Note: Descriptions are shown in the official language in which they were submitted.
~2~
ARTICLES EMBODYING A WEAR RESISTANT SURFACE LAYER
AND A METHOD OF MANUFACTURE THEREOF
BACKGROUND OF THE INVENTION
This invention relates to articles of the type
S that are designed to be subjected to highly abrasive operating
conditions which in turn renders it necessary that such
articles have at least the outer surface layers thereof formed
of a material which possesses good wear resistant qualities.
More specifically, this invention in par-ticular relates both to
10 the grinding rolls which are employed in a pulverizer of the
type that is particularly suited to be used to effect the
pulverization therewithin of a material such as coal, and to
the mill liners that are employed in selected interior regions
of the pulverizer.
An essential component of any steam generation system
in which coal is utilized as a Fuel is obviously the apparatus
that is employed for purposes of accomplishing the
pulverization of the coal so as to render it suitable For use
as a fuel. To this end, one apparatus in particular which has
20 frequently been utilized to accomplish -the pulverization of
coal so as to render it suitable For use as a fuel in a
coal-fired steam generation system is that which those in the
industry commonly refer to as a bowl mill. The bowl mill
obtains its name principally from the fact that the
25 pulverization, i.e., grinding, of the coal that takes place
therewithin occurs on a grinding surface which in confiyuration
bears a resemblance somewhat to that of a bowl.
C840a,,20
~3~2~
2--
In connection with the discussion that follows,
particular reference is made herein to the fact that two of the
essential components of such a bowl mill are one the body
portion, i.e., housing, within which the grinding surface,
i.e., grinding table, from which the bowl mill derives its name
is mounted for rotation, and two the plurality oF grinding
rolls that are supported in equally spaced relation one to
another within the housing of the bowl mill so as to be able to
coact with the grinding table such that the coal disposed on
the surface of the grinding table is capable of being ground,
i.e., pulverized, as a consequence of the grinding force that
the plurality of grinding rolls apply to the coal. For this
purpose the grinding rolls are each designed to be mounted on a
shaft-like member. Furthermore, in order to effect the
assembly of the grinding roll with the aforesaid shaft-like
member, the grinding roll preferably has a through passage
provided through the centPr thereof. This through passage
enables the shaft-like member to be positioned therewithin so
that the grinding roll is thereby positioned in mounted
relation thereto. In order, therefore, to facilitate the task
of providing the grinding roll with such a through passage, it
is desirable that the grinding roll be made of a material that
is characterized by its ease of machinability, i.e., a
relatively soft material such as gray iron.
In contradistinction to the desirability of forming
the grinding roll from a relatively soft material, there also
e~ists a requirement that at least the external, i.e., outer,
surface layer of the grinding roll be of a material that is
characterized by its good wear resistant qualities. The reason
for this is that in the course of effecting the pulverization
of material with these grinding rolls, the latter are of
necessity subjec-ted to a harsh abrasive action by virtue oF the
nature of the material being pulverized as well as by virtue of
the manner in which the pulverization takes place. The result
thus is that the grinding rolls are susceptible to being
rendered unusable because of excessive wear in a relatively
short period of time, i.e., the rolls are found to have a
C840420
~ 3~ 2;~
--3~
relatively short operating life. Obvlously, such a result is
to be avoided, if possible. In this context, note is made of
the fact that the wear which grinding rolls employed in bowl
mills actually experience is influenced principally by the
5 grinding characteristics of the material that is being
pulverized as well as by the productive output of the bowl
mill, i.e., the amount of material that is being pulverized
within the bowl mill in a given period of time.
When the outer surface layer of the grinding, i.e.,
pulverizer, roll becomes sufficiently worn so as to preclude
the further use thereof for purposes of accomplishing therewith
the pulverization of material, the remaining portions of the
roll normally are still usable. Namely, but for the fact that
the outer surface layer thereof is worn, the grinding roll
would still be capable of being utilized. As such, it is,
therefore, not surprising to find in the prior art evidence of
the fact that there have been various efforts undertaken in the
prior art heretofore directed towards realizing improvements in
the wear life of grinding rolls.
For ease of reference, it is possible to classify
into three basic categories the efforts that have heretofore
been undertaken in an attempt to realize improvements in the
~ear life of grinding rolls. First, there are the efforts
which have been directed towards realizing improvements in the
manner in which the original manufacture of the grinding rolls
is accomplished and/or in the manner in which the grinding
rolls are resurfaced after having become ~orn. Secondly, there
are the efforts which have been directed towards producing an
improved high chromium alloy that is capable of being utilized
for purposes of fabricating therefrom at a minimum, the wear
surface, i.e., the outer surface layer, o-f the grinding rolls.
Thirdly, there are the efforts which have been directed towards
producing an improved nickel-chromium alloy that is capable of
being utilized for purposes of fabricating therefrom at a
minimum, -the wear surface, i.e., the outer surface layer, of
the grinding rolls.
C840D,2 0
- 4 - 62898-1348
Insofar as the first of the categories w'hich have been
enumerated above is concerned, reference may be had in this
regard, by way of exemplification and not limitation, to U.S.
Patent No. 4,389,767, which issued on June 28~ 1983, and which is
assigned to the same assignee as the presen-t application. U.S.
