Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGROUND OF THE INVENTION
My invention relates to the production of pulp from fibrous
ligno-cellulose materials, such as wood chips and other fibrous
vegetable materials and more particularly to pulplng processes
which are generally termed "mechanicalprocesses" in which the
ligno-cellulose material is fiberized between the grinding discs
of a refiner. ^~
1 ~
~6;~4(~5
The refiner discs may be of the counter-rotating kind, or
one of the discs may rotate while the other one is stationary.
In the latter instance, the raw material is fed through the
center of the stationary disc into the space between the discs,
and, by the action of elements affixed to the rotary grinding disc,
the material is accelerated and, by centrifugal forces, finally
conducted in between the grinding elements of the grinding zone.
The pulp produced is mainly intended for use in the manu-
facture of newsprint, cardboard, tissue paper and similar products,
and fibrous ligno-cellulose materials from wood or other plants,
e.g. bagasse, may be used as raw material. The method used can
. .
be classified as a mechanical process and can be carried out under
normal atmospheric conditions or in a steam atmosphere at temper-
atures above 100C, generally at a temperature between 110~ up
to 140C, or, under special conditions, in the temperature range
between 150C and 170C. When the mechanical process is carried -
out at a temperature above 100C, it is generally classified as
"thermomechanical".
S~$MARY OF THE INVENTION
One of the purposes of the invention is to improve the pro-
duction of pulp in such a way that the fibers of the raw material
are separated from each other without being unduly shortened and
so that the fibers are further refined to improve their paper-
making properties, this process being accomplished by frictional
forces generated within the moist fibrous ligno-cellulose material.
In the following, the material being processed between the grind-
ing discs will be called "grist". As the individual fibers in
the "grist" have a considerable springiness, the grist will de-
velop a considerable volume of capillary voids increasing its
capability to hold moisture.
A further purpose of the invention is to reduce the energy
required for the pulping process.
During the process of refining, the grist is a moist agglom-
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634(?5
eration of the processed raw material, which, if it is of conif-
erous origin, e~g. spruce, consists mainly of 2mm. to 3 mm. long
tracheids with a slenderness ratio of around 100 to 1. The trach-
eids in their turn are anatomically built up from three concentric
layers of lamellae with a thickness of about one-thousandth of
one millimeter and a layer of fibrillae helically arranged around
a fourth lamella surrounding the innermost tubular space, the lu-
men. The fibril has a slenderness ratio of about 1000 to 1, but,
taken together, it is estimated that they constitute about 70% to
80% of the substance of one tracheid. One of the objects of my
invention is to separate with a high degree of efficiency the fi-
bers from each other and, furthermore, by a surface abrasion pro-
cess, to affect the lamellae to such a degree that the fibrils are
partially liberated. This improves the papermaking properties of
the pulp produced.
