DE19911284C2 - Process for producing a socket connection for cross-linked polyethylene pipes (PE-X pipes) by rotary friction welding - Google Patents

Description

The invention relates to a method for producing a socket connection Rotary friction welding for cross-linked polyethylene pipes (PE-X pipes) for use of these pipes in industrial and underground pipeline construction. The high abrasion and wear resistance of the cross-linked polyethylene pipes (PE-X pipes) parts in the wastewater sector and for cable ducts as well as in the laying technology of Water pipes because they have a higher resistance to drawing marks than the uncrosslinked polyethylene pipes.

Cross-linked polyethylene pipes (PE-X pipes) stand out compared to polyethylene high-density pipes (PE-HD pipes) due to their excellent properties Lich higher strength, aging stability, temperature resistance, resistance ge aggressive media as well as high impact strength and resistance to Stress corrosion cracking and are therefore for underground gas and what Ideally suited for pipeline construction. They are also used for compressed air locations, hot water pipes and industrial plants.

A major problem in the manufacture of piping systems Cross-linked polyethylene (PE-X) is the connection technology.

The degree of crosslinking of polyethylene (PE) worsens namely its weldability.

Connection method, which is characterized by high cost-effectiveness in the traditional PE industrial pipeline construction, such as heating element welding for Pipe diameter <110 mm and heating element socket welding for small ones Diameters up to 125 mm are not suitable for cross-linked PE pipes (PE-X pipes) settable. Cross-linked polyethylene (PE-X) melts due to its molecular structure under the influence of heat in the welding temperature range for high density polyethylene (PE-HD) no longer, but only becomes rubber-elastic soft.  

According to the general state of knowledge, it can be assumed that cross-linked polyethylene cannot be welded to each other (specialist lecture "The pipe material PE-X: pipe material properties, quality assurance and main areas of application" conference proceedings and lecture on the Wiesbaden plastic pipe days 1998 on April 27 and 28, 1998) ,

It has been known since the mid-1980s that cross-linked polyethylene pipes (PE-X- Pipes) in the area of domestic drinking water installation, in heating and hot water in the meantime also in district heating and gas pressure lines enforce. As connecting elements between the pipes were specially Hose nozzle and crimp connector made of brass and steel developed to the the pipe ends were attached and additionally secured with stainless steel clamps (Trade journal gwf - Gas-Erdgas, 131, 1990, issue 10/11, pages 477-482). The disadvantage of this solution is the high cost and assembly costs in the area the connection technology.

Currently, cross-linked polyethylene pipes (PE-X pipes) are replaced by mechanical ones Crimped or sliding sleeve fittings made of brass connected. This connection Molded parts are costly in terms of materials and costs, on the other hand they are material-related defects in the property profile of cross-linked polyethylene. she are preferably used for compressed air systems, hot water pipes and Industrial plants.

The great interest of all pipeline builders, especially gas and water multiple, in the use of the excellent properties of the cross-linked poly ethylene pipes (PE-X pipes) led to investigations of connections Possibilities of PE-X pipes and the reliability of such connections. According to the general state of knowledge, it was again assumed that networked Polyethylene (PE-X) is not weldable. The investigations domestic and foreign Institutes and pipeline construction companies showed that it is possible to ver to weld meshed polyethylene (PE-X) with uncrosslinked polyethylene (PE-HD) SEN. However, it was also found that cross-linked polyethylene (PE-X) with ver wetted polyethylene (PE-X) is not weldable.  

Heating element welding connections between cross-linked polyethylene pipes (PE-X- Pipes) and pipes made of high density polyethylene (PE-HD pipes) reached ei a welding factor of <0.5 ("Use of the pipe material PE-X in the gas supplier gung ", member information Nov. 1997 of the Plastic Pipe Association eV Bonn). However, a PE-X pipe / PE-HD pipe connection is of no economic importance tung.

