US3160355A - Fiber pulp refining apparatus - Google Patents

Description

1964 J. CHIAVERINA 3,160,355

FIBER PULP REFINING APPARATUS 1 Filed March 28, 1961 2 Sheets-Sheet 1 INVENTQR Jean Chia'verma HIS ATTORNEYS Dec. 8, 1964 J. CHIAVERINA FIBER PULP REFINING APPARATUS 2 Sheets-Sheet 2 Filed March 28. 1961 United States Patent 22,9?3 1 Claim. (Cl. 241-291) This invention relates to the construction of apparatus for the refining of fiber pulp, especially paper pulp.

Paper and similar fibrous sheet materials are composed of dispersed fibers varying in shape and dimensions depending on the particular (usually'vegetable) source from which they were derived and on the particular treatments to which they were exposed. The fibers are formed into a Wet pulp or lap containing a large amount of water together with various additions and are subjected to a number of mechanical (so-called refining) treatments while suspended in water before they are passed through the dehydrating or forming machines which finmly deliver the dry web of final paper or similar end product. These refining treatments to which the wet pulp is subjected prior to dehydration exert a very important infiuence on the mechanical strength and other physical characteristics of the final sheet.

The pulp refining operations may be carried out in any of various types of apparatus such as stamping throughs or rotary refining mills which usually comprise rotor and stator members provided with cutter vanes between which the pulp is passed. The over-all efiect of the refining treatment on the fibers comprises complex and profound mechanical and physical modifications in the fiber structure, although the accompanying chemical modifications are generally so slight as to escape analysis. The fibers are cut up, broken down and frayed, a process sometimes known as fibrillation, so that they are made more flexible and their capacity for water absorption is greatly increased. This increase in capacity for water absorption or hydration of the fibers is the chief over-all effect of the refining treatment and can be taken as a measure for quantitatively characterizing the effectiveness of a given refining process. As a general rule, the strength and other mechanical characteristics of the final sheet material all increase with the effectiveness of the refining treatment to which the pulp was subjected, as measured by the degree of hydration.

The degree of hydration of a pulp can be determined by various types of test devices that have been developed for the purpose, one widely used device being the Schopper-Riegler tester. This device determines the so-called SR-index of a given pulp as the rate of flow of water from the pulp through a wire screen of predetermined mesh size. A low SR-index characterizes a lean pulp, and a high SR-index indicates a rich pulp. The index increases with the time of refining and the shape of the graph plotting the variations of this index against refining time is well-known in the paper-making art for characterizing the refining process used.

As regards the strength characteristics of the final paper or other fibrous sheet, one important and widely used physical test characteristic is the breaking length, which is the length of paper web of arbitrary, constant, width, which'when freely suspended from one end of the web will break under its own weight. For example, in the case of Kraft paper and bisulfite bleached fir-wood paper, the breaking length assuming adequate refining of the pulp is in the range of 8,000 to 10,000 meters. For chestnut wood pulp, a high degree of refinement cannot be obtained and the breaking length does not generally exceed 5,000 meters. For bleached straw pulp, with the normal degree of refinement the breaking length is in the range of 6,000 to 8,000 meters.

It should further be noted that the refining process which constitutes an essential step in the paper-making processes consumes a considerable amount of power. Conventional pulp mills and refining machines as used in paper mills currently use drive motors in a range of power ratings from to 300 horsepower.

In the refining of a pulp; the elficiency of the refining 7 process is found to depend rather critically on the characteristics of the cutters or vanes of the pulp mills or other refining apparatus used, such as the contour, spac-- ing, and general arrangements of said cutters. As regards the material from which such cutters are made, this.

has been selected heretofore chiefly with regard to its subjected at high-speed operation from the pulp; Usually, the vanes or cutters of the rotors and stators of pulp mills have been made either from various grades of steel,

ronze and other hard alloys, or from natural minerals such as lava.

Long practice has shown that all of the materials so far used have certain drawbacks. Pulp mills when provided with metallic cutters of steel or bronze of the types heretofore used are strong and have a long useful life; however such pulp mills do not perform very satisfactorily in that they require comparatively long times of operation to achieve a prescribed degree of refining of the pulp. Pulp mills fitted with cutters or vanes made from'lava are more satisfactory in this respect. However, lava material lacks uniformity, and is both difficult to work and brittle, so that the resulting equipment is expensive and short-lived, and moreover there is the constant danger of small pieces of the cutter material being free of the above deficiencies of prior equipment and which in addition will bring important new advantages with it.

