WO1996039287A1

WO1996039287A1 - Apparatus for cutting tubular material

Info

Publication number: WO1996039287A1
Application number: PCT/SE1995/000648
Authority: WO
Inventors: Ingvar Gustavsson
Original assignee: DALUMVERKEN AB
Current assignee: DALUMVERKEN AB
Priority date: 1993-12-21
Filing date: 1995-06-06
Publication date: 1996-12-12
Anticipated expiration: 1997-12-06

Abstract

An apparatus for cutting tubular material, for example extruded plastic pipes or tubes, which apparatus comprises a sharp-edged tool (11) and a holder (12) for non-rotatable holding of the pipe (10) with reference to the sharp-edged tool (11). This tool is provided with an opening (11a) oriented substantially in a plane across the longitudinal axis of the pipe (10), with a section which is larger than the pipe section (10). Drive means (18-20) are arranged to cause a mutual displacement, either of the sharp-edged tool in relation to the pipe, or vice versa, which displacement forms an eccentric cutting movement. According to the invention, the sharp-edged tool (11) is provided with an edge pointing to the centre of the opening (11a) and running at least along a substantial part of the border of the hole opening. The hole opening (11a) is designed so that it enables a free passage of the material.

Description

TITLE

Apparatus for cutting tubular material

TECHNICAL FIELD

The present invention refers to an apparatus for cutting tubular material, for example extruded plastic pipes or tubes, which apparatus comprises a sharp-edged tool and a holder for non-rotatable holding of the pipe with reference to the sharp-edged tool which is provided with an opening oriented substantially in a plane across the longitudinal axis of the pipe, with a section which is larger than the pipe section, and wherein drive means are arranged to cause a mutual displacement, either of the sharp-edged tool in relation to the pipe, or vice versa, which displacement forms an eccentric cutting movement.

BACKGROUND OF THE INVENTION During continuous extrusion of plastic pipes or plastic tubes, an apparatus for flying cutting in suitable lengths for handling the "endless" material which is fed out of the extruding apparatus. The cutting must be rapid because the cutting must be made rapid, because the cutting tool moves along with the material during cutting and then moves in the opposite direction back to a initial position in order to meet the next following point of cutting.

Usually, the cutting is performed by means of a serrated cutting wheel, which produces noise and chips during cutting. The cutting wheel is subjected to wear and must be changed at certain intervals, which means that the extrusion must be stopped.

THE TECHNICAL PROBLEM

One object of the present invention is therefore to provide an apparatus for cutting, which does not exhibit the above described drawbacks with noise and chips, and which facilitates rapid cutting operations.

THE SOLUTION For this purpose, the apparatus according to the invention is characterized in that the sharp-edged tool is provided with an edge pointing to the centre of the opening and running at least along a substantial part of the border of the hole opening, and that the hole opening is designed so that it enables a free passage of the material.

DESCRIPTION OF THE DRAWINGS

The invention will be described here below with reference to embodiments shown in the accompanying drawings, in which Fig. 1-7 schematically shows the working cycle of the apparatus in seven steps, Fig. 8 shows a cutting apparatus according to a first embodiment of the invention in a view from the front, Fig. 9 is a section along the line IX-IX in Fig. 8, Fig. 10 is a section along the line X-X in Fig. 8, Fig. 11 shows the cutting apparatus according to Fig.

8-10 in a view from behind, and Fig. 12 shows an alternative embodiment of the sharp- edged tool of the cutting apparatus.

DESCRIPTION OF EMBODIMENTS

The principle of cutting, which is shown schematically in Fig. 1-7, is especially suitable for use during production of extruded pipes and tubes, wherein the extruded material into suitable lengths, without interruption of production. However, it is possible to use the cutting principle for other purposes.

Fig. 1-7 show a pipe 10 and a sharp-edged tool 11 with an opening 11a oriented in a plane substantially across the longitudinal direction of the pipe. The pipe 10 is insertable in its axial direction into a holder 12, which is shown in Fig. 9, but is not depicted in Fig. 1-7. The holder 12 is designed as a slide, which is displaceable supported in the direction of the arrow 13, and can be moved between two positions by means of a cylinder 14, 15.

These two positions are marked in Fig. 9, in such a way that the left part of the holder 12 is located in an upper position corresponding to the pipe 10 shown with unbroken lines in Fig. 1. The right part of the holder 12 is in a lower position, corresponding the pipe 10 shown with broken lines in Fig. 1.

The upper position of the holder is used during displacement of the cutting apparatus along the pipe, and displacement of the pipe with reference to the cutting apparatus, respectively. When moving the holder to the lower position in the figures, the pipe will come into contact with the edge of the sharp-edged tool 11, which is designed with a circular shaped opening 11a and with the edge directed towards the centre of the opening, wherein a incision is started into the pipe wall, completely through the pipe wall to the inside of the pipe wall. At the same time, the pipe is fixed against rotation by means of the clamp surface 16 which is rigidly connected to a stand member 17 which forms an attachment for the piston 15 of the cylinder 14.

Then the sharp-edged tool 11 starts to work according to Fig. 2-4 and is driven around in an eccentric movement.

This takes place according to the embodiment shown in Fig.

