ZA200603045B

ZA200603045B - Device for cutting a rotationally symmetrical body

Info

Publication number: ZA200603045B
Application number: ZA200603045A
Authority: ZA
Inventors: Grassberger Wolfgang; Unterzaucher Christian
Original assignee: Knoch Kern & Co
Priority date: 2004-10-15
Filing date: 2006-04-13
Publication date: 2007-12-27
Also published as: WO2006042580A1; RU2339488C2; RU2006118687A; KR20070054137A; DE102004050155B3; KR100929738B1

Description

Device for Cutting a Rotationally Symmetrical Body

Description

The invention pertains to a device for cutting a rotationally symmetrical body. The rotationally symmetrical body may be, for example, a pipe for conveying drinking water or waste water or a drainage pipe. It may have a cylindrical or tubular shape or consist of solid material.

Such tubular bodies can be manufactured from plastic, for example, by means of a so-called rotational moulding method. Such a rotational moulding method is described in greater detail, for example, in EP 0 360 758 A2. :

In this method, the wall of the pipe is built up within a rotating mould. When the pipe is removed from the mould, it has constant inside and outside diameters. The free end faces of the pipe, however, may contain certain irregularities caused by the manufacturing process. In other words, the two end faces of the tubular body do not always extend within a plane that lies perpendicular to the pipe axis. Slight irregularities in the geometry of the pipe end faces can be accepted for certain applications.

However, an exactly plane end face of the tubular body is required in other applications. This is true for the so- called “advanced pipes”. In this case, the pipes are directly installed in the ground without prior excavation.

They are hydraulically pressed into the ground. In some instances, the pipes need to be installed in this fashion over distances of several hundred meters. Accordingly, the pipeline consists of several pipe sections that are successively pressed into the ground and adjoin one another on their end faces. Stress concentrations inevitably occur if the end faces of these advanced pipes are not exactly plane and not aligned exactly perpendicular to the pipe axis, wherein these stress concentrations may be so significant that locally permissible stress limits are exceeded and disruptive effects are triggered during the pipe-pushing process.

It is known to cut the ends of pipes with a circular saw in order to produce exactly plane pipe end faces. For this purpose, the pipes are placed onto a table, on which at least two supports for receiving the body to be placed onto the table are arranged such that they are spaced apart from one another in the axial direction of the body. Each support consists of at least two rotatable rollers that are spaced apart from one another such that the pipe to be cut can be received between the respective rollers.

The pipe is subsequently cut by means of the aforementioned saw while being turned on the table, for example, such that a small end section is cut off. However, it was determined that an axial displacement of the pipe takes place on the table during this process. Due to this axial displacement, the cutting surface does not lie exactly perpendicular to the pipe axis, but rather extends helically.

One reason for the axial displacement of the pipe, for example, is that the aforementioned rollers of the pipe supports do not extend exactly parallel to the axial direction of the pipe or that their position changes over time during the operation of the cutting device.

In this respect, the observed deviations from an exactly vertical «cut (on a pipe that is exactly supported horizontally) amounted to several centimeters and consequently are unacceptable.

It is therefore an object of the invention to offer a device for cutting a rotationally symmetrical body that makes it possible to produce an exact cut in a plane that lies perpendicular to the longitudinal axis of the rotationally symmetrical body.

In attaining this objective, the following aspects were taken into account:

In practical applications, it is practically impossible to ensure a precise alignment of the support rollers over extended periods of time. Even if such a precise alignment could be ensured, it would not be possible to prevent the axial displacement of the rotationally symmetrical body (for example, a pipe) on the table that is caused by the forces generated during the cutting process.

Consequently, a first aspect of the invention pertains to causing a specific and positive axial displacement of the body by aligning the rollers of the supports at a specific angle.

A second aspect of the invention pertains to simultaneously compensating this undesired axial displacement of the body.

In this respect, it is not sufficient to merely provide a static counter support for the end face of the rotationally symmetrical body to be cut, namely because the body is turned during the cutting process such that an irregular cutting surface would be produced.

Consequently, a third aspect of the invention pertains to designing the counter support in such a way that it is freely movable in all three directions of the coordinate system. Of course, the counter support as a whole needs to have a stable position.

