PARKES RICHARD (GB)
STARSMORE NEIL (GB)
PARKES RICHARD (GB)
| WO2003022439A2 | 2003-03-20 | |||
| WO2003055635A1 | 2003-07-10 |
| FR1323514A | 1963-04-12 |
| CLAIMS: 1. A method of electrically heating a component, comprising cyclically driving first and second electric currents through the component, wherein the first electric current is driven along a first current path defined between a first pair of end points, and the second electric current is driven along a second current path that is different from the first current path and defined between a second pair of end points. 2. The method according to claim 1 , wherein the first and second current paths have different end-points. 3. The method according to claim 1 , wherein the first and second current paths have at least one common end point. 4. The method according to any preceding claim, comprising cyclically driving at least one further electric current through the component along at least one further current path which is different from the first and second current paths. 5. The method according to any preceding claim, comprising selecting end- points of the current paths so that the end-points of each current path are uniformly distributed around a periphery of the component. 6. The method according to any preceding claim, comprising selecting end- points of the first and/or second current paths so that the end-points are located on substantially opposite sides of the component such that a current flows from one side of the component to the other. 7. The method according to any preceding claim, comprising holding at least one of the electric currents at a predetermined current level for a predetermined period of time. 8. The method according to any one of claims 1 to 6, comprising increasing and/or decreasing at least one of the electric currents from a first predetermined current level to a second predetermined current level. 9. The method according to claim 8, comprising increasing and/or decreasing at least one of the electric currents from the first predetermined current level to the second predetermined current level at a predetermined rate. 10. The method according to any preceding claim, comprising measuring a temperature of the component and controlling one or more of the electric currents in response to the measured temperature. 11. The method according to any preceding claim, comprising cyclically driving a current for an associated portion of a switching cycle period. 12. The method according to any preceding claim, comprising cyclically driving each of the electric currents one at a time while the other electric current is switched off. 13. The method according to any one of claims 1 to 12, comprising driving alternating electric currents simultaneously, wherein the alternating electric currents have a predetermined phase relationship. 14. The method according to any preceding claim, wherein the end-point of each current path is established at a point of contact between the component and an electrode. 15. The method according to any preceding claim, configured for heating a portion of a component for welding to a further portion of the component. 16. The method according to any preceding claim, configured for heat treating a component. 17. A heating apparatus comprising: at least three electrodes adapted to engage a component to be heated; an electrical supply adapted to provide an electric current; and an electrical processing device adapted to process the electric current provided from the electrical supply so as to cyclically drive a first current between a first pair of the electrodes and a second current between a second pair of the electrodes. 18. The apparatus according to claim 17, wherein the electrodes constituting the first pair of the electrodes are different from the electrodes constituting the second pair of the electrodes. 19. The apparatus according to claim 17, wherein the first and second pairs electrodes comprise at least one common electrode. 20. The apparatus according to claim 17, 18 or 19, wherein the electrical processing device is adapted to cyclically drive the first and second currents at different times. 21. The apparatus according to claim 17, 18 or 19, wherein the electrical processing device is adapted to cyclically drive the first and second currents simultaneously. 22. The apparatus according to any one of claims 17 to 21 , wherein the electrical processing device is adapted to couple the first and second pairs of the electrodes to the electrical supply. 23. The apparatus according to any one of claims 17 to 22, comprising a further electrical supply, wherein the electrical processing device is adapted to couple the first and second pairs of the electrodes to different electrical supplies. 24. The apparatus according to any one of claims 17 to 23, wherein the electrical processing device is adapted to alter a characteristic of the electric current provided by the electrical supply. 25. The apparatus according to any one of claims 17 to 24, wherein the electrical processing device is adapted to process the electric current provided from the electrical supply so as to cyclically drive a third current between a third pair of the electrodes. |
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for heating a component and, in particular, but not exclusively, for heating a component in a welding operation.
