Note: Descriptions are shown in the official language in which they were submitted.
; A TRIMETAL PULVERIZER ROLL AND A METHOD OF MANUFACTURE THEREOF BACKGROUND OF THE INVENTION
This invention relates to rolls, and more
specTfically to a trimetal pulverizer roll of the type that is
intended to be used in bQwl mills for purposes of effecting
the pul-verization therein of material such as, for example,
coal and to a method ox manufacturing such a trimetal
pulverizer roll.
An essential component of any steam generation system
of the type, which u~i1izes pulverized coal as a fuel, is the
apparatus in which the coal is pulveri7ed in order to render
it suitable for such usage. Although the prior art ls replete
with examples of vari OU5 types of apparatus that have been
employed for purposes of accomplishing coal pulverization,
15 one form of apparatus, which in particular has frequently been
; used for th7s purpose, is that commonly referred to as a bowl
mill. The latter obtains its name principally from the fact
that the pulverization, i.e., gr7nding, of the coal that takes
place therewithin occurs on a grinding surface, which insofar
as configuration is concerned resembles somewhat a bowl.
For an exemplary showing of a prior art form of bowl
mill, reference may be had to U.S. Patent No. 3,465,971, which
is assigned to the same assignee as the present invention.
Patent No. 3,465,971 contains a teaching of both the nature of
the construction and the mode of operation of a bowl mill that
is suitable for use for purposes of effecting the
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pulverization of the coal that is used to fuel a coal-fired
steam generator. As set forth in this patent, the essential
components of such a bowl mi11 are a body portion, i.e.,
housing, within which a grinding table is mounted for
rotation, a plurality of grinding rolls that are suppsrted in
equally spaced relation one to another, the plurality of
grinding rolls are suitably arranged in such a manner so as to
coact with the grinding table such that coal ~Ihich is disposed
on the surface of the grindTng table is capable of being
ground, i.e., pulverized, by the rolls, coal supply means for
feeding to the surface of the grinding table the coal which is
to be pulverized in the bowl mill, and air supply means for
providing to the interior of the body portion the air that is
required in ths operatlon of the bowl mill.
In order to satisfy the demands for pulverized coal
of a coal-fired steam generation system that embodies a
conventional form of construction, there commonly exists a
need to employ a plurali+y of bowl mills of the type which are
shown in the aforereferenced patent. In this regard, note is
further made here of the fact that in terms of capacity each
of these bowl mills may have a capacity of up to one hundred
tons per hour of pulverized coal. In addition to possess;ng
the capability of operating a its maximum capacity, each of
these bowl m711s must also be capable of operating at less
than full capacity, i.e., at some percentage thereof, e.g.,
25%, 50~, 75%, etc. Finally, these bowl mills must also be
capable of use with a variety of types of coal that have
dissimilar grinding characteristics.
With further reference to the aforementioned patent,
the mode of construction of the grinding rolls that are
depicted therein is such that each grinding roll is designed
to be mounted on a shaft-like member. As a result the
grinding rolls are each capable of movement relative to the
surface of the grinding table. To effect the assembly of the
grinding roll with the aforesaid shaft-like member, each
; grinding roll preferably has a through passage formed through
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the center thereof. The function of this +hrough passage is
to enable the shaft-like member to be positioned therewithin
in mounted relation thereto. Accordingly, in order to
facilltate the task of providing the grinding roll with such
a through passage, it is desirable that the grinding roll be
composed of a material thaw is characterized by its ease of
machinability, i.e., a relatively soft material such as gray
iron.
On the other hand, in addition to it being desirable
to form the grlnding roll of a material that is relativeiy
soft, there exists also a need for at least the external,
i.e., outer, surface of the grinding roll to consist of a
material that is characterT~ed by its good wear-resistant
qualitles. The primary reason for this is that the grinding
rolls in the course of effecting the pulverizatTon of material
therewith are of necessTty subjected to a harsh abrasive
action, the latter being occasioned by virtue of the nature of
the material that is being pulverized as well as by virtue of
the manner in which th1s pulverization takes place. The
result, therefore, is that the grinding rolls exhibit a
susceptibllTty to being rendered unusable in a relatively
short period of time. That is, the rolls are found to have a
relatively short operating Itfe. Fur obvious reasons, it is
desirable thaw such a result be avoided, if possible. As is
known to those who are sk711ed in this art, the wear, which
the grindTng rolls that are employed in bawl mills actually
experience Ts influenced principally by the grinding
characteristTcs of the materTal that is being pulverized as
well as by the productive output of the bowl mill, i.e., the
amount of material that is being pul~erTzed in the bowl mill
in a given period of time.
hen the external, 7.e., outer, surface of the
pulverTzer, i.e., grinding, roll becomes sufficiently worn so
as to preclude any further use thereof for purposes of
effectTng the pulverTzatTon of materTal therewith, the
remaining portions of the roll are normal still functional.