In its most general embodiment the invention relates to a device for cutting a rotationally symmetrical body in a

- 4 -~ plane perpendicular to the longitudinal axis of the body, including the following features: -a table with at least two supports arranged thereon, wherein said supports serve for receiving the body to be placed onto the table and are spaced apart from one another in the axial direction of the body, wherein -each support comprises at least two rotatable rollers that are spaced apart from one another in such a way that their axes extend parallel to one another and offset relative to the axial direction of the body by no more than 3°, -a counter support provided with a central ball bearing, from which at least three arms radiate in different directions along a plane, wherein -the counter support is arranged in such a way that the arms abut against a free end face of the body to be placed onto the table, and -a cutting device, moveable relative to the body perpendicular to its longitudinal axis.

It is sufficient to angle the rollers by < 3°, for example, 1° or 2°.

The specific minimal angle of the rollers (relative to the longitudinal axis of the table and the axial direction of the tubular body, respectively) causes the turning body to be axially displaced in the direction of the counter support (counter bearing) on the supports such that a certain pressure is exerted upon the counter support.

The counter bearing has a fixed position, wherein the central ball bearing makes it possible for the counter bearing to practically act in a cardanic fashion. In this case, the aforementioned arms that radiate from the ball bearing are adjusted in accordance with the geometry of the end face of the body, namely into a position in which the arms contact the still irregular end face of the body. The design of the counter bearing provided with a ball bearing, as well as the stationary mounting of the arms on this ball bearing, make it possible to fix the axial position of the rotationally symmetrical body even while it is turned (during the cutting process).

The corresponding cutting device, for example, a circular

Saw, can now be aligned relative to the pipe (rotationally symmetrical body) such that the saw blade extends exactly perpendicular to the longitudinal center axis of the body, wherein a cutting surface is produced that extends in a plane lying perpendicular to the longitudinal center axis of the pipe over the entire circumference of the tubular body.

The cutting device may as well be, for example, a water jet cutter or a laser cutter.

According to one embodiment, it is proposed to arrange the counter (end) support such that it can be adjusted in the axial direction of the rotationally symmetrical body.

However, the counter support is then fixed in the respectively adjusted position. It would also be conceivable to arrange the counter support such that its height can be adjusted. This is required and practical, in particular, when bodies with different diameters need to be cut on the same system (device). The position of the ball bearing is also fixed at the respectively adjusted height in this case.

In another embodiment that also pertains to the cutting of bodies with different diameters, the length of the counter bearing arms is variable. This can be achieved by attaching extension pieces to the existing arms. However, the arms may also be realized in a telescopic fashion. In any case, the arms need to have such a length that they can contact the end face of the pipe.

On the side that faces the rotationally symmetrical body, the arms may be realized such that they all lie within one plane. However, this is not absolutely imperative because the counter support is provided with a ball bearing. The counter support, in principle, may also comprise only two arms, which then preferably extend in opposite directions.

It would also be conceivable to provide a planar end support, for example, in the form of a circular disk, the pressure surface of which (contact surface against the end face of the body) being reversibly deformable within certain limits, so that the pressure surface may adapt to the irregular end face of the body. In the context of this invention, this would correspond to an embodiment “with an infinite number of arms.” However, the central ball bearing needs to be provided in all instances in order to absorb the desired wobbling movement during the rotation of the body on the table without causing an axial displacement of said body.

The arms may be provided with a friction lining in order to improve the static friction between the arms of the counter support and the corresponding end face of the rotationally symmetrical body. Such a friction lining may also be provided on the rollers of the supports.

A radiating arrangement of the counter support arms can be realized in such a way that the arms are respectively angled relative to one another by 120° i.e., like a star.

This embodiment is described below.

The inclined position of the support rollers may be chosen such that the rollers are offset relative to the axial direction of the tubular body by up to 5 mm (particularly by 0.5-1.5 mm) on their free ends. However, it always needs to be ensured that the axes of the support rollers extend parallel to one another.

- 7 =

In order to precisely adjust the roller position, one embodiment proposes to align the roller shafts with the aid of adjusting screws.

Other features of the invention are disclosed in the sub- claims, as well as in the other application documents.

