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Патент USA US3034743

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May 15, 1962
E. P. CADWELL
LEAD FILLED CERAMIC MEDIA F‘OR GRINDING
3,034,735
Filed Sept. 29, 1953
BY
ATTO R N EY
United States Patent 0.” rice
3,034,735
Patented May 15, 1962
1
2
3,034,735
Edward, P. Cadwell, Santiago, Chile, assignor to Ameri
FIG. 4 is a broken perspective view of a grinding rod
LEAD FILLED CERAMIC MEDIA FOR GRINDING
can Cyanamid Company, New York, N.Y., a corpora
tion of Maine
Filed Sept. 29, 1953, Ser. No. 383,055
5 Claims. (Cl. 241-184)
shell; and
I
FIG. 5 shows a lead-?lled grinding rod shell partly in
section.
5
FIG. 1 shows a grinding ball covered with a hard
ceramic 1. The holes 2 in the ceramic shell 1 allow lead
to be poured into the interior of the ceramic shell.
Usually two holes as illustrated in FIG. 1 are better than
This invention relates to the crushing and grinding of
one since entrapped gases and air inside the shell can
solids and more particularly to a grinding medium for
tumbling mills. It also relates to a process of grinding 10 escape ‘from one hole as lead is being poured in the other.
In FIG. 2 the shell of the ceramic 1 is shown surround
solids in tumbling mills,
ing the lead core 3. The thickness of the ceramic 1 is
The crushing and grinding of various solids often re
immaterial since it may be adjusted at will. Since the
quires the use of tumbling mills. Tumbling mills is a
speci?c gravity of the grinding ball decreases as the thick
generic name sometimes‘ used referring to ball, pebble,
rod, tube, and compartment mills, ecause of the action 15 ness of the ceramic increases, it is possible to adjust the
speci?c gravity of the grinding ball to any desired value.
of the grinding medium. These mills are usually made
Although the speci?c gravity can be adjusted to any value
up of a s-teel- or stone-lined cylindrical shell, containing
between that. of uncoated lead to that of the un?lled
a charge of steel rods or balls or stone pebbles. On
rotation of the cylindrical steel shell crushing and grind 20 ceramic shell, it is usually desirable to achieve the spe
ci?c gravity of iron or steel balls which runs around 7.
ing is eifected by the tumbling of the balls or pebbles on
the material between them.
,
Although steel or iron balls or rods are commonly used
The speci?c gravity of 7 is usually excellent in practice.
FIG. 3 shows a shell of ceramic 1, the holes 2 for ?ll
ing and the lead core 3. As shown the lead core 3 ?lls
in tumbling mills, their use is prohibited in certain grind
ing operations. For example, where contamination of 25 the holes 2 to the surface of the ceramic 1. This can be
achieved in ?lling the shell of ceramic 1 with molten
a comminuted product by iron is not permissible, steel
lead to the capacity of the shell and then allowing the
or iron balls cannot be used. Or where corrosive action
lead to cool. This will result in shrinkage of the lead.
such as oxidation is particularly acute iron or steel grind
Additional lead can then be poured in the holes in order
ing media may not be employed.
that
the lead will completely occupy the holes 2 to the
To overcome these handicaps it has been suggested that
outer surface of the shellof ceramic 1. The ?lling of
?int stones be used as a grinding media. However, the
the holes 2 with lead 3 helps minimize any chipping that
low speci?c gravity of ?int stones has limited their grind
might tend to take place at or near the site of the holes
ing capacity exceedingly. Thus, ?int stones are unsatis
2. Any other suitable method of completely ?lling the
factory for many grinding operations.
It has also been suggested to prepare grinding media, 35 ceramic‘shell with lead may be used such as using a lead
alloy which does not shrink when the liquid metal cools
particularly balls, by coating a leadlcore with rubber.
and turns solid.
‘
Such a grinding medium has the advantage of high spe
FIG. 4 shows a shell of ceramic in the form of a tube.
ci?c gravity and high resistance to corrosion. Rubber
Although this tube 4 can be made with the ends 5 closed
coated lead balls serve very well for grinding soft solids
and
then?lled with lead through the holes 6, it-is pref.
such- as vegetable. or plant material. However, many 40
erable not to do so. Instead, the tube 4 is cast of a
types of grinding operations, for example, the grinding
suitable ceramic, the tube is placed on one end 5 thus
of quartz, call for a hard, brittle surface on the grinding
sealing that end, and lead is poured in the other end 5.
medium. Rubber-coated lead balls ‘fail in this respect.
In FIG. 5 the tube 4 is ?lled with an inner core of lead
Furthermore, many grinding operations are carried out
in the presence of a liquid, usually water. If, however, 45 7. The end 5 of the core of lead 7 need not be covered
with ceramic since the end 5 is not part of the grinding
(the grinding is to be carried out in the presence of a liquid
surface of the tube 4. With open-ended rods the lead
‘such as, for example, a hydrocarbon, then rubber-coated
core adheres better if a lead alloy is used that does not
grinding media are unsatisfactory since the rubber may
shrink as it passes from the liquid phase to the solid
dissolve in such solvents. Also, Where lead is used as
a core in a grinding medium it is desirable that the lead 50 phase on cooling.
