GB2112306A - Temperature or pressure sensing element - Google Patents
Temperature or pressure sensing element Download PDFInfo
- Publication number
- GB2112306A GB2112306A GB08136976A GB8136976A GB2112306A GB 2112306 A GB2112306 A GB 2112306A GB 08136976 A GB08136976 A GB 08136976A GB 8136976 A GB8136976 A GB 8136976A GB 2112306 A GB2112306 A GB 2112306A
- Authority
- GB
- United Kingdom
- Prior art keywords
- capillary tube
- sensing element
- bellows device
- capsule
- joint
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G12—INSTRUMENT DETAILS
- G12B—CONSTRUCTIONAL DETAILS OF INSTRUMENTS, OR COMPARABLE DETAILS OF OTHER APPARATUS, NOT OTHERWISE PROVIDED FOR
- G12B1/00—Sensitive elements capable of producing movement or displacement for purposes not limited to measurement; Associated transmission mechanisms therefor
- G12B1/04—Hollow bodies having parts which are deformable or displaceable under pressure, e.g. Bourdon tube, bellows
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K5/00—Measuring temperature based on the expansion or contraction of a material
- G01K5/32—Measuring temperature based on the expansion or contraction of a material the material being a fluid contained in a hollow body having parts which are deformable or displaceable
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H35/00—Switches operated by change of a physical condition
- H01H35/24—Switches operated by change of fluid pressure, by fluid pressure waves, or by change of fluid flow
- H01H35/32—Switches operated by change of fluid pressure, by fluid pressure waves, or by change of fluid flow actuated by bellows
Abstract
A temperature or pressure sensing element of the kind having an expansible capsule or bellows (1) connected a capillary tube (2) by way of an hermetic seal is fabricated by sealing the capillary tube (2), which may be of aluminium, stainless steel, brass or copper, to the bellows or capsule (1) with a synthetic resin bonded joint (14). The resin joint also serves to connect the capillary tube (2) to a rigid support plate (9).
Description
SPECIFICATION
Temperature or pressure sensing element
This invention relates to the manufacture of temperature or pressure sensing elements, in particular temperature sensing elements of the type comprising an expansible capsule or bellows device connected to a capillary tube which is closed at its end remote from the capsule or bellows device to form a hermetically sealed system.
Fluid filled hermetically sealed temperature
sensing elements of the type referred to above are
commonly employed in thermostatic controls and
the like, the fluid filling of the sealed system
comprising a gas, vapour, or liquid/vapour in
equilibrium, according to the intended practical
application and range of temperatures for which
the element is to be used.
The walls of the expansible capsule or bellows
device are commonly made of spring steel and the
capillary tube is most commonly made of copper.
The capsule or bellows device is usually supported
by a mild steel support plate in the region where
the capsule or bellows device adjoins the capillary
tube. The joint between the capillary tube and the
capsule or bellows device has to be mechanically
strong and hermetically sealed. This joint is, in the
known manufacturing technique, formed by
soldering. Thus in the most usual arrangement the
expansible capsule or bellows device is connected
to a rigid support plate having an aperture through
which the capillary tube passes, this aperture
being sealed by the solder joint, which also forms
a mechanical bond between the support plate
and the adjoining end of the capillary tube.
After soldering the joint between the capillary
tube and the capsule or bellows device the
assembly has to be wire-brushed to remove solder
flux residues and the assembly is then heated in
vacuo to effect complete dehydration before the
introduction of the gas or liquid filling.
The high cost of copper renders the use of
alternative materials for the capillary tube
attractive. The use of aluminium capillary tube in
place of copper capillary tube has certain
advantages, not least of which is a significantly
lower cost. A problem arises, however, in the
provision of a satisfactory sealed joint between
the capillary tube and the capsule or bellows
device to which it is connected, given that a
conventional soldered joint cannot be used to
effect a sealed bond between aluminium and steel
surfaces.
It has been found that a satisfactory sealed joint
can be made using a resin bonding material.
Accordingly the present invention provides, in one
aspect, a temperature or pressure sensing element
comprising an expansible capsule or bellows
device connected to a capillary tube, in which the
capillary tube is sealed to the capsule or bellows
device by a synthetic resin bonded joint.
