GB2071625A

GB2071625A - Device for spreading or tensioning a moving sheet or web

Info

Publication number: GB2071625A
Application number: GB8107545A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-03-11
Filing date: 1981-03-10
Publication date: 1981-09-23
Also published as: GB2071625B

Abstract

A bowed roll (1) comprises a bowed shaft (2) on which a number of spools (3) are individually rotatably mounted. A helical coil (8) forms a sleeve which embraces the outer cylindrical surface of each spool (3) so as to be rotatable with the spools (3). Two coils end to end may be carried on shaft (2). In order to prevent individual coil windings from falling into the gaps between the spools (3) the spools may be provided with castellated rims for engaging in interdigitated manner with the castellated rims of adjacent spools. The coil can be made of steel or plastics optionally coated with zinc or cadmium and the turns may have a circular or rectangular cross section. The coil can be coated with plastics before or after fitting to the shaft or be fitted with a rubber sleeve. The spools are made of nylon or PTFE. The coil (8) provides a relatively inexpensive and hard-wearing outer surface for the roll (1). <IMAGE>

Description

SPECIFICATION Device for spreading or tensioning a moving sheet or web This invention relates to a device for spreading or tensioning a moving sheet or web transverse to its direction of movement.

In order to remove wrinkles and prevent creasing of the web at critical points in any continuously moving web process, such as printing, coating, laminating, calendering, slitting and rewinding, it is known to pass the web over a bowed roll comprising a fixed shaft which is slightly bowed along its length, a pluraiity of rotatable spools mounted side-by-side along the shaft, and a rubber sleeve embracing the outer cylindrical surfaces of the spools so as to be rotatable with the spools. The shaft is bowed in the direction in which the web is moving so that the web comes into contact with the roll on the concave side and parts contact with the roll on the convex side. Since each portion of the web tries to pass around the roll at right angles to the axis of the shaft, the web is subjected to a transverse spreading action outwardly from the middle of the web.

However, these bowed rolls are expensive to manufacture mainly on account of the high cost of the rubber sleeve, as well as being costly to maintain due to the fact that the rubber sleeve is subject to wear and accordingly requires periodic replacement. Moreover, although it is desirable for these rolls to be free running, it often proves necessary to drive the rolls from an external source in order to overcome the stiffness of the roll.

It is an object of the invention to provide a device for spreading or tensioning a moving sheet or web which device is capable of being manufactured and maintained at low cost and which is hard-wearing.

According to the invention there is provided a device for spreading or tensioning a moving sheet or web transverse to its direction of movement, comprising a bowed shaft, at least one spool mounted on the shaft so as to be rotatable with respect to the shaft and at least one helical coil forming a sleeve which embraces the outer cylindrical surface of the or each spool so as to be rotatable with the spool(s).

Such a coil may be produced at low cost and may be made of a hard-wearing material.

Moreover the coil is easily engaged with the spools by being pushed over the spools, ready wound, whilst being rotated in the direction in which the convolutions of the coil tend to open out. The coil is advantageously close coiled when fitted on the spools.

In a preferred embodiment of the invention the sleeve comprises two coils, one of which is wound in a clockwise direction and the other of which is wound in an anti-clockwise direction, as viewed from one end of the shaft, the two coils being arranged such that the coil windings themselves exert a spreading action on the sheet or web which reinforces the spreading action outwardly from the middle of the sheet or web due to the bowing of the shaft. The spreading action of the coil windings is due to the combined effects of the first helical coil frictionally engaging the sheet or web and tending to move the sheet or web in a first direction as the coil rotates and the second helical coil frictionally engaging the sheet or web and tending to move the sheet or web in a second direction as the coil rotates.

The or each coil can be a steel or plastics spring which may be plated with zinc or cadmium where it is to be used in the presence of water. The elongate member from which the or each coil is wound may have a circular section or a rectangular section for example.

The gaps between adjacent windings of the or each coil may be sealed by dip coating the coil in a plastics sealing compound before or after the coil has been fitted to the roll. The compound on the outside of the coil will generally wear off in use, leaving the compound between the windings.

Alternatively a thin rubber sleeve may be rolled on to or pulled over or bonded to the coil.

The ends of the coil(s) in the vicinity of the ends of the shaft are preferably fixed in relation to the spools so as to minimise any tendency of the coil(s) to unwind during rotation in contact with the sheet or web. For this purpose the ends of the coil(s) in the vicinity of the ends of the shaft may be attached to pegs or turned inwards so as to engage in holes in the spools, adjacent the ends of the shaft. Alternatively, or in addition, the ends of the coil(s) in the vicinity of the ends of the shaft may be clamped to the spools by surrounding bands, for example by crimping. These bands can be attached to, or integral with, members for sealing the free ends of the spools. In an alternative embodiment the members for sealing the free ends of the spools are fixed to the shaft and sealed in relation to the spools by cup seals.

Where two coils are provided the ends of the coils in the vicinity of the middle of the shaft may be coupled together, for example by welding.

Additionally or alternatively these ends may be attached to pegs or turned inwards so as to engage in one or more holes in the spools.

In view of the bowing of the shaft, slight gaps, of the order of 2 to 4 mm, will exist at the outer periphery of adjacent spools on the shaft. If spools of conventional shape are used, the individual windings of the or each coil might tend to work their way into these gaps.

Accordingly the invention also provides a device for spreading or tensioning a moving sheet or web transverse to its direction of movement, comprising a bowed shaft, and a plurality of spools mounted on the shaft so as to be rotatable with respect to the shaft, adjacent spools being provided with portions which overlap one another in the direction of the axis of the shaft.

