US2596724A - Method and apparatus for determin - Google Patents

Description

May 13, 1952 w. G. REYNOLDS METHOD AND APPARATUS FOR DETERMINING THE FREENESS OF WOOD PULP Filed Dec. 8, 1949 2 SHEETSSHEET l AI AHA AHHWAA INVENTOR WILL/RM G. Q'Y/VOLDS ATTORNEY y 1952 w. G. REYNOLDS 2,596,724

METHOD AND APPARATUS FOR DETERMINING THE FREENESS 0F woon PULP Filed Dec. 8, 1949 2 SHEETSSHEET 2 I NVE N TOR w/z. 4mm a. KEY/V0405 RWMW ATTOR NEYJ Patented May 13, 1 952 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR DETERMIN- ING THE FREENESS OF WOOD PULP William G. Reynolds, Cottondale, Ala.

Application December 8, 1949, Serial No. 131,707

7 Claims.

This invention relates to a method and apparatus for determining the freenes's and quality of hydration of pulp suspensions from which paper is manufactured.

The principal object of the invention is to provide a method and apparatus of the character designated which shall be effective to determine the freeness of a pulp suspension independent of the consistency thereof.

Another object is to provide a method and apparatus for testing the freeness of pulp suspensions from the rate of deceleration in drainage between two areas on a moving screen.

Another object is to provide a method and apparatus for testing the quality of hydration of pulp suspensions from the change in rate of deceleration in drainage between two areas on a moving screen.

A still further object is to provide a method and apparatus for determining the freeness of pulp suspensions whereby the refining machines may be accurately controlled, thereby causing them to deliver a pulp of uniform freeness.

Heretofore, so far as I am aware, there have been no satisfactory means to measure accurately the freeness and quality of hydration of pulp suspensions, particularly during the manufacture of paper on paper making machines. Conventional testers, known to me, all measure the velocity with which the liquid drains through a wire screen from a pulp suspension. The thus drained liquid flows into a container having an orifice in the bottom thereof. If the pulp has high freeness the liquid will flow through the screen faster than it can flow through the orifice and will overflow through an overflow pipe into a graduate. The volume of liquid thus caught in the graduate is taken as the index of freeness of the pulp. Such conventional methods of testing the freeness of pulp suspensions have been fundamentally incorrect because they determine an average drainage velocity-time characteristic of a pulp suspension whereby any freeness value obtained may represent several different combinations of pulp characteristics and qualities of hydration. Speaking in terms of the mathematical calculus processes, such conventional methods amount to' a partial integration of the drainage velocity with respect to time. This integration is partial because drainage velocity components which do not cause overflow into the graduate are excluded from the integration. The drainage velocity components which do not cause overflow into the graduate consists of that portion of the total drainage velocity which is insufficient to I develop a hydrostatic head large enough to cause flow of the drained water through the overflow pipe into the graduate. Since the freeness is determined by the volume overflowed into a graduate, this excluded drainage introduces disproportion into the determination of freeness. The ratio of the excluded drainage velocity in the initial stages of the drainage operation is relatively small. However, as the drainage operation proceeds and the total drainage velocity decreases that portion of the total drainage velocity insufficient to cause overflow represents a steadily increasing proportion of the total drainage velocity. In order to be consistent for stocks having varying characteristics, means must be provided whereby the ratio of drainage velocity excluded from the total velocity remains constant throughout the operation. Later I shall show that the opposite calculus process of differentiation must be applied if the true freeness factor of the pulp is to be obtained. The velocity of drainage cannot, in itself, define pulp freeness since it varies throughout the drainage operation and is directly affected by factors other than the freeness of the pulp suspension.

