Field of application of the invention

The present invention refers to a processing machine and a method for restoring the functionality to abrasive disks, and in particular for the dressing of such disks.

Review of the prior art

In the art of industrial processing, there is often the need to operate on the surfaces of a product substantially ready for the desired use, in order to confer definitive characteristics and shape to such product: in particular, there is the elim- ination of the casting feedhead, the removal of the molding burrs, the rounding of the edges, the polishing of the surfaces and other similar processing.

All of such processing is generally carried out with abrasive devices, i.e. having the work surface composed or coated with very hard small grains with material, composition, size and density suitable for the material to be worked.

Nevertheless, during processing, the device progressively loses effectiveness since the abrasive surface is deteriorated, partly because of the loss of aforesaid grains and the rounding of their edges, partly because the surface retains the abraded material scraps between the grains. The restoration of the working effectiveness can be obtained by substituting the device when its cost is sub- stantially insignificant (sheets, discs and strips of sandpaper) or by dressing the abrasive surface, in a manner so as to bring it back to the initial conditions.

This operation is common with the devices generically known as abrasive disks: these disks are substantially discs with different thicknesses constituted by a composition of known abrasive materials such as cubitron®, abral® and other super-abrasive materials, mixed with a Bakelite binder, having the edge and/or the surface strongly abrasive. The abrasive disks work the material to be ground by operating on the same with the edge or with the surface, or with both, and in any case by rotating at a higher or lower speed depending on the material to be worked. These disks are particularly employed for grinding the surfaces of metal elements, in particular the surfaces of springs, in order to confer a shape thereto with bases that lie on parallel planes.

When the abrasive disk requires being dressed, a small roller is used, generally formed by one or more metal discs, which is brought into contact with the surface of the abrasive disk, along the periphery thereof, and made to slowly advance towards the center, simultaneously maintained in rotation by the rotation of the abrasive disk itself.

Alternatively, in place of the aforesaid small roller, a small roll is used having a diamond end, which is moved exactly as described above and with the same modes of the roller.

By working in this manner, the tool brings out the rounded and worn grains from the abrasive surface, raising the grains with new cutting edges and thus restor- ing the effectiveness of the abrasive disk.

The Applicant has observed that the above manner of working is not satisfactory: the noise is very high,- no longer tolerable today; the dressing time, also high, considerably increases the production costs; and a considerable quantity of pulverulent waste is produced.

In addition, in particular in the operation of grinding springs, due to the high quantity of material to be removed, the abrasive surface of the abrasive disks is deteriorated in a very specific manner: the abrasive surface loses its coplanar- ity, which is compromised by undulations and recesses generated on the work surface. In this case, in order to restore the functionality of the abrasive disks, such surface must also be leveled/smoothed.

Objects of the invention

The Applicant has thus perceived that the methods described could be substi- tuted by a new method, and consequently by an improved plant, capable of overcoming the abovementioned defects and obtaining an increase in productivity, cost savings and improvement of the ergonomical characteristics of the work environment.

Summary of the invention

The present invention therefore refers to a method for dressing and restoring the effectiveness of an abrasive disk, characterized in that it cleans the surface of the abrasive disk with a diamond wheel rotating in a direction and with a speed independent from the direction/speed of the abrasive disk.

In a second aspect thereof, the present invention also regards a plant for actuating the aforesaid method, and more particularly a plant for dressing the work surface of abrasive disks, characterized in that it comprises a diamond wheel which is conducted on the surface of the abrasive disk with autonomous movements.

It is specified herein, in the following description, that with the word 'dressing' it is intended all the operations, included cleaning and leveling/smoothing, that are necessary for restoring the effectiveness of an abrasive disk.

Brief description of the figures

The present invention can be better understood from the following description and with the aid of the enclosed figures, provided exclusively as a non-limiting example, since other embodiments are possible in compliance with and in the scope of the definition of the aforesaid method and the aforesaid plant according to the following claims.

• Figure 1 shows the plant with the device according to the invention, in a par- tial side cross-section view along the plane A-A of figure 2.

• Figure 2 illustrates, in front view, the dressing device according to the invention.

• Figure 3 shows, in side perspective view, the device of figure 2.

• Figure 4 illustrates, in partial perspective view, the dressing device according to the invention in operative position on the support plant.

