BACKGROUND OF THE INVENTION
[0001] This invention relates to rolls, and more specifically to a trimetal pulverizer roll
of the type that is intended to be used in bowl mills for purposes of effecting the
pulverization therein of material such as, for example, coal and to a method of manufacturing
such a trimetal pulverizer roll.
[0002] An essential component of any steam generation system of the type, which utilizes
pulverized coal as a fuel, is the apparatus in which the coal is pulverized in order
to render it suitable for such usage. Although the prior art is replete with examples
of various types of apparatus that have been employed for purposes of accomplishing
coal pulverization, one form of apparatus, which in particular has frequently been
used for this purpose, is that commonly referred to as a bowl mill. The latter obtains
its name principally from the fact that the pulverization, i.e., grinding, of the
coal that takes place therewithin occurs on a grinding surface, which insofar as configuration
's concerned resembles somewhat a bowl.
[0003] For an exemplary showing of a rrior 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 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 mitt are a body
portion, i.e., housing, within which a grinding table is mounted for rotation, a plurality
of grinding rolls that are supported 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 which is disposed on the surface of the grinding
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 the operation of the bowl milt.
[0004] 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 plurality 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 possessing the capability of operating at its maximum
capacity, each of these bowl mills 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 cf types of coal that
have dissimilar grinding characteristics.
[0005] 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 the center thereof. The function of this through
passage is to enable the shaft-like member to be positioned therewithin in mounted
relation thereto. Accordingly, in order to facilitate the task of providing the grinding
roll with such a through passage, it is desirable that the grinding roll be composed
of a material that is characterized by its ease of machinability, i.e., a relatively
soft material such as gray iron.
[0006] On the other hand, in addition to it being desirable to form the grinding roll of
a material that is relatively 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 characterized
by its good wear-resistant qualities. The primary reason for this is that the grinding
rolls in the course of effecting the pulverization of material therewith are of necessity
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 th,is pulverization takes place. The result, therefore, is that the grinding
rolls exhibit a susceptibility to being rendered unusable in a relatively short period
of time. That is, the rolls are found to have a relatively short operating life. For
obvious reasons, it is desirable that such a result be avoided, if possible. As is
known to those who are skilled in this art, the wear, which the grinding rolls that
are employed in bowl mills actually experience, is influenced principally by the 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 in
the bowl mill in a given period of time.
[0007] When the external, i.e., outer, surface of the pulverizer, i.e., grinding, roll becomes
sufficiently worn so as to preclude any further use thereof for purposes of effecting
the pulverization of material therewith, the remaining portions of the roll are normally
still functional. That is, 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 significantly less than the cost associated with the manufacture of an entirely
new grinding roll.
[0008] In addition 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 life which is achievable
with a resurfaced worn grinding roll as contrasted to that which is obtainable with
an entirely new grinding roll. Namely, in 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 obtain from a new grinding roll. That is, any savings
which are achievable from making use of a resurfaced worn grinding roll as contrasted
to employing an entirely new grinding roll should not be dissipated as a consequence
of the fact that the operating life of a worn grinding roll is such that several resurfacings
thereof are required in order to realize the same operating life that can be realized
with a grinding roll that is totally new. To summarize, if in the interest of obtaining
comparable operating lives, multiple resurfacings would have to be had of the worn
grinding roll such that the cost thereof would probably equal, if not exceed, the
cost of providing an entirety new grinding roll, then, the advantages accruing from
reusing a worn grinding roll vis-a-vis replacing the latter with a new grinding roll
would undoubtedly not be realized.
[0009] 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 providing the external surface of new grinding rolls with a
hard facing. Unfortunately, however, such attempts applied to new grinding rolls have
not heretodate met with much success.
[0010] 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 is that it
would enable the period to be extended between when shutdowns are required to accomplish
the removal of worn grinding rolls and the replacement thereof with new grinding rolls.
Furthermore, when consideration is given to the fact that each bowl mill normally
embodies three grinding rolls, each of which periodically must be removed and replaced
when it becomes worn, as well as the fact that a plurality of bowl mills are commonly
employed to provide the requisite amount of pulverized coal to a coal-fired steam
generation system, the magnitude 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 grinding rolls while concomitantly ensuring that the power generation system
retains the capability to provide continuous uninterrupted service should be readily
apparent.