Patent No. 4,389,767 discloses a method of manuEacturing a grind-
ing roll which is characterized in that the wear surface, i.e.,
the outer sur-Eace layer, of the grinding roll is shaped in accord-
ance with the predicted wear characteristics that the grinding
roll is expected to experience based on the nature of the use to
which the grinding roll is intended to be pu-t suc'h that the con-
tour thereof replicates that of a worn grinding roll, and a
substantially uniform layer of a material characterized by its
wear resistan-t qualities i8 applied to -the outer surface of the
grinding roll so as to form the wear surface of -the grinding
roll.
A further illustration of the prior art efforts which
are deemed to fall into the first of the categories that have been
enumerated above is that w'hich forms the subject matter of U.S.
Patent No. 4,610,401, issued September 9, 1986. The latter U.S.
patent is assigned to the same assignee as the present applica-
tion. To this end, U.S. Patent No. 4,6L0,401 is directed to a
trimetal grinding roll w'hich embodies a trimeta:L form of construc-
tion and wherein the core material, i.e., the first or inner
Layer, of t'he trimetal ro:L:L consists of a reLatively soft material
that is noted Eor its good machinability, the next, i.e., second
or intermediate, layer of the trimetal roll comprises a material
~.
~ 5 - 62898-1348
that has medium wear resistant qualities and -t'he last, i.e., third
or outer, layer of the trimetal roll comprises a material having
highly abrasive resistant qualities.
Attention will next be focused on a second category, as
enumerated above, of t'ne prior art efforts that have been under-
taken heretofore in an attempt to improve the wear life of the
grinding rolls that are employed in a bowl mill. By way of exem-
plification and not limitation, reference is had here to one such
particular effort. More specifical.ly, the effort to which refer-
:10 ence is had here is that whic'h culminated in the development of-the material known to those in the industry as "Stoody 103". This
material, i.e., Stoody 103, has been availab:le for purchase from
The Stoody Company of California. ~eportedly, the composition of
Stoody 103 material is such that among ot'ners, this material
includes in the approximate amounts, by weight percentages, set
forth hereinafter the following elements: Carbon - 4.0%,
Manganese - 5.0%, and C'hromium - 27.0% to 28.0%. On the other
hand, Stoody 103 material is said to include neither molybdenum
nor boron, except perhaps in quantities whic'h are barely discern-
ible. Insofar as the -fabrication of grinding rolls is concerned,
the material known as Stoody 103 most commonly is employed in the
form of a weld overlay that is applied to the grinding roll so as
to comprise the outer surface thereof, i.e., so t'hat t'he layer o:E
Stoody 103 mater:ia:L which is applied thereto forms the wear sur-
face of the grinding roll. It 'has been alleged that t'he wear
resistant qualities of Stoody 103 material are, by a factor of one
and one-half to two times, better than those of the material which
~ ~,
- 6 - 62~98-13~8
for ease of reEerence is referred to hereinafter as ordinary
Nihard.
Another example of a prior art effort which can be
classified in-to the second category, as these categories have been
enumerated hereinbefore, of prior art ef-forts that have been
undertaken in an attempt to improve the wear life of the grinding
rolls of a bowl mill is that which resul-ted in -the development of
an abrasion resistant white cast iron. More specifically, the
white cast iron comprises a base of iron, and, by weight percent-
ages, 2.0% - 4.5% Carbon, .001. - 4.0% Boron and one or more of
the following alloying elemen-ts: .001% . 30% Vanadium, Titanium,
Niobium, Tantalum, Molybdenum, Nickel, Copper, or Chromium, or
mixtures thereof.
Yet ano-ther example of those prior ar-t efforts which are
deemed to fall within the second ca-tegory thereof, as the ca-te-
gories have been enumerated hereinbefore, is that which led to the
development of a highly abrasion resistant alloy which is par-ticu-
larly suitable for use as the material from which to fabricate the
outer surface layer, i.e., the wear surface of a grinding, i.e.,
pulverizer, roll tha-t is designed to be employed in a bowl mill so
as to be operative therein for purposes of accomplishing the
pulverization of a material such as coal through the coact-ion of
the grinding roll with another surface with which the bowl mill is
suitably provided for this purpose. The high:Ly abrasion resistan-t
alloy to which reference is had here comprises, by weight percent--
ages, ~.0% - 6.0% Carbon, 3.0% - 1~.0% Manganese, 1.0~ - 2.5~
Silicon, 15.0% - 30.0% Chromium, and ~.0~ - 6.0% Molybdenum, with
,, ~
,~
, ' ~3~L2~iP~
- 7 - ~2898-134~
0.5% - 2.0~ Boron being added thereto, the balance being iron and
incidental impurities. Based on test results that have been
conduc-ted to date, the highly abrasion resistant alloy is predic-
ted to have -twice the wear life of that o-f a prior art form of
standard hardfacing material such as the material previously
discussed herein known as Stoody 103.
Moving on to a consideration of t'he third category, as
the categories have been enumerated hereinabove, of the prior art
efforts that have been undertaken here-tofore in an attempt to
improve the wear life of the grinding rolls o-f a bowl mill,
reference is had here to a further white cast iron alloy. It has
long been known to those skilled in this art to -fabricate -the
outer surface layer, i.e., the wear surface, of -the grinding rolls
of the -type tha-t are employed in a bowl mill from that material
whic'h is commonly re-ferred to as Nihard. The white cast iron
alloy, however, has been referred to as "Premium Nihard".