As a sheet is formed on a screen the liquid initially flows through very rapidly as only the screen resists its passage. For each unit of drainage volume passing through the screen a unit weight of pulp proportional to the consistency of the pulp suspension will be deposited on the screen and will retard further drainage. The degree of such retardation is uniquely dependent on the character of the pulp. Each unit of drainage volume passing through the screen also represents a corresponding decrease in the hydrostatic head of the pulp suspension above the screen, this hydrostatic head constituting the primary driving force which causes the drainage operation to occur. Also, since the pulp particles in any pulp suspension are of random sizes it also occurs that the smaller particles which can pass through the screen or a very thin mat of pulp existing at the beginning of the drainage operation cannot pass through the thicker pulp mat existing later in the drainage operation. Such smaller particles when caught on the pulp mat will tend to plug up the pulp mat more completely and to retard drainage more substantially, so that the retarding effect of the deposition of a unit weight of pulp in the latter partof the sheet-making process will be greater than the corresponding retarding efiect during the. earlier part of the sheet making process. It follows that the degree of difference in such retarding effects will serve as a definitive indication of the relative proportion of smaller pulp particles, or fines, present in the pulp suspension. This indication is of great importance to the papermaker as it tells him the extent to which he is cutting pulp fibers instead of hydrating them. Conventional testers cannot discriminate between a freeness value obtained by destructive cutting of fibers and the same value obtained by proper hydration of uncut fibers.

From the foregoing it can be seen that the drainage operation is affected by many substantial factors other than the freeness of the pulp. I have discovered that the basic factor which determines the freeness value of any pulp is the rate of change of free drainage velocity caused by the deposition of an extremely thin layer of the pulp, and I have devised a method and apparatus which permits: (1) the isolation of this basic factor from myriad other Fourdrinier paper machine operating variables; (2) continuous indication of the factor; (3) continuous indication of any change in the factor caused by variations in quality of hydration; and (4) control of the refining machines to cause them to deliver a pulp of uniform freeness.

To avoid confusion it should be recognized that pulp freeness conventionally has been defined to be the result obtained by testing pulp in some particular device of arbitrary design. In such a case it is obvious that the result obtained will depend upon the particular design of device used as much as it will depend upon the character of the pulp tested. This fact accounts for the serious discrepancies in freeness values obtained when the same pulp is tested on different conventional devices. I have defined true pulp freeness as the reciprocal of the rate of change of free drainage velccity caused by the deposition of an extremely thin layer of the pulp, and this value will be consistent for a particular pulp regardless of the design of any test device so long as it measures the variable soughtl In calculus terms this definition may be expressed practically as freeness AV and theoretically as freeness 05- wnere V represents free drainage velocity, and P represents pulp mat thickness.

To avoid confusion it should also be noted that in my use of the term quality of hydration, I am considering good quality of hydration of pulp fibers as that treatment which exposes the fibers to intense gross and molecular stresses Without causing the mechanical dilapidation of a substantial proportion of the fibers; and poor quality of hydration as the similar treatment of the fibers which does cause the mechanical delapidation of a substantial proportion of the fibers. I have discovered that pulp freeness as herein defined, is substantially uniform throughout the drainage operation when pulp has been subjected to good quality hydration, and that the freeness is not uniform throughout the drainage operation when pulp has been subjected to poor quality hydration. Speaking again in calculus terms the quality of hydration can be expressed as the reciprocal of the second derivative of the free drainage velocity; or, practically 1 quality of hydration oc F and, theoretically,

- 1 quality of hydration ocfl dP where V represents free drainage velocity, and P represents pulp mat thickness.

