EP1231022B1

EP1231022B1 - Apparatus for polishing and conveying products

Info

Publication number: EP1231022B1
Application number: EP02002163A
Authority: EP
Inventors: Fabio Corradini
Original assignee: Ancora SpA
Current assignee: Ancora SpA
Priority date: 2001-02-01
Filing date: 2002-01-29
Publication date: 2008-09-24
Anticipated expiration: 2022-01-29
Also published as: EP1231022A3; DE60229015D1; EP1231022A2; ATE409099T1

Abstract

An apparatus for polishing products (3) having a flat supporting base, in particular unfired ceramic tiles, comprises moving means (2) suitable for advancing said products (3) along an advancing direction (F), operating head means (13) provided with abrasive disc means (14) suitable for machining an outer surface of said products (3) and further operating head means (35) provided with further abrasive disc means (36); said abrasive disc means (14) and/or said further abrasive disc means (36, 23) may have a continuous band (24) of abrasive material. An apparatus for conveying objects (3) with flat supporting base comprises conveying means (102) suitable for moving said objects (3) along an advancing direction (F) and guiding means (106) which can be operatively associated with said conveying means (102) and suitable for guiding said objects (3) along said advancing direction (F); said guiding means (106) can be removably fixed to said conveying means (102). <IMAGE>

Description

The invention relates to an apparatus for polishing flat ceramic products, for example tiles or slabs made of porcelain stoneware.
The invention further relates to an apparatus for conveying objects having a flat supporting base, in particular ceramic tiles along a conveying line during a step of the production cycle.
Machine tools are known which are fed with tiles that have already been fired in kiln, so that such tiles can be treated on the surface thereof by means of abrasive or cutting tools, through which the tiles are subjected to polishing on the face that will be visible after tile laying.
The above mentioned polishing machine tools are provided with cooling means for cooling the interface region between tool and tile, said cooling means consisting of jets of lubricant-coolant liquid, in particular water, which completely floods the surface of tiles to be worked. The liquid jets can be manually positioned quite roughly and exaggerated water flows are therefore required, to be sure that the working surface is properly sprayed.
This implies a drawback consisting in a high production of sludge, containing particles of ceramic material removed from tiles suspended in the cooling liquid.
Therefore, expensive and bulky systems for purifying such sludge are needed, said systems comprising many sludge settling tanks and requiring long sludge treatment times and preparation of appropriate stonework.
For at least partially overcoming the above described drawbacks, polishing devices have been developed, said polishing devices being suitable for treating "green" tiles, i.e. pressed and dried, but not yet fired tiles.
The Italian Patent for industrial invention no. 1.269.384 discloses a polishing machine, particularly for ceramic tiles made of porcelain stoneware, comprising a first polishing unit and a second polishing unit, consecutively arranged, through which said tiles are advanced along a pre-established direction by means of a conveyor belt of a conveying line.
The first polishing unit is provided with a polishing tool having cylindrical shape and advantageously made of abrasive material, said polishing tool being positioned above the conveyor belt so as to interact with the surface of the tiles carried by the conveying line.
The tool is rotationally supported by a supporting frame so as to be able to rotate around a respective longitudinal axis arranged perpendicularly to the advancing direction of the tiles.
The second unit is provided with a further polishing tool having the shape of a disc, also advantageously made of abrasive material.
The further tool is positioned above the conveying line and is rotated by a motorized shaft arranged substantially in a vertical position: thus, the further tool can interact with the upper surface of the tiles removing from said tiles part of the material forming the tiles for obtaining on each tile a polished surface.
The second unit further comprises, at the active surface of the disc shaped tool, a conduit suitable for blowing pressurized air, arranged for removing from said active surface the powders generated during the polishing operations.
To make expelling such powders easier, the disc shaped tool is obtained by mutually placing side by side a plurality of abrasive sectors so that the escapes between a sector and the adjacent ones form a preferred path for the outflow of the pressurized air.
