DE3926662A1 - Welding together polypropylene pipes - by using inner sleeve with centre outer rib, heating this and one pipe, pressing pipe over sleeve, cooling , and repeating with second pipe - Google Patents

Abstract

Joints are produced in central heating pipes of plastics and polypropylene in partic. In the process the surface of one end of a socket and one pipe are heated, these are pressed together and then cooled, the same procedure being followed also on the other end of the same socket and on the end of another pipe if necessary. The o.d. of the socket is heated at its end, and the i.d. of each pipe end concerned is also heated; the pipes are then forced over each end of the socket. ADVANTAGE - The method avoids the problems of conventional spigot/socket joints (e.g. variations in the end ring used, difficulties in obtg. a snug fit of pipe end into a socket, risks of the joined pipes meeting inside the socket and forcing their heated ends to move radially inwards and hence attenuate the pipe dia. etc.).

Description

The invention relates to a method for producing Pipe connections according to the preamble of claim 1 and an apparatus for performing the method.

From the leaflet DVS 2207, part 11, Aprilil 1985 "heating element welding of thermoplastics - pipelines Polypropylene (PP) "is the so-called heating element socket welding known. This welding process is carried out using a heating element tes that a heating mandrel on one side and on the other Overlying side has a heating socket, an end portion a fitting on the one hand and an end section of a pipe on the other hand, heated before the heated pipe end into the  Fitting sleeve used and both parts until the cooling heated sections are held together. With the heater Socket welding is carried out through the inside surface of the fitting sleeve the mandrel is heated while at the same time through the heating bush the outer surface of a pipe end portion is heated. Here is the warming up time of the fitting sleeve and the pipe given. The assembled parts are essentially chen about the same length of time as the warm-up time, and only after A predetermined cooling time can expire Connection are claimed. The same process can be done with regard to the fitting sleeve and a second pipe end ren, so that by means of the fitting sleeve a connection between two pipe ends can be produced.

The fittings sleeves generally used have one inner circumferential annular approach, the inside of which knife is smaller than the rest of the fitting socket inside diameter and which defines an axial length within the fitting sleeve, over which the associated pipe end is to be used. Here it is desirable that after heating the fitting sleeve on the one hand and the pipe end on the other hand the pipe up to this approach in the fitting sleeve is inserted and then the two parts up be cooled down for a firm connection.

The use of such a fitting sleeve is disadvantageous this ring-shaped on the inner circumference of the sleeve Approach, because during the manufacture of such fittings bumps or the like in the area of the annular attachment can result, due to the internal arrangement of the ring-shaped approach are not or difficult to see from the outside. This can cause inaccuracies when inserting the pipe into the fitting sleeve results in a full contact of the forehead term pipe end section on the annular approach of the fittings sleeve is not always guaranteed what to do with manual welding slight displacements between pipe and fitting sleeve  while holding the pipe and fitting sleeve in the course of the cooling process, which in turn can cause alignment problems me and / or sealing problems.

Another disadvantage in the production of such connections can be seen in the fact that the pipe end sections with the molten zenen end faces are pushed into the fitting sleeve and both due to the insertion depth, which cannot be seen from the outside Pipes are inserted so far that the melted ends converge and the melted material towards the pipe axis is pressed. This can lead to a narrowing of the Pipe cross section within the fitting sleeve and even to one complete welding within the fitting sleeve.

According to section 3.2.2 of the DVS 2207 leaflet, the fitting sleeve must be inside with a cleaning agent, e.g. alcohol, and absorbent, non-fibrous material must be thoroughly cleaned, before the welding process can take place. Obviously calls this is very difficult with the usual heating pipe diameters due to the inner surface of the fitting sleeve being difficult is accessible. Another disadvantage is that after cleaning the inside surface of the fitting sleeve from the outside cannot be easily recognized, for example, whether fibers of the paper material or the like on the inner surface are left, so that errors within the welding cross section or there is a discontinuous weld can. Fittings sleeves of this type are produced as molded parts poses. Inaccuracies, in particular, can occur during spraying occur on the inner wall surface, for example unevenness etc., due to the comparably small inside diameter are not easily recognizable with the eye.

The invention has for its object a method of type mentioned so that the above  described disadvantages are eliminated.