By using a resin bonded joint it is possible to
form an extremely strong connection between the
capillary tube and the capsule or bellows device, using a fabrication method which is significantly cheaper than the soldering technique used when copper capillary tube is employed. The capillary tube may be fabricated in, for example, aluminium, stainless steel or brass. Where aluminium is employed the capillary tube is preferably anodised, at least on its external surface. Various resins may be employed to form the resin bonded joint. An epoxy resin has proved satisfactory, preferably a single part epoxy resin which is heat-cured. The heat-curing of the resin joint assists the dehydration of the assembly. A further incidental advantage of employing resin as the bonding material is that no separate wire brushing step is necessary to remove flux residues.
The resin bonded joint is preferably reinforced by a metal sleeve which surrounds the end of the capillary tube adjoining the capsule or bellows device and which is embedded at least partly in the resin of the joint.
Figure 1 is a diagrammatic sectional view of a temperature sensing element fabricated by a known process according to the prior art;
Figure 2 is a diagrammatic sectional view, corresponding to Figure 1, illustrating a temperature sensing element according to one embodiment of the present invention;
Figures 3 and 4 are diagrammatic sectional views, similar to Figure 2, illustrating alternative embodiments of temperature sensing elements according to the invention;
Figure 5 illustrates diagrammatically the sequence of operations in one method of sealing the end of the capillary tube in a temperature sensing element according to the invention, and
Figure 6 illustrates diagrammatically an alternative method of sealing the end of a capillary tube in a temperature sensing element according to the invention.
Throughout the drawings the same reference numerals are used to indicate the same or corresponding component parts.
Referring first to Figure 1, a typical temperature sensing element made by a known prior art fabrication process is illustrated. A flexible-walled expansible capsule or bellows device 1 is connected to a capillary tube 2 which is closed at its end remote from the bellows device 1, forming a hermetically sealed system containing a gas, vapour or liquid/vapour filling. The bellows device 1 comprises two stainless steel diaphragms 3, 4 which are welded together peripherally. A rigid mild steel boss 5 is projection welded to a central part of the diaphragm 3 and acts as a force transmitting member for applying an actuating force to a thermostat or other mechanism (not shown) in response to temperature variations in the sealed system.A rigid base member 6 of mild steel is projection welded to a central part of the other diaphragm 4, which has a central hole 7 aligned with and slightly smaller in diameter
Figure 1 is a diagrammatic sectional view of a temperature sensing element fabricated by a known process according to the prior art;
Figure 2 is a diagrammatic sectional view, corresponding to Figure 1, illustrating a temperature sensing element according to one embodiment of the present invention;
Figures 3 and 4 are diagrammatic sectional views, similar to Figure 2, illustrating alternative embodiments of temperature sensing elements according to the invention;;
Figure 5 illustrates diagrammatically the sequence of operations in one method of sealing the end of the capillary tube in a temperature sensing element according to the invention, and
Figure 6 illustrates diagramatically an alternative method of sealing the end of a capillary tube in a temperature sensing element according to the invention.
Throughout the drawings the same reference numerals are used to indicate the same or corresponding component parts.
Referring first to Figure 1, a typical temperature sensing element made by a known priort art fabrication process is illustrated. A flexible-walled expansible capsule or bellows device 1 is connected to a capillary tube 2 which is closed at its end remote from the bellows device 1 , forming a hermetically sealed system containing a gas, vapour or liquid/vapour filling. The bellows device 1 comprises two stainless steel diaphragms 3, 4 which are welded together peripherally. A rigid mild steel boss 5 is projection welded to a central part of the diaphragm 3 and acts as a force transmitting member for applying an actuating force to a thermostat or other mechanism (not shown) in response to temperature variations in the sealed system.A rigid base member 6 of mild steel is projection welded to a central part of the other diaphragm 4, which has a central hole 7 aligned with and slightly smaller in diameter than a central hole in the base member 6. The base member 6 is formed with an upstanding tubular portion 8 which projects through an aperture in a mild steel support plate 9.
The boss 5 and base member 6 of the bellows device are electroplated with nickel sulphamate to resist corrosion and assist welding. The mild steel support plate 9 is copper piated.
