RU2432517C1 - Method of connection of multi-layer metal-polymer pipes - Google Patents

Abstract

FIELD: machine building. ^ SUBSTANCE: here is disclosed method for connection of multi-layer metal-polymer pipes. Pipes are connected by welding through a connecting device having not less, than two connecting elements with seats for end sections of pipes. Welding is performed along external, internal and end surfaces of the end section of the pipe enveloped with internal surfaces of the seat of the connecting device. Also, the end section of the pipe and seat of the connection device are preliminary simultaneously heated. Successively, preliminary heated sections of the pipe and the connection device are matched. To avoid destruction of polymer layers and exposure of an internal metal layer and for removal of adhesion layers of the pipe applied on the metal layer the end section of pipe is heated to softening temperature of material of external and internal layers of the pipe at pipe and the connecting device matching. The seat of the connecting device is made in form of a circular slot coaxial with an internal orifice of the connecting element of the connecting device. The circular slot has a cylinder wall from the side of external surface of a connected pipe and a conic wall truncated along plane of the end of the connecting element from the side of internal surface of the connected pipe. The seat is preliminary heated to melting temperature of material of the connecting device. The end section of the pipe and seat are preliminary heated by means of a welding device equipped with a control unit and a heater whereon there are arranged a tool of the pipe and a tool of fitting. Temperature of the heater and tool of fitting directly contacting surface of the heater equal to temperature of connecting device material melting is set with the control unit and is maintained at a constant level within ranges of preset error. Securing the tool of the pipe on the heater through a transit bush facilitates limit of end section of the pipe heating to temperature not exceeding softening temperature of material of external and internal layers of the pipe. The tool of the pipe can travel along axis of the transit bush for adjustment of heating temperature at external conditions change. ^ EFFECT: upgraded quality and reliability of connection of multi-layer metal-polymer pipes. ^ 7 dwg

Description

The invention relates to compounds of plastics, and more particularly to the connection of multilayer metal-polymer pipes, and can be used, for example, when installing pipelines of hot and cold water supply systems.

Currently, technologies for manufacturing pipelines from multilayer metal-polymer pipes, the outer and inner layers of which are made of polymer material, are widely used. An embodiment of a five-layer construction of such a pipe is shown in FIG. The pipe contains an outer polymer layer 1, adhesive coatings 2 and 4, an aluminum layer 3 and an inner polymer layer 5.

In the manufacture of pipelines from such pipes, their connection is usually performed using threaded (compression) fittings (SP 40-103-98 group Zh24, Code of design and construction rules. Design and installation of pipelines for cold and hot domestic water supply systems using metal-polymer pipes; СП 41-102-98 Group Ж24. Code of rules for design and construction. Design and installation of heating system pipelines using metal-polymer pipes) or using press fittings (for example, press fi HERZ) (http: //www.herz-vl/d/67920/d/hress-fitingi_gerc.pdf).

The disadvantages of connections with threaded fittings include possible errors during installation (the thread is not tightened enough), the need for periodic monitoring during operation, since the tightening of the crimping nuts weakens over time and a leak occurs at the junction. When using press fittings, the connection is much more reliable and durable. However, both methods are characterized by a rather complicated technology and a large number of parts necessary for the installation of the pipeline.

At the same time, when installing pipelines from single-layer polymer pipes, methods of one-piece connection of pipes from thermoplastic materials without dissolving or changing the chemical composition, exclusively due to heating, are widely used. The most widely used method is welding with a heated tool butt (http://www.polyplastic.ru), thermistor welding using fittings with embedded heaters (http: //www/etp/com/ua/news/vid_svarki.html) and the welding method heated tool with a socket using fittings (http://www.polyplastic.ru).

