United States Patent: 3552664

[US Patent & Trademark Office, Patent Full Text and Image Database]

( 14108 of 14108 )

United States Patent	3,552,664
Herbert , et al.	January 5, 1971

DISC-TYPE

Abstract

A disc-type fibrous cellulosic stock refiner has bar-and-groove-type rotating and stationary refining plates in which the working or bar section has a D.sub.i/D.sub.0 ratio of between 0.55 and 0.85, and in which the operation of the refiner work input into the stock is analogized to the absorption of energy in a clutch or disc brake.

Inventors:	Herbert; William (Middletown, OH), Riedel; James H. (Middletown, OH)
Assignee:	The Black Clawson Company (Hamilton, OH)
Appl. No.:	04/740,884
Filed:	June 28, 1968

Current U.S. Class: 241/261.3

Current International Class: D21D 1/00 (20060101); D21D 1/30 (20060101); B02C 7/12 (20060101); B02C 7/00 (20060101); B02C 7/06 (20060101); B02c 007/06 (); B02c 007/12 ()

Field of Search: 241/296--8,255--6,260,162,163

References Cited [Referenced By]

U.S. Patent Documents


2035994	March 1936	Sutherland
2537570	January 1951	Bossert
2589307	March 1952	Symons
2971704	February 1961	Johansson
3032282	May 1962	Asplund
3117603	January 1964	Keuren
3241775	March 1966	Clendaniel

Primary Examiner: Kelly; Donald G.

Claims

We claim:

1. A disc-type refiner for fibrous cellulosic stock having improved refiner efficiency with decreased power requirements, comprising a refiner housing having a stock inlet and an outlet, at least one annular stationary plate and an adjacent rotating plate, the adjacent annular faces of each plate having means defining an inner relatively smooth portion and an outer working portion, said working portion being formed with a pattern of alternate bars-and-grooves for receiving stock from said inlet, refining the stock therebetween, and for discharging the stock in a radially outward direction, the smooth portions of the plates extending radially outwardly over more than a predetermined critical fraction of the diameter of the plates to provide for reduced loss of power and greater efficiency in the refining action of said working portions, the ratio of the diameters of the smooth portions to the diameters of the working portions being in the range of 0.55 to 0.85.

2. The refiner of claim 1 in which said smooth portions comprise a pair of oppositely-disposed fill plates positioned radially inwardly of said bar-and-groove pattern forming a throat leading from a region adjacent the axis of said refiner rotor to said pattern.

3. The refiner of claim 2 in which at least one of said fill plates is formed with a radially tapered surface defining said throat of decreasing width with increasing radial distance and terminating at the base of said grooves.

4. An improved refiner plate for a disc-type paper pulp refiner, comprising a plurality of arcuate plate segments each having a portion of an annular bar-and-groove pattern formed thereon adapted for assembly on a backing support in a refiner and together defining a full annular bar-and-groove pattern in which the ratio of inside diameter to outside diameter of said pattern is between 0.55 and 0.85.

5. The refiner plate of claim 4 further comprising means defining a fill plate having an outer circumference which coincides with the inner circumference of said segments and having a generally smooth radially disposed surface leading into said bar-and-groove pattern, and in which the portion of said surface adjacent said arcuate segments is in general alignment with the bottoms of the grooves of said pattern.

Description

BACKGROUND OF THE INVENTION

Cellulosic fibers such as paper pulp, bagasse, insulation or fiber board materials, cotton and the like, are commonly subjected to a refining operation, which consists of the mechanical rubbing of the fibers between sets of relatively rotating bar and groove elements. In disc-type refiners, these elements have consisted of plates having annularly arranged alternate bar-and-groove patterns formed therein, with the groove pattern extending in a somewhat radial direction, but frequently at some angle to a true radius.

Often, refiners are used to cut or shorten the length of the fibers. Also, where the fibers are already sufficiently short, the refiner may be used to develop fiber strength, by the working and rubbing of the fibers between the bars. This may open or split the outer wall or shell, and expose a new surface of fresh fibrils, to form fibers capable of forming bonds with other fibers, for increasing the strength, opacity, or other qualities of the resulting product.

