Note: Descriptions are shown in the official language in which they were submitted.
8s~3
PROCESS FOR SHREDDING TOBACCO STEMS
Background of the Invention
- The processing of tobacco stems has been complicated in
the past because of the structural dissimilarity of the rod-like
stems in comparison with the laminar portions of the tobacco leaf.
The sheet-like quality of the laminar portions results in a resili-
ent curliform shred when cut. Such shreds of laminar material,
when agglomerated, result in a cigarette filler material which
exhibits predictable qualities of filling power, density, and
texture. These qualities derive from the tortuous configuration
and springiness of individual shreds which curl and otherwise
arrange themselves in convoluted patterns. Such shreds exhibit
enough springiness so that the total filling capacity of a ciga-
rette filler in which they appear is enhanced. These character-
istics of cigarette fillers containing laminar leaf shreds are thefocus around which the elements of cigarette making machinery
design have developed.
eigarette making machines incorporate a high degree of
automation capability. They are designed to accept and handle --
tobacco filler having particularly those characteristics described
above which are peculiar to cut leaf blend. Any significant depar-
ture from these characteristics may make a cigarette filler blend
unsuitable for proper feeding into automatic cigarette making
equipment. ~lends of cigarette filler which contain a mixture of
shreds cut from leafy material and from stems wherein tbe cut stem
content is proportionately above a certain level may not be a
suitable feed material for such machines. When the percentage of
cut stem shreds is too high, problems may be experienced in the
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85C~3
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operation of the equipment's tobacco filler feed mechanism. There
may also be produced a certain excessive percentage of cigarettes
which are rejected because of improper appearance or feel.
The basic problem arises from the dense texture of those
stem shreds which are produced when cut across the grain of the
stem shards according to methods of shredding widely used in
tobacco cutting machinery. As stated, leaf shreds exhibit re- -
siliency; while stemsS when cut across the grain under like condi-
tions, may produce stick-like shreds or hard chunks of relatively
high density. These hard stick-like shreds and chunks are less
suitable as cigarette filler constituents. In addition, the rela-
tively short length and lack of springiness of cut stems reduces
their contribution to blend filling power and increases their
tendency to separate from the blend on handling. It is desirable
to carry out stem processing in such a way as to produce stem shred
fragments which more nearly duplicate the texture of leaf shreds.
Some prior art stem shredding methods have been used in
an attempt to convert stems into such leaf-like fragments which
would be compatible with leaf shreds in a filler mixture blend.
Some progress has been made toward this objective by rolling the
stems under pressure between pressure rolls. Thus, the stems are
crushed, flattened, macerated, and otherwise modified in overall
structure prior to shredding. This process, known as "rolling and
cutting," is a current industry standard.
~n such a process, threshed bright and/or burley stems
are moistened to 25 to 35% moisture content and then passed between
press rolls to flatten the stems to a form more like leaf lamina.
These flattened stems are then cut into shreds on a tobacco cutter
an~d reordered to a moisture content suitable for blending with
other tobacco filler components.
Methods-such as the above have produced stem shreds of
varying acceptability. The physical form and appearance of the
shreds so produced has resulted in inconsistent quality and yields.
This lack of consistency has limited the ready use of stems in
spite of the present need to increase the percentage of stem shred
fragments in the make-up of filler blends. In addition, some
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undesirably large stem particles are produced which cannot be
recycled to the process of rolling and cutting.
To the end that stem shreds be made more like leaf shreds
in appearance and texture, it has been suggested that a new
and different stem shredding process be devised. More particu-
larly, it is desired to shred tobacco stems in such a way as to
cause the stems to separate into fragments of curliform fibrous
strands.
Summary of the Invention
This invention relates to a method of shredding
tobacco stems which comprises the steps of:
a. supporting tobacco stem shards in a shredding
zone for free movement within a fluid medium; and
b. striking said stem shards violently with suffi-
cient force to separate said stem shards into
fibrilliform shred fragments.
An object of the present invention is to shred tobacco
stems by splitting or parting the stems along the grain to
produce light, pliable, low bulk density fibrillar shreds. Such
shreds exhibit sufficient resiliency so that when maseed they
approximate or exceed the filling capacity of cut leaf shreds.
Rolled and cut stem shreds tend to separate out on handling,
while fibrilliform stem fragments of the present invention when
mixed with leaf shreds counter this tendency toward separation.
The present process utilizes blunt rotatable blade-
like elements as hammers used to strike stem shards. Such bladesare arranged to revolve at high speed within a moving stream of
fluid-supported, dispersed, water-softened tobacco stem shards.
