SE447307B - SET AND DEVICE FOR SEATING FIBER FLEXIBILITY - Google Patents

Abstract

FIBRE FLEXIBILITY METER A method and apparatus are disclosed for obtaining an indication of fibre flexibility by spraying a pulp sample of preselected average fibre length against the bottom of a horizontal screen having a negative pressure thereabove whereby a selected pressure drop is applied across the screen and the pulp sample is divided into a retained and a passed fraction. The flexibility index is obtained by a ratio indicative of the fibre mass in the passed fraction or retained fraction to the fibre mass in the feed.

Description

It is therefore an object of the present invention to provide a method and apparatus for measuring fiber flexibility in a pulp sample which operates relatively quickly and which can be used for online monitoring of fiber flexibility.

This is achieved by a method according to the present invention, characterized in that a slurry of said fibers is sieved to obtain an feed fraction with a selected average fiber length, that the concentration of the feed fraction is adjusted to a selected concentration in the range 0.05 ~ 0.3%, that said feed fraction is sprayed against the bottom of a substantially horizontal screen. whose apertures have minimum dimensions which substantially correspond to a b / L ratio of 0,3 ~ 0,7 for a screen with square apertures, where b corresponds to the dimension on one side of the square aperture and L corresponds to the average fiber length in the square aperture. entered the fraction. that a sufficient negative pressure is maintained above said horizontal screen, so that a flow of the slurry is obtained through said screen without a mat being formed below said screen and to divide said fed fraction into a retained and a passed fraction, that a ratio produced indicating a fiber mass in the permeated or retained fraction of the fiber mass in said feed, to thereby obtain an indication of the fiber flexibility, and by an apparatus for measuring the fiber flexibility which is characterized by a substantially horizontal screen, an upper housing , which communicates with the upper part of said screen, means for spraying a fiber slurry to be tested with said fibers in random orientation towards the bottom of said horizontal screen. means for maintaining a negative pressure in said upper housing to effect a flow of a permeated slurry through said strainer without mat formation on the bottom of said strainer and dividing said infiltrated slurry into a passed and retained fracture. means for removing said permeable fraction from the upper housing. Further features, objects and advantages of the invention will become apparent from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic view of the screen equipment for measuring fiber flexibility; is a schematic view of a device for obtaining a fiber fraction of predetermined average fiber length, Fig. 3 is a schematic plan view of a flexibility measuring equipment according to the present invention comprising means for obtaining a preselection of preselected fiber length and the screen device, fig. H is a diagram where the ratio of fibers in the retained fraction (Fr) to the fibers in the feed (Ff) is plotted against the ratio between the size of the screen opening to the fiber length to be tested, Fig. 5 is a diagram showing the concentration ratio (Cp). / Cf) and the fiber ratio (Fp / Ff) in the passed fraction to the feed plotted against the pressure differential across the screen, Fig. 6 is a diagram showing the concentration ratio (CP / Cf) and the fiber ratio (Fp / Ff) in the permeation fraction against the feed plotted against the vacuum in the upper housing in mm water column, Fig. 7 is a diagram of the ratio of the concentrations in the permeation fraction to the concentration in the feed (C / Cf) plotted against the feed concentration (Cf ) as percent dry oven (0.D.) at a pressure drop across the sieve of 15 mm H 2 O, Fig. 8 is a graph plotting flexibility index (CP / Cf) against freeness throughout the mass in Canadian standard freeness (CSF) for two different f bleached softwood pulp, Fig. 9 is a graph where the flexibility index (CP / Cf) is plotted against the specific refining energy of a softwood refiner pulp retained on a 35 mesh screen, Fig. 10 is a graph showing the bulk volume and tensile strength of the the transmitted 1H-retained 28-fraction and the transmitted-28-retained-H8-fraction are plotted against flexibility index (CP / Cf), and Fig. 11 is a diagram where the breaking factor, tear factor, tensile strength and bulk density are plotted against flexibility density index (Fp / Ff) for different fractions of a thermomechanical mass, a 50-50 mixture of thermomechanical mass and force mass and for force mass.

The fiber flexibility measuring apparatus 10 consists essentially, as schematically indicated in Fig. 1, of a device with an upper housing 12, connected to a lower housing 1H by a quick-release valve 16. Across the lower housing 1U, at a distance from its upper end, a horizontal strainer 18 is arranged, and at a distance below this strainer a nozzle 20 is arranged to direct a slurry of pulp fibers towards the bottom of the strainer 18. The pulp fiber slurry is fed to the nozzle 20 via a pipe 22.

