WO1989000356A1

WO1989000356A1 - Wall-traversing inlet, and procedure for implementing such inlet

Info

Publication number: WO1989000356A1
Application number: PCT/FI1988/000100
Authority: WO
Inventors: Tapio Toivanen
Original assignee: Tapio Toivanen
Priority date: 1987-06-30
Filing date: 1988-06-22
Publication date: 1989-01-12
Also published as: FI872893A0; FI872893A; AU1980488A

Abstract

The invention concerns an inlet, and a corresponding procedure, for carrying a conductor electrode (1) in galvanically insulated mode through a wall (2). As taught by the invention, the inlet comprises an inlet duct (3) of the same material as the wall, an insulator plug (5) of a material having a thermal expansion coefficient substantially equal to that of the inlet duct, and a conductor electrode of a material having a thermal expansion coefficient substantially equal to that of said insulator plug.

Description

WALL-TRAVERSING INLET, AND PROCEDURE FOR IMPLEMENTING SUCH INLET

The present invention concerns an inlet as defined in the preamble of Claim 1, and a procedure for implementing an inlet, as defined in the preamble of Claim 10.

In measurements of potential in metallic con¬ tainers, when said containers are pressurized or at high temperature or when they contain corrosive substan¬ ces, it is common practice to insulate and seal the conductor electrodes against the container with a Teflon packing. For instance in measurements of potential in cellulose digesters such measuring pick-ups designed with Teflon are unsatisfactory as regards reliability because, being inelastic, Teflon begins to leak in the course of time. Likewise, as a rule, in various inlets, e.g. in those passing electric leads, or pipes, through walls, if there is need of a tight-sealing and insulat- ing inlet, conventional insulator and sealing materials "work" under influence of ambient conditions, thus impairing the qualities which the inlet is desired to possess.

Therefore the object of the present invention is to eliminate the drawbacks evident in the state of art and, particularly, to provide a simple and reliable sealing design for carrying conductor electrodes, or equivalent, through the wall into metallic containers, or through walls in general. Regarding the features which characterize the invention, reference is made to the Claims section.

As taught by the invention, the inlet comprises an inlet duct which belongs to the wall as a substan¬ tially integral part and which is of the same material as the container itself, e.g. of pressure-vessel steel. The inlet also comprises, fitted in said duct, an in¬ sulator plug of a material having a thermal expansion coefficient substantially equal to that of the inlet duct material and provided with a conductor aperture, said plug substantially conforming in shape to the inside configuration of the inlet duct so that the plug can be applied with tight sealing on the end of the inlet duct. Furthermore, the inlet comprises a conductor electrode of a material having a thermal expansion coefficient substantially equal to that of the insulator plug, said electrode being disposed to extend through the conductor aperture of the inlet duct, the conductor aperture in the insulator plug having a diameter sub¬ stantially equal to the diameter of the conductor elect¬ rode so that the conductor electrode can be installed with tight seal in the conductor aperture. It is essential in the inlet, and procedure, of the invention that the inlet duct, the insulator plug and the conductor electrode all consist of ma¬ terials having substantially equal thermal expansion coefficients, construction and sealing of the inlet being then accomplished e.g. according to the following procedure. With the inner diameter of the inlet duct and the outer diameter of the insulator plug substan¬ tially equal in shape and consistent with each other, or the diameter of the insulator plug being slightly larger when they are at the same temperature, the inlet duct is heated so that its inner diameter becomes larger. The insulator plug can then be inserted in the inlet duct, and owing to their substantially equal thermal expansion coefficients they will be tightly locked together on reaching the same temperature. They are thereafter heated both together so that the conduc¬ tor aperture in the insulator plug expands, whereby the conductor electrode, which has substantially equal thermal expansion coefficient but is at a lower tempera- ture, can be pushed into the conductor aperture in the insulator plug. Subsequently, after the temperatures have levelled out, the insulator plug and conductor electrode will be tightly fixed to each other and they will also maintain this tight sealing under varying service temperature conditions, because owing to their substantially equal thermal expansion coefficients they expand and shrink in step.

Advantageously, the electrode may be provided within the inlet duct with an insulation, either an integral insulating shell or various loose insulating materials to be placed around the conductor. Advantageously, the wall which is employed, such as a metallic container, and the inlet duct thereto attached consist of pressure-vessel steel, but other materials may also be contemplated.

In practical tests, using pressure vessel steel, molybdenum has been found to be a suitable ma¬ terial for the conductor electrode and a ceramic con¬ sisting of zirconium oxide, for the insulator plug. However, e.g. platinum, silver, stainless steel may equally be used for conductor electrode material, and e.g. aluminium oxide in replacement of zirconium oxide.

In an advantageous embodiment of the invention, the major part of the electrode consists of an inexpen¬ sive, and commonly used, metal and only the sealing part, i.e., the part of the conductor which will be sealed in the ceramic, consists of molybdenum, for instance. In that case, this part of the electrode may have greater thickness than the rest of the electrode, constituting e.g. a conical plug which has sealing grooves on its surface and is insertable in a conductor aperture of equivalent size in the ceramic.

The advantage of the present invention over prior art is accomplishment of a simple and reliable inlet which retains complete sealing capacity also under variable conditions and in corrosive electrolytes. The invention is described in detail in the following, referring to the attached drawing, wherein:- Fig. 1 presents an inlet according to the invention, and Fig. 2 presents another inle^*c according to the inven¬ tion.

