GB2028302A

GB2028302A - Improvements in or relating to glass cutting

Info

Publication number: GB2028302A
Application number: GB7833350A
Authority: GB
Original assignee: Vidrierias de Llodio SA
Current assignee: Guardian Llodio SL
Priority date: 1978-08-09
Filing date: 1978-08-15
Publication date: 1980-03-05
Also published as: FR2433490A1; GB2028302B; DE2835297A1; CH626554A5

Abstract

A method and apparatus for cutting glass, particularly glass thicker than 6 mm, wherein a roulette cutter is applied perpendicularly to the glass surface with a force that is maintained constant as the roulette cutter is moved over the glass surface whilst being maintained perpendicular thereto. The constant force applied is related to the thickness of the glass being cut. The cutting angle of the roulette cutter is also related to the thickness of the glass being cut, the relationship being: A = 2 arc sine (1-0.18/t> where A is the cutting angle and t is the glass thickness. <IMAGE>

Description

SPECIFICATION Improvements in or relating to glass cutting This invention relates to glass cutting, particularly but not exclusively to glass having a thickness of 6 mm or more.

In the past glass up to 6 mm thick has been but by means of a roulette having a sharp circumferential edge, the roulette being rolled under pressure across the glass surface to provide an incision therein. The glass is cut or broken off at the incision and the resultant edge(s) subsequently polished and/or chamfered. With glass having a thickness greater than 6 mm, a long and arduous cutting procedure has been necessary, e.g. by using special punches or by using special erosion chemicals. Various other methods of glass cutting have also been proposed, e.g. in USA Patents Nos. 3800991, 3865293, 3865294 and 3865673.

It is considered desirable to provide a glass cutting method and apparatus which can be simply used for cutting glass even if the glass is thicker than 6 mm.

According to a first aspect of this invention there is provided a method of cutting glass, wherein a roulette cutter is held generally perpendicular to the glass surface and applied thereto with a force that is maintained constant as the roulette cutter is moved over the glass surface.

Preferably said force is predetermined to accord with the thickness of the glass to be cut, e.g. is approximately 85 Kgs for a glass thickness of 8 to 10 mm and is approximately 170 Kgs for a glass thickness of 24.4 mm.

Preferably the cutting angle of the roulette cutter is predetermined to accord with the thickness of the glass to be cut. Advantageously the cutting angle and glass thickness have the following relationships: A = 2 arc sine -0.18/t) where A is the cutting angle, and t is the glass thickness. For example, for a glass thickness of 25.4 mm the cutting angle is approximately 167" and for a glass thickness of 8 to 10 mm the cutting angle is approximately 157".

According to a second aspect of this invention there is provided apparatus for cutting glass, the apparatus comprising a support for glass to be cut, means mounting a roulette cutter above the support such that the roulette can move over the surface of glass supported by the support and generally perpendicularto the glass surface, and means to apply a constant force to the roulette cutter as the latter is moved over said glass surface.

Preferably the means to apply a constant force is adjustable to adjust the force in accord with the thickness of the glass to be cut. Advantageously said force applying means comprises a pneumatic piston-cylinder arrangement.

Preferably the roulette cutter is removably mounted on said mounting means and is one of a plurality of such roulette cutters P -ch to be used for a different glass thickness.

Conveniently the mounting means comprises a movable head from which the roulette cutter is carried by a horizontal shaft.

Preferably the support bears glass having a thickness related to the cutting angle of the roulette cutter in accordance with the relationship: A = 2 arc sine (1 -0.18/t) where A is the cutting angle, and t is the glass thickness.

By way of non-limiting example, one embodiment of this invention will now be described with reference to the accompanying drawing of which: Figure 1 is a schematic cross-sectional view through a glass sheet and illustrating an internal stress diagram.

Figure 2 is a schematic cross-sectional view through a glass sheet of large thickness (e.g. greater than 6 mm) when cutting by a conventional prior art procedure has been commenced, Figure 3 shows a roulette cutter in end and side view, Figure 4 is a diagram illustrating irregularities in the edge of a glass sheet when cut in accordance with this exemplary embodiment, Figure 5 is a diagram illustrating irregularities in the edge of a glass sheet when cut by a prior art method, Figure 6 is a schematic representation of a cutting operation according to this invention, Figure 7 is an enlarged view similar to Figure 6, and Figure 8 is an enlarged view of part of a roulette cutter for the said exemplary embodiment of this invention.