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The blunt blades travel at very high velocity within the
stream of softened shards and strike the individual shards
with force sufficient to cause spalling of the shards into
fibers parting them along the grain of the stem to produce long
fibrous shred fragments.
The shards to be shredded are first wetted to a
given desired moisture content. Wetting makes the shards
pliable and avoids the production of an excessive number of
short fibers. The shredding through spalling action, according
to the present invention, is thought to result from impinge-
ment of the fast-moving blunt blades on the floating stems and
stem shards by converting kinetic energy into internal stem
energy on impact thereby causing shattering of the shards
along the lines of the internal grain structure. This forms
elongated fibrous shreds which are thence driven protreptically
forward of the blades by the transfer of kinetic energy. They
are thus repositioned to be struck again and again by succeed-
ing blades. This action proceeds until the
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repeated spalling results in producing finer and finer shreds until
the desired degree of fineness results. These fine fibrillar
shreds are then separated and removed as a finished product by
screening, air classification, or centrifugal force. In this way,
the stem shards are not exposed to a tearing or cutting action
resulting from contact with opposing surfaces while under violent
protreptic movement induced by blade action.
Long, light fibrous shreds are thus produced which
exhibit the desirable characteristics of resilience similar to
shreds cut from leaf tobacco. In addition~ they possess the
characteristic of forming into helical convolutions thought to be
the result of dissimilar inherent strains in the shard structure in
its natural state, thus impart;ng springiness to the shreds for
better f;ll;ng power and curl;ness better to cause the stem shreds
to intertwine w;th leaf shreds ;n a blend.
In contrast, as prev;ously indicated, stem shreds made
according to the pr;or art in a rolling process and cut by opposed
shearing elements tend to exhibit undesirable features. Such
features are short shred length, a high degree of hardness, and
high bulk dens;ty which in each case results in lower filling power
and poorer blendability with shredded leaf in cigarettes. However,
the shreds produced by the present process possess improved ciga-
rette filling power per unit of weight over shreds produced by
these former methods and exhibit greater resil;ence and subjec-
tively produce a cigarette which has a smoother feel~
An important aspect of the process of the present inven-
tion is that the stems and stem shards are resiliently supported in
a fluid medium against impact action of the blades. An "anvil-
type" chopping block support for the shards or a shearing or cut-
ting action by a traveling cutter blade against a rigid support isavoided in the present process which effects shredding and f;beri-
z;ng by spall;ng act;on through the transfer of k;netic energy at
the po;nt of coll;sion between a blade and a float;ng stem frag-
ment. This results in explosive spallation and produces an un-
expectedly superior fibrous shredded stem product which is bettersu;ted for use ;n c;garette filler combinations than shreds pro-
- duced by prior methods.
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Description of the Drawin~s
Figure 1 is a lJaring Blendor illustrated to show modifi-
cation for adaptation to the present process.
Figure 2 is a view in elevation showing a blade arrange-
ment of a typical hammermill and screening apparatus; i.e., a
Fitzmill and a Sweco vibrating screen.
Figure 3 is a diagrammatic showing of the related steps
of the process.
Figure 4 is a photograph of feed stock of stem shards.
Figure 5 is a photograph showing the finished product of
the present process.
Description of the Presently Preferred
Practices of the Invention
In accordance with the present invention, stem midribs
separated from a tobacco leaf in any satisfactory way are first
treated with water in such a manner as to thoroughly moisten the
stems uniformly throughout. This moistening step may be effected
by spraying, steaming, or immersing the stems in a water bath for a
period of time as needed to achieve the desired level of moisture
content. Moistening of the stems by subjecting the stems to the
action of steam within a pressure vessel or at ambient pressures
will result in accelerating the penetration of moisture into the
stems.
Regardless of the method chosen to moisturize the stems,
it is desired to bring the moisture content to a level of from 40
to 75~ with a preferred level being at least about 60% by weight,
wet basis. A significantly lower moisture content will cause the
production of an undesirable percentage of short shreds due to
brittleness of the tobacco in the drier state.