In the apparatus according to the invention, the grist is
introduced between grinding discs of a refiner. Each disc is e-
quipped with a series of pockets separated by radially arranged
bars forming pockets displaced leng~hwise relatively to each other ;
in the opposing grinding rings. The pockets have a curved form in
cross section, which, at least in the stationary grinding disc,
gives the pocket the form of a circle segment. The grist enters
the rotating pockets through the gates and is acted upon by centri-
fugal forces. At the centrally innermost rotating pocket, the
grist is deflected by the rotating surface axially towards the sta-
tionary disc to cause the grist to pass through friction surfaces
which are formed by the interaction between the bars of the ro-
tating and the stationary discs, whereafter the grist is forced into -
the opposing pockets in the stationary grinding discs, where it be-
comes compacted with the fibers oriented principally parallel in
a radial direction at a right angle to the bar. The grist collect-
e~ in the stationary pockets will form a relatively compacted body, -
a portion of which is caused by successive deposits of grist from ~ -
--3--
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.. ~ : - , . ,
1()634~5
the rotating disc to gradually tilt over into the rotating pocket
of the rotating disc. The latter portion of the grist collected
- in the stationary pocket will then be successively sheared off
by the bars of the rotating disc. The friction surfaces generated
in the compacted grist by the rapidly moving bar create forces of
very high intensity which will act on ~he individual fibers to
mechanically refine the grist. The grist will in this manner be
conveyed outward stepwise in a radial direction between the rotary
and stationary pockets. Each time a portion of the accelerated
grist is transferred from a rotating pocket into an opposing sta-
tionary pocket, the velocity of the grist is reduced to zero. The
kinetic energy of the moving grist is transformed into a mechanical
force which will compact the grist in the stationary pocket effic-
iently. When the grist comes to a full stop, this kinetic energy
will have raised the temperature of the grist 3C-5C depending
uopn the angular speed of the refiner disc. This compacting force
~ will greatly enhance the formation of frictional surfaces between
`~ the bars and the grist and within the grist. - -~ -
The curved bottom of the pockets is shaped so as to efficient-~
. 20 ly change the direction of the flow of the grist axially. The
grist in these pockets may move with a tangential velocity of 50
m/sec to 120 m/sec, depending upon the size of the refiner. The
frictional surfaces generated within the grist will delaminate and
?,
~ fibrillate the fibers of the raw material.
-~ 25 BRIEF DESCRIPTION_OF THE DRAWINGS
My invention will be understood by reference to the accompany-:
ing drawings, which form a part of this specification and show var-
;i ious forms of apparatus by means of which the process may be car-
ried out.
Fig. 1 is a vertical view partly in section of a refiner ac-
cording to the invention.
-, Fig. 2 is a sectional view of a part of Fig. 1 in a larger
` scale.
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1(~63405
Fig. 3 shows in perspective a part of the grinding disc ac-
cording to the invention, with the portion parallel to the central
axle of the refiner shown in section~
Fig. 4 shows an axial section through the refiner disc.
Figs. 5A-5C show a section along the line V-V in Fig. 3.
Fig. 6 shows a vertical section through a refiner disc
according to a modified embodiment of the invention.
DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION
On the drawings the numeral 10 designates the housing of the
refiner carrying the stationary grinding disc 12. This grinding
- disc works together with the grinding disc 16 fixed to rotating
shaft 12 driven by motor (not shown). The shaft 14 is on each side
'~.` of the grinding disc 16 supported by bearings which also are not
- shown on the drawings. In the stationary grinding disc 12, there
are three grinding zones 18, 20 and 50, concentrically arranged. -
Likewise, the grinding disc 16 has three concentrically arranged
~ zones 22, 24 and 30. Three grinding zones are thereby formed,
`~ namely, one between the elements 18 and 22, in which a prelimin-
ary crushing of the admitted raw material, for instance wood chips,
takes place. In a second zone formed by the grinding elements 20
and 24, a further coarse defibering takes place before the grist
passes into the third grinding zone 30 and 50 of the grinding el-
ements according to the invention. The two innermost grinding
zones can be equipped with elements and ribs according to formerly
~i 25 known designs.
~, . .
` The raw material, e.g,, chips from wood or other fibrous
ligno-cellulose ~aterial, is fed through an opening 32 in the hous-
; ing 10 and is conveyed therefrom by a helical screw 34 equippedwith flights 36 through the openings in the central parts of the
stationary and rotating grinding discs. A central ring 38 with
.
flights 39 is fastened on the rotating disc 16 to convey the chips
further towards the first grinding zone.
According to the invention, in the third grinding zone, the
:,1 .
; ~ 5
6;~4()S
two grinding elements 30 and 50, preferably carried out as circle
rings with the grinding surfaces opposing each other, are equipped
with bars for~ing the radially arranged pockets 41 to 46, in the
ring 30, and 61 to 66 in the ring 50.
S A minor variation from the radial direction of these pockets
can be accepted. The pockets of the rotating disc should be form-
ed so as to assist in diverting the grist moving in the pockets
sideways from a radial to an axial direction. The curved bottom
of the pockets in the stationary discs should preferably have the
. lO form of a circle segment.
