Toroidal flow pulper for difficult materials

To defiber a wide variety of materials, rotor and stator constructions are varied 1) to increase the agitation of stock in a tank or 2) to increase defibering effectiveness and increase flow rate through a recirculation line or to downstream equipment. To increase agitation, lobes of the stator are configured and sized to reduce the stator-rotor interface below 50% of its maximum possible value. To increase defibering effectiveness and increase the recirculation flow rate, the stator lobes are configured and sized so the stator area at the interface exceeds 50% of its maximum possible value. These lobe area changes are made in a way that also preserves a desired acquisition angle on cutting edges on rotor for the given material so that the lobes reliably "acquire" and reduce the stock. To increase homogeneity of treatment, deflectors on the stator and/or rotor require that all the stock traverses the defibering interface between peripheral teeth on the rotor and opposed stator bars. To increase the operational life of the rotor-stator pair, the rotor has an axially-thickened, cylindrically-shaped peripheral flange and is periodically axially advanced toward the stator to compensate for wear. To extend rotor-stator life when operating on very abrasive materials, the leading edges of the rotor blades are profiled at their tips to distribute the wear more evenly. To defiber more finely or more coarsely, the number and spacing of the rotor teeth are changed. For coarse milling, at least the tooth before each of a set of equiangularly spaced rotor blades is omitted.

BACKGROUND OF THE INVENTION 
This invention relates in general to reduction and defibering machinery and 
methods. More specifically, it relates to an improved pulper rotor-stator 
that defibers a wide range of difficult materials, that can increase 
selectively the agitation flow or defibering and recirculation flow of a 
stock, and can do so with an extended service life. 
Pulpers are typically used in the paper and pulp industry to reduce a stock 
material, such as wood pulp, into a watery slurry suitable for making 
paper. The stock material is added to a tank of water incorporating a 
rotor-stator pair where the stock material is broken down into fibers of a 
suitable size and consistency to make the desired paper product. 
Until the introduction of the pulper described and claimed in U.S. Pat. No. 
4,365,761, it was impossible to defiber a variety of materials in pulpers. 
These "unconventional" or "difficult" materials include cotton, hemp, 
flax, rag, leather, high wet strength papers, synthetic fibers, sheets of 
stock formed of fibrous material bound by adhesives, and in particular, 
the high wet strength board known as "shoe board". The defibering 
difficulty affects not only the cost and quality of the final paper 
product, but also the ability to recycle old paper products into new paper 
products, thereby avoiding landfill and saving trees. 
The pulper described in U.S. Pat. No. 4,365,761 uses a rotor and stator 
operating at close clearance (e.g. 0.010 inch). The rotor and stator are 
configured to "acquire" and cut difficult materials with a scissor-like 
action at a size reduction interface having a truncated conical geometry. 
This interface is defined in part by a series of generally triangular 
segments, or lobes, of the stator, which each curve along the outer edge 
of a generally circular base. Each lobe also inclines inwardly. The inner 
surface of these lobes defines a conical, as opposed to a cylindrical, 
interface. An outer cutting edge of blades, on the base of the rotor 
define the inner boundary of this interface. Scissoring occurs between 
these blade cutting edges and the leading edge of each triangular stator 
lobe. Once acquired and reduced to a sufficiently small size, the material 
is defibered in the attrition zone of the pulper between the lobes and the 
outer edges of the blades. 
This interface reduces in size large stock such as large sheets of shoe 
board and woven or natural cotton into "flakes" that can be further 
defibered without clogging. To date the '761 pulper, sold by 
Bolton-Emerson Americas, Inc. under the registered trade designation 
"Tornado.RTM." is the only commercial pulper which can handle such 
materials. The Tornado.RTM. pulper is believed to be used to prepare the 
slurries that make about half of the paper currencies now in circulation 
throughout the world. 
The energy input to the Tornado.RTM. pulper is used to reduce in size and 
defiber the material, to recirculate the flow of defibered stock back to 
the pulper (or, alternatively, to transfer stock downstream on a 
continuous basis), and to agitate the stock held in the tank using a 
toroidal flow. The pulper must also effectively deal with problems such as 
the tendency of some stock to float or settle in the tank ("submergence"), 
plugging of the defibering mechanisms, and "slugging" due to the rapid 
introduction of a mass of difficult material to the acquisition and 
attrition zones of the rotor-stator pair. 
While the '761 Tornado.RTM. rotor-stator design works well, it is adapted 
for use in conjunction with a standard size tank (7.5 foot inside 
diameter) and designed principally for defibering materials used in making 
paper and cardboard products. If it is placed on a larger size tank, 
(e.g., one with a 12 foot inside diameter), more power is required to 
produce sufficient agitation in the tank to mix the stock and draw it to 
the pulper. But more importantly, there is now a demand for a pulper which 
can effectively defiber a much wider range of materials to produce 
products very different from paper. 
