BIMETALLIC ACTUATORS

Abstract: A method of making snap-acting thermally sensitive bimetallic actuators in which a series of actuator blanks (6) is formed in a strip (2) of bimetallic material. Adjacent blanks (6) are joined by one or more bridges (8) of the strip material. The blanks (6) are indexed through one or more deforming operations whilst they are joined together by the bridges (8), by indexing means (28) associated with the bridges (8). The blanks (6) are then separated to form individual actuators.

Description: Bimetallic Actuators The present invention relates to bimetallic actuators, and more particularly to a method of making snap-acting thermally responsive bimetallic actuators. Typically such actuators may comprise a domed bimetallic disc which moves to an oppositely domed configuration when it exceeds a predetermined temperature. One particular actuator of this type which is very widely used today is disclosed in GB 1542252, and a method of manufacturing that actuator is disclosed in GB 1546578. In that method of manufacture, individual actuator blanks are stamped out from a strip of bimetallic material and subjected to a number of pressing operations to give the actuator the desired domed configuration, whereafter they are heat-treated to stabilise their operating temperature. Whilst this method has proved very successful, it has the drawback that the various operations are performed on individual blanks which have to he moved individually from process step to process seep. This slows down production, which may have serious implications where high volumes of actuators are being produced. The present invention seeks to alleviate this problem, and from a first aspect provides a method of making snap-acting thermally sensitive bimetallic actuators comprising forming a series of actuator blanks in a strip of bimetallic material, adjacent blanks being joined by one or more bridges of the strip material, indexing said blanks through one or more deforming operations whilst they are joined together by the bridges, by indexing means associated with the bridges and then separating the blanks to form individual actuators . In accordance with the invention, therefore, the blanks remain joined to one another whilst having one or more deforming operations performed on them. They are indexed through a number of operation stages, by indexing means associated with the bridges. This allows for accurate movement and positioning of the blanks whilst obviating the need for separate means for transferring individual blanks between production stages. This will significantly improve production times and thereby reduce costs. The bridges should be sufficiently flexible to allow the deforming operations to be performed on the blanks without breaking the bridges. For example, in the case of domed bimetals the doming operation will decrease the effective length of each blank. Thus, in order to maintain the integrity of the strip of blanks during the subsequent processing steps, the bridges must be able to extend as the effective length of the blank decreases. Preferably, therefore, the bridges do not run linearly between successive blanks but are at least partially curved or angled such that they may extend during deformation of the blank. Preferably two bridges are formed between adjacent blanks. Preferably, the bridge(s) is/are arranged offset from the axis of the series of blanks, and more preferably two bridges are provided linking adjoining sides of adjacent actuator blanks, most preferably being symmetrically arranged with respect to the said axis. Most preferably, the various operations are performed sequentially on the bimetallic material as it moves in a stepwise manner through a progression tool having a succession of work stages. Preferably the desired profile of the finished actuator is punched or stamped out of the strip material so as to leave the bridge(ε) between adjacent blanks. To facilitate eventual separation of the formed actuators, the end positions of the bridges may be scored on the strip material so that the bridges can more easily be broken at those positions. The scoring is preferably performed on the bimetallic material before the bridges are formed. The bimetals formed by this process will generally be used as control sensors and it is therefore highly desirable that the bimetals are kept within clearly defined tolerances. The scoring of the ends of the bridges ensures that the bridges may be broken from the resultant bimetals at precisely the correct position with regard to the required tolerances. In this way, the shape of the bimetal is maintained within the desired tolerances. As stated above, the blanks are indexed through one or more deforming operations by indexing means associated with the bridge(s) . Preferably, therefore, the bridge(s) is/are provided with formations, for example one or more openings, for engagement by the indexing means. For example, strip indexing or