Traditionally, the design of paper pulp refiners has been dictated by a consideration of the number and radial extent of refiner bars which can be placed within a given refiner on the basis that if some refiner bars were desirable, therefore a greater number would be more desirable. Many formulas and analytical approaches have been proposed to explain the operation of a refiner, and terms such as "inch-cuts-per-minute" were developed as a measure of refiner performance, on the basis that the more cutting action which can be effected between the bars of the rotating and the stationary discs the more refining would result. "Inch-cuts-per-minute" is a measure of the number of inches of cutting surface produced in a minute of time, based upon the r.p.m. and the amount of cutting surface in a given refiner disc. As a result of this concept, refiners have commonly been made with the bars being extended as long as practical toward the center of the refiner, with the result that the ratio of inside to outside diameter (D.sub.i/D.sub.o) has commonly been less than 0.5 and frequently in the range of 0.45.

Such refining discs with the bars extending one-half or more of the radius of the disc have frequently caused special problems in bar design, as it is necessary either to stagger groupings of the bars by making a plurality of separate plates, or by specially tapering the bars and intermediate grooves, or both . Attempts to increase the inch-cuts-per-minute factor have resulted in refiner plates of complex design which are expensive to manufacture.

SUMMARY OF THE INVENTION

The present invention is the result of a new approach to the analysis of refiner operation. A new theory of operation of a disc-type refiner has been developed by analogy to the horsepower formula for clutches and brakes. As a result of this theory, it is possible to improve the design of a refiner disc by specially selecting the D.sub.i/D.sub.o ratio to provide the highest degree of refining requiring the least power input. In other words, a refiner plate design is provided which has the least loss for the amount of refining produced.

This is accomplished, by separately considering the work loss factors in a disc refiner, arriving at an optimized and improved refiner disc construction which produces more refining, with less loss of energy. In other words, the refiner of the present invention is one in which more of the work put into the refiner goes into the stock and less of the work is wasted on nonproductive loss factors.

It is accordingly an important object of this invention to provide a disc-type cellulosic fiber refiner which has refiner plates of improved efficiency.

A further object of the invention is the provision of a disc refiner, and refiner plates therefor, in which the ratio of inside diameter to outside diameter of the working portion is between 0.55 and 0.85.

Another object of the invention is the provision of a refiner plate which is particularly adapted for replacement into existing refiners, having an improved pattern of refiner elements.

A further object is the provision of a fill plate which forms a taper leading from the region adjacent the refiner axis to the bar and groove pattern of the refiner plates.

These and other objects and advantages of the present invention will become apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of a twin disc type refiner constructed according to this invention;

FIG. 2 is an elevational view, partially in section, of the refiner of FIG. 1;

FIG. 3 is a fragmentary plan diagram of one of the improvements in refiner plates;

FIG. 3A is a plan fragment of a typical prior plate which is replaced by the plates of this invention;

FIG. 4 is an enlarged vertical section through the stationary and rotating discs and the supported refiner plates; and

FIG. 5 is a graph on which D.sub.i/D.sub.o is plotted against horsepower for various conditions.

THEORY OF REFINER OPERATION

W The work put into a disc refiner, for the purpose of analysis, can be broken into four main parts: (1) the hydraulic friction loss when a disc rotates in a liquid; (2) the pumping work (loss) due to acceleration of the liquid to the exit velocity; (3) the mechanical friction loss due to friction in the bearings, etc. (this item is a small percentage of the total, and since it is a constant can usually be ignored); and (4) the work put into refining the stock.

Referring to the loss items 1, 2 and 3 above, only item 1 is of a substantial nature, and its percentage to the total work can be reduced by proper consideration of the inside and outside diameter ratios of the refiner plates. The pumping work factor (item 2) need not be ignored, but in reality forms only about 1--2 percent of the total horsepower input into a refiner.

Referring to item 4), the present invention is the result of a new approach to understanding the work put into the stock, by a direct analogy to the horsepower formula for an annular type clutch or disc brake. This factor will be developed below in greater detail.

