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Title:
ABRASIVE TOOL FOR SMOOTHING MACHINES
Document Type and Number:
WIPO Patent Application WO/2000/030812
Kind Code:
A1
Abstract:
This modular abrasive tool with radial swing (27) for rotary heads of smoothing machines for granite, marble, ceramic, resinous stone and the like, has a shape in the form of an angular sector (36, 37) tapered with converging inclinations which are accentuated (21, 22) in those regions of lesser peripheral speed, and a structure which offers a plurality of points (4, 9, 11) at which the slab being machined is abrasively attacked, said plurality of points deriving from cooperation with soft elements (3), preferably of graphite, which interrupt the continuity of the abrasive structure.

Inventors:
Di Giuseppe, Andrea (Via Filolao, 3 Roma, I-00100, IT)
De Gennaro, Giovanni (Via Val di Fiemme, 18 Milano, I-20128, IT)
Application Number:
PCT/IT1999/000381
Publication Date:
June 02, 2000
Filing Date:
November 24, 1999
Export Citation:
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Assignee:
REPLA S.R.L. (Via Piave, 609 Calusco D'Adda, I-24033, IT)
Di Giuseppe, Andrea (Via Filolao, 3 Roma, I-00100, IT)
De Gennaro, Giovanni (Via Val di Fiemme, 18 Milano, I-20128, IT)
International Classes:
B24B41/047; B24D3/34; B24D7/06; B24D18/00; B24D99/00; (IPC1-7): B24D17/00; B24B41/047; B24D3/34; B24D7/06; B24D18/00
Foreign References:
EP0561610A1
US5076023A
EP0395162A1
US4776885A
Attorney, Agent or Firm:
Luksch, Giorgio (Ing. A. Giambrocono & C. S.r.l. Via Rosolino Pilo, 19/B Milano, I-20129, IT)
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Claims:
Claims
1. A modular abrasive tool with radial swing (27) for rotary heads of smoothing machines for granite, marble, ceramic, resinous stone and the like, characterised by having an abrasive body (1) with its perimeter (43) shaped as an angular sector (36,37) tapered with converging inclinations which are accentuated (21, 22) in those regions of lesser peripheral speed, and a structure which offers a plurality of lines or points (4,9,10,11,12,13, 14,15,1 16,17,18,19,20) at which the slab being machined is abrasively attacked, said plurality of points deriving from cooperation with soft elements, preferably of graphite, which interrupt the continuity of the abrasive structure.
2. A tool as claimed in the preceding claim, characterised in that the abrasive body (1) has a shape (43) comprising large radius curves (5,6) at its ends.
3. A tool as claimed in the preceding claims, characterised in that the soft elements are in the form of substantially parallelepiped graphite bars (3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H, 3L, 3M, 3N, 3P).
4. A tool as claimed in the preceding claims, characterised in that the soft elements or inserts are in the form of granular elements distributed uniformly within the abrasive body (1).
5. A method for forming the tool of the preceding claims, characterised by using a mould having a through hole which is closed at its resting base by an insert (39) shaped to match the profile of said hole and being concave to create the necessary cylindrical convexity (25) of the abrasive body, on said concavity there then being laid a shaped paper sheet (41) to which graphite bars (3) are glued in predetermined positions, to then be covered with a mixture of powdered bronze binder and abrasive diamond powder, which is finally subjected to known sintering to complete the structure.
Description:
Description Abrasive tool for smoothing machines Technical Field This invention relates to a modular abrasive tool with radial swing for rotary heads of smoothing machines for granite, marble, ceramic, resin incorporating stone granules, known as resinous stone, and the like. The invention also relates to a method for forming said abrasive tool.