In contrast, the use of electric welding sleeves made of high-density polyethylene (PE-HD) has been successfully tested and is now state of the art. During the welding process, the PE-HD is melted, the PE-X only becomes rubber-elastic soft. Strength tests have shown that this connection is suitable for the gas and water supply sector. Some pipes are in operation ("The pipe material PE-X; pipe material properties, quality assurance and main areas of application", conference proceedings and lecture on the international Wiesbaden Plastic Pipe Days 1998 on April 27 and 28, 1998 and "Decision criteria for the selection of pipe materials in the gas supply", also from the cited conference proceedings).

A disadvantage of this connection method with electrofusion fittings is that Costs for larger pipe diameters due to the expensive electrical weld fittings rise sharply and this process for relining ailing Piping systems is also unsuitable because of the electrofusion fittings disrupt when pulling in the PE-X pipes.

DD-WP 139 544 became a procedure for ver bind cross-linked semi-finished products, especially pipes made of cross-linked polyethylene len, known. Then the joining surfaces of the pipe ends to be welded with a flat heating element whose working temperature is at least 450 ° C is heated in a warm-up time of maximum 8 seconds and after the Removing the heating element assembled under high pressure, the Maintain pressure until the joint zone cools down to ambient temperature will. This method has not found its way into practice because none  reproducible and no satisfactory weld strength was achieved the.

About friction welding processes and friction welding can be found in the specialist literature detailed information. Friction welding of thermoplastics was already mentioned by Henning in 1942 (Kunststoffe, year 32, 1942, issue 4, Page 104). According to the principle of rotation friction welding, the Heat required to plasticize the material through interfaces created friction between the parts to be welded. Usually one becomes the parts are set in a rotating movement, the other is in a recording recorded. The friction is generated in that at the same time a perpendicular to the friction surface pressure is exerted. Rotary friction welding can can only be used for molded parts that have a rotationally symmetrical connecting surface own (balls, tubes, discs, etc.). The welding time is with the Rotati friction welding at about a second and thus in a very economical way Area (plastics, year 71, 1981, issue 10, pp. 764-768).

Thermoplastics suitable for friction welding are described in the specialist literature. a. polyamide (PA), polyethylene (PE), polypropylene (PP), polycarbonate (PC), polystyrene (PS) and Called polyvinyl chloride (PVC). It can be used for connections to parts from the same plastic a seam strength of 80 to 100% of the base work material (welding and cutting, Düsseldorf, born 22, 1970, Issue 2, pages 56-62 and plastics, year 62, 1972, Issue 8, pages 478-482). Friction welding connections for pipes made of polypropylene (PP) and polyethylene (PE) are mainly used in chemical plant construction. To this end special friction welding machines were developed and built.

The friction welding connection was used to create a flange connection ses used for a detachable pipe connection with so-called loose flanges. The the flange bushings required for this purpose were friction-welded onto the End faces of the pipe ends welded on (plastic processor, born 25, 1974, Issue 4, pages 225-228).  

Furthermore, JP 10281381 A Abstract of Japan describes a rotary friction welding Process for producing a socket connection between a networked bottom known polyethylene tube and an overlap rotary sleeve. Between sleeve and The pipe will be connected to an additional ring-shaped connecting part with peroxide orderly. By rotating the sleeve on the fixed pipe for more than 25 s and the resulting frictional heat of 250 ° C becomes the connecting part melted and connects pipe and welding socket. Find in the welding zone a crosslinking reaction takes place and one occurs between the pipe and the pipe socket heat-resistant welded joint.

Rotary friction welding is increasingly used in industry, but only refers to the welding of non-cross-linked thermoplastic ter plastics. A method of connecting cross-linked polyethylene pipes (PE-X pipes), which are not thermoplastic but thermoelastic cha are not known from rotary friction welding.

The object of the invention is to provide a method for producing a material key butt or socket connection for cross-linked PE pipes (PE-X pipes) preferably for small pipe diameters up to 125 mm characterized by high weld seam strength, economy and practical relevance.

The invention is based on the rotary friction welding method known per se in which the heat for plasticizing the seam material through interfacial friction between the parts is generated. Here, a part is in one order ne axis brought rotating movement, the other is fixed in a support. The friction is generated in that both parts by an axially acting Pressure force are merged.

