14
1
r1
'
l
utC\-I~MICAL
CORPORAT\ON
L35 East
42nd
Street
New York, N.Y. 10011
-. ---- -~-.,~-~-~
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!•c
.
. " .• •
.
.
•
...
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.
AN EVOLUTION
OF
QUALITY
PRODUCTS
Broad
Experience and Years
of
Development
are
reflected
in the MARCY MILL
For more than fifty years the names MINEAND SMELTER and MARCY have been the symbol of dependable quality ore milling ma -chinery, industrial and mining equipment, and supplies created for your specific needs. Dur-ing this period thousands of operators have experienced continuous economical and un -equalled service through their use.
No exact date is recorded as to when the
need first arose for some mechanical means
of reducing particles in size, but considering that it has been many years, it is perhaps sur-prising that grinding is still an "art" and not an "exact science".
The Mine and Smelter Supply Company, through its Manufacturing Division, during these years has continuously accumulated knowledge on grinding applications. It has contributed greatly to the grinding process through the development and improvement of such equipment.
Just what is grinding? It is the reduction of lump solid materials to smaller particles by the application of sheari'lg forces, pressure, attrition, impact and abrasion. The primary consideration. then, has been to develop some mechanical means for applying these forces.
The modern grinding mill applies power to rotate the mill shell and thus transmits energy to some form of media which, in turn, frac -tures individual particles.
Just how this can best be done reverts to our history of grinding. In 1914 Mr. Frank E.
Marcy established the "Marcy principle of
grinding". This principle is simply stated "rapid change of mill content is necessary for high efficiency". This principle is incorpo
-rated in all Marcy Mills and has been proven in hundreds of operating installations until it is now generally accepted as a world-wide axiom. Since the first Marcy installation oper -ators of every class. small as well as large. have shown their preference for Marcy Mills. We point with pride to the great number of large installations throughout the world where Marcy Mills are doing the grinding. Small
mills profit from the experience of these large operations.
Through constant and extensive research. in the field of grinding as well as in the field of manufacturing. Mine
&
Smelter continues to pioneer. Constantly changing conditionsprovide a challenge for the future. Meeting
this challenge keeps our company young and progressive. This progressive spirit, with the knowledge gained through the years. assures top quality equipment for the users of our mills.
Today Mine
&
Smelter's modern manu-facturing facilities. rigid controls. and close inspection assure excellence in uniformity of our products and satisfactory performance even under the most severe conditions.
You are urged to study the following
pages which present a detailed picture of our facilities and discuss the technical aspects of grinding. You will find this data helpful when considering the selection of the grinding equi p-ment.
THE MINE AND SMELTER SUPPLY
THE ORE & CHEMICAL CORPORATION
235 East 42nd Street
New York, N
.
Y. 10017
El Paso, Texas
Copyright 1958 by The Mine & Smelter Supply Co.
Main Office: Denver 16, Colorado, U.S.A.
3800 Race St. P.O. Box 9041
122 East 42nd St., New York Salt Lake Ctty, Utah
-Eight of seventeen 9' x 12' Marcy Rod Mills at Anacondo, Montana
Marcy Quality and Service Selection of a Grinding Mill From Theory to Practice General Construction Method of Discharge Drives
Feeders Rod Mills
End Peripheral Discharge Rod Mills
Center Peripheral Discharge Rod Mills Ball Mills Tube Mills Pebble Mills Special Applications Cement Grinding Useful Information Alphabetical Index 2- 3 4- 5 6-13 14-19 20-21 22-23 22-23 24-29 28-29 28-29 30-33 34-35 34-35 36-37 38-39 40-43 44-45
1
OVER
SO YEARS OF EXPERIENCE
It
is quite understandable
that The Mine
&
Smelter
Supply Company takes pride in the
quality of its
Marcy Mills because of the
tradition
established
and carried forward in
the
history of
our company.
Complementing the human craftsmanship
built
into these
mills, our plants are equipped
with
modern
machines of advanced design
which
permit
accurate manufacturing of each
constituent
part
.
Competent supervision
en-courages
cl
o
se inspection
of each mill both
as
to qu
ality
and
proper fabrication
.
Each
mill
pr
oduced i
s
assured of meeting the high
requ
i
r
ed stan
dards
.
New and higher speed
machines
have
replaced former pieces of
equipment to provide up-to-date procedures.
The use
of
high speed cutting and drilling
tools has
stepped
up production
,
thereby
re-ducing costs and permitting us to add other
refinements and pass these savings on to you,
the consumer.
Each foundry heat is
checked
metallurgic-ally
prior
to pouring. All first castings of any
new design are
carefully examined
by the use
of an X-ray machine to be certain of
uniform-ity
of structure. The X-ray
is
also used to
check welding work, mill heads,
and other
castings.
Each Marcy Mill, regardless of size, is
de-signed to meet the
specific grindi
ng
condi-tions under which
it
will be used.
The
speed
of the mill
,
type of liner, discharge
arrange-ment,
size
of feeder, size of bearings,
mill
diameter and length, and other factors are
all considered to take care of the size of feed,
tonnage, circulating sand load
,
selection of
balls
or
rods,
and the final size of
gri
nd
.
All Marcy Mills
are
built with jigs and
tem-plates
so
that any part may be duplicated.
A full
set of
detailed drawings
is
made for
each mill
and its
parts. This record is kept
up to date during the life of the mill.
This
assures accurate duplication for the
replace-ment
of
wearing parts during the future years
.
Views
of
our manufacturing plant in
Den-ver
are shown
on these pages
.
Other
manu-facturing plants
are
located
in
Canada,
Eng-land, Australia, Sweden, South Africa, and
Finland.
MARCY
TECHNIC
A
L SERVICE
As
a part of our service
our staff includes
experienc
ed engineers, trained
in the
field of
metallur
gy, with special emphasis on
grind-ing work
.
Th
is
k
no
wl
edge, as well as a b
a
ck-ground
g
ain
e
d
fro
m
intimate contact with
various operat
i
n
g co
m
panies throughout the
world
,
pro
vi
d
es a sound basis for
consulta-t
i
on on your
grin
d
i
n
g problems
.
