GB2373308A

GB2373308A - Elongate spiral thermal guard

Info

Publication number: GB2373308A
Application number: GB0202558A
Authority: GB
Inventors: John Anthony Billett
Original assignee: GRESHAM WOOD IND Ltd
Current assignee: GRESHAM WOOD IND Ltd
Priority date: 2001-03-15
Filing date: 2002-02-05
Publication date: 2002-09-18
Anticipated expiration: 2022-02-05
Also published as: GB0106386D0; GB2373308B; GB0202558D0

Abstract

A thermal guard 10 for at least partially thermally isolating a member is fabricated from a thermally insulating material formed into an elongate spiral. The material preferably has a Shore A hardness between 70 to 90 degrees and comprises silicone rubber capable of withstanding an ambient temperature of at least 300{C. A dye may be included in the rubber which renders it less susceptible to thermal discolouration. At least part of the spiral can be formed in a clockwise or anti clockwise sense, and may include at least one direction reversal. The guard 10 may be installed on an elongate member of an oven tray which is susceptible to being contacted in personal use. Methods of fabricating and installing the guard are also provided.

Description

THERMAL GUARD Field of invention The present invention is concerned with a thermal guard. Moreover, the invention is also concerned with a method of fabricating the guard. Furthermore, the invention also tn relates to a method of applying the guard.

Background to the invention Thermal guards are conventionally employed in products such as ovens to provide thermal breaks therein, for example around oven doors. Contemporary thermal guard materials include woven fibre glass and urea-formaldehyde plastics which are capable of withstanding temperatures of 300OC or more. However, such contemporary guards are often relatively costly to manufacture and their installation in apparatus is frequently labour intensive and complex.

The inventor has appreciated that thermal guards can be more cheaply manufactured and more readily installed than the aforementioned conventional thermal guards. Thus, the inventor has therefore devised an alternative type of thermal guard.

Summary of the invention According to a first aspect of the present invention, there is provided a : t ouard a least partiaily thermally isolating a member about v/hich the guard. s irstalied. the guard being fabncad from a themmaHy insulating material termed into an elonse spiral.

The invention provides the advantage that the thermal guard is capable of being manufactured and installed more economically than conventional known types of thermal guards.

The guard can be used in a number of potential applications such as in the automotive field, for example where hot engine environments are encountered, and also in domestic appliances where thermal heating occurs, for example in convector or storage heaters, and in thermal ovens.

For a material to be regarded as thermally insulating, it preferably exhibits a thermal conductivity of less than 1 W m''K''. Most preferably, the material exhibits a thermal conductivity of less than 0.4 W m'l K-l.

The guard beneficially is of suitable hardness that makes it easy to handle during installation. Thus, preferably, the material is flexible and has a Shore A hardness in a range of 70'to 90'. More preferably, the material is flexible has a Shore A hardness in a more limited range of 75'to 850.

The materially beneficially is thermally stable in use and preferably also substantially flexible and thereby resiliently deformable. Hence, the material preferably comprises a silicone rubber material. Other materials can however be used, for example vulcanized rubber or PTFE. Moreover, the rubber material in use preferably is capable of withstanding an ambient temperature of at least 250OC, more preferably at least 300Oc.

Visibility of the guard is potentially important to indicate to personnel where they can safely grip. Moreover, the guard beneficially is aesthetically pleasing after prolonged use at elevated temperatures. Thus, the material preferably includes a dye which renders it less susceptible to thermal discolouration in use in comparison to corresponding undyed material.

Retention of the guard around the member is important in use. In order to improve such retention, the guard may, in one embodiment, be fabricated from a material which includes an activatable hardening ingredient for hardening the guard after installation around the member. The hardening ingredient is preferably heat-activatable, for example the hardening ingredient is preferably a thermo-setting polymer.

As a majority of people are right handed, the guard is preferably fabricated so that at least part of the spiral is formed in a clockwise sense. Such a spiral sense eases installation of the guard when wrapping it about the member, the member typically p c, being an elongate rod-like or tube-like structure (such as a peripheral member of a mesh-like oven tray). In practice, assembly personnel are often most familiar with manipulating objects in a clockwise manner, for example when screwing threaded components together. Alternatively, at least part of the spiral is formed in an anticlockwise sense.

