Note: Descriptions are shown in the official language in which they were submitted.
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TOOTH FLANK POLISHING TOOL
The invention relates to a tooth flank polishing tool and the use of such
tool.
An important criterion for the quality of tooth gears is the roughness or
smoothness of
the tooth flanks. Roughness values Ra ranging from 0.4 pm to 1.6 pm can be
attained by grinding, which correspond to peak-to-valley heights Rt of 1.6 pm
to 6.3
pm; roughness values of Ra <_ 0.2 pm can be attained by vibratory grinding.
For
vibratory grinding, the work pieces to be worked on are placed as bulk
material in a
working container, together with abrasive products, so-called chips, and
frequently an
additive in aqueous solution. A relative movement between workpiece and the
abrasive product is produced by an oscillatory and rotational motion of the
working
container which causes removal of material from the workpiece, in particular
on its
edges. Vibratory grinding can produce excellent surface smoothness.
Disadvantageously, vibratory grinding can take a long time, between 4 hours
and 24
hours. In addition, the size of the components to be worked on is limited with
vibratory grinding, because the components together with the chips must fit
inside a
working container.
Larger tooth gears which are not suitable for vibratory grinding according to
the
aforedescribed process due to their size, must therefore be worked on manually
with
fine polishing tools. Disadvantageously, manual processing is unable to
produce a
uniform surface quality. As a result, some sections on the tools flanks may
have
different roughness, causing portions of the bearing support surface to be
different
which can adversely affect the load bearing capacity of the tooth. The sliding
properties of any manually polished tooth gear are therefore not uniform over
the
entire periphery, which may lead to increased wear during operation and
increased
noise generation.
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Another problem when working with fine-grained polishing tools is so-called
burning,
or overheating during grinding. Burning occurs when abrasive material with
very
small of fine grain size is used. This is due to the fact that the coefficient
of friction
between the abrasive material and the workpiece becomes very high with
decreasing
grain size, with heat generated by friction potentially causing material
changes of the
workpiece. The material can, for example, become brittle which would adversely
affect the service life.
It is therefore an object of some embodiments of the invention to provide a
tooth flank
polishing tool which is capable of producing tooth flanks with particularly
small
roughness, in particular on tooth gears that had not been worked on by
vibratory
grinding, thereby obviating the disadvantages of conventional manual polishing
methods, as well as to elucidate various uses for such tooth flank polishing
tool.
According to one aspect of the present invention, there is provided tooth
flank
polishing tool, comprising a base which can rotate about a central axis and to
which
there is attached a polishing fleece which can be introduced into at least one
tooth
gap of a gear that is to be polished, wherein at least some sections of the
polishing
fleece have an external contour which is adapted to the shape of a tooth
flank,
wherein the polishing fleece comprises an organic, synthetic and/or mineral
material,
selected from cotton or sisal, synthetic resin fibres, tangled synthetic resin
fibres or
nylon.
In some embodiments, the tooth flank polishing tool is used to remove
roughness
peaks, i.e., the surface structure of the tools flanks is at least partially
plastically
deformed with very little material removal and hence smoothed. With the tooth
flank
polishing tool of the invention, a tooth flank can advantageously be polished
so
smoothly so that it has a very small surface roughness Ra of preferably <_ 0.4
pm, in
particular <_ 0.2 pm. In this way, the percentage of the bearing support
surface and
hence the tooth load bearing capacity is increased and the sliding properties
of the
tooth gear are improved. The
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basic geometry of the previously generated tooth gear arrangement is not
changed.
The damage of the tooth surfaces from thermal overheating, which can occur
when
fine-grained grinding disks that do not match the geometry of the tools flanks
are
used, can thus be reliably prevented with proper handling. Advantageously, the
tooth
flank polishing tool can be adapted to any size of a tooth gear.
With the tooth flank polishing tool of the invention, tooth gears having a
very large
diameter, i.e., a diameter greater than 1000 mm, can be worked on in order to
generate a surface in the region of the tooth flanks which is able to prevent,
for
example, gray stippiness. Gray stippiness refers to a wear characteristic of
regions
near the surface of highly stressed metallic components, for example the tooth
flanks
of tooth gears. Gray stippiness can be identified on dull gray surfaces with
the naked
eye. The origin is a large number of very small nicks and pores caused by
mixed
friction and sliding friction and the resulting plastic deformation of regions
near the
surface. Gray stippiness can eventually cause deep incipient cracks and nicks
on the
tooth flanks. Another important aspect of the invention is that the tooth
flank polishing
tool can be integrated in an automated process, so that, unlike with manual
surface
processing, predetermined surface qualities with the required small variation
range
can be obtained.