In accordance with my invention the freeness and quality of hydration of pulp suspensions may be determined independently of the consistency of the suspension, by determining the effect on drainage caused by the settling of fibers on a moving screen or Wire of a Fourdrinier machine. In carrying out my invention, I install a plurality of troughs under the Fourdrinier wire at difierent distances from the head box of a paper making machine which empty into containers of equal dimensions having drainage orifices therein of 0 equal size. The first trough is located near the head box of the paper machine, at a suflicient distance to allow the preliminary formation of a thin fiber mat on the Fourdrinier wire. A second trough is located closely adjacent to the first trough and the other trough or troughs are lo cated further away from the head box. Since the drainage velocity decreases throughout the sheet making operation there will always be a greater volume of water in the first container than in the second container. It will be understood that the drainage orifices in the containers are of such sizes to accommodate the drainage through the wire and from the troughs after suficient head has been built up. By this means I am enabled to determine simultaneously the drainage rate at a plurality of hydrostatic heads and a plurality of thicknesses Of fiber mat on the wire. At any given condition of Fourdrinier operation the ratio of the volume of liquid collected in the first container to the volume of liquid collected in the second container is proportional to the freeness of the pulp suspension. The reason for this is that the effects of consistency variation, decrease in drainage velocity caused by decrease of hydrostatic head, variation of water viscosity caused by temperature variation, and similar factors apply to each trough, whereas the efiect of the pulp mat added proportional to the drainage into the first trough applies only to the second trough. Thus this measurement isolates the variable sought from the other variables and determines the deceleration in drainage due to pulp freeness during the sheet forming process.

In the accompanying drawings forming a part of this application,

Fig. 1 is a diagrammatic view showing apparatus for determining the rates of deceleration in drainage through the Fourdrinier wire at different distances away from the headbox; and

Fig, 2 is a diagrammatic view showing apparatus for indicating the ratio between the difference in volume in adjacent containers and the greaterlvolume.

Referring now to the drawing for a better understanding of my invention I provide a trough l0 beneath the moving Fourdrinier wire H of a papermaking machine a sufficient distance from the head box 12 to allow the preliminary formation of a thin fiber mat l3 on the Fourdrinier wire. A second trough M of the same width as trough I0 is provided relatively close, but further away from the head box I2, than trough II]. The troughs In and I4 discharge the drained liquid through conduits Ill and I4 into containers l6 and I1, respectively, having the same dimensions. The ratio of the volume of liquid collected in container I6 to the volume of liquid collected in container I! is proportional to the deceleration of drainage between the troughs ID and I4 respectively.

Volume 16 Volume l7 deceleration of drainage for the time interval between trough I0 and trough I4.

A second set of similar troughs I3 and I9 may be located similarly to troughs II] and I l but further along the Fourdrinier wire. The troughs l8 and I9 discharge the drained liquid into containers 2I and 22 respectively through conduits I8 and I9 respectively. The ratio of the volume of liquid thus drained into the container 2| to the volume drained into container 22 is an indication of the rate of change in drainage for the time interval between troughs I8 and I9. A comparison of the ratio of volumes drained in troughs I0 and I 4 with the ratio of volumes drained in troughs l8 and I9 is proportional to the change in deceleration of drainage velocity between said pairs of troughs. This comparison of ratios gives the change of freeness during the sheet forming process and indicates to the paper maker the quality of hydration of the pulp on the paper machine. The reason for this is that good quality hydration leaves the greater proportion of fibers intact so that the mechanics of sheet formation are substantially uniform throughout the sheet forming process; whereas, poor quality hydration causes a greater proportion of fibers to become dilapidated or cut into tiny pieces fines and these fines pl-ug up the true pulp mat to increase drainage retardation in the later stages of sheetmaking, which in turn causes a false (and lower) freeness value to be obtained in the later stages of the sheet making process.

When a pulp suspension of high freeness is used on the paper machine a relatively large volume of liquid will be collected in container I6 and, because the drainage retarding effect of such pulp is small, the volume of liquid collected in container I! will also be relatively large. The ratio Volume 16 Volume 1 7 is in such case low and is inversely proportional to the freeness of the pulp. When a pulp suspension of low freeness is used on the paper machine the volume of liquid collected in container I6 is less than in the first case, and the volume of liquid collected in container I1 is proportionately much less than in the first case because of the substantially greater drainage retarding effect of the slow pulp. The ratio Volume 16 Volume 17 with slow pulp, therefore, is high and thus indicates lower freeness of the pulp suspension.

