KR20050003670A - Method for manufacturing high tension bolts - Google Patents

Abstract

PURPOSE: To provide a method for manufacturing high strength bolts, the method for extending strength and life of bolts formed by heat treatment or cold rolling working, preventing the bolts from easily being cracked during forming and manufacturing bolts having excellent processing efficiency. CONSTITUTION: The method comprises a step of cutting a carbon steel or alloy steel wire rod on which heat treatment or cold rolling working is performed to a plurality of wire rods in a certain size; a step of partially heating portions(8) of the cut wire rods corresponding to a bolt head part and a screw front part to a temperature of 400 deg.C to A1 transformation temperature; and a step of forming the partially heated wire rods in a bolt shape in the temperature of 400 deg.C to A1 transformation temperature, wherein the heating step is performed by using a small capacity heating equipment such as a high frequency heating coil.

Description

Method for manufacturing high tension bolts

The present invention relates to a high-strength bolt, and more particularly to a method for producing a high-strength bolt excellent in stress ratio of 80kgf / mm 2 or more tensile strength used in automobile parts, industrial machinery, bridges, civil engineering buildings and the like.

Looking at the conventional high-strength bolt, the so-called material adjustment bolt is applied to give the required strength by the material adjustment process of the hardling, tempering ring after forming the annealed rod from cold to bolt.

However, this material adjusting bolt requires a lot of heat treatment processes, which increases the manufacturing cost.

Therefore, as a method of reducing the heat treatment step, a method has been proposed in which cold rods are formed from cold to bolts which have increased the strength to a value close to the final bolt strength by heat treatment or cold rolling.

However, this method includes a problem that the life of the mold is shortened due to the high strength at the time of bolt forming, cracking is likely to occur at the time of molding, and the processing rate is not high.

Therefore, in order to solve these problems, the warm forming method, which proposes a method of forming bolts in the temperature range of 400 ° C to A1 point, requires a large-capacity heating facility because it heats the entire material, and the heating temperature is high. This involves a problem that the strength of the screw portion is lowered.

In addition, since the whole material is heated when the heating temperature is changed, the change in temperature is connected to the change in strength.

Therefore, the strength of the materials used is urgently required in the field for fastening members for efficient construction of steel structures and for weight reduction, multifunction, and high performance of automobile parts.

The present invention has been made in order to satisfy the above requirements, and extends the strength and life of the bolt formed by heat treatment or cold rolling, etc., as well as preventing easily cracking during molding, as well as excellent bolt It is to provide a method of manufacturing a high strength bolt to provide.

1 is a process chart showing a heating, cutting state in the bolt molding of the present invention

Figure 2 is a flow chart illustrating a process of the heating portion is formed into a bolt shape after heat cutting by the manufacturing method of the present invention.

Explanation of symbols on the main parts of the drawings

1: feeding stand 2: conveying roller

3: high frequency heating coil 4: dies

5: knife 6: stopper

7: vanguard 8: heating part

In order to achieve the above object, the present invention is to heat a plurality of bolt heads of carbon steel or alloy steel rods subjected to heat treatment or cold rolling to a temperature of 400 ° C to A1 transformation point, and to form a bolt at the temperature. It features.

The reason for performing heat treatment or cold rolling on the rod before warm processing is to give the rod almost the same strength as that of the target bolt in advance.

This makes it possible to omit the heat treatment for imparting strength after bolt forming.

That is, the reason that the heating temperature is defined in the range of 400 ° C to A1 transformation point is that when the heating temperature is less than 400 ° C, the deformation capacity required for bolt head molding is not obtained, and cracking occurs easily during molding, while cutting load and molding The load will increase.

On the other hand, when the heating temperature exceeds the A1 transformation point, the temperature rise of the shaft portion due to heat conduction is large, leading to a decrease in strength and an increase in strength variation.

In addition, during the molding process or during the cooling process, the unevenness of the hardened portion is generated, which partially degrades the toughness of the neck.

For this reason, heating temperature shall be in the range of 400 degreeC-A1 transformation point.

Hereinafter, described in detail by the accompanying drawings as follows.

1 illustrates a heating portion and a cutting position in a process diagram showing a heating and cutting state in the bolt molding of the present invention.

The present invention is a feed stand (1) for showing the heating and cutting equipment during bolt forming, the rod 7 on the feed stand (1) coil to the high-frequency heating coil (3) by the conveying roller (2) Supplied.

