Note: Descriptions are shown in the official language in which they were submitted.
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PNEUMATIC HAND GRINDING TOOL
The present invention relates to a pneumatic hand
grinding tool, which has a supporting plate and a com-
pressed-air pipe to be connected to a source of com-
pressed air for driving the supporting plate, the sup-
s porting plate having a flat surface to which an abrasive
sheet is to be attached.
In order to fasten an abrasive sheet, by which is
here meant a piece of abrasive paper, an abrasive cloth
or the like, to a supporting plate, today adhesive abra-
sive sheets are generally used, which have an adhesive
surface that is made to abut against the flat surface of
the supporting plate. Such abrasive sheets are relatively
expensive and are also difficult to handle because of the
adhesive surface which is sensitive to dust and dirt. Be-
sides, they have a limited shelf life and are tempera-
ture-sensitive.
It is also known to use so-called Velcro strips for
attaching an abrasive sheet to a supporting plate. An ef-
ficient attachment of the abrasive sheet is then ob-
tamed, but abrasive sheets for such an attachment are
very expensive. Such abrasive sheets do not allow the
user to change the format of the abrasive sheet or make
dust extracting holes.
Finally, it is also known to attach an abrasive
sheet to a supporting plate by suction of the abrasive
sheet to the flat surface of the supporting plate. For
such a supporting plate use can be made of ordinary abra-
sive sheets, i.e. abrasive sheets which have not been
treated in a specific way, for instance been provided
with an adhesive layer or Velcro strips. Then quick and
easy changes of abrasive sheets may take place.
With a view to attaching the abrasive sheet by suc-
tion to the supporting plate, the supporting plate has
ducts leading into the flat surface which are connected
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to a source of suction. In the known tools in which the
abrasive sheet is attached by suction to the supporting
plate, a source of suction which is disposed outside the
tool is used. In a pneumatic hand grinding tool of this
sort, it is thus necessary, on the one hand, to connect
the tool by means of a compressed-air pipe to a source of
compressed air for driving the supporting plate and, on
the other, to connect the ducts of the supporting plate
to the source of suction by means of a suction pipe. This
complicates the use of the tool and limits the use to
such locations where, in addition to a source of com-
pressed air, also a source of suction is available.
The object of the present invention is therefore to
provide a pneumatic hand grinding tool, in which the
abrasive sheet is attached by suction to the supporting
plate and the use of which is not limited to such loca-
tions where, apart from a source cf compressed air, also
a source of suction is available.
This object is achieved by means of a pneumatic hand
grinding tool, which has a supporting plate and a com-
pressed-air pipe to be connected to a source of com-
pressed air for driving the supporting plate, the sup-
porting plate having a flat surface to which an abrasive
sheet is to be attached by suction, and the supporting
plate having for this purpose ducts leading into the flat
surface, which are connected to a source of suction, the
tool according to the present invention being character-
ised in that the ducts are connected to an ejector unit
forming the source of suction, the ejector unit being ar-
ranged on the tool and having means for connecting the
ejector unit to the compressed-air pipe.
In a preferred embodiment, the ejector unit com-
prises at least two ejectors, which are connected to at
least two separate duct systems comprising the ducts con-
nected to the respective ejectors. The flat surface of
the supporting plate is conveniently, with the aid of
sealing means, divided into sections which are separated
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from each other and associated with the respective duct
systems.
The invention will now be described in more detail
with reference to the accompanying drawings, in which
Fig. 1 is a cross-sectional view of a hand grinding
tool according to the present invention,
Fig. 2 is an exploded view and shows parts included
in the tool according to Fig. 1 in cross-section,
Fig. 3 shows an ejector unit arranged in the tool,
in the direction of arrow III in Fig. 2,
Fig. 4 shows a vacuum distributor arranged in the
tool, in the direction of arrow IV in Fig. 2,
Fig. 5 shows a supporting disc arranged in the tool,
in the direction of arrow V in Fig. 2, and
Fig. 6 shows the supporting disc in the direction of
arrow VI in Fig. 2.
The hand grinding tool shown in Fig. 1 has a casing
1 and a handle part 2 connected thereto. The tool is
pneumatically operated and has a compressed-air motor 3
which by means of a compressed-air pipe 4 extending
through the handle part 2 is connected to a source of
compressed air (not shown).
The output shaft 5 of the motor 3 has a threaded,
axial bore at its end facing away from the motor. A bolt
6, whose head 7 forms a spacing means and is non-
rotatably connected to a circular metal washer 8 that
will be described in more detail below, is screwed into
the end bore of the shaft 5 in order to rotate with the
shaft together with the washer 8. The bolt head 7 also
has a threaded axial bore 9 at its free end, and the cen-
tre hole of the washer 8 is located opposite this bore 9.
A bolt 10 is screwed into the bore 9 of the bolt head 7
to rotate with the bolt head, and thus with the motor
shaft 5.
A circular supporting disc 11, which consists of a
supporting sheet 12 of metal and a rubber sheet 13 pro-
vided with knobs which are directed outwards (downwards
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in Fig. 1), is non-rotatably connected to the bolt 10.
The supporting disc 11 thus rotates with the bolt 10, and
consequently with the bolt 6 and the motor shaft 5. The
supporting disc 11 has a circumferential rubber skirt 14
which forms an outer, peripheral sealing lip.
The supporting disc 11 of the tool is eccentrically
rotated, and for this purpose the tool has an eccentric
device 15 which is of prior-art type and therefore is not
further described here.