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That ls, the grinding roll but for its worn external surface
would still be serviceable. Thus, from the standpoint of
achieving economies of manufacture, it would be desirable, if
possible, to effect a resurfacing of the external surface of
the grinding roll such that the latter might once again be
utilized for the pulverization of material rather than
necessitating that the worn grinding roll be replaced by one
that is entirely new. Further to this point, one would
normally expect that the cost of reconditioning, i.e.,
resurfacing, the outer surface of a worn grinding roll would
be significantiy less than the cost associated with the
manufacture of an entirely new grinding roll.
In additTon to the relative cost of resurfacing the
external, i.e., outer, surface of a worn grinding roll as
contrasted to the cost of manufacturing an entirely new
grinding roll, there also exists the matter of the operating
Iife which ts achievable w7th a resurfaced worn grinding roll
; as contrasted to that which is obtainable with an entirely new
grinding roll. Namely, Tn order to be economically feasible
it is desirable that the operating life of a resurfaced worn
grinding roll be approximately equivalent to that which one
would obtaTn from a new grlnding roll. what is, any savings
which are achievable from making use of a resurfaced worn
grTnd7ng roll as contrasted to employTng an entirely new
grind7ng roll should not be d7ssipated as a consequence of the
fact that the operat7ng 17fe of a worn gr7nd7ng roll is such
that several resurfac7ngs thereof are required in order to
real7ze the same operat7ng life that can be realized w7th a
gr7nding roll that is totally new. To summarize, if in the
interest of obtaining comparable operating lives, muItiple
resurfac7ngs would have to be had of the worn gr7nd7ng roll
such that the cost thereof would probably equal, 7f not
exceed, the cost of prov7d7ng an ent7rely new gr7nding roll,
then, the advantages accruing from reus7ng a worn gr7nd7ng
roll v7s-a-vis replacing the latter with a new grinding roll
would undoubtedly not be real7zed.
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It has been known in the prior art to resurface a
worn grinding roll. Further, the results obtainable therefrom
have proven to be generally satisfactory. Most often, this
resurfacing has been in the form of providing the external
surface of the worn grinding roll with a suitably dimensioned
layer of weld metal. In view of this experience which the
prior art has had with the resurfacing of a worn grinding
roll, there have been attempts made at provid7ng the external
surface of new grlnding rolls with a hard facing.
Unfortunately, however, such attempts applied to new grinding
rolls have not heretodate met with much success.
The motivation behind the attempt to effect a
resurfacing of new grinding rolls has largely resided in the
desire to extend the operating life thereof. One of the major
reasons for seeking to extend the operating life of new
grinding rolls i5 that it would enable the period to be
; extended between when shutdowns are required to accomplish the
removal of worn grTndlng rolls and the replacement thereof
wTth new grinding rolls. Furthermore, when consideration is
given to the fact that each bowl mill normally embodtes three
grTnding rolls, each of which periodically must be removed and
replaced when 7t becomes worn, as well as the fact that a
plurality of bowl mills are commonly emptoyed to provide the
requisite amount of pulverized coal to a coal-fired steam
- 25 generation system, the magnTtude of the problem that is
presented by the need to effect a shut down of the bowl mill
for purposes of accomplishing the removal and replacement of
worn grindTng rolls while concomitantly ensuring that the
power generation system retains the capability to provide
continuous uninterrupted service should be readily apparent.
In addition to the above there 7s also the matter of
the expend7ture of t7me and effort along with the cost per se
that 7s associated with the act of removTng and replacing a
worn grinding roll. Obv70usly, therefore, if one were to be
successful in achieving a reduction in the frequency with
which grinding rolls are required to be replaced as a
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consequence of their having become worn, cost savings could be
realized in terms of the time and sffort that is required to
be expended to effect such replacement. There has been shown
to exist in the prior art a need for a new and improved form
of grinding roll that is characterized by the fact that this
new grinding roll possesses a significantly longer operating
life than that commonly found to be possessed by prior art
forms of grinding rolls, In addition, a need has been
demonstrated for a new and improved method for manufacturing
such a new and improved form of grinding roll.
It is, therefore, an object of the present inventTon
to provide a new and improved form of pulverizer roll.
It is another object of the present invention to
provide such a pulverizer roll which is characterized in that
it embodies a trimetal mode of construction.
It is still another object of the present invention
to provide such a trimetal pulverTzer roll that is primarily
intended to be employed in a bowl mill for purposes of
effecting the pulverization therewithin of a material such as
coal.
A further object of the present invention is to
provide such a trlmetal pulverizer roll that is
distinguishable by its relatTvely long operating life.
A still further object of the present invention is to
provide such a trimetal pulverizer roll having a first portion
thereof that is characterized by its ease of machinability, a
second portion thereof that is characterized by the fact that
it exhibits medium wear-resistant qualit7es, and a third
portion thereof that is characterized by the fact that it
exhibits highly abrasive resistant qualities.
Yet another object of the present invention is to
provide such a trimetal pulverizer roll that while being
readily employable in a bowl mill yet also enables significant
cost savings to be realized through the use thereof insofar as
the operation of the bowl mTII is concerned.