Figure 1 illustrates a glass sheet which can be considered as three layers, in accordance with the actuation direction on it of the internal stresses in the material. In the two outer surface layers 1 and 2 the material's internal stresses are in compression, whilst on the internal layer 3 these stresses are in traction or tension. This is shown by the stress diagram line 4. The dotted line 5 indicates the neutral stress situation, and the passing of this line 5 from one side to the other of the curve 4 indicates the passing from a tension or traction situation to a compression situation or vice versa. The layer separation is located jointly on those cutting points.

On this basis the following may provide a theoretical explanation for a material's cutting in the conventional prior art procedure.

As soon as the incision or fissure is made on the sheet surface in accordance with a line along which the cut is to be performed, a manual actuation is initiated by means of punches with a quick blow in accordance with direction N. The application of this force N gives rise to an instantaneous flexure in the material which makes the internal stress diagram undergo a deformation such that the lower layer 3 tends to increase in thickness and the upper layer 1 tends to decrease in thickness. The separation line 10 between this upper layer 1 and the central layer 2 undergoes an upward motion which moves it to wards the point of incision and as soon as this line reaches or is reached by the incision 10, the stresses in the tension or traction direction of the central area 2 produce the tearing and cutting of the material.

This conventional procedure presents, among others, the following disadvantages: It is a very slow operation requiring qualified and expert staff and runs the risk of unwanted sheet breaking. Also, after the cut, substantial irregularities appear on the resulting edge (See Figure 5) so that the latter needs polishing - an operation which logically incides upon the total cut. Such irregularities are indicated in Figure 5, the irregularity area 9 of sheet 8, i.e. the area 9 between lines R-R which must be removed when polishing.

In this embodiment of the invention a roulette is used (Figure 3) in conjunction with several very special features or qualities for attaining a perfect cut on high thicknesses of glass.

This cutting roulette 6 consists of a disc-shaped body on whose periphery there is a double bevel which provides a central cutting edge A having a certain angle 7 (Figure 8). In the center, the roulette 6 has shaft running through it by which the roulette is removably mounted on a head which, by means of a pantographic or like system, will be able to carry out the necessary movements for following the required cutting line and always maintaining the shaft of the roulette parallel to the plane of the glass sheet which is to be cut, i.e. the cutting edge perpendicular to the glass surface.

This head is also provided with a pneumatic piston-cylinder arrangement which will apply a constant force on the roulette 6 as the latter incides upon the glass sheet to be cut. This force is constant and perfectly perpendicular to the glass sheet, the provision of the pneumatic piston-cylinder arrangement facilitating the achievement of this condition.

For cutting different thicknesses of glass sheet different roulettes 6 are used and also the force applied by the head's pneumatic piston-cylinder arrangement is also adjusted in accordance with the different thickness values. Although the roulette diameter is preferably the same as the thickness of the sheet that is to be cut, the roulette selected for cutting a particular glass sheet is arranged to have a cutting angle 7 appropriate to the thickness of the glass that is to be cut.For example, for an 8 mm sheet thickness, angle 7 of the roulette is approximately 157", and for a 25 mm thickness the angle 7 of the roulette to be used is approximately 167". From tests and experiments that have been conducted it seems that a formula which relates glass thickness to the roulette cutting angle determined by the two bevel surfaces, can be defined as follows; Cutting angle = 2 x arc sine (1 - 0.18 glass thickness As regards the force with which the selected roulette 6 impinges upon the glass, then for a glass thickness of 8 to 10 mm, the pneumatic pistoncylinder is appropriately graduated to provide a force of approximately 85 Kgs, whilst for a maximum glass thickness of approximately 25 mm an appropriate force is approximately 160 Kgs.

Figure 6 provides a general indication of the situation of the selected roulette 6 pressed towards the glass sheet 8 with a force M pneumatic pistoncylinder arrangement (not shown). Point 11 indicates the separation between the top layer of compression internal stresses and the intermediate layer of tension or traction internal stresses.

The following possible theoretical explanation give with reference to Figure 7 will clarify how a cut is attained according to this embodiment of the present invention.

