GB2056541A - Band clamps - Google Patents

Abstract

A worm drive clamp consists of an injection moulded plastics strip (11), an injection moulded plastics housing (10), and a worm screw (12) mounted for rotation in a bore of the housing. One end of the strip (11) is secured to the housing by projections (16) engaging in slots in the housing, and the other end (20) overlaps the fixed end within the housing. The worm screw thread engages serrations formed in a thickened portion (21) of the strip (11). <IMAGE>

Description

SPECIFICATION Worm drive clamps This invention relates to a worm drive clamp which may be used, for example, to clamp a flexible pipe to a fixed hollow spigot.

For many years worm drive clamps have been made of steel. Atypical clamp consists of a flexible steel band with serrations rolled, milled or pierced across the longitudinal axis and extending in from one end. A screw with a thread of the same pitch as the serrations is retained in a suitable housing attached to the other end of the band so that, when the band is formed into a loop having overlapping ends contained in the housing, the screw thread engages with the serrations. Rotation of the screw then expands or contracts the loop to slacken or tighten the clamp respectively.

In a process for producing such a clamp, strip steel is fed into a progression tool and a sequence of seven operations are performed to obtain the appropriately shaped housing. A second steel strip is then cut to provide the band, and two holes are punched in one end of the band. The band is then milled to provide the serrations. The band must then be straightened before being bent at the end containing the two punched holes. This end is then inserted into the housing and two pairs of opposing projections at the bottom of the housing are pressed into the two holes to rivet the band to the housing. The band is then rolled into a loop and the assembly is plated before inserting the worm screw into the housing and overlapping the ends of the band in the housing so that the screw thread engages the serrations.Finally, the housing is crimped around the screw to prevent axial movement of the screw so that when the screw is rotated the loop expands or contracts according to the direction of rotation.

The above process involves a large number of manually controlled operations and is therefore a labour-intensive time consuming operation.

In accordance with one aspect of the present invention a method of producing a worm drive clamp comprises injection moulding a flexible plastics strip with serrations formed transverse to the longitudinal axis of the strip extending in from one end thereof, injection moulding an open-ended tubular housing, inserting the threaded core of a worm screw into the housing, securing the unserrated end of the strip to the housing, forming the strip into a loop, and overlapping the ends of the strip within the housing such that the threaded core of the screw is compressed between the overlapped ends of the strip and the roof of the housing with the screw thread engaged with the serrations on the strip.

In accordance with another aspect of the present invention, a method of producing a worm drive clamp comprises injection moulding an integral assembly consisting of (a) an open-ended housing, (b) a flexible plastics strip depending from the base of the housing and with serrations formed transverse to the longitudinal axis of the strip extending inwardly from the free end thereof, and (c) a worm screw carried at the end of a spur depending from the housing; the method further comprising inserting the threaded core of the screw into the housing, forming the strip into a loop, and inserting the free end of the loop into the housing such that the threaded core of the screw is compressed between the free end of the loop and the roof of the housing with the screw thread engaged with the serrations on the strip.

A clamp produced by either of the above methods thus comprises an injection moulded flexible plastics strip formed into a loop having overlapped ends, an injection moulded plastics housing containing the overlapped ends, and a worm screw mounted for rotation in a bore of the housing, one of the overlapped strip ends being secured to the housing and the screw thread engaging serrations provided on the outwardly facing surface of the other overlapped end such that rotation of the worm causes expansion or contraction of the loop.

The plastics strip, the housing and, if desired, the screw can all be injection moulded in a single tool within about 15 seconds. Once these three components have been injection moulded, they can be assembled either by the manufacturer or by the eventual user. In the latter case, the components would be sold as a kit of parts.

The serrated portion of the strip is preferably thickened with respect to the remainder of the strip, the thickened portion being centrally disposed about the longitudinal axis of the strip and having a width less than that of the strip. This ensures that the depth of the serrations can be made sufficient to give adequate surface area contact with the teeth of the worm screw while at the same time the remainder of the strip has the required flexibility. The method of securing the strip to the housing is preferably by means of mutually engagable slots and projections which releasably retain the strip and the housing together until the free end of the loop is inserted into the housing to provide a compression fit between the two overlapped ends of the strip and the screw.

The screw is preferably moulded with an integral end flange which is spaced from the head of the screw by a distance substantially equal to the length of the housing such that the head and the end flange abut the respective end faces of the housing to prevent axial movement of the screw within the housing when the screw is rotated.

The plastics material is selected to suit the particu lar application of the clip. One particular plastics material which can be advantageously used for some applications is a nylon based material filled with glass fibre. For applications in which the clip is not subjected to extreme pressures or where the torque exerted on the screw is not excessive, a softer injection-moulded resin, such as high density polypropylene, could be used. Conversely, harder injection-moulded resins, such as nylon, could be used to give high torque characteristics.

Particular examples of suitable injection-moulded materials would be polystyrene, polypropylene, polyethylene, polyvinylidene chloride, acrylo nitrile butadene styrene and nylon.

By way of example only, a clamp embodying the invention will now be described with reference to the accompanying drawings in which: FIG. 1 is a side elevational view of the assembled clamp; FIG. 2 is an end view of the clamp; FIG. 3 is a side elevational view of the clamp housing; FIG. 4 is an end view of the clamp housing; FIG. 5 is an end view of the flexible band; FIG. 6 is a plan view of one end of the band; FIG. 7 is a side view of the end of the band shown in Fig. 6; FIG. 8 is a plan view of the other end of the flexible band; and, FIG. 9 is a side view of the end of the band shown in Fig. 8.

Referring to these figures, the clamp consists of three components all of which are formed of plastics material and are injection moulded. The three components are a housing 10, a flexible band 11, and a worm screw 12.