The upper chamber 12 has an overflow tube 24 for extracting the sample to be tested or measured and a connection to a vacuum pump or the like, as indicated by line 26. In this device, the pulp sample is introduced via line 22 and sprayed via the nozzle 20 against the bottom of the screen 18.

Negative pressure is maintained above the screen 18 by opening the valve 16, so that the upper part of the housing 1% above the screen 18 is subjected to a vacuum which is applied via the line 26. The hash fraction which has passed through the screen 18 passes through the quick-closing valve 16 into the upper chamber 12 and is drawn off via line 2U. The valve 16 is only needed to facilitate the generation of the negative pressure above the screen 18 and to close the apparatus.

The fiber length of the fraction fed to the flexibility measuring apparatus 10 must be reasonably controlled to ensure sensitivity and reproducibility of the results obtained with the measuring apparatus. The fiber fraction fed via line 22 can be obtained from a fiber length classifier, such as a "Bauer-McNett Classifier" or alternatively according to a preferred embodiment of the invention, screeners may be provided in the measuring apparatus itself.

Such a device is shown in Fig. 2 and in the illustrated arrangement is composed of two tanks 30 and 32 and two screens 3% and 36. These screens are vertical self-cleaning screens. Dilution is supplied to the two tanks Sd and 32 via lines 38 and HU, the streams of dilution being controlled by sensors H2 and 44 which sense the level in tanks 30 and 32 and control valves 46 and H8 in lines 38 and HD. Pumps 50 and 52 pump the samples into tanks 30 or 32 through lines 5H or 56, respectively, to filters 3a and 36, respectively.

The reject from the screen 3U passes via line 58 back to 447 307 z - the tank 30 and the acceptance passes via the line 60 into the tank 32, while the reject from the screen 36 passes via the line 62 to the tank 32 and the acceptance passes via the line BH for receipt becoming.

To obtain samples with the required fiber length for feeding to the flexibility measuring apparatus of Fig. 1, a sufficiently large sample is placed in the tank 30 and pumped via the pump 50 and line SU to the sieve 3H, where it is divided by a sieve, which may suitably be selected so that it gives a fraction corresponding to e.g. a 28 mesn strainer in a Bauer- fi c fl a CLassifier, so that the material passing through the strainer bra and into the tank 32 would be the 28 part passed through the sample, while the reject is simply returned to the tank 30 and corresponds to the long-fiber fraction ( retained 28) and recycled.

It is obvious that the level in the tank 30 drops and it is then necessary to add water via the line 38, in order to keep the level substantially constant, whereby the concentration in the tank 30 is reduced.

The acceptor that accumulates in the tank 32 is pumped via the pump 52 and the line 56 dll the strainer 38, which can be equivalent to e.g. an H8 mesh strainer in a Bauer-Mc fl a Classifier. The material retained thereon, ie. the reject, passes via line 62 back to the tank 32, whereby the tank 32 accumulates a fraction passed ~ 28 retained-H8, or any desired fraction.

The concentration in the tank 32 changes as material is drawn therefrom via line 64 and water is supplied via a line H0 to maintain a constant level in the tank. Before the test in the flexibility meter, the concentration of the mass fractions in tanks 30 and 32 is adjusted to e.g. 0.15%, either by adding dilution water if the concentration is too high or by closing the dilution valve and running the mass through the strainer, if the concentration is too low.

As shown in Fig. 3, which is a schematic plan view of the combination of the flexibility meter according to Fig. 1 and the fractionation device according to Fig. 2, it can be noted that the meter 10 is arranged on a base 66 and can be moved forward and to wife from a position above the tank 32 to a position above the tank 30, as indicated by the arrow 68.

After stable operation of the fractionation device is achieved, after a predetermined period of time sufficient to form a selected length fraction in the tank 32, the valves 70 and 72 in the lines Su and 55 are closed and the pumps SU and 52 are stopped.

If the flexibility of the mass fraction in the tank 32 is to be tested, the concentration is adjusted as described above to the appropriate sample concentration and the valve 7u is opened and the pump 52 is started to pump the stock from the tank 32 through the valve 7H and line 22 to the flexibility measuring apparatus 10. . to the nozzle 20. Pour which passes through the strainer of the flexibility meter will flow into the tank 12, compare Fig. 1, while the reject falls back to the tank 32.

If the flexibility is to be tested for the sample in the tank 30, the concentration in this tank is adjusted to the required degree, and the flexibility meter 10 is moved as indicated by the arrow 68 so that it ends above the tank 30, the valve 74 is closed and the valve 76 is opened, the pump 50 is started to pump via valve 76 and line 22 to the flexibility meter 10.