For example, it is now desired to pulverize municipal solid waste (MSW) so 
that it can be fed to a reactor to make high energy liquid fuel to fire 
power plants. It is also desired to reduce MSW to fuel pellets for power 
generation. There is also an interest in "atomizing" scrap leather for 
conversion into pure protein for animal and human consumption. Another 
application is defibering old polypropylene carpeting and carpet scraps so 
that the fibers can be re-pelletized to make new plastic products. 
Agricultural products such as hemp, flax, kenaf, and straw, if defibered, 
can be made into various paper products. It is also desired to transform 
(i) "trash" fish and fish parts into liquid fertilizer, (ii) manure into 
fuels or fertilizer, (iii) old books and magazines into mulch, and (iv) 
even process the contents of old landfills in order to reclaim the land. 
These different materials and different end uses for a defibered product 
each present special processing problems. To produce an efficient and 
rapid pulping--without heat and chemicals--the pulper design must somehow 
accommodate significant differences in the raw materials, their flow 
characteristics, and their submergence in the tank as well as operating 
parameters such as consistency of the defibered stock, production rate, 
the amount of agitation required, and the recirculation flow rate. For 
example, where larger tanks are already installed, or they are needed to 
handle the raw material, more of the available power must be directed to 
agitation. Stronger raw materials, on the other hand, require more power 
for ripping and shredding. Homogeneity of the treatment to provide a high 
degree of uniformity of the size of the processed fibers is important in 
other end use applications. Different materials and end applications for 
the stock also influence the degree to which the rotor-stator pair must 
meet the design needs of 1) a scissor-like shearing action 2) a 
refiner-like defibering action, and 3) extraction (of small fibers to an 
extraction chamber and then to a recirculation line or to downstream 
equipment). The rotor-stator design must also be able to alter the 
distribution of power among recirculation, agitation of the stock within 
the tank, and defibering. To date, known pulper construction cannot meet 
these various design considerations for the many possible applications, 
particularly those outside of the paper and pulp industry. 
In addition, known pulpers continue to suffer from wear. Wear is 
particularly troublesome in dealing with highly abrasive materials such as 
those used in certain flooring bases. Replacement of rotor-stator 
components requires costly production down-time as well as the cost of 
replacement parts. 
Further, it may be desired to control the operation of a known Tornado.RTM. 
pulper to defiber materials "coarsely", to an unusually long fiber length. 
The rotor-stator interface is essentially a highly effective moving screen 
that rapidly reduces material to a defibered state. Under normal operating 
conditions, coarse fibers will be reduced in size. There is also a need to 
defiber to unusually short fiber lengths--a "fine" defibering--and within 
reasonable commercial production parameters, e.g., without repeated 
recycling or pre-pulper or post-pulper processing. 
It is, therefore, a principal object of the present invention to provide a 
rotor-stator assembly for, and method of operation of, a pulper which can 
defiber a wide range of difficult raw materials for the production of a 
wide range of end products. 
Another principal object of the present invention is to increase pulper 
production without sacrificing defibering effectiveness or energy usage 
efficiency. 
Yet another object is to provide either increased agitation or a greater 
effectiveness in defibering and increased recirculation. 
A further object is to provide a rotor design and method of operation of a 
rotor-stator pair which can readily compensate for wear at the 
rotor-stator interface while maintaining the aforementioned operational 
advantages, even when processing highly abrasive materials. 
Still another object is to provide a rotor-stator assembly and method of 
operation which can provide greater homogeneity of treatment and thus 
produce a stock with a high degree of consistency in the length of the 
fibers. 
A still further object of the invention is to provide a mechanically simple 
and reliable way to defiber to fine and coarse fiber lengths without 
clogging and without costly additional processing or repeated recycling, 
and without unusual or time sensitive modes of operation of the pulper. 
SUMMARY OF THE INVENTION 
A pulper includes a stock-holding tank with a rotor-stator pair mounted in 
the tank, typically a side-wall of the tank. A motor and drive shaft 
rotate the rotor within the stator. The stator has a generally circular 
base with a side wall typically in a series of generally triangular, 
curved, and inwardly inclined lobes arrayed around its periphery. The 
rotor is a generally circular plate that carries a set of upright blades 
mounted on the plate and configured to interact with an edge of the stator 
lobes in a scissors action as the rotor rotates. The blades and lobes 
define an acquisition zone where the stock is caught and cut in this 
scissor action to reduce it in size to a level where it can be defibered 
by 1) a milling action between the blade edges and cutting edges formed at 
bars and channels on the inner surface of each lobe and 2) a chopping 
action between a series of teeth formed on the outer periphery of the 
rotor and opposing bars on the side wall of the stator at or near its 
base. 
