CN105889414A - Component for metal belt of continuously variable transmission - Google Patents

Abstract

The present invention provides an element for a metal belt of a continuously variable transmission, which can properly reduce the stress generated at the root of the neck of the element when the metal belt is driven, thereby increasing the repeated fatigue strength, thereby improving the torque transmission capacity of the continuously variable transmission, And it is possible to improve the power transmission efficiency of the continuously variable transmission near the overdrive ratio region. The element is manufactured using a steel material having a carbon content of not less than 0.61% and not more than 0.71% as the steel material of the element. At this time, the shape of the base of the neck connecting the saddle surface and the neck side is constituted by three curved surfaces that are smoothly connected to each other and satisfy the relationship of R1<R2<R3 and D/R2≤0.3. A downwardly convex surface (PA-PB(R1)), a downwardly convex surface (PB-PD(R2)), and an upwardly convex surface (PD-PE(R3)). In addition, adjacent curved surfaces sharing the same tangent plane (tangent line) are smoothly connected at each connection portion.

Description

Components for metal belts of continuously variable transmissions

technical field

The present invention relates to an element for a metal belt of a continuously variable transmission, and more specifically relates to an element for a metal belt of a continuously variable transmission that can properly reduce the stress generated at the root of the neck of the element when the metal belt is driven and improve the repeated fatigue strength , so that the torque transmission capacity of the continuously variable transmission can be improved, and the power transmission efficiency of the continuously variable transmission near the overdrive ratio region can be improved.

Background technique

As an element for a metal belt of a continuously variable transmission, as shown in FIG. The roughly triangular ears are formed on the upper part of the main body from the neck. A pair of abutting surfaces capable of abutting against V surfaces of a driving pulley (not shown) and a driven pulley (not shown) are formed at both ends in the left-right direction of the element body. In addition, main surfaces abutting adjacent elements are respectively formed on the front side and the rear side in the traveling direction of the element, and furthermore, a locking edge extending in the left-right direction is formed on the lower part of the main surface on the front side in the traveling direction. There are slopes. Further, in order to connect front and rear adjacent elements, protrusions and holes that can be fitted with each other are respectively formed on the front and rear surfaces of the ear ( FIG. 9( b )). Further, a saddle surface for supporting the inner peripheral surface of the metal ring assembly (the inner peripheral surface of the innermost metal ring) is formed at the lower edge of the left and right annular seams.

Furthermore, the metal belt composed of the above-mentioned metal ring assembly and the above-mentioned element is wound between a pair of pulleys (drive pulley, driven pulley), and the two abutting surfaces of the element are pressed against the V of the pulley. Rotational power from the engine is transmitted from the drive pulley to the driven pulley by the frictional force between the abutment surface and the V surface of the pulley. In this way, when the metal belt rotates, the saddle surface of the element is pressed downward by the metal ring assembly, and the two contact surfaces are pressed by the V surface of the pulley. Furthermore, when the element transmits and transmits torque to the driving pulley and the driven pulley, a bending moment in the front-rear direction acts on the element main body according to the direction of torque transmission. Therefore, stress concentrates on the neck portion of the element, particularly on the base portion of the neck portion (dotted circle portion in the figure) which is the intersection portion with the saddle profile.

A circular-arc concave portion that is smoothly recessed from the neck side surface to the saddle surface is formed at the base of the neck. A known element is characterized in that the cross-sectional shape of the arcuate recess consists of a first arc of curvature radius R1 continuous with the neck side and a second circle of curvature radius R2 continuous with the first arc and forming the bottom. An arc is formed, and the radius of curvature R1 is greater than the radius of curvature R2 (for example, refer to Patent Document 1).

In addition, an element is also known, characterized in that the circular arc concave portion is composed of four circular arcs with radii of curvature R1, R2, R3, R4, and among these radii of curvature, the second circular arc forming the bottom is the radius of curvature R2 is the maximum value (for example, refer to Patent Document 2).

In addition, there is also known an element characterized in that the ratio D/R of the arc depth D from the saddle surface to the radius of curvature R is in the range of 0.3 to 0.75 (for example, refer to Patent Document 3).

