JP2005121056A - Connecting rod, and method and device for manufacturing connecting rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a connecting rod hardened only at a specified position, and a method and a device for manufacturing the connecting rod. <P>SOLUTION: This connecting rod manufacturing device is formed such that when the outline of the connecting rod is formed by forging a steel for machine structural use, the connecting rod is heated to a temperature of approximately 750°C, and the areas of the connecting rod near a small end part 3 and a large end part 4 are clampingly held by a small end tool 8 and a large end tool 9 in the thickness direction. A first air blow tube 13 is formed at the large end tool 8 and a second air blow tube 18 is formed at the large end tool 9. Air shown by the arrow A can be sent out from the first air blow tube and air shown by the arrow B can be sent from the second air blow tube. The connecting rod manufacturing device is formed such that, when the connecting rod is held by the small end tool 8 and the large end tool 9, the air shown by the arrows A and B is sent out, cooling water is sprayed by a shower over the range of a column part 2, and the connecting rod is quenched so that that range can be transformed to a martensitic structure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a connecting rod, a connecting rod manufacturing method, and a manufacturing apparatus.

Conventionally, in a reciprocating engine such as a gasoline engine for automobiles, a connecting rod (hereinafter referred to as a connecting rod) that connects a piston and a crankshaft needs to have excellent buckling strength and fatigue strength due to its usage environment. there were. Therefore, when manufacturing a connecting rod, the hardening process of the whole product is performed by quenching and tempering, or carburizing quenching (for example, refer patent document 1).
JP-A-9-196044

  However, in the method for manufacturing a connecting rod described in Patent Document 1, since the entire connecting rod is subjected to a hardening process, it becomes difficult to perform a cutting process after the hardening process, and the connecting rod is reliably connected to a piston or a crankshaft. Therefore, there is a problem that the necessary cutting process is not performed smoothly.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a connecting rod, a manufacturing method and a manufacturing apparatus for the connecting rod, which are cured only at predetermined positions.

In the following, means for achieving the above object and its effects are described.
According to the first aspect of the present invention, the small end connected to the piston, the large end connected to the crankshaft, and the column portion connecting the small end and the large end are integrated. In the connecting rod formed in the above, the gist is that quenching is performed only in the column portion among the column portion, the small end portion, and the large end portion.

The gist of a second aspect of the invention is that, in the first aspect of the invention, the Vickers hardness of the column portion is 350 HV or higher.
According to invention of Claim 1 and Claim 2, the connecting rod provided with the column part which has high Vickers hardness compared with a small end part and a large end part is obtained. Therefore, a connecting rod having a high Vickers hardness at the column portion and good machinability at the small end portion and the large end portion can be obtained.

  According to a third aspect of the present invention, a small end connected to the piston, a large end connected to the crankshaft, and a column portion connecting the small end and the large end are integrated. In a connecting rod manufacturing method comprising a forging step and a step of blowing cooling water to the column portion, a step of covering the small end portion and the large end portion prior to the step of blowing cooling water to the column portion. The gist is to have prepared.

According to the invention described in claim 3, since the cooling water is not sprayed to the small end portion and the large end portion, quenching is not performed on the small end portion and the large end portion.
According to a fourth aspect of the invention, in the invention of the third aspect, when the small end portion and the large end portion are covered, the small end portion and the large end portion are sandwiched and held from both sides in the thickness direction. The gist is that

According to invention of Claim 4, since a deformation | transformation of a small end part and a large end part is suppressed, a coining process can be abbreviate | omitted and a manufacturing process is shortened.
According to a fifth aspect of the invention, in the invention of the third or fourth aspect, when the small end portion and the large end portion are covered, the small end portion and the large end portion cannot be moved relative to each other. This is the gist.

  According to the fifth aspect of the present invention, expansion due to transformation of the column portion occurs during quenching of the column portion, but since the small end portion and the large end portion are not relatively movable, The transformation expansion force is converted into residual stress, and the column portion is strengthened.

  The invention according to claim 6 is the invention according to any one of claims 3 to 5, wherein the small end portion covering means for covering the small end portion and the large end portion covering means for covering the large end portion are provided. The gist of the invention is that it is provided with a step of heating.

