IE45691B1 - Improvements in or relating to temperature-responsive actuators - Google Patents

Description

This invention relates to temperatureresponsive actuators.

The particular type of actuator in relation to which the invention has been developed, is for use in operating mechanisms for ventilation purposes, for example for opening and closing greenhouse windows, the actuator comprising a pressure cylinder containing a piston which is displaceable outwardly of the cylinder upon expansion of a flowable material contained within the cylinder, said material being wax or other material, such as alcohol or mercury, having a high coefficient of thermal expansion. Such cylinders comprise a tube and two end closure elements, one of which is of solid or continuous form and the other of which is provided with a through-bore to receive the piston rod.

According to the invention, there is provided a method of assembling a temperature-responsive actuator having a pressure cylinder comprising a tube, two end closure elements each secured to a respective end of the tube, a body of flowable material contained within the tube between the end closure elements, and a piston extending through a through-bore in one of the end closure elements and projecting into the body of flowable material, Said method including the step of disposing said body of flowable material within the tube between and abutting said end closure elements, while at least one of said end closure elements is not secured to the tube, so that said body of flowable material determines the distance apart of said end closure elements.

An embodiment of the invention will now be - 2 45691 described by way of example with reference to the accompanying drawing which is a longitudinal crosssection through a thermally sensitive actuator.

The actuator comprises a tube 10, the ends 5 of which are closed by respective end closure elements and 12. The portion of the tube 10 between the - 3 4 5 6 91 closure elements is filled with a body of flowable material^ Buch aa wax, alcohol or mercury, having a high coefficient of thermal expansion. A respective resilient 0 ring 13, 1U is fitted in a groove in the outer periphery of each of the end closure elements 11 and 12 to provide a seal between such end closure element and the inner wall of the tube.

A piaton 15, in the form of a rod, extends through a through-bore 16 in the end closure element 12 and projects into the flowable material. The inner end of the through-bore 16 is enlarged to accommodate a reeilient seal 17 which engages between the end closure element 12 and the piston 15 and is held in place by an inwardly directed lip 18 formed on the edge of such enlarged recess.

Preferably, as shown,, the inner end of the piston 15 tapers to a point 19 so that, should the piston 15 he forced to its fully inward position in which it •makes contact with the end closure element 11, the flowable material in the tube can exert pressure on the tapering surface adjacent the point 19 when expansion next takes place. A pin 20 extends transversely through the piston 15 near the inner end thereof and serves, by engagement with the closure element 12, to prevent complete withdrawal of the piston from the tube 10.

If the flowable material is a material which can be frozen at temperatures not inconveniently lower than room temperature, a unit of flowable material may be formed by producing a casting of the solidified material shaped to fit within the tube 10 and including a central hole to accommodate the piston 15 when the latter 6 01 is inserted into the tube 10 to its maximum extent.

The tube 10, unit of frozen flowable material, piston 15, and end closure elements 11 and 12 may then be assembled together with the unit of flowable material serving to maintain the required spacing between the two end closure elements 11 and 12 which are then secured in position in their respective ends of the tube 10. This latter operation may conveniently be effected by pressing the end edges 21 and 22 of the tube radially inwardly so as to embrace the respective end closure elements 11 and 12.

As an alternative to freezing the flowable material, a unit thereof may be formed by inserting the material, in liquid form, into a skin formed from flexible sheet material such as polyethylene. The package of flowable material so formed is then inserted into the tube 10 and the end closure elements 11 and 12 fitted with the piston 15 withdrawn to its maximum extent. Then, with the end. closure elements 11 and 12 held in position, the piston rod 15 is driven into the tube 10 so as to pierce the polyethylene or other sheet material. Finally the end closure elements 11 and 12 are secured in their permanent positions as described above. The presence of the sheet material in the tube 10 has no effect on subsequent operation.

A further method of assembling the actuator shown in the drawing, for use with a flowable material such as wax which hardens at the lower end of the temperature range encountered in normal use, is initially to fit the end closure element 12, with the piston 15 already installed therein, into one end of the tube 10 and displace the edge of suoh end radially inwardly - 5 45691 to retain the end closure element 12 in position.

