DE19911284A1 - Rotational friction welding of a sleeve connector between crosslinked polyethylene pipes by inserting a sleeve of similar material between the pipe ends and rotating - Google Patents

Abstract

The sleeve connector comprises either a tube section, a butt welding sleeve(3) or an injection molded overlapping rotational welding socket of cross-linked polyethylene. The connector is positioned between the non-rotating pipes(1,2) and rotated about its axis while both pipes are moved axially towards each other to effect friction between the end faces(4,5,6,7) of the connector and pipes and produce a rotational friction weld. Preferred Features: With increasing frictional pressure the temperature of the mating faces(4-7) reaches 420-440 deg C to give a uniform melt viscosity. The friction period is 7-12s and when friction ceases an axial pressure of 0.9-1.2bar is applied to the joint until the melt cools.

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) brings forward 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) are distinguished from polyethylene high density pipes (PE-HD pipes) due to 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) deteriorates namely its weldability.

Connection methods, which are characterized by high economic efficiency 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 general knowledge, it can be assumed that networking tes polyethylene is not weldable to each other (specialist lecture "The pipe mill PE-X material: pipe material properties, quality assurance and main application offer "Conference proceedings and lecture on the Wiesbaden Plastic Pipe Days 1998 on the 27th and April 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 clog. As connecting elements between the tubes 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 (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 conditions with molded parts are expensive in terms of material 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 level 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) eat. 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 polyethylene became higher Density (PE-HD) successfully tested and is now state of the art. When sweat process, the PE-HD is melted, the PE-X only becomes elastic soft. Strength tests showed that this connection for the area the gas and water supply is suitable. Some pipelines 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 27th and 28th, 98 and "Decision criteria in the selection of pipe materials in the gas supply ", likewise 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 Pipe 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 captured. The friction is generated in that at the same time a perpendicular to the friction surface acting pressure is exerted. Rotary friction welding can can only be used for molded parts that have a rotationally symmetrical connection surface own (balls, pipes, 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 that are 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 on parts to be joined 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) have been used primarily 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).  

Rotary friction welding is increasingly used in industry, but only refers to welding thermoplastic uncrosslinked Plastics. A process for connecting cross-linked polyethylene pipes (PE- X-tubes), which are not thermoplastic, but a thermo-elastic cha owning is 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. A part is divided into its own Axis rotating movement brought, the other is fixed in one edition. The Friction is generated in that both parts by an axially acting pressure be brought together by force.

According to the invention, in rotary friction welding of cross-linked polyethylene pipes (PE-X pipes) as a butt or socket connection a pipe section or a Butt welded socket made of cross-linked polyethylene (PE-X) or a sprayed Overlapping sleeve made of cross-linked polyethylene (PE-X) as a connecting element between the axially movable but not rotating tubes 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 rotie The pipe section and the end faces of the pipes create friction and become Friction pressure builds up. When using a networked rotary overlap sleeve the friction arises when the pipes are fed due to the fit tolerances between 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 to the local one in the friction area thermal digestion of the thermoelastic-molecular network structure into one thermoplastic structure due to an increase in temperature <420 ° C but <440 ° C, preferably 430 ° C. Only then does a weldable melt layer form with an integral thermoplastic-viscous character that in the interfaces area has the lowest viscosity and very strong due to the rubbing movement shears and mixes turbulently. After reaching the melt state there is an abrupt stop of the frictional movement while maintaining the axial Pressure until cooling, resulting in a thermoplastic material connection leads.

When using an overlap rotary sleeve made of cross-linked polyethylene (PE-X) the friction is promoted by the fact that the sleeve is a conical sleeve has an 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 friction and sweat 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 rotation welding is depending on the wall thickness and diameter, preferably up to 300 1 / min 700 rpm. 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 the fact that cross-linked polyethylene pipes (PE-X pipes), in particular 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 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 can easily be used for relining piping systems.

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

There should be a rotary friction butt weld connection with a butt weld sleeve and a rotary friction overlap weld connection with an overlap welding sleeve on cross-linked polyethylene pipes (PE-X pipes) Dimensioning d = 90 mm can be produced.

Show it:

Fig. 1 of the positioning elements for a Rotationsreib-butt-welded connection,

Fig. Rotationsreib 2-butt weld joint,

Fig. 3 for a positioning of the elements Rotationsreib-lap weld,

Fig. 4 rotary friction lap weld.

According to Fig. 1 and Fig. 2, a butt welding sleeve 3 of dimensioning d = 90 mm made of cross-linked polyethylene is used to produce a rotary friction butt weld connection of the cross-linked polyethylene pipes 1 and 2 . 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 is formed in a thermoplastic melt layer with high shear and turbulent mixture. 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 feed pressure is maintained until the weld joint 8 ; 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 with respect to the fixed tubes 1 and 2 at a speed of 500 rpm. 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 , with friction 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 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 pressure-producing a welded joint 13 is formed under the melt formed; 14 between the pipe ends and the overlap rotating sleeve 10 . The welded 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 symbols used

1

Polyethylene pipe

2nd

Polyethylene pipe

3rd

Butt weld socket

4th

Face

5

Face

6

Pipe face

7

Pipe face

8th

Welded joint

9

Welded joint

10th

Overlap rotary sleeve

11

Inner sleeve wall

12th

Footbridge

13

Welded joint

14

Welded joint
α cone angle

Claims (3)

1. A process 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, characterized in that a pipe section made of cross-linked polyethylene or a die is used as the socket connection Welded sleeve ( 3 ) made of cross-linked polyethylene or a sprayed overlap rotary sleeve ( 10 ) made of cross-linked polyethylene serves as a connecting element, which is set in a rotational movement between the axially movable but non-rotating tubes ( 1 ; 2 ) around the tube axis, that at the same time an axial Infeed movement of the tubes ( 1 ; 2 ) takes place until boundary surface friction occurs between the friction surfaces of the tubes and the friction surfaces of the connecting element, a friction pressure builds up and a temperature <420 ° C but <440 ° C, preferably 430 ° C is generated, which one On thermal closure of the thermoelastic material in a thermoplastic melt mi t approximately the same viscosity, high shear and turbulent mixture, that a friction time of 7 s to 12 s is maintained, that the friction process is then stopped abruptly and after stopping while maintaining a holding pressure of 0.9 bar to 1.2 bar a cohesive weld 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 web ( 12 ) is arranged.