Severing Apparatus For Severing Lengths Of Tube From A Continuously Fed Flattened Tubular Web

Abstract

The invention relates to a severing apparatus for severing lengths of tube from a continuously fed flattened tubular web which is provided with transverse scorelines such as perforations at intervals along its length.

Description

Usually, such severing apparatus comprises a pair of holding rolls rotatable at a peripheral speed equal to or less than the feeding speed of the web and a pair of severing rolls disposed downstream of the holding rolls at a distance therefrom less than the interval between successive scorelines for advancing the leading end of the web at a higher speed than the holding rolls during each severing operation. Apparatus of this kind is particularly useful in conjunction with tube drawing machines for the continuous formation of staggered tube sections which have a plurality of plies that are laterally offset from one another and which serve for the manufacture of multi-ply bags by the staggered transverse perforation of the required webs of material, laying the webs to form a staggered tubular web and severing the individual staggered tube sections therefrom along the transverse perforations.

Generally, the holding rolls turn at a lower peripheral speed than the feeding speed of the staggered tubular web and the severing rolls turn at a higher speed than the feeding speed, means being provided for displacing an upper roll of each pair towards and away from the other roll in the operating sequence of the staggered tube-making machine.

With such an arrangement, the feed rolls of the tube-making machine feed the flattened tubular web into the severing apparatus whilst the upper holding and severing rolls are raised so that the leading scoreline in the web reaches the space between the pairs of holding and severing rolls. By momentarily lowering the upper roll of each pair, the web is subjected to such a high tension that it will tear along the scoreline. The length of tube so severed is delivered by the severing rolls to a downstream conveyor which discharges the severed lengths from the staggered tube machine.

Free feeding of the leading end of the tubular web into the severing apparatus means that this leading end will be quite slack, the degree of slackness being all the higher if the feeding speed of the web is high. This makes it necessary to have a comparatively high peripheral speed for the severing rolls relatively to the speed of the holding rolls so that the web will be tensioned whilst the leading scoreline is still passing through the space between the pairs of holding and severing rolls. The resultant shock-like tightening of the web until it tears along the leading scoreline gives rise to a very loud report resembling the noise of an explosion and this is extraordinarily disturbing especially in the case of high-speed production.

Another disadvantage caused by free feeding of the leading end of the web and arising especially with the high-speed production of long staggered tube sections is that the slack free end may wander and be fed crookedly to the severing rolls. As a result, each length of tube may be severed unevenly and produce undesirable tears at the ends of the tubes as well as distortion. This gives rise to wastage and interruptions in production.

The invention aims to provide a severing apparatus which operates less noisily and avoids crooked running of the leading end of the web.

According to the invention, there is provided a severing apparatus for severing lengths of tube from a continuously fed flattened tubular web which is provided with transverse scorelines at intervals along its length, comprising a pair of holding rolls rotatable at a peripheral speed equal to or less than the feeding speed of the web, a pair of severing rolls disposed downstream of the holding rolls at a distance therefrom less than the interval between successive scorelines for advancing the leading end of the web at a higher speed than the holding rolls during each severing operation, and a pair of tensioning rolls disposed downstream of the severing rolls to engage the leading end of the web and tightening the web before each severing operation, the peripheral speed of the tensioning rolls during tightening of the web being higher than the feeding speed of the web and the tensile force exerted thereby being set so that the web entering the nip of the tensioning rolls in a slack condition will be pulled taut before each severing operation but without tearing the web along a scoreline. Each severing operation thus takes place only after the web has been tightened.

Tightening of the web at a limited tension before each actual severing operation permits the web to be severed along the scoreline substantially without any shock, only small differences in peripheral speed being required for the holding rolls and the severing rolls. Severing therefore takes place without a loud noise. In addition, tightening of the web will cause it to be pulled straight if it happens to have wandered and the web will therefore be returned to a path at right-angles to the roll axes to ensure clean severing of each tube length.

In one form of the invention, the severing rolls are effectively applied to the web only during each severing operation and the tensioning rolls are located at a distance downstream thereof so that the spacing of the tensioning rolls from the leading scoreline of the web is less than the interval between successive scorelines.

When two pairs of rolls are provided for tightening and severing the web, the tensile force of the pair of tensioning rolls may be adjustable by varying the pressure between these rolls or by means of a controllable friction clutch provided in the drive of the tensioning rolls. The severing rolls downstream of the tensioning rolls may be in constant contact with the web but it may be of advantage for one of the tensioning rolls to be displaceable to and from the other so that the duration of tightening can be reduced at will and so that withdrawal of the severed tube length is possible at a higher speed than the peripheral speed of the tensioning rolls by means of some other conveying equipment.

An example of the invention is diagrammatically illustrated in the accompanying single drawing which is a side elevation of a severing apparatus making use of a pair of severing rolls and a pair of tensioning rolls.

A staggered tubular web St is formed in a staggered tube machine (not shown) from a plurality of webs which are transversely perforated at intervals t along the length of the web corresponding to the desired lengths of tube to be severed. The web St is fed at a uniform speed in the direction a by means of pairs 1, 2 of feed rolls. The leading free end of the web then reaches severing means 3 for tearing a tube section S therefrom.

