CENTRIFUGAL MILL

BROYEUR CENTRIFUGE

English Abstract

ABSTRACT OF THE DISCLOSURE
A centrifugal mill comprising a cylindrical
grinding drum, which rotates on its own axis and
simultaneously revolves at a constant angular velocity
ratio on a circular orbit around a stationary axis of
revolution, which is parallel to the drum axis. The
distance from the axis of the drum to the axis of
revolution is smaller than the radius of the grinding
drum. The ratio of the diameter G of the circular
orbit to the inside diameter D of the grinding drum
is between 0.3 and 1.0 and the ratio R of the angular
velocity of the revolution of the grinding drum on
the circular orbit around the axis of revolution to
the angular velocity of the rotation of the grinding
drum on its own axis is in the range from
<IMG> to <IMG> , the ratio R
being considered to be negative when the two angular
movements are in opposite senses, and positive when
two angular movements are in the same sense. The mill
comprises a feeder provided at one end of the grinding
drum, and discharge means provided at the other end of
the grinding drum.

Claims

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
1. A centrifugal mill comprising: a cylindrical
grinding drum, which rotates on its own axis and simultaneously
revolves at a constant angular velocity ratio on a circular
orbit around a stationary axis of revolution which is parallel
to the drum axis, the distance from the axis of the drum to the
axis of revolution being smaller than the radius of the
grinding drum; a drive mechanism for rotating the grinding drum.
on its own axis and for revolving the drum on the circular
orbit about said stationary axis; a feeder provided at one end
of the grinding drum, and discharge means provided at the
other end of the grinding drum, characterized in that the ratio
of the diameter G of the circular orbit to the inside diameter D
of the grinding drum is between 0.3 and 1.0, and the ratio R
of the angular velocity of the revolution of the grinding drum
on the circular orbit around the axis of revolution to the
angular velocity of the rotation of the grinding drum on its
axis is in the range from <IMG> to <IMG> ,
the ratio R being considered to be negative when the two angular
movements are in opposite senses, and positive when the two
angular movements are in the same sense.
2. A centrifugal mill according to claim 1,
characterized in that the ratio R of the angular velocity of
the revolution of the grinding drum on the circular orbit
around the axis of revolution to the angular velocity of the
rotation of the drum on its own axis is R = - 1.

