CH553368A - Pipe joint sleeve with integral heating wire - made from coaxial components with helically grooved surfaces - Google Patents

Abstract

Thermoplastic pipe welding sleeve made from two coaxial sleeves with an interface which defines a helical groove loaded with a resistance heating wire. The outer sleeve has wells via which electrical contacts may be made with the element. The heater is laid in close pitch turns near end of the sleeve but the linking turns run through a channel with an extended pitch and further from the inner surface of the coupling. Assembled by applying the heater windings to the inner sleeve, then dilating the sleeve on a mandrel to tension the windings before injction moulding the outer sleeve in situ. The position of the heating element is positively and reproducibly controlled. Installation of the wire under tension prevents subsequent loss of contact between the heater and the inner lining during the subsequent welding heat cycle. No direct electrical contact with the surface of the pipes or profiles to be joined, for operator safety under damp conditions.

Description

       

  
 



   The present invention relates to a sleeve made of thermoplastic plastic with a heating wire arranged in the sleeve wall, which can be electrically welded to produce connections to plastic pipes and fittings, as well as a method for producing the same.



   For the connection of pipes and fittings made of plastic, electrically heatable welding sleeves made of plastic are increasingly used today. The known welding sleeves, however, still have significant shortcomings.



   In a first known welding sleeve, in which the heating wire is wound onto a mandrel during manufacture, this mandrel is removed after the injection molding process of the sleeve body, so that the wire winding has to absorb the shrinkage to which the sleeve-shaped sleeve body is subject. The disadvantage here is that when the pipes to be connected are inserted into the welding socket, the pipe edge can strike a turn of the wire coil, so that this wire rises up due to the high shrinkage stress of the welding socket and thus becomes unusable.



   In a further known welding sleeve, the heating wire is covered with a material corresponding to or related to the sleeve material before being wound onto a mandrel. so that there is a firm connection with the sleeve material after the injection process. It is therefore not possible to set up the heating wire when inserting the pipes or fittings to be welded. The disadvantage of this welding sleeve, however, is that the injection pressure and the shrinkage of the material on the wire pressure are opposite, but the wire pressure runs in the opposite direction to the parts to be welded.

  The heating of the sleeve means that the heating wires move into the interior of the sleeve material, so that the welding point is even further away from the heating wire than is already the case during manufacture, and thus a perfect welding becomes even more difficult.



   The evasion of the heating wire into the sleeve material not only causes poorer welding because of the increasing distance to the welding point, but it also opens the welding sleeve because the plastic expands with increasing temperature. If a welding socket opens in this way, this leads to a faulty welding, if there is not only little play between the pipe or fitting to be connected and the socket at the welding point. The shrinkage property of the welding sleeve itself is low in this embodiment and is largely reduced by long storage.



   There is also a known welding method for connecting plastic pipes and fittings, in which a heating tape is placed between the parts to be welded and the welded joint is produced by heating it. There is a risk of short circuits with this procedure. because the winding is arranged bifilar.



   Furthermore, a welding sleeve is known in which the heating wire is subsequently embedded in a groove arranged on the inside of the sleeve-shaped sleeve. The sleeve-shaped sleeve is expanded while it is still warm and then cooled so that it has a certain shrinkage capacity when it is reheated. This welding socket is life-threatening in wet weather because of the bare inner wires and the high electrical welding voltage, around 220 V.



   A major deficiency of the known designs and methods is that the manufacture of the welding socket is expensive. because the production can only be partially automated.



   The present invention is based on the object of designing a welding sleeve of the type mentioned in such a way that it does not have the deficiencies mentioned in the known designs, but rather ensures reliable welding of the parts to be connected without minimal tolerances and is also produced in a fast, automatic production process can. This object is achieved by an inner sleeve part, on the outer circumference of which a heating wire is wound in turns, and by an outer sleeve part that covers the turns of the heating wire.



   The method for producing the socket according to the invention is characterized in that the inner socket part is first produced, then the outside of the inner socket part is wound with the heating wire and the outer socket part is then applied over the inner socket part.