  According to the sixth aspect of the present invention, even when the cooling water is submerged toward the small end or the large end, the cooling water is evaporated by the heat of the small end covering means or the large end covering means. be able to. Therefore, quenching at the small end or the large end is prevented.

  According to a seventh aspect of the present invention, in the invention according to any one of the third to sixth aspects, when cooling water is sprayed on the column portion, the small end portion and the large end portion are directed toward the column portion. The gist of the invention is that it has a process for sending air.

According to the seventh aspect of the present invention, even when the cooling water is submerged toward the small end or the large end, the cooling water is immersed in the air sent toward the small end or the large end. It is suppressed.
According to an eighth aspect of the present invention, a small end connected to the piston, a large end connected to the crankshaft, and a column portion connecting the small end and the large end are integrated. In a connecting rod manufacturing apparatus that forges and quenches by blowing cooling water to the column portion, a small end portion covering means for covering the small end portion, and a large end portion covering means for covering the large end portion The gist is that

  According to the invention described in claim 8, the column portion is hardened by covering the small end portion with the small end portion covering means and covering the large end portion with the large end portion covering means. Quenching is performed only on the part. Therefore, the Vickers hardness of the column portion is improved without impairing the machinability of the small end portion and the large end portion.

  The invention according to claim 9 is the invention according to claim 8, wherein the small end covering means and the large end covering means press and hold the small end or the large end from both sides in the thickness direction. The gist of this is.

According to invention of Claim 9, since a deformation | transformation of a small end part and a large end part is suppressed, a coining process can be skipped and a manufacturing process is shortened.
According to a tenth aspect of the present invention, in the invention according to the eighth or ninth aspect, the small end portion covering means and the large end portion covering means cannot move the small end portion and the large end portion relative to each other. The gist is that it is coated.

  According to the invention of claim 10, expansion occurs due to transformation of the column part during quenching of the column part, but since the small end part and the large end part are not relatively movable, The transformation expansion force is converted into residual stress, and the column portion is strengthened.

  The invention according to claim 11 is the invention according to any one of claims 8 to 10, wherein the small end covering means and the large end covering means are the small end covering means and the large end, respectively. The gist is that a heating means for heating the covering means is provided.

  According to the eleventh aspect of the present invention, even if the cooling water is submerged toward the small end or the large end, the cooling water is evaporated by the heat of the small end covering means or the large end covering means. be able to. Therefore, quenching at the small end or the large end is prevented.

  According to a twelfth aspect of the present invention, in the invention according to any one of the eighth to eleventh aspects, the small end portion covering means includes a column portion extending from a gap between the small end portion covering means and the small end portion. A first air sending means for sending air toward the second end, wherein the large end covering means sends a second air toward the column portion from a gap between the large end covering means and the large end. The gist of the present invention is that it is provided with an air delivery means.

  According to the twelfth aspect of the present invention, even if the cooling water is submerged toward the small end or the large end, the cooling water is immersed in the air sent toward the small end or the large end. It is suppressed.

An embodiment of the present invention will be described with reference to FIGS.
In a reciprocating engine or the like, a connecting rod 1 (hereinafter referred to as a connecting rod 1) that connects a piston and a crankshaft is formed in a substantially Y shape in plan view as shown in FIG. The small end 3 and the large end 4 are provided. The connecting rod 1 is made of steel for machine structure such as carbon steel or alloy steel.

  The column part 2 is formed in an I-shaped cross section in order to achieve high buckling strength and light weight, and a hardening process is performed by quenching over a predetermined range X sandwiched between the straight lines X1 and X2. . The structure of the column portion 2 has a martensite form by quenching, and its Vickers hardness is set to about 350 HV.

  The small end portion 3 is formed to be slightly wider than the column portion 2, and a first connection hole 3a for connecting the small end portion 3 to the piston is formed at the center thereof. The inner peripheral surface of the first connecting hole 3a is smoothly continuous in order to reliably transmit the reciprocating motion of the piston to the connecting rod 1, and its radius is set to r1. The small end portion 3 is formed by cold forging (coining), and its Vickers hardness is set to be less than the Vickers hardness of the column portion 2, that is, less than 350 HV.