The housing 10 includes side walls 13, a roof 14 and a base 15. It also includes a pair of end walls 24,25 having aligned openings forming a bore for receiving the worm screw 12 and the overlapped ends of the band 11 as shown in Figs. 1 and 2.

One end of the plastics band 11 is T-shaped (as shown in Figs. 6 and 7), and each end of the crosspiece 18 is formed with a projecting tongue 16 having a 15, taper. During assembly of the clamp, these tongues 16 are pushed with atightfitinto respective slots 17 formed in the side walls 13 of the housing 10 until the cross-piece 18 (which juts below the strip) abuts the base 15 of the housing 10 as shown in Fig.

1. The band is then formed into a loop and the free end 20, together with the worm screw, is inserted into the space 19 (Fig. 4) between the side walls 13 of the housing. The free end 20 of the band thus over lies the fixed end and, at the same time, it forces the worm screw 12 upwards against the roof 14 of the housing 10. The three components are thus tightly held together.

The free end 20 of the band 11 is moulded with a raised platform 21 having serrations 22 transverse to the longitudinal axis of the strip which engage the worm screw 12 when the clamp is assembled as shown in Fig. 1. When the screw is rotated the free end 20 of the band 11 is moved forwards or backwards to contract or expand the loop formed by the band. Axial movementofthe screw is prevented by a flange23 atthe end of the screw 12 which abuts the end wall 24 (Fig. 1), the head 26 of the screw abutting the opposing end wall 25.

Different lengths of band 11 can be provided with out altering the dimensions of the housing so that the clamp can be used for a wide variety of applications.

The housing 10, the band 11, and the worm screw 12 may be injection moulded as an integral assem bly ifthe worm screw is carried at the end of a spur (not shown) depending from the housing, the spur being bent into a substantial U-shape when the assembly is removed from the mould and the screw is inserted into the housing. In such an assembly, the fixed end of the band would be moulded integrally with the base of the housing.

Claims (14)

1. A worm drive clamp comprising: an injection moulded flexible plastics strip formed into a loop having overlapping ends; an injection moulded plastics housing containing the overlapped ends; and a worm screw mounted for rotation in a bore of the housing, one ofthe overlapped strip ends being secured to the housing and the screw thread engaging serrations provided on the outwardly facing surface of the other overlapped end such that rotation of the worm causes expansion or contraction of the loop.

2. A clamp according to Claim 1 in which the serrated portion of the strip is thickened with respect to the remainder of the strip.

3. A clamp according to Claim 2 in which the thickened portion of the strip is centrally disposed aboutthe longitudinal axis of the strip and has a width less than that of the strip.

4. A clamp according to any of the preceding claims in which the housing includes a pair of opposed substantially vertical side walls spaced apart by a distance substantially equal to the width of the strip such that, when the free end of the strip is inserted into the housing, the serrations cannot be skewed with respect to the thread of the screw.

5. A clamp according to Claim 4 in which the said side walls of the housing are joined by a curved roof, the height of the side walls and the combined thickness of the overlapped ends of the strip being such that the worm screw is displaced upwardly into engagement with the roof when the two ends of the strip are overlapped in the housing.

6. A clamp according to Claim 4 or Claim 5 in which the strip and the housing are provided with mutually engageable projections and slots, the projections being inserted into the slots to secure the strip to the housing.

7. A clamp according to Claim 6 in which the slots are in the side walls of the housing and the projections are at one end of the strip.

8. A clamp according to any one of the preceding claims in which the end of the strip carrying the projections is further provided with a step which abuts the base of the housing when the projections are fully inserted into the slots.

9. A clamp according to any one of the preceding claims in which the screw is injection moulded.

10. A clamp according to Claim 9 in which the screw is moulded with a flange spaced from the head of the screw by a distance substantially equal to the length of the housing such that the head and the flange abut the respective end faces of the housing to prevent axial movement of the screw within the housing when the screw is rotated.

11. A method of producing a worm drive clamp comprising injection moulding a flexible plastics strip with serrations formed transverse to the longitudinal axis of the strip at one end thereof; injection moulding an open-ended tubular housing; inserting a worm screw into the housing; securing the unserrated end of the strip to the housing; form ing the strip into a loop; and overlapping the ends of the loop within the housing such thatthe screw is compressed between the overlapped ends of the loop and the roof of the housing with the screw thread engaged with the serrations on the strip.

12. A method of producing a worm drive clamp comprising injection moulding an integral assembly consisting of (a) a tubular open-ended housing, (b) a flexible plastics strip depending from the base of the housing and with serrations formed transverse to the longitudinal axis of the strip at the free end thereof, and (c) a worm screw carried at the end of a spur depending from the housing; the method further comprising inserting the body of the screw into the housing, forming the strip into a loop, and inserting the free end of the strip into the housing such that the body of the screw is compressed between the free end of the strip and the roof of the housing with the screw thread engaged with the serrations on the strip.

13. A kit-of-parts for assembling a worm drive clamp, the kit comprising an injection moulded flexible plastics strip, an injection moulded open-ended tubular plastics housing, and a plastics worm screw, one end of the strip being formed with serrations transverse to the longitudinal axis of the strip and with a pitch equal to the pitch of the thread on the worm screw, the other end of the strip including means for engaging complimentary means on the housing to secure the said other end of the strip to the housing, the roof of the housing being curved to receive the threaded core of the worm screw when the strip is secured to the housing and formed into a loop with the serrated end overlapping the fixed end within the housing, whereby, with the parts assembled, the screw thread engages the serrations on the strip and rotation of the screw expands or contracts the loop.

14. A clamp according to Claim 1 and substantially as herein described with reference to the accompanying drawings.