The tool has an ejector unit 16 which is non-
rotatably connected to the casing 1 and consists of a
collar 17 and four ejectors 18 attached to its circumfer-
ence. The ejectors 18 are evenly distributed along the
circumference of the collar 17. The ejectors 18 are of
conventional type and have a through compressed-air pas-
sage 19 and a transverse duct 20 connected thereto, which
leads into the radially inwards directed surface of the
ejector 18. The compressed-air passage 19 is at its one
end connected to the source of compressed air through the
compressed-air pipe 4 and an ejector pipe 21 which is
connected thereto.
The collar 17 has in its outwards (downwards in Figs
1 and 2) directed surface, two circular, concentric
grooves or ducts 22 and 23. The grooves 22 and 23 are
sealed radially inwards, between them and radially out-
wards by means of three sealing rings 24, 25 and 26. The
sealing rings 24, 25 and 26 abut against the inwardly di-
rected surface of the washer 8. The collar 17 has, oppo-
site each ejector 18, a duct 27, 28, which constitutes a
radial extension of the duct 20 of the ejector. The duct
27 communicates with the inner annular groove 22, whereas
the duct 28, which is shorter than the duct 27, communi-
cates with the outer annular groove 23. Two of the four
ejectors 18 are in this way connected to the inner annu-
lar groove 22, while the two others are connected to the
outer annular groove 23.
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The ejector unit 16 has four arms 29 which protrude
radially from the collar 17 and which at their free end
have a pin 30. Each pin 30 is introduced into a corre-
sponding hole 31 in a fixing lug 32 which is formed on
5 the casing 1. A compression spring 33 is arranged on each
pin 30 to press the collar 17 against the washer 8 rotat-
ing with the shaft 5.
The washer 8 has two groups of passages 34, 35. In
one of the groups, the passages 34 are distributed along
an inner circle which has the same radius as the inner
annular groove 22 of the collar 17, and in the other
group, the passages 35 are distributed along an outer
circle, which has the same radius as the outer annular
groove 23 of the collar 17. The passages 34 of the washer
8 are thus located opposite the inner annular groove 22
of the collar 17, while its passages 35 are located oppo-
site the outer annular groove 23 of the collar 17. The
passages 34, on the one hand, and the passages 35, on the
other, are sealed radially inwards, between them and ra-
dially outwards by means of three sealing rings 36, 37
and 38. The sealing rings 36, 37 and 38 abut against the
inwardly directed surface of the supporting sheet 12.
The supporting sheet 12 has two groups of through
holes 39, 40. In one of the groups, the holes 39 are dis-
tributed along an inner circle, which has the same radius
as the inner annular groove 22 of the collar 17, and in
the other group, the holes 40 are distributed along an
outer circle, which has the same radius as the outer an-
nular groove 23 of the collar 17.
The rubber sheet 13 has, in its inwardly directed
surface, an inner circular centre recess 41, which ex-
tends a distance into the sheet. A plurality of holes 42,
which lead into the flat outer surface, defined by the
knobs, of the sheet 13 communicate with the recess 41.
The holes 42 are distributed along a circle which is con-
centric with the shaft 5. The rubber sheet 13 has also in
its inwardly directed surface an outer circular groove 43
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and, extending radially outwards therefrom, a plurality
of grooves 44, which terminate a distance from the cir-
cumference of the sheet 13. A hole 45, which leads into
the outer surface of the sheet 13, communicates with each
groove 44 at the radially outer end thereof. The rubber
sheet 13 has a narrow, circular, continuous portion 46
which forms a sealing ring between the openings of the
holes 42, on the one hand, and the openings of the holes
45, on the other.
la As will be evident from the above, the radially in-
ner holes 42, which lead into the flat outer surface of
the sheet 13, communicate with two of the ejectors 18
through the recess 41, the passages 34, the groove 22 and
the ducts 27. The two ejectors 18 form a source of suc-
tion for the duct system which is formed by the holes 42,
the recess 41, the passages 34, the groove 22 and the
ducts 27. As will further be evident, the radially outer
holes 45, which lead into the flat outer surface of the
sheet 13, communicate with the other two ejectors 18
through the grooves 44, the groove 43, the passages 35,
the groove 23 and the ducts 28. The two last-mentioned
ejectors 18 form a source of suction for the duct system
which is formed by the holes 45, the grooves 44, the
groove 43, the passages 35, the groove 23 and the ducts
28. The two duct systems are separated from each other by
means of the sealing rings 25, 37 and 46. The duct system
27, 22, 34, 41, 42 is sealed radially inwards by means of
the sealing rings 24 and 36, and the duct system 28, 23,
35, 43, 44, 45 is sealed radially outwards by means of
the sealing rings 26 and 38 as well as the sealing lip
which is formed by the rubber skirt 14.
A valve 47 is arranged in the compressed-air pipe 4.
The valve 47 is by means of a switch (not shown) adjust-
able from a first position, in which it stops the supply
of compressed air to the motor 3 as well as to the ejec-
tors 18, to a second position, in which it still stops
the supply of compressed air to the motor 3 but keeps the
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connection 21 between the compressed-air pipe 4 and the
ejectors 18 open, and via the second position to a third
position, in which it allows supply of compressed air to
the ejectors 18 as well as to the motor 3. Naturally, the
valve 47 is by means of the switch also adjustable from
the third position to the second position and via the
latter to the first position.
When the valve 47 is in its second position, a suc-
tion effect at the flat surface of the supporting disc 11
is thus produced via the two separate duct systems 27,
22, 34, 41, 42 and 28, 23, 35, 43, 44, 45. By this suc-
tion effect, an abrasive sheet 48 is attached to the sup-
porting disc 11. Subsequently, the valve 47 is adjusted
to its third position, the motor 3 being supplied with
compressed air and driving the supporting disc 11 and the
abrasive sheet 48 attached thereto.