This object is achieved in that the End section of the sleeve in the area of the sleeve outer surface and the End section of each heating pipe in the area of the pipe inner wall is heated and that for joining sleeve and heating pipe end section of the latter on one of the two sleeve sections is postponed.

According to a preferred embodiment it is provided that the Sleeve and the heating pipe each have an oval cross section, the clear cross-section of the heating pipe is approximately that the socket cross-section corresponds to the specified cross-section of the socket, and that before joining sleeve and heating pipe the same are rotated or positioned so that their both major and minor axes are aligned.

The invention provides a welding process in which the fittings sleeve comes to lie within the two associated pipe ends.

The method has the advantage that the surface of the sleeve is on which the heating pipes are plugged on, in a simple way with an eye on possible production errors or inaccuracies ten can be examined, with a fitting sleeve if necessary the outer circumferential central annular approach as Stop for the heating pipe ends to be pushed open. This ring-shaped approach can also and completely on straight Check running contact surfaces with the eye so that defects are easily ascertainable.

According to the invention it is ensured that the surface of the Sleeve, which is used to hold the pipe end sections, with bare Eye can be easily checked before the welding process is initiated.  

Another advantage of the method according to the invention is in that, in contrast to the prior art, the inner surface of the Tube is exposed to heating, in general is cleaner than the pipe outer surface. The in general a cleaner pipe surface requires less complex cleaning measures, so that the cleaning of the pipe end sections itself designed less complex. Such pipes are through Extrusion produced endlessly, which has the consequence that the Inner wall surface is completely smooth. In addition, the Extrusion of such continuous tubes while monitoring the Manufacturing process to avoid defects in the extruded Pipe. The production of smooth wall surfaces is guaranteed chen. Since such an endless pipe is laid in is cut predetermined lengths, it is ensured that the inside of the pipe remains extremely clean.

The method is preferably used for the production of pipe connections between oval plastic pipes, preferred made of polypropylene.

The method can be advantageously used in such Plastic heating pipes, preferably made of polypropylene, the External surface with an additional coating, e.g. to Avoidance of oxygen diffusion is provided. Here there is the advantage that the otherwise required Elimination of such a layer in the known method The prerequisite for establishing the welded joint is superfluous and therefore no difficulties with the subsequent Elimination of such, essentially the oxygen diff fusion serving coating are to be expected.

A device for performing the method has one Heating socket and a heating mandrel, of which the cross section  area of the heating bush approximately that defined by the sleeve circumference th cross-section corresponds, while the cross-section of the heating mandrel the cross-section defined by the inner circumference of the heating pipes area corresponds.

In the following the method and an apparatus for Execution of the method using the drawings to explain described further features. Show it:

Fig. 1 is a partially sectional view of a fitting socket, which shape in accordance with a preferred embodiment having an oval cross section,

Fig. 2 is a front view of the fitting sleeve according to Fig. 1,

Fig. 3 is a sectional view of the fitting socket of FIG. 2 taken along the minor axis 3-3 ',

Fig. 4 is an end view of a welding socket of a heating device according to a preferred embodiment,

Fig. 5 is a sectional view of the welding socket according to Fig. 4,

Fig. 6 is an end view of a welding mandrel of the heating device,

Fig. 7 is a side view of the welding mandrel of Fig. 6, and

Fig. 8 is a sectional view illustrating two heating pipe end portions welded together by an inner fitting sleeve.

Fig. 1 shows a fitting sleeve 1 for use in the method according to the invention, which according to FIG. 2 preferably has an oval cross section. The sleeve has a central, annularly extending along the hub surface approach 1 a, which serves as a stop for both sides to-install on the pipe fitting sleeve 1 ends 18, 20th The approach 1 a is provided in the Darge presented embodiment, but can be omitted if necessary. The defined on both sides of the annular approach 1 sleeve end portions 2 a, 2 b are of a predetermined length and dimensioned such that a secure attachment of the also elliptical or oval cross-section Heizungsroh end portion is guaranteed.

Although the invention with fitting sleeves and heating pipes oval or elliptical cross section is described, can the invention also with corresponding elements with a circular Insert cross section.

