[0001] The present invention relates to polishing machines having tools in the form of sectors
of abrasive materials mounted on rotating units of the machine, used to polish and
grind slabs of natural stones, ceramic floor tiles, porcelain, enameled tiles and
similar materials. Such a machine is known, for example, from DE-A-4119 679 on which
the preamble of claim 1 is based.
[0002] The abrasive sectors are commonly solid bodies of an aggregate of resin loaded with
diamond dust, usually of synthetic origin, having a "shank" shaped to fit into a retaining
slot of a steel bracket fastened to the rotating head of the machine and a grinding
face shaped like a sector of a cylinder whose axis lies on the same plane of the axis
of all the grinding sectors of the rotating unit, all intersecting the axis of rotation
of the grinding head. The rotating head may comprise three to six or even more grinding
sectors, coplanar among each other and radially spaced at regular angular intervals.
[0003] The fastening brackets of the abrasive sectors may be rigidly linked or more preferably
hinged to the rotating unit, allowing for a limited angle of oscillation in opposition
to the contrasting force of robust springs, in order to reduce vibrations caused by
pinnings of a grinding sector against asperities of the surface being ground.
[0004] EP-A-0 395 162 describes a polishing tool for stone material or the like comprising
a dovetail support, a base portion and an abrasive layer of sintered diamond dust
material supported by the base and further including a layer of elastic material interposed
between the base and the dovetail support for dumping the forces generated during
machining.
[0005] EP-A-0 691 182 discloses a mounting insert for an abrasive tool having a laminated
structure including a soft, stroke dampening elastic material and another layer of
other noise dampening material interposed between an abrasive tool and the oscillating
arm of a rotary end of a polishing machine.
[0006] The rotating unit is mounted on the end flange of a driving shaft. The shaft rotates
at a speed of 300 to 700 RPM and is advanced such to force the abrasive sectors against
the material being ground.
[0007] The grinding action is typically that of levelling the surface of the worked material
and is perfectly suitable to many polishing and grinding treatments of natural stone
and ceramic floor tiles.
[0008] By contrast, in case of certain types of floor tiles or of other materials where
it is just required to level the crests of decorative enamel smudgings, pittings,
crevices, corrugations, and the like, such an intrinsic levelling characteristic may
not be ideal. Indeed, if the aim is to give to the material a particular worn aspect,
the rigidity of these polishing machines tends to cut the crests leaving unaesthetical
sharp edges around the levelled areas.
[0009] In order to attenuate the levelling effect and to produce somewhat blunter edges,
machines have been proposed wherein the rotating head assembly is fixed to the drive
shaft through springs for attenuating the levelling effect of the grinding process
by introducing a certain ability of the rotating head to oscillate.
[0010] Such an approach imposes important mechanical modifications of the design of the
machine, and in the majority of cases, it becomes necessary to purchase a new machine
equipped with special adjustments.
[0011] It has now been found and is the object of the present invention, a way to provide
for a grinding operation without an excessive levelling action on the surface being
ground resulting in an appreciable "rounding off" of the edges of the ground crest
areas as well as the perimeter of the tile surface even with a normal polishing machine
without any adjusting mechanisms and/or to accentuate the effect of such adjustments
on specially designed machines.
[0012] Essentially, a structure has been devised for the individual abrasive sectors, to
be mounted on the face of a rotating head, that produces a less accentuated levelling
action. The ground crests of corrugations present on the surface of the material to
be finished assume a convex shape and/or a blunt edge as desirable in specific applications.
[0013] Essentially, the approach of the present invention is to confer intrinsically to
each of the tools or abrasive sectors installed on the operating unit a certain resilience
such to make the working face of the grinding sectors substantially flexible, that
is, capable of slightly inflecting upon increasing the load.
[0014] This effective result is attained by realizing each abrasive tool or sector in a
composite or stratified manner, typically including at least a layer or pad of elastomer,
and by making the body of abrasive material that constitute a working face, geometrically
shaped like a cylindrical sector of the tool which is of an intrinsically rigid material,
in a segmented form capable of undergoing elastic inflections of the cylindrical surface
without fracturing. In practice, the segmental abrasive body is able to follow elastically
the compressions endured by the elastomer layer beneath, placed between the segmented
body of the generally cylindrical face of the tool and a "shank" of rigid material,
shaped to solidly fit into the supporting bracket that is commonly hinged to the rotating
unit.
[0015] The invention is defined in claim 1. Dependent claims 2 to 6 relate to preferred
embodiments of the invention.
