Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a centrifugal mill and
particularly to a centrifugal mill comprising a cylindrical grind-
ing drum, which rotates about its own drum axis and simultaneously
revolves on a cricular orbit around a stationary axis of revolution,
which is parallel to the drum axis, at a constant anguIar velocity
ratio.
Centrifugal mills for intermittent pilot operation have
been described in "Rock Product", February 1951, pages 93-97.
Printed German Application 10 13 946 describes a cen-
trifugal mill which is used for batch operation and in which the
distance betwèen the drum axis and the axis of revolution'is less
than the radius of the grinding drum so that'there is allegedly
no critical or limited speed of revolution of the mill. The
- critical velocity is the velocity above which the material being ' '
ground and the grinding elements form under the action of centrifugal
force a covering on the wall of the grinding drum so that ~here is
no longer a grinding action. On the other hand, the spacing of
~' the drum axis and the axis of revolution by a distance which is
j~ smaller than the radius of the grinding drum does not in itself
ensure sub-critical conditions and a high grinding rate. ''
The present invention provides a centrifugal mill
which enables a continuous operation in the sub-critical range at '~
a high grinding rate per unit of volume of the grinding drum and
' in which the grinding drum is readily accessible and can be replaced ~ '
quickly and simply and in which a simple mounting for the drum is
provided and the transmission of uncontrolled stresses'and vibra-
tion is avoided while the structural expenditure is small.
According to the present invention, there is provided '~
a'centrifugal mill comprising a cylindrical grinding drum, which
rotates about its own drum axis and simultaneously revolves on a
circular orbit'around a stationary axis of revolution, which is
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parallel to the drum axis, at a constant angular velocity ratio,
whereby the grinding drum is mounted in substantially horizontal
position in at least one rocker, each limb of the rocker is mounted
in an eccentric bearing, each eccentric bearing is secured to an
eccentric driving shaft, the eccentric driving shafts are provided
with courlterweights and are mounted in bearings, a charging device
is provided on one end portion of the grinding drum and a discharge
device is provided at the other end portion, characterized in
that~
- said grinding drum is mounted in at least one U-shaped rocker,
~ a bearing is provided at a lower portion of said at least one
` U-shaped rocker, said bearing being rigidly connected in ver-
tical direction to said lower portion and being movable in all ~ `
other directions, ~` -
- two abatments are associated with the respective limbs of said ;~
at least one rocker, said grinding drum being mounted between
said two abatments. ~;
, The limbs of the U-shaped rocker may extend at right -~
;~ angles or at another angle to the lower portion of ~he rocker or -
may extend along arcs of circles to the lower portion of the rocker.
;~ Alternatively, the entire rocker may have the configuration
of an arc of a circle.
The bearing in the lower portian of the rocker may
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consist of a ball-type pivot bearing or of a pin having a suitable
~ play on that side of the bearing which faces the
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grinding drum and on which the ~earing is connected to the
grinding drum. That side of the bearing which faces the lower
portion of the rocker may be suitably connected to the rocker
- by a screw-threaded joint.
The abu-tments provided on the limbs of the rocker
extend suitably horizontally but may alternately be somewhat
inclided.
There is either a small play between the abutments
and the grinding drum or the abutments contact the grinding
~ 10 drum.
! The eccentric bearings may consist suitably of
roller-type pivot bearings.
The drive shafts may ~e suitably connected to one or
more trancmissions by highly elastic couplings, which are
torsionally rigid, and these transmissions may be driven by
one motor or a pl~rality of motors< Where two transmissions
ff are provided, they must be coupled to each other so that a
synchronous operation of both eccentric shafts is ensured.
According to a preferred feature, the bearings of
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one eccentric-driving shaft are pivotally connected to a base
frame at one point. This ensures that manufacturing tolerances
of the rockers and levers cannot result in additional loads
~` on these parts.
According to another preferred feature, one abutment
~1 of each rocker consists of a resilient bearing. The resiliency
.f~, of the bearings may be due to the provision of springs or of
pneumatic or hydraulic means. This ensures that the grinding
~ drum is held by a defined force and that a transmission of
`~ forces due to thermal expansion to the rockers is avoided.
According to another preferred feature, one abutment
of each rocker is provided with a sensor for measuring the
reaction force of the grinding drum. The sensor consists
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suitably of a load cell. Such arrangemen-t enables a simple and
accurate monitoring and automatic control of the operating
conditions of the grinding drum.
