Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a sandblasting machine
and method for finishing moulded or cast pieces, particularly
for trimming mouldings of thermo-setting plastics.
The practice of finishing, or more generally
surface-treating articles under production by means of sand-
blasting is very widespread in modern technology. It is used
on all metal pieces to be painted, enamelled, metallized, etc.,
on metal pieces produced by casting or moulding to re ve
burrs, on plastics pieces to be painted or metallized to
improve adhesion, and on moulded plastics parts for trimming
and finishing, to cite just some examples related to the
field of the invention, which, although having been developed
to satisfy specific problems of resin products, is not limited
to these and is extended in its application to related
sectors such as those stated.
The moulding, die-casting and injection moulding of
resin or plastics pieces has been developed particularly in
the electrotechnical field for economical reasons and for
the ease of incorporating metal parts in the mouldings, which
;20 ~ ~ would be impossible in the case of the more esteemed a~nd
costly ceramic insulant material. Thus objects have been
; produced by moulding which are increasingly complicated and
in their final stages of assembly, or at least in very advanced
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stages, such as single or multi-6tage electrical switches and
; commutators. The great economy of such production is due to
the complete automation and high productivity rate attained,
~ such that the intervention of direct labour has nearly dis-
;~ appeared. The pieces produced in this manner require only
surface finishing to remove casting or moulding burrs.
Initially, this operation was carried out by an operator
using a jet of sand in a box, and wearing a protective ~ k.
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However, this manual operation, besides giving rise to some
criticism and preoccupation from the health aspect, is out
of step with the whole economy of the production process.
Thus completely automatic sandblasting was necessarily
brought in.
The method used at the present time consists of
disposing a load of pieces in a cavity or cradle on to which
a wide jet of sand or grit is directed while the load is con-
tinuously agitated or turned in such a manner that the entire
surface of each piece is exposed to the jet in various posi-
tions. ~his method has proved valid from the point of view
of working efficiency and economy in the amount it contributes
to the cost of each sandblasted piece, but has a serious
drawback which is intrinsic to its system and cannot be
eliminated unless the system itself is changed, namely that
the pieces inevitably collide with each other as they are
turned, and if the pieces comprise delicate projections
such as is the case with switches and the like, these can
become damaged or broken, and this is reflected in an
excessive number of production rejects. To obviate this
serious drawback, it has been attempted to pass the objects
to be sandblasted one by one in front of the sand jet in
various positions, either by passing the piece se~eral times
in different positions in front of the same jet, or by
passing the piece in front of different jets disposed in
different positions. To pass the piece again in a different
position, the conveyor, belt, chain or wire carrying the
objects is returned in front of the jet, but this allows
only two passes with two fixed positions. More simply, the
pieces are loaded several times in different positions on
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the same conveyor belt passing in front of the fixed jet.
This requires an operator for the loading and unloading,
An attempt has also been made to load the pieces on to
rotatable supports on the conveyor. This can be successful
in the case of large costly pieces, but would be too expensive
for common pieces. Thus the problem of sandblasting pieces
having a shape even slightly complicated has not yet found
a general satisfactory olution.
The general object of the present invention is
therefore to obviate the drawbacks of the aforesaid sand-
blasting methods.
One particular object of the invention is a con-
tinuous sandblasting method which enables the individual
pieces to be sandblasted practically in all directions.
A further particular object is a sandblasting machine
which enables the new method to be carried out.
A further particular object is a device for a sand-
- blasting machine which enables a piece to be presented in a
single pass in front of a jet of sand or grit while making it
assume all the required positions, without any danger of
impact damaging to the method,
These and further objeats have been attained
accordiny to the invention by a sandblasting method for
finishing moulded or cast pieces, particularly for trimming
mouldings of thermo-sett1ng plastics, wherein the pieces to
be sandblasted are made to roll in front of a sandblasting
jet, individually in a single pass, within a reticulated
portion of a conduit.