[0016] The various aspects and advantages of the invention will become even more evident
through the following description of several embodiments and by referring to the annexed
drawings, wherein:
Figure 1 is a general view of a rotating head of a polishing machine;
Figures 2 and 3 are a general view and a detail view of an abrasive sector mountable on the rotating
head of Fig. 1, realized according to the present invention.
Figures 4 and 5 are an assembly view and an exploded view, respectively, of a grinding sector according
to an alternative embodiment of the invention.
[0017] Fig. 1 shows an operating unit or rotating head 1 of a polishing machine that may
be connected by means of the flange 2 to the end of a driving shaft of the machine.
The working face of the unit 1 is constituted by a plurality of abrasive tools or
sectors 3. The illustrated head has six abrasive sectors, fitted by means of brackets
4, that are hinged to the body of the rotating unit.
[0018] Generally, the abrasive tools, whose working surface has the shape of a cylindrical
sector, are blocks of an aggregate of particles (grains) of an abrasive material and
of a bonding resin. The bonding resin may be for example an epoxy, phenolic or melaminic
resin or any other suitable thermosetting resin, or even a mixture of a thermosetting
and of a thermoplastic resin such as a polyurethane or a polyolefin.
[0019] Commonly, synthetic diamond powder is used as the abrasive substance; the granules
may have a size ranging between 30 and 6000 mesh. The finer part may be constituted
by particles with a diameter of 0.5 to 1.0 µm and the coarse part may pass through
a 30 and 40 mesh sieve.
[0020] The cylindrical sectors 3 are mounted on the same plane generally normal to the axis
of rotation of the rotating head 1.
[0021] The orientation of the axis of all the sectors 3 is radial and the sectors are uniformly
spaced on the face of the rotating unit.
[0022] The upper part of each sector has a shape functional to solidly fit into a receiving
slot of the supporting steel bracket, hinged to the rotating head.
[0023] Fig. 2 depicts a sector 3 made according to a preferred embodiment of the invention
and an exploded view of the composite sector is shown in Fig. 3.
[0024] The composite structure of the sector, object of the present invention, comprises
a "shank" or shaped body 5 of a rigid and mechanically strong material, generally
of aluminum or of a light-weight alloy or most preferably of a reinforced polyammidic
resin, e.g. of nylon ®, loaded with fiberglass or carbon fiber molded to a shape suitable
to fit solidly into a recovery slot of the bracket of the rotating head of the polishing
machine.
[0025] The composite includes one or more layers, two in the illustrated example, 6 and
8 respectively, of an elastomer with a hardness generally comprised between 25 and
95 Shore, for example of a natural rubber, a synthetic rubber or a silicon rubber
and the like.
[0026] In the illustrated example, an intermediate layer 7 of a substantially rigid material,
for example of a reinforced nylon, has a convex face shaped as a cylindrical surface.
The association of the intermediate element 7 and of the two-elastomer layers 6 and
8 constitute a resilient pad.
[0027] The aggregate body of particles of abrasive material and of bonding resin with a
working surface geometrically equivalent to the surface of a cylindrical sector of
the same radius of the convex face of the intermediate element 7 of the resilient
pad is, according to another essential aspect of the present invention, realized in
a segmented form. The aggregate body is formed in a plurality of levelled protrusions
or mesas 9 rising from a relatively thin base layer 10 of the same aggregate, preferably
incorporating during the molding operation, reinforcement fibers or preferably a reinforcing
mesh, for example of nylon, fiberglass, carbon fiber or the like.
[0028] The segmented structure imparts to the aggregate body 9, 10, a certain flexibility
and allows for the elastic inflection of the generally cylindrical surface defined
by the end faces at the vertex of the protrusions 9.
[0029] The various elements or layers that compose the tool are permanently joined together
by a structural adhesive, for example a ciano acrylate resin.
[0030] Of course, as well as the "shank" 5, also the body of aggregate 9-10 is manufactured
by molding.
[0031] The aggregate body 9-10 may be formed in a mold, eventually pressing over the face
of the flexible thin reinforced base layer 10, an the elastomer layer 8 in order to
bond the elastomer layer 8 directly onto the coupling face of the aggregate body formed
in the mold. The elastomer layer 8 so incorporated during the polymerization of the
aggregate in the mold, promotes a good facilitates the adherence through the adhesive
to the other elastomer layer 7 of the resilient pad of the assembly, practically functioning
as a priming layer.
