JP3925206B2 - Manufacturing method of endless metal belt - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an endless metal belt. The present invention can be used for manufacturing, for example, a CVT (Continuously Variable Transmission) belt.
[0002]
[Prior art]
Since the endless metal belt is wound around a roller and is rotated, it is desirable that a repeated stress is applied between the bending stress when passing through the roller and the disappearance of the bending stress at the linear portion to improve the fatigue strength. It is.
Fatigue strength is usually improved by performing shot peening on the surface portion of the endless metal belt. In order to further improve the fatigue strength, as proposed in JP-A-2000-225567, the surface of the endless metal belt is subjected to surface hardening treatment and then shot peened.
In improving fatigue strength by shot peening, the peripheral length of the endless metal belt is increased by shot peening. Conventionally, a large number of endless metal belts were produced, the circumferences were measured after shot peening, and the ones with circumferences similar to each other were selected, and the layers were multilayered so that the interlayer clearance was below the allowable value.
[0003]
[Problems to be solved by the invention]
When shot peening treatment is applied to an endless metal belt, its fatigue strength is greatly improved. On the other hand, the inner circumference of the endless metal belt (hereinafter referred to as the circumference) increases once in the shot peening treatment, and is shot peened. It has been found that if left untreated after treatment, it decreases as the standing time increases. This is as shown in the case of non-heating in FIG. 1, and the rate of change decreases with the passage of the standing time, but the amount of change increases with the passage of the standing time.
This phenomenon is extremely inconvenient from the viewpoint of the use in which multiple layers are combined. In other words, when the number of layers is increased, the clearances between the layers are managed and combined with high accuracy, while the circumferential length of each layer changes with time, which means that the clearance value becomes unstable.
The objective of this invention is providing the manufacturing method of the endless metal belt which can suppress the change of the perimeter of the endless metal belt which performed the shot peening process.
[0004]
[Means for Solving the Problems]
The present invention that achieves the above object is a method of manufacturing an endless metal belt in which a surface of an endless metal belt made of maraging steel is subjected to shot peening treatment, and the endless metal belt is heated after the shot peening treatment. The heat treatment is performed at a temperature of 70 to 300 ° C. during the heat treatment .
The heat treatment temperature may be set to 70 to 100 ° C. during the heat treatment.
[0005]
It has been found that if the endless metal belt is subjected to heat treatment after the shot peening treatment, the subsequent change in the circumference of the endless metal belt can be suppressed. The phenomenon in which the circumference of the endless metal belt decreases as the standing time after shot peening increases, is due to dislocations (changes in the arrangement of metal atoms in the metal crystal lattice) caused by significant plastic deformation during shot peening. It is presumed that there is a change in the material structure around the dislocation or around the dislocation, and this change is significantly accelerated and saturated by heating. It is presumed that the change in length could be suppressed. As a result, according to the method of the present invention for performing the heat treatment of the endless metal belt after the shot peening treatment, when the endless metal belt is combined in multiple layers, the clearance between the layers can be prevented from becoming unstable, and the clearance can be reduced. It becomes possible to manage with high accuracy.
Further, in the endless metal belt material maraging steel is less than the heat treatment temperature of 70 ° C. during the heat treatment, large changes in the peripheral length of the after heat treatment of the endless metal belt, i.e., an endless metal shot peening process is applied It has been found that the effect of suppressing the change in the belt circumference is small, and the compressive residual stress applied to the endless metal belt surface portion by the shot peening process is reduced above 300 ° C. Then, since heat processing temperature was prescribed | regulated to 70-300 degreeC, the change of the peripheral length of the endless metal belt to which the shot peening process was performed suitably can be suppressed, suppressing a compression residual stress reducing.
If the heat treatment temperature is set to 70 to 100 ° C. during the heat treatment, it can be easily and uniformly heated by heating water and immersing the endless metal belt therein.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Below, the manufacturing method of the endless metal belt of this invention Example is demonstrated with reference to FIGS.
