Patent Publication Number: US-10758791-B2

Title: Iron-type golf club head

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a golf club head, more particularly to an iron-type golf club whose club face is improved in the rebound performance in a sole-side region of the club face. 
     The following patent documents 1-3 disclose iron-type golf club heads comprising a face plate forming a club face for hitting a ball, and a head main body supporting a peripheral part of the face plate. Accordingly, these iron-type golf club heads are constructed such that the central part of the club face can easily deflect and exhibits high rebound performance. On the other hand, the iron-type golf club heads have a tendency that the rebound performance decreases toward the sole from the central part of the club face.
     Patent document 1: Japanese Patent Application Publication No. 2012-166093   Patent document 2: Japanese Patent Application Publication No. 2013-59680   Patent document 3: Japanese Patent Application Publication No. 2006-149964   

     SUMMARY OF THE INVENTION 
     In general, an iron-type golf club has many opportunities to hit a ball lying on lawn, therefore, the ball hitting position tends to become on the sole-side (under side) of the center of the club face. In other words, there is a tendency that a ball is hit at a sole-side position where the rebound performance is relatively low. 
     Thus, the iron-type golf club heads disclosed in the patent documents 1-3 have a room for improvement in order to increase the carry distance of the ball. 
     It is therefore, an object of the present invention to provide an iron-type golf club head, in which the club face can exhibit high rebound performance in the central region as well as in a sole-side region of the club face. 
     According to the present invention, an iron-type golf club head having a club face for hitting a ball and a sole forming an under surface of the club head, comprises: 
     a face plate made of a titanium or a titanium alloy, and 
     a head main body made of a metal material having a specific gravity larger than that of the face plate and supporting a peripheral part of the face plate, wherein 
     the face plate is provide with a plurality of grooves extending in the toe-heel direction of the club head, 
     in a grooved range in the toe-heel direction which is defined between a position in the toe-heel direction of the most toe-side end of the grooves and a position in the toe-heel direction of the most heel-side end of the grooves, 
     a distance of at least part of a sole-side edge of the face plate is not more than 2.5 mm when measured in the up-down direction from a sole-side profile line of the club head appearing in a front view of the club head under the upright state. 
     Definitions 
     In this application, dimensions, positions, directions and the like relating to the club head refer to those under a standard state of the club head unless otherwise noted. 
     Here, the standard state of the club head is such that the club head is set on a horizontal plane HP so that the axis of the club shaft (not shown) is inclined at the specified lie angle while keeping the axis on a vertical plane, and the club face forms the specified loft angle. Incidentally, in the case of the club head alone, the center line of the shaft inserting hole can be used instead of the axis of the club shaft. 
     The toe-heel direction is a direction parallel with the horizontal plane HP and perpendicular to a front-back direction. 
     The front-back direction is a direction parallel with a straight line projected on the horizontal plane HP, wherein the straight line is drawn normally to the club face passing through the center of gravity G of the club head. 
     The sole-side profile line of the club head means the profile line of the sole of the club head appearing when the club head is viewed from the front of the club head under the upright state as shown in  FIG. 1 . 
     The upright state of the club head is such that the club head under the standard state as shown in  FIG. 4  is rotated around a horizontal axis extending along the club face so that the loft angle alpha becomes 0 degree as shown in  FIG. 3 . 
     The iron-type golf club according to the present invention may further include the following features (1)-(7): 
     (1) the above-mentioned at least part of the sole-side edge extends in the toe-heel direction across the center in the toe-heel direction of the grooved range; 
     (2) the distance is not more than 2.4 mm; 
     (3) the sole-side edge includes a linear part extending linearly along the toe-heel direction, and 
     in the grooved range, the distance of the sole-side edge in the linear part is not more than 2.5 mm over the entire length of the linear part; 
     (4) the distance of the sole-side edge in the linear part is gradually decreased from the center of the linear part in the toe-heel direction toward the toe-side end of the linear part and toward the heel-side end of the linear part; 
     (5) the distance of the sole-side edge in the linear part is not more than 2.0 mm at the toe-side end of the linear part, and not more than 2.0 mm at the heel-side end of the linear part; 
     (6) in the grooved range, at least part of the sole-side edge of the face plate forms the sole-side profile line; 
     (7) the face plate has, on its sole-side, a contact surface with the head main body, and a height (Q) of an upper edge of the contact surface from the sole-side edge is in a range of from 0.8 to 2.2 mm when measured in the up-down direction in the front view of the club head under the upright state. 
     Therefore, in the iron-type golf club head according to the present invention, as the face plate is made of a titanium or a titanium alloy and excels in the rebound characteristic when hitting a ball, the club head may exert high rebound performance. 
     Further, as the distance of the sole-side edge is not more than 2.5 mm, the face plate which excels in the rebound characteristic is enlarged toward the sole, and the rebound performance in a sole-side region of the club face can be effectively improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of an iron-type golf club head as a first embodiment of the present invention under the upright state of the club head. 
         FIG. 2  is a rear view thereof under the upright state. 
         FIG. 3  is a cross sectional view thereof under the upright state taken along line A-A of  FIG. 1 . 
         FIG. 4  is a cross sectional partial view of the iron-type golf club head shown in  FIG. 1  under its standard state taken along line A-A of  FIG. 1 . 
         FIG. 5  is an exploded perspective view of the iron-type golf club head. 
         FIG. 6  is a closeup of  FIG. 1  showing a sole-side part of the club head. 
         FIG. 7  is a front view of an iron-type golf club head as a second embodiment of the present invention under the upright state of the club head. 
         FIG. 8  is a cross sectional view thereof under the upright state taken along line A-A of  FIG. 7 . 
         FIG. 9  is an enlarged cross sectional view showing a modification of the junction structure of the face plate and the head main body of the second embodiment. 
         FIG. 10  is a graph showing a relationship between restitution coefficients and ball hitting positions. 
         FIGS. 11( a ) and 11( b )  are cross sectional views of an iron-type golf club head according to the present invention and a conventional iron-type golf club head, respectively. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described in detail in conjunction with accompanying drawings. 
     In the following embodiments, the lie angle is preferably set in a range of from 50 to 70 degrees, and the loft angle is preferably set in a range of from 15 to 70 degrees. But, the lie angle and the loft angle are not necessarily limited to these ranges. 
     As shown in  FIG. 1  to  FIG. 3 , an iron-type club head  1 , as a first embodiment of the present invention, comprises a flat club face  2  for hitting a ball, a sole  3  forming the under surface of the club head, a top  4  forming the upper surface of the club head, a heel  5  as an end of the club head  1  on the side to which a shaft is attached, a toe  6  as an end of the club head  1  on the opposite side of the heel  5 , and a tubular hosel portion  7  to which the shaft is attached. 
     In the first embodiment, as shown in  FIGS. 1 to 3 , the club head  1  is composed of a head main body  11  and a face plate  10  fixed thereto. 
     The face plate  10  has a top-side edge  10   a , a toe-side edge  10   b , a heel-side edge  10   c  and a sole-side edge  10   d , wherein, as shown in  FIG. 1 , the top-side edge  10   a , the toe-side edge  10   b  and the sole-side edge  10   d  extend along the profile line of the club face  2  in substantially parallel thereto, and the heel-side edge  10   c  in this example extends in the vertical direction. 
     The front surface of the face plate  10  forms a major part of the club face  2 . 
     The face plate  10  is provided in the front surface with a plurality of grooves  12  having a small width and a small depth according to the limitations provided in the Golf rules. 
     The grooves  12  extend straight in parallel with the toe-heel direction. 
     The grooves  12  increase the frictional coefficient of the club face  2  to give appropriate spin to the hit ball to improve the flying distance. 
     Given that a grooved range  20  is a range defined as extending between the positions in the toe-heel direction of the most toe-side end  12   a  and most heel-side end  12   b  of the grooves  12 , it is not essential but preferable that, in view of variations of ball hitting positions of the average golfers, the width in the toe-heel direction of the grooved range  20  is set in a range of from about 40 mm to about 60 mm, and the grooved range  20  is positioned substantially at the center in the toe-heel direction of the club face  2 . 
     The face plate  10  is made of a titanium or a titanium alloy (hereinafter, generically, “titanium based materials”). Such titanium based materials are, owing to their lower Young&#39;s moduli, bent easily when hitting a ball and exhibit good rebound characteristics. Therefore, the use of a titanium based material is preferred. 
     The titanium of the titanium based material making up the face plate  10  may be an alpha-phase titanium, beta-phase titanium or alpha-beta-phase titanium. It is desirable to use an alpha-beta-phase titanium alloy having high strength such as Ti-5Al-1Fe. 
     The front surface of the face plate  10  is substantially flat excepting the grooves, namely dents caused thereby. On the other hand, the back surface  10 B of the face plate  10  in this example is non-flat or stepped. Thereby, the face plate  10  has multi-thickness changed stepwise. However, the face plate  10  is not to be limited to such configuration. 
     The face plate  10  in this example comprises 
     a first part  21  extending annularly along the outer circumference or edge of the face plate  10 , 
     a second part  22  extending annularly on the inside thereof, and 
     a third part  23  surrounded by the second part  22 . 
     The thickness t 1  of the first part  21  is largest, the thickness t 3  of the third part  23  is smallest, and the thickness t 2  of the second part  22  is therebetween. 
     The thicknesses of the first part  21 , the second part  22  and the third part  23  are decreased step by step. 
     The third part  23  has an area largest in the face plate  10  and covers substantial ball hitting positions including the sweet spot SS. 
     The third part  23  having the thickness t 3  smallest in the face plate  10  is bent easily, and contributes to improve the rebound performance. 
     Incidentally, the sweet spot SS is an intersecting point of a normal line, which is drawn from the center of gravity G of the club head to the club face  2 , with the club face  2 . 
     The face plate  10  in this example is provided with a concave portion  24  at the corner between the front surface and the outer circumferential surface  10 A of the face plate  10 . 
     The concave portion  24  in this example is formed annularly, namely, continuously around the face plate  10 . 
     The concave portion  24  is utilized when the face plate  10  is fixed to the head main body  11  by a caulking technique as described hereinafter. 
     The head main body  11  in this example includes the hosel portion  7  and a face plate receiving frame  30  as shown in  FIG. 5 . 
     The face plate receiving frame  30  extends annularly so as to form a through hole O penetrating the head main body  11  in the front-back direction. 
     The face plate receiving frame  30  comprises a top frame  31 , a sole frame  32 , a toe frame  33  and a heel frame  34 . 
     The top frame  31  forms the top  4  of the club head  1 . 
     The sole frame  32  forms the sole  3  of the club head  1 . 
     The toe frame  33  connects between the top frame  31  and the sole frame  32  on the toe  6  side. 
     The heel frame  34  connects between the top frame  31  and the sole frame  32  on the heel  5  side. 
     The heel frame  34  is formed integrally with the hosel portion  7 . The face plate receiving frame  30  is further provided with a club face mount portion  40  onto which the face plate  10  is mounted. 
     The club face mount portion  40  is formed annularly surrounding the though hole O as shown in  FIG. 3 . 
     The club face mount portion  40  comprises an inner surface  41  facing toward the center of the club head, and a front surface  42  facing toward the club face  2  side of the club head, and the inner surface  41  and the front surface  42  form an internal corner therebetween.
 
To the inner surface  41 , the outer circumferential surface  10 A of the face plate  10  is fitted. To the front surface  42 , the back surface  10 B of the face plate  10  is fitted. Thereby, movements of the face plate  10  in the up-down directions, right-left directions, and backward direction are restrained.
 
     The face plate  10  is fitted in the club face mount portion  40  and finally fixed thereto by joining means, for example, adhesive bonding, press fitting, caulking, welding, fastening screws and the like. 
     In this example, the face plate  10  is fixed to the club face mount portion  40  by caulking. 
     Incidentally, the caulking is a technique for fixing the face plate  10  to the club face mount portion  40  by plastically deforming a part of the face plate  10  and/or club face mount portion  40 . 
     Preferably and in this embodiment, after the face plate  10  is fitted in the club face mount portion  40 , the face plate receiving frame  30  is partially pressed and plastically deformed so that the deformed part engages with the concave portion  24  of the face plate  10 . Thus, the face plate  10  is prevented from being demounted toward the front by the plastically deformed part of the face plate receiving frame  30 . 
     Incidentally, an adhesive agent can be used between the face plate  10  and the head main body  11  when making the caulking operation. 
     In the first embodiment, the peripheral part of the face plate  10  supported by the head main body  11  is the first part  21  which has the thickness t 1  largest in the face plate  10 . Therefore, the club head  1  can be improved in the durability of the junction part of the face plate  10  with the club face mount portion  40 . 
     On the other hand, the other part of the face plate  10  (namely, the second part  22  and third part  23 ) is not supported by the head main body  11 . 
     As the second part  22  and the third part  23  have the relatively small thicknesses t 2  and t 3 , in cooperation with the lower Young&#39;s modulus of the titanium based material, these parts  22  and  23  can be elastically deformed when hitting a ball to bent toward the back of the club head without being hindered by the head main body  11 . Thereby, the club head  1  in the first embodiment can exhibit further improved rebound performance. 
     It is preferable that the head main body  11  has a specific gravity more than that of the face plate  10 . 
     The head main body  11  is made of a metal material. For example, a single kind or plural kinds of metal materials selected from stainless steels, maraging steels, Ni-base alloys, soft iron and the like can be used. 
     It is also possible that the head main body  11  is constructed by two or more separate parts made of different metal materials having different specific gravities. 
     In this case, it is preferable that a part made of a metal material having a larger specific gravity is incorporated in the sole  3  of the club head main body  11  as a weight member, for example. 
     Given that the distance D is that of the sole-side edge  10   d  of the face plate  10  measured from the above-mentioned club head sole-side profile line  8  in the up-down direction of the club head under the upright state along the club face  2 , the distance D of at least part of the sole-side edge  10   d  positioned in the grooved range  20  is in a range of not more than 2.5 mm. 
     Thus, the face plate  10  is extended to near the club head sole-side profile line  8  so that the region capable of exhibiting good rebound characteristic is enlarged toward the sole. Accordingly, even if the ball hitting position is on the sole-side of the center or sweet spot, the golfer can enjoy good rebound performance. 
       FIGS. 11( a ) and 11( b )  show the club head  1  in this embodiment and a conventional club head  1 ′, respectively. Both heads  1  and  1 ′ are the same in respect of the position of the top-side edge of the face plate  10  and the indicated width B. It is necessary that the width B is more than a certain value from the aspect of the strength and the durability. 
     Although, both heads  1  and  1 ′ have the same width B, the face plate  10  of the club head  1  in this embodiment is provided with a deflectable part L which is larger in the up-down direction than that of the conventional club head  1 ′ by being expanded toward the sole. Therefore, it is possible to provide an iron club which is advantageous to off-center hits on the sole-side of the club face. Thus, even if the ball hitting position is on the sole-side of the club face, the club head  1  in this embodiment can exert high rebound performance, without sacrificing the strength and the durability of the face plate  10 . Accordingly, it is possible for the average golfers to improve the carry distance. 
     For the average golfers, a typical hitting position of iron-type golf club heads is 15 mm above from the club head sole-side profile line  8  along the club face  2 . 
     As the club head  1  in this embodiment has the above described structure, it is possible to increase the restitution coefficient at a position 15 mm above from the club head sole-side profile line  8  along the club face  2  and at the center of the grooved range  20  in the toe-heel direction. 
     When the restitution coefficient of the club head according to the present invention is measured at a measuring position on the club face  2  at the center in the toe-heel direction of the grooved range  20  which measuring position is spaced apart from the club head sole-side profile line  8  by a distance of 15 mm in the up-down direction along the club face  2 , the restitution coefficient is preferably not less than 0.808, more preferably not less than 0.810, still more preferably not less than 0.812. 
     Here, the restitution coefficient is measured according to the “Procedure for Measuring the Velocity Ratio of a Club Head for conformance to Rule 4-1e, Appendix II, Revision 2 (Feb. 8, 1999), United States Golf Association.” 
     It is preferable that, in the grooved range  20 , the distance D of at least part of the sole-side edge  10   d  is not more than 2.4 mm. 
     It is preferable that a part of the sole-side edge  10   d , in which the distance D is not more than 2.4 mm, extends in the toe-heel direction across the center in the toe-heel direction of the grooved range  20 . 
     In the first embodiment, as shown in  FIG. 6 , the sole-side edge  10   d  of the face plate  10  has a linear part  50  extending linearly in the toe-heel direction and positioned in the grooved range  20 . 
     Preferably, the distance D (D 1 , D 2  and D 3  in  FIG. 6 ) of the linear part  50  is not more than 2.5 mm over the entire length of the linear part  50 . 
     Incidentally, the linear part  50  may be utilized as a reference line when making the grooves  12  extending parallel with the toe-heel direction. 
     In the first embodiment, the club head sole-side profile line  8  appearing when the club face  2  is viewed from the front of the club head  1  is, as shown in  FIG. 1 , smoothly curved and convex downward. 
     Due to the convex shape of the club head sole-side profile line  8  and the sole-side edge  10   d  of the face plate  10  including the linear part  50 , the distance D of the linear part  50  is gradually decreased from the center  50   c  of the linear part  50  toward the toe-side end  50   a  and the heel-side end  50   b  of the linear part  50 . 
     In order to effectively improve the rebound performance of the club face  2  in its sole-side part, the distance D 1  of the sole-side edge  10   d  at the center  50   c  of the linear part  50  is preferably set in a range of not more than 2.5 mm, more preferably not more than 2.4 mm, still more preferably not more than 2.3 mm. And, at the toe-the side end  50   a  and the heel-side end  50   b  of the linear part  50 , the distances D 2  and D 3 , respectively, of the sole-side edge  10   d  of the face plate  10  are preferably set in a range of not more than 2.1 mm, more preferably not more than 2.0 mm, still more preferably not more than 1.9 mm. 
     In the first embodiment, as explained above, the sole-side edge  10   d  of the face plate  10  is positioned on the upper side of the club head sole-side profile line  8 . Therefore, as an example, a caulking technique utilizing the concave portion  24  is available over the entire circumference of the face plate  10 . Accordingly, the club head  1  can achieve both of high rebound performance and good durability in a sole-side region of the club face. 
     In the first embodiment, in order to effectively derive this advantage effect, it is preferred that the minimum of the distance D of the sole-side edge  10   d  of the face plate  10  from the club head sole-side profile line  8  is set in a range of not less than 1.5 mm, more preferably not less than 1.8 mm. 
     In order to improve the rebound performance by enlarging the face plate  10  toward the toe  6 , the distance D 4  between the toe-side edge  10   b  of the face plate  10  and the outer edge of the club face  2  is preferably set in a range of not more than 2.5 mm, more preferably not more than 2.3 mm, still more preferably not more than 2.0 mm when the club face  2  is viewed from its front. 
     In order to improve the rebound performance by enlarging the face plate  10  toward the top  4 , the distance D 5  between the top-side edge  10   a  of the face plate  10  and the outer edge of the club face  2  is preferably set in a range of not more than 2.8 mm, more preferably not more than 2.6 mm when the club face  2  is viewed from its front. 
     Preferably, the distance D 4  is equal to or less than the distance D 5 . 
     In order to further improve the rebound performance of the club head  1 , the thickness t 3  of the third part  23  of the face plate  10  is preferably not less than 1.6 mm, more preferably not less than 1.8 mm, but preferably not more than 2.5 mm, more preferably not more than 2.3 mm, and 
     the thickness t 2  of the second part  22  is preferably not less than 2.1 mm, more preferably not less than 2.3 mm, but preferably not more than 2.9 mm, more preferably not more than 2.7 mm. 
     In order to increase the strength of the junctional part of the face plate  10  with the head main body  11  while improving the rebound performance of the club head  1 , 
     the thickness t 1  of the first part  21  of the face plate  10  is preferably not less than 3.0 mm, more preferably not less than 3.1 mm, but preferably not more than 3.5 mm, more preferably not more than 3.4 mm, and 
     the width w of the first part  21  is preferably not less than 1.3 mm, more preferably not less than 1.5 mm, but preferably not more than 2.7 mm, more preferably not more than 2.5 mm. 
     In the example shown in  FIG. 3 , in order to enlarge the deflectable part L (shown in  FIG. 11 ) of the club head  1  toward the sole without deteriorating the durability of the club head, the height Q in the up-down direction between the sole-side edge  10   d  and the upper edge P of the contact surface of the face plate  10  with the head main body  11  is preferably not less than 0.8 mm, more preferably not less than 1.1 mm, but preferably not more than 2.2 mm, more preferably not more than 2.0 mm. 
       FIG. 7  and  FIG. 8  show an iron-type club head  1  as a second embodiment of the present invention. 
     The second embodiment will be described hereunder wherein, for the parts corresponding to those in the first embodiment, the same reference numbers are used, and redundant descriptions are omitted. 
     In the second embodiment, at least part of the sole-side edge  10   d  in the grooved range  20  forms the club head sole-side profile line  8 . 
     The top-side edge  10   a , the toe-side edge  10   b  and the heel-side edge  10   c  of the face plate  10  are positioned inside the outer edge of the club face  2  as shown in  FIG. 7 . 
     But, the sole-side edge  10   d  of the face plate  10  reaches the sole  3  and is exposed in the surface of the sole  3  to form a front part of the sole  3  as shown in  FIG. 8 . Thereby, a part of the sole-side edge  10   d  of the face plate  10  forms the club head sole-side profile line  8 .
 
Thus, the face plate  10  is further enlarged toward the sole in comparison with the first embodiment, and the rebound performance in the sole-side part of the club face can be further improved.
 
Similarly to the first embodiment, the top-side edge  10   a , the toe-side edge  10   b  and the heel-side edge  10   c  of the face plate  10  are firmly fixed to the club face mount portion  40  by caulking. Thereby, movements of the face plate  10  in the up-down directions, right-left directions, and backward direction are restrained.
 
     In the second embodiment, since a major part of the sole-side edge  10   d  of the face plate  10  forms the club head sole-side profile line  8 , it is difficult to cover and secure the sole-side edge  10   d  of the face plate  10  from the front side of the face plate by the plastically deformed part of the club head main body  11 . 
     Therefore, it is preferable that, as shown in  FIG. 8 , the sole-side edge  10   d  of the face plate  10  is provided at the rear corner with a concave portion  45  formed by cutting out the rear corner. 
     The concave portion  45  is formed by two surfaces, namely, a front surface and an upper surface in the cross section. 
     In the example shown in  FIG. 8 , the front surface is parallel with the club face, and the upper surface is perpendicular to the club face. 
       FIG. 9  shows a modification of the concave portion  45  shown in  FIG. 8 . 
     In the example shown in  FIG. 9 , the front surface is parallel with the club face, and the upper surface is a slant surface  45   a  which is inclined with respect to the direction N perpendicular to the club face, downwardly toward the back of the club head. 
     In eighth case, the concave portion  45  is filled with a part of the club head main body  11  protruding frontward to engaged with each other. This protruding part can be a plastically deformed part of the club head main body  11 . 
     The slant surface  45   a  is particularly preferable in order to prevent the face plate  10  from being dislocated toward the front and serve to achieve both of good rebound performance and high durability. 
     While detailed description has been made of especially preferable embodiments of the present invention, the present invention can be embodied in various forms without being limited to the illustrated embodiments. 
     Comparison Tests 
     Based on the structures shown in  FIG. 1  to  FIG. 8 , iron-type golf club heads having specifications listed in Table 1 were experimentally manufactured and measured for the restitution coefficient. 
     Common specifications are as follows. 
     Club head: for six iron 
     Lie angle: 61.5 degrees 
     Loft angle: 27 degrees 
     Face plate 
     material: titanium alloy (Ti-5Al-1Fe) 
     first part width W: 2.5 mm 
     first part thickness t 1 : 3.25 mm 
     second part thickness t 2 : 2.55 mm 
     third part thickness t 3 : 2.15 mm 
     height Q: 2.0 mm 
     Head main body 
     material: stainless steel (SUS630) 
     The restitution coefficient was measured according to the “Procedure for Measuring the Velocity Ratio of a Club Head for Conformance to Rule 4-1e, Appendix II, Revision 2 (Feb. 8, 1999), United States Golf Association”. But, instead of the sweet spot, the measuring position was 15 mm upward from the sole-side profile line of the club face along the club face and at the center in the toe-heel direction of the grooved range of the club face. 
     As explained above, such measure position reflects actual hitting positions of the average golfers. 
     The results are show in Table 1, wherein the larger the value, the better the restitution coefficient. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
                 comparative 
                 comparative 
                 comparative 
                 working 
               
               
                 Head 
                 example 1 
                 example 2 
                 example 3 
                 example 1 
               
               
                   
               
               
                 distance D1 (mm) 
                 3.3 
                 4.3 
                 3.1 
                 2.3 
               
               
                 distance D2 (mm) 
                 2.8 
                 3.8 
                 2.6 
                 1.9 
               
               
                 distance D3 (mm) 
                 2.8 
                 3.8 
                 2.8 
                 1.9 
               
               
                 distance D4 (mm) 
                 2.0 
                 2.0 
                 2.5 
                 2.0 
               
               
                 distance D5 (mm) 
                 2.5 
                 1.5 
                 2.0 
                 2.5 
               
               
                 restitution 
                 0.804 
                 0.792 
                 0.805 
                 0.812 
               
               
                 coefficient 
               
               
                 (measured value) 
               
               
                 restitution 
                 100 
                 98.507 
                 100.124 
                 100.995 
               
               
                 coefficient 
               
               
                 (relative value) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 working 
                 working 
                 working 
               
               
                   
                 Head 
                 example 2 
                 example 3 
                 example 4 
               
               
                   
                   
               
               
                   
                 distance D1 (mm) 
                 2.4 
                 2.5 
                 0 
               
               
                   
                 distance D2 (mm) 
                 2.0 
                 2.1 
                 0 
               
               
                   
                 distance D3 (mm) 
                 2.0 
                 2.1 
                 0 
               
               
                   
                 distance D4 (mm) 
                 2.0 
                 2.0 
                 2.0 
               
               
                   
                 distance D5 (mm) 
                 2.5 
                 2.5 
                 2.5 
               
               
                   
                 restitution coefficient 
                 0.810 
                 0.808 
                 0.817 
               
               
                   
                 (measured value) 
               
               
                   
                 restitution coefficient 
                 100.746 
                 100.498 
                 101.617 
               
               
                   
                 (relative value) 
               
               
                   
                   
               
            
           
         
       
     
     Form the test results, it was confirmed that, in comparison with the comparative examples, the working examples according to the invention were significantly improved in the rebound performance at typical hitting positions of the average golfers. 
     Further, working example 1 and comparative examples 1 and 2 were each measured for the restitution coefficient of the club face at various measure positions. The measure positions were on the center line (center in the toe-heel direction) of the grooved range of the club face and in a range between 4 mm and 25 mm above from the above-mentioned sole-side profile line of the club head. 
       FIG. 10  shows the results of measurements, wherein the measured values are plotted, and polynomial approximate curves therefor are also shown. The axis of ordinate denotes the restitution coefficient, and the axis of abscissas denotes the distance in millimeter of the measuring position above from the sole-side profile line. 
     As shown in  FIG. 10 , the club head as working example 1 exhibited the restitution coefficient of more than 0.790 at hitting positions in a range between plus/minus 2 mm of the center of the distribution of the typical hitting positions of the average golfers, and it was confirmed that, in comparison with the comparative examples 1 and 2, the restitution coefficient of working example 1 was significantly increased. Further, in the club head as working example 1, the maximum (about 0.828) of the restitution coefficient occurred at a position of less than 20 mm above from the sole-side profile line, whereas the maximum of the restitution coefficient of comparative examples 1 and 2 occurred at positions more than 20 mm above from the sole-side profile line. Thus, it was confirmed that working example 1 was improved in the rebound performance in the sole-side part of the club face. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  iron-type golf club head 
               2  club face 
               3  sole 
               8  club head sole-side profile line 
               10  face plate 
               10   d  sole-side edge 
               11  head main body 
               12  groove 
               20  grooved range 
               50  linear part