We take
pride
i
n man
u
f
acturi
n
g Marcy Mills for the
metallur
g
ical
, rock products, cement, process.
and chemi
cal indus
t
ries
Partial view of Pattern Shop
-TEST F
A
CI
L
ITIES
As an additional service we offer our test-ing laboratories to check your material for grindability. Since all grinding problems are different some basis must be established for recommending the size and type of grinding equipment required. Experience plays a great part in this phase; however, to establish more direct relationships it is often essential to con-duct individual grindability tests on the spe-cific material involved. To do this we have established certain definite procedures of lab
-Portion of Foundry
oratory grinding work to correlate data ob-tained on any new specific material for com-parison against certain standards. Such stand-ards have been established from conducting similar work on material which is actually being ground in Marcy Mills throughout the world. The correlation between the results we obtain in our laboratory against these standards, coupled with the broad experience and our company's background, insures the proper selection and recommendation of the required grinding equipment.
4
When selecting a grinding mill there are many factors to be taken into consideration. First let us consider just what constitutes a grinding mill. Essentially it is a revolving, cylindrical shaped ma-chine, the internal volume of which is approxi -mately one-half filled with some form of grinding media such as steel balls, rods or non-ferrous pebbles.
Size of feed to a mill may be considered: coarse ( l" to 2"); medium (1/4" to
3/.!"):
or fine•(less than 1/4"). Feed may be classified as hard, average or soft. It may be tough, brittle, spongy, or ductile. It may have a high specific gravity or a low specificgravity. The desired product from a mill may range in size from a 4 mesh down to 200 mesh, or into the fine micron sizes. For each of these properties a different mill would be indicated.
The Marcy Mill has been designed to carry out specific grinding work requirements with em-phasis on economic factors. Consideration has been given to minimizing shut-down time and to provide long, dependable trouble•free operation. Wherever wear takes place renewable parts have been designed to provide maximum life. A Marcy Mill, given proper care, will last indefinitely.
Marcy Mills have beer manufactured in a wide variety of sizes ranging from laboratory units to mills l2V2' in diameter, with any suitable length.
Each of these mills, based on the Marcy principle of grinding, provides the most economical grind -ing apparatus.
Marcy offers you the following advantages: l. Power requirements and consumption of
liners and media are kept at a minimum. 2. Superior mechanical construction provides
continuous low cost operations.
3. They are available in a large selection of sizes and capacities.
4. Low pulp level grinding provides an active effective grinding mass within the mill to act on particle size reduction only. There is no wasteful cushioning of grinding action by high pulp levels.
5. For any given capacity, Marcy Low Dis -charge Level Mills require less floor space, lower transportation costs, and minimum required erection material.
ROD M
I
LLS
For a number of years ball mill grinding was the only step in size reduction between crushing and subsequent treatment. Subse-quently rod mills have altered this situation, providing in some instances a more econom-ical means of size reduction in the coarser fractions. The principal field of rod mill usage is the preparation of products in the 4-mesh to 35-mesh range. Under some conditions it may be recommended for grinding to about 48 mesh. Within these limits a rod mill is often superior to and more efficient than a ball mill. It is frequently used for such size reduction followed by ball milling to proE:luce a finished fine grind. It makes a product uni -form in size with only a minimum amount of tramp oversize.
The basic principle by which grinding is done is reduction by line contact between rods extending the full length of the mill. Such line contact results in selective grinding carried out on the largest particle sizes. As a result of this selective grinding work the i n-herent tendency is to make size reduction with the minimum production of extreme fines or slimes.
The rod mill has been found advantageous for use as a fine crusher on damp or sticky materials. Under wet grinding conditions this feed characteristic has no drawback for rod milling whereas under crushing conditions those characteristics do cause difficulty. This asset is of particular importance in the man-ufacture of sand, brick, or lime where such material is ground and mixed with just suffi-cient water to dampen, but not to produce a pulp. The rod mill has been extensively used for the reduction of coke breeze in the 8-mesh to 20-mesh size range containing about l 0% moisture to be used for sintering ores.
-BALL MILLS
Grinding by use of nearly spherical shaped
grinding media is termed ball milling. Strictly
speaking, such media are made of steel or
iron. When iron contamination is detrimental, procel.3in or natural non-metallic materials are
used and are referred to as pebbles. When ore particles are used as grinding media this is known as autogenous grinding.
Other shapes of media such as short
cyl-inders, cubes, cones, or irregular shapes have
been used for grinding work but today the
nearly true spherical shape is predominant and
has been found to provide the most economic form.
In contrast to rod milling the grinding action results from point contact rather than
line contact. Such point contacts take place
between the balls and the shell liners, and
between the individual balls themselves. The
material at those points of contact is ground to extremely fine sizes. The present day
prac-tice in ball milling is generally to reduce
ma-terial to
35
mesh or finer. Grinding in a ballmill is not selective as it is in a rod mill and
as a result more extreme fines and tramp over -size are produced.
Ball mills generally operate at slightly
higher speeds than rod mills and thereby
im-part a cascading action to the grinding media. Ball mills are generally recommended not only for single stage fine grinding but also have wide application in regrind work. The Marcy Ball Mill with its low pulp level is
especially adapted to single stage grinding
as evidenced by hundreds of installations
throughout the world. There are many appli-cations in specialized industrial work for either continuous or batch grinding.
WET AND DRY CRINDINC
Wet grinding may be considered as the grinding of material in the presence of water
or other liquids in sufficient quantity to pro
-duce a fluid pulp (generally 60% to 80%
solids). Dry grinding on the other hand is carried out where moisture is restricted to a very limited amount (generally less than 5%). Most materials may be ground by use of either
method in either ball mills or rod mills. Se-lection is determined by the condition of feed
to the mill and the requirements of the ground product for subsequent treatment. When grinding dry some provision must be made to permit material to flow through the mill. Marcy Mills provide this necessary
gra-dient from the point of feeding to point of dis-charge and thereby expedites flow.
ADVANTAGES OF WET GRINDING
l
.
No dust problem.2. Damp and sticky feed may be treated. 3. Low power consumption.
4. Simplified material handling.
5. Higher mill capacity.
6. Size classification is simplified.
ADVANTAGES OF DRY GRINDING
l.
Lower steel consumpti.on.2. Elimination of drying or filtering f
in-ished product.
FINENESS OF GRIND
The fineness to which material must be
ground is determined by the individual mate-rial and the subsequent treatment of that
ground material. Where actual physical
sepa-ration of constituent particles is to be real -ized grinding must be carried to the fineness where the individual components are
sepa-rated. Some materials are liberated in coarse
sizes whereas others are not liberated until extremely fine sizes are reached.
