GB1559739A

GB1559739A - Method of fastening a length of metal tube in a circular aperture in a metal plate

Info

Publication number: GB1559739A
Application number: GB843477A
Authority: GB
Original assignee: Rosemount Engineering Co Ltd
Current assignee: Emerson Process Management Ltd
Priority date: 1977-02-28
Filing date: 1977-02-28
Publication date: 1980-01-23
Also published as: DE7800015U1

Description

(54) A METHOD OF FASTENING A LENGTH OF METAL TUBE IN A CIRCULAR APERTURE IN A METAL PLATE (71) We, ROSEMOUNT ENGINEERING COMPANY LIMITED, a British Company, or Durban Road, Bognor Regis, Sussex P022 9QX do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the fastening of lengths of metal tubes in circular apertures in metal plates. The invention is particularly concerned with fastening the end portion of a tube in such a circular aperture. Known methods of fastening metal objects together which can be employed to fasten a tube in an aperture in a plate, include soldering, brazing and welding. However, each of these methods requires specialist tools and equipment and a fair degree of skill and experience.

In one aspect, the present invention provides a method of fastening an end portion of a length of metal tube in a circular aperture in a metal plate, the aperture being formed with a cylindrical flange portion having an internal diameter slightly greater than the external diameter of the tube, and the internal surface of the cylindrical flange portion having at least one circumferentially extending ridge thereon, the method comprising the steps of fitting the end portion of the length of tube into the flange portion, forcing into the open end of the tube adjacent the end portion thereof at least a part of a tool which part having in cross section the shape of a polygon with a diametrical extent greater than the internal diameter of the tube so as to deform the end of the tube and expand it firmly against the cylindrical flange portion of the aperture in the plate, and then withdrawing the tool from the end of the tube leaving the tube secured in the aperture of the plate. The performance of this method requires no special skills and only the use of simple hand tools such as a hammer and a vice, which are, with the exception of said tool with a polygonal cross section, commonly available in a small workshop. As the polygonal tool is forces into the open end of the tube the tube is expanded against the internal surface of the flange portion of the plate, causing the tube to be firmly fixed to the plate. Normally, the expansion of the end portion of the tube will cause a corresponding deformation of the sleeve portion as the polygonal tool is forced home. The or each ridge provided on the internal surface of the sleeve portion provides a firm gripping engagement between the internal surface and the external surface of the expanded portion of the tube.

One application of the above described method is in the assembly of resistance thermometers and thermocouples. It is known to make resistance thermometers and thermocouples with the sensing element mounted at a closed end of a length of metal tube, forming a sheath or probe. The other end of the tube is open and is secured in a circular aperture in a metal mounting plate, with the plate in a plane perpendicular to the axis of the tube. A terminal block of insulating material is fastened to the plate and the leads from the sensing element run the length of the tube emerging from the open end and are connected to terminals provided on the terminal block. When assembled in a factory, it is quite convenient to fasten the mounting plate to the open end of the sheath described above by welding or brazing. Since the length of the sheath from the mounting plate to the closed end is not adjustable once the thermometer or thermocouple is manufactured, it has been found necessary to offer for sale thermometers and thermocouples with ranges of sheath lengths, although having otherwise substantially identical characteristics.

The present invention further envisages, accordingly, a method of assembling a resistance thermometer or a thermocouple which comprises a sheath in the form of a length of metal tube closed at one end, a metal mounting plate for the sheath having a circular aperture in the plate formed with a cylindrical flange portion having an internal diameter slightly greater than the external diameter of the tube and the internal surface of the flange portion having at least one circumferentially extending ridge thereon the thermometer or the thermocouple further comprising a sensing element with leads which is positionable in the sheath adjacent the closed end and a terminal block mountable on the mounting plate and for providing connections to the sensing element leads, the method of assembling comprising the steps of cutting the tube, if required, to a desired length between the closed end and the open or cut end, fastening the open or cut end portion of the tube in the circular aperture of the mounting plate in accordance with the steps of the method of the invention described above and then fitting the sensing element in the tube mounting the terminal block on the mounting plate and connecting up the leads.

