IT201900005226A1 - REINFORCEMENT NET FOR ABRASIVE WHEELS AND RELATIVE ABRASIVE WHEEL - Google Patents

Description

DESCRIPTION

of the Italian Patent for Industrial Invention entitled:

“REINFORCEMENT NET FOR ABRASIVE WHEELS AND RELATIVE WHEEL

ABRASIVE "

TECHNICAL FIELD

The present invention relates to a reinforcing mesh for abrasive wheels, an abrasive wheel, for example with a depressed or flat center, for emery or cutting, a process for making a reinforcing mesh, a method of manufacturing an abrasive wheel and a procedure for controlling the production of abrasive wheels. PRE-EXISTING TECHNIQUE

As is known, there are abrasive wheels, of the discoidal type with depressed center or flat, conical, semi-flexible or rigid, particularly used on portable electric, compressed air or more rarely hydraulic high-speed grinding machines (60-100 m / s of peripheral speed ) also known as grinders to perform deburring and / or cutting operations. These abrasive wheels are essentially made up of an abrasive mixture reinforced by armatures consisting of one or more fabric nets, one or two annular metal elements, commonly called washers or ring nuts, which delimit the hole for fixing the wheel to the shaft of the grinding machine. and a possible label in paper or other commonly used primer, adhering to one of the two faces of the grinding wheel (usually the convex one).

The abrasive mixture is generally made up of grains of abrasive material (silicon carbide light green, dark green, black, corundum, corundum modified with zirconium, semi-permeable, red brown, white, pink, ruby, ceramic, monocrystalline, abrasive sol- gels or sintered ceramics or other) of predefined granulometry (normally measured in mesh) which are mixed with resins, for example phenolic, liquid and / or powdered and possibly modified with epoxy resins, and / or others, possibly modified with organic compounds and / or vegetable or synthetic, and other types of polyamide resins, etc., and with additives and fillers.

The hardness of the abrasive wheel is defined based on the percentage of resin in the mixture, in particular the greater the percentage by weight of the resin abrasive weight, the greater the hardness of the abrasive wheel.

The reinforcement nets are normally woven with glass fiber yarns, but other types, both natural and even more advanced types, such as carbon, Kevlar or other, could be used; the nets woven on looms in height of the order of 1.5 m, are previously immersed in a solution of liquid resins and solvents, squeezed between pairs of rollers and dried in suitable ovens in which the resin dries without polymerizing (the polymerization is subsequently completed together with the grinding wheel firing in special polymerization ovens).

From the mesh fabric, so impregnated with resin and dried, the mesh discs needed to reinforce the wheels are obtained by die-cutting or other cutting technique. Other manufacturing methods of abrasive wheels provide that the reinforcing nets are used in rolls with lamination techniques and coupling to the abrasive compound through roller conveyors; in other applications they can be punched into square or other shaped slabs used to compose sandwich slabs of abrasive compound and reinforcing nets which are then punched to obtain the definitive abrasive wheels.

The nets can optionally be pre-glued to a sheet of paper or polymeric material of thin thickness as well as to the labels.

The labels are made of paper or other synthetic material and normally have the shape of a circular crown, (however, they can have any other shape) they can occupy either the entire face of the grinding wheel or a limited area of the face to which they adhere and report the identification data and information of the grinding wheel.

The reinforcing nets are preferentially arranged so that a first reinforcing mesh is substantially in correspondence with the rear face (or back) of the abrasive wheel and a second reinforcing net is found in correspondence with the opposite front face.

In addition, for example in particular for emery wheels, there are also one or more reinforcement meshes interposed between the first and second reinforcement mesh, within the thickness of the abrasive wheel. Finally, there are also wheels without reinforcement nets (for low rotation speeds) and others equipped with a single reinforcement mesh positioned in the center of the abrasive wheel itself.

The abrasive wheels are produced in most cases by pressing inside molds consisting of a ring in which an open forming cavity, called female, and a complementary punch, called male, is housed.

The pressed and formed abrasive wheel (green) is subsequently subjected to heating at a slowly increasing temperature from 80 ° C to 125 ° C; in these conditions the resins of the abrasive mixture and those that impregnate the reinforcing mesh (s) become fluid, "fusing" together and "penetrating", in this way the abrasive mixture adheres to the mesh (s) together with which it creates a single block with very high mechanical resistance.

The subsequent heating up to 170 - 200 ° C (but also lower) determines the irreversible polymerization process of the resin.

A deeply felt need in the sector is to have the absolute certainty that the reinforcing meshes, especially the first and second reinforcing mesh, are always present in the abrasive wheel and that their presence is ensured, as these reinforcing meshes have the important task of preserving the integrity of the abrasive wheel and ensuring its safety in operation.

Therefore, both for the manufacturer and for the distributor and / or the user there is a need to detect and guarantee the correct presence of all the reinforcing nets that the abrasive wheel is intended to contain in accordance with its project, for example having an automatic, safe, fast, reliable and economical control that makes it possible to identify any anomalies - or the absence of the foreseen reinforcement nets - with the possibility of preventing the marketing and use of potentially dangerous abrasive wheels which, erroneously, they do not have one or more of these reinforcing nets. Normally this check is carried out visually by trained personnel and is however only possible for the nets placed on the surface of the grinding wheel, while there is no certainty of the correct presence of the intermediate nets. Obviously the cost of the control operations carried out by means of people is considerable and the quality of the control relatively low as the staff after having viewed a few hundred pieces can easily make mistakes and not notice wheels without reinforcement nets due to the monotony of the process by placing dangerous masses on the market.

An object of the present invention is to satisfy the aforementioned needs and the intrinsic limits of the known art, within the context of a simple, rational and low cost solution.

These purposes are fully achieved by the characteristics of the invention reported in the independent claims. The dependent claims outline preferred and / or particularly advantageous aspects of the invention.

EXHIBITION OF THE INVENTION

The invention, in particular, makes available a reinforcing mesh for abrasive wheels which includes:

- a fabric (or non-woven fabric) of fibers; And

- at least one recognition element made of conductive material (for example electrically conductive) adhered to the fiber fabric.

