Polishing head

The invention relates to a polishing head, in particular a polishing head for stone materials.

Polishing heads are known that are used for polishing surfaces of stone material with the assistance of water, in particular slabs or tiles for floors or walls made of ceramics, marble, gres, granite and various forms of stone. The polishing heads are mounted singularly or in groups on an operating machine. Each polishing head comprises a shaft positioned centrally, provided at a first end with a flange, through which a rotational movement is taken from a motor associated with the operating machine. The shaft is rotatably and coaxially connected to a casing element that is fixed to the operating machine and which has a greater diameter than the diameter of the shaft. A cylindrical portion that projects to a second end of the shaft opposite the first end is internally fixed to the casing element. Inside the cylindrical portion the shaft is rotatably supported by means of bearings. At the second end there is fixed a further casing element comprising a circular base, that is rotated by the shaft during operation. The circular base is provided peripherally with a cylindrical wall that projects to the casing element so as to define a closed volume inside the polishing head. Inside the polishing head there is provided a first gearwheel, provided externally with a first toothing and arranged coaxially to the shaft. The first gearwheel is fixed by means of the cylindrical portion to the casing element . Within the polishing head there is provided a second gearwheel arranged coaxially to the shaft and having an external diameter that is greater than the first gearwheel. The second gearwheel is fixed to the cylindrical portion in such a way as to be further away from the circular base with respect to the first wheel.

The second gearwheel is provided peripherally with a peripheral annular portion projecting to the circular base. On the annular portion a second toothing facing the shaft is obtained internally. The polishing head is provided with a plurality of tool- holding shafts for grinding wheels, which shafts are rotatably connected and arranged transversely to the circular base, in such a way as to be able to be rotated by the latter around a central axis of the shaft. The plurality of tool-holding shafts for grinding wheels is positioned in such a way as to have first ends arranged inside the polishing head and second ends, opposite the first ends, and positioned outside the polishing head for supporting grinding wheels. The plurality of tool-holding shafts for grinding wheels comprises first tool-holding shafts, for first grinding wheels, and second tool-holding shafts for second grinding wheels. The first tool-holding shafts and the second tool- holding shafts are arranged together in an alternating manner, are uniformly distributed along a peripheral zone of the circular base and have respectively first rotation axes and second rotation axes arranged parallel to the shaft. The first rotation axes and the second rotation axes are arranged at the same distance from the shaft. The first tool-holding shafts are provided at the first ends with first pinions that engage with the first gearwheel in such a way that during operation, the first tool-holding shafts rotate around the first rotation axes at a preset angular speed and in a first rotating direction that corresponds to a rotating direction of the shaft.

The second tool-holding shafts are provided at the first ends with second pinions that engage with the second gearwheel in such a way that during operation, the second tool-holding shafts rotate at the preset angular speed but in a second rotating direction opposite the first rotating direction .

During operation, the first tool-holding shafts and the second tool-holding shafts rotate respectively around the first axes and the second axes and at the same time rotate around the central axis of the shaft. The first grinding wheels, as they rotate in a direction that corresponds to the rotating direction of the shaft, have peripheral zones that are further from the central axis that move at a greater cutting speed than further peripheral zones of the second grinding wheels that are further from the central axis, the second grinding wheels rotating in the opposite direction to the shaft.

If on the one hand it has been found to be extremely positive for the purposes of machining to provide first and second grinding wheels rotating in opposite directions to one another, it has nevertheless been found to be complicated to devise operating parameters for the polishing head to make the cutting speeds between the first grinding wheels and the second grinding wheels more homogenous. An object of the invention is to improve the polishing heads, particularly for stone materials.

In particular, it is desirable to obtain a polishing head for which suitable operating parameters are defined that are such as to make the cutting speeds of the first grinding heads and of the second grinding heads more homogenous. This enables polishing to be improved and a more careful and homogenous surface finish to be obtained.

According to the invention, there is provided a polishing head, comprising first tool-holding shafts rotating in a first rotating direction and associated with first transmission means, and second tool-holding shafts rotating in a second rotating direction opposite said first rotating direction and associated with second transmission means, characterised in that said first transmission means and said second transmission means are such that said first tool- holding shafts and said second tool-holding shafts have

cutting speeds that are not too different from one another as absolute values.

