Shaft for golf club with overlapped joint   

TECHNICAL FIELD

The present invention relates, in general, to shafts for golf clubs having overlapped joints and, more particularly, to a shaft for a golf club having overlapped joints, which provide effects of increasing the distance that a golf ball is driven and of preventing the shaft of the golf club from being momentarily twisted when impact energy is applied from the golf club head to the golf ball.

BACKGROUND ART

Generally, a shaft for a golf club is manufactured through an inner layer forming step of winding a double-layered sheet, which has bias-angled grains and determines the basic strength and weight of the shaft of the golf club, around the circumferential outer surface of a mandrel, a step of forming a triangular subsidiary sheet on the circumferential outer surface of the inner layer to increase the thickness and strength of a tip part of the shaft, a middle layer forming step of winding one or two sheets having straight grains around the inner layer and the triangular subsidiary sheet, a step of forming an outer layer around the circumferential outer surface of the middle layer in the same manner as that of the middle layer forming step, and a step of winding heat-shrink tape around the circumferential outer surface of the outer layer, baking it using a heat treatment furnace, and removing the mandrel.

In the case of the conventional method, because one kind of sheet having constant strength and elasticity is used in each layer, and constant tonnage is applied thereto, when the golf club, which is manufactured by coupling a club head to the tip part and by coupling a handle, that is, a grip, to a butt part of the shaft, strikes a golf ball, a single kick point is formed, in other words, the shaft is bent and elastically returned to its original state only at a single point. Therefore, to increase the distance that the golf ball is driven and the directional controllability, high strength, high elasticity and high tonnage of carbon fiber prepreg, which is very expensive, must be used to form each layer. This induces a problem of an increase of the cost of manufacturing the shaft.

If relatively low strength, elasticity and tonnage of carbon fiber prepreg is used to reduce the manufacturing cost, the restoring force, that is, the elasticity, for increasing the distance that a golf ball is driven is unsatisfactory, and twist resistance is not ensured. Furthermore, in the conventional arts, typically, several sets of sheets are used to increase the twist resistance of the shaft. However, this causes a problem of an increase in the weight of the shaft.

Meanwhile, as representative examples of conventional techniques pertaining to the present invention, there are techniques, which were proposed in Korean Patent Registration No. 10-0654365, entitled “REINFORCING SHEET STRUCTURE FOR GOLF SHAFT”, in Korean Patent Registration No. 10-0404713, entitled “METHOD OF BRAID FIBER REINFORCEMENT GOLF SHAFT USING IMPROVEMENT OF CARBON FIBER REINFORCEMENT GOLF SHAFT”, and in Japanese Patent Laid-open Publication No. 2005-152613, entitled “GOLF CLUB SHAFT”. These conventional techniques are regarded as being included in the specification of the present invention.

Particularly, in Japanese Patent Laid-open Publication No. 2005-152613, entitled “GOLF CLUB SHAFT”, the shaft is constructed such that maximum bending rigidity points are formed at several positions and reduced bending rigidity regions are formed between the maximum bending rigidity points. Thus, the shaft bends consistently along the entire length of the shaft, and the head speed of the golf club is increased, thus increasing the distance that a golf ball is driven. To achieve the above-mentioned purpose, several sheets of prepreg having straight grains are arranged in the longitudinal direction of the shaft. However, this technique is constructed such that the prepreg sheets merely contact each other, and do not form overlapped joints.

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a shaft for a golf club which is constructed such that overlapped joints are formed therein, thus providing effects of increasing the distance that a golf ball is driven, and of preventing the shaft of the golf club from being momentarily twisted when impact energy is applied from the golf club head to the golf ball.

In order to accomplish the above object, the present invention provides a shaft for a golf club having an overlapped joint, including an inner layer provided at an innermost position, a middle layer laminated around a circumferential outer surface of the inner layer, and an outer layer laminated around a circumferential outer surface of the middle layer, wherein the middle layer comprises a plurality of middle layer sheets arranged in a longitudinal direction of the golf shaft such that the middle layer sheets partially overlap each other to form an overlapped joint.

Preferably, a joint protrusion may be formed on a circumferential outer surface of the shaft of the golf club by the overlapped joint.

Furthermore, each of the middle layer sheets may differ from an adjacent middle layer sheet in one or more of strength, elasticity and tonnage applied thereto.

In addition, the overlapped joint may be formed in a direction perpendicular to the longitudinal direction of the golf shaft.

As well, the overlapped joint may be formed in a direction inclined with respect to the longitudinal direction of the golf shaft.

The middle layer may include a first middle layer having an overlapped joint inclined upwards with respect to the longitudinal direction of the golf shaft, and a second middle layer having an overlapped joint inclined downwards with respect to the longitudinal direction of the golf shaft.

The inner layer may be formed by laminating double-layered sheets, each of which has grains angled at a predetermined bias.

Preferably, a triangular subsidiary sheet, which is made of carbon fiber prepreg, may be wound between the inner layer and the middle layer to reinforce a shaft tip.

Furthermore, the middle layer may be formed by laminating at least one sheet of carbon fiber prepreg having grains oriented in a longitudinal direction.

In addition, heat-shrink tape may be wound around a circumferential outer surface of the outer layer.

The shaft for golf clubs according to the present invention is constructed such that overlapped joints, that is, joint protrusions, are formed therein, thus providing effects of increasing the distance that a golf ball is driven, and of preventing the shaft of the golf club from being momentarily twisted when impact energy is applied from the golf club head to the golf ball.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a shaft for a golf club, according to an embodiment of the present invention;

FIG. 2 is a sectional view taken along the line A-A of FIG. 1;

FIG. 3 is views illustrating a method of manufacturing the shaft for the golf club of FIG. 1;

FIG. 4 is a sectional view showing a middle layer of FIG. 3;

FIG. 5 is views illustrating a method of manufacturing a shaft for a golf club, according to another embodiment of the present invention; and

FIG. 6 is a perspective view of the shaft for the golf club, manufactured by the method of FIG. 5.

1: tip part 2: butt 3: joint protrusion 10: mandrel 110: inner layer 111: triangular subsidiary sheet 120: middle layer 121: first middle layer 122: second middle layer 130: outer layer 131: rectangular subsidiary sheet

Hereinafter, the construction and operation of embodiments of the present invention will be described in detail.

FIG. 1 is a perspective view of a shaft for a golf club, according to an embodiment of the present invention. FIG. 2 is a sectional view taken along the line A-A of FIG. 1. FIG. 3 is views illustrating a method of manufacturing the shaft for the golf club of FIG. 1. FIG. 4 is a sectional view showing a middle layer of FIG. 3.

As shown in FIG. 1, the shaft for the golf club according to the embodiment of the present invention includes a shaft tip 1, which is provided on the upper end of the shaft for coupling a club head thereto, and a butt 2, which is provided on the lower end of the shaft for coupling a grip, which is a handle, thereto. Furthermore, four joint protrusions 3 are formed on the shaft such that kick points can be formed at three positions P1, P2 and P3. A method of forming the joint protrusions 3 will be explained with reference to FIG. 3.

A mandrel 10 is a mold used to manufacture the shaft for the golf club.

All of an inner layer 110, middle layers 120 and an outer layer 130, which will be described below, are made of carbon fiber prepreg.

The inner layer 110 is a double-layered sheet, each layer of which has grains oriented at predetermined bias angles, for example, 30°, 35°, 40°, 45°, etc., and the layers of which overlap each other such that the grains thereof cross, thus forming an X shape. The inner layer 110 is formed by winding one or more double-layered sheets around the mandrel, and determines the flex and the weight of the shaft.

A triangular subsidiary sheet 111, which has straight grains oriented in the longitudinal direction of the golf shaft, is wound around the circumferential outer surface of the inner layer 110 to enhance the strength, elasticity and durability of the shaft tip 1 and to set the thickness of the shaft such that it is suitable for the size of an insert coupling part of the club head.

Here, each grain of the triangular subsidiary sheet 111 may be oriented at an angle perpendicular to the shaft or at other various angles, as well as at a longitudinal angle.

In this embodiment, the middle layer 120 comprises a first middle layer 121 and a second middle layer 122. Depending on the weight and flex of the shaft, or depending on the intended purpose, for example, depending on whether the user is a man or a woman, one or more middle layers 120 are used.

Furthermore, in this embodiment, to form the first middle layer 121, five middle layer pieces s1, s2, s3, s4 and s5 are arranged in the longitudinal direction of the golf shaft such that the parts thereof overlap each other to form four overlapped joints j1, j2, j3 and j4.

Each of the middle layer pieces s1, s2, s3, s4 and s5, which constitute the first middle layer 121, is made of material having straight grains oriented at a longitudinal angle. The middle layer pieces s1, s2, s3, s4 and s5 differ from each other in strength, elasticity and tonnage. Furthermore, as shown in FIG. 4, the middle layer pieces s1, s2, s3, s4 and s5 partially overlap each other, so that the overlapping parts form the respective overlapped joints j1, j2, j3 and j4. The overlapped joints j1, j2, j3 and j4 form respective joint protrusions 3 of the golf shaft, which is the final product.

The second middle layer 122 is manufactured through the same process as that of the first middle layer 121.

The outer layer 130 is wound around the circumferential outer surface of the middle layer 120 and is made of one kind of material, which has grains oriented at an angle parallel to the longitudinal direction of the golf shaft and has strength, elasticity and tonnage appropriate for preventing the overlapped joints j1, j2, j3 and j4 of the middle layer 120 from being separated from each other when executing a golf swing and to ensure sufficient durability of the golf shaft. The outer layer 130 comprises one or more sheets.

A rectangular subsidiary sheet 131 is wound around the circumferential outer surface of the outer layer 130 to enhance the strength, elasticity and durability of the shaft and to set the thickness of the shaft such that it is suitable for the size of the insert coupling part of the club head, in the same manner as that of the triangular subsidiary sheet 111. The grains of the rectangular subsidiary sheet 131 may be oriented at various angles, for example, at an angle parallel to or perpendicular to the longitudinal direction of the golf shaft.

Thereafter, processes of winding heat-shrink tape, conducting thermal treatment, and removing the mandrel are conducted, in the same manner as in the conventional art.

FIG. 5 is views illustrating a method of manufacturing a shaft for a golf club, according to another embodiment of the present invention. FIG. 6 is a perspective view of the shaft for the golf club manufactured by the method of FIG. 5.

The manufacturing process of this embodiment remains the same as that of FIG. 3, excluding the middle layer 120.

In this embodiment, middle layer sheets s1, s2, s3, s4 and s5 are cut at inclined angles such that the inclined ends thereof have widths r1, r2, r3 and r4. Thereafter, the middle layer sheets s1, s2, s3, s4 and s5 are partially overlapped with each other such that overlapped joints j1, j2, j3 and j4 are formed.

Preferably, the direction in which the ends of middle layer sheets of a first middle layer 121 are inclined is opposite that of the second middle layer 122, thus further enhancing the durability of the golf shaft.

In the case where the golf shaft is manufactured through this process, joint protrusions 3 having widths r1, r2, r3 and r4 are formed, as shown in FIG. 6. In other words, the width of each joint protrusion 3 of FIG. 6 is markedly greater than that of the overlapped joint 3 of FIG. 1.

As such, in the case where the overlapped joints are formed in the middle layer or the joint protrusions are formed in the shaft by the overlapped joints, the following effects are achieved.

1) Multiple kick points (multiple joints) are formed in the shaft by the joint protrusions, so that the inertial moment is increased such that almost all of the swing energy of a golfer can be converted to kinetic energy, thus increasing the distance that a golf ball is driven.

2) Because the overlapped joints, that is, the joint protrusions, are relatively thick compared to other portions, they serve to prevent the shaft from momentarily twisting, in other words, to restrain the shaft when impact energy is applied from the golf club head to the golf ball. This restraining effect reduces the momentary twisting force when impact energy is applied, such that the golf club head can strike the golf ball in a state of being parallel therewith, thus increasing the size of the area of the club head that can be used to strike the golf ball, and enhancing the directional controllability. Furthermore, in the golf game, which is a mental sport, the present invention makes it possible for the golfer to maintain psychological stability.

3) The clutch effect of the multiple kick points (multiple joints) and the joint protrusions increases the momentary restoring force of the shaft, thus preventing the loss of swing energy. Furthermore, the clutch effect generates energy over a wide area and disperses impact, thus reducing the impact applied to the golfer, thereby preventing the golfer from being injured.

Although the preferred embodiments of the present invention have has been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible. Furthermore, the modifications, additions and substitutions must be regarded as falling within the bounds of the present invention, so long as they do not depart from the scope and spirit of the invention.

As described above, the present invention provides effects of increasing the distance that a golf ball struck by a golf club is driven, and of preventing a shaft of the golf club from momentarily twisting.