   The invention is described below with reference to an embodiment shown in the accompanying drawing. It shows:
Fig. 1 is an axial section through a plastic sleeve provided with a heating wire for the formation of connec tions on plastic pipes and fittings, Fig. 2 is an axial section through an inner sleeve part with two expanding mandrels, in apart
Presentation,
3a shows an axial section of the expanding mandrel and
3b shows a plan view of the outer ring of the expanding mandrel.



   The welding socket shown in FIG. 1 has an inner socket part 7 which has two groove parts located on its outside, in the grooves 1 of which a heating wire 4 is laid. The heating wire 4, which expediently consists of one piece, is provided at both ends with an electrical connection 5 which can be connected in various ways, e.g. can be designed as a plug pin with a holder 2.



   It is desirable that the heating wire 4 is arranged in the groove parts as close as possible to the inside of the inner sleeve part 7. Between the two groove parts lies a middle part 7a of the inner sleeve part 7, over which a piece 4a of the heating wire 4 runs in the vicinity of the outside of the inner sleeve part 7.



   The inner socket part 7 is expediently injected in the form shown in FIG. The heating wire is wrapped at the prescribed spacing given by the spacing of the grooves 4, so that there is no risk of the heating wire having a coil short at any point.



   An outer socket part 8 is located around the inner socket part 7.



  which is also expediently sprayed on and has the corresponding recesses for the electrical plug connections. In Fig. 1, an annular collar 9 is also arranged around this.



   Above the heating wire 4 located in the middle part 7a of the inner socket part 7, the wall thickness of the outer socket part 7a is weakened, for example by a recess 11. In the recess 11, a temperature indicator, for example a Tbermochrome point, is arranged, which enables an exact temperature measurement on the outside of the outer one Socket part 7a allows, so that an assessment is possible as to whether the socket has reached the temperature necessary to achieve a perfect weld.



   On the inside of the inner sleeve part 7 there is a stop 3, which is expediently injected with the injection molding of the inner sleeve part 7, but has a weak point so that it can be easily removed if necessary. The stop 3 serves to limit the insertion depth and can also consist of two or more segments distributed around the circumference.



   To produce the sleeve shown in FIG. 1, the inner sleeve part 7 is injected in a first operation, onto which the electrical heating wire 4 is then subsequently wound. After completion, the inner sleeve part 7 is expediently expanded by means of the expanding mandrel 6 shown in FIGS. 2, 3, whereby the heating wire 4 receives an additional tensile stress. The expanding mandrel 6 consists of an outer ring 10 formed from ring segments and a conically shaped inner mandrel 6a. Expediently, two of the expanding mandrels 6 described are used for expanding the inner socket part 7 (FIG. 2).



   The inner sleeve part 7 pretensioned in this way is surrounded by the outer sleeve part 8 in an injection mold.



  The sleeve produced in this way has a high shrinkage capacity and holds the heating wire 4 close to the inside of the welding sleeve, so that good heat transfer to the plastic pipe or shaped piece to be welded is guaranteed. Due to the temperature indicator attached to the outside, any incorrect welding is practically impossible.



   PATENT CLAIM 1
Sleeve made of thermoplastic material with a heating wire arranged in the sleeve wall, which can be electrically welded to produce connections to plastic pipes and fittings, characterized by an inner sleeve part (7), on the outer circumference of which a heating wire (4) is wound in turns , and by an outer sleeve part (8) covering the turns of the heating wire.



   SUBCLAIMS
1. Sleeve according to claim I, characterized in that the turns of the heating wire (4) are laid in the grooves (1) of the inner sleeve part (7).



   2. Sleeve according to claim I and dependent claim 1, characterized in that the grooves (1) of the inner socket part (7) are divided into two groove parts and separated by a central part (7a), within which the near the outer wall of the inner socket part (7) arranged heating wire connects the two groove sections.



