RU2849117C1 - Method for welding polymer pipes with connecting parts with built-in heaters - Google Patents

Abstract

FIELD: welding.

SUBSTANCE: invention relates to the field of welding polymer pipes with connecting parts using an embedded heater and can be used for welding polyethylene pipes at ambient temperatures below those specified in regulatory documents. The result is achieved by bringing the temperature in the melting zone between the pipe and the coupling to a value between minus 15 and plus 45° C, as specified in regulatory documents. The cooling rate is set to be the same as at ambient temperatures within the regulated range. Before welding polymer pipes, a certain amount of power is supplied through the coupling terminals using the welding machine itself, and preheating is performed. For welding at low ambient temperatures, a programme with calculated data for the power supplied for preheating, technological pause and adjustment of the cooling rate of the welded joint is set in the welding machine software. The temperature in the melting zone and the cooling rate of the welded joint at any low temperatures are forcibly set as for welding in a regulated temperature range, taking into account the ambient air temperature.

EFFECT: obtaining a high-quality welded joint without the construction of a special heated shelter.

1 cl, 5 dwg

Description

Field to which the invention relates

The invention relates to welding polymer pipes using connecting parts with embedded heaters and can be used in welding polyethylene pipes at low ambient temperatures.

State of the art

There is a technical solution known (1. Design and construction of gas pipelines from polyethylene pipes and reconstruction of worn-out gas pipelines SP 42 - 103 - 2003. - Official publication. - M. ZAO POLIMERGAZ, 2004. - 84 p.), according to which, with a wider range of ambient air temperatures than from minus 15 ° C to plus 45 ° C, welding work is recommended to be performed in rooms (shelters) that ensure compliance with the specified temperature range (p. 6.48). The disadvantage of this method is the labor intensity and large time costs for the construction of the shelter and for achieving the regulated air temperature inside the shelter and on the welded sections of the polymer pipes.

The closest technical solution is (2. Patent No. 2744141. Method for welding polymer pipes using connecting parts with an embedded heater. Published 03.03.2021, Bulletin No. 7), in which, during welding at low air temperatures (below minus 15°C), preheating is performed before welding and the cooling of the welded joint after welding is controlled by applying a certain voltage through the terminals of the embedded heater of the part. The applied voltage for preheating and cooling control is calculated using methods of mathematical modeling of thermal welding processes and is embedded in the developed software of the welding machine. A disadvantage of the technical solution is that, at a given low ambient air temperature, the amount of heating energy, determined by the heater exposure time, and the time-varying heating power for cooling control by applying voltage to existing welded parts are provided by the embedded heater with a large error. This is due to the fact that embedded heaters in existing components are made of different materials. It is also due to the fact that the electrical resistance of conductors increases with increasing temperature and decreases with decreasing temperature. The dependence of the resistance R ( T ) of a wire on temperature T is described by the formula:

where temperature T is specified in degrees Celsius; R ₂₀ is the conductor resistance at 20°C; α is the temperature coefficient of resistance (TCR) with the dimension 1/°C, depending on the material. The power of the embedded heater is determined by the formula:

Where U is the applied voltage. The TCS is not indicated in the barcode for parts with embedded heaters. When applying the same voltage to the terminals of parts with embedded heaters made of different materials, the power will not be the same. Therefore, voltage control is not universal and requires calculating a mathematical model for each part variant, manufacturer, and size to ensure high-quality welds and to program it into the machine.

Disclosure of invention

The objective of the proposed invention is to universalize the welding method using parts with embedded heaters and to obtain a high-quality welded joint of a polymer pipe at ambient temperatures below the regulated one.

The technical result achieved in solving the assigned problem consists of using the welding machine's own software, which allows for the correction of power changes during preheating and maintaining the required cooling rate of the welded joint, taking into account the ambient air temperature, which is below the standard value.

The method for welding polymer pipes using fittings with an embedded heater involves preparing the pipe ends, installing and securing the ends of the pipes to be welded in the clamps of a centering fixture while simultaneously seating the fitting with the embedded heater, connecting the fitting to the welding machine, programming the welding process, initiating the welding process, and heating and cooling the weld joint. This method is distinguished by the fact that the temperature in the fusion zone is preliminarily brought to a value within a specified temperature range, and the required cooling rate of the weld joint is maintained by applying time-varying power from the welding machine itself. The welding machine's system is programmed to perform preheating, maintain a process pause to equalize the temperature field of the weld zone within the specified ambient temperature range, and maintain the required cooling rate of the weld joint, as during cooling within the permissible welding temperature range, regardless of the temperature coefficient of resistance of the embedded heater material.

Essential features characterizing the invention

Limiting: welding is performed by installing and securing the ends of the pipes to be welded in the clamps of the centering device with the simultaneous seating of the part with the embedded heater, connecting the part with the embedded heater to the welding machine, and starting the welding process.

