IMPROVED TRIGGER DEVICE FOR HEAT PACK

Abstract: A trigger device for a heat pack comprises three helically-coiled, resilient metallic filaments (1, 2, 3) nested one within the other and of inwardly decreasing diameter, the filament (2) being wound in a sense opposite to that of filaments (1) and (3). Flexing the assembly of nested helices about its longitudinal axes produces a rubbing action between adjacent turns thereof which initiates crystallisation. Other devices comprises two nested helices wound in the same sense; a single helix having a pressure plate at one end and an external or internal cap at the other; and a body of randomly convoluted or woven matallic filament.

Description: IMPROVED TRIGGER DEVICE FOR HEAT PACK This invention concerns improvements in and relat¬ ing to trigger or activator devices for so-called 'heat packs' . 5 In the so-called 'heat packs' latent heat of crystalli¬ sation is stored in a supercooled solution of a crystal¬ line material. It is known that such packs can be stored in a. stable condition and used as a heat source as and when required, by triggering or initiating crystall- "L Q isation of the supercooled solution whereby the latent heat of crystallisation is given up in the resulting exothermic reaction. British Patent Specification No. 1585808, for example, describes a self-contained heat pack comprising a flexible container incorporating *L5 * the appropriate supercooled solution, together with an activator device in the form of a fissured activator strip capable of being flexed to initiate crystallisation of the solution. U.S. Patent Specification No. 2220777 describes 20 a heat pack comprising a container, which may have rigid or flexible walls, for the supercooled solution and an activator device which may take the form of a rod having one end which is attached to a flexible wall portion and is manipulable to cause the other 25 end to scrape the inside of the container wall; in another embodiment opposed wall portions of a flexible container are provided with metal inserts which may be manipulated so that their internal surfaces come come into scraping contact. In yet another, rather 30 conjectural, embodiment 'various pieces of metal' may be placed within the container and crystallisation initiated merely by shaking the container. Although various activator devices for initiating such crystallisation have hitherto been proposed, the mechanism whereby crystallisation is initiated is not fully understood. It is an object of the present invention to provide a reliable activator device for initiating crystallisat¬ ion of a supercooled solution, for example in a so- called "heat pack 1 . An activator device in accordance with the invention • is characterised in that it comprises one or more con¬ voluted metallic filaments so disposed that flexing of the filamentary metallic material, and consequent rubbing contact of contacting metallic surfaces, is effective to initiate crystallisation of a supercooled solution within which the activator device may be immersed. According to a first preferred form of the invention the activator device comprises two or more resilient helical filaments nested one within the other, optionally with a flexible core. Each helix may be wound in a sense the same as or opposed to that of its immediate neighbours; moreover the diameter of the filaments may decrease in a radially inward direction. According to a second preferred form of the invention the device comprises a helical spring fitted with a cap or terminal insert, the surface of which is brought into rubbing contact with that of the spring on compression, extension or flexing thereof. In a third preferred form the device comprises a body of flexible convoluted filament which may be random or woven. In each form of the invention flexing of the con¬ voluted flexible metallic filaments, for example the - 3 - one or more springs, causes the rubbing contact which triggers crystallisation. In the case of the first and third forms -of the invention the contact is between surfaces of convoluted flexible filament and in the second form between the surface of the convoluted flex¬ ible filament (the spring) and the insert or cap. An activator device in accordance with the invention may take a variety of forms, some specific examples of the invention being illustrated in the accompanying drawings, in which Figure 1 is a side elevation of one embodiment of device according to the invention; Figure 2 is a part sectional elevation corresponding to Fig. 1; Figure 3 is a plan view corresponding to Fig. 1; Figures 4, 5 and 6 are views corresponding to Figs. 1 to 3 respectively and illustrating another embodiment of the invention; Figures 7, 8 and 9 are corresponding views of a yet further embodiment of the invention, and; Figures 10, 11 and 12 are each an elevation of a yet further embodiment of device in accordance with the invention. Referring to Figs. 1 to 3, there is shown a device intended for immersion within the supercooled solution retained within the outer envelope of a heat pack, the heat pack, apart from the presence of the activator of Figs. 1 to 3, being of known construction and there- fore not illustrated. The activator device comprises three helically coiled metallic filaments 1,2,3, nested one within the other. The helical filaments possess an inherent spring characteristic tending to retain the helices of the nested filaments symmetrical about a rectilinear longitudinal axis, whilst permitting bending of the assembly of the nested filaments against this restoring force. As in the case of known arrang- ments, the flexible wall of the outer envelope of the 5 heat pack (not shown) is such as to enable manipulation of the activator device. It will be appreciated that the action of flexing the assembly of nested helices is such as to produce a rubbing action between the adjacent turns thereof, this being sufficient to initiate 10 crystallisation of the surrounding supercooled solution. It will be noted that the configuration of the nested helices is such that each helix is wound in a sense that is in opposition to that of the adjacent inner and/or outer helix. It will be further noted that 15 the respective diameters of the filaments forming the helices are different from one another, being reduced in a direction towards the central longitudinal axis of the assembly, such that whereas each helix is of approximately the same axial length, each helix has 2.0 a smaller pitch and thus a correspondingly greater number of turns than the neighbouring outer helix. It will be seen that the arrangement of Figs. 4 to 6 is essentially similar to that of Figs. 1 to 3, with the exception that only two helical metallic fila- 25 ments are provided, both being wound in the same sense. The method of operation of the device is otherwise similar to that of Figs. 1 to 3. The device of Figs. 7 to 9 comprises a single helical metallic compression spring 6, at one end of which 0 is located a circular pressure plate 7. The other end of the spring is enclosed within a generally cylin¬ drical end cap 8 the internal surface of which is in rubbing contact with the outer periphery of the adjacent helices of the spring. In operation of the device. compression of the end cap towards the pressure plate 7 and/or relative angular movement of the pressure plate 7 and end cap 8 is effective to cause friction between the contacting metallic surfaces, in order to activate crystallisation of the surrounding super¬ cooled liquid. Figs. 10 to 12 show activators comprising randomly convoluted metallic filament, such as wire wool, forming a body of material the compression and/or flexing of which is sufficient to effect crystallisation of the surrounding liquid. In each case the body of material forms a coherent structure having the shape illustrated, the structure being disposed within larger outer envelope of the heat pack itself. In any of the above described embodiments, the fila¬ mentary material may be confined within a sleeve or apertured envelope of resilient rubber or like material in order to cover any sharp edges of the filamentary material and thus prevent puncture of the outer envelope of the heat pack, whilst allowing the required flexing of the activator assembly. The various embodiments of activator described above provide varying degrees of sensitivity of actuation. That is to say the degree of flexing of the actuator required to trigger crystallisation of a given solution will be less as the sensitivity is increased. In general the sensitivity of the activator device is increased by increasing the overall area of contact between met¬ allic surfaces, reducing the localised areas of contact and/or increasing the local contact pressure. Thus factors tending to increase sensitivity of the activator include: increased number of nested helices (Figs. 1 to 6); nested helices of opposite pitch (Figs. 1 to 3); reduced diameter of metal filament; tighter interengage ent of windings of nested helices; smaller pitch of wound helix. It will be appreciated from the above disclosure that the invention accordingly provides a reliable and versatile activator arrangement having a response capable of being tailored to suit the requirements o'f a given design of heat pack. Moreover, the activator device according to the invention lends itself to being housed in a small compartment separate from, but in fluid communication with, the main' compartment of a flexible walled container containing the working solution * Various modification and alterations may be made to the illustrated embodiments of the invention without departing from the underlying inventive concept. Thus, for example, in the arrangement of Figs. 7 to 9 the end cap 8 may be replaced by a metallic body located within the spring 6. In the arrangements of Figs. 10 to 12, the randomly convoluted filament may be woven in a regular manner.