It is considered that a thermometer or a thermocouple can be assembled employing this method without the need for specialist tools on equipment and without the application of special skill. As a result, it is considered that the described method of assembling can be performed by the user of the device, who can then ensure that he cuts the sheath of the device to a length specifically suited to his own application.

Very conveniently, the internal surface of the flange portion of the plate is screw threaded to provide a plurality of circumferentially extending ridges. Further, said tool cross section is preferably a regular hexagon. The tool or part thereof may be forced into the tube by hammering. As one example, the tool may be withdrawn from the end of the tube by providing a screw thread on a portion of the tool which still extends from the tube when the tool is forced home, and screwing a nut on the screw thread so that the nut bears on the end face of the tube and/or on the plate and so that continued screwing of the nut pulls the tool from the tube.

Preferably the end portion of the tube is fitted into the flange portion such that the flange portion is directed away from the adjacent end face of the tube. Preferably the tube is held firmly clamped when the tool or part thereof is being forced into the tube.

The present invention still further envisages the provision of a kit for assembling a resistance thermometer or a thermocouple, the kit comprising a sheath in the form of a length of metal tube closed at one end, a metal mounting plate for the sheath having a circular aperture in the plate formed with a cylindrical flange portion having an internal diameter slightly greater than the external diameter of the tube and the internal surface of the flange portion having at least one circumferentially extending ridge thereon, a sensing element with leads which is positionable in the tube adjacent the closed end, a terminal block mountable on the mounting plate and for providing connections to the sensing element leads, and a tool of which at least a portion has in cross section the shape of a polygon with a diametrical extent greater than the internal diameter of the tube of the sheath, whereby the tool or a polygonal part thereof can be forced into the open end of the tube when this is fitted in the aperture in the mounting plate so as to deform the end portion of the tube and expand it firmly against the cylindrical flange portion of the aperture in the plate.

Preferably the polygon is a regular hexagon.

In one embodiment, the tool includes a screw threaded portion substantially co-axial with the polygonal portion and a nut threaded on the screw threaded portion, whereby the nut can be screwed, when the polygonal portion is forced home, to bear on the end face of the tube and/ or on the plate and continued screwing of the nut tends to pull the tool from the tube. Preferably also the tool includes a cylindrical end portion extending co-axially from the polygonal portion and having a diameter slightly less than the internal diameter of the tube. This cylindrical end portion can be fitted into the open end of the tube to position the tool before the polygonal portion is forced home.

Conveniently, the kit further includes a clamping jig comprising a split block shaped for engaging the tube and to enable the tube to be firmly clamping between the parts of the block without substantial deformation of the tube as a result of the clamped force. The clamping jig may comprise a portion of hexagonal rod, axially bored through with a bore diameter slightly greater than the external diameter of the tube, and diagonally split in half to enable the tube to be clamped between the halves when seated in the bore.

Where the internal diameter of the flange portion of the plate is described herein as being "slightly" greater than the external diameter of the tube, it is intended that the difference in diameters should be only sufficient to allow the tube to fit readily into the flange portion without significant effort. Although the relative sizes of the tube and the flange portion are not critical, it will be appreciated that an excessive difference between the diameters would make it difficult if not impossible to fasten the tube and plate firmly together without exceeding the limits of expansion of the end portion of the tube.

The present invention yet further envisages a resistance thermometer or thermocouple device having an elongate metal tube, forming a probe, closed at one end and open at the other, a metal mounting plate having an aperture in which the open end of the tube is fastened, a terminal block mounted on the mounting plate, a temperature sensor, i.e. a resistance thermometer sensor or a thermocouple sensor, located in the tube near the closed end and lead wires extending along the tube and connecting the sensor to terminals on the terminal block, the aperture in the mounting plate being formed with a cylindrical flange portion having at least one circumferentially extending ridge on the internal surface thereof, the open end portion of the tube extending inside the flange portion and being expanded, relative to the diameter of the rest of the tube, into a polygonal crosssection forming a pressure connection with the flange portion and with the or each said ridge biting into the outer surfaces of the end portion of the tube.

