Note: Descriptions are shown in the official language in which they were submitted.
CA 02244264 1998-07-24
WO 97/2?032 PCT/US96/20709
A KNIFE SHAFT ASSEMBLY
FIELD OF THE INVENTION
This invention relates to a knife shaft assembly for a rotary die cutter. More
i
specifically, this invention relates to a knife shaft assembly with die
cutting inserts and
means for preventing a buildup of material waste between adjacent inserts.
BACKGROUND OF THE INVENTION
A rotary die cutter includes a rotatable anvil roll which cooperates with a
rotatable
knife shaft assembly. The knife shaft assembly has an outer circumference with
two or
more die cutters mounted thereon. The knife shaft assembly cooperates with the
anvil roll
to form a nip through which a web of material can pass. As the web of material
passes
between the nip, the die cutter wilt cut the material into a predetermined
shape.
It is common practice to form the knife shaft assembly from a single die shaft
by
machining the cutting edges into the outer circumference thereof. By doing so,
one can
control to very close tolerances the outside diameter of the knife shaft
assembly and
therefore maintain a predetermined dimension between the nip. However, it is
very
expensive to machine the knife shaft assembly from a single metal piece. It is
much more
advantageous to machine individual die cutting inserts and then mount the
inserts onto the
outer circumference of a die shaft. Doing so substantially reduces the cost of
producing
the knife shaft assembly. However, the use of reptaceable die cutting inserts
present two
challenges. First, up until now, when an insert was interchanged with another
insert, it was
necessary to regrind alt of the knife edges of alt of the inserts mounted on
the
circumference of the die shaft in order to assure that the nip dimension would
not change.
A second challenge with the use of replaceable die cutting inserts is that cut
waste material
could build up between the adjacent cutting edges. A buildup of such waste
would reduce
the ability of the knife shaft assembly to completely cut through the web
passing through
the nip.
CA 02244264 2004-08-17
Now, a knife shaft assembly has been invented which utilizes a compressible
material between adjacent cutting edges of the inserts to prevent the build-up
of waste
material.
SUMMARY OF TIE INVENTION
Briefly, this invention relates to a knife shaft assembly for a rotary die
cutter. The
knife shaft assembly includes a rotatable die shaft having an outer
drcumference and
having a defined width. At least two die cutting inserts, preferably
replaceable andlor
interchangeable die cutting inserts, are mounted on the outer drnumference of
the die
shaft. Each of the inserts has a first surface and a knife formed about the
periphery of the
first surface. The knife shaft assembly also includes a compressible material
positioned
between each pair of adjacent die cutting inserts which prevent the buildup of
waste
material.
The invention may provide a knife shaft assembly with at least
iwo die cutting inserts and means for preventing a buildup of waste material
between the
inserts. A more spedfic object of this invention is to provide a knife shaft
assembly with
replaceable andlor interchangeable die cutting inserts and a grid work of a
compressible
material kxated between the inserts for preventing the accumulation of cut
waste material.
The invention may provide a knife shaft assembly with a plurality
of die cutting inserts and means for preventing a buUdup of waste material so
as to improve
the die life.
The invention may provide a knife shaft assembly with
replaceable and/or interchangeable die cutting inserts utilizing multiple
pieces of a
compressible material to reduce waste material.
The invention may provide a knife shaft assembly with
replaceable andlor interchangeable die cutting inserts utilizing compressible
material
between adjacent inserts to improve the efficiency of cutting various
materials.
The invention may provide a knife shaft assembly with
replaceable and/or interchangeable die cutting inserts utilizing a grid work
of compressible
material to reduce the initial cost to building a knife shaft assembly.
Other advantages of the present invention will become more apparent
to those skilled in the art in view of the following description and the
accompanying
drawings.
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WO 97/Z7032 PCTlUS96/20709
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic of a rotary die cutter showing a ~otatable anvil roll
cooperating
with a rotatable knife shaft assembly to form a nip therebetween and having a
web of
° 5 material passing through the nip.
Fig. 2 is a perspective view of a replaceable and/or interchangeable die
cutting
insert.
Fig. 3 is a top view of the circumference of a die shaft extended in planar
form
depicting the arrangement of the replaceable and/or interchangeable die
cutting inserts and
the compressible material positioned therebetween.