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Yet still another object of the present inventton is
to provide a new and improved method of manufacturing such a
trimetal pulverizer roll.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present
invention there is provided a pulverizer, i.e., grinding roll
of the type that is particularly suited for employment in a
bowl mill. When mounted in the bowl mill, the subject roll is
designed to be operatlve to coact with another surface of the
bowl mill in order to accomplish the pulverization within the
bowl mill of material such as coal. To this end, the subject
roll embodies a trimetal form of construction. More
speciflcally, the subJect roll incorporates a first, i.e.,
7nner, portion whtch is made of material that is characterized
by its ease of machinability, as for example, gray iron.
Further, this inner portion has formed therethrough a passage
which is suitably dimensioned for receiving therewithin a
shaft-like member on which the roll is designed to be mounted
in supported relation thereto. Next, the subject roll
Tncorporates a second, i.e., intermediate, portion of material
that 7s suitably supported in adhered relation on the inner
portion. This intermediate portion, which is substantially
un7form in thickness, is composed of a material that is voted
for Tts medium wear~resistant qualities such as a material
like Raymix, the latter being obtainable from applicant's
assignae. Lastly, the subject roll incorporates a third,
i.e., outer, port70n that is suitably supported in adhered
relation on the intermediate portion. This outer portion is
substantially uneven in thickness. That is, those areas of
the outer portion of the subject roll that are known to wear
most rapidly are provTded with a thicker thickness of
material. Finally this outer portion is composed of a highly
abrasive resistant material such as a weld overlay material.
In'accordance with another aspect of the present
invention there is provided a method of manufacturing such a
tri~etql pulverizer, i.e., grinding roll. The subject method
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includes the steps of forming from a material that is
characterized by its ease of machinability a body having the
general configuration of a roll, providing through the center
of the body a suitably dimensioned through passage capable of
having a shaft-like support member positioned therewithin in
mounted relation thereto, affixing in supported relation to
the body a first substantially uniform layer of material
having medium wear-resistant characteristics, and affixing in
supported relation to the first layer of material a second
substantially nonuniform layer of material having highly
abrasive resistant characteristics.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a side elevational view partly in section
and with some parts broken away of a bowl mill embodying
pulverizer rolls constructed in accordance wifh the present
invention and manufactured in accordance with the method of
the present invention;
Figure 2 is a sectional view on an enlarged scale of
a pulverizer roll constructed in accordance with the present
invention and manufactured in accordance with the method of
the present inventlon; and
Figure 3 is a sectional view on an enlarged scale of
a pulverized roll constructed in accordance with the present
invention and manufactured in accordance with the method of
the present invention, illustrating in exaggerated form +he
uneven nature of the thickness of the outer portion of the
pulverizer roll.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to the drawing, and more particularly
to F7gure l thereof, there is depicted therein a pulverizing
bowl m711, generally designated by reference numeral 10.
Inasmuch as the nature of the construction and the mode of
operation of pulverizing bowl mills per se are well-known to
those skilled in the art, it is, therefore, not deemed
necessary to set forth herein a detailed description of the
bowl mill lO, which is illustrated in Figure l. Rather, it is
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deemed sufficient for purposes of obtaining an understanding
of a pulverizing bowl mill lO, which is capable of being
equipped with pulverizer rolls constructed in accordance with
the present 7nvention and manufactured by means of the present
inventton, that there merely be presented herein a generalized
description of the nature of the construction and the mode of
operation of the components of the pulverizing bowl mill lO.
For a more detailed description of the nature of the
construction and the mode of operation of the components ot
the pulverizing bowl mill lO, which are not described in depth
herein, one may have reference to the prior art, e.g., U.S.
Patent No. 3,465,971, which issued September 9, 1969 to J. F.
Dalenberg et al., and/or U.S. Patent No. 4,002,299, which
issued January ll, 1977 to C. J. Skalka.
ReferrTng further to Figure l of the drawing, the
pulverizing bowl mill lO, as illustrated therein, includes a
substantially closed separator body 120 A grinding table 14
is mounted on a shaft 16, which in turn is operatively
connected to a suitable drive mechanTsm (not shown), so as to
be capable of being rotatably driven thereby. With
aforedescrTbed components arranged within the separator body
12 in the manner depicted in Figure 1 of the drawing, the
grtnding table 14 Ts designed to be driven in a clockwise
direction.
Continuing with description of the pulverizing bowl
mill 10, a plurality of pu3verizer, i.e., grinding, rolls 18,
preferably three in number in accord with conventional
practice, are suitably supported within the interior of the
separator body 12 so as to be spaced equidistantly one from
another around the circumference of the latter. The nature of
the construction as well as the method by which each of the
grinding rolls 18 is manufactured comprises the subject matter
that forms the essence of the present invention. A
description of the nature of the construction of the grinding
rolls 18 as well as a description of the method by which such
a grinding roll 18 is manufactured will be found set forth
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hereinafter. First, however, note is made here of the fact
that in tha interest of maintaintng clarity of illustration in
the drawing only one grinding roll 18 has been shown in Figure
1.