Distinctive features: preheating is carried out by providing constant power in the embedded heater for a certain period of time, and cooling of the welded joint after heating is carried out by providing power that varies over time.

It is known that the welding process program takes into account, in addition to the barcode data attached to the part with the embedded heater, also the ambient air temperature via the welding machine's temperature sensor.

Brief description of the drawings

Fig. 1 shows the temperature field in the vertical section of the walls of the pipe section and the part at the time of completion of heating at an ambient air temperature of -40°C. Fig. 2 shows the temperature field in the vertical section of the walls of the pipe section and the part at the time of completion of temperature equalization at an ambient air temperature of -40°C. Fig. 3 shows the time dependence of the heater (1) power at the cooling stage under conditions of an ambient air temperature of -40°C with controlled cooling. Fig. 4 shows the dynamics of the 120°C isotherm (2) in the section of the coupling and the pipe in a vertical plane at an ambient air temperature of 20°C at the end of heating and the 100°C isotherm at different times: (3) - 2 min; (4) - 4 min; (5) - 6 min of cooling, respectively. In Fig. 5 shows the dynamics of the isotherm, the dynamics of the 120°C isotherm (2) in the cross-section of the coupling and the pipe in a vertical plane at an ambient air temperature of -40°C using the technology with preliminary heating at the end of heating and the 100°C isotherm at different points in time: (3) - 2 min; (4) - 4 min; (5) - 6 min of cooling, respectively.

Implementation of the invention

The method is as follows. The surfaces of the polymer pipes to be welded are cleaned of contaminants and degreased. The pipes are then installed and secured in the clamps of a centering fixture, while the part with the embedded heater is simultaneously seated. The part with the embedded heater is connected to the welding machine. The welding machine's reader scans the barcode and initiates preheating. A preset power level is applied, which depends on environmental conditions and the size of the part. After preheating, a period of time (a process pause) is maintained to equalize the temperature in the fusion zone of the part with the embedded heater and the pipe. The part is then welded to the pipe, and the weld joint is cooled at a preset rate. The preset cooling rate is achieved by supplying power from the welding machine through the part's terminals. The parameters for preheating, process pause, welding and cooling of polymers are pre-programmed into the welding machine for each pipe and coupling size, regardless of the type of embedded heater, taking into account the ambient air temperature.

Example. For welding PE 100 SDR 11 polyethylene pipes with a diameter of 110 mm and a wall thickness of 10 mm using a part with an embedded heater at an ambient temperature of -40°C, the heating time is 200 s, cooling time is 15 minutes, and the heater voltage during heating is 40 V. The heater power was calculated using the formula:

where resistance R = 0.96 Ohm; temperature coefficient of resistance of the coil β = 4.3 · 10 ^-3 1/°C.

Preheating is performed at a constant heater power of 107 W for 24.5 minutes. Temperature fields in the vertical cross-section of the pipe section and part walls at the end of preheating are shown in Fig. 1. After preheating, a 4-minute break begins to equalize the temperatures. After this break, the temperature fields in the pipe and part walls become more uniform (Fig. 2).

After the temperatures have equalized, the welding process begins in standard mode, as permissible temperatures. After welding, the formed weld joint begins to cool, with the cooling rate controlled by varying the welding machine's power input over time (Fig. 3, curve 1). Formulas for determining the heater power, depending on the ambient temperature and pipe dimensions, were pre-programmed into the welding machine's software.

During the welding process under conditions of ambient air temperature of -40°C with the cooling rate set by control by changing the power over time, the same processes of formation of the structure of the welded joint material are achieved as at a temperature of 10°C. This is evidenced by the graphs of the 120°C isotherms (2), recorded in the welded joint material after heating and the 100°C isotherm at different moments of cooling time (3, 4, 5), as shown in Fig. 4 and Fig. 5. It is known that at a temperature of 120°C the crystallization process of polyethylene begins, and at a temperature of 100°C it ends.

Claims (1)

A method for welding polymer pipes using connecting parts with an embedded heater, which consists of preparing the ends of the pipes, installing and securing the ends of the pipes to be welded in the clamps of a centering device with the simultaneous seating of the part with the embedded heater, connecting the part to the welding machine, setting a welding process program, starting the welding process, heating and cooling the welded joint, characterized in that the temperature in the melting area is preliminarily brought to a value from a regulated temperature range and the required cooling rate of the welded joint is maintained by supplying time-varying power by the welding machine itself, the system of which contains a program that allows for preliminary heating, maintaining a process pause to equalize the temperature field of the welding area within the values of the regulated range of ambient air temperatures and maintaining the required cooling rate of the welded joint as during cooling in the permissible range of welding temperatures, regardless of the temperature coefficient of resistance of the material of the embedded heater.