According to another preferred feature the grinding
drum is mounted in two interconnected rockers. Two rockers
constitute a structurally simple, satisfactory holder. The
connection between the rockers prevents a parallel displacement
thereof.
A preferred embodiment of the invention will be
explained more fully and by way of example with reference to
the drawings, in which
Fig. 1 is a top plan view showing a mill, ~ ~-
Fig. 2 is a side elevation showing a mill viewed
from its discharge side, -`
Fig. 3 is a side elevation like Fig. 2 but partly
in section and
Fig. 4 shows the mechanical movement of the rocker
and of the grinding drum.
The illustrated grinding drum 1 has a smooth lining. -
In practice, however, lifting bars are provided on the inside
or a lining is provided which has an irregular surface so that
the movement of the material to be ground in the drum is
improved. These means are not shown for the sake of clearness.
The grinding drum 1 is mounted in two U-shaped rockers 2, 2a,
which have limbs extending at right angles to the lower
portion of the rocker. The bearing 3 provided in the lower
portion of each of the rockers 2, 2a is designed to be rigid
in the vertical direction and to be movable in all other
; directions. On the side facing the grinding drum 1, the bearing
' 30 3 consists of a ball-type pivot bearing. On its side facing
~` the lower portion of each rocker 2, 2a, the bearing 3 is
screw-connected to the lower portion by means of a screw-
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threaded pin, which extends through the bearing, and lock nuts.
As a result, the bearing 3 is vertically rigid and is movable in
all other directions owing to the provision of the ball-type
pivot bearing.
Two abutmen-ts 4, 5 are secured -to the inside of the
limbs of each of the rockers 2, 2a. The abutments 4 on one
side constitute resilient bearings comprising built-in springs.
The abutments 5 on the other side are provided with load cells
18. The bearings 3, 4 and 5 retain the grinding drum 1 at its
end walls 22, 23. When it is desired to remove the drum 1, it
is sufficient to eliminate the screw connections of the bearings
3. The limbs of the roc]cers 2, 2a are mounted in respective
eccentric bearings 6, 7, which consist of self-aligning roller
bearings~ The eccentric bearings 6, 7 are secured to respective ...
eccentric-driving shafts 8, 9, which are provided with counter- ~ .
weights 10, 11 an~l mounted in bearings 12, 13, 14, 15. Lead
plates 24 are mounted in the counterweights 10, 11 and may be .
used to control the mass of the counterweights 10, 11~ The ::
bearings 12, 13 are firmly screw-connected to the base frame 16.
The bearings 14, 15 are pivoted to the base frame 16 by pins
having centers 17. The lower portions of the two rockers 2, 2a
are interconnected by a flanged tube 19. The eccentric-driving
shafts 8, 9 are connected to the transmission and drive unit
by couplings 24, 25.
Fig. 4 shows only the rocker 2, the grinding drum 1,
the eccentric-driving shafts 8, 9, and the eccentric bearings
6l 7. The di3tances between t:he centers 26 of the eccenbric-
driving sha.fts 8, 9 and the centers 27 of the eccentric bearings
6, 7 define the radii of the circular orbits of revolution G.
In the embodiment shown by way of example, the ratio of the
diameter of the circular orbits of revolution G to the inside
diameter D of the grincling drum is about 0.4. The distance
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between the axis 28 of the grinding drum 1 and the imaginary
stationary axis of revolution 29 of the gringind drum 1 is
smaller than the radius of the grinding drum 1. ~`
The advant~ges afforded by the invention reside in that -
owing to the rat~o R = -1 (R being the ratio of the angular ~ -
velocity of the grinding drum 1 on the circular orbit about the
stationary axis of revolution to the angular velocity of the
grinding drum about its own drum axis) a particularly high grinding :~
rate is ensured, the centrifugal forces are equal at all points ~`
of the cross~section of the grinding drum, and the vectors of
j acceleration àt all points are parallel and have the same direc- ~.
tion, that the mill operates always in the sub-critical range
even at a high grinding rate, the design ensures an exactly
. circular motion in a simple manner, the grinding drum can be.
.. mounted and replaced quickly and simply wlthout need for a high ~ :
expenditure of work, the shut-down tlmes are short, a satisfac-
tory mounting and holding of the grinding drum is ensured with
a small structural expenditure, a transmission of uncontrolled
~:. vibration to the rockers and other parts is avoi.ded, the grinding ~.
drum and the charging and emptying devices are well accessible,
` and additional drive means Eor rotating the grinding drum on its ;
own axis are not rèquired.
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