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Патент USA US3021091

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Feb. 13, 1962
R. M. E. SULLIVAN
3,021,032
VIBRATORY BALL MILL SYSTEM
Filed Jan. 21, 1960
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INVENTOR
RALPH MAJOR EDWARD SULLIVAN
? ire States Patent
3,�,�
Patented Feb. 13, 1%62
2
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fice
In an externally excited system for vibrating a load
the present invention provides a primary resilient sus
3,021,082
VIBRATORY BALL MlLL SYSTEM
pension for the load which is designed so as to- transmit
Ralph Major Edward Sullivan, llayswater, London, Eng
a major pro-portion of the total input excitation force.
land, assignor to National Research Development Cor
This means that the primary suspension is tuned at least
poration, London, England, a British corporation
approximately to resonance when under load and, al
Filed Jan. 21, 1966, Ser. No. 3,759
though the damping effects of a granular or pulverulent
Claims priority, application Great Britain Jan. 22, 1959
charge in a ball mill are complex and di?icult to esti
5 Claims. (Cl. 241-175)
mate, in practice the resonance curve normally exhibits
This invention relates to the generation of vibrations 10 a sharp peak. For all practical purposes, therefore an
excitation frequency of the order of 0.9 times the reso
in loads, and aims at providing a method of and means
nant frequency is adequate in a ball mill operated in
for vibrating a load in the most e?icient manner. In
accordance with the present invention.
particular, the invention relates to vibratory systems in
A resilient suspension of. high rate imposes on its
which the frequency and mode of vibration of a load
is imposed by an external exciter. A common example 15 anchorages a relatively high static loading at high fre
quency, so that the system will normally be required
of such systems is the vibratory ball mill, to which par
to be designed with a view to isolating the high fre
ticular reference will be made hereinafter.
quency excitation transmitted by the suspension from sur
rounding buildings. Known techniques may be adopted
Investigations have been made into the relative effec
tiveness of linear and circular or orbital forms of vibra
of such a mill is much greater when circular or orbital
excitation is applied than when either horizontal or ver
tical rectilinear excitation is applied. In this connec
for this purpose, as will be understood, but as the fre
quency of excitation increases in order to increase the
grinding rate, the static loading on the anchorages of
a resonant suspension also increases. Consequently,
heavier foundations are required, and the known tech
tions preferably at right angles, and adjusting either in
tion, and the problem of isolating heavy foundations is
tion in ball mill grinding, and it has been observed that
the vibratory energy reappearing as heat in the contents
tion it must be noted that the vibratory displacement of 25 niques for isolating them from their surroundings be
come much more di?icult and costly to apply. Although
a ball mill normally takes place in one plane, i.e. it is
experiments have shown that the size of a mill, and
two-dimensional, its components being normally hori
hence its weight, can be reduced almost in proportion
zontal and vertical linear displacements.
to the increase of resonant frequency excitation, and
Normally, a large vibrating ball mill is operated at
a frequency in excess of the resonant frequency of the 30 that this offsets to a signi?cant degree the above~men~
tioned increase in static loading on the anchorages of
mill. It has been found, however, that by varying the
the resonant suspension, the relative stiffness of a reso
form of the vibration at constant frequency, a large varia
nant or near-resonant suspension compared with that
tion in rate of grinding is produced. Such variation in
of a conventional suspension still imposes very large
form can only be obtained by segregating the compo
nents of displacement in two mutually inclined direc 35 forces on its anchorages at high frequencies of excita
still formidable.
The present invention reduces this problem to a sub
stantial extent by providing a secondary suspension, be
mutually inclined directions is controlled by a primary 40 tween the primary suspension and the foundation, which
has a different rating from that of the primary suspen
resilient suspension anchored to a foundation through
sion. Preferably, this secondary suspension has a reso
a secondary resilient suspension. The primary resilient
nant frequency much lower than that of the primary
suspension may consist of respective individual resilient
suspension, so that it can absorb the major proportion
units each having one degree of freedom of de?ection
only, viz. that of the relevant component direction. A 45 of the loading on the primary suspension anchorages.