Allegedly, the latter alloy has better wear resistant qualities
than that of what is being referred to herein as ordinary Nihard,
i.e., that rnaterial which those skilled in this art have long
referred to as Ni'hard. As described therein, the white cast iron
alLoy, i.e., Premium 'Nihard, comprises, by weight percentages,
2.~% - 3.56 Carbon, 0.6% - 2.0% Silicon, 0.05% - 0.56 Manganese,
0.05% - 0.25% Sulfur, 0.5% - 1.5% Phosphorus, 3.56 - 5.0% Nickel,
2.5% - ~.56 Chromium, 0.2% - 0.7% Molybdenum, with the balance
being iron and incidental impurities. Further, it 'has been stated
that this white cast iron alloy, may also contain up to .O:L%
Bismut'h, by weig'ht percentage, to ensure against possible graphite
.'. ,! `,
~ 3~2~7
- 7a - 62898-13~8
formation particularly in heavy section castings.
A major reason why the attainment of a longer operating
li~e for new grinding rolls is sought is that it would enable one
to extend the point in time at which it becomes necessary to shut
down the bowl mill for purposes of enabling the removal therefrom
of the worn grinding roll and the replacement thereof with an
unworn grinding rolL. In this regard, it is important to note
that a plurality of bowl mills are commonly employed to provide
the required amount of pulverized coal to a coal-fired steam
].0 generator, and that each of these bowl mills normally embodies
three grinding rolls -that are each suscep-tible to having to be
removed and replaced as they become worn. ~lso, there is the
matter o-f ~he time and effort as well as the cost associated
therewith that needs to
~.~
~1 3~ 2!~7
be expended in the course of effecting such removal and
replacement of a worn grinding roll. Obviously, therefore, if
one were able to reduce the frequency with which grinding rolls
become sufFiciently worn as to require replacement, cost
savings could be realized in terms of the time and effort that
is required to be expended to effect such replacement.
Apart from the grinding rolls which have been the
subject of discussion in the preceding paragraph, there are
also a number of other components of a bowl mill that are
equally likely during the operation of the bowl mill to be
subjected to wear. By way of exemplification and not
limitation, reference is had here in this regard to the upper
surface of the grinding table, which as was mentioned herein
previously, is designed to coact with the grinding rolls such
that through the coaction therebetween material such as coal
which is disposed on the upper surface of the grinding table
becomes pulverized as a consequence of the force being applied
thereto by the grinding rolls. Continuing, other components of
the bowl mill which are known to be prone to suffer from wear
are those which lie in the path of movement that the coal
particles follow as they are being conveyed by a gas such as
air through the interior of the bowl mill. More specifically,
the components to which reference is had here suffer wear by
virtue of the abrasive action to which they are subjected when
they are struck by the coal particles as the latter are being
transported through the interior of the bowl mill. To this
end, it has long been known to selectively emplace liners in
those regions of the interior of the bowl mill where from past
experience wear has most frequently occurred.
Insofar as the upper surface o-f the grinding table of
the bowl mill is concerned, this upper surface commonly takes
the form of what is known to those skilled in this art as a
bull ring. In accord with the teaching of the prior art the
bull ring has-been known to be formed as an integral member as
well as in the form of a multiplicity of individual segments
which collectively comprise the bull ring. The bull ring is
designed to be suitably supported on the grinding table so as
C840420
9 -
to be rotatable therewith. The mode of operation of the
grinding table of the bowl mill is such that the material to be
pulverized is fed in a suitable manner on to the bull ring.
Then, as the grinding table and thereby also the bull ring
rotates by the grinding rolls the material that is disposed on
the bull ring becomes pulverized by virtue of the force applied
thereto by the grinding rolls as the bull ring is made to
rotate past the grinding rolls.
After being pulverized in the aforedescribed manner,
the coal particles are then picked up and become entrained in a
stream of air that flows upwardly around the circumference of
the grinding table. Once entrained in this stream of air the
coal particles are conveyed in suitable fashion through the
interior of the bowl mill. In the course of being so conveyed,
those coal particles which are larger than desired are made to
return to the grinding table for further pulverization, whereas
those coal particles which are of the desired size continue
their passage through the interior of the bowl mill and
eventually exit therefrom. It is while the coal particles are
being conveyed in this fashion that the components housed
within the interior of the bowl mill are struck thereby which
in turn occasions the wear to which reference has been had
hereinbefore.
A need has thus been demonstrated in the prior art
for articles having at least the outer surface layers thereof
formed of a new and improved material which is characterized by
its highly abrasion resistant qualities. In addition, a need
has been evidenced for such a highly abrasion resistant
material which, at a minimum, would be suitable for employment
as the outer surface layer, i.e., the wear surface, of a
grinding roll and which would in turn enable a yrinding roll to
be provided that would be characterized by the fact that the
grinding roll possesses an improved wear liFe. Moreover, there
has been evidenced a need for such a highly abrasion resistan-t
material which would be suitable for employment for purposes of
resurfacing a worn grinding roll wherein the highly abrasion
resistant material would, at a minimum, form the outer surface
C840~20
~`3 ~
~lo--
layer, i.e., the wear surface, of the grinding rol1. Such a
highly abrasion resistant material should be suitable for
employment for resurfacing a worn grinding roll notwithstanding
the nature of the material which had originally been utilized
as the outer surface layer, i.e., wear surface, of the grinding
roll. Further, such a highly abrasion resistant ma-terial
should be suitable for employment to form the bull ring that is
designed to be emplaced on the grinding table of the bowl mill
irrespective of whether the bull ring is intended to be in the
form of an integral member or in the form of a multiplicity of
individual segments. Also, such a highly abrasion resistant
material should be suitable for employment for purposes of
forming therefrom the liners that are designed to be
selectively emplaced in those regions of the interior of the
bowl mill that are known to be susceptible to wear of the type
that is occasioned by the coal particles striking thereagainst
in the course of their passage through the bowl mill interior
while entrained in a fluid medium such as air.