As further regards +he grinding rolls 18, each of the
latter, as best understood with reference to Figure 1 of the
drawing, is preferably supported on a suitable shaft (not
shown) such as to be rotatable relative thereto. Moreover,
the grinding rolls 18 are also each suitably supported in a
manner yet to be described for movement relative to the upper
surface, as viewed wtth reference to Figure 1, of the grinding
table 14. To this end, each of the grinding rolls 18 has
cooperatively associated therewith a hydraulic means,
gensrally designated in Figure 1 by reference numeral 20.
Each of the hydraulic means 20, as will be described more
fully hereinafter, is operafive to establish a hydraulic
loading on the grlnding roll 18 that is associated therewith.
The effect of this loading is to cause the roll 18, which is
subject thereto, to exert the requisTte degree of force on the
coal that is disposed on the grinding table 14, and thereby
accomplish the desired pulverTzation of this coal.
The material, e.g., coal, that is to be pulverized in
the bowl mtll 10 is fed thereto by means of any suitable
conventional form of feed means. By way of exempllfication 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 22, with which the separator
body 12 is suitably provided. In accordance with the
embodiment of the pulverizing bowl mill 10 illustrated in
Figure 1, the coal supply means 22 includes a suitably
dimensioned duct 24 having one end thereof, which extends
outwardly of the separator body 12 and preferably terminates
in a funnel-like member (not shown). The latter mamber (not
shown) is suitably shaped so as to facilitate the collection
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of the coal particles entering the bowl mill 10, and the
guiding thereafter of these coal particles into the duct 24.
To this end, as shown 7n Figure 1 of the drawing, the duct end
26 preferably is suitably supported within the separator body
12 through the use of any suitable form of conventional
support means (not shown) such that the duct end 26 is
coaxially aligned with the shaft 16 that supports the grinding
table 14 for ro+ation, and is located in spaced relation to a
suitable outlet 28 provided in the classifier, generally
designated by reference numeral 30, through which the coal
flows in the course of being fed onto the surface of the
grinding table 14.
In accord wlth the mode of operation of pulverizing
bowl mills that embody the form of construction depicted in
FTgure 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
pulver7zing bowl mill 10. The air that is made use of in this
regard enters the separator body 12 through a suitable opening
(not shown) formed therein for this purpose. From +he
aforesa7d opening snot shown) in the separator body 12, the
aTr flows to a multiplicity of annular spaces 32 suitably
- formed between the circumference of the grinding table 14 andthe inner wall surface of the separator body 12. The air upon
- 25 exiting from the annular spaces 32 is deflected over the
grinding table 14 by means of suitably positioned deflector
means (not shown). One such form of deflector means (not
shown), which is suitable for use for this purpose in the bowl
mill 10 of Figure 1 comprises the subject matter of U.S.
Patent No. 4,234,132 which issued to applicant on November 18,
1980, and which is assigned to the same assignee as the
present applicatTon.
While the air is flowing along the path described
above, the coal which is dTsposed 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
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partlcles are by centrifugal force thrown outwardly away from
the center of the grinding table 14. Upon reaching the region
of the circumference of the grinding table 14, the coal
particles are picked up by +he air exiting from the annular
spaces 32 and are carried along therewith. The combined flow
of air and coal particles is thereafter captured by the
deflector means (not shown), which has been referred to
previously hereinabove. The deflector means (not shown),
in turn, is operative to cause this combined flow of air and
coal particles to be deflected over the grinding table 14.
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
partTcles, because they have more inertia, become separated
from the air stream> and fall back onto the surface of the
grinding table 14, whereupon they undergo further
pulverization. The lighter coal particles, on the other hand,
because they have less inertTa continue to be carried along in
the air stream.
After leaving the influence of the aforedescribed
deflector means (not shown), the combined stream consisting of
air and those coal particles that rematn entrained therein
flows to the classifier means 30 to which reference has been
had herein previously. In accord with conventional practice
and in a manner which is well-know~ to those skilled in this
art, the classifier 30 operates to effect a further sorting of
the coal particies that remain in the air stream. Namely,
those particles of pulverized coal, which are of the desired
parttcle size, pass through the classifier 30 and along with
the air are discharged therefrom and thereby from the bowl
mill 10. This discharging of the coal particles is effected
through the outlets 34 with which the bowl mill 10 is suitably
provided for this purpose.
On the other hand, those coal particles, which in
size are larger than desired, are returned to the surface of
- the grinding table 14 whereupon they undergo further
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pulverization. Thereafter, these coal particles are once
again subjected to the process that has been described above.
That 7s, these particles are thrown outwardly of the grinding
table 14, are picked up by the air exiting from the annular
spaces 32, are carried along with the air to the deflector
means (not shown), are deflected back over the grinding table
14 by the deflector means (not shown), the heavier particles
drop back onto the grinding table 14, the lighter particles
are carried along to the classifier 30, and finally those
particles which are of the proper size pass through the
classifier 30 and exit from the bowl mill 10 through the
outlets 34.