On the other hand, it is known that the carbon content (C% contained) of the element material has a large influence on the stress concentration at the base of the neck. It is known that wear resistance and fatigue resistance of the element can be improved when the element is made of steel having a carbon content (C %) of 0.50 to 0.70% (for example, refer to Patent Document 4).

prior art literature

patent documents

Patent Document 1: Japanese Patent No. 4766064

Patent Document 2: Japanese Patent No. 3975791

Patent Document 3: Japanese Patent No. 4321119

Patent Document 4: Japanese Patent No. 5594521

The aforementioned Patent Documents 1 and 2 are techniques for reducing the stress generated at the base of the neck by connecting the saddle surface and the neck side surface with a smooth arc (curved surface). That is, it is a technique for reducing the stress generated at the base of the neck by increasing the curvature radius R of the arc without changing the overall shape of the element.

However, according to strength analysis, it has been found that the distance (depth) D from the saddle surface to the lowest arc has a greater influence on the stress generated at the base of the neck than the radius of curvature R. In the above-mentioned Patent Documents 1 and 2, the distance (D) from the saddle surface to the lowermost portion of the arc is not considered.

FIG. 10 shows analysis results obtained by strength analysis when a downward load is applied to the saddle surface of the element while the element is restrained as shown in FIG. 9( a ). In addition, FIG. 11 shows that the rear surface in the middle position between the saddle surface and the locking edge is convex from the hole side in the state where the element is restrained as shown in FIG. 9 (b) through strength analysis. Analysis results of the stress generated at the base of the neck when a load is applied to the head side. According to (a) and (b) of Figure 10 and (a) and (b) of Figure 11, it can be seen that even in the relationship of R1<R2 (R1/R2<1) and R3<R2 (R3/R2<1) , the resulting stresses are still high and largely discrete. Therefore, the above-mentioned Patent Documents 1 and 2 do not necessarily have a large effect on reducing the stress at the base of the neck.

In addition, in the above-mentioned Patent Document 3, the distance (D) from the saddle surface to the lowest portion of the arc is considered.

However, it can be seen from (c) of FIG. 10 and (c) of FIG. 11 that a very high stress occurs at the root of the neck when 0.3≤D/R≤0.75. Therefore, the above-mentioned Patent Document 3 does not necessarily have a great effect on reducing the stress at the base of the neck.

Contents of the invention

Therefore, the present invention has been accomplished in view of the above-mentioned problems in the prior art, and its object is to provide a metal belt element of a continuously variable transmission, which can properly reduce the stress generated at the root of the neck of the element when the metal belt is driven. By improving the repeated fatigue strength, the torque transmission capacity of the continuously variable transmission can be improved, and the power transmission efficiency of the continuously variable transmission near the overdrive ratio region can be improved.

With regard to the element for the metal belt of the continuously variable transmission of the present invention for achieving the above object, a plurality of the elements are aligned in phase by a metal ring assembly formed by laminating a plurality of belt-shaped metal rings and along the metal ring assembly. stacked in a ring shape, and the element has a saddle surface supporting the metal ring assembly and a neck extending upward from the saddle surface, and the element is characterized in that,

At the root of the neck where the saddle surface intersects with the neck, there is formed a concave portion that is sunken toward the saddle surface side. A downwardly convex first curved surface (R1) in the range of the bottom surface portion of the concave portion; a downwardly convex second curved surface ( R2); and an upwardly convex third curved surface (R3) smoothly connected to both the second curved surface and the saddle surface, the first curved surface (R1), the second curved surface (R2) The radii of curvature of the third curved surface (R3) increase in the order of the first curved surface (R1), the second curved surface (R2) and the third curved surface (R3), and the third curved surface 2 The ratio of the depth (D) of the curved surface to the radius of curvature (R2) of the second curved surface is a value equal to or less than 0.3.

In the above structure, the neck base (corner) where the saddle surface and the neck intersect is configured such that the radius of curvature increases sequentially from the neck to the saddle surface, and the radius of curvature of the portion forming the bottom depends on the angle from the saddle surface. The three above-mentioned curved surfaces (arcs) of the depth are smoothly connected. That is, if the radius of curvature of the first curved surface connected to the neck side is R1, the radius of curvature of the second curved surface forming the bottom part is R2, and the radius of curvature of the third curved surface connected to the saddle surface is R3, the saddle surface When the depth of the second curved surface as a reference is D, the base of the neck (corner portion) where the saddle-shaped surface intersects the neck is formed by satisfying R1<R2<R3 and D/R2≤0.3. ). In particular, by increasing the radius of curvature sequentially and making the radius of curvature R2 forming the bottom surface dependent on the depth D from the saddle surface, the stress generated at the base of the neck can be appropriately reduced.