pilot holes may be formed in appropriate positions on the strip material prior to formation of the bridges. The deforming operations performed on the blanks may comprise standard operations as disclosed, for example, in GB 1546578. These may include, therefore, doming the blank in a first direction, doming it in the opposition direction and then "trimming" the curvature. After forming, the actuators may be heat-treated either after, or more preferably before, they have been separated from each other. The method of the invention is not limited to any particular shape or configuration of actuator. It is most suited, however, to producing generally circular actuators, for example of the type disclosed in GB 1542252 which have a centrally released tongue, or solid circular bimetallic discs. It will also be appreciated that the invention extends to a snap-acting bimetallic actuator produced by the method of the invention. A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 shows a strip of bimetallic actuators of the type described in GB 1542252 being produced in accordance with a method of the invention; and Fig. 2 shows, schematically, a progression tool for carrying out the invention. Referring to the figures, a strip 2 of bimetallic material is indexed in a stepwise manner through a progression tool 4 (Fig. 2) in which a number of operations are performed sequentially on a given portion of the strip 2 at a succession of stations A to J. As can be seen from Fig. 1, a number of actuator blanks 6 are first formed through stations A to F, the blanks being joined by a number of frangible bridges 8. The bridges 8 are symmetrically formed offset from the axis of the blanks 6, such that the blanks 6 may be closely positioned together, with the bridges being formed within the width of the bimetallic strip, so that they are formed of material which would, ir. any event become scrap. This optimises use of the bimetallic material and reduces cost. The joined blanks are then subjected to a number of deforming operations at stations G to I and are finally separated into individual actuators 10 at station J. The finished actuators 10 are of the type disclosed in GB 1542252 which are domed and have a generally circular outer periphery 12, and a tongue 14 formed in an inner arcuate opening 16. The tool 4 comprises a fixed base platen 18 and an upper platen 20 movable towards and away from the base platen 18. The upper platen 20 abuts an upper plate 22 which mounts a number of punch or press tools which extend through a sprung, movable, intermediate plate 24 for engagement with complementary tool parts formed in a fixed base plate 26, as the upper platen 4 is moved downwardly. These will be described further below. The successive stations A to J of the tool will now be described. The first operation performed on the strip 2 is performed at station A, where a pair of pilot holes 28 is formed on either side of the strip 2 by a punch and die 30. These holes 28 will allow for accurate location and indexing of the actuator blanks 6 between stations, and are engaged by indexing means (not shown) . As can be seen from Fig. 1 the pilot holes 28 are formed in positions such that they will lie within the bridges 8 formed between the blanks 6. The next operation, performed at station B, is the formation of score marks 32 on the strip 2 at locations corresponding to the ends of the bridges 26. This will facilitate subsequent separation of the blanks 6 at these locations. The scores 32 are produced by a punch 34 having projecting scoring portions (not shown) and an adjustable die plate 36, which can be moved up or down in the base plate 26 by a mechanism 38 so as to adjust the depth of the score produced in the material. In this embodiment four scores are produced at one time. At station C, two holes 40,42 are produced in positions such that they will lie at the free end of the tongue 14 of the finished actuator 10. These are produced by punches and dies 44 in the tool 4. The inner arcuate opening 16 and the tongue 14 of the actuator are then formed by punch and die 46 at station D, and the outer periphery 12 of the actuator 10 then punched out in two stages at stations E and F by respective punches and dies 48,50. The shapes of the respective punches 48,50 are shown shaded in Fig. 1, from which it will be seen that the first punch and die 48 define the sides of the actuator and the second punch and die 50 the opposed edges of adjacent blanks 6. Between them, they also define the bridges 8 between adjacent blanks 6, which are joined to the blanks 6 at the score marks 32. The bridges 8 have an enlarged central section 9 formed around the pilot holes 28, and curved end portions where they connect to respective blanks. The curved end portions allow the bridges to extend by deforming, without breaking during processing. It will be seen that the base platen 6 has an opening 52 to allow metal removed through stations A to F to fall