  The large end portion 4 is constituted by a first large end portion 4a and a second large end portion 4b which are divided into two branches from the column portion 2 and extend. A semicircular continuous end surface is formed between the first large end 4a and the second large end 4b, and the radius of the semicircle is set to r2 larger than r1. The large end portion 4 is formed by coining, and its Vickers hardness is set to be less than the Vickers hardness of the column portion 2, that is, less than 350 HV.

  In the large end portion 4 formed in this way, a second connecting hole 7 for connecting to the crankshaft is formed by integrally attaching a facing member 5 indicated by an imaginary line with a bolt 6. The inner peripheral surface of the second connecting hole 7 is smoothly continuous in order to reliably transmit the movement of the connecting rod 1 to the crankshaft.

  Here, the range X in which the connecting rod 1 is quenched will be described. The straight lines X <b> 1 and X <b> 2 are set within a range in which the machinability of the inner peripheral surfaces of the first connection hole 3 a and the second connection hole 7 can be secured and high buckling strength can be imparted to the column portion 2. Specifically, the straight line X1 is set at a position separated from the center of the first connection hole 3a by a distance L1, and the distance L1 is not less than the radius r1 of the first connection hole 3a and the diameter of the first connection hole 3a ( That is, the radius is set to be less than r1 × 2). The straight line X2 is set at a position separated from the center of the second connection hole 7 by a distance L2, and the distance L2 is not less than the radius r2 of the second connection hole 7 and the diameter of the second connection hole 7 (that is, the radius r2). × 2) set to less than

  The conditions of the Vickers hardness of the column part 2, the small end part 3 and the large end part 4 or the conditions of the distance L1 and the distance L2 are calculated from the experimental values shown in FIG. Specifically, the connecting rod 1 in which the radius r1 of the first connecting hole 3a is set to 10 mm and the radius r2 of the second connecting hole 7 is set to 30 mm is used, and various evaluations are performed using the connecting rod. It has been broken.

  That is, the distance L1 from the center of the first connection hole 3a to the straight line X1, the distance L2 from the center of the second connection hole 7 to the straight line X2, the Vickers hardness H1 of the column part 2, the small end part 3 and the large end part 4 The appropriateness of the strength of the connecting rod 1 and the machinability of the small end portion 3 and the large end portion 4 when the Vickers hardness H2 is variously changed is determined.

Next, the manufacturing method of the connecting rod 1 mentioned above is demonstrated.
The connecting rod manufacturing apparatus first shapes the outer shape of the connecting rod 1 by forging machine structural steel. When the outer shape of the connecting rod 1 is formed, the connecting rod manufacturing apparatus heats the connecting rod 1 to a temperature of about 750 ° C. or more, and as shown in FIGS. 2 (a) and 2 (b), the portion excluding the range X, that is, the small end The vicinity of the portion 3 and the vicinity of the large end 4 are sandwiched and held in the thickness direction by a small end jig 8 as a small end covering means and a large end jig 9 as a large end covering means, respectively.

  Here, the small end jig 8 for clamping the vicinity of the small end portion 3 and the large end jig 9 for clamping the vicinity of the large end portion 4 will be described. The small end jig 8 includes a first small end jig 8a and a second small end jig 8b that can be divided in the thickness direction of the connecting rod 1 (vertical direction in FIG. 2B). 9 includes a first large end jig 9a and a second large end jig 9b that can be divided in the thickness direction of the connecting rod 1 (vertical direction in FIG. 2B). A first clamping recess 10 is formed in the first small end jig 8a, and a second clamping recess 11 is formed in the second small end jig 8b, respectively. The tool 8b is formed so as to be able to cover the small end portion 3 from both sides in the thickness direction by both sandwiching recesses 10 and 11. The first clamping recess 10 and the second clamping recess 11 are set to a depth that allows the small end 3 to be clamped and held in the thickness direction when the small end 3 is clamped.

  The first small end jig 8a and the second small end jig 8b are respectively formed with semicircular concave grooves 12 at corresponding positions on the contact surfaces. Accordingly, when the first small end jig 8a and the second small end jig 8b are brought into contact with each other, the first air blower serving as the first air delivery means having a circular cross section is formed by the concave grooves formed in the both small end jigs. A tube 13 is formed. As shown in FIG. 2 (a), the first blower pipe 13 is connected to the first sandwiching recess 10 and the second sandwiching recess from the blowing port 13a formed at one end of the small end jig 8 (left end in FIG. 2 (a)). After extending toward 11, it branches off to both sides in the width direction of the connecting rod 1 at a substantially central position of the small end jig 8 and communicates with the side walls of the first clamping recess 10 and the second clamping recess 11. The small end jig 8 formed in this way is formed between the first sandwiching recess 10 and the second sandwiching recess 11 and the connecting rod 1 by supplying air into the first blowing tube 13 from the blowing port 13a. Air can be blown out from the gap.