THE FRICTION LOSS FACTOR

The total horsepower HP.sub.t is defined above as being the sum of four factors, one of which is the disc friction loss by reason of a disc rotating within a fluid media. In essence, this loss can be expressed as a function of rotational speed cubed, and the diameter to the fifth power times a constant. Included in the constant is the mass of the fluid and a moment coefficient which is dependent upon Reynolds number and relative roughness. The basic formula for disc friction loss horsepower can be written as follows: ##SPC1## in which K.sub.d is a constant, N is the speed of rotation, and D is the disc diameter. However, since the disc in a refiner is annular, the portion forming the loss may be expressed as a difference in diameter. In addition, it has been determined experimentally that the constant K.sub.d for a conventional bar and groove plate is at least three times as high as that of a smooth plate. Therefore, the above formula can be written as follows: ##SPC2## in which K.sub.dN.sup.3(D.sub.o.sup.5-D.sub.i.sup.5) represents the losses in the bar and groove area and represents the losses caused in the smooth area. It can be seen from formula (2) that the larger the area having no bars and grooves, the smaller will be the unproductive friction loss. Since the friction losses represent between 30--50 percent of the total power applied to the disc refiner, any reductions in this loss may provide corresponding improvements in the overall efficiency of the refiner. Accordingly, any analysis of refiner efficiency must include a consideration of the disc friction loss, as related to the total work input and as related to the effective work applied to the refiner, as described below.

EFFECTIVE WORK

As previously indicated, the present invention makes use of an analogy to disc type brakes and clutches for an understanding of the effective horsepower (HP.sub.e) applied to the stock. This is a valid assumption due to the fact that in actual operation, the relatively moving and stationary bars have an interface clearance of between .003 and .010 of an inch, for example. The fibers which flow into the space between the bars become stapled across the bars and exert an axial force tending to separate the rotating and stationary elements, which is a substantially greater force than the hydraulic forces within the refiner. They also exert a friction drag between the relatively rotating elements not unlike that of an annular disc-type brake. Thus, in the operation of a typical disc-type refiner, a pair of opposed stationary plates are brought axially into working relation with opposite sides of a center rotating disc, and a clearance is established only during actual flow of the stock through the refiner, since the stock, and the fibers within the stock, maintain the necessary axial separating force to prevent physical contact and ultimate destruction of the relatively rotating elements. A suitable control system for effecting control of the refiner plates, is shown and claimed in the copending application of Frank Hayward, Ser. No. 698,931 filed Jan. 18, 1968 and assigned to the assignee of this application.

The remaining work put into the refiner, subtracting the loss items above, is the effective useful work in refining the stock. It was found that the refining factor cannot be increased merely making further increases in the area of the bar and groove pattern within a given refiner. Rather, the ratio of the effective power to the total can only be increased by properly selecting the D.sub.i/D.sub.o ratio of the bar-and-groove pattern.

In a disc brake, the horsepower which is dissipated is equal to a constant, multiplied by the r.p.m. multiplied by the difference of the cube of the O.D. and the cube of the I.D. of the contacting surfaces, assuming that the forces between the plates are equal between the I.D. and the O.D., and can be written as follows: ##SPC3## The constant K.sub.e includes pressure in psi or other dimensions, and includes the coefficient of friction.

Formula (3) applies when the refiner plates are new, and the pressure over the entire contacting surfaces is uniform. Refiner plates wear in use, and the wear is a function of the work performed and is proportional to the product of speed, pressure, and coefficient of friction. Assuming the coefficient of friction remains constant, in order to achieve uniform wear, the work expended must be constant over the surface. However, the linear speed varies directly with diameter, and thus the pressure tending to separate the plates must vary inversely with diameter. Accordingly, at the inside diameter of the refiner plates there is a condition of high pressure and low speed, generally considered to be a cutting condition, while at the outside periphery of the disc there is a an area of high speed and lower pressure, considered to be hydrating or fibrillating condition.

Formula (3) for a disc-type refiner, can be rewritten as follows: ##SPC4## K.sub.e is a constant which includes the coefficient of friction between the fibers and the plate and fiber-to-fiber, and the available operating pressure between the adjacent relatively rotating surfaces.

PLOTTING THE EFFECTIVE WORK AND LOSSES AS A FUNCTION OF D.sub.i/D.sub.o

The disc friction loss formula (2A) can be rewritten as follows: ##SPC5## Dividing each side of the equation (5) by a constant, the total horsepower (HP.sub.t), produces the following: ##SPC6##

The term K.sub.dN.sup.3D.sub.o.sup.5/HP.sub.t, in formula (6) is a constant when comparing refiners of the same speed and diameter. Therefore, it will be seen that the ratio of disc friction horsepower HP.sub.d to the total horsepower HP.sub.t is equal to a constant times a function of D.sub.i/D.sub.o and may be written as follows: ##SPC7## Where C.sub.d is a dimensionless constant.