The second feature of the element for the metal belt of the continuously variable transmission of the present invention is that the steel material constituting the element contains at least carbon (C), silicon (Si), manganese (Mn) and chromium (Cr) as additives, so The carbon content (%) is 0.61% or more and 0.71% or less.

In the above-mentioned structure, by using the steel with the above-mentioned carbon content, it can interact with the shape of the above-mentioned arcuate concave portion, which can appropriately reduce the stress generated at the root of the neck and improve the repeated fatigue strength of the element.

The effect of the invention

According to the element of the present invention, the above-mentioned shape characteristics of the neck base interact with the above-mentioned material characteristics of the steel constituting the element, so that the stress generated at the neck root of the element can be appropriately reduced, and the repeated fatigue strength of the element can be improved. . In addition, in the element of the present invention, the distance (D) from the saddle surface to the bottom portion is small, and the stress generated at the base of the neck is small, so that the locking edge can be moved to the saddle surface side. As a result, in the vicinity of the overdrive ratio region, torque loss due to slippage occurring between the ring and the saddle surface can be reduced, which can contribute to the improvement of the power transmission efficiency of the continuously variable transmission.

Description of drawings

(a) and (b) of FIG. 1 are explanatory cross-sectional views of main parts showing the base of the neck of the element of the present invention.

(a) and (b) in Fig. 2 show the analysis results obtained by strength analysis when a downward load (that is, a load from above) is applied to the saddle surface of the element of the present invention at the base of the neck. chart.

(a) and (b) in Fig. 3 show that the back surface in the middle position between the saddle surface and the locking edge of the element of the present invention is applied a load from the hole side to the nose side by strength analysis (that is, A graph of the analysis results of the stress generated at the root of the neck when the load comes from the rear).

Fig. 4 is a graph showing the correlation between steel material, neck base shape, and repeated fatigue strength.

Fig. 5 is a graph showing the relationship between the carbon content, the shape of the base of the neck, and the repeated fatigue strength.

Fig. 6 is an explanatory view showing the locking edge of the element of the present invention, the left side shows the shape of the conventional element, and the right side shows the shape of the element of the present invention.

Fig. 7 is an explanatory diagram showing power transmission efficiency of a continuously variable transmission using the element of the present invention.

Fig. 8 is a perspective view showing a conventional element.

(a) and (b) of FIG. 9 are explanatory views showing the direction of the load applied to the element.

(a), (b) and (c) in Fig. 10 show the stress generated at the base of the neck when a downward load (i.e., a load from above) is applied to the saddle surface of a conventional element obtained by strength analysis A graph of the analytical results at time.

(a), (b) and (c) in Fig. 11 show that the back surface of the existing element in the middle position between the saddle surface and the locking edge is applied from the hole side to the convex head side through strength analysis. It is a graph of the analytical results of the stress generated at the base of the neck when the load is applied (that is, the load is applied from the rear).

FIG. 12 is an S-N diagram explaining the “equivalent load for fatigue strength of repetition number 1.0E+5 times” in FIGS. 4 and 5 .

Label description

100: element, C1, C2, C3, C4: arc center, L1, L2, L3, L4, L5: tangent, n1, n2, n3, n4, n5: normal, PA, PB, PD, PE: connection Point, PC: the deepest point, PF: the top of the saddle surface, PA-PB, PB-PD, PD-PE: curved surface (arc), R1, R2, R3: radius of curvature, D: from the top of the saddle surface to the deepest Point distance (depth), W: distance from the neck side to the R start point of the saddle profile.

detailed description

Hereinafter, the present invention will be described in further detail through the embodiments shown in the drawings.

FIG. 1 is an explanatory cross-sectional view showing a main portion of a neck base portion of an element for a metal belt (hereinafter referred to as "element") 100 of a continuously variable transmission according to the present invention. In addition, (b) of FIG. 1 is a graph which shows the correlation of each curvature radius R and depth D. In addition, the symbol D is the depth (distance) from the end of the saddle surface to the deepest part (point) PC, and the symbol W is the distance from the neck side to the R start point PE of the saddle surface.