Fig. 4 is an exploded cross-sectional view taken along line 4--4 of Fig. 3
depicting
the cutting edges of a pair of adjacent die cutting inserts with a
compressible material
sandwiched therebetween when mounted an a die shaft.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Fig. 1, a rotary die cutter 10 is shown which includes a
rotatable anvil
roll 12 cooperating with a rotatable knife shaft assembly 13. The anvil roll
12 can be
constructed of a ferrous or non-ferrous metal and should have a smooth
surface. The anvil
roll 12 can be formed from a material which is compressible, such as natural
or neoprene
rubber or from a non-compressible material, such as steel. For most
applications, it is
preferred that the anvil roll 12 be a metal roll.
The knife shaft assembly 13 includes a rotatable die shaft 14 having an outer
circumference 16 and a defined width "w,~ see Fig 3. The die shaft 14 should
be
constructed out of a metal material, such as steel, and can vary in diameter
to meet one's
particular needs. The die shaft 14 can also vary in diameter. For most rotary
die cutting
applications, the diameter of the die shaft 14 can be between about 2 inches
to about 12
inches. Larger diameters can be used if required. The die shaft 14 can have
two or more
inserts 18 mounted around its outer circumference 16. The exact number of
inserts 18
which are utilized will depend upon a number of factors, including the size of
each
insert 18, the circumferential area and width of the die shaft 14, and the
actual
arrangement of the inserts 18 about the circumference of the die shaft 14,
etc. For cutting
articles, such as sanitary napkins and pantiiiners, out of a web of absorbent
material, the
' die shaft 14 can be constructed to have a diameter of between about 6 inches
to about 18
inches, preferably, between about 6 inches to about 12 inches. The actual
number of
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CA 02244264 1998-07-24
WO 97/27032 PC'T/US96/20709
inserts 18 which can be mounted to the die shaft 14 can range from between
about 2 to
about 100, preferably between about 16 to about 52, and most preferably,
between about
16 to about 24.
It should be noted that the efficiency of the knife shaft assembly 13 will
increase
when a plurality of die cutting inserts 18 are mounted onto the outer
circumference 16 of
the die shaft 14. As shown in Fig. 1, there are four die cutting inserts 18
mounted in a
spaced apart configuration about the outer circumference 16 of the die shaft
14. Each of
the inserts 18 has a central longitudinal axis X-X and a central transverse
axis Y-Y. The
inserts 18 can be arranged about the outer circumference 16 of the die shaft
14, such that
each longitudinal axis X-X extends around at least a portion of the outer
circumference 18
of the die shaft 14.
The anvil roll 12 and the knife shaft assembly 13 cooperate to form a nip 20
therebetween through which a web of material 22 can pass. As the anvil roll 12
and the
knife shaft assembly 13 are rotated in opposite directions, the web of
material 22 can pass
through the nip 20 and be cut by the die cutting inserts 18 into individual
articles 24. The
articles 24 can be transported by conventional means, such as a conveyor 26,
to a location
where they can be stacked, packaged and later shipped. Any design waste, also
referred
to as 'Srvaste trim" 30 from the rotary die cutter 10 can be directed away
from the nip 20 by a
conduit 28 using vacuum, air pressure, gravity or mechanical means. The waste
trim 3fl
can then be collected in a hopper 32 for possible recycling or some other
means of
disposal.
Refer-ing to Fig. 2, a die cutting insert 18 is shown before it is secured to
the die
shaft 14. The die cutting insert 18 can be a replaceable and/or
interchangeable insert. By
replaceable, it is meant that the insert 18 can be unbolted and removed from
the die
shaft 14 to be cleaned, reground or machined in some fashion and then bolted
back onto
the die shaft 14 in its original location. By interchangeable, it is meant
that each of the die
cutting inserts 18 is capable of being mutually interchanged with any other of
the die cutting
inserts 18. This interchangeability feature is very important because, up
until now, it has
been virtually impossible to produce replaceable and/or interchangeable
inserts for a rotary
die cutter 10 while still maintaining the nip dimension between the anvil roll
12 and the knife
shaft assembly 13.