It is, therefore, an object of the present invention
to provide articles that embody a wear resistant surface layer
formed of a new and improved material that is characterized by
its good wear resistant qualities.
It is another object of the present invention to
provide such articles embodying a wear resistant surface layer
that are particularly suited for employment in a bowl mill of
the type which is designed to be utilized for purposes of
effecting the pulverization therewithin of a material such as
coal.
It is still another object of present invention to
provide such articles embodyiny a wear resistant surface layer
wherein the art;cles include the grinding rolls which are
designed to be employed in a bowl mill.
A further object of the present invention is to
provide such articles embodyiny a wear resistant surface 1ayer
wherein the articles include the bull ring which is designed to
be emplaced on the grinding table of the bowl mill.
C840420
1 3 ~
62898-1348
Yet another object of the present invention is to
provide such articles embodying a wear resistan-t surface layer
wherein the articles include the liners which are designed to
be selectively emplaced in those regions of the bowl mill that
based on prior experience are known to be susceptible to wear.
Yet still anot'her object of the present invention is
to provide suc'h articles embodying a wear resistant surface layer
wherein the articles are relatively inexpensive to provide, are
relatively easy to employ, and are c'haracterized by t'heir improved
10 wear life.
SUMMARY OF THE INVE'NTION
In a broad aspect, the invention resides in an improve-
ment in a bull ring for a bowl mill embodying at least one grind-
ing roll, -the bull ring including a first portion and a second
portion, the second portion being inclined relative to the first
portion at a predetermined angle so as to enable the second
portion to mate with -the outer surface of said one grinding roll
for purposes of accomplis'hing the pulverization, wit'h said second
portion and said one grinding roll of material disposed -there-
20 between. The improvement comprises al: least an outer surfacelayer formed on each of the first portion and the second portion
of an abrasion resistant material having as cast a composition, by
weight percentages, of 3.5%-3.7-6 Carbon, 1.2%-1.66 Si:Licon, 0.46
maximum Manganese, 4.36-5.096 Nickel, 3.7~6-4.4% Chromium, 0.156-
0.25% Phosphorus, 0.9P~-0.1:L6 Sulfur, 0.46-0.66 Molybdenum and
0.0156 nominal Bismuth so that said outer surface Layer formed on
eac'h of the first portion and the second portion without being
`~,
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:~ 3 ~
- 12 - 62898-1348
heat treated has as a norm a hardness of 700 Brinell.
In a further broad aspect, the invention resides in an
improvement in a liner for a bowl mill including a first portion
that extends in a first plane, and a second portion that e~tends
in a second plane so as to be inclined at a predetermined angle to
-the first plane. The improvement comprises at least t'ne outer
surface layer of the liner being formed of an abrasion resistant
material having as cast a composition, by weight percentages, of
3.5%-3.7% Carbon, 1.2~-1.6% Silicon, 0.~ maximum Manganese, 4.3~-
5.0% Nickel, 3.7%-~.4~ Chromium, 0.15~-0.25% Phosphorus, 0.9~-
0.11% Sulfur, 0.4~-0.6% Molybdenum and 0.0L5% nominal Bismuth so
that said outer surface layer o-E the liner without being heat
treated has as a norm a hardness of 700 Brinell.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a side elevational view partially in section
and with some parts broken away of a bowl mill embodying articles
constructed in accordance with the present invention having at
leas-t -the outer surface layer thereof formed of a material charac-
terized by its good wear resistant qualities;
Figure 2 is a sectional view on an enlarged scale of a
bowl mill grinding roll embodying an outer surface layer -Eormed of
a material characterized by its good wear resistant qualities
constructed in accordance with the present invent:ion;
Figure 3 is a sectional view of a bull ring embodying an
outer surface layer formed oE a materia:L characterized by its good
wear resistant quali-ties constructed in accordance with the
present invention and illustrated emplaced on the grinding table
of a bowl mill,
i'`'`~,
~ ~3~L2~
- 12a - 62898-13~8
Figure 4 is a top plan view of a first type of bowl mill
liner embodying an outer surface layer formed of a material
characterized by its good wear resistan-t qualities constructed in
accordance with the present invention'
Figure 5 is a side elevational view of a second type of
bowl mi:ll liner embodying an outer surface layer formed of a
material characterized by its good wear resistant ~ualities
constructed in accordance with the present inven-tion, and
Figure 6 is a sectional view of a third type of bowl
mill liner embodying an outer surface layer formed of a material
characterized by its good wear resistan-t qualities constructed in
accordance with the present invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
,~
. . ,
` ~3~ 2~
-13-
Referring now to the drawing, and more particularly
to Figure 1 thereof, there ;s depicted therein a bowl mill,
generally designated by reference numeral 10. Inasmuch as the
nature of the construction and the mode of operation of bowl
mills per se are well-known to those skilled in the art, it is
not deemed necessary, therefore, to set forth herein a detailed
description of the bowl mill 10 illustrated in Figure 1.