Thanks to the particular properties of the conductive materials, this solution makes it possible to satisfy the aforesaid needs of the prior art in a precise, rational, economical and functional way.

In particular, thanks to the recognition element, the certain, repeatable, economic, safe and automated identification of each reinforcement mesh is made possible, for example when it is incorporated into an abrasive mixture of an abrasive wheel or in any case in each production step. of an abrasive wheel itself.

According to an aspect of the invention, the recognition element can comprise a conductive strip elongated along a longitudinal axis, and equipped with a transverse width with respect to the longitudinal axis prevailing with respect to its thickness. The longitudinal axis of the strip can be curved or straight or have any desired shape.

Thanks to this solution, it is possible to identify the recognition element easily and with certainty through a simple and inexpensive sensor, for example an inductive sensor (also called micro jargon).

Advantageously, the recognition element can have a flexural strength less than or equal to the flexural strength of the fiber fabric.

Thanks to this solution, the addition of the recognition element to the reinforcement mesh does not substantially change the rigidity of the reinforcement mesh, which - therefore - can be adapted, like traditional reinforcement meshes, to the shape of the mold. , without negatively interfering with the formation process of an abrasive wheel.

According to an aspect of the invention, the conductive material can be selected from the group, preferably but not exclusively, among aluminum, copper, zinc, tin, lead, iron and their alloys as well as carbon fiber (or a conductive composite material) nickel, tungsten , magnesium, lithium, chromium and carbon or other elements of the group of metals in the periodic table of elements.

Advantageously, the reinforcing mesh can further comprise a sheet, for example made of a polymeric material or a paper material, which can be provided with a face adhering to a face of the fiber fabric.

Advantageously, the recognition element can be preferably interposed between the face of the fiber fabric and the face of the sheet.

Thanks to this solution, the production of the reinforcement mesh can be facilitated and automated.

According to one aspect of the invention, the thickness of the recognition element can be less than or equal to the (maximum) thickness of the fiber fabric and / or sheet.

Furthermore, the width of the recognition element is large enough to be identified by a sensor, for example an inductive sensor.

Thanks to this solution, the introduction of the recognition element in the reinforcement mesh does not significantly change the thickness and functionality of the fiber fabric and / or sheet and, therefore, of the reinforcement mesh as a whole.

Preferably, the reinforcing mesh can comprise a plurality of recognition elements distributed (uniformly or randomly or otherwise) on one face or both of the fiber fabric or in any case fixed thereto.

According to a further aspect (alternative or in addition), the recognition element can be obtained by depositing, on the fiber fabric, at least one conductive powder, preferably along a strip elongated along a longitudinal axis, and having a transverse width with respect to to the prevailing longitudinal axis with respect to its thickness.

Advantageously, moreover, the recognition element can be deformable in a plastic (and not elastic) way.

A further aspect of the invention makes available an abrasive wheel which includes:

- an abrasive mixture; And

- at least one reinforcing mesh, as described above, in which the reinforcing mesh is at least partially incorporated within the abrasive mixture and which, as mentioned, is equipped with a recognition element.

Thanks to this solution, the technical problems set out in the preamble are solved with an advantageous, easy to implement, safe and controllable solution.

A further aspect of the invention makes available a process for making a reinforcing mesh which includes the steps of:

- make a fabric of fibers; And

- make the recognition element made of conductive material adhere to the fiber fabric.

Advantageously, the process can further (but not necessarily) include the step of punching the fiber fabric with the recognition element attached to it, creating a reinforcing mesh disk equipped with at least a portion of a conductive material element attached to it.

Still, a further aspect of the invention makes available a method of manufacturing an abrasive wheel which includes the steps of:

- making a reinforcing mesh with the procedure described above; And

- at least partially incorporate a portion of the reinforcing mesh within an abrasive mixture;

- press the abrasive mixture and the reinforcement mesh incorporated in it; and - heat treating the abrasive mixture and the reinforcing mesh incorporated therein previously pressed.

A further aspect of the invention makes available a control procedure for abrasive wheels which includes the steps of:

- producing an abrasive wheel with the above method; And

- determine the presence of the reinforcing mesh incorporated in it by detecting, by a sensor, the recognition element attached to the reinforcing mesh.

The sensor, as mentioned, can be any sensor suitable for detecting the presence of the recognition element placed (inside) the abrasive wheel (or incorporated within the abrasive mixture that constitutes it).

For example, the sensor can work in various ways, the simplest of which is the inductive type, which detects the magnetic field mutations induced on the conductive material of which the recognition element is composed.

Other sensors and detection methods may provide for detecting the presence of the recognition element by means of thermal vision (thermal imaging camera), having previously subjected the abrasive wheel to a variable high-frequency magnetic field which raised the temperature of the conductive parts only (heating to induction), or only the element of recognition. As known, only conductive materials are heated by induction heating, therefore from the detection of the area that has been heated (most), the presence (or not) of the recognition element is detected (and therefore the presence or absence of the relative reinforcement mesh) not only if it is placed near the surface, or rather a face, of the abrasive wheel but also if it is placed inside it; this is due to the propagation of heat towards the surface of the abrasive wheel itself following the heating of the conductive recognition element.

Other sensors and detection methods may involve the use of (a myriad of) needles that feel one face of the abrasive wheel and when any of them comes into contact with the recognition element of conductive material they allow the electric current to flow along a length of it and, therefore, the measurement of electric current at the ends of the needles. From the measured electric current, the presence (or not) of the recognition element is detected (and therefore the presence or absence of the relative reinforcement mesh is determined).

Other sensors and detection methods may provide for the use of an X-ray sensor, which generates an image of the abrasive wheel crossed by X-rays (commonly called radiography), which allows to identify - in correspondence with each recognition element of conductive material (especially if made of metal) - areas of contrast (for example dark) with respect to the rest of the abrasive wheel. The presence of the recognition element is therefore detected from the identified contrast area (and therefore the presence of the relative reinforcing mesh is determined).

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become evident from reading the following description provided by way of non-limiting example, with the aid of the figures illustrated in the attached tables.