The function represented by formula (1) has been plotted on FIG. 5 by the broken line 20, for a particular disc having a D.sub.i/D.sub.o ratio of 0.45 in which the constant C.sub.d is an arbitrary 0.334. It will be seen by reference to FIG. 5 that curve 20, at its right hand extent, approaches assymptotically a value of about 34 percent of the total power input, but drops off rapidly with D.sub.i/D.sub.o ratios greater than 0.5. A power saving can thus be effected by choosing D.sub.i/D.sub.o ratios of greater than 0.5.

The effective horsepower can also be plotted against D.sub.i/D.sub.o. Formula (5) can be rewritten as follows: ##SPC8## Dividing each side of the equation by HP.sub.t gives the following: ##SPC9## In formula (9) the term K.sub.eND.sup.3/HP.sub.t is again a dimensionless constant when comparing refiners of the same speed and diameter. Therefore, formula (9) may be simplified as follows: ##SPC10## Where C.sub.e is a dimensionless constant.

Formula (10) relates the ratio of effective-to-total horsepower in terms of D.sub.i/D.sub.o. It is plotted on line 25 in FIG. 5, again assuming the same conditions as previously assumed, that is, assuming a value for the constant C.sub.e of 1.87 which has been determined for conventional refining plates having a D.sub.i/D.sub.o ratio of 0.45.

EFFICIENCY

The D.sub.i/D.sub.o ratio for maximum efficiency does not coincide exactly with the maximum value for HP.sub.e at approximately .6 as plotted in FIG. 5, due to the fact that the friction loss factor HP.sub.t continues to decrease with increasing D.sub.iD.sub.o ratio. The formula for efficiency .eta. can be written as follows: ##SPC11## From formula 11 it will be seen that efficiency is a function of the effective power HP.sub.e divided by the sum of the effective power and the friction power. All other terms in the efficiency formula are constants. Therefore, a curve can be plotted of HP.sub.e/HP.sub.d = R which will correspond to efficiency. The efficiency will be at its maximum value when the ratio R = HP.sub.e/HP.sub.d is a maximum. The corresponding D.sub.i/D.sub.o value for this condition can be calculated by establishing R as a function of D.sub.i/D.sub.o and putting the first derivative of this equation to zero, as follows: ##SPC12## Again, as indicated above in connection with formulas (6) and (9), the first term of the horse power equation is a constant and has no bearing upon the derivative. Thus, equation (12) can be rewritten as follows in which the ratio of effective horsepower to disc loss horsepower is defined as a function of D.sub.i/D.sub.o: ##SPC13##

Differentiating and setting the first derivative of the equation to zero and solving for D.sub.i/D.sub.o given a D.sub.i/D.sub.o optimum of 0.64. The curve for formula (13) is plotted at 30 in FIG. 5 in which it will be seen that the optimum portion at the top is relatively flat, and near maximum efficiency is obtained for D.sub.i/D.sub.o ratios of between 0.55 and 0.85.

DESCRIPTION OF PREFERRED EMBODIMENT

The teachings of the invention have been applied to a disc-type refiner 35 in FIG. 1. The refiner 35 includes a rotatably mounted shaft 36 upon which a central disc 38 is mounted for rotation between a pair of axially adjustable nonrotating plates 39 and 40. The refiner plates are contained within a housing 42 with twin inlets 43 and 44 into which the stock to be refined is admitted, and a single outlet 45. The stock from the inlets 43 and 44 is applied to a region adjacent the axis of the shaft 36, as shown in FIG. 2, and is thus directed to a region radially inwardly of the stationary and rotating discs.

The rotating discs 38 and the stationary or nonrotating plates 39 and 40 each have mounted thereon refining plate structure, as shown in greater detail in FIGS. 3 and 4. The plates 39 and 40 are each mounted on a pair of transversely disposed arms 48 and 49. The arms are mounted in turn on oppositely threaded shafts 50, and are positionable by a drive mechanism 52 to move in unison axially toward and away from the rotating disc 38. The drive mechanisms 52 are normally remotely and automatically controlled, such as for example by the apparatus disclosed in the above-identified copending application, to cause a predetermined load on a meter driving the shaft 36.

As mentioned above, the disc 38 and the adjacent plates 39 and 40 each support annularly arranged refiner plate structure such as shown generally at 60 in FIG. 3. The refiner plates are formed preferably as a direct substitute for prior refiner plates, such as that shown by the segment of the plate 60a in FIG. 3A. Also, since the left-hand and right-hand refiner plates mounted in opposed working relation are substantially identical in construction that the plate arrangement or assembly 60 is typical of each of the four sets of plates used in the twin disc refiner 35.