Rather, it is deemed sufficient for purposes of obtaining an
understanding of a bowl mill 10, which is capable of being
equipped with articles embodying in accordance with the present
invention an outer surface layer formed of a material
characterized by its good wear resistant qualities, that there
be presented herein merely a generalized description of the
nature of the construction and the mode of operation of the
components of the bowl mill 10. For a more detailed
description of the nature of the construction and the mode of
operation of the components of the bowl mill 10, which are not
described in detail herein, one may have reference to the prior
art, e.g., U.S. Patent No. 3,465,971, which issued September 9
1966 to J. F. Dalenberg et al, and/or U.S. Patent No.
4,002,299, which issued January 11, 1977 to C. J. Skalka.
Referring further to Figure 1 of the drawing, the
bowl mill 10 as illustrated therein includes a substantially
closed separator body 12. A grinding table 14 is mounted on a
shaft 16, which in turn is operatively connected to a suitable
drive mechanism (not shown) so as to be capable of being
rotatably driven thereby. With the aforereferenced components
arranged within the separator body 12 in the manner depicted in
Figure 1 of the drawing, the grinding table 14 is designed to
be driven in a clockwise direction.
Continuing with a description of the bowl mill 10, a
plurality of grinding, i.e., pulverizer, rolls 18, preferably
three in number in accord with conventional practice, are
suitably supported within the interior o-F the separator body 12
so as to be spaced equidistantly one from another around the
circumference of the latter. Note is made here of the fact
that in the interest oF maintaining clarity of illustration in
C840420
2 ~ ~ 7
1~--
the drawing only one grinding roll has been depicted in Figure
1.
With further regard to the grinding rolls of the bowl
mill 10, each of the latter as best understood with reference
to the grinding roll 18 depicted in Figure 1 oF the drawing is
preferably supported on a suitable shaft, seen at 20 in Figure
1, for rotation relative thereto. In addition, each of the
grinding rolls, as best understood with reference to the
grinding roll 18 of Figure 1 is also suitably supported for
movement relative to the upper surface, as viewed with
reference to Figure 1, of -the grinding table 14. To this end,
each of the grinding rolls of the bowl mill 10 including the
roll 18 illustrated in Figure 1 has a hydraulic means,
generally designated in Figure 1 by the reference numeral 22,
cooperatively associated therewith. The hydraulic means 22 in
a manner well-known to those skilled in the art of bowl mills
is operative to establish a hydraulic loading on the grinding
roll 18 associated therewith whereby the latter grinding roll
18 is made to exert the requisite degree of force on the coal
that is disposed on the grinding table 14 for purposes of
accomplishing the desired pulverization of this coal.
~ he material, e.g., coal, that is to be pulverized in
the bowl mill 10 is fed thereto by means of any suitable
conventional form of feed means. By way of exemplification in
this regard, one such -feed means that may be employed for this
purpose is a belt feeder means (not shown). Upon being
discharged from the feed means (not shown), the coal enters the
bowl mill 10 by means of a coal supply means, generally
designated by reference numeral 24, with which the separator
body 12 is suitably provided. The coal supply means 24 is
operative to cause the coal to flow on to the surface of the
grinding table 14.
In accord with the mode of operation of bowl mills
that embody the form of construction depicted in Figure 1, a
gas such as air is utilized to effect the conveyance of the
coal from the grinding table 14 through the interior of the
separator body 12 for discharge from the bowl mill 10. The air
C840420
~3~2~
-15~
that is used in this regard enters the separator body 12
through a suitable opening (not shown) formed therein for this
purpose. From the aforesaid opening (not shown) in the
separator body 12 the air flows to and through the annulus, the
latter-being denoted in Figure 1 by the reference numeral 26,
which consists of the ring-like space that exists between the
circumference of the grinding table 14 and the inner wall
surface of the separator body 12. The air upon passing through
the annulus 26 is deflected over the ~rinding table 1~
preferably by means of a vane wheel assembly, constructed in
accordance with the teachings of U.S. Patent No. 4,523,721
which issued on June 18, 1985 to T. V. Maliszewski et al, and
which is assigned to the same assignee as the present
application. For purposes of maintaining clarity of
illustration in the drawing, only the deflector portion, the
latter being seen at 2~ in Figure 1, of the vane wheel assembly
which forms the subject matter of U.S. Patent No. 4,523,721 has
been depicted in the drawing. Moreover, it is deemed that the
depiction of the deflector portion 28 in Figure 1 of the
drawing is sufficient for purposes of enabling one to obtain a
complete understanding of the subject matter of the present
invention to which the instant application is directed.
~lowever, should further information be desired concerning the
nature of the construction and/or the mode of operation of the
vane wheel assembly that the bowl mill 10 shown in Figure 1
embodies, reference may be had for this purpose to U.S. Patent
No. 4,523,721.