The polishing fleece can be made of a composite material or a single material.
Preferably, the polishing fleece includes an organic, synthetic and/or mineral
material. Organic materials for a polishing fleece include cotton or sisal.
Synthetic or
chemical materials for a polishing fleece may be resin fibers, tangled resin
fibers or
nylon. A suitable mineral material is particularly aluminum oxide (A12O3),
preferably in
the form of corundum.
In an advantageous embodiment, the polishing fleece is applied at least over
sections of a surface of the base. For example, the polishing fleece is
attached on
the base with an adhesive.
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In another embodiment, the polishing fleece is strung over the surface of the
base.
This requires a clamping device for securing the polishing fleece. Covering
the area
has an advantage over using an adhesive in that the polishing fleece can be
exchanged if needed.
In another particularly advantageous embodiment, the polishing fleece is
inserted in
a radial circumferential groove or a seat of the base. In this way, the
polishing fleece
can be permanently and stably affixed.
A combination of the base and the polishing fleece can have the shape of a
polishing
disk. The tooth flank polishing tool can then advantageously be clamped in
conventional polishing machines, such as rotary tables, gear hopping mills or
tooth
flank grinding machines. Machining is performed incrementally, i.e., the tooth
gear is
rotated commensurate with its pitch and the tooth flank polishing tool is
moved
between two tooth flanks.
According to another embodiment, the combination of the base and the polishing
fleece can have the shape of a polishing worm gear. With a polishing worm
gear, the
flanks of the tooth gear can be polished in a continuous process. The
polishing worm
gear can also be clamped in conventional polishing machines, such as rotary
tables,
gear hopping mills or tooth flank grinding machines. The polishing fleece
hereby
formed a tooth of the polishing worm gear or a surface region of the tooth.
The tooth
can also be formed on the base and the polishing fleece can be attached
outside on
the tooth.
The combination of the base and the polishing fleece (73, 85, 94) can have the
shape of a polishing finger. The polishing finger can be versatilely used.
This type of
tooth flank polishing tool is suitable for rotary tables and gear hopping
mills.
The tool flank polishing tool is primarily intended for polishing tooth gears,
for
example, spur tooth gears and pinions, spur ring gears, bevel spur gears and
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pinions, as well as worm gears and shafts, in particular with diameters
greater than
1000 mm.
In an advantageous modified embodiment of the invention, the base is at least
indirectly coupled with an oscillation generator. The oscillation generator is
provided
for superimposing on the rotary motion of the base an oscillatory motion. The
oscillatory motion occurs in at least one spatial direction, for example in an
axial or a
radial direction of the base. Also feasible in the context of the invention is
a
superposition of two spatial directions, thereby producing circular or
elliptical motion
in at least one plane in three-dimensional space. The oscillation generator
can be a
tubular oscillator or a rotor oscillator, in particular a piezoelectric
oscillator.
Longitudinal oscillations or flexural oscillations can be combined and
superimposed.
The invention is not limited to the type of oscillation generator or the
particular
oscillation direction, or to a particular oscillation frequency. It is
important, however,
that an improved polishing result can be obtained with the additionally
generated
oscillation.
In general, the tooth flank polishing tool can also be used to polish a
thread. Threads
have a tooth-like shape with tooth flanks, so that these can also be polished
using
the tooth flank polishing tool.
The invention will be described hereinafter in more detail with reference to
exemplary
embodiments depicted schematically in the drawing. It is shown in:
FIG. 1 a tooth flank polishing tool in form of a polishing disk;
FIG. 2 a cross section through the polishing disk of FIG. 1 according to a
first
embodiment;
FIG. 3 a cross section through the polishing disk of FIG. 1 according to a
second
embodiment;
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FIG. 4 a tooth flank polishing tool in form of a polishing worm gear;
FIG. 5 a cross section through the polishing worm gear of FIG. 4 according to
a
first embodiment;
FIG. 6 a cross section through the polishing worm gear of FIG. 4 according to
a
second embodiment;
FIG. 7 a tooth flank polishing tool in form of a polishing finger;
FIG. 8 a cross section through the polishing finger of FIG. 7 according to a
first
embodiment; and
FIG. 9 a cross section through the polishing finger of FIG. 7 according to a
second
embodiment.
