Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IMPROVED FIX~D ROLLER PULVERIZING MILL
BACKGROUND OF THE INVENTION
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There are several common uses for mills which are used
to pulverize solids. One example is the pulverization of coal
to prepare it for firing in a furnace.
One type of mill, commonly known as a ball mill, as its
name implies, uses large metal balls to pulverize the material.
Ball mills ~re generally reliable but have several disadvanta~es.
For any given quantity of coal or other material to be pulverized
they are comparatively large and therefore require a rather large
capital expenditure. Further, they consume much energy in their
operation.
When a less expensive mill is required, roller mills
are often employed. Roller mills which are presently used to
pulverize coal generally employ several rollers which bear down
on a rotating table onto which the coal is fed to pulverize the
coal. In some designs, the rollers have flat tread portions
which tend to wear unevenly over a period of time. This results
in a pulverized coal in which the particulate size is not
uniform. Other designs have structure which urge the rollers
down against the rotating table in such a way that when the coal
be~ween the table and roller exerts an upward force on a roller,
the other rollers are jostled. The result is the creation of
vibration during operation and a consequent excessive degree of
wear and a loss of efficiency.
In other designs, the rollers begin to yaw a~ter a period
of operation because of wear in the parts which are designed to
guide the rollers. This creates excessive rolling frictiQn so that
the rollers often skid over the table rather that roll over it.
When this happens, the skidding roller is not pulveri~ing the
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coal properly! and consequently the efficiency of the mill
quickly deteriorates.
SUMM~RY OF TXE IN~EN~ION
The present invention seeks to overcome drawbacks
found in the prior art such as those discussed above.
Accordingly, a roller mlll is provided with a rotating table
and a plurality- of rollers whlch bear down on the table at
a circular trough therein. Each of the rollers are individ-
ually spring biased down against the table so that movement
of the axis of rotation of one of the rollers will not affect
any of the other rollers.
More particularly, the inYention pertains to a
pulverizing mill including, an outer shell, a table rotatably
mounted within the outer shell, the table having an annular
track including an annular recess and means for rotating the
table. Means are provided for placing material to be pulverized
on the table and a plurality of rollers, each having a tread
portion bearing on the table are within the recess. Each of
a plurality o~ supports, each having one of the rollers
rotatably mounted thereon, is pivotally secured to the outer
shell and a plurality of spring means, each engaging one of
the supports but supported independently thereof, urges the
associated roller toward -the table.
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BRIEF DESC~IPTION OF THE DR~INGS
Fi~ 1 is a side view partly in section showing a
pulverizing mill made in accordance with the present
invention, and
Fi~ 2 is a view partly in section and in larger
scale than is Fig 1 showing a detail of the preferred embodiment.
Fi~ 3 is a plan view partly in section taken
substantially along the line 3-3 of Fig l; and
Eig 4 is a view showing certain parts of the
present invention positioned for servicing.
DETAILED D:æSCRIPTION OF THE PREFERRED EM~ODIMENT
Eig. 1 shows a coal pulveriziny mill indicated
generally as 10 having an outer shell 12 which has an upper
portion 14, which is joined to a middle portion 16 at a flange
seam 17 and a lower portion 18. The shell 12 is mounted on
a platform which in turn is supported on legs 22 and 24 which
extend upwardly from footing 26 and 28 respectively. Located
within the shell 12 is a circular table 30 which is mounted
as by bolts 32 on a wheel 34 which is rotated by a motor 36
directly ~elow the wheel 34. The tahle 30 which has
a hollow center portion 38 includes an annular
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trac~ 40 of wear resistance material which may be hard steel.
The track 40 is recessed at 42. A cover 44 bridges the hollow
center portion 38 to prevent particulate matter from entering the
hollow portion 38.
The cover 44 is secured to the table 30 by bolts 45 and
the annular track 40 is secured to the table by bolts 48 so
that the cover 44 and track 40 rotate with the table 30 when it
is turned by the motor 36.
- Unpulverized coal is introduced into the mill through
a coal pipe S0 which extends down through the top 52 of the mill
10 to a location above the center of the table 30. The coal
falls on the table to be moved radially outward by centrifugal
force to the annular track 40. The coal then passes ~etween the
track ~0 and rollers 54, wh-ich bear down on the trac~ 40, within
the recess 42. Although the preferred embodiment employs several
rollers 54, only one is shown in Fig l for the sake of
simplicity.
The roller 54 has a tread portion 56 which is curved in
cross section so that it has the shape of the outer portion of a
torus. The tread 56 is the peripherial surface of a tire portion
58 which is made of hardened metal and which is secured to a
wheel portion 60 positioned within the tire portion 56. The
roller 54 includes an outer race 62 which rotates about bearings
64 which in turn rotate about an axle 66. The axle 66 includes
a jGurnal portion 68 which in effect forms the inner race for the
bearings 64 and an increased diameter portion 70 positioned
bet~,Jeen the journal portion 68 and a tapered portion 72. The
tapered portion 72 is integrally connected to the end of a shaft
portion 74. The axle 66 is mounted rigidly with a support 76.