The force M supplied by the pneumatic-cylinder arrangement creates a first incision upon the glass sheet, and the action of the components of the force M orthogonal to the lips T1 and T2 of roulette 6 create an instantaneous material bending, which deforms the material's Internal stress diagram thus diminishing the thickness of the first compression layer until the roulette cut reaches the intermediate tension or traction layer and thus produces tearing of the material.

Also, given the uniformity or constancy of the force M, the cutting irregularities produced will tend to be much smaller than those apparantly produced with the conventional prior art procedure. Figure 4 shows this cut end, and it can be seen how the irregularity area 9 of sheet 8, which area is between lines R-R, is much thinner than area 9 of Figure 5 which corresponds to the conventional prior art procedure.

It will be appreciated that, for the broad usage of this embodiment, it is appropriate to have available several roulettes 6 having different features in accordance with the different thickness of glass to be cut, and it is also appropriate to regulate, vary or adjust, in each case, the force applied to the roulette carried by the head.

To cut a particular glass sheet it is placed on the support therefor of the apparatus and the selected head mounted roulette cutter 6 is applied perpendicularly to the glass surface with a force that is maintained constant as the roulette cutter is moved over the glass surface whilst being maintained perpendicular thereto. The constant force applied is related to the thickness of the glass being cut. The cutting angle of the roulette cutter is also related to the thickness of the glass being cut, the relationship being: A = 2 are sine (1 - 0.18/t) where A is the cutting angle and t is the glass thickness.

From the foregoing it will he appreciated that embodiments of this invention may achieve glass cutting in a single operational step and without the application of any bending moment to the glass.

Also such glass cutting may be achieved quickly and safely, even for the highest glass thickness, without requiring a highly skilled operative. Furthermore such glass cutting may be achieved without requiring extensive polishing of the cut edge.

Claims

1. A method of cutting glass, wherein a roulette cutter is held generally perpendicular to the glass surface and applied thereto with a force that is maintained constant as the roulette cutter is moved over the glass surface.

2. A method according to Claim 1, wherein said force is predetermined to accord with the thickness of the glass to be cut.

3. A method according to Claim 1 or Claim 2, wherein the glass is 8 to 10 mm thick and the said force is approximately 85 Kgs.

4. A method according to Claim 1 or Claim 2, wherein the glass is 24.4 mm thick and the said force is approximately 170 Kgs.

5. A method according to any preceding Claim, wherein the cutting angle of the roulette cutter is predetermined to accord with the thickness of the glass to be cut.

6. A method according to Claim 5, wherein the cutting angle, A, and the glass thickness, t, have the following relationship: A=2arcsine(1 -0.18/t)

7. A method according to any preceding Claim, wherein the glass is 25.4 mm thick and the cutting angle is approximately 167".

8. A method according to any one of Claims 1 to 6, wherein the glass is 8 to 10 mm thick and the cutting angle is approximately 157".

9. A method according to Claim 1 and substantially as herein described with reference to the drawings.

10. Apparatus for cutting glass, the apparatus comprising a support for glass to be cut, means mounting a roulette cutter above the support such that the roulette can move over the surface of glass supported by the support and generally perpendicular to the glass surface, and means to apply a constant force to the roulette cutter as the latter is moved over said glass surface.

11. Apparatus according to Claim 10, wherein the means to apply a constant force is adjustable to adjust the force in accord with the thickness of the glass to be cut.

12. Apparatus according to Claim 10 or Claim 11, wherein said force applying means comprises a pneumatic or like piston-cylinder arrangement.

13. Apparatus according to any one of Claims 10 or 12, wherein the roulette cutter is removably mounted on said mounting means and is one of a plurality of such roulette cutters each to be used for a different glass thickness.

14. Apparatus according to any one of Claims 10 to 13, wherein the support bears glass having a thickness t related to the cutting angle A of the roulette cutter in accordance with the relationship: A 2arcsine (1 -0.18/t)

15. Apparatus according to any one of Claims 10 to 14, wherein the mounting means comprises a movable head from which the roulette cutter is carried by a horizontal shaft.

16. Glass cutting apparatus substantially as herein described with reference to and/or as illustrated in the accompanying drawing.