[0011] In addition to the above there is also the matter of the expenditure of time and
effort along with the cost per se that is associated with the act of removing and
replacing a worn grinding roll. Obviously, therefore, if one were to be successful
in achieving a reduction in the freauency with which grinding rolls are required to
be replaced as a consequence of their having become worn, cost savings could be realized
în terms of the time and effort 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.
[0012] It is, therefore, an object of the present invention to provide a new and improved
form of pulverizer roll.
[0013] It is another object of the present invention to provide such a pulverizer roll which
is characterized in that it embodies a trimetat mode of construction.
[0014] It is still another object of the present invention to provide such a trimetal pulverizer
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.
[0015] A further object of the present invention is to provide such a trimetat pulverizer
roll that is distinguishable by its relatively long operating life.
[0016] 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 qualities, and a third portion thereof that is characterized by the
fact that it exhibits highly abrasive resistant qualities.
[0017] 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 mill is concerned.
[0018] Yet still another object of the present invention is to provide a new and improved
method of manufacturing such a trimetal pulverizer roll.
SUMMARY OF THE INVENTION
[0019] 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 operative
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 specifically, the subject roll incorporates
a first, i.e., inner, portion which 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 incorporates a second, i.e., intermediate, portion
of material that is suitably supported in adhered relation on the inner portion. This
intermediate portion, which is substantially uniform in thickness, is composed of
a material that is noted for its medium wear-resistant qualities such as a material
like Raymix, the latter being obtainable from applicant's assignee. Lastly, the subject
roll incorporates a third, i.e., outer, portion 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 provided with a thicker thickness of material. Finally
this outer portion is composed of a highly abrasive resistant material such as a weld
overlay material.
[0020] In accordance with another aspect of the present invention there is provided a method
of manufacturing such a trimetal pulverizer, i.e., grinding roll. The subject method
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
[0021]
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 with 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 invention; 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 the uneven nature of the
thickness of the outer portion of the pulverizer roll.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0022] Referring now to the drawing, and more particularly to Figure 1 thereof, there is
depicted therein a pulverizing bowl mill, 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 10, which
is illustrated in Figure 1. Rather, it is deemed sufficient for purposes of obtaining
an understating of a pulverizing bowl mill 10, which is capable of being equipped
with pulverizer rolls constructed in accordance with the present invention and manufactured
by means of the present invention, 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 10. For a more detailed description of the nature of
the construction and the mode of operation of the components of the pulverizing bowl
mill 10, 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 11, 1977 to C. J. Skalka.
[0023] Referring further to Figure 1 of the drawing, the pulverizing 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
aforedescribed 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.
[0024] Continuing with a description of the pulverizing bowl mill 10, a plurality of pulverizer,
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 hereinafter. First, however, note is made here of the fact that
in the interest of maintaining clarity of illustration in the drawing only one grinding
roll 18 has been shown in Figure 1.
[0025] As further regards the 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 with 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, generally designated in Figure 1 by reference numeral 20. Each
of the hydraulic means 20, as will be described more fully hereinafter, is operative
to establish a hydraulic loading on the grinding roll 18 that is associated therewith.
The effect of this loading is to cause the roll 18, which is subject thereto, to exert
the requisite degree of force on the coal that is disposed on the grinding table 14,
and thereby accomplish the desired pulverization of this coal.
[0026] The 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 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 member (not shown) is suitably shaped
so as to facilitate the collection 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 in 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 rotation, 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.
[0027] In accord with the mode of operation of pulverizing 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 pulverizing 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 the aforesaid opening (not shown) in the separator
body 12, the air flows to a multiplicity of annular spaces 32 suitably formed between
the circumference of the grinding table 14 and the inner wall surface of the separator
body 12. The air upon 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 application.
[0028] 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 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
the 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 particles, 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 inertia continue to be carried
along in the air stream.
[0029] After leaving the influence of the aforedescribed deflector means (not shown), the
combined stream consisting of air and those coal particles that remain 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-known to those
skilled in this art, the classifier 30 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 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.
[0030] 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 pulverization.
Thereafter, these coal particles are once again subjected to the process that has
been described above. That is, 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 I;ghter particles are carried along to the classifier
30, and finally those particles which are of tne proper size pass through the classifier
30 and exit from the bowl mill 10 through the outlets 34.
[0031] Considering further the matter of the pulverizing action to which the coal 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 pulverization 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 pulverize the coal will be a function of the grindability of the coal to be pulverized,
i.e., 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 output rate at which the
bowl mill 10 is being operated.