ConsiderTng further the matter of the pulverizing
action to which the coat disposed on the upper surface, as
viewed with reference to Figure 1, of the grinding table 14 is
subjected by the grinding rolls 18, the amount of force that
must be exerted on the latter in order to effect the desired
degree of pulverizatton of the coal mill vary depending on a
number of factors. For example one important consideration
in this regard is the nature of the coal itself. That is, the
amount of force required to pulverlze the coal will be a
function of the grindability of the coal to be pulverized,
ire., the grinding characteristics 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 14, which in turn is a function
of the outpu+ rate at which the bowl mill 10 is being
operated.
As best understood with reference to Figure 1 of the
drawing, the amount of grinding force which the grinding rolls
18 apply to the coal on the grinding table 14 is a function of
the amount of force with which the grinding rolls 18 are
biased into engagement with the coal on the table 14. In
accord with the nature of the construction shown in Figure 1,
; the grinding roll 18 depicted therein, which is suitably
36~
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mounted for rotation on a shaft (not shown), is suitably
supported so a: to be pivotabie about the pivot pin 36 into
and out of engagement with the coal that is disposed on the
grinding table 14. Although only one grinding roll 18 is
shown in Figure 1 and although this discussion is directed fo
this one grinding roll 18, it is to be understood that as has
been mentioned previously hereinbefore the bowl mill 10 is
normally provided with three such grinding rolls 18.
Therefore, this discussion is intended to be equally
applicable to each of these three grinding rolls 18.
Continuing with the matter of the force exerted by
the gri.nding roll 18~ the latter in accord with the nature of
the construction illustrated in Figure 1 is designed to be
biased hydraulically into and out of engagement with the coal
that is on +he grinding table 14. More specifically, to this
end the hydraulic means 20 is cooperatively associated with
the grinding roll 18~ As depicted in Figure 1, the hydraulic
means 20 includes a cylinder 38 suitably mounted to the
exterior wall surface of the separator body 12. Wlthin the
cylinder 38, a piston 40 is suitably supported for movement
therewithin. Attached to the piston 40 is a piston rod 42 of
sufficient length so as to extend into the interior of the
separator body 12 whereupon the free end of the piston rod 42
engages an upstanding member 44 that comprises a portion of
the support means for the grtnding roll 18. A suitable
opening 46 Ts formed in the separator body 12 to enable the
piston rod 42 to project into the interior of the latter. In
a manner well-known to those skilled in the art of hydraulics,
the cylinder is filled with a suitable hydraulic fluid, such
that a hydraulic pressure is applied by the fluid to both
faces of the piston 40. The hydraulic fluid which fills the
- cylinder 38 is provided thereto from a suitable source thereof
(not shown).
Accordingly, the extent to which the free end of the
piston rod 42 projects into the interior of the separator body
12 for engagement with the member 44 is a function of the
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difference in hydraulic pressure, which is applied to the
faces of the piston 40. In turn, the extent to which the free
end of the piston rod 42 extends into the interior of the
separator body 12 determines the extent to which the grinding
roll 18 is hydraulically biased into engagement with the coal
on the grinding table 14, and concomitantly the amount of
grinding force being applied to the coal by the grinding roll
18. That is, the piston rod 42 is fixedly attached to one
face of the piston 40 such that as the piston 40 moves in
response to the difference in hydraulic pressure being applied
- to the faces thereof, the piston rod 42 moves along
therewith. It is to be understood in this connection that the
opening 46 provided in the separator body 12 through which the
piston rod 42 passes is equipped with suitable sealing means
(not shown) operative to prevent the leakage through the
openlng 46 of hydraulic fluid from the cylinder 38 to the
interior of the body 12.
By way of exemplification, the more the free end of
the piston rod 42 extends into the interior of the separator
body 12, the more it will cause the member 44 to move in a
clockwise direction, as viewed with reference to Figure 1,
abouf the pivot p7n 36, and thereby have the effect of
increasing the amount of grinding force that the grindlng roll
18 exerts on the coal that is on the grinding table 14.
Conversely, the less the free end of the piston rod 42
projects into the interior of the separator body 12, the less
clockwise movement there will be of the member 44 about the
pivot pin 36, and thus the less grinding force the roll 18
will exert on the coal that is disposed on the table 14.
Lastly, in accord with the preferred form of
construction, the hydraulic means 20 is provided with an
accumulator 48. The.function of the latter is to obviate any
potentially damaging consequences that might otherwise flow
from the occurrence of some form of transient operating
condition. For example, should some foreign object be
introduced into the bowl mill 10 along with the coal that is
121Z3~i~
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to be pulverized, and should this foreign object become
disposed on the grinding table 14, the effect of the grinding
roll 18 engaging this foreign object would be to raise the
roll 18 away from the table 14, to would be to cause the
roll 18 to move about the pivot pin 36 in a counterclockwise
direction, as viewed with reference to Figure 1. As a
consequence of this action, the member 44 would be made to
apply a force against the free end of the piston rod 42
tending to cause the piston 40 to move in a direction away
from the wall surface of the separator body 12. further, as
the piston 40 moves in this manner, the hydraulic fluid
located in that portion of the cylinder 38 towards which the
piston 40 is moving would tend, absent the presence of the
accumulator 48, to resist the movement of the piston 40. This
could result in damage being incurred by the various
components that are operatively associated with the grTnding
roll 18.