Occasionally a sufficient amount of
valu-able particles are liberated in coarser sizes to
justify separate treatment at that grind. This treatment is usually followed by regrinding
for further liberation. Where chemical
treat-ment is involved, the reaction between a solid and a liquid, or a solid and a gas. will
gen-erally proceed more rapidly as the particle sizes are reduced. The point of most rapid
and economical change would determine the fineness of grind required.
Laboratory examinations and grinding tests
on specific materials should be conducted to
determine not only the fineness of grind
required, but also to indicate the size of commercial equipment to handle any specific
problem.
The following f e w pages are devoted to the subject "From Theory to Practice" taking you step by step through some of the vari-ables encountered in grinding and how each of these affect your operations.
As previously pointed out, grinding must still be considered an art and not an exact science. As a result many theories have been expounded on the numerous variables w h i c h enter into grinding work. Should it be pos-sible to reduce all of these variables to a sim-ple mathematical formula the selection of a grinding mill would, of course, be simple. Many approaches to this have been made but to date a fool-proof formula, both mathe-matically and practically applicable, has not been devised. W e must, therefore, take each variable into consideration on its o w n merits and then correlate such ideas into a single selection. To do this a broad experience and understanding of the complete subject of grinding is essential. This is a part of the problem of your engineers and our o w n con-sulting staff. On page 5 t w o general points have been discussed briefly — wet or dry grinding, and fineness of grind. T w o main categories of grinding equipment, namely rod mills and ball mills, have also been mentioned.
Whether grinding is to be performed wet or dry, or in a ball mill or rod m i l l , a choice must be made between open or closed cir-cuit. Other factors which require thought are mill size, speed of mill rotation, moisture con-tent, retention time, circulating load, type and sizes of grinding media, mill pulp level, mill shape, power, and relation between diameter and length. These all influence operating re-sults and are evaluated and incorporated in the selection and design of the Marcy M i l l .
A NOTE ABOUT M I L L SHAPE
Marcy mills are essentially cylindrical ir""" shape and this design has been selected for very definite reasons.
M i l l capacity is a function of the mill vol — ume and the load of grinding media. There-fore to obtain a mill of greatest capacity for any given space, pure logic dictates a mill having the greatest volume. W h i l e a square— section w o u l d provide the greatest volume, smooth continuity of operation and uniformity of media action must also be considered and thus a true circle is the only practical answer.— Should the diameter vary f r o m one end to an-other there is but one thing which occurs— reduced volume, or in other words, reduced
capacity. — The cylinder simplifies mill construction,
resulting in a m i n i m u m amount of mainte-nance and reflecting in less downtime. Power-wise, cylindrical mills provide the most eco-nomical piece of equipment for grinding work. Floor space for any mill is proportional to the diameter of the mill and its length. Therefore, floor space is kept at a m i n i m u m . A m i l l . ~ keeping u n i f o r m diameter throughout its full length obtains m a x i m u m volume for a given floor space.
LENGTH OF M I L L
The relationship of mill diameter to length, is of considerable importance. Rod mills should have a length greater than the diameter to avoid entanglement' of rods. The construction of ball m'ills is different in that the diameter, may be larger, equal to, or smaller than the length.
The selection of mill length is depend-ent upon the size of feed, size of product a n d ' type of grinding circuit selected. Considera-tions given a short mill are the reduced floor space, shorter retention time producing less fines in the discharge product, and the possi-' bility of producing a slight amount of tramp oversize particles. Corresponding conditions to be expected f r o m a longer mill are greater floor space requirements, higher capacity' (closely proportional to mill length), greater retention time thereby producing a finer mill discharge product and a greater amount of ex-treme fines, less tramp oversize in the product." Since most mill variables act as a function of the mill length, this consideration is relatively simple. On pages 10 and 1 1 considerable dis-cussion is provided on the subject of m i l l " diameter.
-OPE
N AND C
LOSED C
I
RCU
I
TS
SING
LE
A
N
D TWO
-
STAGE
GRINDING
The method of operating a grinding mill may be classified into two methods. open cir-cuit or closed circir-cuit. In open circir-cuit grind-ing feed enters one end of the mi II at a pre-determined rate so as to make the desired
fin-ished product during a single pass through
that mill. In other words there is no size
classification made on the discharge product. One important application is on ores
contain-Advantages of open circuit grinding: 1. Simplicity of mill layout.
2. May be used where classifying is not practical.
3. May be used where control of pro
d-uct size is not important.
4. The use of rod mills will produce an
ideal fine feed for ball mills.
5. May be used where classifier dilutuion would be objectionable.
Advantages of closed circuit grinding:
1
.
Prov1des a close control of finishedproduct size.
2. Mill capacity is greatly increased. ing damp and clay-like material which causes
difficulty in fine crushing. This problem is generally solved by wet grinding in a rod - mill or in this case it may be called wet fine
crushing.
3. Power requirements per ton of fi
n-ished material are lower.
4. Less overgrinding or production of ex
-treme fines.
-In closed circuit grinding the feed enters
one end of the mill and is discharged from the other end into some type of classifier.
This classifier is to limit maximum particle
size removed from the mill circuit. The
over-size material is returned to the grinding mill for additional size reduction. Such material returhed to the mill is defined as the
circulat-ing load. Classifying equipment may consist
of vibrating screens on coarse separations for
wet or dry grinding. For wet grinding in the finer size ranges wet classifiers and/or cy-clones are employed, generally to make a size
separation from
20
mesh down to325
mesh. Under dry grinding conditions air classifiersare used to make the size classification.
Single stage grinding may be defined as
grinding original feed to finished size in a
single mill. It may o;:>erate in either open cir-cuit or closed circuit.
Two stage or multiple stage grinding may be defined as grinding in two or more units with each unit making a step in size redu c-tion. Each mill may operate either as open circuit or closed circuit.
r
-
0-o
F •FEEDD : DISCHARGE O=OVERSIZE
RETURN SANDS
F
-Advantages of single stage grinding:
1. Less equipment to purchase. install and maintain.
2. Less floor space requirements. Advantages of two-stage grinding:
1. Less overgrinding.
2. Provides a simplified fine crushing plant and grinding section.
3. May be used to increase capacity of
existing single stage operation.
4. Provides an opportunity for recovery of desirable material between stages of size reduction.
CIRCULATING LOAD
Generally speaking circulating loads for rod mill operation will be less than
200
%.
In most cases it will more closely approach1
00%
to120
%.
In ball mill operations the circulating load will vary between300
%
and100
0
%
depending upon the grind requiredand type of material. As an average it will
approach 3
5
0
%
.