Owing to the invention, there is provided a polishing head that enables surfaces of stone materials to be polished evenly. In particular, the first transmission means and the second transmission means are associated respectively with suitably selected first transmission ratios and second transmission ratios. Further, the first tool-holding shafts and the second tool-holding shafts are distant from a central longitudinal axis of the polishing head respectively by a first amount and by a second amount that are suitably preset. In this way, during operation, abrasive surfaces associated with the first tool-holding shafts, and further abrasive surfaces associated with the second tool-holding shafts act on the surfaces to be machined at substantially the same cutting speeds. In particular, with respect to known polishing heads, the differences in peripheral speed are considerably reduced that are generated between zones of the abrasive surfaces and further zones of the further abrasive surfaces that are further from the longitudinal central axis.

This enables uniform surface finishes to be obtained and the grooves to be homogenised that are generated on the surfaces during machining. The invention will be better understood and carried out with reference to the attached drawings that illustrate an embodiment thereof by way of non-limiting example, in which: Figure 1 is a perspective view of a polishing head. Figure 2 is a schematic view that shows the operation of the polishing head in Figure 1.

Figure 3 is a section view taken along a through plane III- III passing through a longitudinal axis of the polishing head in Figure 1. Figures 1 to 3 show a polishing head 1 that is suitable for polishing surfaces of stone material, such as slabs or tiles for floors or walls for example, of ceramic, marble, gres,

granite, and various types of stone. The polishing head 1 comprises shaft means 2 that extends along a central longitudinal axis A and is rotatably connected to a casing element 3 that is fixed firmly to an operating machine (not shown) . The shaft means 2 is rotatably housed through bearings 12 inside a cylindrical portion 10 that is fixed to the casing element 3. To a first end 5 of the shaft means 2 a flange 4 is fixed by means of which a rotational movement supplied by a motor of the operating machine is transferred to the shaft means 2. To a second end 6 of the shaft means 2, opposite the first end 5, there is fixed a further casing element 32 comprising a base 11 of cylindrical shape. Peripherally to the base 11 there is provided a cylindrical wall 13 that projects towards the casing element 3 in such a way as to define volume that is closed above by an upper circular portion 14 arranged transversely to the shaft means 2 and immediately below the casing element 3. The upper circular portion 14 prevents, by means of sealing elements 31 and gaskets 33, undesired objects from entering inside the polishing head 1. On the base 11 there are obtained housing cavities 8 arranged peripherally at regular intervals in such a way as to house rotatably, through further bearings 15, in an alternating manner, first tool- holding shafts 9 and second tool-holding shafts 20. The polishing head shown in Figures 1 to 3 is provided with five first tool-holding shafts 9 and with five second tool- holding shafts 20, but it is possible to provide another desired number of first tool-holding shafts 9 and of second tool-holding shafts 20. To the first tool-holding shafts 9 and to the second tool- holding shafts 20 there can be fixed, for example through screws, respectively first grinding wheels 60 and second grinding wheels 61 that are positioned jutting over the base 11.

The first grinding wheels 60 and the second grinding wheels 61 are provided with abrasive surfaces 25 that are able to polish the surfaces to be treated.

The first tool-holding shafts 9 and the second tool-holding shafts 20 comprise respectively stem portions 62, having first rotation axes X, and further stem portions 63, having second rotation axes Y, extending parallel to the central longitudinal axis A. The stem portions 62 are rotatable around first rotation axes X, and the further stem portions 63 are rotatable around the second rotation axes Y.

The first rotation axes X are positioned at a first distance Rl from the central longitudinal axis A, and the second rotation axes Y are positioned at a second distance R2 from the central longitudinal axis A. The first grinding wheels 60 and the second grinding wheels 61 can be mounted in such a way as to have longitudinal axes slightly tilted by an angle E with respect to the first rotation axes X and to the second rotation axes Y. In this way, when the first tool-holding shafts 9 and the second tool-holding shafts 20 rotate respectively around the first rotation axes X and the second rotation axes Y the planes of the abrasive surfaces 25 are varied continuously in such a way as to adapt better to the surface roughnesses that are treated. The polishing head 1 comprises first transmission means 50, associated with the first tool-holding shafts 9, and second transmission means 51, associated with the second tool- holding shafts 20. The first transmission means 50 comprises a first gearwheel 26, having a first external radius F, arranged coaxially to the shaft means 2 and fixed to the cylindrical portion 10 by means of screws 64. The first gearwheel 26 is provided peripherally and externally with a first toothing 27. The first transmission means 50 comprises first pinions 21, having a second external radius C, that are fixed to upper connecting ends 17 of the first tool-holding shafts 9. The

first pinions 21 are externally and circumferally provided with further first toothings 22 that engage with the first toothing 26. Between the first gearwheel 26 and the first pinions 21 there is defined a first transmission ratio Zl, i.e. a first ratio between a first number of teeth Nl provided on the first gearwheel 26 and a second number of teeth N2 provided on each first pinion 21.

