FR2466441A1 - Cutting of glass panes by scoring, then bending to cause fracture - using asymmetric scoring wheel so smooth cut edges are obtd. which do not need grinding - Google Patents

Abstract

Cutting of glass panes by scoring and bending to cause fracture. A wheel with an asymmetric profile is used to score the panes, the periphery of the wheel consisting of a double cone converging to a point. The cones possess two different angles, alpha and beta, where alpha is pref 77-83 deg., and beta is pref. 25-35 deg. The force exerted on the scoring wheel is pref 35-70 N, and the wheel pref travels at 0.5-1 m/s when making the score. A stress above 5 N/cm is pref applied asymmetrically w.r.t the score to cause fracture of the pane, esp when the latter rests on two rollers, and a third roller is driven dowwards between the two to cause fracture. A very smooth cut edge is obtd on the pane, so the edge does not require final grinding, esp when the pane is used to form a window in a building, or a fixed window in a motor vehicle.

Description

Method and device for cutting
and breaking a sheet of glass
The invention relates to the cutting and breaking of a glass sheet.

 In many uses, the edges of the glass sheets must be shaped after cutting to avoid the risk of injury when handled. Shaping, which consists of felling the edges of the edges of the sheets, is generally carried out using abrasive grinding wheels or belts. This operation is therefore expensive.

 The present invention relates to a method and a device for cutting by tracing and breaking glass sheets which make superfluous the shaping operation, especially in all cases where the edges of the glass sheets are recessed (window glazing, glazing fixed vehicles, etc.).

 The devices used industrially for cutting glass sheets are knobs, generally made of tungsten carbide, shaped disks movable about an axis of rotation and having on their periphery two bevels forming a cutting angle. Such knobs are described in particular in the French patent publication 2 179 817 and in the journal GLASS-DIGEST of February 15, 1978, pages 50-52.

 When applied under a suitable pressure on the sheet to be cut, these wheels trace in the glass, from the surface, a crack substantially perpendicular to this surface. The depth of the crack depends on the cutting angle of the wheel and the pressure with which it is applied to the glass sheet. This is then broken by exerting a bending by means of a device having as a rule, on the face opposite to that which contains the crack, a pressing member (bar or cylinder) applied to the right of the tracing. The application of the pressing member causes the extension of the tracing face and a concentration of stresses at the tip of the crack which thus progresses towards the opposite face, causing the rupture of the glass sheet.

 The known knobs are normally applied to the sheet and the bevels defining their cutting angle are symmetrical, thus also the faces of the dihedron according to which the tracing pressure is exerted.

 We thus obtain fracture planes perpendicular to the faces, but having four sharp edges.

 The Applicant has established that, if the tracing of a sheet of glass is carried out by exerting a pressure - aissymmetric pressing, using a dial with an angle of dissection, and then shifting in a judicious way the í -zzure thus traced with respect to the pressing member which puts it in extension during the breaking of the sheet, so as to exert a further asymmetric force, it is possible to obtain fracture profiles including two edges are not sharp.

 The invention therefore has for its first object a method for cutting a glass sheet using a wheel, a method according to which the faces of the dihedron of pressing during the tracing are asymmetrical, the wheel itself remaining preferably perpendicular to the surface of the glass, while the faces of said wheel defining the cutting angle form different angles with its plane of rotation.

 As will be explained in detail below, this method makes it possible to trace in a sheet of glass a continuous cutting crack which is arranged obliquely with respect to the surface of the sheet in a direction approximately extending the bisector dihedron and which allows, when one breaks this sheet in the desired conditions, to obtain, in addition, on the opposite side to the cutting crack (tracing), a non-cutting edge.

 The tracing is preferably performed by exerting on the wheel a force of between 35 and 70 N and moving the wheel at a speed of 0.1 to 1 m / s, the dihedral being inclined towards the portion of the sheet to be preserved.

 To then put the crack in extension, in order to effect the breaking, the breaking process according to the invention uses an asymmetrical bending, the bending moment on the crack decreasing from one edge to the other of the crack and preferably from the side to be used to the side to be eliminated.

Applied to the breaking of a glass sheet comprising a tracing carried out using an asymmetrical wheel, or possibly a glass sheet having a crack traced with a conventional wheel, whose rotation plane is a plane of symmetry, but has obliquely, it allows to obtain in particular a bossa has two non-cutting edges on the part used.

