GB2034361A - Tenter clip - Google Patents

Abstract

A tenter clip for holding the edge (12) of a web (11) of material being stretched, has two identical clamping elements (8, 8') with edge-gripping surfaces (16, 16') curved eccentrically with respect to the axes of respective pivot pins (14, 14') on which the clamping elements are rockably mounted. These elements have respective arms (10, 10') extending away from them on the remote side of the pins (14, 14'). The arms have ends (9, 9') which ride on the outer surfaces (18, 18') of rails or bars (19) which extend along the length of the material. The clip is carried along a clip chain track in known manner. The surfaces (18, 18') have upwardly and downwardly inclined regions, (extending along the said length), respectively for opening and closing the clamping elements. Between these regions are horizontal surface regions for holding the clamping elements open when necessary. The control rails or bars may be mounted internally, Fig. 1, or externally, Fig. 3 (not shown), of the clip chain track carrier (1). <IMAGE>

Description

SPECIFICATION Tenter clip This invention relates to a tenter clip for holding the edge of a web or length of material in a clamping plane in which the material lies, the clip having clamping elements engaging the edge of the material on respective sides of the clamping plane and adapted to pivot about pivot pins arranged parallel to the direction of longitudinal stretching of the material.

Numerous tenter clips for holding and guiding a length of material in tentering, drying and stretching apparatus are known in the textile industry and also for foil stretching installations (e.g. U.S. Patent No. 2,878,546, German Patent No. 568,508, German Petty Patents Nos. 1,896,724 and 1,916,100, British Patent No. 1,1 25,024 and German Patent No. 2,351,996). In all these disclosures, the material is gripped at its edges and stretched by tenter clips which are joined together to form chains extending along both sides of the tentering frame. The edges of the material are usually clamped between a smooth clamping plate, mounted in the clip table, and a stretching bar, which is equipped with one or more knife-like blades and is attached to the lower end of a pivotal flap arranged above the clamping plate.

According to British Patent No. 1,125,024, a clip may also be constructed in such a manner that its clip table, which has a curved clamping plate, is pivotal about a pin arranged in an arm of the clip body, this arm serving as a carrier for the clamping table.

The angle through which the clip table can pivot is adjusted by an adjustment or stop screw. Opposite the clamping table with its clamping plate is a flap pivotal about an axis parallel to the axis of the clamping table and urged into the open position by a spring. The pivot pins of the clamping table and flap, which pins are arranged one above the other and parallel to the direction of movement of the clips, are situated in two planes perpendi cular to the clamping plane. The flap carries a curved clamping plate whose curvature is opposite to that of the lower clamping plate.

The flap with its tentering bar is pressed against the material by a spring, or drops on it by its own weight. The arrangement of the tentering bar in relation to the clamping plate is such that the direction in which the flap swings and the direction of pull exerted on the material by way of the clips, during e.g.

stretching of a length of foil, coincide. The material is firmly clamped between the clamp ing plate and the tentering bar.

The tenter clip disclosed in German Patent No. 2,351,996 has a clamping element in which the pivot bearing is formed by at least one blade arranged in the region of the clip remote from the edge of the material and adapted to tilt in at least one tilting edge arranged in the clamping table.

These known tenter clips have the disadvantage that the coefficient of friction and hence the grip by friction between the clamping plate, the material and the tentering bar is liable to vary according to the nature of the material (e.g. its thickness, substance, surface). it has therefore been proposed to provide beads on the edge of the material, especially in the case of foil, to prevent the material slipping from the clips. This proposal is limited in application since foil extrusion is difficult and the formed beads are not uniform. It can therefore only be used for foils of comparatively large initial thickness. However, difficulties arise in opening the clips if the material is too thick because the force required for opening is too great and the clips wear out prematurely due to the impact on the opening device of the clip and the clip chain.If the foils are thin on the other hand, the high speed of transport of the material presents difficulties.

It is an object of the invention to provide a tenter clip in which opening and closing of the clamping elements for releasing or gripping the edge of the web of material are effected with less application of force than in known clips. Opening of the clamping elements should be carried out if possible without loss of friction in the pivot pins of the clamping elements and the resulting opening forces which are necessary, particularly if the clips and clip chains are moving at high speed. Further, the clamping elements should be simpler and should be more easily replaceable, and opening and closing should also be simplified.