BACKGROUND TO THE INVENTION
When welding a first component to a second component the temperatures of the components and the temperature distributions across the components may be critical. When an end-face of the first component is to be welded to a corresponding end-face of the second component, for example, variations in temperature across either of the end-faces may lead to variations in hardness which may lead to an unacceptable weld quality such as insufficient weld strength or unacceptable weld dimensions. To improve the weld quality, therefore, a more uniform temperature distribution across the component end-faces is desirable.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a method of electrically heating a component comprising the step of cyclically driving first and second electric currents through the component, in which the first electric current is driven along a first current path and the second electric current is driven along a second current path that is different from the first current path.
Cyclically driving the first and second electric currents along different current paths through the component in this way may result in establishing a more uniform temperature distribution within the component. Such a uniform temperature distribution may be critical for some applications such as welding of the component to a further component. The inventor has discovered that improved temperature uniformity within the component may lead to improved hardness uniformity across a surface of the component resulting in an improved weld quality between the component and the further component.
The first current path may define a first pair of end points between which the first current is passed.
The second current path may define a second pair of end points between which the second current is passed.
The first and second current paths may have different end-points. The first and second current paths may have at least one common end point. For example, the first current path may have an end-point that is also an end-point of the second current path.
The method may further comprise cyclically driving at least one further electric current through the component along at least one further current path which is different from the first and second current paths.
The method may comprise selecting end-points of the current paths so that the end-points of each current path are uniformly distributed around the component. This arrangement may permit a more uniform temperature distribution through the component.
The method may comprise selecting end-points so that the end-points of each current path are uniformly distributed around a periphery of the component.
The method may comprise selecting end-points distributed in the region of an end-face of the component. This arrangement may result in establishing a more uniform temperature distribution across the end-face of the component in preparation for welding the end-face of the component to a further component.
The method may comprise selecting end-points of the first and/or second current paths so that the end-points are located on substantially opposite sides of the component such that a current flows from one side of the object to the other. Such an arrangement may provide that the current flows across a component or, in the case of a hollow component such as a pipe having an aperture, that the current may flow from one end-point before splitting evenly around the aperture and recombining at the corresponding end-point.
The method may comprise selecting end-points of a current path, which end- points are diametrically opposed across a component having a generally circular cross-section.
Choosing end-points in this way may be critical for temperature uniformity. For example, in the case of a hollow component having a generally circular cross- section such as a pipe having an aperture, choosing end-points in this way may ensure that substantially equal currents flow either side of the aperture between the end-points.
The method may comprise controlling at least one of the electric currents.
The method may comprise maintaining or varying at least one of the electric currents.
The method may comprise holding at least one of the electric currents at a predetermined current level. For example, the method may comprise holding at least one of the electric currents at a predetermined current level for a predetermined period of time.
The method may comprise increasing and/or decreasing at least one of the electric currents from a first predetermined current level to a second predetermined current level.
The method may comprise increasing and/or decreasing at least one of the electric currents from the first predetermined current level to the second predetermined current level at a predetermined rate.
Varying one or more of the electric currents in this way may further improve the uniformity of the temperature distribution within or across a component at any instant.
The method may comprise measuring a temperature of the component and controlling one or more of the electric currents in response to the measured temperature.
The method may comprise measuring at least one further temperature of the component and controlling one or more of the electric currents in response to the measured at least one further temperature.
The method may comprise controlling the one or more of the electric currents so that the measured temperature or each of the measured temperatures approach a respective target temperature.
The method may comprise measuring temperatures of the component at several different locations. The method may comprise controlling one or more of the electric currents so that the average of the temperatures measured at the different locations is controlled to approach a target temperature. In such an arrangement, any deviation of each of the measured temperatures from the target temperature may be minimised. Such a method may permit the heating of a component towards a target temperature whilst maintaining temperature uniformity across the component. The method may comprise cyclically driving one or more of the electric currents over multiple switching cycles.