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WO 97/27032 PCT/US96/20709
The die cutting insert 18 has a base 34 formed on a predetem~ined radius. The
base 34, which can have an arcuately-shaped profile, has first and second
spaced apart
ends, 36 and 38 respectively, and first and second oppositely aligned
surfaces, 40 and 42
respectively. The first surface 40 will face the anvil roll 12 when the
inserts 18 are
' S assembled onto the knife shaft assembly 13. The second surface 42 will be
concave so as
to match the outer circumference 16 of the die shaft 14 onto which the insert
18 is to be
' secured. ft is common to machine the second surface 42 to have a tolerance
of plus or
minus .0001 inches so as to facilitate a proper attachment between each of the
die cutting
insert 18 and the die shaft 14. If the second surface is not machined to a
close tolerance to
match the outer circumference 16 of the die shaft 14, then it is possible for
additional
compressive forces to develop as each insert 18 is secured to the die shaft
14. The
presence of such compressive forces can alter the dimension of the nip 20, and
this is
undesirable.
As shown in Fig. 2, the die cutting insert 18 has a knife 44 which is
integrally formed
about the periphery of the first surtace 40. Preferably, the knife 44 is a
continuous element
but could be serrated if desired. The knife 44 has a cutting edge 46 and first
and second
side walls, 48 and 50 respectively. The cutting edge 46 has a width of less
than about .005
inches. Preferably, the width of the cutting edge 46 is between about .0005 to
about .004
inches, and most preferably, the width is between about .001 to about .002
inches. The
width of the cutting edge 46 is very important because if the width becomes
too great, it will
be more difficult to cleanly cut the material 22 passing through the nip 20.
For example,
instead of making a clean cut, the cutting edge 46 could compress the material
22 and
allow the material 22 to be tom or broken and thereby produce a ragged cut.
The first side wall 48 is aligned approximately perpendicular to the cutting
edge 46.
tn other words, the first side wall 48 is coextensively aligned with the
outside periphery 52
of the base 34. Preferably, the first side wall 48 is aligned perpendicular,
that is at 90
degrees, to the cutting edge 46. The second side wall 50 is aligned at an
angle of at least
about 15 degrees relative to the cutting edge 46. The second side watt 50 is
located
inward of the first side wall 48 and terminates at a third surface 54. The
third surface 54 is
located intermediate the first surface 40 and the second surface 42. The third
surface 54 is
spaced below the first surface by a relatively small distance. The actual
distance between
the first surface 40 and the third surface 54 can vary but normally will be
about equal to the
. thickness of the article which is to be cut. For example, when cutting a
compressible article
having a total thickness of about .125 inches, the distance of the third
surface 54 below the
first surface 40 can be between about 0.1 inches to about .125 inches. This
distance is
5
CA 02244264 2004-08-17
equivalent to the height of the knife 44. The height of the knife 44 can be
affected by the
type of material 22 which is being cut, the thickness of the material, whether
the material is
compressible, whether the material is formed from a single layer or from a
plurality of
layers, whether the layers are bonded together by an adhesive, as well as the
particular
characteristics of the material itself. For example, a thermoplastic film may
react differently
to being cut than a fibrous nonwoven web. It should also be noted that when
cutting
thinner materiats, the height of the knife 44 could be less than the thickness
of the
material 22 because the cut may not have to extend as far through the material
as with a
thicker product. When cutting the material 22, it is not necessary that the
cutting edge 46
actually contact the anvil roll 12. In fact, the life of the cutting die
insert 18 can be extended
when the cutting edge 46 does not physically contact the anvil roll 12.
The second side wall 50 is aligned at an angle of at least about 15°
relative to the
cutting edge 46. Preferably, the angle is between about 15° to about
50° relative to the
cutting edge 46, and more preferably, the angle is between about 15° to
about 40°
relative to the cutting edge 48. It is important that the second side wall 50
be angled
relative to the cutting edge 46 at an angle of at least about 15°
because the design of the
insert 18 leaves very little support for the knife 44. Since the first side
wail 48 is
approximately perpendicularly aligned to the cutting edge 46, all support
provided to the
knife 44 will have to come from the material present between the first side
wall 48 and the
second side wail 50. If the angle is less than about 15°, there is a
high probability that
the cutting edge 46 will crack or chip as the material 22 is being cut because
the forces
acting on the cutting edge 48 can become very high.