A drawback of such machine is that, if the cylindrical tool of the first unit is rotated around a rotation axis that does not exactly coincide with its geometrical axis, polished tiles are obtained having a non perfectly flat upper face. In particular, if the cylindrical tool rotates in a slightly eccentric manner, the resulting tiles may be provided with a face that is to be visible after laying, the surface of which has a series of undulations consisting of a plurality of protrusions alternated with a respective plurality of depressions.
Another drawback of the above described machine consists in that the cylindrical tool can comprise, at one or more points of the active surface thereof, grains of abrasive material having particular hardness that produce, on the tiles with which said grains come into contact, grooves extending longitudinally through the whole extension of the tiles. Said groove can compromise the aesthetical properties of the tiles, sometimes even making said tiles unusable for being laid.
In addition, particles of material removed from a transiting ceramic product can remain "trapped" between the tile surface and the portion of the tool interacting with said tile, causing scratch defects similar to those described above. Such defects are particularly evident if the removed particles have significant size and/or particular hardness.
A further drawback of the machine disclosed in IT 1.269.384 consists in that the disc shaped tool of the second polishing unit tends to adhere to the ceramic supports with which it interacts, since the pressurized air flowing through the escapes arranged between an abrasive sector and the adjacent ones is subjected to a centrifugal motion and tends, therefore, to create a depression between the tool and the underlying tiles. Said depression keeps the tiles attached to the tool. Thus, a "suction cup" effect is created between the tile face and the tool active surface, which makes difficult transferring the tiles on the conveying line, particularly when said tiles leave the second polishing unit. This can cause damage, or breakage of the tiles, which are quite brittle since they have not yet been fired.
Prior art comprises apparatuses for conveying ceramic tiles comprising a conveyor belt whereon the tiles that are to be moved along an advancing direction lie. The conveyor belt is wound on a pair of end rollers, one of which is motorized by suitable actuating means. The apparatuses for conveying ceramic tiles further comprise adjustable guiding tapes performing a lateral guiding function for the tiles and enabling tiles of different size to be moved. Said guiding tapes lie on the two peripheral regions above the plane defined by the conveyor belt so as to leave uncovered a central portion of such belt. Such portion can be used for moving the tiles. Said guiding tapes rest on the conveyor belt along the whole plane involved in moving the tiles and are wound on a portion of the end rollers, always remaining in contact with such conveyor belt. The apparatus further comprises a roller driven independently from said conveyor belt, such roller enabling said tapes to move at a peripheral speed exactly equal to the conveyor belt speed.
When the apparatus has to be adjusted to change from conveying tiles having a certain transverse dimension with respect to the advancing direction to conveying tiles of a different transverse dimension, it is necessary to replace said pair of guiding tapes with another pair of tapes of different width, allowing a central portion of the conveyor belt, having a width exactly equal to the width of the tiles that it is desired to move, to be left uncovered.
Alternatively, it is possible to change the width of the central portion of conveyor belt suitable for moving the tiles by varying the position of one or both the guiding tapes, i.e. by moving the guiding tapes closer to, or away from, a symmetry plane of the conveyor belt parallel to the tile advancing direction.
A drawback of such apparatus consists in that it requires a pair of driving devices, the first of which is arranged for actuating the conveyor belt, the second for moving the guiding tapes. That causes a significant increase of the apparatus costs, and multiplies the breakage risks and the maintenance charges.
A further drawback consists in that, if the apparatus has to be adjusted for changing the size of the tiles to be conveyed, the guiding tapes have to be removed and then repositioned, or replaced with other guiding tapes of suitable width, which implies a decrease in the machine efficiency and a loss of productivity.
It is known from EP-0879677 a planing machine provided with one drive head for planing tiles translated by a planing line comprising a slat conveyor belt formed by a plurality of slats constrained one consecutively to another by flexible joints. A wheel, on which the slat conveyor belt is partially wound, can be displaced with a vertical direction component. A cam, solidly associated to the wheel, rests on a fixed roller, and is shaped so that a flexible joint joining a first slat interacting with the wheel and an adjacent slat not interacting with the wheel is not subject to vertical displacements.