The bellows device 1 is secured to the support plate 9 by swaging of the tubular portion 8, the diameter of the latter being slightly greater than that of the capillary tube 2. The capillary tube passes through the tubular portion 8 of the base member 6 and abuts the portion of the diaphragm 4 surrounding the hole 7. Before being fitted to the bellows device 1 the capillary tube 2 is formed with a bend so that the end ofthe capillary tube which is joined to the bellows device 1 is perpendicular to the plane of the bellows device 1 and its support plate 9. The capillary tube 2 is anchored to the support plate 9 by means of deformable lugs 10 formed integrally with the support plate 9.With the capillary tube 2 correctly positioned sealing is then effected by the injection of solder 11 into a shallow annular well 12 in the support plate 9 surroundinq the capillary tube 2. The solder 11 forms a mechanical joint between the support plate 9 and the capillary tube 2, and also enters the space between the capillary tube 2 and the tubular portion 8 of the base member 6, forming a hermetic seal.
After cooling of the soldered joint the joint itself is wire brushed to remove flux residues and the entire assembly is then dehydrated by heating in a chamber in vacuo. This is followed by charging of the interior of the capillary tube 2 and the bellows device 1 with the appropriate quantity of gas or liquid, following which a cold weld is made in the end of the capillary tube 2 remote from the bellows device 1 to seal the interior of the capillary tube. The sealed end of the capillary tube is then swaged, crimped and fused to form a sealed tip 1 3. The completed and sealed temperature sensing element may be electroplated with tin prior to inspection.
The present invention makes use of an alternative material for the capillary tube 2, in this example aluminium capillary tube. The aluminium tube 2 is anodised on its external surface. The assembly of the temperature sensing element is similar to that illustrated in Figure 1, except that the bonding of the capillary tube 2 to the support plate 9 is effected by means of a synthetic resin bonding material 14, in this case a single part epoxy resin. A suitable resin for this purpose is
ESP 109 resin manufactured by Permabond
Adhesives Ltd. The resin 14 forms a joint similar to the soldered joint 11 of Figure 1, hermetically sealing the capillary tube both to the support plate 9 and to the base member 6 of the bellows device 1. Curing of the resin is effected by heating, for example to 1 800C for 20-30 minutes.The heat-curing of the resin also assists dehydration of the bellows device and capillary tube 2, avoiding the need for this as a separate step.
Reinforcement of the resin bonded joint is afforded by a metal sleeve 1 5 which surrounds the end of the capillary tube 2 adjoining the bellows support plate 9, the end of the sleeve 1 5 adjacent
the bellows device 1 being flared outwardly and located in the well 12, so that, upon formation of the resin joint 14, it is embedded in the resin.
By providing a pre-anodised aluminium capillary tube 2 the need for a separate finishing coating of electroplated tin can be avoided, particularly if the bellows support plate 9 is electroplated, for example, with nickel sulphamate, prior to assembly.
Figure 3 illustrates a variant of the embodiment shown in Figure 2, in which a weld 1 6 is formed between the aluminium capillary tube 2 and the crimped end of the tubular portion 8 of the base plate 6. This weld 16, which may alternatively comprise a soldered joint, is carried out before the formation of the resin bonded joint 14, and forms a preliminary seal.
Figure 4 shows a further variant of the temperature sensing element illustrated in
Figure 2 in which the reinforcing sleeve 1 5 is omitted, the joint 14 being formed with resin only.
The end of the capillary tube 2 adjoining the
bellows device 1 may be strengthened by the
provision of a preformed bulge portion 17, as
shown diagrammatically.
The filling of the capillary tube 2 of the
temperature sensing element, and its subsequent
closure, can be performed in a single cold-forging
operation when aluminium is used as the material
for the capillary tube. One sequence of operations
for closure of the capillary tube 2 is illustrated in
Figures 5(a)-(d). The capillary tube 2 and its
associated bellows device 1 is charged with fluid
under pressure, in this example, refrigerant gas; from a charging manifold or reservoir 1 8 (Figure
5(a)) with which the open end of the capillary tube 2 communicates through a seal 1 9. After filling to the required pressure the capillary tube 2 is crimped externally of the charging manifold 18 at 20 (Figure 5(b)).The crimping operation forms a cold-weld and is followed by parting of the capillary tube 2 at the site of the crimp 20. The closed end of the capillary tube 2 is then finally sealed by a cold-forging operation in which the end of the capillary tube 2 is inserted in a die 21 and deformed by a punch 22 which acts axially on the closed end of the capillary tube 2, forming an enlarged sealed end 23 (Figure 5(d)). The resulting sealed end 23 would not necessarily have an enlarged diameter as shown.