FIG. 1 shows in a simplified schematic diagram a tooth gear 1 and a tooth
flank
polishing tool 2 in form of a polishing disk, which are jointly clamped in an
un-
illustrated tooth flank polishing machine. The tooth flank polishing tool 2
has a base 4
rotating about a central axis 3. The central axis 3 can be moved by the tooth
flank
polishing machine in two different radial directions 5, 6. The polishing disk
2 is driven
with a defined angular velocity and pressed with a likewise defined pressing
force
against the tooth gear 1. A polishing fleece 15 is attached on the base 4. The
polishing fleece 15 engages in a tooth gap 7 of the tooth gear 1 and has in
the
section where it makes contact with a tooth flank 8 an outside contour that
matches
the shape of the tooth flank 8 of the tooth gear 1. The tooth gear 1 is
clamped in the
tooth flank polishing machine for rotation about its longitudinal axis 9.
Accordingly,
one tooth flank 8 after another tooth flank 8 of the tooth gear 1 can be
polished.
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FIG. 1 also shows schematically an oscillation generator 95 which is coupled
to the
base 4 in a manner that is not illustrated in detail. More particularly, the
oscillation
generator is a piezoelectric ultrasound motor which superimposes an
oscillatory
motion on the rotary motion of the base 4 or of the polishing fleece, wherein
the
oscillatory motion can point longitudinally in one of the illustrated spatial
directions x,
y, z or any other additional spatial direction. Longitudinal oscillations can
also be
superimposed, resulting in a rotation oscillation in an arbitrary spatial
plane. The
oscillatory motion of the base improves the polishing efficiency of the tooth
flank
polishing tool of the invention.
FIG. 2 illustrates the polishing disk 16 in cross-section. The base 4 having
an inner
cylindrical hollow space 10 is rotationally symmetric with respect to its
central axis 3
and has on the radially outward peripheral side 11 a circumferential groove 12
in
which the polishing fleece 15 is inserted. It can be seen that the polishing
fleece 15
has on two surfaces 13, 14 an outside contour that matches the shape of two
adjacent tooth flanks 8 (see FIG. 1). The polishing fleece 15 includes an
organic
material, for example cotton or sisal.
Another embodiment of the polishing disk 17 is illustrated in FIG. 3 in cross-
section.
Unlike in the polishing disk 16 (see FIG. 2), at the base 23 a circumferential
bead 18
is formed, with a polishing fleece layer 20 applied on its radially outside
19. The bead
18 has an outside contour formed by two surfaces 21, 22 and matching the shape
of
adjacent tooth flanks 8 (see FIG. 1).
FIG. 4 shows schematically a tooth gear 30 and a tooth flank polishing tool 31
in form
of a polishing worm gear, which are jointly clamped in an unillustrated gear
hobbing
mill. The tooth flank polishing tool 31 includes a base 32 on which once more
a
polishing fleece 33 is attached. The base 32 is supported for rotation about
its central
longitudinal axis 34 and can be moved by the gear hobbing mill in two
different
directions 35, 36. The polishing worm gear 31 is driven with a defined angular
velocity and is pressed with a likewise defined pressing force against the
tooth flanks
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37 of the tooth gear 30. Like in the tooth flank polishing machine according
to FIG. 1,
the tooth gear 30 is clamped in the gear hobbing mill for rotation about a
central axis
38.
The polishing fleece 33 engages simultaneously in several adjacent tooth gaps
39 of
the tooth gear 30. In this exemplary embodiment, the polishing worm gear 31
has a
tooth 40 which protrudes from the radially outward peripheral side of the base
32 and
winds in a helical pattern about the base 32. The outer contour of the tooth
40
matches the shape of the tooth flanks 37 with which it is in contact. The
tooth gear 30
rotates about its longitudinal axis 38 in unison with the rotation of the
polishing worm
gear 31. In this way, all tooth flanks 37 can be polished in a continuous
process.