  The first small end jig 8a and the second small end jig 8b are each inserted with a nichrome wire heater 14 as a heating means at a substantially central position in the thickness direction. The nichrome wire heater 14 is arranged so that the first small end jig 8a or the second small end jig 8b can be heated, and the first small end jig 8a and the second small end jig 8b are small end portions. When sandwiching 3, it is heated to about 500 to 700 ° C.

  A third clamping recess 15 is formed in the first large end jig 9a, and a fourth clamping recess 16 is formed in the second large end jig 9b. The tool 9b is formed so as to be able to cover the large end portion 4 from both sides in the thickness direction by both sandwiching recesses 15 and 16. The third clamping recess 15 and the fourth clamping recess 16 are set to such a depth that the large end 4 can be clamped and held when the large end 4 is clamped.

  The first large end jig 9a and the second large end jig 9b are each formed with a semicircular concave groove 17 at a corresponding position on the contact surface. Accordingly, when the first large end jig 9a and the second large end jig 9b are brought into contact with each other, the concave grooves 17 formed in the two large end jigs 9 serve as the second air delivery means having a circular cross section. Two blower pipes 18 are formed. As shown in FIG. 2 (a), the second blower pipe 18 is branched from the blower opening 18a formed at one end of the large end jig 9 (the right end in FIG. 2 (a)) to both sides in the width direction of the connecting rod 1. The third clamping recess 15 and the fourth clamping recess 16 communicate with the side walls. The large-end jig 9 formed in this way is formed between the third sandwiching recess 15 and the fourth sandwiching recess 16 and the connecting rod 1 by supplying air into the second blower pipe 18 from the blower port 18a. Air can be blown out from the gap.

  The first large end jig 9a and the second large end jig 9b are each inserted with a nichrome wire heater 19 as a heating means at a substantially central position in the thickness direction. The nichrome wire is arranged so that the first large end jig 9a or the second large end jig 9b can be heated. The first large end jig 9a and the second large end jig 9b When sandwiched, it is heated to about 500-700 ° C.

  The connecting rod manufacturing apparatus sandwiches and holds the small end portion 3 and the large end portion 4 of the connecting rod 1 in the thickness direction by the small end jig 8 and the large end jig 9 formed as described above, and the connecting rod 1. The small end jig 8 and the large end jig 9 are brought into contact with both end portions in the longitudinal direction so that the small end portion 3 and the large end portion 4 do not move relative to each other in the longitudinal direction of the connecting rod 1.

  When the connecting rod 1 is clamped by the small end jig 8 and the large end jig 9, the connecting rod manufacturing apparatus supplies air to the first blower pipe 13 and the second blower pipe 18 and showers in the range X of the column portion 2. Then, cooling water is sprayed and quenching is performed so that the range X changes to a martensite form.

  Since the connecting rod manufacturing apparatus supplies air to the first blower pipe 13 and the second blower pipe 18 when quenching the column portion 2, the first sandwiching recess 10, the second sandwiching recess 11, the connecting rod 1, The air shown by the arrow A can be sent out from the gap formed between the two. In addition, the air indicated by the arrow B can be sent out from the gap formed between the third clamping recess 15 and the fourth clamping recess 16 and the connecting rod 1. Therefore, the connecting rod manufacturing apparatus can suppress cooling water from flowing from the column portion 2 toward the small end portion 3 or the large end portion 4 by blowing off the cooling water with the air indicated by the arrows A and B.

  Further, since the small end jig 8 and the large end jig 9 are both heated to about 500 to 700 ° C. by the nichrome wire heaters 14 and 19, the cooling water flows from the column portion 2 to the small end portion 3 or Even when the water is going to be immersed toward the large end 4, the cooling water can be evaporated by the heat of the small end jig 8 or the large end jig 9 before reaching the small end 3 or the large end 4. it can. Therefore, the connecting rod manufacturing apparatus can surely prevent the small end portion 3 or the large end portion 4 from being quenched.