As mentioned above, the die cutting insert 18 can be replaceable and/or
interchangeable onto the die shaft 14. One means for removeably attaching the
die cutting
insert 18 to the die shaft 14 includes forming at least one aperture 58
adjacent to each of
the first and second ends, 38 and 38 respectively. Preferably, a pair of
apertures 56 are
formed adjacent to each of the ends, 38 and 38 respectively, so as to permit
each insert 18
to be con-ectiy secured to the die shaft 14 without introducing unwanted
forces into each
insert 18. Each of the apertures 56 extends completely through the base 34
from the third
surface 54 to the second surface 42. The apertures 56 are not threaded but do
contain a
counterbore 58 located adjacent to the third surtace 54. Each counterbore 58
is sized and
configured to receive the head of a machine bolt which can be used to attach
the insert to
the die shaft 14.
6
CA 02244264 2004-08-17
Each of the die cutting inserts 18 can also contain a pin hole 80 formed at
the
intersection of the central lorroitudinal axis X-X and the central transverse
axis Y-Y. The
pin hole 60 is designed to be coaxia0y aligned with a hole or bore formed in
the die shaft 14
such that a pin (not shown] can be inserted through the pin hole 60 and served
to
physically align the insert 18 onto the die shaft 14. Once the insert is
aligned and held in
position by the pin, the machine bolts can be inserted into the apertures 56
and be
threaded into threaded bores formed in the die shaft 14. It should be noted
that the pin
hole 60 is an optional feature and is present only for convenience in
mountinfl the insert 18
onto the die shaft 14.
Referring to Figs. 3 and 4, the knife shaft assembly 13 dudes msaM 82 fa
preventing the buikf-up of cut waste material between adjacent die cut5nfl
inserts 18. The
means 82 fs a oompnessible material such as natural a synthetic rubber, or
some other
type of malarial having comprea:ible charsdsriatics. When artting absorbent
amides 24,
such as sanitary napkins and paMiliners, it is necessary that the oomprossible
materlaf 82
be approved by the U.S. Food and Drug Administration (FDA). A material which
is FDA
approved is neoprone rubber, model tIf8818K24 is oorrrnerdaly available from
McMaster-Carr S~ply Company, P O Box 4355, Chicago, Illinois, 80880.4355. Thia
putiarlu neoprone rubber cartiss in sheet form and can be cut or stamped Into
any
destrod shape. The neoprone rubber :houki have s tsn:ik st<enpth of between
about 100
s ~ ~~° ~ ~~ t° 2~~ ~. prefuebly between about 500 psi to about
1,500
psi, end most preferably, between about 1,000 bo about 12,000 p:l. Thb
particular material
is oft-wMts in color having a dtu~ometer hardness das:Hied as Shoro 'A.' The
neopnrte
has an operable temperature range of between shout -25~ F to about 220°
F. Neoprene is
a synthetic rubber pr~oduoed by polyrnsrization of chloroprons and used in
v~roalher
roslstaM products, adhesives, shoe sobs, paints and rocket fuels. The
compnss(bk
mater(al 82 can have a thid<rwu ert>idt can vary from between about .001
inches to about
.5 inches. Preferably, the compressible material 82 has a thickness of between
about .01
7
CA 02244264 1998-07-24
WO 97/27032 H'CT/US96/20709
inches to about .25 inches, and most preferably, has a thickness of between
about .01
inches to about .1 inches. For most applications, the use of a compressible
material 62
having a thickness of less than about .25 inches will suffice.
As shown in Fig. 3, the die cutting inserts 18 are arranged in an end-to-end
configuration about the outer circumference 16 of the die shaft 14. The
inserts 18 can be
arranged in a spaced apart configuration having an opening of from between
about .001
inches to about .5 inches between each adjacent insert. In Fig. 3, one will
also notice that
the inserts 18 are arranged in a side by side, offset configuration across the
width "vr~' of the
die shaft 14. Preferably, there will be at least one roll of inserts arranged
about the outer
circumference 16 of the die shaft 14. More preferably, for increased
efficiency, it is
advantageous to arrange the die cutting inserts 18 across the entire width "w"
of the die
shaft 14 so as to be able to cut a greater number of articles 24 for each
revolution of the
die shaft 14. In Fig. 3, four die cutting inserts 18 are shown arranged in an
offset pattern
across a major portion of the width "w" of the die shaft 14. It should be
noted that the
particular configuration of the die cutting inserts 18 will dictate as to how
each of the
inserts 18 can be nested so as to produce the most cuts while obtaining the
least amount
of cut waste material. It has been found that the use of two to twelve, side
by side rolls
across the width "v~' of the die cutter 18, works well. The number of inserts
18 aligned end
to end around the outer circumference 16 of the die shaft 14 will be dependent
upon the
length of each insert and the diameter of the die shaft 14. It should be noted
that all of the
inserts 18 do not have to be identical in size or dimension. For example, two
or more
different articles can be produced by mounting different shaped inserts 18 on
the die
shaft 14.