Referring now to Fig. 1, the wall 2 of steel comprises a flange 9 presenting a bore 10, through which a tubular inlet duct 3 has been passed. To the flange has been attached, with bolts 12, a fixing plate 13, the mating faces of flange and fixing plate having been ground to be level, whereby they require no other seal¬ ing means. The fixing plate presents a bore 14 matching the bore 10, the inlet duct being disposed to pass through both bores and being welded (11) to the fixing plate 13. This end of the duct comprises, within the duct, a cylindrical insulator plug 5 sealing tightly against its inner surface and presenting a conductor aperture 6.

On the inner end 7 of the inlet duct 3 has been provided an insulator plug 5, the shape of the inner surface of the inlet duct substantially conforming to this plug. The plug also presents in its centre a conductor aperture for the conductor electrode. Further¬ more, the embodiment here depicted comprises insulator beads or disks 8, which have been threaded to surround the conductor electrode in the inlet duct, in order to keep the conductor electrode apart from the inlet duct. The insulator beads may for instance consist of alu¬ minium oxide, or of another suitable insulating ma¬ terial.

The inlet duct depicted in Fig. 1 is assembled as follows. The inner end 7 of the inlet duct 2 is heated, which causes it to expand, and the insulator plug is pushed tight into this end of the inlet duct. After the temperature has levelled out between duct and plug, the plug will be tightly clamped in the duct. Next, both are heated so that the conductor aperture in the plug expands, whereby it becomes possible to push the conductor electrode therethrough, this electrode being tightened up in similar manner with the insulator plug as the temperatures equalize. The next step is to thread insulator beads on the conductor electrode over the entire length of the inlet duct, and attachment, in the manner described, of the plug and electrode on the other end of the duct. The inlet duct may then be intro¬ duced in the bore 10 and fixed in place by welding (11). In Fig. 2 is presented another inlet duct according to the invention. Here, a tubular inlet duct 3 of the same material as the wall has been welded (15) to the wall 2. On the inner end of said duct has, ac¬ cording to the invention, been provided a cylindrical plug 16 of suitable ceramic material and having an outer surface consistent with the cylindrical inner surface of the tube, in its centre belonging a conductor aper- ture 17. Inside the duct has been placed a conductor electrode 1 insulated from the inlet duct with an in¬ sulator 18, e.g. Teflon; the electrode may for instance consist of stainless steel or of another suitable metal. However, at the sealing portion of the inlet duct, that is, at the plug 16, the electrode consists of a piece 18 of different metal, e.g. molybdenum, which has a thermal expansion coefficient substantially equal to that of the surrounding plug 16 and that of the duct 3 surrounding the plug. It is thus understood that the expensive metal appropriate for the electrode need not be used for the entire length of the structure.

The other end 19 of the inlet duct 3 is merely closed in conventional manner, e.g with a threaded plug 21. The invention has been described in the forego¬ ing in detail, referring to some of its advantageous embodiments, without in any way confining the invention; its different embodiments being allowed to vary within the inventive idea delimited by the claims.

Claims

1. An inlet for carrying a conductor electrode (1) or equivalent in galvanically insulated mode through a wall (2) for instance into a metallic container, to be used e.g. in measurements of potential e.g. inside boilers, characterized in that the inlet comprises

- an inlet duct (3) of the wall material, belonging to the wall; - an insulator plug (5) of structural ceramic material, provided with a conductor aperture (6) , disposed in the inlet duct and having a thermal expansion coefficient substantially equal to that of the inlet duct;

- and a conductor electrode of a material having a thermal expansion coefficient substantially equal to that of said insulator plug, extending through the conductor aperture in the insulator plug.

2. Inlet according to claim 1, characterized in that the inlet duct consists of a hole in the wall.

3. Inlet according to claim 1, characterized in that the inlet duct consists of a tube (3) substan¬ tially integrally attached to the wall.

4. Inlet according to claim 3, characterized in that on at least one end of the tube belongs said insulator plug (5).

5. Inlet according to any one of claims 1-4, characterized in that the mutually opposed surfaces of the duct (3) and of the insulator plug (5) conform to each other.

6. Inlet according to any one of claims 1-4, characterized in that the mutually opposed surfaces of the conductor electrode (1) and of the insulator plug (5) conform to each other.

7. Inlet according to any one of claims 1-6, characterized in that the wall (2) and the inlet duct

(3) integrally attached thereto are metallic.

8. Inlet according to claim 7, characterized in that the conductor electrode (1) consists of molyb¬ denum, platinum, silver or steel.

9. Inlet according to any one of claims 1-8, characterized in that the insulator plug (5) consists of ceramic material, e.g. zirconium oxide or aluminium oxide.

10. Procedure for carrying a conductor, pipe, rod or equivalent in galvanically insulated mode through a wall, characterized in that for sealing and insulating material between the conductor and the wall is used structural ceramic material having a thermal expansion coefficient substantially equal to that of the wall, such as aluminium oxide or zirconium oxide, and for conductor is used metal having a substantially equi- valent thermal expansion coefficient, e.g. molybdenum, platinum or pressure vessel steel, the juncture between the components being accomplished with the aid of ther¬ mal expansion and shrinking, as a shrink joint.