TW533086B - Golf club head made of metal - Google Patents

Abstract

A golf club head which includes a ball hitting face having a central portion and a peripheral portion surrounding at least a part of the central portion. The golf club head is made of a metal, and the hardness of the peripheral portion is smaller than the hardness of the central portion. The difference in the hardness between the central portion and the peripheral portion is equal to or greater than 50 in terms of the Vickers hardness, and the width of the peripheral portion of the hitting face is in a range between about 5 and 20 mm.

Description

533086 V. Description of the invention (Background of the invention) The present invention relates to the use of metal Gaol for such as wooden poles, / stems, etc. More specifically, the present invention relates to iron rods and practical punishment. _ # Yu Zhi's golf club head, the related techniques explain the best flight distance characteristics and durability. Golf balls such as those of metal, iron, and practical metal golf balls #Master, by making the face members separately , Acetylene m, then a dry reduction component, a bottom component, an F component, etc., weld each structure into an early one, and make a single piece 7 at the same time. Balanced and polished to make the final product. The face member of the golf club head can be made by processing the metal into sheet metal. Similarly, the face member can also be subjected to further surfaces such as electroplating or iontophoresis. Treatment process to improve its flight distance and durability. In addition to the above four-piece heads, there are other types of golf club head structures, such as three-piece and two-piece heads. However, in traditional golf ball In the head, there is a problem that even if the surface member undergoes a surface treatment process such as electroplating or ion plating, the flying distance and durability are still insufficient. SUMMARY OF THE INVENTION After considering the above environment, the objective of the present invention is to provide excellent flight Distance and long-term golf club heads. After unremitting research to achieve the above goals and extensive tests of various materials and structures used for golf club heads, the inventors have found that the flight distance performance can be compared by The hardness of the center of the ball striking surface reduces the hardness of its peripheral parts. The paper size is adapted to the Chinese National Standard (CNS) A4 specification (210 X 297 mm) 533086. 5. Description of the invention (2) and improved. Similarly, the inventor found The hardness of the periphery of the ball striking surface can be reduced by subjecting only the ball striking surface to the heat treatment process and then melting it with other components. It does not need to first melt each component and then accept the dazzling parts as in the conventional process. Heat treatment process. Therefore, the present invention provides a golf club head, which includes a center portion on the hitting surface and surrounds at least a portion The peripheral part of the heart part, in which the golf club head is made of metal, and the hardness of the peripheral part is lower than the hardness of the central part. The present invention also provides a golf club head including a front part constituting a hitting surface, and the hitting surface includes a The central part and the peripheral part surrounding at least a part of the central part, in which the method of manufacturing a golf club head, includes the following steps. K is different from other raw materials used for golf club head members to produce a surface member; and then other members are welded In the periphery of the face member, a golf ball; f thousand heads are made of Mons, and the hardness of the peripheral part is lower than the hardness of the central part. According to another aspect of the present invention, the width of the peripheral part of the hitting surface is in the range of about 5 to 20 mm. The measurement of the width of the peripheral part is to measure the hardness distribution of the ball striking surface by measuring any point A on the edge of the ball striking surface and passing the center of the ball striking surface to point B on the edge of the ball striking face. The average hardness measured on the central area of the sphere determines the hardness of the central part. The hardness difference in the area is within 5% of the soil. The average hardness measured in the area of a determines the hardness of the surrounding parts near point A, and the hardness difference in the area is within ± 5%; the determination of a measurement point, the hardness value is closest to the medium to 4 hardness and the surrounding The median value of the hardness of the part; and determine the width of the peripheral part as the distance between point A and the measurement point. -5- 533086 A7 ___ B7 V. Description of the invention (3) According to another aspect of the present invention, the hardness difference between the center and peripheral parts of the striking surface is equal to or greater than 50 Vickers hardness, and the hardness of the center and peripheral parts Measure the hardness distribution of the ball striking surface by measuring any point A on the edge of the ball striking surface and passing the center of the ball striking surface to a point B on the edge of the ball facing surface. The average hardness measured determines the hardness of the central part, and the hardness difference in the region is