Patent Application
20090069109
This application claims priority on Patent Application No. 2007-236779 filed in JAPAN on Sep. 12, 2007, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a golf club shaft.
2. Description of the Related Art
As a golf club shaft, so-called steel and carbon shafts have been known. The carbon shaft is constituted by CFRP (carbon fiber reinforced plastic).
Most of the carbon shafts are manufactured by a so-called sheet winding process. In the sheet winding process, a prepreg sheet including a fiber and a matrix resin is used. In the process, a sheet formed of prepreg is wound around a metallic core member and the matrix resin is then cured by heating, and the core member is pulled out after the curing. By the process, there is formed a shaft which is obtained by winding and curing the prepreg sheet.
Japanese Laid-Open Patent Publication No. 2003-24489 has disclosed a carbon shaft in which a straight layer, an angle layer and a hoop layer are provided and a tensile modulus of elasticity of a fiber or the like is specified. Referring to the shaft, it is possible to achieve a lightweight property and a high strength. US Patent Application No. US2003/022728 A1 corresponds to the Japanese Laid-Open Patent Publication No. 2003-24489.
In a carbon shaft, a partial layer (a partial reinforced layer) can be provided partially in a longitudinal direction of the shaft in addition to a full length layer provided wholly in the longitudinal direction of the shaft. The partial layer can be provided in a tip portion of the shaft, a rear end of the shaft, a central portion of the shaft and the like, for example. It is possible to select a position, a length and a thickness of the partial layer and the like. By the partial layer, it is possible to enhance a degree of freedom of design in the shaft. The enhancement in the degree of freedom of design can contribute to an increase in a flight distance and an improvement in a hitting feeling.
In recent years, there is a tendency that a resilience coefficient of a golf club head is regulated. It has been hard to increase the flight distance depending on the characteristic of the head. For this reason, it has been required to increase the flight distance depending on the characteristic of the shaft. A lightweight shaft contributes to the increase in the flight distance. Since the partial layer can selectively reinforce a portion having a low strength, it is useful for a reduction in the weight of the shaft.
However, it has been found that a durability of the shaft is apt to be deteriorated due to the presence of the partial layer. Furthermore, it has been found that the durability of the shaft is particularly apt to be deteriorated if a large number of partial layers are provided.
It is an object of the present invention to provide a golf club shaft which has a partial layer and can enhance a durability.
A shaft according to the present invention is obtained by winding and curing a prepreg sheet including a matrix resin and a fiber. The sheet includes a full length sheet provided wholly in a longitudinal direction of the shaft and a partial sheet provided partially in the longitudinal direction of the shaft. The number of the full length sheets is equal to or greater than two. The number of the partial sheets is equal to or greater than four. When four sections obtained by dividing the shaft into four equal parts in the longitudinal direction are set to be first, second, third and fourth sections from a tip end side in order, the total number of end(s) of the partial sheets positioned in the first section is represented as N1, the total number of end(s) of the partial sheets positioned in the second section is represented as N2, the total number of end(s) of the partial sheets positioned in the third section is represented as N3, and the total number of end(s) of the partial sheets positioned in the fourth section is represented as N4, all of N1, N2, N3 and N4 are equal to or greater than one.
It is preferable that a difference (Nx−Nn) should be equal to or smaller than four when a maximum value of N1, N2, N3 and N4 is represented as Nx and a minimum value of N1, N2, N3 and N4 is represented as Nn.
It is preferable that a ratio (Px/Pn) should be equal to or lower than 1.5 when the total number of the sheets belonging to the first section is represented as P1, the total number of the sheets belonging to the second section is represented as P2, the total number of the sheets belonging to the third section is represented as P3, the total number of the sheets belonging to the fourth section is represented as P4, a maximum value of P1, P2, P3 and P4 is represented as Px, and a minimum value of P1, P2, P3 and P4 is represented as Pn.
A golf club according to the present invention comprises a head, a grip and a golf club shaft. The golf club shaft is obtained by winding and curing a prepreg sheet including a matrix resin and a fiber. The sheet includes a full length sheet provided wholly in a longitudinal direction of the shaft and a partial sheet provided partially in the longitudinal direction of the shaft. The number of the full length sheets is equal to or greater than two. The number of the partial sheets is equal to or greater than four. When four sections obtained by dividing the shaft into four equal parts in the longitudinal direction are set to be first, second, third and fourth sections from a tip end side in order, the total number of end(s) of the partial sheets positioned in the first section is represented as N1, the total number of end(s) of the partial sheets positioned in the second section is represented as N2, the total number of end(s) of the partial sheets positioned in the third section is represented as N3, and the total number of end(s) of the partial sheets positioned in the fourth section is represented as N4, all of N1, N2, N3 and N4 are equal to or greater than one.
In the golf club shaft according to the present invention in which the partial sheet is distributed in the longitudinal direction of the shaft, the end of the partial sheet is distributed in the longitudinal direction of the shaft. In the shaft, a stress acting on the end of the partial sheet is distributed. Therefore, a durability can be enhanced.
The present invention will be described below in detail based on a preferred embodiment with reference to the drawings.
As shown in
The head 4 and the grip 8 are not restricted. Examples of the head 4 include a wood type golf club head, an iron type golf club head, a so-called utility type head, a patter head and the like.
The shaft 6 is a so-called carbon shaft. The shaft 6 is obtained by curing a prepreg sheet. In a typical prepreg sheet, a fiber is oriented in one direction. The prepreg sheet has a fiber and a matrix resin. Typically, the fiber is a carbon fiber. Typically, the matrix resin is a thermosetting resin.
The shaft 6 is manufactured by a so-called sheet winding process. The shaft 6 is obtained by winding and curing a prepreg sheet. The curing can be achieved by heating. A process for manufacturing the shaft 6 includes a heating step. Through the heating step, the matrix resin of the prepreg sheet is cured.
The shaft 6 has a straight layer, an angle layer and a hoop layer. In the developed views of
In the straight layer, an orientation of a fiber is substantially parallel with the axial direction of the shaft. Due to an error made in winding or the like, usually, the orientation of the fiber is not perfectly parallel with the axial direction of the shaft. In the straight layer, an angle Af formed by the orientation of the fiber and the axial direction of the shaft is equal to or greater than approximately −10 degrees and is equal to or smaller than approximately +10 degrees. In the shaft 6, the straight layer is constituted by the sheets a1, a4, a6, a8, a9, a11 and a12. The straight layer has a high correlation with a bending rigidity and a bending strength in the shaft.
The angle layer is provided to enhance a torsional rigidity and a torsional strength in the shaft. The angle layer is constituted by at least two sheets in which orientations of fibers are reverse to each other. The angle layer includes a layer having the angle Af which is equal to or greater than −60 degrees and is equal to or smaller than −30 degrees and a layer having the angle Af which is equal to or greater than 30 degrees and is equal to or smaller than 60 degrees. In the shaft 6, the angle layer is constituted by the sheets a2 and a3.
The hoop layer is provided to enhance a crushing rigidity and a crushing strength in the shaft. The crushing rigidity indicates a rigidity against a force for crushing the shaft inward in a radial direction thereof. The crushing strength indicates a strength against the force for crushing the shaft inward in the radial direction. The crushing strength can also be related to the bending strength. A crushing deformation can be generated interlockingly with a bending deformation. In a lightweight shaft having a small thickness, particularly, an interlocking property is great. By an enhancement in the crushing strength, it is also possible to improve the bending strength.
In the hoop layer, an orientation of a fiber is substantially perpendicular to the axial direction of the shaft. In other words, in the hoop layer, the orientation is substantially parallel with a circumferential direction of the shaft. Due to an error made in winding or the like, usually, the orientation of the fiber is not perfectly perpendicular to the axial direction of the shaft. In the hoop layer, the angle Af is usually 90 degrees ±10 degrees. In the shaft 6, the hoop layer is constituted by the sheets a5, a7 and a10.
In a manufacture of the shaft 6, a cored bar (mandrel) is prepared. The cored bar has a circular section. An external surface of the cored bar is tapered. In an embodiment of
The developed views of
In the present invention, first, second, third and fourth sections are defined. As shown in
As shown in
A plurality of sheets constituting the shaft 6 includes a full length sheet provided wholly in the longitudinal direction of the shaft and a partial sheet provided partially in the longitudinal direction of the shaft. In an embodiment shown in
As shown in
In the present invention, the position of the end in each partial sheet is distributed in the longitudinal direction of the shaft. It was found that a stress concentration on the end of the partial layer can be relaxed and a durability of the shaft can be enhanced by the distribution.
In the present invention, the ends of the partial sheet are distributed into all of the four sections. When the total number of the ends of the partial sheet which are positioned in the first section is represented as N1, the total number of the ends of the partial sheet which are positioned in the second section is represented as N2, the total number of the ends of the partial sheet which are positioned in the third section is represented as N3, and the total number of the ends of the partial sheet which are positioned in the fourth section is represented as N4, all of N1, N2, N3 and N4 are equal to or greater than one.
The end of the partial sheet is positioned on one of sides (the tip end T side) or the other side (the bat end B side) in the longitudinal direction of the shaft. The end of the partial sheet is present in a position excluding the tip end T and the bat end B. For example, in the embodiment shown in
In the case in which the partial sheet takes a triangular shape, any of sides of the triangle is not regarded to be the end of the partial sheet. In the case in which the partial sheet takes the triangular shape, it is regarded to have no end.
The side h1 constituting the end t1 of the partial sheet a1 is inclined to the axial direction of the shaft. By the inclination, the end t1 is distributed in the longitudinal direction of the shaft. By the distribution, a stress concentration can be relaxed. As shown in
In the embodiment shown in
The position of the end of the partial sheet is determined by a middle point of the end. For example, in a partial sheet z1 shown in
It is assumed that the boundary p2 belongs to the first section, the boundary p3 belongs to the second section and the boundary p4 belongs to the third section. Accordingly, in the case in which the middle point of the end is positioned on the boundary p3, for example, the end is assumed to belong to the second section.
When a maximum value of N1, N2, N3 and N4 is represented as Nx and a minimum value of N1, N2, N3 and N4 is represented as Nn, it is preferable that a difference (Nx−Nn) should be equal to or smaller than four. Consequently, the position of the end of the partial sheet is further distributed. Therefore, the durability of the shaft can be enhanced still more. In the embodiment shown in
In the present invention, the total number of the sheets belonging to the respective sections is taken into consideration. The total number of the sheets belonging to the first section is represented as P1, the total number of the sheets belonging to the second section is represented as P2, the total number of the sheets belonging to the third section is represented as P3, and the total number of the sheets belonging to the fourth section is represented as P4.
In order to calculate P1 to P4, the number of the sheets in each of the sections is counted. A method of counting the number of the sheets will be described with reference to
The numbers of all the sheets are counted. The numbers of both the full length sheets and the partial sheets are counted. The number of the sheets is counted irrespective of the shape of the sheet.
The number of the sheets is different from that of plies. In the present application, the number of plies indicates the number of winds. For example, in the sheet a8 of
The P1 to the P4 are obtained by totalizing the numbers of the sheets thus counted every section. For example, in the embodiment shown in
When a maximum value of P1, P2, P3 and P4 is represented as Px and a minimum value of P1, P2, P3 and P4 is represented as Pn, it is preferable that a ratio (Px/Pn) should be equal to or lower than 1.5. Consequently, the number of the sheets is distributed into each section. Therefore, it is possible to enhance the durability of the shaft. In the embodiment shown in
In respect of the durability of the shaft, the number of the full length sheets is preferably equal to or greater than two and is more preferably equal to or greater than three. In respect of a lightweight property and a productivity in the shaft, the number of the full length sheets is preferably equal to or smaller than eight and is more preferably equal to or smaller than six.
In respect of the durability of the shaft, the number of the plies of the full length sheet is preferably equal to or greater than four, is more preferably equal to or greater than six, and is further preferably equal to or greater than eight. In respect of the lightweight property and the productivity in the shaft, the number of the plies of the full length sheet is preferably equal to or smaller than 12 and is more preferably equal to or smaller than 10.
It is preferable that the full length layer constituted by the full length sheet should include a layer having the angle Af which is equal to or greater than −60 degrees and is equal to or smaller than −30 degrees and a layer having the angle Af which is equal to or greater than 30 degrees and is equal to or smaller than 60 degrees. These can enhance a torsional rigidity, a bending rigidity and a crushing rigidity. Furthermore, it is preferable that the full length layer should include a layer having the angle Af which is equal to or greater than −10 degrees and is equal to or smaller than 10 degrees. This layer can enhance the bending rigidity.
In the case in which a large number of partial sheets are provided, a degree of freedom of design can be enhanced. In respect of the degree of freedom of design, the number of the partial sheets is preferably equal to or greater than four, is more preferably equal to or greater than five, is more preferably equal to or greater than six, and is further preferably equal to or greater than seven. In respect of an enhancement in the productivity, the number of the partial sheets is preferably equal to or smaller than 16, is more preferably equal to or smaller than 12, and is further preferably equal to or smaller than 10.
All of N1, N2, N3 and N4 are set to be equal to or greater than one so that the degree of freedom of design is enhanced and the position of the end of the partial sheet is distributed in the longitudinal direction of the shaft. By the distribution, the stress concentration can be relaxed and the durability of the shaft can be enhanced. N1, N2, N3 and N4 have no upper limit. In respect of a suppression in a reduction in the productivity with an increase in the number of the sheets, it is preferable that all of N1, N2, N3 and N4 should be equal to or smaller than four.
If the difference (Nx−Nn) is great, the end of the partial sheet easily concentrates in a specific section. For this reason, the stress concentration is apt to be generated in the same section. In respect to an enhancement in the durability through a relaxation of the stress concentration, the difference (Nx−Nn) is preferably equal to or smaller than four, is more preferably equal to or smaller than three and is further preferably equal to or smaller than two.
If the ratio (Px/Pn) is high, the stress easily concentrates in a section in which the total number of the sheets is Pn. Consequently, the durability is apt to be deteriorated. In respect of the enhancement in the durability through the relaxation of the stress concentration, the ratio (Px/Pn) is preferably equal to or lower than 1.5, is more preferably equal to or lower than 1.4 and is further preferably equal to or lower than 1.35.
When a number Lh of plies constituted by a full length sheet is increased, the sheet width Ws is made greater. If the sheet width Ws is excessively great, winding failures such as wrinkles are easily generated. In this respect, the number Lh of plies is preferably equal to or smaller than four, is more preferably equal to or smaller than three and is further preferably equal to or smaller than two. In respect of an enhancement in a uniformity in the circumferential direction of the shaft, it is preferable that the number Lh of plies should be equal to or greater than one.
When a number Lp of plies constituted by a partial sheet is increased, the sheet width Ws is made greater. If the sheet width Ws is excessively great, winding failures such as wrinkles are easily generated. In this respect, the number Lp of plies is preferably equal to or smaller than four, is more preferably equal to or smaller than three and is further preferably equal to or smaller than two. In respect of an enhancement in a uniformity in the circumferential direction of the shaft, it is preferable that the number Lp of plies should be equal to or greater than one except for a portion constituting an end. The portion constituting an end implies a portion formed by an inclined end to the axial direction of the shaft. For example, in the sheet a6 shown in
In respect of an enhancement in the strength and the productivity, thicknesses of the full length sheet and the partial sheet are preferably equal to or greater than 0.025 mm, are more preferably equal to or greater than 0.058 mm, and are further preferably equal to or greater than 0.083 mm. In respect of a lightweight property, the thicknesses of the full length sheet and the partial sheet are preferably equal to or smaller than 0.150 mm, are more preferably equal to or smaller than 0.145 mm and are further preferably equal to or smaller than 0.136 mm.
In respect of an enhancement in a strength, fiber content rates of the full length sheet and the partial sheet are preferably equal to or higher than 60% by mass, are more preferably equal to or higher than 63% by mass and are further preferably equal to or higher than 70% by mass. If the fiber content rate is excessively high, a content rate of the matrix resin is reduced so that a tacking property of the sheet is deteriorated. Due to the deterioration in the tacking property, the winding failures such as wrinkles are apt to be generated. In this respect, the fiber content rates of the full length sheet and the partial sheet are preferably equal to or lower than 85% by mass, are more preferably equal to or lower than 80% by mass and are further preferably equal to or lower than 75% by mass.
The shape of the full length sheet is not restricted. In the case in which the numbers of the plies in all of the positions in the longitudinal direction of the shaft are set to be equal to each other, the full length sheet takes a trapezoidal shape shown in
The shape of the partial sheet is not restricted. Examples of the shape of the partial sheet include a polygon such as a triangle or a square. In respect of a forming property (a workability in the winding step), it is preferable that the partial sheet should take a square shape.
The partial sheet and the full length sheet have a parallel side h5 which is almost parallel with the longitudinal direction of the shaft (see
An angle a formed by a side constituting the end and the parallel side h5 is shown in
In respect of a strength, a weight of the shaft is preferably equal to or greater than 30 g, is more preferably equal to or greater than 34 g and is further preferably equal to or greater than 38 g. A lightweight shaft can enhance a head speed and a flight distance. In this respect, the weight of the shaft is preferably equal to or smaller than 60 g, is more preferably equal to or smaller than 58 g, and is further preferably equal to or smaller than 56 g.
A specific example of the prepreg sheet which can be used in the present invention is not restricted. The following Table 1 shows an example of a prepreg sheet on the market which can be used in the present invention. The Table 1 shows an item number of the prepreg sheet, an item number of a carbon fiber used in the prepreg sheet, a tensile modulus of elasticity of the carbon fiber, a tensile strength of the carbon fiber, a thickness of the prepreg sheet, and a fiber content rate. The prepreg sheet shown in the Table 1 is manufactured by TORAY INDUSTRIES, INC. or MITSUBISHI RAYON CO., LTD. In the present invention, it is also possible to use a fabric sheet obtained by weaving a fiber in addition to a UD prepreg sheet (a unidirection prepreg sheet). As described in the Table 1, TR1100M, TR1120M and TR3110M manufactured by the MITSUBISHI RAYON CO., LTD. can be used as the fabric sheet, for example. TR1100M, TR1120M and TR3110M manufactured by the MITSUBISHI RAYON CO., LTD. are prepreg sheets in which a plain weave fabric is impregnated with a resin.
In respect of the strength and the elastic modulus, a carbon fiber is preferable for a fiber constituting the prepreg sheet. In respect of the strength, the tensile strength of the fiber constituting the sheet is preferably equal to or greater than 300 kgf/mm2, is more preferably equal to or greater than 400 kgf/mm2, and is further preferably equal to or greater than 500 kgf/mm2. In consideration of physical properties of available carbon fibers, it is preferable that the tensile strength of the fiber should be equal to or smaller than 680 kgf/mm2.
The shaft according to the present invention may have a hoop layer. The hoop layer is formed by a fiber reinforced resin and has an orientation angle of a fiber which is substantially perpendicular to the axis of the shaft. 805S-3 manufactured by the TORAY INDUSTRIES, INC. which is described in the following Table 1 or the like is used as the hoop layer, for example. As compared with other types of the prepreg, 805S-3 has a smaller weight per unit area and a smaller carbon fiber mass per unit area, and a smaller thickness. Since such a thin prepreg can easily be wound while the carbon fiber is bent, it is suitable for the hoop layer.
When the full length L of the shaft is greater, the position of the sheet end is distributed in the longitudinal direction of the shaft more easily. In this respect, the full length L of the shaft is preferably equal to or greater than 35 inches (889 mm), is more preferably equal to or greater than 41 inches (1041 mm), is more preferably equal to or greater than 43 inches (1092 mm), is more preferably equal to or greater than 44 inches (1117 mm), and is particularly preferably equal to or greater than 45 inches (1143 mm). In respect of a maintenance of the strength of the shaft, the full length L of the shaft is preferably equal to or smaller than 52 inches (1321 mm), is more preferably equal to or smaller than 50 inches (1270 mm), and is particularly preferably equal to or smaller than 48 inches (1219 mm).
For the method of manufacturing a shaft according to the present invention, a sheet winding process is preferred. For the matrix resin of the prepreg sheet, it is possible to use a thermosetting resin, a thermoplastic resin and the like other than an epoxy resin in addition to the epoxy resin.
In the case in which the crushing rigidity in the bat portion (rear end) of the shaft is low, a crushing deformation in the radial direction of the shaft is increased in the bat portion. When the crushing deformation is increased, a head speed in hitting is apt to be decreased. In this respect, it is preferable to cause the crushing rigidity in the bat portion to be higher than that in the conventional art. The crushing deformation implies such a deformation that the sectional shape of the shaft is changed from a circle to an almost ellipse.
In respect of an enhancement in the crushing rigidity of the bat portion, a shaft to satisfy the following (A1) is preferred.
(A1) A position placed apart from the tip end T of the shaft by 30 mm is set to be a first position r1, a position placed apart from the bat end B of the shaft by 30 mm is set to be a twelfth position r12, positions for dividing a portion between the first position r1 and the twelfth position r12 into eleven equal parts are set to be a second position r2, a third position r3, a fourth position r4, a fifth position r5, a sixth position r6, a seventh position r7, an eighth position r8, a ninth position r9, a tenth position r10 and an eleventh position r11 from the chip end T side in order,
crushing rigidities EI measured in twelve portions from the first position r1 to the twelfth position r12 are set to be EI (1), EI (2), EI (3), EI (4), EI (5), EI (6), EI (7), EI (8), EI (9), EI (10), EI (11) and EI (12) from the tip end T side in order, points obtained by plotting measured values in the twelve positions in an XY coordinate plane in which a distance (mm) from the tip end T of the measuring position is represented as an X axis and a value (kgf/mm2) of the crushing rigidity EI is represented as a Y axis are set to be T (1), T (2), T (3), T (4), T (5), T (6), T (7), T (8), T (9), T (10), T (11) and T (12) from the tip end T side in order, respectively,
a straight line K passing through the T (7) and the T (12) in the XY coordinate plane is expressed in an equation of [Y=aX+b7],
values (kgf/mm2) of Y-intercepts of straight lines which are parallel with the straight line K and pass through the T (1), T (2), T (3), T (4), T (5), T (6), T (8), T (9), T (10) and T (11) are represented as b1, b2, b3, b4, b5, b6, b8, b9, b10 and b11, respectively, and
when a maximum value of the b7, b8, b9, b10 and b11 is represented as bmax,
a gradient a of the straight line K is equal to or greater than −0.006 and is equal to or smaller than −0.003,
all of the b8, b9, b10 and b11 are greater than b7,
the bmax is b8, b9, b10 or b11, and
(bmax−b7) is equal to or greater than 2 (kgf/mm2) and is equal to or smaller than 12 (kgf/mm2).
In the shaft to satisfy the (A1), a minimum value of the b1, b2, b3, b4, b5, b6, b7, b8, b9, b10 and b11 is more preferably b6 or b7 and is further preferably b7.
In the shaft to satisfy the (A1), it is more preferable that the following expression should be set up.
EI (1)>EI (2)>EI (3)>EI (4)>EI (5)>EI (6)
In the shaft to satisfy the (A1), it is more preferable that the following expression should be set up.
b1>b2>b3>b4>b5>b6
For a shaft which can achieve physical properties of the (A1), a shaft to satisfy the following (B1) is preferred.
(B1) there is provided a partial layer (a partial reinforced layer) which is constituted by a cloth layer including a plain weave fabric or a hoop layer,
the partial layer has an end on the tip end T side which is provided on the bat end B side from the seventh position r7 and the end on the bat end B side which is provided on the tip end T side from the twelfth position r12,
the partial layer is present in at least the ninth position r9, and
a length Lz in the longitudinal direction of the shaft in the partial layer satisfies the following expression (F1).
[(L−60)×(2/11)]≦Lz (F1)
In the expression (F1), L represents a full length (mm) of the shaft.
The method of measuring the crushing rigidity is as follows. A shaft is cut in each position (W/2) at the chip end T side and the bat end B side in the axial direction of the shaft around a measuring point and a ring-shaped specimen having a length W is cut out. The specimen thus cut out is mounted on a pedestal jig and a load N is applied by an indenting jig. The load N is applied in an orthogonal direction to the axial direction of the shaft and a deformation δ (mm) of the specimen through the load N is measured. δ (mm) indicates a displacement of the indenting jig. The load N is uniformly applied in a longitudinal direction of the specimen. A crushing rigidity G is calculated in G=N/(δ×W). In the measuring method according to the present application, N is set to be 5 kgf and W is set to be 10 mm. A compressed surface is formed into a plane for the pedestal jig for mounting the specimen thereon and the indenting jig for applying the load.
The first position r1 to the twelfth position r12 are shown in
Although the advantages of the present invention will be apparent from examples, the present invention should not be construed restrictively based on the description of the examples.
A durability was evaluated. A head and a grip were attached to a shaft to fabricate a golf club. The golf club was attached to “SHOT ROBO III-1” (trade name) manufactured by MIYAMAE CO, LTD. and was caused to repetitively hit a golf ball at a head speed of 54 m/s. The number of hitting operations was confirmed until the shaft was broken. The number of the hitting operations was indexed with that in a comparative example 1 set to be 100. The index is shown as a “durability test result (index)” in the following Tables 2 to 8. When the index is greater, the durability is more excellent.
In the same manner as the shaft 6 according to the embodiment, there was obtained a shaft shown in the developed view of
A shaft according to an example 2 was obtained in the same manner as in the example 1 except for the developed view of the shaft (the view showing a structure of a sheet) illustrated in
A shaft according to an example 3 was obtained in the same manner as in the example 1 except for the developed view of the shaft (the view showing a structure of a sheet) illustrated in
A shaft according to an example 4 was obtained in the same manner as in the example 1 except for the developed view of the shaft (the view showing a structure of a sheet) illustrated in
A shaft according to an example 5 was obtained in the same manner as in the example 1 except for the developed view of the shaft (the view showing a structure of a sheet) illustrated in
A shaft according to an example 6 was obtained in the same manner as in the example 1 except for the developed view of the shaft (the view showing a structure of a sheet) illustrated in
A shaft according to a comparative example 1 was obtained in the same manner as in the example 1 except for the developed view of the shaft (the view showing a structure of a sheet) illustrated in
A difference between the examples 1 and 2 includes a length of a sixth sheet from an inside of the shaft and a length of a twelfth sheet from the inside of the shaft. A difference between the examples 1 and 3 includes the length of the sixth sheet from the inside of the shaft, a length of a tenth sheet from the inside of the shaft, and the length of the twelfth sheet from the inside of the shaft. A difference between the examples 1 and 4 includes the length of the sixth sheet from the inside of the shaft and the length of the twelfth sheet from the inside of the shaft. A difference between the examples 1 and 5 includes the length of the sixth sheet from the inside of the shaft and the length of the twelfth sheet from the inside of the shaft. A difference between the examples 1 and 6 includes the length of the sixth sheet from the inside of the shaft, the length of the tenth sheet from the inside of the shaft, and the length of the twelfth sheet from the inside of the shaft. A difference between the example 1 and the comparative example 1 includes a length of a seventh sheet from the inside of the shaft and a length of a ninth sheet from the inside of the shaft.
In the example 2, particularly, the durability is lower than that in the example 1 because the difference (Nx−Nn) is two. In the example 3, particularly, the durability is slightly lower than that in the example 2 because the ratio (Px/Pn) is high. In the example 4, particularly, the durability is slightly lower than that in the example 2 because the difference (Nx−Nn) is three. In the example 5, the position in the longitudinal direction of the shaft of the end of the sheet e6 is coincident with that in the longitudinal direction of the shaft of the end of the sheet e9 and a stress concentration is apt to be generated in the same positions. For this reason, the durability in the example 5 is slightly lower than that in the example 4. In the example 6, the durability is slightly lower than that in the example 4 because the difference (Nx−Nn) is four.
As shown in the Tables 2 to 8, each of the examples has a higher evaluation than that in the comparative example. In the comparative example 1, particularly, the durability is deteriorated because N2 is zero. From the result of the evaluation, the advantages of the present invention are apparent.
The present invention can be applied to all golf club shafts, for example, a shaft for a wood type golf club, a shaft for an iron type golf club and a shaft for a patter.
The above description is only illustrative and various changes can be made without departing from the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-236779 | Sep 2007 | JP | national |