Background Art The aforesaid materials are generally smoothed by machines provided with special heads 28 rotating about a vertical axis 31 with a direction of rotation 29 (Figure 2). These machines are known as abrasive machines with Fichert swing action heads. Said smoothing heads are composed of a plurality of interchangeable or modular abrasive tools 26. These abrasive tools move with a slow swinging movement along directions 32A and 32B about their own specific radial axes 27 while they orbit about the vertical axis 31 of the rotary head. These modular swing-orbiting tools consist of an abrasive body 1 generally formed from sintered bronze-based material including diamond granules. The modular tools are usually in the form of"blocks"with a concave top 25 and generators parallel to said radial axis of swing 27. The blocks are usually of rectangular shape with their rectangular base 30 mounted on the rotary head 28. Each of these rectangular blocks is arranged radially on said machine rotary head, and hence tends to rub against the underlying machined slab 35 at a speed which is low in regions 33 close to the centre or axis of rotation 31 of the head, and high in regions 34 distant from said axis of rotation (Figure 3). In this respect, the peripheral parts 34 of these modular abrasive tools travel through a greater distance and undergo greater wear, however in spite of this they cannot be lowered to increase the passage depth because of the obstacle offered by the most central region 33 of the tool, which is

usually less worn. Hence the wear of such modular tools 25 or blocks is irregular, preventing their abrasive surface 25 from operating under optimum conditions on the underlying slab 35 being machined. The low contact force within the worn peripheral region 34 of the modular tool 26 favours undesired polishing of this region and prevents surface-emergence of the diamond granules embedded in its abrasive body 2. The result is a reduction in its abrasive capacity. As a result of this drawback the rotary head 28 has to be pushed against the machined slab 35 with a considerable force which in certain cases can damage the slab.

Such damage can consist of deep scratching due to the irregularity with which the abrasive granules are detached. The damage can also consist of breakage of certain slabs. This considerable force can also cause the slab 35 to bend, this being incompatible with the formation of a perfectly flat machined surface. The considerable force with which such usual irregularly wearing modular tools 26 have to be thrust against the machined slab results in a short tool life. Another intrinsic drawback of these usual modular abrasive tools 26 is the fact that in swinging from right to left, 32A, 32B, they offer only two"entries"or attack angles or cutting lines against the material of the slab 35 to be machined. These entries are represented by the left and right side edges of said rectangular swinging base 30.

The negative consequence of this characteristic of known modular abrasive tools is that the abrasive body 1 of the tool 26 is not fully utilized.

An object of this invention is to define a modular abrasive tool with radial swing for rotary heads of smoothing machines for granite, marble, ceramic, resinous stone and the like, having a form suitable for optimum use of its abrasive material. A further object is to define a modular abrasive tool as above having a structure which gives it greater abrasive capacity independently of the grain fineness of its incorporated abrasive elements. A further object is to define a method for forming such tools.

Disclosure of Invention

These and further objects will be seen to be attained from the ensuing detailed description of a modular abrasive tool with radial swing for rotary heads of smoothing machines for granite, marble, ceramic, resinous stone and the like, having a shape in the form of an angular sector tapered with converging inclinations which are accentuated in those regions of lesser peripheral speed, and a structure which offers a plurality of points at which the slab being machined is abrasively attacked, said plurality of points deriving from cooperation with soft elements, preferably of graphite, which interrupt the continuity of the abrasive structure. The method for forming the aforesaid modular abrasive tool is characterised by the details specified in the appropriate claim.

Brief description of drawings The invention is illustrated by way of non-limiting example on the accompanying drawings, on which: Figure 1 is a sectional perspective view of an abrasive body to be fitted to a tool 26 to be mounted radially on usual rotary smoothing heads 28 for operation by typical swing movements 32A and 32B; Figure 2 is a schematic view of a usual rotary machine head 28 illustrating the special manner in which abrasive body of Figure 1 operates; Figure 3 is a view from below showing the woking surface of a first embodiment of said abrasive body, associated with a usual rectangular support base; Figure 4 is a view from below showing the woking surface of a second embodiment of a abrasive body, associated with a usual rectangular support base; Figure 5 is a view from below showing the woking surface of a third embodiment of a abrasive body, as stated; Figure 6 is a section through a sintering mould having graphite inserts in the form of substantially parallelepiped bars located in the required position by a paper reference sheet which rests on the floor of the mould and carries said bars glued on it.

