JPS6346126B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is an improvement of a cooling device for high-frequency induction hardening, and more specifically, a cooling device for inductively heating a steel material (including special alloy steel) as a workpiece, moving it, and quenching it mainly using cooling water as a coolant. Regarding improvements. The quality of surface hardening of a steel material lies in whether the maximum quenching hardness of the steel material is exhibited evenly throughout the entire hardened layer and without quenching cracks, and one factor that determines this is the cooling method. The conventional high-frequency induction heating hardening apparatus shown in FIG. 2), and the work W1, which has been induction heated by the work coil 1, is placed in the cooling jacket 2.
The cooling jacket 2 is a jacket unit 21 equipped with a large number of jet holes 20 on the front surface of the work W.
A plurality of ejection holes 20 are provided at intervals in the circumferential direction of the ring unit, or a single ring unit is provided with ejection holes 20 (however, for convenience, the latter example is shown in Fig. 1). When hardening a rod-shaped steel workpiece such as a ball screw using such a hardening apparatus, the following problems occur. In order to obtain the maximum hardness, the amount of water ejected from the cooling jacket 2 within a unit time is increased as much as possible. A part of the fountain that collided with the workpiece surface returns to the workpiece coil side (heating range) (as water flows along the surface of the workpiece W1). (backwards to the work coil side), this unnecessarily lowers the surface temperature of the heated workpiece W1 before it reaches the jacket 2, and the critical zone (high temperature cooling zone) becomes gradual, making it impossible to provide a sudden temperature difference. In the end, due to the above-mentioned phenomenon, a nodular troostite structure is created on the surface of the workpiece, and the maximum hardness cannot be obtained by quenching (sufficient martensitic transformation cannot be achieved). On the other hand,
Low temperature cooling range (approximately 400℃ or less) due to large amount of cooling water
The process progresses easily and the martensitic transformation starts point Ms (approximately
Cooling proceeds rapidly below 350℃ (however, this varies depending on the steel quality), resulting in an increased risk of quench cracking. In this way, in the case of conventional equipment, even if an attempt is made to increase the quenching effect, due to the limitations of the equipment itself, the cooling in the critical area is insufficient and the cooling in the low temperature area is excessive, resulting in the maximum hardness being quenched. They are faced with the dilemma of not being able to achieve this, but risking quench cracking. In view of the above, as a result of various experimental studies, the present inventors found that
Cooling is divided into two stages, and in the first cooling (critical area), the fountain force (there are other refrigerants other than water, but only water will be used as an example) is made stronger, but the amount of water is reduced to keep the surface temperature of the workpiece approximately the same. Rapid cooling to around 500℃ is followed by second cooling (low-temperature cooling range) to about 200℃, in which the fountain force is weak but the workpiece surface is cooled with a relatively large amount of water. He learned that by slowly cooling the material so that it is surrounded by a film of applied water, it is possible to quench the material with high hardness and without quenching cracks. The strength of the fountain force in the first cooling described above destroys the formation of a steam film on the workpiece surface and strengthens the contact cooling between the workpiece surface and the fountain. This is to prevent the migration of waves. The weak fountain force and large amount of water in the second cooling process are achieved by wrapping the surface of the workpiece in water and cooling it slowly and uniformly, allowing the transition from the start to the end of martensitic transformation to occur gradually and sintering. This is to prevent cracking. The cooling device of the present invention for carrying out such a method uses a conventionally used shower-type jacket for the second cooling, and uses a cooling device for the first cooling, which is the same as the one for the first cooling. The second cooling jacket is equipped with a properly narrowed fountain so that the fountain force is stronger than that of the second cooling jacket, and the total number of fountains involved in the fountain is far smaller than that of the second cooling jacket. The cooling nozzle and the cooling jacket are arranged in the order in which the work is carried out. The present invention will be explained in detail below based on the drawings. Second
The figure is a temperature one-hour characteristic graph of the cooling method of the present invention. In this cooling method, the cooling time t ₁ from the maximum heating temperature A of the workpiece to approximately 500°C B is assumed to be rapid, for example, 0.5 seconds, and this is the primary cooling.
The cooling time _t2 to reach around 200℃ is relatively slow (for example, 5 seconds), and this is considered secondary cooling, and the temperature drop curve is steep.
It is said that the curve is relatively gentle. The first cooling rapidly cools the steel to approximately 500°C, followed by the slow second cooling, which allows for smooth martensitic transformation, resulting in unprecedented quenching hardness. It is clear from the results described below that this can be achieved. Next, a cooling device of the present invention for implementing such two-stage cooling will be described. FIG. 4 is a perspective view showing one embodiment of the cooling device of the present invention, and FIGS.
The front views of each of the cooling means and the second cooling means are shown.
In this example, each of the first and second cooling means has a water passage (not shown) therein, and the two cooling means are held in parallel with each other.
A plurality of (seven in this case) cooling nozzle units 22 are arranged at equal intervals on the two arcuate arms 23 and 24 as the first cooling means, and the same number of cooling jacket units are arranged as the second cooling means. 21...
are shown as an example in which they are provided at equal intervals. Among these, the cooling nozzle unit 22 has only one narrow slit 221 bored in the front of the hexagonal columnar nozzle body 220 as shown in FIGS. 4 and 5, and the fountain flows from this slit 221 into a narrow beam shape. It will be done.
On the other hand, the cooling jacket unit 21 has a rectangular columnar jacket main body 210 with a large number of circular ejection holes 211 bored in a staggered manner on the front surface of the jacket body 210, and water is emitted from the ejection holes 211 in a funnel shape. In FIG. 4, reference numerals 25 and 26 are water inlets, each connected to a water supply source (not shown). The slit 221 of the unit 22 is sufficiently narrowed (for example, 0.5 mm in length and 15 mm in width) to make the fountain force strong, and its opening area is sufficiently smaller than the total opening area of the circular jet hole 211 (number of slits). As an example, the ratio is 7:120). Therefore, if we assume that the pipe resistance and the water pressure on the water supply side of each of the units 22 and 21 are equal, the jet pressure from the slit 221 is much higher than that from the jet hole 211, but the unit time On the contrary, the amount of water in the unit 21 is clearly larger than that in the unit 22. Note that the water pressure and amount of water from the slit 221 are determined by taking into consideration the transfer speed of the workpiece W.
The design shall be such that water running on the workpiece W does not return to the workpiece coil 1 side. Instead of the above embodiment, the cooling nozzle and cooling jacket shown in FIGS. 6a and 6b may be applied.
That is, the nozzle in figure a has a ring-shaped nozzle body 2.
The cooling jacket 21 also has ejection holes 211... arranged in a row on the inner circumference of the ring-shaped jacket body 212.
It is a list of... The cooling device of the present invention has the above-mentioned configuration, and includes a first cooling means for the workpiece W1 that maintains the maximum heated temperature;
That is, by receiving a small but strong jet of water from the cooling nozzle 22, the surface of the workpiece W1 is rapidly cooled to about 500° C. in a short period of time without forming a water curtain, thereby completing the first cooling. During this period, the phenomenon in which the applied water returns to the work coil 1 side does not occur.
The workpiece W2 that has been rapidly cooled by the nozzle 22 is then slowly cooled by a large amount of water, albeit with a weak jetting force, from the cooling jacket 21, which is a second cooling means. By enveloping the material, even and gentle cooling is achieved, thereby sufficient martensitic transformation is achieved, and the second cooling to about 200° C. is completed. Because of this slow cooling, the fear of causing quench cracks in the workpiece can be sufficiently avoided. As a result, the hardness distribution diagram showing the relationship between the depth from the surface of the workpiece W3 that has been cooled according to the present invention and the hardness is as shown in FIG. 7. In FIG. 7, Carvey indicates the present invention, B indicates Comparative Example 1, and C indicates Comparative Example 2. Table 1 shows the results of comparing and comparing this figure with numerical values obtained by cooling using a conventional device equivalent to that shown in FIG. 1, and cooling only with the cooling nozzle 22 as an experimental example of the present invention.