From Fig. 1 and Fig. 3 it can be seen that the annular projection 1 a has a surface 3 a running parallel to the tube axis and two laterally adjoining end faces 3 b, 3 c, which are at right angles to the surface 3 a. The height of the side surfaces 3 b, 3 c is chosen such that it is approximately equal to the wall thickness of the heating pipes used, so that after connecting the fitting sleeve 1 and the heating pipe end section, the upper surface 3 a is flush with the outer wall of the welded heating pipes. It is essential that the lateral Stirnflä surfaces 3 b, 3 c run as exactly as possible perpendicular to the axis of the fitting sleeve 1 and if possible a 90 ° angle between the lower end of the end faces 3 b, 3 c on the one hand and the sleeve sections running parallel to the axis of the fitting sleeve 2 a, 2 b is observed so that after heating the pipe end section and the associated socket end section, the heating pipe abuts the associated end face 3 b or 3 c. The length of the sleeve end sections 2 a, 2 b is chosen so large that, on the one hand, an easy application of the pipe end section is ensured, and on the other hand, after the heating pipe is placed on the fitting sleeve, a coaxial arrangement between the heating pipe and the fitting sleeve is ensured until the previously heated parts have cooled. In the illustrated embodiment, the fitting sleeve 1 has a total length of mm 35, while the fittings muffenendabschnitte 2 a, 2 b each have a length of about 15 mm have.

According to a preferred embodiment, the fitting sleeve 1 a has bevels 4 a, 4 b at its two ends. From the cross-sectional drawing according to FIG. 3 it follows that the bevels 4 a, 4 b taper the front ends of the fitting sleeve 1 from the center to the outside, thereby making it easier to push the end sections (not shown in FIG. 3) onto the fitting sleeve 1 becomes. The bevel 6 b pointing to the axis of the fitting sleeve can also provide fluidic advantages after the production of a fitting sleeve-heating pipe connection, since the bevel 6 b causes an oblique transition from the inner wall of the heating pipe to the inner wall of the fitting sleeve 1 and thus turbulence in the flow are largely excluded.

The fitting sleeve 1 a according to Fig. 1 to 3 is heated by the in Figs. 4 and 5 shown welding socket 10 of a heating apparatus in the area of the surfaces b designated 8 a, 8. The following the representations according to FIGS. 4 to 7 are compared to the representation of FIGS. 1 to 3 on a reduced, approximately half-scale. For this purpose, the fitting sleeve 1 a with one of the surface sections 8 a or 8 b is inserted into the welding bush 10 . At the same time, a tube end section is pushed onto a welding mandrel 14 according to FIGS . 6 and 7 and is heated internally over a predetermined length corresponding to the length of the mandrel.

Both the fitting sleeve 1 a and the associated Rohrendab section are jerkily removed from the heating device or from the heating device and then the Rohrendab section is plugged with its previously heated end onto the heated surface section 8 a or 8 b of the sleeve 1 a. Before joining the fitting sleeve and heating pipe end section in the illustrated embodiment with an oval or elliptical cross-section, of course, both parts must be aligned with one another in such a way that their larger axes or smaller axes each overlap, while such alignment is not required if the sleeve 1 a and the associated heating pipe have a circular cross-section. Then both parts, preferably without relative movement in the axial direction, are held fixed to one another and are subjected to a cooling process, as a result of which an intimate connection takes place between the respective sleeve surface and the associated inner pipe surface. The still free Endab section of the sleeve 1 a is heated in the same way together with the end section of another heating pipe and the same process takes place, whereby a pipe connection in the form of two pipe end sections attached to the sleeve 1 a is obtained, as shown in Fig. 8 is shown. In Fig. 8, the two pipe end sections are designated 18, 20 .

From Fig. 8 it can be seen that the clear cross section of the sleeve 1 a is smaller than the clear cross section of each pipe end section 18 , 20th It was suspected that such a reduction in the clear cross-section leads to an increase in the flow resistance due to the use of an inner sleeve 1 a, that is to say an inner sleeve 1 a in the tube end sections 18 , 20 . As shown in FIG. 8, the clear cross section, ie the cross-sectional area defined by the inner wall of each heating pipe in the area of the pipe connection according to FIG. 8, is reduced by the wall thickness of the sleeve 1 a. Such a problem does not arise in the case of heating element socket welding according to the prior art, since there, after completion of the socket-pipe connection, the clear cross section corresponds to that which is defined by the pipe radius, after the pipe ends according to the prior art into one Fitting sleeve are used.

