| JP04203586 | PIPE COUPLING HOLDER |
| JP09070894 | ELECTRIC FUSING AND WELDING APPARATUS |
| JP2539747 | ELECTRIC MELT WELDING APPARATUS OF RESIN PRODUCT |
ABRAHAMSSON, Johan (Thor Modéens gata 4K, Kungsör, S-736 32, SE)
ANDERSSON, Thomas (Skottvägen 6, Kungsör, S-736 32, SE)
ABRAHAMSSON, Johan (Thor Modéens gata 4K, Kungsör, S-736 32, SE)
| Claims 1. Device for joining together, by means of electrically generated fusion, at least two plastic pipes (2, 3) which are insertable into the device, which device comprises - a welding sleeve (1) containing a fusible material and an electrical conductor having connecting members (6a, 6b) for connecting the conductor to a power source ( 7 ) , characterized by - an indicating device (9), which is insertable into the welding sleeve (1) and comprises a member which is elastically deformable in the axial direction of the welding sleeve, the said member having at least one magnet (10a), which is axially displaceable in the welding sleeve, and - a sensing device (11), which is disposed outside the welding sleeve (1) and is arranged to detect a change in the magnetic field generated by the magnet (10a). 2. Device according to Claim 1, in which the elastically deformable member comprises a generally helicoidal member having ends which overlap in the circumferential direction. 3. Device according to Claim 2, comprising two magnets (10a, 10b), which are disposed, in mutually repelling arrangement, on a respective end of the generally helicoidal member. 4. Device according to any one of Claims 1-3, in which the sensing device (11) comprises at least one Hall element or at least one reed element. 5. Device according to any one of Claims 1-4, comprising a power source (7) connectable to the connecting members (6a, 6b) of the welding sleeve (1), the sensing device (11) being connected to the power source (7) and arranged to allow the power source to supply current to the connecting members (6a, 6b) of the welding sleeve only when the sensing device (11) detects a state of the indicating device (9) corresponding to the fully inserted position of the plastic pipes (2, 3) in the welding sleeve (1). 6. Device according to any one of the preceding claims, in which the indicating device (9) and the welding sleeve (1) are configured with interacting engagement members along a portion of the indicating device (9) and along a corresponding portion of the welding sleeve (1) in order to prevent rotation of the indicating device (9) inside the welding sleeve (1). 7. Device according to Claim 6, in which the said engagement members are constituted by a stepped portion of the indicating device ( 9 ) and corresponding grooves in a corresponding portion of the welding sleeve (1). 8. Method for joining together at least two plastic pipes (2, 3) by means of a welding sleeve (1) having a corresponding number of openings, which welding sleeve comprises a fusible material and an electrical conductor having connecting members (6a, 6b), which method involves - introducing the plastic pipes (2, 3) into a respective opening in the welding sleeve (1) and - connecting an electrical power source (7) to the connecting members (6a, 6b) in order, by resistive heating of the conductor, to fuse the fusible material to the plastic pipes (2, 3), characterized by - the generation of a magnetic field by means of an indicating device (9), comprising at least one magnet (10a), which is inserted in the welding sleeve (1), - the influencing of the indicating device (9), through the displacement of those ends of the plastic pipes (2, 3) which are inserted in the welding sleeve (1), so as to change the state of the magnetic field, and - the detection of the change in the state of the magnetic field by means of a sensing device (11) disposed outside the welding sleeve (1). 9. Method according to Claim 8, involving the detection, by means of the sensing device (11), of axial displacement of or change in the magnetic field generated by the at least one magnet (10a) • 10. Method according to Claim 9, in which the detection of the axial displacement of or change in the magnetic field is achieved by means of at least one Hall element or reed element belonging to the sensing device (11). 11. Method according to any one of Claims 8-10, involving the supply of current to the connecting members (6a, 6b) of the welding sleeve, by means of the power source (7), in order to produce the resistive heating only when the sensing device (11) detects a state of the indicating device (9) corresponding to the fully inserted position of the plastic pipes (2, 3) in the welding sleeve (1). 12. Method according to any one of Claims 8-10, involving interruption of the resistive heating of the welding sleeve (1) when the sensing device (11) detects a change in the state of the indicating device (9), which change corresponds to a non-fully inserted position of the plastic pipes (2, 3) in the welding sleeve (1). |
Field and background of the invention The invention relates to a device which is configured to join together, by means of electrically generated fusion, at least two plastic pipes. The device comprises a welding sleeve, which can be constituted, for example, by a jointing sleeve for joining together two or more plastic pipes. The invention also relates to a method for joining together at least two plastic pipes.
