Novel Disc Refiner And Method

Abstract

Novel refining disc plate for use in a disc refiner, the plate being characterized by flow channels between the refining bars which flow channels are of substantially constant cross section, thereby to allow constant velocity of fluid through the channels and markedly reduce turbulence within the disc refiner. The diminished turbulence results in better power efficiency, a reduction in maintenance requirements and an improved defiberized pulp product. Most advantageous plates formed according to the invention include a peripheral flow-retarding ring having a number of flow-dividing ribs and flow paths between the ribs, which flow paths are offset at a small angle from the aforesaid channels.

Description

BACKGROUND OF THE INVENTION

This invention relates to a novel disc refiner apparatus such as is used in refining of pulp in paper making operations.

Disc-type refiners comprise opposed, relatively rotating discs, which may be two rotors or may be a stator and a rotor. A paper pulp slurry is passed between the two discs and is defiberized by the shearing action caused by the relative rotation of the discs. A primary problem encountered in such operations is to obtain the most effective use of power, that is to have a maximum proportion of power converted utilized in defiberizing and a minimum proportion of power dissipated in nonfiberizing power-consuming phenomena within the refiner. A particularly troublesome problem with respect to such undesirable power consuming losses is the fact that they usually result in a fast wear rate on the refining discs (2) and a consequent further loss in efficiency and, eventually, a shut-down during which time the refining discs must be refurbished or replaced. Indeed in some operations it has been found desirable to change discs after from one to four days operation.

It is manifest, therefore, that it would be desirable to provide refining plates which have efficient defiberizing surfaces, but which wear more slowly. A number of approaches can be used to improve wear and still obtain effective defiberizing. For example, one can select a highly abrasion-resistant metal, or one can adopt a yielding elastic surface or backing material, as did Sutherland in the devices disclosed in U.S. Pat. No. 2,156,321 of May 2, 1939. In any event, even more effective economical solutions to the problem would be of value in the paper making industry.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide refining apparatus capable of achieving effective defiberizing of wood pulp and having exceptional wear characteristics.

Another object of the invention is to provide a refining, i.e. defiberizing, disc which is particularly efficient with respect to power utilization.

Still another object of the invention is to provide rotary refining disc apparatus which yields a higher quality defiberized pulp.

A further object of the invention is to provide a novel, improved paper pulp refining process which markedly reduces the maintenance of equipment utilized therein and provides a higher quality defiberized pulp for papermaking.

Other objects of the invention will be obvious to those skilled in the art on reading this disclosure.

The above objects have been substantially accomplished by construction of a double disc refiner having two opposed rotating refiner discs, each the mirror image of the other, which are constructed to have generally radially extending refiner bars defining channels between them, as is generally known in the art. However, these channels are of substantially constant cross sectional area because, as they extend outwardly toward the periphery of each disc, they become constantly wider and shallower in such relative proportion as to preserve their cross sectional area.

It has been discovered that the use of such channels markedly reduces turbulence, increases power efficiency, extends plate life from about 1,000 to 3,000 per cent, and yields a longer fiber. The longer fiber is believed to be attributable to the relatively small amount of turbulence and the consequently greater tendency for longitudinal flow along the channels between the refining bars. Apparently the fibers tend to "roll" over the bars in radial alignment. This allows a kind of peeling action along the axis of an idealized fiber, rather than a cutting action across the width of the fiber.

All these advantages are maximized when the peripheral section of the refining disc, i.e. that between the outer circumference and the outlet end of the aforesaid channels, comprises a flow-retarding ring consisting of a series of alternate grooves and ribs disposed along the edge. These ribs and grooves are offset angularly from the refining bars and channels of the central portion of the disc to retard flow. The ring is not a dam but does present a sufficient resistance to flow to increase the dwell time of the fluid between the refining segments of the discs. The flow paths, or grooves, between these ribs are also constant velocity-inducing because of their size, albeit the velocity of pulp between the ribs of the retarding ring may differ somewhat from the velocity of the pulp between the refining bars.

In practice, the number of ribs will be from about 1.1 to 2 times that of the refining bars.

ILLUSTRATIVE EXAMPLE OF THE INVENTION

In this application and accompanying drawings, where is shown and described a preferred embodiment of the invention and suggested various alternatives and modifications thereof, but it is to be understood that these are not intended to be exhaustive and that other changes and modifications can be made within the scope of the invention. These suggestions are selected and included for purposes of illustration in order that others skilled in the art will more fully understand the invention and the principles thereof and will be able to modify it and embody it in a variety of forms, each as may be best suited in the condition of a particular case.

IN THE DRAWINGS

FIG. 1 is a plan view of a major portion of one segment of a refining disc constructed according to the invention.

FIG. 2 is a section of this segment taken along line 2--2 of FIG. 1.

FIG. 3 is a section of this segment taken along line 3--3 of FIG. 1.

FIG. 4 is a section of this segment taken along line 4:4 of FIG. 1.

FIG. 5 is a section of this segment taken along line 5:5 of FIG. 1.

FIGS. 3, 4 and 5 are fragmentary in that they do not show a section through the entire depth of the disc segment base. These drawings are not necessarily shown to scale and should be read with the following description to be understood.

It will be understood by all skilled in the pulp refining art that the invention is being defined with reference to a disc segment forming one-sixth of a circle, that six such segments are ordinarily mounted on a support plate to form a disc for use in a refining unit. It will also be understood that such a disc can be used as a stator, or as rotor, or -- as is of particular advantage with respect to the instant plate -- with a second disc cast to be a mirror image of the one shown, one disc being the rotor and the other the stator.