The method may comprise cyclically driving a current for an associated proportion of a switching cycle period. For example, the method may comprise cyclically driving each of the currents for an associated respective proportion of the switching cycle period.
The switching cycle period may be a fixed period.
The method may comprise cyclically driving each of the electric currents one at a time while the other electric current or currents is/are switched off. Cyclically driving the electric currents in this way may improve temperature uniformity across the component. Additionally, this arrangement may permit heating to be achieved with the use of a single electrical supply, in combination with a switching arrangement, for example.
The electric currents may be alternating electric currents.
The method may comprise controlling a root mean square value of at least one of the electric currents. For example, the method may comprise maintaining or varying a root mean square value of at least one of the electric currents.
The method may comprise controlling an amplitude of at least one of the electric currents. For example, the method may comprise maintaining or varying an amplitude of at least one of the electric currents.
The method may comprise controlling a bias level or DC offset of at least one of the electric currents. For example, the method may comprise maintaining or varying a bias level or DC offset of at least one of the electric currents.
The method may comprise driving alternating electric currents simultaneously, wherein the alternating electric currents have a predetermined phase relationship. Cyclically driving the alternating electric currents simultaneously in this way may improve temperature uniformity across the component.
The method may comprise driving alternating electric currents simultaneously using a single-phase current supply in combination with one or more phase shift devices.
The method may comprise driving alternating electric currents simultaneously using a multi-phase current supply.
The method may comprise driving first, second and third alternating electric currents simultaneously wherein each of the first, second and third alternating electric currents have a phase difference of 2π/3 radians with respect to each of the other alternating electric currents. Each of the first, second or third alternating electric current may, for example, comprise a different phase of a three-phase alternating electric current supply.
The end-point of each current path may be established at a point of contact between the component and an electrode.
The method may be used for heating a portion of a component for welding to a further portion of the component.
The method may be used for heat treating a component, for example, for annealing or quenching a component.
According to a second aspect of the present invention there is provided a heating apparatus comprising:
at least three electrodes adapted to engage a component to be heated; an electrical supply adapted to provide an electric current; and
an electrical processing device adapted to process the electric current provided from the electrical supply so as to cyclically drive a first current between a first pair of the electrodes and a second current between a second pair of the electrodes.
The electrodes constituting the first pair of the electrodes may be different from the electrodes constituting the second pair of the electrodes. Alternatively, the first and second pairs of the electrodes may comprise a common electrode.
The electrical supply may comprise a power supply.
The electrical supply may comprise a radio frequency (RF) or a high frequency (HF) power supply.
The electrical supply may comprise an alternating current (AC) or a direct current (DC) electrical supply.
The electrical supply may comprise a voltage source or a current source. The electrical supply may be common to the first and second pairs of the electrodes.
The electrical processing device may be separate from or integral with the electrical supply.
The electrical processing device may be adapted to cyclically drive the first and second currents at different times. Alternatively, the electrical processing device may be adapted to cyclically drive the first and second currents simultaneously.
The electrical processing device may be adapted to couple the first and second pairs of the electrodes to the electrical supply. For example, the electrical processing device may be adapted to cyclically connect the electrical supply to and disconnect the electrical supply from the first and second pairs of the electrodes. For example, the electrical processing device may comprise a switch for switching the electrical supply between the first and second pairs of the electrodes.
The electrical processing device may be configured to connect the electrical supply to the first pair of the electrodes and disconnect the electrical supply from the second pair of the electrodes for a first period and to connect the electrical supply to the second pair of the electrodes and disconnect the electrical supply from the first pair of the electrodes for a second period.
The first period may comprise a first proportion of a switching cycle period and the second period may comprise a second proportion of the switching cycle period.
