Flexible Strap

p-0002The present invention relates to an improved strap of flexible material, in particular, an improved strap of flexible material for use with a harness for breathing apparatus.

p-0003Self-contained breathing apparatus (SCBA) harnesses comprise a back plate (or frame) to which a cylinder of breathable gas is mounted. The cylinder of gas is retained on the back plate using a flexible cylinder-retaining strap that is attached to the back plate and tensioned around the cylinder. Typically two flexible shoulder straps are each attached at a first end to an upper portion of the back plate and at a second end to a lower portion of the back plate. A flexible waist strap (or belt) is also attached to the back plate. This enables the harness to be carried on the back of a user.

p-0004For breathing apparatus of the above kind which is used by fire-fighters, it is important that the cylinder-retaining, waist and shoulder straps are flame retardant because the harness must be capable of withstanding high-temperatures.

p-0005It is known to use straps that are woven from Kevlar (®) or Nomex (®) fibres. Such straps are intrinsically flame retardant but are relatively expensive due to the cost of Kevlar and Nomex. The straps that are produced from the aforementioned materials must also be sealed at their edges in order to prevent fraying. However, it is not possible to heat-seal the ends because of the flame retardant properties of the fibres. The ends of the straps must therefore be folded over twice and stitched. This results in additional manufacturing expense and time.

p-0006According to one aspect of the present invention there is provided an elongate strap of flexible material for use with a harness for breathing apparatus, the strap comprising a core substrate provided on first and second surfaces with a flame retardant layer. Preferably the flame retardant layer is a coated layer. The core substrate is preferably a textile. The strap can be manufactured cheaply and easily and the flame retardant layers allow the strap to be used in high-temperature environments. In a particularly preferred arrangement the flame retardant layers are non-slip. Use of the non-slip material means that the strap can grip adjacent objects.

p-0007In one embodiment the flame retardant layers are rubber. The rubber may be a synthetic rubber, a butyl/nitrile synthetic rubber mix; silicone rubber or flexible PVC. The flame retardant layers may have anti-oxidant additives to improve the flame retardant properties. The thickness of the flame retardant layers may be between 0.3-1 mm.

p-0008The textile material may be a polyamide such as nylon. The thickness of the textile may be 0.5-1.5 mm. The textile may be woven, comprising warp threads and weft threads. Preferably the strap is formed such that the warp threads of the textile extend in a direction of elongation of the strap, to provide strength.

p-0009The invention also comprises a gas-cylinder retaining strap, or a shoulder strap, or a waist strap for a harness for breathing apparatus comprising a strap according to any statement herein.

p-0010The invention also comprises a breathing apparatus having a strap according to any statement herein.

p-0011According to a second aspect of the present invention there is provided a method of manufacturing a strap of flexible material for use with a harness for breathing apparatus, the method comprising applying a flame retardant layer to first and second surfaces of a textile. Preferably the flame retardant layer is provided as a coating. The flame retardant layer may be non-slip. The flame retardant layer may be applied to the first and second surfaces of the textile under heat and/or pressure.

p-0012In one embodiment the strap is formed from a woven textile having warp threads and weft threads. Preferably the strap is formed such that the warp threads extend in the direction of elongation of the strap.

p-0013The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

p-0014Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

p-0015<figref idrefs="DRAWINGS">FIG. 1</figref> schematically shows an elongate strap of flexible material according to the present invention;

p-0016<figref idrefs="DRAWINGS">FIG. 2</figref> schematically shows the cross-section A-A of <figref idrefs="DRAWINGS">FIG. 1</figref>;

p-0017<figref idrefs="DRAWINGS">FIG. 3</figref> schematically shows a method of manufacturing a strap according to the present invention;

p-0018<figref idrefs="DRAWINGS">FIG. 4</figref> schematically shows a sheet of material from which a number of straps can be cut; and

p-0019<figref idrefs="DRAWINGS">FIG. 5</figref> schematically shows a number of straps used on a harness for breathing apparatus.

p-0020<figref idrefs="DRAWINGS">FIG. 1</figref> shows a flexible elongate strap <b>10</b> according to the present invention. The strap <b>10</b> has a layered structure as shown in <figref idrefs="DRAWINGS">FIG. 2</figref>. The layered structure comprises a woven textile <b>12</b> with coated layers <b>14</b>, <b>16</b> on first and second surfaces, of a flame-retardant non-slip material.