Figure 1 is an exploded view of three embodiments of reinforcement mesh according to the invention, in a possible installation configuration inside an abrasive wheel.

Figure 2 is an axonometric view of an abrasive wheel according to the invention. Figure 3 is a sectional view along a section plane containing the axis of rotation of the abrasive wheel in figure 2.

Figure 4 is a sectional view of a mold for forming abrasive wheels.

Figures 4a-4e are schematic views of a sequence of forming an abrasive wheel, according to the invention.

Figure 5 is a flow chart of a production method of an abrasive wheel, according to the invention.

Figure 6 is a flow chart of a process for making a reinforcement mesh, according to the invention.

Figure 7 is a flow chart of a control procedure for abrasive wheels, according to the invention.

BEST WAY TO IMPLEMENT THE INVENTION

With particular reference to these figures, the numeral 10 globally indicates an abrasive, cutting and / or emery wheel.

The abrasive wheel 10 comprises an annular body 20, provided with a central axis, which annular body 20 is for example substantially flat (see Figures 2-3) or with a depressed center (not illustrated).

The annular body 20 is substantially circular and is provided with a central attachment hole 21 coaxial with the annular body 20.

The attachment hole 21 can be associated, substantially coaxially, with the free end of a rotating shaft of a grinding (or grinding) or cutting-off machine, not shown as it is of a known type.

The annular body 20 comprises two opposite faces 22 and 23, of which a front face 22 and an opposite rear face 23.

In an embodiment, shown in the figures, the faces 22 and 23 are globally parallel to each other and orthogonal to the central axis of the abrasive wheel 20.

In an alternative embodiment, the faces 22 and 23 can be globally inclined to each other, for example they are substantially conical with opposite tapers, for example converging towards the center of the annular body 20 (so-called biconical wheels, used to reduce friction on the sides during cutting).

In general, the front face 22 faces the free end of the rotating shaft of the grinding machine, when the abrasive wheel 20 is fixed to the rotating shaft itself (i.e. the attachment hole 21 is fitted on it), and the rear face 23 faces the grinding machine.

In particular, in depressed-center abrasive wheels, the front face 22 is substantially concave (or has at least one central concave portion) and the rear face 23 is substantially convex (or has at least one central convex portion).

The annular body 20 has a substantially layered structure and has at least one or more layers of abrasive mixture 24.

Each layer of abrasive mixture 24 (once pressed and fired) defines a substantially monolithic body.

For example, each layer of abrasive mixture 24 is made from a mixture of abrasive powders which is compacted and stably bonded by a binder resin.

In practice, the abrasive mixture layer 24 is obtained by pressing a mixture of granules of abrasive material, such as for example natural corundum, sand, recycled artificial corundum or the like, sol-gel or sintered ceramic abrasives, zirconium corundum, or other, and mixed with a suitable binder, for example based on binder resins, for example phenolic, liquid and / or powder resins and possibly modified with phenoxy and / or other epoxy resins, modified with organic and / or vegetable or synthetic compounds , and other types of polyamide resins, etc., and / or with additives and fillers.

For example, the amount of resin is between 8% and 40% by weight with respect to the weight of the powder mixture of abrasive material.

The abrasive material of the layer of abrasive mixture 24 has a particle size substantially comprised between 8 and 180 mesh (the use of abrasive mixtures with a particle size greater or less than the range reported according to requirements is not excluded, however).

The annular body 20 comprises one or more reinforcing nets, globally indicated with the number 30, each substantially incorporated or at least partially incorporated in a layer of abrasive mixture or interposed between them.

In practice, each layer of abrasive mixture 24 (or the layers of abrasive mixture) surrounds (no), in particular axially, the entire surface (lower and / or upper) of each reinforcement mesh 30, or at least a portion (relevant ) of it.

Furthermore, a layer of abrasive mixture 24 can also incorporate more than one reinforcing mesh 30.

Each reinforcing net 30 is shaped like a net disk obtained by punching from a wider net sheet or from a net reel, as will be better described below.

In practice, each reinforcing mesh 30 has a discoidal shape provided with a central hole and preferably has an external diameter substantially equal to (or slightly smaller) than the external diameter of the annular body 20 and an internal diameter substantially equal to (or slightly greater) than the diameter of the attachment hole 21. In some cases the reinforcing mesh 30 may also have an external diameter which is significantly smaller than the external diameter of the abrasive wheel 10 in which it is used.

Each reinforcing net 30 comprises a layer of fiber fabric 31, i.e. a fabric (or non-woven fabric) made with fiber yarns, preferably glass fiber, but other types of fibers could also be used such as carbon fibers, carbon fibers. Kevlar or other material.

The layer of fabric of fibers 31 comprises a pair of opposite faces, of which a first face 310, for example intended to be turned towards the front face 22 of the annular body 20, and an opposite second face 311, for example intended to be turned towards the rear face 23 of the annular body 20.

At least one reinforcing mesh 30 could comprise a sheet 32 (thin), permeable / perforated or non-permeable / non-perforated, which in turn comprises a first face 320, for example intended to face the front face 22 of the annular body 20, and an opposite second face 321, for example intended to be turned towards the rear face 23 of the annular body 20.

The sheet 32 has a thin thickness, preferably less than the thickness of the fabric layer of fibers 31.

Furthermore, the sheet 32 exhibits a stiffness or flexural strength less than the stiffness or flexural strength of the fiber fabric layer 31.

Each sheet 32 is fixed, or made adherent, to a respective layer of fabric of fibers 31.

In particular, at least one of the first face 320 and the second face 321 of the sheet 32 is adherent (and in contact) to at least one of the first face 310 and the second face 311 of the layer of fabric of fibers 31.

The adhesion between the first face 320 or second face 321 of the sheet 32 with the first face 311 or second face 312 of the fiber fabric layer 31 can be achieved by gluing, as will be better described below, for example by means of an adhesive ( or resin) appropriate.

For example, in a first embodiment, the sheet 32 can be made of a polymeric material, for example polyethylene, polypropylene, PVC, nylon, etc ...

Preferably, the reinforcing mesh 30 proximal to the rear face 23 (or back mesh) of the annular body 20 has the sheet 32 made of polymeric material.