The severing means 3 comprise a pair of holding rolls 4, 4' and, downstream thereof, a pair of severing rolls 5, 5'. The center-to-center spacing x between these pairs of rolls is less than the smallest interval t likely to be encountered between successive scorelines P, i.e., less than the length of the shortest tube section S that might be desired to be severed. This arrangement ensures that even if very short lengths are to be severed only one scoreline P of the web St will be located along the path x between the holding and tensioning rolls. The two lower rolls 4, 5 of each pair are driven at different peripheral speeds. The holding roll 4 has a peripheral speed which is about one half percent less than the feeding speed of the web imparted by the pairs 1, 2 of feed rolls whilst the severing roll 5 has a peripheral speed of about 12 percent higher than the feeding speed. The upper rolls 4', 5' are mounted for free rotation on pivotable levers 6, 6'. The latter are pivotable by means of bars 7, 7' in synchronism with the operating sequence of the staggered tube machine so that the upper rolls are moved to and from the lower rolls. Any desired drive means may be provided for the bars 7, 7' and these are so coupled with the drive of the staggered tube machine that reciprocation of the rolls 4', 5' always takes place whilst a scoreline P is moving along the path x between the pair of holding rolls 4, 4' and the pair of severing rolls 5, 5'. Provided downstream of the severing rolls, there is a pair of tensioning rolls 8, 8' which is driven at a peripheral speed about 35 percent higher than the feeding speed of the web St imparted by the pairs of feed rolls. The upper tensioning roll 8' is loosely rotatable at both ends in sliding pads 9 and pressed against the lower roll 8 by means of springs 10. The pressure with which the upper roll is applied to the lower roll is adjustable by altering the spring tension with the aid of set screws 11.

The spacing y of the pair of tensioning rolls 8, 8' from the pair of severing rolls 5, 5' is such that the distance of the pair of tensioning rolls from the leading scoreline located between the rolls 4, 4' and 5, 5' during each severing operation is less than the interval t between successive scorelines P so that the leading end of the web will be gripped by the tensioning rolls whilst the leading scoreline is still passing along the path x between the rolls 4, 4' and 5, 5'.

Downstream of the pair of tensioning rolls a double-belt conveyor 12 is provided for advancing the severed tube sections S and still further downstream there is a deviator 13 which can lead each severed tube section to a selected one of a plurality of base-laying machines (not shown) for forming bases on the tube sections if the latter are to be made into bags.

The web St is fed by the feed roll pairs 1, 2 at a constant speed when the upper holding roll 4 and the upper severing roll 5 are lifted from their respective backing rolls. As soon as the leading end of the web has been engaged by the tensioning rolls 8, 8', the web is tightened between the tensioning rolls and the feed rolls because the tensioning rolls are turning at a higher speed than the feed rolls. The pull exerted on the web is limited by appropriately adjusting the pressure between the rolls 8, 8' with the aid of the set screws 11 so that the web will not tear along the leading scoreline during tightening. It is only after the rolls 4' and 5' have been lowered and applied to the web against the lower rolls 4, 5 that the tension will increase to an extent necessary for severing the leading end of the web along the leading scoreline which will be located between the rolls 4 and 5. The severed tube section is led by the tensioning rolls to the conveyor 12.

Instead of adapting the tensile force exerted on the web to requirements by changing the pressure between the two tension rollers, the force could be set by means of a variable-torque friction clutch 14 which is indicated in chain-dotted lines. This has the advantage that when the tensioning rolls have attained the set tensile force they will not slide on the web as would be the case if the tensile force is limited by the pressure between the two tensioning rolls.

Instead of having the tensioning rolls 8, 8' in constant contact with the web, the upper roll 8' may, as already described for the rolls 4', 5', be freely rotatable in a pivotable lever and move to and from the roll 8 in synchronism with the operating cycle of the tube-making machine, the arrangement being such that the roll 8' will descend before the rolls 4' and 5' descend. The severed tube section S can in this case be discharged by the double belt conveyor 12 at as high a speed as may be desired as soon as the upper rolls 4', 5', 8' have been raised again. This leaves sufficient time between successive severed tube sections to enable the deflector 13 to be operated.

Claims

I claim:

1. Severing apparatus for severing lengths of tube from a continuously fed flattened tubular web which is provided with transverse scorelines at intervals along its length, comprising a pair of holding rolls rotatable at a peripheral speed equal to or less than the feeding speed of the web, a pair of severing rolls disposed downstream of the holding rolls at a distance therefrom less than the interval between successive scorelines for advancing the leading end of the web at a higher speed than the holding rolls during each severing operation, and a pair of tensioning rolls disposed downstream of the severing rolls to engage the leading end of the web and tighten the web before each severing operation, the peripheral speed of the tensioning rolls during tightening of the web being higher than the feeding speed of the web and the tensile force exerted thereby being set so that the web entering the nip of the tensioning rolls in a slack condition will be pulled taut before each severing operation but without tearing the web along a scoreline.

2. Apparatus according to claim 1, wherein the severing rolls are effectively applied to the web only during each severing operation and the tensioning rolls are located at a distance downstream thereof so that the spacing of the tensioning rolls from the leading scoreline is less than the interval between successive scorelines.

3. Apparatus according to claim 2, wherein the tensile force of the pair of tensioning rolls is adjustable by varying the pressure between said rolls.

4. Apparatus according to claim 2, wherein the tensile force of the pair of tensioning rolls is adjustable by means of a controllable friction clutch provided in its drive.

5. Apparatus according to claim 2, wherein one of the tensioning rolls is displaceable to and from the other.