According to the invention in rotary friction welding of cross-linked polyethylene pipes (PE-X pipes) as a butt or socket connection a piece of pipe or a  Butt welding socket made of cross-linked polyethylene (PE-X) or a sprayed Overlap sleeve made of cross-linked polyethylene (PE-X) as a connecting element between the axially movable but not rotating pipes in a rotary movement offset around the pipe axis.

At the same time there is an axial feed movement of the tubes until between the ro ting pipe section and the end faces of the pipes friction occurs and one Friction pressure builds up. When using a networked rotary overlap sleeve The friction occurs when the pipes are fed in due to the fit tolerances between the inner circumference of the overlap sleeve and the outer circumference of the pipes.

In contrast to friction welding of non-cross-linked polyethylene pipes (PE-HD pipes), whose friction surfaces change into a thermoplastic melt at approx. 160 ° C, In the case of cross-linked PE pipes (PE-X pipes), friction occurs according to the invention of the thermoelastic material up to the local thermi in the friction area the thermal-elastic-molecular network structure into a thermopla static structure due to an increase in temperature <420 ° C but <440 ° C, preferably 430 ° C. Only then does a weldable melt layer form with one integral thermoplastic-viscous character, which in the interface area the has the lowest viscosity and shears very strongly due to the rubbing movement mixes turbulently. After reaching the melt state, a abruptly stopping the frictional movement while maintaining the axial pressure until for cooling, which leads to a thermoplastic material connection. When using an overlap rotary sleeve made of cross-linked polyethylene (PE-X) friction is promoted by the sleeve being a conical sleeve inner wall with a stop bar in the middle of the sleeve. The angle of the conical sleeve bore is preferably up to 3 °.

An expansion of the overlap rotating sleeve during the rubbing and welding the process by radial forces is achieved by a clamping device encompassing the sleeve direction prevented.  

For pipe diameters up to 125 mm, the speed of the rotary welding sleeve is preferably 300 1 / min to 700 1 / min depending on the wall thickness and diameter, the friction time 7 s to 12 s and the specific holding pressure 0.9 bar to 1.2 bar.

The advantages achieved with the rotary friction welding method according to the invention consist in particular that cross-linked polyethylene pipes (PE-X pipes), ins special up to a pipe diameter of 125 mm, high quality and inexpensive with a simple tubular welding sleeve or overlap Welding socket made of the same type of material easily to any length of pipe lines can be welded. When welding the PE-X pipes with a butt welding socket corresponds to the pipe diameter at the welding point the original diameter, so that rotationally butt-welded PE-X pipes per can easily be used for the relining of piping systems.

An embodiment of the invention is shown in the drawings and will described in more detail below.

There should be a rotational friction butt weld connection with a butt weld sleeve and a rotary friction overlap weld connection with an overlap welding socket on cross-linked polyethylene pipes (PE-X pipes) of dimension tion d = 90 mm.

Show it:

Fig. 1 positioning of the elements for a rotary friction butt weld connection

Fig. 2 rotary friction butt weld connection

Fig. 3 positioning of the elements for a rotary friction overlap welded joint

Fig. 4 rotary friction lap weld

According to Fig. 1 and Fig. 2 is used to produce a rotary friction butt weld connection of the cross-linked polyethylene pipes 1 and 2 a butt-welding socket 3 of dimensioning d = 90 mm from cross-linked polyethylene. The butt welding sleeve 3 is axially aligned between the tubes 1 and 2 and arranged in a rotating movement around the tube axis. The speed is 600 1 / min. The tubes 1 and 2 are firmly clamped and fixed in position but axially movable. Through them, an axially acting feed pressure of 1 bar is applied to the end faces 4 and 5 of the rotating butt welding socket 3 , whereby a temperature of preferably 430 ° C. is generated and generated by the boundary surface friction of the pipe end faces 6 and 7 on the end faces 4 and 5 of the butt welding socket 3 thermal digestion of the PE-X in a thermoplastic melt layer with high shear and turbulent mixture is formed. After reaching the melt state of the interfaces 4 ; 5 and 6 ; 7 after a rubbing time of 10 s there is an abrupt stopping of the rubbing movement of the butt welding sleeve 3 while maintaining the feed pressure, which leads to a material weld connection 8 and 9 between the pipe end faces 6 ; 7 and the end faces 4 ; 5 of the butt welding socket 3 leads.