This method of determining the freeness of pulp suspensions is affected very little by variations in consistency since the volume discharged from each trough into its associated container 6 will vary inversely as the consistency varies without affecting the ratio of Volume 16 Volume 17 which is the primary variable desired.

To obtain the rate of deceleration of drainage velocity from the volume of liquid collected the following apparatus may be employed. Referring to Fig. 1, the containers I6 and I! are substantially of the same dimensions and are separated by a common wall in the form of a plate 23 having a hinge 24 at the bottom thereof. The compartments thus formed are sealed apart by a flexible diaphragm 26. Both compartments are provided with drainage orifices 21 and 21' of the same size and of such size that the drainage from the compartments is restricted permitting. the building up of a hydrostatic head therein. When the volume in container I6 is greater than the volume in the container I1 a higher hydrostatic head will exist in container IS. The volume in container I6 is always greater because the liquid drains faster when the sheet is first formed. At 28 I show an air jet which is located closely adjacent and is directed toward the movable wall .or plate 23. The air jet 28 is attached to an air line 29 which communicates with an air pump 3 I, a pressure indicator 32, and a bellows 33, The bellows 33 bears against the plate 23 so that when pressure builds up in the bellows the plate is pushed away from the jet. If the pressure in the bellows 33 builds up sufiiciently so that, aided by the volume in container I! it overcomes the pressure of the volume of liquid in compartment I6, the plate or wall 23 moves away from the jet 28 and'the pressure in the airline drops, until an equilibrium is established between the force exerted by the liquid in container I1 and the bellows 33 and the higher hydrostatic head in container I6. The pressure indicated on the pressure indicator is a function of Volume 17 or rate of deceleration. This device may also be used to obtain the rate of deceleration between troughs I8 and I9.

The change in rate of deceleration for the time interval between troughs I0 and I4 and the troughs I8 and I9 may easily be determined by connecting the pressure line 29 and the pressure line 29 associated with the troughs l8 and [9 to a differential pressure gauge 34.

It will be seen that with the apparatus so far described, the volumes of water draining into the troughs and their associated containers will depend upon the speed of the Fourdrinier wire, so that, to evaluate the data obtained, separate ratios would have to be calculated for each speed at which the machine is operated.

constant the value of which is determined by the freeness and quality of hydration of the pulp suspension, where It represents the indicated rate of drain-age or hydrostatic head in the first container away from the head box and hi the indicated-rate of drainage or hydrostatic head in the second container. In accordance with my invention, I have provided means whereby this ratio is indicated constantly during the operation of the paper machine by means of a Wheatstone bridge.

Referring now to Fig. 2 of the drawing I show apparatus adapted for indicating the free ness factor, continually, as above set forth. At 40 I show a source of direct current, such as a battery, one terminal of which is connected by means of a flexible connection 4| to the sliding contact 42 of a slide'wire bridge divided into resistor portions 43a and 43b by the contact 42. The contact 42 is moved back and forth along the resistor portions, as hereinafter described, by means of a reversible motor 44 adapted to be energized from a circuit 46. Connected to resistor portion 43b is a wire 4'! which leads toa resistor 48 and thence through a wire 49 to the other terminal of the battery 46. The wire 41 is also connected by a wire to one connection of the coil of a polarized relay 6|. Mounted in the container I6 is a float 5| which is connected to and insulated from a sliding contact 52 for the resistor 48. The contact 52 is mounted on a conducting bar 53 which is connected at its upper end to the upper end of the resistance coil of the resistor 48 and to the wire 49. Accordingly, the resistance circuits 41, 48 and 49 varies directly in response to the hydrostatic head in the container l6.