The invention essentially provides fiber pulp, e.g. paper pulp, milling or refining apparatus, comprising station ary and/or movable cutters through-which the pulp is passed, which apparatus is characterized in that said cutters are formed, at least in the active surface areas thereof that are to engage the pulp, from a porous synthetic material, especially porous metallic materials such as porous sintered powder metals.

. As will be later explained in detail, it is found that pulp refining mills equipped with the improved cutters of the invention not only are hard and long-lived and relatively inexpensive, as are the solid metallic cutters heretofore used, but that they give superior refining performance permitting the satisfactory refining of wood pulps in shorter times than was possible before, and/or the attainment of high degrees of hydration in certain types of wood pulps that were not earlier considered amenable to such effective refining.

The improved pulp mill cutters of the invention may be produced by various conventional techniques, preferably by molding or pressure molding, followed by suitable heat treatment. The'rnanufacturing process should be such that the finished cutters present open pores connecting with the outer pulp-engaging surfaces of the cutters and intercommunicating within the mass of the cutter. The porosity of the improved cutters, defined'as the volume percentage of cavities to the total apparent volume of the cutters in the porous areas, is preferably within the approximate range from 20 to 60%.

The improved porous cutters are preferably made from porous metals, e.g. bronze, one desirable grade of which, for the purposes of the invention, is 90% copper and 10% tin. Various grades of stainless steel, such as steel containing nickel and chromiumteg. 18% Ni and 8% Cr, or 18% Ni, 8% Cr and 2% Mo) may also be used. Other alloys, including Cupronickel, Monel metal, and substantially pure metals such as nickel, can also be used in the manufacture of the porous cutters of the invention.

As indicated above, the porous material can constitute. all or only part of the stationary and/ or movable cutters of the improved refining pulp mill. Thusthe porous material may be used to provide only the outer tips of the cutter elements and may be attached to the main bodies of the elements by any suitable means. 7

In the accompanying drawings, I have shown preferred embodiments of my invention in which:

FIGURE 1 is a perspective view of one pulp cutter element of my invention;

FIGURE 2 is a perspective view of a second pulp cutter element of my invention;

FIGURE 3 is 'aperspective view element of my invention; and

FIGURE 4 is a graph which shows a comparison between performance of conventional pulp cutter elements and my pulp cutter elements from the standpoint of pulp refining times. 7 ,7

Referring to FIGURE 1, it shows a pulp cutter element 1 composed entirely of open-por'ed sintered powder metal. FIGURE 2 shows a cutter element comprising a backing or support 3 of non-porous metal and a cutting tip 2 of open-pored sintered powder metal aflixed to the backing 3. This cutting tip 7. engages the pulp during refining operations. FIGURE 3 shows a cutter element similar to that of FIGURE 2, and includes a'support and a cutting tip 4 of the open-pored sintered powder metal afiixed to the backing 5.

The preferred method of manufacturing the improved cutter elements is'by pressure-molding and sintering powder metals. In this respect conventional powder-metal techniques well-known in the art may be used, provided the porosity characteristics indicated above are obtained together of course with the usual requisite mechanical strength characteristics for the finished cutter elements. The elements may be pressure-molded from powder metal of a third pulp cutter particles of spherical or other form, being heat treated at suitable temperatures and in appropriate atmospheres and possibly being subjected to further known treatments such as carbide hardening, nitride hardening or the like, applied simultaneaneously with or subsequent to the actual sintering treatment.

The improvement of the invention can be applied to a wire variety of types of refining apparatus or pulp mills, including the types using plain cylinders, displaced cylinders and multiple cylinders, and/or multiple pulp channels, as well as mills using moving plates and stationary cylinders, disks, straight or conical, and soon.

The improved porous materials of the invention may be incorporated both in the stationary and rotary cutters, or only one set, preferably the rotor cutters, while the other set of cutters may then be made from conventional materials. The contouring and dimensioning of the cutters would of course be predetermined in dependency on the type of fiber to be processed and the type of end' products to be obtained, in accordance with well-known rules of procedure.

The cutters made of the improved porous metallic materials of the invention show greatly increased mechanical strength as compared to the natural porous substances such as lava sometimes heretofore used in the manufacture of the cutters. They are moreover easily produced with a much higher degree of uniformity in their physical structure.

