U.S. patent application number 14/423470 was filed with the patent office on 2015-10-22 for golf club shaft.
This patent application is currently assigned to Mitsubishi Rayon Co., Ltd.. The applicant listed for this patent is Mitsubishi Rayon Co,Ltd.. Invention is credited to Takashi KANEKO, Satoshi SHIMONO.
Application Number | 20150297963 14/423470 |
Document ID | / |
Family ID | 50183608 |
Filed Date | 2015-10-22 |
United States Patent
Application |
20150297963 |
Kind Code |
A1 |
SHIMONO; Satoshi ; et
al. |
October 22, 2015 |
GOLF CLUB SHAFT
Abstract
The present invention provides a high-balance-point shaft
capable of increasing ball speed. A golf club shaft formed by
laminating fiber-reinforced resin, wherein the balance point
obtained by formula below is set to be 53% or higher; and the
kickpoint obtained by formula below is set to be 44% or higher.
Inventors: |
SHIMONO; Satoshi;
(Toyohashi-shi, JP) ; KANEKO; Takashi;
(Toyohashi-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Rayon Co,Ltd. |
Chiyoda-ku TK |
|
JP |
|
|
Assignee: |
Mitsubishi Rayon Co., Ltd.
Chiyoda-ku
JP
|
Family ID: |
50183608 |
Appl. No.: |
14/423470 |
Filed: |
August 29, 2013 |
PCT Filed: |
August 29, 2013 |
PCT NO: |
PCT/JP2013/073212 |
371 Date: |
February 24, 2015 |
Current U.S.
Class: |
473/319 |
Current CPC
Class: |
A63B 60/0081 20200801;
A63B 60/42 20151001; A63B 53/10 20130101; A63B 60/00 20151001 |
International
Class: |
A63B 53/10 20060101
A63B053/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2012 |
JP |
2012-191090 |
Claims
1. A golf club shaft formed by laminating fiber-reinforced resin,
wherein a balance point obtained by formula (1) below is set to be
53% or higher; and a kickpoint obtained by formula (2) below is set
to be 44.5% or higher and 48% or lower, wherein a mass of the shaft
M [g] and a full shaft length (L.sub.S) [mm] satisfy the following
formula 35.ltoreq.M.times.(L.sub.S/1168)75 balance point
(%)=(L.sub.G/L.sub.S).times.100 (formula 1) L.sub.G: distance from
the gravity center of the shaft to a tip end of the shaft L.sub.S:
full length of the shaft kickpoint (%)=(L.sub.K/L.sub.B).times.100
(formula 2) L.sub.K: when a the shaft is curved by a compression
load exerted on both ends of the shaft so that the linear distance
between both ends is 98.5.about.99.5% of the shaft length, the
distance from the tip end of the shaft to a point where a straight
line connecting both ends intersects with a perpendicular line
drawn from an apex of the curve. L.sub.B: when the shaft is curved
by a compression load exerted on both ends of the shaft so that the
linear distance between both ends is 98.5.about.99.5% of the shaft
length, the linear distance between both ends of the shaft.
2. The golf club shaft according to claim 1, wherein a tip-side end
of a weight layer (W) that weights 10.about.30% of the shaft weight
is positioned at 800 mm or greater from the tip end of the shaft,
and a flexural modulus of the weight layer (W) in a longitudinal
direction of the shaft is 70 GPa or lower, wherein an average
thickness of the weight layer (W) is set at 0.5 mm or less, and the
weight layer (W) is preferred to be disposed on a sixth layer from
an outermost layer or closer.
3. (canceled)
4. (canceled)
5. The golf club shaft according to claim 1, wherein the shaft is
formed in a tube shape; an inner diameter of the shaft tapers,
gradually increasing from the tip end toward a butt end; the
inner-diameter taper has an inner-diameter taper bending point
(Pm); the inner-diameter taper bending point (Pm) is positioned at
550.about.750 mm from the tip end of the shaft; and when an
inner-diameter tapering gradient is set as (Tm) to indicate an
inner-diameter inclination between the tip end and the
inner-diameter taper bending point (Pm), and when an inner-diameter
tapering gradient is set as (Tb) to indicate the inner-diameter
inclination between the inner-diameter taper bending point (Pm) and
the butt end, Tm>Tb is satisfied.
6. The golf club shaft according to claim 5, wherein the
inner-diameter taper has an inner-diameter taper bending point (Pt)
positioned 40.about.140 mm from the tip end of the shaft; and when
an inner-diameter tapering gradient is set as (Tt) to indicate the
inner-diameter inclination between the tip end and the
inner-diameter taper bending point (Pt), and when an inner-diameter
tapering gradient is set as (Tm') to indicate the inner-diameter
inclination between the inner-diameter taper bending point (Pt) and
the inner-diameter taper bending point (Pm), the following are
satisfied: Tt<Tm' 0.1/1000.ltoreq.Tt15/1000
7. The golf club shaft according to claim 5, wherein the (Tm) and
the (Tb) satisfy 1.5.ltoreq.Tt.ltoreq.5.5.
8. The golf club shaft according to claim 1, wherein an outer
diameter at the tip end is set to be 8.5 mm.about.9.3 mm, and an
outer diameter at the butt end is set to be 14.0 mm.about.16.5
mm.
9. The golf club shaft according to claim 2, further comprising an
angle layer made of fiber-reinforced resin where a fiber
orientation is set diagonally to the longitudinal direction of the
shaft; the weight layer (W); a straight layer made of
fiber-reinforced resin where the fiber orientation is set to be
parallel to the longitudinal direction of the shaft; and a hoop
layer where the fiber orientation is set to be perpendicular to the
longitudinal direction of the shaft.
10. The golf club shaft according to claim 9, further comprising a
reinforcement layer made of fiber-reinforced resin, wherein the
reinforcement layer is disposed 400 mm or less from the tip end
side of the shaft, and its fiber orientation is set to be parallel
to the longitudinal direction of the shaft.
11. A golf club comprising the golf club shaft according to any of
claim 1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a shaft used for a golf
club. The present application is based upon and claims the benefit
of priority to Japanese Patent Application No. 2012-191090, filed
Aug. 31, 2012. The entire contents of the application are
incorporated herein by reference.
BACKGROUND ART
[0002] Since restitution regulations on golf club heads were added
to the rules, various methods have been attempted to compensate for
lower restitution at the head. Designing heavier heads is one such
attempt. That technology aims to extend carry distance by
increasing the clubhead weight so as to increase the kinetic energy
of the head during the swing motion.
[0003] However, if the clubhead weight is set greater, the moment
of inertia of the club increases, resulting in a "heavy" feel
during the swing motion. To solve the problem, golf shafts are also
being improved, and a so-called high-balance-point shaft, in which
the gravity center is shifted closer to the grip, is drawing
attention. By so setting, even with a heavier head, the gravity
center of the club is closer to the grip, preventing a "heavy" feel
during the swing motion.
[0004] Patent publication 1 describes a shaft designed to increase
the clubhead weight to the extent allowable by making the portion
closer to the grip heavier so that even with the heavy head, a
"heavy" feel during a swing motion is prevented. More specifically,
patent publication 1 discloses a shaft where the balance point of
the shaft, namely, the percentage of the distance from the tip end
to the gravity center, is 56.5% or greater of the entire length of
the shaft.
[0005] Patent publication 2 describes a specific method for
manufacturing a so-called high-balance point shaft, where the
portion closer to the grip is made heavier. The tip side of a
high-balance point shaft is thinner. Thus, the publication
discloses a technology so that strength is increased while the
tip-side thickness is decreased to the extent allowable. Using the
technology, the shaft is designed to have the gravity center
positioned at a balance point of 53.0% or higher.
[0006] Theoretically, ball speed (carry distance) is expected to
increase by a heavier head on a high-balance-point shaft as
described in aforementioned publications. However, the problem is
that ball speed does not always increase as theoretically
predicted.
PRIOR ART PUBLICATION
Patent Publication
[0007] Patent publication 1: Specification of U.S. Patent
Publication No. 2012/0071266
[0008] Patent publication 2: JP H09-239082A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0009] In view of the aforementioned problems, the objective of the
present invention is to provide a high-balance-point shaft capable
of increasing ball speed.
Solutions to the Problems
[0010] The inventors of the present invention have carried out
intensive studies and found that the above problems are solved by
designing a shaft to have both a high balance point and a high
kickpoint. Namely, the embodiments of the present invention are
described in the following [1].about.[11]. [0011] [1] A golf club
shaft formed by laminating fiber-reinforced resin in which the
balance point obtained by formula (1) below is set at 53% or
higher, and the kickpoint obtained by formula (2) below is set at
44% or higher.
[0011] balance point (%)=(L.sub.G/L.sub.S).times.100 (formula 1)
[0012] L.sub.G: distance from the gravity center of a shaft to the
tip end of the shaft [0013] L.sub.S: full length of the shaft
[0013] kickpoint (%)=(L.sub.K/L.sub.B).times.100 (formula 2) [0014]
L.sub.K: when a shaft is curved by a compression load exerted on
both ends of the shaft so that the linear distance between both
ends is 98.5.about.99.5% of the shaft length, the distance from the
tip end of the shaft to a point where a straight line connecting
both ends intersects with a perpendicular line drawn from the apex
of the curve. [0015] L.sub.B: when a shaft is curved by a
compression load exerted on both ends of the shaft so that the
linear distance between both ends is 98.5.about.99.5% of the shaft
length, the linear distance between both ends of the shaft. [0016]
[2] The golf club shaft described in [1] above, in which the
tip-side end of a weight layer (W) which weighs 10.about.30 wt. %
of the shaft weight is positioned 800 mm or greater from the tip
end of the shaft, and the flexural modulus of the weight layer (W)
in a longitudinal direction of the shaft is 70 GPa or lower. [0017]
[3] The golf club shaft described in [1] or [2] above, in which the
average thickness of the weight layer (W) is 0.5 mm or less. [0018]
[4] The golf club shaft described in any of [1].about.[3] above, in
which the mass of the shaft (M) [g] and its full length (L.sub.S)
[mm] satisfy the following formula.
[0018] 30.ltoreq.M.times.(L.sub.S/1168).ltoreq.80 [0019] [5] The
golf club shaft described in any of [1].about.[4] above, where the
shaft is formed in a tube shape; the inner diameter of the shaft
tapers, gradually increasing from the tip end toward the butt end;
the inner-diameter taper has an inner-diameter taper bending point
(Pm); the inner-diameter taper bending point (Pm) is positioned
550.about.750 mm from the tip end of the shaft; and when an
inner-diameter tapering gradient is set as (Tm) to indicate the
inner-diameter inclination between the tip end and the
inner-diameter taper bending point (Pm), and when an inner-diameter
tapering gradient is set as (Tb) to indicate the inner-diameter
inclination between the inner-diameter taper bending point (Pm) and
the butt end, Tm>Tb is satisfied. [0020] [6] The golf club shaft
described in [5], in which the inner-diameter taper has an
inner-diameter taper bending point (Pt) positioned 40.about.140 mm
from the tip end of the shaft, and when an inner-diameter tapering
gradient is set as (Tt) to indicate the inner-diameter inclination
between the tip end and the inner-diameter taper bending point
(Pt), and when an inner-diameter tapering gradient is set as (Tm')
to indicate the inner-diameter inclination between the
inner-diameter taper bending point (Pt) and the inner-diameter
taper bending point (Pm), the following are satisfied:
[0020] Tt<Tm'
0.1/1000<Tt<5/1000 [0021] [7] The golf club shaft described
in [5] or [6] above, where (Tm) and (Tb) as defined above satisfy
1.5<Tm/Tb<5.5. [0022] [8] The golf club shaft described in
any of [1].about.[7] above, where the outer diameter at the tip end
is 8.5 mm.about.9.3 mm, and the outer diameter at the butt end is
14.0 mm.about.16.5 mm. [0023] [9] The golf club shaft described in
any of [1].about.[8] above, further including the following: an
angle layer made of fiber-reinforced resin where the fiber
orientation is set diagonally to the longitudinal direction of the
shaft; the weight layer (W); a straight layer made of
fiber-reinforced resin where the fiber orientation is set to be
parallel to the longitudinal direction of the shaft; and a hoop
layer where the fiber orientation is set to be perpendicular to the
longitudinal direction of the shaft. [0024] [10] The golf club
shaft described in [9] above, further including a reinforcement
layer made of fiber-reinforced resin; the reinforcement layer is
disposed 400 mm or less from the tip end side of the shaft and has
a fiber orientation set to be parallel to the longitudinal
direction of the shaft. [0025] [11] A golf club formed by using the
golf club shaft described in any of [1].about.[10] above.
Eeffects of the Invention
[0026] A golf club shaft according to one aspect of the present
invention and a golf club made of such a golf club shaft are
capable of lowering the rate of reduction in head speed relative to
a gain in head weight. As a result, when a gain in head weight
causes the initial ball speed to increase, the effect is maximized,
and carry distance of the ball increases.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1: a view showing the laminated structure of an
embodiment of the present invention;
[0028] FIG. 2: a half sectional view of a shaft (including a
mandrel) of an embodiment of the present invention;
[0029] FIG. 3: a half sectional view of a shaft (including a
mandrel) of another embodiment of the present invention;
[0030] FIG. 4: a half sectional view of a shaft (including a
mandrel) of yet another embodiment of the present invention;
[0031] FIG. 5: a view showing three examples of a hoop layer
employable in each embodiment of the present invention;
[0032] FIG. 6: a graph illustrating the results showing the
relationship between head weight and head speed in simulations
conducted on an embodiment of the present invention;
[0033] FIG. 7: a view schematically illustrating the balance point
in an embodiment of the present invention; and
[0034] FIG. 8 a view schematically illustrating the kickpoint in an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0035] In the following, examples of the embodiment of the present
invention are described in detail. In the present application, the
widest end of a shaft is referred to as the butt end, and the
narrowest end as the tip end. In addition, depending on the
situation, the butt-end side or the butt side may be referred to as
the grip side, and the tip-end side or the tip side as the tip
side.
[0036] A golf shaft according to an embodiment of the present
invention is manufactured by a sheet wrapping method. In such a
method, a fiber-reinforced resin layer, made by impregnating resin
into a reinforcing fiber sheet having a unidirectional fiber
orientation, is wrapped around a mandrel (core member) multiple
times (usually 2-4 times, depending on the size of the resin
layer), which is then thermoset to be shaped.
[0037] In the present embodiment, examples of the fiber used in a
fiber-reinforced resin layer are glass fiber, carbon fiber, aramid
fiber, silicon carbide fiber, alumina fiber, steel fiber and the
like. Especially, a polyacrylonitrile-based carbon fiber is the
most preferred, since it forms a fiber-reinforced plastic layer
that exhibits excellent mechanical characteristics. Such
reinforcing fibers may be used alone or in combination of two or
more.
[0038] A matrix resin of a fiber-reinforced resin layer is not
limited to any specific kind, but epoxy resin is generally used.
Examples of epoxy resin are bisphenol-A epoxy resin, bisphenol-F
epoxy resin, bisphenol-S epoxy resin, phenol novolac epoxy resin,
cresol novolac epoxy resin, glycidylamine epoxy resin,
isocyanate-modified epoxy resin, alicyclic epoxy resin and the
like. Such epoxy resins may be liquid or solid, and in addition,
may be used alone or in combination thereof. Also, a curing agent
is often mixed into epoxy resin.
[0039] The fiber weight, resin content and the like in a
fiber-reinforced resin layer are not limited specifically, and are
determined properly from the thickness, wrap-around diameter and
the like required for each layer.
[0040] A golf club shaft according to the present embodiment
requires a balance point of 53% or higher and a kickpoint of 44% or
higher. By so setting, when a ball is hit by a golf club made of
such a shaft, the ball speed effectively increases. The details are
described later. The effect on the increase in ball speed cannot be
sufficiently achieved when the balance point and kickpoint are
low.
[0041] As shown in FIG. 7, a balance point is defined as a
percentage of distance (L.sub.G) from tip end 61 to gravity center
70 of shaft 60 to the full length (L.sub.S) of the shaft. Namely, a
balance point is obtained by the following formula (1).
balance point (%)=(L.sub.G/L.sub.S).times.100 (1)
[0042] A balance point allows the position of the gravity center to
be determined quantitatively. In the present embodiment, a shaft
with a balance point lower than 50% is referred to as a low-balance
shaft, a shaft with a balance point of 50% or higher but lower than
53% as a mid-balance shaft, and a shaft with a balance point of 53%
or higher as a high-balance shaft. Generally speaking, when the tip
end 61 side of shaft 60 is made thinner and the butt end 62 side of
shaft 60 is made thicker, the value of the balance point increases;
that is, a high-balance shaft is achieved.
[0043] As shown in FIG. 8, a kickpoint is defined as follows. Shaft
60 is curved by being compressed from both of its ends. At that
time, compression load (P) exerted on both ends differs depending
on the bending rigidity of the shaft; compression load (P) is
exerted so that the linear distance between both ends is
98.5.about.99.5% of the shaft length prior to exerting compression
load on shaft 60. More specifically, both ends of shaft 60 are
fixed by rotatable fixing jigs 81, and the distance between both
ends of the shaft is reduced to the above range by moving a fixing
jig on one side so as to set fixing jigs 81 closer to each other.
When the linear distance is within the above range, apex 80 of the
curvature is found substantially at the same position. Length
(L.sub.D), which is the contraction amount of the length of shaft
60 when compression load (P) is exerted, is approximately 10 mm in
an example shown in FIG. 8.)
[0044] In shaft 60C, which is the curved shaft 60, apex 80 is at
the most protruding point in the peripheral direction of curved
shaft 60C. Then, distance (L.sub.K) from apex 80 and tip end 61 is
measured. The value of a kickpoint is determined as the percentage
of distance (L.sub.K) to shaft length (L.sub.B) when it is curved
as above (linear distance between both ends of the curved shaft),
namely, the value is obtained by the following formula (2).
kickpoint (%)=(L.sub.K/L.sub.B).times.100 (formula 2)
[0045] In the present application, values are obtained by using a
shaft kickpoint gauge "FG-105RM," made by Fourteen Corporation. For
example, a shaft with a kickpoint of lower than 43.5% is classified
as a low kickpoint shaft, a shaft with a kickpoint of 43.5% or
higher but lower than 44.0% as a mid kickpoint shaft, and a shaft
with a kickpoint of 44% or higher as a high kickpoint shaft.
Generally speaking, when the tip end 61 side of shaft 60 is made
harder and the butt end 62 side of shaft 60 is made softer, the
value of the kickpoint increases. Namely, a high kickpoint shaft is
achieved.
[0046] In addition, (L.sub.K) and (L.sub.B) are defined precisely
as follows.
[0047] L.sub.K: when a shaft is curved by a compression load
exerted on both ends of the shaft so that the linear distance
between both ends is 98.5.about.99.5% of the shaft length, the
distance from the tip end of the shaft to the point where the
straight line connecting both ends of the shaft intersects with a
perpendicular line drawn from the apex of the curve
[0048] L.sub.B: when a shaft is curved by a compression load
exerted on both ends of the shaft so that the linear distance
between both ends of the shaft is 98.5.about.99.5% of the shaft
length, the linear distance between both ends of the shaft
[0049] In the embodiment, to enhance the effect on the increase in
ball speed by achieving both a high balance point and a high
kickpoint, a balance point of 54% or higher and a kickpoint of
44.5% or higher are preferred; more preferably a balance point of
55% or higher and a kickpoint of 45% or higher, even more
preferably a balance point of 56% or higher and a kickpoint of
45.5% or higher, and especially preferably a balance point of 57%
or higher and a kickpoint of 46% or higher.
[0050] When a balance point is too high, the ratio of a weight
layer (W) to the entire shaft 60 becomes too high, causing the tip
end 61 side to be thinner and increasing the risk of breakage.
Thus, the balance point is preferred to be 63% or lower, more
preferably 61% or lower. In addition, if the kickpoint is too high,
there may be a strange feel (feel while swinging a club). Thus, the
kickpoint is preferred to be 48% or lower, more preferably 47.5% or
lower.
[0051] A golf club shaft 60 of the present embodiment is preferred
to include a weight layer (W) whose weight is 10.about.30% of the
shaft weight. The material for forming a weight layer (W) may be
selected from the above listed fiber-reinforced resins, but a
weight layer needs to be designed in consideration of physical
properties related to the design of the shaft 60. If the weight
layer (W) is too light, the weight on the grip side cannot be
increased sufficiently, and a high balance point is not achieved.
If the weight layer (W) is too heavy, the golf shaft will be too
heavy, failing to satisfy the intended functions of the shaft 60.
The weight layer (W) is preferred to weigh 13% or greater but no
greater than 27% of the entire shaft weight, more preferably 15% or
greater but no greater than 25% of the entire shaft weight.
[0052] In addition, the average thickness of a weight layer (W) is
preferred to be 0.5 mm or less. Here, the average thickness is
defined precisely as follows: the entire longitudinal length of a
weight layer (W) is divided by 5 and its circumference is divided
by 4, the thickness at the middle point of each divided portion is
measured, and their average value is calculated. If a weight layer
(W) is too thick, it is hard to achieve a high kickpoint. That is
because the outer diameter increases only where a weight layer (W)
is disposed, and only the portion with a weight layer (W) disposed
underneath will be emphasized because of the enlarged outer
diameter due to the weight layer (W). As described earlier, a high
kickpoint is likely to be achieved if the butt end 62 side is
softer. Accordingly, a weight layer (W) is preferred to be thinner.
It is preferred to be 0.4 mm or less, more preferably 0.3 mm or
less, even more preferably 0.2 mm or less, especially preferably
0.1 mm or less. The lower limit of the average thickness of a
weight layer (W) is preferred to be the smallest value allowable
for a shaft design, but the targeted value is 0.02 mm. Namely, a
weight layer (W) is preferred to be set at 0.02.about.0.5 mm, more
preferably 0.02.about.0.3 mm, even more preferably 0.02.about.0.2
mm, and especially preferably 0.02.about.0.10 mm.
[0053] Furthermore, to position a weight layer (W) effectively,
when shaft 60 is formed by wrapping multiple layers of
fiber-reinforced resin into a tube shape, it is preferred to be
disposed on the outer layer of the tube shape. In particular, a
weight layer (W) is preferred to be disposed on the sixth layer
from the outermost layer or closer. If a weight layer (W) is
positioned closer to the center, it is hard to achieve a high
kickpoint as described above. If a weight layer (W) is positioned
on a layer even closer to the outermost layer, the weight layer (W)
could be shaved off during a polishing process. Accordingly, a
weight layer (W) is preferred to be positioned on the fourth layer
from the outermost layer or closer, more preferably on the second
layer or closer, counted from the outermost layer. If it is located
on the first layer from the outermost layer or closer, the weight
layer (W) is shaved off during a polishing process, causing the
weight or shape of the weight layer (W) to be changed. Accordingly,
the balance of the weight in the shaft is changed and the club may
not perform well.
[0054] Here, physical properties of a shaft 60 in the present
application are defined. In general production procedures, both
ends of a golf club shaft are cut off after a wrapping process is
done so as to minimize production errors during the wrapping
process. The shaft length (L.sub.S) is defined as a full length of
the shaft after such cutting process. The shaft weight, the weight
of a weight layer (W), a kickpoint, a balance point and the like
are defined as their respective values obtained in a shaft as a
product, namely, the values obtained in a shaft that is cut as
above to avoid production errors. In addition, when assembled to
form a golf club, the shaft is further cut. Regarding a shaft after
it is assembled into a golf club (namely, a shaft that is further
cut from the shaft having a full length (L.sub.S)), such a shaft is
also within a scope of the present invention as long as it is
within the scope of patent claims. Furthermore, the position,
length, orientation angle of fibers of each layer and the number of
laminations are defined as follows. The fiber orientation angle
including that in a later-described straight layer is set at
approximately zero degrees to the shaft axis direction unless
otherwise specified. The fiber orientation angles indicate those
with respect to the shaft axis. The number of layers is one unless
otherwise specified. There are three ways to measure the length of
a reinforcement layer. In an example shown in FIG. 1, since a
weight layer (W) is wrapped on a partial portion of the butt side,
it is shaped to be trapezoidal, and the tip side end is cut off to
be triangular so as to prevent the concentration of stress on its
end portion (FIG. 1). The length of the trapezoidal layer does not
include the cut-off portion. On the other hand, since a triangular
reinforcement layer 50 (FIG. 1) does not include any cut-off
portion, its length is measured from one end to the other. In
addition, the length of a weight layer (W) is also measured from
one end to the other.
[0055] Moreover, in the present embodiment, a weight layer (W) is
preferred to be positioned at least 800 mm away from tip end 61 of
shaft 60. If a weight layer (W) is located too close to the tip end
61 side, gravity center 70 of shaft 60 is shifted to the tip end 61
side. As a result, a high balance point will not be achieved. A
weight layer (W) is preferred to be located at least 850 mm from
tip end 61, more preferably at least 900 mm from tip end 61. In the
present embodiment, "a weight layer (W) is located at least 850 mm
from tip end 61 of the shaft" means that a weight layer (W) is
disposed in such a way that of both ends of the weight layer (W),
one end on the tip end 61 side is located at least 800 mm from tip
end 61. The dimensions of a weight layer (W), namely, the
dimensions in the longitudinal direction and radial direction of
shaft 60 when the weight layer (W) is assembled into the shaft, are
preferred to be 200.about.400 mm in the longitudinal direction and
0.02.about.0.5 mm in the radial direction, although they may vary
depending on the weight of a weight layer (W) and the targeted
balance in shaft 60.
[0056] Moreover, when it is assembled into a shaft 60, the flexural
modulus of a weight layer (W) in the longitudinal direction of the
shaft is preferred to be 70 GPa or lower in the present embodiment.
If the flexural modulus of a weight layer (W) is too high, the butt
end side hardens even if its aforementioned weight and position are
satisfied. As a result, a high kickpoint will not be achieved. The
flexural modulus of a weight layer (W) is preferred to be 50 GPa or
lower, more preferably 20 GPa or lower. On the other hand, if the
flexural modulus is too low, adhesiveness to prepreg decreases and
the weight layer may be peeled off. Since the flexural modulus of a
resin used for adhesion purposes is usually 3 GPa or higher, the
flexural modulus of a weight layer (W) of the present embodiment is
at least 3 GPa. In particular, the flexural modulus in one
direction is set at 70 GPa or lower for a material to form a weight
layer (W). In the present embodiment, the flexural modulus of a
weight layer (W) in the longitudinal direction indicates a value
measured according to JIS K7017; more specifically, a value
obtained when a three-point bending test is conducted on a test
piece of a predetermined size by setting the distance at 80 mm
between supporting pins, and the size of a test piece is 100 mm
long, 15 mm wide and 2 mm thick.
[0057] Examples of material having a flexural modulus of 70 GPa in
a longitudinal direction are as follows: prepreg formed with low
elastic pitch-based fibers laminated to have a fiber orientation of
approximately zero degrees to the longitudinal direction of shaft
60; prepreg made of glass fiber or prepreg with dispersed metal
powder such as tungsten; prepreg formed with carbon fibers having a
higher strength and a mid-range elasticity which are laminated to
have a fiber orientation of approximately .+-.45 degrees to the
longitudinal direction of a shaft 60; prepreg formed with carbon
fibers having a higher elasticity which are laminated to have a
fiber orientation of approximately 90 degrees to the longitudinal
direction of a shaft 60; and the like. However, those are not the
only options. Specific product names and properties are shown in
Table 2.
[0058] A shaft of the present embodiment is formed to have a weight
of 60 grams, frequency of 250 cpm and a full shaft length (L.sub.S)
of 1168 mm. Depending on the functions intended for the club, the
weight, frequency and length of a shaft may be determined properly
by the engineer who designs the club. A frequency measuring device
made by Fujikura Ltd. is used to measure the frequency. The grip
portion is located at 180 mm from the butt end, and the tip weight
is set at 196 grams.
[0059] An example of a golf club shaft according to the present
embodiment is described below with reference to FIG. 1.
[0060] Around mandrel 10, fiber reinforced resin layers such as an
angle layer 20, a weight layer (W), a first straight layer 30, a
second straight layer 40, and a tip reinforcement layer 50 are
wrapped in that order. As a mandrel 10, any conventional material
for a golf club may be used. After the fiber reinforced resin
layers wrapped around a mandrel 10 are thermoset, the mandrel 10 is
pulled out. Then, sections 10 mm from the tip end 61 and 12 mm from
the butt end 62 are respectively cut off and the remaining portion
is polished. Accordingly, a tube-shaped shaft 60 is obtained. In
the present embodiment, a shaft 60 for a wood is structured to have
a full shaft length (L.sub.S) of 1092.about.1220 mm, a narrow-end
outer diameter of 7.50.about.9.00 mm, and a wide-end outer diameter
of 15.0.about.15.8 mm An example shown in FIG. 1 is a shaft 60 with
a full shaft length (L.sub.S) of 1168 mm, and a narrow-end outer
diameter of 8.50 mm.
[0061] Here, the fiber orientation of the angle layer 20 is set
diagonal to the longitudinal direction of a shaft 60. A diagonal
direction means that a fiber orientation is in any direction but
excludes an orientation perpendicular or parallel to the
longitudinal direction of a shaft 60. In the example shown in FIG.
1, the angle layer 20 is made of fiber reinforced resin where a
first fiber material 20A and a second fiber material 20B are
adjacent to each other. The fiber orientation of the first fiber
material is set at angle (D1), inclining counterclockwise at
greater than zero but less than 90 degrees to the longitudinal
direction of a shaft 60. The fiber orientation of the second fiber
material 20B is set at angle (D2), inclining clockwise at greater
than zero but less than 90 degrees to the longitudinal direction of
a shaft 60. The materials for an angle layer 20 are carbon fiber or
the like, and may be selected properly from the above-listed
materials for fiber reinforced resin layers that have a fiber
orientation angle of 30.about.60 degrees. However, since angles
(D1, D2) are preferred to be close to 45 degrees, those having a
fiber orientation of 40.about.50 degrees are especially preferable.
The most preferable material is one having an orientation angle of
45 degrees. In the example of FIG. 1, angle (D1) is approximately
45 degrees, and angle (D2) and angle (D1) are the same at
approximately 45 degrees (in other words, fiber orientations are
set at +45 degrees and -45 degrees respectively to the longitudinal
direction of a shaft). The dimensions of an angle layer 20, namely,
dimensions corresponding to longitudinal and radial sizes when
assembled into a shaft 60, may vary depending on the weight of the
angle layer 20 and on the targeted balances of a shaft 60, and thus
are selected according to the balances to be set in the shaft
60.
[0062] A straight layer means a layer with a fiber orientation
parallel to the longitudinal direction of a shaft 60. In
particular, fibers with a fiber orientation parallel to the
longitudinal direction of a shaft 60 indicate that the fiber
orientation is set at -5 to +5 degrees to the longitudinal
direction of a shaft 60. It is especially preferable if the fiber
orientation is set at zero degrees in a measurable range to the
longitudinal direction of a shaft 60. The material for a straight
layer may be carbon fiber or the like, and selected properly from
the above-listed materials for fiber reinforced resin layers. It is
an option to form multiple straight layers. It is especially
preferable if there are two or three straight layers. In the
example shown in FIG. 1, there are a first straight layer 30 and a
second straight layer 40. Dimensions of first and second straight
layers 30 and 40 are determined properly in consideration of the
balances set for a shaft 60.
[0063] A tip reinforcement layer 50 is set to adjust the outer
diameter and shape on the tip end side of a shaft 60. The material
for a tip reinforcement layer 50 may be carbon fiber or the like
and may be selected properly from the above-listed materials for
fiber reinforced resin layers. The shape and dimensions of a tip
reinforcement layer 50 are described later.
[0064] In the present embodiment, the outer diameter of a tip end
61 is preferred to be 8.5 mm.about.9.3 mm. If the tip diameter is
too small, it may cause insufficient strength, and if the tip
diameter is too wide, it is difficult to achieve a high balance
point. The outer diameter is more preferable if it is 8.5
mm.about.9.1 mm. Regarding a butt diameter, the outer diameter of a
butt end is preferred to be 14.0 mm.about.16.5 mm. The grip may
feel strange if the outer diameter of the butt end is too narrow or
too wide. It is more preferable if the outer diameter is 14.5
mm.about.16.0 mm, even more preferable if it is 15.0 mm.about.15.5
mm.
[0065] To assemble a shaft 60 into a club, the butt end side of a
shaft 60 is cut off. In the example shown in FIG. 1, 48 mm of the
butt end side of a shaft 60 with a full shaft length (L.sub.S) of
1168 mm is cut so that the full length of the assembled shaft is
1120 mm, which is the regular club size of 46 inches. Here, "R9"
made by TaylorMade Golf Company, Inc. (Loft 9.5.degree.) is used as
a head. But that is not the only option.
[0066] As described above, the shaft length of a golf club shaft
differs depending on purposes such as shafts for drivers, fairway
woods, utilities, irons or the like. Examples of a club that
requires a long carry distance, which is the objective of the
present invention, are golf shafts for woods such drivers and
fairway woods. The full shaft length (L.sub.S) for such a club is
usually set at 1092 mm.about.1220 mm as described above. However,
when the full length (L.sub.S) is made different, the weight of the
shaft changes, making it difficult to define. Thus, to simplify
descriptions in the present application, a shaft weight is defined
as shown in the following formula by converting its full shaft
length (L.sub.S) to 1168 mm.
shaft weight after conversion=M.times.(L.sub.S/1168) [0067] M=shaft
weight [0068] L.sub.S=full shaft length
[0069] Also, when a shaft is assembled into a club, the shaft is
further cut as described above. The length to be cut differs
depending on the type of a head, since the length inserted into the
head is different. Since the exact weight at that time is also
difficult to define, the same conversion as in the above formula is
employed.
[0070] Based on the above formula, a shaft 60 in the present
embodiment is preferred to have a shaft weight in the range of
30.ltoreq.M.times.(L.sub.S/1168).ltoreq.80. If the shaft weight is
too light, the feel may be strange during a swing motion and
performance of the shaft decreases. Also, the risk of breakage may
increase. If the shaft weight is too great, an intended increase in
carry distance will not be achieved. A weight in the range of
35.ltoreq.M.times.(L.sub.S/1168).ltoreq.75 is more preferable, and
a weight in the range of 38.ltoreq.M.times.(L.sub.S/1168).ltoreq.70
is even more preferable.
[0071] Furthermore, the golf shaft of the present embodiment is
formed to have a balance point of 53% or higher and a kickpoint of
44% or higher.
[0072] The inventors of the present invention have found the
following two issues from multiple test results.
[0073] (1) When a balance point is lower than 53%, it is difficult
to sufficiently increase the head weight, and thus the ball speed
cannot be increased.
[0074] (2) When a kickpoint is lower than 44%, the head speed
decreases significantly even if the head weight is increased. Thus,
the same as in (1) above, the ball speed cannot be increased.
[0075] When a high-balance point shaft is formed to have a balance
point of 53% or higher, the tip side is usually thinner and the
butt side is thicker as shown in patent publication 2. Thus, the
butt side is stiffer relative to the soft tip side, resulting in a
so-called low to mid kickpoint shaft having a kickpoint of lower
than 44%. Namely, conventional technologies cannot produce a shaft
having both a high balance point and high kickpoint.
[0076] As described above, setting a high balance in a shaft
inevitably result in a low to mid kickpoint shaft when conventional
technologies are employed. Accordingly, the aforementioned
"theoretically expected increase in ball speed derived from a gain
in head weight" is not achieved. To solve the problem, it is
required to achieve both a high balance point and high
kickpoint.
[0077] Therefore, as one of the solutions for such a problem, the
inventors of the present invention have found that when a weight
balance of a shaft is adjusted by a weight layer (W) described
below, both a high balance point and high kickpoint are achieved.
[0078] the weight of a weight layer (W) is at least 10% but no
greater than 30% of the entire shaft weight. [0079] the weight
layer (W) is disposed at a location at least 800 mm away from the
tip side. [0080] the flexural modulus of the weight layer (W) in
the longitudinal direction of a shaft is 70 GPa or lower.
[0081] To form a high kickpoint shaft, a large reinforcement member
needs to be disposed on the tip side. Thus, the weight of the
reinforcement member causes the balance to be shifted to the tip
side. Accordingly, the method shown in FIG. 2 is preferred for
forming a shaft.
[0082] FIG. 2 is a half-sectional view of a shaft 60 and a mandrel
10. As described above, a shaft 60 is obtained when predetermined
materials are wrapped around a mandrel 10 and then the mandrel 10
is pulled out toward the butt end (butt end 62 side). As a result,
the shaft 60 has a shaft inner diameter equal to the outer diameter
of the mandrel. To specify the shape of a shaft using the outer
diameter of a mandrel, the description would be complex. Thus, the
shape of the shaft will be described using the inner diameter of
the shaft.
[0083] As shown in FIG. 2, the inner surface of tube-shaped shaft
60 is set so that the inner diameter of the tube-shaped shaft
tapers, increasing from the tip end 61 of the shaft toward the butt
end 62. On the inner surface of shaft 60, an inner-diameter taper
bending point (Pm) is formed so that the tapering degree of the
inner diameter reduces on the butt end 62 side. Here, the
inner-diameter taper bending point (Pm) is set to be positioned 550
mm.about.750 mm from the tip end 61. When the position of a point
(Pm) is closer to the tip side, the kickpoint is shifted to the tip
side, making it difficult to achieve a high kickpoint. When the
position of a point (Pm) is closer to the butt side, the kickpoint
is also shifted to the tip side, making it difficult to achieve a
high kickpoint. Positioning a point (Pm) at 600 mm.about.700 mm
from the tip end 61 is preferred. When an inner-diameter tapering
gradient is set as (Tm) to indicate the inner-diameter inclination
between the tip end 61 and the inner-diameter taper bending point
(Pm), and when an inner-diameter tapering gradient is set as (Tb)
to indicate the inner-diameter inclination between the
inner-diameter taper bending point (Pm) and the butt end 62, the
tapering gradient is adjusted to satisfy Tm>Tb. By so setting,
the kickpoint is moved toward the grip side, resulting in an even
higher kickpoint.
[0084] In addition, the shaft is formed so that the inner diameter
increases from the tip end 61 toward the butt end 62. Namely, in
the shaft, the inner diameter increases from the tip so as to flare
out toward the butt, and at the point (Pm) the diameter further
enlarges toward the periphery with respect to a virtual line (Th)
that connects the tip and the butt end (namely, a shaft is formed
to satisfy Tm>Tb). By so setting, without using a reinforcement
member on the tip side as described above, a high kickpoint shaft
is more likely to be achieved.
[0085] Also, when Tm>Tb is satisfied, there is an advantage that
even with a weight layer (W) disposed on the butt side, the outer
diameter is unlikely to be enlarged. When the outer diameter on the
butt side is enlarged, the butt side is inevitably made stiff and a
high kickpoint is hard to achieve. However, when the inner diameter
is set as in the present embodiment, the space for a weight layer
(W) is secured, making it easier to achieve a high kickpoint.
[0086] To make it even easier to achieve a high kickpoint,
1.5<Tm/Tb<5.5 is preferred. When the value of Tm/Tb is too
small, the effect of moving a kickpoint toward the grip side is
reduced, making it harder to achieve a high kickpoint. When Tm/Tb
is too great, the kickpoint is shifted toward the tip side, making
it harder to achieve a high kickpoint. The range is more preferred
to be 2.5<Tm/Tb<3.5.
[0087] As described in patent publication 2, it is necessary to
reduce the tip side thickness in a high balance point shaft. In
addition, as described above, on the tip side of a high kickpoint
shaft, a reinforcement member is necessary, namely, the tip side
thickness is required to be increased. There are two methods to
make it easier to achieve a high kickpoint without increasing the
tip side thickness. One is to form the aforementioned
inner-diameter taper bending point (Pm). The other is to use a
material containing fiber with a higher elastic modulus for the tip
side. However, material with a higher elastic modulus is fragile
and easy to snap. Since the tip side of a high balance shaft is
thinner, using a material with a higher elastic modulus in the tip
side means a higher risk of breakage.
[0088] Therefore, it is preferred to employ a third method as
follows. FIG. 3 shows an example with such a third method employed
therein. [0089] an inner-diameter taper bending point (Pt) is
positioned at 40.about.140 mm from the tip side. [0090] when the
inner-diameter tapering gradient is set as (Tt) to indicate the
inclination between the inner diameter at the tip end and the inner
diameter at the inner-diameter taper bending point (Pt), and when
the inner-diameter tapering gradient is set as (Tm') to indicate
the inclination between the inner diameter at the inner-diameter
taper bending point (Pt) and the inner-diameter taper bending point
(Pm), the following is satisfied:
[0090] Tt<Tm'
0.1/1000.ltoreq.Tt.ltoreq.5/1000
[0091] A shaft 60A according to the third structure is formed to be
thicker only where the greatest load is exerted when hitting a
ball, and thus is capable of preventing breakage from occurring
when a ball is hit.
[0092] The portion 40.about.140 mm from the tip side is said to
sustain the greatest deformation when striking a ball and thus is
the portion most likely to break. By setting Tt<Tm', the
position of a point (Pt), namely, any portion located 40.about.140
mm from the tip side, is locally made thicker, and breakage is thus
prevented. Moreover, by employing the present structure, the
thickness of the portion on the tip side of a point (Pt) is
maintained. Thus, both a high balance point and a high kickpoint
are more likely to be achieved.
[0093] When the position of a point (Pt) is shifted much closer to
the tip side, the effect of preventing breakage is low in the
manufacturing process and use of shaft 60. Also, when the position
of a point (Pt) is shifted much closer to the butt side, the
balance point is shifted to the tip side, making it harder to
achieve a high balance point. The position of a point (Pt) is more
preferred to be 70.about.110 mm from the tip side.
[0094] When the value (Tt) is too small, tapering is closer to
being parallel. Thus, friction increases when the mandrel is pulled
out during the manufacturing process of a shaft 60, and the tip
side of the shaft may crack. When the value (Tt) is too great,
since the portion closer to the tip side from a point (Pt) is too
thick, it is harder to achieve a high balance point. The value (Tt)
is more preferred to be 1/1000.ltoreq.Tt.ltoreq.4/1000, even more
preferred to be 2/1000.ltoreq.Tt.ltoreq.3/1000.
[0095] For producing a high balance and high kickpoint shaft, the
above structure is preferred to be employed from the viewpoint of
preventing breakage during actual use.
[0096] Next, by referring to FIG. 4, (Pm), (Pt), (Tb) and (Tt) are
each defined in further detail. A shaft 60A of the present
embodiment may have multiple inner-diameter taper bending points.
In such a case, inner-diameter taper bending points are arranged
from the tip side in the order of P1, P2, . . . Pn (n is a whole
number). Among the inner-diameter taper bending points located
550.about.750 mm from the tip side, the point closer to the 550 mm
side is set as a point (Pm) (P4 in FIG. 4), and among the
inner-diameter taper bending points located 40.about.140 mm from
the tip side, the point closer to the 40 mm side is set as a point
(Pt) (P1 in FIG. 4).
[0097] Also, (Tb) is set as the inner-diameter tapering gradient
made when a point (Pm) and the butt end are connected; (Tm) is set
as the inner-diameter tapering gradient made when the tip end and a
point (Pm) are connected; (Tt) is set as the inner-diameter
tapering gradient made when the tip end and a point (Pt) are
connected; and (Tm') is set as the inner-diameter tapering gradient
made when (Tt) and (Pm) are connected.
[0098] In addition, a shaft 60A of the present embodiment has a tip
reinforcement layer 50 (FIG. 1) which is also used for adjusting
the outer diameter. One end of the tip reinforcement layer 50 is
preferred to be positioned at the tip end, and the other is
preferred to be positioned 50.about.400 mm away from the tip end 61
toward the butt end 62. When a tip reinforcement layer is present
from the tip end 61 to a point less than 50 mm away from the tip
end, reinforcement of the tip is insufficient, and the risk of
breakage increases when striking a ball. When a tip reinforcement
layer is present from the tip end to a point further than 400 mm
away from the tip end, the weight concentrates on the tip end 61
side, making it harder to achieve a high balance point.
[0099] Moreover, a shaft 60A may have a hoop layer 90 laminated
with a fiber orientation angle set to be perpendicular to the
longitudinal direction of a shaft 60. Here, "set to be
perpendicular" means a fiber orientation of approximately 90
degrees to the longitudinal direction of a shaft 60. It may be
approximately 85.about.95 degrees, but it is preferred to be 90
degrees in a measurable range. The arrangement of a hoop layer 90
may be patterns A.about.C shown in FIG. 5, for example. Patterns
A.about.C are defined as follows.
[0100] A: at least one hoop layer 90 is arranged on the entire
length of a shaft 60.
[0101] B: a hoop layer 90 is arranged in such a way that one end of
a hoop layer 90 is positioned at least 300 mm away from the tip end
61 and on the tip end 61 side of the center of the shaft 60, while
the other end is positioned at the butt end 62.
[0102] C: a hoop layer 90 is arranged in such a way that one end of
a hoop layer 90 is positioned at least 300 mm away from the tip end
61 and on the tip end 61 side of the center of the shaft 60, while
the other end is positioned at least 700 mm away from the tip end
61.
[0103] The size and position of the hoop layer 90 are preferred to
be A, B or C, since the risk of breakage is reduced when actually
striking a ball. The effects of reducing breakage by the hoop layer
90 are high on the butt end side of the 300-mm point, but low on
the tip end side of the 300-mm point. Accordingly, from the
viewpoint of achieving both breakage reduction and a high balance,
a structure where one end of a hoop layer 90 is positioned at least
300 mm away from the tip end 61 and on the tip end 61 side of the
center of the shaft 60, while the other end is positioned at the
butt end 62, namely, the structure of B, is most preferred. Such a
structure is especially effective to be employed on a shaft 60 with
a weight of 60 grams or lower. Such a structure may also be
employed in a shaft 60A as well.
EXAMPLES
[0104] In the following, examples of the present embodiment are
described in detail. However, the present invention is not limited
to such examples. As for fiber-reinforced resin layers, carbon
prepregs (made by Mitsubishi Rayon Co., Ltd.) shown in Table 1, for
example, may be used. As for a weight layer (W), combinations of a
prepreg and a lamination angle shown in Table 2, for example, may
be used (combinations in which the flexural modulus of a weight
layer (W) is 70 GPa or lower in a direction corresponding to the
longitudinal direction of a shaft 60 when the weight layer (W) is
assembled in the shaft 60).
[0105] Flexural moduli in Table 2 are measured according to JIS
K7107 as described above. When the fiber orientation angle is
changed, the orientation angle is required to be changed when a
test piece is formed so that the relationship of the fiber
orientation angle in the fiber-reinforced resin to the longitudinal
direction of a shaft 60 corresponds to that described above.
However, measuring methods and the size of test pieces are the
same. Generally speaking, when the orientation angle is closer to
zero degrees, the flexural modulus is higher, whereas when the
orientation angle is closer to 90 degrees, the flexural modulus is
lower.
TABLE-US-00001 TABLE 1 laminate: flexural fiber: modulus resin
tensile JIS content thick- pre- product elasticity K7017 weight
[mass ness preg number [GPa] [GPa] [g/m.sup.2] %] [mm] A TR350C075S
235 176 75 25 0.062 B TR350C100S 235 176 100 25 0.083 C TR350C125S
235 176 125 25 0.103 D TR350C150S 235 176 150 25 0.124 E TR350C175S
235 176 175 25 0.145 F TR350J050 235 147 54 37.5 0.058 G TR350E100R
235 165 100 30 0.091 H TR350E125S 235 165 125 30 0.113 I TR350E150S
235 165 150 30 0.136 J MR350C050S 295 221 58 25 0.05 K MRX350C075R
295 221 75 25 0.063 L MRX350C100R 295 221 100 25 0.085 M
MRX350C125R 295 221 125 25 0.106 N MRX350C150R 295 221 150 25 0.127
O MRX350K020S 295 177 23 40 0.026 P MRX350J050S 295 184 54 37.5
0.058 Q HRX350C050S 390 293 58 25 0.048 R HRX350C075S 390 293 69 25
0.057 S HRX350C100S 390 293 92 25 0.076 T HRX350C125S 390 293 116
25 0.096 U HSX350C050S 450 338 58 25 0.047 V HSX350C075S 450 338 69
25 0.056 X HSX350C100S 450 338 92 25 0.075 Y HSX350C125S 450 338
116 25 0.095
TABLE-US-00002 TABLE 2 0.degree. laminate: .+-.45.degree.
90.degree. flexural laminate: laminate: fiber: modulus flexural
flexural tensile JIS modulus modulus resin product elasticity K7017
JIS K7017 JIS K7017 weight content thickness prepreg number [GPa]
[GPa] [GPa] [GPa] [g/m.sup.2 ] [mass %] [mm] W1 E1026C-10N 98 66 16
5 149 33 0.099 W2 GE352G135S 76 53 13 4 200 30 0.111 W3 TP013GE3417
-- 5 5 5 700 -- 0.090 W4 E0526A-12N 45 30 8 2 198 33 0.136 W5
TR350C100S 235 176 44 13 100 25 0.083 W6 MRX350C100R 295 221 55 17
100 25 0.085 W7 HRX350C100S 390 293 73 22 92 25 0.076 W8
HSX350C100S 450 338 84 25 92 25 0.075
Example 1
[0106] Example 1 of the present invention is described with
reference to FIG. 1. Around the mandrel 10 of FIG. 1 (diameter at
the tip end=6.0 mm, diameter at the butt end=13.3 mm), the
following layers were wrapped in that order: an angle layer 20
(prepreg K: two sheets of prepreg K were laminated with fiber
orientation angles of .+-.45 degrees to the longitudinal direction
of a shaft), a weight layer (W) (prepreg W1: laminated with a fiber
orientation angle of zero degrees to the longitudinal direction of
a shaft), a first straight layer 30 (prepreg D), a second straight
layer 40 (prepreg D), and a tip reinforcement layer 50 (prepreg H:
wrapped from the tip end to a point 250 mm upward). After
thermosetting the resin, the mandrel 10 was pulled out. Next, a
section 10 mm from the tip end and a section 12 mm from the butt
end were cut off and the remaining portion was polished.
Accordingly, a shaft was obtained to have a full length (L.sub.S)
of 1168 mm, a narrow-end outer diameter of 8.50 mm, and a wide-end
outer diameter of 15.1.about.15.3 mm. The weight of the shaft was
60 grams and the frequency was 250 cpm.
[0107] Here, regarding "a weight layer (W) (prepreg W1: laminated
with a fiber orientation angle of zero degrees to the longitudinal
direction of a shaft)" as described above, the flexural modulus of
the weight layer (W) in the longitudinal direction of a shaft is
"0.degree. laminate: flexural modulus" in Table 2. In the examples
below, a suitable orientation angle is selected from Table 2, and
the value in the column is set as "the flexural modulus of a weight
layer (W) in the longitudinal direction of a shaft."
[0108] A weight layer (W) was disposed to be positioned 800 mm from
the tip end of the shaft to the butt end. Also, the number of
wrappings in the weight layer (W) was adjusted so that its weight
is 10% of the total weight of the shaft.
Example 2
[0109] The shaft was produced the same as in Example 1 except that
the number of wrappings in the angle layer was changed and the
following modification was made to adjust the total weight of the
shaft. The number of wrappings in the angle layer was adjusted not
only in the present example but in each example. However, that
description is omitted.
[0110] The weight percentage of the weight layer (W) was set at
13.5%.
Example 3
[0111] The shaft was produced the same as in Example 1 except for
the following change.
[0112] The weight percentage of the weight layer (W) was set at
17.0%.
Example 4
[0113] The shaft was produced the same as in Example 3 except for
the following change.
[0114] As a weight layer (W), two sheets of prepreg (W5) were
laminated to have fiber orientation angles of.+-.45 degrees to the
longitudinal direction of the shaft.
Example 5
[0115] The shaft was produced the same as in Example 3 except for
the following change.
[0116] The weight layer (W) was switched to prepreg (W3).
Example 6
[0117] The shaft was produced the same as in Example 1 except for
the following change.
[0118] The weight layer (W) is disposed to be positioned 900 mm
from the tip end of the shaft to the butt end.
Comparative Example 1
[0119] The shaft was produced the same as in Example 1 except for
the following change.
[0120] As a weight layer (W), two sheets of prepreg (W8) were
laminated to have fiber orientation angles of.+-.45 degrees to the
longitudinal direction of the shaft.
Comparative Example 2
[0121] The shaft was produced the same as in Example 1 except for
the following change.
[0122] Prepreg (W5) was laminated as the weight layer (W).
Comparative Example 3
[0123] The shaft was produced the same as in Example 1 except for
the following change.
[0124] The weight percentage of the weight layer (W) was set at
6.5%.
Comparative Example 4
[0125] The shaft was produced the same as in Example 1 except for
the following change.
[0126] The weight percentage of the weight layer (W) was set at
3.0%.
Comparative Example 5
[0127] The shaft was produced the same as in Example 1 except for
the following change.
[0128] The weight layer (W) is disposed to be positioned 700 mm
from the tip end of the shaft to the butt end.
<Evaluation of Test>
[0129] Clubs were assembled using the shafts produced in the
examples and comparative examples above, and robot testing was
conducted under the following conditions.
(Assembly of Club)
[0130] As described earlier, the club length was set at 46 inches,
and the club balance was set at D0. As a head, "R9 Loft:
9.5.degree. " made by TaylorMade was used.
(Club Balance)
[0131] When a golf club is assembled, club balance is measured. By
measuring club balance, the moment of inertia in the direction of
swing can be estimated by approximation. Since the moment of
inertia in the direction of swinging the club is "weight" that is
felt during a swing motion, the weight felt during a swing motion
is the same if the club balance is the same. In the present test,
the head weight was adjusted to have a club balance of D1. Club
balance was measured using the "Golf Club Scale," a swing weight
scale made by the Kenneth Smith Golf Company.
(Robot Testing)
[0132] For robot testing, a swing robot "ROVO IV" made by Miyamae
Co., Ltd., was used. Five balls were test hit for each shaft. To
track the trajectory of a ball, "TrackMan," a trajectory tracking
device made by TrackMan, was used.
[0133] Average values obtained by the test are shown in Table
3.
TABLE-US-00003 TABLE 3 example example example example example
example comp. comp. comp. comp. comp. 1 2 3 4 5 6 example 1 example
2 example 3 example 4 example 5 shaft: total weight g 60 60 60 60
60 60 60 60 60 60 60 shaft: frequency cpm 250 250 250 250 250 250
250 250 250 250 250 shaft: full length L.sub.S mm 1168 1168 1168
1168 1168 1168 1168 1168 1168 1168 1168 grip weight g 50 50 50 50
50 50 50 50 50 50 50 club balance Pt D0 D0 D0 D0 D0 D0 D0 D0 D0 D0
D0 head weight g 203 205 207 207 207 205 203 203 201 199 201
balance point % 53.0 54.0 55.0 55.0 55.0 54.0 53.0 53.0 52.0 51.0
52.0 kickpoint % 44.0 44.0 44.0 44.5 45.0 44.0 43.5 42.5 44.0 44.0
43.5 weight layer W: % 10.0 13.5 17.0 17.0 17.0 13.5 10.0 10.0 6.5
3.0 10.0 weight weight layer W: GPa 66 66 66 44 5 66 84 176 70 70
70 elastic modulus weight layer W: mm 800 800 800 800 800 900 800
800 800 800 700 position head speed m/s 40.3 40.0 39.9 40.0 40.1
40.0 39.7 39.5 39.9 40.3 39.8 ball speed m/s 62.0 62.1 62.6 62.7
62.9 62.1 61.1 60.7 60.8 60.8 60.6 ball carry distance yrd 222.8
223.4 225.0 225.5 226.1 223.4 219.5 218.4 218.5 218.4 217.9
[0134] Compared with the comparative examples, the ball speed is
increased significantly in the examples as shown in Table 3
(t-test: P<0.05). As a result, carry distance of the ball is
significantly extended. That is based on the following
principles.
[0135] Head weight is increased when it is a high balance shaft;
however, in mid-kickpoint and low-kickpoint shafts as seen in
Comparative Examples 1 and 2, head speed is significantly reduced
and ball speed cannot be increased. In the same manner, in the case
of mid-balance point shafts as seen in Comparative Examples 3 and
4, even when they are set to have a high kickpoint, head weight is
not increased sufficiently. Thus, the ball speed cannot be
increased.
[0136] By contrast, as seen in Examples, when a shaft has both a
high balance point and a high kickpoint, the rate of reduction in
head speed is lowered. Thus, a significantly extended carry
distance is achieved from an increase in impulse caused by a gain
in head weight.
(Confirming the Effects by Simulations)
[0137] To confirm more clearly the aforementioned effects
(principles), simulations were conducted using FEM. A
general-purpose "ABAQUS" analysis software made by SIMULIA Corp.
was used. The results are shown in Table 4 and FIG. 6. In the
simulations, gravity centers of a low kickpoint (kickpoint=42%) and
high kickpoint (kickpoint=44%) were changed every 1% from
50%.about.59%, and the head weight was changed corresponding to
each gravity center.
TABLE-US-00004 TABLE 4 simulation number 1 2 3 4 5 6 7 8 9 10 Low
Kickpoint head weight g 195 197 199 201 203 205 207 209 211 213
balance point % 50.0 51.0 52.0 53.0 54.0 55.0 56.0 57.0 58.0 59.0
kickpoint % 42.0 42.0 42.0 42.0 42.0 42.0 42.0 42.0 42.0 42.0 head
speed m/s 41.38 41.21 41.12 40.85 40.67 40.43 40.34 40.14 39.88
39.67 High Kickpoint head weight g 195 197 199 201 203 205 207 209
211 213 balance point % 50.0 51.0 52.0 53.0 54.0 55.0 56.0 57.0
58.0 59.0 kickpoint % 44.0 44.0 44.0 44.0 44.0 44.0 44.0 44.0 44.0
44.0 head speed m/s 41.42 41.39 41.22 41.18 41.11 40.80 40.75 40.71
40.62 40.50
[0138] As shown in the simulation results, when head weight is
increased, the head speed is significantly reduced in a
low-kickpoint shaft, whereas the rate of reduction in head speed is
low in a high-kickpoint shaft. Namely, the simulation results
confirmed the test results obtained above.
[0139] Other examples are described below.
Example 7
[0140] In Example 7, a mandrel shown in FIG. 2 was used (tip-end
diameter=4.2 mm, diameter at point (Pm)=11.0 mm, butt-end
diameter=13.1 mm) In Example 7, the inner-diameter taper bending
point (Pm) was set at 650 mm from the tip side. Also, Tb=4.0/1000
and Tm=10.5/1000 were set. The rest of the structure was the same
as in Example 1. The structure is shown in Table 5, but the same
components as those in Example 1 were omitted.
Example 8
[0141] The shaft in Example 8 was prepared the same as in Example 7
except that the position of the inner-diameter taper bending point
(Pm) was set at 550 mm from the tip side.
Example 9
[0142] The shaft in Example 9 was prepared the same as in Example 7
except that the position of the inner-diameter taper bending point
(Pm) was set at 750 mm from the tip side.
Example 10
[0143] The shaft in Example 10 was prepared the same as in Example
7 except that Tm/Tb was set at 1.5.
Example 11
[0144] The shaft in Example 11 was prepared the same as in Example
7 except that Tm/Tb was set at 5.5.
Example 12
[0145] The shaft in Example 12 was prepared the same as in Example
7 except that a mandrel shown in FIG. 3 was used (tip-end
diameter=5.1 mm, diameter at point (Pt)=5.3 mm, diameter at point
(Pm)=11.0 mm, butt-end diameter=13.1 mm), the inner-diameter taper
bending point (Pt) was set at 90 mm from the tip side, and
Tt=2.5/1000, Tm'=12.0/1000 and Tt<Tm' were set.
Example 13
[0146] The shaft in Example 13 was prepared the same as in Example
12 except that the position of (Pt) was set at 40 mm.
Example 14
[0147] The shaft in Example 14 was prepared the same as in Example
12 except that the position of (Pt) was set at 140 mm.
Example 15
[0148] The shaft in Example 15 was prepared the same as in Example
12 except that Tt=0.1/1000.
Example 16
[0149] The shaft in Example 16 was prepared the same as in Example
12 except that Tt=5/1000.
Example 17
[0150] The shaft in Example 17 was prepared the same as in Example
12 except that a hoop layer (prepreg P) was added along the entire
length. By so setting, the breakage risk factor is reduced.
Example 18
[0151] The shaft in Example 18 was prepared the same as in Example
12 except that a tip reinforcement layer was formed from the tip
end to a point 400 mm upward. By so setting, the breakage risk
factor is reduced.
Example 19
[0152] The shaft in Example 19 was prepared the same as in Example
1 except that prepreg (W1) was used for the weight layer (W) and
its average thickness was set at 0.45 mm. The balance point was
53.2% and the kickpoint was 44.2%.
Example 20
[0153] The shaft in Example 20 was prepared the same as in Example
1 except that prepreg (W2) was used for the weight layer (W) and
its average thickness was set at 0.25 mm. The balance point was
53.2% and the kickpoint was 44.6%.
Example 21
[0154] The shaft in Example 21 was prepared the same as in Example
1 except that prepreg (W3) was used for the weight layer (W) and
its average thickness was set at 0.15 mm. The balance point was
53.2% and the kickpoint was 45.0%.
Comparative Example 6
[0155] The shaft in Comparative Example 6 was prepared the same as
in Example 1 except that prepreg (W5) was used for the weight layer
(W) and its average thickness was set at 0.55 mm. The balance point
was 53.2% and the kickpoint was 43.8%.
[0156] In Table 5, a list of production conditions for Examples
7--16 is shown. By so setting, both high balance point and high
kickpoint are more likely to be achieved. In addition, in Examples
19.about.21, both high balance point and high kickpoint are more
likely to be achieved, although they are not shown in the
table.
TABLE-US-00005 TABLE 5 example example example example example
example example example example example 7 8 9 10 11 12 13 14 15 16
balance point % 53.2 53.2 53.2 53.2 53.2 53.2 53.2 53.1 53.2 53.1
kickpoint % 44.2 44.2 44.2 44.1 44.1 44.1 44.1 44.1 44.1 44.1
position of Pm mm 650 550 750 650 650 650 650 650 650 650 Tb 1/1000
4.0 4.0 4.0 7.0 1.9 4.0 4.0 4.0 4.0 4.0 Tm 1/1000 10.5 10.5 10.5
10.5 10.5 10.5 10.5 10.5 10.5 10.5 Tm/Tb -- 2.6 2.6 2.6 1.5 5.5 2.6
2.6 2.6 2.6 2.6 position of Pt mm -- -- -- -- -- 90 40 140 90 90 Tt
1/1000 -- -- -- -- -- 2.5 2.5 2.5 0.1 5.0 Tm' 1/1000 -- -- -- -- --
12.0 12.0 12.0 12.0 12.0
INDUSTRIAL APPLICABILITY
[0157] The golf shaft related to the present invention is capable
of lowering the rate of reduction in head speed when head weight is
gained. As a result, the effect on the increase in ball speed
derived from a gain in head weight is maximized, and carry distance
of the ball increases.
DESCRIPTION OF NUMERICAL REFERENCES
[0158] 10 mandrel [0159] 20 angle layer [0160] 20A first fiber
material [0161] 20B second fiber material [0162] 30 first straight
layer [0163] 40 second straight layer [0164] 50 tip reinforcement
layer [0165] 60, 60A, 60C: shaft [0166] 61 tip end [0167] 62 butt
end [0168] 63 compressed shaft [0169] 70 gravity center of shaft
[0170] 80 kickpoint position [0171] 81 fixing jig [0172] 90 hoop
layer [0173] L.sub.S full length of shaft [0174] L.sub.G, L.sub.K,
L.sub.B, L.sub.D length [0175] P load [0176] W weight layer
* * * * *