An alternative method of closing and sealing the capillary tube 2 is illustrated in Figure 6, in
which the cold-forging of the end of the capillary tube to form the enlarged end 23 is effected in a
single operation. The end of the open capillary tube 2 is inserted in the charging manifold 18 through the seal 19, as illustrated in Figure 5(a)
and is held firmly in a clamp or jaws. A punch 22
moves axially with respect to the end of the capillary tube 2 and passes through the charging
manifold 18, through a further seal 24. The punch 22 cold-forms the enlarged end 23 of the capillary tube 22 in the manifold 18, immediately after the charging operation, forming a finished end 23 similar to that illustrated in Figure 5(d).
The cold-forged sealed end 23 of the capillary tube 2 is stronger and less vulnerable to damage than the sealed capillary tube ends formed by the traditional method. Moreover, the joint between the capillary tube and the bellows device is stronger and more easily made than the traditional soldered joint.
Other capillary tube materials which may be bonded using the method of the present invention are stainless steel, copper, brass and copper plated mild steel. Aluminium is, however, preferred because of its relative cheapness and its greater flexibility, rendering the sensing element easier to install.
The capillary tube 2 in the temperature sensing element of the present invention is preferably preanodised, as stated previously. Alternative surface treatments may, however, be employed, including a pre-coating with paint or plastic materials including epoxy, epoxy polyester of ethyl vinyl acetate applied by dipping, spraying, electrophoretic or powder coating methods. The coating material may be applied either as a precoat to the capillary or may be applied as a coating after the assembly of the sensing element.
Similarly, other environmentally compatible plating finishes may be applied to the other component parts of the sensing element according to the intended field of application.
Although the invention has been described with particular reference to a temperature sensing element, it will be appreciated that it is also applicable to pressure sensing elements, in which case the capillary tube connected to the capsule ol bellows device would be open-ended.
Claims (14)
1. A temperature or pressure sensing element comprising an expansible capsule or bellows device connected to a capillary tube which is closed at its end remote from the capsule or bellows device to form a hermetically sealed system, in which the capillary tube is sealed to the capsule or bellows device by a synthetic resin bonded joint.
2. A sensing element according to Claim 1, in which the capillary tube is fabricated in aluminium, stainless steel, brass or copper.
3. A sensing element according to Claim 1 or
Claim 2, in which the capillary tube is bonded to the capsule or bellows device by an epoxy resin joint.
4. A sensing element according to Claim 1,
Claim 2 or Claim 3, in which the resin bonded joint is reinforced by a metal sleeve which surrounds the end of the capillary tube adjoining the capsule or bellows device and which is embedded at least partly in the resin of the joint.
5. A sensing element according to any one of the preceding claims, in which a rigid base member of the capsule or bellows device is attached to a rigid support plate having an
aperture through which the capillary tube passes,
the capillary tube being bonded to a surrounding
part of the support plate by the resin joint, which
also forms a hermetic seal between the capillary
tube and the capsule or bellows device.
6. A sensing element according to Claim 5, in
which the base member has a tubular portion
which projects through the aperture in the support
plate and which is swaged to attach the base
member to the support plate, the said tubular
portion being embedded in the resin joint.
7. A method of making a temperature or pressure sensing element in accordance with
Claim 1, in which one end of a capillary tube is connected to a support member of a diaphragm or bellows device by the formation of a resin-bonded hermetically sealed joint and the other end of the capillary tube is closed by a forging operation.
8. A method according to Claim 7, in which the cold-forging operation is preceded by a cold welding or crimping step to close the said other end of the capillary tube.
9. A method according to Claim 7, in which the cold-forging operation is carried out while the said other end of the capillary tube is in communication with a supply of charging fluid under pressure.
10. A method according to Claim 7, Claim 8 or
Claim 9, in which the cold-forging is effected by van impact tool acting axially on the said other end of the capillary tube.
11. A temperature or pressure sensing element substantially as herein described with reference to and as shown in any of Figures 1 to 4 of the accompanying drawings.
New claims or amendments to claims filed on 1
July 1982.