Alternatively, the apparatus may comprise a further electrical supply and the electrical processing device may be adapted to couple the first and second pairs of the electrodes to different electrical supplies. In this arrangement the electrical processing device may be adapted to connect and disconnect the respective electrical supplies to the respective pairs of the electrodes. For example, the electrical processing device may comprise a switch for connecting the electrical supply to and disconnecting the electrical supply from the first pair of the electrodes and for connecting the further electrical supply to and disconnecting the further electrical supply from the second pair of the electrodes.
For example, the apparatus may be arranged to connect the first pair of the electrodes to the electrical supply and disconnect the second pair of the electrodes from the further electrical supply for a first period and to disconnect the first pair of the electrodes from the electrical supply and connect the second pair of the electrodes to the further electrical supply for a second period.
The first period may comprise a first portion of a switching cycle period and the second period may comprise a second portion of the switching cycle period.
The electrodes may be arranged around a periphery of the component to be heated.
The electrodes may be arranged around an outer periphery.
The electrodes may be arranged around an inner periphery.
The electrodes may be uniformly distributed about the periphery of the component to be heated. Alternatively, the electrodes may be distributed non- uniformly.
Distribution of the electrodes may be selected in accordance with, for example, the material or geometrical properties of the component, the required temperature profile, the intended function of the component when heated and the like.
The electrical processing device may be adapted to alter a characteristic of the electric current provided by the electrical supply, such as a temporal or waveform characteristic of the electric current. For example, the electrical supply may provide an alternating current and the electrical processing device may comprise a phase shift device. In this arrangement, the phase shift device may be adapted to modify the phase of the alternating current provided from the electrical supply. For example, the phase shift device may be configured to impose or impart a phase difference between the first and second currents. The phase shift device may be configured to impose or impart a phase difference between the first and second currents of π/2 radians. The electrical processing device may be adapted to process the electric current provided from the electrical supply so as to cyclically drive a third current between a third pair of the electrodes.
The electrodes constituting the third pair of the electrodes may be different from the electrodes constituting the first and/or second pairs of the electrodes.
The electrodes constituting the third pair of the electrodes may comprise an electrode common to the first pair of the electrodes and/or an electrode common to the second pair of the electrodes.
The electrical processing device may be adapted to process the electric current provided from the electrical supply so as to cyclically drive further currents between respective further pairs of the electrodes.
The electrodes constituting one of the further pairs of the electrodes may be different from the electrodes constituting the first, second and/or the other further pairs of the electrodes.
The electrodes constituting the third pair of the electrodes may comprise an electrode common to the first pair of the electrodes, an electrode common to the second pair of the electrodes, and/or an electrode common to the other further pairs of the electrodes.
The apparatus may comprise a controller.
The controller may be adapted to control the first and/or second electric currents.
The controller may be adapted to communicate with the electrical supply. The controller may be adapted to control the electrical supply so as to control an electric current provided by the electrical supply.
The controller may be adapted to control the electrical supply so as to maintain, increase or decrease an electric current provided by the electrical supply.
The controller may be adapted to control the electrical supply so as to maintain an electric current provided by the electrical supply at a predetermined level for a predetermined period of time.
The controller may be adapted to control the electrical supply so as to increase or decrease an electric current from a first predetermined current level to a second predetermined current level at a predetermined rate.
The controller may be adapted to control the electrical supply so as to control a root mean square value of an electric current provided by the electrical supply. For example, the controller may be adapted to control an amplitude or a DC offset of an alternating electric current provided by the electrical supply. The controller may increase the one or more of the electric currents from the first predetermined current level to the second predetermined current level at a predetermined rate.
The controller may be adapted to communicate with the electrical processing device.
The controller may be adapted to control the electrical processing device.
The controller may be adapted to control the electrical processing device so as to control a temporal or waveform characteristic of an alternating electric current provided by the electrical supply. The controller may, for example, be adapted to control the electrical processing device so as to control a phase value of an alternating electric current provided by the electrical supply.
The apparatus may comprise one or more temperature sensors.
The one or more temperature sensors may be remote temperature sensors, such as image sensors and/or infrared sensors or the like.
