Field of the Invention

This invention relates to electron beam welding apparatus and in particular to high- voltage connectors for the electron beam welding apparatus.

Background to the Invention

For electron beam welding apparatus, a high-voltage supply is connected to a cathode element so as to generate the electrons required for welding. The high-voltage supply cable generates a large amount of heat where it connects to an electron gun assembly and insulated connectors and insulating fluids have been used to absorb heat and extend the operational lifetime of the electron gun. However the insulating fluids generally used are corrosive and can result in failure of seals over time, causing the fluid to leak into the apparatus and cause damage.

Summary of the Invention

In accordance with the invention, there is provided electron beam welding apparatus comprising socket means formed with a first channel configured to receive a high- voltage supply member, for example a cable, so as to enable electrical communication with a cathode element, wherein the socket means further comprises a tubular plug having a second channel configured to receive the high-voltage supply member, the diameter of the first channel being greater than the diameter of the second channel, thereby in use to define an annular passage around the high-voltage supply member.

The diameter of the second channel preferably corresponds to a diameter of the high- voltage supply member, such that in use the high-voltage supply member is in sealing engagement within the second channel.

Desirably the diameter of the first channel is approximately 50 to 20mm greater than the diameter of the second channel, in use with a high-voltage supply member defining an annular passage of sufficient width to allow circulating flow of fluid. The tubular plug may comprise at least one internal conduit to facilitate water cooling, such that water entering and leaving the internal conduit will remove heat absorbed by the tubular plug. The tubular plug may further comprise a fluid reservoir to supply thermal transfer fluid to the first channel, with preferably the thermal transfer fluid being Silicone oil 200, 10 centistokes. Thus in use with a high-voltage supply member the thermal transfer fluid will fill the annular passage. The socket means is preferably sealable at one end to an assembly comprising a cathode element, typically at a rear end of the socket means distal to a front end of the socket means in which the tubular plug is locatable.

The socket means may further comprise a heat exchange element, preferably located proximal to an assembly comprising a cathode element.

The heat exchange element may comprise a third channel configured to receive a high-voltage supply member, such that both the tubular plug and heat exchange element act to locate a high-voltage supply member within the socket means.

The heat exchange element may further comprise a plurality of grooves formed in an external wall, the grooves increasing the external surface area of the heat exchange element. The heat exchange element may further comprise a plurality of axial grooves located within the third channel and if desired a plurality of supplementary channels extending radially from the third channel to the exterior surface of the heat exchange element so as to further assist with fluid flow in and around the heat exchange element.

Preferably at least a portion of the tubular plug extends into the first channel, with the portion formed with external grooves, the grooves increasing the external surface area of the tubular plug. Desirably when the socket means is in use with a high-voltage supply member, an annular gap configured to retain thermal transfer fluid and allow circulation of such fluid surrounds the high-voltage supply member. The invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of electron beam welding apparatus with power supplied by a high-voltage source;

Figure 2 is a partial cross-section through part of an electron beam welding apparatus illustrating a prior art connector used to connect a high-voltage source to the apparatus;

Figure 3 is a partial cross-section through part of an electron beam welding apparatus with a high-voltage connector in accordance with the invention;

Figure 4 is a cross-section through the high-voltage connector of Figure 3 with a high- voltage cable in position;

Figure 5 is a perspective view of part of the high-voltage connector of Figure 3;

Figure 6 is a perspective view of a heat exchanger;

Figure 7 is a detailed cross-section of part of the high-voltage connector of Figure 3; and Figure 8 is a view from above of a plug associated with the high-voltage connector. Description

A schematic diagram of electron beam welding apparatus 10 is shown in Figure 1 where a workpiece 12 is welded under vacuum using electron beam 14. A high- voltage supply provided by cable 15 is connected to gun housing assembly 18 to be in electrical communication with cathode 20 and cause cathode 20 to generate a beam of electrons. Electrons in beam 14 are accelerated, focussed and directed to workpiece 12 using elements such as bias cup 22, anode 24, focussing coil 26 and deflection coil 28. It will be appreciated that Figure 1 is an illustrative example of such welding apparatus.