It is known from DE-4436336 a method which involves tiles being automatically placed and fixed in a position in which they are clamped between a conveyor and pressure piece. The tiles are then conveyed through at least two spaced apart planing units. The positions of the free ends of the planes are continuously checked by optical sensors during operation. Their nominal and actual positions are compared and the result is converted into control impulses.
A first purpose of the present invention is to improve the apparatuses for polishing unfired flat ceramic products.
A second purpose of the invention is to provide an apparatus for polishing unfired flat ceramic products that is provided with high productivity.
A third purpose of the invention is to provide an apparatus which allows unfired polished, flat ceramic products having a very high surface finishing level to be obtained.
A fourth purpose of the invention is to provide an apparatus for polishing unfired flat ceramic products, said apparatus allowing finished products having a visible face substantially free from scratching defects to be obtained.
A fifth purpose of the invention is to obtain a polishing apparatus for unfired ceramic products wherein transferring such products through the working units is not compromised by the action of the abrasive means.
A sixth purpose of the present invention is to improve the apparatuses for conveying objects with flat supporting base, in particular ceramic tiles.
A seventh purpose of the invention is to provide an apparatus for conveying objects with flat supporting base wherein said objects are precisely guided along their path.
An eighth purpose of the invention is to provide an apparatus for conveying objects with flat supporting base wherein the mechanical components are subjected to less heavy working conditions.
A ninth purpose of the invention is to make less onerous and quicker adjusting the line in case of size change of the objects to be conveyed.
In a first aspect of the invention, an apparatus is provided for polishing products as defined by the features of claim 1.
Owing to this aspect of the invention, it is possible to obtain an apparatus allowing the surface of the visible face of unfired ceramic products to be uniformly polished. The presence on said surface of defects such as grooves or scratches can thus be limited.
In a preferred version, the apparatus is provided with adjusting means arranged for controlling the pressure exerted on the ceramic products by the operating head means and by the further operating head means. Thus, it is possible to polish ceramic products which are not fired, and therefore highly brittle, without causing the damage or breakage thereof.
In a further preferred version, the adjusting means consists of a detecting device for detecting the electric current absorbed by a motor coupled with a spindle shaft supporting the abrasive disc means, or the further abrasive disc means, such device being suitable for sending an electric signal to an actuator coupled with the spindle shaft in order to change the axial position thereof and, respectively, to change the pressure of the abrasive disc means, or of the further abrasive disc means, on the ceramic supports.
In a second aspect of the invention, an apparatus is provided for polishing products, in particular unfired ceramic tiles, comprising operating head means provided with abrasive disc means suitable for machining an outer surface of said products, characterized in that, said abrasive disc means has a continuous band of abrasive material.
Advantageously, moving means is provided suitable for advancing said products along an advancing direction so as to bring said products into an operating configuration below said abrasive disc means.
Owing to this aspect of the invention, it is possible to obtain an apparatus for polishing unfired ceramic products, wherein the interaction between the operating head means and the ceramic products does not hinder the transferring of said ceramic products on and away from said moving means.
In a third aspect of the invention, tool means is provided arranged for polishing products, in particular unfired tiles, comprising abrasive disc means suitable for interacting with an outer surface of said products, characterized in that, said abrasive disc means has a continuous band of abrasive material.
Owing to this aspect of the invention, it is possible to obtain a polishing tool that does not tend to adhere to the surface of the products which it contacts during the polishing operations.
Owing to this aspect of the invention, it is possible to obtain an apparatus for conveying objects having a flat supporting base wherein the guiding means may be easily and rapidly repositioned.
In a preferred version, said guiding means comprises fixing means which can be associated with coupling means with which said conveying means is provided.
In a further preferred version, said coupling means is obtained in said conveying means so as to define a plurality of rows arranged parallel to said advancing direction.