Hence, a much lighter foundation becomes possible, and
source of excitation is advantageously applied to the
?nal isolation thereof from a surrounding building be
load directly or at the point of its attachment to the
relation to the other.
The present invention is essentially a compound sus
pension in which each of two or more displacements in
comes a much simpler problem.
compound system.
The present invention also aims at further reducing
In the design of vibratory systems generally, a well
the
problem of foundation size and isolation by intercon
50
known parameter of the design to ensure effective iso
necting a plurality of grinding vessels or containers by
lation of the vibratory system from its surroundings is
means of an inter-vessel suspension arranged as a self
the resonant frequency of the loaded suspension. As
balancing or substantially self-balancing system having a
a general rule, if the excitation frequency is approxi
minimum external resultant force, and mounting the as?
mately four times the resonant frequency, little or no
vibration is transmitted through the suspension anchor 55 sembly on a relatively light ?foundation by means of a
suspension having a substantially different resonant
ages to the foundations of the system. This principle
frequency.
has also been assumed to have the further advantages
Preferably, the vessels or containers are located, at the
that the spring stresses are low and their anchorages light.
corners of a polygon in a closed loop and each container
It has now been found, however, that in vibratory
ball mills a much increased rate of grinding can be ob
60 is connected to its neighbour on either side by a suspen
tained by the use of high frequency excitation with low
amplitudes of displacement of the load. This kind of
excitation produces ?fluidisation? of at least the grind
ing balls, i.e. a state of random agitation extending
throughout the mass with substantially uniform ampli
tude so as to give an apparent reduction in density
throughout the mass. Furthermore, in such a modi?ed
system, power loss is considerably reduced, so that a
lower power input can be tolerated for the increased
grinding rate. Where excitation is provided by rotary 70
eccentric masses, these can be much lighter, with a cor
responding reduction in the size of bearings.
sion designed so as to transmit the major proportion of
the input excitation force. Where four vessels are inter
connected in the form of a square, each vessel is excited
in anti-phase with its immediate neighbours.
As an alternative to a rotating out-of-balance system,
the vibration may also be induced electro-magnetically
by a suitable arrangement of electro-magnets between the
individual grinding vessels, the coils of the magnets being
energised from a suitable A.C. source.
When operating a vibration ball mill at or near natural
frequency of the system, changes in the damping effects
of the loose charge in a container, due to the cushioning
3,021,082
3
4
action of the increasing ?neness of the charge, cause rela
for very heavy and expensive foundations and their in
sulation from surrounding structures.
tively large changes in amplitude of vibration. In order
to control these amplitude changes, the present invention
also provides for some form of continuous amplitude
monitoring device. If the out-of-balance force is gener
An alternative form of excitation mechanism is a poly
phase electromagnetic system in which four or more elec
tromagnets (not shown) are mounted on a ring yoke
ated by means of a rotating eccentric mass system, the
around the vessel assembly and use the vessels or con
tainers 1 . . . 4 as armatures. Alternatively, armatures
output signal from the detector unit when the vibration
may be ?xed to, or constituted by extensions of, the spacer
amplitude rises above a predetermined level may be used
blocks 11!. If space permits, the magnets may be mounted
to vary the excitation frequency in the sense for reducing
the amplitude of vibration. If the vibration is excited 10 within the ring of vessels 1 . . . 4'. Such a field system
could be excited from the public mains supply, a fre
electro-magnetically, the signal may be used to vary the
quency of 50 cycles per second giving a vibration rate of
input voltage to the coil of the electro-magnet.
3000 cycles per minute.
