JP6561412B2 - Sinter hardening method and sintering furnace for sinter hardening - Google Patents

Description

  The present invention relates to a sintering hardening method and a sintering furnace for sintering hardening suitable for the sintering hardening method.

  Conventionally, as a method of producing a high-strength sintered product, a method in which a workpiece formed by compression molding a powder material is sintered, cooled, and then subjected to heat treatment such as carburizing and quenching in a separate process. However, in this method, since heating is performed in each of the sintering and the subsequent heat treatment, distortion due to expansion / contraction due to heating is likely to occur, and a reduction in the dimensional accuracy of the sintered product cannot be avoided.

  On the other hand, in recent years, a technique called sinter hardening has been developed (for example, Patent Document 1). Sinter hardening is a method in which a workpiece formed by compression molding a powder material is heated to sinter, and then the workpiece is hardened by rapidly cooling the workpiece in a subsequent cooling process. According to this method, since the sintering and quenching can be performed by one heating, the generation of distortion due to the heating can be suppressed.

Japanese Patent Laying-Open No. 2015-14041

  Conventionally, when a high-hardness sintered product is manufactured by the above-mentioned sinter hardening, whether or not the obtained sintered product has a predetermined quenching structure is determined by manual eddy current inspection in the post-sinter hardening process. It was.

  That is, sinter hardening comprises a plurality of transport rollers for transporting a workpiece, a sintering chamber for heating the workpiece to a sintering temperature on the transport path of the transport roller, and a quenching chamber located downstream of the sintering chamber. Using a continuous sintering furnace. If the workpiece cooling rate in the quenching chamber is sufficiently high, a sintered product having a predetermined quenching structure can be obtained. If there is any abnormality in the quenching chamber, the workpiece cooling in the quenching chamber is performed. There is a possibility that the speed is insufficient and a predetermined quenched structure cannot be obtained.

  Therefore, in order to inspect whether or not the obtained sintered product has a predetermined quenching structure, eddy current inspection is performed on each sintered product discharged from the continuous sintering furnace, and a high hardness sintered product is obtained. Reliability was ensured. In eddy current inspection, a sintered product is placed in an alternating magnetic field to generate an eddy current due to electromagnetic induction inside the sintered product, and a hardened structure is inspected based on the induced magnetic field induced by the eddy current. It is. And this eddy current test | inspection was performed by the operator setting each sintered product discharged | emitted from the continuous sintering furnace manually to the eddy current test | inspection apparatus.

  However, manual eddy current inspection of individual sintered products discharged from the continuous sintering furnace has been complicated.

  An object of this invention is to provide the sintering hardening method which can test | inspect efficiently whether the predetermined quenching structure | tissue was obtained.

A sintering hardening method according to an aspect of the present invention includes:
A workpiece formed by compression molding powder material is conveyed by a plurality of conveyance rollers,
Heating the workpiece to a sintering temperature in a sintering chamber provided on the conveying path of the conveying roller;
In the quenching chamber located on the downstream side of the sintering chamber on the transport path of the transport roller, quenching by blowing a cooling gas to the workpiece,
When cooling gas is blown to the workpiece in the quenching chamber, the cooling rate of the workpiece in the quenching chamber is detected by a temperature sensor, and whether or not the detected cooling rate is within a preset range is checked.
Sinter hardening method.

  Based on the above, it is possible to efficiently inspect whether or not a predetermined quenched structure has been obtained.

It is sectional drawing which shows the continuous sintering furnace used with the sintering hardening method concerning embodiment of this invention. It is the partially expanded sectional view which fractured | ruptured the quenching chamber of FIG. 1 along the cross section orthogonal to the conveyance direction of a workpiece | work. It is a figure which shows an example of the time change of the output of the temperature sensor shown in FIG.