In this element 100, the connecting surface at the base of the neck that smoothly connects the saddle surface and the neck side is gradually increased from the neck side to the saddle surface, and the curvature radius R2 of the bottom surface depends on the curvature radius from the saddle surface to the saddle surface. The three curved surfaces (arcs) of the depth D are smoothly connected, and the three curved surfaces are the downwardly convex curved surface (arc) PA-PB and the downwardly convex curved surface (arc) PB -PD and upwardly convex curved surface (arc) PD-PE. In addition, although the details will be described later, steel materials having a carbon content (mass %) of 0.61 to 0.71% are used as the steel materials constituting the element 100 . In addition, here, for convenience of description, the use of curved surface and circular arc means the same meaning.

In addition, "smoothly" here refers to the case where adjacent curved surfaces (arcs) are connected by the same tangent plane (tangent line). Therefore, the center of each arc is obtained as the intersection of the normal lines at the two connection points, and the radius of curvature thereof is obtained as the distance from the center of the arc to the connection point. Conversely, when the arc centers and curvature radii of each curved surface are known, the straight line connecting the two arc centers becomes the normal line, and the position of the connection point is automatically obtained from the normal line and the curvature radius. position to automatically determine the length of the arc. For example, the position of the connection point PB and PD of the arc PB-PD can be automatically calculated by the normal line n2 connecting the arc centers C1 and C2, the normal line n3 connecting the arc centers C2 and C3, and the radius of curvature R2 out, and automatically determine the length of the arc PB-PD according to the position of the connection point PB, PD.

The circular arc PA-PB is smoothly connected to the neck side at the connection point PA, and is smoothly connected to the circular arc PB-PD at the connection point PB which does not reach the deepest part PC. The arc PA-PB is a downwardly convex arc whose curvature radius is R1 and whose arc center C1 is located outside the plane. In addition, the arc PA-PB is connected tangentially with the neck side and the arc PB-PD and thus has common tangents L1, L2, so the arc center C1 is taken as corresponding to the common tangents L1, L2 at the connection points PA, PB The intersection point of each normal line n1, n2 is obtained. In addition, the height position of the connection point PA, which is the starting point of the arc PA-PB, coincides with the upper end PF of the saddle surface in this embodiment, but it is preferably located at the upper and lower distance rings from the upper end PF of the saddle surface (Fig. 8) The position within half of the plate thickness, that is, within ±1/2Δ.

The circular arc PB-PD is smoothly connected with the circular arc PA-PB at the connection point PB and is formed within the range including the deepest point PC from the connection point PB to the connection point PD, and the arc center C2 is located on the surface and the curvature A downwardly convex arc with a radius of R2. In addition, the arc PB-PD tangent is connected to both the arc PA-PB and the arc PD-PE, so it has common tangents L2, L3, so the arc center C2 is taken as the common tangent L2, The intersection point of each normal line n2, n3 corresponding to L3 is obtained. In addition, as will be described later, the depth D from the upper end PF of the saddle surface to the deepest point PC and the radius R2 depend on each other, and have a relationship of D/R2≦0.3.

The arc PD-PE is smoothly connected with the arc PB-PD at the connection point PD, and is smoothly connected with the saddle surface at the connection point PE, and the center C3 of the arc is located in the plane and the radius of curvature is R3. Convex arc on top. The arc PD-PE tangent is connected to the arc PB-PD and the saddle surface, so it has common tangents L3, L4, so the arc center C3 is taken as the corresponding to the common tangents L3, L4 at the connection point PD, PE. Find the intersection point of normal lines n3 and n4.

In addition, as for the distance W from the neck side surface to the R start point of the saddle surface, if it is increased, the contact surface between the ring and the saddle surface will become smaller, which will adversely affect the operation of the ring, so it is preferably 1.6. ~1.7mm.

The radii of curvature R1, R2, and R3 have a relationship of R1<R2<R3 as shown in (b) of FIG. Therefore, in the case where the connection point PA and the connection point PE are fixed, if the depth D is determined, the radius of curvature R2 can be determined according to the relationship D/R2≦0.3. At the same time, the arc center C2 is also automatically determined (because the arc center C2 is located at a distance R2 from the deepest point PC on the normal line n5 corresponding to the tangent line L5 at the deepest point PC). Then, according to the relationship of R1<R2 and the constraint condition of tangent connection (the center of the arc is located on the normal line passing through the connection point), the arc center C1, the radius of curvature R1 and the connection point PB are respectively automatically determined. Similarly, according to the relationship of R2<R3 and the constraint condition of tangent connection, the arc center C3, radius R3 and connection point PD are also automatically determined respectively. In this way, in the element 100 of the present invention, if the depth D and the radius of curvature R2 are determined, the neck (formed by smoothly connecting the arcs PA-PB, arc PB-PD, and arc PD-PE) will be automatically determined. root shape.