The second transmission means 51 comprises a support ring 29 of a second gearwheel 30, arranged coaxially with respect to the shaft means 2 and fixed to the cylindrical portion 10 by further screws 65. The second gearwheel 30 is provided in the interior thereof with a second internal toothing 28 arranged along a circumference coaxial to the central longitudinal axis A. The second toothing 28 has an internal radius G that is greater than the second distance R2.

The second transmission means 51 comprises second pinions 18, having a third external radius D, that are fixed to further upper connecting ends 34 of the second tool-holding shafts 20, in such a way as to be further from the base 11 than are the first pinions 21. The second pinions 18 are provided externally and circumferally with further second toothings 19 that engage with the second toothing 28. Between the second gearwheel 30 and the second pinions 18 there is defined a second transmission ratio Z2, i.e. a second ratio between a third number of teeth N3 provided on the second gearwheel 30 and a fourth number of teeth N4 provided on each second pinion 18.

During operation, the base 11, which is rotated in a first direction L by the shaft means 2, drags with it the first tool-holding shafts 9 and the second tool-holding shafts 20 that travel along a revolution trajectory around the central longitudinal axis A. Simultaneously, the first toothing 27, which is fixed, interacts with the further first toothings 22 in such a way that the first pinions 21 rotate in a direction corresponding to the first direction L around the first rotation axes X. In this way the first grinding wheels

60 rotate around the first rotation axes X and at a first angular speed Wl .

The second toothing 28, which is fixed, interacts with the further second toothings 19 in such a way that the second pinions 18 rotate in a second direction M opposite the first direction L around the second rotation axes Y. In this way, the second grinding wheels 61 rotate around the second rotation axes Y at a second angular speed W2. By selecting suitable values of the first distance Rl, of the second distance R2 and/or of the first transmission ratio Zl and of the second transmission ratio Z2 it is possible to reduce significantly the differences in cutting speed between the first grinding wheels 60 and the second grinding wheels 61, due to rotations in opposite directions, in particular between zones of the first grinding wheels 60 and further zones of the second grinding wheels 61 that are further from the central longitudinal axis A. This enables the first grinding wheels 60 and the second grinding wheels

61 to move on the surfaces to be machined at cutting speeds that are not very different from one another as an absolute value .

In a first example, the polishing head 1 has a first transmission ratio Zl=3.78, (with Nl=151, N2=40) at a first distance Rl=191 mm (distance between diametrically opposite first tool-holding shafts 9 equal to 382 mm) , a second distance R2=194 mm (distance between second diametrically opposite tool-holding shafts 20 equal to 388 mm) , a second transmission ratio Z2=13.12 (with N3=210, N4=16) and a first angular input speed nl of the shaft means 2 equal to 200 rpm.

With such design parameters, peripheral zones of the first grinding wheels 60 move, in regions that are further from the shaft means 2, at a first cutting speed Vtl=9.01m/s . The first cutting speed VtI is generated by the algebraic sum of a first speed contribution equal to 3.96m/s provided by the rotation of the first grinding wheels 60 around the first

rotation axes X and a second speed contribution equal to 5.05m/s, provided by the rotation of the first grinding wheels 60 around the central longitudinal axis A. Further peripheral zones of the second grinding wheels 61 move in regions that are more distant from the shaft means 2, at a second cutting speed Vt2=8.63m/s. The second cutting speed Vt2 is generated by the algebraic sum of a further first speed contribution equal to 13.74m/s provided by the rotation of the second grinding wheels 61 around the second rotation axes Y, and a further second speed contribution equal to 5.11m/s, provided by the rotation of the second grinding wheels 61 around the central longitudinal axis A. In a second example, the polishing head 1, differs from the first example only by having a second angular input speed n2 of the shaft means 2 equal to 265 rpm. In this case, there is a first cutting speed VtI=Il .93m/s . The first cutting speed VtI is generated by the algebraic sum of a further first speed contribution equal to 5.24m/s provided by the rotation of the first grinding wheels 60 around the first rotation axes X, and a further second speed contribution equal to 6.687m/s, provided by the rotation of the first grinding wheels 60 around the central longitudinal axis A. In this example, there is a second cutting speed Vt2=ll .43m/s . The second cutting speed Vt2 is generated by the algebraic sum of a still further first speed contribution equal to 18.20m/s provided by the rotation of the second grinding wheels 61 around the second rotation axes Y, and a still further second speed contribution equal to 6.77m/s, provided by the rotation of the second grinding wheels 61 around the central longitudinal axis A.

It is possible to note how the values of VtI and Vt2, in the first example and in the second example disclosed above, differ from one another by less than 5%.