When butt welding, as shown in FIG. 1, the surfaces to be welded are heated with a metal heated tool. The essence of the method is to heat the ends of the pipes to be welded until the material melts and then compress the heated ends to cool. At the same time, to obtain a high-quality welded joint, a number of conditions must be observed. The main parameter of the process is the heating temperature of the welding tool, which must be kept constant to an accuracy of ± 10 K. The heating time — the melting of the ends of the pipes to be welded with the welding tool — depends on the ambient temperature, the wall thickness of the pipes, and the preparation of the ends of the pipes for welding. Reducing the duration of heating at a constant temperature of the tool leads to insufficient softening of the material and, as a consequence, to a deterioration in the quality of the weld. Exact observance of the heating time does not always guarantee a stable heating depth; it can vary depending on environmental conditions. When heated, the welding tool should touch the edges of the pipes around the perimeter. With proper process management, a uniform burr of molten material in the form of a roller with a height of not more than 2-3 mm should be formed along the entire perimeter of the pipe. After melting the ends of the pipes, it is necessary to quickly remove the heater and precipitate the pipes. The time between removal of the heater and pipe sludge should not exceed a certain value, otherwise there is a decrease in the strength of the weld as a result of rapid cooling of the surfaces being welded. When the upsetting pressure increases, the molten material is excessively squeezed out and into the pipe, which affects the quality of the welded joint. The duration of cooling under pressure is determined taking into account the wall thickness of the pipes being welded, the ambient temperature and the type of plastic. The welded joint must be kept under pressure until the material is completely cooled, since the movement of the ends of the pipes immediately after welding can lead to the creation of additional internal stresses in the joint.

Thermistor welding or welding using fittings with a built-in heating element, one of the options of which is presented in figure 3, is one of the most high-performance welding methods. Its essence lies in the supply of electricity to the heating element (wire) located on the inside of the molded connecting part (fitting). The wire is heated by passing an electric current through it, and under the influence of heat, the connected surfaces of the pipe and fitting are melted and welded together.

A device for connecting multilayer composite pipes (Patent RU No. 93127, F16L 13/00, 04/20/2010), made in the form of a coupling with an internal fastener with a cylindrical socket covering the inner, end and outer surfaces of the pipe, is pressed into the walls of the cylindrical socket or when inserting a sleeve, a heating element is installed to melt the inner, outer and end layers of the sleeve and pipe with the terminals brought out of the sleeve to connect to a constant or pulsed electric current source.

When heated to the melting temperature of the coupling material, the linear temperature elongation of the embedded heating element can lead to a convergence of its coils and the formation of overheating groups of local sections, which will lead to increased deep heating of the pipe and coupling and, as a result, to deformation of their surfaces.

When welding the socket, illustrated in FIG. 4, the pipe 5 and the connecting element (fitting) are welded using a welding device 1. The welding device consists of a fitting tool 2 and a pipe tool 4, which are mounted on the heater 3. The outer surface of the pipe is heated by the pipe tool, at the same time with this, the inside surface of the fitting is heated by the fitting tool. Upon reaching the fusion of the outer surface of the pipe and the inner surface of the fitting, the welding fixture is removed from the welding zone, and the pipe and fitting are combined and cooled.

This method is the most technologically advanced of the known and is widely used in practice, characterized by high quality and reliability of the connections of single-layer polymer pipes obtained with its help. However, due to the design features of multilayer metal-polymer pipes, this method has not found wide application for their connection.

The problem to which the claimed invention is directed is to develop a method for joining multilayer metal-plastic pipes that is not inferior in terms of manufacturability and quality to a method for joining single-layer pipes of thermoplastic materials with a heated tool using fittings. At the same time, the design features of metal-polymer pipes determine additional requirements:

- to obtain a high-quality and reliable connection of multilayer metal-polymer pipes, their welding with a fitting must be carried out both on the outer surface of the outer polymer layer and on the inner surface of the inner polymer layer of the pipe;

- during the welding process, it is necessary to exclude the destruction and deformation of sufficiently thin polymer and adhesive layers of the pipe and exposure of the inner metal layer of the pipe, since otherwise it is impossible to ensure reliable adhesion of the welded surfaces of the pipe and fitting.

