JPH0499126A - Production of high-fatigue strength valve spring by high frequency heating - Google Patents

Abstract

PURPOSE:To produce the high-fatigue strength valve spring by high-frequency heating by subjecting a steel wire specified in carbon content to high-frequency inductive heating at a specific temp. at the center in a high-frequency inductive coil while continuously moving the steel wire, then rapidly cooling the steel wire at a specific temp. immediately thereafter while winding the steel wire to a coil shape, and adjusting the pitch and number of turns at a specific temp. CONSTITUTION:A spring blank material 1 of 0.5 to 0.86% carbon content is fed at an arbitrary speed to a heating coil 3 by feed rolls 2 which are driven to rotate. This blank material is thereby subjected to the high-frequency inductive heating from 850 to 1050 deg.C. The blank material is then immediately fed to a spring forming mechanism section and is taken up on a take-up drum 6 driven by a revolving motor 4 and a cross feed motor 5, and is rapidly cooled at >=70 deg.C. The heating blank material 1 fed to the take-up drum 6 is tightly wound up to the first 1 to 2 turns and is thereafter wound in 4 to 5 turns in the effective winding coil part at an equal pitch interval. The valve spring constituted of an intricate shape and size is thus coiled and formed at >=650 deg.C with good accuracy. The valve spring from which working flaws are entirely removed and which has the excellent fatigue strength is obtd. in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of manufacturing a valve spring for a four-wheeled vehicle or an auto-high engine, which has particularly excellent fatigue strength, by forming it into a coil shape without high-frequency heating. It is something.

[Prior Art] Conventionally, springs have generally been manufactured according to JIS-G3502 (
piano wire), 3505 (hard steel wire) or 4801
Many cars are hardened and tempered using wire rods specified in the (Spring Steel Materials) and then formed into coils at Reima.

In addition, some valve springs of automobile engines are carbonitrided at a low temperature of around 500° C. as described in Japanese Patent Publication No. 36-9406 as a means of increasing fatigue strength. This is well known as a method for surface hardening mechanical parts, and the above-mentioned Japanese Patent Publication No. 36-9406 is an example of applying this principle to a valve spring. However, in this method, in order to harden the surface, after forming into a coil shape,
Since the carbonitriding treatment must be carried out at a low temperature of around 0°C for several hours, there is a drawback in productivity.

In addition, induction heating using high-frequency current is often used to harden the surface of mechanical parts. For example, if a coil spring to be processed is left in a high-frequency heating coil and the material of the coil spring is adjusted uniformly, 8 conductive heating coils are required depending on the shape and dimensions of each coil spring. This results in high equipment costs and poor workability. In addition, the literature “
Tetsu to Hagane J Vol, 73 (1987), P2290 and “
As described in ``Spring Papers'' No. 27 (1978), p. 28, as well as in Japanese Patent Publication No. 30736/1983, spring wires that have been hardened and tempered by high-frequency heating are used in a completely different process and cold-heated. High fatigue strength coiled springs are already known. however,
All of these materials are subjected to high-frequency heating to obtain the required material quality and strength level, and then cold-formed, so in the case of extremely high-strength materials, there is a problem with the workability of coiling.

Furthermore, Japanese Patent Application Laid-Open No. 59-38329 discloses a method of connecting a high-frequency power source to the blade before or after molding and directly passing a high-frequency current to harden the surface of the blade. For example, since a high-frequency power source is directly connected to the spring material, there are problems with the stability of hardening accuracy due to variations in the surface condition of the contact surface, the wire diameter, or uneven feeding speed.

[Problems to be Solved by the Invention] With the increasing performance and output of automobile engines, valves with high fatigue strength are strongly desired. In order to realize these demands, the present invention aims to solve problems such as productivity, coiling performance, and hardenability, and to provide a method for manufacturing a valve spring that can guarantee the required characteristics.

