U.S. patent application number 10/825902 was filed with the patent office on 2004-10-07 for polymer composite bat.
Invention is credited to Fitzgerald, Stephen, St. Laurent, Frederick, Sutherland, Terrance W..
Application Number | 20040198539 10/825902 |
Document ID | / |
Family ID | 37235177 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040198539 |
Kind Code |
A1 |
Sutherland, Terrance W. ; et
al. |
October 7, 2004 |
Polymer composite bat
Abstract
A baseball bat is described having of an elongated cylindrical
handle portion for gripping, a cylindrical barrel portion for
striking and a tapered cylindrical mid-section connecting the
handle portion and the barrel portion, wherein at least the barrel
portion is tubular and is constructed solely of a polymer composite
material with a three-dimensional fiber reinforcement architecture
resulting in improved durability versus conventional polymer
composite bats, without any sacrifice in playing performance. Also
disclosed are polymer composite baseball bats where the polymer
composite material includes between 85% and 100% fiberglass
reinforcement fibers, and/or where the central cavity is filled
with a damping material such as polymeric foam or a low-density
granular material, and/or where the bats are constructed of
multiple layers of intertwined tubular braid forms using a
precision molding process.
Inventors: |
Sutherland, Terrance W.;
(Ottawa, CA) ; Fitzgerald, Stephen; (Halifax,
CA) ; St. Laurent, Frederick; (Val des Monts,
CA) |
Correspondence
Address: |
Jeffrey S. Sokol
ANDRUS, SCEALES, STARKE & SAWALL, LLP
Suite 1100
100 East Wisconsin Avenue
Milwaukee
WI
53202-4178
US
|
Family ID: |
37235177 |
Appl. No.: |
10/825902 |
Filed: |
April 16, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10825902 |
Apr 16, 2004 |
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10080085 |
Feb 21, 2002 |
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6723012 |
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Current U.S.
Class: |
473/567 |
Current CPC
Class: |
A63B 60/002 20200801;
A63B 2209/023 20130101; A63B 60/08 20151001; A63B 2102/18 20151001;
B29L 2031/52 20130101; A63B 60/54 20151001; B29C 70/48 20130101;
A63B 59/50 20151001; A63B 59/54 20151001; A63B 2102/182 20151001;
A63B 2209/00 20130101 |
Class at
Publication: |
473/567 |
International
Class: |
A63B 059/06 |
Claims
I claim:
1. A baseball bat comprising: a handle portion for gripping; a
cylindrical tubular hollow void barrel portion for striking; and a
tapered mid-section portion connecting said handle portion and said
barrel portion; said handle, barrel and mid-section portions
constructed solely of a polymer composite material, said polymer
composite material comprising a thermoset resin and continuous
length reinforcement fibers, said continuous length reinforcement
fibers comprising multiple intertwined tubular braid forms, said
intertwined tubular braid forms being arranged in multiple
layers.
2. The baseball bat of claim 1, wherein said bat is constructed
using a precision molding process.
3. The baseball bat of claim 1, wherein said thermoset resin is
selected from a group of thermoset resins consisting of epoxy,
vinyl ester, polyester and urethane.
4. The baseball bat of claim 1, wherein said multiple layers of
said multiple intertwined tubular braid forms comprise at least
four layers.
5. The baseball bat of claim 1, wherein said handle portion has a
handle length and said barrel portion has a barrel length, and
wherein said continuous length reinforcement fibers in said handle
portion have a handle fiber length and said continuous length
reinforcement fibers in said barrel portion have a barrel fiber
length, and wherein said handle fiber length is greater than said
handle portion length and said barrel fiber length is greater than
said barrel portion length.
6. The baseball bat of claim 1, wherein the baseball bat has a bat
length, and each of said multiple intertwined tubular braid forms
has a braid form length, and wherein said braid form length of at
least one of said multiple intertwined tubular braid forms is
substantially equal to said bat length, and wherein said braid form
length of at least another one of said multiple intertwined tubular
braid forms is less than said bat length.
7. The baseball bat of claim 1, wherein said continuous length
reinforcement fibers are arranged at a resultant fiber angle
relative to a central longitudinal axis of the bat, and wherein an
average of the absolute values of all of said resultant fiber
angles in said handle portion is less than an average of the
absolute values of all of said resultant fiber angles in said
barrel portion, thereby providing said handle portion with
desirable mechanical properties that differ from said desirable
mechanical properties of said barrel portion.
8. The baseball bat of claim 7, wherein said average of the
absolute values of all of said resultant fiber angles in said
handle portion is between 5.degree. and 30.degree. less than said
average of the absolute values of all of said resultant fiber
angles in said barrel portion.
9. The baseball bat of claim 7, wherein said average of the
absolute values of all of said resultant fiber angles in said
handle portion is less than 20.degree. and said average of the
absolute values of all of said resultant fiber angles in said
barrel portion is greater than 25.degree..
10. The baseball bat of claim 7, wherein said desirable mechanical
properties in said handle portion include a first bending mode
frequency of 100 to 600 hertz and said desirable mechanical
properties in said barrel portion include a first hoop frequency of
800 to 2000 hertz.
11. The baseball bat of claim 7, wherein said desirable mechanical
properties in said handle portion include an axial stiffness of
between 50,000 lb/in.sup.2 and 250,000 lb/in.sup.2, and said
desirable mechanical properties in said barrel portion include a
radial stiffness of between 70,000 lb/in.sup.2 and 350,000
lb/in.sup.2.
12. The baseball bat of claim 1, wherein said handle portion
includes at least one layer of said continuous length reinforcement
fibers arranged in a stitched tubular form, said continuous length
reinforcement fibers in said stitched tubular form having a
resultant fiber angle of 0.degree. relative to a central
longitudinal axis of the bat.
13. The baseball bat of claim 1, wherein said barrel portion has a
barrel portion wall thickness less than 0.2 inches.
14. The baseball bat of claim 1, wherein said continuous length
reinforcement fibers are comprised of between 85% and 100%
fiberglass fibers.
15. The baseball bat of claim 2, wherein said precision molding
process comprises the steps of: placing said multiple layers of
said multiple intertwined tubular braid forms of said continuous
length reinforcement fibers over a solid precision mandrel; placing
said mandrel into a closeable external precision mold; closing and
sealing said mold; heating said mold; injecting said mold with said
thermoset resin, thereby combining said thermoset resin with said
continuous length reinforcement fibers in a resin-fiber matrix;
allowing said resin to cure, thereby forming said polymer composite
material; extracting said mandrel and said polymer composite
material from said mold; and extracting said mandrel from said
polymer composite material.
16. The baseball bat of claim 15, wherein, said barrel portion has
a finished outside diameter having a barrel portion outside
diameter tolerance of .+-.0.001 inches, said barrel portion has a
finished wall thickness having a barrel portion wall thickness
tolerance of .+-.0.001 inches, said barrel portion has a finished
roundness having a barrel portion roundness tolerance of .+-.0.003
inches, and the bat has a finished bat weight having a bat weight
tolerance of .+-.{fraction (1/16)}th ounces.
17. A precision molding process for making a baseball bat,
comprising the steps of: placing multiple layers of continuous
length reinforcement fibers over a solid precision mandrel; placing
said mandrel into a closeable external precision mold; closing and
sealing said mold; heating said mold; injecting said mold with a
thermoset resin, thereby combining said thermoset resin with said
continuous length reinforcement fibers in a resin-fiber matrix;
allowing said resin to cure, thereby forming a polymer composite
material; extracting said mandrel and said polymer composite
material from said mold; and extracting said mandrel from said
polymer composite material.
18. The process of claim 17, wherein said continuous length
reinforcement fibers comprise multiple intertwined tubular braid
forms.
19. The process of claim 18, wherein said multiple layers of said
multiple intertwined tubular braid forms comprise at least four
layers.
20. The process of claim 18, wherein the baseball bat has a handle
portion and a barrel portion, and said handle portion has a handle
length and said barrel portion has a barrel length, and wherein
said continuous length reinforcement fibers in said handle portion
have a handle fiber length and said continuous length reinforcement
fibers in said barrel portion have a barrel fiber length, and
wherein said handle fiber length is greater than said handle
portion length and said barrel fiber length is greater than said
barrel portion length.
21. The process of claim 18, wherein the baseball bat has a bat
length, and each of said multiple intertwined tubular braid forms
has a braid form length, and wherein said braid form length of at
least one of said multiple intertwined tubular braid forms is
substantially equal to said bat length, and wherein said braid form
length of at least another one of said multiple intertwined tubular
braid forms is less than said bat length.
22. The process of claim 17, wherein the baseball bat has a handle
portion and a barrel portion and said continuous length
reinforcement fibers are arranged at a resultant fiber angle
relative to a central longitudinal axis of the bat, and wherein an
average of the absolute values of all of said resultant fiber
angles in said handle portion is less than an average of the
absolute values of all of said resultant fiber angles in said
barrel portion, thereby providing said handle portion with
desirable mechanical properties that differ from said desirable
mechanical properties of said barrel portion.
23. The process of claim 22, wherein said average of the absolute
values of all of said resultant fiber angles in said handle portion
is between 5.degree. and 30.degree. less than said average of the
absolute values of all of said resultant fiber angles in said
barrel portion.
24. The process of claim 22, wherein said average of the absolute
values of all of said resultant fiber angles in said handle portion
is less than 20.degree. and said average of the absolute values of
all of said resultant fiber angles in said barrel portion is
greater than 25.degree..
25. The process of claim 22, wherein said desirable mechanical
properties in said handle portion include a first bending mode
frequency of 100 to 600 hertz and said desirable mechanical
properties in said barrel portion include a first hoop frequency of
800 to 2000 hertz.
26. The process of claim 22, wherein said desirable mechanical
properties in said handle portion include an axial stiffness of
between 50,000 lb/in.sup.2 and 250,000 lb/in.sup.2, and said
desirable mechanical properties in said barrel portion include a
radial stiffness of between 70,000 and 350,000 lb/in.sup.2.
27. The process of claim 17, wherein the baseball bat has a handle
portion and a barrel portion and said handle portion includes at
least one layer of said continuous length reinforcement fibers
arranged in a stitched tubular form, said continuous length
reinforcement fibers in said stitched tubular form having a
resultant fiber angle of 0.degree. relative to a central
longitudinal axis of the bat.
28. The process of claim 17, wherein a barrel portion of the
baseball bat has a barrel portion wall thickness less than 0.2
inches.
29. The process of claim 17, wherein said continuous length
reinforcement fibers are comprised of between 85% and 100%
fiberglass fibers.
30. The process of claim 17, wherein, a barrel portion of the
baseball bat has a finished outside diameter having a barrel
portion outside diameter tolerance of .+-.0.001 inches, said barrel
portion has a finished wall thickness having a barrel portion wall
thickness tolerance of .+-.0.001 inches, said barrel portion has a
finished roundness having a barrel portion roundness tolerance of
.+-.0.003 inches, and the bat has a finished bat weight having a
bat weight tolerance of .+-.{fraction (1/16)}th ounces.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to baseball and
softball bats and in particular to such bats wherein at least the
striking portion is constructed solely of polymer composite
materials having a fiber reinforcement architecture that provides
the required durability for a baseball bat, which is subject to
repeated ball impacts, while at the same time providing superior or
equivalent performance when compared to existing all wood, all
metal, all composite, or hybrid material baseball bats.
BACKGROUND
[0002] Since the inception of the game of baseball, almost a
century ago, manufacturers of baseball bats have continually sought
out new materials and designs to make bats both better performing;
that is, easier to hit, and/or longer hitting; and more durable;
that is, less prone to breakage.
[0003] Baseball bats were initially made of wood. Today, wood
baseball bats are all made of heavy and strong hardwoods, primarily
ash. The rule of thumb for baseball bats made of ash (or other
similar hardwoods such as hickory or birch) is that the length in
inches equals the weight in ounces. Thus, today's wood baseball
bats limit bat speed, and are also prone to catastrophic breakage.
Such catastrophic breakage could lead to injury of not only players
but also to bystanders and is a real concern to authorities. Also,
as wood bats lose moisture and dry out, they lose strength and
breakage increases. Replacing broken wood baseball bats is a major
cost over the course of a baseball season. For these reasons, today
the use of wood baseball bats is restricted mainly to major
professional baseball leagues.
[0004] More recently, beginning in the mid 1970's, aluminum
baseball bats captured a large majority of the market share versus
wood bats, even though they are more expensive and players complain
about vibrations and the "pinging" sound when a baseball is hit.
There are three reasons for the success of aluminum baseball bats:
1) they are lighter than wood bats, thus increasing bat speed and
increasing hitting distance; 2) they are locally less stiff than
wood bats providing a "trampoline" effect upon ball impact, thus
increasing hitting distance; and 3) they are less prone to breakage
than wood bats.
[0005] Most recently, in an attempt to further lower the weight of
aluminum bats and increase the "trampoline" effect, thinner walled
and multi-walled aluminum bats have been produced, however,
problems have been encountered with balls leaving dents or
depressions in the bat and also, bat breakage.
[0006] Recently as well, beginning in the late 1980's, hybrid
material baseball bats have been produced, incorporating polymer
composite materials with both wood and aluminum. The objective of
these hybrid bats is to improve either bat performance and/or
durability. Such hybrid material baseball bats are described in
U.S. Pat. No. 5,364,095 to Easton, U.S. Pat. No. 4,569,521 to
Mueller, U.S. Pat. No. 5,395,108 to Souders, and U.S. Published
application No. 20010046910A1 of Sutherland, all of which disclose
means to improve the performance and/or durability of aluminum
baseball bats by combining composite-like materials with aluminum.
U.S. Pat. No. 6,139,451 to Hillerich, discloses another class of
hybrid material baseball bats, which combine traditional ash wood
bats reinforced full length with a fiberglass composite material,
while earlier U.S. Pat. No. 3,129,003 to Mueller discloses an ash
bat reinforced in the handle portion, with a composite-like
material.
[0007] U.S. Pat. No. 4,014,542 to Tanikawa discloses a
five-component hybrid baseball bat having a softwood balsam core, a
main member made of foam, a metal tube having apertures for bonding
fixed to the barrel portion only of the main member, and an outer
layer of glass fiber painted with a synthetic resin.
[0008] U.S. Pat. Nos. 5,114,144, 5,458,330, and 6,152,840 to Baum
disclose a hybrid multi-component bat having between five and
eleven layers. Baum's bat includes external layers of wood veneer
over a plurality of resin impregnated fabric socks, which in turn
surround inner cores of foam, wood or aluminum which may include
cavities.
[0009] The foregoing references describe hybrid material baseball
bat structures, but do not disclose bats wherein at least the
striking portion is constructed solely of polymer composite
materials.
[0010] U.S. Pat. No. 4,848,745 to Bohannan discloses a
two-dimensional filament winding process, which could be used to
make an all polymer composite baseball bat, using layers (typical
of today's existing composite laminate architecture) of continuous
fiber reinforcement in a thermoplastic resin matrix. Bohannan
describes an outer composite shell comprised of layers of helical,
longitudinal, and circumferential fiber rovings impregnated in a
thermoplastic resin.
[0011] U.S. Pat. No. 5,301,940 to Seki discloses a method of
manufacturing a bat using a resin injection technique, with the
resin being reinforced with layers of fiber.
[0012] The above two references concern possible methods for making
polymer composite bats without any discussion of the fiber
reinforcement architecture to be employed.
[0013] U.S. Pat. No. 5,303,917 to Uke discloses a bat comprising
two telescoping tubes, made of plastic or plastic with fiber
reinforcement, that overlap in the region between handle and
barrel.
[0014] U.S. Pat. No. 5,395,108 to Souders discloses a synthetic
wood composite bat composed of a shell of layers (or plies) of
fiber-reinforced resin, a dry fiber tube inside the shell, and a
rigid foam filling the shell. Souders specifically describes the
existing two-dimensional fiber reinforcement architecture
comprising "a plurality of cured layers of fiber resin reinforced
material." Such existing fiber reinforcement architecture, as
described by Souders, is well known to perform poorly under impact
loading situations, as repeatedly encountered by baseball bats.
This poor performance is due to inter-laminar (that is, interlayer
or inter-ply) failure between the laminates, layers, or plies of
polymer composite material. Further, Souders describes an inner dry
fiber tube, which is not a polymer composite material.
[0015] Moreover, polymer composite baseball bats are typically
constructed using a mixture of fiber reinforcement materials such
as fiberglass, graphite and aramid. Usually the mix ranges from 67%
to 84% by volume of fiberglass combined with from 16% to 33% of
other fibers. Generally, the reason for using a mixture of fibers
is to achieve a suitable combination of weight, strength, and
stiffness. The problem with such fiber reinforcement mixtures is
that they tend to suffer from limited durability due to the
presence of the stiffer and stronger graphite and aramid fibers,
which are less durable under impact loads due to relatively low
elongation under impact and relatively poor resin adhesion.
[0016] Further, all polymer composite bats of the prior art have
been constructed by one of the processes commonly referred to as
filament winding, tube rolling, bladder molding, compression
molding, or hand lay up. All such prior art processes originated in
the aerospace industry and, as such, have limitations when used to
produce baseball bats at high volume and low cost.
[0017] None of the above references describe a polymer composite
baseball bat wherein at least the striking portion is constructed
solely of polymer composite materials having the laminate
architectures or fiber reinforcement techniques required to yield a
bat with the necessary combination of thickness (which affects
stiffness) and durability, required to ensure the maximum
"trampoline" effect, and thus good hitting performance, while at
the same time being able to withstand repeated impacts without
damage.
[0018] A polymer composite material consists of a non-homogenous
combination of reinforcement fibers in a polymer resin matrix
whereby the resultant polymer composite material has superior
properties when compared to either the reinforcement fibers or the
polymer resin matrix taken separately. The reinforcement fibers
employed in a typical polymer composite material may be graphite
(or carbon), aramid (or Kevlar.TM.), fiberglass, or boron, or other
suitable fibers, or combinations thereof. The polymer resin may be
any suitable resin, such as epoxy, vinyl ester, polyester,
urethane, nylon, urethane, or other suitable resins, or mixtures
thereof.
[0019] The following is a specific properties chart showing the
density, stiffness and strength properties of various possible
materials for use in making baseball bats. All data is taken from
standard textbooks available in the field. Specific stiffness and
specific strength are actual stiffness and strength divided by
density respectively. Strengths for composite materials are given
as tensile strength measured along fiber direction in a
unidirectional part. Strength for wood is given as the minimum of
tensile and compressive ultimate strength. Strength for metal is
given as ultimate tensile strength.
1 Density Stiffness Specific Strength Specific Materials
lbs/ft.sup.3 Msi Stiffness Ksi Strength Steel AISI 304 487 30.00
3.90 85.00 10.90 Aluminum 6061-T6 169 10.00 3.70 45.00 16.60
Aluminum 7075-T6 169 10.00 3.70 83.00 30.50 Titanium Ti-75A 283
17.00 3.70 80.00 17.70 High Modulus 102 38.00 23.30 165.00 100.00
Graphite Intermediate 102 34.00 19.50 180.00 109.80 Modulus
Graphite Commercial 98 21.00 13.30 210.00 132.90 Graphite E-Glass
130 17.00 3.10 135.00 64.30 S-Glass 124 8.00 4.00 155.00 77.60
Kevlar 49 86 11.00 8.00 210.00 152.20 White Ash 42 2.00 3.00 8.00
12.10 Bigtooth Aspen 27 1.00 2.30 4.00 9.30 Yellow Poplar 29 1.10
2.40 4.50 9.80
[0020] Polymer composites are over 16 times stronger than ash and
60% stronger than aluminum. However, they are over three times
heavier than ash, while approximately 20% lighter than aluminum,
the aluminum bats being hollow, therefore lighter than solid
composite bats, on an equal volume basis. While a solid all polymer
composite baseball bat would be much stronger than either a solid
ash or aluminum bat, it would be much too heavy for regular use.
However, a tubular all polymer composite bat could be made both
stronger and stiffer than a similar tubular aluminum or titanium
bat.
[0021] In summary, polymer composite materials can theoretically be
employed to manufacture baseball bats, wherein at least the
striking portion is tubular and made solely of a polymer composite
material, which are both stronger and stiffer than today's
predominantly all aluminum tubular baseball bats. However, the two
dimensional layered fiber architecture used in current polymer
composite materials performs poorly under impact loading conditions
such as when baseball bats are impacted by baseballs. Thus, the
limited attempts, to date, to commercially produce an all polymer
composite baseball bat have largely been unsuccessful, primarily
due to premature bat failure or breakage. To improve durability,
the wall thickness of the polymer composite tube could be
increased, however, increasing wall thickness dramatically
increases stiffness and weight, which in turn lowers bat
performance due a decreased "trampoline" effect as the thicker bat
wall springs back less after impacting the ball.
[0022] What is needed then, is a baseball bat having at least a
tubular striking portion made solely of a polymer composite
material with a fiber reinforcement architecture, which can
withstand repeated impacts with a baseball, thus providing the
required durability, while at the same time having a wall thickness
thin enough to ensure hitting performance that is at least
equivalent to that of the best currently existing baseball
bats.
[0023] Further, what is also needed, is a high precision, high
volume, and low cost process for manufacturing all polymer
composite bats, resulting in desirable, and differentiated,
mechanical properties in the bat handle and barrel portions
required for optimal bat performance.
SUMMARY
[0024] In view of the foregoing, there is a need for a polymer
composite bat having at least the striking portion made solely of a
polymer composite material, which is as durable, or more durable,
than conventional baseball bats made of wood, aluminum, hybrid
wood/composite, hybrid aluminum/composite, or multi-layer polymer
composites.
[0025] There is also a need for a polymer composite bat having at
least the striking portion made solely of a polymer composite
material, which is of equivalent, or lower weight, than
conventional baseball bats made of wood, aluminum, hybrid
wood/composite, hybrid aluminum/composite, or multi-layer polymer
composites.
[0026] There is a further need for a polymer composite bat having
at least the striking portion made solely of a polymer composite
material, with equivalent, or better, hitting performance as
measured by hit distance, than baseball bats made of wood,
aluminum, hybrid wood/composite, hybrid aluminum/composite, or
multi-layer polymer composites.
[0027] There is yet another need for a polymer composite bat having
at least the striking portion made solely of a polymer composite
material, with a barrel length or hitting surface equivalent to, or
longer than, conventional baseball bats made of wood, aluminum,
hybrid wood/composite, hybrid aluminum/composite, or multi-layer
polymer composites.
[0028] There is still another need for a polymer composite bat to
provide having at least the striking portion made solely of a
polymer composite material, and having a structure, which improves
damping so as to minimize vibrations on the hands of the user.
[0029] There is another need for a process for manufacturing a
polymer composite bat in high volumes, at reasonably low costs, and
with high precision in order to achieve desired and differentiated
mechanical properties in the bat handle and barrel portions
required for optimal bat performance.
[0030] According to one aspect then, the present polymer composite
bat comprises a handle portion for gripping; a cylindrical tubular
hollow void barrel portion for striking; and a tapered mid-section
portion connecting the handle portion and the barrel portion; the
handle, barrel and mid-section portions constructed solely of a
polymer composite material, the polymer composite material
comprising a thermoset resin and continuous length reinforcement
fibers, the continuous length reinforcement fibers comprising
multiple intertwined tubular braid forms, the intertwined tubular
braid forms being arranged in multiple layers.
[0031] According to another aspect, there is provided a precision
molding process to manufacture all polymer composite bats in high
volumes, at reasonably low costs, and with high precision
comprising the steps of: placing multiple layers of continuous
length reinforcement fibers over a solid precision mandrel; placing
the mandrel into a closeable external precision mold; closing and
sealing the mold; heating the mold; injecting the mold with a
thermoset resin, thereby combining the thermoset resin with the
continuous length reinforcement fibers in a resin-fiber matrix;
allowing the resin to cure, thereby forming a polymer composite
material; extracting the mandrel and the polymer composite material
from the mold; and extracting the mandrel from the polymer
composite material.
[0032] Advantageously, all polymer composite baseball bats made in
accordance with the descriptions contained herein are equivalent or
lower in weight and are as durable or more durable, than
conventional baseball bats made of wood, aluminum, hybrid
wood/composite, hybrid aluminum/composite, or multi-layer polymer
composites. The applicant's polymer composite bats as described
herein, provide equivalent or better, hitting performance as
measured by hit distance, and permit the construction of bats
having equivalent or longer barrel lengths or hitting surfaces than
such conventional bats. Further, the applicant's polymer composite
bats can be constructed with a structure, which improves damping so
as to minimize vibrations on the hands of the user.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The applicant's polymer composite baseball bats will be
further understood from the following description with reference to
the drawings in which:
[0034] FIG. 1 is a longitudinal cross-section of a typical all
polymer composite baseball bat of the prior art.
[0035] FIG. 1A is an enlargement of a section of FIG. 1 showing the
typical two-dimensional multi-layer fiber reinforcement
architecture employed in the prior art.
[0036] FIG. 1B is a horizontal cross-section of the typical
multi-layer polymer composite baseball bat of the prior art shown
in FIG. 1.
[0037] FIG. 1C is a three-dimensional enlargement of a section of
FIG. 1B, showing the typical two-dimensional multi-layer fiber
reinforcement architecture employed in the prior art.
[0038] FIG. 2 is a longitudinal cross-section of one embodiment of
the applicant's polymer composite bat, having a tubular handle, a
tubular tapered mid-section, and a tubular striking or barrel
portion constructed solely of a polymer composite material.
[0039] FIG. 2A is an enlargement of a section of FIG. 2, showing
the three-dimensional fiber reinforcement architecture of one
embodiment of the applicant's polymer composite bat.
[0040] FIG. 2B is a horizontal cross-section of the barrel portion
of the baseball bat shown in FIG. 2.
[0041] FIG. 2C is a three-dimensional enlargement of a section of
FIG. 2B, showing the three-dimensional fiber reinforcement
architecture employed in accordance with one embodiment of the
applicant's polymer composite bat.
[0042] FIG. 3 is a longitudinal cross-section of a further
embodiment of the applicant's polymer composite bat, having a solid
handle portion.
[0043] FIG. 3A is an enlargement of a section of FIG. 3, showing
the three-dimensional fiber reinforcement architecture in the
barrel portion.
[0044] FIG. 3B is an enlargement of a section of FIG. 3, in the
area where the solid handle joins the tapered tubular
mid-section.
[0045] FIG. 4 is a longitudinal cross-section of a further
embodiment of the applicant's polymer composite bat, having a solid
handle portion and a solid tapered mid-section.
[0046] FIG. 4A is an enlargement of a section of FIG. 4, showing
the three-dimensional fiber reinforcement architecture in the
barrel portion.
[0047] FIG. 4B is an enlargement of a section of FIG. 4, in the
area where the solid mid-section joins the tubular barrel
portion.
[0048] FIG. 5 is a longitudinal cross-section of a further
embodiment of the applicant's polymer composite bat, having a
tubular handle made of a different material than the tapered
mid-section and the barrel portion.
[0049] FIG. 5A is an enlargement of a section of FIG. 5, showing
the three-dimensional fiber reinforcement architecture in the
barrel portion.
[0050] FIG. 5B is an enlargement of a section of FIG. 5, in the
area where the handle joins the tapered mid-section.
[0051] FIG. 6 is a longitudinal cross-section of a further
embodiment of the applicant's polymer composite bat, having a
tubular handle portion and a tubular tapered mid-section made of
different material than the barrel portion.
[0052] FIG. 6A is an enlargement of a section of FIG. 6, showing
the three-dimensional fiber reinforcement architecture in the
barrel portion.
[0053] FIG. 6B is an enlargement of a section of FIG. 6, in the
area where the tubular mid-section joins the tubular barrel
portion.
[0054] FIG. 7 is a longitudinal cross-section of a further
embodiment of the applicant's polymer composite bat comprised of
multiple intertwined two-dimensional tubular braid forms arranged
in multiple layers.
[0055] FIG. 7A is a horizontal cross-section of the barrel portion
of the baseball bat shown in FIG. 7.
[0056] FIG. 7B is a three dimensional enlargement of a section of
FIG. 7A showing the multiple layers of intertwined tubular braid
forms.
[0057] FIG. 7C is a magnified top view of a single layer of a
typical intertwined tubular braid form used in the construction of
the bat shown in FIG. 7.
[0058] FIG. 8 is a block diagram showing the steps in the
applicant's precision molding process for manufacturing polymer
composite bats.
[0059] FIG. 9A is a top plan view of a precision mandrel used in
the applicant's precision molding process.
[0060] FIG. 9B is a top plan view of a two-piece precision external
mold used in the applicant's precision molding process.
DETAILED DESCRIPTION
[0061] FIG. 1, shows a tubular all polymer composite baseball bat
typical of the prior art, having a bat body 1.
[0062] FIG. 2, illustrates one embodiment of the applicant's
baseball bat, having a tubular bat body 12 constructed solely of a
polymer composite material.
[0063] The bats shown in FIGS. 1 and 2, each have a handle portion
4 for gripping, a barrel or striking portion 2 for striking,
impacting, or hitting, and a tapered mid-section 3, connecting
handle portion 4 with barrel portion 2. A conventional endcap 6 and
knob 7, constructed of any materials, are located at the ends of
barrel 2 and handle 4, respectively. The interiors 5 of bat bodies
1 and 12 are hollow.
[0064] In one preferred embodiment, as discussed in further detail
below, but not shown in the drawings, interior 5 could,
alternatively, be filled partially or entirely with foam or a
low-density granular material.
[0065] In further preferred embodiments, as shown in FIGS. 3, 4, 5,
and 6, handle portion 4 and/or mid-section 3 can be solid or
tubular and can be made from a polymer composite material, or from
other materials such as wood, metal, aluminum, plastic, foam,
composite, or other suitable materials.
[0066] FIG. 1A is an enlargement of a section of FIG. 1 showing the
typical two-dimensional multi-layer fiber reinforcement
architecture employed in the polymer composite materials of the
prior art. FIG. 2A is an enlargement of a section of FIG. 2,
showing the three-dimensional fiber reinforcement architecture of
the polymer composite material of the applicant's polymer composite
bat.
[0067] FIG. 1B is a cross-sectional view along lines 1B of FIG. 1,
and FIG. 2B is a cross-sectional view along lines 2B of FIG. 2.
[0068] Bat bodies 1 and 12 have a length 8, a circumference 9,
which varies in diameter along length 8, and a wall thickness 10,
which may vary along length 8.
[0069] FIG. 1C is a three-dimensional enlargement of a section of
FIG. 1B, showing the typical two-dimensional multi-layer fiber
reinforcement architecture employed in the polymer composite
materials of the prior art. FIG. 2C is a three-dimensional
enlargement of a section of FIG. 2B, showing the three-dimensional
fiber reinforcement architecture employed in accordance with the
applicant's polymer composite bats as described herein.
[0070] The bats illustrated in FIGS. 1 to 6 are three-dimensional
and have physical properties such as strength, stiffness and
durability (toughness). These characteristics are important
considerations in all three dimensions, along length 8, around
circumference 9, and through thickness 10.
[0071] While a polymer composite baseball bat is three-dimensional,
the reinforcement fibers, which largely determine the bat's
physical properties, are supplied in their raw material form as
continuous filaments or strands, which are grouped together and
made available in a bundled form. These one-dimensional fiber
bundles, known as yarns, tows, or rovings, have maximum physical
properties along their length, and are placed along the length 8 or
around circumference 9 of the bat. Commonly, reinforcement fibers
are made into flat sheets, or broad goods, with the fibers arranged
and held in two-dimensions by a knitting, braiding, or weaving
processes. These two-dimensional reinforcement fibers are
positioned in cylindrical planes covering both length 8 and
circumference 9 of the bat. The length direction (0 degrees) is
referred to as the warp direction while the width direction or
circumference (90 degrees) is referred to as the weft direction.
Fibers can be arranged all oriented in the warp direction at 0
degrees, all in the weft direction at 90 degrees, in both the warp
and weft directions at 0 and 90 degrees, or at various angles to
each other, such as +45 degrees and -45 degrees, etc. The typical
tubular all polymer composite baseball bat, as shown in FIG. 1, and
in particular in FIGS. 1A, 1B, and 1C, is made by layering one or
two-dimensional reinforcement fibers to achieve the required
thickness 10. Consequently, such polymer composite products are
often called laminates.
[0072] Typically, ten to thirty individual layers or laminates,
positioned in cylindrical planes defined by length 8 and
circumference 9, are used for existing tubular all polymer
composite bats. Since the fiber reinforcements within the layers
have much higher physical properties (such as strength) than the
polymer matrix, the baseball bat properties in cylindrical planes
along length 8 and around circumference 9, are much greater than
the physical properties through thickness 10. Thus, at a typical
laminate boundary 11, as shown in FIG. 1C, between the layers, also
known as the inter-laminar interface, the bat's physical properties
are largely determined by the properties of the much weaker polymer
resin matrix. For this reason, under impact loading, such as that
which occurs in a bat-ball collision, bats having at least the
striking portion 2 constructed solely of a polymer composite
material, typically fail interlaminarly (that is, between the
laminate layers), at a typical laminate boundary 11, and typically
at much lower physical property (strength) levels than those of the
fiber reinforcements. Consequently, the relatively few bat designs
attempted to date, having at least the striking portion constructed
solely of a polymer composite material, have not been commercially
successful due to a lack of durability and premature failure
resulting from the use of a two-dimensional fiber reinforcement
architecture. In some cases, in an attempt to compensate for the
lack of strength under impact loading, the wall thickness 10 of the
bats has been increased. Such bats have suffered from poor
performance due to increased weight and high stiffness resulting in
little or no "trampoline" effect.
[0073] To solve these problems, the bat body 12 of one embodiment
of the applicant's polymer composite bat, incorporates a
three-dimensional fiber reinforcement architecture at least in the
barrel or striking portion 2, which includes, in addition to fiber
reinforcement placed on cylindrical planes defined by length 8, and
circumference 9, fiber reinforcements that intersect the
cylindrical planes of bat body 12, through thickness 10. The result
is a bat 12, having at least the tubular barrel or striking portion
2 constructed solely of a polymer composite material, and having
improved durability and increased hitting performance, due to its
thinner-walled construction, and relatively low weight compared to
similar conventional polymer composite bats using a two-dimensional
fiber reinforcement architecture. The wall thickness 10 of bats
made using this three-dimensional fiber reinforcement architecture,
at least in the striking portion 2, is normally less than or equal
to 0.25 inches. The resulting reduced weight of the applicant's
polymer composite bat can be used to design longer barrel portions
2, having larger sweet spots.
[0074] As illustrated in FIG. 2, it is preferable that the entire
bat body 12 be tubular and constructed solely of a polymer
composite material using the three-dimensional fiber reinforcement
architecture described above, however, the advantages of the
applicant's polymer composite bats are also realized if only the
barrel or striking portion 2 is tubular and constructed solely of a
polymer composite material using the three-dimensional fiber
reinforcements described herein. In this case, as shown in FIGS. 3
to 6, handle portion 4 and/or tapered mid-section 3 can be tubular
or solid and can be made from polymer composite materials or other
materials such as wood, metal, aluminum, plastic, foam, composite,
or other suitable materials. For example, FIG. 3 shows bat body 12
having a solid handle portion 4 made of a different material than
the remainder of the bat, FIG. 4 shows bat body 12 having a solid
handle portion 4 and a solid tapered mid-section 3 made of
different materials than barrel portion 2, FIG. 5 shows bat body 12
having a tubular handle portion 4 made of different material than
the remainder of the bat, and FIG. 6 shows bat body 12 having a
tubular handle portion 4 and a tubular tapered mid-section 3 made
of different materials than barrel portion 2.
[0075] The use of a fiber reinforcement architecture that
incorporates three-dimensional fiber forms at least in the tubular
all polymer composite barrel portion 2 of bat body 12,
significantly improves durability while maintaining, or improving
performance. The applicant has utilized several types of
three-dimensional fiber reinforcements in constructing the polymer
composite bats described herein. These include random chopped
strand mats, formed by chopping roving, yarn or tow into short
lengths and pressing them together into thick layers with fibers
randomly arranged in all directions, and continuous strand mat
where the fibers are not chopped but instead are laid down by
randomly swirling the fibers. Included as well, are
three-dimensional fiber forms made by weaving, knitting, stitching,
or braiding continuous fibers in a third vertical (thickness)
direction. In making such three-dimensional broad goods, multiple
layers of two-dimensional fabric, which are produced at the same
time in parallel sheets, are simultaneously interlaced with fiber
bundles or roving in the perpendicular or thickness direction.
Because fiber bundles have maximum physical properties along the
length of the fibers, the use of such three-dimensional broad goods
and/or random chopped or continuous strand mats in the applicant's
polymer composite bats, greatly reduces the typical weaknesses
found at the inter-laminar boundaries 11, under impact loading,
resulting in a much stronger and more durable all polymer composite
tubular baseball bat 12 than was previously possible.
[0076] Advantageously, at least in the barrel portion 2, a single
layer of three-dimensional fabric is used in a polymer resin
matrix. This results in zero inter-laminar boundaries 11 and
eliminates the problem of inter-laminar failure. A single layer of
three-dimensional fiber reinforcement fabric provides the best
combination of low weight, high strength, increased durability and
reduced thickness. For a number of reasons, it may not be possible
to use a single layer of three-dimensional fiber reinforcement. For
example, the required wall thickness 10 may be greater than the
thickness of available three-dimensional fabric. In these
situations, multiple layers of three-dimensional fiber
reinforcement can be used. However, because of the increased
thickness of three-dimensional fiber forms, and their increased
strength in the thickness direction compared with two-dimensional
fiber materials, the number of layers required to achieve the same
strength and durability is greatly reduced. The fewer number of
layers and increased strength in the thickness direction greatly
lessens the likelihood of inter-laminar failure and reduces the
weight and thickness of the resulting bat.
[0077] To further reduce the likelihood of inter-laminar failure in
a bat having multiple layers of three-dimensional fiber
reinforcement, the applicant has found it advantageous to alternate
the type of three-dimensional fiber from layer to layer. For
example, a layer of three-dimensional random chopped or continuous
strand mat can be used to separate layers of a three-dimensional
broad good such as a woven fabric. The multi directional fibers of
the random chopped or continuous strand mat reduces the likelihood
of inter-laminar failure by interconnecting and binding together
the two layers of woven fabric through the polymer resin matrix.
Other combinations of knitted, woven, braided or stitched
three-dimensional fibers offer similar advantages. Moreover,
alternating layers of three-dimensional random chopped or
continuous strand mat, with layers of two-dimensional reinforcement
fibers will similarly reduce the likelihood of inter-laminar
failure inherent in two-dimensional fiber reinforcement
material.
[0078] Generally, the fiber reinforcement materials used in making
the applicant's polymer composite bats as described herein are
selected from a group consisting of fiberglass, graphite, aramid,
and boron or other suitable fibers, or mixtures of any of
these.
[0079] The polymer resin matrix used to bind the reinforcement
fibers may be any suitable resin, such as epoxy, vinyl ester,
polyester, urethane, nylon, urethane, or other suitable resins, or
mixtures thereof. The polymer resin may be left to retain its
natural color, or a color pigment may be added to the resin to
result in bats of any desired color.
[0080] In addition to the above, the applicant has found that
fiberglass has two important characteristics not present in other
reinforcement fibers typically used to make baseball bats wherein
at least the barrel portion 2 is tubular and made solely of a
polymer composite material. These characteristics are significant
in determining baseball bat toughness, impact resistance, and
durability regardless of whether one- two- or three-dimensional
fiber reinforcements are used. First, adhesion of the polymer
matrix to the fiberglass fibers is significantly greater than the
adhesion to other fiber candidates. Second, the elongation
properties of fiberglass are far greater than those of other
fibers, such as graphite, used in making existing all polymer
composite bats. The greater elongation properties of fiberglass
allow it to stretch without failure under impact loading. Thus, a
bat having at least the barrel portion 2 made solely of a tubular
polymer composite material composed of a higher percentage of
fiberglass reinforcement fibers in a polymer resin matrix, results
in a bat with increased durability relative to a similar bat having
a lower percentage of fiberglass reinforcement fibers. The
applicant has found that the greatest advantage from using
fiberglass occurs when the percentage of fiberglass reinforcement
fibers versus other fibers is between 85% and 100%. Ideally, having
100% fiberglass reinforcement fibers in a polymer matrix will have
the greatest durability, toughness and impact resistance.
[0081] The ideal principle design objectives for baseball bats are
high axial or longitudinal bending stiffness in the handle portion
4 to reduce bending mode vibrations resulting from ball impacts,
which cause unfavourable feel or sting in the player's hands, high
axial strength in the handle portion 4 to eliminate handle
breakage, and low transverse stiffness in the barrel 2 to increase
the trampoline effect and thus increase bat performance. Referring
to FIGS. 7, 7A, 7B, and 7C, the applicant has determined that a
baseball bat 13 made solely of a polymer composite material,
comprising predominantly two-dimensional continuous length
intertwined tubular braid fiber forms 14, combined in a thermoset
resin matrix and arranged in multiple layers 15, is advantageous in
being able to achieve all three of the above-stated design
objectives, resulting in a durable, high performance baseball bat
having a good feel and desirable and differential mechanical
properties in the handle portion 4 and barrel portion 2. Such bats,
though not as light weight as polymer composite bats made with
three-dimensional fiber materials as described by the applicant
herein above, have proved in both laboratory and field testing to
be at least as durable as prior art aluminum bats. Further,
intertwined tubular braid fiber forms 14 arranged in multiple
layers 15 have been found by the applicant to be advantageous
during bat construction, as they readily conform to a bat-shaped
mandrel 40 (see FIG. 9A) used in the applicant's precision molding
manufacturing process (as described below) and can extend full
length 8 and/or partial length of the bat 13 to thereby produce
different mechanical properties in the handle portion 4 compared to
the barrel portion 2.
[0082] Two-dimensional intertwined tubular braid fiber forms 14 are
produced from continuous length fiber tows 16 (see FIG. 7C),
sometimes referred to as rovings or yarns. In each tubular braid
fiber form 14, continuous length fiber tows 16 are interwoven such
that a first set 17 is intertwined with a second set 18 in a
continuous spiral pattern. Thus, such intertwined tubular braid
forms 14 have fiber continuity from end to end of the form and the
two sets 17, 18 of continuous length fiber tows 16 are mechanically
interlocked or intertwined to each other. Because all the fiber
tows 16 are continuous and mechanically locked or intertwined,
tubular braid fiber form 14 has superior mechanical properties
compared to other fiber forms. In particular, as required in
baseball bats, tubular intertwined braid forms 14 have good impact
resistance resulting from the mechanical intertwining of the two
sets 17, 18 of fiber tows 16, and the natural nesting that occurs
at the interlaminar interfaces 11 (see FIG. 7B) between adjacent
layers of tubular braid forms 14, which further increases
interlaminar strength over other two-dimensional fiber forms. This
nesting effect is due to uniform hills 20 and valleys 21 (see FIG.
7C) formed by the intertwining of the two sets 17, 18 of fiber tows
16 across the surface of two-dimensional tubular braid form 14.
[0083] Tubular braid forms 14 are typically manufactured in a wide
range of base tubular diameters, with one to four inches being the
most common for use by the applicant in the manufacture of polymer
composite bats described herein. The mechanical intertwining of the
two sets 17, 18 of individual fiber tows 16 in two-dimensional
tubular braid forms 14 results in the tows 16 being set at a fiber
angle 22 relative to a central longitudinal axis 30 (see FIGS. 7
and 7C). When tubular braid form 14 is fixed at its base tubular
diameter, the fiber angle 22 is referred to as the base fiber
angle. For example, .+-.45.degree. is the most common base fiber
angle for intertwined tubular braid forms 14 used by the applicant.
Tubular braid forms 14 of a given base tubular diameter can be
expanded or contracted to conform to diameters that are somewhat
greater than or somewhat less than the base tubular diameter. As
tubular braid form 14 is expanded to conform to a larger diameter,
the absolute value of fiber angle 22 increases (i.e. becomes
greater than 45.degree.). As tubular braid form 14 is contracted to
conform to a smaller diameter, the absolute value of fiber angle 22
decreases (i.e. becomes less than 45.degree.). The fiber angle 22
in the finished bat 13 is referred to as the resultant fiber angle.
Since barrel portion 2 has an outside barrel diameter 23 that is
larger than an outside handle diameter 24 of handle portion 4 (see
FIG. 7), a single tubular braid form 14 extended over the full
length 8 of bat 13 has different resultant fiber angles 22 in the
handle portion 4 relative to the barrel portion 2. The ability of
the applicant to produce bats having different resultant fiber
angles 22 in the handle portion 4 compared to the barrel portion 2,
is advantageous in achieving the above-described desirable and
differentiated mechanical properties in the handle portion 4
relative to the barrel portion 2.
[0084] In a first example, tubular braid form 14 constructed solely
of fiberglass tows 16, having base fiber angles 22 of
.+-.45.degree., and base tubular diameter of two (2) inches, will
have resultant fiber angles 22 of .+-.54.degree. when expanded to
stretch over barrel portion 2 having outside barrel diameter 23 of
2.25 inches, and resultant fiber angles 22 of .+-.19.degree. when
contracted to fit over handle portion 4 having outside handle
diameter 24 of 0.9 inches.
[0085] As a second example, tubular braid form 14 constructed
solely of fiberglass tows 16, having base fiber angles 22 of
.+-.45.degree., and base tubular diameter of three (3) inches, will
have resultant fiber angles 22 of .+-.32.degree. when contracted to
fit over barrel portion 2 having outside barrel diameter 23 of 2.25
inches, and resultant fiber angles 22 of .+-.12.degree. when
contracted to fit over handle portion 4 having outside handle
diameter 24 of 0.9 inches.
[0086] Referring to FIG. 7C, due to the anisotropic nature of
polymer composite structures, their stiffness and strength are
significantly greater in a fiber length direction 25 parallel to
the direction of fiber tows 16, as compared to a cross fiber
direction 26 perpendicular to the direction of fiber tows 16. Thus,
in the first example referred to above, for a two (2) inch tubular
braid 14, axial stiffness (along the length 8, parallel to
longitudinal axis 30) of barrel portion 2 is 22% less and axial
strength is 37% less, than the same barrel made with the resultant
fiber angles 22 of .+-.45.degree.. Transverse stiffness
(perpendicular to length 8 and longitudinal axis 30) of barrel
portion 2 is 31% greater and transverse strength is 83% greater.
Similarly, in handle 4, axial stiffness is 97% greater, axial
strength is 519% greater, transverse stiffness is 44% less, and
transverse strength is 60% less. Such resultant and differentiated
mechanical properties between barrel portion 2 and handle portion 4
are particularly desirable to optimize both bat performance and
feel.
[0087] In the second example referred to above, for tubular braid
14 have a base tubular diameter of three (3) inches, used on bat 13
having outside barrel diameter 23 of 2.25 inches and outside handle
diameter 24 of 0.9 inches, axial stiffness of barrel portion 2 is
45% greater and axial strength is 136% greater, than the same
barrel made with the resultant fiber angles 22 of .+-.45.degree..
Transverse stiffness of barrel portion 2 is 29% less and transverse
strength is 45% less. Similarly, in handle 4, axial stiffness is
116% greater, axial strength is 702% greater, transverse stiffness
is 48% less, and transverse strength is 64% less.
[0088] The longitudinal or axial stiffiness and strength of a
standard all fiberglass polymer composite tube with all fiber
angles 22 oriented at 0.degree. to the longitudinal axis of that
tube, is typically 8 Msi (million lbs/in.sup.2) and 155 Ksi
(thousand lbs/in.sup.2), respectively. This compares to 2.4 Msi and
17 Ksi, respectively, for the same standard polymer composite tube
having all fiber angles 22 oriented at .+-.45.degree.. Thus, to
achieve even higher axial strength and stiffness in handle portion
4, the applicant has found it useful to include in the handle
portion 4 only, at least one layer of continuous length
reinforcement fibers arranged in a stitched tubular form having all
resultant fiber angles 22 of 0.degree. relative to the central
longitudinal axis 30 of bat 13. The tows 16 of stitched tubular
forms are not braided or intertwined, but are merely stitched
together in a tubular construction. This at least one layer of
0.degree. stitched tubular fibers in the handle portion 4 does not
affect the strength or stiffness of barrel portion 2, thus
resulting in improved bat durability and feel without negatively
affecting performance.
[0089] To further differentiate resultant stiffness and strength
properties between handle portion 4 and barrel 2, the applicant has
found it useful to include, within a selected single layer 15, one
intertwined tubular braid form 14 that extends only the length of
handle portion 4 or only the length of barrel portion 2 and a
second intertwined tubular braid form 14 that extends the balance
of the length 8 of bat 13. These two tubular braid forms 14, within
the selected single layer 15, may have base tubular diameters and
base fiber angles that are varied and differentiated as required to
achieve the desired stiffness and strength differentials between
handle portion 4 and barrel portion 2. Additional layers 15 of
intertwined tubular braid forms 14 extending the full length 8 can
be added either above or below the selected single layer 15.
Multiple such selected single layers 15, each combining two
differentiated tubular braid forms 14, may be included in the same
bat 13.
[0090] The applicant's polymer composite bat 13 made predominantly
of tubular braid forms 14, arranged in multiple layers 15,
preferably has resultant fiber angles 22 in the handle portion 4
that range from 0.degree. to .+-.45.degree., wherein an average of
the absolute values of the resultant fiber angles 22 is less than
20.degree. and generally in the range of 5.degree. to 20.degree..
In the barrel portion 2, the resultant fiber angles 22 range from
.+-.20.degree. to .+-.60.degree., wherein an average of the
absolute values of the resultant fiber angles 22 is greater than
25.degree. and generally in the range of between 25.degree. to
35.degree.. Thus, the average of the absolute values of the
resultant fiber angles 22 for all layers 15 in the handle portion 4
is preferably between 5.degree. and 30.degree. less than the
average of the absolute values of the resultant fiber angles 22 for
all layers 15 in the barrel portion 2.
[0091] Further, as demonstrated in laboratory testing (i.e.
frequency and model analysis), handle portion 4 of bat 13 has an
axial stiffness of between 50,000 and 250,000 lb/in.sup.2 and a
first bending mode frequency of between 100 and 600 hertz. Barrel 2
of bat 13 has a transverse or radial stiffness of between 70,000
and 350,000 lb/in.sup.2, and a first hoop mode frequency of between
800 to 2000 hertz, which both directly relate to the differential
stiffness achieved in the handle 4 versus barrel 2 of bat 13.
[0092] Further, the nesting which results between each of the
multiple layers 15 of intertwined tubular braid forms 14, due to
the unique hills 20 and valleys 21 on the surface thereof, plus the
mechanical intertwining of the tows 16, contribute to a significant
increase in the durability of the applicant's polymer composite
baseball bats made therewith.
[0093] Since intertwined tubular braid forms 14 are constructed of
tows 16 that follow a spiral path around the circumference of
tubular braid form 14, the fiber length of tows 16 is always
greater than the braid form length of the corresponding tubular
braid form 14. Accordingly, the length of fiber tows 16 in the
handle portion 4 of bat 13 is always greater than the length of the
handle portion 4, and the length of the fiber tows 16 in the barrel
portion 2 of bat 13 is always greater than the length of the barrel
portion 2.
[0094] The force produced in a ball-bat collision in a typical game
of adult baseball can approach 10,000 lbs. Extensive testing
conducted by the applicant has determined that to consistently and
continually withstand these high ball/bat collision forces, the
wall thickness 10 of barrel portion 2 of bat 13, as described
herein by the applicant, is preferably in the range of 0.2 inches
or less. Of course, if less strength and durability is required,
for example for bats used in youth baseball or slow pitch, a
thinner bat can be produced.
[0095] Due to the limitations imposed by commercially available raw
material rovings or tows 16, intertwined tubular braid forms 14 are
generally only available in thicknesses varying from 0.015 inches
to 0.050 inches. Thus, a minimum of four layers 15 are required to
achieve a resultant barrel wall thickness 10 of 0.2 inches. Of
course, more layers could be necessary if thinner braid forms are
used, and fewer layers may be required to make a thinner bat
barrel, if desired.
[0096] Polymer composite materials are known to have superior
damping properties relative to metals. Thus, bats of the
applicant's polymer composite bats vibrate less and result in less
stinging of the user's hands.
[0097] Further, as shown in FIGS. 2 to 6, tubular sections of the
applicant's polymer composite bats have an internal cavity 5, that
can be filled with a suitable damping material, such as a polymeric
foam or low-density granular materials, or other suitable
materials, in at least barrel portion 2, but also in tapered
mid-section 3, or handle portion 4, or combinations thereof.
Filling cavity 5, or parts thereof, with foam can be used to
selectively weight the bat, and/or produce a differentiated more
pleasing sound relative to the metallic pinging of an aluminum bat,
and/or reduce vibrations providing less sting in the user's hands,
and/or lower the trampoline effect, or hitting performance, if
required by regulations. As shown in FIGS. 3 and 4, handle portion
4 and/or tapered mid-section 3 may be solid so that only the
internal cavity 5 of barrel portion 2 is filled with damping
material.
[0098] Moreover, filling cavity 5, or parts thereof, with a damping
material such as polymeric foam or the like, creates a "structural
sandwich" comprised of a thin, high strength, high stiffness
external polymer composite sleeve or skin covering and bonded to a
relatively thick, relatively weak lightweight foam core. The
combination provides lightweight bats with high strength and
stiffness and improved durability. In the case of the "structural
sandwich" construction, the external all polymer composite sleeve
or skin is constructed around the foam core, ensuring bonding of
the polymer skin to the foam core. In the alternative, the foam
core can be coated with resin and inserted into the previously
constructed all polymer composite tube.
[0099] The types of polymeric foam used to fill cavity 5 include
polystyrene, polyurethane, polyvinyl, polymethacrylimide,
polyamide, syntactic, styreneacrylonitrile, polyolefin, or other
similar foams, or combinations thereof. Typical foam densities
range from approximately 3 lbs/ft.sup.3 to 20 lbs/ft.sup.3.
[0100] The applicant's polymer composite bats as described herein
can be lower in weight than wood, metal, or hybrid metal bats.
Lower weight results in faster bat speed, which in turn increases
performance (hitting distance) and also allows a player more time
before reacting to a pitched ball. A three-mile per hour (mph)
increase in bat speed results in approximately 10 feet of
additional hitting distance. Also, the increase in bat speed allows
a player 3% more reaction time. This equals approximately 2 feet
more of pitch length before the decision to swing or not must be
made. The result is a further increase in performance, resulting in
a better hitting average. Where the minimum weight of a bat is
regulated, the lower weight properties of the applicant's all
polymer composite bats can be used to lengthen the hitting area,
that is barrel portion 2, and thus increasing the sweet spot,
relative to conventional bats. This allows increased opportunity
for the player to optimally contact the ball, which further
increases performance and hitting average.
[0101] Also, lower weight polymer composite bats as described
herein, can have secondary weights added evenly to both ends
(balanced load) or at either end (end loaded), which can further
improve performance and hitting distance.
[0102] Polymer composite bats as described herein by the applicant,
may be manufactured by a variety of polymer composite processes
including resin transfer molding, compression molding, hand lay-up,
filament winding, and other processes known within the industry.
The hollow tubular all polymer composite portions of the
applicant's polymer composite bats are typically formed around a
solid mandrel or tool, which is subsequently withdrawn, extracted,
or dissolved. In the embodiment where cavity 5 includes a damping
material such as polymeric foam, to form a "structural sandwich",
the foam core may serve as the mandrel and remain as part of the
finished bat.
[0103] Preferably, the applicant's polymer composite bats and bat
components are constructed or manufactured using a precision
molding process (See FIGS. 8, 9A, and 9B). The precision tooling
employed by the applicant in the preferred precision molding
process consists of a solid internal mandrel 40 (shaped in a
positive form of the desired bat) having a barrel portion 42 and
handle portion 44 and external diameters corresponding to the
internal tubular diameters of the desired bat, and a solid
two-piece precision external mold 50, consisting of a top mold
portion 52 and a bottom mold portion 54, and mold cavities 56, all
precision machined of a hardened tool steel (for example, P-20
steel). When fitted together, top mold portion 52 and bottom mold
portion 54 conform to the precise outside diameters of the desired
bat. A rubber "O" ring 60 circles mold cavity 56 to provide a means
of sealing the mold 50 when the two mold portions 52, 54 are fitted
together and placed into a hydraulic press (not shown). Machining
of the mandrel 40 and the mold 50 is preferably accomplished by
computer numerically controlled (CNC) machine tools capable of
holding precise tolerances. Further finishing of the precision
tooling 40, 50 by grinding and polishing results in final tool
tolerances of .+-.0.0001 inches.
[0104] Referring to FIG. 8, the precision molding process used by
the applicant in manufacturing the polymer composite bats described
herein consists of arranging fiber preforms, such as the tubular
braid forms 14 shown in FIG. 7C, in multiple layers 15 (see FIG.
7B) over the precision internal mandrel 40 (step 100). Some of the
fiber preform layers 15 are arranged to cover the full length of
the mandrel 40, while others cover only a portion of the full
length, for example, only the barrel portion 42 or only the handle
portion 44. The sequence of preform layers 15, whether covering the
full length or partial length of the mandrel 40, is determined by
the desired physical characteristics of the finished bat. The
precision mandrel 40 is then placed within the cavity 56 of bottom
portion 54 of the two-piece precision external mold 50 (step 102),
and the top portion 52 is fitted in place and inserted into a
hydraulic press to seal the cavity (step 104). The mold 50 is
heated, preferably using electric platens (step 106), and a
two-part thermoset liquid resin is simultaneously mixed and
injected into the mold cavity 56, through a conduit 62 using a pump
preferably at 25 to 45 psi air pressure, thereby combining the
thermoset resin with the reinforcement fibers of the fiber preforms
in a resin-fiber matrix (step 108). The mold 50 is continually
heated to a thermoset resin curing temperature of between
190.degree. F. and 300.degree. F. Once the thermoset resin has
cured or hardened (approximately 3 minutes) (step 110), the mold 50
is opened, and the mandrel 40, including the hardened polymer
composite material on its exterior surface, is removed (step 112).
The mandrel 40 is subsequently extracted from the polymer composite
material using a pneumatic extractor (step 114) and the ends are
trimmed to a final desired length (step 116).
[0105] Polymer composite bats made using the above-described
precision molding process require no additional finishing
operations, such as sanding and/or machining, as required in other
polymer composite manufacturing processes, such as filament
winding, hand lay-up and tube rolling. None of these other
processes employ external mold 50, comprising precision top and
bottom mold portions 52 and 54 and cavities 56, as described above
by the applicant, and thereby result in polymer composite bats that
are relatively imprecise with respect to outside diameter, wall
thickness, and weight. The bladder molding process, which does not
use an internal mandrel, results in similar imprecise dimensions.
Subsequent sanding and/or machining steps, while improving
achievable tolerances in these other processes, are unable to
produce bats having tolerances that match those of the applicant's
polymer composite bats made using the above-described precision
molding process. Typically, tolerances achieved by the applicant's
precision molding process are three times greater than those
achievable with other polymer composite manufacturing
processes.
[0106] In addition, bats made using other polymer composite
manufacturing processes, such as filament winding, result in bats
that have only continuous fibers extending from the bat handle end
all the way through to the bat barrel end. Moreover, these
continuous fibers are all placed at resultant fiber angles 22 that
are constant within a particular layer 15, thus limiting optimal
bat performance. Such other polymer composite manufacturing
processes compare unfavourably to the applicant's precision molding
process, as described herein, which uses intertwined tubular braid
forms 14, which when extended over the full length 8 of the bat 13,
produce different resultant fiber angles 22 in the barrel portion 2
compared to the handle portion 4, thus improving bat performance.
Also, when smaller diameter tubular braid forms 14 and stitched
tubular fibers aligned at 0.degree. to the longitudinal axis 30 are
placed only in the handle portion 2, handle axial stiffness is
increased and bat performance is further improved.
[0107] Tolerances achievable on a consistent basis by the precision
molding process described herein by the applicant include:
.+-.0.001 inches for the outside barrel diameter 23 and outside
handle diameter 24; .+-.0.001 inches for the barrel portion 2 wall
thickness 10; .+-.0.003 inches for the barrel portion 2 roundness
(also referred to as out-of-roundness); and .+-.{fraction (1/16)}
ounces for the finished bat weight. The precise tolerances
achievable by the applicant's precision molding process as
described herein, compare favourably to aluminum bats, where
tolerances are determined largely by the raw aluminum tubes used in
their manufacture. For example, raw aluminum tube specifications
are typically in the range of .+-.0.006 inches (drawn) or .+-.0.015
inches (extruded), which directly translates to the wall thickness
of the finished aluminum bat barrel. Both barrel diameter and
barrel wall thickness are subsequently unchanged in the typical
swaging process used to produce most aluminum bats. Also, the
swaging process typically has a stated barrel roundness tolerance
of .+-.0.005 inches, with many aluminum bats having greater
roundness tolerances. Further, aluminum bats, because of their
greater inherent dimensional tolerances, have a weight tolerance of
.+-.0.5 ounces.
[0108] The importance of achieving low and consistently precise
physical dimension tolerances is fundamental to achieving optimal
bat performance. For example, a larger outside barrel diameter 23
improves bat performance by increasing the trampoline effect. Also,
a larger outside barrel diameter 23 increases the hitting surface
area and thus increases the probability of contacting the ball. The
outside barrel diameter 23 of bats used in competition is regulated
to an allowed maximum barrel diameter. This maximum limit must be
taken into account so that manufacturing tolerances do not result
in bats that exceed the regulated maximums. Because of the
exceptionally low tolerances achieved by the applicant's precision
molding process, as described herein, bats produced using this
process have outside barrel diameters 23 that are capable of being
consistently much closer to the regulated allowable maximum
diameters than bats produced using any other manufacturing process.
Also, reducing barrel wall thickness 10 is directly related to
lower transverse stiffness in barrel portion 2 and thus to
increased trampoline effect and increased bat performance. However,
decreasing barrel wall thickness 10 to improve performance is
offset by a decrease in durability. Precise control of barrel wall
thickness 10, as achieved by bats manufactured using the
applicant's precision molding process as described herein, allows
for optimally thinner barrel wall thickness 10 for a given
acceptable durability. Further, the low and consistently precise
dimensional tolerances of the applicant's precision molding
process, result in much tighter weight tolerances, which allow
consistent and accurate bat moments of inertia, resulting in
consistent feel and swing weight, highly favoured by players using
bats in all bat categories.
[0109] The applicant's polymer composite bats as described herein
may be embodied in other specific forms without departing from the
spirit or essential characteristics thereof. The present
embodiments are therefore to be considered as illustrative and not
restrictive, the scope of the invention being indicated by the
appended claims rather than by the foregoing description, and all
changes that come within the meaning and range of equivalency of
the claims are therefore intended to be embraced therein.
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