Detailed description of several preferred embodiments of the invention

In the following present description, for descriptive ease, reference is only made to a preferred embodiment of the invention; it must be clear that the method and plant described are not limited to the aforesaid case, but regard the dressing of abrasive disks for any type of working and grinding.

One mechanical element whose grinding is generally required before its final use is the compression spring, obtained with a round metal bar helically wound in successive coils along the axial direction thereof. Due to this packing method, the axially opposite ends of the spring do not lie on planes parallel to each other, and this leads to installation difficulties and possible malfunctions in operation. The grinding operation, with removal of material from the ends of the spring, arranges said ends in planes parallel to each other.

With reference to figure 1 , the plant for grinding mechanical elements in general, and helical springs in particular, and for dressing the work surface of the abrasive disks which carry out the grinding operation, comprises a base 1 , associated with a work station 2 where the elements to be ground are arranged, generically per se known and insignificant with regard to the invention. Such elements, specifically a helical spring 3, are arranged in the work station mounted on movement and support means, not illustrated since they are known or can be easily inferred, adapt to maintain said elements stably positioned in said station during the grinding operation. Present in the station is an abrasive disk 4, rotating around a rotation axis Y-Y, defined below as the first rotation axis; such disk is arranged at one end of said work station, with the abrasive surface directed towards the element to be ground. Without this constituting any type of constraint, the abrasive disk is generally formed by a composition of super- abrasive elements and Bakelite binder, having a thickness comprised between 20 and 150 mm, preferably on the order of 20 mm, and a diameter comprised between 200 and 1200 mm.

Any orientation can be selected for the axis of the abrasive disk 4, and consequently for that of the element being worked; however, according to a preferred embodiment, the abrasive disk is arranged with axis Y-Y set vertically with re- spect to the ground. According to another preferred embodiment, the work station associated with the plant comprises a pair of coaxial abrasive disks 4-4', mutually axially movable, arranged at opposite ends of said work station, in a manner so as to be able to simultaneously work both ends of the mechanical element to be ground. The mutual movement between such abrasive disks can be attained by making only one abrasive disk (4') movable with respect to the other (4), or vice versa, or both with respect to a fixed external reference.

The aforesaid abrasive disks can be axially moved and commanded to rotate, in a direction and with a speed, in an independent manner with respect to each other.

On the plant 1 , a slide 5 is present, illustrated in side section in figure 1 , in front view in figure 2 and in perspective view in figure 3, which supports a rotation axis X-X, hereinbelow defined the second rotation axis. On the slide 5, the dressing device of the invention is mounted; such dressing device comprises an abrasive disk, and more specifically a diamond wheel 6, mounted at the end of said axis X-X directed towards the work station, and rotating around said second rotation axis. The slide is axially slidable on the base in both directions along said rotation axis; alternatively it can be moved between a front position, in which the dresser device is situated (figure 4) inside the work station, and a rear position, in which said dresser device is situated (figure 1) in a position outside said work station. The actuations that command the movements of the slide and the rotation of the second rotation axis are not described herein since they are of substantially known type, and in any case can be easily obtained by the man skilled in the art who knows the object to be attained.

Without this constituting any type of constraint, the diamond wheel is generally constituted by a disk of sintered or electrodeposited material, having a thickness comprised between 1 and 50 mm, preferably on the order of 20 mm, and a di- ameter comprised between 50 and 200 mm, preferably on the order of 100 mm. According to the invention, the diamond wheel 6 has its speed and rotation direction commanded independently from the speed and rotation direction of the abrasive disk 4.

The diamond wheel 6 operates on the abrasive disk 4, as will be stated below, via contact between its edge and the work surface of the abrasive disk. When a pair of facing abrasive disks (4, 4') is present, the diamond wheel operates after having been inserted between said pair of abrasive disks. In order to allow the contact between the abrasive disks, the distance between the edge of the diamond wheel and the surface of the abrasive disk can be adjusted as desired, according to requirements: this can be achieved by making the abrasive disk or the abrasive disks axially movable along the rotation axis thereof, as said above. In order to allow the coupling between the diamond wheel and the abrasive disk, or the abrasive disks, according to the invention, the second rotation axis is moved by means of the movement of the slide, parallel to itself, in both directions along the first rotation axis. The end of the slide which supports the diamond wheel 6 can have different degrees of freedom, in a manner so as to be able to vary the angular value and the orientation of the plane in which the disc 6 rotates with respect to the plane of the surface of the abrasive disk 4; preferably, however, the second rotation axis X-X is arranged perpendicular to the first rotation axis Y-Y, and still more preferably, said first and second rotation axes lie in a same plane "p". In conclusion, the second ro- tation axis, and with this the diamond wheel, can be axially movable along the direction of the first rotation axis, via the use of means of known type which allow the sliding of the slide 2 in both vertical directions on the plant 1.