The delivery pressure is maintained until the weld joint 8 has cooled; 9 maintained at ambient temperature.

The rotary friction lap welding of cross-linked polyethylene pipes (PE-X pipes) is shown in Fig. 3; 4 shown. As a connecting element of the cross-linked polyethylene pipes (PE-X pipes) 1 and 2 , an overlap rotating sleeve 10 made of cross-linked polyethylene (PE-X) is used. The overlap rotary sleeve 10 has a conical sleeve inner wall 11 with a cone angle α of 1 ° to 3 °, preferably 2 ° and a stop web 12 in the middle of the sleeve bore. In order to carry out the rotary friction overlap welding connection, the overlap rotary sleeve 10 is set in a rotating movement about the tube axis and at a speed of 500 rpm relative to the fixed tubes 1 and 2 . At the same time, the tubes 1 and 2 are moved by a mutual feed movement with their tube ends in the rotating overlap rotary sleeve 10 to the impact web 12 , wherein between the inner wall 11 of the overlap rotary sleeve 10 and the outer surface of the tube ends due to the interfaces caused by friction the cone angle α of the inner wall 11 of the sleeve is increased, a temperature of <420 ° C. but <440 ° C., preferably 430 ° C. is reached and a thermoplastic, turbulently sheared melt layer is formed.

After a rubbing time of 12 s there is an abrupt stopping of the rotational movement of the overlap rotary sleeve 10 , and there is a cohesive weld joint 13 under the melt formed; 14 between the pipe ends and the overlap rotating sleeve 10 . The weld joint 13 ; 14 remains fixed at ambient temperature until it cools down.

The expansion of the overlap rotating sleeve during the friction and welding process by radial forces is by a not shown Spannvor direction prevented.  

List of the reference numerals used

1

polyethylene pipe

2

polyethylene pipe

3

Butt welding sleeve

4

face

5

face

6

Pipe face

7

Pipe face

8th

welded joint

9

welded joint

10

Overlap rotary sleeve

11

Muffeninnenwandung

12

stop web

13

welded joint

14

welded joint
α cone angle

Claims (3)

1. A method for producing a socket connection for cross-linked polyethylene pipes (PE-X pipes) by rotary friction welding, preferably for PE-X pipes up to a pipe diameter of 125 mm with a sprayed overlap rotary sleeve made of cross-linked polyethylene as a connecting element, which is between axial movable but non-rotating pipes in a rotary movement around the pipe axis, whereby at the same time an axial movement of the pipes takes place until interface friction occurs between the friction surfaces of the pipes and the friction surfaces of the connecting element and a frictional pressure builds up, characterized in that the sleeve connection a pipe section made of cross-linked polyethylene or a butt welding sleeve ( 3 ) made of cross-linked polyethylene serves as a connecting element that a temperature <420 ° C but <440 ° C, preferably 430 ° C is generated by the boundary friction known per se, which thermal decomposition of ther moelastisc hen materials in a thermoplastic melt with approximately the same viscosity, high shear and turbulent mixture forms that a friction time of 7 s to 12 s is observed, that the rubbing process is then stopped abruptly and after stopping while maintaining a holding pressure of 0.9 bar up to 1.2 bar a cohesive welded connection is created. 2. The method according to claim 1, characterized in that the speed of the Connecting element is 300 1 / min to 700 1 / min. 3. The method according to claims 1 and 2, characterized in that the connecting element is an overlap rotary sleeve ( 10 ) having a conical sleeve inner wall ( 11 ) with a cone angle α to 3 ° and that in the middle of the overlap rotary sleeve ( 10 ) a stop bar ( 12 ) is arranged.