 According to this method, the previously drawn glass sheet is brought into contact on the face opposite to the tracing with a support system sufficiently offset from the tracing figure, towards the part of the sheet that will be used, so that the shear force accompanying the bending acquires a significant value, preferably of the order of 2 to 5 N at least per centimeter of the length of the plot.Si tracing is rectilinear, the support system may comprise for example one or two rolls of parallel to the tracing and exerting the bending force extending the face traced with a counter-support system, which may consist of one or two rollers also parallel to the tracing, the drawing being placed between support and counter-support on the outside of the counter-supports and at a sufficient distance from the nearest of them.

 In the case of a tracing having a rounded closed profile, for example a circular profile whose inner part is used, the support system will be similarly constituted by an inner frame to the outline of the cut and the setting in flexion provided by the force exerted on the sheet by means of a counter-support consisting of pressing members outside the path.

 The approximation of the support and counter-support members is conveniently carried out at a speed of between 0.5 and 2.5 cm / min.

 This breaking process, applied to glass sheets comprising a tracing performed with a conventional wheel, leads to asymmetrical fracture profiles of which one of the opposite edges to the tracing is rounded. Applied to a glass sheet having a tracing performed with an asymmetrical wheel according to the invention, it produces fractures whose edge on the side of the tracing includes a chamfer and one of whose opposite edges is rounded. The sheets or glass articles thus obtained by breaking are of course within the scope of the invention.

 Finally, a last object of the invention is constituted by the asymmetrical rollers used in the drafting pro.-edé described above.

Other features of the invention will become apparent from the detailed description which follows, in which reference is made to the accompanying drawings. On these drawings
Figure 1 is a schematic view of a wheel according to the invention, in a direction perpendicular to its axis of rotation;
FIGS. 2a and 2b show the profile of the fracture obtained by breaking a glass sheet previously drawn with the aid of an asymmetrical wheel
Figure 3 is a diagram illustrating the breaking process according to the invention; ;
FIGS. 4 and 5 illustrate various fracture profiles obtained by breaking, by the method of the invention, glass sheets previously drawn using a conventional symmetrical wheel and using an asymmetrical wheel
Figure 6 is a schematic view illustrating the breaking method according to the invention in the case of a glass sheet having a circular pattern, the useful part to be the disc.

 Figure 1 shows an asymmetrical wheel according to the invention. It consists, in a manner known per se, of a disc 1 pivoting on an axis 2 and having a cutting edge 3. The flanks forming the cutting angle are two truncated cone-shaped bevels forming with the plane of the angle wheel, respectively α and ss, not equal, the bisecting plane of the corresponding dihedral, visible Figure 2a, being inclined at an angle Y on the perpendicular to the glass sheet when the wheel is straight. The choice of these angles determines the quality of the tracing of the cutting line in the glass sheets.

 The angle Oc is preferably of the order of 800 with a tolerance of +30. An angle of 850 is not suitable because, if the play of the axis of the wheel or the play of the wheel on its support are too large, the flank 4 of the wheel is sometimes parallel to the surface of the glass sheet which is no longer drawn.

The choice of the angle ss is also very important. It is obvious that if it is equal to α, we obtain a ssmetric wheel that produces a crack perpendicular to the surface of the glass sheet. When the angle ss decreases, decreases,
The crack tilts towards the angle y and forms with the normal ci on the surface an angle all the greater as the angle 3 is smaller.

 This angle F is preferably equal to 300 + 50.

 This leads to an angle Y of the order of 25q which would make it difficult to use a symmetrical but inclined wheel.

 After asymmetrical breaking, it can be seen (FIG. 2b) that the edge obtained is more or less inclined, the edge on the crack side 5 made in the sheet 6 having a regular chamfer Sa whose inclination with respect to a perpendicular plane to the faces, corresponds to the inclination of the crack created during the tracing of the sheet of glass.

 FIG. 3 represents a breaking device according to the invention.

 The glass sheet 7 rests on supports 8 and the approximation of a pressure support 9 causes it to bend, then break, under an effort R.

 Table 1 below gives the characteristics of the crack obtained with an asymmetrical wheel where o (= 800 and ss = 300, oil-lubricated, loaded at 34, 39, 44 and 59 N approximately and moved to 30 to 40 cm / s approximately The angle # and the length of the crack under tracing were measured.