The one or more temperature sensors may be arranged so as to measure one or more temperatures distributed around the component.
The one or more temperature sensors may have a uniform angular distribution around a periphery of the component.
The one or more temperature sensors may provide a continuous temperature profile around a periphery of the component.
The controller may control the first and second electric currents in response to one or more temperatures sensed by the one or more temperature sensors. For example, the controller may control the electrical supply and/or the electrical processing device according to one or more temperatures sensed by the one or more temperature sensors.
The apparatus may be configured for heating a portion of a component for welding to a further portion of the component.
The apparatus may be configured for heat treating a component, for example, for annealing or quenching a component.
According to a third aspect of the present invention there is provided a method of electrically heating a component comprising the steps of:
bringing at least three electrodes into engagement with the component to be heated; and
cyclically driving a first current between a first pair of the electrodes and a second current between a second pair of the electrodes. According to a fourth aspect of the present invention there is provided a method of welding a component to a further component comprising heating the component using a method or apparatus according to any other aspect.
The method may further comprise heating the further component.
The component and/or the further component may be hollow.
The component and/or the further component may be steel pipes.
According to a fifth aspect of the present invention there is provided an apparatus for welding a component to a further component, the apparatus comprising an apparatus according to any other aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 is a schematic front elevation of an apparatus for heating a component constituting a first embodiment of the present invention;
Figure 2 is a schematic cross-section on AA of the apparatus of Figure 1;
Figure 3 shows a first electric current and a second electric current as functions of time corresponding to the electric currents driven along different current paths through the component using the apparatus of Figures 1 and 2;
Figure 4 is a schematic front elevation of an apparatus for heating a component constituting a second embodiment of the present invention;
Figure 5 shows a first electric current and a second electric current as functions of time corresponding to the electric currents driven through the component by the apparatus of Figure 4;
Figure 6 is a schematic front elevation of an apparatus for heating a component constituting a third embodiment of the present invention;
Figure 7 is a schematic cross-section on AA of the apparatus of Figure 6; and
Figure 8 is a schematic front elevation of an apparatus for welding a first component to a second component.
DETAILED DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 show an apparatus generally designated 2 for heating a component 4. The apparatus 2 may be used for heating the component 4 in preparation for welding the component 4 to a further component (not shown). Other uses may include heating a portion of the component 4 for welding to a further portion of the component 4 and heat treating of the component 4, for example, annealing or quenching the component 4. As shown in Figure 1 , the apparatus 2 is arranged to heat the component 4 in the vicinity of an end-face 5 of the component 4. In the embodiment shown, the component 4 is formed of an electrically conductive material such as steel and, as shown in Figures 1 and 2, the component 4 is provided in the form of a pipe such that the end-face 5 is annular.
The apparatus 2 comprises a first electrode 6, a second electrode 8, a third electrode 10 and a fourth electrode 12 which are circυmferentially arranged around the component 4 and are in contact with the outer surface thereof. As shown most clearly in Figure 2, the electrodes 6, 8, 10 and 12 are in contact with the outer surface of the pipe 4 at a first contact position 14, a second contact position 16, a third contact position 18 and a fourth contact position 20 respectively. The contact positions, 14, 16, 18 and 20 are located in the region of the end-face 5 and have a uniform angular distribution around the component 4 in a plane perpendicular to the longitudinal axis 7 of the component 4. Thus, the angular separation of any two adjacent contact positions is 90 degrees such that the first contact position 14 and the third contact position 18 are diametrically opposed, and the second contact position 16 and the fourth contact position 20 are diametrically opposed.