In Fig. 3, the compressible means 62 is shown in a grid-like arrangement
having
one or more ring or band members 64 of compressible material extending
circumferentially
about the outside circumference 16 of the die shaft 14. The ring or band
members 64 can
be continuous about the 360° circumference or they can be arcuate
segments which are
assembled so as to form a complete circle or a portion of a complete circle.
The grid work
also includes one or more transverse member 66 positioned between the ends of
each pair
of adjacent inserts 18. The ring members 64 and the transverse member 66 can
have a
thickness "Y' as labeled in Fig. 4, of between about .001 inches to about .5
inches.
Preferably, the thickness is less than .025 inches, and most preferably, the
thickness is
between about .01 inches to about .1 inches. If one has the opportunity to
size the
diameter of the die shaft 14 so as to maximize the number of inserts 18 which
can be
mounted onto the outer circumference 16 thereof, one can reduce the distance
between
8
CA 02244264 1998-07-24
WO 97!27032 PCTJUS96/20709
the ends of adjacent inserts 18. By reducing the distance therebetween, one
can minimize
the amount of cut waste material in the manufacturing process. This is a very
advantageous feature. For this reason, it is preferable to dimension the end-
to-end
clearance distance to range between about .01 to about .05 inches, if
possible.
It is likewise important to minimize the clearance distance between two
adjacent
side-by-side inserts 18. However, the outer configurations of the inserts 18
may require
Y
that the clearance be larger than that between the end-to-end arrangement. It
is
anticipated that the ring or band members 64 may have a thickness which is
slightly larger
than the thickness of the transverse member 66. By slightly larger, it is
meant that the
thickness may be in the range of between .001 inches to about .1 inches, and
preferably,
will be about .05 inches. It should also be noted that the ring members 64 and
the
transverse member 66 do not have to be physically bonded or attached together
but can be
merely held in position by the physical arrangement of the inserts 18. One
wilt notice that
in Fig. 3, a first flange 68 is secured to the left-hand side of the die shaft
14 and a second
flange 70 is attached to the right-hand side of the die shaft 14. The flanges
68 and 70 are
configured to conform to the outer profile of the circumferencial row of
inserts 18 and assist
in sandwiching the ring member 64 against the cutting edges 46 of the aligned
inserts 18.
Located between each circumferential row of inserts 18, is the compressible
material 62.
The compressible material 62 will be sandwiched between each pair of cutting
edges 46 by
the physical engagement with the inserts 18. it should be noted that in
assembling the
compressible material 62, it is anticipated that the compressible material 62
will be
squeezed to a certain extent in the assembly process. The amount that the
compressible
material 62 is squeezed will be dependent upon one's manufacturing process and
the type
of tooting used.
Fig. 4 shows an embodiment wherein the compressible material 62 is positioned
between two adjacent inserts 18. The compressible material 62 contains a top
surface 72
which is aligned approximately flush with a horizontal plane aligned
tangential to the tips of
the cutting edges 46. It should be noted that the top surface 72 can be
positioned slightly
below the plane of the cutting edges 46 but should not be at a distance below
the plane
which is greater than the thickness of the web of material 22 which is being
cut. For
example, if the web is about .125 inches thick, the top surface 72 of the
compressible
material 62 should not be below the plane by more than about .1 inches or the
benefit of
utilizing the compressible material 62 wi0 be lost. Preferably, the
compressible material 62
is equal to or slightly below the plane created by the adjacent cutting edges
46. It is
possible to have the compressible material 62 extend above the plane of the
cutting
9
CA 02244264 1998-07-24
WO 97/27032 PCT/US96/20709
edges 46 but in this position, the compressible material may intertere with
the ability of the
cutting edges 46 to properly cut the web of material cleanly. A very slight
extension, in the
range of between about .0001 to about .1, above the plane of the adjacent
cutting
edges 46 should be acceptable. !t should also be noted that if a compressible
material 62
is used which has a soft or medium compressibility value, a value which allows
the material
to be easily compressed, that a greater distance above the plane of the
cutting edges 46
could possibly be used. For a compressible material having a firm or hard
compressibility
value, it is recommended that the top surface 72 of the compressible material
62 does not
extend above the plane of the cutting edges 46.