FIG. 5 shows a cross-section through a polishing worm gear 51 according to a
first
embodiment. As shown, the base 53, which has an interior hollow space 52,
includes
on its radially peripheral side 54 a groove 55 which winds around the base 53
in a
helical pattern and into which the polishing fleece 56 is inserted. The
polishing fleece
56 forms the tooth 40 (see FIG. 3) of the polishing worm gear 51. The
polishing
fleece 56 has an outside contour 57 that matches the shape of the tooth flanks
37
(see FIG. 3). The polishing fleece 56 includes a synthetic material, for
example resin
fibers, tangled resin fibers or nylon.
FIG. 6 shows a second embodiment of the polishing worm gear 58 in cross-
section.
Unlike in the preceding embodiment (see FIG. 4), the tooth 59 is formed on the
base
53, and a polishing fleece layer 60 is applied on the tooth 58. The polishing
fleece
layer 60 is attached on the base 53 with an adhesive and includes a mineral
material,
for example aluminum oxide (A1203), preferably in form of corundum.
FIG. 7 shows a tooth flank polishing tool 70 in form of a polishing finger and
a
simplified schematic diagram of a tooth gear 71, which are jointly clamped in
an
unillustrated rotary table. The polishing finger 70 has a base 72 on which a
polishing
fleece 73 is attached. The polishing finger 70 rotates about its longitudinal
axis 74
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during polishing and is also adjustable in the direction of the longitudinal
axis 74 of
the polishing finger and the longitudinal axis 75 of the tooth gear. The
polishing finger
70 is inserted in a tooth gap 77 and pressed with a predefined pressing force
against
(the) tooth flanks 76 to be polished and is guided in a translational motion
parallel to
the longitudinal axis 75 of the tooth gear along the surfaces of the tooth
flanks 76.
FIG. 8 shows in cross-section a polishing finger 80 according to a first
embodiment.
The polishing finger 80 has a base 81 on which a shaft 82 is formed as a
single
piece. A seat 84 for a polishing fleece 85 is provided on the end 83 opposite
the shaft
82. The polishing fleece 85 is held with a rotation lock in this seat 84. The
base
surface of the seat 84 and of the insertion section 86 of the polishing fleece
85 are
hereby shaped as a polygon. The outside of the polishing fleece has a conical
contour 87 that matches the shape of the tooth flanks 76 (see FIG. 7) with
which the
contour 87 makes contact. The polishing fleece 85 is made of nylon.
The embodiment illustrated in FIG. 9 shows another configuration of the
polishing
finger 90. Unlike in the embodiment of FIG. 8, the base 91 has a polishing
cone 92. A
polishing fleece layer 94 is applied on the outside 93 of the polishing cone
92. The
polishing fleece layer 94 includes tangled resin fibers.
The polishing fleeces 16, 51, 80 of the embodiments illustrated in FIGS. 2, 5
and 8
are shown as a single piece. However, these polishing fleeces could also be
produced with a stiffening core made of a different material, wherein the
polishing
fleece is arranged only on the outside of this core.
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List of references symbols
1 Tooth gear
2 Tooth flank polishing tool
3 Central axis of 4
4 Base
Radial direction
6 Radial direction
7 Tooth gap
8 Tooth flank
9 Longitudinal axis of 1
Hollow space
11 Peripheral side of 4
12 Groove
13 Outer surface of 15
14 Outer surface of 15
Polishing fleece
16 Polishing disk
17 Polishing disk
18 Bead
19 Outside of 18
Polishing fleece layer
21 Outer surface of 20
22 Outer surface of 20
23 Base
Tooth gear
31 Tooth flank polishing tool
32 Base
33 Polishing fleece
34 Central axis of 32
Radial direction
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36 Radial direction
37 Tooth flank
38 Longitudinal axis of 30
39 Tooth gap
40 Tooth
51 Polishing worm gear
52 Hollow space
53 Base
54 Peripheral side of 53
55 Groove
56 Polishing fleece
57 Outside contour of 56
58 Polishing worm gear
59 Tooth
60 Polishing fleece layer
70 Polishing finger
71 Tooth gear
72 Base
73 Polishing fleece
74 Longitudinal axis of the polishing finger
75 Longitudinal axis of the tooth gear
76 Tooth flank
77 Tooth gap
80 Polishing finger
81 Base
82 Shaft
83 End of 81
84 Seat
85 Polishing fleece
86 Insertion section
87 Contour
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90 Polishing finger
91 Base
92 Polishing cone
93 Outside of 92
94 Polishing fleece layer
95 Oscillation generator
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