JP3622663B2 - 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 example, for adjusting the circumference in the manufacture of a CVT (Continuously Variable Transmission) belt or the like.
[0002]
[Prior art]
Since the endless metal belt is wound around two rollers and rotated, for example, when the belt passes through the roller part, a tensile bending stress is generated on the outer peripheral side of the belt, and the belt passes through the roller part and the next roller. Until reaching the site, the belt is linear, and there is no tensile stress due to bending on the outer peripheral side of the belt. Therefore, it is desired that the outer peripheral surface of the belt is repeatedly subjected to tensile stress due to bending during the rotation of the belt, thereby improving the fatigue strength.
In JP-A-61-42402, JP-A-63-96258, etc., by subjecting only the outer peripheral surface of the endless metal belt to shot peening, a compressive residual stress is generated on the outer peripheral surface, and the fatigue strength of the outer peripheral surface. An endless metal belt has been proposed which improves the above.
[0003]
[Problems to be solved by the invention]
However, in an endless metal belt made of a thin plate, the thickness of the plastic deformation layer (about 20 to 25 μm) on the surface is not negligible compared to the belt plate thickness (about 0.2 mm). For example, an increase in circumference (about 720 mm) (an increase of about 2 mm), a change in crowning R, and the like. Here, the crowning R is a curvature of a cross section perpendicular to the circumferential direction as shown in FIG.
For metal belts, high shape accuracy is often required for these values, and when the conventional shot peening process of the prior art is applied, the variation in the shot peening process is added to the accuracy variation of the processed product existing before the process. It becomes a problem on the product function.
In particular, endless metal belts are often laminated and used as products in multiple layers (for example, 9 layers), and in this case, circumferential length accuracy is extremely important. For example, when the permissible clearance between the laminated belts is 10 μm, the permissible difference in circumferential length is 60 μm, which is 2π times that. In the past, many endless metal belts were produced, and one with a difference in length within an allowable range was selected from the belts and assembled into a laminated belt. It is a very inefficient production method.
The object of the present invention is to use the shot peening process, which has been one of the causes of the decrease in accuracy in the past, as a fine adjustment method for the belt periphery length accuracy. An object of the present invention is to provide an endless metal belt manufacturing method capable of manufacturing a metal belt.
[0004]
[Means for Solving the Problems]
The present invention for achieving the above object is as follows.
(1) An endless metal belt having a shot peening process for performing shot peening on an endless metal belt, wherein the endless metal belt is adjusted by adjusting the shot peening process. Manufacturing method.
(2) The circumference of the endless metal belt is adjusted by measuring the circumference of the endless metal belt before the shot peening treatment, and setting the conditions for the shot peening treatment based on the measurement result. A method for producing an endless metal belt.
(3) The endless metal according to (1), in which the circumference of the endless metal belt is measured during shot peening and the circumference of the endless metal belt is adjusted by ending the shot peening based on the measurement result. A method for manufacturing a belt.
[0005]
In the manufacturing method of the endless metal belt of the above (1), the shot peening treatment is used not only for improving the fatigue strength but also for fine adjustment of the belt circumferential length, and the shot peening treatment conditions (for example, shot peening treatment time, etc.) The circumference of the endless metal belt is adjusted by adjusting (), so that an endless metal belt with higher productivity and higher circumference accuracy can be manufactured than before.
As the shot peening treatment conditions, for example, taking the shot peening treatment time, as a result of examining the change in the circumference of the endless metal belt accompanying the shot peening treatment, the endless metal belt circumference increases with the shot projection time and increases the circumference. The rate was found to show a gradual decrease with time. On the other hand, since the compressive residual stress of the surface applied to the endless metal belt saturates early (for example, in 9 seconds) with the passage of the shot time, the fatigue strength having a strong correlation with the compressive residual stress is relatively short ( It was found that it can be secured by the shot peening process (for example, in 9 seconds). Therefore, by performing shot peening for more than the projection time (for example, 9 seconds) required to ensure fatigue strength, high accuracy is achieved in a region where the rate of increase in circumference is moderate while maintaining improved fatigue strength. In addition, it is possible to finely adjust the endless metal belt in the direction of increasing the circumference. However, the shot peening processing time must be adjusted in a range of a projection time (for example, 9 seconds) or more necessary for ensuring fatigue strength.
Since the method of the present invention is a method of adjusting the circumference of each belt itself by adjusting the shot peening process, as in the conventional case of producing a large number of belts and selecting one having a similar length. It is not necessary to produce a lot of extra belts, and it is highly productive.
In the method (2) for producing an endless metal belt, the circumference of the endless metal belt before the shot peening process is measured. As a result of the measurement, it is understood how many mm the circumference should be lengthened. For example, the necessary projection time can be obtained from the relationship between the circumference variation obtained in advance and the projection time (for example, the graph of FIG. 3 described later). Therefore, shot peening is performed only for that time, and the circumference of the endless metal belt is set to the target circumference.
In the endless metal belt manufacturing method of (3) above, the circumference of the endless metal belt during the shot peening process is continuously measured, and the shot peening process is terminated when the circumference of the endless metal belt reaches the target value. . In the case of the above method (2), if a constant relationship between the peripheral length change amount and the projection time is used, the peripheral length change amount versus the projection time depends on conditions such as nitriding or soft nitriding before shot peening. When the relationship changes, the circumference of the endless metal belt changes, but this method (3) continuously measures the circumference of the endless metal belt during the shot peening process, and the measurement result reaches the target value. Then, since the shot is stopped, the final belt circumference is not affected by conditions such as nitriding or soft nitriding before shot peening, and the belt circumference is adjusted to the target circumference with high accuracy. be able to.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Below, the manufacturing method of the endless metal belt of this invention is demonstrated with reference to FIGS. In addition, the same code | symbol is attached | subjected to the common part over all the Examples of this invention over all the Examples of this invention.
