Note: Descriptions are shown in the official language in which they were submitted.
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"HIGH TORQUE DRIVE MEANS FOR TWO VERY COO E SHAFTS WHICH ARE Also
SUBJECTED TO STRONG AXIAL THRUSTS AND APPLICATION THEREOF TO A
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DOUBLE SCREW EXTRUDE"
This invention relates to drive means capable ox
moving a set of two shafts arranged at a close distance iron each
other, either parallel or with converting axes, being said shafts
subjected to strong axial thrusts. These shafts are used, for
example, in a double screw extrude for plastic materials.
In the case of two adjacent shafts moving in opposite
10. direction to each other, the simplest way for rotating them is to
transmit the entire torque of the motor only to one of the two
shafts, and then impart a rotation to the second shaft by a pair of
identical gears, each one keyed to each of the two shafts, such as
to mesh with the other gear. On the other hand, when the shafts
rotate in a same direction, the rotation imparted to the first
shaft, always by a single motor, is transmitted to the second shaft
by means of an intermediate gear.
However, in these embodin~nts, the high speed of
rotation of the shafts leads to a severe wear and to a very short
20- life of the plasticizing screws. On the other hand a low speed would
cause high torques and accordingly occasional breakage. Moreover,
being the shaft distance very small, the gears must have very small
pitch diameters.
In the late few years, two ways have been followed to
overcome this drawback.
The first way consists in mixing shafts carrying
conical extruding screws, so that at Skye distance run the cone
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apex the gears may have larger dimensions. However,
this complicates the whole construction.
A second approach was to separate the shaft
actuation providing a reduction unit with two outlets
each of which imparts the movement to the free end of
each shaft, that is to the end opposite to the one
carrying the screw. The disadvantage of this system is
that the two very close shafts, subjected to a strong
torsion become very long in order to leave along their
axis the necessary space for the housing of the thrust
bearings. These are usually positioned in such a way
that each thrust bearing of a shaft is offset with
respect to thrust bearing of the other. Therefore this
solution is still not acceptable, because the shafts,
for resisting the torsional stress, must greatly
increase their diameters.
Attempts were also made to increase the gear
sturdiness by lengthening the latter or increasing their
number. However, this also considerably adds to costs.
Therefore, it is the object of an aspect of the
present invention to provide a structurally economical
solution to the problem of driving two close parallel
or converging shafts arranged at a close distance from
each other which are also subjected to strong axial
thrusts.
Various aspects of the invention are as follows:
An apparatus rotationally driving two closely
spaced shafts, comprising:
a driven gear on each shaft;
two respective drive gears for directly driving
each said driven gear;
a separate drive means for driving each respective
drive gear; and
synchronizing means, secured on each respective
shaft, for constraining each of said two closely spaced
shafts to rotate at the same speed.
An apparatus rotationally driving two closely
spaced shafts, comprising:
a driven gear on each shaft;
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two respective drive gears for directly driving
each said driven gear;
a separate drive means for driving each respective
drive gear;
synchronizing means for constraining each of said
two closely spaced shafts to rotate at the same speed;
and
said respective drive gears and said synchronizing
means comprises an idler gear, said idler gear engaging
one terminating gear of one drive means of each driven
gear.
An apparatus rotationally driving two closely
spaced shafts comprising:
a first driven gear on a first of said shafts;
a first drive gear and a second drive gear, said
first drive gear and said second drive gear being for
directly driving said first driven gear;
a first independent drive means for driving said
first drive gear and a second independent drive means
for driving said second drive gear;
a second driven gear on a second of said shaft;
a third drive gear and a fourth drive gear, said
third drive gear and said fourth drive gear being for
directly driving said second driven gear; and
a third independent drive means for driving said
third drive gear and a fourth independent drive means
for driving said fourth drive gear,
whereby torque applied to said first driven gear by
said first drive gear and said second drive gear and to
said second driven gear by said third drive gear and by
said fourth drive gear at points along the circumference
of said first driven gear and said second driven gear,
respectively is distributed so as to be reduced in
magnitude.
An apparatus for rotationally driving two closely
spaced shafts, comprising:
a first driven gear on a first of said shafts;
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a first drive gear and a second drive gear, said
first drive gear and said second drive gear being for
directly driving said first driven gear;
a first independent drive means for driving said
first drive gear and a second independent drive means
for driving said second drive gear;
a second driven gear on a second of said shafts;
a third drive gear and a fourth drive gear, said
drive gear and said fourth drive gear being for directly
driving said second driven gear;
a third independent drive means for driving said
third drive gear and a fourth independent drive means
for driving said fourth drive gear;
a synchronizing means for constraining each of said
closely spaced shafts to rotate at the same speed; and
said drive means each include a terminating gear
for driving said respective drive gears and said
synchronizing means comprises an idler gear, said idler
gear engaging one terminating gear of one drive means of
each driven gear;
whereby torque applied to said first driven gear by
said first drive gear and said second drive gear and to
said second drive gear by said third drive gear and by
said fourth drive gear at points along the circumference
of said first driven gear and said second driven gear,
respectively is distributed so as to minimize stresses.