Connected to the upper end of portion 43a of the resistance element is a wire 54 which is connected to one end of the resistance element of a resistor 56, the other end being connected to the wire 49 leading back to the battery 46. The resistance in the resistor 56 is varied by means of a sliding contact 51 mounted on a conducting bar 53, which is connected at its opposite end to the wire 54 and to the end of the resistance element of resistor 56. It is also connected to a wire 59 leading to the other connection of the coil of the polarized relay 6|.

The sliding contact 51 is-operated by means of an air cylinder 52 having a piston 63 therein which is connected to the sliding contact 51 by means of a rod 64 and adjusting nuts 66. The contact 57 is separated and insulated from the rod 64 as by means of insulating material 61. A spring 63 is mounted on the rod 64 and bears against a fixed abutment 69 at its outer end and against a collar I! mounted on the rod 64 at its opposite end. The cylinder 62 is connected to the conduit 29, already described, in which the pressure varies directly responsive to the difference in hydrostatic head of the water in container Hi and that in container Thus, the resistance in resistor 56 varies directly responsive to the difference in hydrostatic heads in the two con tainers.

It will be seen that the circuits described comprise a Wheatstone bridge which includes as one side resistance portion 43b of the potentiometer 45 and as a second side the resistor 48; as the third side the resistor '56, and as the fourth side the upper resistance portion 43a of the slide bridge 45. The cross circuit includes the wires 59 and 55 and the coil of the polarized relay 6|. Whenever the resistance in the resistor 48 is in the 8 greater than that in resistor 56, current will flow from the battery through 4|, 43a, 54, and 59, and through the polarized relay 6|. When the resistance is greater in the resistor 56 than in 48, the current will flow from the battery hrough 4|, 43b, 41 and 55 through the relay 6|.

The relay 6| controls the circuit to the motor 44 asfollows. Associated with the relay 6| is a switch having contacts 16 and 11 controlled by the armature of the relay 6| constituting a switch arm 15 which is connected at 18 to a common wire 19 leading to the motor. The contact I6 is connected to a wire 8| leading to the motor 44 and the contact 11 is connected to a wire 82 leading to the motor 44.

It will be seen that when the relay 6| is energized to actuate its armature, which is the switch arm 15, upwardly, as viewed in the drawing, the motor 44 will be energized through the wires 8| and 19 to run in one direction and when the relay BI is energized to move the armature l5 downwardly to engage the contact 11, the motor 44 will be energized to run in the opposite direction. Connected to the motor 44 is a threaded shaft 83 upon which is mounted a nut 86 connected to a pointer 31 which is connected to and insulated from the sliding contact 42 of the slide bridge 45. At 85 is shown a graduated scale which indicates the relative resistances in the circuits hereinbefore described, and accordingly the freeness of the pulp. Inasmuch as the ratio between the difference in heads in containers I6 and I! and the head in container I6 is a constant, independently of the velocity of movement of the wire II, the indication of the pointer 8! will be a constant the value of which stands in the relation of From the foregoing it will be apparent that I have devised an improved method and apparatus for determining the freeness of pulp suspensions during the manufacture of paper which indicates the freeness and quality of hydration of the pulp, and which is substantially unaffected by the consistency of the pulp suspension.

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications, without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What I claim is:

1. The method of determining the freeness of paper pulp suspensions while a sheet is being formed on a Fourdrinier wire comprising, collecting the drained liquid at at least two different positions beneath the sheet, and measuring the ratio of drainage between said positions.

2. The method of determining the freeness of paper pulp suspensions while on the wire of a Fourdrinier paper machine having a head box comprising collecting the drained liquid at a pair of adjacent positions along the moving Fourdrinier wire a sufficient distance from the head box to allow a preliminary mat of fiber to form thereon, collecting the drained liquid at a second pair of adjacent positions further along said wire, and measuring the ratio of deceleration of drainage at said pairs of points.