The rotation of the rotor, particularly the paddle-action of the blades 
projecting from the rotor plate, pumps the water and stock material in the 
tank. The pumped flow is split between a radial flow between the lobes and 
a recirculation flow through channels in the stator side wall into an 
annular extraction chamber formed outside the tank wall to receive the 
defibered stock. An outlet conduit directs the defibered stock for 
recirculation back to the tank and/or to an outlet conduit that feeds 
downstream equipment. 
To increase the agitation while still providing excellent defibering and 
recirculation without plugging, slugging, or cavitation, the lobes are 
constructed so that they occupy less than 50%, and for most applications 
preferably about 1/3, of the total surface area of the conical 
rotor-stator reduction interface. This reduction is made while maintaining 
a high degree of rotational symmetry. 
In a preferred form, the stator has six lobes with pairs of adjacent lobes 
spaced circumferentially by distance that would otherwise be occupied by a 
lobe. In another form, the lobes are uniformly truncated so that their 
maximum axial height from the stator base is less than the axial height of 
the rotor vanes. In yet another form the lobes are all mutually spaced 
circumferentially, preferably by a distance equal to the circumferential 
width of one of the lobes. In still another form the lobes are continuous 
around the periphery, but are each "flattened" to a uniform degree. The 
total surface area of the lobes at the interface controls distribution of 
agitation/recirculation flow and the surface area available for 
"bar-and-channel" milling-action attrition. 
To increase defibering effectiveness and increase the recirculation flow 
rate, the lobes are configured and sized to occupy more than 50% of the 
interfacial area. Additional lobes are added, and/or the size of the lobes 
is increased. The lobes are truncated, or retain their peaks. The angle of 
the lobe edges, however, is generally the same as with a standard nine 
lobes around the stator. 
To increase homogeneity, deflectors on both the stator and rotor force the 
flow of stock to traverse the interface between the teeth formed in the 
outer edge of the rotor and the stator. 
To compensate for wear at the reduction interface, the rotor plate is 
thickened axially at its outer periphery with a cylindrical outer surface 
and the axial position of the rotor is adjustable. As wear widens the 
clearance between the cooperating elements of the rotor and stator, the 
rotor is advanced towards the stator until the desired clearance is 
re-established. This process is repeated until the highest points of the 
rotor vanes and the stator lobes become generally coincident. Initially, 
the lobes and vanes are sized so that the lobes extend over the vanes. The 
extent of this initial height mismatch is reflected in the amount of 
peripheral thickening of the rotor plate. The rotor flange maintains the 
desired area of engagement between the rotor and the stator at the 
interface. For operation with highly abrasive materials, the upper, outer 
end of the rotor blade is profiled to distribute the wear more evenly over 
the blade end. The profiling is in the form of a wedge-shaped relief that 
thins the blades as it extends toward its upper end. 
It has been found that the number, spacing, and, in some instances, size, 
of the peripheral rotor teeth produce fine or coarse defibering, without 
modification of the stator or other equipment. For fine defibering, the 
number of the rotor teeth is increased over the number heretofore standard 
on a comparably-sized Tornado.RTM. rotor, e.g. by about 50% to about 100%, 
with a corresponding reduction in the inter-tooth spacings, and usually in 
the width of the teeth as well. For coarse defibering, the tooth size need 
not change, but at least three equiangularly spaced teeth, ones that each 
lead an associated rotor blade, are omitted to create large inter-tooth 
spacings or "pockets". In another form such pockets are created before all 
of the rotor blades, but not at other circumferential locations. In still 
another form such pockets are formed between all of the rotor teeth lying 
between adjacent rotor blades. Elimination of teeth to create the pockets 
is rotationally symmetric. The number and size of the pockets is varied 
depending on the desired degree of coarseness in the defibering and with a 
given application. 
Viewed as a process, the invention where increased agitation is required 
involves decreasing the area of the lobes at the reduction interface to a 
value below 50% of the total area of the interface and distributing this 
decrease uniformly about the stator. This reduction is done while 
maintaining the acquisition, attrition, and recirculation qualities 
necessary to defiber the particular material being processed. The area 
decreasing can be by spacing lobes circumferentially, truncating them, 
flattening them axially, or combinations of the foregoing. To enhance 
defibering and recirculation, the area of the lobes at the reduction 
interface is increased above 50% by filling in the region between lobes or 
increasing lobe size, with or without truncation of the lobe. The wear 
compensation invention, viewed as a process, includes thickening the 
periphery of the rotor in an axial direction and with a cylindrical outer 
configuration, and then periodically advancing the rotor toward the stator 
to maintain a slight clearance therebetween at a pre-set value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1-3 show a system 10 according to the present invention which 
includes a stock-holding tank 12 and a defibering pulper 14 with a 
stationary stator 16 and a nested, rotatable rotor 18 which together 
define a reduction and attrition interface 20. For many applications the 
interface has a slight clearance, typically 0.005 to 0.010 inch, that is 
uniform around the interface. However, for some applications the clearance 
may be reduced to zero, and, in still other applications, it is desired to 
use thrust, that is, to advance the rotor further to increase the power 
demand and to increase significantly the effectiveness of the pulper. 