Such rows are spaced by pre-established distances, said distances being chosen so as to allow objects belonging to a wide range of sizes to be moved.
Thus, for adjusting the apparatus so as to change from conveying objects having a certain transverse dimension to conveying objects having a different transverse dimension, it is sufficient to remove said fixing means from the coupling means with which said fixing means is associated, and to couple said fixing means with coupling means of a different row after having repositioned the guiding means.
In a still further preferred version, said guiding means comprises a plurality of curb means successively arranged at a pre-established distance one from another.
Thus, the guiding means are quite flexible and therefore the risks of damaging and breaking said guiding means when it is arranged along non rectilinear trajectory, for example when it is wound around rollers, are remarkably reduced.
In a fifth aspect of the invention, conveyor belt means is provided comprising coupling means arranged for removably coupling with guiding means suitable for guiding said objects along an advancing direction.
In a sixth aspect of the invention, guiding means is provided which can be operatively associated with conveyor belt means for guiding objects having a flat base resting on said conveyor belt means, comprising fixing means suitable for removably fixing said guiding means to said conveyor belt means.
The invention will be better understood and carried out with reference to the attached drawings, that illustrate some not restrictive embodiments thereof, wherein:

Figure 1 is an elevation, side view of a polishing apparatus according to the invention;
Figure 2 is a top view of the polishing apparatus of Figure 1;
Figure 3 is an enlarged interrupted cross section taken along a plane III-III of Figure 1;
Figure 4 is a front view of the abrasive disc means of the polishing apparatus of Figure 1;
Figure 5 is a top view of a conveying apparatus according to the invention;
Figure 6 is an enlarged and interrupted section, taken along a vertical plane, of the conveying means and the guiding means of the transporting apparatus of Figure 5 according to a particular construction mode;
Figure 7 is a section like Figure 6, showing the conveying means and the guiding means made according to a further construction mode.

With reference to Figures 1 and 2, a polishing apparatus 1 is shown, comprising a conveying line 2 arranged for advancing ceramic tiles 3 along an advancing direction indicated by the arrow F. The conveying line 2 comprises a conveyor belt 4 wound on a pair of end rollers 5, one of which is motorized, the conveyor belt 4 extending between a removal line 6 for removing the tiles 3 from a pressing station, or from a drying station, and a transferring line 7 for transferring said tiles towards the firing kiln.
The polishing apparatus 1 comprises a first polishing unit 8, supported by a frame 9 by means of a bridge support 10 extending above the conveying line 2, and a second polishing unit 11, positioned upstream of said first unit 8 with respect to the advancing direction of the tiles 3 and similarly supported by the frame 9 by means of a respective further bridge support 12.
The first polishing unit 8 is provided with a polishing head 13 comprising a disc shaped polishing tool 14, advantageously consisting of abrasive material, possibly comprising diamond inserts. The polishing tool 14 is fixed to a spindle 15 by means of a support 16, having a section corresponding to the section of the polishing tool 14. The support 16 is coupled to the free end of a shaft 17 of the spindle 15: the other end of said shaft 17 being coupled with an electric motor 18.
The end of the shaft 17 coupled to the support 16 is provided with a cavity 19 intended to receive pressurized air through an annular fitting 20, or rotating joint, peripherally rotationally coupled with such shaft: it is noted that inserting pressurized air through the annular fitting 20, as shown by the arrow F1, allows the polishing powders to be removed from the working region.
It is further noted that the belt 4 is slidingly supported by a sliding plane 21 which is part of the frame 9 of the polishing apparatus 1, a layer 22 of anti-wear material being possibly arranged therebetween, said layer 22 being removably coupled with said sliding plane 21.
As shown in Figure 4, the polishing tool 14 comprises grinding wheel means 23 so shaped as to have a continuous annular band 24 of abrasive material.