An example of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a cross-sectional representation of a metal plate for use in performing the present invention; Figure 2 is a view in elevation of a metal plate and a metal tube positioned ready to be fastened together, together with a tool positioned ready to be forced into the end of the tube; Figure 3 is a partial view in cross section showing the end portion of the tube fastened in the flange portion of the plate after withdrawal of the tool; Figure 4 is a sectional view of the clamping jig taken along line 4-4 of Figure 2 and Figure 5 is a view of a complete resistance thermometer or a thermocouple assembled in accordance with the present invention.

Referring to Figure 2, a length of tube 10 is illustrated firmly held between the jaws 11 and 12 of a vice, the rest of which is not shown in the Figure. The length of tube 10, of which only a portion is shown in Figure 2, is typically of stainless steel, and though open at the end visible in Figure 2 is closed at the lower end.

The tube 10 is clamped between the jaws 11 and 12 by means of a clamping jig 13. The jig 13 comprises a length of hexagonal rod with an axial bore 14 having a diameter slightly greater than the external diameter of the tube 10. The rod 13 is split in a diagonal plane into two halves 15 and 16. The tube 10 is seated in the portions of the bore 14 provided in each of the two halves 15 and 16 and the halves are pressed firmly together by the jaws 11 and 12 of the vice, in this way, the tube 10 is firmly held without substantial deformation over the length where it is gripped by the bore 14 of the jig 13.

At an upper end 17 the jig 13 has a recess 18 formed by an enlargement of the bore 14 near the end 17. The purpose of the recess 18 will become apparent later. The jig 13 may be split completely into the two halves 15 and 16.

However, as shown in Figure 4, a web 50 of the material of the hexagonal rod may be left connecting the two halves together along one side of the rod. The web 50 should be sufficiently small to enable the two halves to move together when held between the jaws of the vice, in effect hinging at the web 50.

In Figure 2, there is shown fitted onto an end portion 19 of the tube 10 a metal plate 20, typically also of stainless steel. In the described example the metal plate 20 is formed as a circular disc and has an aperture 21 at the centre.

The aperture 21 is formed by a cylindrical flange portion 22 extending perpendicular to the plane of the plate 20. The flange portion 22 is formed integrally with the plate 20 and has an internal screw thread 23 (Figure 1). As shown in Figure 2, the end portion 19 of the tube 10 is fitted into the aperture 21 with the flange portion 22 pointing away from the adjacent open end 24 of the pipe and being located in the recess 18 in the clamp jig 13.

The plate 20 rests against an end face 25 of the jig 13 and the tube 10 is positioned relative to the jig 13, before firmly clamped, so that the end 24 of the pipe is substantially in or slightly above the plane of the plate 20.

When the end portion 19 of the tube 10 has been fitted into the aperture 21 of the plate 20 as shown and the tube 10 is firmly clamped between the jaws 11 and 12 of the clamp, a tool 26 is inserted into the open end 24 of the pipe.

The tool 26 includes a portion 27 having the shape, in cross section, of a regular hexagon.

The diametrical extent of the hexagonal portion 27, that is to say the largest cross sectional dimension through the axis of the portion is made greater than the internal diameter of the tube 10. The tool 26 includes a cylindrical portion 28 which extends co-axially from the lower end, in Figure 2, of the hexagonal portion 27 and has a diameter slightly less than the internal diameter of the tube 10 so that it can fit into the open end 24 of the pipe as shown in the Figure. The cylindrical portion 28 is effective to locate the tool 26 so that the hexagonal portion 27 of the tool can be forced into the end portion 19 of the pipe.

In operation, the tool 26 is positioned by inserting the cylindrical 28 into the end of the tube and the hexagonal portion 27 is then forced into the end portion of the tube, for example by hammering an upper end 29 of the tool. As the hexagonal portion 27 is forced into the end portion 19, the end portion is deformed and expanded against the internal surface of the flange portion 22 of the plate of 20. It will be appreciated that the external diameter of the tube 10 is only slightly less than the internal diameter of the flange portion 22 sufficient to enable the tube to be readily ed into the aperture 21. Thus, as the end portion 19 of the tube is expanded, the flange portion 22 of the plate 20 is also deformed and expanded and both the end portion 19 and the flange portion 22 adopt a hexagonal shape corresponding to the shape of the hexagonal portion 27 of the tool. As the end portion 19 of the tube is expanded against the flange portion 22, the circumferentially extending ridges of the screw thread 23 on the internal surface of the flange portion 22 tend to bit into the external surface of the expanded part of the tube, thereby ensuring a firm and rigid engagement between the tube and the plate 20.

