GB2077341A

GB2077341A - Flexible locking tie

Info

Publication number: GB2077341A
Application number: GB8018198A
Authority: GB
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1980-06-04
Filing date: 1980-06-04
Publication date: 1981-12-16

Abstract

A flexible tie for bundling electric cables or the like has a lever (2) mounted in a head (1) and rotatable between a release position and two locking positions in which different forces are applied to hold strap (4) against a tooth (9) in the head. In one position (Fig. 3) the strap may be pulled in directon (A) to tighten it but not in direction (B); in the other (Fig. 4) it cannot be pulled in either direction. <IMAGE>

Description

SPECIFICATION Flexible locking tie This invention relates to methods of securing a toothed strap in a tie head and to flexible ties; such ties are suitable for either bundling together or securing and supporting electric cables and other elongate articles. Such ties have a head on which is mounted a lever rotatable between a release position and a locking position in which it exerts a force to hold the strap in interlocking engagement with at least one tooth on the head.

The invention is applicable both to single piece ties, in which the head is integral with the toothed strap, and to multi-piece ties in which the head and toothed strap are separate.

Single piece ties are suitable for wrapping around and securing together a bundle of cables, with the toothed strap passing from the head, around the bundle, and back through the head in which it is locked by engagement of the transverse tooth with a part of the head.

Two piece ties are suitable for attaching a cable, or a bundle of cables, to a support, such as a cable tray; the head will normally be mounted on the free end of a plain flexible strap, attached at its other end to the support, and the toothed strap will be attached at one end to the support with its free end available fc, passing through and locking to the head. Other configurations of tie head and toothed tie strap are possible.

In accordance with the invention, a method of securing a strap to the tie head comprises:- (i) inserting the strap in the head; (ii) tensioning the strap with the lever in a first locking position in which it exerts a resilient biassing force to hold the strap in such engagement which force can be overcome by a sufficient tension at least in the direction tending to move the strap through the head in a tightening direction; and (ii) rotating the lever to a second locking position in which it exerts a force to hold the strap in such engagement, which force cannot be overcome by a tension in the strap that would be sufficient to overcome the force applied in the first locking position.

Preferably, the rotation towards the second locking position applies shearing and/or tensile forces to a torsion bar formed by a beam located between, and connecting the lever and the head.

In accordance with another aspect of the present invention, in a tie the lever has a bearing surface forming a cam with two sections, each section establishing a stable position of the lever, one stable position corresponding to a first locking position of the lever in which it exerts a resilient biassing force to hold the strap in such engagement which force can be overcome by a sufficient tension at least in the direction tending to move the strap through the head in a tightening direction and the other stable position corresponding to a second locking position of the lever in which it exerts a force to hold the strap in such engagement, which force cannot be overcome by a tension in the strap that would be sufficient to overcome the force applied in the first locking position.

In order that the invention may more readily be understood, a description is now given by way of example only, reference being made to the accompanying drawings in which: Figure 1 is a plan view of the head of a tie embodying the present invention; Figure 2 is a cross-section on the line Il-Il in Figure 1 of a head and strap in a release position in which the strap may pass through the head; Figure 3 is a similar cross-section of the head and strap in a first locking position; Figure 4 is a similar cross-section of the head and strap in a second locking position.

The tie shown has a head 1 of U-shaped crosssection, the head being moulded integrally with a lever 2 and a strap 3 which, for one-piece ties, is the plain end of a toothed strap 4 and for multipiece ties is separate from toothed strap 4. Head 1 supports lever 2 by beams 5 which are deformable in torsion to permit the lever to rotate about axis 6.

When lever 2 is in its moulding position, i.e.

there is no torsional stress in the beams, the minimum spacing between surfaces 7 and tooth 9 is less than the thickness of strap 4, typical valves being 0.7 mm and 1 mm respectively.

In order to permit strap 4 with teeth 8 to pass freely between two arcuate bearing surfaces 7 of lever 2 and a transverse tooth 9 on the inside of the base of head 1 , the lever can be rotated by hand and then held in its release position (Figure 2) to give a sufficient clearance between surfaces 7 and tooth 9. When a suitable position of strap 4 in head 1 has been achieved, the lever can be released so that it moves under its own resilience to a first locking position (Figure 3) in which the two arcuate surfaces 7 of lever 2 bear against the strap thereby exerting a resilient biassing force on the strap tending to urge one of its teeth 8 into interlocking engagement with tooth 9.

