Washer-assembled bolt and manufacturing method therefor

Abstract

To provide a washer-assembled bolt having superior mechanical properties that can be used in a severe use environment where a large load such as vibration is applied, and a manufacturing method therefor.SOLUTION: In a washer-assembled bolt with a spring washer assembled between a head part and a thread part of a bolt, a surface hardness of the spring washer is 450 HV or more, and a ratio of a free height after a compression test to that before the test is 90% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a washer assembled bolt, and more particularly to a washer assembled bolt in which a washer can be assembled into the bolt before heat treatment, and a method for manufacturing the same. [Background technology]

[0002] In a washer assembled bolt, a washer is inserted into the bolt and assembled into the bolt head by forming the threaded portion so that it cannot be pulled out, and by incorporating the washer into the bolt in advance, workability in the assembly process using robots, etc. These washer assembled bolts are standardized as washer assembled hexagon bolts (JIS B 1187) and cross recessed head machine screws (JIS B 1188), but in reality, due to strong user demand, they are also manufactured as high-strength hexagon bolts and hexagon socket head bolts with a strength classification of 10.9 to 12.9, for example.

[0003] These high-strength bolts are given the strength and hardness specified by JIS by undergoing heat treatment at specified temperatures through quenching and tempering. The spring washers used in these bolts are already given the strength and hardness specified by JIS during the production process. Flat washers, on the other hand, are either given the hardness specified by JIS by the rolls used during thin plate rolling, or given the hardness specified by JIS through heat treatment.

[0004] However, in the case of bolts with assembled washers, if the bolt is subjected to heat treatment while the washer is already assembled into the bolt, the appropriate tempering temperatures differ between the bolt and the washer, which causes the hardness of the washer to decrease, resulting in a problem where the hardness and spring properties (in the case of spring washers) do not meet the standard values.

[0005] For this reason, conventionally, after the head and body of the bolt are formed using a header, the bolt blank is first heat treated to obtain the strength and hardness specified by JIS. Next, a washer whose hardness and springiness (in the case of a spring washer) already meets the standard values ​​is inserted, and then the threaded portion is formed in a rolling process to produce the finished product.

[0006] However, in conventional methods for manufacturing washer-assembled bolts, the tensile strength and hardness of the bolt blank after heat treatment are increased compared to before heat treatment, which means that the lifespan of rolling tools such as dies is significantly reduced to one-quarter to one-fifth when rolling the threaded portion, resulting in a problem of significantly increasing the manufacturing costs of washer-assembled bolts.

[0007] Furthermore, in the manufacturing method for a single bolt, the head is formed in a header on a bolt blank, the thread portion is formed in a rolling process, and then the bolt is heat treated to complete the product. However, in the manufacturing method for the conventional washer-assembled bolt described above, the rolling and heat treatment processes are performed in the reverse order, which causes a loss of consistency in the manufacturing line and leads to confusion in production management.

[0008] In light of the problems with the above-mentioned conventional washer assembled bolts, the present applicants have previously proposed and put into practical use a washer assembled bolt and a manufacturing method thereof that allows a washer to be assembled into the bolt before the heat treatment process by selecting a material that increases resistance to tempering softening in the case of spring washers, and by selecting a material that achieves a standard hardness through quenching and tempering in the case of flat washers (see Patent Document 1). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 3510184 Summary of the Invention [Problem to be solved by the invention]

[0010] This has made it possible to incorporate washers into high-strength hexagonal washer assembled bolts and hexagonal socket washer assembled bolts with strength classifications of 10.9 to 12.9 before the heat treatment process. The object of the present invention is to provide, by further improving this, a washer assembled bolt with superior mechanical properties that can be used in harsh operating environments where large loads such as vibration are applied, and a method for manufacturing such a bolt. [Means for solving the problem]

[0011] In order to achieve the above object, the washer assembled bolt of the present invention is a washer assembled bolt in which a spring washer is assembled between the head and threaded portion of the bolt, and is characterized in that the surface hardness of the spring washer is 450 HV or more and the ratio of the free height before and after a compression test to that after the test is 90% or more.

[0012] In this case, the spring washer may be made of a spring wire containing vanadium.

[0013] Furthermore, the method for manufacturing a washer-assembled bolt of the present invention is a method for manufacturing the above-mentioned washer-assembled bolt, characterized in that after incorporating a spring washer into a bolt blank, a thread portion is formed through a rolling process, and then quenching is performed at 850 to 890°C, followed by tempering at 420 to 480°C. [Effects of the Invention]

[0014] According to the washer-assembled bolt and manufacturing method of the present invention, by subjecting the spring washer, while it is already assembled in the bolt, to the same heat treatment as the bolt, it is possible to incorporate a spring washer with high hardness and excellent compression performance into the bolt, thereby obtaining a washer-assembled bolt with superior mechanical properties that can be used in harsh operating environments where large loads such as vibration are applied. Furthermore, because the spring washer can be assembled in the bolt before the heat treatment process, it is possible to perform the rolling process before the heat treatment process, which allows washer-assembled bolts to be manufactured at low cost without shortening the life of the rolling tools, and because they can be manufactured using the same manufacturing process as single bolts, it is possible to maintain consistency in the manufacturing line and facilitate production management. [Brief explanation of the drawings]

[0015] [Figure 1] 1A to 1C are process diagrams showing an embodiment of a method for manufacturing a washer-assembled bolt according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a washer assembled bolt and a method of manufacturing the same according to the present invention will be described with reference to the drawings.