  When the column part 2 is quenched and the quenched part changes into a martensite form, the volume of the column part 2 tends to expand, and the connecting rod 1 mainly has a longitudinal direction of the column part 2. Stress toward is generated. However, since the connecting rod manufacturing apparatus holds the small end 3 and the large end 4 so as not to move in the longitudinal direction of the connecting rod 1, the connecting rod 1 does not actually expand in the longitudinal direction, and the connecting rod 1 is elongated. The force to expand in the direction remains in the column portion 2 as a compressive stress.

  FIG. 3 is a characteristic diagram showing the relationship between the depth from the connecting rod surface and the residual stress. The horizontal axis indicates the depth from the connecting rod surface, and the vertical axis indicates the residual stress. The solid line D1 is the surface of the column part 2 when the column part 2 is quenched in the present embodiment, that is, with the small end jig 8 and the large end jig 9 suppressing expansion of the connecting rod 1 in the longitudinal direction. It is a characteristic view which shows the relationship between the depth from and its residual stress. A broken line D2 indicates the relationship between the depth from the surface of the column portion 2 and the residual stress when the column portion 2 is quenched without suppressing the expansion of the connecting rod 1 in the longitudinal direction. FIG. As shown in the figure, by quenching the column portion 2 while suppressing the expansion of the connecting rod 1 in the longitudinal direction, a larger stress remains in the column portion 2 than in the past, and the strength of the connecting rod 1 is improved. To do.

As described above in detail, according to the connecting rod, the manufacturing method, and the manufacturing apparatus according to the above-described embodiment, the excellent effects listed below can be obtained.
(1) The connecting rod manufacturing apparatus sprays cooling water onto the column portion 2 in a state where the small end portion 3 and the large end portion 4 are covered with the small end jig 8 or the large end jig 9, respectively. Quenching is performed. Therefore, when the column part 2 is quenched, the small end part 3 and the large end part 4 are not unexpectedly cooled, and the connecting rod manufacturing apparatus can reliably perform the hardening process only on the column part 2. it can. As a result, it is possible to obtain a connecting rod provided with the column portion 2 having a higher Vickers hardness than the small end portion 3 and the large end portion 4, and the small hardness with good machinability while setting the hardness of the column portion 2 high. A connecting rod having an end 3 and a large end 4 can be obtained.

  (2) When the connecting rod manufacturing apparatus quenches the column portion 2, the small end portion 3 and the large end portion 4 are clamped and held by the small end jig or the large end jig 9. Therefore, the connecting rod manufacturing apparatus can prevent the small end portion 3 and the large end portion 4 from being deformed by the stress accompanying the quenching of the column portion 2. Therefore, the coining process accompanying the deformation of the small end 3 and the large end 4 can be omitted, and the connecting rod manufacturing process can be shortened.

  (3) When the connecting rod manufacturing apparatus quenches the column portion 2, the small end jig 8 and the large end jig 9 are brought into contact with both longitudinal ends of the connecting rod 1, and the small end portion 3 and the large end portion 4 are brought into contact with each other. The connecting rod 1 is fixed so as not to move relatively in the longitudinal direction of the connecting rod 1. Therefore, even if the quenching portion of the column portion 2 expands, the relative position between the small end portion 3 and the large end portion 4 does not change, and the expansion force remains in the column portion 2 as a compressive stress. And the intensity | strength of the column part 2 can be raised with this compressive stress.

  (4) The connecting rod manufacturing apparatus holds the small end 3 and the large end 4 while the small end jig 8 and the large end jig 9 are heated. Therefore, even if the cooling water is submerged from the column portion 2 toward the small end portion 3 or the large end portion 4, the cooling water can be evaporated by the heat of the small end jig 8 and the large end jig 9. Therefore, it is possible to prevent quenching of the small end portion 3 and the large end portion 4 due to the cooling water being submerged when the column portion 2 is quenched.

  (5) When the connecting rod manufacturing apparatus quenches the column portion 2, it is possible to suppress the infiltration of the cooling water into the small end portion 3 and the large end portion 4 with the air indicated by the arrow A. Therefore, the occurrence of quenching of the small end portion 3 and the large end portion 4 can be suppressed.