One embodiment of the invention is described in greater detail below. The only figure shows--in the form of a schematic representation--the device according to the invention with a pipe lying thereon, an end section where- of needs to be cut off.

The reference symbol 10 identifies a table comprising two parallel beams 12, 14 that are connected to one another by

Ccrossbeams 16. Two supports 18, 20 are arranged between the beams 10 and spaced apart from one another (referred to the longitudinal direction of the beams 10). Each support 16, 18 comprises two rollers 22, 24, the axes 26 of which are respectively offset by 0.5° relative to the longitudinal center axis M of a pipe 30 placed onto the table 10. The two rollers 22, 24 of each support 18, 20 are spaced apart from one another (referred to a direction that extends perpendicular to the longitudinal direction of the beams 12, 14) such that the pipe 30 can be received between the two respective rollers.

A counter support 32 is arranged on one end of the table 10, wherein the mounting of the counter support is not shown in the figure in order to provide a better overview.

The counter support 32 comprises a centrally arranged annular body 34, in which a (schematically indicated) ball bearing is arranged. Three arms 36, 38, 40 extend radially outward from the annular body 34, wherein the arms 36, 38; 38, 40; 40, 36 are respectively angled relative to one another by 120°. The surfaces of the arms 36, 38, 40 that point to the corresponding end face 30s of the pipe 38 lie in one plane.

The ball bearing enables the counter support 32 to move in all three directions of the coordinate system independently of the geometry of the end face 30s of the pipe 30. After being turned on the supports 18, 20, the pipe 30 moves toward the arms 36, 38, 40 in the axial direction (M) until it contacts said arms. The pipe 30 cannot be additionally displaced in the axial direction on the table 10 once this position is reached.

A saw 42 that is arranged on the other end 30a of the pipe and mounted on a swivel arm 44 can now be perpendicularly guided toward the surface of the pipe 30.

Due to the exact axial positioning of the pipe 30, it is possible to produce a cutting surface on the rotating pipe 30 that extends exactly perpendicular to the longitudinal center axis M of the pipe 30.

In the embodiment shown, an end section with the length L is cut off the pipe 30.

A suction tube 46 mounted on the beam 12 ensures that dust accumulating during the cutting process is immediately removed.

The end face 30s of the pipe 30 is in contact with the arms 36, 38, 40 during the entire cutting process, wherein said arms rotate about the ball bearing in accordance with the rotation of the pipe 30.

Claims

ON CLAIMS

1. A device for cutting a rotationally symmetrical body (30) in a plane perpendicular to the longitudinal axis M of the body (30), with the following features: a) a table (10) with at least two supports (18, 20) arranged thereon, wherein said supports serve for receiving the body (30) to be placed onto the table (10) and are spaced apart from one another in the axial direction of the body (30), wherein b) each support (18, 20) comprises at least two rotatable rollers (22, 24) that are spaced apart from one another in such a way that their shafts extend parallel to one another and offset relative to the axial direction of the body (30) by no more than 3°, Cc) a counter support (32) provided with a central ball bearing, from which at least three arms (306, 38, 40) radiate in different directions along a plane, wherein ; d) the counter support (32) is arranged in such a way that the arms (36, 38, 40) abut against a free end face (30s) of the body (30) placed onto the table (10) during the rotation of the body (30), and e) a cutting device (42) moveable relative to the body (30) perpendicular to its longitudinal axis.

2. The device according to Claim 1, wherein the counter support (32) is adjustable in the axial direction of the body (30).

3. The device according to Claim 1, wherein the height of the counter support (32) is adjustable.

4. The device according to Claim 1, wherein the length of the arms (36, 38, 40) of the counter support (32) is telescopically variable.

5. The device according to Claim 1, wherein the counter : support (32) comprises three arms (36, 38, 40) that are angled relative to one another by 120°.

6. The device according to Claim 1, wherein the arms (36, 38, 40) of the counter support (32) are provided with a friction lining on their side that faces the body (30).

7. The device according to Claim 1, wherein the rollers (22, 24) of the supports (18, 20) are offset relative to the axial direction of the body (30) by £ 5 mm at their free ends.

8. The device according to Claim 1, wherein the position of the rollers (22, 24) of the supports (18, 20) being adjustable by means of screws.