The stems, after moistening, are introduced at a given
rate of feed into a partially confined area in which striker blades
are arranged to rotate at high speeds in accordance with the modes
of the invention as hereinafter described. The moistened stems are
shredded in the practice of one mode of the present invention in a
3s specially adapted one-quart Waring Blendor as shown in Figure 1
equipped with a commercial electric motor 10 and a bowl 12 in which
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11~85~3
the wall 13 has been provided with an exit slot 14 as shown in
Figure 1. A funnel-like feeder 15 is positioned within the steel
bowl 12. The feed material 16 consists of tobacco stem shards
which have been prepared by any suitable means (not shown) to a
desired length known as "short stems" and preferably 1 to 3 inches
in length prior to entry into the upper cone-like feed section 17
of the funnel 15. In operation, the shards 16 are fed by hand or
mechanically into the funnel 15 at a suitable rate thence through
the upper end 18 of the feed tube 19.
The blade element 20 is rotated at approximately 21,000
revolutions per minute by means of a standard Waring Blendor
motor 10. Shards are thus thrust centrifugally outward and
accelerated forwardly, recirculated, and struck again repeatedly.
A fresh supply of shards is fed through the funnel 15 until an
equilibrium rate of feed of material entering at that point is
matched to the effluent rate of finished product exited through the ---
slot 14. The gate element 21 is adjusted to a height of closure in
slot 14 to control the depth of material in proximity to the
blade 20. This determines the fineness of the shreds which are
forced to the top of the torus 22 formed around the vortex 23 over
the blade 20. The recirculation time of the shards and shreds
within the vortex 23 determines the fineness and final curliform
characteristics in the completed shreds.
Thus, factors in controlling the fineness of the shreds
are the rate of feed of the shards and'the height of the lower end
of the exit slot 14. This maintains the depth of the shards in
proximity to the revolving blades which in combination with the
rate of feed of fresh shards through the feed funnel 15 is critical
in determining the degree of fineness of finished shreds discharged
at the effluent slot 14. Once the balance of feed rate and height
of the effluent slot are determined, the process may be carried on
continuously w;th fresh stem shards 16 being fed through the feed
funnel 15 at a desired rate consistent with the rate of effluent 24
of finished shreds as described above.
The wide mouth funnel 15 as fitted to the jar top of the
bowl 12 facilitates continuous addition of feed stems and ~erforms
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the additional function of preventing stem shards and product from
being ejected from the top of the jar by the force of blade impact.
During operation, threshed stems, softened by moistening
to 40 to 75% moisture content, preferably above 60~, and holding or
"bulking" l to 24 hourss preferably l to 2 hours, are added through
the funnel 15 at a rate determined by the rate of shredded stem
efflux through the slot 14 for a given preset height of the gate
element 21. The blade 20, as driven by the blendor motor lO at
about 21,000 revolutions per minute, shatters the stems into finer
and finer fragments on recirculation within the torus 22. The
shards and shreds in the rotating vortex 23 are supported above the
shredding zone by air and centrifugal forces. Thus, as a suitable
size and shape of shred is attained, they rise to the top of the
torus 22 being carried upward by support of surrounding movement of
air exiting by centrifugal action through slot 14. Larger stem
shards remain in the shredding zone until they are shattered into
lighter fragments and become air supportable at the upper part of
the torus for removal. The height of the bottom edge of the side-
wall slot 14 is adjusted vertically by repositioning of the gate
element 21 to a height to permit an optimum size, shape, and weight
range of shredded stems to exit the bowl according to their rela-
tive position in the circulating torus of finished product.
The product removed through the slot 14 may be further
separated (i.e., with a standard or preferably a slotted classi-
fying screen, by centrifugal force or by air classification) anddried to a moisture content suitable for incorporation in a ciga-
rette blend.
Oversized material which remains after screening on a
slotted classifying screen, not shown, may be recycled alone,
d;rectly to the blendor, or mixed with fresh stem feed. Thus, no
oversized material ultimately remains by this mode of the process.
The final product is composed totally of suitable filler and a
small amount of fines which are separated for use elsewhere.
An alternate form of the present process may be imple-
mented with a Model M Fitzmill as shown in Figure 2 which is fittedwith blunt-faced impact blades 34 and a 4-mesh exit screen 35. The
particular unit is manufactured by The Fitzpatrick Company of
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Elmhurst, Illinois. Threshed stems, softened by moistening to 40
to 75% moisture content, preferably above 60%, and then holding or
"bulking" for 1 to 24 hours, preferably 1 to 2 hours, are submitted
to the shredding zone of the Fitzmill at a rate which permits free
circulation of the stems and ready access to spalling thereof by
the rapid rotation of blades 34. rhe shredding mass of stems is
forced by centrifugal action against the exit screen 35. As size
and shape permit, the shredded steTn fragmerlts go through the
screen 35.