The high frequency heating coil (3) can be changed in position depending on the length of the bolt to be manufactured.

The vane 7 intermittently heated by the high frequency heating coil 3 is inserted into the die 4, the cutting length is adjusted by the stopper 6, and then cut into a predetermined length by the knife 5. It is then exposed to the heating section 8.

Although the high frequency heating coil 3 may be one as shown in FIG. 1, the high frequency heating coil 3 may be divided into two parts depending on the length of the bolt depending on the length of the diameter bolt and the production speed.

Figure 2 shows the process of manufacturing the bolt in the cutting state, preforming, finishing molding in a flow chart showing the process of the heating portion is formed into a bolt shape after heat cutting by the manufacturing method of the present invention.

In addition, the oblique part in the figure shows the heating part 8.

The reason why the high frequency heating coil 3 is used as a heating method is to rapidly heat the heating portion corresponding to the bolt head to prevent the temperature rise of the shaft portion, and to prevent the fluctuation of the heating temperature from affecting the strength of the screw portion.

In addition, in forming the bolt head, since the deformation capacity is sufficiently obtained, no cracking occurs during molding.

In addition, the device for rapidly heating the heating portion 8 is not limited to the high frequency heating coil (3).

As shown in Fig. 2, the cutting position is such that the heating portion 8 remains at the head of the bolt and the screw tip (about 1/5 of the thread length), thereby reducing the resistance at the time of cutting and the knife 5 And the life of the die 4 can be extended.

In addition, the screw manufacturing of FIG. 2 does not necessarily need to continuously perform the head molding process of the bolt, but may be performed separately after cooling.

(Example)

The configuration of the present invention is as described above, but the following embodiments will be described.

The material provided for the test was prepared with a 10 mm diameter wire rod containing C: 0.27%, Si: 0.18%, Mn: 0 95%, and Cr: 0.32%, and the tensile strength was increased to 105 kgf / mm2 before molding. According to the manufacturing conditions given in Fig. 1, M10 and 85 mm long bolts were completed.

Specimens were taken from the completed bolts and subjected to a tensile test.

The results are shown in Table 1.

Table 1 shows the required heater capacity, wire tensile strength before molding, heating temperature, molding load of bolts and tensile strength of bolts, respectively.

TABLE 1

* Table shows cracks in the head of the bolt during molding

The heater capacity required for the present invention 1 and 2 of Table 1 is conventionally 1/3 of that, and sufficient deformation capacity is obtained because the heating temperature is more than 400 ° C., and the molding load of the bolt is less than 30 ton, and the bolt No cracking of the head occurred during molding, and the tensile strength of the bolt was 107 kgf / mm 2, and there was no decrease in strength, and the standard deviation was as small as 0.46 to 0.50.

In Comparative 3, since the temperature was lower than 350 ° C. compared with the heating temperature of the present invention, the deformation capacity was insufficient, the molding load of the bolt was 33 tons, and cracking occurred during bolt molding.

Conventional 4 is a warm molding method of heating the entire material.

For this reason, the required heater capacity is 75 KVA, which is three times that of the present invention, and the bolt shaft portion is also heated to lower the tensile strength of the screw portion to 102 kgf / mm 2.

In addition, since the variation of the heating temperature affects the strength of the bolt shaft part, the average deviation of tensile strength is large, 0.82.

Since the conventional 5 is a cold forming method, the deformation capacity is insufficient, the molding load of the bolt is large to 38 tons, and cracking occurs during bolt forming.

As is apparent from the above embodiment, the method of manufacturing the high strength bolt according to the method of the present invention corresponds most to the method of manufacturing the high strength bolt which prevents the decrease and fluctuation of the strength of the screw portion with a small heating device.

As described above, since the manufacturing method of the high strength bolt according to the present invention is based on the above configuration, there is no fluctuation caused by the decrease in the strength of the threaded portion with a small capacity heating device, there is no cracking during molding, and furthermore, the life of the mold is damaged. It has an excellent effect that molding with a large processing rate is possible without doing.

On the other hand, the present invention exemplified the best embodiment thereof, but is not limited to this, if limited to the appended claims can be carried out without departing from the scope of the invention in view of the modifications of the embodiments described so far Can be.

Claims (1)

Manufacture of high strength bolts characterized by heating a plurality of bolt heads of carbon steel or alloy steel rods subjected to heat treatment or cold rolling to a temperature of 400 ° C to A1 transformation point and forming a bolt at the temperature. Way.