   3. Sleeve according to dependent claim 2, characterized in that a temperature indicator is arranged above the heating wire (4a) on the outside of the outer sleeve part (8).



   4. Sleeve according to claim I, characterized in that on the outer edge of the groove parts in the inner sleeve part (7) mounted electrical connection, for. B. a contact pin (5) is arranged.



   5. Sleeve according to claim I, characterized in that a stop (3) with a weak point is arranged on the inner wall of the inner sleeve part (7).



   PATENT CLAIM II
Method for producing the sleeve according to claim 1, characterized in that first the inner sleeve part (7) is produced, then the outside of the inner sleeve part (7) is wound with the heating wire (4) and then the outer sleeve part (8) over the inner sleeve part (7) is applied.



   SUBCLAIMS
6. The method according to claim II, characterized in that the heating wire (4) is wound at a distance determined by grooves (5) on the outside of the inner sleeve part (7).



   7. The method according to claim II, characterized in that before the outer sleeve part (8) is applied, the inner sleeve part (7) is widened, e.g. by means of an expanding mandrel (6) with a segmented outer ring (10) and a conical inner mandrel (6a).

** WARNING ** End of DESC field could overlap beginning of CLMS **.



   


    

Claims (1)

** WARNING ** Beginning of CLMS field could overlap end of DESC **. which then subsequently the electrical heating wire 4 is wound. After completion, the inner sleeve part 7 is expediently expanded by means of the expanding mandrel 6 shown in FIGS. 2, 3, whereby the heating wire 4 receives an additional tensile stress. The expanding mandrel 6 consists of an outer ring 10 formed from ring segments and a conically shaped inner mandrel 6a. Expediently, two of the expanding mandrels 6 described are used for expanding the inner socket part 7 (FIG. 2). The inner sleeve part 7 pretensioned in this way is surrounded by the outer sleeve part 8 in an injection mold. The sleeve produced in this way has a high shrinkage capacity and holds the heating wire 4 close to the inside of the welding sleeve, so that good heat transfer to the plastic pipe or shaped piece to be welded is guaranteed. Due to the temperature indicator attached to the outside, any incorrect welding is practically impossible. PATENT CLAIM 1 Sleeve made of thermoplastic material with a heating wire arranged in the sleeve wall, which can be electrically welded to produce connections to plastic pipes and fittings, characterized by an inner sleeve part (7), on the outer circumference of which a heating wire (4) is wound in turns , and by an outer sleeve part (8) covering the turns of the heating wire. SUBCLAIMS 1. Sleeve according to claim I, characterized in that the turns of the heating wire (4) are laid in the grooves (1) of the inner sleeve part (7). 2. Sleeve according to claim I and dependent claim 1, characterized in that the grooves (1) of the inner socket part (7) are divided into two groove parts and separated by a central part (7a), within which the near the outer wall of the inner socket part (7) arranged heating wire connects the two groove sections. 3. Sleeve according to dependent claim 2, characterized in that a temperature indicator is arranged above the heating wire (4a) on the outside of the outer sleeve part (8). 4. Sleeve according to claim I, characterized in that on the outer edge of the groove parts in the inner sleeve part (7) mounted electrical connection, for. B. a contact pin (5) is arranged. 5. Sleeve according to claim I, characterized in that a stop (3) with a weak point is arranged on the inner wall of the inner sleeve part (7). PATENT CLAIM II Method for producing the sleeve according to claim 1, characterized in that first the inner sleeve part (7) is produced, then the outside of the inner sleeve part (7) is wound with the heating wire (4) and then the outer sleeve part (8) over the inner sleeve part (7) is applied. SUBCLAIMS 6. The method according to claim II, characterized in that the heating wire (4) is wound at a distance determined by grooves (5) on the outside of the inner sleeve part (7). 7. The method according to claim II, characterized in that before the outer sleeve part (8) is applied, the inner sleeve part (7) is widened, e.g. by means of an expanding mandrel (6) with a segmented outer ring (10) and a conical inner mandrel (6a).