[0032] 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 mounted for
rotation on a shaft (not shown), is suitably supported so as to be pivotable 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 to 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.
[0033] Continuing with the matter of the force exerted by the grinding 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 the
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. Within 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 grinding .roll 18. A suitable opening 46 is 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).
[0034] 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 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 opening 46 of hydraulic fluid
from the cylinder 38 to the interior of the body 12.
[0035] By way of exemplification, the more the free end of the piston rod 42 extends into
the interior of the separatdr body 12, the more it will cause the member 44 to move
in a clockwise direction, as viewed with reference to Figure 1, about the pivot pin
36, and thereby have the effect of increasing the amount of grinding force that the
grinding 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.
[0036] 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
+he bowl mill 10 along with the coal that is 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,
i.e., 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 grinding roll 18.
[0037] Accordingly, the function of the accumulator 48 is to permit hydraulic fluid to flow
thereinto as the fluid is 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 grinding
roll 18 is once again restored to its normal position, i.e., nontransient condition.
This occurs by virtue of the flow from the accumulator 48 into the cylinder 38 of
the hydraulic fluid which had been made to flow into the former from the latter, because
of the counterclockwise movement, as viewed with reference to Figure 1, of the grinding
roll 18 about the pivot pin 36 caused by the raising of the roll 18 as the latter
engaged and passed over the foreign object located on the table 14.
[0038] For p
Jrposes of setting forth a detailed description of the structural nature of a pulverizer
roll 18 constructed in accord with the present invention as well as the method by
which such a pulverizer roll 18 is manufactured in accord with the present invention,
reference will now be had particularly to Figures 2 and 3 of the drawing. It is important
to take note here of the fact that Figure 2 in contrast to Figure 3 is intended to
simply provide a general illustration of a pulverizer, i.e., grinding, 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 particularly the specific details
of construction of a pulverizer roll 18 that is manufactured in accordance with the
present invention.
[0039] With the above as a frame of reference, it can be seen from Figures 2 and 3 that
the grinding roll 18 embodies a trimetat 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 material arranged in layered
relation to each other as well as to the body portion 50. To this end, one of these
two portions, i.e., that denoted generally by the reference numeral 52 in Figures
2 and 3 of the drawing, is suitably positioned in superimposed relation to 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 superimposed relation to the portion 52.
[0040] 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, with 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 capable of receiving therewithin in assembled
relation thereto the shaft-like member (not shown) to which reference has 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.
[0041] Next, with regard to the portion 52, i.e., the intermediate layer, with which the
trimetal pulverizer roll 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 portion
50 will be found set forth with more particularity hereinafter.
[0042] 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 invention, of a material that is characterized by the fact that it is highly
abrasive resistant. One material, which is 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 trimetal pulverizer roll 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.
[0043] 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
that the outer surface of the pulverizer roll 18 is subjected to a harsh 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 machinable 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 the 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.
[0044] Insofar as concerns the illustrations 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.e., grinding, roll 18. Figure 3, on the other hand, is intended to illustrate
a grinding roll 18 constructed in accordance with the present invention wherein 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, i.e.,
portion 52, which is of substantially uniform thickness. More specifically, the external
surface of the outer portion 54, i.e., that denoted by the reference numeral 58 in
Figure 3 is 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 suitably 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 material in those areas whereat it is expected 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 intentionally 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.
[0045] Next, a description will now be had of the method by which in accord with 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 is 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 intermediate portion 52 of the pulverizer roll 18 is poured in known fashion into
a suitable mold. In accordance with the known techniques of centrifugal casting, the
Raymix under the influence of centrifugal force moves 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 the known techniques of centrigual
casting, the gray iron under the influence of centrifugal force forms a layer in abutting
engagement with the inner surface of the interme iate portion 52. A suitable bonding
agent is preferably utilized to cause the outer surface of the inner portion 50 to
adhere to the 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 embodiment 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 thickness 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 put, 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.
[0046] 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 pulverizer 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 trimetal 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.
Moreover, 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 portion 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.
[0047] 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 intermediate portion 52 is 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
damaging the roll, i.e., so to preclude the resurfacing of the worn roll. In contradistinction,
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 the roll 18 after the outer portion 54 thereof 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 before 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.
[0048] Another advantage that derives from the use of dissimilar materials 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 nihard of outer portion
54. To further enhance this visual recognition, it is possible to color with a suitable
medium, e.g., red paint, the outer surface of the intermediate portion 52 so as to
provide the latter with a readily viewable surface before the outer portion 54 is
affixed thereto.