within 5% of the soil; and by using the average hardness measured on the area near the point A, the hardness of the peripheral part near the point a is determined. The hardness difference in the region is within 5% of the soil. The drawings have briefly described some features and advantages of the present invention, others will be more apparent from the following detailed description and the accompanying drawings, of which: FIG. 1 is a schematic diagram showing a golf club head according to an embodiment of the present invention 2A is a schematic view showing the front part of a golf club (wooden) head according to Example 1 of the present invention; FIG. 2B is a diagram showing the hardness distribution of the golf club head shown in FIG. 2a FIG. 3A is a schematic view showing a front portion of a golf club (iron) head according to Example 7 of the present invention; and FIG. 3B is a diagram showing the hardness distribution of the golf club head shown in FIG. 3a. Detailed Description of the Invention The invention, as outlined above and defined by the scope of the listed patent applications, can be better understood by reference to the following detailed description, which should be read with reference to the drawings. -6-This paper size applies Chinese National Standard (CNS) A4 regulations ^^ 297, p

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The detailed description of the specific preferred embodiment uses the specific implementation of the present invention, but it is not only used as a specific example of the present invention. 'Although the following is proposed and established by people and is intended to limit the scope of patent applications listed, FIG. 1 is not FIG. 'Shows a golfer's face according to an embodiment of the present invention. F knife. It is noted in FIG. 1 that although the golf club (wooden) head: the face trowel 1 'is formed with the hosel la-body according to this embodiment of the present invention, {this month is not limited to this way, and The front part ^ and the sheath h can be opened with a knife. Also in FIG. I, the front part i is dazzled with other components, and its peripheral parts constitute a bottom part and a crown part for making golf talents. Therefore, the front part 1 is made of at least one material different from other components. Fabrication, but other components such as the bottom and crown can be formed integrally with other components or separately. — In Figure 1, the hardness of the peripheral part 3 of the front part 1 is lower than that of the central part 2 of the front part 1. In the front part, the width W (W1 & W2) from the edge of the peripheral part 3 to the center of the front part 1 is the range of about 5 to 20 mm. Similarly, the difference in Vickers hardness between the central portion 2 and the peripheral portion 3 is preferably 50 or more. If the Vickers hardness difference between the central part 2 and the peripheral part 3 is 50 or higher, and the width W of the peripheral part 3 is between about 5 to 20 mm, the flying distance performance of the club head is improved, and at the same time, Durability can be enhanced. On the other hand, it is preferable that the Vickers hardness of the center portion 2 is 500 degrees or less. If the Vickers hardness of the center part 2 exceeds 500, the flying distance performance and durability of the head will be reduced. In addition, although the wooden head has been explained in the above embodiment, it is also best to use a Chinese or Japanese standard (CNS) A4 specification for the hardness of the peripheral part 3 lower than that of the central part, such as an iron or practical head. (210 X 297 mm)

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Line 533086 A7 B7 V. Description of the invention (5) Bit 2 hardness. The hardness of the peripheral part 3 and the hardness of the central part 2 will be explained below, while explaining the width W of the peripheral part 2 in the embodiment of the present invention. The Vickers hardness of the front part 1 shown in Fig. 1 is measured from the point A on the edge of the peripheral part 3, and the point b on the opposite edge of the peripheral part 3 is measured by the point 0 located at the center, and the hardness distribution of the front part is obtained. Next, the average hardness of the higher portions near point 0 'can be calculated based on the obtained hardness distribution. The elevated part can be defined, for example, as a region with a hardness difference within ± 5%, and the average hardness of the elevated part can be used as the central part 2 hardness. Similarly, the average hardness of the higher portions near the points A and B respectively located on the edge of the peripheral portion can also be obtained. The protruded part near points a and B can also be defined as the area with a hardness difference within the range of ± 50/0. At the same time, the average hardness of the higher part obtained for each point A and B can be further averaged and used as Peripheral part 3 hardness. Similarly, the width in the peripheral portion 3 can be calculated as follows. The median hardness between the peripheral part 3 and the central part 2 can be obtained. Then, points eight and 扪 with hardness equal to the median value can be determined, and at the same time, the width wi can be measured, that is, the width from point A to point A1 on the periphery of the peripheral part 3 and the width W2, that is, since The width from point B to point m on the peripheral edge of the peripheral part 3. Finally, the width w can be calculated by averaging