According to this invention there is provided a tenter clip for holding the edge of a web or length of material in a clamping plane formed by the material, the clip having clamping elements adapted to grip the edge on both sides of the clamping plane and pivotal about pivot pins arranged parallel to the direction of movement of the material, wherein the clamping elements are congruent in structure and pivot in pincers-like manner about the pivot pins which are arranged symmetrically on both sides of the clamping plane, and which lie substantially the same vertical plane as the said edge, the clamping elements being each in the form of a lever having an opening and closing arm on the side of the pivot pin remote from the said edge and wherein opening and closing of the clamping elements is controlled by control bars or rails acting on the arms.

The main advantage of the invention is that due to the congruent formation of the clamping elements and their symmetrical, pincerlike pivotal arrangement on either side of the clamping plane at the height of the edge of the material and in the same vertical plane as the edge of the material, virtually no friction losses and opening forces occur during opening and closing. Opening and closing of the clamping elements is controlled by the leverlike arms on the side remote from the material and by the control bar or rail acting on the arms from the inside or outside. Opening and closing of the clamping elements takes place symmetrically to the clamping plane and has the advantage that the edge of the material is always gripped equally from above and below in pincer-like fashion and is always clamped under identical conditions of force.The congruent formation of the clamping elements not only simplifies manufacture and supply but gives the advantage that with appropriate construction of the clips, clip chain track carrier and clamping elements, the opening and closing arms and hence the clamping elements can be controlled either from inside or from outside.

If the opening and closing arms are controlled from the inside, they are bent upwards and downwards like shears on their inner ends, remote from the material. These bent ends bear with their inner surfaces against symmetrically arranged control surfaces which merge one into the other and which are formed on control bars or rails arranged at the inlet and outlet regions of the clip chain track carrier. The angles of inclination of the control surfaces are adapted to the requirements of opening and closing of the clamping elements and may form an upward slope in a clipopening region, run parallel in a clip holdopen region, and slope downwards in a clipclosing region.The clamping surfaces of the clamping elements are curved eccentrically relative to the axes of their pivot pins, and during opening the two eccentrically curved clamping surfaces move away from each other until they reach the open position.

If the opening and closing arms are controlled from outside, the ends of the arms are straight and the surfaces of their clamping parts are curved, e.g. they may have a smaller, eccentrically curved clamping surface.

Opening and closing is in principle the same as that when the arms are controlled from the inside. During opening and closing, the surfaces of the opening and closing arms slide along control surfaces which are arranged above and below the chain track and are shaped according to the opening and closing movements of the clamping elements. The edge of the material is again gripped and clamped symmetrically from above and below by the clamping elements.

Embodiments of the invention will now be described by way of example, with reference to the drawings, in which:~ Figure 1 is a vertical section through one embodiment of clip chain track carrier and clip chain, showing the clamping elements of a tenter clip controlled by a control bar inside the carrier; Figure 2 shows a control bar viewed from the right of Fig. 1; and Figure 3 is a vertical section through another embodiment, showing the clamping elements of a tenter clip controlled by a control bar from outside the carrier.

Referring to Fig. 1, a clip chain track carrier 1 with a clip chain 2 transports a tenter clip 7 which is supported and guided by rollers 3, 4; 3', 4' on running and guide rails 5, 6; 5', 6'.

The clip 7 comprises two congruent clamping elements 8, 8' controlled from inside the carrier and, extending in the opposite direction, two opening and closing arms 10, 10' in the form of levers bent upwards and downwards at their ends 9, 9' in the form of shears. The clamping elements 8, 8' and the arms 10, 10' are mounted, symmetrically above and below a clamping plane 13 in which lies the edge 12 of a web or length of material 11, on pivot pins 14, 14' arranged one above the other in a common plane 15 which is at right angles to the clamping plane 13. The clamping surfaces 16, 16' of the clamping elements 8, 8' are curved towards each other with a curvature which is eccentric in relation to the pivot pins 14, 14'.Opening and closing of the clamping elements 8, 8' is effected by the arms 10, 10' in that the surfaces 17, 17' of their ends 9, 9' slide along control surfaces 18, 18' formed on a control bar or rail 19 which is situated opposite to the clamping surfaces 8, 8' and arranged symmetrically above and below the clamping plane 13. The bar or rail 19 is of a wear-resistant material, e.g. hard metal or a self-lubricating material. When the clamping elements 8, 8' are in the closed or clamping position, the surfaces 17, 17' are at the end of a downwardly sloping closing region c of the control surfaces 18, 18' (see also Fig. 2).