While the air is flowing along the path described
above, the coal which is disposed on the surface of the
grinding table 14 is being pulverized by the action of the
grinding rolls 18. As the coal becomes pulverized, the
particles are thrown outwardly by centrifugal force away from
the center of the grindiny table 14. Upon reaching the region
of the circumference of the grinding table 14, the coal
particles are picked up by the air exiting from -the annulus 26
and are carried along therewith. The combined flow of air and
coal particles is thereafter captured by the deflector portion
C840420
~ 3 ~ 7
-16-
28 of the vane wheel assembly constructed in accordance with
the teachings of U.S. Patent No. 4,523,72l. The effect of this
is to cause the combined flow of thi~ air and coal particles to
be deflected over the grinding table l4. This necessitates a
change in direction in the path of flow of this combined stream
of air and coal particles. In the course of effecting this
change of direction, the heaviest coal particles, because they
have more inertia, become separated from the air stream, and
fall back on to the surface of the grinding table 14 whereupon
they undergo further pulverization. The lighter coal
particles, on the other hand, because they have less inertia
continue to be carried along in the air stream.
After leaving the influence of the aforesaid
deflector portion 28, the combined stream consisting oF air and
those coal particles that remain flows to the classifier 30.
The classifier 30 in accord with conventional prac-tice and in a
manner which is well-known to those who are skilled in this art
operates to effect a further sorting of the coal particles that
remain in the air stream. Namely, those particles of
pulverized coal, which are of the desired particle size, pass
through the classifier 30 and along with the air are discharged
therefrom and thereby from the bowl mill lO. On the other
hand, those coal particles, which in size are larger than
desired, are returned to the surface of the grinding table l4
whereupon they undergo further pulverization. Thereafter,
these coal particles are subject to a repeat of the process
described above.
With further regard to the matter of the pulverizing,
i.e., grinding, action to which the coal disposed on the
grinding table l4 is subjected by -the grinding rolls l8, the
amount of force that must be exerted by the latter in order -to
effect the desired degree of pulverization of the coal will
vary depending on a number of factors. For example, one
important consideration in this regard is the nature o-f the
coal itself. That is, the amount of force required -to
pulverize the coal will be a function of the grindability of
the coal to be pulverized, i.e., the grinding characteristics
C840420
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of the latter. Another important factor in determining the
amount of force that the grinding rolls 18 must exert to
accomplish the desired degree of pulverization of the coal is
the depth to which the coal is disposed on the grinding table
l4, which in turn is a function of the output rate at which the
bowl mill lO is being operated.
For purposes of setting forth a detailed description
of a bowl mill grinding roll which embodies an outer surface
layer formed of a material characterized by its good wear
resistant qualities and which is constructed in accordancP with
the present inventiont reference will be had in particular to
Figure 2 of the drawing. Note is made here of the fact that
Figure 2 is intended simply to provide a general illustration
of the nature of the construction which a grindingt i.e.t
pulverizert roll 18 often embodies. Referring to Figure 2t it
will be readily apparent therefrom that the grinding roll 18
often consists of a main body portiont generally designated by
reference numeral 32t that embodies the overall configuration
of a roll, and a layered external surface 34 formed of a
different materialt e.g.t a material which in accordance with
the present invention is characterized by its good wear
resistant qualitiest than that from which the body portion 32
is formed. To this endt the body portion 32 is preferably made
of a relatively softt easily machinable material such as gray
iront while the outer surface layer 34 is made of a relatively
hard material which has good wear resistant qualitiest i.e.,
exhibits good abrasion resistant characteristics. Further, as
best understood with reference to Figure 2, the body portion 32
has a through passage 36 formed through substantially the
center thereof. The through passage 36 is suitably dimensioned
so as to be capable of receiving therewithin in assembled
relation thereto the shaft 20 to which reference has previously
been had hereinbeForet and on which the grinding roll 18 is
suitably supported so as -to be capable of functioning in the
manner described above and as shown in Figure l.
In essencet the reasons for fabricating the grinding
roll 18 from two dissimilar materials is to give equal
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-18-
recognition to first the fact that there is a need to provide
the body portion 32 with the through passage 36 and secondly to
the fact that the outer surface 34 is subjected to a hard
abrasive action in the course of effecting the pulverization of
coal. The result, therefore, is that on the one hand it is
desirable that the body portion 32 be made of a relatively
soft, easily machinable material so as to facilitate the
formation therein of the through passage 36. In
contradistinction to this, there is a need for at least the
outer portion, i.e., that encompassed by the outer surface
layer 34, to be made of a relatively hard material
characterized by its capability to resist wear, and in
particular the wear caused by abrasive action.
With the preceding discussion serving as a proper
background for an understanding of the invention, the outer
surface layer 34 of the grinding roll 18 in accordance with the
present invention is formed of a material which embodies
abrasion resistant qualities and which is particularly suited
to be employed for purposes of forming therefrom the outer
surface layer, i.e.; the wear surface, 34 of the grinding roll
18. Moreover, the material from which the outer surface layer
3~ of the grinding roll 18 is formed in accordance with the
present invention is further characterized in that it is
capable of being cast as well as being it is capable of being
utilized to hardface a new grinding roll 18. Typically, the
material from which the outer surface layer 34 of the grinding
roll 18 is formed, as cast, comprises, by weight percentage~,
3.2% - 3.4% Carbon, l.45% - l.65% Silicon, 0.4% maximum
Manganese, 4.5% - 5.0% Nickel, 4.0% - 4.25% Chromium, 0.4% -
0.5% Phosphorus, 0.9% - 0.ll% Sulfur, 0.4% - 0.6% Molybdenu~
and no Bismuth.