The crude shredded stem shards a~ter passing through
screen 35 are further separated from the finer shreds on a two-deck
classifying screen assembly containing a suitably sized slotted
upper screen 36 which may have slots ranging in size from 1~" x
~" to 1" x 1/16" and a regular 30 mesh lower screen 37. Those stem
shards remaining on the upper slotted screen 26 are called "heavies" -
and are recycled to the hammermill, either alone or in admixture
with fresh stem feed. The fraction retained on the 30-mesh
screen 37 is the product desired and is thereafter dried to a
moisture suitable for cigarette blends. The smaller stem particles
which pass through the 30-mesh screen 37 are not recycled to the
mill. These are called fines and are carried away for use else-
where. Thus, only suitable product and fines are produced in this
process with the "heavies" being recycled.
Example 1
- Batch Waring Blendor Shredding
A standard one-quart glass Waring Blendor bowl is
equipped with a lid and a standard blade set of four blades and is
powered by a commercial two-speed motor, Model 5011, 21,000 RPM, as
illustrated in Figure 1.
Threshed burley tobacco stem shards up to approximately
three inches in length are softened by moistening to over 60%
moisture content and held or "bulked" for one hour in a sealed
container. The softened stems are Waring Blendor shredded in 10 9
batches for 30 seconds each.
A fraction of the shredded product which passes through a
standard Sweco 4-mesh screen and retained on a 30-mesh Sweco screen
35()3
g
is dried and equilibrated under standard conditions in air of 60%
relative humidity at 75F. The shredded stems so equilibrated
exhibit a cylinder volume of 92 cc for a weight of 10 9 at 12n6Db OV
(oven volatiles) compared to burley stems prepared by the usual
rolling and cutting process which exhibit a cylinder volume of
49 cc for a like weight with 12.5% nv .
Exam~le 2
Continuous Waring Blendor Shredding
A standard one-quart metal Waring Blendor bowl as illus-
trated in Figure 1 is equipped with a vertical rectangular slot of
1 x 3 inches in one side wall and provided with a height adjustable
bottom edge by means of an adjustable closure. The bowl is also
fitted with a standard blade set and a wide mouth plastic funnel
and is powered by a standard commercial two-speed motor, Model
5011, which is capable of turning at 21,000 RPM, as shown in
Figure 1.
Threshed burley stems of up to 3 inches in length are
softened by moistening to 65% H20 and holding for one hour in a
sealed container. The softened stems are added slowly at the rate
of 5 to 10 9 per minute through the funnel 15, and the bottom edge
of the slot 14 is height adjusted by gate element 21 to permit exit
of a subjectively optimum fraction of shredded stems.
A fraction of the product produced as passed through a
standard Sweco 4-mesh screen and as further retained on a 30-mesh
Sweco screen is dried and equilibrated under standard conditions.
The shredded stems thus treated exhibit a cylinder volume of 90 cc
per 10 9 of weight at 12.5% OV compared to burley stems prepared by
the usual rolling and cutting process which exhibit a cylinder
volume of 49 cc per 10 9 of weight at 12.5% OV.
The fraction of heavies of shredded stems retained on the
4-mesh screen is mixed with fresh feed and recycled through the
Blendor. Ultimately, the process gives a 92% yield of product
which is retained on a 30-mesh screen.
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Example 3
Fitzmill Shredding Utilizing
a 4-Mesh Exit Screen
A Model M Fitzmill equipped to turn at 5,000 RPM is
equipped with blunt impact blades of Type D-625 and a 4-mesh exit
screen, Type A, No. 4, as shown in Figure 2.
Threshed burley stems of up to three inches in length are
softened by moistening to above 60% moisture and held for one hour
in a sealed container. The softened stems are passed through the
Fitzmill at about five pounds per hour.
A fraction of the crude shredded stems passing through a r
slotted Sweco screen with openings of 1~ x 3/32 inches and retained
on a regular 30-mesh Sweco screen is dried and equilibrated under
standard conditions. The shredded stems exhibit a cylinder volume
of 70 cc per lO g of weight at 12.5% OV compared to 49 cc per lO g
of weight at 12.5% OV for burley stems prepared by the usual roll-
ing and cutting process.
The fraction retained on the slotted Sweco screen con-
sisting of the "heavies" of shredded stems is mixed with fresh feed
and recycled through the Fitzmill. This process gives a 90% yield
of usable product through a slotted 4-mesh screen and retained on a
30-mesh screen with a 10% yield of fines which pass through the 30-
mesh screen and are removed for use elsewhere.