In the method of manufacturing an endless metal belt according to the present invention, as shown in FIG. 6, in order to improve the fatigue strength of the endless metal belt 1 made of a thin plate having a welded start and end, Curing treatment (for example, nitriding treatment or soft nitriding treatment) is performed, and then shot peening is performed. Shot peening is applied to the inner and outer surfaces of the endless metal belt 1. By shot peening, compressive residual stress is generated in the surface portion of the endless metal belt 1.
After the shot peening process, the endless metal belt 1 is heated.
[0007]
The material of the endless metal belt is usually maraging steel. However, it may be other than maraging steel, for example, stainless steel.
When the material of the endless metal belt is maraging steel, the heat treatment temperature is set to 70 to 300 ° C. during the heat treatment. The lower limit value is set to 70 ° C. and the upper limit value is set to 300 ° C. When the temperature is less than 70 ° C., the effect of suppressing the change in the circumference of the endless metal belt subjected to the shot peening treatment is small. This is because the compressive residual stress applied to the endless metal belt surface is reduced.
[0008]
Moreover, up to 70 to 100 ° C. can be easily and uniformly heated by heating water and immersing an endless metal belt therein. The holding time may be longer than the time during which the entire endless metal belt can be uniformly heated, but in the case of heating with warm water, heat transfer between the hot water and the endless metal belt is good, and it may be about 5 seconds or longer.
At 100 ° C. or higher, heating is performed by hot air or radiation. In that case, heat transfer is not good, and thus the holding time is longer than that in the case of hot water heating.
[0009]
Specific examples of the present invention are shown below.
The test material was 1800 MPa class maraging steel, processed into a ring shape having a plate thickness of 190 μm and a circumferential length of about 720 mm, and then subjected to nitriding treatment and further shot peening treatment. The shot peening was so-called stress peening performed by applying a pre-tension stress to the surface. However, it is not limited to stress peening.
[0010]
In the shot peening process, as shown in FIG. 7, the endless metal belt 1 includes a first roller 2 that applies a pretension stress (preload) to the inner peripheral surface of the endless metal belt 1, and the endless metal belt 1. It is wound around three or more rollers 2, 3, 4 including a second roller 3 that applies a pre-tension stress (preload) to the outer peripheral surface, and is endless from the projection nozzle 5 from the inner peripheral side of the endless metal belt 1. The shot grain 6 is projected toward the portion where the metal belt 1 is wound around the first roller 2, and the endless metal belt 1 is wound around the second roller 3 from the outer peripheral side of the endless metal belt 1 through the projection nozzle 7. Shot grains 8 were projected toward the portion. A preload curvature in the direction opposite to the projection position on the outer peripheral side was given at the projection position on the inner peripheral side. The preload radius of curvature R was 20 mm. Reference numerals 9 and 10 are shutters which control the projection time by opening and closing the shutters.
[0011]
The shot peening conditions were a shot grain average hardness of 675 HV and a projection speed of 90 m / s. The difference in the residual stress distribution form was changed by changing the average grain size of the shot grains to be used to 70 μm and 110 μm.
After the shot peening treatment, the endless metal belt 1 was heated to a predetermined temperature, held at each temperature for a predetermined time (300 sec), and then cooled to room temperature. The change with time in the circumference of the endless metal belt 1 from immediately after that to 720 hours was investigated.
The results are shown in FIGS. FIG. 1 shows the case where the average grain size of the shot grains is 70 μm, and FIG. 2 shows the case where the average grain size of the shot grains is 110 μm. From this result, it became clear that the change with time of the circumference was suppressed at 70 ° C. or higher under any shot conditions.
[0012]
On the other hand, in order to see the influence of the holding time, the change in the circumferential length was measured by changing the holding time at each temperature to 30 sec and 300 sec. The results are shown in FIGS. FIG. 3 shows the case where the average grain size of the shot grains is 70 μm, and FIG. 4 shows the case where the average grain size of the shot grains is 110 μm. 3 and 4, it can be seen that there is almost no influence of the holding time at 70 ° C. or higher.