[0032] An alternative embodiment is shown in Figures 4 and 5.
[0033] According to this alternative embodiment, the aggregate body is segmented in a different
way, in this case in a unidirectional fashion.
[0034] Also in this case, the segments 9 erect from a relatively thin and flexible base
layer 10, preferably reinforced by incorporating a suitable reinforcing mesh during
the polymerization process in the mold.
[0035] Differently from the embodiment illustrated in Figures 2 and 3, in this case the
cylindrical working face of the tool, is defined by the shape of the molded body 9-10
of aggregate, and the assembly does not contain a cylindrically shaped element 7 of
rigid material as in the preceding example.
[0036] Even in this alternative embodiment, the coupling face of the aggregate body may
incorporate, during the polymerization phase of the bonding resin, an elastomer layer
8, to facilitate the subsequent bonding to another elastomer layer 6 that is bonded
on the face of the rigid body 5.
[0037] In this case the inflections of the cylindrical working face of the tool occur by
virtue of the flexibility of the thin reinforced base layer 10, present at the base
of the transversal cuts between the substantially rigid subsectors 9 raising from
the base layer 10.
[0038] The grinding sectors of the invention may substitute conventional rigid sectors,
monolithically formed, whenever a nonlevelling grinding is desired.
[0039] The capacity of resiliently inflecting of the grinding sectors of the invention,
produce a slightly convex grinding action of the crests of the worked surface, determining
an appreciable rounding off at the edges.
[0040] Moreover, this important result is obtained by using a standard polishing machine
without any resilience adjusting mechanisms of the rotating unit. Naturally, in the
case of machines equipped with such adjusting mechanisms, the use of grinding sectors
with the composite structure of the invention enhances the effects beyond those obtainable
by the adjustment of the machine.
[0041] The segmented structure of the aggregate body may also have different geometries
than those illustrated in the reported examples, remaining fundamental for the aim
of the present invention to form the abrasive body in a way such to ensure a capacity
of resiliently inflecting.
[0042] The elastic properties of the elastomer pad of the composite structure of the grinding
sectors of the invention are designed in function of the desired degree of flexibility
of the aggregate body, in order to modulate the resilience of the grinding sectors
according to the type of material to be ground and in function of the desired finish.
1. A polishing machine comprising at least a rotating head (1), connected through a flange
(2) to the end of a drive shaft, the working face of the rotating head carrying a
plurality of grinding sectors (3), held hingedly in brackets (4) connected to the
rotating head (1) at uniformly spaced angular positions, each grinding sector (3)
having a laminated structure including a shaped shank portion (5) of a rigid and mechanical
resistant material fitting into a receiving slot of the holding bracket (4), at least
a resilient pad at least partly made of elastomer (6, 8) interposed between a face
of said shank portion (5) and an aggregate body of abrasive particles and of a bonding
resin (9, 10) having a substantially cylindrical working face, characterized in that said cylindrical working face is discontinuous and defined by a plurality of end
faces of as many protrusions (9) of said aggregate rising from a relatively thin and
flexible base layer (10) of said aggregate incorporating reinforcing fibers.
2. The polishing machine according to claim 1, characterized in that said shank (5), said resilient pad of elastomer (6, 8) and said body of aggregate
(9, 10) are glued together.
3. The polishing machine according to claim 1, characterized in that said resilient pad comprises a first layer of elastomer (8) partly incorporated on
the coupling face of said base layer of reinforced aggregate and at least a second
layer (6) of elastomer.
4. The polishing machine according to claim 3, characterized in that said resilient pad includes an insert (7), shaped as a cylindrical sector, of a rigid
material sandwiched between said two layers (8, 6) of elastomer.
5. The polishing machine according to claim 1, characterized in that said abrasive aggregate body has a bidimensional array of said protrusions.
6. The polishing machine according to claim 1, characterized in that said abrasive aggregate body has a monodimensional array of said protrusions.