TABLE 1

<tb> Effort <SEP> on <SEP> the <SEP> f <SEP> o <SEP><SEP> Length <SEP> of <SEP> the <SEP> crack
<tb><SEP><SEP> wheel under <SEP> tracing
<tb><SEP> 34 <SEP> N <SEP> 320 <SEP> 250
<tb><SEP> 39 <SEP> N <SEP> 330 <SEP> 295
<tb><SEP> 44 <SEP> N <SEP> 320 <SEP> 325
<tb><SEP> 59 <SEP> N <SEP> 370 <SEP> 408
<Tb>
A first series of breaking tests was carried out on a rectangular glass sheet having a length of 110 mm, a width of 40 mm and a thickness of 2.83 mm, in which a transverse crack was drawn using a wheel loaded at 39 N and moved at a speed of 1 m / s.These tests were carried out with a device of the type of Figure 3, the supports having a diameter of 9.9 mm, the fixed supports 8 being separated by 70 Ma, and the support 9 being located in the middle, by varying the distance x between the crack Ui of the support 8. The loading speed at the right of the support 9 was 9.7 MPa / s.

 It has been found that if a conventional wheel having a cutting angle of 1500 is used, a very regular non-cutting edge is obtained on the side opposite to the tracing. The comparative tests, carried out with a glass sheet on a surface from which the preliminary crack has been drawn using an asymmetrical wheel in accordance with the invention and axes parallel to the plane of tracing of the sheet, show that two non-cutting edges are obtained.

 The breaking profiles obtained are shown in FIG. 4, while the breaking conditions and the corresponding profiles are shown in Table 2 below.

TABLE 2

<tb><SEP> Dial <SEP> x <SEP> R <SEP><SEP> Profile of
<tb><SEP> mm <SEP> daN <SEP> fracture
<tb> Symmetric <SEP> 35 <SEP> 2.5 <SEP> a
<tb> 1500 <SEP> 25 <SEP> 3.6 <SEP> b
<tb><SEP> 15 <SEP> 6.2 <SEP> c
<tb><SEP> 5 <SEP> 19.0 <SEP> d
<tb> Unsymmetrical <SEP> 35 <SEP> 2,4 <SEP> e
<tb> 80 -30 <SEP> 25 <SEP> 3,4 <SEP> f
<tb><SEP> 15 <SEP> 5.8 <SEP> g
<tb><SEP> 5 <SEP> 18.0 <SEP> h
<Tb>
FIG. 4 shows that the profile of the fracture changes significantly when the distance between the crack 10 and the nearest end support 8 varies. On the edge opposite this crack, we obtain a connection angle with the surface of the glass sheet less than 900 moving towards a rounded profile. The ridge is very regular and very little cutting.

 For the last tests, one obtains an opposite edge to the tracing which presents, if x is small enough so that the shearing force is important, a rather strong radius of curvature, close to 150 em for the profile (g), 200 m for the profile (h) and 300 Um for the profile (i).

 In comparison with the previous profiles, it can be seen that neither the direction of the fracture at the outlet of the crack nor its general shape is significantly affected by the inclination of this crack.

 The edges are not sharp and the rounded edge has the appearance of a burnished edge.

 A second series of tests was carried out on identical sheets of glass, previously cut with an asymmetrical wheel (tC = 800, p = 300) always loaded at 39 N and moved at a speed of 1 m / s, then on sheets of almost double thickness.

 The break is effected with a charging speed of 230 MPa / s, the fixed supports 8 being separated by 88 mm, the support 9 having a diameter of 12 mm. The fracture profiles obtained by varying the distance x separating the crack from the fixed support are shown in FIG.

These profiles correspond to the following x distances

<tb><SEP> Foil <SEP> of <SEP> 2.83 <SEP> mm <SEP> Foil <SEP> of <SEP> 5.85 <SEP> mm
<tb> Distance <SEP> x
<tb><SEP> (mm) <SEP> R <SEP> Profile <SEP> R <SEP> Profile
<tb><SEP> daN <SEP> daN
<tb><SEP> 32 <SEP> 2.8 <SEP> (e) <SEP> 11.5 <SEP> (i)
<tb><SEP> 14 <SEP> 6.8 <SEP> (g) <SEP> 28 <SEP> (j)
<tb><SEP> 10 <SEP> 10 <SEP> (h) <SEP> 41 <SEP> (k)
<Tb>
It emerges from this that the profile obtained depends essentially on the value of R, that is to say on the shear force undergone during the rupture.

 It is advantageous, on the other hand, that the breaking operation be done quickly after the tracing operation and not more than 5 minutes after this operation.

 In order to measure the mechanical strength of the sheet, samples have been subjected to bending tests perpendicular to the cut edge, tests which show that this resistance is largely equal to that of the edges cut with a symmetrical wheel and that it is often superior. .

