HEAT RECOVERABLE ARTICLES

The present invention relates to a device and a method for heating heat recoverable articles and more particularly but not exclusively to such a device and such a method for effecting recovery of heat shrinkable cable closures.

Heat recoverable sleeving is often used to protect joins in electrically conducting cables and in optical fibre signalling lines. In use, a sleeve is passed over one end of a cable, for example a cable having multiple pairs of signalling wires and, once jointing of one cable to another cable has been completed, the sleeve is relocated over the joint area, the sleeve spanning the ends of the respective insulating jackets of the cables. Alternatively after the joint has been formed a split sleeve is positioned over the jointing area and is sealed using a hot melt adhesive or other heat activated sealing material. Heating the sleeve causes it to shrink to grip tightly around the cable jacket and the joint area thereby effecting water resistance and insulation. Care must be taken during the shrinking operation to ensure that air entrapment is limited.

Thus, for example, if the ends of a sleeve are recovered too rapidly so that sealing of the sleeve to the insulating cable jackets prevents air from escaping then the central portion of the sleeve may be prevented from shrinking fully onto the joint area by the entrapped air. Accordingly skilled operators are employed to effect the shrinking operation usually by applying a gas torch to the sleeve area, moving the torch from the centre towards the ends.

However, as will be appreciated, many such jointing operations are performed in restricted areas such as in underground cable chambers where the effects of combustion products may be dangerous to the operator. Furthermore, the use of a naked flame in such chambers, in which a build up of

combustible or explosive gases is possible, should preferabl be avoided.

One solution to the above problem has been disclosed i application EP88307726 (Publication No. 304333) which has bee made by the present applicant. In the aforementione application there is disclosed a portable heating device comprising a body forming an elongate enclosure the interior of which has electrical heating elements being independently energisable whereby the longitudinal temperature profile within the enclosure may be controlled. The body comprises two half cylinders hinged on one side. Thus, by placing a sleeved joint in the elongate body and then energising the heating elements the central portion reaches recovery temperature very quickly while the outer portions reach that temperature more gradually.

It has been found using the heating device disclosed in EP

88307726 (Publication No. 304333) that the quality of the insulation and water resistance of the joint after shrinkage of the heat recoverable sleeve is affected by the temperature inside the enclosure at the time the heating device commences operation. In particular, it has been found that the heating device may produce sleeved joints of poor insulation and water resistance at commencement temperatures below zero degrees fahrenheit. It is therefore one object of the present invention to provide a portable device and a method capable of effecting recovery of a heat shrinkable article in a controllable manner to produce sleeved joints of uniform quality.

According to one aspect of the present invention there is provided a device for applying heat to heat recoverable articles comprising: -

(a)a heating device the interior of which has a plurality of electrical heating elements spaced apart in the heating device each of the heating elements being independently energisable and the interior of which has also at least one sensor for sensing the actual temperature within the heating device, and

(b)connected to the heating elements and the at least one sensor, a control circuit which may independently energise the heating elements and by using the at least one sensor detect the actual temperature within the heating device, the control circuit being arranged to thereby heat the heating device using a uniform or near uniform temperature profile within the heating device until a predetermined temperature is reached within the heating device and subsequently to heat the heating device using a non-uniform temperature profile within the heating device for a period of time sufficient to cause heat recovery.

Further according to the invention there is provided a device for applying heat to heat recoverable articles comprising: a heating device with an interior containing a plurality of electrical heating elements, each of the elements being independently energisable; at least one temperature sensor within the device for sensing the internal temperature of the device; and a control circuit connected to the elements and the at least one sensor for measuring the initial device temperature and selecting a heating profile dependent thereon to effect heat recovery.

Preferably the body of the heating device is cylindrical and comprises two half cylinders hinged on one side to simplify access to the interior of the heating device.

The body of the heating device may have removable end plates which include apertures through which one or more cables and one or more heat recoverable articles may pass. The end plates may be relocated to reduce the size of the interior of the body of the heating device which may also include in its interior one or more support plates and/or thermal baffles.

The control circuit may produce the temperature profile within the interior of the heating device by sequential energisation. The energisation sequence may have a predetermined time interval between each step thereof or the

energisation sequence may be related to the actual temperatur profile within the body of the heating device.

The control circuit may be arranged to cause energisatio of the heating elements closest to the centre of the heat recoverable article prior to energisation of heating elements away from the centre of the heat recoverable article.