The sheet 32, for example, can also be made of dispersed fiber fabric, that is non-woven fabric (called non-woven fabric, TNT, or non-woven in jargon), which can be made, for example, of both synthetic and natural fibers.

Furthermore, the reinforcing mesh 30 proximal to the rear face 23 (or back mesh) of the annular body 20 has the sheet 32 with its first face 320 adherent and in contact with the second face 311 of a respective layer of mesh fabric 31.

In this case, the reinforcing mesh 30 proximal to the rear face 23 (or back mesh) of the annular body 20 is formed by joining a (single) layer of mesh fabric 31 and a (single) sheet 32.

In a second embodiment, the sheet 32 can be made of a paper material.

For example, the sheet 32 is totally closed or provided with through windows or made of a material (paper or synthetic).

For example, the reinforcing mesh 30 proximal to the front face 22 (or head mesh) of the annular body 20 has the sheet 32 made of paper material. Furthermore, the reinforcing mesh 30 proximal to the front face 22 (or head mesh) of the annular body 20 has the sheet 32 with its second face 321 adherent and in contact with the first face 310 of a respective layer of mesh fabric 31.

In this case, the reinforcing mesh 30 proximal to the front face 22 (or head mesh) of the annular body 20 is formed by joining a (single) layer of mesh fabric 31 and a (single) sheet 32.

It is not excluded that both the head and back reinforcement meshes 30 may be associated with a sheet of polymeric or paper material or that, alternatively, the head reinforcement mesh 30 is associated with a sheet of polymeric material and the mesh back reinforcement 30 to a sheet of paper material.

Furthermore, it is not excluded that in a third embodiment, the reinforcement mesh 30 - for example when the reinforcement mesh 30 is intended to be interposed between a back reinforcement mesh 30 and a head reinforcement mesh 30 - present only the layer of fabric of fibers 31, in which both the first face 310 and the second face 311 are free, i.e. they are not adherent and / or in contact with any sheet 32.

At least one reinforcing mesh 30, for example each of them or at least one of them (preferably at least both the head and back reinforcement meshes 30), comprises a recognition element 33 made of conductive material, which is made adherent or fixed to the layer of fiber fabric 31 (in direct contact or not in direct contact with it).

For example, the recognition element 33 has a flat shape (for example ribbon-like) and elongated along a longitudinal axis A, which determines the prevailing size of the recognition element.

For example, the recognition element 33 then has a width, or a first transverse dimension with respect to the longitudinal axis A, prevailing with respect to its thickness, or a second transversal dimension with respect to the longitudinal axis A orthogonal to the width.

For example, the recognition element 33 has a width substantially between 0.3 mm (which substantially corresponds to the detection limit of the sensor used to detect it) up to covering 100% of the surface of the reinforcing mesh 30 to which it is associated.

For example, the recognition element 33 could occupy (in length and / or width) a (limited) portion of the (width of) the reinforcing mesh 30 (and therefore of the abrasive wheel 10 to which it is associated) or extend (in length and / or width) for a prevalent portion of the (width of) reinforcing mesh 30 (and therefore of the abrasive wheel 10 to which it is associated), up to the limit to extend (in length and / or width) for the entire (width of the) reinforcing mesh 30 (and therefore of the abrasive wheel 10 to which it is associated).

the recognition element 33 has a thin thickness, preferably less than the thickness of the fiber fabric layer 31 to which it is attached, and / or for example less than or equal to the thickness of the sheet 32 (where provided).

Preferably, the recognition element 33 (in each of its axial stretches) has a stiffness or resistance to bending which is less than or equal to the stiffness or resistance to bending of the layer of fabric of fibers 31 to which it is fixed, for example less than or equal to the stiffness o flexural strength of sheet 32 (where provided).

the recognition element 33 is preferably deformable in an (exclusively) plastic way, that is, without elastic return or with an elastic modulus substantially null or, in any case, negligible.

the recognition element 33 comprises a first face 330 (substantially parallel to the longitudinal axis A and its width), for example intended to be turned towards the front face 22 of the annular body 20, and an opposite second face 321, to example intended to be turned towards the rear face 23 of the annular body 20.

Each reinforcing mesh 30 (or at least one of them) can comprise a plurality of recognition elements 33, for example arranged in a pre-ordered way, for example in parallel or random strips, preferably lying on a plane parallel to one of the first face 310 and the second face 311 of the fabric layer of fibers 31 or both.

Each recognition element 33 is fixed, or made adherent, to a respective layer of fabric of fibers 31 (and / or to sheet 32 where provided).

In particular, at least one of the first face 330 and the second face 331 of each recognition element 33 is adherent (and in contact or not in contact) to at least one of the first face 310 and the second face 311 of the layer of fiber fabric 31 and / or one between the first face 320 and the second face 321 of sheet 32, where provided.

The adhesion between the first face 330 or second face 331 of the recognition element 33 with the first face 311 or second face 312 of the fiber fabric layer 31 and / or with the first face 320 or the second face 321 of the sheet 32 , where foreseen, it can be made by physical / chemical adhesion and / or gluing, as will be better described below.

For example, in a first embodiment, where a sheet 32 is provided, the recognition element 33 can be interposed between the layer of fiber fabric 31 and the sheet 32, or between the faces in mutual contact of the same.

In this case, the recognition element 33 can be fixed to the mesh fabric layer 31 by means of the same adhesive that fixes the mesh fabric layer 31 to the sheet 32.

In practice, in the first embodiment described above (i.e. in the case of the back reinforcement mesh 30), the recognition element 33 is arranged with its first face 330 adherent and in contact with the second face 311 of the layer of fabric of net 31 and with its second face 331 adherent and in contact with the first face 320 of sheet 32.

In the first embodiment described above (i.e. in the head mesh), the recognition element 33 is arranged with its first face 330 adhering to and in contact with the second face 321 of the sheet 32 and with its second face 331 adhering and in contact with the first face 310 of the mesh fabric layer 31.