The two circular rings 30 and 50 of the grinding discs have
been machined to form radial or nearly radial grooves. These
;- grooves should preferably have perpendicular radial extensions
which are rectangular in cross-section. In circular ring 30 of the
: 15 rotating grinding disc, the six pockets are designated by numerals
41-46. They are formed by the bars 47 and grooves recessed in the
circular rings. In the embodiment shown, the pocket 41 serves as
- an entrance. The number of the following pockets can, if desired, ~-
`~ be varied within considerable limits. The pockets of the station-
'l 20 ary disc are designated by the numerals 61-66, and the separating
bars, with numeral 67. The pockets are walled in at the sides by
the flat bars 67. This can be observed in Fig. 3. The bottom of
`.i the stationary pockets 61-66 should have the form of a circle seg-
-, ment. The geometrical center of these segments should be at a -
', 25 point which is somewhat sbove the edge of the bars defining the
radial sides of the pocket. Otherwise, the movement of the body
~ of the grist will be hampered. The rotating pockets 42-46 can
`~ have the same form, but, in the section shown, this pocket has
been extended somewhat to increase its cross section, giving it
, 30 a larger volume than that of the semi-circular segments of the
stationary disc~ This can be seen in Fig. 4. The series of pock-
ets in the two grinding discs are radially offset relative to
each other, for instance, one-half the length of a pocket. The
. 6
~' .
... . ~ ,..... . .. . .. ~ . ~ . . -
~63~05
grist is introduced through a gate 40 which forms the entrance of
the innermost pocket 41. The outermost pocket 66 of the stationary
grinding element is open to allow the ground fibrous pulp or the
girst to be discharged into the housing of the refiner,
The bars 47 and 67 radially separating each pocket as shown by
the numerals 51 and 52 in Fig. 4 should be made from a material hav-
ing considerably higher abrasion resistance than the material of the
circular rings 30, 50. These pockets extend to the surface of the
narrow edges of the bars 47 and 67. The distance between the grind-
ing surfaces of the rings 30 and 50 in axial direction is regulated
- by the axial adjustment of the refiner shaft. This is often done by
hydraulic servo-motor which in some cases may be adjusted to exert
an axial pressure of 30 tons to keep the grinding space constant.
The distance may vary between 0.5 mm down to 0.05 mm, or even less,
to obtain the desired refining effect. A distance of 0.8 mm has
been used for special pulps. The servo-motor should preferably be
able to keep this grinding space constant within a margin ofO.01 mm.
As an example of the actual design of a 50" refiner equipped
according to the invention, may be mentioned that the rotating cir-
cular rings 30, 50 may have an outer dia~leter of 1270 mrn and an in- --
ner diameter of 1016 mrn. The rotating "grinding disc" or the "ro-
tor" 16 is designed to be driven with a speed of 1500 rpm to 1800
rpm. The individual pockets 41 to 46 may have a width of 0.33 cm
and a cross-section of 1.5 cm2, which gives a volume of 0.57 cm3.
The bars may have a thickness of 3 mrn and a width of 15 mm and a
.
length of 127 mm. Such a disc may, around the circumference, have
504 bars arranged in 72 groups of 7 parallel bars, creating scissor-
` like cuts instead of the long parallel cuts obtained when the bars
are all radially arranged. In the stationary disc 50, the pockets
;~, 30 and bars can be arranged in substantially the same way as in the
rotating disc 30e The grouping with parallel bars contributes to a
more even distribution of the angular torque during operation. Such
`` parallel arrangement of ~he bars in groups also sirnplifies the ma-
- chining of the ~rinding elements 30 and 50 by allowing a greater
~7~
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634~5
number of slots to be milled in one operation.