Welding sleeves are used, for example, to join together plastic pipes for the conveyance of petrol and other fuels in petrol stations. A simple type of welding sleeve for straight joining together or jointing of two plastic pipes usually comprises a substantially cylindrical casing having a continuous axial opening. The casing comprises an outer, dimensionally stable layer and an inner layer of a fusible material. An electrical conductor is wound in the shape of a coil in or around the inner layer. The conductor has at both its ends a pin or the like for the connection of an external power source. The pin is disposed on the outer side of the casing for simple connection of the power source.
In the joining together of two plastic pipes, one end each of the same is threaded into a respective end of the casing, such that a part of each pipe end is placed radially inside the casing. After this, the power source is connected to the conductor. Due to the resistance which arises in the conductor, the inner fusible material is heated, whereupon this material melts and is joined together with the peripheral surface of the respective plastic pipe. After a certain time, the power source is disconnected, whereupon the material recools. In this way, a leak-tight joint is produced between the two pipes, which joint is constituted by the material fused together with the peripheral surface of the pipes and that portion of the casing which is present between the molten material. The welding sleeve itself thus forms part of the produced joint and therefore remains seated between the pipes during use of the same following the conclusion of the joining operation.
WO99/46532 describes a similar type of welding sleeve with which double-walled pipes can be joined together.
The above-described and other previous known welding sleeves entail problems, however. In order to ensure a perfect joint, it is very important that the two pipe ends are fully inserted in the welding sleeve throughout the welding process. The operator therefore usually makes markings on the outer side of both pipes and checks throughout the welding process that these markings do not shift in relation to the welding sleeve. This procedure is relatively complicated and calls for precise monitoring. Despite such monitoring of markings on the pipes during the welding operation, it can happen that the pipes are not held fully inserted in the welding sleeve throughout the welding operation. This gives rise to a defective joint, which can cause serious failures during use of the pipes.
Summary of the invention
One object of the invention is therefore to provide an improved device for joining together at least two plastic pipes by means of electrically generated fusion.
Another object is to provide a device of this kind with which the above-described problems and risks can be reduced. A further object is to provide a device of this kind which is relatively cheap and simple to produce.
Yet another object is to provide a device of this kind which is simple and safe to use.
These and other objects are achieved with a device of the type defined in the introduction to Patent Claim 1 and having the distinctive features defined in the characterizing parts of the claim.
The device is designed to join together, by means of electrically generated fusion, at least two plastic pipes which are insertable into the device. The device comprises a welding sleeve containing a fusible material and an electrical conductor having connecting members for connecting the conductor to a power source. According to the invention, the device comprises an indicating device, which is insertable into the welding sleeve and comprises a member which is elastically deformable in the axial direction of the welding sleeve, the said member having at least one magnet, which is axially displaceable in the welding sleeve, and a sensing device, which is disposed outside the welding sleeve and is arranged to detect a change in the magnetic field generated by the magnet.
In detail, the indicating device comprises a magnet which is arranged to be axially displaced in the welding sleeve as the plastic pipes are inserted. The sensing device is in this case designed to detect axial displacement of the magnetic field generated by the magnet of the indicating device .
With the device according to the invention, it is thus possible to automatically and contactlessly monitor the axial position of the respective end of the plastic pipes in the welding sleeve, from the outside of the welding sleeve, throughout the welding process. In this way, it is easily- possible to reduce the incidence of a defective joint. As a result of the invention, such monitoring can take place wholly without the operator needing to make any markings or needing to take other measures than to insert the plastic pipes into the welding sleeve.
The axially elastically deformable member comprises a generally helicoidal member having ends which overlap in the circumferential direction.
Such an indicating device helps to produce a simple, cost- effective and yet very functionally reliable indication of the correct positions of the plastic pipes.
