Abstract
A security device has a flexible strap (26) with a lock unit (28) attached at each end. The strap (26) comprises a plurality of longitudinally extending multi-filament cables or ropes (2) arranged in a substantially planar array embedded in an elastomeric material (4). The cables or ropes (2) have a coating of primer for creating a bond with the elastomeric material (4). The primer may be restricted to the external surface of the cables or ropes (2), or some of the surfaces of the filaments may be free of primer. This facilitates relative movement of the filaments during flexure or compression of the strap (26). Moreover, an extrusion process for manufacturing the strap (26) including a priming station (12) is disclosed.
Claims
1. A security device comprising a flexible strap with a lock unit attached at each end, the strap having a plurality of longitudinally extending multifilament cables arranged in a substantially planar array embedded in a thermoplastic or thermosetting elastomeric material wherein the cables have a coating of primer for creating a bond with the material, wherein some of the surfaces of the cable filaments within the strap are free of primer.
2. A security device according to claim 1 wherein the elastomeric material is polyurethane.
3. (canceled)
4. A security device according to claim 1 wherein filaments having different tensile strengths are included in each cable.
5. A security device according to claim 1 wherein each cable comprises a plurality of multifilament wires.
6. A security device according to claim 5 wherein the wires are twisted around a core.
7. A security device according to any claim 5 wherein each wire itself comprises multiple filaments twisted around a core.
8. A security device according to any claim 6 wherein the core also comprises multiple filaments twisted around a core.
9. (canceled)
10. A security device according to claim 1 wherein the filaments of the cables are of different materials.
11. A security device according to claim 10 wherein the materials are metallic and non-metallic.
12. A security device according to claim 1 having a heatproof outer coat.
13. A security device according to claim 12 wherein the outer coat comprises a sleeve.
14. A security device comprising a flexible strap with a lock unit attached at each end, the strap having a plurality of longitudinally extending multifilament cables arranged in a substantially planar array embedded in a thermoplastic or thermosetting elastomeric material wherein the cables have a coating of primer for creating a bond with the material wherein the cross-section of the strap is linear on one side of the array and indented on the other side between the cables, or indented on both sides of the array between the cables.
15. (canceled)
16. A security device according to claim 14 wherein the minimum thickness of the strap between the cables is half the diameter of a single cable.
17. A security device according to claim 14 wherein the minimum spacing between the cable is half the diameter of a single cable.
18. (canceled)
19. A security device according to claim 14 wherein the cross-section of the strap has a width-to-thickness ratio in the range 5:1 to 8:1.
20. A security device according to claim 14 wherein at least some of the cables project at the ends of the strap for attachment to the lock units, and the projecting cables at each end of the strap are received and held in a bracket attached to the respective lock unit.
21-22. (canceled)
23. A security device according to claim 20 wherein the cables are held in the brackets by one of crimping, gluing and welding.
24-25. (canceled)
26. A method of making a security device wherein a plurality of multifilament cables coated with a primer and arranged in a planar array extending in a common longitudinal direction are drawn through a die with a mass of heated thermoplastic or thermosetting elastomeric material, which die forms indents on at least one side of the array between the cables, the material then being cooled with the cables embedded therein to form a strap in which the primer enhances a bond between the cables and the material; and attaching complementary lock units to the strap ends.
27. A method according to claim 26 wherein the heated elastomeric material is under pressure.
28. A method according to claim 26 wherein the heated elastomeric material is polyurethane.
29. A method according to claim 26 including the preparatory step of coating the surfaces of the cables with primer while ensuring that some of the surfaces of the cable filaments are free of primer.
30-32. (canceled)
33. A method according to claim 26 wherein projecting cables at each end of the strap are received and held in a bracket attached to the respective lock unit and the cables are held in the brackets by one of crimping, gluing or welding.
34. A security device according to claim 1 wherein the minimum spacing between the cables is half the diameter of a single cable.
Description
[0012] Further details of the invention will be apparent from the following description of preferred embodiments in which reference will be made to the accompanying schematic drawings wherein:
[0013] FIG. 1 is a cross-section of a strap for use in a device according to the invention;
[0014] FIG. 2 is an enlarged cross-section of an alternative strap for use in a device of the invention;
[0015] FIG. 3 is a further enlarged cross-section of one form of cable suitable for use in straps of the kind shown in FIGS. 1 and 2;
[0016] FIG. 4 illustrates a process for making a strap for use in a security device according to the invention;
[0017] FIGS. 5 and 5A shows a security device incorporating a device according to the invention;
[0018] FIG. 6 is a perspective view of the ends of a strap for use in a device of the invention; and
[0019] FIG. 7 shows an exploded view of one of the strap ends of FIG. 5, revealing the cable ends.
[0020] The strap shown in FIG. 1 has an array of six cables 2 embedded in a cooled and cured elastomeric material 4. The strap shown is around 5 cms wide and around 1 cm thick; its cross-section has flat upper and lower faces as shown and is semi-circular on either side. Each cable has a diameter of around 6 mms, and the array is located centrally in the material leaving a minimum of at least 1 mm of material around each cable. The spacing between the cables is in the range 1.5-2.0 mm, and the spacing between the outermost cables and the outer extremity of the strap is around 2 mms. these dimensions can of course vary, but the ratio of strap width to thickness will normally be in the range 5:1 to 8:1.
