Fiber length indicating apparatus and method

A standpipe is connected into a fiber processing system such as a pressurized stock line of a paper making system, containing refined stock, or unrefined pulp, at operating consistencies. Automatic controls cycle a measurement chamber, in the standpipe, through intake measure and exhaust. An imperforate plate mounted across the measurement chamber has at least one hole of predetermined cross dimension, or diameter, substantially equal to the relative length of fiber desired. Automatic timing establishes a set intake time for slurry, or suspension, to pass through the hole and contact lower and/or upper liquid level sensors, or other level indicators, in the chamber. Instantaneous, periodic read out is provided to indicate "too short", "too long" or "correct length" with each cycle. Differential pressure, across the hole, or orifice during measure, as well as approach velocity, is appropriately controlled.

BACKGROUND OF THE INVENTION 
In the grinding of rags and the like for the preparation of a furnish for 
roofing felt, for example, it is necessary to determine when the stock has 
arrived at desired condition. Threads that are too long are difficult to 
handle and result in an inferior product. Fibers that are too short drain 
slowly and interfere with efficient manufacturing. Presently, the only 
available method for determining quality is to manually examine a handful 
of stock. Not only is such procedure time consuming, but it is also most 
imprecise depending on the skill and experience of the operators involved. 
As a result, product quality is impaired, productivity is reduced and 
operating cost increased. 
In recent years, continuous digesters have replaced batch digesters, i.e. 
wood chips and chemicals are continuously introduced to, and pulp is 
delivered from, a complex system of vessels, piping, etc. In many 
continuous pulp mills, a problem is encountered inasmuch as several 
species of wood are utilized and it is essential to segregate resulting 
pulp according to specie, i.e. a pulp made from softwood must be 
segregated from pulp made from sawdust, etc. 
The problem is that, as it emanates from the pipeline, all pulps are 
virtually indistinguishable. There is, however, one factor which 
quantitatively identifies virtually all species, namely fiber length. By 
continuously monitoring fiber length of pulp as it passes through the 
pipeline, a change from one specie to another becomes immediately evident, 
positively precluding any possibility of a customer receiving incorrect 
pulp. 
Thus, an instrument which will automatically monitor fiber length of 
refined paper stock, or of unrefined paper pulp, while in slurry form, at 
operating consistencies and while in the paper making system will 
obviously be most useful. 
The principal object of this invention is to provide such an apparatus and 
method so that a signal is generated to inform the operator when a pulp 
interface passes, or that stock is refined to the correct fiber length and 
quality. 
Use can be made of the signal to automatically control the refining effect 
of refiners to optimize, and maximize, uniformity. 
It has, heretofore been proposed in U.S. Pat. No. 1,580,166 to Reid of Apr. 
13, 1926 to provide a laboratory type device with a screen having 
elongated, narrow, slots, a tank entirely separate from a stock pipeline 
system and a vacuum mechanism for drawing stock through the screen. The 
slots are about one hundreth of an inch in width so that a dilute slurry 
is used and the stock is treated as discrete fibers, rather than as a 
fiber aggregate. The Reid device would not be capable of instantaneous 
"read out" in "on-line" operation since one would have to count, or weigh, 
the fibers which do not pass the screen. 
In U.S. Pat. No. 2,973,000 to Pearson of Feb. 28, 1961, a sharp edged 
orifice plate is used to determine consistency of diluted stock in a 
laboratory type device. All of the fibers pass through the orifice without 
regard to length. 
In U.S. Pat. No. 3,846,231 to Crosby et al of Nov. 5, 1974 the stock is 
drawn across a perforated partition to measure freeness just as in my two 
patents on freeness testers cited thereagainst namely U.S. Pat. No. 
3,538,749 of October 1970 and U.S. Pat. No. 3,186,215 of June 1965 both to 
Danforth. No claim, or teaching, is made in these patents for measuring or 
monitoring fiber length. 
A prior patent which more closely relates to measuring fiber length is U.S. 
Pat. No. 3,873,416 to Forgacs of Mar. 25, 1975 but the device requires the 
stock to be substantially diluted rather than at operating consistency in 
the paper making system. The Forgacs device works on a continuous flowing 
stream principle and not on a sampling sequence and makes use of a 
fractionating screen which is vertically oriented and vibrates. 
As far as I am aware, none of the devices of the above patents are 
available in the trade and no instantaneous, automatic, "read-out" of 
fiber length, has been developed, except as disclosed herein. 
There are no other references in the prior art, known to me, disclosing a 
device to monitor fiber length directly in the production system. 
SUMMARY OF THE INVENTION 
In this invention, an apparatus and method for monitoring the length of 
fibers in refined paper stock, or in unrefined paper pulp, is provided, 
wherein the read-out is instantaneous, and achieved periodically, while 
the fibrous slurry is in the paper making system at operating consistency. 
