JPS6047881B2 - Induction hardening method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized by stopping the induction heating of the outer peripheral surface of a workpiece by applying a high-frequency current to a heating coil, and by supplying refrigerant from a refrigerant injection jacket to the heated outer peripheral surface. The rapid cooling is stopped by a predetermined elongation using a precision length measuring device, respectively.
This paper relates to an induction hardening method controlled by detection of shrinkage.

Up until now, the heating conditions have been high-frequency induction hardening by supplying a refrigerant to the outer circumferential surface of the heated object to rapidly cool it after induction heating the work by passing a high-frequency current through a heating coil that surrounds the work. The cooling conditions have been controlled by the amount of voltage (KW) and heating time (seconds), and the injection amount (llmln) of refrigerant at a predetermined temperature and the injection cooling time (seconds).

In other words, the stopping of heating and cooling is regulated by a set timer, and the heating and cooling conditions are kept uniform by using an automatic voltage regulator to deal with fluctuations in power supply voltage, and by using a constant temperature maintaining device to set the refrigerant temperature. Efforts have been made to maintain high repeatability and minimize variations in heat treatment quality. However, this conventional method was expensive due to the highly accurate automatic voltage regulator, and was indirect quenching management that did not directly grasp information on the heating and cooling conditions from the state of the workpiece to be quenched. The current situation is that quality control requires a great deal of effort and man-hours, even though expensive equipment is used and is affected by disturbance factors such as variations in the precision of component equipment and variations in the installation precision of coils. In view of the above points, the present invention was developed with the intention of managing induction hardening work from a standpoint different from the conventional work management using heating power and heating time. The elongation of the steel material to be hardened, which can be most closely related to the hardening quality such as layer depth, can be captured using a precision length measuring device, and the final hardening quality of the steel can be determined more directly during heating and cooling. The purpose of the present invention is to provide a high-precision induction hardening method using a relatively simple device with a configuration that allows for accurate understanding.

An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG. 2 is a chart showing the relationship between temperature change and elongation of medium carbon copper material (for example, S4OC). The principle of the method of the present invention will be explained with reference to the embodiments shown in Figs. 1 and 2. In the workpiece W of S4OC (annealed state) round steel as the member to be quenched, the elongation decreases as the heating temperature increases. The change takes the form of a nearly straight line as shown in FIG.

At point B, contraction occurs due to ACl transformation, and then AC3 transformation progresses within a certain temperature range, causing some contraction, and at point C, this A. 3 Metamorphosis is completed.
The workpiece W exhibits simple thermal expansion in the high temperature region A after completion of the AO3 transformation and in the low temperature region A up to the ACl transformation. In general heat treatment, the heating temperature for quenching is set at point D, which is 30 to 50 degrees higher than point C, where AC3 transformation is completed, but because high-frequency heating is rapid heating, it is set to an even higher temperature. expected to shift. The heating temperature for induction hardening actually depends on the steel type, preheat treatment condition, heating rate,
It is well known that the heating temperature is determined by various factors such as the quality specifications of the baked product, but in actual work, the heating temperature is generally determined by the heating power and heating time, not by a thermometer. Various combinations are used to determine the final quality of the hardened product. The present invention uses a commercially available precision length measuring device 10b to check the final quality, particularly the elongation of the product under heating, which is directly related to surface hardness, hardened layer depth, etc. The value has been reached. When the heating is stopped and the heated surface W1 is rapidly cooled, the surface W1 is cooled exactly as indicated by the broken line in FIG. 2, passing through the maximum contraction point G, and cooling to the complete cooling region where martensite is generated. After passing the maximum contraction point G, it is slowly cooled to purify martensitic formation and reduce dimensional changes as much as possible! This is to minimize cooling. Regarding steel materials used for induction hardening, including S4OC in this example, the average line between 0℃ and heating temperature 700℃ *However, K = 0.8 ~
0.9--If the diameter becomes even larger than when the above empirical formula was obtained, and the ratio of the thickness/diameter of the heating layer becomes smaller, it is expected that the value of K will become smaller than the above value r+[;
1,12 Ete 110/. :FOZ Mi2 expansion coefficient is approximately 1
3 to 15 x 10-6/°C, and the difference depending on the steel type is extremely narrow.Also, at high temperatures above point C, excluding shrinkage during transformation, the coefficient of linear expansion at the entrance of the region is the coefficient of linear expansion of the region A. ing.