Example 4
Fitzmill Shredding with 'i-Inch Exit Screen
The process of Example 3 is performed except that a
Fitzmill exit screen with ~2-inch round holes is used. Yery little
shredding action takes place due to the rapid exit of the stems
from the vicinity of the rotating blades.
Example 5
Fitzmill Shredding with 8-Mesh Exit Screen
The process of Example 3 is performed except that a
Fitzmill exit screen with round holes of 8-mesh is used. The crude
product exiting the Fitzmill under these conditions is very finely
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"
divided with a high proportion of dust and undesirable fines due to
an excessive time spent in contact with the rotating blades.
Example 6
Fitzmill Shredding with a Regular
4-Mesh Classifying Screen _
The process of Example 3 is performed except that a
(Square hole) 4-mesh size classifying screen is used for separation
of the recycle stream of "heavies" from the usable shreds. The
recycle stream of heavies is found to contain a relatively large
proportion of desirable shreds. The product passing through this
4-mesh screen and retained on a 30-mesh'screen also contains some
undesirable flat rectangular stem chips.
- Example 7
Batch Waring Blendor Shredding
with Bright Stems
- The process of Example 1 is performed with bright stems
at above 60% moisture content replacing the burley stems. The
product passing through a 4-mesh and retained on a 30-mesh screen
has a cylinder volume of 45 cc per 10 9 of weight at 12.5X OV
20 compared with 36 cc per 10 g of weight at 12.5% OV for bright stems
prepared by the usual rolling and cutting process.
Example 8
Fitzmill Shredding with Bright Stems
The proc,ess of Example 3 is performed with-bright stems
at above 60% W r6~placing the burley stems. The passing'through a
4-mesh onto a 30-mesh product fraction had a cylinder volume of
43 cc per 10 9 of weight at 12.5% W compared with 36 cc per 10 9
of weight at 12.5% OY for bright stems prepared by the usual roll-
ing and cutting process.
Additional Comments and Discussion
In Figure 4, a photograph of typical feed stock at
4 times magnification shows stem,shards which have been prepared
for processing in accordance with the invention by treatment in a
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preliminary threshing step. The finished shreds are shown in
Figure 5 and are photographed in equal magnification to that of
Figure 4.
It can be seen that in Figure 5, the shreds are of very -
fine strand thickness and are lying in curliform convoluted pat-
terns of somewhat helical nature. Such shreds exhibit spring-like
qualities and intertwine readily with tobacco leaf shreds.
Since the moisture content of the finished shreds is
similar to that of the feed stem shards, these shreds are dried to
a reordered moisture content of 12.5%; and the "cylinder volume,"
which is a means for gauging the ability of a particular cigarette
filler product to pack a cigarette to a desired firmness, is
evaluated by way of reading the height of stem shred product pro-
duced by different methods in columns of equal weight within a
standard graduated cylinder under a standard pressure.
In this way, a test for filling power is made. The same
amount of pressure in the form of a weighted piston with small
clearance within the cylinder is placed at the top of the samples
in each case, and the height of the tobacco column in the cylinder
under the piston is observed after it has been weighted for a
suitable time interval. The following relative volumes of stem
shreds made by the different methods is as shown in the repre-
sentative comparisons in Table 1 below.
Table 1
Representative Cylinder Volume
for Processed Stems
At 12.5% OV
1. Rolled and cut bright stems 33 cc/10 9
2. Shredded bright stems "Fitzmill"43 cc/10 9
3. Rolled and cut burley stems 49 cc/10 9
4. Shredded burley stems "Fitzmill"70 cc/10 9
The data of Table 1 demonstrate that the present processyields a product of greatest filling power when applied to the
shredding of burley stems. HoweYer, both bright and burley stems
when shredded in accordance with the present process are produced
at lower cost and with the elimination of several processing steps
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in comparison with prior art methods. In the case of burley stems,
which are the most difficult to process by prior methods, there is
a large increase in filling power as is shown in Table l when
shredded according to the present invention.
The process of the present invention makes possible the
conversion of stems of both flue-cured and air-cured tobacco into a
usable blending component for cigarette filler. The final product
in the form of fibrillar stem shreds is very well suited for use in
cigarette filler blends and offers considerable economic advan-
tages. Moreover, a high capital investment is not required for the
process which can be carried out using readily available equipment.
While presently preferred embodiments and practices of
the invention have been described, it will be apparent that the
invention may be otherwise variously embodied and practiced within
the scope of the following claims.
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