Further according to the invention there is provided a method for applying heat to heat recoverable articles in a device which comprises a body the interior of which has a plurality of independently energisable electrical heating elements and a means for sensing and indicating the actual temperature within the body, comprising the steps of: i) placing the heat recoverable article together with the joint or joints to be covered within the body, ii)energising the heating elements to produce a uniform or near uniform temperature profile within the body until a predetermined temperature is indicated, and iii)energising the heating elements to produce a non-uniform temperature profile within the body for a period of time.

Further according to the invention there is provided a method for applying heat to heat recoverable articles in a device having an interior with a plurality of independently energisable electrical heating elements and temperature sensing means, the method comprising the steps of: placing the heat recoverable article together with the joint or joints to be covered within the device interior; sensing the internal temperature of the device and selecting a heating profile dependent on the sensed temperature to effect heat recovery.

A device in accordance with the invention will now be described by way of example only with reference to the accompanying drawings in which: -

Figure 1 is an isometric view of a heating device for effecting shrinkage of a heat recoverable cable joint sleeve.

Figure 2 is a schematic diagram indicating the apparatus used to control the temperature of the heating device, and

Figure- 3 is a flow diagram indicating the operation of the apparatus.

Referring to Figure 1 the heating device comprises a housing in the form of two half cylinders 1 of thermally insulating material. The two half cylinders 1 are linked together by "lift-off" hinges 2 on one edge and have the respective halves of a clamp arrangements 3 of known kind on the opposed edges. Thus the two halve cylinders 1 may in use be locked together using the clamps 3 to form a cylindrical oven enclosure.

Embedded in the walls of the body of the heating device a number of groups of electric heating elements 4 to 7 (only some of which are shown) are provided, each having an individual connection wire (not shown) for power to be supplied from a controller. Between each group of heating elements 4 to 7, and at each end of the half cylinders, mounting guides 8, 9 may be provided to which end plates 10 may be fitted.

Each end plate 10 includes one or more semicircular grooves 11 arranged on closure of the cylinder to form an aperture. The grooves 11 each carry a support plate 12 which, in use, provides support to the ends of a jointed cable (not shown). Several pairs of interchangeable end plates may be provided to cater for different cable sizes. For example the end plates 10 are adapted for use with a single cable of a larger diameter while the end plates 10 takes a similar cable and a smaller cable.

Other exemplary end plates for a single smaller diameter cable, three such cables and a cable of intermediate diameter are also shown.

For the avoidance of doubt the term cables as used herein includes not only multi cored electrical signalling cables but also cables comprising of multiple optical fibres, co-axial cables and the like.

The interior of the half cylinder shells 1 comprises heat radiating surface 14 which is preferably coated with

"non-stick" material such as Teflon (trademark) to facilitat the removal of (e. g. ) hot melt adhesives which may have bee used in the jointing process.

As shown in the diagram, adjacent the groups of heatin elements 4 nearest the longitudinal centre of the enclosure further pair of plates 15 are provided. The plates 15 hav two functions the first of which is to give support to a cabl when it is in the enclosure and the second of which is to ac as a thermal baffle to prevent premature temperature rise along the length of the cylinder.

It will be realised that, as with the end plates 10, th plates 15 may be located in different positions along th length of the half cylinders 2 either using the same mounting 8 or additional mountings (not shown). It will also b appreciated that the plates 15 may carry extensions similar t the shells 12 to provide additional longitudinal support.

To enable the control of the temperature profile along th length of the enclosure one or more thermocouples 16 ar incorporated in the walls of the shells 1 as thermal sensors.

Referring to Figure 2 the sensor 16 and heating element

4, 5, 6 and 7 perform the functions as previously describe and are connected to a first control circuit 17 and a secon control circuit 18.

If the temperature sensed by sensor 16 within the bod

(internal temperature) is below the trigger temperature th first control circuit 17 energises the heating elements 4, 5,

6 and 7 to produce a uniform or near uniform temperature profile within the body (the pre-heat cycle) until the internal temperature reaches a pre-set temperature (the pre-set temperature). If the internal temperature is at or above the trigger temperature the first control circuit 17 will wait until the internal temperature falls below the trigger temperature before energising, in the mode referred to above (i. e. the pre-heat cycle) the heating elements 4, 5, 6 and 7. A typical trigger temperature is 30° Centigrade and a typical pre-set temperature is 40° Centigrade.

