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Oct. 15, 1946a
53 E, E, AHLFQRS ‘
METHOD OF STRAINING FIBROUS SUSPENSIONS
, Filed Jan. 30. 1942
2,409,524
Patented Oct. 15, 1946
2,409,524
UNITED STATES PATENT OFFICE
2,409,524
METHOD OF STRAINING FIBROUS
SUSPENSIONS
Sten Eskil Einarsson Ahlfors, Hedemora, Sweden
Application January 30, 1942, Serial No. 428,930
In Sweden July 22, 1940
4 Claims.
(CI. 92-33) .
2
1
This invention relates to straining of ?brous
The embodiment of my improved strainer above
suspensions, particularly paper pulp.
described operates as follows:
One of its objects is to provide a straining
method resulting in a thickening of the pulp
strained as compared with the pulp to be strained.
Other objects are to increase the output of
the strainer and decrease the weight thereof.
The invention consists in the novel method
The pulp to be strained is supplied to the pulp
vat 2 at any suitable point, such as at I9 in Fig. 1
and the supply of the incoming pulp is so con
‘
trolled as to maintain a suitable level of liquid
in the pulp vat 2 as indicated at a in Figs. 1 and 2.
The pulp thus introduced tends to move upwards
hereinafter fully described and particularly
through the slotted strainer bottom l2 which is
10 caused to vibrate rapidly by means of the actu
pointed out in the claims hereunto appended.
ating mechanism above described. The matter
The invention is illustrated by way of example
passing through the slots 13 is continuously dis
on the annexed drawing in which:
Fig. 1 shows a longitudinal section along line
charged at the top face of the strainer bottom
I--I in Fig. 2 of an embodiment of my improved
I2 by the suction tube [6. On the other hand
strainer;
15 the matter rejected by the strainer, such as knots
or ogher coarse matter is continuously discharged
Fig. 2 shows a transverse section along line
II—II in Fig. l of the strainer illustrated in Fig. 1.
Fig. 3 shows an enlarged fragmentary plan
at
.
In practising the above method of straining I
have found that by suitable choice of the oper
view of the bottom of the strainer vat and one
of the sprinkle tubes in Fig. 1.
20 ation conditions, particularly of the characteris
On the drawing i represents the supporting
tics of the vibratory motion of the strainer Vat,
the pulp strained will be thickened as compared
frame of the strainer, 2 the stationary pulp vat
with the entering pulp to be strained whereas the
and 3 the vibratory strainer vat. The latter is
resiliently supported by means of springs d de
pulp in the vat 2 becomes thinner during the
pending from the frame I. Associated with the 25 course of the straining. This action is con
trary to what happens in all straining methods
strainer vat 3 is an actuating mechanism therefor
comprising a rotary shaft 5 journalled in bearings
hitherto known in which the entering pulp be
6 supported by the strainer vat 3 by means of
longitudinal and transverse bars ‘I and 8 respec
tively. Carried by the shaft 5 intermediate its
ends is a pulley 9 adapted to be rotated by means
comes thicker as the straining proceeds which as
a rule necessitates the addition of larger or
smaller quantities of diluting water at the input
side of the strainer to prevent cloggingof the
strainer at that side. Such addition of water
of a belt I0 from a source of power not illus
for diluting the pulp in the pulp vat is entirely
trated. At its ends the shaft 5 supports unbal
avoided by my present method of straining. Be
anced or eccentrically arranged masses H serv
ing to vibrate the strainer vat 3 in rotating the 35 sides, if desired thicker pulps can be strained
according to my method without incurring the
shaft 5. The bottom l2 of the strainer vat 3
risk of clogging of the strainer at the input side.
forms the strainer proper and is provided with
slots i3 extending in the longitudinal direction
This means a considerable increase of the output
of the strainer per unit of surface of the strainer
of the strainer from the lower surface of the
strainer bottom l2 and communicating with re 40 area.
cesses M at the top surface of the strainer bot
In practising my improved method I have
tom said recesses successively increasing in
found that the velocity of the vibratory motion
width from the upper end of the slots it to the
of the strainer must be relatively high to obtain
top surface of the strainer bottom I2.
The pulp vat 2 is provided with an outlet 15 for
the material rejected by the strainer, and at Hi
satisfactory straining. Thus, in practice I have
4k in
obtained excellent results of straining, for in
stance, by using a frequency of vibration of about
there is indicated a stationary suction tube for
1200-1400 vibrations per minute and an ampli
discharging the strained pulp.
tude of vibration of about 2-5 millimetres.
Greater or smaller departures from these values
Associated with the strainer vat 3 are spout
ing or sprinkling members consisting of a plu 50 are, however, permissible in practice depending on
rality of tubes ll spaced at some distance from
the characteristics of the entering pulp and the
the top surface of the bottom E2 of the strainer
desired pureness of the strained pulp. As a rule
and extending thereacross.
Said tubes are
I have, however, found that the frequency of
adapted to be supplied with liquid under pressure
vibration should not be diminished below about
either continuously or intermittently by any suit 55 900 vibrations per minute as the output of the
able means not illustrated on the drawing and
strainer then materially decreases, and on the
other hand an increase of the frequency of vibra
are provided with a series of discharge apertures
tion to a value above about 1800 vibrations per
or nozzles 98 pointing towards the recesses 14
minute has been found to appreciably impair the
and extending in a direction sloping towards the
straining effect.
end of the strainer bottom [2 where the discharge
During the straining operation water is ejected
tube It is situated.