The refiner operates as follows~ In the first zone formed
by the elements 18 and 22, the raw material, e.g., the wood chips,
is fragmented with moderate energy consumption. In the second
grinding zoneJ the material is further broken down between the el-
` ements 20 and 24. The grist may then have a "freeness" of 800 ml
determined according to the "Canadian Standard Freeness" method -
(CSF). The grist then is introduced through the gate 40 and enters
- pocket 41 in the rotating grinding ring 30. The exit part 48 of the -
pocket 41 now directs the grist laterally toward the innermost pock-
et 61 of the stationary grinding disc 50. The grist then alter-
nately passes between the pockets of the rotating and stationary
~"` discs until finally leaving the grinding zone from pocket 66. ~ ~
- In Fig. 4, it is shown how the pockets in both grinding discs -
are in open communication with each other corresponding to the po-
sition shown in Fig. 5A. When the grinding disc moves in the di-
~'J rection indicated by the arrow 31, the bars 47 move from the po-
sition shown in Fig. 5A, where the pockets are in full open com-
munication with each other. In Fig. 5B, this communication is
. ......................................................................... .
closing, and, in Fig. 5C, the communication is fully closed, with
~, the exception of the narrow grinding space set by the hydraulic
servomotor controlling the axial position of the rotating shaft.
In this manner, any specific pocket in the stationary disc is passed
by 10800 pockets in the rotating disc every second, corresponding
~d 25 to one-tenth of a millisecond for each pocket to pocket communi-
^~ cation. Despite this short dwell time, the flow of grist from the
1 pockets in the rotating disc to the pockets in the stationary disc
;~ is not clogged, This can be observed if the flow of chips fed to
-, the refiner is shut off and the refiner disc is brought to a stand-
still~ When the refiner is opened for inspection, the pockets of
.:,
the rotating disc are found completely empty. When the propelling
action of the grist coming from the rotating disc has ceased, pulp ~-
will remain in the stationary pockets.
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, ~ .. . ~
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1~63405
The grist coming from the pocket 41 moves with very high
velocity, around 82 m per second~ and has thus acquired a consid-
erable quantity of kinetic energy of motion. When the grist is
projected into the stationary pocket, it exerts a considerable
mechanical pressure on the grist already collected therein, com-
pressing it to a density of about 0.79 g per cm3. The internal
friction created when the edge of the next oncoming bar cuts into
the body of grist provides the required refining effect. This ac-
tion can be modified by the setting of the distance between the
grinding discs~ e.g., when pulp for newsprint is produced, a dis-
tance between 0.1 mm and 0.2 mm may be used. When tissue paper is
produced, a distance of 0.3 mm to 0.5 mm may be used. Pulp for egg
containers may be produced with a setting of up to 0.7 mm.
When the grist from the rotating pocket 41 is pressed against
the mass of grist collected in the stationary pocket 61, as shown
: by the arrow A in Fig. 4, a wedge-shaped portion of this mass will
"tilt" into the pocket 42. This portion will then be "shaved off"
by a bar 67 and subsequently accelerated by the centrifugal force
and finally deflected into the pocket 62.
Each time the grist is arrested, the kinetic energy of ro-
tation is transformed into heat, raising the temperature of the
; grist. As the temperature of the grist affects the quality of the
` pulp, it is of certain importance to counteract these fluctuations.
~ As the whole process of refining is carried out at a temperature
-~ 25 very close to the boiling point of water, whether this is done un-
^, der atmospheric conditions or under steam pressure in a pressur-
-,` ized refiner, this heat will also cause evaporation to such an ex-
tent that the moisture content of the grist may be reduced. As
the intensity of the shearing forces developed in the friction
surfaces within the body of grist is highly dependent upon the a-
mount of moisture present, the water evaporated must, therefore,
~ be compensated for. This is done by injecting an appropriate a- ~
: mount of water, e.g., through the conduit 55. -
The grist diverted from the pocket 41 has a velocity of about
~ B -9- ~ ~
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. - ........... . - . .. ..