the different widths W1 and W2, which is used as the width of the peripheral portion 3. Next, a method for manufacturing a golf club according to a second embodiment of the present invention will be explained. First, the surface member, the bottom member, and the crown member are obtained by molding a metal such as a titanium alloy using a sheet metal processing process. The sheathing member can be -8-This paper size applies Chinese National Standard (CNS) A4 specification (2ΐ〇χ 297mm) ------_____ 533086 A7 _______ B7 V. Description of the invention ^ ^ "-乂 = 'Making clothing. Attention should be paid to the surface and hosel members, which can be shaped as described above. Next, only the surface members undergo a heat treatment process. The heat treatment system can be obtained by performing the aging treatment after the solution treatment is performed, or by performing the aging treatment only. The solution treatment can be performed at a temperature of about 700 to 90 ° C. At the same time, the cape effect treatment can be performed in the air at a temperature of about 400 to 600 ° C. IY for about 5 to 10 hours. The surface member undergoes heat treatment, The moxibustion bottom, the fun part, the hosel member and the face member are fused to produce a golf club head. It is best to perform a dazzle process under an argon atmosphere with a dazzle current of about 30 to 90 amps. If the face member is in the After the aging process before the welding process, the peripheral parts of the surface member are heated by the welding heat energy applied during the welding process, while the hardness of the peripheral parts is reduced. S; The idea is to increase as long as the strength of the metal, solution treatment and heat treatment such as heat treatment. Then, according to the embodiment of the present invention, it is also possible to use a metal different from titanium alloy, and obtain the effect of reducing the hardness of the peripheral part during the welding process after the heat treatment process. If the hardness of the peripheral part of the surface member is reduced as described above, then the constitution The central part of the hitting surface has a relatively increased hardness, so because the peripheral part has a lower hardness than the central part, the elastic effect is obtained. The performance of the flying distance of the head is improved compared with the conventional club head with the same hardness of the front part. In addition, the durability of the golf club head according to the embodiment of the present invention is not like the conventional club head due to the impact applied to the hitting surface. Only the front part is absorbed by the entire head because the entire head is strained due to the low hardness of the peripheral part. As described above, according to the present invention, the peripheral part of the front part can be dazzled by the face member. Before the process, the heat treatment can reduce the hardness of the center part by -9- This paper size applies the Chinese National Standard (CNS) A4 specification (210 X 297 mm) 533086 5. Description of the invention (low. Similarly, the periphery of the front part The size of the part can be controlled by the size of the dazzling current used to connect the surface to other components. This is when the welding current: Xi Ri ^, the area of the peripheral part with lower hardness is enlarged, so the 'peripheral 2 area' can be borrowed Reduced by the use of a smaller welding current. If the hardness of the front part of the mountain 4 is lower than the hardness of the center part in the above manner, the flight distance of the golf club head The performance is enhanced 'and its durability is improved. It should be noted that according to the present invention, as long as the hardness of the peripheral part can be small = the hardness of the center part, any manufacturing method can be used, therefore, the golf club head does not need to use the front face described above. The parts are produced separately and produced by a heat treatment process before the welding process. Example 1 The benefits of the present invention will be explained below by comparing a golf club head according to the present invention with a comparative example. Dry Example 1 The titanium alloy and the sheet metal processing process are used to make the surface member, the bottom member and the crown member. Similarly, the sheath member is made by a mechanism. The surface structure is made of a β-type titanium alloy, which undergoes an aging treatment at 430 ° C for 10 hours. In this way, the aging treatment is performed before the welding process, and the hardness of the perimeter of the front part is reduced compared to the center part. Next, the face member, the bottom member, the crown member, and the sheath member are welded under an argon atmosphere, and the welded members are polished to form the golf club (wooden) head of Example 1 shown in FIG. 2A. Example 2 'By using a titanium alloy and using a sheet metal processing process, a face member, a bottom member, and a crown member are separately produced. In the same way, the sheathing member is made by the mechanism of this paper with the national financial standard (CNS) -10- 8) 5. Description of the invention (: = mining:: _ alloy production, which under the war _ bottom member, crown The component is h and the welded part is polished to make Fancang J 3-inch aging treatment. Next, the face member insert sheath member 'welds the golf club (wooden) head of 2 in an argon atmosphere. Example 3 In Example 3 The