The compressible material 62 also includes a bottom surtace 74 which can be
flush
with the bottom surface 40 of each of the inserts 18. As shown in Fig. 4, when
the bottom
surtace 74 is flush with the bottom surface 40 of the inserts 18, all of the
surfaces will mate
with the outer circumference 16 of the die shaft 14. This wilt assure that as
the
compressible material 62 is compressed from above, by contacting the material
web 22,
that it will not be pushed down to a permanent lower position which is below
the plane of
the cutting edges 46. The purpose of the compressible material 62 is to
compress down
below the cutting edges 46 as the material web 22 is being cut and then to
extend back to
its normal position expelling any potential fibers or waste material which may
be present.
The waste material located between the adjacent cutting edges 46 can then be
removed
as the knife shaft assembly 13 rotates about its center axis. The compressible
material 62
should be selected to have a particular tensile strength and compressibility
value. These
values can vary depending upon the type of material selected, the thickness of
the
material, the type of material being cut, as welt as other factors. A
compressible material is
normally classified as being a "soft, medium, firm or hard" grade. For this
invention, the
compressible material 62 should be selected to be either "soft, medium or
firm" grade but
not "hard" grade. The "soft grade 35-45 A" and the "medium grade 45-55 A"
seems to
work best when using the compressible material 62 between adjacent cutting
edges 46 for
cutting absorbent articles, such as sanitary napkins and pantiliners. The
"firm grade 55-65
A" might work better for a harder material which is to be cut. It is
anticipated that the
compressibility values of the material 62 will range from between about .1X to
about 10X,
preferably between about .1X to about 5X, and most preferably, the
compressibility value is
less than about 3X. By 1X, it is meant that the compressible material 62 can
be
compressed to half of it's thickness. The tensile strength of the material 62
can also vary
CA 02244264 1998-07-24
WO 97/27032 PCT/US96/20709
and should range between about 450 psi to about 1,500 psi, more preferably
between
about 750 to about 1,500, and most preferably, between about 1,000 psi to
about 1,300
psi.
It should be noted that the compressible material 62 can be positioned about
at
least a portion of the periphery of the first surface 40 of each of the
adjacent inserts 18.
The top surface 72 of the compressible material 62 can be curved or arcuate in
shape so
as to match the profile of the cutting edge 46 of the knives 44. It should
also be noted that
if the cutting edges 46 are flat or linear, then the top surtace 72 of the
compressible
material 62 can also be flat or linear. The compressible material 62 can be
positioned
about the outer circumference of each of the inserts 18 but does not have to
be in physical
contact with the entire outer circumference of each of the inserts 18. For
example, if one
looks at Fig. 3, one will notice that the compressible material 62 actually
forms an
approximately rectangular grid work around the hourglass shape inserts 18.
Physical
contact about the entire periphery of the insert 18 does not occur.
It should also be noted that it is possible for one to form a particular grid-
like
arrangement of the compressible materials 62 and then to place it, like a
template, over the
outer circumference 16 of the die shaft 14. Once the grid work of the
compressible
material 62 is in place, each of the individual inserts 18 can then be bolted
onto the die
shaft 14. This and other particular configurations will be obvious to those
skilled in the art
and are considered part of the present invention.
While the invention has been described in conjunction with several specific
embodiments, it is to be understood that many alternatives, modifications and
variations will
be apparent to those skilled in the art in light of the aforegoing
description. Accordingly,
this invention is intended to embrace a!I such alternatives, modifications and
variations
which fall within the spirit and scope of the appended claims.
11