High-voltage cable 15 generates a large amount of heat in the region where it connects to cathode 20. As shown in Figure 2, a high-voltage insulator is formed as a receptacle 30 with a tapered opening matching the dimensions of cable 15 such that walls 32 of receptacle 30 adjoins cable 15, with cable 15 secured in position to connect to corona ring 33 associated with a cathode. Walls 32 of receptacle 30 are formed with internal channels 34, 34’ along which an insulating fluid travels to reach the rear region near corona ring 33 so insulating the rear region and reducing the amount of heat that the gun assembly elements are exposed to. The fluid is Flutec 200, with a viscosity of 1000 centistokes. However this fluid is corrosive and leaks into gun assembly 18, causing other elements to break down and prevent the apparatus from working.

Figures 3 to 7 show an arrangement in accordance with the present invention for securing a solid, substantially rigid high-voltage cable 16 to gun housing assembly 18. As shown in Figures 3 and 4, cable 16 is secured within an internal channel 38 of solid-walled resin-moulded receptacle 40 using insulating plug 42. Receptacle 40, see Figure 5, comprises a front section 44, a middle section 46 and a rear section 48 proximal corona ring 33. Middle section 46 has a front end 50 and a rear end 52, front end 50 formed with circular grooves 54 for retaining o-rings 56, and rear end 52 externally tapered to fit within corona ring 33. Rear section 48 seals middle section 46 at the end proximal corona ring 33 whilst ensuring electrical communication between cable 16, corona ring 33, and a cartridge element 36 comprising a cathode.

The internal diameter of hollow receptacle or socket 40, and thus the diameter of channel 38, exceeds the diameter of cable 16 such that an annular gap 60 extends along the length of cable 16 when cable 16 is positioned centrally within socket 40 and held in place within second channel 39 formed within plug 42, see Figure 4 where the inserted cable 16 is shown in position. Second channel 39 has a matching diameter to that of cable 16. Annular gap 60 typically has a width of between 25 to 10mm, and more preferably 18mm, each side of cable 16, as can be seen in Figures 4 and 5. A heat exchanger 62, shown in more detail in Figure 6, is positioned proximal rear end 52, near corona ring 33. Annular gap 60 is reduced in width where heat exchanger 62 is located, see Figure 4. Heat exchanger 62 is formed from a thermally conductive material, such as Copper Chrome, and is substantially tubular with a plurality of external circumferential grooves 70 formed in external wall 72 to increase the surface area available for heat exchange. Cable 16 locates within central channel 74 with internal wall 76 of heat exchanger 62 formed with a plurality of axial grooves 78 and also channels 80 extending between the internal and external walls 76, 72 so as to allow increased fluid flow through and around heat exchanger 62 and improved thermal transfer to a surrounding fluid. Reservoir 90, see Figure 7, is connected to plug 42 so as to supply a non-viscous high- voltage insulator fluid, such as Silicone oil 200, 10 centistoke, to annular gap 60 through passage 92, with the fluid having flow properties similar to water. Using a non-aggressive fluid, such as Silicone oil, avoids issues with corrosion leading to leakage.

Plug 42 is typically formed as a potted housing and is formed with an integral internal channel 96 through which water, or other cooling fluid, is circulated, passing from inlet 98 along channel 96 to reach outlet 100 as shown in Figure 8. The integral channel 96 prevents leakage of water into annular gap 60 and ensures cooling water can be recycled. Plug 42 is formed with a plurality of external circumferential grooves 102 so as to increase the surface area of plug 42 exposed within annular gap 60.

In use, cable 16 is fed through channel 39 of plug 42, along channel 38 and inserted into central channel 74 of heat exchanger 62 so as to be in electrical communication with corona ring 33. Plug 42 is secured in position using one or more bolts 104 and Silicone oil from oil reservoir 90 introduced into annular gap 60 so as to fill gap 60. This forms a closed system with the Silicone oil unable to enter any other parts of gun assembly 18. Water is continuously run through channel 96 to cool plug 42.

During operation of the electron gun, heat generated proximal cable 16, corona ring 33 and cathode is absorbed by the oil with heat exchanger 62 increasing the rate of heat transfer into the oil. The oil heats up where cable 16 is proximal to corona ring 33 and the oil circulates within annular gap 60 by convection, moving to the cooler outer or front end where water-cooled plug 42 is situated, with the water-cooled plug increasing the heat gradient along annular gap 60. Water-cooled plug 42 removes heat from the oil, with cooled oil returning by convection to the rear end close to corona ring 33 so as to continue to remove heat from the rear end. This ensures thermal stability in the rear region near corona ring 33. This arrangement is responsive to power changes and overshoots when power settings are changed.