To carry out the method according to the invention
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there is provided a sandblasting machine for finishing
moulded or cast pieces, particularly for trimming mouldings
of thermo-setting plastics, comprising a conduit in which
the pieces to be processed are caused to move forward under
gravity by rolling, and a sandblasting jet which is directed
into the interior of the conduit transversely
In accordance with a particular embodiment of the
invention, a sandblasting machine for finishing moulded or
cast pieces, particularly for trimming mouldings of thermo-
setting plastics, comprises a rotatable conveyor tube forthe pieces to be sandblasted, said conveyor tube having its
axis i~clined downwardly in the feeding direction of said
pieces thereby to feed by gravity said pieces therethrough, - : -
said conveyor tube having at least one aperture in an inter-
mediate portion thereof, blasting jet generating means having
blades directing the sandblast jet towards said aperture in a
direction transverse to said axis, characterized in that
said aperture extends over the entire circumference of said
intermediate portion of said conveyor tube, said intermediate
portion comprises an open mesh structure covering said
aperture and the machine includes rotatable supports allowing
full continuous rotation of said conveyor tube about its axis
and drive means for imparting a full continuous rotation to
said conveyor tube about its axis, thereby to impart a random
rolling to said pieces both in a circumferential and axial
direction of the conveyor tube.
The characteristics and advantages of the invention
will be apparent from the detailed description of a preferred
embodiment given by way of example, with reference to the
accompanying drawings, in which:
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1097080
Fig. 1 is a perspective view of a sandblasting
machine for carrying out the method according to the invention,
Fig. 2 is a view in the direction II of Figure 1,
Fig. 3 is an axial section in elevation of the
device for single pass sandblasting according to the invention,
and
Fig. 4 is an axial section through a turbine which
generates the sand jet.
Reference will now be made in particular to Figures
1 and 2 which show a machine or installation for carrying out
the invention, indicated overall by the reference numeral 1.
It consists of a housing 2 with an upper support surface 3
from which projects a stepped part 4, which is connected by
way of a connector 5 to a suction fan 6 comprising a tor 6'.
The housing 2 is supported on four feet 7, between
which there extends a hopper 8 in the form of a lower
appendix to the housing 2. A unit formed from an electric
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motor 10 and a centrifugal sand jet turbine 11 is fixed on to
the surface 3 by way of a base 9. A vertical screw conveyor
tube 12 is connected to the discharge mouth of the hopper 8
(Fig. 2) to gravity-feed the turbine or turbo-ejector 11 with
sand in closed cycle. The screw inside the tube of the con-
veyor 12 is driven by an electric motor 13. The housing 2 is
traversed, in a plane normal to the axis-of the turbine 11, by
a tubular conduit 14 (Fig. 3) which represents the feeder and
single-pass conveyor for the pieces to be sandblasted. The
turbine 11 feeds its sand jet towards the interior of the
housing, along the axis of the conveyor 14 as described here-
inafter. A door 15 enables the interior of the housing 2 to
be inspected and maintained.
Figure 3 shows an axial section, in a vertical plane,
through the entire portion of the conveyor 14 which traverses
the housing 2, together with part of the two conveyor projec~
tions thereof. The conveyor tube 14 is disposed with its axis
inclined downwards from left to right in Fig. 3, to ensure
that the conveyed pieces move forward while rolling, when the
tube is rotated. It is mounted in the opposing walls of the
housing 2 by way of two rotatable supports 16, each consti-
tuted by a flange 17 and backing flange 18 which clamp between
them the edges of the perforated wall of the housing 2, and
house between them three rolling bearings 19 distributed
peripherally 120 apart, on which the tube 14 rolls by way of
a sleeve 20 rigid with the tube. A coupling covering 21 is
provided to protect the bearing from the sand.
The sleeve 20 of the upstream coupling is also used
for transmitting rotary motion to the tube, generated by an
electric motor 22 and transmitted to the tube via a reduction
gear 23 and belt 24. The conveyor tube 14 is interrupted over
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at least the entire portion corresponding to the sand jet,
indicated orientatively by the dashed lines running from the
turbine 11, of which the impeller is indicated diagrammatic-
ally in Fig 3.
Over this portion, the tube is replaced by a cylindri-
cal basket or cage 25, of the same diameter as the tube 14, and
mounted in alignment therewith by means of two end flanges 26.
