AU659109B2 - Welding apparatus - Google Patents

Description

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AUSTRALIA

Patents Act 1990 9 109 AGRU ALOIS GRUBER GMBH

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Irr

II

I

4$

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0 S99 Invention Title: WELDING APPARATUS The following statement is a full description of this invention including the best method of performing it known to us:i_ -2- BACKGROUND OF THE INVENTION 1. Field of Invention The invention relates to a device for the joining of tubular parts made from plastic, especially polyvinylidene fluoride, polypropylene and polyethylene (wherein the aligned parts exhibit about the same diameter) by being pushed together and welded on the abutting surfaces of the tubular parts by the effect of heat. More specifically, the invention provides a heating element for softening the area of the beveled abutting surface, of at least one tubular part, and the contact surface of the heating element on the abutting surface of the tubular part is designed corresponding to the abutting surface and is provided on a circular or disk-shaped lug on the heating element and the heating element is provided with a centering and/or calibrating lug for the tubular part.

2. Backaround Ar The uniting or joining of pipes, fittings or other tubular plastic parts made of PE, PP, PVDF, ECTFE, PPS, PEEK, etc.) heretofore has taken place by *t butt-welding. In this case the tubular parts are cross-cut evenly and then butt-jointed. Then along the butt joint the material of the two parts to be connected is heated to the softening or melting point, whereupon the flowing togethers of the plastic of the two parts leads to a welding. Also in this know butt-welding technique, a o welding bead which is at least two to four millimeters thick is formed on the inside surface of the pipe thus produced which, if it is not removed in an expensive way, entails considerable flow losses and/or deposits in the pipe in the area of these welding beads. But often it is technically impossible to machine away such welding seams later on from the pipe inside wall. In this case, an undesirable rise in the flow resistance in the pipe as well as such deposits occurs if liquids with solid ;1 i 1 1 3 particles are transported in the pipe.

Various ways for reduction of these welding beads have already been proposed. Thus DE-A-3510552 explains the placing of technically relatively complicated recesses along the abutting surfaces of the two pipe parts to be welded together. These recesses are softened by a tool partially filling them so that after removal of the tool the pipe parts can join one another and be connected to one another. But also in using this known process a significant inside bead appears, which leads to the already mentioned undesirable increase of the flow resistance in the pipe. Also in DD-A-197216 it is pointed out that, mold heating elements as well as inside bevels and also reduction of the welding pressure are to le 1 to a reduction of the inside beads.

A device for reliable production of a pipe welding joint with practically smooth inside wall is disclosed in WO 88.06966.

Brad Description of the Invention 20 The object of the invention is to provide a device f "e the initially mentioned type, with which the formati of 46 i a welding bead on the inside surface of the tubu r parts when they are joined from two plastic tubular arts with Sessentially the same diameter is practica y completely prevented.

o0 This object is achieved in th process according to the invention by the fact that e abutting surfaces of 0 *4 the tubular parts in the di ction of the inside pipe space are undercut or r essed so that the edge formed by the inside surface o the tubular part and the abutting surface springs ck opposite the edge formed by the outside surf of the tubular part and the abutting surface, d so that the parts in the area of the abutting surfa s in the axial direction essentially are softened e ily in depth, then pushed together and, as a result, Y 2 4 It has been shown that in welding of pipes of sizable diameter difficulties can arise in adhering to the necessary tolerances. Plastic pipes with a diameter of about 150 to 250mm perhaps could not be welded optimally with the device of the parent case.

It would be desirable to provide a device for welding plastic pipes of the initially mentioned type, with which (in a reliable and thus economical way) even pipes made from plastic of said diameter can be joined to one another while adhering to the condition that the welding connection take place practically inside bead free to avoid flow disturbances of the mediui,: flowing in the pipes.

Disclosure of the Invention In one broad form the present invention provides a device for joining plastic tubular parts of about the same diameter and minimising the size of a bead of material formed on an interior of the tubular parts during the joining, with corresponding ends of the tubular parts S"which are intended to be joined together having been 20 recessed around an interior end edge thereof, the device comprising: a heating element for contacting with and for softening an end surface of at least one tubular part which is intended to abut a corresponding softened end 25 surface of another tubular part, with said softened o *e S. surfaces forming an abutting surface when joined together; wherein a circular or disk-shaped lug is provided on the heating element to define the contact surface, said lug including a heating ring and an alignment disk which are both miade from metal and which hold a heat-resistant plastic ring therebetween, said plastic ring being sized and positioned to serve as a contact surface which corresponds to the recessed end surface of said at least one tubular part.