Since the surface of the grinding wheel means 23 is free from radially arranged grooves or escapes and since pressurized air flows out of the cavity 19, phenomena of adhesion of the polishing tool 14 to the tiles 3 are prevented. Thus the tiles 3 can more easily exit from the first unit 8 when the polishing operations are over without being subject to damages or breakage.
The shaft 17 is rotatably supported by a sleeve 25, which can slide vertically in a guiding case 26 connected to the bridge support 10.
At the upper end of the sleeve 25 a plate 27 is fixed, a height adjusting device 28 for adjusting the height of the polishing tool 14 being supported by said plate 27.
As shown in Figure 3, the device 28 comprises a plate 27 fixed to the upper end of the sleeve 25, said plate 27 being laterally provided with an extension 30 provided with a seat for rotatably coupling with a positioning screw 31, extending parallel to the sleeve 25: said screw 31 being actuated by a gear motor unit 32, supported by the plate 27.
The positioning screw 31 is engaged with a nut screw 33 inserted into a seat housed into a block 29 connected to the case 26.
The control of the gear motor unit 32 is obtained by means of an electric signal proportional to the absorption of the motor 18, so that, when such absorption exceeds a pre-established threshold value, the gear motor unit 32 acts on the screw 31 to raise the polishing tool 14: thus it is also possible to polish brittle supports, without causing their undesired damages or breakages.
The polishing unit 8 is provided with suction hoods 34 coupled with vacuum means 34, not shown, for removing the polishing powders, as shown by the arrow F2.
The second polishing unit 11 is provided with a further polishing head 35 comprising a further disc shaped polishing tool 36, substantially equal to the disc shaped polishing tool 14 of the polishing head 13.
As far as the construction details are concerned, the further polishing head 35 is exactly similar to the polishing head 13; a corresponding similarity can be found also between the respective operations.
In particular, the further polishing head 35 is provided with a further height adjusting device 28a for adjusting the height of the disc shaped polishing device 36, said further height adjusting device 28a being carried out in the same manner as the adjusting device 28 described with reference to Figure 3.
Finally, similarly as described with reference to Figure 4, the further polishing tool 36 is made so as to have a continuous annular band of abrasive material.
In Figures 5, 6 and 7 a conveying apparatus according to the invention is shown, suitable for being associated with the polishing apparatus described above, so as to work as conveying line 2.
With reference to Figure 5, a conveying apparatus 101 is shown comprising conveying means 102 arranged for conveying ceramic tiles 3 along an advancing direction indicated by the arrow F. The conveying means 102 comprises a conveyor belt 104 wound on a pair of end rollers 105, one of which is motorized. Each of such end rollers has an outer cambered surface 105a, i.e. such that the diameter of the roller measured on the centreline is slightly greater than the diameter measured of the end sections. This allows the belt 104 to be kept centred on said rollers 105, preventing the translation of said belt 104 in a transverse direction with respect to the advancing direction F.
The conveying apparatus 101 further comprises guiding means 106, capable of being removably associated with the belt 104 and arranged for guiding the tiles 3 during the conveying operations.
The guiding means 106 comprises a plurality of mutually aligned curbs 107. Each curb is spaced from the adjacent curbs 107 by a pre-established distance. Thus, when the belt 104 winds on the end rollers 105, the curbs 107 fixed to said belt 104 are free to elastically deform, adapting to the curvature of the end rollers 105, without being subjected to damages or breakages.
With reference to Figures 6 and 7, the guiding means 106 comprises fixing means 108 that can be associated with coupling means 109, with which said conveying means 102 is provided.
As shown in Figure 6, the coupling means 109 comprises a plurality of inserts 110, each of which provided with a threaded hole 111, having a shaped profile 110a and inserted into respective dovetail seats 112 obtained in the conveyor belt 104 during the production thereof. The inserts 110 are therefore embedded into the material, for example elastomeric material, forming the belt 104, so that the threaded hole 111 opens to the outer face 104a of the belt 104, i.e. onto the face on which the tiles 3 to be conveyed are resting.
