GB2046651A

GB2046651A - Cutting Head for Filter Assembler

Info

Publication number: GB2046651A
Application number: GB8010220A
Authority: GB
Original assignee: Molins Ltd
Current assignee: Mpac Group PLC
Priority date: 1979-04-05
Filing date: 1980-03-26
Publication date: 1980-11-19
Also published as: GB2046651B

Abstract

A cutting head for a cigarette filter attachment machine comprises a drum (10) carrying a number of knives (13) each of which is urged radially outwards by at least one spring (17, 18) against an adjustable retaining device (15) by which the normal distance of the cutting edge from the axis of the drum can be adjusted. <IMAGE>

Description

SPECIFICATION Cutting Head for Filter Assembler This invention is concerned with a cutting head for a filter assembly, which is a machine for making filter cirgarettes by joining filter portions to tobacco rods by means of uniting bands. These bands are cut from a web which is often of corklike appearance and is for that reason usually referred to as "cork".

A common form of cutting head comprises a drum carrying a number of circumferentially spaced knives which cooperate with anvil inserts in a drum carrying the cork web, each cut being achieved by a pinching action. In one common cutting head, each individual knife is pivotally mounted on its carrier drum and is radially adjustable with respect to the axis of the drum. This allows the cutting edge of each knife to be set at a desired distance from the axis of the drum, while the freedom of pivotal motion accommodates any lack of parallelism between the axis of the cutting head drum and that of the drum carrying the cork web.

There are normally fewer knives on the cutting drum than anvils on the cork drum. Accordingly, it is not possible to set each knife so as to take account of any slight variation in regard to the distance of each anvil surface from the axis of the cork drum. Therefore the load of the knives on the anvils can vary, especially if the cork drum is heated, as in the Molins PA8 filter attachment machine.

The same problem arises in connection with the cutting drum described in Molins Limited British Patent No. 1,469,684, in which each knife is secured to the cutting drum, which is itself universally pivoted on its drive shaft.

According to the present invention a cutting head for a filter attachment machine comprises a drum carrying a number of knives each of which is urged radially outwards by at least one spring against an adjustable retaining device by which the normal distance of the cutting edge from the axis of the drum can be adjusted.

During cutting, each knife moves radially inwards against the action of the spring or springs, which thus provide a controlled cutting force. This controlled force contrasts with prior arrangements in which the cutting force was transmitted through a pivot without inherent flexibility (apart from any flexibility in the shaft supporting the cutting drum) so that an excessive cutting force could arise if the cutting head was incorrectly adjusted in regard to the radial position of one or more knives and/or in regard to the distance of the cutting head from the cork drum.

In one possible form the adjustable retaining device for each knife comprises a spindle lying substantially along a cord of the drum (e.g.

midway between the ends of the knife) and having an eccentric portion engaging the knife so that rotation of the spindle alters the normal radial position of the knife (i.e. the position while the knife is not cutting).

Each knife is preferably engaged by two springs at or near its opposite ends. In one possible arrangement according to this invention, a ring of elastic material near each end of the drum serves as a spring engaging all the knives.

Aternatively, each knife may have its own separate spring at each end, for example in the form of one or more spring washers.

According to another aspect of this invention, in a cutting head for a filter attachment machine, each knife is located along a spring beam which is resiliently flexed and engages the knife so as to urge it radially outwards; preferably the centre of the beam is pivotable on the bottom surface of a slot containing the knife and the beam, or serves as a fulcrum for the knife. Preferably pivotal motion is provided by a rounded projection on the inner surface of the beam serving as a fulcrum; alternatively a fulcrum (possibly in the form of an insert with a rounded head) may be fitted in the bottom of the groove.

During assembly, the beam for each knife may be pre-stressed by a retaining device which displaces the knife radially inwards through a predetermined or adjustable distance. For example, the retaining device may comprise a pin which is inserted through an aperture in the body of the knife and has an eccentric portion which displaces the knife when the pin is rotated about its axis.

Examples of cork cutting heads according to this invention are shown in the accompanying drawings. In these drawings:- Figure 1 is a sectional view of one cutting head taken on the line I-I in Figure 2; Figure 2 is an end view of the drum shown in Figure 1, with part of the end plate broken away to show one of the knives; Figure 3 is an end view of the spindle acting as a retaining device for one knife; Figure 4 is a side elevation of the spindle shown in Figure 3; Figure 5 is a fragmentary section similar to Figure 1 but shown in a different form of cutting head; Figure 6 is similar to Figure 5, but shows another different cutting head; and Figures 7 to 11 show a different form of cutting head.

As shown in Figures 1 and 2, the cutting head comprises a drum 10 mounted on a shaft 11 and driven via a key 12. The drum carries five circumferentially spaced knives 1 3 in radial slots 14, only one knife being shown in Figure 1.