Once the tool 26 has been hammered fully home, that is to say when the hexagonal portion 27 of the tool has been forced home so that the entire length of the hexagonal portion 27 is forced into the end of the tube, the tool 26 is withdrawn. In order to facilitate this withdrawal, the tool is formed with a screw threaded portion 30 substantially coaxial with the hexagonal portion 27, and at the opposite end of the hexagonal portion form the cylindrical portion 28. When the hexagonal portion 27 is forced fully home, the screw threaded portion 30 still extends from the end of the tube 10 with the lower end 31 of the screw threaded portion substantially abutting the end face of the tube. A nut 32 is provided threaded on the portion 30 and the tool 26 is withdrawn by screwing the nut 32 down the threaded portion 30 until the bottom face 33 of the nut engages the top face of the plate 20. The tool 26 is then withdrawn from the tube 10 by continuing to screw the nut 32 down against the plate 20 so that the screwing action causes the hexagonal portion 27 of the tool to be pulled out of the end of the tube 10. Lubrication may be provided between the face 33 of the nut 32 and the upper surface of the plate 20. To prevent excessive torque being applied by the tool 26 to the tube 10 during the withdrawing operation, a further hexagon 34 is provided substantially co-axial with the screw threaded portion 30. The hexagon 34 is firmly fixed relative to the screw threaded portion 30 and the hexagonal portion 27 of the tool. The hexagon 34 can be engaged by a second spanner when the nut 32 is being screwed down so as to absorb the torque transmitted to the tool 26 when turning the nut 32.

When the tool 26 is withdrawn from the tube 10, the pipe and plate assembly is removed from the clamping jig 13. A typical join between the end portion 19 of the tube and the plate 20 is illustrated in Figure 3.

Referring now to Figure 5, a complete resistance thermometer or a complete thermocouple device is illustrated including the tube 10 and the plate 20 secured together as described above with reference to Figures 1-4. The end 35 of the tube 10 remote from the plate 20 is closed. The length of pipe 10 forms a sheath or probe for the device. A sensing element 36 is inserted into the pipe 10 and positioned adjacent the closed end 35. Leads 37 for the element 36 extend inside the length of the tube 10 emerging at the open of the tube.

The plate 20 constitutes a mounting plate, typically made of stainless steel on which there is mounted a terminal block 38. The terminal block 38 is usually made of insulating material and is fastened to the side of the plate 20 opposite to the flange portion 22. The terminal block 38 may be fastened to the plate 20 by means of screws 39. The terminal block 38 has mounted on the upper surface thereof terminals 40. The leads 37 of the element 36 extend right through the terminal block 38 via a central bore 41 which is substantially coaxial with the tube 10. The leads 37 are then connected to the terminals 40. The terminals 40 enable the resistance thermometer to be connected to a utilisation circuit as required.

Where the device is a resistance thermometer, the element 36 is a resistance element or sensor. Where the device is a thermocouple, the element 36 is a thermocouple element.

One of the problems with resistance thermometers or thermocouples having elongate probes is that the desirable length of the probe is different for different applications of the device. Thus, manufacturers typically offer for sale resistance thermometers and thermocouples having ranges of probe lengths, although the other parameters of the devices may all be identical. In accordance with an embodiment of the present invention, a manufacturer offers for sale a standard kit of parts which enables the purchaser to assemble a device which has a probe length of his choice.