` ~6~405
80 m/sec, giving it a centrifugal acceleration of 1330 g, and -
is pressed against the grist in the pocket 61, where it comes to
an instant stop. The stationary pocket 61 is filled with com-
pressed grist with the fibers oriented perpendicularly to the bars.
The kinetic energy of the grist is converted into heat, which
evaporates moisture. This transfer is repeated each time the pock-
ets in the two grinding discs open into each other. When the bars
47 shear through the compacted grist, frictional surfaces are de-
veloped between which the fibers are separated from each other
and fibrillated. The power from the driving motor is thus trans- -
ferred to the grist by means of the bars 47 to kinetic energy of --
rotation by centrifugal acceleration of the grist on the order of
1000 g to 1500 g. By directing the flow of grist, it is possible - ~ -
.~i to develop the internal frict.onal forces necessary to effect the
fiber separating and obtain the desired fibrillation.
It has been mentioned that each time a communication takes
place between the pockets 41 and 61 of the rotating and the sta-
~ tionary pockets as shown in Fig. 5A, a new quantity of grist is
;.,i transferred to the pocket 61. It has also been mentioned that the
grist compacted in the stationary pockets, thanks to its geometri-
j cal form of a circle segment, will pivot in the pocket around its
-' geometrical center point 49 of the sector, as indicated by the
~, line 69 in Fig. 4. This means that the flow of grist through the
refiner is maintained as long as new material is supplied through
1 25 the gate 40 to the pocket 41. This in turn implies that, when
-~ grist is continuously supplied to and compacted in the entrance ;
part of the stationary pocket 61, a corresponding quantity of ~-
grist is pressed out and sliced off from the exit part of the
pocket 61 into the pocket 42 of the refining member 30 of the ro- ~-
-~ 30 tating disc. During the passage to this pocket, new friction
surfaces will be developed within the grist as the rapidly moving
bar 47 cuts through the compacted body of fibrous grist which is
, prevented from being passed into pocket 42 by the bar 67. In
this manner, the grist will alternately move between the moving
B
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.. . . ~ ~ ... . . . . .. .. - `
,.. . . . . .~ . . . . .. ... . . . .
6~40S
and the stationary pockets until it finally leaves the stationary
member 50 through one of its exits 66 at the periphery of the
grinding disc.
Depending upon the adjustment of the distance between the
grinding discs and also upon the relative quantity of grist carried
in the stationary pockets, a portion of the grist may pass di-
rectly radially from the pocket 41, passing through surfaces of
friction developed by an edge designated by the numeral 51 in
Fig. 4.
In Fig. 5A to 5C, it is shown that, when the bars 47 pass by
the bars 67, the passage between the pockets of the rotating and
moving members of the refiner is alternatley opened and closed.
In a 50" refiner, which herein has been used as an example, this is
repeated for each bar with a frequency of nearly 10,000 times per
second. The bodies of grist emerging from the stationary pockets
have then been acted upon by forces varying between a magnitude of
a few kg per cm2 to zero, which accomplished the transfer of the
grist through the pockets. This vibratory effect also assists in
compacting the grist so as to make possible the development of
frictional forces of high intensity as the grist passes from a sta-
tionary pocket to a rotating pocket.
The distance between the opposing narrow edges of the bars
: of the rotating and stationary refiner members in Fig. 5A, numbered
` 47 and 67 respectively, corresponds to the "refiner disc distance",
an important operating factor of the refiner, depending upon oper-
ating conditions, type of raw material and type of fibrous pulp
desired. In some cases, when a very finely refined pulp is de-
:;
sired, the distance may even be reduced to 0~05 mm, but, in such
a case, the capacity of the refiner is reduced. Pulp of a CSF -
freeness of down to 2 millimeters may then be produced,
~` The grinding disc distance will in most cases be a multiple
of the diameter of a fiber of most vegetable raw materials which,
:~ e.g., for the tracheids of spruce generally is around 0.02 mm and
0.03 mm. A direct cutting of the fibers between the surfaces of
,,
.- ~ . ................. - . ., .... . - . . - ~
. .
