US3144763A

US3144763A - Freeness tester

Info

Publication number: US3144763A
Application number: US116862A
Authority: US
Inventors: Ned H Mayo
Original assignee: Armstrong Cork Co
Current assignee: Armstrong World Industries Inc
Priority date: 1961-06-13
Filing date: 1961-06-13
Publication date: 1964-08-18
Anticipated expiration: 1981-08-18

Description

Aug-18,1964. I N. H. NYIAYO 3,144,763

FREENE SS TESTER Filed June 'l5, 19.61

STOP START GROUND ELECTRODE ELECTRODE ELECTRODE GAlN CONTROLS.

MAM-- Fi 3 I IN V EN TOR. N E D H. MAYO United States Patent Pennsylvania Filed June 13, 1961, Ser. No. 116,862 6 Claims. (Cl. 7363) This invention relates generally to a freeness tester, and more particularly to an automatic freeness tester for measuring the freeness of fiber stock. Still more particularly the invention relates to an automatic cyclic freeness tester adapted to measure sufficiently and accurately the freeness of a wide variety of fiber stocks made of suspensions of various kinds of fibers in water.

Freeness is defined as the rate of drainage of water through a pulp. Many devices have been developed to conduct such freeness measurements, these measurements sometimes being given in terms of seconds. The most widely used, the Canadian standard, gives its measurements in terms of milliliters of water.

However, there has been a need for a freeness measuring device which operates automatically without an operator, which is self-cleaning and not subject to fouling or clogging, and which is sensitive to a broad range of freeness encountered in the manufacture of paper, felt, and fiberboard.

It is the primary object of the present invention to supply such a freeness tester.

The invention contemplates a freeness tester for determining freeness of fiber stock wherein the tester comprises an elongated shell having an opening at each end thereof. A wire screen is positioned over the opening at one end of the shell. Inside the shell are positioned indicating means for measuring the rate of water rising up through the interior of the shell through the screen.

The invention will be better understood with reference to the attached drawing in which:

FIG. 1 is a side, sectional view of one embodiment of the invention;

FIG. 2 is a top view of FIG. 1; and

FIG. 3 illustrates a timing circuit suitable for use with the freeness tester of the present invention.

Referring to the drawings, the elongated shell 1 is preferably of cylindrical shape, although a shell having a cross-sectional shape in the form of a square or other polygon is possible. The handles 2 allow the shell to be dipped into the stock to be measured or to be physically suspended in said stock by means of suitable support, not shown. One end of the shell 1 is closed with a screen 3 which may be of suitable mesh for admitting the water into the interior of the shell while retaining the mat of fibers on the exterior or bottom side of the screen. The mesh size of the screen 3 may be varied depending on the fineness of the fibers in the stock, but for use in the manufacture of cellulosic fiberboard it is preferred that the screen 3 be of 24-mesh, United States standard. The screen itself should be made of a suitably corrosion-resistant material such as Phosphor bronze wire cloth or the like.

It is preferred that a turbulence guard 4 be positioned on the shell 1 at the screen end of the shell in order that the mat which forms on the bottom of the screen 4 be protected from erosion due to turbulence of the stock during the freeness measurement. It will be apparent that the turbulence guard 4 may be nothing more than the lower portion of the shell 1 when the screen 3 is mounted up inside the shell 1 instead of directly at the opening thereof.

One of the advantages of the freeness tester of the present invention is that it is particularly well adapted to the electrical measuring of the time interval required 3,144,763 Patented Aug. 18, 1964 ice for water to rise inside the shell 1 from a starting point to a stopping point; these two points merely serve to define the distance the water rises inside the shell. Although these distances can be set off with visible markings merely, it is preferred for the best accuracy and for unattended operation of the freeness tester to utilize electrodes mounted within the freeness tester. The starting electrode 5 is positioned so that the bottom thereof is located just above the screen 3. The ground electrode 6 is positioned so that its bottom corresponds with the bottom of electrode 5. It will be apparent that ground electrode 6 may reach below the bottom of starting electrode 5 in a direction toward the screen, but the ground electrode should never be above the bottom of starting electrode 5. If a potential is impressed across starting electrode 5 and ground electrode 6, the appearance of stock water between these two electrodes will be manifest by a slight fiow of current between the two electrodes 5 and 6. This current may be amplified and used to activate a timing device '7 shown in FIG. 3. As the water continues to rise through the screen 3 above the bottom of starting electrode 5, it will eventually reach the bottom of stopping electrode 8 at which point current will flow between the ground electrode 6 and stopping electrode 8. This current can be amplified and used to stop the timer 7 and thus indicate in an extremely accurate manner the time interval it has taken the water to rise from the bottom of starting electrode 5 to the bottom of stopping electrode 8. This rate of flow of the water into the interior of the shell 1 will be a measure of the freeness of the fiber stock. Water enters the shell 1 through the screen 3, rapidly at first, then more slowly as a mat of fiber builds up on the under side of the screen 3. The time required for the water level in the shell 1 to rise between the two reference points at the bottom of

electrodes

5 and 8 is used as the measure of freeness.