Surprisingly, however, it has been found that in the case of a pipe connection of the type shown in FIG. 8, the increase in the flow resistance due to the internal sleeve 1 a is so small that it is negligible. In particular, the flow resistance is so insignificantly increased by such constrictions in the pipe register of an underfloor heating system that no pump with a higher pumping capacity than in the comparable case in which the entire underfloor heating system is designed without pipe ends connecting inner sleeves.

The taper 6 b described in connection with FIG. 3 on the end face of each sleeve 1 a in the manner shown in FIG. 3 together with the external taper 6 a ( FIG. 3) gives the effect described below. By heating the outer surfaces 8 a, 8 b of the sleeve end sections 2 a, 2 b, the sleeve wall in the region of the taper 6 a is so soft that it lies completely against the inner wall of the pipe end sections 18 , 20 according to FIG. 8, and after Solidification of the preheated parts only the taper 6 b remains, that is, a gently rising surface 6 b between the inner pipe wall of the heating pipe placed on the one hand and the inner sleeve wall on the other hand. The taper 6 b is practically no longer available in the finished pipe-socket connection, since the surface section 6 a bears intimately on the inner wall of the heating pipe and firmly connects it. This caused by the inclined surface 6 b smooth transition from the Rohrendab section 20 to the sleeve 1 a or from the pipe end section 18 to the sleeve 1 a is decisive for the negligible increase in flow resistance in the area of the pipe-sleeve connection.

In the inventive method, the Oberflächenab are sections 8 a, 8 b of the sleeve 1 a respectively before the heating thereof by the heater cleaned. The same applies to the welding bush and the heating mandrel. The surface of the sleeve 1 a is vorzugwei se cleaned with a solvent and non-fibrous paper or the like. In most cases, cleaning the inner surface of the plastic tube is unnecessary, since the inner surface of the tube is generally clean, in contrast to the outer surface of the tube. Then the respective sleeve surface 8 a or 8 b and the associated pipe inner surface section are heated or heated over a predetermined period of time. Then the two parts, namely sleeve 1 a and pipe end section, preferably jerkily, are removed from the heating device or from the heating device and quickly joined to the welding bead 1 a. Make sure that the two parts are properly aligned axially. As already described above, in the case of oval or elliptical sleeves 1 a and heating pipes, the alignment of the two parts must be carried out before the two parts are joined so that their large or small axes coincide. The two parts are then held together until they have cooled down.

The welding bush and welding mandrel described in connection with FIGS. 4 to 7 are firmly connected to the associated heating devices, not shown in the drawings, such that, for example, the end of a possibly oval heating pipe on the heating mandrel and the other side from the one Sleeve 1 a can be inserted into the heating socket.

As can be seen from FIGS. 4 and 5, the welding bushing 10 has a base body 10 a with an essentially circular cross section, in which the recess 12 is formed axially and centrally to the base body 10 a. For the preferred embodiment of the method, the welding bush 12 has an elliptical cross section. for heating the sleeve section 2 a or 2 b, this is inserted into the recess 12 from the side labeled 13 in FIG. 5. On the front side 13 ( FIG. 5) opposite side of the base body 10 a is provided with a bore 13 a, which together with the recess 12 forms a continuous opening through the base body 10 a. The bore 13 a is circumferentially provided with bores 16 arranged radially around the axis of the base body 10 a, at least one such bore 16 being provided and serving to hold a fixing pin (not shown).

The welding pin according to Fig. 6 and 7 has a bore 13 a corresponding hole 17, which is preferably provided with an internal thread 18. On the side surface of the welding mandrel 14 opposite the side 19 containing the bore 17 , a projection 20 is formed, which represents the actual welding mandrel and protrudes with a corresponding length from the base body 21 containing the bore 17 . The base body 21 is provided with at least one bore 22 which is formed with a radius to the axis of the base body 21 which corresponds to the radius of the bore 16 in the base body 10 a of the welding bushing according to FIG. 5. Fixing pins can be used by means of the bores 16 , 20 , as a result of which the base body 10 a can be fixed relative to the base body 21 . Preferably by means of a screw or the like., Which is inserted through the recess 12 of the base body 10 a through bore 13 a therethrough, the base body 10 can be a fix and the base body 21 a, the screw into the thread 18 of the base body 21 engages . Obviously, the attachment between the base bodies 10 a and 21 can also be done in other ways.