PRIMARY MILL - D-t
0-,
DI
OPEN CIRCUIT OR C =CLASSIFIER FINISHED PRODUCTTwo sTAGE:PRIMARY OPEN CIRCUIT
Ll
cLAssiFIERLc
SECONDARY CLOSED CIRCUIT '-· _ _ _ _ _ _
___,!
F SINGLE STAGE!-
o
~
W
~ ~
iii (/) <{LD-
d
h
TWO STAGE: BOTH MILLS CLOSED CIRCUITED WITH SEPARATE CLASSIFIERSF
I
LD
-l
c
TWO STAGE:PRIMARY OPEN CIRCUIT
(PRODUCT CLASSIFIED) SECONDARY CLOSED CIRCUIT
F
I
- 0 --, SPLIT I O ~L
D
-I
C
TWO STAGE: BOTH MILLS CLOSED CIRCUITED
WITH ONE CLASSIFIER
SINGLE STAGE CLOSED CIRCUIT jC
From Theory to Practice
MILL SPEEDS
Proper speed, or most efficient speed, at which mills are to operate depends upon the action desired by the grinding media, the amount of media, its size and shape, percentage of solids in each mill, and shape of liners. In the follow-ing discussion we refer to critical speed
apply-ing to ball mills and peripheral speed referring to rod mills. Reference gr~phs giving these
speeds for various mill diameters will be found
on page 9.
Critical speed may be considered as the speed at which an infinite particle will con-tinue its travel around the periphery of the mill, thus becoming part of a flywheel action. Grinding balls actually will not centrifuge at this theoretical critical speed since they are larger than an infinite particle and also because of slippage.
The following table illustrates the action of a normal ball charge at various percentages of critical speed. %Critical Speed 10 20 30 40
so
60 70 80 90 Sliding 3 3 3 2 2 2 1 1 Cascading 1 1 1 2 3 3 2 • Centrifuging 1 1 2 2 31 indicates slight amount, 2
indicates great amount. indicates appreciable amount, 3 The following table illustrates the effect of va
ry-ing the amount of ball charge.
Ball Charge 5-15 15-25 25-35 % (Mill Volume) Sliding Cascading Centrifuging
*
3
*3
*
*
1 *2
* *
2*
*
1
35-45 * 1 *3
**
2
45-50 * 1*
2
*
3
I indicates slight amount, 2 indicates appreciable amount 3
indicates great amount. '
• effective at all speeds, • * only effective at higher speeds.
Generally speaking ball mills operate within the range of 50% to 90% of critical speed.
The average is found to be approximately 75%.
Pebble Mills have been found to operate more efficiently at higher speeds than ball mills.
When reaching the higher percentages of critical speed caution must be used and consideration given the action of the scoop feeder (see page 22).
When considering rod mills, peripheral speeds only should be considered. In the case of ball milling, with a free moving grinding me-dium, ball paths obtained are based on critical speeds. ln a rod mill with a comparatively rigid grinding medium, a certain cascading and roll of rods are obtained, which does not resemble the action of loosely projected ball paths. There-fore to simulate similar rod actions in mills of various diameters it is necessary to operate be-tween 60% and 98% of critical speed. There -fore, Critical Speed is misleading if used in con-junction with rod mills. It has been found that Marcy low pulp level rod mills show increases in efficiency as peripheral speeds are increased from 300' per minute to the present practical maximum of around 500' per minute.
To illustrate the comparison between critical speeds and peripheral speeds and the misleading use of critical speed for rod mills, we submit the follow-ing illustrative table:
BALL MILLS @
76% C.S.
ROD MILL SPEEDSMill Criti- RPM Peri-
I
At 330' /Min. At 470' /Min.Dia. cal At pheral
Inside Speed 76% Speed Mill % Mill %
Liners RPM
c.s
.
Ft./Min. RPMc.s.
RPM C.S. 4' 38.3 29.1 366 26.2 68_4 37.4 97.7 6 31.3 23.8 44? 18.1 57.8 24.9 79.5 8 27.1 20.6 518 13.1 48.3 18.7 69.1 9 25.6 19.5 552 11.7 45.7 16.6 64.8 10 24.2 18.4 578 10.5 43.4 15.0 62.0SLOW SPEED MEDIUM SPEED HIGH SPEED
8
Above are three illustrations showing the action of balls in a mill at differ-ent speeds. The action at medium speeds (around 75% critical speed) is gener-ally most desirable and efficient for Marcy grate discharge mills.
-Theoretically critical speed is the point at which centrifugal and gravity forces acting on an infinite particle traveling on the shell liner offset each other or become equal. The formula used in calculating critical speed is shown on the graph below.
Zl ::::i .J .J
w
I: Cl)w
9
Cl)z
a::e
40% 0% 60% 70% 80% 90% 100% ~ 45% 65% 75% 85% 95%w
~ <(40
_J _J ~ ~ Wl2 w La..J,
~8 ii; ~a:
w
t-6
w
~ <(0
_J4 _J ~ 10 15 2025
30MILL R.P.M
.
PERIPHERA
L:
SPEED
P. S.= IT X D X R.P.M. I ' I IICRITICAL SPEED
Cs.
. ..JR
= 54.19 .S.=CRITICAL SPE DIN R.P.M.R= RADIUS IN FEET INSIDE SHELL LINING. 35 40 45
z!:>~P
·
""
·
30 Rf>·""· 50 35R.e
·
""
·
4o
R
.
P.""
·
45 R.f>.""· 50 Rf>·""· 200 300 400 500FEET P
ER M
I
NU
TE
The above graph provides peripheral speeds for various mill diameters. Such speeds are measured on the inside diameter of shell liners.
55
600
from Theory to Practice
POWER AND CAPACITY
Often grinding capacity and power are used
hand in hand since power is an index to the
potentialities of any grinding mill. The grind
achieved is in direct relation to the power applied
in rotating a mill. This rotation transmits energy input to the grinding media and energy is
con-sumed in reducing particle sizes. When any particle is split, producing two or more smaller particles, the total surface area of the smaller
particles will be greater than the surface area of the initial size. Therefore surface area often
is used to express the amount of grinding work
which is performed.
There are two methods of looking at power.
First and easily understood is the reference to
connected horsepower, or the actual consumed
horsepower required to drive the mill. The
sec-ond is basing power on the amount of work done.
We prefer to express this as kilowatt hours per
ton of material ground. The following formula
containing three factors may be found useful in
calculating power consumed per ton of material
ground. Wherever two of the factors are avail-able, the third may easily be solved.