Best mode of carry'nu out the invention In the ensuing description reference is made to some preferred embodiments of the invention, illustrative of possible variants of the invention by way of non-limiting example.

Figure 1 shows an abrasive body 1 of a modular smoothing tool 28.

The abrasive body 1 incorporates graphite bars 3 of substantially parallelepiped shape. Graphite is the preferred material, but its function could be performed by other soft materials of high melting point. These bars extend along the entire extent of the abrasive working surface 2 (25 in Figure 2) to divide it into regions of abrasive material 2A, 2B, 2C, 2D alternating with graphite regions 3A, 3B, 3C. Said abrasive material consists of sintered metals, preferably bronze, with included diamond particles of size inversely proportional to the degree of smoothing which they are required to achieve. On said working surface 2,25 of the abrasive body 1 of the tool 26, the inert material strips 3 are arranged parallel to each other in the direction longitudinal to the radial extension of the modular abrasive body 26. This radial direction is expressed in Figure 2 by a point 27, representing the radial axis of swing of the abrasive tool 26 to the head 28, which rotates in the direction 29. Particular examples of these abrasive surface arrangements 2 or 25 are shown in Figures 3,4,5.

Figure 3 is a view from below showing the form of the abrasive tool working surface, which is contained within the rectangular perimeter of the base 30 of a steel support for the abrasive body 1 (Figure 2). This working surface comprises the three strips of graphite or other inert material 3A, 3B, 3C. Figure 4 is a view from below showing the form of a working surface defined by edges 43 which taper in the manner of those of Figure 3, and includes four graphite strips 3D, 3E, 3F, 3G. Figure 5 is a similar view showing a surface form (of the abrasive body 1) comprising five graphite strips 3H, 3L, 3M, 3N, 3P.

In all these cases, the graphite or inert material bars or strips are arranged longitudinally and parallel to each other. When the abrasive tool is mounted on the machine head 28, this longitudinal

direction becomes radial along the axis 27 (perpendicular to the drawing of Figure 2)). As graphite is less abrasion resistant than the sintered metal (indicated on the drawings by said regions 2), the presence of the graphite strips 3 creates raised regions presenting a multiplicity of lines of attack 4 against the material of the slab 35 to be smoothed (Figure 1). Cutting angles, present along these raised lines of attack 4, are formed on both the right side and the left side of each of the graphite strips 3. During said right-left swing, traditional abrasive tools present only two"entries"or lines of attack or cutting edges against the material to be machined. In contrast, the abrasive tools of the invention present a much greater number of cutting edges. In this respect, an abrasive body with a working surface provided with five graphite strips or bars 3H, 3L, 3M, 3N, 3P such as that shown in Figure 5 advantageously has six lines of attack 13,14 when the head rotates in a certain direction 29 (ie which act when the module advances in a direction 23), and six lines of attack 15,16,17,18,19,20 which cut in the opposite direction to the preceding (ie which act when the module advances in a direction 24). As stated, this results in better engagement between the tool and the material to be machined, with the consequent advantages of higher machining speed, better worn diamond regeneration and lower machining pressure.

The method for forming the abrasive body 1 of the tool 26 comprises preparing a sintering mould 38 with precisely located inserts of soft inert material, preferably consisting of graphite bars 3, arranged to create a plurality of points or lines 4 along which the abrasive diamond granules attack the slab 35 being machined. Said mould preparation involves the use of a mould having a hole of through profile which is closed at its base by a suitable insert 39. Said insert matches the profile of said hole and has its upper or inner face 40 shaped and recessed to create the typical cylindrical convexity at the working surface 25 of the abrasive body 1 of the tool 26 to be formed. On the face 40 there is rested a sheet of paper 41 on which parallelepiped graphite