[Description of Embodiment of the Present Invention]
(1) A sintering hardening method according to an aspect of the present invention includes:
A workpiece formed by compression molding powder material is conveyed by a plurality of conveyance rollers,
Heating the workpiece to a sintering temperature in a sintering chamber provided on the conveying path of the conveying roller;
In the quenching chamber located on the downstream side of the sintering chamber on the transport path of the transport roller, quenching by blowing a cooling gas to the workpiece,
When cooling gas is blown onto the workpiece in the quenching chamber, the cooling rate of the workpiece in the quenching chamber is detected by a temperature sensor, and whether or not the detected cooling rate is within a preset range is inspected. ,
Sinter hardening method.
If it does in this way, based on the cooling rate when hardening a workpiece | work in a quenching chamber, it can be test | inspected indirectly whether the predetermined hardening structure | tissue was obtained by the workpiece | work. That is, it is possible to inspect whether or not a predetermined quenched structure is obtained in the process of sinter hardening, and individual sintered products obtained by sinter hardening are processed in the post-sinter hardening process. There is no need for manual inspection. Therefore, it is possible to efficiently inspect whether or not a predetermined quenched structure has been obtained.
(2) The following configuration can be added to the above sinter hardening method.
The temperature sensor is a radiation thermometer that detects the temperature of the workpiece by measuring the intensity of infrared rays emitted from the workpiece,
While the temperature sensor detects the cooling rate of the workpiece in the quenching chamber, the conveyance roller that supports the workpiece repeats normal rotation and reverse rotation so as to reciprocate the workpiece back and forth in the conveyance direction.
In this way, while the temperature sensor detects the cooling rate of the workpiece in the quenching chamber, the workpiece reciprocates back and forth, so that the workpiece surely enters the temperature measurement area by the radiation thermometer, enabling stable inspection. It becomes.
(3) Moreover, the thing of the following structures is provided as a continuous sintering furnace for sinter hardening which concerns on 1 aspect of this invention.
A plurality of conveying rollers for conveying a workpiece formed by compression molding a powder material;
A sintering chamber for heating the workpiece to a sintering temperature on a conveying path of the conveying roller;
A quenching chamber located on the downstream side of the sintering chamber on the conveying path of the conveying roller, and quenching the workpiece by blowing a cooling gas;
A cooling temperature inspection device that detects the cooling rate of the workpiece in the quenching chamber with a temperature sensor and inspects whether or not the detected cooling rate is within a preset range;
A continuous sintering furnace for sintering hardening.

[Details of the embodiment of the present invention]
A sinter hardening method according to an embodiment of the present invention and a continuous sintering furnace suitable for the sinter hardening method will be described below with reference to the drawings. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

  1 and 2 show a continuous sintering furnace used in a sintering hardening method according to an embodiment of the present invention. This continuous sintering furnace is a continuous sintering furnace in which a workpiece W formed by compression molding an iron-based powder material is heated to a sintering temperature of 1100 ° C. or higher and sintered. This continuous sintering furnace has a dewaxing chamber 2, a preheating chamber 3, a sintering chamber 4, a slow cooling chamber 5, a quenching chamber 6, and a cooling chamber 7 in order from the upstream side to the downstream side.

  Each of the chambers 2 to 7 is provided with conveying rollers 8 to 13 for moving the carbon tray 1 on which a plurality of works W are placed from the upstream side to the downstream side. A plurality of conveyance rollers 8 to 13 are provided in each of the chambers 2 to 7 with an interval in the conveyance direction of the workpiece W. That is, the chambers 2 to 7 are sequentially provided on the transport path of the workpiece W by the transport rollers 8 to 13.

  Between the dewaxing chamber 2, between the dewaxing chamber 2 and the preheating chamber 3, between the preheating chamber 3 and the sintering chamber 4, between the sintering chamber 4 and the slow cooling chamber 5, between the slow cooling chamber 5 and the quenching chamber 6. Between the rapid cooling chamber 6 and the cooling chamber 7, and at the outlet of the cooling chamber 7, shutters 14 to 20 are provided, respectively. These shutters 14 to 20 are individually opened and closed.