KWH/ton x tons per 24 hours
17.9
HP
There are several variables in mill horsepower
-the most important has to do with mill diame-ter. Several of these variables also reflect
simi-larly on capacity. There have been various
state-ments made as to how power and capacity vary
with mill diameter, each using a figure of the
diameter raised to some power, such as 03
, 02.65,
02.6, and 02
·5. For your convenience we have
listed on page 11 a table giving these various
diameters raised to the appropriate figures. We
have found in the Marcy low pulp level mills
that the capacity varies closely as the diameter
cubed. The mill power varies closely as the
diameter to the 2.5 power. With overflow type
mills, or high pulp level mills, the theoretical
ex-ponents more closely approach the 2.6 or 2.65
power. The difference lies in the waste of energy
when transmitted through a cushioning deep
quantity of pulp.
Power required in relationship to mill length
is a straight line function or direct proportion
within limits. In other words each foot of mill
will require a definite amount of power.
Capac-ity of a mill also varies in the same manner.
Example:
You are operating a No. 86 Marcy Mill
con-suming 245 HP and grinding 500 tons per day
to 65 mesh. What will be the capacity of a
54 Marcy Mill? From the table on page 11. the
86 diameter cubed is 512; the 54 diameter
cubed is 125; the 86 diameter to the 2.5 power
is 181 ; and the 54 diameter to the 2.5 power
is 55.91. Such diameters are inside new liners. Capacity 125 x4 x 500 = 81 tons 512 X 6 Horsepower 55.91 X 4 X 245 = 50 HP 181 X 6
Therefore the 54 mill will have a capacity of
81 tons and wi II consume 50 H P.
Power consumed is a reflection of the fine-ness of grind. The finer a material is ground the
more power is consumed.
Power consumption is also a reflection of
the amount of media carried within the mill.
The maximum power requirements for any mill
will be when it is 45% to 50% filled with
grinding media. Above or below this power
drops off. Similarly mill capacity will behave
the same way. Within limits the effect of
add-ing or decreasadd-ing grindadd-ing media will be
pro-portional to that weight.
Power is again reflected in mill dilution. A
mill carrying a high percentage of solids will
consume less power than a mill carrying a low percentage of sol ids.
The above refers to wet grinding. Under dry
grinding conditions it has been found that the
power will be between 60% and 90% that of
a wet grinding mill. Wet grinding capacity will
-,....
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3 4 5 1 7 8 t l 0 1 1 1 2MILL DIAMETER INSIDE SHELL~Feet
The above graph illustrates how power
con-sumed for various grinds changes with ball mill
diameter. It is noted that as the diameter of the
mi II increases the kilowatt hours consumed per ton
decrease. This shows the advantage of selecting as
large a diameter mill as possible for any grinding
application. (Curves may be used within limits of
about 3 or 4 feet diameter variance.)
Below is a graph showing the effect on mill
capacity by varying the size of feed. As feed size
decreases capacity increases: Example: 1" feed
equals 24.5%:
Y
2"
feed equals 43%. Decreasingfeed would increase capacity (43-24.5) 18.5%.
~
~roc
2c
:to ·
! FEED: ZE: INC HES i
fit I :j:!'Eff
i
~
-The table below tabulates mill diameter in feet or
inches raised to various exponents. This table will be
found useful in calculating power and capacity figures.
DIAMETER Feet Inches 2
3
45
67
8
9
10 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 99 102 105 108 111 114 117 120 122 123 126 129 11 132 135 138 141 12 144 147 150 153 13 156 159 162 165 D2S D26 5.657 6.061 7.596 8.236 9.879 10.83 12.54 13.87 15.59 17.40 19.04 21.43 22.92 25.98 27.23 31.07 32.01 36.77 37.24 43.03 42.95 49.92 49.18 57.47 -55.91 65.68 63.18 74.56 70.97 84.14 79.30 94.45 88.20 105.5 97.68 117.3 107.7 129.9 118.4 143.3 129.7 157.5 141.5 172.5 154.1 188.5 167.2 205.2 181.0 222.9 195.6 241.5 210.7 260.9 226.5 281.3 243.0 302.6 260.2 325.0 278.2 348 3 296.8 372.8 316 2 398.1 329.6 409.1 336.3 424.4 357.3 452.0 379.0 480.5 401.4 510.0 424.6 540.9 448.5 572.5 473.1 605.3 498.9 639.6 525.0 674.6 552.5 711.0 580.6 748.7 609.3 787.2 639.0 827.4 669.6 868.6 701.1 911.3 Dl6S Dl 5.761 8.00 8.576 11.39 11.34 15.63 14.59 20.80 18.38 27.00 22.73 34.33 27.66 42.88 33.20 52.73 39.41 64.00 46.28 76.77 53.83 91.33 62.13 107 2 71.17 125.0 81.00 144.7 91.65 166.4 103.1 190.1 115.4 216.0 128.6 244.1 142.6 274.6 157.6 307.5 173.6 343.0 190.5 381.1 208.4 421.9 227.3 465.5 247.4 512.0 268.4 561.5 290.4 614.1 313.6 669.9 337.8 729.0 363.3 791.5 389.9 857.4 417.8 926.9 446.7 1000 466.7 1051 476.9 1077 508.4 1158 541.0 1243 575.0 1331 610.6 1424 647.0 1521 684.7 1623 724.4 1728 764.7 1839 806.9 1953 850.4 2073 895.0 2197 .941.5 2327 989.3 2460 1039 2600From Theory to Practice
GRINDING
MEDIA
The subject of grinding media is still con-troversial. The following information is
gen-eral and based upon facts gathered from many
operations.
General statements can be made and are
worthy of consideration when selecting
grind-ing media. For the best results it has been
found that the smallest diameter ball or rod which will break down the particular material to
be ground is desirable since greatest surface area
is obtained. From the standpoint of economy.
the larger the media the higher will be the liner
consumption and media consumption. The mini
-mum size of grinding balls should be selected with caution since there will be a tendency for
such balls to float out of the mill in a dense
pulp (this is minimized by the use of a Marcy
grate discha'rge mill). Also the smaller the media
the quicker it will reach its reject size.
For the first stage of grinding, media will
generally be in the 4" to 2" size (in some cases
as high as 5"). In secondary finer grinding the
initial charge will begin at around 3" and in
the case of balls will grade down to about 3_4".
