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Technological parameters for welding polypropylene pipes into the socket at low temperatures

DOI: 10.17586/1606-4313-2018-17-3-29-36
UDC 621.791.461:678.029.43

Technological parameters for welding polypropylene pipes into the socket at low temperatures

Starostin N. P. , Ammosova O. A.

For citation: Starostin N.P., Ammosova O.A. Technological parameters for welding polypropylene pipes into the socket at low temperatures. Vestnik Mezhdunarodnoi akademii kholoda. 2018. No 3. p. 29-36

Abstract
According to the regulatory documents welding of polypropylene pipes with a heated instrument into the socket is recommended at positive ambient temperatures. The proposed technology for welding polypropylene pipes at air temperatures below the standard includes the following operations: preheating the welded sections of pipes and couplings with special nozzles, free cooling to equalize the temperatures in the zone of thermal impact of the joint to the allowable for welding, reflow in the standard mode, and cooling the welded joint in a heat-insulating chamber with an air layer of calculated thickness. In this paper, we propose a technique for determining the technological parameters for welding polypropylene pipes into the socket at low temperatures from the condition of ensuring the flow of the thermal process according to the regularities corresponding to the temperature change during welding under conditions acceptable for welding air temperatures. Calculation of technological parameters of welding is carried out on the basis of mathematical modeling of the heat process of welding taking into account a two-phase zone in which the substance is in both solid and liquid state. The fraction of the liquid phase is proposed to be determined using the temperature dependences of the amount of heat released (absorbed) during the phase transformation, obtained by differential scanning calorimetry. Assuming that the pre-heating has been carried out, the calculation of the technological parameters of socket fusion of a given size is carried out at an ambient temperature below the standard one. It is shown that it is effective to cool the welded joint in a heat-insulating chamber with an air layer, in comparison with the use of a layer of thermal insulation. The proposed welding technology can be used for installation and repair of hot and cold water supply systems made of polypropylene pipes at low temperatures.

Keywords: polypropylene pipes, socket welding, mathematical model, phase transition, technological parameters, cooling, thermal insulation.

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