During commercial manufacture, speed of assembly is important. In view of such speed, the spiral preferably includes at least one spiral direction reversal, thereby rendering the guard potentially quicker to install. Such reversal provides personnel installing the guard with relatively shorter lengths of guard to handle when installing around a member. For example, during a first step of installation of the guard, a central portion of the guard can be secured to an elongate member to yield two free ends. During a second step of installation, the two free ends are concurrently wrapped in their respective directions around the member. The two free ends will be shorter than the full length of the guard; such a full length can be unwieldy to manipulate during installation.

The guard is especially useful when included as part of an oven tray ; the oven tray preferably includes an elongate member onto which a thermal guard according to the first aspect is installed. More preferably, the elongate member is a peripheral member of the tray susceptible to personnel contact. As a result of the spiral form, the guard is capable of being retrofitted to existing trays to render them safer in use.

According to a second aspect of the present invention, there is provided a first method of fabricating a thermal guard according to the first aspect, the method including the steps of : (a) ejecting a fluid material from an orifice to form a solid material strand, the orifice being moved in a substantially circular or elliptical path about a longitudinal axis of the guard to form the strand into a spiral about the axis; and (b) periodically severing the spiral strand to provide one or more of the guards.

Preferably, the rotational direction of movement of the orifice about the axis is periodically reversed to provide the guard with one or more spiral direction reversals.

The present invention also provides a second method of producing a guard according to the first aspect, the method including the steps of : (a) extruding a fluid material to form a hollow tube of resilient solid material; (b) mounting the tube onto a support member; and (c) rotating the support member and tube relative to cutting means engaging onto the tube and traversing the cutting means relative to the tube to form a spiral cut into the tube, thereby forming the tube into an elongate spiral constituting the guard.

Preferably, the direction of rotation of the support member and tube relative to the cutting means is periodically reversed so that the spiral includes at least one spiral sense reversal.

According to a third aspect of the present invention, there is provided a method of installing a guard according to the first aspect onto an elongate member, the method including the steps of : (a) affixing the guard at a central region thereof onto the member; and (b) concurrently winding end regions of the guard around the member so as to at least partially enclose the member.

Detailed description of the invention Embodiments of the invention will now be described, by way of example only, with reference to the following diagrams in which: Figure 1 is an illustration of a first embodiment of a thermal guard according to the first aspect of the invention; Figure 2 is an illustration of a second embodiment of a thermal guard according to the first aspect of the invention, the second embodiment having a spiral sense which periodically reverses along the guard;

Figure 3 is an illustration of a method of manufacturing the thermal guards as illustrated in Figures 1 and 2 ; and Figure 4 is an illustration of a thermal oven incorporating a thermal guard as shown in Figures 1 and 2 affixed to a tray of the oven.

Referring to Figure 1, there is shown a thermal guard according to the invention indicated by 10. The guard 10 comprises a spiral of resilient silicone rubber material. although other resilient materials capable of withstanding temperatures at which the guard 10 is employed can alternatively be used. Alternative materials include vulcanized elastomers for example. The rubber material has nominally thermal !) insulating properties, namely a thermal conductivity of preferably less than 1.0 W m K-l. Most preferably, the rubber material exhibits a thermal conductivity of less than 0. 4 W m-l K-'.

The rubber material is preferably capable of withstanding a sustained temperature of at least 250 C. More preferably, the material is capable of withstanding a sustained temperature of at least 3000C. Moreover, the shore A hardness of the rubber material is preferably in a range of 70'to 90', although a Shore A hardness value in a more limited range of 750 to 850 is found by the inventor to be especially preferable as this hardness makes the guard easier to handle when affixing around elongate members. However. it will be appreciated that Shore A hardness values outside these two ranges can also be

employed for implementing the invention. The rubber material is thus flexible and resiliently deformable.

