GB2195935A

GB2195935A - Rotary cutting apparatus for tubes

Info

Publication number: GB2195935A
Application number: GB08623084A
Authority: GB
Inventors: Martin John Watson
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1986-09-25
Filing date: 1986-09-25
Publication date: 1988-04-20
Also published as: GB8623084D0

Abstract

Apparatus for cutting tubes comprises a fixed frame 2 defining a central axis 5 and providing an axial passage for the tube 6. A rotary cutter head 10 is mounted for rotation on a hub 7 and supports two cutting blades mounted for movement towards and away from the central axis on pivotally mounted arm. Rollers 22 connected to the arms engage a frustoconical cam surface 25 provided on an annular cam member 22 mounted for axial sliding movement within the hub 7. An actuating cylinder 33 acts to move the cam member via an operating lever 32 forked levers 29, and pins 26 connected to the cam member. <IMAGE>

Description

SPECIFICATION Rotary cutting apparatus The invention relates to rotary cutting apparatus, especially for cutting tubes. The invention is particularly applicable to apparatus for cutting tubes of plastics materials but may also be applied to cutting tubes of other materials such as metal, cardboard, etc. Further, whilst the apparatus has been primarily designed for cutting hollow plastics tubes it may also find use in the cutting of solid rods of various materials.

The invention relates to rotary cutting apparatus of the kind comprising a fixed frame defining a central axis and providing an axial passage for a tube to be cut, a rotary cutter head mounted on the frame for rotation about the central axis, and at least one cutting element mounted on the cutter head for movement towards and away from the central axis.

British Patent 572217 relates to rotary cutting apparatus of the kind described in which the cutting elements are mounted on the cutter head for radial sliding movement towards and away from the central axis. The sliding supports for the cutting elements are connected to a cam plate which rotates with the cutter head and a brake acts on the cam plate to retard it relative to the cutter head causing the cutting elements to move towards the central axis.

Cutting apparatus of the kind described is also known from our prior UK Patent No.

2037642. In this prior apparatus the cutting elements are mounted on the cutter head via pivot arms and movement of the pivot arms such that the cutting elements are brought into engagement with the tube is brought about by means of relative rotational movement between the cutter head and a brake drum which normally rotates with the cutter head but may be retarded in relation thereto by the action of a brake.

It is a disadvantage of the prior apparatus that the use of a brake involves frictional wear of the parts concerned and imposes a substantial load on the drive motor for the cutter head. It is the object of the present invention to provide an improved cutting apparatus in which this disadvantage is avoided or reduced.

According to the present invention there is provided rotary cutting apparatus, especially for cutting tubes, comprising a fixed frame defining a central axis and providing an axial passage for a tube to be cut, a rotary cutter head mounted on the frame for rotation about the central axis, at least one cutting element mounted on the cutter head for movement towards and away from the central axis, a cam follower connected to the or each cutting element, and a cam member mounted Icr axial movement on the frame and having a cam surface which engages the cam follower(s); whereby axial movement of the cam member causes movement of the cutting element(s) towards the central axis.

An embodiment of the invention is described below with reference to the accompanying drawings in which: Figure 1 shows a front view of the apparatus; Figure 2 shows a cross-section of the apparatus along line A-A in Fig. 1; and Figure 3 shows a section of a portion of the apparatus along line B-B of Fig. 1.

The apparatus 1 comprises a frame 2 which is mounted on a bench 3 or other suitable support. The apparatus defines a central axis 5 and provides an axial passage for a tube 6 which is to be cut. Fixedly mounted on the frame, and surrounding the axial passage is a hub 7 which, as shown, comprises a first annular body member 8, and, bolted thereto, an axially extending ring 9.

A rotary cutter head 10 is mounted for rotation on the hub by means of bearings 11. In the embodiment shown the ring 9 and bearings 11 are housed with an annular recess 12 formed in the rotary cutter head. The cutter head 10 rotated continuously and at a constant speed by a motor 13 via a belt 14 which passes around the radial outer surface of the cutter head.

Cutting elements in the form of blades 15 are rigidly mounted on pivot arms 16. As shown best in Fig. 3, each pivot arm 16 is pinned to one end of a shaft 17 which is journalled for rotation in the cutter head about a pivot axis parallel to but spaced from the central axis of the apparatus. Springs 18 acting between the cutter head 10 and an end of each lever arm adjacent the pivot axis bias the lever arms into a position away from the central axis of the apparatus. The other end of each lever arm is guided by a guide 19.

These guides restrain any axial movement of the pivot arms and ensure that the blades cut only in a plane transverse to the axis of the tube.