The function of the horizontal screen for determining flexibility is affected by variables of the pulp fibers themselves and by the operating variables of the equipment.

The most important or significant fiber variables are fiber length and fiber flexibility. In order to eliminate as far as possible the possible effect of fiber length on the determination of flexibility, the pulp sample is first filtered to obtain a fraction with a preselected fiber length, eg the fraction which passes 1Q mesh but is retained at 28 mesh in a Bauer -McNett Classifíer, or any other suitable fiber length fraction.

The operating variables for the process or equipment shall be maintained substantially the same for each sample.

One of the main variables is the size of the sieve openings of the flexibility meter 447 307, which must be correlated with the fiber length fi of the fraction to be tested, ie. the openings must be smaller than the average fiber length of the masses to be tested but still have a relatively high throughput for the more flexible fibers. In practice, it has been found that the 1U / 28 fraction, i.e. the fraction that has passed 1H mesh but is retained on 28 mesh screen in a Bauer-Hc fl a Classifier, for softwood pulps should preferably be tested with a 16 mesh screen and the 28/48 fraction with a 3D_gesh screen.

For a more adequate description of the mesh size requirements, reference may be made to Fig. H, which shows a curve where Fr / Ff, i.e. the amount of fiber in the retained fraction / amount of fiber in the feed, plotted against b / L, where b is the length on one side of the square sieve opening in the flexibility meter and L is the fiber length in the feed. In order to obtain a significant difference in the ratio Fr / Ff, it is necessary that the ratio b / L is in the range of about 0.3-0.7. Preferably, the operation takes place at about the 0.5-0.6 range, which means that the dimension b for the screen should normally constitute about half of the fiber length of a material being tested. Dimension b has been specified for a screen opening that is square, but equivalent values for other shapes of the openings, e.g. rectangular etc., can be determined.

The dissertation of Ronald Estridge in TAPPI April 1962 volume 45 no.

H provides a theoretical way to obtain equivalent values or alternatively they can be determined empirically.

In Fig. H, the open circles represent a force mass and the filled circles a mechanical mass for a 14/28 fraction, while the open triangles represent force mass and the filled triangles mechanical mass for the 28 / H8 fraction. The center curve is the theoretical curve for rigid fibers derived according to Estridge above for wire drainage or screening on a paper machine.

Another parameter is the pressure differential across the screen 18 on the flexibility meter, as this has a very significant effect on the fiber division. This pressure differential should not be so strong that a fiber mat builds up on the bottom of the screen, which can happen especially with rigid fibers, which would significantly affect the operation of the screen and interfere with the passage of a fraction therethrough. This relationship is clearly indicated in Fig. 5.

The open circles represent a mass of force and the filled circles a refiner mass (RHP). CP / Cf is the ratio between the concentration of the passed fraction and the feed concentration and Fp / Pf is the ratio between the fiber mass flow in the passed fraction to the fiber mass flow in the feed. It is obvious that in order to obtain a division between flexible power fibers and mechanical fibers a pressure differential must be maintained over the screen, however care must be taken to ensure that the pressure drop is not so high that a mat is formed on the screen, but still high enough to provide a bending force on the fibers. The allowable range for the pressure drop varies depending on the stiffness and / or type of fibers being tested and is generally in the range of 10-150 mm H 2 O, but should preferably be the same for all samples and be in the range of 20-25 mm H 2 O.

The build-up of fibers on the screen 18 is determined in part by the flow rate through the screen which in itself is partly determined by the negative pressure maintained in the upper housing 12. This negative pressure must at least be sufficient to maintain a flow into the housing. 18 and out through the overflow line 24 and should at least be sufficient to maintain stable operation, as will be apparent from the discussion in connection with FIG.

Fig. 6 shows the unfilled markings for the 14/28 fraction and the filled markings for the 28 / H8 fraction. The circles denote softwood mass and the squares thermomechanical IEIâSSOP.