[Means for solving the problem] The gist of the present invention is that the carbon content is 0.5 to 0.86
While continuously moving the steel wire rod, it is heated by high frequency conduction to 850℃ or more and 1050℃ or less at the center of the high frequency conduction coil, and then immediately wound into a coil shape and rapidly cooled at a cooling rate of 70℃/sec or more. Cooled and 650℃
The above provides a method for manufacturing a valve spring with high fatigue strength by high-frequency heating, which is characterized by adjusting the pitch and number of turns.

[Function] Therefore, the present inventors conducted various studies on the possibility of applying such means in terms of productivity, coiling property, and hardenability in order to improve the fatigue strength of a valve spring for an automobile engine.

The details of the present invention will be explained below.

Among the chemical components according to the present invention, in particular, the carbon content is 05 to 0.
The reason for setting the range to 86% is to increase the tensile strength or hardness to satisfy the requirement for high fatigue strength, and furthermore, the high frequency conduction heating temperature of the present invention is set to 850°C or higher 105
If the temperature is 0° C. or lower and rapid cooling is performed at 70° C./sec or higher, a very fine martensitic structure can be obtained.

In addition, it is possible to generate fine structures and crystal grains obtained by austenitization (γ) during high-temperature and short-time heating, improving toughness such as elongation and drawing, and obtaining higher fatigue strength. Here, if the carbon content is less than 0.5%, the fatigue strength level will be extremely high due to the sagging phenomenon, whereas if it exceeds 0.86%, the toughness will deteriorate significantly and it will not be able to withstand use. In addition, if necessary, Si may be added from 0.10 to
1.5%, Mn 0.40-0.55%, Cr 0.
Addition of 0.01 to 0.08% improves the hardenability of the steel wire, resulting in a stable and high-strength steel wire even when a large-diameter coil is bounced.

Furthermore, the structure obtained by austenite (γ) formation during high-temperature, short-time heating becomes even finer. In this case, Si, Mn, and Cr are each 0.10.0.
If it is less than 40.0.01%, sufficient strength cannot be obtained, and if it exceeds 1.5, 0.55, or 0.8%, the hardness of the rolled wire increases, making pre-processing such as peeling or drawing difficult. become.

In addition, if the temperature at which the steel wire is heated by high-frequency 8 conduction while moving is less than 850°C, sufficient austenitization will not occur, so it is difficult to secure the necessary strength, and if it exceeds 1050°C, it will be heated more than necessary. As a result, the crystal grains become coarser and the properties and toughness deteriorate. Then, immediately cool it quickly while winding it into a coil shape, or if the cooling rate is 70℃/
If it is cooled for less than sec, it will not harden and the target strength will not be obtained. Moreover, there is no expectation of improvement in fatigue strength in subsequent use characteristic evaluation tests.

The optimal conditions for high-temperature, short-time heat treatment are shown in Figure 1.If you move the center of the coil in which the steel wire is heated by high-frequency induction, the temperature can be uniformly distributed throughout the interior without any unevenness, and in a short time.
High frequency heating becomes possible at 850-1050°C. 650℃
The reason why we decided to adjust the pitch and number of turns of the seat part and the effective winding part while immediately winding it into a coil shape is to form it in the austenite phase state, and the temperature is 650°C.
This is extremely effective because at temperatures lower than This is a requirement.