surface members are made of rolled alloys. It is known to use the cold rolling process without annealing. At the same time, the sheet metal process is used as the surface member components, that is, the crown and the bottom members. Si pure titanium is manufactured using the sheet metal processing process. The ground member is made of a round rod. The face member is subjected to a 30-minute% efficiency process in the air under the avoidance of 4. The face member, the bottom member, the crown member, and the sheath member I are exposed to argon with a current of 60 amps. Welding under atmospheric conditions, and at the same time the welded parts were polished to make the golf club (wooden) head of Example 3. Therefore, only the materials used for the surface members and the aging process time of Example 3 are different from those of Example 1. Example 4 In Example 4, each construct It is made of the same material as in Example 丨, and the surface member is subjected to aging treatment in the air at 430 tT as in Example 1. After that, the golf club (wooden) head of Example 4 is different from the example. 1 welding conditions, that is, using 90 ampere current in the dazzle welding process under argon environment, which is 5 times the current used in Example 1. After the polishing process, 'obtained using a material, has the same as Example 1 Head shape Example 4 Golf club (wooden) head. The width of the peripheral part of the front part of the head with lower hardness is 22 mm due to the increase in welding current. -11-This paper size applies to China® standards (CNS) A4 specification (210X297 mm) Example 5: The parent component is the same as in Example 1—the surface components are made as in Example 1 at 43 °. Shizhi gave birth to Ligan 4. In the second gas experienced 10 hours Example 5 of \. / ", Using a different connection condition from Example 1, making a Fan Erfu club (wooden) head, that is, using 3. Ampere: In the course of performing ΓΓ, it is the example of using current in Example 1: V head; Γ was post- ′ obtained using the same material and having the same example 5 golf club (wood) head as the head / side. Has a small hardness mm. , And it is 3 due to the reduction of welding current. Example 6 'The surface member adopts _ titanium alloy, and the member that uses sheet metal plus the member surface member', that is, the crown member and the bottom member 'uses pure titanium metal and uses sheet metal-inserts the member from Production of round rods made of pure titanium; Similarly, . . Next, go through 3. Minute aging place ...; Surface :: The surface component is 430 1 plus the surface component, the bottom component, the core 4 component and the hosel component, using 60 χΛ 〇 < dumplings under the argon ring grave, and the welded parts are polished and Get an example of a clever golf club head. Therefore, the time for aging treatment in Example 6 is different from Example W, but the shape of each part of the shoulder condition ’and the head. Example 7 The same as that in Example 1. Person: Example 7 in the clothes-hardcore. The surface components of the iron head are made of titanium and made of sheet metal. Different from the surface structure, the plug sheath member and the rod frame member are integrally cast. The cow also uses β type 533086 A7.

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Line 533086 A7 B7 V. Description of the invention (11) Table 1 Head material aging treatment welding electric hardness hardness hardness difference width condition (° c X hours) flow (ampere) (center) (periphery) Example 1 wood β Ρ 430χ 10 60 340 260 80 8 Example 2 α + β Ρ700χ 2 60 400 350 50 10 Example 3 β ρ 430χ 0.5 60 460 260 200 5 Example 4 β ρ 430χ 10 90 340 260 80 22 Example 5 β ρ 430χ 10 30 340 260 80 3 Example 6 β ρ 430χ 0.5 60 280 260 20 5 Comparative Example 1 β 430χ 10 60 340 340 0 0 Example 7 Iron β β 430χ 10 60 340 260 80 8 Comparison Example 2 β 430χ 10 60 340 340 0 0 * β: β Type titanium alloy; α + β: α + β type titanium alloy; P: process before welding; A: process after welding; and W: width. Similarly, the hardness distribution of the front part of each golf club head can be measured. In fact, each golf club head is cut from the golf club head to the bottom member, and the Vickers hardness from one end of the cut surface to the other is measured at a distance of about 1.2 to 1.6 mm . The hardness of the peripheral and central parts can be obtained based on the measurement results. Then, the median hardness between the peripheral part and the central part can be calculated to determine the measurement point with the closest median hardness, and this measurement point is used to define the boundary between the peripheral part and the central part. In Table 1 above, the hardness of the peripheral part and the central part, the hardness difference between the two, and the width of the peripheral part are also shown. -14- This paper size is in accordance with Chinese National Standard (CNS) A4 specification (210X297 mm) 533086 A7 B7 V. Description of the invention (12) Figure 2B is a diagram showing Example 1 golf club (wooden) shown in Figure 2A ) The head is at the cut surface 10 and compared with the Vickers hardness of the golf club head of Comparative Example 1. In Fig. 2B, the Vickers hardness of the golf club head of Example 1 is indicated by a dot (·), and the golf club head of Comparative Example 1 is indicated by a triangle point (▲). Similarly, FIG. 3B graphically shows the Vickers hardness of the golf club (iron) head of Example 7 shown in FIG. 3A at the cut surface 20, as compared with