Alternatively, the strap 4 can be passed between surfaces 7 and tooth 9 by applying a force in the direction A sufficient to make tooth 8 pass over tooth 9 while forcing lever 2 to rotate anticlockwise (the lever moving from the first locking position to the release position and back again for each tooth 8).

The strap can be undone, if necessary, by releasing tooth 8 from engagement with tooth 9 by turning the lever or pulling the strap in direction A and then maintaining lever 2 in its release position, while moving the strap 4 in direction B (opposite to A). Each bearing surface 7 forms a cam with two sections 10 and 11, each section establishing a stable position of the lever when strap 4 is held in the head; cam section 10 corresponds to the first locking position of lever 2.

A force similar in magnitude to that needed to pull the strap through the head in the direction A when the lever is in its first locking position but in direction B cannot overcome the biassing force and thereby affect loosening of the load, because not only the relevant abutting faces of tooth 8 and tooth 9 in this case are perpendicular to B, but also downward movement of the strap will not rotate the lever 2 anticlockwise but rather tends to rotate it clockwise and increase the grip.

Moreover, if the load held by the tie is big enough to make the strap 4 bear on the lower part of bearing surfaces 7, this produces an additional torque tending to urge the strap against tooth 9.

Rotation of arm 12 anticlockwise through a large angle applies not only torque but also shearing and tensile forces to the beams 5, since the distance from axis 6 to the part of surface 7 bearing on the strap 4 increases significantly, thereby forcing the effective axis of rotation of lever 2 away from tooth 9. Once arm 10 has been rotated anticlockwise through approximately 1300, the lever achieves a new stable position in which part of cam section 11 abuts the strap, this being the second locking position of the lever (see Figure 4). In this second locking position, the location of the effective axis of rotation of lever 2 relative to head 1 is shown by numeral 13 of Figure 4.

Due to this displacement, beams 5 exert forces which additionally urge the strap 4 against tooth 9, thereby greatly increasing the force required to overcome the engagement between trap 4 and tooth 9, also it may make any substantial movement of the strap through head 1 impossible without damage either to the beams or to the strap.

The lever 2 can be released from its second locking position and returned to the first locking position or the release position by clockwise rotation of arm 12, and in some cases can be relocked, though usually only a small number of times.

In the illustrated tie the head, the lever, and the strap can be simultaneously moulded in a two piece mould without retracting parts. A suitable material is nylon.

Claims

1. A method of securing a toothed strap in a tie head having a lever mounted so as to be rotatable between a release position and a locking position in which it exerts a force to hold the strap in interlocking engagement with at least one tooth on the head, characterised by (i) inserting the strap in the head; (ii) tensioning the strap with the lever in a first locking position in which it exerts a resilient biassing force to hold the strap in such engagement which force can be overcome by a sufficient tension at least in the direction tending to move the strap through the head in a tightening direction; and (iii) rotating the lever to a second locking position in which it exerts a force to hold the strap in such engagement which force cannot be overcome by a tension in the strap that would - be sufficient to overcome the force applied in the first locking position.

2. A method according to Claim 1 characterised in that the rotation towards the second locking position applies shearing and/or tensile forces to a torsion bar formed by a beam located between, and connecting the lever and the head.

3. A flexible tie having a tie head, a lever mounted in the head so as to be rotatable between a release position and a locking position in which it exerts a force to hold a toothed strap in interlocking engagement with at least one tooth on the head, characterised in that the lever has a bearing surface forming a cam with two sections, each section establishing a stable position of the lever, one stable position corresponding to a first locking position of the lever in which it exerts a resilient biassing force to hold the strap in such engagement, which force can be overcome by a sufficient tension at least in the direction tending to move the strap through the head in a tightening direction, and the other stable position corresponding to a second locking position of the lever in which it exerts a force to hold the strap in such engagement, which force cannot be overcome by a tension in the strap that would be sufficient to overcome the force applied in the first locking position.

4. A method of securing a strap to a tie head substantially as herein described with reference to the accompanying drawings.

5. A tie substantially as herein described with reference to and as illustrated in the accompanying drawings.