8-11, by means of two eccentric shafts 18 with crankshaft pins 20 which for example is shown in Fig. 10. The shafts

18 are supported by means of roller bearings 21 in the stand member 17. Further roller bearings 22 are used for supporting a knife holder 23 upon the crankshaft pins 20.

Locking rings 24 and 25 are used for locking the bearings 21 to the stand member 17 and the eccentric shafts 18 in these bearings respectively. Further locking rings 26 are used for locking the bearings 22 to the knife holder 23. The bearings 23 are in their turn locked to the crankshaft pins 20 by means of bolts 27.

The eccentric shafts 18 are driven around synchronously by means of a rack 28, the cogs of which are in engagement with gear wheels 29 at the end of each respective eccentric shaft. The rack 28 is manoeuvred by means of a piston rod 30, which is displaceable supported in a U- formed slot in a rail 31, which is mounted by means of bolts at the stand member 17.

The movement continuous at least until the crankshaft pins 20 have realized a movement of 360°. In Fig. 4, the movement has continued to about 450°, which is indicated by depicting the pipe 10 with broken lines in this position.

The holder 12 has been moved together with the pipe 10 from this position to the position shown with unbroken lines in Fig. 4. In this position, the tube end may again be fed into the cutting apparatus to the right cutting position, wherein the eccentric movement is repeated in the opposite direction according to Fig. 5-7, so that the working cycle will be completed back to the position shown in Fig. 1.

Fig. 12 shows an alternative to the above described working principle, wherein the sharp-edged tool 11 is provided with a notch 32 in the edge which is facing the centre of the opening of the tool. This notch 32 makes it possible to feed the pipe through the cutting apparatus to the right cutting position, without having to move the pipe sideways across its longitudinal direction according to Fig. 1-7. Then the cutting is preferably executed with the same eccentric movement as described before. Alternatively, the pipe 10 can be made to perform an eccentric movement, while the sharp-edged tool is stationary.

It has appeared, that the length R of the eccentric movement (see Fig. 12), should be as large as or larger than the inner diameter O_± of the pipe, to be able to cut the pipe at an eccentric movement of 360°.

Pipes can be cut rapidly and exactly by means of the above described cutting methods, without generation of chips or noise. The cutting may be repeated with very small time intervals, which results in short cycle times. The sharp- edged tool has a comparatively long edge which distributes the wear. By suitable selection of material, the wear on the sharp-edged tool can be maintained at a level which is approximately insignificant.

The means for driving the eccentric movement, i.e. the cylinder 30 and the rack 28 may be replaced with other means. For example, the eccentric shafts 18 may be synchronous driven by means of a chain or a toothed belt. Further, the cutting do not have to be effected by means of a circular movement, but this movement may be elliptic, and may then follow a sharp-edged tool with an elliptic shape. An electric motor may be used for driving the cutting apparatus.

The invention is not limited to the above described embodiment, but several variants are possible within the scope of the accompanying claims. For example, the cutting apparatus can be designed in many different ways with regard to the area of application.

Claims

1. Apparatus for cutting tubular material, for example extruded plastic pipes or tubes, which apparatus comprises a sharp-edged tool (11) and a holder (12) for non- rotatable holding of the pipe (10) with reference to the sharp-edged tool (11) which is provided with an opening (11a) oriented substantially in a plane across the longitudinal axis of the pipe (10), with a section which is larger than the pipe section (10), and wherein drive means (18-20) are arranged to cause a mutual displacement, either of the sharp-edged tool in relation to the pipe, or vice versa, which displacement forms an eccentric cutting movement, c h a r a c t e r i z e d in that the sharp- edged tool (11) is provided with an edge pointing to the centre of the opening (11a) and running at least along a substantial part of the border of the hole opening, and that the hole opening (11a) is designed so that it enables a free passage of the material.

2. A cutting apparatus according to claim 1, wherein the eccentric cutting movement is brought about by means of a displacement of the pipe (10) in relationship to the sharp-edged tool (11), c h a r a c t e r i z e d in that the holder (12) is manoeuvrable for causing circular eccentric movement, and that the holder is provided with bearing means enabling non-rotatable holding of the pipe

(10) in relation to the sharp-edged tool (11) during the eccentric movement.

3. A cutting apparatus according to claim 1, wherein the eccentric cutting movement is brought about by means of a displacement of the sharp-edged tool (11) in relationship to the pipe (10), c h a r a c t e r i z e d in that the sharp-edged tool

(11) is circular and that the drive means comprise two synchronously driven eccentric shafts (18) for providing a circular eccentric movement.

4. A cutting apparatus according to claim 2 or 3, c h a r a c t e r i z e d in that the opening (11a) of the sharp-edged tool (11) is circular and provided with a notch (32) with a depth at least corresponding to the material thickness of the pipe is to be cut, and with a shape which enables the pipe to be displaced longitudinally into the opening with the inner diameter of the pipe level with the inner border of the edge.

5. A cutting apparatus according to claim 3, c h a r a c t e r i z e d in that eccentric shafts (18) are provided with gearwheels (29) in engagement with a rack (28), which is connected to a piston (30) for driving the eccentric shafts in a reciprocate movement.

6. A cutting apparatus according to claim 1, c h a r a c t e r i z e d in that the length R of the eccentric movement is as large as or larger than the inner diameter O_i of the pipe (10).