U.S. patent application number 11/127331 was filed with the patent office on 2005-09-15 for forged iron-type golf clubs.
Invention is credited to Burnett, Michael S., Gilbert, Peter J..
Application Number | 20050202900 11/127331 |
Document ID | / |
Family ID | 34136107 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050202900 |
Kind Code |
A1 |
Gilbert, Peter J. ; et
al. |
September 15, 2005 |
Forged iron-type golf clubs
Abstract
Forged cavity back iron-type clubs and oversize clubs are
disclosed. These forged clubs have thin, durable hitting face and
relatively large cavity volumes. These clubs have high rotational
moments of inertia to minimize distance and accuracy penalties
associated with off-center hits. Long irons with hitting face of
about 0.100 inch thick are achievable by the present invention.
Also disclosed are forged irons made from stainless steels and
annealed to achieve the desired hardness and ductility.
Inventors: |
Gilbert, Peter J.;
(Carlsbad, CA) ; Burnett, Michael S.; (Carlsbad,
CA) |
Correspondence
Address: |
ACUSHNET COMPANY
333 BRIDGE STREET
P. O. BOX 965
FAIRHAVEN
MA
02719
US
|
Family ID: |
34136107 |
Appl. No.: |
11/127331 |
Filed: |
May 12, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11127331 |
May 12, 2005 |
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10640537 |
Aug 13, 2003 |
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Current U.S.
Class: |
473/342 |
Current CPC
Class: |
A63B 53/0458 20200801;
A63B 53/0454 20200801; A63B 53/047 20130101; A63B 53/0408 20200801;
A63B 2209/00 20130101; A63B 60/00 20151001; A63B 53/04
20130101 |
Class at
Publication: |
473/342 |
International
Class: |
A63B 053/04 |
Claims
We claim:
1. An iron-type golf club comprising: a club head having a hosel, a
front and a back, wherein the back comprises a cavity defined by a
perimeter member and the front has a hitting zone located opposite
to and coinciding with the cavity, and wherein the club head is
forged from stainless steel and then annealed, wherein the cavity
volume is greater than or equal to 8.68 cc.
2. The iron-type golf club of claim 1, wherein the cavity is
further adjoined by a first portion and a reinforced portion
located on the back of the club head and wherein the reinforced
portion is thicker than the first portion.
3. The iron-type golf club of claim 2, wherein the first portion is
located on top of the reinforced portion.
4. The iron-type golf club of claim 2, wherein the thickness of the
reinforced portion is about 1.2 times to about 3 times higher than
the thickness of the first portion.
5. The iron-type golf club of claim 2, wherein the first portion
occupies from about 50% to about 90% of the total area of the
hitting zone.
6. The iron-type golf club of claim 5, wherein the first portion
occupies from about 60% to about 80% of the total area of the
hitting zone.
7. The iron-type golf club of claim 1, wherein the perimeter member
is thicker on the bottom of the club head than on the top.
8. The iron-type golf club of claim 1, wherein the stainless steel
has a yield strength less than about 90,000 psi and an elongation
of greater than about 13%.
9. The iron-type golf club of claim 8, wherein the yield strength
is less than about 85,000 psi and the stainless steel has an
ultimate elongation of about 15% to about 21%.
10. The iron-type golf club of claim 1, wherein the stainless steel
comprises more than about 10% of chromium.
11. The iron-type golf club of claim 1, wherein the grain size of
the forged and annealed stainless steel is greater than about 10
.mu.m.
12. The iron-type golf club of claim 11, wherein the grain size of
the forged and annealed stainless steel is between about 10 .mu.m
and about 50 .mu.m.
13. The iron-type golf club of claim 1, wherein the club head is a
unitary club head.
14. The iron-type golf club of claim 1, wherein the club head
further comprises a forged face insert, and wherein the face insert
is made from stainless steel.
15. The iron-type golf club of claim 1, wherein the club head
further comprises a stamped face insert and wherein the face insert
is made from the stainless steel.
16. The iron-type golf club of claim 1, wherein the club head has a
hardness of less than about 90 Rockwell Hardness B.
17. The iron-type golf club of claim 1, wherein the stainless steel
is selected from a group consisting of 410 stainless steel, 403
stainless steel, 431 stainless steel, 416 stainless steel, 303
stainless steel, 304 stainless steel, 329 stainless steel, 316
stainless steel, 259 stainless steel, Nitronic 40, Nitronic 50 and
Nitronic 60.
18. The iron-type golf club of claim 1, wherein the club head is
selected from a group consisting of the number 1-9 irons, the
pitching wedge, the sand wedge and the gap wedge.
19. The iron-type golf club of claim 1, wherein the rotational
moment of inertia about a shaft axis is greater than about 500
kg.multidot.mm.sup.2.
20. The iron-type golf club of claim 19, wherein the rotational
moment of inertia about the shaft axis is greater than about 650
kg.multidot.mm.sup.2.
21. The iron-type golf club of claim 1, wherein the hitting zone
has a minimum thickness of less than about 0.2 inch.
22. The iron-type golf club of claim 21, wherein the minimum
thickness is less than about 0.13 inch when the loft angle is less
than about 35.degree..
23. The iron-type golf club of claim 21, wherein the minimum
thickness is about 0.1 inch.
24. The iron-type golf club of claim 1, wherein the hitting zone
has an aspect ratio in accordance to the following equation: aspect
ratio.gtoreq.-((1/4.5).times.loft angle.degree.)+25, wherein the
aspect ratio is the area of the hitting zone (inch.sup.2) divided
by a minimum thickness (inch) of the hitting zone.
25. An iron-type golf club comprising: a club head having a hosel,
a front and a back, wherein the back comprises a cavity defined by
a perimeter member and the front has a hitting zone located
opposite to and coinciding with the cavity, and wherein the club
head is forged from stainless steel and then annealed, wherein the
cavity volume is greater than or equal to 13.05 cc.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of co-pending U.S.
application Ser. No. 10/640,537, which was filed Aug. 13, 2003.
FIELD OF THE INVENTION
[0002] This invention generally relates to golf clubs, and, more
particularly, to iron-type clubs.
BACKGROUND OF THE INVENTION
[0003] Individual iron club heads in a set typically increase
progressively in face surface area and weight as the clubs progress
from the long irons to the short irons and wedges. Therefore, the
club heads of the long irons have a smaller face surface area than
the short irons and are typically more difficult for the average
golfer to hit consistently well. For conventional club heads, this
arises at least in part due to the smaller sweet spot of the
corresponding smaller face surface area.
[0004] To help the average golfer consistently hit the sweet spot
of a club head, many golf clubs are available with cavity back
constructions for increased perimeter weighting. Perimeter
weighting also provide the club head with higher rotational moment
of inertia about its center of gravity. Club heads with higher
moment of inertia have a lower tendency to rotate caused by
off-center hits. Another recent trend has been to increase the
overall size of the club heads, especially in the long irons. Each
of these features increases the size of the sweet spot, and
therefore makes it more likely that a shot hit slightly off-center
still makes contact with the sweet spot and flies farther and
straighter. One challenge for the golf club designer when
maximizing the size of the club head is to maintain a desirable and
effective overall weight of the golf club. For example, if the club
head of a three iron is increased in size and weight, the club may
become more difficult for the average golfer to swing properly.
[0005] In general, the center of gravity of these clubs is moved
toward the bottom and back of the club head. This permits an
average golfer to get the ball up in the air faster and hit the
ball farther. In addition, the moment of inertia of the club head
is increased to minimize the distance and accuracy penalties
associated with off-center hits. In order to move the weight down
and back without increasing the overall weight of the club head,
material or mass is taken from one area of the club head and moved
to another. One solution has been to take material from the face of
the club, creating a thin club face. Examples of this type of
arrangement can be found in U.S. Pat. Nos. 4,928,972, 5,967,903 and
6,045,456.
[0006] Iron-type clubs, which include wedge clubs, are typically
made by investment casting, machining or forging. Forged club heads
are coveted by the higher skilled amateur golfers and professionals
for its superior playing characteristics. On the other hand,
forgeable alloys are malleable and typically have low yield
strengths. For forged clubs, the face of the club cannot heretofore
be made thin, because of this drawback.
[0007] Commercially available forged iron-type clubs are typically
the muscle back type, such as the Titleist.RTM. Forged 670, 680 and
690 series, Mizuno's MP-33 irons and Kenneth Smith's Royal Signet
clubs. The Royal Signet.RTM. muscle back clubs concentrate the club
weight near the center sweet spot, thereby reducing its moment of
inertia. Forged cavity back iron-type clubs are also available, as
midsize clubs with relatively thicker hitting face, such as the
Titleist.RTM. 690-CB, the Hogan Apex Edge Pro or the Royal
Signet.RTM. Titanium. The Hogan Apex Edge Pro irons are
single-piece clubs forged from carbon steel, but the Hogan CFT
clubs have a stamped titanium face in a cast body. The Royal
Signet.RTM. Titanium clubs are cast stainless steel clubs with a
forged titanium full face insert for additional strength.
[0008] Hence, a need still exists for improved forged iron-type
golf clubs.
SUMMARY OF THE INVENTION
[0009] Hence, the invention is directed to forged golf clubs.
[0010] The present invention is directed to golf clubs wherein the
entire club head is forged from metal ingot.
[0011] The present invention is also directed to forged iron-type
golf clubs.
[0012] The present invention is further directed to oversize forged
iron-type clubs.
[0013] The invention is also directed to an iron-type golf club
comprising a club head having a hosel, a front and a back, wherein
the back comprises a cavity defined by a perimeter member and the
front has a hitting zone located opposite to and coinciding with
the cavity. The club head is forged from a malleable metal, such as
stainless steel, and then preferably annealed. The cavity and the
substantially flat front face form a hitting zone having a first
portion and a thicker reinforced portion. The reinforced portion is
preferably located below the first portion and may have one or more
depressions defined therein. The thickness of the reinforced
portion is about 1.2 times to about 3 times higher than the
thickness of the first portion.
[0014] The first portion occupies from about 50% to about 90% of
the total area of the hitting zone, and more preferably from about
60% to about 80% of the total area of the hitting zone. The
perimeter member is preferably thicker on the bottom of the club
head than on the top.
[0015] The present invention is also directed to an iron-type golf
club comprising a club head made from single-piece or
multiple-piece forged stainless steel. The club head comprises a
hosel, a front and a back defining a cavity, and the front
comprises a hitting zone located opposite to the cavity and is
defined by the cavity area. The cavity has a volume equal to or
greater than about 10 cc. A set of inventive irons has cavity
volumes defined as greater than or equal to curve A in FIG. 11.
More preferably the cavity volume through a set is greater than or
equal to curve B in FIG. 11. Preferably, the forged stainless steel
is annealed after forging.
[0016] The present invention is further directed to an iron-type
golf club comprising a club head made from forged metal, said club
head comprises a hosel, a front and a back defining a cavity,
wherein the front comprises a hitting zone located opposite to and
coinciding with the cavity and wherein the hitting zone has an area
equal to or greater than about 2.25 inch.sup.2 and the cavity has a
volume equal to or greater than about 9 cc. A preferred set of such
irons has an average hitting zone equal to or greater than about
2.25 inch.sup.2 and average cavity volume equal to or greater than
about 9 cc. More preferably, the hitting zone is equal to or
greater than about 2.4 inch.sup.2 and average cavity volume equal
to or greater than about 12 cc.
[0017] The present invention is further directed to an iron-type
golf club comprising a club head made from forged metal, said club
head comprises a front face and a back defining a cavity, wherein
the front face comprises a hitting zone opposite to the cavity and
the hitting zone has a minimum thickness less than about 0.2 inch
for the set. More preferably, the thickness is less than about 0.13
inch for clubs having loft angles (LA) less than about
30.degree..
[0018] The present invention is further directed to an iron-type
golf club comprising a club head made from forged metal, said club
head comprises a hosel, a front and a back defining a cavity,
wherein the front comprises a hitting zone located opposite to and
coinciding with the cavity and wherein the hitting zone has an
aspect ratio (AR) defined by the following equation:
AR.gtoreq.-((1/4.5).times.LA)+25,
[0019] wherein the aspect ratio is defined as the area of the
hitting zone divided by its minimum thickness.
[0020] The malleable or forged metal is preferably stainless steel
having yield strength of less than or equal to 90,000 psi and over
about 13% in elongation. More preferably, the material has yield
strength of less than about 85,000 psi and ultimate elongation of
about 15% to about 21%. The forged metal preferably contains more
than 10% chromium (Cr).
[0021] The iron-type golf club head can be any of the number 1-9
irons, the pitching wedge, the sand wedge and the gap wedge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] In the accompanying drawings, which form a part of the
specification and are to be read in conjunction therewith and in
which like reference numerals are used to indicate like parts in
the various views:
[0023] FIG. 1 is a front view of a club head in accordance with an
embodiment of the present invention, with the grooves omitted for
clarity;
[0024] FIG. 2 is a back view of the club head of FIG. 1;
[0025] FIG. 3 is an isometric back view of the club head of FIG.
1;
[0026] FIG. 4 is a top view of the club head of FIG. 1;
[0027] FIG. 5 is a sole view of the club head of FIG. 1;
[0028] FIG. 6 is a heel view of the club head of FIG. 1;
[0029] FIG. 7 is a toe view of the club head of FIG. 1;
[0030] FIG. 8 is an isometric back view of a club head in
accordance with another embodiment of the present invention;
[0031] FIGS. 9(a) and 9(b) are magnified photographs of the
microstructure of a forged material suitable for use in the club
heads of the present invention;
[0032] FIGS. 10(a) and 10(b) are magnified photographs of the
microstructure of the forged material of FIGS. 9(a) and 9(b) after
annealing;
[0033] FIG. 11 is a graph showing the cavity volume of the club
heads in accordance with the present invention;
[0034] FIG. 12 is a graph showing the areas of the hitting zones of
the club heads in accordance with the present invention;
[0035] FIG. 13 is a graph showing the exemplary minimum thickness
of the hitting zones of the club heads in accordance with the
present invention;
[0036] FIG. 14 is a graph showing the aspect ratios between the
areas of the hitting zones of FIG. 12 and the minimum thickness of
FIG. 13; and
[0037] FIG. 15 is a cross-sectional view of the club of FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Club head 10 in accordance with an embodiment of the present
invention is illustrated in FIGS. 1-7. Club head 10 comprises front
12, back 14, top 16, sole 18, heel 20, toe 22 and hosel 24. The
club head is a single-piece forging, i.e., it is forged from a
single ingot and does not include a face insert, or it is formed
from a stainless steel body and stainless steel insert. The body is
forged and the face insert is forged or stamped. A shaft (not
shown) is connected to the club head at hosel 24 and a grip (not
shown) is provided at the top end of the shaft. The grooves on the
front 12 are omitted from the figures for clarity. Front 12
comprises hitting zone 26, which preferably is defined by the rear
cavity area and is located opposite to top portion 28 and
reinforced portion 30 as best illustrated in FIGS. 2 and 3. Club
head 10 is a "cavity back" club, i.e., a substantial portion of the
mass of the club head is positioned on the back side around
perimeter 32 of the club head. As explained further below, the
cavity back design provides the club with larger rotational moments
of inertia to resist the club's tendency to rotate caused by
off-center hits. Inside perimeter 32, top portion 28 is the
thinnest member of hitting zone 26. The minimum thickness of front
12 is in top portion 28. Reinforced portion 30 is thicker than top
portion 28 to provide some structural support to the hitting face.
Taken together, top portion 28 and reinforced portion 30 resemble a
traditional "muscle-back" forged club. Club head 10 also has a
distinctive appearance of having a muscle-back within a cavity
back. Reinforced portion 30 may have depressions 34 to provide the
club with more distinctiveness.
[0039] Additionally, the mass distribution within perimeter 32 is
biased toward sole 18, so that the center of gravity of club head
10 is both behind and below the geometric center of the face. The
geometric center can be defined as the intersection of a vertical
centerline and a horizontal centerline of front 12, or it can be
defined as the midpoint of the grooves. As best illustrated in
FIGS. 3, 4 and 7, the thickness at the top of perimeter 32 is
substantially thinner than the thickness at the bottom of perimeter
32. When the center of gravity is below and behind the geometric
center of the hitting face, the club can launch the golf ball to
higher trajectory and longer flight distance.
[0040] Another embodiment of the present invention is illustrated
in FIG. 8. This embodiment is substantially similar to the
embodiment of FIGS. 1-7, except that this club head is an
"oversize" club head. As used herein, oversize club head includes,
but is not limited to, club heads that are dimensionally larger
than the traditional club heads, club heads that have larger
"sweet-spots" than traditional club heads, and cavity back club
heads that have a relatively higher cavity volume. Cavity volume is
defined as the volume within a three-dimensional shape bounded by
the surface of the back of hitting zone 26, i.e., the combined
surfaces of portions 28 and 30, the inner surface of perimeter
weight 32 and an imaginary planar or curvilinear plane formed by
outer edge 36 of perimeter 32. Outer edge 36 is best illustrated in
FIG. 7. The club head of FIG. 8 is the oversize version of the club
head of FIGS. 1-7, because of the relative difference in cavity
volumes. This cavity volume difference is best illustrated by the
relative difference in thickness 38 of perimeter 32 shown in FIG. 3
and in FIG. 8. FIG. 15 illustrates a cross-sectional view of this
club showing minimum thickness t.sub.1 of top portion 28 and
thickness t.sub.2 of reinforced portion 30.
[0041] The table below shows the preferred cavity volumes for the
clubs in accordance with the present invention:
1 Inventive Clubs Inventive Oversize Clubs Club Cavity Volume
Cavity Volume Type Loft.degree. (cm.sup.3) Loft.degree. (cm.sup.3)
1 17.5 12.36 2 19.5 11.58 19.0 14.1 3 22.0 11.75 21.5 13.62 4 25.0
10.78 24.0 13.35 5 28.0 10.45 27.0 13.31 6 31.0 10.64 30.0 13.05 7
35.0 8.68 34.0 13.18 8 39.0 8.92 38.0 13.24 9 43.0 9.10 42.0 13.05
PW 47.0 9.09 46.0 13.37 SW 51.0 8.96 50.0 13.66
[0042] The cavity volumes for these two embodiments of club head 10
are plotted in FIG. 11 as a function of the loft angle of the club
head. As depicted in FIGS. 11, 13 and 14, curve A depicts the
characteristics of the inventive clubs and curve B depicts the
characteristics of the inventive oversize clubs. FIG. 11 readily
shows that the cavity volume for the oversize clubs is always
larger than the cavity volume for the other clubs. Furthermore, for
clubs with loft angle (LA) less than about 32.degree., the cavity
volume is greater than about 10 cm.sup.3 (cc). The cavity volume is
at least about 8 cc for all clubs. For the oversize clubs, the
cavity volume is at least about 12 cc for all clubs, and preferably
the cavity volume is greater than about 13 cc. Additionally, as
discussed below, the larger cavity volumes of the inventive
oversize clubs produce the desirable high rotational moment of
inertia.
[0043] In accordance with one aspect of the present invention,
malleable stainless steel is a preferred material for the forging
process. Typically carbon steel had been used for forging due to
its softness. However, because carbon steel rusts, the club head is
chrome plated for protection. Chrome plating is not ductile and
thus subject to cracking. This limits the lie, loft and bending
ability of the club head. Chrome plating also limits the ability of
golf club manufacturers to grind the finished head to customize
weight, shape and/or sole configuration, since the thin chrome
plating would be eliminated.
[0044] Preferred stainless steels have yield strength of less than
about 90,000 psi and over about 13% in elongation. More preferably,
the material has yield strength of less than about 85,000 psi and
ultimate elongation of about 15% to about 21%. Preferred stainless
steels also have a Rockwell Hardness of less than about 25 HRC
(Hardness Rockwell C scale). Suitable stainless steels include the
410 stainless steel, which has the following chemical composition:
86.98% Fe, 11.3% Cr, 0.723% Mn, 0.366% Si, 0.297% Ni, 0.11% C,
0.034% P, 0.033% Cu, 0.03% Mo, 0.02% V, 0.017% S, and 0.01% Al.
Another suitable stainless steel is the 403 stainless steel, which
has the following chemical composition: 86% Fe, 12.3% Cr, max 1%
Mn, max 0.5% Si, max 0.15% C, max 0.04% P and max 0.03% S.
[0045] A forged club head made from 410 stainless steel has a
hardness in the range of about 14.2 to about 17.3 HRC. The forging
process may comprise multiple forging steps, wherein each forging
step is followed by other processing steps such as grinding,
sandblasting, removing flash, and trimming, among others. For
example, the forging process may have a primer forging step
followed by grinding and/or sandblasting before multiple rough
forging steps are carried out. More grinding and sandblasting can
occur before the grooves are cut or stamped and fine forging steps
are performed to finish the forging process.
[0046] In accordance with another aspect of the present invention,
the forged club head is further treated by annealing (heating) to
decrease its hardness to less than about 40 HRC and preferably less
than about 90 HRB, more preferably about 80 HRB. In one embodiment,
the hardness is annealed to between 20-40 HRC for durability. In a
preferred embodiment, the club is made softer for customization and
has a hardness less than about 90 HRB. In one example, the forged
club head is heated to about 1050.degree. C. for about 90 minutes
and then to about 650.degree. C. for about 120 minutes.
[0047] The post-forging heat treatment brings the hardness of the
forged club head to any desired hardness. Advantageously, the
increased hardness resolves the problem of the forged club head
being too hard and being easily customized in loft and lie. The
hardness of the annealed forged material is also advantageously in
the same range as the hardness of the cast materials, e.g., cast
431 stainless steel or cast 8620 carbon steel, used in the high-end
cast clubs, such as Titleist.RTM. DCI irons. The physical
properties of these materials are shown below:
2 Tensile Tensile Strength Strength Material Density Hardness
(Ultimate) (Yield) Elongation 410 SS (forged 7.72 g/cm 24 HRC-77
97,000 psi 70,000 psi 16% & annealed HRB 403 SS (forged (same
as 410 SS) & annealed) 416 SS 7.64 21 HRC 107,000 81,900 20%
(machined) 431 SS (cast) 7.67 20-28 HRC 95,000 60,000 18% S20C
(forged) 7.87 85-95 HRB 80,000 55,000 20% 8620 (cast) 7.75 85-90
HRB 85,000 60,000 20%
[0048] Hence, the present invention resolved the thick hitting face
problem of forged irons by selecting a ductile or malleable
forgeable stainless steel that is better than chrome-plated soft
carbon steel and annealing the forged club head.
[0049] Another advantage realized by the annealing step is that the
crystalline structure of the forged material improved. As
illustrated in FIGS. 9(a) and 9(b), the microstructure of the
forged club head comprises relatively small grain size, and as
shown in FIGS. 10(a) and 10(b) the grain size has significantly
increased. Metals with larger grain size microstructure have higher
ductility. Preferably, the grain size is greater than about 10
.mu.M to about 50 .mu.m. As shown in the above table, the ductility
of annealed and forged 410 SS has elongation properties approaching
that of cast 431 SS. The chemical composition for 431 stainless
steel is 82% Fe, 15-17% Cr, 1.25%-2.5% Ni, max 1% Mn, max 1% Si,
max 0.2% C, max 0.04% P and max 0.03% S.
[0050] Additionally, the bending ability of forged and annealed 410
SS surpassed 17-4 PH SS, another commonly used metal for iron-type
clubs and similar to cast 431 SS. Other suitable materials include,
but are not limited to, forgeable 403 SS, 431 SS, 416 SS, 303 SS,
304 SS, 329 SS, 316 SS, 259 SS, Nitronic 40, Nitronic 50 and
Nitronic 60. Suitable stainless steels have at least 10% Cr. The
forging and annealing processes can readily be adjusted to reach
the desirable hardness, tensile strength and ductility in
accordance with the process described above.
[0051] The inventive iron-type clubs can have a hitting zone
minimum thickness in the same range as the thickness of cast
iron-type clubs. In one embodiment, the thickness of hitting zone
26 can be less than about 0.100 inch. The inventors of the present
invention have produced clubs with a hitting zone as thin as about
0.098 inch for the long irons, i.e., the no. 1, 2 and 3 irons. In
other embodiments, particularly in the two-piece embodiment, i.e.,
a forged body and a forged or stamped insert, the thickness can be
as low as 0.060 inch.
[0052] The minimum thickness of hitting zone 26 can be
characterized in terms of the clubs' aspect ratio, which is the
ratio of hitting zone 26 over its minimum thickness. Referring to
FIG. 2, the area of hitting zone 26 within front 12 is estimated as
the product of the length L of hitting zone 26 and the average
height of hitting zone 26. Two representative heights, H.sub.1 and
H.sub.2, are illustrated. In other words, hitting zone 26 is the
area within front 12 opposite to and coinciding with top portion 28
and reinforced portion 30 of the cavity back. The minimum thickness
t.sub.1 is measured within top portion 28. The defined aspect ratio
covers hitting zone 26, where the area of top portion 28 makes up
from about 50% to about 90%, more preferably from about 60% to
about 80%, of the total area of hitting zone 26. The thickness of
reinforced portion 30 can be about 1.2 times to about 3 times the
thickness of top portion 28. The relative thickness between top
portion 28, t.sub.1, and reinforced portion 30, t.sub.2, is
illustrated in FIG. 15.
3 Inventive Clubs Face Area of Hitting Club Front 12 Zone 26
Thickness Aspect Ratio Type Loft.degree. (inch.sup.2) (inch.sup.2)
(inch) (inch) 1 17.5 4.165 2.548 0.110 23.16 2 19.5 4.185 2.503
0.110 22.75 3 22.0 4.202 2.538 0.110 23.07 4 25.0 4.231 2.373 0.115
20.63 5 28.0 4.216 2.330 0.120 19.42 6 31.0 4.317 2.338 0.125 18.70
7 35.0 4.379 2.240 0.130 17.23 8 39.0 4.545 2.346 0.135 17.38 9
43.0 4.660 2.323 0.140 16.59 PW 47.0 4.755 2.345 0.145 16.17 SW
51.0 4.800 2.277 0.150 15.18
[0053]
4 Inventive Oversize Clubs Face Area of Hitting Club Front 12 Zone
26 Thickness Aspect Ratio Type Loft.degree. (inch.sup.2)
(inch.sup.2) (inch) (inch) 2 19.0 4.258 2.506 0.110 22.78 3 21.5
4.322 2.363 0.110 21.48 4 24.0 4.304 2.421 0.115 21.05 5 27.0 4.383
2.466 0.120 20.55 6 30.0 4.391 2.377 0.125 19.02 7 34.0 4.476 2.377
0.130 18.28 8 38.0 4.644 2.471 0.135 18.30 9 42.0 4.750 2.498 0.140
17.84 PW 46.0 4.864 2.528 0.145 17.43 SW 50.0 4.920 2.535 0.150
16.90
[0054] As used herein, club nos. 1-9, pitching wedge (PW) and sand
wedge (SW) have common accepted descriptions used in the golf club
art. A set of irons typically includes clubs ranging from 3-iron to
PW or 5-iron to PW with other clubs being available for custom
orders. It is also noted that a manufacturer can make different
clubs within a set in different manners, such as cavity back/muscle
back sets. Iron-type clubs may also include a gap wedge. These
clubs can also be described by other variables including, but not
limited to, the loft angle. The areas of hitting zone 26 are
plotted in FIG. 12, the minimum thicknesses of top portion 28 are
plotted in FIG. 13 and the aspect ratios between the areas of
hitting zone 26 and minimum thickness are plotted in FIG. 14. In
FIGS. 12 and 14, Curves A illustrate the areas of hitting zone 26
and the aspect ratios for the inventive clubs and Curves B
illustrate the areas of hitting zone 26 and aspect ratios for the
inventive oversize clubs.
[0055] FIG. 12 illustrates large hitting zones for the inventive
clubs and for the inventive oversize clubs, which are the results
of having large face areas combined with large cavity volumes. FIG.
13 illustrates the thin single-piece stainless steel forged face
having a minimum thickness of less than or equal to about 0.200
inch, and preferably the less than about 0.130 inch for clubs with
LA of less than about 35.degree.. FIG. 14 shows the aspect ratios
(AR) of the clubs of the present invention, and the advantages of
having a large hitting area and a thin face. The AR can be
expressed as
AR.gtoreq.-((1/4.5).times.LA)+25.
[0056] Curve C is the linear line representing this equation in
FIG. 14.
[0057] Rotational moment of inertia ("inertia") in golf clubs is
well known in art, and is fully discussed in many references,
including U.S. Pat. No. 4,420,156, which is incorporated herein by
reference in its entirety. When the inertia is too low, the club
head tends to rotate excessively from off-center hits. Higher
inertia indicates higher rotational mass and less rotation from
off-center hits, thereby allowing off-center hits to fly farther
and closer to the intended path. Inertia is measured about a
vertical axis going through the center of gravity of the club head
(I.sub.yy), and about a horizontal axis about the center of gravity
(c.g.) of the club head (I.sub.xx), as shown in FIG. 1. The
tendency of the club head to rotate around the y-axis through the
c.g. indicates the amount of rotation that an off-center hit away
from the y-axis causes. Similarly, the tendency of the club head to
rotate in the around the x-axis through the c.g. indicates the
amount of rotation that an off-center hit away from the x-axis
through the c.g. causes. Most off-center hits cause a tendency to
rotate around both x and y axes. High I.sub.xx and I.sub.yy reduce
the tendency to rotate and provide more forgiveness to off-center
hits.
[0058] Inertia is also measured about the shaft axis (I.sub.sa),
shown in FIG. 1. First, the face of the club is set in the address
position, then the face is squared and the loft angle and the lie
angle are set before measurements are taken. Any golf ball hit has
a tendency to cause the club head to rotate around the shaft axis.
An off-center hit toward the toe would produce the highest tendency
to rotate about the shaft axis, and an off-center hit toward the
heel causes the lowest. High I.sub.sa reduces the tendency to
rotate and provides more control of the hitting face. High
I.sub.xx, I.sub.yy and I.sub.sa have been achieved in high-end cast
iron-type clubs. This can now be realized in high-end forged
iron-type clubs in accordance with the present invention.
[0059] As discussed above, the hitting zone of the club head can be
as thin as about 0.100 inch for a 2-iron and about 0.150 inch for a
sand wedge (SW). The weight is moved to the perimeter of the club
head, and the sole can be as thick as about 0.540 inch to about
0.780 inch and the top can be as thick as about 0.180 inch to about
0.380 inch, preferably about 0.240 inch to about 0.320 inch.
Exemplary inertias of the inventive clubs calculated by computer
aided design (CAD) are shown below and compared to the inertia of a
traditional forged muscle back (with no perimeter weighting). The
comparative clubs are the Titleist.RTM. 670 Forged Irons.
5 CAD-generated Inventive Oversize Clubs Inventive Clubs
Comparative Clubs Club type 3 6 9 3 6 9 3 6 9 I-xx (kg-mm.sup.2)
52.7 56.5 70.0 50.5 55.7 70.7 47.3 54.6 72.8 I-yy 234.8 244.8 270.3
228.0 240.5 264.7 189.3 202.4 238.9 I-sa 526.6 595.2 662.5 472.2
536.7 608.6 389.4 435.3 488.3 CG-y (mm) 18.6 18.5 18.7 18.3 18.4
18.7 19.6 19.7 19.6 CG-sa 37.8 37.6 37.6 34.8 35.8 36.1 32.1 32.2
31.6 weight (kg) 0.243 0.261 0.283 0.241 0.260 0.282 0.240 0.259
0.281 * data created from CAD files.
[0060] As discussed above, the relative large cavity volumes of the
inventive oversize clubs produce high rotational moments of
inertia, particularly I.sub.sa and I.sub.yy.
[0061] The locations of the center of gravity are also listed
above. GC-y is measure from the ground when the club rests in the
address position; CG-x is measured from the center of the face in
the same position; and CG-sa is measured from the shaft axis in the
same position. The center of gravity is located behind and below
the geometric center of hitting face. The geometric center can be
defined as the midpoint of the grooves or score lines, as stated
above. It is readily apparent that the moments of inertia of the
inventive clubs are higher than the moments of inertia of the
comparative clubs.
[0062] While it is apparent that the illustrative embodiments of
the invention disclosed herein fulfill the objectives stated above,
it is appreciated that numerous modifications and other embodiments
may be devised by those skilled in the art. Therefore, it will be
understood that the appended claims are intended to cover all such
modifications and embodiments, which would come within the spirit
and scope of the present invention.
* * * * *