?A LL 0 In another broad form, the present invention provides a device for joining together plastic tubular parts of about the same diameter and minimizing the size of a bead of material formed on the interior of said tubular parts during said joining, with corresponding ends of said tubular parts which are intended to be joined together having been recessed, said device comprising: a) a heating element adapted to fit between said tubular parts; b) said heating elemeht including two circular or disk-shaped lugs, one of said lugs being disposed on each side of said heating element, each of the lugs including a heating ring and an alignment disk which are both made from metal and which hold a heat resistant plastic ring therebetween, tit 15 said plastic ring being sized and positioned to serve as part of a contact surface of the lug and which, in use, comes into contact with the recessed end surface of the tubular part; c) the configuration of the contact surfaces of said lugs being adapted to mate with said recessed ends of said tubular parts, whereby the heating and softening of said tubular pieces by said heating element is maximized and oo: whereby said recessed ends of said tubular parts are heated to a substantially equal degree and depth across t 25 the thickness of said tubular parts.

In an earlier welding device the lug of the heating m element as well as the centering and/or calibrating lug consist of solid polytetrafluoroethylene (PTFE), and these could also be provided as two disks separated from one another. But nevertheless they consist in their i -6entirety of said plastic. It has now been shown that the described drawbacks of a problematic tolerance accuracy of the welded joint, especially with sizable diameters, can be avoided, if in the indicated way the lug and the centering and/or calibrating lug basically consist of metal material, preferably aluminium or an aluminium alloy and if the projection thus formed on the heating element exhibits a comparatively thin plastic ring, that is with relatively large inside diameter so that during the welding process it is provided as a corresponding contact surface on the inner recessed surface of the one pipe to be welded. It is assumed that the described tolerance difficulties with the earlier device are attributed especially to heat expansions or heat stresses, which come from the solid PTFE lugs of the heating element. In any case it has been surprisingly shown that te the tolerance deviations, observed so far, are avoided if lugs and plastic ring are designed in the way according to "the invention. In this case, it is especially important 20 that with the device according to the invention it is possible at all for the first time to weld plastic pipes with a sizable diameter, approximately 150 to 250mm, especially 160 to 225mm, to one another inside bead-free.

It should also be stressed that with the device according to the present invention, which consists of metal (preferably aluminium) lugs and plastic ring, can be produced more inexpensively than for example a solid plastic lug.

In this respect, the subunit is especially economical to produce, if in the area of the plastic ring it is divided parallel to its main plane. In this case, the PTFE ring can simply be inserted between the two lugs, which then are screwed together.

According to another feature of the invention it is provided that the plastic ring is radially surrounded by a i 7projection of the lug. In this way, the plastic ring is not only reliably fastened but also a conceivable radial expansion under the influence of heat during the welding process is limited, which is especially conducive to the desired dimensional stability.

Other details, features and advantages of the invention are brought out from the following description of a preferred embodiment of the invention as well as by the diagrammatic drawing and the claims.

Brief Description of the Drawings In the drawings: Fig. 1 to 3 shows the welding of two plastic parts I+ corresponding to the process according to the invention; 0. Fig. 4 shows an essential part of a device according r a 0 O 15 to the invention for carrying out the process according to oo the invention; oo Figs. 5.1 to 5.4 show various configurations of beveled or undercut abutting surfaces of the pipe parts to be joined, in enlarged representation; Fig. 6 shows the heating element (according to a4 Fig. further including the improvements relative to aa the parent application.

Detailed Description of the Invention The two plastic pipe parts to be joined to one °a 25 another, shown in Figures 1 to 5, are identified by o numerals 10 and 11. They exhibit the same or Gai approximately the same diameter. The plastic is oDuo polyvinylidene fluoride, polypropylene, polyethylene or a similar plastic.

Although two straight pipe pieces 10 and 11 are shown in the drawing, it is obvious that curved pipe parts can also be joined by the process according to the invention as well as the device according to the invention, just as straight pipes can be joined to elbows or curved parts.

All that matters is that the two tubular parts to be 1 L n 8 joined exhibit the same or approximately the same diameter in the area of their abutting surfaces.

