RU2615890C1 - Welding method by the heated tool into the polimeric pipes flared end - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: method is carried out by reduction of residual stresses in the pipe and coupling walls by reduction of the temperature distribution non-uniformity in the welded flared end joint due to the gradient pre-heating from the opposite to the welding surfaces pipe and coupling sides.

EFFECT: quality welding joint production without the construction of special facilities.

5 dwg

Description

FIELD OF THE INVENTION

The invention relates to the welding of polymer pipes with a heated tool into a socket and can be used when welding polypropylene pipes at low ambient temperatures.

State of the art

Known technical solution (1. SP 40-101-96. Design and installation of pipelines made of polypropylene "Random copolymer"; introduced. 04/09/96. - Official publication, Ministry of Construction of Russia. M: GUP TsPP, 1997), which consists in reflowing the surface the pipe to be welded and the socket of the sleeve using a sleeve and mandrel of a tool heated to or above the melting temperature of the pipe material, joining after removing the tool melted surfaces and holding for a certain time, dictated by the cooling rate and relaxation processes in the welded joint.

The disadvantage of this technical solution is to obtain low-quality welded joints at low ambient temperatures.

A technical solution is known (2. Departmental building codes for the design and installation of internal water supply systems from polypropylene pipes "Random copolymer" (PPRC) VSN 47-96; introduced. 01.08.96. - M.: Rotaprint Mosorgstroya. 1996), in which the need for welding and installation work at an outdoor temperature below 0 ° C, pipe welding should be performed in heated rooms (Section 4.13).

The disadvantage of this method is the complexity and time-consuming construction of the structure and the achievement of a regulated air temperature inside the structure and at the ends of the welded polymer pipes and fittings.

The closest is the technical solution (3. Starostin NP, Ammosova OA, Botvin GV Thermal process of welding polypropylene pipes into a socket at low temperatures // Welding and diagnostics. 2015. No. 6. P. 57- 61), in which when welding polypropylene pipes with a heated tool into a socket at negative ambient temperatures, in order to ensure uniform temperature distribution and reduce temperature stresses in the wall of the pipe and coupling being welded, it is necessary to preheat the pipe to a length of departure exceeding the depth in the socket, and a box a depth of the socket to a temperature above 20 ° C special interchangeable nozzles for the heating to be established to the additional heat plate welding machine. After heating, the parts to be welded are freely cooled to obtain a uniform temperature distribution from the interval allowed for welding in the walls of the pipe and coupling ends being welded. After heating, welding is carried out at permissible temperatures (welding of polypropylene pipes is allowed at ambient temperatures above 0 ° C, polyethylene pipes from -15 ° C to + 45 ° C). Cooling of the welded joint after welding is carried out in a heat-insulating chamber. The thickness of the insulation is calculated in such a way as to ensure the cooling rate of the welded joint is the same as with standard welding in conditions of positive ambient temperatures.

The disadvantage of this solution is the large temperature gradient between the welded section and the cold part of the pipe, due to which residual stressed sections arise in the welded joint.

Disclosure of invention

The objective of the invention is to obtain a high-quality welded joint of a polymer pipe without the construction of a special structure at negative ambient temperatures.

The technical result achieved by solving the problem lies in obtaining at low ambient temperatures a weld with reduced residual stresses in the walls of the pipe and coupling.

The essential features characterizing the invention.

Restrictive: before welding, the ends of the pipe and coupling to be welded are preheated, welding is performed by melting the outer surface of the pipe and the inner surface of the coupling with a tool heated to or above the melting temperature of the pipe material, and joining the fused welded parts after removing the tool. Cooling of the weld and the pipe zone is carried out in a heat-insulating chamber.

Distinctive: the pipes and couplings are preheated from the side of the opposite welding surface, i.e. the pipe is heated from the side of the inner surface, and the coupling from the side of the outer surface, to the maximum working temperature of the parts to be welded (for polypropylene 95 ° C, for polyethylene 80 ° C, etc.).

Since the residual stresses in the walls of the pipe and coupling appear due to the uneven distribution of temperatures, a decrease in the temperature gradient in the welding area will also reduce the temperature stresses in the walls of the parts being welded.

Brief Description of the Drawing

In FIG. 1 shows a diagram of preheating, welding and cooling in a heat-insulating chamber of polymer pipes. In FIG. Figure 2 shows the temperature distribution along the radius r of the socket weld at the time of welding of polypropylene pipes of the PPRC PN20 63 × 10.5 grade at ambient temperatures T _okr = 20 ° C and T _okr = -40 ° C.

The implementation of the invention

The method is as follows. On the heating plate (1) of the additional welding machine for socket welding, heated to the maximum working temperature of the polymer, nozzles are installed for preheating the end of the pipe and coupling (2) (Fig. 1, a). The shape of the nozzles is such that the heating is carried out from the side opposite to the welding surface, the pipe (3) is heated from the side of the internal surface, the coupling (4) from the side of the external surface (Fig. 1, b). Heating is carried out until the temperature of the welded surfaces of the pipe and coupling is reached to a temperature from the regulated interval of welding production (gradient heating). The duration of the gradient heating is found by solving the heat conduction problem based on the ambient temperature, thermophysical properties and geometric dimensions of the pipe and the connecting part (3. Starostin NP, Ammosova OA, Botvin GV. Thermal process of welding polypropylene pipes into a socket at low temperatures // Welding and diagnostics. 2015. No. 6. P. 57-61). Next, welding with a heated tool (5) is carried out in the socket of polymer pipes as at permissible temperatures (Fig. 1, c). Cooling is carried out in a heat-insulating chamber 6) (Fig. 1, d) of certain sizes, in which the temperature is maintained in a regulated temperature range due to the heat of the welded joint accumulated during welding.

Example. When welding polypropylene pipes of the PPRC PN20 brand with a diameter of 63 mm at an ambient temperature of minus 40 ° C, nozzles (sleeve and mandrel) are installed on the plate of the additional welding machine heated to 95 ° C (maximum working temperature of polypropylene) for preheating. Using the sleeve, the pipe is heated from the inside, with the mandrel - the coupling from the outside. The duration of the gradient heating, according to the calculations, was: for the pipe - 420 s, for the coupling - 360 s, therefore, the heating of the pipe should be started 60 s earlier to simultaneously start the heating (reflow) process. Next, welding is carried out with a tool heated to 270 ° C into the socket of polypropylene pipes.

In FIG. 2 shows the temperature distribution along the radius of the socket welded joint at the time of welding at ambient temperatures T _okr = 20 ° C and T _okr = -40 ° C. It can be seen that after welding with preliminary gradient heating at an ambient temperature of 40 ° C in the middle of the welded socket joint, the same temperature distribution as after welding at T _okr = 20 ° C. To maintain the required cooling rate, the welded socket joint is held in the heat-insulating chamber.

Thus, under these conditions, welding at negative ambient temperatures with preliminary gradient heating provides reduced residual stresses in the walls of the pipe and coupling.

Claims (1)

A method of welding polymer pipes, which consists in melting a preheated pipe and sleeve with a heated tool into a socket, joining the melted surfaces after removing the heated tool and keeping the cooling time in a heat-insulating chamber, characterized in that the pipe and coupler are preheated using a sleeve and mandrel, heated up to the maximum working temperature of the materials being welded from sides opposite to the welding surfaces, until the temperature of the surfaces being melted is reached from regulated temperature range of welding production.

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