Automatic controls are provided similar to those provided for the standpipe 
of my above mentioned patents on freeness testers, now well known in the 
trade as the "Drainac" manufactured by Bolton-Emerson, Inc. of Lawrence, 
Mass. In one embodiment of my freeness tester, an upstanding standpipe is 
mounted on a stock, or pulp, line with the lower end directly connected 
into the line and the upper portion forming a measurement chamber by 
reason of a transverse screen in the freeness tester. Timing control 
cycles the measurement chamber through intake by exhausting air therein to 
cause flow through the screen, a pair of electrodes sense the liquid 
levels attained by the filtrate and air pressure discharges the filtrate 
through the screen, thus transporting the fibers thereon back into the 
system. 
If equalization of stock pressure is desired, the measurement chamber of 
the freeness tester can be exposed to ambient atmospheric pressure, rather 
than to negative pressure, and a constant level head box used between the 
stock line and the tester as in the Myers U.S. Pat. No. 2,734,378 of Feb. 
14, 1956. 
A significant feature of this invention is that instead of using a meshed 
screen, or a slotted plate, the fiber length indicator disclosed herein 
makes use of an imperforate plate extending across a measurement chamber 
and having at least one, orifice, or hole, of predetermined area or 
configuration preferably substantially circular, or tubular, cylindrical, 
and of predetermined cross dimension, or diameter, substantially equal to 
the relative length of the fiber to be detected as of changed specie or as 
of desired relative length. 
When change of pulp specie in a pulp line is to be detected the upstanding 
container has its lower end directly connected into the system, with no 
by-passing or resort to laboratory manual testing. The fiber length 
indicator, or detector, automatically and periodically cycles through 
intake, measure and discharge with the electric probes, or other level 
sensing means, in the measurement chamber repeatedly signalling "correct" 
as long as the predetermined set intake time signals that the fiber length 
of the species is flowing. When another pulp species interface is 
encountered, it will result in fibers of a different length so that the 
read-out will be "incorrect length". 
It will be udnerstood that a meshed screen, or multiperforated plate 
corresponding to a screen, such as used in a freeness tester will not 
function as the partition across the measurement chamber of the fiber 
length indicator of this invention because the stock being measured is of 
high consistency and cannot be screened in the normal sense. A single 
orifice is sometimes preferred, but multiple such orifices of similar, or 
different, diameters such as four have usually been found preferable. The 
range of orifice diameters depends on the length of fibers to be measured 
and may range from one millimeter for extremely fine, synthetic fiber to 
about twenty millimeters for relatively unrefined rag fiber. 
Since a single fiber processing mill may produce a number of different 
grades, the fiber length indicator of the invention may have a variety of 
replaceable plates, each with at least one substantially circular orifice 
of different diameter, or area to accomplish "coarse tuning" the fine 
tuning being accomplished by the operating variable of differential 
pressure across the orifice. Over a reasonable range, the same orifice can 
differentiate different fiber lengths depending on the driving force, the 
best operation appearing to be from 0.5 to 1.5 p.s.i.

DESCRIPTION OF A PREFERRED EMBODIMENT 
A paper stock system 20 is shown diagrammatically in FIG. 1, the system 
including a beater 21, valve 22, stock conduits 23, pump 24, conduit 25, 
and a stock refiner 26 of the disc, Jordan or "Claflin" type. The refiner 
26 discharges into a conduit 27, conduit 27 having a fiber length 
indicator 28, of the invention, installed therein, with a control system 
such as shown in FIG. 7 or FIG. 11. Conduit 27 includes a valve 29 and 
discharges back into the beater 21 or elsewhere as desired. 
As best shon in FIG. 2, the fiber length indicator 28, includes an 
upstanding, stock container 31, similar to the above mentioned "Drainac" 
freeness tester, and connected directly to a paper, or pulp, conduit 27, 
which forms a part of stock system 20, and contains paper stock, or pulp 
32, at operating consistency so that it is relatively high consistency and 
has not been diluted for laboratory, or by-pass, testing. 
The stock container 31 is divided, intermediate of its height, by an 
orifice plate 33, to form an upper portion 34, which is the measurement 
chamber, and a lower portion 35, the lower end 36 of the lower portion 35 
being connected to the stock, or pulp, supply 27 to receive the stock, or 
pulp, 32 therefrom, at operating consistency and incorporate said lower 
portion into the paper, or pulp, conduit 27 of the paper stock system 20. 
The orifice plate 33 is not a meshed, perforate screen, but instead is of 
imperforate material, such as metal, and includes at least one orifice 37 
formed, by the rim 38 in the plate. The orifice 37 is preferably 
cylindrical and is of predetermined diameter substantially equal to the 
relative length of the fibers, such as 39, to be monitored in the 
measurement chamber 34. The orifice 37 could be of other shapes, 
configurations or cross sectional areas, such as triangular so long as 
it's cross dimension is of predetermined width corresponding to the 
predetermined relative length of the fiber to be measured, but a 
cylindrical orifice is found much preferable. 