[0049] In summary, not only does the pulverizer roll 18 constructed in accordance with the
present invention provide a roll that has a measurably longer operating life than
do the rolls which have heretofore been constructed in accordance with the teachings
of the prior art, but also the pulverizer roll 18 is characterized by the fact that
even when the outer portion 54 thereof becomes worn through, by virtue of the presence
of the intermediate portion 52 continued usage may be made of the pulverizer roll
18 for effecting the pulverization of a material without the roll 18 sustaining damage
thereto. This obviates 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
thickness, additional wear is obtainable from the pulverizer roll 18 before the outer
portion 54 thereof wears through; namely, those areas of the outer portion 54 which
experience shows are subjected to the greatest wear are provided with the thickest
layer of material.
[0050] 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 construction. 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 trimetal 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 is provided which
has 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
qualities, and a third portion thereof that is characterized by the fact that it exhibits
highly 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.
[0051] While only one embodiment of my invention has 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. I, therefore, intend by the appended
claims to cover the modifications alluded to herein as well as all the other modifications,
which fall within the true spirit and scope of my invention.
1. A pulverizer roll of the type suitable for use in a bowl mill for purposes of effecting
the pulverization therewithin of a material such as coal comprising:
a.) a first portion formed of a material characterized by its ease of machinability,
said first portion having a through passage formed therein suitably dimensioned so
as to be capable of receiving therewithin a member operative for effecting the mounting
thereon of the pulverizer roll in supported relation thereto;
b.) a second portion formed of a material noted for its medium wear-resistant qualities,
said material of said second portion being different from said material of said first
portion, said second portion being adhered to said first portion in layered relation
thereto; and
c.) a third portion formed of a material noted for its highly abrasive resistant qualities,
said material of said portion being different from both said material of said second
portion and said material of said first portion, said third portion being affixed
to said second portion in layered relation thereto.
2. The pulverizer roll as set forth in Claim 1 wherein said material of said first
portion comprises gray iron.
3. The pulverizer roll as set forth in Claim 2 wherein said first portion comprises
a layer of substantially uniform thickness of gray iron.
4. The pulverizer roll as set forth in Claim 1 wherein said material of said second
portion comprises Raymix.
5. The pulverizer roll as set forth in Claim 4 wherein said second portion comprises
a layer of substantially uniform thickness of Raymix.
6. The pulverizer roll as set forth in Claim 1 wherein said material of said third
portion comprises nihard.
7. The pulverizer roll as set forth in Claim 6 wherein said third portion comprises
a layer of nonuniform thickness of nihard with the thickest thickness of nihard being
located at those areas of said third portion that are predicted to be subject to the
greatest wear.
8. The pulverizer roll as set forth in Claim 1 wherein the dissimilarity between said
material of said third portion and said material of said second portion enables a
visual recognition to be had of when said third portion has worn through.
9. A method of manufacturing a pulverizer roll having a trimetal form of construction
and of the type suitable for use in a bowl mill for purposes of effecting the pulverization
therewith of a material such as coal comprising:
a.) forming from a material characterized by its ease of machinability a first portion;
b.) providing the first portion with a passage extending therethrough substantially
at the center thereof;
c.) forming from a material noted for Its medium wear-resistant qualities a second
portion;
d.) adhering the second portion on the first portion in layered relation thereto;
e.) forming from a material noted for its highly abrasive qualities a third portion;
and
f.) affixing the third portion on the second portion in layered relation thereto.
10. The method as set forth in Claim 9 wherein the first portion is formed as a layer
of substantially uniform thickness of gray iron.
11. The method as st forth in Claim 10 wherein the first portion is formed by means
of a centrifugal casting process.
12. The method as set forth in Claim 9 wherein the second portion is formed as a layer
of substantially uniform thickness of Raymix.
13.. The method as set forth in Claim 12 wherein the second portion is formed by means
of a centrifugal casting process.
14. The method as set forth in Claim 9 wherein the third portion is formed as a layer
of nonuniform thickness of nihard with the thickest thickness of nihard being located
at those areas that are predicted to be subjected to the greatest wear.
15. The method as set forth in Claim 14 wherein the third portion is formed as a weld
overlay.
16. The method as set forth in Claim 9 wherein the second portion is adhered to the
first portion through the use of a bonding agent.
17. The method as set forth in Claim 9 wherein the third portion is affixed to the
second portion by means of welding.