the filler, it is ensured that the thread of the sealing connection is a dry sealing pipe thread. There are no dry seal pipe threads in the inch pipe thread system.

The sealing pipe thread has two functions of mechanical connection and sealing; the non-sealing pipe thread has only one function of mechanical connection. Therefore, the accuracy of the sealing pipe thread is stricter than the precision of the non-sealing pipe thread. Some people see that the medium-diameter tolerance of the unsealed pipe thread is half of the diameter of the seal pipe thread. It is considered that the accuracy of the unsealed pipe thread is higher than that of the seal pipe thread. This view is incorrect. Type accuracy is required. The tolerances of the large diameter, the medium diameter and the small diameter are the same; the flank angle and the pitch error have a great influence on the sealing performance. Non-sealed pipe threads have essentially no requirements for tooth accuracy. The top diameter tolerance is greater than the medium diameter tolerance; the bottom diameter has no tolerance requirements. In addition, some people think that the non-sealed cylindrical internal thread can be combined with the external sealing thread. This view is also wrong. This is equivalent to relaxing the accuracy requirements of the internal threads of the seal, and the sealing of the pipe threads may be problematic.

Due to the use of sealing pipe threads, machining accuracy, assembly and inspection techniques, current pipe thread standards do not guarantee that all screw parts that meet the standard requirements can be sealed. In the inch seal pipe thread standard, the accuracy requirement of uniform thread single parameter cannot be proposed. These single thread parameters have a direct impact on sealing performance. The fundamental way to solve the problem is to develop your own internal control measures for your specific products and industries. The internal control indicators of these parameters are generally kept secret. It is also not common for companies in other industries, and manufacturers must have a clear understanding of this. Sealing pipe thread standards are not omnipotent, and sealing problems may require the manufacturer to pay attention to it. Before 1987, China did not have American and British pipe thread standards. However, in the production, these two internationally widely used pipe thread standards cannot be avoided. For this reason, the old mechanical drawing standards have previously specified the marking codes of the American and British pipe threads. These thread codes are derived from the Chinese pinyin letters and are not considered at all. Whether the foreign standard pipe thread standard code is consistent. Since this standard only specifies the thread code and does not specify the thread parameters, the thread parameters indicated by the same thread code in different companies or industries may also differ. There is no basis for judging who is right or wrong when there is a waste. From 1987 to 1991, China issued the British Standard Pipe Thread Standard. From then on, the pipe thread code and marking shall be subject to the provisions of the pipe thread standard.