For additionally increased reliability, the indicating device, according to one embodiment of the invention, can comprise two magnets, which are disposed at one end each of a, in the axial direction, helicoidal member, which ends are overlapping in the circumferential direction and are arranged close together. The two magnets are arranged such that one repels the other one. When the magnets are forced together, the magnetic field is strengthened and the sensing device can detect this. If the two magnets come into contact with each other, the magnetic field is extinguished. The sensing device can likewise detect this.
This embodiment has many advantages compared with an embodiment of the indicating device having only one magnet.
In practice, the detection of an axial displacement of just one magnet works in the same way as in the detection of the strengthening of the magnetic field when two repelling magnets are pressed together. A magnet typically has a north end and a south end. The magnetic field is strongest precisely at the respective pole, so as then to be weakened the farther away you come from the respective pole. The sensing device is typically disposed radially outside the indicating member on the magnet or magnets. The sensing device is configured to sense the magnetic field in a position corresponding to the fully inserted positions of the plastic pipes, which means that the magnet or magnets are in precisely this position. In the single-magnet embodiment, the magnetic field will be strengthened precisely in the position corresponding to the fully inserted positions of the plastic pipes, since this means that the north and south poles of the magnet are in precisely this position. The difference between the single- magnet embodiment and that having two repelling magnets is that the strengthening is greater with two repelling magnets than with one magnet, if a fully inserted position of the plastic pipes means that they are very close together without coming into contact with each other. If a fully inserted position of the plastic pipes means that the two repelling magnets come into contact with each other, the magnetic field will be extinguished when the plastic pipes are in a fully inserted position. This means that the sensing device must be more sensitive in the single-magnet embodiment compared with the embodiment having two repelling magnets. The sensing device is cheaper and simpler, and also more reliable in its indication that the plastic pipes are fully inserted in the welding sleeve, in the dual-magnet embodiment.
The means of the sensing device for detecting displacement of/change in the magnetic field can expediently comprise at least one Hall element or at least one reed element.
In this way, a wholly contact-free and functionally reliable detection of the position of the plastic pipe in the welding sleeve is enabled in a cost-saving manner .
The device expediently comprises a power source connectable to the connecting members of the welding sleeve. The sensing device is in this case expediently connected to the power source and arranged to allow the power source to supply current to the connecting members of the welding sleeve only when the sensing device detects a state of the indicating device corresponding to the fully inserted position of the plastic pipes in the welding sleeve. In this way, the device automatically ensures that the welding process proceeds only once the plastic pipes have assumed and are maintaining the correct position in the welding sleeve.
The indicating device and the welding sleeve are expediently- configured with interacting engagement members along a portion of the indicating device and along a corresponding portion of the welding sleeve in order to prevent rotation of the indicating device inside the welding sleeve.
It is important that the magnet or magnets are situated in a predetermined position inside the welding sleeve in order for the sensing device to be able to function optimally and be able correctly to detect an axial displacement of the magnet or magnets, with an accompanying change in the magnetic field.
The engagement members are expediently constituted by a stepped portion of the indicating device and corresponding grooves in a corresponding portion of the welding sleeve.
One object of the invention is also to provide an improved method for use in joining together at least two plastic pipes. This and other objects are met with the method defined in the independent Claim 8. The method according to the invention has corresponding characteristics and advantages to the above- described device according to the invention.
Further objects and advantages of the device and method according to the invention emerge from the following detailed description of illustrative embodiments and of the patent claims.
Brief description of the figures.
An illustrative description of embodiments of the invention is given below with reference to the figures, of which:
Figs. Ia and Ib are schematic plan views, partially in cross section, of a device according to the invention, and show the device before and after the insertion of two plastic pipes into the welding sleeve of the device.
Fig. 2 is a perspective view of an indicating device belonging to the device shown in Figs. Ia and Ib.
Fig. 3 is a perspective view of an alternative embodiment of the indicating device.