Turning next to a consideration of -the bull ring
which is designed to be emplaced on the grindiny table 14 of
the bowl mill 10 and which embodies at least an outer surface
layer that is characterized by its good wear resistant
qualities and is constructed in accordance with the present
invention, reference will be had -For -this purpose in particular
C840~20
--19--
to Figure 3 of the drawing.- With reference to Figure 3, the
bull ring which is denoted therein generally by the reference
numeral 38 is formed of a material that is characterized by its
good abrasion resistant qualities. More specifically, the bull
ring 38 embodies a first portion, the latter being denoted by
the reference numeral 40 in Figure 3, and a second portion
which is identified by the reference numeral 42 in Figure 3.
The first portion 40 is suitably inclined relative to the
second portion 42 of the bull ring 38 so as to mate with the
outer surface layer 34 of the grinding roll 18. That is, the
angle at which the first portion 40 of the bull ring 38 is
inclined is suitably selected so as to conform to the angle at
which the outer surface layer 34 of the grinding roll 18 is
inclined, i.e., the angle at which the first portion 40 oF the
bull ring 38 is inclined is designed to be complementary to the
angle of inclination of the outer surface layer 34 of the
grinding roll 18. In accord with the best mode embodiment of
the invention, the bull ring 38 preferably is comprised oF a
multiplicity of individual segments. However, it is to be
understood that the bull ring 38 could equally well without
departing from the essence of the present invention take the
form of a single integral member. Typically, the material From
which the bull ring 38 of the grinding roll 18 is -formed, as
cast, comprises, by weight percentages, 3.5% - 3.7% Carbon,
1.2% - 1.6% Silicon, 0.4% maximum Manganese, 4.3% - 5.0%
Nickel, 3.7% - 4.4% Chromium, 0.l5% - 0.25% Phosphorus, 0.9% -
0.ll% Sulfur, 0.4% - 0.6% Molybdenum and 0.0l5% nominal
Bismuth.
For purposes of completing the description o-f the
articles embodying in accordance with -the present invention an
outer surface layer characterized by its abrasion resistant
qualities, reference will be had in particular to Figures 4, 5
and 6 of the drawing wherein there is to be found depicted a
first type of bowl mill liner identified generally by reference
numeral 44 in Figure 4, a second type of bowl mill liner
identified generally by the reference numeral 46 in Figure 5,
and a third type of bowl mill liner identified generally by the
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reference numeral 48 in Figure 6. The bowl mil1 liner 44
constructed as depicted in Figure 4 of the drawing is designed
to be employed in the deflector portion 28 of the vane wheel
assembly to which reference has been had hereinbefore in
connection with the discussion of the bowl mill lO shown in
Figure 1. More specifically, in accordance with the mode of
construction of the deflector portion 2~, a plurality of bowl
mill liners 44 are utilized to form each of the various rows of
deflector liners with which the deflector portion 28 is
suitably provided. To this end, each of the bowl mill liners
44 embodies a configuration which is preestablished in order to
enable each of the bowl mill liners 44 to be cooperatively
associated one with another in a suitable fashion as required
in order to function as an operative component of the deflector
portion 28. That is, as best understood with reference to
Figure 4 of the drawing, the bowl mill liner 44 embodies a
configuration wherein two sides thereof, i.e., those denoted by
the reference numerals 44a and 44b in Figure 4, extend
substantially in parallel relation one to another, a third side
thereof, i.e., the side denoted by the reference numeral 44c in
Figure 4, extends substantially at right angles to both the
sides 44a and 44b of the bowl mill liner 44, and the fourth
side thereof, i.e., the side denoted by the reference numeral
44d in Figure 4, is inclined relative to both the sides 44a and
44b and in addition extends in nonparallel relation to the side
44c of the bowl mill liner 44. Fur~her, the edge surfaces of
-the bowl mill liner 44 of Figure 4 are suitable configured such
as by being beveled so as to enable them to mate with the
complementary edge surfaces of the bowl mill liners 44 that
adjoin thereto. This is not only to facilitate the initial
installation of the bowl mill liners 44 within the separator
body 12 of the bowl mill 10 of Figure l, but also to facilitate
their removal and subsequent replacement when they become worn.
Finally, because of the abrasive action to which they are
subjected by virtue of the air having coal particles entrained
therein striking thereagainst the bowl mill liners 44 are
formed of a material that is noted for its good abrasion
C~40420
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~21~
resistant qualities. Typically, the material from which the
bowl mill liners 44 are formed, as cast, comprises, by weight
percentages, 3.5% - 3.7% Carbon, 1.2% - 1.6% Silicon, 0.4%
maximum Manganese, 4.3% - 5.0% Nickel, 3.7% - 4.4% Chromium,
0.15% - 0.25% Phosphorus, 0.9% - 0.11% Sulfur, 0.4% - 0.6%
Molybdenum, and 0.015% nominal Bismuth.
