Leadthrough arrangement

Abstract

 A leadthrough arrangement for providing an electrical connection through the wall of a furnace, comprises a tubular body (2) having an electrical conductor (4) passing therethrough and electrically isolated therefrom, there being an insulating sheath (10) surrounding the conductor (4) throughout its length within the body (2), and a heat sink (9) mounted on the conductor (4) externally of the body (2). The body (2) is adapted to be mounted over an opening in a furnace wall in vacuum tight manner.

Description

[0001] This invention relates to a leadthrough arrangement for providing an electrical connection through the wall of a furnace.

[0002] In plasma thermochemical treatment apparatus, for example in apparatus for plasma carburising workpieces in a vacuum furnace, there is a need for a leadthrough arrangement which serves to take the HT electrical supply for the glow discharge through the wall of the furnace.

[0003] Normally the furnace wall itself constitutes the anode of the electrical supply, and thus the leadthrough arrangement must be capable of passing an electrical conductor through an opening in the wall of the furnace in vacuum tight manner, with the conductor electrically isolated from the wall of the furnace, and must not be adversely affected by the high temperatures, of the order of 1000 C, which can occur in the furnace.

[0004] A particular difficulty which arises with known leadthrough arrangements when used in plasma carburising furnaces is that sooty deposits can build up on parts of the arrangement and provide arc tracking paths. to earth for the HT supply.

[0005] According to this invention there is provided a leadthrough arrangement, for providing an electrical connection through the wall of a furnace, comprising a tubular body adapted to be mounted over an opening in said wall in vacuum tight manner; an electrical conductor passing through said body and electrically isolated therefrom; an insulating member serving to mount said conductor in said body; and an insulating sheath surrounding said conductor throughout its length within said body.

[0006] A leadthrough arrangement embodying this invention will now be described by way of example with reference to the drawing which is a longitudinal sectioned view of the arrangement.

[0007] The arrangement comprises a tubular body 1 of high- nickel steel, having welded to one end thereof a mounting flange 2 by which the body 1 is in use secured over an opening in a furnace wall (not shown! in vacuum tight manner, for example by means of a clamp.

[0008] At its other end the body 1 carries an annular ceramic insulating member 3 which is secured by vacuum brazing in an end portion of the body 1 and which projects therefrom.

[0009] Passing through the body 1 and insulating member 3 is a relatively small diameter metal conductor rod 4 which within the furnace is connected to a worktable (not shown) and which serves to take an HT electrical supply into the furnace for establishing a glow discharge therein between the worktable and the furnace wall which constitutes the other electrode of the supply.

[0010] The rod 4 projects beyond the free end of the insulating member 3 and has secured thereon a metal _; coupling member 5 which is carried by the insulating member 3 by way of a steel cap member 6 which is secured about a free end portion of the insulating member 3 and which has a hole therein through which a portion of the coupling member 5 projects. The coupling member 5 has a flange 7 which abuts the cap member 6, and the free end portion 8 of the coupling member 5 is externally threaded.

[0011] Screwed onto the portion 8 of the coupling member 5 is a finned heat sink 9 which also serves as the electrical connection to the rod 4 an HT supply lead (not shown) being connected to the heat sink 9, for example by means of a screw connection (not shown).

[0012] The rod 4 is thus held in position relative to the body 1 by means of the coupling member 5, cap member 6 and insulating member 3, and extends through the body 1 in electrically isolated manner.

[0013] Surrounding the rod 4 throughout its length within the body 1 is a ceramic insulating sheath 10 which extends through the insulating member 3 and terminates within the cap member 6.

[0014] The space defined by the cap member 6, the free end of the insulating member 3 and the end of the ceramic sheath lO is filled with a potting material comprising refractory cement material 11 which has been fired to remove all traces of moisture.

[0015] In use of a leadthrough arrangement as described above, the body 1 is secured over an opening in a furnace wall, by means of the flange 2, with the conductor rod 4 and its surrounding sheath 10 extending into the furnace, the rod 4 being electrically connected as required at a worktable within the furnace. The HT electrical supply is then connected up with the furnace wall serving as the positive earth connection and the rod 4 serving as the negative connection, the voltage accross the connection being of the order of 1000V. During operation of the furnace any heat conducted down the conductor rod 4 is dissipated by the heat sink 9 which would normally be fan cooled, thus ensuring that the arrangement is not subjected to excessive temperatures

[0016] If the leadthrough arrangement is used in a plasma carburising furnace, the sheath 10 serves to prevent tracking between the rod 4 and the body 1 which is at the potential of the furnace wall, which tracking could be caused by soot deposits forming in the body 1.

[0017] The use of the refractory cement material 11 serves to prevent the possibility of a discharge within what would otherwise be an empty space, and in particular serves to avoid the occurrence of hollow cathode effects.

[0018] Further, the cooling effected by the heat sink 9 maintains the arrangement at a temperature which reduces soot formation to a minimum within the arrangement.

Claims

1. A leadthrough arrangement, for providing an electrical connection through the wall of a furnace, characterised by a tubular body (1) adapted to be mounted over an opening in said wall in vacuum tight manner; an electrical conductor (4) passing through said body (2) and electrically isolated therefrom; an insulating member (3) serving to mount said conductor in said body; and an insulating sheath (10) surrounding said conductor (4) throughout its length within said body (2).

2, An arrangement as claimed in Claim 1, characterised in that said insulating member (3) projects from one end of said body (1) and carries at its free end a cap member (6) having a hole therein through which said conductor (4) passes, and within which said sheath (10) terminates, the space defined by said cap member (6), the free end of the insulating member (3), and the end of the sheath (10) being filled with a potting material (11),

3. An arrangement as claimed in Claim 2, characterised in that the potting material (M) is a refractory cement material which has been fired to remove all traces of moisture.

4, An arrangement as claimed in Claim 2 or Claim 3, characterised in that said conductor. (4) carries a coupling member (5) having a portion received in the hole in said cap member (6), and an externally threaded portion (8) projecting outside said cap member (6).

5. An arrangement as claimed in Claim 4, characterised in that said externally threaded portion (8) of said coupling member (5) carries a heat sink (9).

6, An arrangement as claimed in any preceding claim, characterised in that said sheath (10) is of ceramic material.

Drawing