Therefore, the linear expansion coefficient above point C can be estimated to be 15 x 10-6/°C or more. To explain the results of an investigation as to whether the method of the present invention is practicable with respect to the reading accuracy (1 pTr1.) of the precision length measuring device 10b currently on the market, the length of the heated area l for a temperature rise x°C above point C ) The elongation of the gourd Δl is given by the following formula. The reading accuracy of the length measuring device is 1μ, i.e. 1x″=6
The change in length corresponding to the synergistic change in temperature and length with a minimum unit of 6.5 can be measured.

The appropriate control range for the heating temperature in heat treatment is ±5°C even when it is particularly strict, and about ±15°C especially in the case of induction hardening which requires rapid heating. Therefore x=30
℃, it becomes l″.2.2w0n. This shows that when performing induction hardening of the S4OC round steel W of this example, it is sufficient if the hardened length is about 2.2T!Rln. .The minimum quenching width currently being performed is 5.5wr!n
That's about it. Since induction hardening is surface hardening, the core is not heated to the same temperature, so the linear expansion indicated by the temperature rise on the surface and the linear expansion in the relatively low temperature part of the core are ideal, and this can be calculated mathematically. Although it is difficult to analyze it visually, each part of the core of the round steel W of the workpiece is in a state of elongation corresponding to its temperature. That is, as the state of change shown in the temperature-elongation curve shown in FIG. It appears as a stretch as a whole. Length 200~ in order of 20~30φ including this example
According to the experimental results when the outer circumferential surface W1 of the workpiece over the entire length of 80D1wt was rapidly heated by high frequency, the following equation was established as the relation between the surface heating temperature and the elongation in the axial direction.
--Todoroki k^1 Choran 1 Reni -1 -4■Q~IP
However, by selecting an appropriate value for K, the elongation at that heating temperature can be estimated.

Even if the surface is rapidly heated at the quenching heating temperature of normal steel, the value of K is 0.5 or more due to its relatively high thermal conductivity.
+ mouth 12E1) 0/. ;It is thought that it will not be below qζ.

Now, if K=0.5, the minimum unit of the measurable synergistic value of temperature and length is; 1.51x(0.5)/10
From 0=, 1X=133, and at x=30℃, 1=
It will be 4.47m.

mosquito! Furthermore, the current length measuring device measuring in units of 1 μm can be used even on a narrow outer peripheral surface. As described above, judging from the basic experimental results of the present invention, the method of the present invention can be applied to both heating a very narrow part and heating the entire length of a long round steel. A1ru. In the induction hardening method according to this embodiment, an input terminal is connected to a semi-loop heating coil 20 that surrounds the outer circumferential surface W1 of a workpiece w, which is an axially symmetrical rotating body such as an S4OC round steel that rotates due to rotational drive by a drive source such as a motor. , 22 to generate an induced current on the outer circumferential surface W1, and heat it by induction to a high temperature D above the end of point C. When a predetermined elongation value is reached, the heating is stopped and the refrigerant is injected from the refrigerant injection jacket 30. In this method, the workpiece is supplied by injection and rapidly cooled until it passes through a temperature G at which the contraction is maximum. 43
The rotational drive side W is restrained from moving in the axial direction by the spring, and the rotation axis of the workpiece W is thermally expanded toward the other free end side W2. The high frequency current supply is cut off and terminated via the controller 10c by detection via the sliding support shaft 44, and then cooling of the heated outer circumferential surface W1 is started,
Induction hardening is performed by stopping the supply of the refrigerant for cooling when the length measuring device 10b detects contraction up to a preset length of the rotating shaft.

These optimum elongation and shrinkage values are calculated and verified empirically. Experimental example/
...A certain relationship was confirmed between elongation and firing quality.

The entire length of the S4OC normalized material (diameter 25φ x length 3001 mm) was surface hardened using a 10 KHZ 1250 KW high frequency oscillator, and complete cooling was performed under the same conditions.