The detector unit may be a photo-electric device, the
So long as the vessels or containers 1 . . . 4- are ar
light beam of which is arranged to be obturated to a
greater or less extent as the vibration amplitude rises 15 ranged symmetrically and each is excited in anti-phase
with its immediate neighbours, the machine is very largely
above a predetermined level or alternatively, a variable
self-balancing with respect to resultant external vibra
inductance or capacitance detecting device may be pre
tions, so that there is no theoretical limit to the number
ferred.
of vessels used. Clearly, however, practical considera
A practical embodiment of the present invention'will
now be described by way of illustration only with refer
ence to the accompanying drawings in which:
FIGURE 1 is an end view, partly in section, of a four
vessel mill, and
FIGURE 2 is a plan view of FIGURE 1.
High grinding rates are obtainable with greatly reduced 25
quiring fairly close dynamic matching, together with con
siderations of accessibility and space occupied, will limit
the number adopted in any one design of ball mill accord
ing to the invention.
bearing stresses and consequent simpli?cation of bear
ing design and improved efficiency? due to lower heat
losses. Both capital and running costs per unit weight
of ground material can thus be substantially reduced.
motor speed controller to keep the vibration amplitude
tions of complication and multiplicity of components re
FIGURES l and 2 also show a schematic arrange
ment of vibration amplitude detector which can be used
in conjunction with a conventional form of electrical
below a predetermined maximum value. The detector
consists of a light source 50 and photocell 51 mounted
on opposite sides of the bed structure 21, and an aper~
tured shutter 52 mounted on the vessel 4 with its aper
ture on the axis of the light beam from the source 50.
So long as the amplitude of vibration of the vessel 4
FIGURES 1 and 2 of the drawings show a vibrating
ball mill having four cylindrical grinding vessel-s or con
tainers 1, 2, 3, 4 whose axes are parallel and equi-angular
ly spaced at the corners of an imaginary cube. Each pair
of adjacent vessels 1 and 2, 2 and 3, etc. are coupled to
gether by a respective primary suspension unit 5, 6, 7, 8 35 remains within the predetermined limit, the photocell out
put is constant. Excessive amplitude of vibration, how
each of which is tuned to resonance or substantially to
resonance at a relatively high excitation frequency. Each
such inter-vessel primary suspension unit is shown as
ever, causes partial or total obscuration of the light
falling on the photocell 51 during part of each half cycle
of vibration of the vessel, with a corresponding change
in output from the photocell which can operate an indi
comprising a pair of similar leaf springs 9, '10 clamped
together by a rigid spacer 11 at their mid-points and
anchored at their ends by rigid blocks 12 to the respective
cator or a motor speed controller.
The vessels 1 . . . 4 may be replaced by any other
vessel.
.piece of apparatus or equipment which it is desired to
subject to oscillation. For example, the vibratory system
may be used for classifying a mixture of granular mate?
Through each vessel \1 . . . 4 passes a shaft 13? carry
ing small out-of-balance weights 14 at either end of the
vessel. The shafts 13 are coupled through universal
joints 15 to respective outputs 16 from a common gear
rials having different particle sizes.
19. The gear ?box 17 drives each pair of weights 14 in
anti-phase with the corresponding pair associated with an
adjacent vessel, each pair of shafts 13 being contra
rotated.
natively, bodies of liquid or liquid/solid mixtures may
be vibrated to emulsify them or to promote intimate
admixture where one constituent is insoluble in the liquid
phase. In these applications of the? invention, it may be
necessary or preferable to induce the vibrations in the
The entire assembly of vessels or containers 1 . . . 4
.and high natural frequency primary suspension units
horizontal plane.
5 . . . 8 is supported by a low natural frequency sec
,ondary suspension system consisting of helical springs 20
Each vessel 1 . . . 4
would then be replaced by the tray or plate on which
the granular material is placed for classi?cation. Alter
box 17, and an electric motor 18 drives a common input
55
on a common foundation or bed 21, each spring 20 having
an anchorage 22 ?xed on or integral with a correspond
ing vessel 1 . . . 4.