The kit comprises a length of stainless steel tube 10 which is closed at one end and having a length greater than the likely maximum probe length desired by the purchaser. The kit further includes a mounting plate of stainless steel similar to that illustrated in Figure 1, the sensing element suitable to be inserted in the tube 10 and positioned adjacent the closed end of the tube, with its leadout wires extending along the length of the tube, the terminal block for mounting on the mounting plate and for providing connections to the leads of the element. Also provided in the kit is a tool, similar to the tool 26, for use in fastening the mounting plate to the length of tube. Before assembling the resistance thermometer, the length of tube provided is, if necessary cut to the desired length. Then the tube and the mounting plate are secured together as described above. Finally, the remaining parts of the device are assembled including inserting the element 36, mounting the terminal block 38 on the mounting plate and connecting up the sensor leads to the terminals 40. The resulting fully assembled resistance thermometer, or thermocouple as the case may be, is as illustrated in Figure 5. The kit may also include the clamping jig 13.

It can be seen therefore, that the kit of parts described above enables a resistance thermometer or a thermocouple device to be assembled having a chosen probe length and using only straight-forward hand tools available in any small workshop. The only tools required apart from the tool 26 and the clamping jig 13 supplied with the kit would be a hammer, a vice and of course a screw driver.

WHAT WE CLAIM IS: 1. A method of fastening an end portion of a length of metal tube in a circular aperture in a metal plate, the aperture being formed with a cylindrical flange portion having an internal diameter slightly greater than the external diameter of the tube, and the internal surface of the cylindrical flange portion having at least one circumferentially extending ridge thereon, the method comprising the steps of fitting the end portion of the length of tube into the flange portion, forcing into the open end of the tube adjacent the end portion thereof at least a part of a tool which part having in cross section the shape of a polygon with a diametrical extent greater than the internal diameter of the tube so as to deform the end of the tube and expand it firmly against the cylindrical flange portion of the aperture in the plate, and then withdrawing the tool from the end of the tube leaving the tube secured in the aperture of the plate.

2. A method of assembling a resistance thermometer or a thermocouple which comprises a sheath in the form of a length of metal tube closed at one end, a metal mounting plate for the sheath having a circular aperture in the plate formed with a cylindrical flange portion having an internal diameter slightly greater than the external diameter of the tube and the internal surface of the flange portion having at least one circumferentially extending ridge thereon the thermometer or the thermcouple further comprising a sensing element with leads which is positionable in the sheath adjacent the closed end and a terminal block mountable on the mounting plate and for providing connections to the sensing element leads, the method of assembly comprising the steps of cutting the tube, if required, to a desired length between the closed end and the open or cut end, fastening the open or cut end portion of the tube in the circular aperture of the mounting plate in accordance with the steps of the method as claimed in claim 1 and then fitting the sensing element in the tube mounting the terminal block on the mounting plate and connecting up the leads.

3. A method of assembling a resistance thermometer or a thermocouple as claimed in claim 2 wherein the internal surface of the flange portion of the plate is screw threaded to provide a plurality of circumferentially extending ridges.

4. A method of assembling as claimed in either of claims 2 and 3, wherein said tool cross-section is a regular hexagon.

5. A method of assembling as claimed in any of claims 2 to 4 wherein the tool or part thereof is forced into the tube by hammering.

6. A method of assembling as claimed in any of claims 2 to 5 wherein the tool is withdrawn from the end of the tube by providing a screw thread on a portion of the tool which still extends from the tube when the tool is forced home, and screwing a nut on the screw thread so that the nut bears on the end face of the tube and/or on the plate and so that continued screwing of the nut pulls the tool from the tube.

7. A method of assembling as claimed in any of the claims 2 to 6 wherein the end portion of the tube is fitted into the flange portion such that the flange portion is directed away from the adjacent end face of the tube.

8. A method of assembling as claimed in any of claims 2 to 7 wherein the tube is held firmly clamped when the tool or part thereof is being forced into the tube.

9. A kit for assembling a resistance thermometer or a thermocouple, the kit comprising a sheath in the form of a length of metal tube closed at one end, a metal mounting plate for the sheath having a circular aperture in the plate formed with a cylindrical flange portion having an internal diameter slightly greater than the external diameter of the tube and the internal surface of the flange portion having at least one circumferentially extending ridge thereon, a sensing element with leads which is positionable in the tube adjacent the closed end, a terminal block mountable on the mounting plate and for providing connections to the sensing element leads, and a tool of which at least a portion has in cross section the shape of a polygon with a diametrical extent greater than the internal diameter of the tube of the sheath, whereby the tool or a polygonal part thereof can be forced into the open end of the tube when this is fitted in the aperture in the mounting plate so as to deform the end portion of the tube and expand it firmly against the cylindrical flange portion of the aperture in the plate.