~(~634(~5
` the leading edges of the bars of the refiner, therefore, is not
possible. The grist is refined by the interaction between the
edge of the bar and the body of compacted grist. The mechanical
effect on the fiber is, therefore~ dependent upon the state of the
frictional forces developed within the grist. This is, of course,
in turn dependent upon the mechanical stability of the refiner,
which should be rigid enough to prevent direct metallic contact
' between any surfaces of the grinding discs.
To accomplish a separation of the fibers from each other and
for a further segregation of, e. g., the anatomical parts of a
coniferous tracheid and to accomplish the desired refining effect
on the pulp, the grist has to be compressed to such a degree that,
within the grist, regions of stresses of sufficient magnitude are
developed.
The pre-requisite for such conditions is accomplished es-
pecially within such regions of compressive stresses which are de-
veloped at passages between the rotating pockets 41-46. ~Depend-
` ing upon the diameter of the refining discs, the moving grist may
be compressed by a centrifugal force of around 500 g, and even up
to 1500 g, when it comes to a sudden stop in one of the stationary
I pockets 61-66.
The fields of frictional forces developed at the crossings
from the stationary grinding disc 50 to the rotating disc 30 have,
on the other hand, another character, more like a "slap on the
ear". When the grist is accelerated by the bar 47 into the pocket
42, the action is different. The strains there are more like the
~ action of a blunt knife cutting through a piece of cheese. In
-~ the compressed grist fo~ced from the stationary grinding disc,
./ .
' 3 the rotating bars will, thus, also create surfaces of friction.
~, 30 Then, in the rotating pocket 42, the grist sliced off and fluffed
. by the bars 47 is accelerated to a considerable velocity. and the
.~ grist is diverted from the rim 49 in the pocket 42. From there, -
it is transferred to the stationary pocket 62 and there again ar-
- -12-
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~6a4~5
rested to zero angular velocity with a loss of kinetic energy and
a repeated rise in temperature.
The lignocellulose substance is hydrophilic, and, when
moist, thermoplastic. When its temperature is raised to the boil-
ing point of water (100C), it starts to soften, and, when thetemperature reaches 140C-150C for different lignocellulose mater-
ials, the strength of the bond between the fibers is very weak.
The refining process according to the invention is prefer-
ably carried out in closed refiners generally called "pressurized
refiners", in which the refining process can be carried out under
. steam pressure. The desired temperature can then be maintained
during the refining process. The energy required to raise the tem-
perature to the desired level is obtained from the heat liberated
in the refining process. The quantity (amount) of mechanical en-
ergy used for the refining process, generally around 800 kWh, up
to 2000 kWh per ton of pulp produced, will liberate more heat than
is required to keep the grist at the appropriate temperature, e.g.,
130C. The heat will then evaporate a portion of the moisture con-
.
tained in the grist. Thus, if the mechanical work needed to carry -~
~:: 20 out the refining process according to the invention corresponds to
~`?~ 800 kWh per ton of dry wood substance, the heat used will corres-
?~:~
pond to 688,000 kcal per ton of dry substance. If the process is
"
carried out at 120C (and at a corresponding steam pressure), to .
. take advantage of the thermoplastic softening of the wood at that
temperature, 1309 kg water per ton of wood processed will evaporate.
Assuming that, in the example quoted, the wood chips fed to
, the refiner had a moisture ratio of 2:1, the moisture ratio would
be reduced to 0.7:1 by evaporation. If a moisture ratio of the
grist of 2:1 during the process is necessary for obtaining accept-
.j 30 able refining result, a corresponding amount of water should be - -
added to the grist in the zone of refining Conduits for such ad-
-i dition are shown at the numeral 55, in Figs. 1 to 5. ~n the pro-
-. cess according to the invention, the amount of water added may be
.. -13-
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- . - -; .. ~ ~ .. . . .... ... , .. . ,.. ,,, .. . ... " .:
40S
automatically controlled.