It should be understood that virtually all fiber slurries represent a range 
of fiber lengths from several millimeters to less than one millimeter with 
distribution similar to a probability curve. The shorter fibers pass the 
orifice while the longer fibers do not until eventually sufficient long 
fibers collect to prevent further passage. Thus, the volume of the stock 
passing the orifice is a measure of relative fiber length, other 
conditions being equal. 
The slurry is not dewatered as a result of passing through the orifice. In 
operation in a fiber processing plant, plates each with a different sized 
orifice can be substituted in the fiber length indicator of the invention 
until a particular sized orifice, in the preset intake time indicates the 
desired relative length of fiber to meet the standards, or production 
requirements, of the processing plant. Thereafter, the same plate and 
orifice will repeatedly by cycled to monitor production and indicate any 
variation in quality revealed by a change of relative length of fiber in 
the slurry. 
The tubular, cylindrical orifice 37, in each plate 33, has a diameter which 
is within the range of about twenty millimeters for rag fibers suitable 
for roofing felt base to one millimeter for highly refined flax pulp 
suitable for cigarette tissue. 
In FIG. 5, the diameter illustrated is about one millimeter for highly 
refined flax pulp suitable for cigarette tissue, or for fine synthetic 
fibers. 
In FIG. 3 an orifice plate 41, similar to plate 33 is shown, wherein the 
rim 42 forms a substantially cylindrical orifice 43 of about twenty 
millimeters in cross dimension, or diameter, for use in measuring fibers 
in relatively unrefined rag pulp suitable for roofing felt base. 
In FIG. 4, an orifice plate 44 is shown which is similar to plate 33 and 41 
except that it is formed with a plurality of identical orifices, such as 
five, designated 45, 46, 47, 48 and 49, which may be circular, triangular 
square, or other configurations of relatively uniform cross dimension. 
Multiple orifices, of similar or different diameters, can be used to 
average out the testing the fiber length measurement results. 
In FIG. 6, an orifice plate 51 is shown having an orifice 52 of variable 
area, configuration and cross dimension together with means 53 for varying 
the same. The orifice 52 may be formed as a camera shutter or preferably, 
as shown, by a pair of oppositely disposed, sliding gates 54 and 55 each 
with a V-shaped cut out 56 or 57 therein and actuated from outside the 
container, during operation by suitable push rods 58 or 59. 
The orifices such as 37, 43, 45, and 52 are preferably of the standard type 
formed in thin plate with a downstream and upstream sharp square edge. 
They are not designed to create a jet but more properly might be 
designated holes or apertures. 
Preferably a baffle, or target plate 61 is provided at a spaced distance 
above each orifice such as 37 to spread out and dampen any jet of paper 
stock or pulp up into the measurement chamber 34. The target plate 61 is 
preferably the lower end of a cylindrical, solid rod 62 supported from 
above, to avoid interference with incoming material. 
A set of orifice plates such as 33, 41, 44 or 51, each with an orifice of 
different diameter, and perhaps totalling ten to twenty plates in the set, 
may be provided with each fiber length indicator 28. The plates are each 
seated in a plate recess 63 at the split 64 so that the upper portion 34 
may be released and hinged rearwardly on hinge 65 to permit replacement of 
the plates in the set and refastened by bolt 66. The container 31 is not 
only separable at mid-height 64, but the upper portion is preferably a 
transparent tube seated on an annular gasket 70. 
Slurry level sensing means 67 is provided within the upper portion, 
constituting the measurement chamber 34, and formed by at least one, and 
preferably by both a lower electric probe 68, and an upper electric probe 
69. Other suitable slurry level sensing means may be used. 
A differential pressure controller 71 (FIG. 11) is included in the system 
20 to insure precision of control conditions. A differential pressure is 
essential (of the order of 1 p.s.i.) and while one can subtract pressure 
in the measurement chamber 34 from the line, or stock, pressure in stock, 
or pulp, line 27, the guage 71 avoids arithmetic error and makes the 
system simpler and more foolproof. 
A check valve 72 may be incorporated with each orifice plate to prevent 
upstream passage anywhere through the plate except through the orifice but 
to permit ready downstream passage through the plate during the exhaust 
cycle back into the stock line. 
A dump valve 73 may also be provided to facilitate discharge from the 
measurement chamber through an auxiliary opening during the exhaust cycle. 
A water valve 74 provides dilution water from a supply conduit 75 to flush 
out the parts and assure that all fibers are returned to the pipe line 27. 