The rigid connection between the axle 66 and the support 76 is
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accomplished by a press fit between the support 76 and the
tapered portion 72.
The shaft portion 74 is of a diameter small enough to
define between it and the support 76 an annular cham~er 78 which
is supplied with seal air of sufficient pressure so that air
will flow Lrom the chamber 78 through a port 80 to an annular
space behind a co~er 82 so that air will constantly flow out from
between the cover 82 and the wheel portion 60 of the roller 54.
This will prevent coal dust from getting into the bearings 64.
Seal air is provided only at the outer side at the roller 54
because the inner side can be protected by a cover 83 which is
fixed to the wheel portion 60 to prevent coal dust from entering
the bearings from the inner end of the wheel 54.
The wheel support 76 is mounted on a shaft 84 which
at each of its ends is rigidly fixed to and concentric with a
sleeve 86 as shown best perhaps in Fig 2. The sleeve 86 is force
fitted onto the shaft 84 and is itsel~ encircled by a flexible
bushing 88 which is force fitted on the sleeve 86. An outer
sleeve 90 is force fitted around the flexible bushing 88 and is
itself fitted in a journal 91 and secured therein again~st rotation
as by welding. The journal 91 is mounted in an opening in the
outer shell 12 and secured thereto by bolts 92, as shown in Fig
2 and 3.
The seal air is supplied through a channel 93 in the
shaft 84, and escapes through openinys therein within the support
76 SG that seal air will flow into the chamber 78.
It has been explained that the support 76 is biased
downwardly against the table 30. To this end the support
includes an upwardly extending lug 94 which is acted upon by
plungers 9~ each of which is slideable mounted within one ot
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two spring housings 98. Each spring housing 38 includes at one
end a circular plate 100 having a centrally located opening
througn which projects the plunger g6. Both spring housings g8
are shown in Fig. 3 while one is shown in section in Fig. 1.
The spring housings 98 are fixed to the outer shell 10
at an access door 102 and are spaced apart in a direction
perpendicular to the axis of the associated roller 54. Also
within each spring housing 98 is an axially moveable spring
base 104. Coil spring 106 is positioned between the plunger 96
and the spring base 104 to urge the plunger 96 against the lug
94.
It has been explained that coal introduced through
the coal pipe 50 passes between the roller 54 and the table 30.
It is desirable that the roller 54 be allowed to oscillate
vertically to allow for non-uniform distribution of coal below
it and for variation in the particulate size of the coal being
pulverized. This is possible because the flexible bushing 88
allows the shaft 84 to oscillate with respect to the journal 91
so that vertical movement of the roller is facilitated by a
pivotal action of the support 76 about the axis of the shaft 84.
Upward mo~ement of the roller 54 will be resisted because as
the roller 54 moves upward, the lug 94 will move the plunger 96
to the right (as shown in Fig. 1) against the action of the
coil spring 106.
It is desirable to be able to adjust the force exerted
on the lug 94 by each of the coil springs within spring housings
98 at the time when the roller 54 is bearing directly against
the table 30 that is when no coal is between the roller 54 and
the table 30. This is so because when no coal is being pulver-
ized, excessive wear will result if the roller bears down di-
rectly agains-t the table 30 with excessive force. Adjustment of
, -~ the force exer-ted by the coil sprincJ 106 when the roller 56 is
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bearing directly on the table 30 is controlled by means of a
shaft 108 which is secured to the plunger 96 and which is
threaded through a sleeve 110 which in turn is threaded through a
bushing 112 which is secured to the access door 102. The oushing
112 is fixed to the spring base 104 so that axial movement of the
bushing 112 will move the spring base 104 axially within the
spring housing 98.
The bushing 112 can be turned by means of a turning nut
114 which is secured to it. The shaft 108 can be turned by means
of a turning nut 116 which is fixed to the shaft 108.
When it is desired to adjust the spring force, which is
applied against the lug 94 when the roller 54 is bearing directly
against the table 30, the nut 116 is rotated. Rotation of the
nut 116 turns the shaft 108 and since the shaft is threaded with
the sleeve 110 the shaft 108 is moved axially. This-moves the
plunger 96 axially. It is possible to adj~st the plunger 96 so
that it just touches the lug 94 when the roller 54 is bearing
directly on the table 30, that is, when there is no coal on the
table 30 under the roller 54. It is also possible to adjust the
plunger 96 so that there is a gap between it and the lug 94.
After the plunger 96 has been adjusted as desired, a
locking nut 118, -~hich is threaded to the shaft 108, is tightened
against a bushing 120 which is positioned bet-~een locking nut 118
and the turning nut 114.
At times it is desirable to adjust the position of the
spring base 104. For example, it may be found that for particular
coals the force exerted on the roller 54 by the spring 106 at any
given position of the roller 54 should be increased or decreased.