bars 3 are glued. The mould defined in this manner is filled with bronze powder (90% copper, 10% tin) 1A acting as a binder, and diamond granules acting as the abrasive. The powder 1A is then pressed with a force S by a presser block 42, also having a profile which matches that of the hole. By way of example, this hole can be expressed by a curvilinear perimeter 43 such as that shown on the drawings of Figures 3,4,5. Finally, the mould is inserted into a usual sintering furnace, which incorporates and fixes the graphite bars 3 into the abrasive structure 2 of the tool 26 being formed, and to its rectangular steel base 30. After extraction from the mould 38, the said graphite bars 3 will be visible on the convex working surface 25 of the modular abrasive tool 26. In this respect, the paper 41 with which they were covered burns away during the sintering of said bronze powder 1A.

This method forms modular abrasive tools having a relatively coarse grain, and hence requiring cavities which during the abrasive action enable the removed hard particles to find a soft seat (graphite) into which they can penetrate in order not to scratch the machined slab, until they are expelled. This expulsion is facilitated by the sludge created by the water used for cooling and dust removal, with which the slab 35 is fed during machining. In the case of modular abrasive tools 26 for fine smoothing, and hence provided with very small diamonds, these "soft seats"are provided by graphite in the form of graphite granules. These granules are distributed uniformly within the bronze structure, together with the diamond powder of suitable particle size. This use of graphite granules is particularly advisable in micro-grain abrasive tools from 140 to 1400 mesh. To achieve a uniform distribution of these graphite granules, during the mixing of the materials to be sintered the said graphite granules are previously coated with Diesel oil (or with liquid paraffin) and then mixed mechanically with the binder (bronze) and abrasive powder (diamond).

With the said arrangement of parallel graphite bars there is the important advantage, compared with the state of the art, of obtaining along the tool working profile 25 a plurality of lines 4

(9,10,11,12,13,14,15,16,17,18,19,20) along which the abrasive attacks the stone material of the slab 35 to be machined.

In addition the abrasive"thread"remains constantly present along the tool cutting lines until it has worn away, because the graphite, which is less resistant to abrasion, tends to wear more than the working surfaces of the tool. As these latter are metallic and abrasive they are raised beyond the graphite surface.

This greater graphite wear is favoured by the said abrasive sludge which the machining produces. This results in a better abrasive action of the tool 26 on the stone material of the slab 35 to be smoothed. As a consequence the machining rate is higher, with improved evacuation of the worn diamonds. The perimetral shape 43 of the abrasive body 1 of the tool 26, shown on the accompanying drawings, has the ideal proportions to offer lateral lines of attack suitable for machining stone materials in general. The oblique side taper in the geometrically radial direction and the rounding of the corners of the resultant trapezoid result in substantially uniform wear and cutting, and excellent removal of the residual abrasive sludge. As stated, the tools 26 swing on the rotary head 28 about a radial axis 27 of it, with the result that in the end-of-swing positions, those parts 33 closest to the centre of rotation 31 (ie those of lower peripheral speed) are proportionally disengaged. When the tool 26 lies with its axis of swing 47 aligned with the vertical axis of rotation 31 of the head, the abrasive line is of maximum length, as indicated by 44 in Figure 3. When the tool 26 is inclined to its maximum extent, ie with its axis of swing 47 at an inclination 45 (Figure 2), the line of contact 7 between the abrasive body 1 and the slab 35 being machined is of minimum length 46.

The abrasive body 1 of tools 26 formed in accordance with the invention has an end part 21 tapering along two terminal portions 8,22 which converge more than the more peripheral edges 36,37.

These portions 8,22 are positioned in that region which when mounted on the machine head is closest to its centre or axis of rotation 31. This enables an abrasive surface to be obtained which, in a circumferential direction with its centre on 31, is proportional to the orbiting speed of its regions. When viewed in plan, the abrasive body 1 has a shape which is completed by connecting curves 5 and 6.