A lever arm 20 is fixed to the other end of each shaft 17 and a frustoconical roller 21 is mounted on the free end of each lever arm for rotation about an axis parallel to the pivot axis.

The rollers 21 provide cam followers for a cam member 22 which is mounted for axial sliding movement in a bearing sleeve 23 supported within the annular body member 8 of the hub 7. The cam member 22 has a cylindrical outer surface and is provided with a frustoconical inner surface which forms a cam surface 25 which engages with the rollers 21.

Axial movement of the cam member 25 causes pivotal movement of the lever arms 20 which, through the shafts 17, causes pivotal movement of the pivot arms 16 so that the blades 15 are moved towards the central axis 5 of the apparatus. Return movement of blades 15 is effected by the springs 18.

A pair of axially extending pins 26 are screwed to the cam member 25 at diammetrically opposite positions. Each pin passes through a guide opening 27 in the frame 2, is provided with a pair of spaced annular flanges 28, and is engaged by a lever 29 having a forked end which passes around the pin 26 between the flanges 28. A collar 30 at the other end of each lever 29 is pinned to a shaft 31 supported on the frame for rotation about its axis. An operating lever 32 is also pinned to the shaft 31, and an actuating cylinder 33 which may be a hydraulic or pneumatic ram, acts between the frame 2 and the free end of the operating lever 32. The end positions of the lever 32 and thus of the cam member 25 and the blades 15, can be adjusted by means of a turn-buckle 34. Similarly, the stroke of the cam member 25 and the blades 15 can be adjusted by varying the stroke of the cylinder 33.

Operation of the cutting apparatus is as follows. With the actuating cylinder contracted, the cam member 22 is held in its extreme left position (looking at Fig. 2) and the pivot arms 16 are urged by the springs 18 to their radially outermost position. With the apparatus in this position a tube 6 to be cut can be moved through the cutting apparatus along the axial passage therein until the part of the tube to be cut aligns with the plane of the blades 15.

When the tube has been correctly positioned for cutting, the actuating cylinder 33 is extended and the cam member 22 is urged axially of the apparatus by means of the cranked lever formed by the lever 32 and the forked arms 29 acting on the pins 26. As the cam member 22 moves to the right (looking at Fig. 2) the rollers 21 engaging the frustoconical cam surface 25 are caused to move radially inwardly. The radial movement of the rollers 21 acts through the lever arms 20 and the shaft 17 to cause pivotal movement of the pivot arms 16. Thus the blades 15 are swung inwardly to contact and cut the tube.

When the tube has been cut, the actuating cylinder is retracted and the cam member withdrawn allowing the blades to swing away from the tube. The tube is then indexed through the apparatus for a further length to be cut and so on.

Claims

1. Rotary cutting apparatus, especially for cutting tubes, comprising a fixed frame defining a central axis and providing an axial passage for a tube to be cut, a rotary cutter head mounted on the frame for rotation about the central axis, at least one cutting element mounted on the cutter head for movement towards and away from the central axis, a cam follower connected to the or each cutting element, and a cam member mounted for axial movement on the frame and having a cam surface which engages the cam follower(s); whereby axial movement of the cam member causes movement of the cutting element(s) towards the central axis.

2. Apparatus as claimed in claim 1, wherein the cutter head is journalled for rotation on a hub which is fixed to the frame. and the cam member is slidably mounted within the hub for axial movement.

3. Apparatus as claimed in any preceding claim, wherein each cutting element is mounted on a pivot arm which is mounted on one end of a shaft journalled for rotation in the cutter head about a pivot axis parallel to but spaced from the central axis, and each cam follower is a roller mounted for rotation about an axis parallel to the pivot axis on one end of a lever arm; the other end of the lever arm being mounted on the other end of the shaft such that radial movement of the cam follower causes pivotal movement of the pivot arm.

4. Apparatus as claimed in any preceding claim, wherein the cam member is annular and the cam surface is an inner frustoconical surface of the cam member.

5. Apparatus as claimed in claim 3 or claim 4, wherein an end of each pivot arm remote from the pivot axis is axially restrained by guide means during pivotal movement of the pivot arm.

6. Apparatus as claimed in any preceding claim, comprising actuating means for moving the cam member wherein the actuating means comprises a ram connected between the frame and a lever arm coupled to the cam member.

7. Apparatus as claimed in any preceding claim, wherein the cutter head is driven in rotation from a motor mounted on the frame via a flexible belt passing around the cutter head.

8. Rotary cutting apparatus substantially as described herein with reference to the accompanying drawings.