SLEEVE-SHAPED WELD CONNECTING PIECE OF THERMOPLASTIC MATERIAL WITH WELD INDICATOR ELEMENT, AND WELDED JOINT FORMED THEREWITH

Abstract: A sleeve shaped weld connecting piece (1) of thermoplastic material for connecting thermoplastic pipes (2) by means of a weld connection. The connecting piece comprises a heating element (4) embedded near the inside wall (3) and bearing connecting parts (9, 9a) accommodated in chambers (10, 10a). A pin shaped weld indicator element (7, 7') extending to the region of the heating element (4) is disposed in a bore (5) in the wall (6) of said connecting piece. The indicator element is provided with additional means (15, 18, 19, 20, 21, 27 and 27') enhancing the visibility of a welding action through heating element (4) at the outer side of the connecting piece, said additional means being activated by heat generated during welding. The pin shaped element (7) may consist of a metal pin (7) extending from the vicinity of the heating element (4) to the vicinity of the outer wall of the connecting piece, said pin shaped element (7) bearing at the upper side a sticker (27, 27') of colour changeable material, changing its colour under influence of heat generated during welding.

Description: Sleeve-shaped weld connecting piece of thermoplastic material with weld indicator element, and welded joint formed therewith. The invention relates to a sleeve-shaped weld connecting piece of thermoplastic material for connecting thermoplastic pipes comprising a heating element embedded near the inside wall, and also a pin- shaped weld indicator element which is disposed in a bore in the wall and retained therein. Such a sleeve-shaped weld connecting piece provided with a pin-shaped weld indicator element by means of which it can be seen from the outside whether a welding operation has actually produced a weld is known. In this known sleeve-shaped weld connecting piece the weld indicator element comprises a pin which is retained in a bore and has a flange-shaped element at its bottom side. During the production of the weld plastic softens around the bottom of the bore, so that as a result of shrinkage of the sleeve and thermal expansion of the material in the welding zone plastic is pressed into the bore and the flange with pin is moved upwards. This known sleeve-shaped weld connecting piece has the disadvantage that only an extremely small difference in size between the internal dimensions of the weld connecting piece and the external dimensions of the pipe is permitted, since with greater play between weld connecting piece and pipe the gap between the two parts is not always closed by shrinkage of the weld connecting piece, and one cannot therefore be sure of the required pressure build-up for moving the pin, while welding still takes place. In the case of weld connecting pieces with wide tolerances required in practice, this known weld indicator element therefore often does not meet the requirements set. On the other hand it is known to provide the outer wall of a weld connecting piece with a colour changeable indicator element in the form of a sticker showing a colour change at a certain temperature and the resulting colour remains after cooling. However, this known colour changeable indicator element presents the disadvantage that due to the rather great wall thickness of the connecting piece a long time is required before the small temperature increase generated during welding reaches the colour changeable indicator element. Furthermore due to the low heat conductibility of the wall of the connecting piece it is necessary to use a colour changeable element showing a colour change at rather low temperature. Often this low temperature is reached during storage and transport of the connecting piece so that the colour of the colour changeable element already changes before its use and becomes unusable. The object of the invention is now to provide a weld connecting piece of the type mentioned at the beginning with which, even where there is greater play between weld connecting piece and pipe to be connected thereto, or where there is a great wall thickness between the actual welding site and the outer side of the connecting piece a faultless indication is given by the weld indicator element when the weld is produced. This object is achieved according to the invention in that the weld indicator element is provided with additional means enhancing the visibility of the welding action at the outer side of the connecting piece and said additional means being activatable by heat generated during welding. Very preferably the weld indicator element is provided with additional means in the form of pressure means which subject the weld indicator element to an outward-directed pressure at least during welding together of the weld connecting piece and the pipe part, so that the weld indicator element is thereby pressed out. It will be clear that, as a result of the presence of the above-mentioned pressure means, the movement of the weld indicator element is no longer dependent on a build-up of pressure in the welding zone, but is purely dependent on the heat supply which occurs during the formation of the weld and, for example, softens the part of the weld connecting piece which ensures that the weld indicator element is retained, so that the weld indicator element is no longer retained and the pressure means can press the weld indicator element out. The pressure means particularly advantageously subject the weld indicator element constantly to an outward-directed pressure force. With the presence of such pressure means the weld indicator element is subjected constantly to an outward-directed pressure force, so that immediately after softening of the bottom part of the bore the weld indicator element is no longer retained and is pressed out by the pressure means. It is particularly advantageous for the pressure means to contain a spring means placed in a bore part, said spring means interacting with a projecting part of the weld indicator element, in