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Патент USA US2115820

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May 3, 1938.
Filed July 27, 1936
4 Sheets-Sheet 1
May 3, 1938.
Filed July 27, ‘1936
‘4 SIhQets-Sheet 2
May 3, 1938.
Filed July 27, 1936
4 Sheets-Shget 3
Patented May 3, 1938
2,115,820 '
'~ Frank 1:.Ill]!
‘ ?st-fame»,
1936, Serial No.
_ 92,887
' 3 Claims.
This invention relates to ball mills and is par
. ticularly directed to improvements in means for
discharging‘ materials from ball mills.
A principal object or the invention is the pro
5 vision of means for the discharge of materials
from ball mills whereby the content of mate
rial in the mill may be maintained substantially
constant at a predetermined amount regardless
. of ?uctuations or surges in the feed to the mill
10 or in other operating conditions.
A further object of the invention is to provide
ball mills having discharge means of simple and
rugged construction which are e?‘ective and de
pendable in their operation.
Another object -of the invention is the pro
vision of means for the discharge of materials
from ball mills whereby the height of the dis
charge may be varied to a substantial degree
without ailecting the level of the material in the
ball mill.
Other objects and advantages of the invention
will be apparent from the detailed description of
illustrative embodiments of the invention herein
after appearing.
The, invention is particularly valuable in con
nection with ball mills operated with a relatively‘
small mill content or with a low “pulp line”,
which has been found by a number of yearsoi.’
experiment and practical operation to be the
30 condition under which ball mills operate at the
greatest capacity and efdciency.
of Fig. 13; and
- ~
Fig. 15 is a fragmentary partial section on line
i5—l5 of Fig. 14.
In Figs. 1 and 2, I6 is the shell of a ball mill
provided at the discharge end with a drilled
?ange ii, and hawng an annular boss l2 on
which is mounted a tire I 3 whereby the mill is
supported for rotation upon rollers it. The mill
is driven by conventional means, not ‘shown,
which may be located at the feed end of the mill.
“Inside the shell are provided liner membersv i5, 15
and adjacent the end of the shell there is pro
vided the discharge grate assembly it.
‘The discharge grate assembly includes a plu
rality of grate sectors i7, shown in further detail
in Figs. 3-5, connected by means “described here
inafter into a strong, rugged annular grate, readi 20
ly removable for repairs and replacements.
The grate sectors ll, comprise a plurality of
rolled steel bars l8, positioned in parallel align
ment and in suitable spaced relation by means
of side plates I 9 to which the bars are welded.
The positioning of the hers is aided and the
structure is strengthened by spacing pads 28
suitably placed between and welded to adjacent
plates. . The sector is further strengthened by
means of rods 20 which may be welded to both
scribed for thepurpose of illustration with ref
erence to the accompanying drawings in which:
Fig. 1 is a fragmentary elevation in partial
taching thesectors to the shell of the mill and
for connecting them together into the grate as
Fig. 3 is a front elevation and Fig. 4 is a side
elevation of a discharge grate section of the form
shown in Figs. 1 and 2;
Fig. 5 is a fragmentary view in partial section
showing a detail of the discharge grate section
45 of Figs. 3 and 4; '_
Fig. 6 is an elevation of a bottom closure mem-'
Fig. '7 is a perspective view of an angle brace
of the'embodiment of Figs. 1 and 2;
Fig. 8 is a fragmentary elevation of the dis
charge end of a ball mill provided with a modi
?ed form of discharge grate;
Fig. 9 is a fragmentary sectional view of the
form of the invention shown in Fig. 8, taken on
Cl CA the line 9—9 of Fig. 8;
Fig. 10 is an elevation and Fig. 11 is a side
view of a three-scoop discharge device which
may be used in connection with the ball mills of
Figs. 1 and 10; j
on the discharge side thereof and serve for at
The sectors are advantageously connected to.
Fig. 2 is an end elevation of the embodiment
shown in Fig. 1 with the end plate removed;
m Fig. 14 is a fragmentary section on line [4
‘the bars and the side plates. As is indicated, the
side plates l9 "project beyond the‘grate bars
bodying the principles of the invention;
tion of another form of discharge grate embody
ing the principles of the invention;
The invention will'be more particularly de
section of the discharge end of a ball mill em
Fig. 12 is an end view and Fig. 13 is an eleva
the shell by means of angle braces 2| (see Fig. '1) ,
the bolts 22 attaching the braces to the sectors
also serving to connect adjacent sectors together 40
at ‘their peripheral ends. The central ends of the
sectors are similarly connected by bolts 23 passing
through side‘ plates IQ of adjacent sectors and
advantageously the same bolts pass through lugs
25 of an annular center plate 28. ~
The space between the peripheral ends of the
sectors and the shell Ill oi‘ the mill is closed by
clamp bars 26 (see Fig. 6) thrust ‘against the
peripheral end bars of the grate sectors by means
of screw bolts 2?.
A particularly valuable feature oi’ the grate of
the invention is'the progressive variation in the
openings between the bars which has been found
to be very advantageous in-maintaining a sub
stantially constant pulp level in the ball-mill; 55
By increasing the width of the openings in the
grates towards the center of the grate the rate
of discharge increases very rapidly as the pulp
level rises and clogging of ‘the mill with surges
in the feed or other variations in operating con
ditions is eliminated. This is particularly valu
able in dealing with thick pulps since with such
materials the rate of flow increases more rapidly
with increasing area of the discharge opening
than is the case with ?uids like water.