The apparatus 2 further comprises a switch 22 and an electrical supply 24. In the embodiment of Figures 1 and 2, the electrical supply 24 is a 300 kVA electrical supply having a frequency f ac , of 22 kHz. The switch 22 is switchable between a first state shown in Figures 1 and 2 and a second state (not shown). In the first state the electrical supply 24 is connected across a first pair of electrodes 6,10. In the second state (not shown) the electrical supply 24 is connected across a second pair of electrodes 8, 12. The apparatus 2 further comprises a controller 28. As indicated by the dotted lines in Figures 1 and 2, the controller 28 is adapted to communicate with the electrical supply 24.
In the first switching state the electrical supply 24 drives a first electric current ii through the component 4 along a first current path between contact positions 14 and 18. In the second switching state the electrical supply 24 drives a second electric current i 2 through the component 4 along a second current path between contact positions 16 and 20. In the present embodiment, the switch 22 cyclically switches between the first and second switching states at a regular switching frequency f which defines a cycle period T according to the relationship T = 1/f. In the embodiment shown in Figures 1 and 2, the switching frequency f may be 5 Hz. It should be understood, however, that any switching frequency may be chosen and that f may, for example, be in the range 0.5 to 5 Hz, and possibly more. In conjunction with the switch, the electrical supply 24 is operable to provide first and second alternating currents H 1 i 2 that vary as a function of time t as shown in Figure 3. As shown in Figure 3, the switch 22 is operable so as to switch on the first current H and to switch off the second electric current i 2 during a first period T 1 . Similarly, during a second period T 2 , the switch 22 is operable so as to switch off the first electric current J 1 and to switch on the second electric current i 2 . Cyclically driving the first and second electric currents H, i 2 along first and second current paths respectively in this way results in a more uniform temperature distribution through the pipe wall around a circumference of the pipe 4 through the contact points 14, 16, 18 and 20 and, in particular, improves the uniformity of the temperature distribution across the annular end-face 5 of the pipe 4. It should be understood that, although T 1 and T 2 are shown as being equal in Figure 3, in general, T 1 and T 2 may be different.
As indicated by the dashed-dotted line in Figure 3, the controller 28 also controls the electrical supply 24 so as to control root mean square values of the first and second currents H, i 2 by controlling amplitudes of the first and second currents I 1 , i 2 . This has the effect of further improving the uniformity of the temperature distribution across the end-face 5 of the pipe 4. More specifically, the controller 28 controls the electrical supply 24 so as to hold root mean square (RMS) values of the first and second electric current ii and i 2 at a predetermined lower threshold current l th1 for a predetermined period between times t=0 and t=ti. Subsequently, the controller 28 controls the electrical supply 24 so that the RMS values of the first and second electric currents H and i 2 are increased at a predetermined rate until they reach the predetermined upper threshold current l th2 at time t=t 2 . For example, studies have shown that, when raising the temperature of steel pipes having an external diameter of 219 mm (8 5/8 inches), a suitable current profile has a predetermined lower threshold current I t ni of 1000 A RMS for 5 seconds and rises at a rate of 1000 A/second to a predetermined upper threshold current l th2 of 4000 A RMS.
The apparatus 2 further comprises a temperature sensing apparatus (see, e.g., Figure 2) comprising a first temperature sensor 30, a second temperature sensor 32, a third temperature sensor 34 and a fourth temperature sensor 36 in which the temperature sensors 30, 32, 34 and 36 are arranged in the region of the end-face 5 of the component 4. The temperature sensors 30, 32, 34 and 36 are remote temperature sensors such as thermal imaging cameras. As indicated by the dotted lines in Figures 1 and 2, the temperature sensors 30, 32, 34 and 36 are configured to communicate with the controller 28. As shown in Figure 2, the temperature sensors 30, 32, 34 and 36 have a uniform angular distribution around the longitudinal axis 7 of the component 4 so that adjacent temperature sensors have an angular separation of 90°. In addition, each temperature sensor 30, 32, 34, 36 has a field of view that extends circumferentially from one contact point to an adjacent contact point. Thus, the temperature sensors 30, 32, 34, 36 provide a continuous circumferential temperature profile of the pipe 4 in the vicinity of the end- face 5.