  In the dewaxing chamber 2, the preheating chamber 3, the sintering chamber 4, and the slow cooling chamber 5, heaters 21 to 24 for heating the respective indoor atmospheres are provided. The sintering chamber 4 is filled with an atmosphere of an inert gas (for example, nitrogen gas), and the workpiece W is heated in the atmosphere of the inert gas.

  A blower fan 25 is connected to the quenching chamber 6, and the cooling gas circulates between the quenching chamber 6 and the blower fan 25. The cooling gas is an inert gas (for example, nitrogen gas). A chiller (not shown) for cooling the cooling gas is connected to the cooling gas circulation path between the quenching chamber 6 and the blower fan 25.

  As shown in FIG. 2, the quenching chamber 6 is provided with a temperature sensor 26 that detects the temperature of the workpiece W in the quenching chamber 6. The temperature sensor 26 is a radiation thermometer that detects the temperature of the workpiece W by measuring the intensity of infrared rays emitted from the workpiece W. The temperature sensor 26 is used for a cooling temperature inspection device 27 that inspects whether or not the cooling rate of the workpiece W in the quenching chamber 6 is within a preset range when the cooling gas is blown onto the workpiece W in the quenching chamber 6. It is connected.

  The temperature sensor 26 is provided on the side wall 28 of the quenching chamber 6 so as to avoid directly above the workpiece W conveyed in the quenching chamber 6. In this manner, by disposing the temperature sensor 26 so as to avoid the position directly above the workpiece W, damage to the temperature sensor 26 due to heat generated by the workpiece W is prevented. Further, an electric motor 29 that drives the transport roller 12 of the quenching chamber 6 is attached to the side wall 28 of the quenching chamber 6.

  As shown in FIG. 1, the cooling chamber 7 is provided with a cooler 30 that cools the indoor atmosphere and a circulation fan 31 that circulates the indoor atmosphere.

  Next, an example of a method for sintering and hardening the workpiece W using this continuous sintering furnace will be described.

  First, as shown in FIG. 1, a plurality of workpieces W are placed on the carbon tray 1, and the workpieces W are transported into the dewaxing chamber 2 in this state. When the workpiece W enters the dewaxing chamber 2, the workpiece W is heated to a temperature of about 500 to 750 ° C. At this time, the wax component present in the workpiece W burns and the wax component is removed.

  Thereafter, the workpiece W is conveyed from the dewaxing chamber 2 to the preheating chamber 3 by the conveying rollers 8 and 9. In the preheating chamber 3, the workpiece W is heated to a temperature of about 800 to 1000 ° C., which is lower than the sintering temperature.

  Thereafter, the workpiece W is conveyed from the preheating chamber 3 to the sintering chamber 4 by the conveying rollers 9 and 10. In the sintering chamber 4, the workpiece W is heated until reaching a sintering temperature of about 1100 to 1300 ° C., and is maintained at the sintering temperature for a predetermined time. Thereby, the powder which comprises the workpiece | work W sinters and integrates.

Thereafter, the workpiece W is transported from the sintering chamber 4 to the slow cooling chamber 5 by the transport rollers 10 and 11. Slow cooling chamber 5, the ambient temperature of the room is lower than 900 ° C., and a temperature higher than the austenitic transformation point (the so-called _{A 3} transformation point) (e.g., a temperature range of 840 to 870 ° C.) so as to keep the The temperature is controlled. The work W is transported by the transport roller 11 so as to stay in the slow cooling chamber 5 for about 10 to 20 minutes. As a result, the workpiece W is cooled and held at a temperature lower than 900 ° C. and higher than the austenite transformation point.

