Description

ABRASIVE TOOL

The present invention relates to an improved abrasive tool.

The abrasive tool is a part, having any shape, provided with abrasive and mounted on grinding machines that transmit a cyclic, linear, oscillatory, rotary motion to the tool, or, more in general, a mix of these motions; the abrasive-holding tool comes in contact with the machined piece to grind it.

A special type of abrasive tool is the so-called pad: it is a disk-shaped abrasive tool that is specially suitable to be driven in rotary motion.

The abrasive tools, and especially the pads of the known art are composed of a rigid bearing body, whose surface is coated with a layer of abrasive powders of solid or synthetic diamonds mixed with a binder, such as adhesive or similar substances.

A first inconvenience of the abrasive tools of the known art consists in the fact that, during the machining process, the abrasive tool vibrates with respect to the grinding machine with vibrations induced by the machining operation and proportional to the irregularities of the machined part: the more the irregularities, the higher the vibrations will be.

This problem is more serious in case of grinding machines that are manually supported by the operator, who gets very tired because of the vibrations; moreover, the quality and accuracy of the grinding process are likely to get worse.

Another inconvenience of the vibrations transmitted by the tool to the grinding machine is related to the life of the tool and/or grinding machine: the vibrations create high-frequency cyclic mechanical stress that results in the creation and propagation of cracks both in the material of the abrasive tool and in the parts of the grinding machine that are subjected to the vibrations, typically the drive shaft that transmits motion to the abrasive tool. The creation and propagation of the cracks causes the failure of the abrasive tool or grinding machine, thus requiring either to change the tool or repair the

machine.

The purpose of the present invention is to overcome these and other inconveniences of the abrasive tools of the known art by means of an abrasive tool as claimed in claim 1. The abrasive tool of the present invention is composed of an elastically flexible bearing structure, on which the abrasive material or element is applied, which advantageously absorbs part of the vibrations generated during the grinding process of the machined part, in particular the high- frequency vibrations that cause the aforementioned cracks and tire the operator who supports the grinding machine with his hand during the machining operation.

Another purpose of the present invention is the manufacturing process of a pad according to the present invention.

Further advantageous characteristics are the subject of the enclosed dependant claims.

These and other advantages will become evident after the description of the enclosed figures, whereby: fig. 1 is a perspective view of the non-abrasive side of an abrasive tool according to the present invention; fig. 2 is a perspective view of the abrasive side of the tool of 1 ; fig. 3 is a side view of the tool of fig. 1 ; fig. 4 is an exploded view of the bearing structure of fig. 1 ; fig. 5 is a view of the bearing structure of the tool of fig. 4 in assembled condition; fig. 6 is a cross-sectional view of the tool of fig. 1 ; fig. 7 is an enlarged view of the tool of fig. 6; fig. 8 illustrates an advantageous executive embodiment of a grid of the bearing structure for an abrasive tool, in particular a pad, according to the present invention; fig. 9 illustrates an alternative advantageous executive embodiment of a grid of the bearing structure for an abrasive tool, in particular a pad, according to the present invention;

fig. 10 illustrates an executive drawing (in mm) of a specially advantageous executive embodiment of a part of a grid of the bearing structure for an abrasive tool, in particular a pad, according to the present invention. The enclosed figure illustrate a circular abrasive tool normally defined as pad, for illustrative purposes.

The present invention also relates to a different shape of the abrasive tool, either with axial symmetry around the rotation axis of the tool or without axial symmetry, such as in the case of rectangular, square or similar tools, since experts of the art will be able to obtain such an abrasive tool according to the precepts contained herein without any inventive effort.

Figures 1 , 2 and 3 illustrate the advantageous case of an abrasive tool (1) shaped as a pad comprising a rear side (2) designed to be mounted facing the grinding machine (not shown) without abrasive and coupled with a lateral shell (3) that identifies the thickness of the pad, and a machining side (4) designed to be mounted facing the piece to be machined (not shown) with abrasive. The pad is coupled with the machine tool by means of a flange (5) designed to transmit motion to the pad that rotates around its axis.

As shown in figs. 1 , 2 and 3, the pad, or more in general the abrasive tool of the present invention comprises a bearing structure composed of: an elastic grid (6) on which the abrasive material is fixed, the said elastic grid (6) being associated with an elastic body (7) and coupled with the flange (5).

The bearing structure gives elasticity or elastic flexibility to the abrasive tool (1), which is advantageously able to absorb the vibrations, especially high-frequency vibrations, that are generated during the machining process.

According to a specially advantageous feature, the elastic grid (6) is made of metal material, while the body (7) is made of plastic, especially polymeric or silicone material.

The elasticity of the metal grid (6) is guaranteed by the reduced thickness and shape, as illustrated hereinafter, while the elasticity of the body

(7) is intrinsic to the plastic material; the flange (5) is rigid, being designed to transmit the tool (1) the torque generated by the machine on which the tool is

fixed by means of the flange (5).