2,409,524
3
4
through the apertures 18 of the tubes i‘! as il
er element so as to cause a thickening of the
lustrated diagrammatically in Fig. 1 to prevent
clogging of the strainer surface‘facingthe pulp
:pulp when passing upwards'throughgsaid strainer
element, discharging the thickened strained pulp
strained which, as stated in the foregoing, ac
at the top of said strainer element and the ma
terial rejected by said strainer element at the
cording to the present process is thickened, that - Cl
is partly dewatered during the straining opera
tion. In the embodiment shown merely the-re
bottom thereof, the discharges being regulated
cesses It need be scavenged by the jets of wa
so ‘as to maintain a thin layer of strained pulp
on the screen, and cleaning the slots of said
ter projected by the sprinkle system H, 18 to
strainer element by spraying liquid against the
remove any matter collecting .in said recesses 10 side thereof facing the pulp strained.
during the process of straining. Thus, when us
2. A method of straining ?brous suspensions,
ing slots increasing in width upwards as shown
particularly paper pulp, comprising supplying the
on the drawing the cleaning water from the-sprin
pulp to be strained to the bottom surface of a
kle system needs not be pressed through the
strainer element having straining slots therein
strainer slots from the top face of the strainer
which have side walls which are divergent up
to the bottom face thereof which generally might
wardly, causing the pulp thus supplied to ,pass
cause a reduction of theoutput of the strainer.
upwards through said strainer element, impart
.The .water of the jets sweeping clean the recesses
M is discharged through the tube l6 together
ing vibratory motion of a frequency of about 1200
to 1400 vibrations per minute to said strainer ele
with the strained pulp.
In the embodiment illustrated the jets of clean~
.ing water are projected substantially in the lon
passing upwards through said strainer element,
ment so as to cause a thickening of the pulp when
discharging the thickened strained pulp at the
gitudinal direction of the strainer and also in
top of said strainer element and the material
the longitudinaldirection of the recesses l4 fa~
rejected by said strainer element at the bottom
cilitating an effective cleaning of the ‘upper sur 25 thereof, maintaining the thinnest possible layer
of strained pulp upon said strainer element, and
faceof the strainer proper and assisting in the
cleaning the slots of said strainer element by
flow of the pulp strained along the preferably in~
spraying liquid on the side thereof facing the
clined bottom I2 towards the discharge tube l6.
pulp strained.
In straining paper pulp-or other ?brous sus
3. A method of straining ?brous suspension,
pensions according to the present method the
particularly paper pulp, comprising supplying the
‘strained pulpshould be maintained in a relative
pulp to be strained to the bottom surface of a
ly thin layer, preferably at the thinnest possible
strainer element having straining slots therein
layer on the strainer proper. This not only se~
which have side walls .which are divergent up
,curesan effective cleaning of the upper face of
wardly, causing the pulp thus supplied to pass
the strainer from ?brous matter tending to clog
upwards through said strainer element, impart
the slots of the strainer'but also prevents an ex
ing vibratory motion of .a frequency of about
cessive dewatering of the strained ‘pulp Which
1200 to 1400 vibrations per minute and an ampli
might result in an excessive deposition of ?brous
tude of about 2 to 5 millimeters to said strainer
matter in the recesses at the top surface of the
strainer. In addition, by maintaining the thin 40 element so as to cause a thickening of the pulp
when passing upwards through said strainer ele
nest possible layer of liquid in the strainer vat
ment, discharging the thickened strained pulp at
the entire strainer device obtains the lowest pos
the top of saidstrainer element and the material
sible height. Thus, the level of liquid in the
rejected by said strainer element at the bottom
strainer vat ?rstly reduces the necessary height
of the pulp vat containing the strainer vat and 45 thereof, the discharges being regulated so as to
receiving the pulp to be strained as the level of
this pulpwhich must-be at a certain height above
maintain a thin layer of strained pulp on the
screen, and cleaning ‘the slots of said strainer
element by spraying liquid on the side thereof
facing the pulp strained towards the zone at
level of the strained pulp. Secondly also the 50 which the pulp strained is discharged.
4. A method of straining ?brous suspensions,
height of the strainer vat and the part thereof
particularly paper pulp, comprising supplying the
immersed into the ?brous suspension are reduced
pulp to be strained to the bottom surface of a
and the weight thereof diminished whereby the
strainer element "having straining slots therein
strainer vat may be vibrated more easily re
which ‘have side walls~which are divergent up
sulting in a reduction of the size of the unbal
wardly, causing the pulp thus supplied to pass
anced masses ordinarily used for vibrating the
upwards through said strainer element, impart
strainer vat, of the necessary driving power and
ing vibratory motion of a frequency of about
also of the stresses to which the material of the
1200 to 1400 vibrations per minute and an ampli
strainer vat is subjected during the vibration.
The invention is susceptible of various changes 60 tude of about 2 to 5 millimeters to said strainer
element so as to cause thickening of the pulp
as to the details of-the method and apparatus
when passing upwards through said strainer ele
describedand the right is herein reserved to make
ment, discharging the-thickened strained pulp at
such changes as properly fall within the scope
the top of said strainer element and the mate
of the-appended claims.
rial rejected by said strainer element at the bot
What I claim is:
tom thereof, the discharges being regulated so
1. A method of straining ?brous suspensions,
the level ofthestrained pulp in the strainer vat,
is lowered witha reduction of the thickness or
particularly paper pulp, comprising supplying the
as to maintain a thin layer of strained pulp on
the screen, and cleaning the slots of said strainer
element by spraying jets of water on the side
strainer element having straining slots therein
which have side walls which are divergent up 70 facing the pulp strained projected in the lon
gitudinal direction of the slots of said strainer
wardly, .causing the pulp thus supplied to pass
element towards the zone at which the pulp
upwards through said strainer element, impart
strained is discharged.
ing vibratory motion of a frequency of about
STEN ESKIL EINARSSON AHLFORS.
1200 to 1400 vibrations per minute to said strain
pulp to be strained to the bottom surface of a
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