With typical pulp, the direction of rotation of the rotor segment shown in FIG. 1 is clockwise and the clearance between the rotor and stator is about .+-. 0.010 inch.

Referring to FIG. 1, it is seen that a refining disc segment 10 is provided upon its face 11 with three holes 12 to accommodate fasteners used to attach segment 10 to a base plate not shown in the drawings. Also integrally cast or molded into face 11 are refining bars 14. Bars 14 define, with face 11, flow channels 16. These flow channels are relatively narrow and deep nearest the center of the disc, i.e. as at 18 and in FIG. 5, but the channels widen and become more shallow as seen at 20 and in FIG. 4 at their termination nearer the circumference of the disc. This modification of the channel diameter is a consequence of the shape of the bars 14. In the example shown, bars 14 do not have to be narrow because the increasing circumferential path along the outwardly extending radial path of the bars provides sufficient room for expansion of the width of the flow channels. However, the depth of the bars, i.e. the distance from the top of the bars to the face 11 of the disc, must be reduced to achieve the desired constant cross sectional area of the flow channels as they extend radially. This is achieved by slanting the face of the bed upwardly as it extends radially. The bars 14 are preferably of uniform width throughout their length, as shown in FIG. 1, but may be of progressively reduced width as they extend radially, as shown in FIG. 5.

When using the term radially herein, the term is used in a broad sense. In fact, it is desirable to have the outwardly extending bars offset by a small angle, say 8.degree. from the radius of the circle formed by the disc.

Thus, fibers flowing in a slurry outwardly along channels 16 tend to have a uniform velocity, are not subjected to turbulence, which is thought to be an inevitable consequence of a changing velocity profile. The fibers, therefore, apparently tend to align axially with the center line of the channels. This causes the bars to rotate normal to the fiber axis and, consequently, there is a relatively small amount of fiber breakage along the lengths of the fibers.

Along the outer periphery of disc segment 10 is a circular flow-restraining ring 22 comprised of a series of ribs 24 which define grooves, or flow paths, 26 with face 11. Both ribs 24 and grooves 26 are angularly offset from the radius of the disc by about 15.degree.. In the example, there are about 360 ribs spaced along the periphery of a completed disc, i.e. a disc comprising six 60.degree. segments.

As seen in FIGS. 2 and 3, the flow paths 26 also become somewhat shallower and wider as they approach the periphery of the disc segment. Between restraining ring 22 and refining central portion 30 is an annular area 28 free of ribs and grooves which forms a transition zone between the restraining ring 22 and refiner bars 14.

It is to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which might be said to fall therebetween.

Claims

I claim:

1. A disc refiner plate of the type suitable for use in defiberizing wood pulp, said disc refiner plate comprising:

a plurality of generally radially extending bars upstanding above the face of said disc;

said bars defining open channels therebetween and said bars gradually changing in cross sectional area as they extend toward the circumference of each disc to maintain each channel at an approximately constant cross sectional area as that channel extends toward the circumference of the disc.

2. A disc plate as defined in claim 1, wherein:

said bars and channels terminate at a spaced distance inside the circumference of said disc;

a circular flow-restraining ring extends around said circumference; and

an annular space is provided between said ring and the terminus of said bars, which is free of ribs or grooves.

3. A disc as defined in claim 2, wherein:

said restraining ring is formed of a series of spaced ribs raised from the surface of said disc and numbering from about 1.1 to 2.0 the number of said bars on said disc.

4. A disc as defined in claim 3, wherein:

said spaced ribs gradually change in cross section along their length and define flow paths, of constant cross sectional area therebetween.

5. A disc as defined in claim 1, wherein:

said open channels become progressively wider and more shallow as they extend toward the circumference of the disc.

6. A disc as defined in claim 2, wherein:

said open channels become progressively wider and more shallow as they extend toward the circumference of the disc.

7. A disc as defined in claim 3, wherein:

said channels become progressively wider and more shallow as they extend toward the circumference of the disc.

8. A disc as defined in claim 4, wherein:

said channels become progressively wider and more shallow as they extend toward the circumference of the disc.

9. In a process for defiberizing wood fibers as they are carried in a liquid slurry comprising the steps of passing the slurry between and proximate the center of two refining discs rotating one with respect to the other, said discs having radially extending refining bars on the working faces thereof, the improvement wherein all slurry moving toward the circumference of said discs between said refining bar is maintained at a constant flow velocity, maximizing the alignment of said fibers in said channels with said bars, and causing the relative movement of said bars and said fibers to be substantially normal to the path or rotation of said bars.

10. A disc refiner plate segment having a central portion formed with a series of integral, upstanding refining bars, each of uniform width, extending outwardly from proximate the center of the plate toward the periphery thereof, said bars defining, with the face of said plate, a series of flow channels, each of uniformly decreasing depth and uniformly increasing width from the center of said plate to the outer terminal ends of said bars;

said bars being of uniformly decreasing height above said face from the center of said plate to said terminal ends and the cross sectional area of said flow channels being constant from one end to the other;

whereby constant stock velocity and reduced turbulence is achieved.

11. A disc refiner plate as specified in claim 10, plus:

an arcuate, flow-retardation ring segment fixed to the outside of said plate, said ring segment having alternate ribs and grooves angularly disposed to the bars and channels of said central portion, each rib reducing in width and each groove increasing in width from the inner end to the outer end thereof.