The bowl mill liners 46 constructed as depicted in
Figure 5 of the drawing are designed to be employed in the
deflector portion 28 of the vane wheel assembly to which
reference has been had hereinbefore in connection with the
discussion of the bowl mill 10 shown in Figure 1. Namely, in
accordance with the mode of construction of the deflector
portion 28, the bowl mill liners 46 are designed to be employed
therein as side liners. More specifically, the plurality of
bowl mill liners 46 are utilized in the deflector portion 28
wherein each of the bowl mill liners 46 is installed so that
the back edge thereof is arranged to be flush with the
separator body 12 of the bowl mill 10 of Figure 1 and so that
the bottom edge thereof is arranged to be flush with the
intermediate liner (not shown). To this end, each of the bowl
mill liners 46 embodies a configuration which is preestablished
in order to enable each of the bowl mill liners 46 to be
cooperatively associated one with another in a suitable fashion
as required in order to function as an operative component of
the deflector portion 28. That is, as best understood with
reference to Figure 5 of the drawing, the bowl mill liner 46
embodies a configuration wherein a first side thereof, i.e.,
the side denoted by the reference numeral 46a in Figure 5,
extends in a first plane, a second side thereof, i.e., the side
denoted by the reference numeral 46b in Figure 5, extends in a
second plane which is substantially perpendicular to the plane
of the side 46a, a third side thereof, i.e., the side denoted
by the reference numeral 46c in Figure 5, is inclined relative
to the side 46a and in addition extends in nonparallel relation
to the side 46b of the bowl mill liner 46, and a -fourth side
thereof which includes a first portion, denoted by the
reference numeral 46d in Figure 5, that extends in parallel
C84042 0
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--22
relation to the side 46a of the bowl mill liner 46 and a second
portion, denoted by the reference numeral 4~e in Figure 5, that
is inclined relative to the side 46c and in addition extends in
nonparallel relation to the side 46a of the bowl mill liner 46.
Because of the abrasive action to which they are subjected by
virtue of the air having coal particles entrained therein
striking thereagainst the bowl mill liners 46 are Formed of a
material that is noted for its good abrasion resistant
qualities. Typically, the material from which the bowl mill
liners 46 are formed, as cast, comprises, by weight
percentages, 3.5% - 3.7% Carbon, 1.2% - 1.6% Silicon, 0.4%
maximum Manganese, ~.3% - 5.0% Nickel, 3.7% - 4.4/~ Chromium,
0.15% - 0.25% Phosphorus, 0.9% - 0.11% Sulfur, 0.4% - 0.6%
Molybdenum, and 0.015% nominal Bismuth.
The bowl mill liners 48 constructed as depicted in
Figure 6 of the drawing are designed to be employed in the
deflector portion 28 of the vane wheel assembly to which
reference has been had hereinbefore in connection with the
discussion of the bowl mill 10 shown in Figure 1. More
specifically, in accordance with the mode of construction of
the deflector portion 28, the plurality of bowl mill liners 48
are utilized in the manner of intermediate liners with which
the deflector portion 28 is suitably provided. To this end,
each of the bowl mill liners 48 embodies a configuration which
is predetermined in order to enable each of the bowl mill
liners 48 to be cooperatively associated one with another in a
suitable fashion as required in order to function as an
operative component of the deflector portion 28. That is, as
best understood with reference to Figure 6 of -the drawing, the
bowl mill liner 48 includes a first portion denoted by the
reference numeral 48a in Figure 6 which extends in a first
plane, and a second portion denoted by the reference numeral
48b in Figure 6 which extends in a second plane that in turn is
inclined at a predetermined angle to the plane of the first
portion 48a. Because of the abrasive action to which they are
subjected by virtue of the air having coal particles entrained
therein striking thereagainst the bowl mill liners 48 are
C840420
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--23--
formed of a material that is noted for its good abrasion
resistant gualities. Typically, the material from which the
bowl mill liners 48 are formed, as cast, comprises, by weight
percentages, 3.5% - 3.7% Carbon, 1.2% - 1.6% Silicon, 0.4%
maximum Manganese, 4.3/O - 5.0% Nickel, 3.7% - 4.4% Chromium,
0.15% - 0.25% Phosphorus, 0.9% - 0.11% SulFur, 0.4% - 0.6%
Molybdenum, and 0.015% nominal Bismuth.
Thus, in accordance with the present invention there
has been provided articles that embody a wear resistant surface
o layer which is formed of a new and improved material that is
characterized by its good wear resistant qualities. Moreover,
the articles of the present invention embodying a wear
resistant surface layer are particularly suited for employment
in a bowl mill of the type which is designed to be utilized for
purposes of effecting the pulverization therewithin of a
material such as coal. In addition, in accord with the present
invention the articles embodying a wear resistant surface layer
include the grinding rolls ~hich are designed to be employed in
a bowl mill. Additionally, in accordance with the present
invention the articles embodying a wear resistant surface layer
include the bull ring which is designed to be emplaced on the
grinding table of the bowl mill. Also, the articles of the
present invention embodying a wear resistant surface layer
include the liners which are designed to be selectively
emplaced in those regions of the bowl mill that based on prior
experience are known to be susceptible to wear. Furthermore,
in accord with the present invention the articles embodying a
wear resistant surface layer are relatively inexpensive to
provide, are relatively easy to employ, and are characterized
by their improved wear life.
While several embodiments of our invention have been
shown, it will be appreciated that modifications thereof, some
of which have been alluded to hereinabove, may still be readily
made thereto by those skilled in the art. We, therefore,
intend by the appended claims to cover the modifications
alluded to herein as well as all the o-ther modifications which
fall within the true spirit and scope of our invention.
C8 4 04 2 0
