Note: Descriptions are shown in the official language in which they were submitted.
~3~7~70
This applica-tion is a division of Canadian Patent Appli-
cation, Ser. No. 479,860, filed April 23, 1985,
Backqround Of_The Invention
1. Field of The Invention
The invention relates to an assembly of a carrier and a
shaped charge for use in an elongated perforating gun of the
type generally used to perforate oil and gas wells. The
invention particularly pertains to the manner in which the
shaped charge is held in place relative to the carrier of
the perforating gun.
2. Description Of The Prior Art
Perforating guns commonly used in wireline service
operations for perforating an oil or gas well typically
include an elongated cylindrical outer housing within which
is received an elongated carrier which has a number of
shaped charges in place in the carrier. The carrier is
located relative to the housing so as to locate each of the
shaped charges adjacent reduced thickness portions of the
housing.
~; It is known ln the prior art to utilize either triangu
lar or hexagonal cross-section tubular carriers constructed
to receive three 120 circumferentially spaced shaped
charges in a given horizontal plane. When a hexagonal
carrier is utilized, longitudinally adjacent layers of
charges ma~ be rotated 60 relative to each other to spread
~ut th~ pclt'cern of perforations along the length of well
whl~h i~, 'o he perforated.
~'piCc-ll-l y~ the shaped charges have been held in place
tive to the carrier by snap rings which interlock both
~L23~ 7~
with the outer case of the shaped charge and with the
carrier.
Furthermore, a number of structures for attachment of
shaped charges to ~he carrier have been developed.
For example, in U. S. Patent ~o. 4,326,462 to Garcia et
al., a plastic retaining clip fits over a shoulder of the
outer case of the shaped charge. The plastic retaining clip
includes flexible arms which snap into holes in the wall of
the carrier.
Another arrangement i5 shown in U. S. Patent No.
3,773,119 to Shore wherein a square cross-section flexible
carrier tube has cut-out portions thereof which engage
notches in the outer case of the shaped charge.
Additionally, a threaded plug, received in the housing of
the perforating gun, itself engages the shaped charge to
snugly hold it in place within the housing.
Another example of a manner in which a shaped charge may
be retained in place relative to a carrier is shown in U. S.
Patent No. 3,636,875 to Dodson wherein the shaped charge has
spaced shoulders between which is received a wire-type frame
member.
From these various examples just discussed, it is seen
that the prior art has long recogni~ed the need for a
reliable means for retaining shaped charges in place within
a carrier of a perforating gun. The present invention pro-
vides a much improved, very economical, reliable, and easily
assembled construction for the assembly of a shaped charge
with a carrier.
2--
~;236~77~
Summary Of The Invention
The present invention provides a shaped charge carrier
assembly for use in a perforating gun. The assembly includ-
es at least one shaped charge having an outer case which
itself includes an outer surface and a first shoulder
extending radially outward from the outer surface. The
assembly further includes a carrier having an opening
-therethrough large enough to receive the outer surface of
the case of the shaped charge. The carrier includes resi-
lient tab means extending into the opening thereof for fric-
tionally engaging at least a first portion of the outersurface of the case of the shaped charge, and for thereby
holding the shaped charge in place relative -to the carrier
with the shoulder of the shaped charge abutting the carrier.
The present invention also provides a shaped charge
case comprising a unitary body having an interior cavity,
a subs-tantially open forward end in communication with the
in-terior cavity and an outer surface including a first
grooved portion. The case has a first shoulder which
extends radially outward therefrom beyond the first grooved
portion and a rearward end which extends from and is of
lesser diameter -than the first grooved portion.
Numerous objects, features and advantages of the pre-
sent invention will be readily apparent -to those skilled
in the art upon a reading of the following disclosure when
taken i.n conjunction with the accompanying drawings.
~23~
Brief Description Of The Drawings
FIG. 1 is an elevation, partly section view of a per-
forating gun showing a carrier in place within the per-
forating gun, with a plurality of shaped charges in place
within the carrier.
FIG. 2 is a section view taken along line 2-2 of FIG.
1 showing a layer of three 120 circumferentially spaced
shaped charges in place within the hexagonal cross-section
carrier of FIG. 1.
FIG. 3 is a cross-section view taken along the length
of an outer case of one of the shaped charges shown in FIG.2,
-3a-
~1 23~7~C31
this particular case being constructed for use only with the
hexagonal cross-section carrier.
FIG. 4 is a side elevation view o~ the outer case of the
shaped charge shown in FIG. 3.
FIG. 5 is an elevation view of one of three identical
stamped panels, which when assembled provide a hexagonal
cro5s~section tubular carrier like that illustrated in FIGS.
1 and 2.
FIG. 6 is a detail view of one of the openings in the
hexagonal cross-section tubular carrier of FIG. 5.
FIG. 7 is a sectional view taken along line 7-7 of FIG.
6, showing the manner in which the tabs are initially bent
out of the plane of the wall o the carrier.
FIG. 8 is an elevation view of one of three stamped
sheet-metal sections, which when assembled provide a
triangular cross-section carrier like that illustrated in
FIG. 12.
FIG. 9 is an enlarged detail view of one o~ the openings
o the triangular cross-section carrier of FIGS. 8 and 12.
FIG. 10 is a cross-section view similar to FIG. 3 of a
modi~ied embodiment of the outer case of a shaped charge
which is constructed so that it may be utilized in either a
he~agonal or a triangular cross-section tubular carrier.
FIG. 11 is a side elevation view of the charge case of
FIG. 10.
FIG. 12 is a view similar to FIG. 2, illustrating the
manrer in which the alterna-tive charge case o FIGS. 10 and
ll is assembled with a triangular cross-section tubular
carrier.
PIG. 13 is a view similar to FIG. 7, but showing a
sha~ed charge in place within the carrier.
~23~
Detailed Descript n of The Invention
Referring now to the drawings, and particularly to FIG.
1, a perforating gun is thereshown and generally designated
by the numeral 10. The perforating gun 10 includes an
elongated cylindrical outer housing 12, the upper end of
which is closed by a top plug 14 and the lower end of which
i5 closed by a bottom plug 16.
Top plug 14 is threadedly connected to housing 12 at
threaded connection 18 and a seal is provided therebetween
by the O-rings 20 and 22. The bottom plug 16 is threadedly
connected to housing 12 at the threaded connection 24 and a
resilient seal is provided therebetween by O-rings 26 and
28.
In place within the housing 12 adjacent the lo~er end of
top plug 14 and the upper end of bottom plug 16 are upper
and lower carrier mounting plates 30 and 32, respectively.
Held in place between the upper and lower mounting
plates 30 and 32 is an elongated charge carrier 34. The
carrier illustrated in FIG. 1 is a generally hexagonal
cross-section tubular carrier.
The carrier 34 has disposed through the walls thereof a
plurality of openings 36 for receiving shaped charges 38
therein.
The carrier 3~ is attached to the end plates 30 and
32 in such a manner as to specifically define its orien-
tation about its longi-tudinal axis relative to the housing
12, so that each of the shaped charges 38 is located imme-
diately adjacent a reduced thickness portion 40 of the
housing 12 in a manner well known to those skilled in the
art.
~L236'~i7~
Disposed through a central opening 42 of top plug 14 is
a firing means 44 which generally comprises a length of pri-
macord and associated apparatus for firing the shaped
charges 38 in response to an electrical signal directed down
a wireline (not shown) from a surface location at the top of
the oil well which is being perforated. As will be
understood by those skilled in the art, the firing means 44
extends downward through the carrier 34 and is operatively
connected to each of the shaped charges 38.
~ ach of the shaped charges 38 constructed in accordance
wi-th the present invention has an outer case 46 as is best
illustrated in FIGS. 3 and 4. FIG. 3 is a cross-sectional
view ~olely of the outer case of the shaped charge 3~, and
as will be understood by those skilled in the art:., the
interior 48 of the case 46 will contain appropriate explo~
sives and liners.
The case 46 has a forward end 50 and a rearward end
52. An opening 53 is disposed through rearward end 52 to
permit the connection of the firing means 44 to the explo-
sive contalned in case 46. Case 46 inc].udes a generally
cylindrically shaped outer surface 54 and a rearwardly
Eacing first shoulder 56 extending radially outward from
outer surface 54.
As is best seen in FIG. 6, each of the oE)enings 36
disposed through the wall of carrier 34 is generally cir-
cular in shape and as illustrated in FIGS. 1 and 2 is large
enough to receive the outer surface 54 of the case 46
therethrough .
The carrier 34 also includes resilient tab means 58
correspo:llding to each opening 36, which -tab means extend
~3~7~
into the opening 36 for frictionally engaging at least a
first portion 60 of outer sur~ace 54 of the case 46 and for
thereby holding the shaped charge 38 in place relative to
the carrier 34 with the first shoulder 56 of shaped charge
38 abutting the carrier 34 as best illustrated in FIGS. l
and 2.
Preferably, the first portion 60 of cylindrical outer
surface 54 is a grooved first portion 60 having a plurality
of longitudinally spaced circumscribing grooves as best seen
in FIG. 4. Although the grooves of first portion 60 of
outer surface 54 may be formed in any number of ways, a pre-
ferable manner of forming the grooves is by machining a
spiral thread-like surface on first portion 60 as best
illustrated in FIG. 4.
The tab means 5~ of carrier 34 engages the grooves of
grooved first portion 60 of outer surface 54 of case 46 when
the shaped charge 38 is in place with the shoulder 56
abutting the carrier 34.
The outer surface 54 of case 46 further includes a
reduced diameter portion 62 located rearward of the grooved
first portion 60. The reduced diameter portion 62 has an
outside diameter 64 less than an internal diameter 66 tsee
FIG. 6) of opening 36 of carrier 34 at the tab means 58, so
tha-t the reduced diameter portion 62 of the outer surface 54
of the case 46 may freely pass through the opening 36.
The cylindrical outer surface 54 of case 46 further
includes a tapered portion 58 located between the reduced
diarneter portion 62 and the grooved first portion 60.
Preferably, the tapered portion 68 slopes at an angle 70 of
about 15~ frorn a central axis 72 of the case 46.
~3~7~
The generally circular opening 36 has an inside diameter
74 (see FIG. 6) which is greater than the outside diameter
64 ~see FIG. 4) of reduced diameter portion 62 and which is
also greater than the outside diameter 76 (see FIG. 4) of
grooved first portion 60 of outer surface 54.
The first shoulder 56 of case 46 is annular in shape and
has an outside diameter 77 (see FIG. 4) greater t.han the
inside diameter 74 (see FIG. 6) of opening 36 so that the
shoulder 56 cannot fit through the opening 36.
As illustrated in FIG. 6, the resilient tab means 58 of
the carrier 34 preferably includes two diametrically opposed
tabs 78 and 80 located on opposite sides of opening 36, said
tabs 78 and 80 extending into the opening 36 toward each
other. Preferably, the opposed tabs 78 and 80 lie along a
line substantially parallel to a longitudinal axis of
carrier 34,
The internal diameter 66 of the opening 36 at the tab
means 58, which may also be defined as the diametrical
distance between radially innermost ends 8~ and 84 of tabs
78 and 80, is less than the inside diameter 74 of the
generally circular portion of opening 36, and is also less
than the outside diameter 76 of first portion 60 of
cylindrical outer surface 54 of case 46.
Thus, the dimensional relationships jus-t defined for the
case 46 and the opening 36 provide a carrier 34 and outer
case 46 of shaped charge 38 which are so arranged and
constructed that when the cylindrical outer surface 54 of
case ~6 is inserted in a rearward direction through the
opening 36 of carrier 34 until the shoulder 56 abuts the
car~Aicr 34, the tabs 78 and 80 of resilient tab means 58
~3~7~7~
frictionally engage the first portion 60 of outer surface 54
and are deflected rearwardly from an initial position of the
tabs. The reduced diarneter surface 62 is freely received
between tabs 78 and 80. The tape~ed surface 68 engages the
tabs 78 and 80 and deflects them before they engage the
Eirst portion 60 of outer surface 54.
This is best understood by viewing FIGS. 7 and 13. FIG.
7 is a sectional view taken along line 7-7 of FIG. 6 and
illuskrates the initial position of tabs 78 and 80 of resi-
lien-t tab means 58 prior to insertion of the shaped charge
38 in the opening 36. In FIG. 7, the numeral ~6 designates
the outer surface of the wall 88 of carrier 34, and the
numeral 90 designates the inner surface of wall 88. As
shown in FIG. 7, the tabs 78 and 80 are preferably initially
deformed to a slightly rearward position out of the plane of
wall 88 so as to promote the ease of insertion of the shaped
charge 36 therebetween.
The tabs 78 and 80 are so dimensioned and constructed
that when they are deflected from their initial position
shown in FIG. 7 to the position shown in FIG. 13, they are
resilientl~ deformed, and while they are so deflected the
tabs 78 and 80 continuously exer-t opposed lateral forces
ayainst the threaded firs-t portion 60 of outer surface 54 oE
case 46 so as to tightly hold the case 46 in place relative
to the carrier 34. In the illustrated embodiment, this
resilient deformation is partially elastic. Although the
tabs are to some extent permanently deformed during the
irsertion of the case 46, the tabs still press against the
sides of case 46.
The appropriate dimensions and shape of the tabs will,
oE courser depend upon the particular material utilized, the
:~L2~
nurnber of tabs utilized, -the shape and size of the outer
surface of the shaped charge, and the desired insertion
force.
Preferably, the tab means 58 is constructecl so that the
shaped charges 38 may be inserted in the openings 36 by
manually applied pressure against the outer forward end of
the shaped charge 38. The tab means 58 is preferably
constructed to provide the maximum frictional holding Eorce
against the case 46, while still heing flexible enough that
the case 46 may be inserted manually.
As illustrated in FIG. 6, the preferred embodiment of
the present invention utilizes a resilient tab means 58
having first and second diametrically opposed tabs 78 and
80. The present invention is not, however, limited to such
an embodiment, and it is possible to utilize the principles
of the present invention with a tab means having one, two,-
three or more tabs circumferentially spaced about the
opening 36.
The tab means 58 illustrated in FIG. 6 is designed so
that if either one of the tabs 78 or 80 is damaged, i.e.,
bent out of shape so that it cannot engage the case 46, the
remaining functional tab 78 or 80 will still hold the case
46 firmly in place relative to the carrier 34. This feature
is accompllshed as follows. A distance 92 (see FIG. 6) bet-
ween t~e radially innermost end 84 of tab 80 and the inner
e~se of gererally circular opening 36 immediately adjacent
the other tab 78 is sufficiently less than the outside
~liameter ?6 (see FIG. 4) of grooved first portion 60 of
outer s~ ace 54 of case 46 so that if either of the tabs 78
or 80 i~ deform2d so that it canno-t engage the case 46, the
--10--
~3~7~7~
other of the tabs 78 or 80 will still frictionally engage
the grooved first portion 60 of cylindrical outer surface 54
of case 46 to hold the shaped charge 38 in place relative to
carrier 3~ with the shoulder 56 of shaped charge 38 abutting
the carrier 34.
The carrier 34 is preferably constructed from sheet
metal, and in the embodiment disclosed in the present appli-
c~tion for the hexagonal cross-section tubular carrier 34 as
seen in FIGS. 1, 2, 5, 6 and 7, the tubular carrier is
formed by joining three sheet metal sections. One of those
sheet metal sections is shown in FIG. 5 and designated by
the numeral 93. The sheet metal section 93 is a single
integral piece of metal formed from a metal sheet by
appropriate stamping and cutting operations.
A central imaginary line 94 represents the line along
which the sheet metal section 93 will be creased to form one
of the six points of the hexagonal cross section of the
carrier 34. Similarly, imaginary lines 96 and 98 represent
lines where the sheet metal parts will be creased to form
the points of the hexagonal cross section immediately adja-
cent to that formed at crease line 94.
The sheet metal section 93 is formed with a plurality of
le~tward ex-tending tabs 100 on its left side which are cir-
cumEerentially opposed to raised pockets 102 along its right
side. When the section 93 is assembled with two identical
sections, the tabs 100 will fit within pockets 102 of the
adjacent section. Also, the section 93 includes a series of
right:ward extending tabs 104 and a corresponding series of
raise(l pockets 106 on its left side. Again, when section 93
is assembled with two identical sections, the rightward
~;~3~
extending tabs 104 will fit ~ithin the poc~ets 106 of the
adjacent section.
Each of the tabs 104 includes a rivet hole 108, and each
of the raised pockets 106 includes a rive-t receiving hole
110. When the tabs 104 are received in the pockets 106 of
the adjacent similarly designed sections, they are rigidly
Eixed together by rivets (not shown~ disposed through the
hole5 108 and 110 which will be in registry.
The sheet metal section 93 includes elongated slots such
as 112 and 11~ which are utilized in forming the connection
between the carrier 34 and the end plates 30 and 32 pre-
viously described with regard to FIG. 1. That end plate
connection is not material to the present invention and the
details thereof need not be described herein.
As is best seen with reference to the lower end of FIG.
6, the tabs 78 and 80 of the tab means 58 are formed by
creating two spaced slots, such as 116 and 118, on either
side of tab 80, said slots having open ends 120 and 122
joining the substantially circular opening 36 of carrier 34.
~ lso, as shown in FIG. 6, a hole 124 may be formed
through the wall of carrier 34 near the root of tab 80 to
increase the flexibility of tab 80.
When utilizing the substantially hexagonal cross-section
carrier 3~, it will be appreciated that the hexagonal tubu-
lar carrier 34 defines six planar outer surfaces of substan-
tially equal width 126.
In FIG. 6, one of these six planar outer surfaces is
cl-!sicJnated by the numeral 128.
The generally circular opening 36, shown in FIG. 6, has
its central axis 130 oriented perpendicular to the planar
-12-
~L~3~
outer surface 128 of carrier 34. This central axis 130 is
substantially centered across the width 126 of the planar
outer surface 128.
As is apparent in viewing FIG. 6, the inside diameter 74
of generally circular opening 36 and the outside diameter 76
(see FIG. 4) of grooved first portion 60 of cylindrical
outer surface 54 of case 46 are each greater than the width
126 of the planar outer surface 128 of carrier 34. Thus,
the generally circular opening 36 extends partly into each
of the planar outer surfaces 132 and 134 of the carrier 34
immediately adjacent to the planar outer surface 128.
When the sheet metal sections such as 93 seen in FIG. 5
of carrier 34 are initially formed, and are still laid out
flat, the opening 36 has egg-shaped extensions 136 a.nd 138
which extend over the imaginary lines 94 and 98 i~to the
adjacent planar outer surfaces 132 and 134.
The egg-shaped extensions 136 and 138 are shaped such
that when three of the sheet metal sections like 93 are
creased along the lines 94, 96 and 98 and then assembled in
the fashion illustrated in FIG. 2, the opening 36 with its
egg-shaped extensions 136 and 138, when viewed along the
central axis 130 of opening 36 presents a substantially cir-
cular opening for receipt of the cylindrical outer surface
54 of case 46.
Alternative Embodiment Of FIGS. 8-12
Referring now to FIGS. 10 and 11, views are thereshown
very sirnilnr to FiGS. 3 and 4 of an alternative embodiment
for a shaped charge case which is designed to be utilized
ei~er W7 ~h the hexagonal cross-section -tubular carrier 34
'7~
previously described with regard to FIGS. 1; 2, 5 and 6 or a
triangular cross-section tubular carrier 34A seen in FIGS.
8, 9 and 12.
For purposes of the following description of this alter-
native embodiment, those fea-tures identical to or closely
analogous to features of the hexagonal cross-section carrier
3~ will be designated by the identical numexal with the
addition of a suffix A.
A modified case 46A seen in FIGS. 10 and 11 has a
cylindr.ical outer surface 54A, a radially outward extending
shoulder 56A, a grooved first portion 60A, a first reduced
diameter portion 62A, and a tapered portion 68A joining the
grooved first portion 60A and the first reduced diameter
portion 62A.
The case 46A can be utilized in place of the case 46
previously described and assembled in a hexagonal cross-
section tubular carrier 34 just as illustrated in FIG. 2 for
the previously described cases 46.
The modified case 46A includes a second grooved portion
lgO. The location of the second grooved portion 140 may be
deEined as being located on a side of first grooved portion
60A opposite from the first shoulder 56A. The second
grooved portion 140 has an outside diameter less than an
outside diameter oE both the first grooved portion 60A and
the reduced diameter portion 62A.
The modified case 46A further includes a second shoulder
. The location of second shoulder 142 may be deEined as
being located between the first and second grooved portions
60A and 140 of outer surface 54A, and in the particular
em~ocliment shown in FIGS. lO and 11, second shoulder 142
--1~
~23~t~
joins second grooved surface 140 and reduced diameter por-
tion 62A.
The modified case 46A further includes a second reduced
diameter portion 1~4 having an outside diameter less than
that of second grooved portion 140. The second reduced
diameter portion 144 and the second grooved portion 140 are
joined by a second tapered portion 146.
When the modified case 46A is utilized with a triangular
cross-section tubular carrier 34A such as shown in FIG. 12,
it is the second grooved portion 140 and the second shoulder
142 which interact with the tab means 58A to hold the case
46A in place within an opening 36A of the carrier 34A.
The relationships of the dimensions of opening 36A to
the dimensions of the second grooved portion 140 and second
reduced diameter portion 144 are similar to the rela-
tionships previously described with regard to the dimensions
of the opening 36 in relation to the first grooved portion
60 and first reduced diameter portion 62.
With reference to FIG. 9, the generally circular opening
36A has an inside diameter 148 which is greater than the
outside diameter of both the second grooved portion 140 and
the second reduced diameter portion 144 of case 46A. The
outside diameter of second shoulder 142, however, is greater
than inside diameter 148 of opening 36A so that the second
shoulder 142 cannot pass through opening 36A but instead
abuts the wall of carrier 34A.
A diametrical distance 150 be-tween radially innermost
ends 82A and 84A of tabs 78A and 80A is less -than the inside
cliameter 148 of opening 36A and is also less than the out-
Si(l? diameter of second grooved portion 140 of cylindrical
o~lter surface 54A of the case 46A.
~L23~
The distance 150 between tabs 78A and 80A is, however,
greater than the outside diameter of second reduced diameter
portion 144.
Thus, when case 46A is inserted in a rearward direction
through the opening 36A, the second reduced diameter portion
144 freely passes between tabs 78A and 80A. As the
inserting movement continues/ the ends 82A and 84A of tabs
78A and 80A first engage the tapered portion 1~6 and then
engage the second grooved portion 140 OL outer surface 54A.
The inserting movement stops when second shoulder 142 abuts
the outer surface of carrier 34A. At that point, the ends
82A and 84A o~ tabs 78A and 80A will be in engagement with
one of the grooves of second grooved portion 140 in a manner
similar to that previously described with regard to E'IG. 13
and with regard to the ~irst embodiment of the invention.
Also, the opening 36A is similar to the opening 36 in
that if either of the tabs 78A or 80A is damaged, the
remaining tab will still firmly engage the second grooved
portion 140. A distance 152 between radially innermost end
84A of tab 80A and the edge of generally circular opening
36A immediately adjacent the other tab 78A is less than the
outside diameter of second grooved portion 140 of the
cylindrical outer surface 54A so l:hat the :functional tab 80A
will. still frictionally engage the second grooved portion
140 to hold the case 46A of shaped charge 38A firmly in
place relative to the carrier 34A with the shoulder 142
.utt.lnr car~ier 34A.
Ei-.-,t and second grooved portions 60A and 140 of
Ol`;. surface 54A of case 46A, and the first and second
stlolllders 56A and 142 thereof, are so dimensioned that Eor
--16--
~3~7~
any given size of perforating gun the case ~6A of shaped
charge 38A may be received in either a hexagonal cross-
sectional tubular carrier 34 or a triangular cross-sectional
tubular carrier 34A in a pa~tern of three 120 circumferen-
tially spaced charges 38 or 38A per horizontal plane, as
seen in FIGS. 2 and 12. The first shoulder 56A abuts the
carrier 34 when the hexagonal cross-sectional carrier is
utilized. The second shoulder 142 abuts the carrier 34A
when the triangular cross-sectional carrier is utilized.
FIGS. 2 and 12 represent identical siæed perforating
guns having identical outer housings 12, and the casings 46A
have identical dimensions from their forward end to the
second shoulder 142 as are present on the case 46 shown in
FIGS. 2-4.
Thus, the single case 46A may be stocked for use in
either the hexagonal or the triangular cross-section tubular
carriers for use in any given size of perforating gun.
The chcice of whether to use a triangular or hexagonal
cross-sectional tubular carrier depends upon the particular
pattern of charges which is desired, as will be understood
by those skilled in the art. If the hexagonal cross~section
carrier is utilized, the three ~harges in immediately adja-
cent longitudinally spaced layers are rotated 60 about the
longitudinal a~is o~ the carrier. With the triangular
cross-section carrier of FIG. 8 and 12, on the other hand,
the shaped charges of adjacent layers are longitudinally
aligned.
Thus, it is seen that the apparatus and methods of the
present invention readily achieve the ends and advantages
rne~ ioned as well as those inherent therein. While certain
'7~
preferred embodiments of the present invention have been
illustrated for the purposes of this disclosure, numerous
changes in the arrangement and construction of parts and
steps may be made by those skilled in the art, which changes
are embodied within the scope and spirit of the present
invention as defined by the appended claims.
