Keyword: «phase transition»

This paper is proposed to take into account in the mathematical model of thermal process the heat of phase transformation when developing the technology of welding polymer pipes at ambient air temperatures below the normative values. The used function of the degree of crystallinity on temperature is determined according to DSC data. A formula is given for determining the effective heat capacity coefficient in the shock-capturing method for solving the heat conduction problem with a phase transition in the temperature range.

The paper studies the evolution of the thermal process during electrofusion welding of polyethylene pipes at low ambient temperatures. It is proposed to preheat the pipe assembly with a coupling by means of a built-in heater mounted in the body of the connecting part. To obtain a temperature distribution close to uniform in the heat-affected zone, alignment is carried out. The duration of heating and leveling are determined by calculation. It is proposed to control the cooling process using a built-in heater. The power of the embedded heater with controlled cooling is determined by the solution of the inverse problem of controlling the thermal regime of the technological process.

A fundamental hypothesis has been made in technology development for welding polyethylene pipes at low ambient temperatures. The priority of the thermal process is shown, which is the key for all processes occurring during welding. We propose to introduce additional preheating operations, equalize temperatures in the heat-affected zone (HAZ) to the temperature acceptable for welding, and ensure cooling of the HAZ according to a pattern typical for welding at regulated temperatures. Mathematical modeling methods are used to determine the parameters of heating, temperature equalization, the dimensions of the heat-insulating chamber, or the thickness of the layer of heat-insulating material for specific low ambient air temperatures.