This is made possible by turning the turning nut 114 to move the
sleeve 110 axially in the desired direction to position the
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spring base 104. The sleeve 110 and the spring base 104 are fixed
in position by means of a locking nut 122 which is threaded on
the sleeve liO and is turned against washer 124 which bears against
the bushing 112. After the spring base 104 is positioned, the
plunger 96 can be adjusted in the manner previously described.
Coal drops down the coal pipe 50 to impinge on the
cover 44 and move radially outward because of the centrifugal
force exerted by the rotating table 30. The coal passes into
- the recess 42 to be pulverized by the rollers 54 which are
rotating over the coal within the recess 42. The shape of the
tread portion 56 of each roller 54 and the shape of the recess 42
tend to confine for a time the coal which is between the roller
54 and the recess 42 so that particles which are not contacted by
the roller 54 and table 30 are exposed to pressure. The pressure
is high enough to break down coal particles and thus
pulverize them even when they are not contacted directly by the
roller 54 and table 30.
The pulverized coal is blown upward by air which is
introduced through a conduit 126. The air flows through an
20 annular air chamber 128 and then up through air ports 130 into
the space within the outer shell 12 above the table 30. The air
then moves the pulverized coal upward in the direction of arrows
"A" to pass through a series of vanes 132 which impart rotation
to the mixture of air and coal around the longitudinal axis of
the coal pulverizing mill 10. This acts as a centrifugal
separator in that the heavier particles are thrown outward and
eventually drops down in a housing 134 in the direction of the
arrows "B". These coarse particles drop through doors 136 which
are hinged and free to move inward as shown in phantom line under
the weight of the coarse particles. The doors help prevent
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pulverized coal moving upward in the direction of the arrows "A"
from passing into the housing 134.
The fine particles move inward and are entrained in air
moving in the direction of the arrows "C" to pass up through a
coal collector 138 defined by a vertical annular plate 140 which
is concentric with and joined to the bottom of an outwardly flared
plate 142. The mixture consisting of air and coal fines passes
upward through the top 52 to a conduit which is not part of the
present invention and which conveys the mixture of pulverized
coal fines and air to the point of use which may be a coal fired
steam generator.
In practice some particles are large and heavy enough
after passing over the table 30 that they cannot be raised by the
air rushing upward from the air ports 130. Such particles are
actually dropped down through the air ports 130 into the chamber
128. They then drop down through chutes 144 and 1~6 to be recycled
into the coal pulverizing mill 10.
When it is desired to service the roller 54 or any of
the parts associated with the support 76, bolts 148 and 150 are
removed so that access door 102 can be swunq outward. The access
door 102 has fastened to its lower end a hinge element 152 which
is rotatably connected to a hinge element 154 secured to the
middle portion 16 of the outer shell 10. Rotation of the access
door 120 outward and downward will move the spring housing 98
as well as the plunger 96 and other elements within the spring
housing 98 outward away from the interior of the coal pulverizing
mill 10. Any roller 54 can be swung out if its associated
journals 91 are removed. As shown in Fig 3, journals 91 are each
positioned between an opening which e~tends into a side of the
30 access door 102 and the main body of the middle portion 16 of the
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outer shell 12. In other words, the journal fits within a
semicircular opening in the access door 102 and a corresponding
semicircular opening the middle portion 16 of the outer shell 12.
Fig 4 shows a roller 54 and its associated supports
76 moved out for servicing. The support 76 has been provided
with a bracket 160 which may be secured to it by bolting or
welding or any other method. Similarly, the associated spring
housing 98 has been provided with bracket 162. The brackets 160
and 162 are fastened together by a bolt 164 which is secured to
the bracket 160 by nuts 166 and 168. Similarly, the bolt 164 is
secured to the bracket 162 by nuts 170 and 172. When the support
76 is so secured to the roller 54, outward movement of the access
door 102 will cause the spring housing 98 and the associated
support 76 and roller 54 to move outward.
Fig 4 shows a suitable apparatus 170 for moving the
access door 102 out. It will not be described in detail because
it is nota part of the present pulverizing mill 10.
Further, a crane 172 can be used to provide additional
support as the access door moves out and additional support is
needed as the center of gravity of the access door, support
76 and roller 54, move out beyond the hinge about which the
access door is pivoted.
Fig 4 shows at 174 the semicircular opening in the
middle portion 16 of the coal pulverizing mill 10 in which the
shaft 84 is supported at one of the ends thereof. The shaft 84
and its associated journal 91 must be moved out of the semi-
circular o~ening 174 and the corresponding semicircular opening
174 in the associated journal 91 (not shown) to allow the support
76 to move to the position shGwn in Fig. 4.
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Once in this position, the roller 54 can be serviced. ~or
instance, if excessively worn, the roller 54 can be replaced.
The bearing 64 can be cleaned and lubricated as desired.
~ he foregoing describes part one preferred embodiment
of the present invention other embodiments being possible
without exceeding the scope of the present invention as desired
in the following claims.
