Technical field

The present invention relates to a grinding wheel, particularly intended for grinding processing operations for sheets of glass, ceramic material or other similar materials, having the features set out in the preamble of main claim 1.

Technological background

The invention involves particularly though not exclusively the specific technical sector of grinding processing for sheets of glass, in which the corners of the sheets are bevelled by means of grinding .

In that field, as well as on the basis of safety standards, the glass sheets which often have substantial dimensions must have bevelled corners in order to make their handling safe as well as for aesthetic matters and matters involving conserving the material integrity, because jagged edges increase the possibility of propagation of cracks and fractures.

To that end, there have been developed types of grinding machines which are specifically dedicated to carrying out that operation.

In accordance with a first known type, there are provided diamond-coated grinding wheels which travel along the peripheral edge of the sheet in order to bevel the corners thereof. A second known type instead provides for the use of intersecting abrasive or diamond-coated belts which are capable of carrying out the bevelling .

The machines with grinding wheels typically have a vertical extent and comprise grinding wheel systems which are directed along the two main Cartesian axes, with a vertical and horizontal orientation, respectively.

Statement of invention

Since the glass sheets are not always cut at 90° along the corners, the main problem which is encountered in this type of machine is to generate homogeneous bevelling actions over the entire extent of the edge of the sheet. In an at least partial solution to that problem, there has been proposed in the prior art a grinding wheel system which is configured so as to place the diamond-coated grinding wheels under constant pressure against the component to be ground . In this manner, the bevelling actions are homogeneous even in the presence of real travel actions of the component to be processed which are different from the theoretical ones defined in the machine.

In accordance with other solutions, the presence of variable bevelling actions is accepted because the operating system of the machine is independent of the cutting of the glass. The invention involves this particular type of grinding machines in order to overcome the technical problem set out above.

The problem is solved by the invention by means of a grinding wheel of the type set out above, constructed in accordance with the appended claims. Brief description of the drawings

The features and advantages of the invention will be better appreciated from the following detailed description of a preferred embodiment which is illustrated by way of non-limiting example with reference to the appended drawings, in which :

- Figure 1 is a perspective view of a grinding wheel constructed according to the invention,

- Figure 2 is a partially sectioned axial view of the grinding wheel of Figure 1,

- Figure 3 is a view corresponding to that of Figure 2 with the grinding wheel illustrated in a different operating condition,

- Figure 4 is a perspective view of the assembly of the grinding wheel of the preceding Figures in a state mounted on a drive shaft,

- Figure 5 is an axially sectioned view of the assembly of Figure 4.

Preferred embodiments of the invention

With reference to the cited Figures, there is generally designated 1 a grinding wheel which is particularly configured for grinding processing operations for sheets of glass, ceramic material or similar materials, and which is constructed according to the present invention.

The grinding wheel 1 is particularly suitable for the operation of bevelling the corners of the edge of the sheet, which operation is necessary following cutting of the sheet in order to make the sheet able to be handled in safe conditions. The bevelling of the sheet corners further serves to remove from the cutting profile any surface irregularities of the edge which are brought about during the operation of cutting the sheet and which can lead to the generation of fracture cracks in the sheet during the subsequent steps (for example, tempering, assembly, etc.). Figure 2 partially shows a sheet of the above-mentioned type which is designated 2 and which is intended to be subjected to operations for bevelling the opposing corners 2a, 2b thereof, by means of a grinding processing operation with the grinding wheel of the invention. The grinding wheel is of the type comprising a disc-shaped support with abrasive material arranged on the circumferential profile of the support and a central hole 3 for attachment to a drive shaft 4 of the grinding wheel. The disc-shaped support is axially symmetrical with respect to a main axis X, about which the grinding wheel is capable of being moved in rotation by the drive shaft 4 during the processing steps.

According to a main feature of the invention, the disc-shaped support of the grinding wheel comprises a pair of disc-shaped bodies 5, 6 which are coupled in a mutually facing position, as clearly shown in Figure 2, and the abrasive portions of which are coupled in a mutually facing position, so as to define together the entire abrasive grinding surface extending along the outermost circumferential profile of the disc-shaped bodies.

More specifically, each disc-shaped body 5, 6 constitutes the base or resilient core, which is advantageously in the form of a plate of spring steel or another low-hysteresis material . The abrasive material being arranged in the region of the outer circumferential profile of the disc-shaped body, and extending from one of the facing faces of the corresponding plate. In a preferred form, the abrasive material in each body 5, 6 is constructed in the form of a respective annular element 5b, 6b which is applied to the corresponding plate of the respective disc-shaped body, there being defined on each element an abrasive annular surface which is designated 5c, 6c, respectively.

The plates of the disc-shaped bodies 5, 6 are provided to be mounted coaxially with the X axis on the shaft 4, with the respective abrasive surfaces 5c, 6c facing each other, in order to define together a groove, which is generally designated 7, of abrasive material which extends circumferentially along the outer profile of the disc-shaped bodies, inside which groove the contact with the opposing corners 2a, 2b of the sheet 2 being processed is brought about.