Once the first and second electric currents I 1 and i 2 have reached the predetermined upper threshold current W at time t 2 , the controller 28 controls the electrical supply 24 so as to vary the RMS values of the first and second electric currents J 1 and i 2 in response to temperature data provided from the temperature sensors 30, 32, 34 and 36, for example, to achieve a predetermined target temperature. Such a target temperature may, for example, be a temperature at a single location on a surface of the component 4 or may be a function of one or more temperatures as measured at one or more locations on a surface of the component
4.
Figure 4 shows a second embodiment of an apparatus 102 for heating a component 104 having an annular end-face 105. The embodiment of Figure 4 is similar to that shown in Figures 1 and 2 and as such like features share like reference numerals, incremented by 100. The apparatus 102 comprises a 300 kVA electrical supply 124 having a frequency f ac , of 22 kHz. Unlike the apparatus of Figures 1 and 2, however, the apparatus of Figure 4 does not comprise a switch. Instead, the electrical supply 124 is permanently connected to a first pair of electrodes 106, 110. In addition, the electrical supply 124 is permanently connected to a phase shift device 140 and the phase shift device 140 is permanently connected to a second pair of electrodes 108, 1 12. As indicated by the dotted lines, a controller 128 is adapted to communicate with the electrical supply 124 and temperature sensors 130 (not shown), 132 (not shown), 134 and 136.
In use, the phase shift device 140 imparts a phase shift to the alternating electric current supplied from the electrical supply 124 such that the second electric current which flows between the second pair of electrodes 108, 112 has a predetermined phase relationship with respect to the first electric current which flows between the first pair of electrodes 106, 110. In the embodiment of Figure 5, the second electric current is π/2 radians out of phase with respect to the first electric current. As shown in Figure 5, the controller 128 controls the electrical supply 124 so as to control the RMS values of the first and second electric currents J 1 and i 2 by controlling the amplitudes of the first and second electric currents J 1 and i 2 . More specifically, the controller 128 controls the electrical supply 124 so as to hold the RMS values of the first and second electric currents u and i 2 at a predetermined lower threshold current l t m between times t=0 and t=ti. Subsequently, the controller 128 controls the electrical supply 124 so as to ramp up the RMS values of the first and second electric currents J 1 and i 2 at a predetermined rate from the predetermined lower threshold current ltm at time I 1 to a predetermined upper threshold current l th2 at time t 2 . Ramping up the RMS current values in this way improves the uniformity of the temperature distribution across the annular end-face 105 of the pipe component 104. Once the RMS value of each electric current I 1 , i 2 has reached the predetermined upper threshold current W, the controller 128 controls the electrical supply 124 so as to adjust the RMS value of each electric current J 1 , i 2 in response to temperature data from temperature sensors 130, 132, 134 and 136 to achieve a predetermined target temperature.
A third embodiment of an apparatus for heating a component is shown in
Figures 6 and 7. This embodiment is similar to that shown in Figures 1 and 2, and, as such, like features are identified with like reference numerals, incremented by 200. The third embodiment of Figures 6 and 7 differs from the earlier embodiments in that the apparatus 202 comprises three electrodes, a first electrode 206, a second electrode 208 and a third electrode 210. Each electrode 206, 208 and 210 is connected to a different phase of a three-phase alternating current electrical supply 224 and has an associated electric current. A controller 228 controls the electrical supply 224 so as to vary an RMS value of the electric current associated with each electrode. The controller 228 controls the electrical supply 228 so as to hold the RMS value of each electric current constant at a predetermined lower threshold current for a predetermined period. The controller 228 subsequently controls the electrical supply 228 so as to increase the RMS value of each electric current from the predetermined lower threshold current to a predetermined upper threshold current at a pre-determined rate. Once the RMS value of each electric current has reached the pre-determined upper threshold current, the controller 228 also controls the electrical supply 228 so as to vary the RMS value of each electric current in response to temperature data from temperature sensors 230, 232, 234 and 236.