Extremely fine grinding will dictate the use of 1
%"
and smaller balls.Grinding media is the working part of a mill. It will consume power whether it is doing grind-ing work or not. The amount of work which it does depends upon its size, its material, its con
-struction and the quantity involved. It is, ther
e-fore, advantageous to select the type of grind
-ing media which will prove most economical,
the size of media which will give the best
grind-ing results, and the quantity of media which will just produce the grind required.
One of the economic factors of grinding is
the wear of the grinding media. This is
de-pendent upon the material used in its manu
-facture, method of manufacture, size of media,
diameter of mill, speed of mill, pulp level main
-tained in the mill, rate of feed, density of pulp maintained, shape of the liner surface, nature
of the feed, and the problem of corrosion. In general practice, tonnage rates and power consumption will be in direct proportion
11
to the specific gravity of the media and approx
i-mately in direct proportion with the amount of
media.
Many shapes of grinding media have been tried over the past years. but essentially there
are only two efficient types of media used. These are the spherical ball and the cylindrical rod.
Other shapes are relatively expensive to
manu-facture and they have shown no appreciable
improvement in grinding characteristics.
It will be found that a seasoned charge will
provide a better grind than a new mill charge. This, of course, is impossible to determine at
the offset, but after continuous operation the
media charge should be checked for size and weight, and maintained at that optimum point. After the charge has been selected, replacement media should be made at the maximum size
used. In some cases it has been found advan
-tageous to add replacement media of two or
more sizes, so as to maintain more closely the
seasoned ratio.
The original charge to a mill is generally between 40% and 50% of mill volume for ball
mills and 35% to 45% mill volume for rod mills. As a general figure rod mills will have a void space within the charge of around 20%
to 22% for new rods. In ball mills the
theo-retical void space is around 42% to 43%. It
has been found that as grinding rods wear a
4
"
or4
Y2"
rod will generally break up at about1
Y2"
diameter. The smaller diameter new rodsdo not break up as easily and will generally
wear down to about 1". In many applications it has been found. that grinding efficiency will
increase if rods are removed when they reach
the 1" size, and also if broken pieces of rods
are removed. The Marcy Open End Rod Mill
has the advantage of allowing the quick and easy removal of such rods.
It is difficult to give figures on media con -sumption since there are so many variables. Rods will be consumed at the rate of 0.2# per
ton on soft easily ground material up to 2#
per ton on harder material. Steel consumption
of balls is spread out over an even greater range.
Some indication as to media consumption can
be obtained from power consumed in grinding.
For example, balls or rods will generally wear at a rate of about 1
#
for each 6 or 7 kilowatt hours consumed per ton of ore. Linerconsump-tion is generally about one-fifth of the media
-GRINDING RODS (NEW)
SIZE Dia. (Inches) by Length (Ft.) 1 X 10 11hx 10 1% X 10
2
x10 2% X 10 3 x10 3% X 10 4 x105
X 10 VOLUME (Cu. ln.) Each 94.2 147.3 212.1 377.0 589.0 848.2 1154.5 1507.9 2356.2 WEIGHT (Pounds) Each 27 42 60 107 167 240 327 427 668 Approx. Approx. NUMBER NUMBER Per Per Cu. Ft. Ton 14.6 9.3 6.5 3.7 2.3 1.6 1.2 0.9 0.6 75 48 33 19 128
6
5
3
SURFACE AREA Each (Sq. ln.) 377.0 471.2 565.5 754.0 942.5 1131.0 1319.5 1508.0 1885.0 SURFACE AREA PER Cu. Ft. (Sq. ln.) 5506 4404 3671 2753 2202 1835 1573 1376 1101 SURFACE AREA PER Ton <Sq. Ft.l 196.1 156.9 130.7 98.0 78.4 65,4 56.0 49.0 39.2 WEIGHT PER UNIT SURFACE .0716 .0891 .1061 .1419 .1772 ·.2122 .2478 .2832 .3544FORGED STEEL GRINDING BALLS (NEW)
SIZE <Diameter Inches)
Y
2
3
,4
'Va
1
11h 1Y
2
]3
,4
2
2%3
3% 44
Y
2
5
VOLUME POUNDS EACH PER Cu. ln. Cu. Ft. .065 .221 .351 .524 1.023 1.767 2.806 4.189 8.181 14.137 22.449 33.510 47.713 65.450 280 280 280 280 280 280 280 280 280 280 280 280 280 280 WEIGHT EACH (Pounds) .019 .063 .099 .148 .290 .501 .795 1.187 2.318 4.006 6.361 9.495 13.519 18.544 NUMBER Per Cu. Ft. 15099 4474 2817 1887 966 559 352 236 121 70 44 29 21 15 NUMBER Per Ton 107851 31956 20124 13481 6902 3994 2515 1685 863 499 314 211 148 108 SURFACE AREA, EACH <S.q. ln.) .79 1.77 2.41 3.14 4.91 7.07 9.62 12.57 19.64 28.27 38A8 50.27 63.62 78.54 SURFACE AREA PER Cu. Ft. (Sq. ln.) 11858.8 7905.9 6776.5 5929.4 4743.5 3952.9 3388.2 2964.7 2371.8 1976.5 1694.1 1482.4 1317.6 1185.9 SURFACE AREA PER TON (Sq. Ft.) 588.24 392.16 336.13 294.12 235.29 196.08 168.07 147.06 117.65 98.04 84.03 73.53 65.36 58.82 WEIGHT PER UNIT SURFACE .024 .036 .041 .047 .059 .071 .083 .094 .118 .142 .165 .189 .212 .236
EXAMPLE: Require Initial Ball Charge of 18000# using 2Y2", 3",
3
Y
2
"
and 4" balls.Ball Dia. X Wt. Ea. 2.318 4.006 6.361 1.~ ~ ~.49_2
u£.,
y Area Eo. 19.64 28.27 38.48 50.27*SEE LAST COLUMNS IN TABLES ABOVE
*
X/Y Wt. /U.1it Surface .118 .142 .165 .189 .614We recommend grinding rods having the fol-lowing approximate specifications:
Carbon Manganese Sulphur Phosphorous Silicon . 85- 1.00% .60- .90 .05 Max. . 04 Max. .10 Max.
%
X/Y of Total 19.2 23.1 26.9 30.8 100.0 %X 18000 3456 4158 4842 5544 18000 No. Balls 1491 1038 761 584 3874 % balls. 38.5 26.8 19.6 15.1 100.0Rods are to be hot rolled, hot sawed or sheared, with standard tolerance and machine straightened .
We have found that a good grade of forged steel grinding balls is generally most efficient for use with our Marcy grate discharge ball mills .