Accordingly, the function of the accumulator 48 is to
permit hydraulic fluid to flow thereinto as the fluid ts being
forced from the cylinder 38 by the advancing piston 40.
- However, as soon as the grinding roll 18 passes over the
foreign object, the grTnding roll 18 Ts once again restored to-
its normal position, i.e., nontransient condition. This
occurs by vtrtue of the flow from the accumulator 48 tnto the
cyltnder 38 of the hydraultc flutd whtch had been made to flow
tnto the former from the latter, because of the
counterclockwtse movement, as vtewed with reference to Figure
1, of the grinding roll 18 about the pivot pin 36 caused by
the ra7sing of the roll 18 as the latter engaged and passed
over the foretgn object located on the table 14.
For purposes of setttng forth a detatled descrtptton
of the structural nature of a pulvertzer roll 18 constructed
tn accord wtth the present tnventton as well as the method by
whtch such a pulvertzer roll 18 ts manufactured tn accord wtth
the present invention, reference will now be had parttcularly
to Ftgures 2 and 3 of the drawing. It is important to take
2365
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note here of the fact that Figure 2 in contrasf fo Figure 3 is
intended to simpiy provide a general illustration of a
pulverizer, i.e., grtnding, roll 18 constructed in accord with
the present invention. Figure 3, on the other hand, as will
be more fully set forth hereinafter, illustrates with more
partTcularly the specific details of construction of 2
pulverizer roll 18 that is manufactured in accordance with the
present inventionO
With the above as a frame of reference, it can be
seen prom Figures 2 and 3 that the grinding roll 18 embodies a
trimetal form of construction. More specifically, as best
understood with reference to Figures 2 and 3, the grinding
roll 18 embodies a main body portion, generally designated by
reference numeral 50, that embodies the overall configuration
of a roll. In addition to the body portion 50, the grinding
roll 18 further embodies two other dissimilar portions of
materlal arranged Tn layered relation to each other as well as
to the body portion 50. To th7s end, one of these two
portions, i.eO, that denoted generally by the reference
numeral 52 in F7gures 2 and 3 of the drawing, is suitably
positioned Tn superimposed relation ,o the body portion 50 of
the grinding roll 18. Similarly, the other of the
aforereferenced two portions, i.e., that denoted generally by
the reference numeral 54 in Figures 2 and 3 of the drawing, is
suitably positioned in super7mposed relation to the port70n
52.
As further regards the body portion 50 of the
grinding roll 18, the latter in accord with the best mode
embodiment of the invention is made of a relatively soft,
easily machinable material, such as gray iron Moreover, w7th
particular reference to Figures 2 and 3 it can be seen
therefrom that the body portion 50 has a passage 56 formed
entirely therethrough at substantially the center thereof.
The through passage 56 is suitably dimensioned so as to be
carable of receiving therewithin in assembled relation thereto
-; the shaft-like member (not shown) to which re$erence has
~Z~Z3~
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previously been made hereinbefore, 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 1.
Next, with regard to the portion 52, i.e., the
intermediate layer, with which the trimetal pulverizer roil 18
is provided, in accord with the best mode of the invention
this portion 52 preferably comprises a material that is noted
for its medium wear-resistant qualities. In this regard, a
material that has been found suitable for use for this purpose
is a material referred to by the name Raymix. Raymix, which
has a known composition, can be obtained from the Monongahela
plant of applicant's assignee. The reasons why a material
having such qualities is selected for use in this context, and
the manner in which the portion 52 consisting of Raymix
preferably is adhered to the body portTon 50 will be found set
forth with more particularity hereinafter.
The last, i.e., portion 54, of the three portions,
which collectively comprise the trimetal pulverizer roll 18
preferably consists, in accord with the best mode embodiment
of the tnventton, of a material that is characterized by the
fact that it is highly abrasive resistant. One material,
which ls suitable for use in this regard, is that known to
those skilled in this art as nihard. As in the case of the
portion 52 the reasons for employing a material to form the
portion 54, i.e., the outer layer of the trime+al pulverizer
roil 18 that has the characteristics described above, and the
manner in which the portion 54 is affixed to the portion 52
will be found set forth hereinafter with more particularlity.
Suffice it to say at this point, however, that the
reasons for constructing the grinding roll 18 from a plurality
of dissimilar materials that are arranged in a layered array
are as a result of recognition being had first to the fact
that there is a need to provide the body portion 50 with the
through passage 56, and secondly to the fact +hat the outer
surface of the pulverizer roll 18 is subjected to a harsh
~2123~5
_19_
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 50 be made of a relatively
soft, easily mach:nable material so as to facilitate the
formulation therein of the through passage 56. In
contradistinction to this, there is a need for at least the
outer surface, i.e., that encompassed by the intermediate
layer, i.e., portion 52, and fhe outer layer, i.e., portion
54, to be made of materials that are characterized by their
capability to resist wear, and in particular that kind of wear
which is occasioned by abrasive action.
Insofar as concerns the illustratTons that comprise
Figures 2 and 3 of the drawing, as was noted previously
herein, Figure 2 is simply intended to illustrate in a general
fashion the nature of the construction in accord with the
present Invention of the pulverizer, i.eO, grinding, roll 18.
