JPH04367346A - Spring having excellent fatigue resistance - Google Patents

Abstract

PURPOSE:To increase the fatigue resistance of the spring and to reduce its size and weight by finishing the surface of a steel wire after drawing by electrolytic polishing or chemical polishing to a specific value or above of ten point surface roughness and further subjecting the steel wire to a shot peening treatment before or after forming to the spring. CONSTITUTION:The surface of the steel wire after drawing or hardening and tempering is finished by the electrolytic polishing or chemical polishing to <=5mum ten point surface roughness (Rz) of the surface roughness specified in JIS B-0601 and further, this steel wire is subjected to the shot peening treatment before or after forming to the spring. The surface roughness of the spring is extremely smoother than the spring which is not previously polished even if the steel wire is subjected to the shot peening treatment before or after the forming to the spring in this way. An important contribution is thus made to the decrease of the generation of stress concn., i.e., the improvement in the fatigue resistance. In addition, the size and weight of the spring are reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to springs for engines and other applications requiring a high degree of fatigue resistance.

0002

2. Description of the Related Art In conventional springs, it is inevitable that minute flaws occur on the wire surface during the wire drawing process or the pass line of the quenching and tempering process. Among these, microscopic flaws of 10 μm or more cause stress concentration in the manufactured spring, becoming a starting point for fatigue failure, and causing a decrease in fatigue resistance.

For this reason, conventionally, before or after forming a spring wire into a spring after drawing or quenching and tempering after drawing, for the purpose of imparting compressive residual stress to the surface of the wire in order to improve the fatigue resistance of the spring, Shot peened.

Furthermore, in order to further improve the fatigue resistance, it has been proposed that after the above-mentioned shot peening treatment, further electrolytic polishing treatment be performed to smooth the wire surface and improve the fatigue strength (Japanese Patent Laid-Open No. 63 -52729).

[0005]

[Problem to be Solved by the Invention] However, if a spring wire that has been subjected to wire drawing or quenching and tempering after wire drawing is subjected to shot peening before or after forming into a spring, minute defects caused by shot peening may cause stress concentration. Further, when electropolishing was further performed to remove these minute defects, there was a problem in that the compressive residual stress layer produced by shot peening, which is effective in improving fatigue resistance, was also removed at the same time.

[0006] The present invention solves these problems, and provides smoother wire surfaces compared to conventional methods in which electrolytic polishing or chemical polishing is not performed after shot peening treatment. It is an object of the present invention to provide a coil spring that has no loss of residual stress layer and has excellent fatigue resistance.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention electropolishes or chemically polishes the wire surface of the wire after drawing or quenching and tempering to improve the surface roughness according to JIS standards.
B-0601 was finished to a ten-point average roughness (Rz) of 5 μm or less, and the spring was constructed by subjecting it to shot peening before or after being formed into a spring.

[0008]

[Operation] By the above means, the surface roughness is determined by electropolishing or chemical polishing to the JIS B-0601 10-point average roughness (R
z) to 5 μm or less, the spring can be formed before or after forming.
Even after shot peening treatment, the surface roughness remains
The surface is much smoother than a surface that has not been polished beforehand, and this greatly contributes to reducing stress concentration caused by scratches and improving fatigue resistance.

[0009] Here, the surface roughness Rz after polishing is determined by JIS
The reason why the ten-point average roughness (Rz) of B-0601 is set to 5 μm or less is as follows. FIG. 1 shows the relationship between the surface roughness (Rz) after polishing and the fatigue strength determined by performing a shot peening treatment after polishing and performing a Nakamura rotary bending fatigue test. From this figure, it can be seen that when the surface roughness (Rz) exceeds 5 μm, the fatigue strength rapidly decreases, and when the surface roughness is 5 μm or less, the fatigue strength is high.

0010

[Example] As an example, quenched and tempered wire SWOSC
-V (C 0.6%, Si 1.4%, Cr 0
．． 7%, Mn 0.7%, balance Fe and unavoidable impurities), wire diameter 4.1 mmφ, the wire was electrolytically polished under the electrolytic polishing conditions shown in Table 1, and the surface roughness was JISB-0.
601 with a ten-point average roughness (Rz) of 2.7 μm, and then coiling molded (free length 64 mm, center diameter 24 mm).
5 mm, effective number of turns 4.5), and was further subjected to shot peening treatment.

[0011] This example, Comparative Example 1 in which shot peening treatment was performed after coiling using the above-mentioned wire that had not been electrolytically polished, and shot peening treatment after coiling and forming using the above-mentioned wire that had not been electrolytically polished. Furthermore, Table 2 shows the results of a spring fatigue test (Nakamura rotary bending fatigue test) performed on three types of Comparative Example 2 which were electrolytically polished under the electrolytic polishing conditions shown in Table 1. From this table, it can be seen that the springs of the examples have significantly better fatigue resistance than either of the springs of Comparative Examples 1 and 2.

Table 3 also shows the JIS values of the wire surface before and after the shot peening treatment of the above example and comparative example 1.
This figure shows the measurement results of the ten-point average roughness (Rz) of B-0601. From this table, compared to Comparative Example 1, the wire surface of Example is smoother not only before shot peening treatment but also after shot peening treatment, and even after shot peening treatment, the effect of electrolytic polishing remains sufficiently. I understand that.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

FIG. 2 shows the relationship between the amount of electrolytic polishing on the wire surface of the cable wire and the ten-point average roughness (Rz) of the surface roughness after polishing measured according to JIS B-0601. This figure shows that in order to ensure that the ten-point average roughness (Rz) of the wire surface is 5 μm or less, it is necessary to polish the wire to a diameter of 10 μm or more. Furthermore, as the amount of polishing increases, the ten-point average roughness (Rz) gradually decreases, but polishing of 50 μm or more has economic disadvantages that outweigh its effects, so the amount of polishing of the line surface is 10 It is preferable to set the thickness to 50 μm. A similar tendency is shown in the case of chemical polishing.

[0017]

[Effect] Since the present invention is constructed as described above, it exhibits extremely excellent fatigue resistance. Therefore, it is more suitable than conventional products as a spring that requires high fatigue resistance, such as a valve spring for an automobile engine, and the spring can be made smaller and lighter.

[Brief explanation of drawings]

[Figure 1] Diagram showing the relationship between the surface roughness (Rz) of a cable wire after polishing and the fatigue strength determined by shot peening after polishing and Nakamura rotary bending fatigue test.

Claims (1)

[Claims] Claim 1: The wire surface of the steel wire after wire drawing or quenching and tempering is electrolytically polished or chemically polished to a JIS surface roughness.
A spring made of B-0601 finished to a ten-point average roughness (Rz) of 5 μm or less, and then subjected to shot peening treatment before or after forming into a spring.