The plate assembly 60 is formed with an outer annular arrangement of arcuate refiner plate segments 65, each of which is formed with a portion of a bar-and-groove pattern formed therein. The arcuate segments 65 together make up a full annular ring of segments forming an annular array of bar-and-groove pattern having the D.sub.o and D.sub.i dimensions as indicated by the respective reference lines in FIG. 3.

The pattern as shown in FIG. 3 comprises parallel and generally radially disposed equally spaced bars 70 separated by intermediate grooves 71. The space between the bars 70 being about generally equal the width of the bars. Each bar is formed with a planar refining face surface 74 which terminates at relatively sharp opposite edges 75, with axially straight walls leading into the grooves 71. The individual spacing of the bars, and the depth of the bars is mainly a matter of choice, within the preferred D.sub.i/D.sub.o ratios of this invention.

Since the refiner plate construction of the present invention, incorporating the bar-and-groove pattern, comprises a relatively narrow radial space, the remaining space in a conventional refiner is completed in the preferred embodiment with a fill plate 80 which is positioned radially inwardly of the plate segments 65. The fill plate 80 is formed with a smoothly tapered face surface 82, which lends from a region adjacent the outer circumference of the axle 36 into the bar-and-groove pattern, with the surface 82 terminating at a plane coincident with the bottoms of the grooves 71. The outer diameter of the fill plate 80 thus coincides with the inner diameter of the assembled plate segments 65. When two of such fill plates 80 are mounted in opposed relation, as shown in FIG. 4, a smoothly tapered throat is formed between the surfaces 82 for guiding the stock radially outwardly into the opposed bar-and-groove patterns for refining.

The arrangement of fill plates 80 defining the tapered lead-in throat tends to eliminate the reverse fluid coupling or circulatory flow which occurs between the planar spaced adjacent surfaces of two relatively rotating plates. Obviously, the occurrence of such counterflow is undesired since it impedes the desired movement of the fibers into the pattern area where it is acted upon by the opposed bars during rotation, for ultimate disposal outwardly of the housing 42 were it is accumulated for exit through the discharge opening 45.

In some instances, it may not be desirable to form the fill plates 80 as separate annular plate inserts. For example, some refiners may not have provision for mounting and supporting a separate plate, and in those instances, it may be preferred to extend each of the arcuate refiner segments or assemblies 60 radially inwardly beyond the above-defined critical bar-and-groove pattern limit to form a smooth throat or lead-in surface corresponding to the surface 82 provided by the annular plates 80. Also, it is within the scope of this invention to design the refiner discs 38 and backup plates 39 and 40 to form integrally the lead-in throat surfaces 82 defined by the plates 80, since these areas are subject to very little, if any, wear, and may accordingly be provided as a more permanent part of the refiner.

While the invention will normally be employed for the refining of paper stock, it is within the scope of this invention to apply the teachings thereof to disc-type refiners in general, which may be used for various types of cellulosic fibrous material, for cutting and/or refining such material, including but not limited to bagasse, cotton, insulation board filler materials, and the like.

The invention accordingly provides a disc-type refiner and plates for such a refiner having improved refiner efficiency with corresponding decreased power requirements. The bar-and-groove pattern on the plate assembly 60 comprise the working portion of the refiner plates and is related to the smooth lead-in portion of the refiner plates so that the bar-and-groove pattern defines and extends over only a predetermined and critical fraction of the total diameter of the combined plates 60 and 80 to provide a greater efficiency in the refining action of the working portions. The preferred ratio of diameters of the smooth to the working portions is in the range of 0.55 to 0.85.

The plate assembly 60 may be employed as direct replacements for plates such as that illustrated at 60' in FIG. 3A presently used in refiners, with a resulting improvement in operating efficiency as depicted in the graphs of FIG. 5. The bar-and-groove refining patterns of the present invention are subject to more uniform radial wear, since they occupy a more restricted and more precisely defined radial range, and since the wear is more uniform the plates tend to last longer before replacement is necessary.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

* * * * *

Current U.S. Class:	241/261.3
Current International Class:	D21D 1/00 (20060101); D21D 1/30 (20060101); B02C 7/12 (20060101); B02C 7/00 (20060101); B02C 7/06 (20060101); B02c 007/06 (); B02c 007/12 ()
Field of Search:	241/296--8,255--6,260,162,163