As brought out by the drawing and especially by the enlarged representations according to Figures 5.1 to 5.4, abutting surfaces 12 and 13 of the two pipe parts and 11 to be welded together are made undercut or recessed, the individual pipe parts are not cut through evenly. Rather, after their separation from a longer pipe piece they are provided with recess or undercut 12. In applying the recess or undercut it is essential to see to it that the edge formed by inside surface 15 of tubular part 10 or 11 and abutting surface 12 springs back opposite the edge formed by outside surface 18 of tubular part 10 or 11 and abutting 15 surface 12.

r If t, rFor the sake of completeness, it can be pointed out that abutting surfaces 12 of tubular part 11 according to Figures 5.1 to 5.4 are made as a mirror image of represented abutting surfaces 12 of tubular part 10, as also shown in Figures 1 and 4.

tc....For welding the two tubular parts 10 and 11ii, abutting 4 surfaces 12 are heated so that in the area of abutting surfaces 12 a melting or heating zone of pipe parts and 12 is produced so that, on the one hand, the contour 25 or topography of selected undercut 12 is essentially maintained and, on the other hand, the phase transition of this melt zone from liquid or softened to the solid o°o material of pipe parts 10 and 11 also exhibits essentially the same contour as undercut or recess 12; cf. broken line representation in Figures 5.1 to 5.4. In other words, this softening or melting zone of the heated plastic extends equally deeply in the pipe wall in the axial direction of the pipe part independently of the respective diameter. Thus, a melting or softening area is obtained in the area of abutting surface 12, whose shape basically i 1 :I ~h 9 corresponds to that of the contour of abutting surface 12.

After abutting surfaces 12 of pipe parts 10 and 11 have been heated for the formation of the described melting zones, cf. Fig. 1; according to Fig. 2 they are axially pushed flush with one another. After the cooling of welding seam 19, the two tubular parts 10 and 11 are solidly joined to one another.

The essential advantage of the invention is brought out in Fig. 2. It can be seen that welding seam 19 on the inside wall of unit 10, 11 practically does not protrude, that rather an essentially smooth inside surface appears.

No further explanation is necessary that in this way favorable flow conditions appear in unit 10, 11, since welding seam 19 does not obstruct at all or only barely obstructs the flow.

By the recess of undercut of abutting surface 12 Ir according to the invention the possibility remains for the I tr softened plastic of pipe parts 10 and 11 to accumulate, during butting of pipe parts 10 and 11, in the free space in the area of the pipe wall formed by the undercut. In S..other words, the softened material in the area of the inside wall of pipe parts 10 and 11 is not forced to flow out over the inside wall of the pipe parts in the free I cross section. It should be noted that the conditions in the area of the outside diameter of unit 10 and 11 are different, cf. Figures 2 and 3. There the softened or

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liquid plastic material goes outward and forms the shown a welding bead 19. But in such location, a welding bead is not disadvantageous for the flow in the inside space of the pipe.

If an absolutely even inside surface is to be achieved in the joining of pipe parts 10 and 11, then, according to Figure 3 in the area of abutting of the two pipe parts a tool 50 can be placed which rests on the inside wall and whose outside diameter is as large as the i;i 1 10 inside diameter of pipe parts 10 and 11. In this way the softened or liquid material in the area of abutting surface 12 is forced to go outward. The tool, for example, may be a polypropylene plug, which can be manipulated by a handle 21. In relation to Figs. 1 to 3 and 5.1 to 5.4 it should also be mentioned that in the representations shown there axial sections through tubular compositions are involved.

In Fig. 4 again it is an axial section through two tubular parts 10 and 11 to be welded to one another with a tool for heating abutting surfaces 12 and 13. The tool is basically a heating element 20 which, for example, can be heated by electric resistance heating (not shown). For this purpose, for example, electric heating coils can be placed in ducts (again not shown). Also a heated heat exchanger liquid can flow in these ducts. As is further t brought out by Fig. 4, in the preferred embodiment shown, the heating device is designed symmetrically so that the two tubular parts 10 and 11 simultaneously, when the heating element is applied in tl way described above, can C be heated and softened or liquefied in the area of their abutting surfaces 12 and 13. For this purpose, according to Figure 4, there are provided laterally at heating element 20 a heatiig ring 21, 22 each as well as a centering and calibrating plug 23, 24. These plugs 23, 24 are used for centering and calibrating the two pipe t parts 10 and 11. The two plus 23, 24 further exhibit t centering lugs 25 for centering relative to ring 21.

Parts 21, 22, 23, 24 and 25 are placed on heating element 20 by means of a centering screw identified as a whole by 26. Calibrating plugs 23, 24 are preferably made from polytetrafluoroethylene or a similar plastic.

Rings 21, 22 are preferably made from aluminium or alloy I (surface coated with TEFLON).

Heating element 20 is heated to the extent that, by ii~o 11 heat transfer, rings 21 and 22 take on such a temperature that during contact with tubular parts 10 and 11, as represented in Fig. 4, the subsequent abutting surfaces of these parts which, as again is shown in Fig. 4, on rings 21 and 22 in the area of their abutting surfaces 12 and 13 rest all-over on rings 21 and 22, are heated to the extend that they melt or soften.