[0021] The strap shown in FIG. 2 also has an array of six cables 2 embedded in a cooled and cured elastomeric material 4. however, in this embodiment the material is indented on one side between the cables. The resistance to bending of the strap is reduced by the removal of the mass from the one side, particularly around an axis on the other side. On either side of the strap the material is formed with a 2.5 mm shoulder 6. The cross-section is flat on its lower face with a minimum of around 1.5 mms between the lower face and each cable 4, and a minimum of around 1 mm over each cable on the upper face. The overall width of the strap is around 5 cms, and its thickness around 8 mms. The depth of each indent is around 5.4 mms, but where indentations are used in any strap of the invention, their depth is normally in the range 55-80% of the strap thickness, preferably 56-70%.
[0022] The elastomeric material is typically thermoplastic, but thermosetting materials can also be used in some applications. The preferred material is polyurethane. The strap as a whole is normally enclosed in a sleeve, or coated with an heatproof layer.
[0023] FIG. 3 shows a further enlarged cross-sectional view of a cable suitable for use in the straps of devices according to the invention. As can be seen it comprises multiple filaments which are themselves arranged in separate wires. The Figure shows six such wires 8 around a seventh core wire 10. Each wire itself consists of multiple filaments; the drawing shows nineteen, with eighteen around the nineteenth core filament. In each wire 8 and 10, the filaments are twisted around the nineteenth core filament, and the wires 8 are twisted around the core wire 10. We have found cables with seven wires performed well in tests. The number of filaments in each wire can vary. We have used nineteen in each wire, as illustrated, and seven in another trial, which also performed well. In a particular embodiment, in an indented strap of the kind illustrated in FIG. 2, each wire had seven 2.6 mm diameter wires with each wire consisting of seven 0.8 mm filaments. The filaments can be of the same material, normally metallic; steel, galvanised or stainless, but combinations of different materials can be used, and bulking fibres can be included.
[0024] A simple procedure for the manufacture of a strap according to the invention is illustrated in FIG. 4. Multifilament cables 2 with the chosen arrangement of filaments as discussed above are coated with a primer at a priming station 12 and delivered in a planar array 14 over a roller 16 to a chamber 18 containing the elastomeric material. The cables and their filaments will normally be cleaned just prior to entering the priming station, and an adhesive may also be added at this stage if needed. The array passes through the chamber and is drawn through a die 20 with the desired cross-section. The elastomeric material is delivered to the chamber 18 and kept under pressure by a screw conveyer 22 and thereby extruded though the die 20 at the same rate as the array 14. As it does so it bonds with the primed surfaces of the cables in the array 14, which bond is established as the material cools and sets in the stabiliser station 24. The resultant strap 26 can then be cut and incorporated in a security device of the invention by attaching a locking unit 28 (see FIG. 5) at either end. The entrance of the cable array to the chamber 18 is sealed by pressurised rollers 30, and at the die 20 by the material itself. The pressure and temperature of the material in the chamber will depend upon the nature of the material, but for polyurethane a temperature in the range 180-225 C. and the pressure generated by a 3:1 compression ratio are appropriate.
[0025] In preferred embodiments of the invention some of the surfaces of the cable filaments are left free of primer. This can be accomplished by coating only the outer surface of the cables and leaving the inner filaments. When the filaments themselves are formed into separate wires within the cables, the external surfaces of the wires can be coated, again leaving the internal filaments uncoated. The filaments without a primer coating are better able to move relative to each other, and this enhances the flexibility of the strap as a whole. This mobility is both longitudinal and lateral, assisting the straps resistance to cutting as the cables and/or wires will compress or shift in response to an attempt to cut the strap with for example a blade or saw.
[0026] A completed security device according to the invention is illustrated in FIGS. 5 and 5A. The strap is enclosed in a knitted sleeve 32, and lock units 28 at either end of the strap are engaged to close the device as shown in FIG. 5. FIG. 5A shows the device open and laid flat. A typical length for the closed device, suitable for use as a bicycle lock, is 736 mm. As can be seen, one of the lock units has a male element 34 projecting from a shoulder 36 on body 38. When engaged with the other lock unit the element 34 and shoulder 36 are received in sleeve 40 with the element latching behind a releasable catch in the sleeve. The element can be released from the catch to unlock the device by a key (not shown) fitted in keyhole 42. A tab 44 is attached to one of the lock units to assist in their separation when the device is unlocked.
[0027] FIG. 6 shows the ends of a strap for use in a device of the invention with the central length omitted to show its cross section. Each end is received in and attached to a bracket 46 as described below. Each bracket 46 consists of matching metal pressings 48, normally of stainless steel, which may be closed by plates 50 at either side. The pressings are formed with openings 52 which combine to form a passage for a rivet by which the pressings are attached to respective lock units. While one rivet 54 is shown in FIG. 5, it is preferred that they not normally be visible in the completed security device. It will be appreciated that attachment mechanisms other than rivets can be used, bearing in mind that the mechanisms are preferably not to be seen. As can be seen, the brackets 46 project from the elastomeric material of the strap at a small angle; typically 10-25 from the strap axis. This can be established by setting the angle at a crease 56 prior to the final curing stage in the manufacture of the strap, and it will be understood in this respect that the requisite length of strap may be cut prior to final curing.
[0028] FIG. 7 illustrates one strap end with the bracket 46 shown separated. As can be seen, the elastomeric material 58 has been stripped back to expose the six cables 2, and the ends of the central cables 60 are cut back to free the space between the openings 52. The brackets can be attached to the exposed cables by suitable means such as welding or gluing, or crimping if the respective bracket is a unitary component. If the means is glue, then a high grade epoxy resin glue is preferred. If the means is welding, the MIG or TIG welding can be satisfactory. The slots 62, which might otherwise be omitted, are useful in this respect as they can be used to puddle weld the bracket 46, or the pressings 48 to the cables, burning off any coating on the cables in the process. A protective coating on the fitted brackets and cables can be added thereafter if required, by painting or dipping.