For many applications of the invention, it is desirable that the guard lO in an urtSlretchc state has an outside dIameter d in a range of 5 mm to 25 mm, although a diameiei in a more limited range of 9. 5 mm to 10. 5 mm is especially preferable for use In conventional domestic thermal ovens. Moreover, the guard 10 has a spire'hall thickness t as illustrated in Figure 1 in a range of 0. 5 mm to 3. 0 mm although a wail thickness in a more limited range of 1.0 mm to 2.0 mm is especially preferred because this renders the guard easier to handle and install. The guard 10 additionally has a spiral width w which is preferably in a range of 1 to 6 mm, although a more limited width

range of 1 mm to 3 mm is especially preferred for rendering the guard easier to affix to elongate members, for example in conventional thermal ovens. If required, the silicone rubber material can include dye materials for improving its visibility or making it less prone to discolouration arising from prolonged operation at a high temperature, for example at 300 C.

Additionally, if required, the silicone rubber material can include a thermosetting additive so that the guard 10 remains flexible during installation around an elongate member by wrapping the guard therearound, after which the member and its guard 10 are subjected to a heating step which hardens the guard 10 to render it more securely retained in position around the member. Such thermosetting additives can include polymers susceptible to molecular cross-linking on application of thermal energy.

Alternatively, or additionally, the rubber material can include a photo-activated additive for hardening the material after installation; such an additive is preferably an ultra-violet radiation activated ingredient.

For convenience, the guard 10 can be manufactured in lengths in a range 0.1 m to 5 m.

More preferably, for ease of working and installing the guard 10, it is desirable that the guard 10 has an unstretched axial length in a range of 295 mm to 305 mm.

Preferably, the guard 10 is manufactured so that its spiral is formed in a clockwise sense as shown in Figure 1. It can alternatively be manufactured so that its spiral is formed in an anticlockwise sense.

Moreover, m order to ease installation of the guard 10., the guard 10 can have a spiral sense which periodically reverses therealong. Such a guard is illustrated in Figure 2 and is indicated generally by 100. Such periodical reversal allows a central region 110 of the guard to be secured to a member to be thermally isolated and then two free end portions of the guard 100 concurrently wrapped around the member during installation, thereby expediting installation of the guard 100.

It will be appreciated that the guard 100 illustrated in Figure 2 includes a single spiral sense reversal. The guard 100 can be further modified to include more than one spiral

sense reversal, for example at a first end of the guard 100, the spiral can have a clockwise sense which changes to a anticlockwise sense in a central portion of the guard and back to a clockwise sense at a second end of the guard 100 remote from the first end.

The guards 10,100 can be fabricated using a continuous injection moulding process, or can alternatively be fabricated using a combination process comprising steps of injection moulding and machining.

In a continuous moulding process, the spiral of the guard 10 is formed as a continuous strand in a moulding apparatus. The apparatus includes an orifice from which fluid silicone material is ejected whilst the orifice is moved in an off-axis spatially substantially circular or elliptical path about a central longitudinal axis of the guard 10. Once the fluid silicone is ejected from the orifice, it polymerizes to form a resilient solid. The strand can be periodically cut to provide practical lengths for the guard 10 as elucidated above; such practical lengths are important when installing the guard 10, such installation involving wrapping the guard 10 around a member to at least partially enclose the member. The member can be a compliant former or, alternatively, a rigid elongate member which is to be thermally insulated by the guard 10.

Spiral sense reversal can be achieved by periodically alternating the direction in which the orifice is spatially rotated about the central longitudinal axis whilst ejecting the silicone rubber material therefrom.

In a combination process for fabricating the guard 10, the silicone rubber material is continuously injection moulded to form an elongate tube. The tube is then cut into sections of convenient length, for example lengths in a range of 250 mm to 3. 50 mm. Such a length of tubing is illustrated in Figure 3 and indicated by 200. The section of tubing 200 is then mounted onto a mandrel 210. The mandrel 210 is subsequently rotated as illustrated about its longitudinal axis A-B in a clockwise direction, the direction as indicated by an arrow 220, relative to a cutting tool 230. The tool 230

comprises a sharp cutting edge 240 which engages into the section 200. As the mandrel 210 is turned, the tool 230 is concurrently traversed in a direction D substantially parallel to the axis A-B. The tool 230 thereby cuts a spiral from the section 200, the

spiral remaining loosely retained on the mandrel 210. When the tool 230 has traversed at least part of the length of the section 200, the tool 230 is then maintained in a spatially constant axial position whilst the section 200 and the mandrel 210 continue to be rotated, thereby severing the spiral cut from the section 200. If necessary to reduce waste material, the tool 230 can be traversed the entire length of the section 200 so that severance is not required to form the spiral.