Before a flow has been established, no reading of either CP or Fp can take place, so it is necessary for the samples to accumulate. If the flow rate is too low, the proportion of fibers to water flowing out of the upper housing 12 can be affected, as shown by the left-hand parts of the curves CP / Cf vs pressure in mm H 2 O. The concentration of the permeate fraction flowing from the upper chamber 12 at low vacuum is substantially higher than when the flow rate increases, thereby indicating a preferred ratio of fiber to 9,447,307: 2 water at low vacuum. It should be noted that the concentration in the permeation fraction (CP) seems to stabilize at a lower value and changes to an extremely small extent after a certain minimum flow rate has been reached. For this reason, it is preferred to operate within what is referred to herein as the "stabilized area", which is the part of the curve that has a relatively small slope and for the specific instrument used obtained with a negative pressure in the upper housing of about 200 There is no point in increasing the applied vacuum significantly beyond this range, as such an increase does not in any way improve the results and if the vacuum is increased too much, the pressure drop across the screen 18 can be increased to a point where a mat formed, whereby the equipment ceases to function.

It should be noted that both the concentration in the permeate fraction and the mass flow of the permeate fraction tend to stabilize within the stabilized range. However, the mass flow is significantly affected by the amount of water transported together with the fibers in the permeated fraction and reduces the differences that can be observed between different masses. preferably the ratio of either the concentration in the retained fraction or in the permeated fraction to concentrations in the feed is used to denote the flexibility. It is very easy to obtain a sample of the passed fraction, so the ratio between the concentration in the passed fraction and the concentration of the feed, ie. CP / Cf, preferred. Selecting the concentration instead of the mass flow ratio (FP / Ff) also simplifies the equipment and samples necessary to obtain the required information.

The female piece 20 should be designed to direct the fibers towards the screen in a uniform manner. This is achieved e.g. by a random distribution of the orientation of the fibers as they hit the screen. The feed rate should also be set for all samples, because if the feed rate changes, the rate at which the fibers hit the screen changes. At lower feed rates, the ratio of the fibers passing through the screen to the cohesive ones decreases, e.g. at a feed rate of 21.5 l / min, the ratio of fibers passing through the screen to fibers fed to the screen is 0.75, while when the flow rate to the screen was reduced to 11 l / min, this ratio for the same fibers decreased to 0.3.

Another important variable is the feed concentration, as shown in Fig. 7, which shows the changes in the concentration ratio of the passed fraction to the feed as a function of the feed concentration for a mechanical mass. If the input concentration changes, the concentration ratio also changes and thus, since the concentration ratio is the indicator for the flexibility equipment, it is important that the input concentration to the measuring equipment is kept substantially constant in the range 0.05-0.3. It is preferred to operate at a concentration of about 0.15%.

Laboratory equipment may suitably have a screen area 18 corresponding to about 100 mm in diameter. For constant meaningful results, the nozzle 20 must have a predetermined shape, which in the preferred arrangement means a whole cone nozzle and the channels must be large enough to allow the passage of the largest particles that can be expected to be present in the slurry. The beam is so directed that it is distributed substantially uniformly over the entire area of the screen 18 with random orientation of the fibers when they hit the screen 18.

The preferred operating conditions are at a feed concentration of about 0.15% using a screen 18 with a b / L ratio of between 0.5 and 0.6 and with square openings, a pressure drop across the screen of between 20 and 25 mm water column, a substantially constant vacuum in the upper chamber 12 of 200 or more for the specific equipment used and preferably within the "stabilized" flow ranges and that the nozzle 20 sprays over an area of about 100 mm diameter on the screen 18 with a random orientation of the fibers when they hit the screen 18. The screens 34 and 36 preferably have mesh sizes of 15 and 30, respectively.

The following examples illustrate the effectiveness of the present invention in distinguishing pulps on the basis of fiber flexibility.

Example 1 The preferred embodiment of the apparatus was used to test similar fractions of different pulp types. Table 1 shows the differences found with regard to yield and pulp production processes. The fiber flexibility is known to decrease with increasing yield and it is usually higher for sulphite than for sulphate pulps.

Table 1 _ 'Yield Flexibility index (C / C Ü Mass% P f 14/28 23 / M8 fraction fraction Mechanical softwood mass 98 0.1-0.2 0.2-0.65 Chemical softwood mass SH-88 0.55 -1.2 0.5-0.95 Bleached kraft pulp from softwood H5 1.1-1.3 1.1 Bleached kraft pulp from hardwood H5 - 1.2 Unbleached bisulfite pulp from softwood 60-70 1.5-1.7 - Example 2 The relationship between the flexibility index determined by CP / Cf and the fiber flexibility was further determined by samples performed using the preferred embodiment of the present invention on bleached softwood pulp samples subjected to varying degrees of grinding.The results are shown in Fig. 8 as a function of freeness for the whole The circles represent the 1 # / 28 fraction and the triangles the 28/48 fraction from Bauer-Hc fl a Classifier.The tested bleached softwood pulp clearly showed that the more the fibers are ground the greater the flexibility index.Similar tests were performed on the softwood refiner pulp. fraction retained on a 35 mesh screen, i.e. the loan the fiber fraction, at different specific refining energies. Again, a clearly increasing flexibility is obtained with increased energy supply, as shown in Fig. 9.