away form the tool for disposal. By the end of station F, it will be seen that an actuator blank 6 has been fully formed. It is then subjected to a number of deforming processes, known per se, at stations G to I. In particular, each blank 6 is subjected to a "doming down" operation at station G by a spring loaded die 54 having a convexly domed lower face 56 which presses the actuator blank 6 against a rubber pad 58 constrained in the lower plate 26. The blank 6 then moves through a rest station to station H where it is subjected to a 'doming up 1 operation by a second spring loaded die 60 having a concavely domed lower face 62 which presses the actuator blank 6 against a second rubber pad 64 mounted in the base plate 26. The blank 6 then moves through a further rest station to station I where it is subjected to a "trimming" operation by an adjustably mounted flat ended die 66 arranged opposite a further rubber pad 68 in the base plate 26. By the end of station I, the actuator is fully formed and may then be heat treated either before or after it is separated from the rest of the strip 2. Separation can be achieved, for example by a punch (not shown) at station J pushing down on the actuator blank 6 sufficiently hard to break the bridges 8 at the scores 32. From the above it will be seen that the actuator blanks 6 move progressively through the tool 4 as a self supporting and self locating strip which avoids the need for separate location and transfer means. Operations are performed sequentially on a section of the strip as it passes through the tool 4 to form an actuator which is eventually separated form the end of the strip 2. It will be appreciated that many variations may be made to the above embodiment within the scope of the invention. For example, the shape of the actuator may be different to that disclosed, as may be the particular deforming operations. Furthermore, the method may also be applicable to trimetallic actuators, and the term "bimetallic" as used herein should be interpreted as embracing any laminated metallic material comprising a plurality of layers of metallic materials having different coefficients of thermal expansion.

Claims: Claims 1. A method of making snap-acting thermally sensitive bimetallic actuators comprising forming a series of actuator blanks in a strip of bimetallic material, adjacent blanks being joined by one or more bridges of the strip material, indexing said blanks through one or more deforming operations whilst they are joined together by the bridges, by indexing meanε associated with the bridges and then separating the blanks to form individual actuators. 2. A method as claimed in claim 1 wherein the bridge(s) is/are offset from the axis of the series of blanks. 3. A method as claimed in claim 1 or 2 wherein two bridges are formed between adjacent blanks. 4. A method as claimed in claims 2 and 3 wherein the bridges are arranged symmetrically about the said axis. 5. A method as claimed in any preceding claim wherein the bridges are deformable so as to increase their effective length in the longitudinal direction of the strip. 6. A method as claimed in any preceding claim wherein the operations are performed successively on the bimetallic material as it moves in a stepwise manner through a tool having a succession of stages. 7. A method as claimed in any preceding claim, wherein the bimetallic material is scored at positions where the bridges join or will join the actuator blanks. 8. A method as claimed in claim 7 wherein said scoring occurs before the bridges are formed. 9. A method as claimed in any preceding claim wherein indexing openings are formed in the bridge(s) for engagement by said indexing means. 10. A method as claimed in claim 9 wherein said indexing openings are formed in the strip prior to formation of the bridges. 11. A method as claimed in any preceding claim wherein said forming operations comprise one or more doming operations. 12. A method as claimed in any preceding claim wherein the actuators are subsequently heat treated. 13. A method as claimed in claim 12 wherein said heat treatment occurs before εaid actuators are separated from each other. 14. A snap-acting bimetallic actuator formed by a method as claimed in any preceding claim. 15. A method or actuator as claimed in any preceding claim wherein said actuator is generally circular. 16. A method of making snap-acting thermally sensitive bimetallic actuators wherein a strip of bimetallic material is moved through a series of process steps to form said actuators by indexing means engaging with portions of the strip which will become scrap after the process steps have been carried out.

Inventors: GARVEY VINCENT JOSEPH, TAYLOR JOHN CRAWSHAW, GARVEY, VINCENT, JOSEPH, TAYLOR, JOHN, CRAWSHAW
Applicants: GARVEY VINCENT JOSEPH, STRIX LTD, TAYLOR JOHN C, GARVEY, VINCENT, JOSEPH, STRIX LIMITED, TAYLOR, JOHN, CRAWSHAW
Application year: 1997
Main classification: H01H37
IPC codes: H01H11, H01H37