In order to achieve spiral direction reversal as described in the foregoing, the direction of rotation of the mandrel 210 relative to the tool 230 can be periodically reversed as the tool 230 is continuously traversed in the direction D. For such spiral direction reversal. the tool 230 is provided with one or more cutting edges so that it can cut in both clockwise and anticlockwise directions into the section 200.

In use, the guards 10,100 can be wrapped around a former to provide a thermally insulating elongate spacing element. Beneficially, the former can itself be fabricated from resilient material, for example a helical spring fabricated from compliant spring steel. Alternatively, the guards can be wrapped around exposed edges of oven trays which are susceptible to being contacted and thereby causing bums to personnel handling the oven trays.

When installed into thermal apparatus, for example a thermal oven, the guards 10,100, with or without associated former, can be retained in grooves. Preferably, the grooves have a restricted aperture opening to provide more positive retention of the guards 10, 100.

Referring now to Figure 4, there is shown an illustration of a thermal oven in which the

thermal guard 10 is utilized. The oven is indicated by 300 and comprises an of en chamber 310 having an associated hinged door 320 for sealing the chamber 310. The chamber 310 includes a plurality of tray retention ridges. for example a ridge 330. onto which an oven tray, for example an oven tray indicated by 340, can be slid for mounting within the chamber 310.

The oven tray 340 includes a welded steel-rod frame having front and rear peripheral elongate tray members 350,'360 respectively and also lateral peripheral elongate

members 370, 380. For convenience, the elongate members 350 to 380 can be fabricated from a continuous bar of 8 mm diameter mild steel material which is bent back onto itself to form the elongate members. A mesh 390 of smaller-diameter mild steel bars, for example bars having a diameter in a range of 1 to 2 mm, are spot welded substantially orthogonally to the elongate members to provide a shelf for the tray 340 as illustrated.

As shown in Figure 4, the guard 10 is included as a component part of the tray 340, the guard 10 being wrapped around the elongate peripheral members 350 to 380 as illustrated. The guard 10 is affixed by sliding one of the peripheral members 350 to 380 through a gap of the guard 10 spiral near one end of the guard 10. The guard 10 is then offered around the member so that the spiral encloses the member. Gaps in the spiral enable members of the mesh 390 to project through the guard 10 where they are spot welded to the peripheral members 350 to 380.

The spiral nature of the guard 10 enables it to be affixed to the tray 340 after the mesh 390 has been spot welded into position. Such installation would not be possible if a thermal guard were provided in the form of woven fibreglass sleeving for enclosing the peripheral members 350 to 380 as the mesh 390 would represent an obstruction.

The guard 10 provides a sufficient thermal barrier so that personnel's hands or wrists momentarily grazing the peripheral members 350,360 are not burned. Moreover, at lower oven temperatures, personnel can remove and insert the tray 340 by gripping onto the guard 10 without employing additional thermal protection, for example thermal gloves.

It will be appreciated that the guard 100 can be employed in substitution for the guard 10 for insulating the tray 340. Spiral direction reversal employed in the guard 100 renders it more easily and quickly affixable to the tray 340 as elucidated in the foregoing.

When installing the guard 100 onto the tray 340, a point of the guard 100 whereat spiral direction reversal occurs, namely at the central region 110 of the spiral, can be clipped to one of the peripheral members 350 to 380 and then the two end regions of the guard

100 concurrently offered around the peripheral members 350 to 380 to enclose them. Concurrent wrapping of the guard 100 enables it to be installed more rapidly and easily than the guard 10.