particular a flange provided on the top side of the weld indicator element. Through the presence of the preferably metal compression spring, the weld connecting piece is constantly subjected to an outward-directed pressure force, but through the retention of the weld indicator element in the bore, it cannot move outwards. However, as soon as the weld indicator element is no longer retained, due to the softening of the plastic mass, the element will be pressed out immediately in order to indicate that a welding operation has taken place. According to another embodiment, the pressure means expediently comprise a coil spring which is integral with the weld indicator element and is connected to the top side of the weld indicator element. In this embodiment the coil spring can be made of the same material as the weld indicator element, for example plastic, since the coil spring lies a great distance away from the heated part of the weld connecting piece. The pressure means can expediently comprise a leaf spring, in which case one can use a pin carrying at its top side a curved plate which is pressed flat when the pin is placed in the bore and is held like this by the pin until during welding the retaining means for the pin can no longer make up for the tension in the deformed plate. This design has the advantage that the weld indicator element can be formed in one operation. According to an entirely different embodiment, the weld indicator element expediently has a container which is open at the top side and contains an expandable solid medium. During carrying out of the welding operation heat is produced and swells up the expandable medium, and therefore a part of the compound in the container is pressed outwards as an indicator showing that the welding operation has taken place. It is particularly advantageous for the expandable medium to be a foa able medium, more particularly a foamable plastic compound. The container for the expandable medium is expediently a metal container. The pin-shaped weld indicator element is advantageously made of a plastic, more particularly of polyoxymethylene. With the use of such a material for the weld indicator element, it can immediately be made integral with a leaf spring or with a coil spring. In another advantageous embodiment the weld indicator element is a well heat conducting element extending to the vicinity of the heating element and engages a colour changeable element changing its colour at elevated temperature. By using a well heat conducting weld indicator the heat generated during welding is rapidly conveyed to the colour changeable element and reaches rapidly a temperature near the temperature in the welding zone. As this temperature in the welding zone is substantially higher than the temperature as reached during storage and/or transport, it is possible to use a colour which will not change at temperatures occurring during transport and/or storage. Appropriately the well heat conducting metal element is broadened at its upper and/or lower side so that the colour changeable element is subjected to the temperature in the welding zone as strong as possible. In a preferred embodiment the weld indicator element comprises a metal pin engaging a colour changeable element at its upper side. In this manner an optimal quantity of heat is supplied to the colour changeable element. The sleeve-shaped weld connecting piece of thermoplastic material is advantageously a polyolefin, for example polyethylene or polypropylene, while the thermoplastic pipes to be welded thereto are also made of a polyolefin. The sleeve-shaped weld connecting piece is in particular suitable for the production of pipelines for carrying gas, but the invention is not limited to this. The invention also relates to a welded joint of a sleeve-shaped weld connecting piece with at least one pipe accommodated therein and connected thereto by welding, which is characterized in that a sleeve- shaped weld connecting piece according to the invention is used. The invention will now be illustrated with reference to embodiments of the invention shown in the drawing, in which: Fig. 1 shows a longitudinal section of a first embodiment of a sleeve-shaped weld connecting piece according to the invention; Fig. la shows a cross-section of a variant of a weld connecting piece according to Fig. 1; Fig. lb shows the same cross-section as that in Fig. la, but after the welded joint has been produced; Fig. 2 shows a view of a variant of a sleeve-shaped weld connecting piece according to the invention; Fig. 2a shows the same view as that of Fig. 2 after the welded joint has been produced; Fig. 3 shows a longitudinal section of yet another embodiment of a sleeve-shaped weld connecting piece according to the invention; Fig. 3a shows the same cross-section as that in Fig. 3, but after the welded joint has been provided; Fig. 4 shows a part of another sleeve-shaped weld connecting piece according to the invention with a foamable medium in a container; Fig. 4a shows the same longitudinal section as that in Fig. 4 after a welded joint has been formed. Fig. 5 shows a longitudinal section of still another weld connecting piece of the invention with a colour change element and Fig. 6 a detail of a variant of a weld connecting piece according to Fig. 5. Fig. 1 shows a longitudinal section of a polypropylene welding sleeve 1 for connecting polypropylene pipes 2 by means of a welded joint. Embedded near the inside wall 3 of the welding sleeve 1 is a metal heating element 4 which at its ends bears connecting parts 9, 9a accommodated in connecting chambers 10 and 10a. The welding sleeve 1 also has two bores 5 in the wall 6 which extend with their bottom 8 to near the heating element 4. The bottom 8 contains a recess 11 in which is clamped a narrowed part 22 of a weld indicator element in the form of a polyoxymethylene pin 7 which at its top side bears a flange 13 formed of polyoxymethylene material. The flange 13 is accommodated in a circular bore part 5' in the outside wall of the