General
The Mine and Smelter Supply Company does not attempt to build a " c h e a p " grinding mill. Engineering based on long experience w i t h mill manufacture enters into the pro-duction of Marcy Mills, w i t h the result that in field operation this equipment yields the lowest possible operating costs, maximum op-erating time, and years of useful service. As such then it is not an expensive mill.
Every Marcy M i l l is engineered and de-signed to meet the specific grinding condi-tions under which it w i l l be used. The speed of the mill, type of liners, grate openings for ball mills, size and type of feeder, size and type of bearings, trunnion openings, mill d i -ameter and length, as well as many other smaller factors are all given careful consid-eration in designing the Marcy M i l l .
Each mill is of proper design, constructed in a workmanlike manner, and guaranteed to be free from defects in material or workman-ship. A l l Marcy Mills are built to jigs and templates so any part may be duplicated when-ever required. A l l parts are accurately ma-chined for fits w i t h close tolerances. Before shipment each mill is assembled in our shops, carefully checked and match marked to fa-cilitate field erection. The mill is given a heavy coat of paint especially prepared for this type of machinery and all machined sur-faces are thoroughly coated w i t h protecting grease.
A complete set of detailed drawings is made for each mill and kept in a fireproof vault. This assures the future supply of per-fectly f i t t i n g replacement parts for the life of the mill. Wearing parts embodying the latest developments are supplied on all orders.
Pages 14-19 are devoted to descriptions of many of the integral parts composing a Marcy M i l l . The discharge parts and the various feeders and drives are discussed on pages 20-23.
In these descriptions you w i l l f i n d the word " M E E H A N I T E " . This is a trade name for metal castings poured under a licensed agreement w i t h The Meehanite Metal Cor-poration. A complete description of its char-acteristics and inherent nature is found on page 19.
The above heavy duty rolls developed for our own use provides a true circular shell having close tolerances. This assures perfect fit for shell liners and heads.
Marcy M i l l shells are fabricated from rolled plate steel. Under special conditions they can be cast of Meehanite, steel, or special alloys. The plate steel shells are rolled accurately to diameter and arc welded accord-ing to ASME specifications, usaccord-ing a Union Melt Auto-matic W e l d i n g Machine. This equipment provides an even flow, u n i f o r m strength weld w i t h f u l l penetration.
On each end of the shell are steel flange rings bored to f i t the shell, set in place and welded to the shell in-side and out by the Union M e l t machine. Large diam-eter shells are stress relieved under temperature and atmosphere control after welding is completed. Such heat treatment relieves any stresses or strains set up during rolling and welding operations.
The method of attaching the flange rings leaves the inside surface of the shell free from any pockets or de-pressions which would cause pulp racing and wear. The flanges are then machined true w i t h the shell axis and w i t h each other and counterbored to gauge for male and female f i t w i t h the separate mill heads. This construc-tion eliminates any possibility of bolt shearing.
One or t w o manholes are provided in ball mill shells, designed so that all interior wearing parts can readily pass through such openings.
Marcy M i l l shells are generally 5 " to 7 " greater in diameter than the nominal mill diameter figure. In other words the diameter of a Marcy M i l l is the measurement inside the average thickness of new liners—not inside the shell as designated by some manufacturers.
Union Melt Welding Ma-chine automatically weld-ing a Marcy Mill Shell.
,...
-HEADS AND
TRUNNIONS
Marcy Feed Head
Marcy feed and discharge heads are detachable. cast of Meehanite metal of ample thickness. either of GA or GC. depending on the size of mill and with cons.ideration to bending stresses. These heads are
generally ribbed for extra strength and stiffness. Such ribs terminate near the center of the head in a trun -nion seat. A male and female fit to the shell flange ring is provided and the back of the connecting flange is faced or spot faced to furnish a true seat for the joint connecting bolts.
The head to which the gear will be attached has a seat or flange with a shoulder turned accurately to
size providing a seat for the gear.
All turning and boring is done in one setting to
assure perfect concentrcity.
Smaller Marcy Mills are constructed with separate trunnions; larger diameter mills have trunnions cast
integral with the heads. Separate trunnions are at -tached to the heads with bolted flanges for male and
female fit. Flanges are faced and counter bored. All
trunnions are cast of Meehanite metal. turned and
carefully polished. All trunnions have a large bear -ing surface capable of carrying the heavy mill load
and to avoid heating during operation. The outer ends of the trunnions are faced and drilled to receive
the trunnion liners. protecting the inside surface from
wear.
Liner bolt holes are drilled to template and spot faced on the outside of the head.
FEED
HEAD
The feed head has ample depth to contain the
feed head liners. The rod mill feed head is conical in shape to give the essential feature of a feed entry pocket in front of the rods.
BALL MILL DISCHARGE HEAD
This head is of considerable depth providing a
pulp lifting chamber, and is designed to contain the
discharge grates, clamp bars. and the lifters which
elevate the mill product through the trunnion. See pages 20 and 21 .
Marcy Discharge Head showing lifters cast integral with head
ROD MILL DISCHARG
E HEAD
For rod mill work the discharge head is conical in shape causing the rods to travel by rotation
later-ally and away from the exceptionally large discharge opening. The discharge opening is larger than the inlet opening. thus providing the Marcy Low Pulp
Line principle of grinding.
TRUNNION
LIN
ERS
The discharge trunnion liner is cast of Meehanite
metal and has a wide mouthed bell to conduct the
mill product away from the mill. with no back drip.
The feed end trunnion liner is also constructed of Meehanite and can be furnished of several
de-signs to _meet each specific application. cor normal
closed circuit grinding work a spiral liner is furnished
to screw new feed and return sands into the mill. For spout fed mills a plain tapered liner is generally
furnished. ~
The mill trunnions are machined with a taper bored seat to receive the trunnion liner. Such ar-rangement permits the trunnion liner weight to be
carried by the seat rather than by the connecting studs. This is of particular importance on the feed
end since the shearing effect of the added feeder would cause breakage of the feeder connecting bolts.
SPIRAL FEED END
TRUNNION LINER
General Construction
TRU
NNION BEAR
I
CS
Swivel
type lead-bronze bushed trunnion
bearings
a
r
e generally
furnished on large diameter
Marcy Mills.
The bearing swivels
are
of Meehanite metal spherically
turned outside and bored and faced
inside
to receive
the removable bushing
.
The bushing
is
bored and
sc
r
aped to fit
the
mill trunnion
.