The tank 12 can assume a variety of shapes. As shown it is generally 
cylindrical with a bottom wall 12a, and a side wall 12b. With the stator 
construction of the present invention that increases power supplied to 
agitation of the stock held in the tank, the tank can have a large 
volumetric capacity as compared to typical tanks for pulpers operating in 
a batch mode. A typical capacity for the tank 12 is roughly 5,000 gallons, 
while a standard tank capacity is about 2,600 gallons. In terms of batch 
capacity in pounds, the standard tank can hold 1,000 pounds at a 5% 
consistency in a 7.5 foot inside diameter tank that is 9.0 feet high. A 
typical large tank, e.g., one with a 12-foot diameter, can handle at least 
a 2,000 pound batch. 
The stock held in the tank is formed by adding to a supply of water a 
charge of a material to be defibered into the water. The invention can be 
used with conventional materials, but it is particularly designed to 
reduce in size and then to defiber difficult materials used in making 
paper and paper products such as raw (or cooked) cotton, stockboard stock, 
hemp, flax, rags, heavy latex impregnated shoe board and the like, as well 
as a wide variety of other materials such as a MSW, the agricultural 
products noted above, fish, manure, used books and magazines, and the like 
to make the fuel, fertilizer, mulch, compost and food products and the 
like, also mentioned above. 
A motor 22 rotates a drive shaft 24 journalled in a set of mutually spaced 
bearings 26a, 26b. A handwheel 28 operating a gear and rack assembly 30, 
or an equivalent linear translation mechanism, moves the drive assembly 
axially to allow adjustment of the rotor-stator clearance at the interface 
20 through an axial movement of the rotor 18 secured to one end of the 
drive-shaft. The drive-shaft is highly rigid to transmit a large torque 
and to resist bending moments that would displace the rotor and destroy 
the uniformity of the clearance 20. 
The rotor 18 is organized about a circular plate 18a that mounts a nose 
cone 32 and a set of circulation blades 34 which project from the plate 
18a into the tank. The blades can be cast integrally with the plate 18a, 
or welded or otherwise attached. The rotor also includes a peripheral 
flange which thickens the rotor axially at its outer edge. The flange 
stiffens the plate, but the flange 70 according to the present invention 
extends axially beyond merely the length needed to stiffen the rotor. This 
extra length, preferably at least double what has been used for stiffening 
alone, has been found useful in extending rotor life due to wear, as will 
be discussed in greater detail below. The flange has a cylindrical outer 
surface which wears to a conical surface. 
The blades are central to the defibering through the interaction of a blade 
edge 34a and cooperating cutting and attrition edges formed or carried on 
the stator. They also act as pumping elements. Their rotation drives 1) a 
defibered stock flow 36 through the interface 20 to an extraction chamber 
38 for recirculation or use and 2) a radial flow 40 out of the interface 
20 which produces a toroidal flow 42 in the tank 12. The toroidal flow 42 
agitates the stock in the tank; it mixes the material in the tank and 
continuously sweeps stock, particularly along the tank walls and along the 
stock surface, to the center of the tank where it is carried to the pulper 
14. The useful energy applied to the system 10 by the pulper 14 is applied 
to size reduction and defibering, recirculation, and agitation. The 
rotor-stator constructions of the present invention can defiber a wide 
range of unconventional materials and maintain a recirculation flow while 
also developing a sufficiently strong toroidal agitation flow 42 so that 
stock held even in a large capacity tank is defibered successfully. 
The recirculation flow 36 of defibered stock exits the extraction chamber 
38 via conduit 44, a valve 46, and a valved "T" connection 48 which 
directs the flow either back into the tank 12 and/or to an outlet conduit 
52, e.g., one that feeds a tank supplying a paper-making machine. The 
system 10 can be operated in a batch or continuous mode, with 
recirculation, or with a variable rate of recirculation as a percentage of 
the total flow through the pulper 14. The valve 48 controls the outflow 
rate from the pulper. 