Advantageously, the basket or cage portion 25 has wide meshes
compatible with the dimensions of the pieces to he sandblasted,
and fairly thin wall wires or bars. To obtain the necessary
mechanical connection for maintaining alignment and transmit-
ting motion between the two portions of the tube 14, a stirrup
coupling is provided externally and consists of two flanges 27,
each disposed at the mouth of a respective portion of tube 14,
and facing the corresponding flange 26 The flanges 27 are
joined firmly together by two external stirrups 28 disposed
180 apart. This mechanical coupling enables the basket 25
to be easily replaced without moving the tube 14.
~ Figure 4 shows the turbine or turbo-ejector 11, which
although representing the essential member of the sandblasting
installation does not form an actual part of the invention,
and is shown because it has been designed and constructed for
use in the preferred embodiment of the invention. The turbine
11 comprises essentially a casing 30 fixed to the base 9.
With the casing 30 there is rigid a sleeve support 31 in which
the turbine shaft 32 is supported on two support bearings 33
and a thrust bearing 34, and is driven by a pulley 35 with
three races. The impeller carried by the shaft comprises two
sets of blades, namely a central set in the form of teeth on
a rotating distributor 36, and a set in the form of centrifugal
injection blades 37. The teeth of the rotating distributor 36
rotate between the teeth of a fixed distributor 38, the teeth
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of which are opposite and external to the former. rrhe turbine
11 is disposed with its axis horizontal and its centrifugal
discharge port pointing downwards, as indicated by the arrow.
An elbow connector 39 gravity-feeds the sand axially to the
turbine, by receiving it from the screw conveyor 12. A nozzle
injector tube 40 feeds water under controlled conditions into
the stream of sand to moisten and lubricate it.
rrhe description of operation of-the installation
will begin with the turbine heretofore described. rrhe sand
reaches its central region where the rotating distributor 36
feeds it by way of the fixed distributor 38 uniformly on to
the blades of the impeller 37, which project it into a volute
delivery path defined by the casing 30, as in the case of a
centrifugal pump As shown in Fig. 3, the wide jet of sand
or grit is directed and centred on the basket 25 of the tubu-
lar conveyor 14. The pieces to be sandblasted, for example
of thermo-setting resin and not shown, are fed continuously
into the conveyor 14 one behind the other, the minimum dis-
tance apart without touching each other. The speed of rot-
ation of the tube and its slope are chosen such that for agiven width and efficiency of the sand jet, each piece rotates
about itself a number of times and remains exposed for the
time necessary for its entire surface to be sufficiently
sandblasted. The rotation of the tube helps the piece to roll
downwards along the tube. rrhe jet also aids the transverse
rolling of the piece, which therefore passes through all
possible positions. As the pieces follow closely behind each
- other, the jet is very well utilized, and as it is proportioned
uniformly over each piece and over the entire surface of each
piece, the exposure thereof can be reduced to the necessary
minimum. rrhis is in contrast to the sandblasting of pieces
which are rotated in a heap, because in this case there is a
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high statistical influence, which means that a factor even
higher than 2 would have to be exceeded in order to obtain a
high probability of sandblasting all the pieces, and even then
there are always pieces which are sanded to an excessive or
insufficient degree. The fan 6 maintains a certain vacuum in
the housing 2, to prevent dust leaving through the tube 14.
The air is then purified or fed to a stack. It is advisable
to make the basket 25 and stirrups 28 of abrasion-resistant
material, or better still make them coated, for example
enamelled, or covered with special anti-abrasive resins, or
coated with rubber specially resistant to sandblasting. The
tube 14 is also preferably coated, for example with plastics,
so that there is no danger of the pieces suffering damaging
impact during rolling. It should be noted that this ideal
operation has been obtained by means of a structure and a
mechanical system which are extremely simple and of low cost.
The entire movement is provided by a small geared motor unit
and a direct belt drive. Thus, relative to equivalent previous
installations, perfect processing with elimination of all the
causes of rejects in this processing stage is obtained, to-
gether with greater productivity, completely auto~atic con-
tinuous operation, and lower installation cost. It is apparent
that the concepts described can be embodied in different forms
without leaving the scope of protection of the invention.
For example, even though of less merit, the turbine sander
could be replaced by any air jet sander, and in all cases the
jet could point in any other sideways direction or from below,
and the tube could be made to vibrate instead of rotate.
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