The spacing between the tips of the electrodes may be varied by changing their respective lengths. This feature gives the tester a high degree of adaptability. For instance, if the tester is to measure the freeness of a very slow stock, the vertical distance between the tips of the starting and stopping electrodes can be made smaller. In this manner a freeness measurement can be made in a reasonable length of time. For very fast stocks, the electrode tip spacing can be increased in order to keep the tester sensitive to minor freeness variations. For each different electrode spacing it is necessary to calibrate the tester against a known freeness scale.

The freeness tester of the present invention is operated by plunging it rapidly into the stock to be tested up to within about an inch of the top. Water enters the tester through a screen at the bottom, rapidly at first, then more slowly as a mat of fiber builds up on the bottom.

It is apparent that the ground electrode 6 may be dispensed with and the shell 1 itself used as a ground for the electrical system if desired. In any case, the electrodes may be mounted on the electrode mount 9 and insulated from the mount 9 by means of insulators 10.

FIG. 3 shows a timing circuit suitable for electrically measuring the time interval for the water to rise between the tips of the two

electrodes

5 and 8. The tips of

electrodes

5 and 8 are preferably pointed in order to eliminate drops of water hanging therefrom and thus destroying the accuracy of the interval between the electrode tips.

The shell 1 may be made of any suitable material. A section of a 6" cast iron pipe has been found to be suitable. The electrodes may be of copper or other conductive material. The insulators may be of rubber, cork, ceramics, or other suitable insulating material.

The freeness tester of the present invention must be correlated or standardized against any desired freeness scale. To correlate freeness readings of the freeness tester of the present invention with those of the standard Oliver freeness tester, measurements have been run by both instruments on the same stock samples. To insure accuracy, four readings were taken by each method on each sample, and the arithmetic mean of the four was used. The stock samples tested ranged in Oliver freeness from 15-90 seconds. Slow stock samples were prepared by the addition of kraft fiber to groundwood pulp, while fast samples were obtained'by blending coarse groundwood with groundwood pulp. In a series of tests for approximately 1000 measurements, there was not a single failure of the outfiowing white water to wash the mat completely free from the bottom of the screen. No build-up or accumulation of solids occurred.

If needed, correction curves may readily be constructed to take into account the efiects of temperature and consistency variations on the freeness tester of the present invention. Such correction curves will be made in known manner.

In order for the freeness tester of the present invention to work continuously and automatically, a constant level sampling box may be built through which a sample of stock to be tested will continuously flow. The sample will continuously be pumped back into the system from which it was withdrawn. It may be convenient to have a small agitator located in the sampling box to break up the cake of fibers formed from the preceding freeness test. The freeness tester itself will automatically be immersed and withdrawn from the stock in the sampling box.

I claim:

1. A freeness tester for determining freeness of fiber stock comprising an elongated shell open at each end thereof, a Wire screen adapted to admit Water but not fibers positioned over the opening at one end of said shell,

and detecting means positioned inside said shell for measuring the rate of rise of water between two spaced apart points, one of said points located above the other of said points, both of said points being situated within said shell and means operable by said detecting means for indicating the rate of the rise of water inside said shell.

2. A freeness tester according to claim 1 wherein said detecting means comprise electrodes.

3. A freeness tester according to claim 1 having a turbulence guard extending beyond said screen.

4-. A freeness tester according to claim 1 wherein said shell comprises a cylinder.

5. A freeness tester for determining freeness of fiber stock comprising an elongated shell open at each end thereof, a wire screen adapted to admit water but not fibers positioned over the opening at one end of said shell, and indicating means for measuring the rate of rise of water inside said shell, said indicating means comprising, in combination, an electrode for detecting a starting point for measuring the rate of water rising inside said shell through said screen, another electrode for detecting a stopping point for measuring the rate of water rising inside said shell, and means operable by said electrodes for indicating the rate of the rise of water inside said shell.

6. A freeness tester according to claim 5 wherein said electrodes are pointed at the bottom thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,292,276 Dysal't Jan. 21, 1919 2,483,450 Wolfner Oct. 4, 1949 2,734,378 Meyers Feb. 14, 1956

Claims

1. A FREENESS TESTER FOR DETERMINING FREENESS OF FIBER STOCK COMPRISING AN ELONGATED SHELL OPEN AT EACH END THEREOF, A WIRE SCREEN ADAPTED TO ADMIT WATER BUT NOT FIBERS POSITIONED OVER THE OPENING AT ONE END OF SAID SHELL, AND DETECTING MEANS POSITIONED INSIDE SAID SHELL FOR MEASURING THE RATE OF RISE OF WATER BETWEEN TWO SPACED APART POINTS, ONE OF SAID POINTS LOCATED ABOVE THE OTHER OF SAID POINTS, BOTH OF SAID POINTS BEING SITUATED WITHIN SAID SHELL AND MEANS OPERABLE BY SAID DETECTING MEANS FOR INDICATING THE RATE OF THE RISE OF WATER INSIDE SAID SHELL.