Next, with the piston 15 fully extended so that the pin 20 abuts againBt the end closure element 12 and the tube 10 held vertical with its open end upwarde, heated flowable material is poured in to completely fill the tube 10«, The assembly is then cooled to a predetermined temperature, causing the flowable material to contract, harden and form a meniscus at the open end of the tube 10. The flowable material is then cut away to a predetermined depth from the open end of the tube and, with the assembly still at the predetermined temperature and with the piston 15 still fully extended, the other end closure element 11 ie inserted so that it rests on the top of the flowable material and the edge of the adjacent end. of the tube 10 is displaced inwardly to hold the end closure element 11 in position. Next, the assembly is heated to a second, higher predetermined temperature, causing the flowable material to expand, forcing the end closure elements 11 and 12 outwards.

The outer edges of the end closure elements 11 and 12, which are initially of very small radius, bite into the overlapping Inwardly displaced ends of the tube 10 and, at the same time, become more rounded. The Overall effect ie to increase the volume of the chamber containing the flowable materiel so that when the assembly is again cooled to a temperature at which the flowable material hardens, the piston 15 is drawn into the tube 10.

In use, the end closure element 11 ie coupled to a first member and the piston to a second member, the positions of which members, one relative - 6 45691 to the other, are to he varied in dependence on ambient temperature.

Claims (11)

1. CLAIMS i1. A method of assembling a temperatureresponpive actuator having a pressure cylinder comprising a tube, two end closure elements each secured to a 5 respective end of the tube, a body of flowable material contained within the tube between the end closure elements, and a piston extending through a through-bore in one of the end closure elements and projecting into the body of flowable material, said method including 10 ' the step-of disposing said body of flowable material within the tube between and abutting said end closure elements, while at least one of said end closure elements is not secured to the tube, so that said body of flowable material determines the distance apart of said end 15 closure elements.

2. A method according to claim 1, comprising forming said body of flowable material into a unit having a solid outer surface and a cross-section such that it can be received within the tube, inserting the 20 unit of flowable material into the tube and inserting a respective end closure element into each end of the tube so as to abut opposite ends of the unit of flowable material, and securing the end closure elements to the tube. 25

3. A method according to claim 2, wherein the unit of flowable material is formed by freezing the flowable material to provide a casting of the solidified material shaped to fit within the tube.

4. A method according to claim 3, wherein the 30 casting includes a central hole to accommodate a portion of the piston projecting into the tube.

5. A method according fo claim 2, wherein the unit of flowable material is formed by inserting the material, in liquid form, into a skin formed from 5 flexible sheet material, and the package of flowable material so formed is then inserted into the tube and the end closure elements secured to the tube with the piston withdrawn to its maximum extent.

6. A method according to claim 1, comprising 10 securing the end closure element through which the piston extends to one end of the tube, fully extending the piston, inserting heated flowable material into the tube with the open end thereof Uppermost, cooling the flowable material to a first predetermined temperature, 15 removing flowable material to a predetermined depth from the open end of the tube to form said body of flowable material, inserting the other end closure element into the open end of the tube and securing it in a position abutting the body of flowable material and heating the 20 body of flowable material to a second higher predetermined temperature whereby the end closure elements are forced outwards from the positions in which they are initially secured.

7. A method according to claim 6, wherein the 25 flowable material is chosen to be solid at said first predetermined temperature and liquid at the temperature to which it is heated before being inserted into the tube.

8. A method according to any of claims 1 to 7, wherein at least one of the end closure elements is 30 secured in position in a respective end of the tube by displacing the peripheral end edge of the tube inwardly so as to embrace the end closure element. -

9. 9. A to claim ?,

10. A to claim 6,

11. A by a method method of assembling an actuator according substantially as hereinbefore described. method of assembling an actuator according substantially as hereinbefore described, temperature-sensitive actuator assembled according to any preceding claim.