To this end each spool may be provided with peripheral formations which project in the direction of the axis of the shaft into peripheral recesses provided in an adjacent spool. In a preferred embodiment each spool is provided with at least one castellated rim for engaging in interdigitated manner with a similar castellated rim provided on an adjacent spool.

Thus, where the device is used in conjunction with the helical coil described earlier, the overlapping portions of the adjacent spools prevent individual coil windings from falling into the gaps between the spools.

Alternatively adjacent spools may be provided with a peripheral rim on one of the spools and a recessed rim on the other spool, the recessed rim fitting within the peripheral rim.

According to a further aspect of the invention each spool is made of a hard-wearing plastics material having a low coefficient of friction, such as nylon or polytetrafluoroethylene. Furthermore each spool, or every alternate spool, is preferably provided with a bearing race made of plastics material, for example nylon. Each spool may be slightly barrelled, so as to make it easier to push the coil(s) over the spools, when such coils are used.

If a nylon bearing race is used instead of a metal bearing race, it is not necessary to prevent moisture from entering the spool and, in particular it is not necessary to provide the spool assembly with sealed ends which tend to make the roll stiff.

The roll may be of the fixed bow type or of the adjustable bow type.

A preferred embodiment of the invention is illustrated, by way of example, in the accompanying drawings, in which: Figure 1 is a section through the ends of the roll; Figure 2 is a perspective view of one of the spools; and Figure 3 is a diagram of the wrap of a web over the roll.

The bowed roll 1 comprises a bowed shaft 2 on which a number of nylon spools 3 are individually rotatably mounted on nylon bearings 4. Cylindrical spacers 5 are provided between adjacent bearings 4, and the complete spool assembly is retained in position on the shaft 2 by two collars 6 which are clamped to the shaft 2 by grub screws 7. A helical coil 8 forms a sleeve which embraces the outer cylindrical surface of each spool 3 so as to be rotatable with the spools 3. The ends of the coil 8 in the vicinity of the ends of the roll 1 are clamped to the endmost spools 3 by surrounding bands 9 which also serve to seal the free ends of the spools 3.

As shown in Figure 2, each spool 3 is provided with castellated rims 10 for engaging in interdigitated manner with similar castellated rims provided on adjacent spools. The castellations prevent individual coil windings from falling into the gaps between the spools 3.

In use of the bowed roll 1, a moving web 11 passes under a roll 12 (see Figure 3) and approaches the bowed roll 1 from the concave side. As the web 11 passes over the roll 1, it is subjected to a spreading action outwardly from the middle of the web due to the fact that each portion of the web tries to pass around the roll at right angles. The web 11 leaves the roll 1 on the convex side and passes under a roll 13.

Claims

1. A device for spreading or tensioning a moving sheet or web transverse to its direction of movement, comprising a bowed shaft, at least one spool mounted on the shaft so as to be rotatable with respect to the shaft and at least one helical coil forming a sleeve which embraces the outer cylindrical surface of the or each spool so as to be rotatable with the spool(s).

2. A device according to claim 1, wherein the sleeve comprises two coils, one of which is wound in a clockwise direction and the other of which is wound in an anti-clockwise direction, as viewed from one end of the shaft, the two coils being arranged such that the coil windings themselves exert a spreading action on the sheet or web outwardly from the middle of the sheet or web which reinforces the spreading action due to the bowing of the shaft.

3. A device according to claim 1 or 2, wherein the gaps between adjacent windings of the or each coil have been sealed by dip coating the coil in a plastics sealing compound before or after the coil has been fitted to the roll.

4. A device according to claim 1 or 2, wherein the or each coil is surrounded by a rubber sleeve.

5. A device according to any preceding claim, wherein the ends of the coil(s) in the vicinity of the ends of the shaft are fixed in relation to the spools so as to minimise any tendency of the coil(s) to unwind during rotation in contact with the sheet or web.

6. A device according to claim 5, wherein the ends of the coil(s) in the vicinity of the ends of the shaft are attached to pegs or turned inwards so as to engage in holes in the spools, adjacent the ends of the shaft.

7. A device according to claim 5 or 6, wherein the ends of the coil(s) in the vicinity of the ends of the shaft are clamped to the spools by surrounding bands.

8. A device according to claim 7, wherein the bands are attached to, or integral with, members for sealing the free ends of the spools.

9. A device according to any one of claims 1 to 7, wherein members for sealing the free ends of the spools are fixed to the shaft and sealed in relation to the spools by cup seals.

10. A device according to claim 2 or any one of claims 3 to 9 when appended directly or indirectly to claim 2, wherein the ends of the coils in the vicinity of the middle of the shaft are coupled together.

11. A device according to claim 2 or any one of claims 3 to 10 when appended directly or indirectly to claim 2, wherein the ends of the coils in the vicinity of the middle of the shaft are attached to pegs or turned inwards so as to engage in one or more holes in the spools.

1 2. A device for spreading or tensioning a moving sheet or web transverse to its direction of movement, comprising a bowed shaft, and a plurality of spools mounted on the shaft so as to be rotatable with respect to the shaft, adjacent spools being provided with portions which overlap one another in the direction of the axis of the shaft.

13. A device according to claim 12, wherein each spool is provided with peripheral formations which project in the direction of the axis of the shaft into peripheral recesses provided in an adjacent spool.

14. A device according to claim 13, wherein each spool is provided with at least one castellated rim for engaging in interdigitated manner with a similar castellated rim provided on an adjacent spool.

1 5. A device according to claim 12, 13 or 14, wherein each spool is made of a plastics material and is provided with a bearing race made of plastics.

1 6. A device according to claim 12, 13, 14 or 15, wherein each spool is slightly barrelled.

1 7. A device for spreading or tensioning a moving sheet or web substantially as hereinbefore described with reference to the accompanying drawings.