The closest analogue is the method of connecting multilayer composite pipes and a device for its implementation (Patent RU No. 2380603, F16L 13/00, 01/27/2010), selected as a prototype, according to which multilayer composite pipes are connected through fittings by welding. At the same time, welding is performed simultaneously on the cylindrical and end surfaces of the pipe, for this, the external, internal and end surfaces at the end of the pipe and the internal surfaces of the fitting connected to the pipe are simultaneously pre-melted. The fitting for connecting the multilayer composite pipes is made in the form of a sleeve with an internal fastener with a cylindrical socket covering the inner, end and outer surfaces of the pipe.

This method does not exclude the destruction of the material, possible during overheating of the polymer layers of the final sections of the pipes to be connected, and, as a result, obtaining poor-quality pipe joints. In addition, when the fitting is heated, there is a direct contact between the heating tool and the end portion of the inner wall of the fitting fastener, which becomes plastic and under the pressure of excess molten polymer changes its geometry, thereby reducing the cross-sectional area of the fitting's through hole. Excess molten polymer will extrude into the inside of the fitting, also reducing the cross-sectional area of the passage opening. This, in turn, will lead to an increase in hydraulic losses and an increase in noise during the transportation of fluid through the pipeline.

The technical result achieved in the claimed invention is to improve the quality and reliability of the connection of multilayer metal-polymer pipes.

The technical result is achieved by the fact that the connection of multilayer metal-polymer pipes by welding is carried out through a connecting device having at least two connecting elements with fittings for the end sections of the pipes. The landing seat of each connecting element is made in the form of an annular groove coaxial with the internal opening of the connecting element with a cylindrical wall on the side of the external surface of the connecting pipe and a conical wall truncated along the plane of the end face of the connecting element. Welding is carried out on the outer, inner and end surfaces of the final pipe section, covered by the inner surfaces of the mounting socket of the connecting device. Welding is carried out with preliminary simultaneous heating of the final section of the pipe and the mounting socket of the connecting device and the subsequent combination of the preheated sections of the pipe and the connecting device. At the same time, to eliminate the destruction of the polymer layers, expose the inner metal layer and remove the adhesive layers of the pipe applied to the metal layer when combining it with the connecting device, the final pipe section is preheated to the softening temperature of the material of the outer and inner layers of the pipe. The seat of the connecting device is preheated to the melting temperature of the material of the connecting device. The preliminary heating of the final pipe section and the mounting socket of the connecting device is carried out using a welding device having a control unit and a heater on which the pipe tool and fitting tool are located. The temperature of the heater and fitting tool, which has direct contact with the surface of the heater, equal to the melting temperature of the material of the connecting device, is set by the control unit and maintained by it at a constant level within the specified error. The limitation of the heating of the final section of the pipe to a temperature not exceeding the softening temperature of the material of the outer and inner layers of the pipe is ensured by fixing the pipe tool to the heater through the adapter sleeve. To adjust the heating temperature when changing external conditions, the pipe tool can move along the axis of the adapter sleeve.

The connecting device, the construction of which is illustrated in FIG. 5, has at least two connecting elements for the end sections of the pipes to be connected, each of which is made with a seat in the form of an annular groove coaxial with the inner hole of the connecting element with a cylindrical wall 2 from the side of the outer surface of the pipe to be connected and conical, truncated along the plane of the end face of the connecting element, the wall 1 from the side of the inner surface of the joined pipe.

The welding fixture, the device of which is illustrated in FIG. 6, is made with a heater 3, on which a pipe tool 1 and a fitting tool 5 are located, and a control unit 4 operably connected to the heater. The heater of the welding fixture is made with a heating element 6 located in the body of the heater, the operation mode of which is set and supported by the control unit. The fitting tool is made in the form of a sleeve with a socket for the fitting on the side of one of its ends. The nest is made in the form of an annular cylindrical groove. The fitting tool is in direct contact with the surface of the heater. The temperature of the heater and fitting tool, equal to the melting temperature of the fitting material, is set and maintained at a constant level using the control unit. The pipe tool is made in the form of a sleeve with a socket for the final pipe section from the side of one of the ends. The socket is made in the form of an annular cylindrical groove coaxial with the inner mounting hole of the sleeve. To ensure the heating of the end section of the pipe to the softening temperature of the material of the polymer layers of the pipe, the pipe tool is fixed to the heater through the adapter sleeve 2. To adjust the heating temperature when changing external conditions, the pipe tool can move along the axis of the adapter sleeve.