Furthermore, it is not excluded that (in the third embodiment and / or in the first and / or second embodiment described above) the recognition element 33 can be fixed to one of the (external) faces of the mesh fabric layer 31 and / or sheet 32 (where applicable).

In particular, in the third embodiment described above, in which the reinforcing mesh 30 is devoid of the sheet 32, the recognition element 33 is fixed to one of the first face 310 or the second face 311 of the mesh fabric layer 31.

Furthermore, it is not excluded that the recognition element 33 may be at least partially intertwined or tied by binding with the fabric that constitutes the mesh fabric layer 31.

In a first embodiment, each recognition element 33 is defined (comprises or consists) of a strip of conductive material, for example, a monolithic strip made of metal.

In a second embodiment, each recognition element 33 is defined (comprises or consists) of a conductive powder (in the form of a strip or dispersion which "colors / impregnates" a part or the entire layer of net fabric 31 and / or of the sheet 32, where provided), for example conveyed by means of a support vehicle, such as for example an adhesive or a resin or other vehicle suitable for the conformation (drafting and realization of a conductive powder strip). In this case, it is possible to deposit the conductive powder, in the form of a strip or any desired pattern, directly on one or both faces 310 and 311 of the layer of net fabric 31 and / or of the sheet 32.

The conductive material with which the recognition element 33 is made is preferably selected from the group consisting (preferably) of aluminum, iron, copper, tin, zinc, lead, titanium, or their alloys as well as carbon, etc ....

Some types of abrasive wheels 10 such as those for cutting (see Figures 2 and 3) can comprise, for example, only a pair of reinforcing meshes 30, of which a head reinforcing mesh 30, as described above, in proximity / correspondence of the front face 22 and a back reinforcement net 30, as described above, in proximity to / correspondence of the rear face 23.

Other abrasive wheels 10 of greater thicknesses, for example from emery (see Figures 4c-4d), could have at least one further intermediate reinforcement mesh 30, for example axially interposed between the head reinforcement mesh 30 and the reinforcement mesh 30 back, which is a reinforcing mesh without the sheet 32 (for example, preferably but not limitedly, provided with the recognition element 33).

Other abrasive wheels 10 could instead have only one (single) intermediate reinforcement mesh 30 without presenting the external reinforcement meshes 30 (i.e. head and back). In this case it is very important to be sure of the presence of the reinforcement mesh 30 in the abrasive wheel 10 itself, failing which the abrasive wheel 10 would become extremely dangerous during use. Each intermediate reinforcement mesh 30, for example, can have a different recognition element 33 (in configuration and / or conductive composition and / or in detectability characteristics) with respect to the recognition element 33 placed in the back or back reinforcement networks 30. head.

An (annular) label can then be applied to the rear face 23 of the annular body 20 of the abrasive wheel 10, in which the technical details of the abrasive wheel itself are reported, in which the label is applied to an annular portion (flat or convex) of the posterior face 23.

Finally, the abrasive wheel 10 comprises one or more annular metal elements, commonly called washers or ring nuts, which delimit the attachment hole 21 of the annular body 20 to the pin of the grinder.

The washer is fixed to the rear face 23 (or to the label) of the annular body 20 and comprises a hollow central tang which is substantially inserted to size in the attachment hole 21 and which has an axial thickness substantially equal to (or slightly less) than the thickness axial of the annular body 20.

In the light of what has been described above, a method M (see Figure 5) for producing an abrasive wheel 10 as described above is the following.

First of all, the aforementioned method M comprises a method P (see Figure 6) for making a reinforcing mesh 30 which can be used for the production of abrasive wheels 10.

The method P for making a reinforcing mesh 30 provides for making (block P1) a sheet of fiber fabric (or a non-woven fabric) starting from a fiber yarn, preferably glass fibers or other material as described above. For example, the step of making the sheet of glass fiber fabric involves making a large sheet or roll, for example with a width greater than 30cm and a length of several meters.

Furthermore, process P could include the step of impregnating the sheet of fabric with fibers of a resin, for example a resin or a solution of liquid resins and solvents.

Subsequently, the process P could include the steps of wringing, for example between pairs of rollers, and drying, in suitable ovens within which the resin dries without completing its polymerization, the impregnated fiber fabric sheet.

The process P could provide, before or after the impregnating step, an adhesion step (block P2) of one or more recognition elements 33 (as described above) made of conductive material, to the sheet of fiber fabric, for example by applying it to one of the faces of the same.

In practice, during the adhesion phase the recognition element 33 is arranged so that one of its faces 330 or 331 is substantially in contact with a face of the sheet of fiber fabric and remains adhered to it.

It is possible that the adhesion phase can be achieved by gluing, for example by means of resins, the recognition element 33 or, alternatively, it is possible that the adhesion phase can be achieved by forming (on site) the recognition element, for example by depositing a recognition element 33 (fluid or semi-solid) on the sheet of fiber fabric.

In particular, it is possible to arrange and make adhere a plurality of recognition elements 33 in the same sheet of fiber fabric, for example randomly or in a predetermined way with a determined distribution pattern, so that in each selected area of the sheet (of equal size or less than an abrasive wheel 10 to be made) at least one recognition element 33 (or a plurality of them) is arranged.

A type of fiber fabric sheets can consist of the aforementioned sheet of fiber fabric and the recognition element 33.

Alternatively, it is possible to complete the sheet of fiber fabric by applying (block P3) a sheet 32 of paper or polymeric material, so as to cover one face of the sheet of fiber fabric.

In one type of fiber fabric sheet, the sheet 32 is a sheet of polymeric material and, in a further type of fiber fabric sheet, the sheet 32 is a sheet of paper material.

In practice, the application of a sheet 32 can be achieved by gluing the sheet 32 on an entire face of the sheet of fiber fabric, for example using the resin or the solution of resins with which the sheet of fiber fabric is impregnated as an adhesive. , and laminating the defined layer structure in suitable laminating rollers.

The application phase of the sheet 32 can preferably take place simultaneously or subsequently (or at least previously) to the adhesion phase of the recognition element 33.

The step of application of the sheet 32 can provide for closing (with a vice) the recognition element 33 between the sheet 32 and the sheet of fiber fabric 31.

