Hot-melt Connection of Precision Seamless Tubes

The process and equipment (tools) for hot-melt joining of precision seamless pipe systems are relatively simple. In recent years, there have been many problems in the connection of precision seamless pipe projects in various places. Difficulties in the field are difficult to detect the quality of the hot melt connection (without breaking the connection). Foreign countries are exploring the use of ultrasonic testing for the quality of hot-melt connections, but the use of the site has not yet been popularized. Currently, it is generally based on “visual inspection”. The guarantee of stable quality of hot-melt joints is mainly based on strict compliance with the specified operating procedures (especially the three parameters of temperature, pressure and time are strictly controlled).

First, it is recommended that precision seamless pipe production enterprises develop more detailed operating procedures suitable for the company’s precision seamless pipes through tests and tests (combined with the characteristics of hot-melt connection equipment) according to relevant regulations (comparative principles). In addition to horizontal diffusion, atmospheric pollutants can also diffuse vertically into the sky. If the atmospheric stratification is stable and the temperature is lower and higher, that is, when the “inversion layer” appears, it covers the near-surface like a large quilt, obstructing the vertical convective motion of the air, so that the height of the mixed layer is higher. The upper kilometer is greatly reduced to several hundred meters or even several tens of meters, resulting in the suppression of the spread of pollutants.

Second, and through the training and consultation to help the builders master the operating procedures. Large companies that produce precision seamless pipe systems internationally have these operating procedures that guide hot-melt connections. In the US PPI manual, a more practical quality control method is introduced: a test hot melt joint is made on site every day, and the “bend belt test” (no destructive test of equipment is required) to judge whether the process and equipment need to be adjusted. The fused connection includes an electrofusion socket connection and an fused saddle connection. The outstanding advantages of fused connections are reliable quality (reducing human factors) and high construction efficiency. Because of the high technical requirements and high cost of electrofusion pipe fittings, the early application was mainly in gas pipe systems with smaller diameters. In recent years, with the advancement of technology, the application of electrofusion connections has become increasingly widespread. It is applied not only to water supply piping systems, drainage piping systems, but also to larger diameters (but the main market for electrofusion fittings is in the DN 20-250 mm diameter range).

In summary, there are two major categories from the technical route: one is to first wind the heating wire around the metal core of the mold or around the pre-made polyethylene thin sleeve, and put it into the injection mold to be injected into the electricity. The fuse of the hot wire. Among them, there are semi-embedded electric heating wires (half exposed metal wires), fully embedded (the metal wires are not exposed), and the heating wires are pre-coated with polyethylene layers (the wires are not exposed) and other different designs (each have advantages and disadvantages); Automatically operated by a robot, with varying degrees of automation for all manual or partial manual operations. The other type is the process route of first injection molding precision seamless pipe and mechanical machining wiring.