3. Apparatus for determining the freeness of paper pulp suspensions while on the wire of a Fourdrinier paper machine having a head box, comprising a trough positioned beneath the wire a short distance from the head box to allow the preliminary formation of a thin fiber mat on said wire and disposed to receive liquid draining through the wire into said trough, a second trough positioned under said Fourdrinier wire further away from the head box than the first trough and also disposed to receive liquid draining through the wire, a pair of equal dimensional receptacles communicating with said troughs, and having restricted drainage orifices of equal size in the lower portions thereof, and means indicating the ratio between volumes of liquid collected in the two receptacles.

4. Apparatus for determining the freeness of paper pulp suspensions while on the wire of a Fourdrinier paper machine having a head box, comprising a trough positioned beneath the wire a short distance from the head box to allow the preliminary formation of a thin fiber mat on said wire and disposed to receive liquid draining through the Wire into said trough, a second trough positioned under said Fourdrinier wire further away from the head box than the first trough and also disposed to receive liquid draining through the Wire, a receptacle communicating with each trough, said receptacles each having a restricted orifice in the lower portion thereof, the orifices being of equal size and so restricted to permit the building up of a hydrostatic head in the receptacles, and means to indicate the difierence in hydrostatic head in the two receptacles.

5. Apparatus for determining the freeness of paper pulp suspensions While on the wire of a Fourdrinier paper machine having a head box, comprising a trough positioned beneath the wire a short distance from the head box to allow the preliminary'formation of a thin fiber mat on said wire and disposed to receive liquid draining through the Wire into said trough, a second trough positioned under said Fourdrinier wire further away from the head box than the first trough and also disposed to receive liquid draining through the wire, a pair of equal dimensional receptacles communicating with said troughs and having restricted drainage orifices of equal size in the lower portions thereof, a movable wall disposed to seal the containers apart, an air pump, an air jet communicating with said pump and sealed against said movable wall when the hydrostatic head in the container opposite the jet is greater than the hydrostatic head on the side adjacent the jet, a bellows communicating with said pump and disposed to push the wall away from the jet thereby causing the pressure to vary in said air line, and a pressure gauge communicating with said air lines.

6. Apparatus for determining the freeness of paper pulp suspensions while on the moving wire I of a Fourdrinier paper machine having a headbox, comprising a pair of troughs positioned beneath the wire a suficient distance from the head box to allow a preliminary formation of a thin fiber mat on said wire and disposed to receive liquid draining through the wire above said troughs, a second pair of troughs further away from the head box than the first two troughs and also disposed to receive the liquid draining through the wire above said second pair of troughs, a pair of equal dimension receptacles communicating with each pair of troughs and having restricted drainage orifices of equal size in the lower portions thereof, means indicating the rates of deceleration of drainage in the respective pairs of receptacles, and other means indicating the change in rates of deceleration occurring between said pairs of receptacles.

'7. Apparatus for determining the freeness of paper pulp suspensions while on the moving wire of a Fourdrinier paper machine havin a headbox, comprising a pair of troughs positioned beneath the wire a sufiicient distance from the head box to allow a preliminary formation of a thin fiber mat on said wire and disposed to receive the liquid draining through the wire above said troughs, a second pair of troughs further away from the head box than the first two troughs and also disposed to receive liquid draining through the wire thereabove, a pair of equal dimensional receptacles communicating with each pair of troughs and having restricted drainage orifices of equal size in the lower portions thereof, a movable wall separating each pair of receptacles, an air pump for each pair of troughs, an air jet communicating with each pump and sealed against said movable wall when the hydrostatic head in the container opposite the jet is greater than the hydrostatic head on the side adjacent the jet, a bellows communicating with each pump and disposed to push the wall away from the jet thereby causing the pressure to vary in said air lines, and a difierential pressure gauge communicating with both of said air lines.

WILLIAM G. REYNOLDS.

REFERENCES (JIEED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,573,850 Naiman Feb. 23, 1926 1,701,331 Merrill Feb. 5, 1929 2,379,835 Sisler July 3, 1945 2,442,888 Cram June 8, 1948

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