The stator 16 is organized around a generally annular, integral base 16a 
which carries a set of curved, circumferentially extending lobes 54. Each 
lobe 54 has the general configuration of a solid triangle that is inclined 
inwardly toward the axis of rotation of the drive-shaft and rotor. The 
inclination and curvature of each lobe is such that the inner surfaces of 
the lobes define a truncated conical surface that is the outer boundary of 
the interface 20. The inner boundary is defined, with a slight clearance 
of a few thousandths of an inch (or essentially no clearance in a "thrust" 
mode of operation), by the locus of the edges 34a of the moving rotor 
blades 34. The lobes 54 are preferably integral with the base 16a. 
As described in detail in the aforementioned U.S. Pat. No. 4,365,761, which 
disclosure is incorporated herein by reference, the blade edges 34a and 
the leading, or "acquisition" blade edges 54a of each lobe 54 meet at an 
angle of 15.degree. to 55.degree., and preferably at about 25.degree. to 
create a scissor-like cutting action as the rotor rotates within the 
stator. This action is termed "acquisition" in the '761 patent, and the 
valleys 58 between lobe peaks are termed "acquisition spaces." This is the 
space where large pieces of the materials are caught and cut into smaller 
pieces which can then enter and be further reduced and defibered in an 
attrition zone 60 defined by the mill-like attrition produced between the 
blade edges 34a and series of "vertically" extending bars 62 and channels 
62a formed on the inner surface of each lobe. Further chopping-action 
attrition occurs through the interaction of a set of teeth 18c formed on 
the outer edge of the rotor with the opposite stator wall with the lower 
portions of the bars 62 and channels 62a. Screws 56 received in axial 
holes 56a at the outer edge of the stator mount it. 
To increase agitation the surface area of all of the stator lobes 54 is 
kept at a value less than 50%, and preferably about 1/3, of the total 
surface area of the truncated conical interface 20. This relationship 
produces a strengthened radial flow out of the pulper, and a 
correspondingly strengthened toroidal agitation flow 42--one sufficiently 
strong to agitate, mix and sweep floating and settling material in the 
tank into the pulper. The precise value of the area reduction will depend 
on the specific application. 
This area reduction must be symmetrical around the stator so as to avoid 
producing moments on the rotor and the drive-shaft which would adversely 
affect the uniformity of the rotor-stator clearance 20. They must also be 
carried out in a way that does not create other problems such as plugging, 
cavitation, or a reduction in the ability of the pulper to acquire, reduce 
in size, and defiber stock material. 
FIGS. 6B-6E each show as linear developments four circular lobe 
constructions which, when used in cooperation with the rotor 18, produce 
this redistribution of energy to the agitation flow. For comparison, FIG. 
6A shows a linear development of a standard, prior art, nine lobe stator 
for a Tornado.RTM. pulper. 
The FIG. 6B form of the invention in effect eliminates in total every third 
one of the nine lobes, leaving six lobes 54, in adjacent pairs, spaced by 
the width of one of the lobes. The lobe height in this embodiment, and 
other construction features, are otherwise the same as in the FIG. 6A 
Tornadoe.RTM. stator. FIG. 6C shows an alternative embodiment where there 
are nine adjacent, non-spaced lobes 54', but each lobe is truncated in a 
common plane parallel to the stator base 16a. FIG. 6D shows a variation on 
the FIG. 6B form, with the lobes 54" narrowed, that is, with a smaller 
included angle 68 at the apex of the lobe. FIG. 6E shows "flattened" lobes 
54'" where the height of each lobe is lowered an equal amount by 
configuring the lobe 54'" with an increased included angle 68' at the apex 
of the lobe as compared to that of the "standard" lobe 54. The degree of 
narrowing or flattening must be balanced against the effect of the change 
of the angle of the acquisition edge 54a in cutting. A typical value, 
corresponding to the FIGS. 1-4 embodiment where 3 of 9 lobes are omitted 
entirely, is 1/3. 
FIGS. 6F-6N show still other alternative stator embodiments useful for 
increasing agitation and falling within the present invention, but in 
front elevation of the stator. The configuration of the standard FIG. 6A 
stator is shown in phantom for comparison. 
In each of these embodiments (FIGS. 6B-6N), these stator lobe arrays are 
used in cooperation with a rotor and rotor blades 34 of the same general 
size as used with the standard lobe 54 shown in FIG. 6A. As a result, the 
increased inter-lobe space and/or lowered lobe height of FIG. 6B and 6E 
allow the tangential pumping action of the rotating vanes to flow with 
less resistance than with prior art approaches, including the FIG. 6A lobe 
configuration, used in the standard commercial form of the Tornado.RTM. 
pulper. 