The bushing
is
pro-vided with end flanges thus assuring that the trunnion
flanges run against a bronze face.
On smaller mills rigid or swivel type bearings sup
-port
the
mill trunnions
.
The lower half of
such
bear
-ings are
lined
with bronze or a special Marcy babbitt
which is peened
in
place
and
bored to
fit
the trunnion
.
In all cases a low bearing pressure is maintained
to assure freedom from overheating, long life and
minimum maintenance. They are designed to provide
support to the mill proper,
its
media and pulp load.
Trunnion bearings are generally supplied with
seals for use with
a
circulating oil lubrication sys
-tem
.
They
can be
designed to accommodate block
grease or
oi I with
wool waste
.
For special
app
lications trunnion bushings can be
furnish
ed
c-
onstructed
of Micarta to allo
w
water
lubri-cation
o
r oi
l lubrication.
In
m
dny
dry
gri
n
ding applications, or
w
here heat
is devel
oped,
the
trunnion bearings can be furnished
for water cooling. This system carries away the
ex-cess heat transmitted through bearings and protects
them.
BRONZE BUSHINCS
M
arcy Lead Bronze has been found to be the
most satisfactory bearing material for large diameter
bea
r
ings, affording the greatest protection against
damage of tru
nn
ions. Lead bronze wi
ll w
i
th
sta
n
d
ex-treme heat for a considerable period
oftime
(
for
ex-ample in the event of lubrication failure). Such heat
will cause the lead to sweat out and act as a lubricant
itself
.
This protection eliminates the possibility of
scoring a trunnion and there is no danger, as with
babbitt, of having the trunnions settle in the bearing
and rub
on
the
bearing l>ase
.
PINION SHAFT BEARINGS
Pinion
shaftbearings are
of
the
SKF anti-friction
typemounted
in
a
common twin beari
n
g assembly
.
Bearings
are
fixed in
place
so
that
the pinion
shaftof
them
ill is
always
in alignment
with
thedrive
com-ponents.
V-belt
driven
mills
are
furnished with
an
outboard bearing
of
similar construction.
Also available are bearings
of
the double
rigid
ring oiling
typefor
special
applications. Such
bear-ings are
castintegral
with a
heavytwin bearing
sole
plate assuring perfect
alignment
and rigidity
.
These
bearings are equipped
withbronze or
babbitted
bush-ings.
16
BASE AND CAP
These are
cast heavy in section of Meehan
i
te
metal. Where
swivel type
bearings are
used
the
base
is spherically bored
inside
to
gauge to receive such
swivels
.
The
bottom
of
the base
is
planed to
fit a
planed
top of
the trunnion bearing sole plate
.
The
bearing cap is provided with a shroud feature
ex-tending
out over drip flanges to
protect
the
bearin
g
from entrance
of dirt or grit.
Slotted
holes are
provided
in the
base for
bolt-ing
the
base
to the sole plate
;
this
permits
move-ment of the bearing
on
the sole plate
for
adjustment
of gear and pinion mesh
.
Such
adjustment is
carri
ed
out by
the
use
of set screws
.
LUBRICANT JACKS
A separate hand
operated lubricant jack can
be
furnished to
be mounted on
the
bearing
base
or
at
some distant point
to provide
a
flow of lubricant prior
to
starting mill
rotation.
This feature assures
lubr
icant
being
present at the bottom
of
the bearing and
re-flects
somewhat in reducing bearing wear and
shows
....
GEARS AND PINIONS
Two general classifications of gearing are used for Marcy Mill drives.
These are the spur gear and the helical gear. Helical gearing may be either
of the single helical or double helical (Herringbone) design. SPUR GEARS
These are generally furnished on the smaller diameter mills using
V-belt drives or reducer drives. Spur gears and pinions are cut with teeth
of the full depth involute tooth form thus assuring maximum tooth strength
and long wearing life. The main gear is cut from a special Meehanite
metal casting and is constructed split and reversible. The pinion is cut
from a steel forging bored, keyseated and mounted on the pinion shaft. The pinion is also reversible.
All spur gears and pinions are carefully machined and the teeth are
accurately cut to obtain proper tooth profile and spacing. thereby utilizing
the maximum potential tooth strength and wear rating.
HELICAL GEARS
Helical gears are used for the larger diameter mills which are to be
direct connected to a low speed motor. There are primarily two main
reasons for use of helical gearing on this drive arrangement. First. in
order to permit higher gear ratios than are obtainable from a practical
standpoint with use of the spur gear. This in turn permits the use of
a higher speed and less expensive motor. Second; in order to take advan
-tage of the smoother continuous overlapping tooth action of helical gearing so essential where there is no intermediate transmission element such as a V-belt drive or speed reducer. All helical gears and pinions are cut with
the full depth tooth form. The main gear is cut from a special gear steel casting and is made split and reversible. The pinion, usually integral
with the pinion shaft, is cut from an alloy steel forging and heat treated
prior to cutting the teeth. The pinion shaft is double ended so it is also
reversible.
All Marcy Mill gearing is designed in accordance with sound
engineer-ing principles and at the same time with consideration given to the long
range economics involved. Extremes such as excessively high ratios or
a very low number of teeth in the pinion are always avoided. This is done
to provide allowance for such later changes in power or capacity
require-ments as changing the mill speed through the use of different sized pinions. Therefore, complete replacement of the main gear and pinion is not required.
Furthermore, all gears and pinions are of ample proportion to
with-stand the dynamic overloads encountered in this service and to provide
satisfactory performance under the conditions peculiar to mill operation .
PINION SHAFTS
As mentioned above pinion shafts used with helical gearing are usually
forged integral with the pinion. For other drives the pinion shaft is care-fully turned and keyseated to accommodate the pinion for press fit.
GEA
R GUARD
A plate steel gear guard, generally in the form of a full circle is fur -nished to protect the gear from entrance of dirt or foreign material. It is
furnished with an inspection door and a door to be used for the application of gear lubricant. It is made dust resistant for operations under extremely
dirty and dusty conditions. The gear guards are designed to be mounted
independently of the mill proper.
SPECIAL
FEATURES
Where specific conditions call for special features. these can be pr
o-vided. For example: Splitters for distributing mill discharge to two separate
classifiers; Rubber lining of heads, shells or feeders for resistance against abrasion or corrosion; sectionalizing for transportation restrictions; special
"""' designs for metal reclaiming work; discharge trammels and elevators;
heavy duty scrubber applications.
SPUR GEARING
SINGLE HELICAL GEARING