the golf club head of Comparative Example 2. In Fig. 3B, the Vickers hardness of the golf club head of Example 7 is represented by a dot (·), and the golf club head of Comparative Example 2 is represented by a triangle point (▲). The hardness of the peripheral part and the central part, and the width of the peripheral part are calculated by using the above-mentioned method for the hardness analysis of each front part. For example, in the golf club head of Example 1 shown in FIG. 2A, the average hardness in the area near points A and B where the difference in hardness is within ± 5%, and the difference in hardness is within ± 5. The average hardness in the area near the 0 point in the% range is 340. Therefore, the center value calculated from the above average value is 300. The hardness is closest to the measurement point of 300, 8 mm away from point A, and 7.5 mm away from point B. Therefore, the width W of the peripheral part is measured to be approximately 8 mm of the average value between the two points. Therefore, the peripheral part of the front part is defined as a region having a width W of 8 mm. The hardness analysis of the golf club head of Example 7 shown in Fig. 3A, and the hardness distribution of other examples and comparative examples are measured respectively in the same manner as above, and the hardness of the peripheral and central parts and the width of each peripheral part are obtained according to the obtained Calculation of hardness distribution. Next, the golf club heads used to estimate Examples 1 to 7 and Comparative Examples 1 and 2 will be explained. Each golf club head is tested for flight distance performance. Flying distance test, by using the shaft attachment example and the comparison example as -15- This paper size applies to China National Standard (CNS) A4 specification (210 X 297 mm) 533086 A7 B7 ___ V. Description of the Invention (13) A golf club head is executed, and a golf club test robot is used to swing the golf ball at the center of the front portion of the club head at a speed of 40 meters per second. Each Nanlf club head was repeatedly tested 10 times. The measured distances of Nanlf clubs are shown in Tables 2 and 3 below. Table 2 Flight distance (m) Shortest average longest example 1 226 230 233 Comparative example 1 216 219 223 Table 3 Flight distance (m) Shortest average longest example 7 167 170 172 Comparative example 2 161 165 167 Similarly, each shot Heads are tested for durability. When the club head swings the golf ball at 3,000, 6,000, and 9,000 times at a head speed of 40 meters per second, the center of the front part of the club head is observed with the naked eye to determine whether a crack or nick is generated. The head endurance test results of Example 1 and Comparative Example 1, and Example 7 and Comparative Example 2 are shown in Tables 4 and 5 respectively. Similarly, the evaluation results of each club head are listed in Table 6. -16- This paper size applies Chinese National Standard (CNS) A4 specification (210 X 297 mm) 533086 A7 B7 V. Description of the invention (14) 3,000 shots after 3,000 shots 9,000 shots after 9,000 shots Example 1 None Change No change No change Comparison example 1 No change There is a crack in the center of the front part Table 4 Table 5 3,000 shots ^ 6,000 shots after 9,000 shots Example 7 No change No change No change Comparison example 2 No change The center of the front part Table 6 Cracked head durability test Flight distance test 3,000 balls 6,000 balls 9,000 average flight distance (meters) Example 1 Wooden NCNCNC 230 Example 2 NCNCNC 228 Example 3 NCNC Crack 227 Example 4 NCNC Notch 228 Example 5 NCNC crack 222 Example 6 NCNC score 221 Comparative example 1 —- ---- NC crack-219 Example 7 ----- ―Iron NCNCNC 170 Comparative example 2 NC crack-165 N. C ·: No change -17 -This paper size is applicable to China National Standard (CNS) A4 (210 X 297 mm) 533086 A7

533086 Five A7 B7 Description of the invention (16) Both are in the better range β ′. Therefore, the flight distance performance and durability are significantly improved compared to the comparison example 2 shown in Tables 3 and 5. Therefore, as described above, according to the example of the sun and moon sound%, the meaning of low I I ~ Mingbei%, because the hardness of the peripheral part of the front part, compared to its central part, the hardness is 伥 // Hungarian, so it has excellent flight. Distance performance and durability of golf club heads. Several examples of the present invention have been described. Those skilled in the art generate various changes, decoration and improvement, although the spirit and scope are not expressed above. Therefore, this publication is limited and defined. After the examples, it is slightly visible that the will be modified, modified and improved at any time. These changes, modifications but still desire and are implied in the present invention are only

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Claims (1)