The open position of the clamping elements 8, 8' is reached by the surfaces 17, 17' sliding along an upwardly sloping opening region a of the control surfaces 18, 18' until they reach the parallel sided open region b of the control surfaces 18, 18'. During this sliding of the surfaces 17, 17' over the control surfaces 18, 18' in the opening region a, the ends 9, 9' are moved apart in the manner of shears and at the same time a pivotal movement of the arms takes place about the pivot pins 14, 14', so that the clamping elements 8, 8' swing and their eccentric curved clamping surfaces 16, 16' move apart.

Closing is caused or assisted by springs 21 supported in the pivot pins 14, 14' and in the middle part 20 of the clip.

The control bar 19 is schematically shown in Fig. 2 (together with sectioned representations of the ends 9, 9') and comprises the opening region a, the keep-open region b and the closing region C. The control surfaces 18, 18', which are arranged above and below symmetrically on both sides of the clamping plane 13 (see also Fig. 1), have an upwardly sloping, slightly trapezoidal form in the clip opening region a, a horizontal form in which the two bars are parallel in the keep-open region b, and a steeply downwardly sloping trapezoidal form in the clip closing region c.

The course taken within the individual regions a, b, c and the transition from one region to another are continuous, so that the surfaces 17, 17' of the ends 9, 9' which are bent away from the opening and closing arms 10, 10' like shears (Fig. 1) slide on these control surfaces smoothly and without undue expenditure of energy, in the direction of sliding, see the arrow at the left hand end of the line in Fig. 2 which represents the plane 13.

Another embodiment is shown in Fig. 3. A cruciform chain track carrier 22 carries a clip chain 23 with a tenter clip 27 supported and guided by rollers 24, 25, 26; and 24', 25', 26'. The tenter clip 27 resembles that of Fig.

1 in having two congruent clamping elements 28, 28', which with their straight opening and closing arms 29, 29' directed up and down, pivot on pivot pins 32, 32' arranged one above the other in a common plane 31 and symmetrically on both sides of the clamping plane 30. Opening and closing of the clamping elements 28, 28' is controlled by the ends 33, 33' of their arms 29, 29' sliding on control surfaces 34, 34' formed on control bars or rails 35, 35' which are situated above and below the plane 30 on the carrier 22.

The clamping elements 28, 28' have equally curved clamping surfaces 36, 36' eccentric to the pivot pins and movable away from each other about the pins. Closing of the two clamping elements 28, 28', i.e. of their clamping surfaces 36, 36', is assisted or actuated by leaf springs 37, 37' in recesses 38, 38' which are in the arms 29, 29', which springs bear at one end close to the respective pivot pin 32, 32' and at the other end against a respective support 39, 39' mounted on the clip chain 23.

The congruent formation and symmetrical arrangement of the clamping elements and opening and closing arms and their control, not only ensures that the edge of the material is gripped pincer-like in a uniform manner under uniform conditions of force, but simplifies manufacture and maintenance in stock of these parts.

Claims (6)

1. A tenter clip for holding the edge of a web or length of material in a clamping plane formed by the material, the clip having clamping elements adapted to grip the edge on both sides of the clamping plane and pivotal about pivot pins arranged parallel to the direction of movement of the material, wherein the clamping elements are congruent in structure and pivot in pincers-like manner about the pivot pins which are arranged symmetrically on both sides of the clamping plane, and which lie substantially the same vertical plane as the said edge, the clamping elements being each in the form of a lever having an opening and closing arm on the side of the pivot pin remote from the said edge and wherein opening and closing of the clamping elements is controlled by control bars or rails acting on the arms.

2. A clip according to claim 1 wherein the clamping elements each have a curved clamping surface which is eccentric to the respective pivot pin axis.

3. A clip according to claim 1 or claim 2 wherein the control bar or rail has control surfaces arranged symmetrically to each other above and below the clamping plane, each control surface having regions with differing angles of inclination, which regions merge one into another.

4. A clip according to any preceding claim wherein the control bars or rails are of wear resistant hard metal, or a self-lubricating material.

5. A clip according to any preceding claim wherein the clamping elements are identical and interchangeable.

6. A tenter clip constructed and arranged substantially as herein described and shown in the drawings.