[0013]
The reason why the change in the circumference of the endless metal belt after heating is suppressed is that the dislocations that occurred due to significant plastic deformation during the shot peening process move over time or change in the material structure around the dislocations. It is inferred that this is caused. This change is remarkably accelerated and saturated by heating the endless metal belt, so that it is considered that the subsequent change with time hardly occurs.
[0014]
In order to see the change in the compressive residual stress on the surface portion of the endless metal belt due to heating after shot peening, after holding for 300 seconds at each temperature after shot peening, air cooling was performed, and the compressive residual stress on the surface portion of the endless metal belt was measured. The results are shown in FIG. From FIG. 5, it can be seen that at 300 ° C. or lower, the compression residual stress of the surface portion of the endless metal belt is not reduced by heating after shot peening. In addition, it can be seen that heating exceeding 300 ° C. is not suitable as a processing condition because it causes a harmful effect of reducing the compressive residual stress applied by shot peening.
[0015]
【The invention's effect】
According to the manufacturing method of the endless metal belt of the first aspect, since the heat treatment of the endless metal belt is performed after the shot peening process, it is possible to suppress the change in the peripheral length of the endless metal belt subjected to the shot peening process. As a result, when the endless metal belts are combined in multiple layers, the clearance between the layers can be prevented from becoming unstable, and the clearance can be managed with high accuracy. Further, in the endless metal belt material maraging steel, so defining the pressurized heat treatment temperature of 70 to 300 ° C., while suppressing the compressive residual stress is decreased, the endless metal belt suitably shot peening process is applied It is possible to suppress the change in the perimeter.
According to the method for producing an endless metal belt according to claim 2, since the heat treatment temperature is set to 70 to 100 ° C. during the heat treatment, the water can be heated and the endless metal belt can be immersed in the endless metal belt easily and uniformly. Can be heated.
[Brief description of the drawings]
FIG. 1 is a graph showing a change in a circumferential length change amount with respect to a standing time after a heat treatment when a shot particle diameter is 70 μm in a method for producing an endless metal belt according to the present invention.
FIG. 2 is a graph showing a change in a circumferential length change amount with respect to a standing time after a heat treatment when a shot particle diameter is 110 μm in the method for manufacturing an endless metal belt of the present invention.
FIG. 3 shows the change in the amount of change in the circumference with respect to the standing time after the heat treatment when the heat treatment time (holding time) is changed in the case of a shot particle size of 70 μm in the method of manufacturing an endless metal belt of the present invention. It is a graph which shows.
FIG. 4 shows the change in the amount of change in circumference with respect to the standing time after heat treatment when the heat treatment time (holding time) is changed in the case of a shot particle size of 110 μm in the method of manufacturing an endless metal belt of the present invention. It is a graph which shows.
FIG. 5 is a graph showing a change in residual stress with respect to a heat treatment temperature after shot peening when a shot particle size is 70 μm in the method for producing an endless metal belt of the present invention.
FIG. 6 is a perspective view of an endless metal belt manufactured by the method for manufacturing an endless metal belt of the present invention and a partial cross-sectional view thereof.
FIG. 7 is a side view of a shot peening machine during execution of shot peening.
[Explanation of symbols]
1 Endless metal belt 2, 3, 4 Roller 5, 7 Projection nozzle 6, 8 Shot grain 9, 10 Shutter

Claims (2)

A method of manufacturing an endless metal belt that performs shot peening treatment on the surface of an endless metal belt made of maraging steel, wherein the endless metal belt is heated after the shot peening treatment. method of manufacturing an endless metal belt that the heating treatment temperature of 70 to 300 ° C.. The method for producing an endless metal belt according to claim 1, wherein a heat treatment temperature is set to 70 to 100 ° C. during the heat treatment.

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