By ceramic is meant any clay or siliceous product
be readily recovered from the coating material. The
brought by the action of heat to a sufficient hardness to
remnants of a rubber coating on such grinding media are
serve in a grinding media; the term also includes certain
often hard to remove.
metal carbides such as silicon carbide, and certain metal
It is, therefore, the principal object of the present in
vention to develop a grinding medium not handicapped 55 oxides such as zirconium oxide. The surface of the
ceramic may be porous or vitreous, glazed or unglazed.
by the shortcomings mentioned above. It is a further
object to develop grinding media suitable for grinding
hard solids. ‘It is a further object to develop a grinding
media having a high speci?c gravity and high corrosion
resistance under the conditions of operation.
The objects of the invention have been accomplished
One of the outstanding advantages of the present inven
tion is that the shell may be made of a ceramic espe
cially selected for a speci?c grinding job. Thus, if quartz
is to be ground a ceramic containing high silica may be
used to minimize contamination of a product. The
ceramic shells for the balls and tubes utilized by the
by developing a grinding medium wherein a core made
present invention may be prepared by any of the means
of lead is surrounded with an outer wearing surface made
for preparing hollow objects well known in the art.
of a hard ceramic. The grinding media and the process
One of the surprising aspects of the grinding media
of using it will be more completely described with refer 65
of the present invention is the strength shown by the
ence to the accompanying drawing in which:
media. Since the lead core completely ?lls the ceramic
FIG. 1 is a perspective view of a grinding ball of the
shell the balls or tubes can withstand a surprising amount
present invention;
of rough handling. There is very little chipping of the
FIG. 2. is a vertical sectional view taken along line 2—2
of FIG. 1;
70 ceramic in actual practice.
Another outstanding advantage of the present inven
FIG. 3 is a vertical sectional view taken along line
tion is that the lead cores of the grinding media may be
3-3 of FIG. 1;
3,034,735
3
readily recovered when the ceramic shell has become
worn away. Any remaining ceramic covering may be
readily removed from the ‘lead core by heavily striking
the worn grinding media with a hammer, or by passing
the media through a jaw crusher or bowl mill. Since
the lead is easily malleable, the ceramic readily breaks
3. A corrosion resistant grinding ball for use in ball
mills consisting essentially of an outer wearing surface
shell of a hard ceramic material, said shell having a plu
rality of adjacent openings therethrough, and a lead core
entirely ?lling said shell and said openings; the volume
of said core and of said shell being so proportioned as
to obtain a predetermined average speci?c gravity.
4. A corrosion resistant grinding rod for use in rod
the order of 90%. Thus the practice of this invention
mills consisting essentially of an outer wearing surface
becomes peculiarly advantageous in those remote regions
which are di?icult of access and where shipping costs are 10 shell of a hard ceramic material, said shell having a plu
rality of adjacent openings therethrough, and a lead core
:high. Once a supply of lead has been accumulated at
entirely ?lling said shell and said openings; the volume
the grinding site only the ceramic shells need be shipped
of said core of said shell being so proportioned as to
into the region; the lead may be easily remelted and
obtain a predetermined average speci?c gravity.
used over and over. Appreciable savings in shipping
5. A corrosion resistant grinding medium for use in
costs can thus be realized.
tumbling mills consisting essentially of an outer wearing
The grinding media of the present invention are par
ticularly useful in grinding operations where corrosion is
surface shell of a hard ceramic, said ceramic shell hav
ing two adjacent openings therethrough, and a lead core
excessive and where contamination due to the oxidation
entirely ?lling said shell and said openings; the volume
of iron balls is detrimental. The lead-?lled ceramic
of said core and of said shell being so proportioend as to
grinding media of the present invention are exceedingly
obtain a predetermined desired average speci?c gravity.
inert and innocuous in grinding mill processes. Excel
lent results can be obtained in processes of grinding solids
References Cited in the ?le of this patent
in tumbling mills in which the lead-?lled ceramic is used.
The new grinding media may be made in any desirable
UNITED STATES PATENTS
size since it is often advantageous to utilize balls or rods 25
324,918
Caspersson ___________ __ Aug. 25, 1885
of varying diameters during a grinding operation. The
329,750
Low _________________ __ Nov. 3, 1885
inertness of the new grinding media of the present inven
504,508
Weswell ______________ __ Sept. 5, 1893
tion is of particular value in grinding wet material where
1,016,272
Johnson ______________ __ Feb. 6, 1912
the grinding media is submerged in water or other liquid.
1,247,545
Kittle _______________ __ Nov. 20, 1917
Tumbling mills can be operated in the same manner with 30
away under such treatment.
Recovery of lead runs on
the new grinding media as they are with any of the grind
ing media of the prior art.
I claim:
1. A corrision resistant grinding medium for use in
tumbling mills consisting essentially of an outer wearing
surface shell of a hard ceramic material, said shell hav
ing a plurality of adjacent openings therethrough, and a
lead core entirely ?lling said shell and said openings;
the volume of said core and of said shell being so pro
portioned as to obtained a predetermined average speci?c 40
gravity.
2. A grinding medium according to claim 1 in which
said grinding medium has an average speci?c gravity of
approximately seven.
1,335,269
1,640,885
2,204,582
2,489,307
Ball ________________ __ Mar.
Curtis _______________ __ Aug.
Donahue ____________ __ June
Miller _______________ __ Nov.
30,
30,
18,
29,
2,518,758
2,653,769
1920
1927
1940
1949
Cook _______________ __ Aug. 15, 1950
Ha-ll ________________ __ Sept. 29, 1953
2,553
26,556
Great Britain _________ __ Feb. 12, 1891
France _______________ __ Oct. 9, 1923
FOREIGN PATENTS
OTHER REFERENCES
Chemical Engineering, September 1950, pages 152 and
154, article, “Ball Mill Media.”
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