The welding process of the pipe and fitting is illustrated in Fig.7. The heater of the welding fixture during the time determined by the parameters of the technological process, depending on the material of the external and internal layers of the pipe and the connecting device, is heated to a predetermined temperature. After that, the final section of the pipe is inserted into the pipe tool of the welding fixture, the connecting device is inserted into the fitting tool of the welding fixture and fixed in the welding fixture for the time of heating. The external, internal and end surfaces of the final pipe section are heated by the pipe tool to the softening temperature of the material of the external and internal layers of the pipe. At the same time, the mounting socket of the connecting device is heated by the fitting tool to the melting temperature of the material of the connecting device. Moreover, due to the lack of direct contact of the surface of the tool of the fitting of the welding fixture with the surface of the end section of the conical wall of the mounting socket of the connecting device, there is no deformation of the final section of the mounting socket of the connecting device. After a predetermined heating time, the pipe and the connecting device are simultaneously removed from the welding fixture. The heated end section of the pipe is inserted all the way into the heated seat socket of the connecting device, followed by fixation in a stationary state. At the same time, the surface of the inner and outer layers of the final pipe section during heat exchange with the surface of the seat socket of the connecting device heated to a higher temperature is heated to the melting temperature of the material of the inner and outer layers of the pipe, thereby ensuring a high-quality connection. In this case, the polymer layers of the final pipe section do not deform and do not shift relative to the inner metal layer of the pipe. The excess molten polymer, filling the cavity between the conical wall of the seat socket and the inner surface of the end portion of the pipe, is not squeezed into the inner hole of the connecting device and does not deform the end portion of the inner wall of the seat socket. After complete cooling, the weld joint is ready.

This method can also be used to connect single-layer plastic pipes, as well as to connect single-layer plastic pipes with multilayer metal-polymer pipes when installing pipelines with increased requirements for the quality and reliability of pipe connections.

Claims (1)

A method of joining multilayer metal-polymer pipes by welding through a connecting device having at least two connecting elements with fittings for the end pipe sections, on the outer, inner and end surfaces of the pipe end section, covered by the internal surfaces of the connector housing of the connecting device, with preliminary simultaneous heating of the final section pipe and mounting socket of the connecting device and the subsequent combination of pre-heated section into pipes and a connecting device, characterized in that in order to prevent destruction of the polymer layers, exposing the inner metal layer and removing the adhesive layers of the pipe applied to the metal layer when combining it with the connecting device, the final pipe section is heated to the softening temperature of the material of the outer and inner layers of the pipe, and the mounting socket of the connecting device, made in the form of a coaxial with the inner hole of the mounting socket of the connecting element of the connecting device The properties of an annular groove with a cylindrical wall on the side of the outer surface of the connecting pipe and a conical wall truncated along the plane of the end face of the connecting element are preheated to the melting temperature of the material of the connecting device, while preheating the end of the pipe and the seat the connecting device is carried out using a welding device having a control unit and a heater on which a pipe tool and a fitting tool are laid, while the temperature of the heater and fitting tool having direct contact with the heater surface equal to the melting temperature of the material of the connecting device is set by the control unit and maintained by it at a constant level within the specified error, while limiting the heating of the final pipe section to a temperature not exceeding the softening temperature of the material of the outer and inner layers of the pipe, is provided by fixing the pipe tool on the heater through the adapter sleeve, while to adjust the heating temperature when changing external conditions, the pipe tool can move along the axis of the adapter sleeve.

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