As is brought out in Fig. rings 21 and 22 are designed in the area of their contact surface with subsequent abutting surfaces 12 and 13 of tubular partk, and 11 with respect to their topography corresponding to abutting surfaces 12 and 13. In this way a snug contact between butting surfaces 12 and 13 and rings 21 or 22 is achieved. In turn this contact causes a practically equally deep penetration of the heat energy from rings 21 and 22 into the area of abutting surfaces 12 and 13, so that an equally deep softening or melting of tubular parts 10 and 11 in the area of abutting surfaces 12 and 13 is achieved, as was described in detail in connection with Figures 5.1 to 5.4. Thus the softened area of pipe rr parts 10 and 11 extends equally deeply in the axial direction over the entire diameter of the pipe walls.

After this state has been reached, pipe parts and 11 are moved in the direction of their longitudinal 25 axis from heating element 20 so that heating element 20 in 6 its entirety can be moved out from its position between LO the two pipe parts 10 and 11. This state corresponds to 6" the position according to Fig. 1.

Then the two pipe parts 10 and 11 are moved together and applied to one another, whereupon, on cooling of welding seam 19 thus formed, a permanent joining of the two pipe parts 10 and 11 is achieved; cf. Fig. 2.

Then it is to be pointed out that basically it is also possible to produce the undercutting or recessing of abutting surfaces 12, 13 by rings 21, 22 melting the

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*i a a ta ac a~ a, U t at a ac a at Ut a a at a a aI a h---2iratta abutting surface, which at first is not undercut, which thus in this case runs perpendicular to the longitudinal axis of pipe parts 10 and 11, and bringing it into the undercut form as reproduced in the drawings. But in this case, special precaution must be taken to remove the plastic material in the pipe interior forced in the direction of the pipe interior.

It is also possible to provide the heating element only on one side with its ring 21 or 22 and optionally associated centering plug 23 and with this first to heat and soften only the abutting surface of one tubular part, then remove it, and then soften the abutting surface of second part 11, then push the two parts together to weld them. But with respect to cost-effective and fast production, the symmetrical design of the heating element with rings 21, 22 and centering and calibrating 23, 24 according to fig. 4 is preferable.

The improvements according to the present invention may be seen in Fig. 6. The assembly shown therein is 20 provided in the device according to the invention on heating element 20 instead of components 21, 23 and 25 of Fig. 4. According to the invention, they are a sLabilizing lug 23' as well as a heating ring 23", each of which have a disk-shape and are produced from aluminium or an aluminium alloy. In the area of the abutting surface of the welding seam to be produced with the device according to the invention of pipes 10 and 11 to be welded a p3astic ring 21' is inserted in a corresponding groove between the two lugs 23' and 23". The plastic 30 ring 21' is preferably made from PTFE. The exposed surface of heating ring 23" is the surface which contacts the abutting surface of the pipe to be welded. The three components 21', 23' and 23" are connected to one another by one or more bolt connections with one bolt 30 each.

The subassembly thus formed which is formed to correspond to the receesed part of the end surface of said at least one tubular part 13 according to Fig. 4 is connected by a bolt 26 through recess 35 to heating element 20. During the course of the heat transfer from heating element 20 to the assembly, heating ring 23" is heated until plastic pipes 10, 11 made from polyvinylidene fluoride, polyethylene or the like in the area of their contact surfaces with the free surface of heating ring 23" are softened or melted. As can be further seen in Fig. 6, heating ring 23" in the area of the outside periphery of plastic ring 21' has a continuous projection 36, which partially surrounds the PTFE ring 21' in the area of its outside surface and in this way reliably holds it in its desired position. Fig. 6 further shows that PTFE ring 21' exhibits a comparatively large inside diameter. In this way, this ring 21' requires only a practically small amount of PTFE material.

The assembly, basically consisting of parts 21', 23' and 23" may be equally used in the device according to Fig. 4 instead of parts 22 and 24 shown there, so that Sf: thus again a symmetrical design of heating element 20 with its lugs, centering and/or calibrating lugs as well as the PTFE ring appears.

yIn conclusion it should be pointed out that the content of WO 88/06966 is hereby being incorporated by referedice in its entirety.

In case a peripheral projection 36 is provided as described, its cross-section according to Fig. 6 should be u designed in such a way that it corresponds to and produces the recessed or undercut abutting surfaces of tubular parts 10 and 11 as explained in connection with Figs. 1 to 5. During the heating procedure of the abutting surfaces the inner surfaces of parts 10 and 11 rest on the outer diameter surface of lug 23' or its oppositely i arranged counterpart (not shown in Fig. 6).