Claims: - 1 - Claims : 1. An activator device for initiating crystallisation of a supercooled solution in aheat pack, characterised in that the device comprises one or more convoluted metal filaments so disposed that flexing of the filamentary metallic material, and consequent rubbing contact of contacting metallic surfaces, is effective to initiate crystallisation of a supercooled solution within which the activator device may be immersed. 2.. A device as claimed in claim 1 and comprising an assembly of two or more filaments each of helical form and nested one within the other. 3. A device as claimed in claim 2, wherein each helix is wound in a sense that is opposed to that of each adjacent inner and/or outer helix. 4. A device as claimed in claim 2, wherein each helix is wound in a sense that is the same as that of each adjacent inner and/or outer helix. 5. A device as claimed in claim 2, 3 or 4, wherein the diameter of each helical filament is reduced in direction towards the longitudinal axis of the assembly. 6. A device as claimed in claim 1 and comprising a single filament in the form of a compression spring and a cap or insert having a surface in nesting contact with one end portion of the spring. 7. A device as claimed in claim 1 and comprising a multiplicity of fibres in random convoluted or woven form. 8. A device as claimed in any preceding claim and further comprising an apertured flexible container in which the filamentary material is contained. 9. A heat pack incorporating an activator device as claimed in the preceding claim.

Inventors: SMITH MARTIN LESLIE, SMITH, MARTIN, LESLIE
Applicants: CREWSAVER MARINE EQUIP LTD, CREWSAVER MARINE EQUIPMENT LIMITED
Application year: 1986
Main classification: A61F7
IPC codes: A61F7, F24J1, F28D20