For example, in a grate having fourteen bars,
the ?rst 7 openings nearest the peripheral end
a may advantageously be % inch, the next 11; inch,
and increasing progressively to H inch at the
central end. In general, the openings between
the grate bars may be varied from openings of,
for example, 1/8 to % inch at the peripheral end
to openings of, for example, 1/2 to 1/4 inch at the
central end of the sectors.
Where the speci?cation and claims refer to
the progressive variation in the width of the
slots in the grate, this shall include structures
in which each slot varies in width from an ad
jacent slot as well as those in which the progres
20 sion is in stages with several slots in each stage
of the same width.
The material ?owing through the grate may
advantageously be discharged, for example, to a
launder not shown, through an annular opening
25 at ‘the periphery‘ of the discharge end of the
shell formed between the annular spout member
29 and end plate 30 ‘spaced from the spout mem
ber- by means of spacers 3| or bolts 32 which
fasten both the spout member and the end plate
to ?ange Ii of shell "I.
The door 33, centrally located in end plate 30,
provides an advantageous means for inspecting
the discharge grate during operation of the ball
mill. The door can be removed or replaced dur
ing operation by pressing button 34 in handle 35,
which retracts catches 36 through levers 31. The
catches when extended engage the inside of the
circular opening in door 310 or any suitable cir
cular holder mounted thereon.
If it is desired to discharge the eiliuent from.
the ball mill at a point above the bottom of the
mill the spout member 29 and end plate 30 may
be replaced by a scoop discharge device such as
is shown in Figures 10 and 11. This device is
45 shown by way of example with three scoops ll,
which lift e?luent material from the peripheral
wall 42 and discharge it through the central
sating annular bulge or convexity 55, the thick
ness of which is proportioned to the normal
amount of wear on the grate ends at various
points along the radius.
The center of the grate is preferably left open
to provide a manhole which may be closed by a
manhole cover 56 bolted to the grate.
A further form of grate sector is shown in Figs.
12 to 15. In this form of sector the bars 6| are
welded in spaced parallel relation to side plates 10
62 which are positioned at an angle of approxi
mately 66° to the longitudinal faces of the bars.
Spacing pads 63 are provided as in the grate sec
tor shown in Figs. 3-5, and rods 64 welded to the
bars and side plates further strengthen the sec
tors. The bars are preferably spaced at distances
increasing from the periphery towards the center
,as described in connection with Figs. 3-5.
The sectors may be connected into a grate as
sembly by means of a spider and suitable con— 20
necting elements as shown in my U. S. Patent
No. 1,629,803.
I claim:
1. Discharge means for ball mills adapted to
automatically regulate the rate of discharge so 25
as to maintain a substantially constant low level
of material in the mill regardless of variation in
the rate of feed comprising a grate member
mounted adjacent the discharge end of the drum
of the ball mill, said grate having a plurality of 30
discharge openings in the form of elongated slots
positioned with their longitudinal axes along
chords of said drum, the width of the slots pro
gressively increasing from the periphery of the
drum towards the center and the slots adjacent 35
the center being substantially wider than those
adjacent the periphery whereby to substantially
accelerate the discharge of material through the
grate as the level of material rises in the drum
above the desired low level.
2. A grate for ball mills adapted to automati
cally regulate the rate of discharge in relation to
the height of material in the mill, said grate com
prising a plurality of sector shaped units, each of
said units comprising a pair of side members, a 45
plurality of grate bar elements supported in
spaced relation between said side members to de
spout 43. The outer wall of the discharge device line a plurality of elongated slots, the spacing
is advantageously provided with hand-holes 44. between said bars progressively increasing in
60 By the use of this device the ei'?uent material may width towards the inner end of the sector and
be discharged at within 5 or 6 inches below the the space between the bars adjacent said inner
end being substantially greater than between the
center of the mill.
Figs. 8 and 9 show a one-piece grate 56 which bars adjacent the outer end whereby the rate of
may replace the grate assembly l6 shown in Figs. discharge of material from the mill will be sub
stantially increased with the‘ rise of the level of
55 1 and 2, and which includes a number of valu
material within the mill.
able improvements. The grate consists of a sin
3. In a grate for ball mills adapted to auto
gle annular member, having an external diameter
slightly less than the internal diameter of the matically compensate for variations in the rate
shell ill of the ball mill. It is provided with a of feed by automatically regulating the rate of
60 plurality of slots 5| cut or cast therein‘. The slots - discharge in relation to the height of material in
are arranged in a plurality of segmental groups. the mill, a grate sector comprising a pair of side
They extend along chords of the annular grate members, a plurality of grate bar elements se
and may be designated as chordal slots. The cured at their ends to said side members in
spaced parallel relation, spacing pads secured be
slots 5! preferably vary in width from the periph
65 ery towards the center, as described in connec
tion with Figs. 3-5.
The grate may be attached to the shell of the
mill by means of bolts 52 passing through holes
in lugs 53 spaced about the periphery of the
70 grate. The grate is tightly positioned by means
of wedges 54 which are preferably bifurcated to
fit around bolts 52. These wedges greatly facili
tate the installation and removal of the grates.
An advantageous feature of the grate shown in
75 Figs. 8 and 9 is the provision of a wear-compen
tween adiacent bars, said pads progressively in-K
creasing in thickness from the outer to the inner
end of the sector and the space between said
bars being correspondingly increased so that the
space between the bars adjacent the inner end
of the sector is substantially greater than be 70
tween those adjacent the outer end thereof
whereby the rate of discharge of material from
the mill is substantially increased as the material
in the mill rises above a desired level.
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