Moreover, because of the presence of the metal grid (6) and the plastic body (7), the abrasive material is fixed to the grid (6) by means of an inexpensive process without using any adhesive, that is to say by means of a galvanic bath, as illustrated hereinafter.

The grid (6) is coupled with the body (7) by partially drowning the grid (6) in the material of the body (7), for instance by means of co-moulding, in such a way at least one side of the grid (6) protrudes or emerges from the body (7) on the side facing the machining side (4). As shown in fig. 2, and also with reference to figs. 6 and 7, part of the grid (6) protrudes from the machining side (4) in alternation with parts of the body (7), in such a way that the machining side (4) has alternate bands of abrasive material, i.e. the grid (6), and bands without abrasive material, i.e. the body (7). Advantageously, as shown in figs. 1 and 6, the machining side of the body (7) is convex, with concavity on the rear side (2) in order to exploit the elasticity of the bearing structure and simplify the operator's work: theoretically, in case of a rigid tool, a convex machining side reduces the contact area between the tool (1) and the part; nevertheless, because of the elasticity of the tool (1 ) of the present invention, the force exerted by the operator or machine tool towards the machined part to press the tool (1) against it generates the elastic deformation of the tool, thus increasing the theoretical contact area, from a contact line to a contact area in which, because of the elasticity of the tool, the contact force is relatively uniform and the vibrations transmitted by the tool to the machine are relatively limited.

Advantageously, the presence of a metal grid (6) coupled with a polymeric body (7) not only gives elastic flexibility to the entire bearing structure of the tool (1 ), but also provides it with higher rigidity only in the areas where it is necessary, that is to say the areas with abrasive material: the areas with abrasive material are the parts of the metal grid (6) that protrude or emerge on the machining side (4), which are relatively more rigid than the polymeric body (7) without abrasive material. Figures 8 and 9

illustrate two especially advantageous constructive embodiments of a metal grid (6).

Although the grid (6) may be given any shape, as long as it is sufficiently thin and elastic, it has been proved that a spiral shape is the most advantageous shape: in fact, the spiral shape permits to mould the metal grid on an ordinary thin flat metal plate, and deform the grid (6) after moulding to give it the concave shape of the body (7) in which it is drown.

Generally, the spiral starts from a perforated central coupling element (8) designed to be coupled with the flange (5) by interference and broadens towards the shell (3).

The spiral pitch can be either constant or variable according to the distance from the centre, but is preferably constant because it is simpler to obtain.

The grid (6) can be shaped as a simple spiral, as shown in figs. 4 and 5, or as a spiral with transversal support arms (9) that depart from the perforated central coupling element (8), as in the grid (6A) of fig. 8, or as in the grid (6B) of fig. 9, in which the grid (6B) is composed of four identical spires staggered by 90° and coupled in the transversal support arms (9).

Another advantage offered by the spiral shape results from the wavelike motion of the spiral during the rotation of the tool (1 ), which allows to cross with the abrasive also while keeping the tool still on the piece to be machined.

Fig. 10 shows a specially advantageous example with dimensions expressed in millimetres of the initial part of the spiral, that is to say the part from which the spiral departs from the perforated central coupling element (8).

The thickness of the grid (6) ranges from 1 to 10 mm; the grid is preferably made of steel, or harmonic steel, although it can be obtained with any electrically conductive material.

The polymers of the body (7) are preferably polyurethanic polymers. The flange (5) is preferably made of aluminium.

Advantageously, the flange (5) transmits the motion to the grid (6) that transmits the motion to the body (7): in such a way, the turning moment of the

motor of the machine tool is not transmitted to the central area of the polymeric body (7), which could be damaged by it, but to the grid (6), which is stronger than the body (7) and distributes it uniformly to the entire body (7), which is driven into rotation and operated without damages. As mentioned earlier, the grid (6) is co-moulded into the body (7), i.e. first the grid (6) is obtained by moulding, shearing or laser cutting starting from a sheet metal and then the grid (6) is positioned in a mould for plastic materials, in which the concave polymeric body (7) is moulded according to the known technique, allowing part of the grid (6) to protrude or emerge from the body (7).

Now or, alternatively, before moulding the body (7) the flange (5) is coupled with the grid (6), for example by means of interference: the flange (5) is coupled with the grid (6) on the perforated central coupling element (8) by means of one or more interference ridges (10) that cooperate with corresponding housings (11 ) provided on the flange (5).

Now, the bearing structure is provided with an abrasive element that is necessary for functioning: the bearing structure is immersed in a galvanic bath in which a powder or granule abrasive element is dispersed.

During the galvanic bath the abrasive powders adhere to the metal surface of the grid (6) that protrudes or emerges from the body (7), on the machining side (4), while the polymeric body (7) is not coated by the abrasive material, being an electrically non-conductive material.