Each knife, as shown in Figure 2, comprises a body 1 3A and an edge member 1 3B formed with a cutting edge 1 30. Midway between the ends of the knife there is a cylindrical aperature 14 through which passes an adjustable retaining device 1 5 shown more particularly in Figures 3 and 4. Near each end of the knife there is a plunger 1 6 which urges the knife radially outwards through the action of compressed spring washers 1 7 and 1 8 engaging between a head 1 6A on the plunger 1 6 and a fixed surface of the drum.

As shown in Figures 3 and 4, each retaining device 1 5 comprises a spindle having coaxial small and large diameter end portions 20 and 21 respectively. Between these end portions there is an eccentric cylindrical portion 22 having an axis 23 which is parallel to but offset from the axis 24 of the portions 20 and 21. The drum 10 has appropriate machined bores forming bearings for the portions 20 and 21, while the eccentric portion 22 lies in the slot 14 containing the knife.

A slot 25 in the end of the portion 21 allows the device 1 5 to be rotated by a screwdriver or similar tool.

During assembly, after the plungers 1 6 have been inserted into the drum, the retaining devices 1 5 are inserted into position, with the axis 23 of the eccentric portion 22 of each retaining device lying outside the axis 24. After that, rotation of the device 1 5 in either direction causes the eccentric portion 22 to displace the knife towards the axis of the drum 20 against the action of the spring washers. This allows the normal distance of the cutting edge 1 3C of each knife from the drum 10 to be adjusted.

It should be noted that the retaining device 1 5 is shown in the drawing after 1 800 of rotation, giving the maximum inward displacement of the knife.

Friction tends to prevent inadvertent rotation of the retaining device 1 5 during use. However, there is a locking device for each retaining device comprising a pin 26 lying parallel to the axis of the drum 10 and capable of engaging and locking the larger diameter portion 21 of the retaining device. As shown in Figures 1 and 3, the locking pin 26 has a part-cylindrical recess 26A which receives the side of the portion 21 of the retaining device, and threaded end portion 26B which is engaged by a nut 27. Tightening of the nut 27 pulls the wall of the recess 26A against the retaining device, which is thus locked against inadvertent rotation.

Circular end plates 28 and 29 cover the ends of the drum 10, being secured by screws 35.

The spring washers 17, 18 may be of the type known as Belleville washers. One of the washers of each pair (e.g. washer 18) may have a lower stiffness than the other. For example, the washer 17 may be one requiring approximately 4001b to flatten it, while the washer 18 may have a flattening load of about a quarter that amount.

This allows adjustment of the radial position of each knife to be made against a relatively light spring force. Also, each knife moves radially inwards slightly during cutting against a relatively light spring force before applying a full cutting force through the action of the stiffer washer. In addition, this allows each knife to align itself with the cooperating anvil surface (i.e. in the event it is not exactly parallel to the anvil) against the resistance of a light spring force.

The surface of the head 16 adjacent to the washer 18 may be slight connical (e.g. with an inclination of 30 40') so as to prevent complete flattening of the washer 18.

Figure 5 shows part of a different form of cutting head 30. This has five knives 31 which are similar to the knives in the previous example, except that the inner surface of each knife body has a slightly different shape as shown. As in the previous example, each knife is held in position by an adjustable retaining device 32 which is identical to the device 15 in the previous example and operates in the same manner.

Figure 5 differs from the previous example in that, in place of the spring washers, there is a sleeve 33 of urethane rubber or other elastomeric material at each end of the drum. The sleeves 33 fit into annular recesses in the ends of the drum and engage and act upon all the knives. Circular end plates 34 secured by screws to the ends of the drum retain the sleeves 33 in position.

Each sleeve may comprise concentric parts of which the outer part is softer and thinner than the inner part to provide a dual spring rate effect similar to that of the Belleville washers in Figures 1 to 4.

As an alternative, in the arrangement shown in Figures 1 and 2, the spring washers at each end of each knife may be replaced by a rubber or other resilient pad or by a different form of spring.

Figure 6 is a longitudinal section through part of a cutting head which comprises a shaft 109 carrying a drum 110 formed with a number of circumferentially spaced longitudinal slots 111 each of which contains a knife body 112 having a cutting edge 113. End plates 114 and 115 on the drum located the knives, for which purpose they have flanges 11 4A and 11 so engaging over the ends of the knife bodies.

A spring beam 116 (e.g. of spring steel) extends parallel to the knife body and has radial projections 11 6A and 11 6B at its ends and a central rounded projection 116C. This last projection serves as a fulcrum on which the knife can pivot relative to the drum to accommodate any lack of parallelism between the knife edge 113 and the surface of the anvil on the cork drum (not shown).