The results when the input density is 0.48KWIc1t are shown in the following table. The induction hardening apparatus according to the embodiment used in this method, as shown in FIG. It is supported on a pair of rollers 41 and 42 for centering, and rotated by a drive source such as a motor via a known chucking device.

A semi-loop heating coil 20 is attached to the rotating workpiece W.
is suitable for mass production, and is set so as to surround the upper half of the workpiece w over the entire length thereof using an appropriate lifting device.

The heating coil 20 of the high-frequency power generation device 100, which does not have an automatic voltage regulator, receives a high-frequency current from the input terminal 22 and heats the outer peripheral surface W1 of the rotating workpiece W by induction. The elongation due to induction heating can be achieved by freely moving the right center 44, which is heated on the workpiece side by a spring, on the axis of the free end side W2 via the superalloy measurement sensor 10a that is held in contact with the right center 44. length measuring device 10b (for example, Njk
There are products such as On's Digimicro ■-501). When the precision length measuring device 10b detects the elongation of the rotation axis of a predetermined workpiece W, it sends a signal to the controller 10c,
The high frequency current is cut off by this command from the controller 10c. At the same time, the coolant is injected and supplied from the coolant injection jacket 30 toward the heated outer circumferential surface W1 in response to a command from the controller 10c. In the case of the present invention, the temperature of the coolant can be controlled to a higher allowable temperature than in the conventional method, and the number of management steps can be greatly reduced. Work W due to this rapid cooling 7
Similarly, the contraction is measured by the length measuring device 1 via the measurement sensor 10a.
0b, and when the contraction to the set shaft length is detected, the controller 10c receives the detection signal, and in response to the command, the electric valve of the refrigerant system that passes through the refrigerant liquid injection jacket 30 is closed, and the refrigerant is discharged. Injection is stopped. Furthermore, as an applied example, if a digital readout system is coupled to the length measuring device 10 of the present invention, the expansion and contraction processes can be visually observed, and heat treatment applications such as selecting the timing to switch from rapid cooling to slow cooling become possible.

In this way, the direct elongation from the workpiece W, which is the member to be hardened,
The method of the present invention that captures the state of contraction using the precision length measuring device 10 may be affected by fluctuations in power supply voltage, accuracy of heating timer,
Non-uniform heating caused by various factors such as misalignment of the relative position of the workpiece and quill, and non-uniform cooling caused by fluctuations in the temperature and flow rate of the coolant are completely eliminated, improving repeatability, i.e., sintering. A further improvement in human quality has been realized, and furthermore, by connecting a digital read-out system to the length measuring device 10b, it is possible to observe the progress of heat treatment during heating or cooling, and it is also possible to perform optimal heat treatment. You can enjoy the effects of

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG. 2 is a chart showing the relationship between temperature change and elongation of carbon steel materials. (Explanation of symbols), 10...Precision length measuring device, 20
... Heating coil, 30 ... Refrigerant injection jacket, W ... Work, W1 ... Workpiece outer circumferential surface, Wl, W2 ... Workpiece edge.

Claims (1)

[Claims] 1. A heating coil 20 surrounding the outer peripheral surface W_1 of the workpiece W.
In the induction hardening method, in which the outer circumferential surface W_1 of the workpiece is induction heated by passing a high-frequency current through it, the outer circumferential surface W_1 of the workpiece is hardened by supplying refrigerant from the refrigerant injection jacket 30 for rapid cooling. The induction heating is performed by detecting the elongation at a preset free end of the work W in the axial direction, which is centered by the precision length measuring device 10 disposed at the end of the work W in the axial direction. Then, cooling of the heated outer circumferential surface W_1 is started, and the supply of the refrigerant for this cooling is detected by the precision length measuring device 10 to detect the contraction to the length of the workpiece W set in advance. This is an induction hardening method that is characterized by stopping. 2 The preset elongation of the work W in the axial direction is
One end w_1 of the workpiece W is restrained in the axial direction, and the other end w_2 is set as a free end, and the precision length measuring device 1 is attached to the free end w_2.
The induction hardening method according to claim 1, wherein the induction hardening method is detected by 0.