In FIG. 7 a fiber length indicator 28 of the invention is shown, connected 
into a paper stock, or paper pulp line 27 containing the high consistency 
liquid 32 to be measured, which may be at any line pressure, with the line 
pressure not affecting differential pressure. 
The liquid 32 is directed into the upstanding open top tube 76 centrally 
located in the upstanding open top tube 77 so that it will flow over the 
rim 78 and into the discharge 79. Thus, the hydraulic head, or pressure, 
remains constant as the liquid is guided out of the bottom 81 of tube 76, 
into the lower portion 35 of container 31, by conduit 82. 
The automatic control means 83 of the invention includes the air input tube 
84 having one end 85 in chamber 34 and leading to a source of air pressure 
86 such as mill air. It also includes the air exhaust tube 87, having one 
end 88 in chamber 34 and leading to the atmosphere or preferably to a 
source of negative air pressure 89. 
The automatic timing means 91 is connected to the two probes, or electrodes 
68 and 69 and the read out means is designated 92. 
As shown diagrammatically, the automatic control means includes a cycle 
timer 93 of known construction, connected by suitable electric circuits 
and to conductors 94 and 95 to the purge, or dump, valve 73, conductors 96 
and 97 to the water dilution valve 74, conductors 98 and 99 to the 
electrodes 68 and 69 and conductors 101 and 102 to the air input valve 103 
and air exhaust valve 104 to actuate the same by suitable solenoids as 
programmed. 
The automatic control means 83 is similar to the control means disclosed in 
my above mentioned U.S. Pat. Nos. 3,186,215 of June 1, 1965 and 3,538,749 
of Nov. 10, 1970 in which the freeness tester disclosed therein is 
automatically cycled through intake, measure and exhaust. 
Thus, a suitable plate 33 having at least one orifice 37 with a cross 
dimension, and area, capable of passing fibers of substantially the 
correct relative length desired is installed in the seat, or recess 33, 
the indicator 28 closed and the cycle timer 93 actuated. The cycle timer 
then cycles the measurement chamber 34 through intake, measure and exhaust 
to obtain the desired automatic, periodic, instantaneous read out by 
opening air exhaust valve 104 to negative pressure, or atmosphere thereby 
enabling the fibers in the stock, or pulp, line to attempt to pass through 
each orifice 37 into the chamber 34. A predetermined set intake time for 
the cycle is established by the cycle timer so that if no stock passes 
through the orifice to reach lower probe 68 before expiration of the set 
intake time "blow down", or exhaust, is initiated and the read out signal 
"too long" is displayed at 92. This is the situation illustrated in FIG. 
8. 
If the stock reaches the upper probe 69 before the set intake time of the 
timer expires, "blow down", is initiated and the signal "too short" is 
displayed on the read out 92 (FIG. 10). 
If the stock reaches the lower probe 68 but not the upper probe 69 before 
the timer times out with the set intake time, blow down is initiated and 
the signal "just right", or its equivalent, is displayed on the read out 
92. 
The differential pressure between stock line pressure and measurement 
chamber pressure is indicated by the differential pressure guage 71 (FIG. 
11) and controlled by the automatic control means 83 to be about 1 psi as 
compared to about 7 psi in the freeness tester of my said patents. 
The check valve 72 in each orifice plate enables the one way return of 
stock from the chamber 34 back into the stock line 27 during the blow down 
or exhaust cycle and the dump valve 73 also enables rapid clearance of 
chamber 34 during exhaust. The cycle timer 93 is programmed to supply 
flush water through valve 74 to clear the plate and orifice of fibers, or 
fibrous mats, during the exhaust cycle also. 
As mentioned above, a constant hydraulic head in the open inner tube, or 
container 76, in the arrangement of FIG. 7 assures that any variations in 
stock line pressure do not affect measurement in the container 31 shown in 
that view. 
It will be understood that air pressure and water pressure are greater than 
line pressure. Intake time may be about ten seconds and exhaust time also 
about ten seconds and the fiber length indicator of the invention may be 
cycled at any desired intervals to provide a read out of exact fiber 
length passing through stock, or pulp line 37 and to warn the operator 
that a different type pulp is passing by the indicator. 
As shown diagrammatically in FIG. 1, a precise control of the quality of 
stock produced by refiners such as 26 is obtained by periodically 
measuring fiber length in a stock line 27, with a fiber length indicator 
28 of this invention, and periodically measuring freeness in the stock 
line 27, with a freeness tester 105 such as the "Drainac" of my above 
mentioned prior patents U.S. Pat. Nos. 3,538,749 and 3,186,215. 
The freeness tester 105, shown in dotted lines, and the fiber length 
indicator 28, are shown as both connected to a control system such as 
illustrated in FIG. 7, including the control means 83 and a circuit 106 to 
the drive means 107 of the refiner so that refining effect is controlled 
automatically to compensate for any variations in fiber length or freeness 
.