Figure 8 illustrates an exemplary use of the apparatus of Figures 1 and 2 for heating two components 304 and 354 in preparation for being welded together. As shown in Figure 8, the components 304,354 are pipes formed of an electrically conductive material, such as steel. Many of the features of the apparatus of Figure 8 are identical to features appearing in the embodiment of Figures 1 and 2 and are thus identified by like reference numerals incremented by 300. The apparatus 302 of Figure 8 differs from the apparatus 2 of Figures 1 and 2 in that the apparatus 302 further comprises a third pair of electrodes 356, 360 and a fourth pair of electrodes 358, 362. The electrodes 356, 358, 360, 362 are arranged to be in contact with an outer surface of the further pipe component 354. In addition, the apparatus 302 comprises a further switch 364 and a further electrical supply 366. In a first state shown in Figure 9, the switch 364 connects the further electrical supply 366 to the third pair of electrodes 356, 360. In a second state (not shown), the switch 364 connects the electrical supply 366 to the fourth pair of electrodes 358, 362. A controller 328 is operable so as to control the electrical supplies 324 and 366 and the switches 322 and 324 so as to raise a temperature of the pipe components 304 and 354 respectively in an identical manner to that described with reference to the apparatus 2 of Figures 1 and 2.
Thus, the apparatus 302 of Figure 8 allows for the uniform heating of an annular end-face 305 of the first pipe component 304 and an annular end-face 368 of the further pipe component 354 for the purposes of welding the end-face 305 to the end-face 368. More specifically, the apparatus 302 provides precise control of a temperature at the end-faces 305 and 368 as well as precise control of temperature distributions across the end-faces 305 and 368 on a critical timescale as required to control the quality of a weld between the end-faces 305 and 368.
In a variant of the apparatus 302, the switches 322 and 364 may be connected in parallel across a single electrical supply. The switches 322 and 364 may, for example, be combined in a single switching unit having two inputs connected to the single electrical supply and having four pairs of outputs, each output pair connected to a pair of the electrodes 306, 308, 310, 312, 356, 358, 360 and 362.
In such a variant of the apparatus 302, the single electrical supply and the switching unit would have a functionality identical to that of the apparatus 302 depicted in Figure 8.
It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made without departing from the scope of the present invention.
For example, in an alternative embodiment of the apparatus of Figures 1 and 2, rather than controlling the RMS values of the first and second currents J 1 and i 2 by controlling the amplitudes of the first and second currents J 1 and i 2 , the amplitudes of the first and second currents J 1 and i 2 may be substantially constant and the controller
28 may control the RMS values of each of the first and second currents J 1 and i 2 by controlling a bias level or DC offset of each of the first and second currents J 1 and i 2 . In other embodiments, the controller may control operation of the switch 22, 322, 364 or the phase shift device 140.
In a further alternative embodiment of the apparatus of Figures 1 and 2, the current supply 24 may be a direct current supply. In such an alternative embodiment, the first and second currents J 1 and i 2 are direct currents and the controller 28 controls the electrical supply 24 so as to control the first and second currents J 1 and i 2 for improved temperature uniformity of the component being heated. More specifically, the controller 28 controls the electrical supply 24 so as to hold the first current ii at a value of l mi between times t=0 and t=t-ι and so as to ramp up the first current J 1 to a value of l th2 at time t=t 2 . After time t=t 2 , the controller 28 controls the electrical supply 24 so as to vary the first current J 1 according to a temperature of the component. Similarly, the controller 28 controls the electrical supply 24 so as to hold the second current i 2 at a value of l tM between times t=0 and t=t t and so as to ramp up the second current i 2 to a value of l tf , 2 at time t=t 2 . After time t=t 2 , the controller 28 controls the electrical supply 24 so as to vary the second current i 2 according to a temperature of the component.