[Table] As is clear from FIG. 7 and Table 1, the present invention was superior to the comparative example in the effective depth of quenching hardness Hv500 or more, and a martensitic structure was confirmed throughout. On the other hand, Comparative Example 2 had a low bainite structure, and Comparative Example 1 had a troostite structure as described above. As described above, the present invention provides an excellent cooling device that further improves the hardenability of the conventional coil and jacket split type, cross-feed type high-frequency induction heating hardening.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a conventional high-frequency induction heating hardening apparatus, Figure 2 is a temperature-time characteristic graph of cooling by the apparatus of the present invention, Figure 3 is a schematic diagram of the apparatus of the present invention, and Figure 4 is a schematic diagram of the apparatus of the present invention.
The figure is a perspective view showing one embodiment of the cooling means of the present invention, FIGS. 5a and 5b are front views respectively showing the first cooling means and the second cooling means in FIG. 4, and FIGS. FIG. 7 is a perspective view of the first cooling means and the second cooling means of another embodiment of the present invention, and FIG. 7 shows the hardness showing the relationship between the depth from the surface of the workpiece and the hardness when it is cooled according to the present invention. It is a distribution map. (Explanation of symbols), 1... Work coil, 2...
Cooling means, 21... Cooling jacket (second cooling means), 22... Cooling nozzle (first cooling means), 22
1...Slit, 211...Blowout hole, 23, 24
... Arc-shaped arm, 210 ... Rectangular columnar jacket body, 220 ... Hexagonal columnar nozzle body, W ... Work, W1 ... Work heated by the coil, W2 ... Work cooled by the cooling nozzle, W
3... Workpiece cooled by a cooling jacket.

Claims (1)

[Scope of Claims] 1. In an apparatus for rapidly cooling and quenching using a cooling liquid ejected from a cooling device after moving a workpiece that has been subjected to high-frequency induction heating by a work coil, the cooling device is connected to the workpiece. It is divided into two parts, a first cooling means and a second cooling means, with respect to the moving direction.
The cooling means has a strong jetting force of the cooling liquid, but is configured to rapidly cool the heated workpiece with a relatively small amount of liquid that is transmitted to the workpiece surface and does not return to the workpiece coil side. A cooling device for high-frequency induction hardening, characterized in that the liquid jetting force is low, but the liquid is slowly cooled with a relatively large amount of liquid that covers the surface of the workpiece. 2. The first cooling means consists of a plurality of cooling nozzle units arranged in the circumferential direction of the workpiece, the second cooling means consists of a plurality of cooling jacket units arranged in the circumferential direction of the workpiece, and each cooling nozzle unit is arranged in one line. 2. The apparatus according to claim 1, wherein each of the cooling jacket units has a plurality of ejection holes arranged in a staggered manner on the front surface thereof.