To retain the guard 10. and likewise the guard 100, in position, a bonding agent, for example a silicone-type adhesive, can be applied to ends of the guard to bind it to the peripheral members 350 to 380. Alternatively, a compliant steel clip or split collar can be inserted over free ends of the guard 10 on the tray 340. In many oven situations. inherent resilience of the guards 10,100 will alone be sufficient to ensure that the guards 10,100 remain in position on the tray 340 during use.

It will be appreciated that modifications and substitutions can be made to the guards 10, 100, and to the tray 340 comprising the guards 10,100 without departing from the scope of the invention. Moreover, it will also be appreciated that modifications can be made to the aforementioned method of manufacturing the guards 10,100 without departing from the scope of the invention.

Claims

CLAIMS 1. A thermal guard for at least partially thermally isolating a member about which the guard in installed, the guard being fabricated from a thermally insulating material formed into an elongate spiral.
2. A guard according to Claim 1 wherein the insulating material exhibits a thermal conductivity of less than 1 W ' K-1.
3. A guard according to Claim 1 or 2 wherein the insulating material exhibits a thermal conductivity of less than 0.4 W mol K"l.
4. A guard according to Claim 1,2 or 3 wherein the material is flexible and has a Shore A hardness in a range of 70'to 900.
5. A guard according to any preceding Claim wherein the material is flexible and

has a Shore A hardness in a range of 75'to 85'.
6. A guard according to any preceding Claim wherein the material comprises a silicone rubber material.
7. A guard according to Claim 6 wherein the rubber material in use is capable of withstanding an ambient temperature of at least 3000C.
8. A guard according to any preceding Claim wherein the material includes a dye which renders it less susceptible to thermal discolouration in use in comparison to corresponding undyed material.
9. A guard according to an-preceding Claim wherein the material includes an activatable hardening ingredient for hardening the guard after installation around the member.
10. A guard according to Claim 9 wherein the hardening ingredient is a thermo- setting polymer.
11. A guard according to any preceding Claim wherein at least part of the spiral is formed in a clockwise sense.
12. A guard according to any preceding Claim wherein at least part of the spiral is formed in an anticlockwise sense.
13. A guard according to any preceding Claim wherein the spiral includes at least one spiral direction reversal.
14. An oven tray including an elongate tray member onto which a thermal guard according to any one of Claims 1 to 13 is installed.
15. A tray according to Claim 14 wherein the elongate member is a peripheral member of the tray susceptible to being contacted by personnel handling the tray in use.
16. A method of fabricating a guard according to any one of Claims 1 to 13, the method including the steps of : (a) ejecting a fluid material from an orifice to form a solid material strand, the orifice being moved in a substantially circular or elliptical path about a longitudinal axis of the guard to form the strand into a spiral about the axis; and (b) periodically severing the spiral strand to provide one or more of the guards.
17. A method according to Claim 16 wherein the rotational direction of movement of the orifice about the axis is periodically reversed to provide the guard with one or more spiral direction reversals.
18. A method of fabricating a guard according to any one of Claims 1 to 13, the method including the steps of : (a) extruding a fluid material to form a hollow tube of resilient solid material ; (b) mounting the tube onto a support member; and (c) rotating the support member and tube relative to cutting means engaging onto the tube and traversing the cutting means relative to the tube to form a spiral cut into the tube, thereby forming the tube into an elongate spiral constituting the guard.
19. A method according to Claim 18 wherein the direction of rotation of the support member and tube relative to the cutting means is periodically reversed so that the spiral includes at least one spiral sense reversal.
20. A method of installing a guard according to any one of Claims 1 to 13 onto an elongate member, the method including the steps of : (a) affixing the guard at a central region thereof onto the member; and (b) concurrently winding end regions of the guard around the member so as to at least partially enclose the member.
21. A thermal guard substantially as hereinbefore described with reference to one or more of Figures I to 4.
22. A method of manufacturing a thermal guard substantially as hereinbefore described and/or illustrated in Figure 3.
23. An oven tray substantially as hereinbefore described with reference to one or more of Figures 1 to 4.