[0017] FIG. 1 shows an embodiment of the method for manufacturing a washer assembled bolt according to the present invention.

[0018] The bolt material is SCM435 chromium-molybdenum steel specified in JIS G 4105, with C: 0.33-0.38%, Si: 0.15-0.35%, Mn: 0.60-0.85%, P: 0.030% or less, S: 0.030% or less, Cr: 0.90-1.20%, Mo: 0.15-0.30% (the balance is Fe and unavoidable impurities; the same applies to the following materials), as shown in Table 1. The head, body, etc. are formed from this bolt material using a header process to produce a bolt blank.

[0019] [Table 1]

[0020] As an example, the material of the spring washer is, as shown in Table 2, SAE of C: 0.60 to 0.68%, Si: 1.30 to 1.60%, Mn: 0.60 to 0.80%, P: 0.025% or less, S: 0.025% or less, Cu: 0.20% or less, Cr: 0.50 to 0.80%, V: 0.25% or less (however, V is an essential element and is preferably contained in an amount of 0.10% or more). A spring wire rod equivalent to standard 9254 was used, and as a comparative example (equivalent to the first material described in Patent Document 1), a spring wire rod equivalent to SAE standard 9254 was used, with C: 0.51 to 0.59%, Si: 1.20 to 1.60%, Mn: 0.50 to 0.80%, P: 0.025% or less, S: 0.025% or less, Cu: 0.20% or less, and Cr: 0.50 to 0.80%, as shown in Table 3. A spring washer was produced using this spring washer material and assembled into a bolt blank.

[0021] [Table 2]

[0022] [Table 3]

[0023] The bolt blank with the washer assembled is then subjected to a rolling process to form a threaded portion, followed by a heat treatment process in which, for a bolt with a strength classification of 12.9, the bolt is quenched at 850 to 890°C and then tempered at 420 to 480°C.

[0024] Next, the mechanical properties of the spring washer of the washer assembled bolt manufactured in this manner were verified by the following method. 1. Exam Content (1)Hardness distribution The cut spring washer is fixed with synthetic resin, and the mirror-finished cut surface is measured for hardness distribution from the surface in accordance with the Vickers hardness test method (JIS Z 2244). (2) Compression test In accordance with the compression test method (JIS B 1251), a test load is applied to the spring washer three times and the change in free height is measured. (3) Torsion test According to the torsion test method for washers (JIS B 1251), the spring washer is clamped in a vice and twisted to approximately 90 Twist to check for damage.

[0025] 2. Test Results (1)Hardness distribution The measured hardness distribution from the surface is shown in Table 4 (Examples) and Table 5 (Comparative Examples). As shown in Table 4 (Examples) and Table 5 (Comparative Examples), it was confirmed that the hardness distribution increases from the surface toward the inside, and that the Examples exhibited a higher hardness (450 HV or more at the surface (0.03 mm from the surface) (approximately 400 HV in the Comparative Examples)) than the Comparative Examples.

[0026] [Table 4]

[0027] [Table 5]

[0028] (2) Compression test The measured values ​​are shown in Table 6 (Examples) and Table 7 (Comparative Examples). As shown in Table 6 (Examples) and Table 7 (Comparative Examples), it was confirmed that the free height after the test of the Examples and Comparative Examples met the judgment criteria (2.5 mm or more), and that the ratio of the free height after the compression test to the free height before the test (free height after the test / free height before the test) of the Examples was larger (90% or more (less than 90% for the Comparative Examples)) than that of the Comparative Examples.

[0029] [Table 6]

[0030] [Table 7]

[0031] (3) Torsion test As a result of the torsion test, it was confirmed that there was no breakage or cracking in the examples and comparative examples.

[0032] The washer-assembled bolt and manufacturing method thereof of the present invention have been described above based on the examples thereof, but the present invention is not limited to the configurations described in the above examples, and the configuration can be changed as appropriate within the scope of the spirit of the invention, such as by adopting various shapes of bolt and spring washer. [Industrial Applicability]

[0033] The washer assembly bolt and its manufacturing method of the present invention have superior mechanical properties that enable them to be used in harsh usage environments where large loads such as vibrations are applied, and therefore can be suitably used for washer assembly bolts.

Claims

1. A washer-assembled bolt in which a spring washer is assembled between the head and threaded portion of the bolt, characterized in that the surface hardness of the spring washer is 450 HV or more, and the ratio of the free height before and after a compression test to that after the test is 90% or more.

2. 2. The washer assembled bolt according to claim 1, wherein the spring washer is made of a spring wire containing vanadium.

3. 3. A method for manufacturing a washer assembled bolt according to claim 1 or 2, characterized in that after the spring washer is assembled into a bolt blank, a thread portion is formed through a rolling process, and then the bolt blank is hardened at 850 to 890°C, and then tempered at 420 to 480°C.

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