welding sleeve. A compressed spring 15, which is supported at one side by a bottom 14 of bore part 5' and at the other side interacts with the flange 13 of the pin 7, exerts a constant outward-directed pressure force on the pin 7 of the weld indicator element. Through the clamping of the narrowed part 22 of the polyoxymethylene pin 7 in the recess 11 of the polypropylene welding sleeve, the pin 7 cannot, however, move outwards. Such a clamping is ensured by the fact that the polyoxymethylene material of the pin 7 has a greater modulus of elasticity than the polypropylene of the welding sleeve. The bore 5 has near its top side a circular boundary edge 17, while the pin can bear near its bottom side a circular collar 18' which has greater dimensions than the edge 17. The opening formed by the circular edge 17 is greater than the dimension of the pin 7, so that the latter can pass the edge 17 during the outward movement. Advantageously, in a variant such as that shown in Fig. la and Fig. lb, in order to ensure a particularly good fixing of the pin 7 in the bore 5, the latter can also bear near its bottom 8 a circular recess 12 into which a projecting rib 16 of the pin 7 snaps. Once the welded connection has been produced, the plastic begins to melt in the region of the circular recess 11, with the result that the pin 7 is no longer retained in the circular recess 12, and therefore through the compression being removed the spring 15 presses the pin 7 upwards. Through a circular boundary edge or projections 17, the outward movement of the pin 7 is now also limited, since the collar 18' hits the edge 17 and stops the outward movement of the pin. Any plastic which might flow, through a build-up of pressure, into the bore 5 after the outward movement of the pin 7 cannot flow out, since the edge 17 and collar 18 shut off the bore 5 at the top side. A suitable tension of the spring 15 lies at approximately 15 to 30 N. Such a design has the great advantage that the weld indicator element is easy to manufacture, very reliable, and creep-resistant, while damage does not affect the reliability, and the weld indicator element does not depend on the welding pressure. Fig. 2 shows another embodiment in which the weld indicator element again comprises a pin 7 of polyoxymethylene material retained in a bore 5. This pin 7 is integral with a coiled strip 23, also made of polyoxymethylene material. This coiled strip, which is connected at a point 24a to an outer closed circular strip 24, forms a coil spring 18 which is retained in a bore 5. The circle is fixed by a circular collar 26 in a widened part 25 of bore part 5'. In Fig. 2a it can be seen how the coil spring 18 has developed after the welded joint has been produced and the pin 7 is therefore pressed out. As can be seen, the helical, line decreases upwards, so that the strip 23 can be deformed to the flat coil shown in Fig. 2. The strip 23 is connected at 26 to the polyoxymethylene pin 7. This weld indicator element is also simple to manufacture and easy to install, and damage does not have any influence on the reliability of the element. Fixing coil spring 18 in bore part 5' in the outside wall of the welding sleeve means that the indicator can be prevented from being pressed fully out of the recess or bore 5. Fig. 3 shows another embodiment, comprising a pin 7 having a leaf spring 19 integral therewith. The leaf spring 19 in its original state has a curved shape. After positioning the pin 7 in the bore 5, the leaf spring 19 is, however, pressed flat, so that it adapts to the shape of the outside wall of the welding sleeve and is accommodated in bore part 5'. After a weld has been produced, softening of the plastic near the bottom of the bore 5 allows the pin 7 to move upwards, as a result of which the leaf spring 19 assumes its original curved position. The bore 5 is here again provided with a boundary edge 17, so that the pin 7 cannot move all the way out, and therefore during welding any molten or fluid polyethylene cannot run out though the bore 5. This weld indicator element 7, 19 is also easy to manufacture and has the advantage that it is in one piece, while the reliability of the indicator is not affected by damage . Finally, Fig. 4 shows another embodiment, in which the weld indicator element comprises a metal box 21 filled with non-expanded polystyrene foam 20. During welding the temperature increases, causing heat to spread through the metal box 21 over the non-expanded polystyrene foam compound. At a particular temperature the polystyrene then expands, so that the material will move out of the box and forms indicator element 7'. The container or the metal box 21 is anchored in the wall of the weld connecting piece in order to prevent plastic flowing through this bore 5 during welding from running out. Such a weld indicator element has the great advantage of small dimensions. Instead of the embodiments shown, it is also possible to choose a weld indicator element made from two boxes which are bonded together, for example by polyethylene, and which contain a compression spring. Through the heat of a weld, the adhesive join is then broken, and one of the boxes is pressed out. Another possibility is to support the pin 7 by a liquid placed in a deformable container and expandable under the influence of welding heat, so that during welding the pin is pressed out through deformation of said container. Fig. 5 shows another embodiment of the invention. The bores 5 contain a metal pin 7 supporting at its upper side a sticker 27 of colour changeable material, which changes its colour at elevated temperatures, such as temperatures near the welding temperature generated by heating element 4. In order to obtain an excellent heat absorbing capacity the pin 7 may be provided with a broadened foot 9a. Advantageously the bore 8 is provided with an enlarged chamber 11 near the welding sleeve outer wall. The chamber 11 accommodates a head 12 of pin 9 bearing an enlarged sticker 10' of colour changeable material (vide fig. 6) .