Upon completion of the pre-heat cycle, the second control circuit 18 will energise the heating elements 4, 5, 6 and 7 to produce a non-uniform temperature profile within the body (the shrinkage cycle) to ensure shrinkage of the recoverable sleeve within the heating device occurs without trapping air within the sleeve (as discussed above).

In use, where two or more cables are to be joined a suitable heat recoverable sleeve is selected and placed over one of the cables. Once jointing or splicing of the cables is completed, the joint area or the inside of the sleeve may be coated with a hot melt adhesive if required and the sleeve positioned thereover. Alternatively a split sleeve pre-coated with hot melt adhesive is selected and wrapped over the joint area after completion of splicing or jointing. Suitable end plates 10 are selected and placed in respective mountings 8, 9 in dependence upon the length of the joint to be sealed together with the intermediate support/thermal baffle plates 15 as necessary. The two half shells 1 are then positioned so that the jointed cables rest in the supports 12 and the enclosure is closed and locked together using the clamps 3. Connection leads from the heating elements 4 to 7 and the thermal sensor(s) 16 may now be connected to the controller. The operator provides the joint parameters on the controller, for example the type and length of joint, the kind of sleeving in use and starts the sequence.

Referring to Figures 2 and 3, the first control circuit 17 and the second control circuit 18 which may be conveniently provided by using custom built Programmed Logic Control or a microprocessor, now steps through the following predetermined sequences releasing the operator to perform other tasks.

In a typical sequence, a signal is sent to the first control circuit 17 instructing it to initiate energisation of the heating device (the commence pre-heat signal). Using sensor 16, the first control circuit 17 senses the internal temperature and if the internal temperature is below the trigger temperature the first control 17 circuit initiates the pre-heat cycle.

During the pre-heat cycle the first control circuit 1 energises the heating elements 4, 5, 6 and 7 either in sequence or randomly to avoid overloading the power supply, which may be conveniently a battery or a generator, to produc a uniform or near uniform internal temperature until th internal temperature reaches the pre-set temperature. Whe the internal temperature reaches the pre-set temperature, th first control circuit 17 ceases energisation of the heatin elements 4, 5, 6 and 7 and sends a signal to the secon control circuit 18 to carry out the shrinkage cycle (th commence shrinkage signal). If on receipt of the commenc pre-set signal, the internal temperature is at or above th trigger temperature, then, the first control circuit 17 will monitor the internal temperature using sensor 16 and wai until the temperature is below the trigger temperature before carrying out the pre-heat cycle and subsequently sending the commence shrinkage signal as described above.

Once the commence shrinkage signal has been received by the second control circuit 18, the second control circuit 18 commences the shrinkage cycle.

In a typical shrinkage cycle the second control circuit 18 first causes the two groups of elements 4 closest to the centre of the enclosure to be energised for a short period of time which may be either a predetermined period (say five minutes) or may be until a given temperature as sensed by sensor 16 is reached.

This initial heating of the central area of the joint ensures that shrinkage if that portion of the recoverable sleeve occurs before any likelihood of the sleeve sealing to the insulated sleeving of the cables thereby allowing entrapped air to escape.

In the next step of the shrinkage cycle, the second control circuit 18 causes the next to centre groups of elements 5 to be energised again for a predetermined period or until a given temperature is sensed during which period the elements 4 may either remain energised or be turned off as required. The groups of elements 6 and 7 may then be energised in turn. It will be realised that a combination of

the time and temperature factors may be used such that at each step mentioned above a predetermined period elapses after a given temperature is reached prior to proceeding to the next step. Whilst as herein described during the shrinkage cycle the heating elements 4, 5, 6 and 7 are controlled to heat a central area first progressing outwardly to the ends it will be appreciated that the longitudinal temperature profile of the enclosure may be controlled in any required manner. For example if sealing of one end is preferred prior to sealing of the opposed end then during the shrinkage cycle the second control circuit 18 may energise the heating elements in the order 7, 6, 5, 4 at one end of the enclosure followed by the corresponding heating elements in the order 4, 5, 6, 7 at the opposed end of the enclosure.

Further although the device has been described with reference to a performed heat recoverable sleeve other thermally responsive mechanisms such as sheets of material wrapped around a joint may be used. The control circuit could include a number of look up tables, for example, to allow different temperature profiles and sequencing including a waiting period to be effected dependent on the initial measured internal device temperature for example.