In addition, the said embodiment can also be implemented as the following forms which changed this suitably, for example.
In the above embodiment, the column portion is formed in an I-shaped cross section, but may be a column portion formed in an H-shaped cross section.

  -In the above embodiment, the Vickers hardness of the quenching portion formed in the column portion was set to about 350 HV, but it is sufficient to provide sufficient buckling strength in the usage environment of the connecting rod, and the Vickers hardness may be changed as appropriate. May be.

  In the above embodiment, the Vickers hardness of the small end portion 3 and the large end portion 4 is set to be less than about 350 HV, but has sufficient buckling strength in the usage environment of the connecting rod, and the first connecting hole 3a or When the two connecting holes 7 are formed, the Vickers hardness may be appropriately changed as long as the machinability of the inner peripheral surface is good.

  Specifically, as shown in FIG. 4, the distance L1 is 10 mm, the distance L2 is 60 mm, the Vickers hardness H1 of the column part 2 is 350 HV, and the Vickers hardness H2 of the small end part 3 and the large end part 4 is 260 HV. It may be a thing. Alternatively, the distance L1 may be 14 mm, the distance L2 may be 40 mm, the Vickers hardness H1 of the column portion 2 may be 350 HV, and the Vickers hardness H2 of the small end portion 3 and the large end portion 4 may be 340 HV.

Explanatory drawing of a connecting rod. (A), (b) is explanatory drawing of the manufacturing process of a connecting rod. The characteristic view which shows the stress which remains in a column part. The evaluation figure of the strength and machinability of the connecting rod corresponding to various conditions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Connecting rod, 2 ... Column part, 3 ... Small end part, 4 ... Large end part, 8 ... Small end jig as small end part covering means, 9 ... Large end jig as large end part covering means, 14 , 19 ... Nichrome wire heater as a heating means.

Claims (12)

In a connecting rod formed integrally with a small end connected to the piston, a large end connected to the crankshaft, and a column connecting the small end and the large end,
A connecting rod, wherein the column portion, the small end portion, and the large end portion are quenched only in the column portion.   The connecting rod according to claim 1, wherein the column portion has a Vickers hardness of 350 HV or more. Forging integrally a small end connected to the piston, a large end connected to the crankshaft, and a column connecting the small end and the large end;
In the manufacturing method of the connecting rod comprising the step of spraying cooling water on the column part,
Prior to the step of spraying cooling water on the column portion, the method of manufacturing a connecting rod comprising the step of covering the small end portion and the large end portion.   4. The method of manufacturing a connecting rod according to claim 3, wherein when the small end portion and the large end portion are covered, the small end portion and the large end portion are sandwiched and held from both sides in the thickness direction.   5. The method of manufacturing a connecting rod according to claim 3, wherein when the small end portion and the large end portion are covered, the small end portion and the large end portion are not allowed to move relative to each other.   6. The connecting rod according to claim 3, further comprising a step of heating the small end covering means for covering the small end and the large end covering means for covering the large end. Production method.   The method according to any one of claims 3 to 6, further comprising a step of sending air from the small end portion and the large end portion toward the column portion when spraying cooling water to the column portion. The manufacturing method of the connecting rod of description. A small end portion connected to the piston, a large end portion connected to the crankshaft, and a column portion connecting the small end portion and the large end portion are integrally forged, and cooling water is added to the column portion. In the connecting rod manufacturing equipment that quenches by spraying
Small end covering means for covering the small end; and
A connecting rod manufacturing apparatus comprising: a large end covering means for covering the large end.   9. The connecting rod manufacturing apparatus according to claim 8, wherein the small end covering means and the large end covering means press and clamp the small end or the large end from both sides in the thickness direction. .   10. The connecting rod according to claim 8, wherein the small end covering means and the large end covering means cover the small end and the large end so as not to move relative to each other. apparatus.   11. The small end covering means and the large end covering means are provided with heating means for heating the small end covering means and the large end covering means, respectively. The manufacturing apparatus of the connecting rod as described in a term.   The small end covering means includes first air sending means for sending air toward a column portion from a gap between the small end covering means and the small end, and the large end covering means includes the The second air delivery means for delivering air from the gap between the large end covering means and the large end toward the column portion is provided. Connecting rod manufacturing equipment.

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