FIG. 2 shows analysis results obtained by strength analysis when a downward load is applied to the saddle surface of the element while the element is restrained similarly to FIG. 9( a ). In addition, (a) of FIG. 2 shows the case of only R1<R2<R3 without the restriction of D/R2≤0.3, and (b) of FIG. 2 shows the case of the restriction of D/R2≤0.3. The case of R1<R2<R3.

According to the drawings, it can be seen that in the case of the constraint condition of D/R2≤0.3, the maximum stress Smax generated at the root of the neck will be further reduced compared to the situation without the constraint condition of D/R2≤0.3. Furthermore, fluctuations in stress are also reduced. In addition, the specific situation is omitted here, but based on the relationship of D/R2≤0.3 and R1<R2<R3 and the condition of tangential connection at the connection point, the value of the radius R2 must be limited to a range of about 1.0 mm or more .

Fig. 3 shows the analysis results obtained by strength analysis when a load is applied to the neck from the hole side to the protrusion side in the state where the element is restrained similarly to Fig. 9(b) . In addition, (a) of FIG. 3 shows the case of only R1<R2<R3 without the restriction of D/R2≤0.3, and (b) of FIG. 3 shows the case of the restriction of D/R2≤0.3 The case of R1<R2<R3.

According to the drawings, it can be seen that in the case of the constraint condition of D/R2≤0.3, the maximum stress Smax generated at the root of the neck decreases and the stress fluctuation becomes smaller than that of the condition without the constraint condition.

Thus, as shown in FIGS. 2 and 3 , it can be seen that the constraint condition of D/R2≦0.3 has a great effect on reducing the stress generated at the base of the neck.

In addition, the characteristics of the material (carbon content: 0.61% to 0.71%, preferably 0.61% to 0.67%), that is, in the case of using a steel material with a carbon content within the above range to produce the neck base having the above-mentioned shape characteristics (R1<R2<R3 and D/R2≤0.3), the element Not only has the effect of reducing stress at the root of the neck, but also has a great effect on the improvement of repetitive fatigue strength. The improvement of the repeated fatigue strength of the element 100 will be described below.

Fig. 4 shows that the same quenching and tempering treatments were carried out on steel material A and steel material B with carbon content [%] of 0.84 and 0.61 respectively, and steel material A and steel material B after these heat treatments were used to process different neck root shapes. (D/R2 = 0.298, 1.0) A total of 4 kinds of elements were carried out, and the individual fatigue test was carried out under the same load conditions as in Fig. The results of obtaining the load corresponding to the fatigue strength at the repetition number of 1.0E+5 times for each element. In addition, the "load corresponding to the fatigue strength at the number of repetitions of 1.0E+5 times" referred to here refers to the load on a test body that is broken when the number of repetitions is 1.0E+5 times or less, as shown in Fig. 12 . The value S at the time of N=1.0E+5 (cycle) in the S-N line graph obtained by statistical processing of the data. In addition, "improvement of fatigue strength" means that the above-mentioned S-N line graph moves upward as a whole.

The C content of steel B is less than that of steel A. Correspondingly, steel B is rich in toughness, and the 1.0E+5 fatigue strength of the material test piece is about 20% higher than that of steel A. However, in the case of the neck root shape of D/R2=1.0, comparing the steel material A and the steel material B, it can be seen that the improvement amount of the strength is about 5%, and almost no difference in the strength of the material itself is obtained. This is due to the high stress concentration at the root of the neck, almost losing the poor material strength.

On the other hand, comparing the results of the steel material A with the result of D/R2 = 0.298 of the steel material B, it can be seen that the fatigue strength was improved by more than 50%. This means that, in the case of using the neck root shape of D/R2=0.298 made of steel material B, the effect of alleviating stress concentration in addition to the above-mentioned shape characteristics (R1<R2<R3 and D/R2≤0.3) In addition, the effect of the material itself is also exerted, and the strength is further increased through the complementary effect of the shape effect and the material effect.

As shown in Fig. 4, it can be seen that the improvement of the fatigue strength due to the material effect differs depending on the shape of the base of the neck, that is, the value of D/R2. Hereinafter, the relationship between the shape of the base of the neck and the carbon content [%] will be described.