Figure 3, on the other hand, Ts intended to illustrate a
grinding roll 18 constructed in accordance with the present
invention whereTn therein is depicted in exaggerated fashion
the fact that the outer layer, i.e., portion 54, embodies an
uneven thickness in contradistinction to the intermediate
layer, l.e., portion 52, whtch is of substantially uniform
thickness. More speciflcally9 the external surface of the
outer portion 54, i.e., that denoted by the reference numeral
58 in Figure 3 Ts provided with a specific configuration which
is intended to constitute a replication of the wear pattern
that a pulverization, i.e., grinding, roll 18 develops as a
consequence of its being utilized to effect the pulverization
of a material such as coal within a bowl mill 10. That is,
the external surface 58 of the outer portion 54 of the
grinding roll 18 is suitabiy configured such that those areas
thereof which based on past experience it can be anticipated
will be subjected to the greatest degree of wear are made to
have a thicker thickness of material, e.g., nihard, thereat.
The intent in doing so is to attempt to achieve a uniform wear
rate of the outer portion 54 by means of providing more
3~
~20-
material in those areas whereat it is expecfed that the roll
18 will experrience the most wear based on past experience
applied to the use to which the roll 18 is intended to be
put. To summarize, the outer portion 54 of the pulverizer,
i.e., grinding, roll 18 is 7ntentionally made to have a
nonuniform thickness such that more material is provided in
those areas whereat more wear is predicted to take place, and
less material is provided in those areas whereat less wear is
expected to occur.
Next, a description will now be had of the method by
which in accord wTth the present invention the pulverizer,
i.e., grinding, roll 18 is preferably manufactured. This will
then be followed by a description of the benefits that flow
from the use of a pulverizer roll 18 which embodies a trimetal
form of construction. Insofar as the method of manufacture of
the pulverizer roll 18 ls concerned, in accord with the best
mode embodiment of the invention a centrifugal casting process
is employed for this purpose. Proceeding with the description
of the subject method, in accord with the first step thereof
the requisite amount of material, e.g., Raymix, needed to form
the 7ntermediate portion 52 of the pulverizer roll 18 is
poured in known fashion into a suTtable mold. In accordance
with the known techniques of centrifugal casting, the Raymix
under the influence of centrifugal force moYes outwardly
within the mold and forms a layer thereof in abutting
engagement to the inner surface of the mold. Once the
intermediate portion 52 of the pulverizer roll 18 is formed,
the next step in accord with the subject method is to effect
the pouring into the mold of the requisite amount of material,
e.g., gray iron, to form the inner, i.e., body, portion 50 of
the pulverizer roll 18. In accord once again with fhe known
techniques of centrigual casting, the gray iron under the
influence of centrifugal force forms a layer in abutting
engagement with +he inner surface of the interme=iate portion
52. A suitable bonding agent is preferably utTlized to cause
the outer surface of the inner portion 50 to adhere to the
23~5
-21-
inner surface of the intermediate portion 52. After the
pulverizer roll 18 has been partially formed in the
aforedescribed manner, the partially formed roll 18 is removed
from the aforereferenced mold and the outer surface of the
intermediate portion 52 to the extent deemed necessary is
prepared for receipt thereon of the outer portion 54. This is
followed by the affixation of the outer portion 54 to the
intermediate portion 52. To this end, in accord with the best
mode embodTment of the method of manufacture of the present
invention, the outer portion 54 is provided in the form of a
weld overlay. Moreover, as described previously hereinbefore,
the outer portion 54 preferably is applied in the form of a
nonuniform thTckness of material such that the thicker
thickness thereof is located in those areas whereat it is
believed, based on the use to which it is known the pulverizer
roll 18 will be put9 the greatest wear will be experienced.
it is to be noted here that in accord with the method
described above, the through passage 56 is formed through
substantially the center of the body portion 50 during the
casting process. Thus, the need to machine such a passage 56
therethrough is obviated except for any minor machining that
may be required to prepare the passage 56 for the receipt
therein of the shaft-like member (not shown) on which the
pulverizer roll 18 is designed to be mounted in supported
relation thereto.
Attention will now be directed to the matter of the
benefits that flow from the use of a pulverizer roll that
embodies a trimetal form of construction. To this end, those
benefits which are to be found enumerated hereinafter are
presented by way of exemplification and not limitation.
First, the pulverlzer roll 18 by virtue of its trimetal form
of construction embodies a body portion 50 that is capable of
being made from a material that is relatively easy to work
thereby enabling economies of manufacture to be realized from
the use for this purpose of this material, e.g., gray iron.
; Secondly, the pulverizer roll 18 that embodies a trime~al
~lZ3~
-2Z-
structure has an external surface that consists of an outer
portion 54 which consists of a relatively hard, i.e., highly
abrasive resistant material such as nihard that is capable of
resisting the abrasive action produced in the course of
effecting the pulverization therewith of a material such as
coal. Moreover7 because of the fact that the outer portion 54
is provided with a thicker thickness of material in the areas
which are most subject to wear, the pulverizer roll 18 is
characterized by the fact that the outer portTon 54 wears more
slowly, i.e., wears more uniformly. That is, before the outer
portion 54 wears through in those areas which are subject to
the greatest wear, a more uniform wearing of the entire outer
portion 54 is realized.
