GB2149706A - Improvements in heating tools - Google Patents

Abstract

A heating tool for soldering or unsoldering copper pipes has jaws (12, 14) with carbon electrodes (16, 18) thereon. A pipe joint (28) to be heated is wedged between the jaws and a current of up to 70 amps is passed between the electrodes. Sufficient heat to melt the solder is developed within a few seconds by resistance heating of the pipe. A temperature sensing device used to control temperature and time of application of current may be provided. The jaws may be fixed as shown or hinged for relative movement. <IMAGE>

Description

SPECIFICATION Improvements in heating tools The present invention relates to heating tools and more particularly to a heating tool which is useful in place of a blowlamp for soldering and unsoldering pipe fittings.

A common form of pipe joint in copper piping is a solder joint wherein abutting ends of adjoining pipe lengths are received within a copper sleeve and are soldered thereto. The solder may be already received within annular grooves within the copper sleeve so that it is merely necessary to apply soldering so that it is merely necessary to apply soldering flux to the joint and then heat the joint in order to melt the solder and cause itto run. In other cases it is necessary to apply the solder separately.

When assembling a soldered pipe joint it is necessary to separate the pipe ends from the sleeve whilst the solder is molten.

The use of a blow lamp is difficult and hazardous.

In exposed positions a draught can blow the flame away from the pipe being heated and in confined situations there is a fire hazard.

There is provided by the present invention a method of heating piping for making or loosening a soldered joint in which a pair of electrodes is applied to the piping at the region to be heated and an electrical current is passed through such region between the electrodes to cause the piping to be heated to a soldering temperature by resistive heating.

Typically a current of up to 70 amps will be used and this can be supplied at two to three volts. The power source can be a step-down transformer of a kind which can be plugged into a domestic power supply.

It has been found efficacious to make the electrodes of carbon or graphite since the relatively high contact resistance and relatively high resistance of the graphite inhibits sparking between the electrodes and the piping. In particular the carbon will not weld to the piping whereby the risk of electrodes becoming welded to the piping is avoided.

An added advantage of the present invention which avoids the use of a blowlamp is that the heating is localized so that in the case of piping in a room there is no risk of damaging of the surrounding decoration.

In a development of the present invention a temperature responsive control may be provided wherein a temperature sensor engages the piping between the electrodes and switches off the power switch when a predetermined temperature is reached, the switch for this purpose being at the primary side of a step-down transformer in the power source. Provision may be made for adjusting the temperature at which such control responds. A timer can also be incorporated in the control to ensure that the heat has sufficient time to spread throughout the joint being soldered or unsoldered before the power is switched off.

The present invention includes a heating tool for heating an electrically conductive workpiece comprising a pair of jaws having thereon carbon electrodes which are spaced apart suitably to receive the workpiece to be heated, and a power source providing a low voltage, high current output connected to said carbon electrodes.

In one embodiment of the tool according to the invention the electrodes are fixed relatively to one another to leave a tapered gap therebetween. When the tool is being used to solder or unsolder piping the jaws are in effect jammed over the piping. The spacing between the jaws can be made adjustable in order to accommodate piping of widely differing diameters.

In another embodiment of the invention the jaws are movable relatively to one another and are biased towards one another so that they can be manually spread apart and clipped or clamped over the piping.

In a more sophisticated embodiment of the invention the heating tool includes a temperature probe disposed between the jaws and spring biased to engage a workpiece placed between the jaws. Such temperature probe can be electrically connected to a switch at the primary side of a step-down transformew to which the electrodes of the heating tool are connected.

Whilst the heating tool according to the invention is advantageously designed for soldering and unsoldering joints in copper piping it can also be used quite generally for heating suitably sized workpieces. Thus, the heating tool may be used for heating chisels which are to be hardened.

The invention is further described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic sectional view of a heating tool according to one embodiment of the invention; Figure 2 is a similar sectional view of a second embodiment of heating tool; and Figure 3 is a diagram of a power source for carrying out the method of the present invention.

Referring first to Figure 1 a heating tool for heating copper piping to be soldered or unsoldered comprises a housing 10 of insulating material which supports a pair of jaws 12 and 14 whose outer diverging ends are provided with carbon electrodes 16 and 18 respectively. The jaws 12 and 14 are made of brass bars 20 which are provided with an insulating coating 22. The electrodes 16 and 18 are electrically conductively secured to the respective brass bars. At their inner ends the brass bars 22 are connected to heavy lead wires 24 and 26 capable of conducting AC current up to 70 amps.

A workpiece in the form of a pipe joint 28 to be soldered or unsoldered is wedged between the electrodes 16 and 18 so as to establish good electrical conduction between the electrodes and the workpiece. The workpiece 28 comprises copper pipe lengths 30 whose adjacent ends are to be interconnected by a copper sleeve 32. In practice the sleeves 32 will be presoldered on their inner surface and these sleeves include internal annular grooves which contain an adequate supply of the solder to form the joint. All that is necessary is to clean the pipe ends and apply flux to them before they are inserted into the sleeve.Upon causing a sufficient current to flow between the electrodes 16 and 18 by connecting the tool to a power source 34 such as is illustrated in Figure 3 the pipe and sleeve in the region of the joint are caused to be heated rapidly to melt the solder to cause the latter to run and so form the joint. Sufficient heat can be developed within a few seconds.