A retaining device 11 7 projects through an aperture 11 8 in the knife body, and is similar to the retaining device in the previous examples.

Adjustment of the normal position of the knife (i.e. while it is not cutting) may be achieved by rotating the retaining device through different angles (up to a maximum of 1800); a locking pin may be provided to lock the retaining device in, any desired position, as in the previous examples.

Alternatively, the retaining device may be arranged to lock only in one position (after 18QO of rotation) to provide a predetermined displacement of the knife.

The clearance space 11 9 between the beam 116 and the bottom of the slot 111 is shown somewhat exaggerated. In practice a smaller clearance may be provided to limit the amount by which the beam can flex to avoid overstressing of the beam.

As an alternative to the arrangement shown, the radial projection 11 6C may extend inwards to engage the bottom surface 119 of the slot in the drum, in which case the projections 11 6A and 11 6B would extend outwards to engage the inner surface of the knife body.

Another possibility is that the central protrusion serving as the fulcrum may be formed or mounted on the knife on the bottom of the slot 111. Projections engaging the ends of the beam may then be formed on the bottom of the slot 111 or on ends of the knife, as the case may be; in that case the beam can be of uniform cross section along its length.

In each of the above-described embodiments of this invention it is possible to use, instead of a single central retaining device for each knife, a pair of similar retaining devices acting on the knife at longitudinally spaced positions along the knife, e.g. near the respective ends of the knife.

Moreover, in place of the dual spring devices (i.e.

those near the respective ends of the knife there may be a single central spring device (Belleville washer, rubber sleeve or the equivalent) lying between the two retaining devices.

Each of the retaining devices mentioned above may be modified as follows. The narrow end portion 20 of the spindle is omitted, and the length of the eccentric portion 22 is reduced; the shortened eccentric portion engages in a recess in the knife, instead of passing through the knife.

An alternative cutting head according to this invention (illustrated by Figures 7 to 11) is in principle as follows. Each knife body is clamped onto the carrier drum by retaining devices engaging the ends of the knife body, and there is an interposed layer of rubber or other resilient material lying at least in the region below the middle of the knife body, each knife body, its retaining devices and its rubber layer being so arranged that when the knife body is secured in position by the retaining devices, it is flexed slightly so that its cutting edge is slightly convex.

We have found that a slightly convex knife edge is desirable, especially if the knife is resilient and is resiliently backed, since each cutting operation then begins at the centre of the knife edge and progresses outwards towards the ends of the knife. In principle, in place of the preferred arrangement described above, it is possible to machine the knife body with a slightly convex cutting edge (instead of with a straight edge) and to support the body at its ends, allowing it to flex in wards during cutting owing to its own resilience, with or without a rubber or spring backing.

Another possibility is as follows. Each knife body may be carried in a groove in the carrier drum which is slightly inclined to the axis of the drum so that each cutting operation starts at one end of the knife and progresses towards the other end. In other words, the knife edge in this case is in effect very slightly helical. The helix may be so small (e.g. less than 1 O)that its effect on the finished cigarettes is substantially invisible to the naked eye while nevertheless producing the desired progressive cut. For this purpose the drum carrying the knife bodies should be rigidly mounted on a substantially rigid drive shaft.

In the example shown in Figures 7 to 11; Figure 7 is an end view of the cutting head; Figure 8 is a fragmentary section on the line VIlI-VIlI in Figure 7; Figure 9 is a plan view of one of the knife body; and Figure 10 is an enlargement of one end of Figure 8.

The cutting head shown in the drawing comprises a carrier drum 200 formed at each end with a shaft 201 by which the head is mounted and driven. A number of longitudinal grooves are machined in the surface of the drum, and each contains a knife body 202 having a cutting edge 203 formed on a hardened insert 204 brazed or bonded to the main part of the knife body.

Below the knife body there is a strip of rubber or similar elastomeric material 205 against which the knife body is clamped by retaining devices in the form of screws 206 passing through slots 207 in flanges 208 at the ends of the knife body.

Around each screw 206 there is a collar 209.

When the screws are tightened, a head 210 on each screw engages a washer 211 which in turn engages one end of the collar, the other end of which engages the bottom of the groove in the drum 200. Thus the- length of the collars determines the amount by which the rubber is compressed. However, the knife body is preferably sufficiently flexible along its length so as to bend slightly under the action of the screws and the resistance-of the rubber, so that the cutting edge 203 becomes slightly convex. Such convexity can hardly be detected by the naked eye and is not shown in the drawings. For example, as an idea of scale, the thickness of the rubber strip may be 4mm; and the difference between the length of the collar 209 and the combined thickness of the flange 208 and rubber strip 205 may be of the order of 0.076 mm.