Detailed description of illustrative embodiments
The illustrative device according to the invention which is shown in Figs. Ia and Ib comprises a welding sleeve 1 for straight jointing of two mutually aligned plastic pipes 2, 3. The welding sleeve 1 comprises an outer casing 4 made of a relatively dimensionally stable material, such as a plastics material. An inner casing 5 made of a fusible plastics material is concentrically accommodated in the outer casing 4. The outer diameter of the inner casing 5 substantially conforms to the inner diameter of the outer casing 4. An electrical conductor (not shown) is wound in the shape of a coil around the inner casing 5 and is accommodated in a groove 5a made in the outer peripheral surface of the inner casing 5. The electrical conductor is coupled at both its ends to connecting members in the form of terminal pins 6a, 6b for connection of an external power source 7 to the conductor. The two pins 6a, 6b are fixed in the outer casing 4 and project radially outwards from the same. The two pins are also each disposed in a respective cylindrical flange 8a, 8b, which projects radially from the outer sleeve 1 and defines an outwardly open cylindrical recess.
An indicating device 9 (see also Fig. 2) is inserted inside the inner casing 5 of the welding sleeve 1. The indicating device 9 comprises an elastically deformable, generally helicoidal member, which is configured in an elastic material. Examples of materials for the elastic member are steel, plastic, aluminium, etc. As can most clearly be seen from Fig. 2, the indicating device 9 also comprises a first 10a and a second 10b permanent magnet, which are arranged axially in line with each other at their respective mutually overlapping end of the helicoidal member. In Figs. Ia and 2, the indicating device 9 is shown when the elastically deformable member is in its unloaded, non-deformed state.
The two magnets 10a and 10b are mutually repelling. When the two pipes which are to be welded together are inserted into the welding sleeve 1, the two repelling magnets 10a and 10b are pressed together, that is to say they are axially displaced, the magnetic field between the two magnets being strengthened when the two repelling magnets 10a and 10b are pressed one against the other. If the two magnets come into contact with each other, the magnetic field will be extinguished.
The device also comprises a sensing device 11, which is disposed radially outside the welding sleeve 1, directly in front of the indicating device 9 inserted in the inner casing 5. The sensing device 11 comprises a Hall element (not shown), which is designed to detect a change in the magnetic field, such as a strengthening or an extinguishment. This change arises, as has been described above, from the fact that the two repelling magnets 10a and 10b on the indicating device 9 in the welding sleeve 1 are axially displaced and are thus pressed together to be either very close to each other or in full contact. The magnets 10a and 10b are preferably permanent magnets. The sensing device 11 is connected to the power source 7 and is designed to direct the power source 7 to allow and break the power supply to the terminal pins 6a, 6b in dependence on the axial positions of the permanent magnets 10a and 10b, which are detected by the sensing device 11. Or, in other words, the strength of the magnetic field is detected, which is dependent on the axial positions of the permanent magnets, which, in turn, is dependent on the positions of the plastic pipes inside the welding sleeve. As is described above, the axial displacement of the two repelling permanent magnets 10a and 10b means a strengthening or, alternatively, extinguishment of the magnetic field, or the magnetic field strength, which can be detected by the sensing device 11.
The sensing device 11 is arranged to allow the power source to supply current to the connecting members of the welding sleeve only when the sensing device 11 detects a state of the indicating device corresponding to the fully inserted position of the plastic pipes in the welding sleeve 1. The sensing device 11 is also arranged to break the power supply to the terminal pins 6a and 6b so as to interrupt the resistive heating of the welding sleeve 1 when the sensing device 11 detects a state of the indicating device 9 corresponding to the fully inserted position of the plastic pipes in the welding sleeve.
Different types of permanent magnets have differently strong field strength. Some examples of common types of permanent magnets are ferrite magnets, neodymium magnets and alnico magnets. These also have a certain depolarization temperature, which depends on the type of permanent magnet. When the welding sleeve is heated in order to fuse with the pipe or pipes and hence form a joint, it is important that the temperature does not reach the temperature at which the magnet or magnets are at risk of depolarization. A suitable type of magnet to use is, for example, neodymium magnets. These have a relatively high field strength, which can be detected by the sensing device 11, and have a depolarization temperature of about 300 degrees Celsius.
The outer casing 4 is made of a material which is transparent to magnetic field strength. An example of suitable materials is polyethylene.
The figures describe an embodiment of the invention having two permanent magnets 10a and 10b. According to an alternative embodiment, the elastically deformable members of the indicating device 9 are configured with just one magnet, which is axially displaceable in the welding sleeve.