However, it is not excluded that the adhesion step may take place in a different way, i.e. by applying the recognition element 33 on one face of the sheet 32 (before or after it has been applied to the sheet of fiber fabric). .

When the sheet of fiber fabric has been added with the recognition element 33 and, optionally, with the paper or polymeric sheet 32, and has been suitably partially polymerized (so that the resin that impregnates it is not sticky, but is not even totally polymerized), it is possible to collect the same in reels, at least one for each type of reinforcing mesh to be made.

Process P, therefore, provides for punching (block P4) the sheet or reel of fiber fabric to which the recognition element 33 (and any sheet 32) has been adhered, so as to form one or more disks reinforcement mesh, suitably shaped.

Each punching, or each reinforcing mesh disk, is such as to include, circumscribe or intersect at least a respective portion of a recognition element 33, which remains defined on the reinforcing mesh 30 which defines the reinforcing mesh disk itself.

At this point the process P can be said to be concluded and the method M can proceed with the actual formation of an abrasive wheel 10, for example by forming and pressing in a suitable mold.

By way of example, a mold for forming (see Figure 4) of abrasive wheels 10 comprises a die matrix adapted to oppose a punch for forming the abrasive wheel 10.

The mold matrix for example comprises a cylindrical jacket which is closed at the bottom by a bottom wall.

In practice, the bottom wall comprises a discoidal body with a circumferential base and for example made of metal material suitable, for example, to be inserted substantially to size inside the cylindrical jacket.

The back wall and the cylindrical jacket define an open molding chamber.

Advantageously, the bottom wall can be associated slidingly with respect to the cylindrical jacket so as to be able to vary the internal volume of the forming chamber, in practice by varying the axial position of the bottom wall with respect to the cylindrical jacket.

The bottom wall has in the center a centering pin rising from the upper face of the same and coaxial with the cylindrical jacket.

The centering pin, in particular, is inserted in a central hole made in the bottom wall and fixed or floating there.

The upper face of the bottom wall can be substantially planar if a flat abrasive wheel 10 is to be made.

The upper face of the bottom wall preferably comprises a central depression coaxial to the bottom wall itself, suitable for defining a central basin, so as to define as a whole a concave bottom wall for the formation of abrasive wheels 10 with a depressed center.

In any case, the bottom wall defines a support surface for the abrasive wheel 10 to be formed substantially orthogonal to the axis of the cylindrical jacket. The punch, for example, comprises an annular / disc-shaped body whose external diameter is substantially equal to the external diameter of the bottom wall of the mold matrix (i.e. slightly less than the internal diameter of the cylindrical jacket), so that it can be substantially inserted to measure in the cylindrical jacket and be superimposed on the back wall itself.

If an abrasive wheel 10 with a depressed center is to be formed, the punch comprises a shape complementary to the bottom wall.

Furthermore, in this case the punch can be made in a monolithic body or with two concentric and separate annular bodies adapted to be axially actuated independently for the independent formation of the external and internal periphery of the abrasive wheel 10.

The punch and the bottom wall are movable towards each other towards / away from each other, respectively for the closing / opening of the forming chamber, as known to those skilled in the art.

The M method, therefore, provides that initially, for example, the washer with the central hollow tang rising from the back wall itself.

Subsequently, where required, the label is placed on the back wall and / or on the washer.

Subsequently, a back reinforcement mesh 30 (for example as described above) is inserted (block M1 and Figure 4a) into the forming cavity, for example resting on the back wall (directly or with the interposition of the label).

In practice, the back reinforcing mesh 30 is obtained by punching from the type of reinforcing mesh 30 which comprises, in addition to the reinforcing mesh layer 31 (portion of the reinforcing mesh sheet), at least one recognition element 33 therein. arranged and, optionally, a sheet 32 (for example made of polymeric material).

The back reinforcing mesh 30 is placed with the second face 321 of the sheet 32 resting (directly or indirectly) on the bottom wall of the forming cavity (ie proximal to it).

The back reinforcing mesh 30 is inserted on the centering pin, so that it is substantially coaxial with the forming cavity.

One (first) layer of abrasive mixture 24 (i.e. one rear layer), for example, so as to completely cover and incorporate the back reinforcement mesh 30 and fill (for a predetermined thickness) the forming cavity

In practice, the amount of abrasive mixture that forms the abrasive mixture layer 24 fills the forming cavity for an axial thickness which exceeds the level of the first face 310 of the mesh fabric layer 31 of the back reinforcing mesh 30, so that the latter is completely incorporated into the layer of abrasive mixture itself.

If the system and the method of forming the abrasive wheel 10 provide for a single station for depositing the abrasive mixture, i.e. the abrasive wheel 10 has a single layer of abrasive mixture, the method M proceeds with the arrangement (block M4 and figure 4e ) a head reinforcement mesh 30 on the layer of abrasive mixture which has just been deposited.

In practice, the head reinforcing mesh 30 is obtained by punching from the type of reinforcing mesh 30 which comprises, in addition to the reinforcing mesh layer 31 (portion of the reinforcing mesh sheet), at least one recognition element 33 therein. arranged and, preferably, a sheet 32 (for example made of paper material).

The back reinforcing mesh 30 is placed with the first face 320 of the sheet 32 facing away from the bottom wall of the forming cavity (ie distal to it).

The back reinforcement mesh 30 is also inserted on the centering pin, so that it is substantially coaxial with the forming cavity.

At this point, method M proceeds with pressing (block M5) the reinforcing nets 30 (back and head) and the layer of abrasive mixture 24 between them interposed in the forming cavity to obtain the abrasive wheel 10 ( raw semi-finished product) of the desired shape (flat or depressed center).

The pressing takes place by the action of the reciprocal approach between the punch and the back wall.

The method of forming by pressing single abrasive wheels 19 described above is not to be construed as limiting, in fact, this method M could foresee the inversion of the sequence of the steps described above for the realization of the abrasive wheel 10 or it could lack one of the steps described , or it could envisage inserting a single central reinforcing mesh 30 inside the compound.