  Thereafter, the workpiece W is transported from the slow cooling chamber 5 to the quenching chamber 6 by the transport rollers 11 and 12. When the workpiece W enters the quenching chamber 6, both the shutter 18 at the entrance and the shutter 19 at the exit of the quenching chamber 6 are closed, and in this state, the blower fan 25 is operated to blow cooling gas onto the workpiece W. Rapid cooling to a temperature lower than the site transformation point (so-called Ms point) (for example, a temperature range of 250 to 350 ° C.). The cooling rate of the workpiece W during the rapid cooling is 2 to 5 ° C./second (preferably 3 to 5 ° C./second). The workpiece W is quenched by this rapid cooling, and the structure of the workpiece W is transformed into martensite.

  Here, when the cooling rate of the workpiece W in the quenching chamber 6 is sufficiently high, a sintered product having a predetermined quenching structure is obtained, but there is some abnormality in the quenching chamber 6 (for example, an abnormality in the blower fan 25 or When there is an abnormality of the chiller that cools the cooling gas circulating between the quenching chamber 6 and the blower fan 25), the cooling rate of the workpiece W in the quenching chamber 6 is insufficient, and a predetermined quenching structure is obtained. There is a risk of not. Therefore, in order to inspect whether or not the work W hardened by the rapid cooling in the rapid cooling chamber 6 has a predetermined quenching structure, the cooling temperature inspection device 27 shown in FIG. When the cooling rate of the workpiece W in the quenching chamber 6 is detected by the temperature sensor 26, and whether or not the detected cooling rate is within a preset range, Indirectly check whether a hardened structure has been obtained. And when the cooling rate of the workpiece | work W remove | deviates from the range set beforehand, abnormality is alert | reported to an operator with the alerting | reporting apparatus which is not shown in figure.

  By the way, when the cooling temperature of the workpiece W is detected by the temperature sensor 26, it is possible to measure the temperature of the workpiece W with the conveyance roller 12 stopped, but the workpiece W with the conveyance roller 12 stopped. When the temperature of is measured, the following problems may occur.

  That is, there is no problem if the workpiece W surely enters the temperature measurement area by the temperature sensor 26 when the conveyance roller 12 stops, but the workpiece W moves from the temperature measurement area by the temperature sensor 26 when the conveyance roller 12 stops. There is a possibility that the temperature sensor 26 stops at the shifted position, and the temperature sensor 26 measures the temperature of the portion between the workpieces W adjacent to each other in the transport direction (that is, the upper surface of the carbon tray 1 that supports the workpiece W). . In this case, not the cooling temperature of the workpiece W but the cooling temperature of the carbon tray 1 that supports the workpiece W is detected, which causes inspection failure.

  Therefore, in this embodiment, while the cooling rate of the workpiece W in the quenching chamber 6 is detected by the temperature sensor 26, the electric motor 29 is driven so that the transport roller 12 repeats normal rotation and reverse rotation, and the workpiece W Are moved back and forth in the transport direction. Thereby, the workpiece | work W enters into the temperature measurement area by the temperature sensor 26 reliably, and the stable test | inspection is attained. Here, the movement distance before and after the reciprocating motion of the workpiece W is set larger than the gap between the workpieces W adjacent in the front-rear direction. Further, the cycle in which the workpiece W makes one reciprocation is set in a range of 15 seconds to 45 seconds.

  FIG. 3 shows an example of an output change of the temperature sensor 26 when the cooling rate of the workpiece W is detected in a state where the workpiece W is reciprocated. The vertical axis corresponds to the temperature measured by the temperature sensor 26, and the horizontal axis corresponds to time. The reason why the output value of the temperature sensor 26 shown in FIG. 3 moves up and down with a width of about 100 ° C. is that the workpiece W is entering and exiting the temperature measurement area of the temperature sensor 26 as the workpiece W reciprocates. Show. Moreover, the fact that the output value of the temperature sensor 26 has decreased as a whole indicates that the temperature of the workpiece W has decreased due to the blowing of the cooling gas in the quenching chamber 6. Based on the output value of the temperature sensor 26, the cooling temperature inspection device 27 inspects whether or not the cooling rate of the work W when the cooling gas is blown onto the work W in the quenching chamber 6 is within a preset range. To do.