In Figure 2 it is also shown how the indicating device 9 is provided with steps. Corresponding steps are configured in the welding sleeve 1 in the inner casing 5 (not shown) and have the function of holding the indicating device 9 in place inside the welding sleeve 1. The steps prevent the indicating device 9 from being able to rotate inside the welding sleeve 1. As stated, the welding sleeve 1 is configured with corresponding grooves. These grooves advantageously run only along the lower part or half of the welding sleeve 1. By the lower part/half is meant that part of the welding sleeve 1 which is situated opposite to the magnet or magnets 10a and 10b. By the upper part or half of the welding sleeve 1 is meant, correspondingly, the part housing the magnet or magnets 10a, 10b and facing towards the sensing device 11, as shown in Figures Ia and Ib.
In Figure 3 is shown an alternative embodiment of the indicating device 9. According to this embodiment, the indicating device 9 is helicoidal, devoid of the steps shown in Figure 2. In this embodiment, the welding sleeve is correspondingly configured with a groove for holding the indicating device 9 in place in the welding sleeve 1. Correspondingly, the groove in the welding sleeve 1 runs along the lower part of the welding sleeve 1.
The indicating device 9 in Figure 3 is, as stated, helicoidal. The indicating device 9 in Figure 2 has the same general shape, with the additional feature that it is configured with steps. By the definition "generally helicoidal" is herewith precisely meant a helicoidal shape configured with steps, projections or the like which diverge slightly from a strict helicoidal form, but which in its basic shape can still be said to be helicoidal.
According to one embodiment, the sensing device 11 can be configured with more than one Hall element or reed element, for example with two of the same. According to one embodiment having two such elements, the respective element is designed to sense the magnetic field strength of the respective magnet 10a and 10b.
The present invention also relates to a method for joining together at least two plastic pipes 2 and 3 by the use of a welding sleeve 1. The welding sleeve 1 has two openings and comprises a fusible material and an electrical conductor having connecting members 6a and 6b. The method involves introducing the two plastic pipes 2 and 3 into a respective opening in the welding sleeve 1 and connecting an electric power source 7 to the connecting members 6a and 6b in order, by resistive heating of the conductor, to fuse the fusible material to the plastic pipes. The method further involves, by- means of an indicating device 9 comprising at least one magnet 10a, which indicating device 9 is inserted in the welding sleeve 1, generating a magnetic field and, through the displacement of those ends of the plastic pipes 2 and 3 which are inserted in the welding sleeve 1, influencing the indicating device 9 so as to change the state of the magnetic field. The method further involves detecting the change in the state of the magnetic field by means of a sensing device 11 disposed outside the welding sleeve 1.
According to the method, the sensing device 11 detects axial displacement or change such as a strengthening or extinguishment of the magnetic field generated by the at least one magnet 10a.
According to the method, the indicating device 9 can comprise a magnet 10a. In this embodiment, the magnet 10a will be axially displaced when the ends of the two plastic pipes 2 and 3 are inserted into respective openings in the welding sleeve 1, which means that the magnetic field to which the magnet 10a gives rise will be axially displaced.
According to the method, the indicating device 9 can comprise two magnets 10a and 10b. In this embodiment, both magnets will be axially displaced and pressed one against the other when the ends of the two plastic pipes 2 and 3 are inserted into respective openings in the welding sleeve 1, which means that the magnetic field to which the magnets 10a and 10b give rise is strengthened the closer they come to each other, since the two magnets are arranged to repel each other. In case of contact, the magnetic field will be extinguished.
The method involves detecting the axial displacement of or change in the magnetic field. This detection is achieved by means of at least one Hall element or reed element belonging to the sensing device 11. The method according to the invention involves the power source 7 supplying current to the connecting members 6a and 6b of the welding sleeve so as to produce the resistive heating only when the sensing device 11 detects a state of the indicating device 9 corresponding to the fully inserted position of the plastic pipes 2 and 3 in the welding sleeve.
The method also involves interrupting the resistive heating of the welding sleeve when the sensing device 11 detects a change in the state of the indicating device 9, which change corresponds to a non-fully inserted position of the plastic pipes 2 and 3 in the welding sleeves.
The invention is not limited to the described embodiments but can be varied within the scope of the claims.
For example, in order to hold the indicating device 9 in place inside the welding sleeve 1 and prevent rotation of the indicating device, the indicating device 9 can be configured in generally helicoidal form by means other than with the steps shown in Figure 2.
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