Iron type golf club head

Provided is an iron type golf club head having an undercut cavity. The iron type golf club head comprises a face portion (2) for hitting a ball; a peripheral edge (2e) of the face portion (2) is provided with a flange portion (7) protruding backward of the head; a rear surface (5) of the face portion (2) is provided with a cavity (C) surrounded by the flange portion (7). The flange portion (7) includes a first flange part (8). The first flange part (8) is provided in its inner surface (8i) side facing to the cavity (C) with a first concave part (10) dented toward the outside of the head so as to form an undercut cavity (c2) extending along the peripheral edge (2e). The cross-section of the first concave part (10) comprises a front wall surface (11) positioned frontward of the head, a rear wall surface (12) positioned backward of the head, and a bottom surface (13) smoothly connecting therebetween, and the cross-section is tapered toward the bottom surface (13). The angle (θ1) formed between the front wall surface (11) and the rear wall surface (12) is not less than 10 degrees and less than 30 degrees, and the bottom surface (13) is formed of a circular arc having a radius (R1) of curvature of not less than 1 mm and less than 2 mm.

TECHNICAL FIELD

The present invention relates to an iron-type golf club head having an undercut cavity.

BACKGROUND ART

The following Patent Documents 1 to 5 disclose iron-type golf club heads. Each of these iron type golf club heads has a face portion with a front surface for hitting a ball. The face portion is provided in its peripheral edge with a flange portion protruding backwardly of the head. The flange portion is formed annularly in a rear surface of the face portion so as to define a cavity (cavity back iron). Since a part of the face portion corresponding to the cavity has a small thickness, the face portion is easy to be bent and produces high rebound performance.

The flange portion may be provided in its inner surface side facing to the cavity with a concave part dented toward the outside of the head. Such concave part forms a so-called undercut cavity. In such a golf club head, the region of the cavity is expanded toward the outside of the head, and a sweet area where the high rebound performance is produced is widened.

PRIOR ART DOCUMENTS

Patent Documents

Patent Document 1: Japanese Patent Application Publication No. 2001-190720Patent Document 2: Japanese Patent Application Publication No. 2005-193069Patent Document 3: Japanese Patent Application Publication No. 2000-288128Patent Document 4: Japanese Patent Application Publication No. H10-234897Patent Document 5: Japanese Patent Application Publication No. H11-178960

SUMMARY OF THE INVENTION

Problem to be Sold by the Invention

In the meantime, there is a problem that the mass of a head increases with increase in the thickness of a flange portion. Especially, if a flange portion having a large thickness in an upper side of the head is formed, the golf club head has an undesirably high center of gravity of the head. Therefore, it is desirable that the thickness of the flange portion, in particular, that in an upper side of the head is made smaller.

In the case of a head whose flange portion has a small thickness, however, it is difficult to form an undercut cavity. For example, if the undercut cavity is manufactured through a lost-wax casting process, molding sand does not fully fill in the inside of the undercut cavity of the wax model. Because of this, there was a problem that it was difficult to form the mold with accuracy.

In view of the circumstances as described above, the present invention was devised, and the primary objective is to provide an iron type golf club head in which it is possible to accurately form an undercut cavity in a flange portion having a small thickness.

Means of Solving the Problems

The present invention is of an iron type golf club head having a face portion with a front surface for hitting a ball, and characterized in thatthe face portion is provided in its peripheral edge with a flange portion protruding backwardly of the head,a rear surface of the face portion is provided with a cavity surrounded by the flange portion,the flange portion includes a first flange part,the first flange part is provided in its inner surface side facing to the cavity with a first concave part dented toward the outside of the head so as to form an undercut cavity extending along the peripheral edge,a cross-section of the first concave part comprises a front wall surface positioned frontward of the head, a rear wall surface positioned backward of the head, and a bottom surface smoothly connecting therebetween, and the cross-section is tapered toward the bottom surface,an angle formed between the front wall surface and the rear wall surface is not less than 10 degrees and less than 30 degrees, andthe bottom surface is formed of a circular arc having a radius of curvature of not less than 1 mm and less than 2 mm.

In the iron type golf club head according to the present invention, the cross-section of the first concave part may have a maximum width of from 2.0 mm to 4.0 mm and a maximum depth of from 1.0 mm to 2.0 mm.

In the iron type golf club head according to the present invention, the first flange part can be formed at least partially in an upper side of the head.

In the iron type golf club head according to the present invention, the first flange part may have a thickness of 5.5 mm to 8.0 mm.

The iron type golf club head according to the present invention can be configured such thatthe flange portion includes a second flange part,the second flange part is provided in its inner surface side facing the cavity with a second concave part dented toward the outside of the head so as to form an undercut cavity extending along the peripheral edge,the cross-section of the second concave part at the deepest part includes a front wall surface positioned frontward of the head, a rear wall surface positioned backward of the head, and abottom surface connecting therebetween, and the cross-section is tapered toward the bottom surface,an angle formed between the front wall surface and the rear wall surface of the second concave part is not less than 10 degrees and not more than 30 degrees, andthe bottom surface of the second concave part has a width of not less than 2 mm.

In the iron type golf club head according to the present invention, the second flange part can be formed at least partially in a bottom side of the head.

Effect of the Invention

The iron type golf club head according to the present invention is provided in the peripheral edge of the face portion with the flange portion protruding backward of the head. The rear surface of the face portion is provided with the cavity surrounded by the flange portion. The flange portion includes the first flange part. The first flange part is provided in the inner surface side facing to the cavity with the first concave part dented toward the outside of the head so as to form the undercut cavity extending along the peripheral edge. Such undercut cavity provides the head having high rebound performance.

The first concave part comprises, in the cross-section thereof, the front wall surface positioned frontward of the head, the rear wall surface positioned backward of the head, and the bottom surface smoothly connecting therebetween, and is tapered toward the bottom surface. The angle between the front wall surface and the rear wall surface is not less than 10 degrees and less than 30 degrees. Further, the bottom surface is formed of a circular arc having radius of curvature of not less than 1 mm. In the first concave part having such cross-section, when the head is manufactured through a lost-wax process, molding sand smoothly comes in to the bottom surface of the first concave part of the wax model, and it becomes possible to form the first concave part with accuracy. Further, since the radius of curvature of the circular arc of the bottom surface of the first concave part is set to less than 2 mm, it becomes possible to form the first concave part having a small width. Thereby, it is possible to reduce the thickness of the flange portion, and the head having a small mass may be provided. Moreover, it is possible to lower the center of gravity of the head while saving a redundant mass. Therefore, the head according to the present invention can be easily provided with high rebound performance and a low center of gravity of the head.

MODE FOR CARRYING OUT THE INVENTION

FIG. 1is a front view showing an iron type golf club head (hereinafter, simply referred to as a “head”)1of the present embodiment in a standard state, andFIG. 2is the rear view thereof.

In this description, the standard state of the head1is a state that the head1is set on a horizontal plane HP at a specified loft angle beta (the loft angle beta is shown inFIG. 3) so that its shaft center line CL is disposed in an arbitrary vertical plane and inclined at a specified lie angle alpha. In this description, unless otherwise noted, the head1is under the standard state.

The lie angle alpha and the loft angle beta of the head1are not particularly limited. Typically, the lie angle is preferably in a range of from 50 to 70 degrees, and the loft angle beta is preferably in a range of from 15 to 70 degrees.

The mass of the head1is not particularly limited. Typically, the mass of the head1is preferably set in a range of from 200 g to 300 g.

As shown inFIG. 1, the head1comprises a face portion2, and a hosel portion3provided on the heel-side thereof. The head1of the present embodiment is made of a metallic material and manufactured through a lost-wax process.

The hosel portion3is formed in a substantially cylindrical form having a shaft inserting hole3einto which a shaft (not shown) is inserted.

The shaft center line of the shaft inserting hole3ecorresponds to the above-mentioned shaft center line CL.

The face portion2comprises a front surface4for hitting a ball, a rear surface5on the opposite side thereof, an outer peripheral surface6between the front surface4and the rear surface5.

The front surface4of the face portion2is, for example, formed of a substantially single flat surface. The front surface4may be provided with an impact area marking M. In the present embodiment, as the impact area marking M, there are provided a plurality of face lines (f) extending in a toe-heel direction. As the impact area marking M, a punch mark may be provided.

The outer peripheral surface6of the face portion2comprises a top surface6aon the upper side of the head, a sole surface6bon the bottom side of the head, and a toe surface6cconnecting therebetween on the toe-side.

In the front surface4of the face portion2, for example, the top surface6aextends from a highest point P1in a toe-side to a lowest point P2in a heel-side.The sole surface6bextends in a region below the top surface6a.The toe surface6cincludes a most toe-side point P3and extends between the top surface6aand the sole surface6b.

InFIG. 3, the section A-A ofFIG. 1is shown. As shown inFIG. 2andFIG. 3, the peripheral edge2eof the face portion2is provided with a flange portion7protruding backward of the head.

The peripheral edge2eof the face portion2is a part of the face portion2on the outer peripheral surface6side. on the other hand, a central part2cof the face portion2is defined as a region including a sweet spot ss of the head1.The sweet spot ss is, as shown inFIG. 3, an intersection point of a normal line N, which is drawn from the center G of gravity of the head to the front surface4, with the front surface4.Since the central part2cof the face portion2is expected to have frequent impacts with a ball, it is preferable that the central part2chas a thickness (ta) of 2.0 to 3.0 mm, for example.

The flange portion7in the present embodiment is formed annularly so as to surround the central part2cof the face portion2. owing to such flange portion7, a cavity c surrounded by the flange portion7is formed in the rear surface5of the face portion2.

The cavity c provides a small thickness to the face portion2. Therefore, when this part hits a golf ball, the face portion2is largely bent, and a long carry distance can be obtained. Further, the flange portion7distributes more mass to the peripheral edge2eof the face portion2.Thereby, the head1of the present embodiment can have a large moment of inertia Ig about a horizontal axis passing the center G of gravity of the head (hereinafter, such moment of inertia may be referred as the “up-down moment of inertia”) so as to obtain stable carry distances, for example.

In the present embodiment, the flange portion7comprises a first flange part8extending along the top surface6aand a second flange part9extending along the sole surface6b.

InFIG. 4, the section x-x ofFIG. 2is shown enlargedly. The first flange part8is provided in its inner surface8iside facing the cavity c with a first concave part10.

The first concave part10dents toward the outside of the head and extends along the peripheral edge2eso as to form an undercut cavity c2as shown inFIG. 2andFIG. 4. The first concave part10is in a groove-like dent. If the head1is viewed from behind in a direction perpendicular to the front surface4, the undercut cavity c2is covered with a cover part8aof the first flange part8and invisible.Therefore, in the head1of the present embodiment, the cavity c includes an open cavity c1not covered with the cover part8aand the undercut cavity c2.

In the face portion2provided with the undercut cavity c2, the region which bends when hitting a ball is further expanded. Thus, the head1of the present embodiment produces high rebound performance. Especially, as the first concave part10reduces the mass on the upper side of the head, the head can be provided with the lowered center G of gravity.

As shown inFIG. 4, the cross-section of the first concave part10comprises a front wall surface11positioned frontward of the head, a rear wall surface12positioned backward of the head and a bottom surface13smoothly connecting therebetween, and is tapered toward the bottom surface13.The angle θ1formed between the rear wall surface12and the front wall surface11of the first concave part10is in a range of from not less than 10 degrees to less than 30 degrees. Moreover, a radius R1of curvature of the bottom surface13of the first concave part10is in a range of from not less than 1 mm to less than 2 mm.

The first concave part10having the above-mentioned cross-section is accurately formed even if the head is manufactured through a lost-wax process.In the lost-wax process, as shown inFIGS. 6 (a) and (b), a wax model30having the same form as the head1is formed. So, the wax model30has the first concave part32.On the surface of the wax model30after immersed in liquid slurry34, molding sand35from which a mold36is made mostly is attached and hardened. Then, the wax model is melted and took out, and the mold36is formed.

As shown inFIG. 6 (a), if the cross-sectional shape of the first concave part32is not desirable, the molding sand35is resisted and cannot smoothly come in to the bottom of the first concave part32of the wax model30.On the other hand, as shown inFIG. 6 (b), if the first concave part32has the improved cross-section as in the present invention, the molding sand35can smoothly come in to the bottom of the first concave part32of the wax model30.Therefore, the mold36having a molding surface substantially same as the outer surface of the wax model30is formed accurately; consequently, the head1can be molded with accuracy.

Since the radius R1of curvature of the circular arc of the bottom surface13of the first concave part10is less than 2 mm, the first concave part10(eventually the undercut cavity c2) having a small width w1is formed. As a result, the first flange part8having a small thickness t1is provided, and the mass of the head, especially the mass on the upper side of the head, is reduced. As a result, the center G of gravity of the head can be lowered, and a surplus mass usable in mass distribution design can be obtained. Therefore, the head of the present embodiment can be provided with high rebound performance and the lowered center of gravity of the head.

If the angle θ1between the rear wall surface12and the front wall surface11of the first concave part10is less than 10 degrees, the molding sand cannot adequately come in to the bottom surface of the first concave part of the wax model. Thus, the undercut cavity c2having a small width cannot be accurately formed. on the other hand, if the angle θ1is not less than 30 degrees, the thickness t1of the first flange part8becomes large. Therefore, the mass on the upper side of the head becomes large, and the lowered center of gravity of the head cannot be achieved. Moreover, the first flange part8cannot achieve sharp and good appearance. Furthermore, if the thickness t1of the first flange part8is large, the appearance configuration of the cover part8apossibly deteriorates.The angle θ1is preferably not less than 15 degrees and not more than 25 degrees.In order to derive such effect more effectively, the front wall surface11and the rear wall surface12are desirably formed in a linear fashion in the above-mentioned cross-section.

Preferably, the front wall surface11is smoothly continued into the rear surface of the central part2cof the face portion2. Thereby, it becomes easy for the molding sand to enter the first concave part of the wax model, and the undercut cavity c2can be accurately formed.

The radius R1of curvature of the bottom surface13of the first concave part10determines a width of an opening of the first concave part10. Thus, if the radius R1of curvature of the bottom surface13is less than 1 mm, the first concave part10(eventually the undercut cavity c2) is hard to be formed accurately through the lost-wax casting process.If the radius R1of curvature is not less than 2 mm, the width w1of the first concave part10(eventually the undercut cavity c2) becomes increased, and accordingly, the thickness t1of the first flange part8becomes increased. This possibly causes increase of the mass of the head and a high gravity center G of the head. Preferably, the radius R1of curvature of the circular arc of the bottom surface13is not less than 1.2 mm and not more than 1.8 mm.

In order to enhance the advantages in the rebound performance and the head mass reduction, it is desirable that the cross-section of the first concave part10has a maximum width w1of from 2.0 to 4.0 mm and a maximum depth D1of from 1.0 mm to 2.0 mm. In the present embodiment, the width w1of the first concave part10is, inFIG. 4, measured in the normal direction to the front surface4. Similarly, inFIG. 4, the depth D1of the first concave part10is measured parallel to the front surface4.

In the first flange part8, it is preferable that the thickness t1is 5.5 to 8.0 mm.If the thickness t1of the first flange part8is less than 5.5 mm, there is a possibility that the strength of the first flange part8deteriorates. If the thickness t1of the first flange part8is over 8.0 mm, there is a possibility that the mass of the head is increased, causing a high gravity center G of the head. Moreover, the first flange part8having sharp appearance cannot be obtained.From these view points, the thickness t1of the first flange part8is more preferably not less than 6.0 mm and not more than 7.5 mm.In this specification, the thickness t1of the first flange part8is a length measured perpendicular to the front surface4from the front surface4to the most rearward position of the first flange part8as shown inFIG. 4.

The length along the outer peripheral surface6of the first concave part10is preferably not less than 10% of the length of the top surface6a.

InFIG. 5, the section Y-Y ofFIG. 2is shown. As shown inFIG. 5, the second flange part9is provided in its inner surface9iside facing to the cavity c with a second concave part19dented toward the outside of the head.As shown inFIG. 2, the second concave part19also extends along the peripheral edge2eso as to form the undercut cavity c2. Similarly to the first concave part10, the second concave part19is also a groove-like dent.

The second flange part9extends in the toe-heel direction along the sole surface6b.As shown inFIG. 3, in comparison with the first flange part8, the second flange part9largely protrudes backward of the head in order to distribute more mass to a bottom side of the head. According to the enlarged second flange part9, the second concave part19has a larger cross-sectional area than the first concave part10. Thus, the mass of the second flange part9can be distributed to further lower and more rear position.

Generally, forming a second concave part19having a large cross-sectional area is comparatively easy.However, if the width is gradually altered toward the deepest portion20, like the widths w4, w3and w2in the second concave part19of the present embodiment, then accurately forming the deepest portion20is as difficult as forming the first concave part10.

In the present embodiment, the cross-section of the deepest portion20of the second concave part19comprises a front wall surface21positioned frontward of the head, a rear wall surface22positioned backward of the head, and a bottom surface23smoothly connecting therebetween, and is tapered toward the bottom surface23.The angle θ2formed between the rear wall surface22and the front wall surface21of the deepest portion20is set to be not less than 10 degrees and not more than 30 degrees.The radius R2of curvature of the bottom surface23of the deepest portion20is not less than 2 mm.

The deepest portion20of the second concave part19having the above-mentioned cross-sectional shape can be formed accurately through the lost-wax process for the same reason as the first concave part10.Preferably, in the deepest portion20of the second concave part19, the front wall surface21and the rear wall surface22are formed in a linear fashion in the cross-section.

The head1of the present embodiment has the up-down moment of inertia Ig which is preferably not less than 550 g sq·cm, more preferably not less than 600 g sq·cm, and preferably not more than 1050 g sq·cm, more preferably not more than 1000 g sq·cm to suppress an increase of the mass of the head and to lessen variations of the carry distance,

Taking a realizable range into consideration, the height of the center G of gravity of the head is preferably not less than 18 mm, more preferably not less than 18.5 mm, and is preferably not more than 21 mm, more preferably not more than 20.5 mm to achieve desirable back spin when hitting a ball.

While the embodiment of the present invention has been described in detail as above, the present invention is not limited to the specific embodiment described above, and the present invention can be carried out by modifying into various embodiments.

EXAMPLES

In order to confirm the effects of the present invention, iron type golf club heads based on specifications shown in Table 1 were tested. Each of the heads had the same configuration except for parameters shown in Table 1.

Main Common Specifications of Each Head Were as Follows.

Lie angle alpha: 61 degreesLoft angle beta: 24 degreesMaterial of head: stainless steelArea of face: 36.0 sq·cmThickness (ta) of most thin part of face portion: 2.27 mmThickness (tb) of face portion in front wall surface part of first concave part: 2.30 mmLength along outer peripheral surface of first concave part/Length of top surface: 100%Manufacturing method head: lost-wax casting process
Test Method Was As Follows.
<Height of Center of Gravity of Head>

The height of the center of gravity of the head, which is a vertical height measured in the standard state from the horizontal plane HP to the center of gravity of the head, was measured. In the results, the smaller value is better.

According to the “Procedure for Measuring the velocity Ratio of a club Head for conformance to Rule 4-1e, Revision 2 (Feb. 8, 1999), United states Golf Association.”, the restitution coefficient was measured. The measuring points were five points: a sweet spot and points 10 mm away from the sweet spot toward the toe-side, the heel-side, the head-upper-side, and the head-bottom-side, respectively; and the average value for the five points was obtained. It is better for the value to approach the upper limit, 0.83, regulated by the golf rules, without exceeding 0.83.

By the naked eyes of a tester, forming accuracy of the first concave part of the head has been checked. If the first concave part was formed according to design values, it was evaluated as “good”. Anything else (metal flew into the first concave part) was evaluated as “defective”. In the wax model, the entire head was formed as one piece.

<Appearance Performance of First Flange Part>

By the naked eyes of the tester, appearance performance of the cover part of the first flange part was checked. If the thickness t2of the cover part was small and the tip was too sharp, it was evaluated as being “defective”. If the thickness t2of the cover part was secured and the tip had a similar form to that shown inFIG. 4, it was evaluated as being “good”.Incidentally, clubs having first flange parts having various shapes were made, and it was found that the appearance of the cover part can be evaluated as being “good” or “defective”, taking 1.7 mm as the criteria for the thickness of the cover part.

The test results and the like are shown in Table 1.

From the test results, it can be confirmed that the heads as Embodiments were accurately manufactured as compared with the comparative examples. Further, it was confirmed that the heads as Embodiments were significantly improved in the height of the center of gravity of the head, the rebound performance and the moment of inertia.

DESCRIPTION OF THE SIGNS