Naturally, the middle region of the rubber strip is also compressed (though less than the ends), so that the difference in "height" between the middle of the cutting edge and ends is considerably less than 0.076 mm; it may, for example, by of the order of 0.0127 mm.

Collars of slightly different lengths may be provided to allow in effect for adjustment of the heights of the ends of the cutting edge.

When viewed from above (i.e. looking directly past the knife edge towards the axis of the drum as in Figure 3) each knife may be slightly inclined to the drum axis so as to provide a progressive cutting action as described above. For this purpose, the knife body may be made more rigid so as to avoid any significant curving of the cutting edge.

The angle of inclination may, for example, be such that, for a knife edge of 90 mm length, the offset of one end with respect to the other is approximately 1 mm.

Other means for securing a slightly inclined knife to the carrier drum may be employed, preferably with some form of resilient backing, e.g. a rubber strip.

Claims

1. A cutting head for a filter attachment machine comprising a drum carrying a number of knives each of which is urged radially outwards by at least one spring against an adjustable retaining device by which the normal distance of the cutting edge from the axis of the drum can be adjusted.

2. A cutting head according to claim 1 in which the retaining device comprises a spindle lying substantially along a cord of the drum and having an eccentric portion engaging the knife so that rotation of the spindle alters the normal radial position of the knife.

3. A cutting head according to claim 2 including a locking device for securing the spindle against rotation.

4. A cutting head according to any one of claims 1 to 3 which each knife is engaged by two springs at or near its opposite ends.

5. A cutting head according to claim 4 in which the retaining device is located between the two springs.

6. A cutting head according to any one of claims 1 to 5 in which the spring comprises a body of elastomeric material.

7. A cutting head according to claim 6 in which the body of elastomeric material comprises a sleeve which engages all the knives.

8. A cutting head according to any one of claims 1 to 5 in which the spring comprises at least one spring washer.

9. A cutting head according to any one of claims 1 to 3 in which the spring comprises a resilient beam which extends along a radially inner face of the knife and is resiliently flexed, and is arranged to engage the knife so as to urge it radially outwards.

10. A cutting head according to claim 9 including a central projection on or cooperative with the beam and serving as a fulcrum about which the knife can pivot.

11. A cutting head according to claim 10 in which the central projection is on the side of the beam adjacent to the knife.

12. A cutting head for a filter attachment machine, comprising a drum carrying a number of knives each of which is located along a spring beam which is resiliently flexed and engages the knife so as to urge it radially outwards.

13. A cutting head according to claim 12 including a central projection on or cooperative with the beam and serving as a fulcrum about which the knife can pivot.

14. A cutting head according to claim 13 in which the central projection is on the side of the beam adjacent to the knife.

1 5. A cutting head according to any one of claims 9 to 14, including retaining means limiting radially outward movement of the knife under the action of the spring, thereby pre-stressing the spring.

1 6. A cutting head for a filter attachment machine, comprising a drum carrying a number of knives each of which is pivotally mounted on the drum and is movable radially inwards against the resistance of a spring.

17. A cutting head according to claim 18 including retaining means limiting radially outward movement of the knife under the action of the spring, thereby pre-stressing the spring.

18. A cutting head according to claim 1 7 in which the retaining means is adjustable for radially adjusting the position of the knife.

19. A cutting head for a filter attachment machine, comprising a carrier drum carrying at circumferentially spaced positions a number of knife bodies each of which is clamped onto the drum by retaining devices engaging the ends of the knife body, and including an interposed layer of rubber or other resilient material lying at least in the region below the middle of the knife body, each knife body, its retaining devices and its rubber layer being so arranged that when the knife body is secured in position by the retaining devices, it is flexed slightly so that its cutting edge is slightly convex.

20. A cutting head according to claim 1 9 in which the retaining devices comprise screws, and in which each screw is associated with a spacer member limiting the movement of the corresponding end of the knife body towards the drum when the screw is tightened.

21. A cutting head according to claim 20 in which each spacer member comprises a collar which surrounds the screw and passes through an aperture or slot in the knife body.

22. A cutting head for a filter attachment machine, comprising a carrier drum carrying, at circumferentially spaced positions, a number of knife bodies each having a convex cutting edge and being capable of flexing while cutting, so that cutting begins at the centre of the knife and progresses outwards towards the ends of the knife.

23. A cutting head for a filter attachment machine comprising a carrier drum carrying, at circumferentially spaced positions, a number of knife bodies each of which is resiliently mounted and is inclined slightly to the axis of the carrier drum so that each cutting-operation starts at one end of the knife and progresses towards the other end.

24. A cutting head for a filter attachment machine, substantially in accordance with any one of the examples described with reference to the accompanying drawings.