The constructive configurations of the abrasive wheels 10 are in fact multiple (only external reinforcement meshes, external reinforcement meshes and internal mesh reinforcement, only internal reinforcement meshes, only one internal reinforcement mesh, more internal reinforcement meshes, etc ...) but in any case, however, the present method provides for inserting at least one reinforcing mesh 30 on at least one of the two faces of the abrasive wheel or at least one reinforcing mesh 30 inside the abrasive wheel 10 in the position deemed most suitable for the functionality of the product and the reinforcement mesh (if one) or the reinforcement mesh (if more than one) detectable by sensors as described below.

Again, alternatively the method M could provide for the production of the individual abrasive wheels 10 by means of a different methodology, which could present a first phase of formation (for example by pressing and / or rolling) of a (large) sandwich structure made of an overlap of reinforcing nets 30 (in the many types of sequences described above) and one or more layers of abrasive mixture 24 (as described above).

This first phase leads to the formation of a large plate (circular or quadrangular or of any desired shape) or a roll consisting of this sandwich structure (raw semi-finished product).

Furthermore, this methodology comprises a subsequent second phase of punching the (large plate or roll) sandwich structure to obtain single abrasive wheels 10, each equipped with at least one (portion of the) reinforcing mesh 30 and, therefore, with at least a (stretch of) identification element 33.

The washers and other elements for finishing and identifying the abrasive wheel itself can then be optionally applied to each of these individual abrasive wheels 10.

It is clear that the present invention is also applicable to the aforementioned alternative methodology, since at least one reinforcing mesh 30 can be of the type described above, or equipped with the respective recognition element 33 of conductive material.

If, on the other hand, the molding method and plant envisages two, three or more sequences of abrasive powder deposition, i.e. the finished abrasive wheel 10 must have several layers of overlapping abrasive material (for example it was an abrasive grinding wheel for emery), before subjecting the abrasive wheel 10 to pressing and firing, one proceeds with the insertion (block M3 and figure 4c) of at least one further intermediate reinforcement mesh 30 of further layers of abrasive mixture (see figure 4d) which will contribute (once superimposed) to form an intermediate layer of abrasive mixture of the annular body 20.

In practice, the intermediate reinforcing mesh 30 is obtained by punching from the type of reinforcing mesh 30 which comprises the reinforcing mesh layer 31 (portion of the reinforcing mesh sheet) and possibly only the recognition element 33 arranged therein, being devoid of sheet 32.

The intermediate reinforcement mesh 30 is also inserted on the centering pin, so that it is substantially coaxial to the forming cavity.

Finally, the abrasive wheel 10 thus formed is subjected to a firing heat treatment (block M6), for example in special polymerization ovens, in which the polymerization of the binder resin is completed, which stably solidifies and retains the abrasive mixture that constitutes the wheel. abrasive itself (or the disc-shaped body that constitutes it) and / or the resins that impregnate the reinforcement meshes 30. In the case of abrasive wheels 10 obtained by die-cutting from a pressed mold or from a laminated roll, the die-cutting of the abrasive wheels themselves can be done also following the polymerization cycle without modifying the advantages deriving from the use of reinforcing nets 30 equipped with a recognition element 33.

In practice, the abrasive wheel 10 is subjected to a thermal cycle which involves its insertion in an oven at a temperature substantially comprised between 70 ° C and 220 ° C for a time substantially comprised between 1 minute and 100 hours, or it can be cooked in situ in the same mold, if it is re-welded. Once the abrasive wheels 10 (semi-finished raw or cooked) have been formed, it is possible to proceed by means of a control procedure C (see figure 7) to check if the abrasive wheel 10 complies with safety standards, in particular if the reinforcement meshes 30 of the abrasive wheel 10 are actually present inside the annular body 20 of the abrasive wheel 10.

The control procedure C is a preferably automatic procedure to grasp all the derived advantages, which provides for having at least one sensor, such as an inductive sensor, a thermal imager, and / or an X-ray sensor or a needle probe. feelers, or the like, operatively connected to an electronic control unit, which is configured to operate a selector or a signaling device which selects or signals the abrasive wheels 10 found not conforming to the standard.

In particular, the control procedure C provides for advancing (block C1) the abrasive wheel 10 along a direction of advancement, for example resting on a front face 22 or on a rear face 23 and / or while they rotate axially or roll on the lateral mantle.

During the advancement of the abrasive wheels 10 they enter a control station, in which the at least one aforementioned sensor is arranged, which is arranged with a detection axis substantially orthogonal to the front face 22 or to the rear face 23 of the abrasive wheel 10 and in an eccentric position (ie arranged at a distance from the axis of the attachment hole 21 of the abrasive wheel 10 greater than the outer diameter of the washer).

In practice, the sensor is configured to selectively detect (block C2) a recognition element 33 fixed to a reinforcing mesh 30 (back, head or intermediate).

Preferably, it is possible to choose the type of sensor according to the type (or material) of the recognition element 33 to be identified.

For example, some conductive materials (such as iron and aluminum) are more suitable for being detected by an inductive sensor, other conductive materials (such as iron) are more suitable for being thermally detected by a thermal imager, other conductive materials (such as those having a higher atomic weight, see copper, lead and tin) are more suitable to be detected with X-ray identification by means of an X-ray sensor; finally, all conductive materials are suitable for being detected by electrical probing and measurement of the relative electrical conduction, by means of a probe with feeler needles.

Furthermore, the control procedure C provides for determining (block C3) the presence of the reinforcing mesh 30 when the recognition element 33 fixed to this reinforcing mesh 30 is detected.

For example, to determine the presence of the back or head reinforcement mesh 30, the sensor could be an inductive sensor (also called micro), which detects the presence of the recognition element 33 when it is within a predetermined distance. detection by the sensor itself.

In practice, the sensor is placed at a predetermined distance from the front face 22 or from the rear face 23 so that its detection distance allows to detect the reinforcement mesh 33 directly facing the sensor but not the reinforcement mesh 33 present on the sensor. opposite face as it is too distant from it.