A preferred solution provides that the drive
members
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are carried out by units completely independent from one another,
that is having fully distinct motors.
In this case, preferably the use is contemplated of
epicyclical reduction units which are readily commercially
available.
In the proposed drive application to a double screw
extrude for plastic materials, it is preferably provided that the
housing containing the extruding screws is directly connected with
10- the support of the thrust bearings, without over stressing the drive
box. Preferably, said connection is obtained by means of tie rods
passing through said drive box.
For the rotation of two shafts rotating in a same
direction, it is provided that the two gears mounted on such shafts
are slightly spaced apart from each other, while the drive members
are synchronized by an idle gear meshing therewith.
If the shafts are convergent it is possible to carry
out all the drive members with conical gears which mesh with the
respective conical gears of each shaft. It is also possible to
20- provide on each shaft two cylindrical gears which do not mesh with
one another; they will be moved by at least two drive members
terminating with a cylindrical gear meshing with the said respective
cylindrical gear.
The invention will now be explained by an exemplary
embodiment as shown in the accompanying drawings, in which:
Fig. 1 is a schematic perspective view of a drive
means according to the present invention, in which the two shafts
rotate in opposite direction;
Fig. 2 is a schematic side view of the same drive
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means, in which also one of the two extruding screws is shown; and
Fig. 3 is a schematic perspective view of another
embodiment, in which the two shafts are caused to rotate in a same
direction.
Figs. 4 and 5 are views of two further embodiments
obtained on the converging shafts.
Referring first to Fig. 1, it will be seen that
reference numerals 1 and 2 denote the two synchronized parallel
10. counter-rotating shafts, which are arranged at a very close distance
from each other. Meshing gears 3 and 4, are mounted on each of the
shafts. According to the present invention, rotation is imparted to
each of such gears 3 and 4 at least by means of two drive members.
Two torques act upon gear 3 by means of gears 6 and 7, which are
located in suitable zones on the circumference of gear 3, to limit
the resulting thrust on said gear 3. Gear 4 is driven by two further
drive members terminating with gears 8 and 9, respectively. In the
particular em w dominate of Fig. 1, the drive members are gears driven
20- by other gears 10, 11, 12 and 13, respectively, which in turn are
driven by independent motors
This solution allows a reduced dimensioning of the
length of gears 3 and 4 since the latter, serving only for
synchronization of the two shafts, do not transmit the full power.
Moreover, a good power division is obtained for the power supplied
to each of the gears, as each torque is applied to the respective
gear 3 or 4 at spaced apart peripheral zones such as to minimize
stresses.
Referring new to Fig. 2, in which an extrude has
been schematically shown, it will be seen that the screws 15 have
30 been wormed on the shafts 1 and 2, although only one screw is shown
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in Fig. 2. The four gears 10, 11, 12 and 13 (of which only two are
shown in Fig. 2) are connected to~çpicyclical reduction units 23 and
24~ which are driven by motors 25 and 26, respectively.
The shafts 1 and 2 must be supported by a series of
axial thrust bearings 16, the strain of which has to be supported by
the support 17. The axial strain caused by the extrusion pressure of
the plastic material has to be supported by the housing 18
containing the extrude screws 15. According to the invention, it is
provided that said housing 18 and support 17 are directly connected
10- to each other, for example by tie rods 19 and 20 which conveniently
are caused to pass through hollow shafts 21 carrying the gears 6, 7,
8-and 9. Thus, the drive box 22, containing the gears 3 to 13, is
released of any stress due to these considerable strains.
Referring now to Fig. 3, it will be seen that also
therein the same reference numerals 1 and 2 are used to indicate two
synchronized parallel shafts which rotate in a same direction and
are arranged at a very close distance. Each of the shafts has gears
3 and 4 mounted thereon, but not meshing with each other. As for the
embodiment of Fig. 1, it is provided that motion is given to each of
20- said gears 3 and 4 at least by means of two drive members. TWO
torques are caused to act upon gear 3 by means of gear 6 and gear 7,
which will be arranged in suitable zones on the circumference of
gear 3 to limit the resulting thrust on said gear 3. Gear 4 is
driven by two further drive members terminating with gears 8 and 9,
respectively. Also in this case, the drive members are gears driven
by further gears 10, 11, 12 and 13, respectively, which in turn are
driven by independent motors.
In this case, synchronism between said shafts 1 and 2
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is provided by gear 30 meshing with gears 6 and 8 forming part of
the drive members operating the two gears 3 and 4, respectively.
Also in this case, the dimensioning of gears 3 and 4 is much
reduced, since such gears serve only to transmit the power share
assigned thereto.
Fig. 4 shows two converging shafts 31 and 32 on which
two conical gears 35 and 34 respectively are mounted meshing with
each other. On each of these, two drive members act, by means of
gears 36, 37, 38, 39, also conical.
10. In Fig. 5 a further embodiment is shown in which the
converging shafts 31 and 32 are each provided with a cylindrical
gear 43 and 44, not meshing one with the other, and with meshing
synchronization gear 35 and 45. The gears 43 and 44 are each driven
by two driving members which act by means of their final gear 46,
47, 48, 40. In this case the driving means can be all carried out
with cylindrical gears.
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