Claims: C L I M S 1. Sleeve-shaped weld connecting piece (1) of thermoplastic material for connecting thermoplastic pipes (2) comprising a heating element (4) embedded near the inside wall (3) , and also a pin-shaped weld indicator element (7, 7*) which is disposed in a bore (5) in the wall (6) and retained therein, characterized in that the weld indicator element (7, 7') is provided with additional means (15; 18, 19, 20, 21; 27 and 27') enhancing the visibility of the welding action at the outer side of the connecting piece and said additional means being activatable by heat generated during welding. 2. Sleeve-shaped weld connecting piece according to Claim 1, characterized in that the weld indicator element (7) is provided with additional means in the form of pressure means (15; 18, 19, 20, 21) which subject the weld indicator element (7) to an outward- directed pressure at least during welding together of the weld connecting piece and the pipe part, so that the weld indicator element is thereby pressed out. 3. Sheeve-shaped weld connecting piece according to Claim 2, characterized in that the pressure means (15, 19) subject the weld indicator element (7) constantly to an outward-directed pressure force. 4. Sleeve-shaped weld connecting piece according to Claim 2 or 3, characterized in that the pressure means contain a spring means (15) placed in a bore part (5'), said spring means interacting with a projecting part of the weld indicator element (7) . 5. Sleeve-shaped weld connecting piece according to Claim 3, characterized in that the projecting part comprises a flange (13) provided on the top side of the weld indicator element. 6. Sleeve-shaped weld connecting piece according to Claim 2, characterized in that the pressure means comprise a coil spring (18) which is connected to the weld indicator element, which spring is connected to the top side of the weld indicator element (7) . 7. Sleeve-shaped weld connecting piece according to Claim 2 or 3, characterized in that the pressure means comprise a leaf spring (19) connected to the top side of the weld formation indicator element (7) . 8. Sleeve-shaped weld connecting piece according to Claim 1, characterized in that the additional means (20, 21) comprise a container (21) which is open at the top side and contains a medium which is expandable under the influence of heat. 9. Sleeve-shaped weld connecting piece according to Claim 8, characterized in that the expandable medium is foamable. 10. Sleeve-shaped weld connecting piece according to Claim 8 or 9, characterized in that the expandable medium is a foamable plastic composition. 11. Sleeve shaped weld connecting piece according to Claim 1, characterized in that, the weld indicator element (7) is a well heat conducting element extending to the vicinity of the heating element (4) and engages a colour changeable element (27, 27') changing its colour at elevated temperature. 12. Sleeve-shaped weld connecting piece according to Claim 10, characterized in that the well heat conducting element (7) is broadened at its upper and/or lower side. 13. Welded joint of a sleeve-shaped weld connecting piece with at least one pipe accommodated therein and connected thereto by welding, characterized in that a sleeve-shaped weld connecting piece according to one or more of the preceding claims is used.

Inventors: LODDER BERNHARD, REGELING HENK JAN, VAN DIJK BEREND JAN, VAN HOUTEN JAN ANNE, LODDER, BERNHARD, REGELING, HENK, JAN, VAN DIJK, BEREND, JAN, VAN HOUTEN, JAN, ANNE
Applicants: WAVIN BV, WAVIN B.V.
Application year: 1990
Main classification: F16L47
IPC codes: B29C65, F16L47, G01K3