10. A kit as claimed in claim 9 wherein the polygon a regular hexagon.

11. A kit as claimed in either of claims 9 and 10 wherein the tool includes a screw threaded portion substantially co-axial with the polygonal portion and a nut threaded on the screw threaded portion, whereby the nut can be screwed, when the polygonal portion is forced home, to bear on the end face of the tube and/ or on the plate and continued screwing of the nut tends to pull the tool from the tube.

12. A kit as claimed in any of claims 9 to 11 wherein the tool includes a cylindrical end portion extending co-axially from the polygonal portion and having a diameter slightly less than the internal diameter of the tube.

13. A kit as claimed in any of claims 9 to 12

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. It can be seen therefore, that the kit of parts described above enables a resistance thermometer or a thermocouple device to be assembled having a chosen probe length and using only straight-forward hand tools available in any small workshop. The only tools required apart from the tool 26 and the clamping jig 13 supplied with the kit would be a hammer, a vice and of course a screw driver. WHAT WE CLAIM IS:

1. A method of fastening an end portion of a length of metal tube in a circular aperture in a metal plate, the aperture being formed with a cylindrical flange portion having an internal diameter slightly greater than the external diameter of the tube, and the internal surface of the cylindrical flange portion having at least one circumferentially extending ridge thereon, the method comprising the steps of fitting the end portion of the length of tube into the flange portion, forcing into the open end of the tube adjacent the end portion thereof at least a part of a tool which part having in cross section the shape of a polygon with a diametrical extent greater than the internal diameter of the tube so as to deform the end of the tube and expand it firmly against the cylindrical flange portion of the aperture in the plate, and then withdrawing the tool from the end of the tube leaving the tube secured in the aperture of the plate.

10. A kit as claimed in claim 9 wherein the polygon a regular hexagon.

13. A kit as claimed in any of claims 9 to 12

and further including a clamping jig comprising a split block shaped for engaging the tube and to enable the tube to be firmly clamping between the parts of the block without substantial deformation of the tube as a result of the clamp force.

14. A kit as claimed in claim 13 wherein the clamping jig comprises a portion of hexagonal rod, axially bored through with a bore diameter slightly greater than the external diameter of the tube, and diagonally split in half to enable the tube to be clamped between the halves when seated in the bore.

15. A resistance thermometer or thermocouple device having an elongate metal tube, forming a probe, closed at one end and open at the other, a metal mounting plate having an aperture in which the open end of the tube is fastened, a terminal block mounted on the mounting plate, a temperature sensor, i.e. a resistance thermometer sensor or a thermocouple sensor, located in the tube near the closed end and lead wires extending along the tube and connecting the sensor to terminals on the terminal block, the aperture in the mounting plate being formed with a cylindrical flange portion having at least one circumferentially extending ridge on the internal surface thereof, the open end portion of the tube extending inside the flange portion and being expanded, relative to the diameter of the rest of the tube, into a polygonal cross-section forming a pressure connection with the flange portion and with the or each said ridge biting into the outer surface of the end portion of the tube.

16. A device as claimed in claim 15 wherein the inside surface of the flange portion is screw threaded.

17. A device as claimed in claim 15 or claim 16 wherein the expanded cross section of the end portion of the tube is hexagonal.

18. A device as claimed in any of claims 15 to 17, wherein the tube and the mounting plate are made of stainless steel.

19. A method of assembling a resistance thermometer or a thermocouple device substantially as hereinbefore described, with reference to the accompanying drawings.

20. A kit of parts, for use in assembling a resistance thermometer or thermocouple device, substantially as hereinbefore described with reference to the accompanying drawings.

21. A resistance thermometer or a thermocouple device substantially as hereinbefore described with reference to and as illustrated in Figure 5 of the accompanying drawings.

22. A resistance thermometer or a thermocouple device assembled by the method claimed in any one of claims 2 to 8 or with the kit claimed in any one of claims 9 to 14.