New or amended claims:
12. A method of making a temperature or pressure sensing element of the kind comprising an aluminium, copper, or other ductile metal capillary tube connected to a diaphragm or bellows device, in which the end of the capillary tube remote from the diaphragm or bellows device is closed by a -old-forging operation.
13. A method according to Claim 12, in which the cold-forging operation is preceded by a cold welding or crimping step to close the said end of the capillary tube.
14. A method according to Claim 12, in which the cold-forging operation is carried out while the said end of the capillary tube is in communication with a supply of charging fluid under pressure.
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08136976A GB2112306A (en) | 1981-12-08 | 1981-12-08 | Temperature or pressure sensing element |
| IT8268432A IT8268432A0 (en) | 1981-12-08 | 1982-12-07 | TEMPERATURE OR PRESSURE SENSOR ELEMENT AND PROCEDURE FOR ITS CREATION |
| PCT/GB1982/000345 WO1983002157A1 (en) | 1981-12-08 | 1982-12-07 | Temperature or pressure sensing element |
| JP83500271A JPS58502065A (en) | 1981-12-08 | 1982-12-07 | Temperature or pressure sensing element |
| DE823249267T DE3249267T1 (en) | 1981-12-08 | 1982-12-07 | TEMPERATURE OR PRESSURE SENSING ELEMENT |
| EP83900200A EP0095494A1 (en) | 1981-12-08 | 1982-12-07 | Temperature or pressure sensing element |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08136976A GB2112306A (en) | 1981-12-08 | 1981-12-08 | Temperature or pressure sensing element |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2112306A true GB2112306A (en) | 1983-07-20 |
Family
ID=10526447
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08136976A Withdrawn GB2112306A (en) | 1981-12-08 | 1981-12-08 | Temperature or pressure sensing element |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0095494A1 (en) |
| JP (1) | JPS58502065A (en) |
| DE (1) | DE3249267T1 (en) |
| GB (1) | GB2112306A (en) |
| IT (1) | IT8268432A0 (en) |
| WO (1) | WO1983002157A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU579117B2 (en) * | 1984-01-27 | 1988-11-17 | Ranco Incorporated | Control device |
| WO1999046569A1 (en) * | 1998-03-12 | 1999-09-16 | Ge Procond Elettronica S.P.A. | Leakproof thermostat |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20140091152A1 (en) * | 2012-09-28 | 2014-04-03 | Invensys Appliance Controls South America | Temperature sensor using aluminum capillary |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2698766A (en) * | 1951-11-19 | 1955-01-04 | Cutler Hammer Inc | Pressure responsive power elements |
| US3654578A (en) * | 1970-05-12 | 1972-04-04 | Gen Electric | Condition responsive switch mechanism |
| GB1378256A (en) * | 1972-06-27 | 1974-12-27 | Springfield Instr Co Inc | Barometer capsule and method of manufacture |
| GB2057686A (en) * | 1979-08-29 | 1981-04-01 | Univ Bath | Thermal Actuators |
| FR2480938A3 (en) * | 1980-04-22 | 1981-10-23 | Ranco Inc | Capillary based temp. sensors with protective resin coating - pref. of polyester, epoxy or saponified EVA resin |
-
1981
- 1981-12-08 GB GB08136976A patent/GB2112306A/en not_active Withdrawn
-
1982
- 1982-12-07 EP EP83900200A patent/EP0095494A1/en not_active Withdrawn
- 1982-12-07 JP JP83500271A patent/JPS58502065A/en active Pending
- 1982-12-07 DE DE823249267T patent/DE3249267T1/en not_active Withdrawn
- 1982-12-07 IT IT8268432A patent/IT8268432A0/en unknown
- 1982-12-07 WO PCT/GB1982/000345 patent/WO1983002157A1/en not_active Application Discontinuation
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU579117B2 (en) * | 1984-01-27 | 1988-11-17 | Ranco Incorporated | Control device |
| WO1999046569A1 (en) * | 1998-03-12 | 1999-09-16 | Ge Procond Elettronica S.P.A. | Leakproof thermostat |
Also Published As
| Publication number | Publication date |
|---|---|
| IT8268432A0 (en) | 1982-12-07 |
| EP0095494A1 (en) | 1983-12-07 |
| JPS58502065A (en) | 1983-12-01 |
| WO1983002157A1 (en) | 1983-06-23 |
| DE3249267T1 (en) | 1984-01-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |