200526300 (1) 九、發明說明 〔相關申請的彼此對照〕 本申請是以2003年12月12日所提出申請的日本國 特許出願特願2 0 0 3 Ml 51 14號爲依據主張優先權，其內容 援用在本申請說明書中。 【發明所屬之技術領域】 本發明是關於高爾夫球桿桿頭。更具體地說是關於金 屬製桿頭本體和強化纖維構件複合形成的鐵頭球棒用的高 爾夫球桿桿頭。 【先前技術】 習知的金屬製桿頭本體和強化纖維構件複合形成的鐵 頭球棒用的高爾夫球桿桿頭，如日本國特許公告公報第 65708/1992號及第88153/1993號或日本國特許公開公報 第173513/1997號所示，爲眾所周知的是將金屬製的打球 面部厚度形成爲薄然後於其背面添設或塡充厚度爲較厚的 纖維強化塑料層的高爾夫球桿桿頭。 這種高爾夫球桿桿頭，是利用低重心構造來提高球的 擊出角，能夠增加高爾夫球的飛行距離。 然而，該習知高爾夫球桿桿頭，是將高爾夫球打球時 施加在板厚薄的金屬製打球面部的衝擊所形成的變形直接 傳達於厚度爲較厚的纖維強化塑料層，利用這些打球面部 與纖維強化塑料之間的反彈力來增加球的飛行距離。 -4 - 200526300 (2) 但是’打球時金屬製打球面部的變形只是些許，將這 些許的變形量只藉由其背後的纖維強化塑料層厚度方向的 變开就算是對球有進行反彈力的作用，也會因其反彈力較 小而無法使球的飛行距離有較大的增加。 【發明內容】 本發明是有鑑於上述問題點而爲的發明，其目的在於 提供一種利用打球時金屬製打球面部的變形，能夠對球作 用著更大的反彈力使球的飛行距離比習知還大的高爾夫球 桿桿頭。 爲達成上述目的，本發明的高爾夫球桿桿頭，是由金 屬製的框形鐵桿頭本體及設置在該桿頭本體的前面部具有 高反彈係數的金屬製板厚薄的正面面部所形成，鐵桿頭本 體是由後跟部、尖端部、聯結該後跟部和該尖端部的上端 之上緣部’及底端部所形成，該桿頭本體具有離開該正面 面部從該底知部後端朝上方伸出的後壁部，於該正面面部 和該底端部和該後壁部之間配設著強化纖維構件，該強化 纖維構件是抵接著正面面部的背面來形成封閉的中空空洞 部，該強化纖維構件的背面其一部份是架在該後壁部上。 如此一來，在打擊高爾夫球時，正面面部會朝後方撓 曲變形，其後方的強化纖維構件的封閉空洞部會被壓縮， 利用該壓縮力使上述封閉空洞部彈性變形。該正面面板的 彈性復原力和封閉空洞部的彈性復原力相結合形成對高爾 夫球作用著反彈力，藉此得以增加高爾夫球的飛行距離。 200526300 (3) 其中，以是將上述強化纖維構件成板狀緊貼於上述正 面面部的背面，用該緊貼成板狀的上述強化纖維構件和其 他的上述強化纖維構件來形成封閉的縱長封閉空洞部爲 佳。 此外，是以從底端部的後端緣朝上方突出的山形伸出 部和傾斜聯結該山形伸出部的頂部和尖端部的上端部的帶 狀伸出部所形成的上述後壁面爲佳。 以下是參照所附圖面來說明本發明的最佳實施形態。 【實施方式】 〔發明之最佳實施形態〕 於以下對本發明的最佳實施例是以參照附圖來說明。 第1圖至第3圖是表示本發明最佳實施形態相關的鐵 頭高爾夫球桿桿頭。該高爾夫球桿桿頭的桿頭本體1 0，從 第1圖的前面看時，是由：長柄（未圖示）插入用的長筒 部1 ;長筒部1下方的後跟部2 ;圓弧狀的尖端部3 ;聯結 後跟部2和尖端部3的上端之帶狀上端緣部4，及，聯結 後跟部2和尖端部3的下端之底端部5形成爲框形。 接著，於桿頭本體1 〇的背面，如第2圖及第3圖所 示’設有：從底端部5的後端緣幾乎直角朝上方突出的山 形伸出部6 ;傾斜聯結該山形伸出部6的頂部和尖端部3 的上端部之帶狀伸出部7。然後，在該兩伸出部6、7和框 形桿頭本體的後跟部及上緣部4之間，形成有從背面側看 是將後跟部側成爲擴徑頭部的紡錘狀間隙部8，此外是於 -6- 200526300 (4) 兩伸出部6、7和框形桿頭本體的尖端部3之間形成有大 致半圓形狀的間隙部9。 上述包括有山形伸出部6和帶狀伸出部7的桿頭本體 1 0，最好是以不銹鋼鑄造形成爲佳。 於形成爲框形的桿頭本體1 〇的前面開口，最好是固 定著利用壓入、焊接、黏結等成一體性的由具高反彈係數 的鈦合金所形成的正面面部1 1的周緣部。該正面面部1 1 其周緣部的厚度爲3〜4 mm，周緣部以外的打球面部的厚度 爲1 · 0〜2.5 m m於該背面一體性黏結著碳等強化纖維所形成 的纖維強化樹脂板1 2。該纖維強化樹脂板1 2的厚度最好 是形成爲要比上述打球面部的厚度還大爲佳。另，於正面 面部1 1的打球面部如習知般設有指定寬度及深度的多數 條橫溝。 本發明，如第3圖所示，是覆蓋著框形的桿頭本體1 0 的底端部5的內周圍面，從其後端幾乎直角豎立配設有框 形的桿頭本體1 〇的後跟部2、尖端部3及上緣部4的整體 及薄片狀纖維強化樹脂（FRP )構件1 3，其周緣的端部是 分別緊貼結合於被黏合在正面面板1 1背面的纖維強化樹 脂板1 2的周緣部。因此，在纖維強化樹脂構件1 3和黏合 在正面面板1 1背面的纖維強化樹脂板1 2之間，如第3圖 所示形成有桿頭本體的中央縱剖面形狀是呈大致三角形密 封的中空封閉部1 4。接著，在纖維強化樹脂構件1 3的外 部背面，於山形伸出部6和帶狀伸出部7所存在的部份結 合於這些伸出部6、7的內面。 200526300 (5) 此外，於山形伸出部6的背面側下方形成著三角形狀 的凹部，於該凹部內埋設有鎢板所形成的錘板1 5。 本發明的鐵頭高爾夫球桿桿頭因是如上述構成’所以 當以正面面板1 1打擊高爾夫球時，是藉由該衝擊來使正 面面板1 1除了架在框形的桿頭本體1 0上的周緣部外其中 央部分是朝後方撓曲。正面面板1 1除了周緣部外因是於 其背面一體性黏合著纖維強化樹脂板1 2，所以其撓曲量會 較大。當正面面板1 1朝後方撓曲時，形成在正面面板1 1 和其後方的纖維強化樹脂構件1 3之間的封閉空洞部1 4會 施加有壓縮力，該壓縮力會使纖維強化樹脂構件1 3未接 觸桿頭本體1 〇的部份，即在纖維強化樹脂構件1 3的後面 沒有山形伸出部6和帶狀伸出部7存在的上述紡錘狀間隙 部8和半圓形狀的間隙部9的纖維強化樹脂構件1 3以微 視性來看時是朝外方膨出變形。 這樣的變形所產生的正面面板1 1的彈性復原力和朝 外方膨出變形的纖維強化樹脂構件的彈性復原力相結合對 高爾夫球作用著反彈力，藉此使打擊高爾夫球的飛行距離 要比習知單靠正面面板彈性變形的高爾夫球桿桿頭還大。 其次，是對：上述實施形態相關的本發明的高爾夫球 桿桿頭；在上述正面面板和山形伸出部6及帶狀伸出部7 之間塡充有碳纖維強化樹脂構件的比較例1的高爾夫球桿 桿頭；及，從上述實施形態的高爾夫球桿桿頭中去除纖維 強化樹脂構件1 3後的比較例2的高爾夫球桿桿頭進行成 品製作’然後使用局爾夫球迅速打擊機器來對這些成品進 200526300 (6) 行比較測試。本發明的高爾夫球桿桿頭和比較例1、2的 高爾夫球桿桿頭都是由正面面板的打球面部爲厚度i.5mm 的欽正面的背面黏合有厚度2mm的碳纖維強化樹脂板所 形成’使用球桿的長度爲3 8.0英吋，球桿末端後傾角度 爲2 5度的高爾夫球桿。桿頭重心特性及反彈係數如表1 所示。 〔表1〕 球桿 名稱 桿頭重心特性 反彈 係數 重心局度 f mm] 重心深度 [mm] 重心距離 [mm] 本發明品 19.6 5.7 4 1.5 0.774 比較例品1 19.9 5.3 4 1.5 0.765 比較例品2 20.8 5.0 39.3 0.746 從表1中可明確得知本發明品是較比較例1、2還要 重心低，此外其反彈係數是比較高。 其次，使用高爾夫球迅速打擊機器進行測試的結果如 表2所示。 200526300 (7) 〔表2〕 _蔓爾夫球迅速打擊機器測試結果 球桿名稱 桿頭速度 飛行距離 初速 打出角 自旋量 [m / s 1 [Yard] [m/s ] [° ] [rpm] 本發明品 33.0 150.8 44.5 18.7 3 166 比較例品1 33.0 148.0 44.0 18.4 3 5 6 7 比較例品2 33.0 144.3 42.7 17.2 3 8 8 9 從表2明確得知，本發明品的打出角是爲較大，與比 較例1及2的高爾夫球桿相比其飛行距離是大爲增加。 第4圖及第5圖是表示本發明第2實施形態相關的鐵 頭高爾夫球桿桿頭。該實施形態的高爾夫球桿桿頭與第1 實施形態的高爾夫球桿桿頭不同之處如下述。 於該高爾夫球桿桿頭中，底端部5的後方部的厚度是 形成爲要比前方部還約厚2倍程度，底端部的後端中央部 1 6如第4圖所示是膨出成山形。接著，於底端部5的後緣 部上端安裝有朝上方伸出的第1金屬製板材1 7，於聯結後 跟部2和尖端部3的上端之帶狀上端緣部4的下面安裝有 朝下方垂下的第2金屬製板材1 8，在兩板材1 7和1 8之間 區隔形成有大致V字型的空洞部。 於該實施形態中，厚度較厚的薄片狀纖維強化樹脂層 1 9 a是緊貼配置在正面面板1 1的背面’較其爲薄的中厚度 的薄片纖維強化樹脂層1 9 b是跨在第1金屬製板材】7和 第2金屬製板材1 8的內面成緊貼配置’於上述兩纖維強 -10- 200526300 (8) 化樹脂層1 9 a、1 9 b的周緣一體性結合著厚度爲較薄的纖 維強化樹脂層1 9 c形成爲封閉的中空空洞部1 4 a。 於該實施形態中，當以正面面板U打擊高爾夫球使 正面面板朝後方撓曲時，因區隔上述中空空洞部1 4 a的周 緣部是形成爲厚度較薄所以中空空洞部1 4a就容易變形， 使該空洞部1 4a的變形量成爲較大比獲得較大的彈性復原 力。 另，本發明並不限於上實施形態，例如：強化纖維除 了碳以外可使用玻璃纖維、芳香族聚醯胺纖維等。 〔產業上之可利用性〕 如上述本發明的高爾夫球桿桿頭，於打擊高爾夫球 時，正面面板會朝後方撓曲變形，其厚度的封閉空洞部會 被壓縮。該正面面板的彈性復原力和被壓縮的空洞部的彈 性復原力相結合形成對高爾夫球作用著反彈力，藉此來增 加高爾夫球的飛行距離。 【圖式簡單說明】 第1圖爲本發明最佳實施形態相關的鐵頭高爾夫球桿 桿頭正面圖。 第2圖爲第1圖相關的鐵頭高爾夫球桿桿頭背面圖。 第3圖爲第2圖III-in剖線的剖面圖。 第4圖爲表示本發明第2實施形態的背面圖。 第5圖爲第4圖v-v剖線的剖面圖。 -11 - 200526300 (9) 【主要元件符號說明】 1長筒部 2 後跟部 3尖端部 4上端緣部（上緣部） 5底端部 6山形伸出部 7帶狀伸出部 8紡錘狀間隙部 9大致半圓形狀的間隙部 1 0桿頭本體 1 1正面面部 1 2纖維強化樹脂板 1 3纖維強化樹脂板 14、14a封閉空洞部（空洞部） 15錘板 1 6底端部的後端中央部 1 7第1金屬製板材 18第2金屬製板材 1 9 a、1 9 b、1 9 c纖維強化樹脂層200526300 (1) IX. Description of the invention [Comparison of related applications with each other] This application claims priority based on Japanese Patent Application No. 2 0 0 3 Ml 51 14 filed on December 12, 2003. The contents are cited in the specification of this application. TECHNICAL FIELD The present invention relates to a golf club head. More specifically, the present invention relates to a golf club head for an iron club formed by combining a metal head body and a reinforcing fiber member. [Prior art] Golf club heads for iron clubs formed by combining a conventional metal head body and a reinforcing fiber member, such as Japanese Patent Publication Nos. 65708/1992 and 88153/1993 or Japan As shown in International Patent Publication No. 173513/1997, it is well-known that a golf club head in which a metal hitting face is formed to have a thin thickness, and a thick fiber-reinforced plastic layer is added or filled on the back surface of the golf club head. . This golf club head uses a low center-of-gravity structure to increase the striking angle of the ball and increase the flight distance of the golf ball. However, the conventional golf club head directly transmits the deformation caused by the impact applied to the thin metal ball face during golf play to the thicker fiber-reinforced plastic layer. The rebound force between fiber reinforced plastics increases the flight distance of the ball. -4-200526300 (2) But 'the deformation of the metal playing face during play is only a little. If the amount of deformation is only changed by the thickness direction of the fiber-reinforced plastic layer behind it, the ball has a rebound force. Effect, because of its small rebound force, the flight distance of the ball cannot be greatly increased. [Summary of the Invention] The present invention is made in view of the above problems, and an object thereof is to provide a deformation of a metal playing face when playing a ball, which can exert a greater rebound force on the ball and make the flight distance of the ball longer than conventional. Also big golf club head. In order to achieve the above object, the golf club head of the present invention is formed by a metal frame-shaped iron head body and a front surface portion of the metal plate with a high rebound coefficient and a thin front surface. The head body is formed by a heel portion, a tip portion, an upper edge portion and a bottom end portion connecting the heel portion and the upper end of the tip portion, and the head body has a rear end away from the front face from the bottom knowing portion. A rear wall portion protruding upward is provided with a reinforcing fiber member between the front surface portion, the bottom end portion, and the rear wall portion, and the reinforcing fiber member abuts against the back surface of the front surface portion to form a closed hollow cavity portion. A part of the back surface of the reinforcing fiber member is supported on the rear wall portion. In this way, when the golf ball is hit, the front face portion is flexed and deformed backward, and the closed cavity portion of the rear reinforcing fiber member is compressed, and the closed cavity portion is elastically deformed by the compression force. The elastic restoring force of the front panel and the elastic restoring force of the closed cavity portion are combined to form a rebound force against the golf ball, thereby increasing the flight distance of the golf ball. 200526300 (3) Among them, the reinforcing fiber member is formed in a plate shape and closely adhered to the back surface of the front surface portion, and the reinforced fiber member and the other reinforced fiber member are formed in a closed shape to form a closed length. It is better to close the cavity. In addition, the rear wall surface formed by a mountain-shaped protrusion projecting upward from the rear end edge of the bottom end portion and a band-shaped protrusion that obliquely connects the top of the mountain-shaped protrusion and the upper end of the tip portion is preferable. . The following is a description of a preferred embodiment of the present invention with reference to the drawings. [Embodiment] [Best Embodiment of the Invention] Hereinafter, the best embodiment of the present invention will be described with reference to the drawings. Figures 1 to 3 show iron head golf club heads according to a preferred embodiment of the present invention. The head body 10 of the golf club head, when viewed from the front of FIG. 1, is composed of: a long barrel portion 1 for inserting a long handle (not shown); a heel portion 2 below the long barrel portion 1; An arcuate tip portion 3; a band-shaped upper end edge portion 4 connecting the upper ends of the heel portion 2 and the tip portion 3; and a bottom end portion 5 connecting the heel portion 2 and the lower end of the tip portion 3 are formed in a frame shape. Next, on the back surface of the head body 10, as shown in FIG. 2 and FIG. 3, a mountain-shaped protrusion 6 protruding from a rear end edge of the bottom end portion 5 at an almost right angle upward is provided; the mountain shape is inclinedly connected A band-like protrusion 7 at the top of the protrusion 6 and at the upper end of the tip 3. Then, a spindle-shaped gap is formed between the two projecting portions 6, 7 and the heel portion and the upper edge portion 4 of the frame-shaped head body, and the heel portion side becomes the enlarged head when viewed from the rear side. In addition, the part 8 has a substantially semi-circular gap part 9 formed between the two protruding parts 6, 7 and the tip part 3 of the frame-shaped head body at -6-200526300 (4). The above-mentioned head body 10 including the mountain-shaped protruding portion 6 and the belt-shaped protruding portion 7 is preferably formed by casting stainless steel. The front opening of the frame-shaped head body 10 is preferably fixed to a peripheral portion of the front surface portion 1 1 formed of a titanium alloy having a high rebound coefficient, which is integrated by press-fitting, welding, bonding, or the like. . The front surface portion 1 1 has a thickness of 3 to 4 mm at the peripheral edge portion and a thickness of 1 to 0 to 2.5 mm at the face portions other than the peripheral portion. A fiber-reinforced resin plate 1 formed by integrally bonding reinforcing fibers such as carbon to the back surface 1 2. The thickness of the fiber-reinforced resin plate 12 is preferably formed to be larger than the thickness of the hitting surface portion. In addition, a plurality of horizontal grooves having a predetermined width and depth are conventionally provided on the playing face of the front face 1 1. The present invention, as shown in FIG. 3, covers the inner peripheral surface of the bottom end portion 5 of the frame-shaped head body 1 0, and the frame-shaped head body 1 0 is arranged at an almost right angle from the rear end thereof. The whole of the heel portion 2, the tip portion 3, and the upper edge portion 4 and the sheet-like fiber-reinforced resin (FRP) member 1 3, and the peripheral edge ends are respectively closely bonded to the fiber reinforcement bonded to the back of the front panel 1 1 The peripheral edge portion of the resin plate 12. Therefore, as shown in FIG. 3, the center longitudinal cross-sectional shape of the head body is hollow between the fiber-reinforced resin member 13 and the fiber-reinforced resin plate 12 adhered to the back of the front panel 11 1 as a substantially triangular seal. Closures 1 4. Next, on the back surface of the outer portion of the fiber-reinforced resin member 13, the portions where the mountain-shaped projections 6 and the belt-shaped projections 7 exist are joined to the inner surfaces of these projections 6,7. 200526300 (5) A triangular recessed portion is formed below the back side of the mountain-shaped protruding portion 6, and a hammer plate 15 made of a tungsten plate is embedded in the recessed portion. The iron-headed golf club head of the present invention is configured as described above, so when a golf ball is hit with the front panel 1 1, the front panel 1 1 is framed in addition to the frame-shaped head body 1 0 by the impact. The central portion of the upper peripheral portion is flexed rearward. The front panel 1 1 has a large amount of deflection because the fiber-reinforced resin sheet 12 is integrally bonded to the back surface except for the peripheral portion. When the front panel 11 is flexed toward the rear, the closed cavity portion 14 formed between the front panel 11 and the fiber-reinforced resin member 13 behind the front panel 11 is subjected to a compressive force, and the compression force causes the fiber-reinforced resin member to be compressed. 1 3 The part that is not in contact with the head body 10, that is, the above-mentioned spindle-shaped gap portion 8 and semi-circular gap portion where the mountain-shaped protruding portion 6 and the belt-shaped protruding portion 7 do not exist behind the fiber-reinforced resin member 13 The fiber-reinforced resin member 1 of 9 is swollen and deformed outward when viewed from a microscopic perspective. The combination of the elastic restoring force of the front panel 1 1 and the elastic restoring force of the fiber-reinforced resin member bulging outward and deformed by such deformation exerts a rebound force on the golf ball, thereby making the flight distance of the golf ball harder. It is larger than the conventional golf club head which is elastically deformed by the front panel alone. Next, the following is a comparison example 1 of a golf club head according to the present invention according to the above embodiment, and a carbon fiber-reinforced resin member filled with a carbon fiber-reinforced resin member between the front panel and the mountain-shaped projection 6 and the belt-shaped projection 7. A golf club head; and a golf club head of Comparative Example 2 after removing the fiber-reinforced resin member 13 from the golf club head of the above embodiment, and finished the product, and then quickly hit the machine with a ball Come to 200526300 (6) for comparative testing of these finished products. Both the golf club head of the present invention and the golf club heads of Comparative Examples 1 and 2 are formed by bonding a carbon fiber reinforced resin plate with a thickness of 2 mm to the back of the front face of the ball face with a thickness of i.5 mm. Use a golf club with a length of 3 8.0 inches and a club tip angle of 25 degrees. The head center of gravity characteristics and rebound coefficient are shown in Table 1. [Table 1] Club name Head center-of-gravity characteristics Rebound coefficient Center-of-gravity degree f mm] Center-of-gravity [mm] Center-of-gravity distance [mm] Product of the present invention 19.6 5.7 4 1.5 0.774 Comparative product 1 19.9 5.3 4 1.5 0.765 Comparative product 2 20.8 5.0 39.3 0.746 It is clear from Table 1 that the product of the present invention has a lower center of gravity than Comparative Examples 1 and 2, and its rebound coefficient is relatively high. Second, the results of tests using a golf ball to quickly hit the machine are shown in Table 2. 200526300 (7) 〔Table 2〕 _Manfring Ball Quick Strike Machine Test Result Club Name Head Speed Flight Distance Initial Velocity Hit Angle Spin Amount [m / s 1 [Yard] [m / s] [°] [rpm ] Product of the present invention 33.0 150.8 44.5 18.7 3 166 Comparative product 1 33.0 148.0 44.0 18.4 3 5 6 7 Comparative product 2 33.0 144.3 42.7 17.2 3 8 8 9 It is clear from Table 2 that the punching angle of the product of the present invention is The distance is large compared with the golf clubs of Comparative Examples 1 and 2. Figures 4 and 5 show iron head golf club heads according to a second embodiment of the present invention. The golf club head of this embodiment differs from the golf club head of the first embodiment in the following points. In this golf club head, the thickness of the rear portion of the bottom end portion 5 is approximately twice as thick as that of the front portion, and the center portion 16 of the rear end of the bottom end portion is expanded as shown in FIG. 4. Out of a mountain shape. Next, a first metal plate 17 protruding upward is attached to the upper end of the rear edge portion of the bottom end portion 5, and is installed below the band-shaped upper end edge portion 4 that connects the upper ends of the heel portion 2 and the tip portion 3. A second metal plate material 18 that hangs downward is formed with a substantially V-shaped cavity portion between the two plate materials 17 and 18. In this embodiment, the thicker sheet-like fiber-reinforced resin layer 1 9 a is placed closer to the back surface of the front panel 1 1. 1st metal sheet material] 7 and the second metal sheet material 1 8 are arranged in close contact with each other at the inner edges of the two fibers -10- 200526300 (8) The peripheral edges of the resin layers 1 9 a and 1 9 b are integrated. The thin fiber-reinforced resin layer 19 c is formed as a closed hollow cavity 1 4 a. In this embodiment, when the front panel U is hit with a front panel U to bend the front panel toward the rear, the peripheral portion that separates the hollow portion 14 a is formed to be thin, so the hollow portion 14 a is easy. Deformation causes the amount of deformation of the cavity portion 14a to be larger than to obtain a large elastic restoring force. The present invention is not limited to the above embodiment. For example, glass fibers, aromatic polyamide fibers, and the like can be used as the reinforcing fibers other than carbon. [Industrial Applicability] As described above, when the golf club head of the present invention hits a golf ball, the front panel flexes and deforms toward the rear, and the thickness of the closed cavity portion is compressed. The elastic restoring force of the front panel and the elastic restoring force of the compressed cavity portion are combined to form a rebound force against the golf ball, thereby increasing the flight distance of the golf ball. [Brief description of the drawings] FIG. 1 is a front view of an iron golf club head according to a preferred embodiment of the present invention. FIG. 2 is a rear view of the iron golf club head related to FIG. 1. Fig. 3 is a sectional view taken along the line III-in in Fig. 2. Fig. 4 is a rear view showing a second embodiment of the present invention. Fig. 5 is a sectional view taken along the line v-v in Fig. 4. -11-200526300 (9) [Description of main component symbols] 1 Long tube portion 2 Heel portion 3 Tip portion 4 Upper edge portion (upper edge portion) 5 Bottom portion 6 Mountain-shaped protrusion 7 Band-shaped protrusion 8 Spindle Shaped gap portion 9 Approximately semicircular gap portion 1 0 Head body 1 1 Front surface portion 1 2 Fiber-reinforced resin plate 1 3 Fiber-reinforced resin plate 14, 14a Closed hollow portion (void portion) 15 Hammer plate 1 6 Bottom end portion Rear center part 1 7 First metal sheet 18 Second metal sheet 1 9 a, 1 9 b, 1 9 c Fiber-reinforced resin layer