  After the workpiece W is rapidly cooled in the quenching chamber 6, the workpiece W is transported from the quenching chamber 6 to the cooling chamber 7 by the transport rollers 12 and 13. In the cooling chamber 7, the workpiece W is cooled to a low temperature of 150 ° C. or lower (for example, about 100 ° C.). When the cooling of the workpiece W in the cooling chamber 7 is completed, the workpiece W is discharged to a replacement chamber (not shown) adjacent to the downstream side of the cooling chamber 7.

  When a high-hardness sintered product is manufactured by the above-described sinter hardening method, it is indirectly inspected whether a predetermined quenched structure is obtained on the workpiece W based on the cooling rate when the workpiece W is quenched in the quenching chamber 6. be able to. That is, it is possible to inspect whether or not a predetermined quenched structure is obtained in the process of sinter hardening, and individual sintered products obtained by sinter hardening are processed in the post-sinter hardening process. There is no need for manual inspection. Therefore, it is possible to efficiently inspect whether or not a predetermined quenched structure has been obtained.

  Further, when a high-hardness sintered product is manufactured by the above sinter hardening method, the workpiece W reciprocates back and forth while the temperature sensor 26 detects the cooling rate of the workpiece W in the quenching chamber 6. W reliably enters the temperature measurement area by the temperature sensor 26, and stable inspection is possible.

DESCRIPTION OF SYMBOLS 1 Carbon tray 2 Dewaxing chamber 3 Preheating chamber 4 Sintering chamber 5 Slow cooling chamber 6 Quench chamber 7 Cooling chambers 8-11 Transport rollers 12, 13 Transport rollers 14-20 Shutter 21-24 Heater 25 Blower 26 Temperature sensor 27 Cooling Temperature inspection device 28 Side wall 29 Electric motor 30 Cooler 31 Circulating fan W Workpiece

Claims (2)

A workpiece formed by compression molding powder material is conveyed by a plurality of conveyance rollers,
Heating the workpiece to a sintering temperature in a sintering chamber provided on the conveying path of the conveying roller;
In the quenching chamber located on the downstream side of the sintering chamber on the transport path of the transport roller, quenching by blowing a cooling gas to the workpiece,
When it is blowing a cooling gas to said workpiece in said quench chamber, the cooling rate of the quenching chamber of the workpiece is detected by the temperature sensor, and determines whether the range to which the sensed cooling rate is set in advance ,
The temperature sensor is a radiation thermometer that detects the temperature of the workpiece by measuring the intensity of infrared rays emitted from the workpiece,
While detecting the cooling rate of the workpiece in the quenching chamber by the temperature sensor, the conveyance roller that supports the workpiece repeats normal rotation and reverse rotation so as to reciprocate the workpiece back and forth in the conveyance direction.
Sinter hardening method. A plurality of conveying rollers for conveying a workpiece formed by compression molding a powder material;
A sintering chamber for heating the workpiece to a sintering temperature on a conveying path of the conveying roller;
A quenching chamber located on the downstream side of the sintering chamber on the conveying path of the conveying roller, and quenching the workpiece by blowing a cooling gas;
A cooling temperature inspection device that detects a cooling rate of the workpiece in the quenching chamber with a temperature sensor and inspects whether or not the detected cooling rate is within a preset range;
I have a,
The temperature sensor is a radiation thermometer that detects the temperature of the workpiece by measuring the intensity of infrared rays emitted from the workpiece,
While detecting the cooling rate of the workpiece in the quenching chamber by the temperature sensor, the conveyance roller that supports the workpiece repeats normal rotation and reverse rotation so as to reciprocate the workpiece back and forth in the conveyance direction.
Continuous sintering furnace for sinter hardening.