 These tests were carried out with a series of sheets of glass traced with an asymmetrical wheel of angles α = 800 and ss = 300, arranged normally, by varying the force P exerted on the wheel.

If we denote by # the angle of the crack with the surface normal and by F the mechanical resistance to bending, the results obtained are as follows:
For P = 39 N = 390,
F = 95 MPa,
For P = 34 N d = 400,
F = 105 MPa.

With an asymmetrical wheel of angles o (= 800 and p = 400, these results are as follows
For P = 39 N
X = 360,
F = 107 MPa,
For P = 34 NX = 14,
F = 110 MPa.

 By way of comparison, the flexural strength of a similar plate, cut with a symmetrical wheel having a cutting angle of 1500 and load at 39 N, was found to be equal to 95 MPa.

On the other hand, the lateral cracks that always occur at the time of incision with a wheel are formed preferentially on the side of the small angle of the asymmetrical wheel. They are therefore mostly localized and more developed on the opposite side to the bevel, that is to say on the part of the unused glass. These lateral fissures are responsible for the appearance of small pieces of glass called srliures resulting from the development of cracks. The splicers can cause, during the handling or trans are glass sheets, scratches on the surface, which adversely affects the optical and mechanical qualities of the glass. These lateral cracks are quite developed in the tests where ss = 400 This angle is therefore less interesting than the angle
P = 300 for which the cracks are rather undeveloped on the side of the large angle of the wheel.

 The wheel according to the invention is also suitable for curvilinear tracing and FIG. 6 shows a device used in a test for detaching circular disks.

 The glass sheet 11, which has a thickness of 2.8 mm, is placed on a circular support 12 with a diameter of 203 mm. The pressing member 13 is concentric with a ball 11 and has a diameter of 125 mm. The glass sheet was drawn in a circle of 156 mm in diameter by means of an asymmetrical wheel.

 By breaking with this device under an effort of the order of 45 daN, a perfectly cut disc is obtained.

 These tests show that the loading speed of the breaking device plays a favorable but rather secondary roll.

 The invention thus provides a simple means for cutting and breaking a sheet of glass, in order to obtain directly an article with sharp edges, without it being necessary to slaughter the edges of the edges of this article.

Claims (14)

 1. A method for cutting a glass sheet by tracing with a wheel and bending break, this method being characterized in that the planes defining the pressing dihedron form different angles with the plane of the leaf.  2. Method according to claim 1, characterized in that the planes defining the pressing angle are with the plane of the sheet angles equal to 300 + 50 and 800 + 30 respectively.  3. Method according to one of claims 1 and 2, charac terized in that the force exerted on the wheel during the tracing operation is between 35 and 70 N.  4. Method according to one of claims 1 to 3, characterized in that the speed of translation of the axis of the wheel is between 0.5 and 1 m / s.  5. Method according to one of claims 4 to 4, charac terized in that the bending moment putting the crack in extension is asymmetrical.  6. A method according to claim 5, characterized in that the bending moment decreases in the direction towards which the penetration of the cutting crack is inclined.  7. Method according to one of claims 5 and 6, charac terized in that the bending force is exerted by a pressing member developing at break a shear force greater than 5 N / cm.  8. Method according to one of claims 5 to 7, applied to a glass sheet having a rectilinear tracing, characterized in that the support system comprises two parallel supports tracing and in that one exerts the effort bending on the face opposite to this tracing with the aid of a pressing member which is also parallel to said tracing, the latter being disposed between a support and the pressing member.  9. Method according to one of claims 5 to 7, applied to a glass sheet comprising a tracing having a rounded closed profile, in particular a circular profile, characterized in that the support system comprises an outer support frame to the trace of the cut and in that the pressing member comprises on the other side of the glass sheet, an inner frame to said plot.  10. Tracing wheel for implementing the method according to claim 1, characterized in that its flanks which define the cutting angle form different angles with its plane of rotation.  11. Wheel according to claim 10, characterized in that its axis of rotation is arranged parallel to the plotting plane.  12. Wheel according to claim 11, characterized in that its flanks which define the angle of cut together with the plane of rotation equal angles-respectively 300 + 50 and 800 + 30  13. Glass sheet having a cutting recess traced on one side, characterized in that said crack is inclined.  14. Glass sheet having on at least one of its edges two non-cutting edges, characterized in that one of them carries a raw chamfer cutting.  i5. A glass sheet according to claim 14, characterized in that the edge opposite the chamfer is a rounded raw cutting edge.