To discriminate between the back and head reinforcement mesh 30 it is sufficient to adopt two sensors facing the two faces of the abrasive wheel 10 and axially opposite each other. The method thus becomes perfectly selective since it allows to detect with absolute precision the presence of the two head and back (external) reinforcement nets 33 independently.

Alternatively, it is possible to provide for the use of different sensors, also in combination with each other such as X-ray sensors or thermal sensors or other to detect the conductive recognition element 33.

For example, to determine the presence of the external or intermediate reinforcement mesh 30, the sensor could be a sensor or an X-ray radiographic machine, which detects, by means of suitable software, the presence of the recognition element 33 of the mesh. reinforcement 30 (made of a conductive material having an atomic weight greater than the prevailing atomic weight of the recognition element 33 of the head and back reinforcement meshes 30 and / or of the material composing the abrasive mixture).

Another example of a sensor to determine the presence of the conductive recognition element associated with the external or intermediate reinforcement mesh 30, may be a thermal imaging camera, which detects the presence of the recognition element 33 suitably heated by induction. This is an indirect detection, that is, by detecting the heat generated by the recognition element 33 which, subjected to induction heating, increases its temperature and by thermal conduction also that of the part of the abrasive wheel 10 in which it lies. The inductive heating can also be modulated with a suitable choice of the conductive material, generating in a pre-selected reinforcement mesh 30 a much greater heating than that generated by the always conductive material of which the recognition elements 33 of the other reinforcement networks present in the abrasive wheel 10. The heating in fact depends on the Joule effect which is directly proportional to the specific resistance of the conductive material so that a less conductive material will heat up a lot while a very conductive one will heat less.

By using a conductive material which heats a lot on a reinforcing mesh 30 and another conductive material which heats very little on the other reinforcing mesh (s) 30, the chosen reinforcement mesh 30 can be clearly highlighted. The heat generation can therefore be easily detected by means of a thermal imager and recognized by means of an appropriate software or even directly by an operator who looks at the image generated by the thermal imager.

The other reinforcing mesh (s) 30 present in the abrasive wheel 10 and equipped with a conductive recognition element 33 can then be selectively identified with the other methods (eg X-rays or inductive sensor).

It is therefore not excluded that a sensor of the thermal imaging camera or X-ray (or other) type may be used to detect the recognition element 33 of a back and / or head reinforcement mesh 30 or, vice versa, that a inductive type can be used to detect the recognition element 33 of an intermediate reinforcement network 30.

Alternatively or in addition, to determine the presence of the back or head reinforcement mesh 30, the sensor could be a probe with feeler needles (which for example comprises a myriad of conductive needles which feel one face of the abrasive wheel 10) .

When the feeler needle probe, or its needles, comes into (electrical) contact with the recognition element 33 of conductive material of a reinforcing mesh 30 proximal to the touched face, the electrical circuit of the feeler needle probe closes and the electric current is allowed to flow along the recognition element 33, allowing to measure - by means of the electronic control unit - the intensity of this electric current.

From the measured electric current intensity, the presence (or not) of the recognition element 33 is detected and therefore the presence or absence of the relative reinforcement net 30 is determined.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept, as claimed below.

Claims (17)

CLAIMS 1. A reinforcement mesh for abrasive wheels which includes: - a fabric or non-woven fabric of fibers; And - at least one recognition element made of conductive material adhered to the fiber fabric. The reinforcing mesh according to claim 1, wherein the recognition element comprises at least one strip of conductive material elongated along a longitudinal axis, and provided with a transversal width with respect to the longitudinal axis prevailing with respect to a thickness thereof, preferably between 0.3 mm up to cover 100% of the surface of the reinforcing mesh to which it is associated. 3. The reinforcing mesh according to claim 1, in which the recognition element has a flexural strength less than or equal to the flexural strength of the fiber fabric. 4. The reinforcing mesh according to claim 1, in which the conductive material is selected from the group among aluminum, iron, copper, zinc, titanium, lead, tin, nickel, tungsten, magnesium, lithium, chromium and carbon or any other element of a metallic nature present in the periodic table of the elements. The reinforcing mesh according to claim 1, which comprises a sheet having a face adhering to a face of the fiber fabric. 6. The reinforcing mesh according to claim 5, in which the recognition element is interposed between the face of the fiber fabric and the face of the sheet. The reinforcing mesh according to claim 5, wherein the sheet is made of a polymeric material. The reinforcing mesh according to claim 5, wherein the sheet is made of a paper material. 9. The reinforcing mesh according to claim 1, in which a thickness of the recognition element is less than or equal to a thickness of the fiber fabric. The reinforcing mesh according to claim 1, which comprises a plurality of recognition elements distributed on one face of the fiber fabric. 11. The reinforcing mesh according to claim 1, in which the recognition element is obtained by depositing on the fiber fabric of at least one conductive powder, preferably along a strip elongated along a longitudinal axis, and having a transverse width with respect to the longitudinal axis prevailing with respect to its thickness. 12. The reinforcing mesh according to claim 1, in which the recognition element is deformable in a plastic way. 13. An abrasive wheel which includes: - an abrasive mixture; And - at least one reinforcing mesh according to claim 1, in which the reinforcing mesh is at least partially incorporated within the abrasive mixture. 14. A process for the creation of a reinforcement mesh which includes the steps of: - make a fabric of fibers; And - making a recognition element made of conductive material adhere to the fiber fabric. 15. The method according to claim 14, which further comprises the step of punching the fiber fabric with the recognition element adhered to it, realizing a reinforcing mesh disk equipped with at least a portion of the recognition element made of conductive material adhered to it. 16. A method of manufacturing an abrasive wheel which includes the steps of: - making a reinforcing mesh with the process according to claim 14; And - at least partially incorporate a portion of the reinforcing mesh within an abrasive mixture; - press the abrasive mixture and the reinforcement mesh incorporated in it; and - heat treating the abrasive mixture and the reinforcing mesh incorporated therein previously pressed. 17. A control procedure for abrasive wheels which includes the phases of: - producing an abrasive wheel with the method according to claim 16; and - determine the presence of the reinforcing mesh incorporated therein by detecting, by a sensor, the recognition element attached to the reinforcing mesh.