Other stator constructions shown in FIGS. 7A-7F also in front elevation, 
increase the defibering action and the recirculation flow of the pulper 
10. In FIG. 7A, the lowest portion of the valley 58 of a nine-lobe (FIG. 
6A) stator is solid (with alternating, generally axially directed bars 62 
and channels 62a formed on its inner surface). FIG. 7B shows an embodiment 
with the stator side wall almost completely filling the valleys 58 of a 
standard nine lobe stator for even greater defibering and recirculation 
action. FIG. 7C shows an alternative embodiment with three equi-angularly 
distributed valleys 58 completely solid. FIGS. 7D-7F show three other 
alternative embodiments which vary the standard, FIG. 6A, nine-lobe 
construction by increasing the size of each lobe and trimming its peak 
(truncating it) to successively increase the stator area at the interface 
20 while maintaining generally the same acquisition angle, about 
25.degree., for each stator acquisition edge 54a. FIG. 7F would be used 
where the acquisition and reduction demands are small, but a maximum 
defibering and recirculation is desired. 
In each of embodiments of FIGS. 7A-7F, the stator-rotor interfacial area is 
greater than 50% of the total interface area. The precise value used and 
the stator configuration used will depend on the particular raw material, 
the desired end product, and desired operating parameters. 
With each of these stator embodiments (FIGS. 6B-7F) it is critical that the 
lobes are angularly symmetrical about the axis of rotation for the pulper. 
Asymmetries will produce bending moments on the drive-shaft through the 
resultant asymmetrical loading on the rotor. Bending moments will in turn 
produce a non-uniformity in the interface clearance which will seriously 
degrade the operation of the pulper. 
FIGS. 8B illustrates deflectors 80, 82 on the stator and rotor, 
respectively, which force the stock being defibered to flow through the 
chopping-action attrition zone defined by the peripheral rotor teeth 18c 
and the opposite channel and bar surface of the stator. In the '761 prior 
art pulper, the channels 62a extended generally in a straight line as 
indicated in FIG. 8A. As a result, material being defibered could flow 
straight into the extraction chamber 38, thus by-passing the chopping 
action of the teeth 18c. Flow arrow 83 shows a by-pass flow through the 
channel 62a; flow arrow 83a shows a by-pass flow through the 
circumferential spaces 66 between the rotor teeth 18c. (Flows 83 and 83a 
together form the defibered stock flow 36.) The deflectors 80, 82 are 
preferably cast in place as integral extensions of the stator base 16a and 
rotor plate 18a, respectively. The deflectors 80, 82 are positioned, 
configured, and sized, as shown, to force the stock flow pumped down the 
channels 62a by rotation of the blades 34 (as shown by flow arrows 84 and 
84a in FIG. 8B) into the attrition region where the teeth 18c can act on 
the fibers. Each deflector 80 can be formed simply by tapering the lower 
end of the channels 62d in the form of a flat ramp that terminates short 
of the rear face of the station. Each deflector 82 on the rotor is 
preferably formed by machining (or casting) the spaces 66' between the 
teeth 18c not to extend through the rotor plate, but rather to curve to 
the outer edge 34a of the blade 34, as shown. It is thus integral with the 
rotor plate 18a. 
While the preferred form of the deflection 80, 82 are shown and described, 
they can assume a variety of forms as long as they: i) divert the flow 
through the channels 62a (defining a first milling-action attrition zone) 
to a second chopping-action attrition zone defined by the teeth 18c and 
the opposed bars 62; and ii) block a by-pass flow that would otherwise 
avoid the second attrition zone by flowing through the openings between 
the teeth 18c. For example, the deflectors 80 can have curved, rather than 
flat, surfaces interacting with the flows. Rather than being integral, the 
deflectors 80, 82 can be solid or sheet metal deflectors welded, or 
otherwise secured, in place on the stator and rotor. The internal shape of 
the deflector 82 can also vary, e.g., it can have a more squared internal 
corner, that is, one that does not thin radially toward the interface 20. 
Further, while there is a loss in performance as compared to using both 
deflectors 80 and 82, it is possible to use only one of the deflectors 80 
and 82 to enhance homogeneity of treatment and uniformity of fiber length. 
This is because with one deflector some portion of the defibered stock 
flow can bypass the second, milling-action attrition zone. 
To cut and defiber these difficult materials, the drive-train must transmit 
a substantial torque. For paper and pressboard applications, typical rotor 
speed is 430 rpm at 350 Hp. For cotton and like applications, a typical 
rotor speed is 380 rpm. A 1200 rpm capacity motor delivers 250 Hp to a 
36-inch diameter rotor steady-state with peak demands in excess of 300 Hp 
when stock is introduced. The reaction forces on the rotor-stator pair are 
likewise substantial. Despite the use of hardened steel alloys for cutting 
and attrition edges, there is steady wear on the rotor and stator at the 
interface 20. 
