GB2185762A - Tentering clip - Google Patents

Abstract

A foil stretching machine has clip chain tracks with tentering clips for transverse stretching of a thermoplastics web. Due to the high speeds at which clip chain tracks operate nowadays, an unpleasant noise is produced, especially during opening of the clips, when the web gripping member 2 of a clip strikes against the clip body, apart from the fact that these parts are then subject to considerable wear. According to the invention, this noise and wear is reduced by introducing an elastic body (4) between the clip body (1) and the web gripping member (2). Since this elastic body (4) can be replaceable, it can easily be replaced when worn without need to remove the whole clip chain or individual members thereof. An arrangement in which a block 6 screwed to the clip body 1 and having the elastic body 4 moulded on it by vulcanization may be provided. The web gripping member 2 is maintained in the open (dashed lines) position or in the closed position (solid line) by a spring 3. <IMAGE>

Description

SPECIFICATION Tentering clip for transverse stretching of a thermoplastics web This invention relates to a tentering clip for transverse stretching of a thermoplastics web in a foil stretching machine and comprising a clip body, a tentering member in the form of a flap pivotally mounted on the body to grip the plastics web along an edge, and a spring mechanism holding the tentering member either in its open position and in its closed position.

For treatment of a thermoplastics web it is known to stretch the web, e.g. a foil, in its longitudinal and its transverse direction. Transverse stretching is carried out in a tentering frame having endless chains moving in guides. These chains are formed by tentering clips placed side by side. One chain track is disposed at each side of the web, and the tentering clips grip the web along its marginal zones. The two chain tracks diverge along part of their path, i.e. the distance between them increases so that the web clamped between them will be stretched in the transverse direction along its path.

The clip has a tentering member in the form of a pivotally mounted flap which grips the edge of the web between itself and a planartentering surface forming a table. The clips are closed as they enter the foil stretching machine or tentering frame and are automatically reopened as they leave.

Considerable tensions are produced during the stretching operation and considerable forces are also required for opening and closing the clips. It is customary also to provide a spring force to bring the tentering member flap from its open position over a dead point position into the closing position and to keep it there. The spring invariably forces the tentering member into one of its two end positions.

It also assists in the process of opening the clip after opening of the clip has been initiated at the exit by an opening rail or an opening wheel. The opening and closing by such devices is known. The opening means (rail or wheel) acrs on a projecting part of the tentering member.

It is especially in the process of opening the tentering clip that the forces mentioned above and the high speeds at which the clip chains nowadays operate (up to 400m/min amounting to a passage of up to 25 clips per second) give rise to harsh impacts when the tentering member strikes against the clip body as it opens. The large number of clips opening in rapid succession produces a very unpleasant noise and the metal parts striking against one another result in rapid wear.

It is an object of this invention to reduce the noise and also to reduce the rapid wear.

According to this invention there is provided a tentering clip for transverse stretching of a thermoplastic web in a foil stretching machine, the clip comprising a clip body, a tentering member in the form of a flap pivotally mounted on the body to grip the web along an edge, and a spring mechanism keeping the tentering member either in its open or in its closed position, wherein an elastic body is provided on the clip body and is disposed between the tentering member and the clip body in the open position. There is great freedom in the choice of material but it is advantageous to use a rubbery elastic material, in particular in the form of a block, although spring combinations with baffle or striking plates or the like could be used. The noisereducing elastic body may be permanently fixed or it may be replaceable.It may be attached by screw fastenings or by adhesive or by vulcanization.

An embodiment of the invention will now be described with reference to the drawing, the single figure of which is a side elevation of a clip, partly in section.

A clip body 1 of a tentering clip has a guide member 7 with rollers 8, 8' and 9, 9' as horizontal guides and for taking up horizontal tension is shown on the right hand side of the figure. The running and guide rails are not shown; they extend in a vertical plane between the upper and lower rollers 8, 9 and 8', 9'. A chain roller 10 for the engagement of a driving gear wheel for the clip chain is also shown.

Fish plates 11 are shown on this chain roller 10 for connecting ittothe next chain link. Vertical rollers for taking up the weight of the clip chain are not shown.

The tentering member 2 of the clip body is shown on the left.

The tentering member 2 is pivoted about a pin 2a like a flap and clamps the plastic web (not shown) to be treated between itself and a tentering table 5. The plane in which the web is clamped is symmetrical to the centre of the chain roller 10 and hence also symmetrical between the horizontal tread rollers 8, 8', 9,9'. The flap forming the tentering member 2 is two-armed. Its lower part comprises a tentering bar (not indicated by reference numeral) for clamping the web. The upper part has a projection (2b) designed to co-operate with a control rail or control wheel or like (not shown) for opening and closing the tentering member 2a in known manner.

Only two positions for the tentering member 2 are shown: The closing position 2 and 2b in solid lines and the open position 2' and 2b' in dash-dot lines.

The tentering member is assisted in opening and closing by a spring 3 which holds it firmly in a respective end position 2 or 2'.

The clip body 1 carries an elastic block which is so positioned that when the tentering member is in its open position 2' a rearward projection of the tentering member bears against the elastic body 4.

Harsh and loud impacts on opening of the clip are thus prevented and the noise is reduced.

There are numerous possible arrangements for positioning and securing the elastic body. Thus it could be either permanently fixed or replaceable. A replaceable arrangement is preferred, e.g. an arrangement having a block 6 screwed to the clip body 1 and having the elastic body 4 moulded on it by vulcanization. Such an arrangement enables the elastic body to be easily replaced when worn without the clip chain as a whole or even single members of the chain having to be removed. It is then a simple matter to replace the elastic body.

Claims (5)

1. A tentering clip for transverse stretching of a thermoplasticweb in a foil stretching machine, the clip comprising a clip body, a tentering member in the form of a flap pivotally mounted on the body to grip the web along an edge, and a spring mechanism keeping the tentering member either in its open or in its closed position, wherein an elastic body is provided on the clip body and is disposed between the tentering member and the clip body in the open position.

2. A clip according to claim 1, wherein the elastic body is rubbery.

3. A clip according to claim 1, wherein the elastic body is replaceable.

4. A clip according to claim 2, wherein the elastic body is a block arranged to be screw fastened to the clip body and having an elastic body moulded thereon by vulcanization.

5. Afastening clip constructed and arranged substantially as herein described and shown in the drawing.