Therefore, in particular, FIG. 2 schematically shows a manufacturing apparatus for carrying out the present invention. Not only the working precision of the material feeding mechanism, heating section, and spring forming mechanism, but also the precision of the construction of these components has a great influence on the quality and performance of the valve springs that are engine parts. It is a lotus. That is, a steel wire rod made of such a component system is used as a spring material 1 and is sent to a heating coil 3 at an arbitrary speed by a feed roll 2 driven and rotated by an electric motor. When the fed material 1 passes through the center of the heating coil 3, which is heated by induction by a high frequency transmitter,
A suitable high frequency induction heating temperature of 850-1050°C is provided. Thereafter, it is immediately fed to the spring forming mechanism and wound onto a winding tram 6 driven by a rotary motor 4 and a transverse feed motor 5. During this winding and forming, 7
Since rapid cooling to 0°C or higher is required, the winding tram 6
The requirements of the present invention can be easily met by providing a ring-shaped nozzle 7 in the direction of travel of the vehicle so as to be able to dissipate cooling debris, cooling water, etc. In addition, the shape of the valve spring consists of a close coil part called an end turn part at both ends and an effective winding coil part with equal pitch spacing in the middle part. 1 is possible by first winding the 1st and 2nd windings, then winding the effective winding coil part 4 to 5 times at equal pitches, and finally winding the 1st and 2nd windings closely. If valve springs with complex shapes and dimensions are coil-formed with precision at temperatures above 650°C, the processing flaws that occur with conventional re-opening molding can be eliminated, resulting in valves with excellent fatigue strength. You can get a splash.

Thus, the formed coil spring does not necessarily require tempering treatment, but is subjected to setting and shot peening treatment at a temperature ranging from room temperature to 350°C.

The effects of the present invention will be illustrated in more detail with reference to Examples below.

[Example] Next, examples will be shown.

Table 1 shows the chemical composition of the high carbon steel wire rods used in the examples, and Table 2 shows the drawn carbon steel wire rods having a diameter of φ3.8 +n+n, which were cut into lengths of 600 mm, and were used as AIO to A3 wire rods.
It was manufactured by the method of the present invention described in No. 3.

The conditions for the method of the present invention were that the spring material was fed to a high frequency heating coil by a feed roll, and the center of the heating coil subjected to high frequency induction heating was moved at a speed of 40 mm/sec. Immediately after heating the spring material to 850-1050℃ with high frequency
While rapidly cooling at a cooling rate of 0°C/sec or more, the winding tram is fed to a winding tram and wound into a coil shape at a temperature of 650°C or higher.At this time, the end winding part is 2 turns, the effective winding part is lo, and 5 turns are made at a pitch of 5 mm. The coils were arranged at equal intervals and a valve spring was formed by high-frequency induction heating. These were set at 200°C and shot peened.

In addition, valve springs were manufactured using the comparative method Bll-B22. The cooling rate and winding temperature in this case were the same as in method A. Note that a high frequency transmitter of 15 kW and 400 KHz was used.

For the valve spring manufactured in this way, the shear stress (τ max = 60 ± 50 kgf
/mm2) was repeatedly applied to determine the fatigue life until fracture. These results are shown in Table 3. As is clear from these results, the valve spring manufactured by the high-frequency heating method of the present invention exhibits high fatigue strength. In addition, we also tested the fatigue life of a valve spring manufactured by the conventional method using A1 steel, so we used C as a reference.
11 Neo.

Table of Contents (%) By overcoming the drawbacks and limitations of fatigue properties shown in Table 1, it has become possible to manufacture a valve spring with high fatigue strength using high-frequency 8 conduction heating. It is clear that the spring material is not limited to a perfectly round material, but also an elliptical material, which is of great industrial value.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between heating temperature and time in the present invention, and FIG. 2 is a schematic diagram showing the manufacturing method according to the present invention. 1...Material 2...Feed roll 3...
Heating coil 4 Rotating motor 5 Transverse feed motor 6 Winding drum 7 Cooling nozzle [Effect of the invention] As described above, the present invention is similar to the conventional means. This is a completely different process, and the workability caused by cold spring forming or spring forming by directly connecting a high frequency power source to the spring material, etc.

Claims (1)

[Claims] 1 While continuously moving a steel wire rod with a carbon content of 0.5 to 0.86%, 850
By high-frequency heating, which is characterized by high-frequency induction heating at a temperature of 1050°C or higher, immediately followed by rapid cooling at a cooling rate of 70°C/sec or higher while immediately winding into a coil shape, and adjusting the pitch and number of turns at 650°C or higher. Method for manufacturing high fatigue strength valve springs.