1. Poliermaschine, die wenigstens einen rotierenden Kopf (1) aufweist, der über einen
Flansch (2) mit dem Ende einer Antriebswelle verbunden ist, wobei die Arbeitsfläche
des rotierenden Kopfes mehrere Schleifsektoren (3) trägt, die in Trägern, die mit
dem rotierenden Kopf (1) an gleichmäßig beabstandeten Winkelpositionen verbunden sind,
schwenkbar gehalten werden, wobei jeder Schleifsektor (3) eine Laminatstruktur besitzt,
die einen geformten Schaftabschnitt (5) aus einem starren und mechanisch beständigen
Werkstoff, der in einen Aufnahmeschlitz des Haltearms (4) eingesetzt ist, sowie wenigstens
ein elastisches Kissen umfaßt, das wenigstens teilweise aus einem Elastomer (6, 8)
hergestellt und zwischen einer Fläche des Schaftabschnitts (5) und einem Aggregatkörper
aus Abriebpartikeln und einem Klebeharz (9, 10) mit einer im wesentlichen zylindrischen
Arbeitsfläche angeordnet ist, dadurch gekennzeichnet, daß die zylindrische Arbeitsfläche unterbrochen ist und durch mehrere Stirnflächen aus
ebenso vielen Vorsprüngen (9) des Aggregats definiert ist, die von einer verhältnismäßig
dünnen und biegsamen Grundschicht (10) des Aggregats, in der Verstärkungsfasern enthalten
sind, nach oben stehen.
2. Poliermaschine nach Anspruch 1, dadurch gekennzeichnet, daß der Schaft (5), das elastische Kissen aus Elastomer (6, 8) und der Aggregatkörper
(9, 10) miteinander verklebt sind.
3. Poliermaschine nach Anspruch 1, dadurch gekennzeichnet, daß das elastische Kissen eine erste Elastomerschicht (8), die teilweise in die Verbindungsfläche
der Grundschicht des verstärkten Aggregats eingebaut ist, und wenigstens eine zweite
Elastomerschicht (6) umfaßt.
4. Poliermaschine nach Anspruch 3, dadurch gekennzeichnet, daß das elastische Kissen einen als zylindrischer Sektor geformten Einsatz (7) aus einem
starren Werkstoff enthält, der zwischen die beiden Elastomerschichten (8, 6) sandwichartig
eingefügt ist.
5. Poliermaschine nach Anspruch 1, dadurch gekennzeichnet, daß der Abrieb-Aggregatkörper eine zweidimensionale Anordnung aus den Vorsprüngen besitzt.
6. Poliermaschine nach Anspruch 1, dadurch gekennzeichnet, daß der Abrieb-Aggregatkörper eine eindimensionale Anordnung aus den Vorsprüngen besitzt.
1. Une machine de polissage comprenant au moins une tête tournante (1), la tête étant
couplée par le moyen d'une collerette (2) à l'extrémité d'un arbre d'actionnement,
la face de travail de la tête tournante portant une pluralité de secteurs de meulage
(3) qui sont tenus par connexion à charnière dans des étriers (4) qui sont connectés
à la tête tournante (1)en positions angulaires uniformément espacées, chaque secteur
de meulage (3) ayant une structure feuilletée comprenant une portion de tige (5) profilée
d'un matériel rigide et mécaniquement résistant placé dans une fente de réception
dans l'étrier de retenue (4), au moins un coussinet résiliant fait au moins en partie
d'élastomère (6, 8) intercalé entre une face de ladite portion de tige (5) et un corps
agrégé de particules abrasives et d'une résine liante (9, 10) ayant une face de travail
essentiellement cylindrique, caractérisée en ce que ladite face de travail cylindrique n'est pas continue et est définie par une pluralité
de faces terminales d'autant de protrusions (9) dudit agrégé qui s'élèvent d'une couche
de base (10) relativement mince et souple dudit agrégé incorporant des fibres de renfort.
2. La machine de polissage revendiquée dans la revendication 1, caractérisée en ce que ladite tige (5), ledit coussinet résiliant élastomère (6, 8) et ledit corps agrégé
(9, 10) sont collés ensemble.
3. La machine de polissage revendiquée dans la revendication 1, caractérisée en ce que ledit coussinet résiliant comprend une première couche élastomère (8) partiellement
incorporée sur la face de couplage de ladite couche de base agrégé renforcé et au
moins une deuxième couche (6) élastomère
4. La machine de polissage revendiquée dans la revendication 3, caractérisée en ce que ledit coussinet résiliant comprend une pièce insérée (7), conformée en secteur cylindrique,
d'un matériel rigide inséré entre lesdites deux couches (8, 6) élastomère
5. La machine de polissage revendiquée dans la revendication 1, caractérisée en ce que ledit corps agrégé abrasif pressente un rangement bidimensionnel desdites protrusions.
6. La machine de polissage revendiquée dans la revendication 1, caractérisée en ce que ledit corps agrégé abrasif pressente un rangement monodimensionnel desdites protrusions.