Fig. 5 shows: steel materials with various carbon contents [%] are subjected to the same quenching and tempering treatment as in Fig. 4 above, and the steel materials after these heat treatments are processed into different neck root shapes (D/R2 = 0.298, 0.4 , 1.0) of various elements, and carry out the same individual fatigue test, obtain the S-N line diagram, and obtain the load equivalent to the fatigue strength of the repetition number 1.0E+5 times for each element.

When D/R2=0.298, the carbon content [%] of the stress-relaxed neck root shape element becomes the maximum strength around 0.6 (0.61~0.71), and the carbon content above or below this will cause the strength to change. Low. The reason for this is considered to be that a region with a low carbon content causes a decrease in strength due to insufficient hardness, and conversely, a region with a high carbon content causes a decrease in strength due to a decrease in toughness. That is, the carbon content [%] corresponding to the above-mentioned characteristics in terms of shape is 0.61 to 0.71, and preferably has an optimum value of 0.61 to 0.67.

When D/R2=0.4, the fatigue strength will rise slowly with the decrease of carbon content [%], and reach the peak state around 0.65. Its material effect is also smaller than that of D/R2=0.298.

When D/R2=1.0, as the carbon content [%] decreases, the fatigue strength increases very slowly, and reaches a peak state around 0.6. The material effect is as shown in Fig. 4, and the increase in fatigue strength is about 5%.

Fig. 6 is an explanatory diagram showing a comparison between the shape of the element of the present invention and the shape of a conventional element.

The depth D of the root of the neck of the element of the present invention is smaller than that of prior art elements. This difference (amount of change) can be used as a margin (amount of movement) for moving the locking edge to the side of the saddle without risk.

When the locking edge is close to the saddle surface, as shown in Figure 7, near the overdrive (OD, overdrive) ratio area, it can reduce the torque loss caused by the slipping between the ring and the saddle surface, thereby making the continuously variable transmission The power transmission efficiency is optimized and improved.

As described above, according to the element 100 of the present invention, the above-mentioned shape characteristics of the root of the neck (R1<R2<R3 and D/R2≤0.3) and the above-mentioned material characteristics of the steel constituting the element (carbon content: 0.61% ~0.71%, preferably 0.61%~0.67%) interact to properly reduce the stress generated at the root of the neck of the element and improve the repeated fatigue strength of the element. The reason for this is that, as shown in FIGS. 4 and 5 , the fatigue limit and the S-N diagram are generally raised. As a result, the torque transmission capacity can be improved without increasing the size of the element. In addition, the distance (D) from the saddle surface to the bottom portion of the element of the present invention is small, and the stress generated at the base of the neck is reduced, so that the locking edge can be moved to the saddle surface side. As a result, in the vicinity of the overdrive ratio region, torque loss due to slip occurring between the ring and the saddle surface can be reduced, contributing to improvement of the power transmission efficiency of the continuously variable transmission.

Claims (2)

1. a metal tape element for buncher, these elements multiple are by the becket of the multiple banding of stacking The becket aggregation that becomes and alignment phase along this becket aggregation annularly stacking, and this element has Support saddle face and cervical region the most extended from this saddle face, the feature of this element of this becket aggregation It is,

Forming the recess of this side, saddle face oriented depression with described cervical region at the neck root intersected in described saddle face, this is recessed Portion is constituted by with lower part: is smoothly connected to the side of described cervical region and is formed at the bottom surface sections not arriving described recess The 1st curved surface the most convexly of the scope divided；Smoothly it is connected to the 1st curved surface and forms described bottom surface portions The 2nd curved surface the most convexly；And be smoothly connected to the 2nd curved surface and described saddle face both sides upward in convex 3rd curved surface of shape,

Described 1st curved surface, described 2nd curved surface and the described 3rd respective radius of curvature of curved surface according to described 1st curved surface, Described 2nd curved surface and the order of described 3rd curved surface and become big, and the degree of depth and the described 2nd of described 2nd curved surface The ratio of the radius of curvature of curved surface is less than the value equal to 0.3.

The metal tape element of buncher the most according to claim 1, it is characterised in that

Constitute and the steel of described element at least contain carbon, silicon, manganese and chromium as additive, the amount of described carbon be More than 0.61% and less than 0.71%.