Ct) ontnt o WO88/696 is erey bingincoportedby

Claims (6)

1. A device for joining plastic tubular parts of about the same diameter and minimising the size of a bead of material formed on an interior of the tubular parts during the joining, with corresponding ends of the tubular parts which are intended to be joined together having been recessed around an interior end edge thereof, the device comprising: a heating element for contacting with and for softening an end surface of at least one tubular part which is intended to abut a corresponding softened end surface of another tubular part, with said softened surfaces forming an abutting surface when joined together; wherein a circular or disk-shaped lug is provided on the heating element to define a contact surface, said lug including a heating ring and an alignment disk which are both made from metal and which hold a heat-resistant plastic ring therebetween, said plastic ring being sized set ti, and positioned to serve as part of the contact surface and 20 which is formed to correspond to the recessed part of the tend surface of said at least one tubular part

2. Device according to claim 1, wherein another part of the contact surface of said heating element which abuts said end surface of said at least one tubular part is 25 defined by the heating ring which is in the form of an rc annular or disk-shape.

3. Device according to claim 1 wherein said heating element includes two circular or disk-shaped lugs each lug being disposed on opposite sides of said heating element and wherein the heating ring of each of the lugs is in contact with said heating element and the respective alignment disk.

4. Device according to claim 1, wherein a molded part is placed in the area of said abutting surface of said C IAv k 4'r i 76 I 15 99t U trU LU U '9

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94. 9. tubular parts so as to be applied to the inside wall of said tubular parts. Device according to claim 4, wherein said molded part is a polypropylene plug. 5. Device according to claim i, wherein the end surface of said at least one tubular part may be softened and formed by the corresponding contact surface of said heating element to produce said undercut or recessed end surface. 7. Device according to claim i, wherein plastic ring in the area of the side facing away from abutting surface of tubular part is radially surrounded by a projection of the heating ring. 8. Device according to claim i, wherein, in the area of the plastic ring, the heating ring and alignment disk divide the lug in a plane parallel to its main plane. 9. Device according to claim i, wherein the plastic ring consists of polytetrafluoroethylene. 10. Device according to claim i, wherein heating ring and 20 alignment disk consist of aluminium or an aluminium alloy. 11. A device for joining together plastic tubular parts of about the same diameter and minimizing the size of a bead of material formed on the interior of said tubular parts during said joining, with corresponding ends of said 25 tubular parts which are intended to be joined together having been recessed, said device comprising: a) a heating element adapted to fit between said tubular parts; b) said heating element including two circular or 30 disk-shaped lugs, one of said lugs being disposed on each side of said heating element, each of the lugs including a heating ring and an alignment disk which are both made from metal and which hold a heat resistant plastic ring therebetween, said plastic ring being sized and positioned to serve as part of a contact surface of the lug and which, in use, 4 C: r I 16 comes into contact with the recessed end surface of the tubular part; c) the configuration of the contact surfaces of said lugs being adapted to mate with said recessed ends of said tubular parts, whereby the heating and softening of said tubular pieces by said heating element is maximized and whereby said recessed ends of said tubular parts are heated to a substantially equal degree and depth across the thickness of said tubular parts. 12. A device for joining tubular parts as hereinbefore described with reference to Figure 6. DATED this 4th day of October 1994 AGRU ALOIS GRUBER Ges.m.b.H j Patent Attorneys for the Applicant: F.B. RICE CO. a 4, i Abstract of the Disclosure Device for joining of tubular parts (10, 11) made from plastic, especially polyvinylidene fluoride, polypropylene or polyethylene, in which aligned parts (10, 11) exhibiting about the same diameter are pushed together and are welded on abutting surfaces (12, 13) by effect of heat. Abutting surfaces (12, 13) of tubular parts (10, 11) in the direction of the inside pipe space are undercut or recessed so that the edge formed by inside surface (15) of tubular part (10, 11) and the abutting surface springs back opposite the edge formed by outside surface (18) of tubular part (10, 11) and abutting surface (12, 13), and so that parts (10, 11) in the area of abutting surfaces (12, 13) in the axial direction essentially are softened equally deeply, then pushed together and, as a result, are welded together. Especially wherein the heating element (20) consists of a fixed disk and a neating ring (23) of metal with a PTFE-ring which may be additionally fixed. 4e 4 *I 0 I 49 45 4 4 4.• 4 4 4 r- -1