As compared to conventional pulp mill cutters made from solid metals and alloys, the porous metallic cutters 6g of the invention show greatly superior refiningperformance. Thus the time required to complete the refining operations can be considerably decreased, and/ or the quality of the final paper product improved.

It should be understood that the porous character of the cutters permits a freer and hence more thorough and effectivercirculation of the liquid pulp constituent relatively to the fibers suspended therein, than can be achieved by solid, compact cutter surfaces. The liquid in the pulp can more readily separate from the fiber by flowing through the pores under the action of the pressure exerted by the cutter surfaces. The more positive propulsion of the liquid phase around and into the fibers subjects the fibers to a rapid alternation of positive and negative'pressure actions which result in draining and re-impregnating the fibers at a rapid rate, so that the liquid is forced into and out of the fiber cells through the cell membranes there-. of, thus bringing about profound modifications in internal physical structure which are conducive to an enhanced degree of hydration in the pulp. This is contrasted with the type of operation that obtains when using the conventional solid metallic cutters wherein the water is only able to depart from and enter the fibers alonga single plane instead of along the three dimensions of space as in the case of the porous cutters of the invention. ,7

. As an example'of a typical practical construction in accordance with the invention, a pulp mill was used comprising a cylinder made of 18/ 8 stainless steel fitted with cutter vanes, and a stationary vaned plate, and this mill was used to demonstrate the advantages of the improved cutters of the invention in connection with the milling of various types of paper pulp, specifically Kraft pulp, bleached fir pulp, chestnut pulp and straw pulp. For each type'of pulp two sets of test runs were carried out, the one using conventional cutters made of stainless steel, grade 18/ 8, and the other with the use of cutters of sintered bronze, grade 90/ 10, having an open porosity of about 50%. In each run of either set the pressure adjustment between the cylinder rotor and the plate was such that the power consumed remained constant throughout each run. The remaining operating characteristics such as pulp concentration and the like were also held constant.

Each run was continued as long as was required to bring the pulp to a given degree of hydration, specifically 60 SR for the Kraft pulp, 78 SR for the bleached firwood, 50 SR for the chestnut pulp and 76? SR for the straw pulp. The tests showed that:

(l) The mechanical strengths of the resulting paper webs as measured by their breaking length, were substantially unchanged as between the runs made with the conventional. and the improved cutters. This showed that the refining process was in fact continued to the same de gree in both cases. a I

(2) The voperatingtimes required to achieve the common prescribed degree of refining in the respective runs were as follows:

Kraft 'Bleached Bleached Bleached Fir Chestnut Straw 60 SR 78 SR 50 SR 76 SR Stainless steel cutters 2 hrs, 15 4 hrs, 45 8 hrs, 20 2 hrs., 30

' min. min, min. min. Porous bronze cutters-.. 1 hr. 15 2 hrs 1 hr 4 hr.

, tional solid metal blades with the porous metal blades of accomplished, thus correspondingly increasing the production rate and decreasing the expense of the paper-making operations. Furthermore, in the case of a non-readily refinable type of pulp such as the bleached chestnut wood pulp tested, the degree of hydration that could be accomplished was greatly enhanced while still retaining a processing time well below that usually applied with that type of pulp with vastly poorer results.

The above findings are summarized by the graph shown on the attached drawing, wherein the SR hydration degree is plotted against refining time for various types of pulp under constant power conditions as explained earlier herein. The full line curves relate to the conventional cutter blades made from 18/8 stainless steel, and the brokenline curves illustrate the use of the impnoved cutters made from porous sintered bronze, grade 90/10.

It will be understood that the invention is not to be construed as being limited to the numerical data, compositions and other details given for illustrative and exemplary purposes, nor is the explanatory theory suggested herein regarding the underlying reasons for the improved performance of the pulp mill cutter blades of the invention to be regarded as restrictive.

What I claim is:

A pulp mill for refining cellulosic pulp which comprises stationary and rotatable pulp-cutter elements between and past which the pulp is passed in operation of the mill, characterized by the improvement that at least some of said cutter elements are formed from waterpermeable open-pored sintered metal in at least the pulpcontacting portions of said elements, the pores in the porous area of said metal being intercomrnunicatingand providing the volume percentage of cavities to the total apparent volume of the cutters in the porous area within the approximate range of from 20 to 60%.

References Cited by the Examiner UNITED STATES PATENTS ANDREW R. JUHASZ, Primary Examiner.

RICHARD D. NEVIUS, EVERETT W. KIRBY,

Examiners.

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