[0001] The present invention refers to an improved lapping head, especially of the type
comprising a plurality of grinding wheels having vertical axis.
[0002] It is known to those skilled in the art that the conventional lapping heads having
wheels with vertical axis and being used for lapping or coarse-grinding stone materials,
comprise a plurality of abrasive wheels carried by relevant shafts whose axes, during
operation, are vertically disposed, that is, substantially orthogonal to the surface
of the material to be worked.
[0003] A drawback in the use of these known lapping heads lies in the fact that, in case
of marked irregularities of the surface under formation, the wheels do not work simultaneously
and their relevant axes do not result in vertical position as the roughness of the
material tends to lift the same wheels which transit thereon, thereby moving them
away from their relevant regions of intervention. Besides being a cause of imperfect
working of the material, this is also a source of impacts and vibrations acting upon
the mechanical and structural members of the head, and thus jeopardizing its reliability.
[0004] The above drawback can be found mostly in the treatment of granite sheets, but it
can also occur in the lapping of other materials, such as grès and porcelained grès.
[0005] The main object of the present invention is to eliminate or at least reducing the
above mentioned drawback.
[0006] This result has been achieved, according to the invention, by providing an apparatus
having the features indicated in the characterizing part of claim 1. Further characteristics
being set forth in the dependent claims.
[0007] The advantages deriving from the present invention lie essentially in that it is
possible to ensure a perfect lapping of stone materials also when the surface to be
treated exhibits marked irregularities or roughness; that an operating head according
to the invention can also be used for surface finish operations by using wheels with
fine-grain abrasive coating; that an operating head according to the invention is
relatively simple to make, cost-effective and reliable even after a prolonged service
life.
[0008] These and other advantages and characteristics of the invention will be best understood
by anyone skilled in the art from a reading of the following description in conjunction
with the attached drawings given as a practical exemplification of the invention,
but not to be considered in a limitative sense, wherein:
- Fig. 1 is a perspective view partially in section of an operating head according to
the invention; and
- Fig. 2 is an enlarged detail of the head of Fig. 1.
[0009] Reduced to its basic structure, and reference being made to the figures of the attached
drawings, an operating head according to the invention has a central shaft (1) with
a flange (2) on top allowing the connection thereof to a machine by which it is driven
into rotation (such a machine usually comprising a plurality of battery disposed lapping
heads). Solid and coaxial to said shaft (1) is a toothed bush (3) whose toothing is
made to mesh with the corresponding inner toothing (4) of a coaxial crown (5) with
which two elastic annular elements (6), coaxial to shaft (1), are associated on opposite
sides. The said crown (5) extends downwardly so as to engage a case (8) from the inside
by screw means (7). Said case (8) fully encloses the inner members of the head, is
coaxial to the shaft (1) and moves along with the latter as it is driven by the element
(5). The lower base of said case (8) is made up of a flange (9) connected to the body
via the same case so as to press, that is, pre-load, said elastic rings (6). The presence
of the elastic rings (6) allows the operating head to effectively absorb the axial
and radial impacts taking place during operation and due to the contact between the
abrasive wheels (19) and the roughness of the material under work. The case (8) exhibits
a plurality of seats for as many vertical axes (10) equally spaced apart from the
main shaft (1) and intended to support the same abrasive wheels (19). Solid and coaxial
to each of said wheel-holder shafts is a gear (11) whose toothing is to mesh the corresponding
toothing of a stationary crown (12) coaxial to the main shaft (1) and whose rotation
is prevented by its being solid (through the body 14 and screws 13) with the machine
to which the head is connected. In this way, as the case (8) rotates together with
shaft (1), the wheels (11) roll around the crown (12) and each wheel-holder shaft
(10) rotates about its vertical axis. As a consequence, each wheel-holder shaft is
driven into rotation about its own vertical axis and, at the same time, about the
axis of shaft (1). The same, of course, holds true for the wheels (19) carried by
the shafts (10). The speed of rotation of shafts (10) is determined by the transmission
ratio of each pair of gears (11, 12). Each wheel-holder shaft (10) is supported on
top by a roller bearing (15) and below by a further roller bearing (16). Moreover,
each wheel-holder shaft (10) is so mounted as to freely translate along its vertical
axis, is associated to elastic means (18) - such as a spiral spring - and exhibits
a stop rod (17) which limits the axial travel of the shaft (10) both downwards and
upwards. More particularly, the upper part of the stop rod (17) is made to strike,
upon reaching the end of its upward stroke, against the corresponding wall of the
case (8) and, upon reaching the end of its downward stroke, against the surface of
an axial ball bearing (20) located in correspondence of its lower portion. Resting
upon a further axial ball bearing (21) is the lower base of the shaft (10).
[0010] Under operating condition, the shafts (10) translate along their vertical axes, so
as to elastically absorb the roughness and irregularities of the surface under treatment
and to ensure no substantial oscillation of the whole operating head will take place,
so that all the wheels (19) will result always adherent to the surface of the material
under work.
1. Improved lapping head, comprising means for supporting and operating a plurality of
abrasive wheels (19) having vertical axis, with a vertical shaft (10) for each wheel
(19), each wheel-holder shaft (10) being fitted into a corresponding seat of a case
(8) driven into rotation by a central vertical axis (1), in which, under operating
condition, each wheel-holder shaft (10) is driven into a rotary motion about its own
vertical axis and into a rotary motion about the axis of said central shaft (1), characterized
in that said wheel-holder shafts (10) are engaged to elastic means acting in their
respective axial direction.
2. Operating head according to claim 1, characterized in that said elastic means consist
of a spiral spring coaxially fitted on said wheel-holder shaft (10).
3. Operating head according to claim 1, characterized in that it is provided with upward
and, respectively, downard stop means for each of said wheel-holder shafts (10) so
as to keep their axial displacement within preset limits.
4. Operating head according to claim 1, characterized in that each wheel-holder shaft
(10) draws its motion from said central shaft (1) via a gear drive.