The jaw 14 is fixed in the housing 10 by means of an insulating block 36 but the jaw 12 is mounted on a pivot 38 in the housing. The spacing between the electrodes 16 and 18 can be adjusted by means of a thumbscrew 40 which is screwed through the jaw 12.

This enables the tool to be used with piping of differing diameters. Standard copper piping varies in nominal diameters between 13 mm and 32 mm.

In the embodiment of heating tool shown in Figure 2, jaws 40 and 42 are mounted in an insulating housing 44. The jaws comprise brass bars 46 provided with an insulating layer 48. At their forward ends the jaws are provided with carbon or graphite electrodes 50 and 52 electrically conductively secured to the brass bars. At their inner ends the brass bars are connected by heavy electrical cables 54 and 56 to the power source 34 shown in Figure 3.

Whilst the jaw 40 is fixed to the housing 44 the jaw 42 is mounted by means of a pivot 58. The jaws are biased towards one another by means of a compression spring 60. A stop 62 of insulating material limits the movement of the jaw 42 towards the jaw 40 and thereby prevents them from contacting one another. The jaws can be opened at their outer end by means of a push button 64 protruding through the wall of the housing 44. The pivoted jaw 42 is connected to the cable 56 by means of a flexible electrical conductor 66. A stop 68 of insulating material limits the pivoting travel of the jaw 42 to avoid the risk of the jaws coming into contact with one another at their inner ends.

The tool shown in Figure 2 can be used in a similar way to the tool of Figure 1. It is simply necessary to press the button 64 and clamp the jaws 40 and 42 over the piping to be soldered or unsoldered.

Because of the pivoting travel of the jaw 42 and the provision of the spring 60 the tool can be used for piping of differing diameters from 13 mm to 32 mm nominal.

In a development of the embodiment of Figure 2, a temperature probe 70 is mounted in the insulating stop 62 so that a spring loaded sensor 72 on the end of the probe protrudes into the gap between the electrodes 50 and 52. The tip of the probe thereby touches the workpiece clamped between the jaws and can send a temperature signal along a connecting wire 74. The connecting wire 74 leads to the power source 34 shown in Figure 3. The power source comprises a step-down transformer adapted to step down from 240 volts to 3 volts AC. The temperature probe 70 controls a switch connected at the primary side of the power source 34. An input lead wire 76 connected to the primary side of the power source can be connected by means of a conventional 13 amp British Standard plug to a domestic power supply. The power source is capable of providing a current of up to 70 amps at the output cables 54 and 56.

Whilst the power source can be provided with an on/off switch 78 preferably at the primary side of the power source it has been found that with the use of carbon electrodes the tool can be applied to the pipe lengths and removed therefrom without sparking between the electrodes and the workpiece even with the power remaining switched on. Because of the provision of the insulation 22 there is no danger of the workpiece coming into contact with a metallic part of the tool so that the risk of the tool becoming welded to the workpiece is avoided.

Claims (17)

1. A method of heating piping for making or loosening a soldered joint in which a pair of electrodes is applied to the piping at the region to be heated and an electrical current is passed through such region between the electrodes to cause the piping to be heated to a soldering temperature by resistive heating.

2. A method as claimed in claim 1, in which a current of up to 70 amps is used.

3. A method as claimed in claim 1 or 2, in which the current is supplied at two to three volts.

4. A method as claimed in claim 1,2 or 3 in which the power source is a step-down transformer of a kind which can be plugged into a domestic power supply.

5. A method as claimed in any preceding claim, in which the electrodes are made of carbon or graphite.

6. A method as claimed in any preceding claim, in which a temperature responsive control is provided in that a temperature responsive control is provided in that a temperature sensor engages the piping between the electrodes and switches off the power switch when a predetermined temperature is reached, the switch for this purpose being at the primary side of a step-down transformer in the power source.

7. A method as claimed in claim 6, in which the temperature at which such control responds is adjusted.

8. A method as claimed in any preceding claim, in which a timer is incorporated in the control to ensure that the heat has sufficient time to spread throughout the joint being soldered or unsoldered before the power is switched off.

9. A heating tool for heating an electrically conductive workpiece comprising a pair of jaws having thereon carbon electrodes which are spaced apart suitably to receive the workpiece to be heated, and a power source providing a low voltage, high current output connected to said carbon electrodes.

10. A tool as claimed in claim 9, in which the electrodes are fixed relatively to one another to leave a tapered gap therebetween.

11. A tool as claimed in claim 10, in which the spacing between the jaws can be made adjustable in order to accommodate piping of widely differing diameters.

12. A tool as claimed in claim 9, in which the jaws are movable relatively to one another and are biased towards one another so that they can be manually spread apart and clipped or clamped over the piping.

13. A tool as claimed in any of claims 9 to 12, in which the heating tool includes a temperature probe disposed between the jaws and spring biased to engage a workpiece placed between the jaws.

14. A tool as claimed in claim 13, in which the temperature probe is electrically connected to a switch at the primary side of a step-down transformew to which the electrodes of the heating tool are connected.

15. A tool as claimed in any of claim 9 to 14, in which each jaw comprises a conductive bar having a respective carbon electrode attached thereto and provided with an insulating coating.

16. Methods of heating pipes substantially as herein described with reference to the accompanying drawings.

17. A heating tool constructed and adapted to be used substantially as herein described with reference to and as illustrated in the accompanying drawings.