As shown in FIG. 6, the projection 20 defining the welding mandrel is of elliptical shape in accordance with the preferred embodiment of the method and has a circumference which corresponds to that of the cross-section of the heating pipes used.

In Figs. 4 to 7, the heating or sealing temperature generating and integrated into the base bodies 10 a, not shown Dende 21 contain means. This device consists, for example, of a coil that is connected to the network via contacts or a transformer for heat generation. For welding polypropylene heating pipes and fitting sleeves, the heating device described in connection with FIGS. 4 to 7 is heated to temperatures which correspond to the value given in the data sheet DVS 2207, part 11.

The method described is particularly advantageous for Connection of plastic pipes or polypropylene pipes, their Outer surface with a special coating e.g. to Avoidance of oxygen diffusion (Eval layer) is provided. In contrast to the known method, the outer layer can the heating pipe are left, while in the known Welding process each pipe end over a predetermined one Section for receiving the outer sleeve should be treated. When using the method according to the invention, customary Imprints provided on the outer surface of the pipe, remain.

The invention provides a method with which pipe ends can be connected to one another in a simple manner, the cleaning of the sleeve surfaces in contrast to the prior art being simplified considerably and in particular also being able to be ascertained easily whether the sleeve outer surface is clean and free of cleaning particles or the like is. The preparations that must be carried out before the welding process can be carried out safely and in a time-saving manner. Each of the separately manufactured sleeves can be easily checked with the eye before the welding process and before cleaning whether they meet the quality requirements and whether, for example, the connecting surfaces of the annular stop 1 perpendicular to the sleeve axis are worked out or not. In this way, a tight fit of the pipe end section to be attached to the annular stop 1 is guaranteed.

Claims (10)

1. Process for the production of pipe connections on heating pipes made of plastic, in particular of polypropylene,
in which a surface of an end section of a sleeve and a surface of the end section of a heating pipe are heated, put together to produce a joining pressure and are subjected to a cooling process,
where appropriate, the same process is repeated with respect to a second end section of the same sleeve and the end section of a further heating pipe, characterized in that
that the end section ( 2 a, 2 b) of the sleeve ( 1 a) in the area of the sleeve outer surface ( 8 a; 8 b) and the end section of each heating tube in the area of the inner tube wall is heated, and that for joining together the sleeve ( 1 a) and Heating pipe end section of the latter is pushed onto one of the two Muffenab sections ( 2 a, 2 b). 2. The method according to claim 1, characterized in that
that the sleeve ( 1 a) and the heating pipe each have an oval cross section,
wherein the clear cross section of the heating pipe corresponds approximately to the cross section of the sleeve ( 1 a) defined by the sleeve circumference, and
that before joining sleeve ( 1 a) and heating pipe they are rotated or positioned in such a way that their two large and small axes are aligned with each other. 3. The method according to claim 1 or 2, characterized in that the outer surfaces of the end portions ( 2 a, 2 b) of the sleeve ( 1 a) are cleaned before heating. 4. The method according to any one of the preceding claims, characterized in that for heating the end portions ( 2 a, 2 b) of the sleeve ( 1 a) or the heating tube the latter are pushed into or on a Heizvor direction, with an axial before sliding Alignment between the heating device and the sleeve on the one hand and the heating device and the heating pipe end section on the other hand is brought about. 5. The method according to claim 4, characterized in that after heating the sleeve outer surface ( 8 a, 8 b) and the heating pipe inner surface sleeve ( 1 a) and Heizungsrohrendab cut at the same time and preferably jerkily removed from the heating device and joined to the weld bead ( 1 a) are by plugging the heating pipe end section onto the associated socket end section ( 2 a, 2 b). 6. sleeve for carrying out the method according to at least one of the preceding claims, characterized in that it has a central, annularly encircling on its outer surface portion ( 1 a). 7. The device for carrying out the method according to at least one of the preceding claims with a heating bush ( 10 ) and a heating mandrel ( 14 ), characterized in that the cross-sectional area of the heating bush ( 10 ) corresponds to the cross-sectional area defined by the sleeve circumference. 9. The device according to claim 6, characterized, that the cross-sectional area of the heating mandrel in the heating pipe cross section corresponds. 10. The device according to claim 6, characterized in that the heating bush ( 10 ) has an oval cross-sectional area. 11. The device according to claim 6, characterized in that the heating mandrel ( 14 ) has an oval cross-section.