The water added will be rapidly distributed on the surfaces
of the fibers of the grist and will, therefore, influence the
state of friction between the fibers and thereby the process of
refining. When the moisture ratio of the grist rises, the thick-
ness of the liquid film will increase. Too thick a film will act
as a lubricant and will lessen the efficiency of the refining pro-
cess. ~hen the moisture ratio decreases to 1:1 or less, there is
considerable risk of formation of microscopic nodules or bundles
of fibers that are difficult to untangle by post-refining. An
- increased amount of water will also increase the energy consumed
- to accelerate the grist in the pockets of the rotating grinding
disc.
When examining microphotographs of a cross-section of spruce
wood fibers (tracheids) magnified 50 times, it is easy to recog-
nize the cross-sections of the individual fibers and how their
size varies within the year rings. A statistical study shows that
tracheids generally have a cross-sectional area of 0.03 mm x
~`~ 0.03 mm, corresponding to about 100,000 fibers per cm2. The fiber
length is about 2.5 mm, giving a number of about 400,000 tracheids
per cm3. The dry weight of spruce wood is about 0.42 g per cm3,
which indicates that one g (= 2.4 cm3) of spruce wood contains -
aboutl,000,000 fibers and that the combined surface of separated
whole fibers is about 3 m2 per g of wood. Refined grist, depend-
`~ 25 ing upon its CSF-value, may have a 10-fold combined surface. The
~`~ liquid film distributed on the particles is calculated to be a -
:~ -
' film of a thickness of less than one-thousandth of one millimeter.
~ However, due to the large su~face involved in refined pulp and the .i
.. J~ thin~wate~ fil~ in addition to the~hydrophilic properties of the
~ 30 wood substance, a limited excess of water can be permitted wi~hout
s.
;~; seriously di~inishing the desired frictional forces within the
grist.
A refiner equipped with grinding discs according to the in-
vention creates a greater number of efficient frictional surfaces
. . ~.~ . ~
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... . .- - ~ :. ~ ; -- . . .. - , , .
1(~6~05
within the grist than has been possible with any previously known
type of refiner. It is also possible in a refiner applying to the
invention to use bars more resistant to abrasion than formerly.
This is possible also because of the novel manner in which the
bars have been embedded in the body of the disc.
The surfaces of friction which are developed wlthin the
grist can also be adjusted in relation to the distance between the
surfaces of the rotating bars and the stationary bars. Efficient
.~ refining action can, therefore, be accomplished when a greater dis-
tance or clearance is used than has been possible with earlier
known designs. This means less abrasions of the opposing surfaces
of the bars. Such increased distance also counteracts excessive;
- shortening of fibers through cutting.
The bars used in the refiner discs according to this inven-
tion will gradually be subjected to wear on the opposing surfaces,
which may result in dullness of the leading edge. Worn bars can
`: easily be replaced with new bars.
With an axially adjustable ring 56 outside the periphery of
the stationary grinding disc 50, it is possible to regulate the
` 20 area of exit from the outermost located stationary pockets 66 to
:~ retar~, if desired, the rate of flow of grist between the grinding
discs 30 and 50 by means of adjusting nut 57.
The bars 47 and 67 can be made from hard abrasive materials
` like carborundum, sillicon carbide or other ceramic materials. The
circular rings 30 and 50 can be made from softer material more
~ easily machined and can, therefore, be made in full circular ring
- construction, depending upon type of refiner. The bars are held
,. .
: in machined radial slots, preferably by high-strength synthetic
organic glues according to known methods, The bars can also be
` 30 cast into such components, Th~nks to the curved contours of the
grooves 41-46 and 61-66, the bars are held with great stability.