FIGS. 9A-9C illustrate a profiled blade end 90 useful in reducing wear when 
very abrasive materials are being defibered, e.g. flooring base material 
containing an abrasive material. The profile 90 is in the form of a 
generally wedge-shaped recess machined in the upper, trailing end of blade 
edge 34a. The widest end of the recess is at the top of the blade 
resulting in the thinnest part of the blade at its uppermost end. This 
configuration avoids a concentration of wear at the upper edge of the 
rotor-stator interface where the abrasive material first enters. Instead, 
the profile reduces the available surface for rotor-stator wear at the 
upper end and facilitates its entry into the interface as a point closer 
to the rotor plate 18a. This distributes the wear more evenly over the 
interface, providing a longer life. The precise shape and size of the 
profile is not critical as long as it performs these functions. The wedge 
shape shown, with a flat, ramp-like configuration, is preferred for ease 
of machining, but it could be curved. By way of illustration, but not of 
limitation for the size of rotor and rotor blades described above, the 
wedge-shaped extends axially for 2.75 inch, leaving the blade with a 
thickness (in the direction of rotation) of 0.25 inch at its tip. The 
wedge in its preferred form shown is uniform and extends over about 80% of 
the height of the blade edge. The wedge recess has a thickness, in this 
example, of about 0.5 inch at the blade tip. Variations in the 
configuration and dimensions of this profiling are limited by the strength 
and rigidity required of the blade and its wear characteristics in use 
which can be determined empirically and/or though conventional stress 
analysis techniques. 
FIGS. 10A and 10B illustrate a rotor-stator construction and method of 
operation of the pulper which can compensate for wear at the rotor stator 
interface and thereby greatly extend the service life of the pulper and 
reduce down-time for maintenance. As shown in FIG. 10A, the rotor has an 
axially thickened (dimension H in FIG. 10B) periphery in the form of a 
rearwardly extending peripheral flange 70. The rotor initially nests in 
the stator only partially--the "upper" edge 34b on the vane lies below the 
upper edge 54b of the lobe at its maximum height. The outer surface of the 
flange 70 is cylindrical with a diameter no greater than the inside 
diameter of the stator. 
As the rotor and stator wear at the interface 70, the rotor is periodically 
advanced into the stator, as by adjusting the axial position of the 
drive-train using the handwheel 28 and gear and rack assembly 30. Each 
advance is sufficient to compensate for wear and reset the interface 
clearance to the desired operating value. Eventually the wear is 
sufficient that the rotor reaches the position shown in FIG. 10B with the 
rotor fully seated in the stator and the upper edges 34b and 54b are 
generally coplanar. Note that the flange 70 progressively nests in the 
stator to maintain a desired rotor-to-stator area of interface. As 
compared to the standard Tornado.RTM. pulper, the stator lobe is also 
thickened so that after wear on the stator it nevertheless has a thickness 
sufficient to provide the necessary rigidity and structural strength. It 
is at least twice the axial thickness of the stiffening peripheral flange 
now used on the rotor of the comparably-sized Tornado.RTM. pulper. By way 
of illustration, but not of limitation, for a nine-lobe, 36 inch diameter 
stator according to this invention, the stator lobes have an initial 
thickness of 1.00 inch at their peak and the flange 70 extends axially for 
about 5.00 inches. 
FIG. 11A shows in detail "standard" rotor teeth 18c that act in cooperation 
with opposed bars 62 on the stator 16 to defiber through a milling action. 
For a 36 inch diameter rotor, the teeth 18c preferably have a width of 
about 5/8 inch, spaced by circumferential gaps 66 of about 7/8 inch. The 
teeth 18c are preferably raked backwardly (with respect to the direction 
of rotation of the rotor) by about 45.degree. measured from a radial line 
passing through the center of rotation and the tooth. 
While this size and configuration works well for many paper and pulp 
industry applications, it does not yield optimal results when used in 
certain other applications, or even in certain paper and pulp 
applications. A major design problem is that the rotor-stator combination 
in operation is in effect a highly efficient moving screen. Because of 
this efficiency, it has proven difficult to achieve a non-standard degree 
of defibering; e.g., in instances where it is important to produce coarse 
(long) fibers. 