When the vessels ll . . . 4 are loaded and the motor
Other forms of excitation can be used if desired-for
example, electromagnetic. In such a system the vessel
assembly 1, 2, 3, 4 is arranged as a four-pole armature
symmetrically located between the poles of four ?xed
electro~magnets respectively whose axes are equiangu
18 is run up to speed, the small out-of-balance weights 14 60 larly spaced. The magnet system is energised from a
Z-phase supply in known manner. Such an armature will
induce high frequency vibrations at or near the resonant
be subjected, when the ?xed ?eld system is energised
or natural frequency of the primary suspension system
from
the supply, to radial forces which appear to rotate
5 . . . 8.
in the same manner as the rotating eccentric weight 7.
Since the vessel assembly is symmetrically arranged, a
An alternative excitation system is a pneumatic or hydrau
high proportion of the excitation forces is balanced out
lic system.
in the primary suspension system 9, It}, 11, each vessel
I claim:
being, in effect, suspended from another mass constituted
1. A vibration ball mill comprising four containers
by the neighbouring vessels. Any resultant unbalanced
symmetrically arranged at equal spacings and adapted
force is absorbed by the low natural frequency secondary 70 to carry grinding elements and a charge of material to be
suspension springs 20 which thus serve to isolate the
ground; a primary suspension unit interconnecting each
foundation or bed 21 from the vibrations. Thus it is
pair of adjacent containers and tuned at least approxi
possible to excite the vessels 1 . . . 4 at high frequencies
with the high ef?ciencies resulting from the use of high
mately to resonance at the frequency which induces a
condition of ?uidization of the mass of grinding elements
natural frequency suspensions 5 . . . 8 without the need 75
in each container, said primary suspension unit consist
8,021,082
6
ing of leaf springs coupled in series and interconnecting
each pair of adjacent containers; an exciter for exciting
coacting element, and means for indicating relative dis
placements of said elements.
each container in at least two mutually inclined direc
4. A vibration ball mill comprising a group of four
tions, the excitation of each pair of adjacent containers
symmetrically disposed vessels for containing a charge
being in anti-phase along one common direction; and a
to be ground and a quantity of grinding elements; a high
secondary suspension system having a lower natural fre
quency of vibration than that of the primary suspension.
2. A vibration ball mill comprising four cylindrical
ing each pair of adjacent vessels for displacement along
frequency primary leaf spring suspension interconnect
mutually inclined directions and tuned at least approxi
containers whose axes are parallel and equiangularly
mately to resonance at the desired high vibration fre
spaced around the circumference of an imaginary cylinder; 10 quency; means for exciting adjacent vessels in phase
2. primary suspension unit interconnecting each pair of
adjacent containers and consisting of a pair of leaf springs
coupled in series and tuned approximately to resonance
opposition; a secondary resilient suspension supporting
said vessels and the primary suspension and having a
natural frequency substantially lower than said vibration
at a relatively high frequency; an eccentric exciting mass
frequency; and vibration amplitude control means com
journalled on the axis of each container; means for driv 15 prising a displacement detector associated with a vessel,
ing each exciting mass in phase opposition to each adja
and means operated by said detector for controlling the
cent mass; and a secondary suspension system support
input energy to said exciter.
ing said primary suspension system and having a natural
5. Apparatus according to claim 4 wherein the vibra
frequency lower than that of said primary system.
tion amplitude detector comprises an apertured shutter
3. A vibrating load system comprising four symmet 20 mounted on the vessel, a ?xed photocell, and a ?xed light
rically disposed load carriers; a high frequency leaf spring
source arranged to irradiate said photocell through the
suspension interconnecting each pair of adjacent carriers
aperture in said shutter.
for displacement in mutually inclined directions; an
References Cited in the ?le of this patent
exciter for vibrating said carriers simultaneously in said
directions at approximately the resonant frequency of 25
UNITED STATES PATENTS
said primary suspension; a secondary suspension sup
2,760,729
Mittag et al. ________ __ Aug. 28, 1956
porting said carriers and said primary suspension and
FOREIGN PATENTS
having a natural frequency remote from said resonant
frequency, and a carrier vibration amplitude detector
633,699
Germany ____________ __ July 16, 1936
comprising an element mounted on a carrier and a ?xed 30
936,003
Germany ____________ __ Dec. 1, 1955
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