The components of the secondary grinding zone of the grind-
ing elements shown in Fig. 1, numerals 20 and 24, may also, as an
-15-
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1~63405
alternative, be designed similar to the elements 30 and 50 in the
same Fig. 1. The working surfaces of the grinding discs should,
after assembly, be finished to the highest possible accuracy for
best performance when the refiner is in operation.
The first pocket 41 of the grinding disc 30 has an innermost
radius of 528 mm. When grist with a moisture ratio of 3:1 is ac-
celerated to a velocity of 83 m per second, the required kinetic
power input will be 14.5 kWh per ton of pulp calculated as oven
dry. When the grist enters the pocket 61 of the stationary grind-
ing disc 50, it is retarded to zero velocity, but, when leaving
this pocket, it is again accelerated in pocket 42. The grist pass-
ing through the refiner is thus accelerated and stopped success--
ively six times, one time for each row of pockets. This would
- correspond to a power consumption of about 95 kWh per ton of pulp
produced. As described above, when the grist in a compacted form
emerges from the stationary pockets, surfaces of friction are gen-
erated by the edges of the bars. The intensity of this friction
- can be modified by setting the grinding disc distance as indicated
. .;. . .
. above. The power used for the refining process may, thus, be var- -
.. .. .
' 20 ied from a few hundred up to 1000 kWh per ton of ordinary types
of pulp. When pulp of special low freeness values is required,
up to 2000 kWh per ton of pulp may be used. With increased grind-
ing disc distance, a short-cut may be created allowing a portion
. .
,f of the grist to pass over the rims 51 directly from a pocket to
the next radial pocket. A considerable loss in refining intensity
~, will occur, but the power consumption per ton will decrease. ~:~
;- In the embodiment disclosed in Fig. 6, the pockets 61-66 and
`~ 71 of the stationary grinding means 50 in an axial section have
the shape of a circle, just as in the preceding embodiment, the
.,
~-~ 30 radius of said segment corresponding to the full depth of the
pocket or being somewhat larger. Also, the individual pockets of
the grinding means 30 are curved in an axial section through the
grinding means. In contrast to the embodiment of Fig. 4, the in-
-16-
,,
1()~3~S
dividual pockets 42-46 and 70 have a gradually sloping wall sec-
tion 72 at the radially outer face thereof, said section being
plane or approximately plane and, at the botto~ of the pocket,
tangentially changing to a wall section 74 extending perpendic-
ularly or approximately perpendicularly to the grinding surface
formed by the edges of bars 47 and rims 51. The arc-like section
73 may have a radius of curvature approximately corresponding to
the full depth of the pocket. In this manner, the rotating pock-
ets will form an outline having a relatively long and flat de-
flection surface for the grist. At the radially inner side of the
grinding means 30, said grist is fed through a port 48 and, at
high speed, is hurled into the innermost stationary pocket 61, as
" disclosed by arrow A, where the grist will be instantaneously
:
stopped and fills up the pocket as a compact plug or body. The
latter slides along the surface 68 and is then brought to the in-
nermost rotating pocket 42, the plug then passing between the bars
46 and 67, respectively, shearing or friction surfaces then being
shaped, in which the separate fibers or fibrilles of the grist are
,~ separated from each other. Due to the circle segment section of
the pockets, the plug of the grist collected therein will be-r~o-
tated about a center 49, as indicated by line 69, by the subse-
.
~.~ quent grist hurled through said port 41. Said plug will then get
,.~
into contact with the rotating bars 47, which disintegrate the
- grist while peeling the same. In the rotating pocket, said grist
is now instantaneously accelerated to the high speed of the
~ grinding means, the grist then being compacted and, due to the
.~ sloping, elongated plane 72 and a favorable distribution of the
'~ components of force in the radial and axial direction, also being
.~
. passed into the next pocket 62, where, once more, a plug in the
shape of a segment of a circle is generated~ The cycle is re-
... peated at the alternate passages outwards of the grist between
the stationary and rotating pockets, and the obtained final pro-
duct is fed out through the last stationary groove 71.
,
- ~ -17- -:
.