533086 Λ 8 Β8 C8 1. A golf club head comprising: a hitting surface at a part of a center portion, which includes a center portion and surrounding at least a peripheral portion, wherein the Γ% golf club head is made of Bema metal today, and the peripheral portion The hardness is lower than that of the central part. A golf club head includes: a face member constituting a hitting surface, and the hitting surface includes a center portion and a peripheral portion surrounding at least a part of the center portion, wherein the golf club head includes a method including the following steps: Making ·· The face member is made of a material separate from other members used in the golf club head; and then the other member is welded to the periphery of the face member, and the golf club head is made of metal and the peripheral portion The hardness is lower than that of the central part. • The golf club head according to item 1 of the patent application scope, wherein: the width of the peripheral portion of the hitting surface is within a range of about 5 to 20 mm. 'The width of the peripheral portion is determined by the following steps: Measure the impact The hardness distribution of the spherical surface from any point A on its edge, through its center, to point B on its opposite edge; by using the average hardness value to determine the hardness of the central part, the hardness value is in the area near the center of the hitting surface Measured, the hardness difference in this area is within the range of 5% of the soil. The hardness of the surrounding area near point A is determined by the average hardness. The hardness is measured in the area near point A. The hardness difference in this area is: t 5% -20- This paper size applies to Chinese National Standard (CNS) A4 (210 X 297 mm) 533086 Λ8 B8 Within the range; determine a measurement point ’whose hardness value is close to the average between the hardness of the central part and the hardness of the peripheral part; and determine the width of the peripheral part as the distance between point A and the measurement point. 4 · The golf club head according to item 2 of the scope of patent application, of which ·· The width of the peripheral part of the hitting surface is within the range of about 5 to 20 mm. The width of the peripheral part is determined by the following steps. The hardness distribution at the center to point B on the opposite edge. The hardness of the center is determined by using the average hardness value. The hardness value is measured in the area near the center of the striking surface. The hardness difference in this area is ± 5 Within the range of% Determine the hardness of the surrounding area near point A by the average hardness value. The hardness is measured in the area near the point A. The hardness difference in this area is within the range of + 5%. Determine a measurement point whose hardness value is close to The average value between the hardness of the central part and the hardness of the peripheral part; and the width of the peripheral part is determined as the distance between the A point and the measurement point. 5. The golf club head according to item 1 of the scope of patent application, wherein: the hardness difference between the central part and the peripheral part is equal to or greater than 50 Vickers hardness value, and the hardness of the central part and the peripheral part is determined by the following Step decision: Measure the hardness distribution of the ball striking surface from any point A on its edge, through its center to point B on its opposite edge; -21-This paper size applies the Chinese National Standard (CMS) A4 specification (210 X 297 directors) 533086 A8 B8 C8 D8 The scope of patent application determines the hardness of the central part by the average hardness value. The hardness value is measured in the area near the center of the ball striking surface. The hardness difference in this area is within the range of ± 5%. And the hardness of the surrounding area near point A is determined by the average hardness value. The hardness is measured in the area near point A, and the hardness difference in this area is within ± 5%. 6. The golf club head according to item 2 of the scope of patent application, wherein: the hardness difference between the central part and the peripheral part is equal to or greater than 50 Vickers hardness value, and the hardness of the central part and the peripheral part is determined by the following steps: Decide: Measure the hardness distribution of the hitting surface from any point A on its edge, through its center, to point B on its opposite edge; by using the average hardness value to determine the hardness of the center part, the hardness value is near Λ Measured in the area of the center of the ball striking surface, the hardness difference in this area is within the range of ± 5%; and the hardness of the peripheral part is determined near the point A by the average hardness, and the hardness is measured in the area near the point A, The hardness difference in this area is within ± 5%. 7. The golf club head according to item 3 of the scope of patent application, wherein: the hardness difference between the central part and the peripheral part is equal to or greater than 50 Vickers hardness value, and the hardness of the central part and the peripheral part is determined by the following steps: Decided: Measure the hardness distribution of the ball striking surface from any point A on its edge, through its center to point B on its opposite edge; -22- The size of the paper is applicable to China National Standard (CNS) A4 (210X297 mm) ) 533086 8 8 8 8 AB c D. The scope of patent application determines the hardness of the central part by the average hardness value. The hardness value is measured in the area near the center of the striking surface. The hardness difference in this area is ± 5%. Within the range; and determine the hardness of the surrounding area near the point A by the average hardness value, and the hardness is re-measured in the area near the point A * The hardness difference in this area is within 5%. -23- This paper size applies to Chinese National Standard (CNS) A4 (210 X 297 mm)