Now that the plant in its entirety has been observed, it will be easier to understand the new and original processing method that is the object of the present invention, for the dressing of the work surface of an abrasive disk used for grinding mechanical elements such as helical springs. The dressing operation begins after the mechanical element has been moved away (figure 4) from the work station. For descriptive simplicity, we only make reference to the abrasive disk 4, given that the actuation of the method of the invention in the presence of the second abrasive disk 4' is fully evident.

The aforesaid method begins with the step of bringing the side surface of a dressing device, i.e. the edge of the diamond wheel 6, against a point of the abrasive surface of the abrasive disk 4. The aforesaid point can be any one point, along the edges or inside said surface; preferably, however, when the abrasive disk has an irregular surface due to the presence of recesses with peaks and depressions, one starts from the highest point of the surface with respect to its normal plane. The movement is actuated by sliding the slide on the base, in a manner so as to move the diamond wheel 6 from the outside towards the work station interior. The abrasive disk 4 is maintained in rotation around the first rotation axis, whereas the dressing device is maintained in rotation around the second rota- tion axis. Now, one begins to move the dressing device radially with respect to the first rotation axis along the abrasive surface of the abrasive disk 4 in the direction of the opposite edge, or in the direction of one of the two edges, external or internal, if the starting point for the movement was selected in a position comprised between said two edges. In this case, in order to cover the entire surface of the abrasive disk 4 it will be necessary to perform a back-and-forth movement from the starting point towards one edge, and then in opposite direction up to the opposite edge, and then once again in the other direction until the starting point is reached.

Preferably, said movement of the dressing device is extended from the external edge of the abrasive surface of the abrasive disk 4 towards the rotation axis of said disk.

The movement of the slide is carried out at a speed comprised between 1 and 200 mm/s. During this movement, the diamond wheel 6 is maintained in rotation, according to a pre-established direction (F1 ), at a constant speed com- prised between 100 and 40000 rev/minute, and still more preferably on the order of 4500 rev/minute. Still during the translation movement of the dressing device along the surface of the abrasive disk, the aforesaid disk is maintained in rotation, preferably in a direction (F2) opposite that of the diamond wheel, at a progressively variable rotation speed; in such a manner, the peripheral speed of the point of contact with the diamond wheel, with the change of the radius size of said point with respect to the axis Y-Y, remains constant and preferably comprised between 1 and 100 meters/second, still more preferably between 10 and 80 meters/second. Preferably, the algebraic sum of the two opposite peripheral speeds of the two contact points - that referred to the point on the abrasive disk and that referred to the point on the diamond wheel - or the difference between the two peripheral speeds when the abrasive disk and the diamond wheel revolve in the same direction, is comprised between 20 and 200 meters/second. Preferably, in the presence of the second abrasive disk 4', the dressing device simultaneously operates on the two opposite abrasive surfaces, that of the abrasive disk 4 and the facing surface of the abrasive disk 4'.

The described invention offers important qualitative and economical advan- tages.

The combination of the translation movement of the dressing device with the opposing rotating speeds of the abrasive disk and the diamond wheel has allowed considerably reducing the leveling/smoothing time and the dressing time for the abrasive disk, which in a specific embodiment has passed from 30 to 5 minutes - with all the consequent economic advantages.

The dressed surface is arranged in optimal conditions of maximum effectiveness with the restoration of its coplanarity, the elimination of all the rounded grains lacking cutting edge, and the elimination of all the scrap accumulated between the grains during the preceding processing. Finally, the noise of the processing is considerably reduced, facilitating improved comfort for the operators in the work setting.

In the present description, not all of the possible structural and size alternatives to the specifically described embodiments of the invention were described: indeed, it did not seem necessary to expand upon the structural details of the sys- tern of the invention, since the man skilled in the art, after the instructions given herein, will have no difficulty designing the most advantageous technical solution, suitably selecting materials and size. Such embodiment variants are nevertheless intended to be equally comprised in the protective scope of the present invention, such alternative forms being per se easily derivable from the descrip- tion outlined herein of the relation that binds each embodiment with the desired invention result.