FIGS. 11B and 11C show a rotor teeth array 18c', according to the present 
invention adapted for fine milling action and rotor teeth arrays 18c" and 
18c'" adapted for coarse milling. For fine milling, the number of teeth 
18c' is increased by approximately 50% to 100% and the inter-tooth 
spacings 66 are reduced in width accordingly. The exact size and 
configuration of the teeth and spacings can vary, provided that: i) there 
is a requisite increase in frequency of the milling action (for a given 
diameter rotor operating at a given speed); ii) the teeth are structurally 
strong enough to withstand the stresses that are applied in operation 
without deforming or breaking; iii) the openings 66 do not plug or clog 
readily; and iv) the mass of the teeth is distributed rotationally 
symmetrically. By way of illustration but not of limitation, for a 36 inch 
diameter rotor, the fine teeth 18c' shown in FIG. 11B are 5/8 inch wide 
(at the outer diameter of the rotor measured in the direction of rotation) 
and ninety in number. The openings 66 extend radially for 1.0 inch and are 
3/8 inch in width at the outside diameter of the rotor. In contrast, the 
standard rotor teeth 18c are 63 in number, with the dimensions and 
spacings noted above. (Except that in each of the FIGS. 11A-11C 
embodiments the tooth at the blade 34 spans a blade and a region on either 
side, typically with a total circumferential length of 2.0 inches, again, 
for a 36 inch diameter rotor.) It has been found that the rotor tooth 18c' 
can reliably produce a fine defibering without modifications to, or a 
re-design of, the stator, particularly the size and configuration of the 
bars 62 and channels 62a. 
The rotor teeth 18c" shown in FIG. 11C are sized and configured like the 
teeth 18c shown in FIG. 11A, except that every other tooth is omitted to 
produce large inter-tooth pockets 67 between adjacent teeth. Also, a 
pocket 67 leads at least each of three equiangularly spaced blades 34. The 
pockets 67 are located so that the rotor teeth 18c' are distributed to be 
rotationally symmetric. With the teeth 18c" and pockets 67, the rotor can 
defiber effectively to a coarse fiber length while operated in a standard 
manner with a stator having a standard array of bars 62 and channels 62a. 
FIG. 11C also shows in phantom an alternative arrangement for coarse 
defibering, which includes rotor teeth 18c'" in pockets 67 except a 
"first" pocket immediately preceding each blade 34, or each of three 
equiangularly spaced blades 34. These teeth 18c'" are, as with the teeth 
18c", sized and configured like the teeth 18c and spaced to produce a 
rotationally symmetric mass distribution. This alternative arrangement, 
using only three equiangularly spaced pockets, has been able to defiber 
rags coarsely for use in paper making without making any other equipment 
modifications or modifications in the operating procedures. 
In all of these examples, the rotor teeth are the standard thickness 
(measured axially) for a 36 inch diameter rotor, 1.25 inch, and the 
leading cutting edges are preferably formed of a hardened steel alloy to 
hold a sharp cutting edge. 
There has been described a stator for a rotor-stator pair of a pulper, as 
well as a complete pulper and pulper system which can operate in 
conjunction with a large size tank to reduce in size and defiber difficult 
materials. The invention provides a readily implemented mechanical 
solution which allows the processing of a wide variety of difficult raw 
materials into a wide variety of end products mechanically, without 
heating and chemicals. This invention also provides a simple mechanical 
solution to the problem of inconsistency in fiber length caused by the 
ability of fibers to bypass the action of the rotor teeth. 
There has also been described a construction and method of operation of a 
rotor-stator pair which compensates for wear at the rotor-stator interface 
without replacement of any parts and the attendant costs for a replacement 
part and production down-time for the replacement. There has also been 
described a rotor blade construction which reduces wear when processing 
very abrasive materials and a rotor tooth construction which can defiber 
to fine and coarse fiber lengths without other changes in the pulper or 
its mode of operation, and without the use of special auxiliary equipment. 
While the invention has been described with respect to its preferred 
embodiments, various modifications and alterations will occur to those 
skilled in the art. For example, while the lobes have been described as 
generally solid isosceles triangles, they can be configured differently as 
long as the acquisition edge is present at the correct angle for the 
scissor action, the attrition zone channels are available, the surface 
area of the lobes conform to the present invention, and the lobes are 
otherwise structurally strong enough to withstand the forces applied to 
them. Similarly the blades can take different forms, and the cutting and 
pump functions could even be divided among separate elements on the rotor. 
A variety of arrangements can be devised to advance the rotor to 
compensate for wear, whether manually or automatically. While nine lobes 
are described as completely surrounding a 36-inch diameter interface, the 
number of lobes can vary for that size pulper, or differently sized 
pulpers. While the tank has been described as cylindrical, it can be oval, 
rectangular, or other more complex shapes, albeit perhaps at great cost or 
with some loss of energy or effectiveness of the agitation flow in the 
tank. Further, while the pulper 14 has been described as mounted in the 
tank side wall, it could be mounted in the bottom wall. They and other 
modifications and variations are intended to fall within the scope of the 
appended claims.