Example 3 Fiber flexibility is related to fiber conformability, measured by the bulk volume or density of laboratory handsheets, and decreases as the bulk volume increases. It is also known that the bonding of the fibers, which is manifested by the tensile strength, increases with increasing flexibility through an increase in the relative bonded area of the fibers. Pig. 10 shows examples of mechanical pulps, filled symbols, and chemical mechanical pulps, unfilled symbols, in which increased fiber flexibility corresponds to an increase in wear length and a decrease in bulk volume, which further indicates that the flexibility index corresponds to the fiber flexibility.

Example H Pig. 11 shows the relationship between flexibility index and strength properties, and the bulk volume of a thermomechanical pulp (THF) and a bleached sulphate pulp (Kraft) and mixtures of these pulps. The diagrams show that the flexibility index increases with wear length, tear factor and burst factor, but decreases with bulk volume. Table 2 shows what the symbols used in Fig. 11 correspond to.

Table 2 Fraction TMP TM? / Force Force 1u / 2a 0 0 Û wa ü _ CJ The ratio CP / Cf and Fp / Pf have both been used to denote fiber flexibility, as it has been shown that both of these ratios indicate the flexibility of the fibers, i.e. there is a specific relationship between these quotas. However, C and Cf are not only the values that are easiest to obtain, but they also make a more large-scale difference, compare Fig. 6, and as indicated above, it is preferable to use these values to denote flexibility index.

Claims (8)

447,307 Patent claims A method of measuring the fiber flexibility of fibers, characterized in that a slurry of said fibers is sieved to obtain an feed fraction with a selected average fiber length, that the concentration of the feed fraction is adjusted to a selected concentration within the range 0 , 05-O.3 t. That said feed fraction is sprayed against the bottom of a substantially horizontal screen (18), the openings of which have minimum dimensions which substantially correspond to a b / L ratio of 0.3-0.7 for a screen with square openings, where b corresponds to the dimension on one side of the square opening and L corresponds to the average fiber length in the fed fraction. that a sufficiently negative pressure is maintained above said horizontal screen. for a flow of the slurry to be obtained through said screen without a mat being formed under said screen and for dividing said input fraction into a retained and a passed fraction. that a ratio is produced which indicates a fiber mass in the passed or retained fraction to the fiber mass in said feed. to thereby obtain an indication of the fiber flexibility. 2. A method according to claim 1. characterized in that the concentration is about 0.15 t. 3. A method according to claim 1, characterized in that said b / L ratio is between 0.5 and 0.6. 4. A method according to claim 1, 2 or 3, characterized in that said negative pressure is within the "stabilized" flow range. i.e. where an increase in the negative pressure in the lower housing no longer gives a marked decrease in concentration in the permeated fraction (Cp) (Fig. 6). 5. S. A method according to claim 1, 2 or 3, characterized in that a pressure drop is maintained over said screen of 20-25 mm H 2 O. 6. A method according to claim 1, 2 or 3, characterized in that said spraying comprises spraying said feed fraction in such a way that the fibers hitting the bottom of said sieve have a random orientation. 7. Apparatus for measuring fiber flexibility, characterized by a substantially horizontal strainer (18), an upper housing (12). which communicates with the upper part of said sieve. means (20) for spraying a fiber slurry to be tested with said fibers in random orientation towards the bottom of said horizontal screen. means (26) for maintaining a negative pressure in said upper housing to effect a flow of a passed slurry through said screen without mat formation on the bottom of said screen and dividing said input slurry into a passed and a retained fraction. means (24) for removing said permeated fraction from the upper housing. Apparatus according to claim 7, characterized in that it further comprises a first container (30) and a second container (32) and a first (34) and a second (36) screen means, said first screen means (34 ) has larger openings than said second screen means (36). means (50) for pumping a slurry from said first container (30) to the first screen means (34). to thereby divide said sample into a retained fraction and a passed fraction, collecting said passed fraction into said second container (32). means (52) for pumping said passed fraction from said second container (32) to said second screen means (36) to form a second passed and a second retained fraction. means (62) for directing said second retained fraction to said second chamber and means for connecting said first or said second chamber to nozzle means (20) for directing a mass fraction. accumulated in said first or second chamber selectively towards the bottom of said horizontal sieve (18). 2