Description

107835Z ; ,
This invention relates to a centrifugal mill
comprising a cylindrical grinding drum, which rotates
on its own axis and simultaneously revolves at a constant
angular velocity ratio on a circular'orbit around a
stationary axis of revolution, which is parallel to the
drum axis, the distance from the axis of the drum to the
axis of revolution being smaller than the radius of the
grinding drum, and a drive mechanism for rotating the
grinding drum on its own axis, and for revolving the drum
on the circular orbit.
Centrifugal mills for intermittent trial opera- `
tion have been described in "Rock Product", February 1951, '~
pages 93-97.
Printed German Application 10 13 946 also dis-
closes a centrifugal mill which is used for batch opera-
tion and in which the distance from the axis of the drum
to the axis of revolution is smaller than the radius of
the grinding drum. As a result, the operation of the
mill shall not be restricted by a critical or limited ~-
angular velocity. The critical velocity is the lowest
velocity at which the material being ground and the
grinding elements are caused by centrifugal force to
form a covering on the inside surface of the grinding
drum so that grinding is no longer effected. On the
other hand, the mere selection of a distance from the
axis of the drum to the axis of revolution which is
smaller than the radius of the grinding drum will not ~-
ensure an operation under subcritical conditions and a
high grinding capacity.
It is an object of the invention to provide
a centrifugal mill which enables a continuous operation
in the subcritical range with a high grinding capacity
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1Cl17~352
,
per unit of volume of the grinding drum.
This object is accomplished according to the present
invention by the provision of a centrifugal mill comprising:
a cylindrical grinding drum, which rotates on its own axis and
simultaneously revolves at a constant angular velocity ratio on
a circular orbit around a stationary axis of revolution which
is parallel to the drum axis, the distance from the axis of the
drum to the axis of revolution being smaller than the radius of
the grinding drum; a drive mechanism for rotating the grinding
drum on its own, axis and for revolving the drum on the circular
orbit about said stationary axis; a feeder provided at one end
of the grinding drum, and discharge means provided at the
other end of the grinding drum, characterized in that the ratio
of the diameter G of the circular orbit to the inside diameter D
of the grinding drum is between 0.3 and 1.0, and the ratio R
of the angular velocity of the revolution of the grinding drum
on the circular orbit around the axis of revolution to the
angular velocity of the rotation of the grinding drum on its
axis is in the range from R = ~ r~ to R = ~
the ratio R being considered to be negative when the two angular
movements are in opposite senses, and positive when the two
angular movements are in the same sense.
The combination of these features ensures that the
mill always operates in the subcritical range and with a high
grinding capacity.
According to a preferred feature of the invention, the
ratio R of the angular velocity of the revolution of the
grinding drum on the circular orbit around the axis of revolution
to the angula'r velocity of the rotation of the drum on its own
axis is R = -1. In this case, the grinding capacity will be
particularly high, the centrifugal forces will be equal at all
points of the,cross-section of the grinding drum, and the
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107835Z
acceleration vectors will be parallel and have the same
direction at all points.
The invention will be explained more fully and by
way of example with reference to the drawings, in which: ;
~ .
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FIGURE 1 is a vertical sectional view showing
a centrifugal mill having a vertical grinding drum,
FIGURE 2 is a sectional view taken on line
I-I in Figure l;
FIGURE 3 is a vertical sectional view showing
different discharge means; and
FIGURE 4 is an enlarged sectional view taken
on line II-II in Figure 3.
In Figures 1 to 4 the grinding drum 1 is shown
to have a smooth liner. Lifting bars are provided on
the inside in practice but are not shown for the sake of
clearness. The grinding drum 1 is provided with hollow
trunnions 2 and 3, which are mounted in bearings 4
arranged in bearing housings 5 and 6. The bearing
housings are integral with a frame, which also includes
longitudinal members 7 and 8. The hollow trunnion 2 is -
connected to a special spiral feeder 9, which rotates
with the grinding drum 1. The hollow trunnion 3 dis-
charges the material into a discharge chute 10, which
discharges into an annular collecting trough 11. A
gear 12 is secured to the hollow trunnion 3 and in mesh
with three gears 13, the last of which is rigidly con-
nected to the mounting pin 14. The frame has end
members 15 and 16, which are rotatably connected by
bearings 17 to a base frame. The base frame carries a
hollow trunnion 18 adjacent to the end member 15 and a
mounting shaft 19 adjacent to the other end member 16.
The mounting shaft 19 and the hollow trunnion 18 define
an axis of revolution 20. A revolution around this
axis is effected by a belt 21 and a belt pulley 22.
The axis of the grinding drum 1 is designated 23 in
Figure 2. The drawings show an arrangement in which
., ... ~ . , . , .' . ; :

~07835Z
the ratio of the diameter G of the circular orbit around
the axis of revolution 20 to the inside diameter of the
grinding drum 1 is approximately 0.5. The transmission
ratio between the hollow trunnion 3 and the mounting pin
14 is important and corresponds to the ratio R. This
transmission ratio determines the relative angular velo-
city of the rotation of the grinding drum 1 in the simu-
lated gravitational field which is produced by the revo-
lution of the axis 23 around the axis 20. A transmission
ratio R = - 1 is preferred so that a certain diameter of
the grinding drum always remains parallel to itself during
the revolution. The belt 21 is driven by drive means
which are not shown. The material is fed through the
hollow trunnion 18 into the feeder 9, which feeds the
material through the hollow trunnion 2 into the grinding
drum 1. Whereas the coarse particles are retained by the
screen 25 in the grinding drum 1, the ground material ;
is discharged to the collecting trough 11. The belt 21
and the belt pulley 22 associated with fixed trunnions
18 and 19 may be replaced by different drive means. The
hub 26 provided with the lower bearing 17 and fixedly
connected to the frame may be driven by another motor
through a belt drive or a gear train. The gear train
12/13 is only an example of means for rotating the grind-
ing drum 1. The highest speed at which the grinding
drum 1 may be rotated is limited only by the mechanical
strength of the mill. To avoid rotary unbalance, the
longitudinal member 7 is weighted to balance out the ,~
weight of the grinding drum 1 and of the charge therein.
In the embodiment provided with the discharge
means shown in Figures 3 and 4, the grinding dxum 1 is
provided with an end plate 27, which has a central

iC~7835Z
opening, which is spaced from the plate 29 by spacers
28. Material which enters the space between the plates
27 and 29 is radially discharged between the spacers.
A spiral discharge member 30, which may consist of round
rod, is arranged to return coarse material into the
grinding drum 1.
A horizontally disposed mill may be similarly
constructed.