Since the seats 112 and the inserts 110 arranged therein have a dovetail section, the risk that the inserts 110 come out of the seats 112 when said conveyor belt 104 winds on the end rollers 105 is substantially prevented.
Such inserts 110 are positioned in the conveyor belt 104 so as to define a plurality of rows 113, 114, 115, 116, 117, 118 arranged parallel to the advancing direction F.
The fixing means 108 comprises a plurality of screws 119 suitable for engaging into the threaded holes 111 to fix the curbs 107 to the conveyor belt 104. If the conveying apparatus 101 has to be adjusted to change from conveying tiles 3 having a certain transverse size, as shown in configuration A of Figure 5, to conveying tiles 3 having a different transverse size, as shown in configuration B of said Figure 5, it is sufficient to remove the screws 119 uncoupling them from the threaded holes 111 in which they were engaged, to remove the curbs 107 from first dual rows 113 and 118 and to reposition said curbs 107 at the inserts 110 respectively belonging to second dual rows 114 and 117. The rows 113, 114, 115, 116, 117, 118 are separated by pre-established distances, chosen so as to allow tiles belonging to a wide range of sizes to be conveyed, said sizes being indicatively specified as Y and Z. In particular, such distances correspond to the most common tile sizes on the market.
As shown in Figure 7, the coupling means 109 may comprise a plurality of further inserts 120, each provided with a further threaded hole 121, said inserts 120 being inserted into respective further seats 122 obtained in the conveyor belt 104. The further inserts 120 are therefore embedded into the material forming the conveyor belt 104 so that the further threaded hole 121 opens to the inner face 104b of the belt 104. In this case, through holes are made in the belt 104, such holes being arranged for allowing the screws 119 of the fixing means 108 to engage into said further threaded holes 121. Since the seats 122 are obtained in the lower portion of the conveyor belt 104, there is no risk that the further inserts 120 are removed from the further seats 122 when said conveyor belt 104 winds on the end rollers 105.
In a further, not shown version, the coupling means 109 and the fixing means 108 may comprise pressure-snapping inserts.
In another version, also not shown, the coupling means 109 and the fixing means 108 may comprise bayonet connecting elements.

Claims

Apparatus for polishing products (3) having a flat supporting base, in particular unfired ceramic tiles, comprising conveying means (2, 102), including a conveyor belt (104), suitable for advancing said products (3) along an advancing direction (F), operating head means (13) provided with abrasive disc means (14) suitable for machining an outer surface of said products (3) and further operating head means (35) provided with tool means suitable for interacting with said surface, said tool means further comprising abrasive disc means (36), characterized in that it comprises guiding means (106) which can be removably associated with the belt (104) and which is arranged for guiding said products (3) during the conveying operation.
Apparatus according to claim 1, wherein the guiding means (106) comprises a plurality of mutually aligned curbs (107).
Apparatus according to claim 2, wherein each curb (107) is spaced from the adjacent curbs (107) by a pre-established distance.
Apparatus according to claim 3, wherein the conveyor belt (104) is wound on a pair of end rollers (105) and the curbs (107) fixed to said belt (104) are free to elastically deform, adapting to the curvature of the end rollers (105), without being subjected to damages or breakages.
Apparatus according to claim 1, wherein the guiding means (106) comprises fixing means (108) that can be associated with coupling means (109), with which said conveying means (102) is provided.
Apparatus according to claim 5, wherein the coupling means (109) comprises a plurality of inserts (110), each of which provided with a threaded hole (111), having a shaped profile (110a) and inserted into respective dovetail seats (112) obtained in the conveyor belt (104) during the production thereof.
Apparatus according to claim 6, wherein the inserts (110) are therefore embedded into the material, for example elastomeric material, forming the belt (104), so that the threaded hole (111) opens to the outer face (104a) of the belt (104).
Apparatus according to claim 7, wherein the inserts (110) are positioned in the conveyor belt (104) so as to define a plurality of rows (113, 114, 115, 116, 117, 118) arranged parallel to the advancing direction (F).