p-0021In this embodiment the textile is woven from polyamide fibres such as nylon. The woven nylon is 1000 denier and has a thickness of approximately 1.25 mm. The flame retardant non-slip material layers <b>14</b>, <b>16</b> are of a butyl/nitrile synthetic rubber mix which is flame retardant. The addition of anti-oxidant additives improves the flame retardant properties of the non-slip layers <b>14</b>, <b>16</b>. Each of the non-slip layers has a thickness of approximately 0.7 mm.

p-0022With reference to <figref idrefs="DRAWINGS">FIG. 3</figref>, a sheet <b>20</b> of the flexible layered material used to make the strap <b>10</b> is manufactured by calendaring the butyl/nitrile synthetic rubber mix onto both sides of a sheet of woven nylon <b>12</b>. This is done by heating the synthetic rubber mix and continuously pouring it onto both surfaces of the woven nylon sheet <b>12</b> whilst feeding the sheet of woven nylon through two oppositely rotating rollers <b>102</b>, <b>104</b>. The pressure of the rollers <b>102</b>, <b>104</b> causes a layer of synthetic rubber mix to become bonded to each side of the woven sheet of nylon. The sheet of woven nylon <b>12</b> coated with layers <b>14</b>, <b>16</b> of synthetic rubber on either side is then fed through a second set of oppositely rotating rollers <b>106</b>, <b>108</b> so as to apply further pressure to the layered material. This manufacturing method results in the layered structure of <figref idrefs="DRAWINGS">FIG. 2</figref>.

p-0023The woven nylon textile <b>12</b> has a textured surface and the synthetic rubber mix is applied to first and second surfaces under the action of pressure and heat. This results in a laminate structure the layers of which are difficult to separate.

p-0024Referring now to <figref idrefs="DRAWINGS">FIG. 4</figref>, the sheet of flexible material <b>20</b> manufactured by the above described process is cut into a series of elongate strips <b>22</b>. The sheet <b>20</b> is cut parallel to the direction of elongation of the warp threads of the woven textile for optimum strength. The strips <b>22</b> can then be cut into the required lengths to form straps <b>10</b>. It is not necessary to seal the ends or edges of the straps <b>10</b> because the rubber layers <b>14</b>, <b>16</b> prevent the woven nylon textile <b>10</b> from fraying.

p-0025The straps <b>10</b> can be manufactured quickly, easily and cheaply. The woven nylon textile <b>12</b> is a relatively cheap material but is not flame retardant. The flame retardant rubber layers <b>14</b>, <b>16</b> shield the woven nylon core <b>12</b> and ensure that the straps as a whole are flame retardant. The strength of the strap <b>10</b> is provided by the woven nylon textile material <b>12</b>. Specifically, the warp threads that extend along the direction of elongation of the strap provide the strength of the strap <b>10</b>. The strap <b>10</b> is also slightly elastic which is particularly useful for certain applications which require a strap to retain an object under tension.

p-0026The strap <b>10</b> has a non-slip surface on either side that in this embodiment is provided by the synthetic rubber layers <b>14</b>, <b>16</b>. This means that the strap <b>10</b> has a relatively high coefficient of friction and therefore exhibits gripping properties.

p-0027<figref idrefs="DRAWINGS">FIG. 5</figref> shows the straps <b>10</b> being used on a harness <b>30</b> for breathing apparatus that is to be worn on the back of a user. The straps <b>10</b> are used as shoulder straps <b>32</b>, a waist strap <b>34</b> and a gas-cylinder retaining strap <b>36</b> (cylinder not shown).

p-0028The non-slip rubber layers <b>14</b>, <b>16</b> of the shoulder and waist straps <b>32</b>, <b>34</b> enable the straps to grip the clothing of the user. This means that the user wearing the harness feels that the harness is held securely and tightly to his/her body. In particular, a secure feeling of the harness against the user's body can be obtained without over tightening the shoulder and waist straps <b>32</b>, <b>34</b> and thus without unduly restricting the wearer's movement.

p-0029The non-slip rubber layers <b>14</b>, <b>16</b> of the gas-cylinder retaining strap <b>36</b> allow the strap to grip a gas-cylinder loaded onto the harness <b>30</b>. This inhibits rotation which would exert an unwanted stress on the connection between the gas-cylinder and the reducer valve <b>38</b> to which it is connected. Conventionally, a separate rubber pad is provided in order to inhibit rotation of the gas-cylinder. The use of a cylinder-retaining strap <b>36</b> having a non-slip coating therefore removes the need for the separate rubber pad which therefore reduces both the cost of the harness and the assembly time.

p-0030As described above, the flame retardant layers <b>14</b>, <b>16</b> of the woven nylon textile <b>12</b> renders the straps <b>10</b> flame retardant. This means that they can be used on a harness for breathing apparatus used by fire-fighters and the like in high-temperature environments.