The groove 7 preferably has a V-like axial cross-section with concavity which is directed towards the sheet which is intended to be subjected to grinding, each side of the V-like section being capable of contact with a respective corner 2a, 2b of the edge of the sheet.

In order to connect the disc-shaped bodies 5, 6, there is provided a first spacer 8 which is in the form of a cylindrical sleeve and which is capable of being mounted coaxially on the drive shaft 4 in a position interposed between the disc-shaped bodies 5, 6, in such a manner that the plates of the bodies are in abutment against the respective, opposing axial ends of the spacer 8. The spacer is further provided with through-passages 10 which extend radially through the thickness of the cylindrical surface thereof and which constitute passages for directly conveying a cooling and/or lubricating liquid onto the surfaces 5c, 6c of abrasive material of the grinding wheel.

An end of the passages 10 is in fluid communication with an annular chamber 11 which in turn communicates with a feeding passage 12 which is formed inside the shaft 4, while the opposite end of the passages 10 is open in the annular cavity which is delimited by the opposing plates of the bodies 5, 6 in such a manner that the liquid supplied into that cavity can reach by centrifugal action (connected with the rotation of the shaft 4) the contact zone between the abrasive surfaces and the sheet being processed . A pair of second spacers both designated 13 are provided in ring-like manner to be mounted coaxially on the drive shaft 4 on the opposite side to the first spacer 8, with respect to the corresponding disc-shaped body 5, 6, in a configuration in which each body 5, 6 is interposed between the first spacer 8 and the corresponding particular second spacer 13.

A pair of limiting flanges whose function will be described in detail below and which are both designated 14 are capable of being coaxially mounted on the shaft 4, each of which is provided in a position abutting the respective second spacer 13, as clearly illustrated in Figure 5. That Figure 5 clearly shows that the disc-shaped bodies 5, 6, the first spacer 8, the second spacers 13 and the pair of outer flanges 14 are clamped together in the form of an assembly on a shank 4a of the shaft 4 by way of a screw type means 15 which blocks the assembly of elements between an abutment 4b of the shaft and an outer closure flange 16. The opposite end of the drive shaft 4 relative to the one involved in the assembly closure system of the grinding wheel is further formed in a cone-like manner for fixing the grinding wheel to a CNC machine.

In each disc-shaped body 5, 6, there is further provision for each annular abrasive element to have circumferentially, in the region of the free end thereof, a regular sequence of projections 18 alternating with recesses 19, which define a front toothed profile 20. The toothed profiles 20 of the bodies 5, 6 are configured so as to be capable of meshing with each other by relative engagement, with limited connection play, of the projections 18 in the recesses 19 of one and other disc-shaped body 5, 6. In other words, there is provided relative engagement with reduced axial connection play between the pair of front toothed rings which are defined by the toothed profiles which are provided on the disc-shaped bodies 5, 6 in the region of the abrasive surfaces 5c, 6c, respectively.

The operating function of the grinding wheel is described in detail below with specific reference to Figures 2 and 3.

The sheet 2 intended to be subjected to grinding is arranged perpendicularly relative to the rotation axis X of the grinding wheel. The grinding wheel is positioned with the sides of the groove 7 in contact with the corners 2a, 2b of the sheet, with an action of light urging into the relative contact.

As a result of the resilience of the plates which form the disc-shaped bodies 5, 6 of the grinding wheel, they are urged to flex resiliently outwards (Figure 3, portion in broken lines) with the result that they apply a pressure (as a result of the urging in terms of resilient return generated in the plates) against the sheet being processed. That resilient behaviour allows the possible different positioning actions of the sheet (connected with the real travel which does not exactly correspond to the theoretical travel) to be made up for, at any rate ensuring that the corners 2a, 2b are bevelled over the entire extent thereof at the edges of the sheet.

It should be noted that the rigidity of the resilient structure defined by the plate of the disc-shaped body is determined, to a main extent, by the thickness of the plate of each disc-shaped body 5, 6 (if comprising spring steel with thicknesses which typically have values between 0.3 mm and 1 mm) and the dimension of the second spacer 13 (the greater the diameter of the spacer, the more rigid the structure of the plate in the disc-shaped body becomes).

In relation to the flexion of the plates of the disc-shaped bodies which moves them away from each other, the outer flanges 14 act as limiting means for the maximum deformation. The flanges actually have such dimensions in diameter as to interfere with the corresponding plates of the bodies 5, 6 during their flexion movement. The maximum resilient deformation brought about is determined by the thickness of the second spacers 13.

As a result of the provision of the front toothed profiles 20 in mutual engagement, the disc-shaped bodies 5, 6 bring about a type of nesting system which allows a portion of the abrasive surface always to be maintained, even in the case of an increase of the groove 7 as a result of a greater degree of introduction of the sheet, inside the groove itself. In that manner, the possibility of carrying out the bevelling at the corners of the sheet is always ensured.

The invention thereby solves the problem set out and achieves the advantages set out with respect to the known solutions.