In addition, it is most important to note here that
the external surface of the pulverizer roll 18 is not
composed of simply the outer portion 54. But rather the
external surface further comprises the intermediate portion
52, which also consists of a material having wear-resistant
qualities, e.g., Raymix. As a consequence, even when the
outer portion 54 is worn through, the pulverizer roll 18 still
remains serviceable in that the intermediate portion 52 is
also capable of performing the wear-resisting function. It is
of course true that the material which comprises the
lntermediate portion 52 ts not as hard, i.e., is not as
abrasive resistant as the outer portion 54. Nevertheless, the
pulverizer roll 18 is still capable of being used with the
intermediate portion 52 exposed, i.e., serving, as the
pulverizing surface. The significance of this is that
continued usage may be made of the pulverizing roll 18.
Namely, no longer is it necessary to immediately replace
pulverizer rolls when the outer surface thereof wears through
for fear of damagTng the roll, i.e., so to preclude the
resurfacing of the worn roll. In contradisttnction, with the
pulverizer roll 18 of the present invention it is possible
most frequently, to await the next scheduled shutdown of the
bowl mill 10 in order to effect the removal and replacement of
365
-23-
the roll 18 after the outer portion 54 thereon has worn
through. This is because the intermediate portion 52 serves
as an adequate surface to effect the continued pulverization
therewith of coal within the bowl mill 10. Normally, the life
of~the intermediate portion 52 Defore it also wears through is
such as to enable a sufficient period of time to expire to
reach the next scheduled shutdown of the bowl mill 10.
Another advantage that derives from the use of
d7ssimilar materTals for the intermediate portion 52 and the
outer portion 54 is that it is possible to visually recognize
when the outer portion 54 has worn through in one or more
places This visual indication is had by noting the different
appearance, e.g., color, etc. of each of the two dissimilar
materials, i.e., the Raymix of intermediate portion 52 and the
! 15 nihard of outer portion 54. To further enhance this visual
recognitton, it is possible to color with a suitable medium,
e.g., red paint, the outer surface of the intermediate portion
52 so as to prov7de the latter w7th a read71y viewable surface
before the outer port70n 54 7s affixed thereto.
In summary, not only does the pulver7zer roll 18
constructed 7n accordance with the present invention prov7de a
roll that has a measurably longer operat7ng life than do the
rolls wh7ch have heretofore been constructed in accordance
with the teachings of the prior art, but also the pulverizer
roll 18 7s characterized by the fact that even when the outer
port70n 54 thereof becomes worn through, by v7rtue of the
pressnce of the intermed7ate portion 52 cont7nued usage may be
made of the pulver7zer roll 18 for effecting the puiver7zat70n
of a mater7al without the roll 18 sustaining damage thereto.
This obv7ates the need to experience many of those shutdowns
of the bowl mill 10 which have been occasioned heretofore by
the need to accomplish the removal and replacement of a
pulverizer roll that had been constructed in accordance with
the teachings of the prior art. Lastly, by providing the
outer portion 54 with a nonuniform th ! ckness, addittonal wear
; is obtainable from the pulverizer roll 18 before the outer
~2~Z~65
-24-
portion 54 thereof wears through; namely, those areas of he
outer portion 54 which experience shows are subjected to the
greatest wear are provided with the thickest layer of
material.
Thus, in accordance with the present invention there
has been provided a new and improved form of pulverizer roll.
Moreover, the pulverizer roll of the present invention is
characterized in that it embodies a trimetal mode of
construçtion. In addition, in accord with the present
invention a trimetal pulverizer roll is provided that is
primarily intended to be employed in a bowl mill for purposes
of effecting the pulverization therewithin of a material such
as coal. Further, the +rimetal pulverizer roll of the present
invention is distinguishable by its relatively long operating
life. Additionally, in accordance with the present invention
a trimetal pulverizer roll 7s provided whTch has a first
portion thereof that is characterized by its ease of
machinability, a second portion thereof that is characterized
by the fact that 7t exhibits medium wear-reststant qualities,
and a third portion thereof that is charac-terized by the fact
- that it exhlbits htghly abrasive resistant qualities. Also,
the trimetal pulverizer roll of the present invention while
being readily employable in a bowl mill yet also enables
significant cost savings to be realized through the use
thereof insofar as -the operation of the bowl mill is
concerned. Furthermore, in accord with the present invention
a new and improved method of manufacturing such a trimetal
pulverizer roll is provided.
While only one embodiment of my invention has been
shown, it will be appreciated that modifications thereof, some
of which have been al!uded to hereinabove, may still be
readily made thereto by those skilled in the art. 1,
therefore, intend by the appended claims to cover the
modifications alluded to herein as well as all the other
modifications, which fall wlthin the true spirit and scope of
my invention.
What is claimed is:
