Pulp refiner element

Abstract

A refining element for a pulp stock refiner having at least its working edges composed of a relatively soft (e.g. nylon), less stiff material, as compared to ferrous metals, whereby fibers of pulp refined in a refiner having such elements are fibrillated and made flexible and have less tendency to be cut into shorter lengths, as compared to pulp fiber refined with ferrous metal elements, as the stock is processed through the refiner.

Description

BACKGROUND OF THE INVENTION

This invention relates to refiners which prepare paper pulp fibers to the desired condition prior to their being delivered to the papermaking machine. More particularly, this invention relates to the fiber contacting blades or disks within the refiners which actually modify the pulp stock fibers to the desired condition.

The structural network that makes up a paper sheet is comprised essentially of cellulose fibers which are randomly distributed and connected to one another by virtue of bonds between hydroxyl groups which are formed when the water is removed from the sheet. The strength characteristics of the resulting sheet are dependent on the extent of the bonding and the strength of the fibers that make up the sheet. Following a conventional pulping process, the pulp stock consists essentially of individual fibers. These fibers are relatively slender tube-like structural elements made up of a number of concentric layers. Each of these layers (called lamellae) consists of finer structural elements (called fibrils) which are helically wound and bonded to one another to form the cylindrical lamellae. The lamellae are in turn bonded to one another thus forming a composite which in accordance with the laws of mechanics has distinct bending and torsional rigidity. In addition, a relatively hard outer sheath (called the primary wall) encases the fiber. The primary wall is often partially removed during the pulping process. The relative stiffness of the fiber, the relative low surface area, and the presence of the primary wall all inhibit bond formation and subsequently limit the strength of the paper formed from these fibers.

It is generally accepted that it is the purpose of a pulp stock refiner, which is essentially a milling device, to remove the primary wall and break the bonds between the fibrils of the outermost layers resulting in a "frayed" surface thus increasing the surface area of the fiber multi-fold. The term "fibrillation" is commonly used to describe this.

Fibrillation alone, however, is not sufficient to produce strong paper. Fiber must also be made more flexible, so that during sheet formation the fibers conform to and around one another producing large areas of intimate contact. This increase in flexibility is accomplished by a rapid and frequent flexure of the fiber until the bonds between the concentric lamellae are broken down (delaminated), the result being equivalent to the delamination of a beam.

It is the purpose of the pulp stock refiner to modify the fibers in accordance with the above requirements without significantly reducing the length or individual strength of these fibers.

Various types of refiners are in use and these can be classified as disk, conical, and beater types. Examples of these refiners and their blade elements are shown and described in U.S. Pat. Nos. 3,118,622; 3,323,732, 3,326,480; 2,779,251; 3,305,183 and 2,934,278, which are incorporated herein by reference.

It is obviously not possible to carry out the required fiber modification on each individual fiber in commercial practice. In fact, it is a purely random statistical application of physical forces within a pulp refiner that accomplishes the average overall effect. As fibers pass through the refiner in a water slurry, they are acted upon by the impinging edges of a rotating blade element and a stationary or oppositely rotating blade element. A characteristic of such prior refiners is the use of metal as the blade element material. The most commonly used metal, steel, has a modulus of elasticity of around 30 .times. 10.sup.6 psi. The material which comprises the pulp fiber, however, has a modulus of elasticity in the range of about 0.8 .times. 10.sup.6 psi to about 2.8 .times. 10.sup.6 psi. Thus, the relative delicacy of the paper fibers is apparent.

Since the energy applied to the refiner is controlled by forcing these blade elements into close proximity, and since steel elements are extremely rigid as compared to the fiber, only an average intensity of applied forces can be controlled, and a wide distribution of force intensity is applied to the multitudes of fibers. In refiners, intensity is a comparative term relating the power required to operate the refiner, considering the speed and pressure forcing the refiner blade elements together, with the relative percent of fibers in a distribution curve which meet certain standards, such as fiber length. The result is that while some fibers might be treated with precisely the required intensity, many are treated insufficiently, and many are treated at an intensity level so high as to cut or otherwise damage the fibers. In order to insure that no fibers are extensively damaged, it would be necessary to reduce the average intensity to a very low level and "gently" refine the pulp repeatedly until, statistically speaking, all of the fibers have received the appropriate treatment. In practice, this could be accomplished by maintaining low pressure levels between blades (many blades per disk or refiner and relatively high speed) and passing the pulp stock through a number of refiners in series, or many times through a single refiner. This, if at all practical, is a costly process due to the non-productive energy expended in the refiner as well as peripheral equipment (pump, agitation tanks, etc.).

Even though steel refiner blades do have a long operating life (anywhere from about 4 months to about 11 months, depending on type of steel, in a disk refiner) and do refine the pulp fibers in a manner satisfactory to produce a quality, saleable paper product, these advantages are tempered by their inherent tendency to cut the fibers into lengthwise segments shorter than actual fiber length.

Attempts have been made to reduce the fiber cutting tendency of refiners by using so called softer metal blade elements such as bronze or aluminum. These materials have moduli of elasticity in excess of 5 .times. 10.sup.6 psi and are also ineffective in accomplishing the objective of not cutting the fibers lengthwise into segments shorter than actual fiber length. In fact, blades formed from these soft metallic materials exhibit a distinct tendency to maintain very sharp edges as they wear and, as a result, increase rather than reduce the degree of fiber cutting.

Attempts have also been made to use very soft materials, such as rubber or polyurethane elastomer. These materials have proven ineffective since their moduli of elasticity are too low (1 .times. 10.sup.3 psi - 20 .times. 10.sup.3 psi) to efficienty produce the required fiber surface modifications. Additionally, high hardness polyurethane elastomers are prone to internal heat build-up, as are hard rubbers, and subsequent failure when subjected to cyclic deformation over an extended period.

SUMMARY OF THE INVENTION

The problems associated with cutting pulp fibers into lengthwise segments have been mitigated by this invention. Instead of hard, metal blade elements, it has been found that plastics, preferably thermoplastics, made from certain synthetic resins fall into the appropriate range of moduli of elasticity and at the same time fulfill the requirements of strength, impact resistance, abrasion resistance, and hydrolytic stability that would be expected in a pulp refiner at normal operating temperatures. Elements made of such materials fibrillate and delaminate the fibers without tending to cut them lengthwise into segments. The use of a softer material permits the element to conform somewhat to the impinging fiber thereby producing a more uniform intensity of treatment on that fiber as well as a more uniform distribution of intensity upon the multitudes of fibers being acted upon at any instant by the many blades in the refiner.

Surprisingly, these materials are relatively soft, having modulii of elasticity of between about 0.1 .times. 10.sup.6 psi to about 2.0 .times. 10.sup.6 psi. They also must exhibit sufficient resistance to abrasion and creep at their operating temperature within the refiner.

Therefore, it is an object of the invention to provide a material for use as a blade element in a pulp refiner having a modulus of elasticity close to the modulus of elasticity of the pulp fiber.

It is another object of this invention to use as the working element of the blade, a material which is sufficiently soft so as not to cut the fiber or otherwise damage it, but stiff enough to produce the required surface modification.

It is another object of the invention to use as the working edge of the blade, a material which has a modulus of elasticity which is sufficiently high so that the required fiber surface modification can be performed efficiently, that is to say with relatively low energy expenditure.

Another object of the invention is to use, for at least the pulp contacting edge of the blade element, a material which has a modulus of elasticity between about 0.1 .times. 10.sup.6 psi to about 2.0 .times. 10.sup.6 psi, which operates in a refiner below its temperature at which creep occurs.

Another object of this invention is to provide a non-ferrous blade element for a paper pulp refiner which fibrillates pulp fibers without reducing the average fiber length as compared to fibers refined with steel blade elements.

Still another object of the invention is to provide a thermoplastic refiner blade element which is hydrolytically stable and abrasion resistant.

Yet another object of the invention is to provide a refiner blade element having such physical properties as to produce pulp fibers to make paper having improved strength properties.

A feature of this invention is a refiner blade material which can be molded into shape.

Another feature of the invention is that a refiner can be constructed without any metallic blade elements for use in industries where any metal in the refined pulp is extremely undesirable.

These and other objects, features and advantages of the invention will be apparent to one skilled in the art as the specification and claims are read in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a face view of a disk for a disk refiner on which a plurality of individual blade elements are formed.

FIGS. 2a and 2b are curves comparing the fiber length of a pulp refined using nickel steel blade elements with the fiber length of a pulp refined using nylon blade elements.

FIGS. 3a-3e, are curves comparing the properties of paper made from a pulp refined using nickel steel with those of paper made from a pulp refined using nylon blade elements.

FIG. 4 is a top view of a beater type refiner.

FIG. 5 is a side elevational view in section of the beater shown in FIG. 4.

FIG. 6 is a side elevational view, partially in section, of a disk type refiner.

FIG. 7 is a side elevational view, partially in section, of a conical type refiner shell.

FIG. 8 is an end view of the conical shaped inner wall of the refiner shown in FIG. 7 and showing the blade elements therein.

FIG. 9 is a perspective view of a conical refiner assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 2a, 2b and 3a-3e, the merits of using a material for refiner blade elements whose modulus of elasticity falls into the previously specified range becomes apparent. In FIG. 2a, the long fiber fraction of the pulp, as measured by the combined percent retention on the 14 and 30 mesh screens of a Clark Classifier, has not been significantly reduced when using nylon for the blade refiner elements, even after refining to a Canadian Standard Freeness as low as 250 ml. In the same figure, the fiber length reduction when using the nickel steel (Ni-Hard) elements is excessive at a C.S. Freeness level of 450 ml. Thus, for increased intensity or refining time, a given quantity of pulp produces a greater number of long, uncut fibers with plastic blade elements than with steel blade elements. Conversely, at a specified freeness, a greater number of longer fibers are produced with plastic blade elements than with steel blade elements. Statistically, this could be expressed on a distribution curve (having the relative percent of fibers having a certain length to the total number of fibers as one coordinate and the applied intensity as the other coordinate) as a greater proportion of the total number of fibers meeting a specified standard of refinement for a given level of refiner intensity. All of these parameters and tests are well known in the paper industry. Further, all tests run to gather data for curves 2a, 2b and 3a-3e were conducted with constant pulping consistency (4 percent) and stock through-put (83 gpm). Canadian Standard Freeness is a rough overall indicator of pulp quality. A high number is desirable because it indicates the pulp is "free," i.e. the water drains from it more rapidly. The faster water drains from the pulp stock in the paper making machine, the faster paper can be made. However, the higher freeness, the less fibrillated and delaminated the stock is, so the best pulp for a given paper machine speed is that having suitable strength at the highest freeness. Conversely, at the same freeness number, better quality pulp fibers will have higher tear factors, breaking lengths and bulk values.

The effect of fiber length on the physical properties of paper made from plups refined with the nickel steel and nylon elements (FIGS. 3b-3e) illustrates the considerable improvements in paper strength which are possible when using a conformable material for the refiner blade element. When using the nickel steel disks, the maximum burst and tensile strengths are achieved at a C.S. Freeness of about 500 ml. When using the nylon disks, the burst and tensile strengths continue to increase until a maximum is reached at about 300 ml. These maximum values for the nylon disks are about 40 percent higher than those for the nickel steel. The fact that the higher strength values were obtained at lower freeness readings is indicative of the greater amount of fibrillation and longer fibers refined with the nylon disks.

Due to the range of modulii of elasticity which is required to obtain the desired intensity (which influences the percent of fibers treated to the desired degree of fibrillation and delamination), the choice of refiner blade material is effectively limited virtually to a plastic. While use of a plastic under such extreme service conditions as would be expected in a high speed, high power attrition mill, seems quite unreasonable, the specific properties of certain plastics render them feasible, in fact, advantageous, under normal refiner operating conditions.

The material to be used for refiner blade elements, in addition to having the appropriate modulus of elasticity (stiffness), must possess certain physical properties in order to economically replace a metallic element in a commercial installation. The broad requirements are (1) hydrolytic resistance, (2) abrasion resistance, (3) creep resistance at operating temperature within the refiner, and (4) heat resistance (related to creep resistance). In general, the poor abrasion resistance of most thermosetting plastics effectively precludes their use and limits the application to a thermoplastic material.

The broad spectrum of requirements further limits the choice of thermoplastic materials. Ultra high molecular weight polyethylene, while exhibiting superb abrasion resistance and hydrolytic stability, has proven unsatisfactory in pure matrix form due to a lack of creep resistance, particularly at temperatures above about 70.degree. F. Creep resistance of ultra-high molecular weight polyethylene is improved to a satisfactory level when it is combined with a fiber material, such as type 610 or type 612 nylon. In addition, due to its relatively low modulus of elasticity, 0.14 .times. 10.sup.6 psi, it is less efficient in refining than the harder thermoplastics. Similarly, modified phenylene oxide sold under the tradename Noryl (reg. TM), while exhibiting excellent hydrolytic stability, creep resistance and heat resistance, has proven unacceptable without being combined, or chemically compounded, with other materials due to its lack of abrasion resistance. Many thermoplastics, such as modified phenylene oxide, can be made sufficiently abrasion resistant by treatment with a flurocarbon compound.

On the other hand, nylon, although processing no outstanding properties, generally exhibits sufficiently high properties in all respects to provide acceptable performance for continuous use. Nylon types 610 and 612 have been found to be especially suitable. In order to provide sufficient hydrolytic stability, type 612 nylon was used for the blade material of the elements used in the tests from which the data of FIGS. 2a, 2b and 3a-3e was obtained. At least one nylon, type 6--6, is hydrolytically unstable and, therefore, unsuitable for this type of use. Fiberglas reinforcement was added to the resin to provide improved creep resistance and heat resistance. Long term tests have indicated that the useful life of the nylon disks is approximately the same as the expected life of a nickel steel disk, although somewhat less than that of a milled stainless steel disk.

Other materials which exhibit suitable properties include the acetal homopolymers, polyarylsulfones, polysulfones, and polyphenylene sulfides. Reinforcing fibers, such as glass, may be added to any of these to enhance creep resistance (this is especially effective as temperatures increase), and they may be compounded with flurocarbons (Telfon which is a registered trademark for tetrafluoroethylene (TFE) fluorocarbon resin, for example) to reduce friction and decrease the wear rate (increase abrasion resistance).

For temperature applications of less than about 90.degree. F., a thermoplastic polyester or a glass reinforced polypropylene might also be used.

Plastics are particularly desirable because they are usually easily molded, extruded and machined, thus lowering manufacturing costs, For example, modified phenylene oxide sold under the tradename Noryl (reg. TM) and the type of nylons sold under the tradename Zytel (reg. TM) have been successfully molded into disk type blade elements. Disk elements can be molded, cast or machined, while blade elements (for conical or beater type refiners) can be extruded and/or machined.

Therefore, contrary to what might appear to be logically concluded, some plastic materials, having particular physical properties, are capable of performing quite well when used to make refiner disks or blades. However, also contrary to what might appear to be logical, the suitability of a material for use as refiner blade elements is not a function solely of its hardness or stiffness (as measured by its modulus of elasticity). It is a function of a combination of these parameters which in turn may be affected by creep and heat and abrasion resistance. More specifically, the creep limit of the material is significant and this is defined as the maximum tensile stress which can be applied to the material at a given temperature without resulting in measurable creep. Therefore, the operating temperature within the refiner becomes important. Depending on the type of refiner (disk, conical or beater) and the applied load, this operating temperature might range from about 50.degree. F. to about 210.degree. F. If the temperature at which creep occurs is within the range of refiner operating temperatures, a particular material may not work in that type of refiner or at a particular intensity, although it may be perfectly satisfactory in another type of refiner having lower operating temperatures.

Shown below are Tables I through III which tabulate the test results of disks made of Zytel (Reg. TM) and Ni-Hard (nickel alloy) steel. The graphs in FIGS. 2a, 2b and 3a-3e were made from some of the data in these tables.

The terms used in the following tables are all well known in the paper industry, but for clarity, they will be identified as follows: "BDT/D" means bone dry tons per day; "BHPD/BDT" means brake horsepower per bone dry ton per day; "C.S. freeness" means Canadian Standard freeness which is a measure of the rate with which water drains from a stock suspension through a wire mesh screen or a perforated plate; "bulk" means the apparent specific volume of a sheet of paper when in a pile under a specified pressure; "burst factor" is a numerical value obtained by dividing the bursting strength in grams per square centimeter by the basis weight of the sheet in grams per square meter; "tear factor" is the tearing resistance in grams (per sheet) multiplied by 100 and divided by the basis weight in grams per square meter; "breaking length" is the length of a strip of paper, usually expressed in meters, which would break of its own weight when suspended vertically; "basis weight" is the weight in grams of a square meter of paper.

TABLE I __________________________________________________________________________ 20" DD-3000 DISK REFINER SUPERIOR KRAFT (BLEACHED SOFTWOOD KRAFT) 1010 RPM MONO-FLO NI HARD DISKS 3,3,4 + 10.degree. __________________________________________________________________________ OPERATING CONDITIONS Trial Raw Cir 1 2 3 4 5 Pass -- 1 1 1 1 1 1 __________________________________________________________________________ Consistency % -- 4.0 4.0 4.0 4.0 4.0 4.0 Through-Put -- 83 83 83 83 83 83 GPM Through-Put -- 20 20 20 20 20 20 BDT/D Applied Gross -- 78 107 117 138 158 175 Energy BHP Net -- -- 29 39 60 80 97 Total Gross -- -- 5.4 5.9 6.9 7.9 8.8 Energy Consumption Net -- -- 1.5 2.0 3.0 4.0 4.9 BHPD/BDT TAPPI PHYSICAL TEST RESULTS C.S.Freeness ml. 655 625 600 580 550 505 455 Bulk cc/gm 1.83 1.78 1.76 1.73 1.68 1.63 1.63 Burst Factor 30.5 36.5 43.3 46.0 52.3 55.9 50.9 Tear Factor 325 335 315 292 255 222 185 Bkg. Length M. 4280 4800 5610 5920 6780 7220 6970 Basis Weight g/M.sup.2 56.9 57.0 57.0 57.2 59.0 60.5 60.3 CLARK CLASSIFICATION RESULTS % FIBER RETAINED ON -- MESH 14 - Mesh % 45.3 51.7 51.6 53.8 53.5 45.7 31.2 30 - Mesh % 33.2 29.8 29.1 26.8 26.4 30.6 37.1 50 - Mesh % 8.7 8.1 8.3 8.1 8.6 10.6 13.8 100 - Mesh % 3.9 4.2 4.2 4.1 4.4 5.9 8.5 Thru 100 - Mesh % 8.9 6.2 6.8 7.2 5.1 7.2 9.4 __________________________________________________________________________

TABLE II __________________________________________________________________________ 20" DD-3000 DISK REFINER SUPERIOR KRAFT (BLEACHED SOFTWOOD KRAFT) 1010 RPM MONO-FLO NYLON DISKS 3,3,4 + 10.degree. __________________________________________________________________________ OPERATING CONDITIONS Trial Raw Cir 1 2 3 4 Pass -- 1 1 1 1 1 __________________________________________________________________________ Consistency % -- 4.0 4.0 4.0 4.0 4.0 Through-Put -- 83 83 83 83 83 GPM Through-Put -- 20 20 20 20 20 BDT/D Applied Gross -- 78 120 138 158 178 Energy BHP Net -- -- 42 60 80 100 Total Gross -- -- 6.0 6.9 7.9 8.9 Energy Consumption Net -- -- 2.1 3.0 4.0 5.0 BHPD/BDT TAPPI PHYSICAL TEST RESULTS C.S.Freeness ml. 655 630 595 575 550 525 Bulk cc/gm 1.83 1.82 1.78 1.72 1.71 1.68 Burst Factor 30.5 37.9 43.9 50.2 54.7 57.4 Tear Factor 325 330 305 283 250 239 Bkg. length M. 4280 4945 5685 6320 6890 7300 Basis Weight g/M.sup.2 56.9 60.2 57.7 60.2 59.6 58.6 CLARK CLASSIFICATION RESULTS % FIBER RETAINED ON - MESH 14 - Mesh % 45.3 58.3 56.6 55.5 56.6 56.1 30 - Mesh % 33.2 26.3 26.4 24.1 22.9 23.0 50 - Mesh % 8.7 8.2 8.2 7.8 7.8 7.7 100 - Mesh % 3.9 4.0 4.0 3.9 3.9 4.0 Thru 100 - Mesh % 8.9 3.2 4.8 8.7 8.8 9.2 __________________________________________________________________________

TABLE III __________________________________________________________________________ 20" DD-3000 DISK REFINER SUPERIOR KRAFT (BLEACHED SOFTWOOD KRAFT) 1010 RPM MONO-FLO NYLON DISKS 3,3,4 + 10.degree. __________________________________________________________________________ OPERATING CONDITIONS Trial Cir 1 2 3 4 5 7 8 9 10 Pass 1 1 1 1 1 1 2** 2** 2** 2** __________________________________________________________________________ Consistency % 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 Through-Put 83 83 83 83 83 83 83 83 83 83 GPM Through-Put 20 20 20 20 20 20 20 20 20 20 BDT/D Total Gross 85 105 125 147 165 187 293 312 334 355 Applied Energy Net -- 20 40 62 80 102 122 142 164 185 BHP Total Gross -- 5.3 6.3 7.4 8.3 9.4 14.7 15.6 16.7 17.8 Energy Consumption Net -- 1.0 2.0 3.1 4.0 5.1 6.1 7.1 8.2 9.3 BHPD/BDT TAPPI PHYSICAL TEST RESULTS C.S.Freeness ml. 610 590 585 555 510 480 390 340 300 270 Bulk cc/gm 1.83 1.79 1.74 1.69 1.67 1.62 1.57 1.57 1.53 1.51 Burst Factor 38.0 39.1 47.2 53.9 62.2 63.5 74.0 79.1 81.0 79.0 Tear Factor 330 345 300 250 240 250 205 190 185 180 Bkg. Length M. 4700 4955 5555 6580 7425 7965 8695 9525 10270 10200 Basis Weight g/M 61.9 60.1 61.9 59.5 61.1 61.2 59.9 58.9 60.8 61.5 CLARK CLASSIFICATION RESULTS % FIBER RETAINED ON - MESH 14 - Mesh % 53.5 53.9 56.4 60.5 59.9 60.5 59.2 56.5 61.8 61.4 30 - Mesh % 29.7 26.8 24.3 22.9 21.1 21.2 21.2 19.8 20.7 20.7 50 - Mesh % 8.4 8.2 8.0 7.9 7.0 7.4 7.0 6.8 7.1 7.1 100 - Mesh % 4.2 3.7 3.7 3.9 3.6 3.7 3.9 3.2 4.4 1.9 Thru 100 - Mesh % 4.2 7.4 7.6 4.8 8.4 7.2 8.7 13.7 6.0 8.9 __________________________________________________________________________

From the tests conducted, knowledge of refiner operating conditions and past experience, it has been discovered that plastics having a modulus of elasticity between about 0.1 .times. 10.sup.6 psi and about 2.0 .times. 10.sup.6 psi, preferably between about 0.2 .times. 10.sup.6 psi and about 1.2 .times. 10.sup.6 psi, with a creep limit temperature (the maximum temperature at which creep will not occur) above the refiner operating temperature will provide an excellent percentage of properly modified individual pulp fibers per unit of refined pulp when used as the material comprising the blade elements in a refiner. Ceramic materials, including glass, tile, concrete and brick, and wood which have modulii of elasticity falling within a 1.0 .times. 10.sup.6 psi - 10 .times. 10.sup.6 psi range, which slightly overlaps the above range for acceptable plastic materials, either do not work nearly as well or not at all; no rubber compounds or rubber-soft materials, such as polyurethane elastomers, work satisfactorily as blade elements in modern refiners for a commercially competitive period of time, and none of these materials is intended to be included within the category of claimed materials. Of course, steel and other materials having modulii of elasticity above the level of about 10 .times. 10.sup.6 psi do perform successfully in that the pulp stock is refined sufficiently to be saleable but, as the tests have shown, stock refined using disks having physical properties set forth above will be of superior quality. The steel disks also have the disadvantages of higher manufacturing costs and maintenance as aforementioned.

In the above discussion, some relative terms are used, such as "relatively low energy expenditure," "fibers treated insufficiently," "economically replace," "sufficiently abrasion resistant," and "acceptable performance." These are used where a numerical value would be either inadequate, impossible, misleading or non-informative, or all of these. Basically, the terms refer to the degree of quality of the fibers refined utilizing refiner elements composed of these materials to the quality of pulp fibers refined with steel blade elements. The same applies to comparisons between physical characteristics and operating economies wherein these terms are used to relate the materials of the invention with steel blade elements. Thus, if the pulp fibers refined by blade elements composed of the materials of this invention, and the costs of installing and utilizing them in refiners, are commercially competitive in the paper industry, then it can be said the particular combination of physical properties allows the refiner to be "economically" operated with "sufficiently" abrasion resistant elements to provide "acceptable" performance. Thus, for example, there is no numerical value to identify what is "sufficient" in the measurement of abrasion resistance.

In summary, the materials which will provide the desired pulp fiber quality and meet the objectives set forth have a modulus of elasticity of between about 0.1 .times. 10.sup.6 psi to about 2.0 .times. 10.sup.6 psi, preferably between about 0.2 .times. 10.sup.6 psi to about 1.2 .times. 10.sup.6 psi. They do not include rubbers, polyurethane elastomers, ceramic materials including glass, tile, concrete and brick, and wood. They must be hydrolytically stable, abrasion resistant, or capable of being made sufficiently abrasion resistant, and able to operate without deforming at the temperatures encountered in the particular type of refiner they are used in. They must be either creep resistance in pure matrix form or capable of being treated to be creep resistant at the temperature of operation within the refiner. Typically, treatment to increase abrasion resistance sould be to chemically treat the material with a flurocarbon compound, and treatment to increase creep resistance would be to fill the material with glass fibers. The preferred embodiment material is preferably plastic, ideally a thermoplastic, but not a thermosetting plastic.

In FIG. 1, a plastic refiner disk 10 is illustrated on which a plurality of grooves 12 are cut at an angle 14 with an imaginary line extending radially from the center axis of rotation 16. Grooves 12 define a plurality of blades 18 which fibrillate and refine the stock as it passes radially outwardly between two such refiner disks in refiner such as shown and described in U.S. Pat. Nos. 2,968,444; 3,118,622 and 3,323,732, all owned by the assignee of this application. The disks are attached to the refiner by cap screws through holes 20.

In FIG. 4, a substantially cylindrical shaped beater 30 is shown rotatably mounted in a tank 32. The individual blade elements 10a, also shown in FIG. 5, are shaped like a rectangular prism and extend radially from the axis of rotation 36 of beater 30. Stock travels in a continuous path about the tank and is refined as it passes between the beater blades 10a and the similarly constructed blades 10b mounted in the tank.

FIG. 6 illustrates the type of refiner 40 in which the disk 10 shown in FIG. 1 would typically be mounted. The stock travels inwardly axially at 42 and is refined between disks 10, 10' as it travels radially outwardly to outlet 44.

The blade elements 10d shown in the conical beater wall 51 in FIGS. 7 and 8, are in a spiral configuration, but they can also extend in a straight line in a plane coextensive with the beater's axis of rotation 52 as the blade elements 10c shown on rotor plug 50 in FIG. 9. Stock travels axially along the periphery of the conical beater plug 50 where it is subjected to varying degrees of refining intensity between the blade elements 10c on rotating plug 50 and blades 10d mounted on the inner conical wall 51 of the beater as it travels from the small end to the larger diamter end.

The construction and operation of all of these beater, disk and conical types of stock refiners is well known in the paper industry.

Naturally, the refiner materials described can also be used with corresponding results when made into, or formed upon, the blade elements for conical and beater type refiners. Thus, only the pulp contacting portions of refiner disk could be made of, or coated with, plastic to lower costs of manufacture and replacement. A more rigid material, such as steel or cast iron, could provide the support for the plastic covering on a plastic coated blade element.

Thus, a set of parameters has been disclosed for a material to be used as a paper pulp refiner blade element which provides unexpectedly good results and achieves the objects, features and advantages set forth. While a preferred embodiment has been discussed in detail, it is understood that other specific materials which meet the described parameters can be used and they also fall within the spirit and scope of the attached claims. Also, while wood constitutes the raw material commonly used for pulp, other materials, such as cotton and bagasse, are used and are intended to be within the scope of the invention.

Claims

What is claimed is:

1. An abrasion resistant, hydrolytically stable fiber refining element for use in a pulp refiner having at least its fiber contacting surfaces comprising a thermoplastic having a modulus of elasticity between about 0.1 .times. 10.sup.6 psi to about 2.0 .times. 10.sup.6 psi and having a creep limit temperature above the operating temperature within the refiner.

2. The refining element as set forth in claim 1, wherein:

the refining element comprises a disk for use in a disk type refiner.

3. The fiber refining element as set forth in claim 1, wherein:

the refining element comprises a blade for use in a conical refiner.

4. The fiber refining element as set forth in claim 1, wherein:

the refining element comprises a blade for use in a beater type refiner.

5. The fiber refining element as set forth in claim 1, wherein:

the material comprises an acetal hompolymer.

6. The fiber refining element as set forth in claim 1, wherein:

the material comprises a polyarylsulfone.

7. The fiber refining element as set forth in claim 1, wherein:

the material comprises a polysulfone.

8. The fiber refining element as set forth in claim 1, wherein:

the material comprises a polyphenylene sulfide.

9. The fiber refining element as set forth in claim 1, wherein:

the material is a pure matrix thermoplastic.

10. The fiber refining element as set forth in claim 1, wherein:

the modulus of elasticity is between about 0.2 .times. 10.sup.6 psi to about 1.2 .times. 10.sup.6 psi.

11. The fiber refining element as set forth in claim 1, wherein:

the material is Type 612 nylon.

12. The fiber refining element as set forth in claim 1, wherein:

the material is Type 610 nylon.

13. The fiber refining element as set forth in claim 1, wherein:

the material is treated with a flurocarbon compound to increase its abrasion resistance.

14. The fiber refining element as set forth in claim 13, wherein:

the material comprises a modified phenylene oxide.

15. An abrasion resistant, hydrolytically stable fiber refining element for use in a pulp refiner having at least its fiber contacting surfaces comprising a thermoplastic material, the pure matrix form having a modulus of elasticity of between about 0.1 .times. 10.sup.6 psi to about 2.0 .times. 10.sup.6 psi and combined with fiber reinforcement to increase its creep resistance, the creep limit temperature of the composite material being above the operating temperature within the refiner.

16. The fiber refining element as set forth in claim 15, wherein:

the material is ultra high molecular weight polyethylene.