Apparatus according to claim 8, wherein the fixing means (108) comprises a plurality of screws (119) suitable for engaging into the threaded holes (111) to fix the curbs (107) to the conveyor belt (104).
Apparatus according to claim 9, wherein the rows (113, 114, 115, 116, 117, 118) are separated by pre-established distances, chosen so as to allow tiles belonging to a wide range of sizes to be conveyed.
Apparatus according to claim 10, wherein the coupling means (109) comprises a plurality of further inserts (120), each provided with a further threaded hole (121), said inserts (120) being inserted into respective further seats (122) obtained in the conveyor belt (104).
Apparatus according to claim 11, wherein the further inserts (120) are embedded into the material forming the conveyor belt (104) so that the further threaded hole (121) opens to the inner face (104b) of the belt (104).
Apparatus according to claim 12, wherein in the belt (104) are made through holes, such holes being arranged for allowing the screws (119) of the fixing means (108) to engage into said further threaded holes (121).
Apparatus according to claim 13, wherein the coupling means (109) and the fixing means (108) comprise pressure-snapping inserts.
Apparatus according to claim 13, wherein the coupling means (109) and the fixing means (108) comprise bayonet connecting elements.
Apparatus according to claim 1, wherein said abrasive disc means (14) and/or said further abrasive disc means (36, 23) have a continuous band (24) of abrasive material.
Apparatus according to claim 16, wherein said continuous band (24) comprises an annulus.
Apparatus according to any one of claims 1, or 16 or 17, wherein said abrasive disc means (14) and/or said further abrasive disc means (36) comprise abrasive elements inserted in an elastic support.
Apparatus according to claim 18, wherein said abrasive elements comprise diamond inserts.
Apparatus according to claim 1 or according to any one of claims 16 to 19, wherein said conveying means (2) comprises conveyor belt means (4) wound on a pair of end rollers (5), one of which is motorized.
Apparatus according to claim 20, wherein said belt means (4) is slidingly supported by sliding plane means (21).
Apparatus according to claim 21, wherein a layer (22) of anti-wear material is removably arranged between said belt means (4) and said sliding plane means (21).
Apparatus according to claim 1 or according to any one of claims 16 to 22, wherein said operating head means (13) and/or said further operating head means (35) comprise spindle means (15) provided with shaft means (17), said abrasive disc means (14) or said further abrasive disc means (36) being respectively fixed at a first end of said shaft means (17).
Apparatus according to claim 23, wherein said shaft means (17) is rotatably supported to sleeve means (25) vertically sliding inside guiding means (26) connected to a supporting frame (9) for supporting said apparatus (2).
Apparatus according to claim 23, or 24, wherein actuating means (18) is connected to a further end of said shaft means, said further end being opposite to said first end.
Apparatus according to claim 25, wherein said further end comprises conduit means (19) arranged for blowing pressurized air at said surface.
Apparatus according to claim 25, or 26, wherein said actuating means comprises an electric motor (18).
Apparatus according to claim 1 or according to any one of claims 16 to 27, and further comprising adjusting means (28, 28a) arranged for keeping the pressure applied by said abrasive disc means (14) and/or said further abrasive disc means (36) on said surface sensibly constant and below a pre-established value.
Apparatus according to claim 28, as appended to claim 27, wherein said adjusting means (28, 28a) comprises a detecting device for detecting the electric current absorbed by said electric motor (18), said device being suitable for sending an electric signal to an actuator (31, 32, 33) coupled with said shaft means (17) in order to change the axial position of said shaft means (17) and, correspondingly, to change the thrust of said abrasive disc means (14) and/or said further abrasive disc means (36) on said products (3).
Apparatus according to claim 29, wherein said actuator comprises a gear motor unit (32) actuating positioning screw means (31) engaged with respective nut screw means (33).
Apparatus according to claim 30, as appended to claim 24, wherein said screw means is connected to said shaft means (17) and said nut screw means is connected to said supporting frame means (9).