[0007]
First, parts common to all the embodiments of the present invention will be described.
In the manufacturing method of the endless metal belt of the present invention, the end and the end of the thin metal belt are welded to form the endless metal belt 6. The endless metal belt 6 is, for example, maraging steel having a plate thickness of about 0.2 mm, a plate width of about 12 mm, and a circumferential length of about 720 mm.
Next, the endless metal belt 6 is subjected to a surface hardening process including nitriding or soft nitriding. The depth of the nitride layer is, for example, about 25 μm.
Next, shot peening is applied to the endless metal belt 6 to improve the fatigue strength. Shot peening is performed on both the outer peripheral surface and inner peripheral surface of the belt so that the endless metal belt does not undergo multiple deformation when shot peening is performed. Shot peening is preferably so-called stress peening performed by applying a pre-tension stress to the surface, but is not limited to stress peening. The shot peening conditions are, for example, a preload radius of curvature of R20 mm, a projected air pressure of 0.3 MPa, a projected particle diameter of Φ70 μm, a shot grain hardness of HV700, and the same inner and outer projection processing conditions.
In the shot peening process, by adjusting the shot peening process conditions (shot peening process time, air pressure, projection amount, particle size, grain hardness, etc., especially shot peening process time), the circumference of the endless metal belt 6 is adjusted. Make fine adjustments.
[0008]
In the shot peening process, as shown in FIGS. 1 and 2, the endless metal belt 6, the first roller 3 that applies pre-tension stress (preload) to the inner peripheral surface of the endless metal belt 6, and the endless metal A projection nozzle is wound around three or more rollers 1, 2, 3 including a second roller 2 that applies a pretension stress (preload) to the outer peripheral surface of the belt 6, from the inner peripheral side of the endless metal belt 6. 5, shot particles 15 are projected toward a portion where the endless metal belt 6 is wound around the first roller 3, and from the outer peripheral side of the endless metal belt 6 to the second roller 2 of the endless metal belt 6 from the projection nozzle 4. The shot grain 15 is projected toward the winding part. A preload curvature in the direction opposite to the projection position on the outer peripheral side is given at the projection position on the inner peripheral side, and the projection timings 4 and 5 on the inner and outer peripheral sides can be controlled independently.
[0009]
Of the three rollers, 1 is a driving roller, and 2 and 3 are driven rollers. Two projection nozzles 4 and 5 are set. Projection on the outer peripheral side is performed by the main nozzle 4, and projection on the inner peripheral side is performed by the sub nozzle 5. The sub-nozzle 5 projects at an angle of about 30 ° with respect to the horizontal plane from obliquely above or obliquely below in order to prevent interference with the endless metal belt 6 at the opposite position in the circumferential direction. In order to increase the effective component V · cos θ of the projection speed V, it is desirable that the angle θ be as small as possible within a range that does not interfere with the endless metal belt 6. However, there is no particular requirement if the equipment has sufficient projection speed. .
[0010]
A tension is applied to the endless metal belt 6 by the spring 11. This tension is for obtaining a frictional force for the endless metal belt 6 to rotate and be fed without slipping, and is compared with a tensile preload generated on the surface of the endless metal belt 6 due to the curvature of the rollers 2 and 3. Small enough. The driven roller 2 is installed on the slide base 10 and is designed so that the spring force acts as the tension of the endless metal belt 6. The driven roller 3 of the inner peripheral projection unit is fixed on the same fixed base 7 as the base of the drive shaft. The drive shaft 13 is driven by a servo motor 12. When the required level of product shape accuracy is low, other conventional motor types other than servo motors may be used. The shot grain projection mechanism uses a normal direct pressure type air blow type, but other ventilation air blow types, impeller types, and other methods may be used.
[0011]
The shot peening used in the present invention includes shot peening (referred to as stress peening) performed by applying a preload (prestress) to the endless metal belt 6. However, the shot peening used in the present invention is not limited to stress peening.
The principle of stress peening will be described with reference to FIG.
When the endless metal belt 6 reaches the part where the endless metal belt 6 is wound around the rollers 1, 2 and 3, the endless metal belt 6 is bent, and a preload A of tensile bending stress is applied to the outer peripheral side of the bend, and the inner peripheral side of the bend is applied. Preload of compressive bending stress is applied. Shot peening is performed in this state. The shot grains 15 are projected onto a portion of the endless metal belt 6 where a pre-load of tensile bending stress is applied. V represents a projection speed, and eV represents a reflection speed. Due to the projection of the shot grains 15, the surface of the endless metal belt 6 is stretched and a compressive residual stress B is generated on the surface portion. Then, as the endless metal belt 6 rotates, when the endless metal belt 6 advances from the roller 1, 2, 3 winding portion and enters the straight portion, the preload of the tensile bending stress is released and the tensile preload A is added. Thus, a large compressive residual stress of A + B = C is formed on the endless metal belt surface. That is, compared with shot peening when there is no preload, stress peening provides a compressive residual stress that is larger by the tensile preload A, which is advantageous in improving fatigue strength.
[0012]
As shown in FIGS. 1 and 2, in fine adjustment of the circumferential length of the endless metal belt 6, the change in the circumferential length of the endless metal belt 6 is measured by the distance between the drive shaft 13 and the driven shaft 14. Specifically, the amount of movement of the arm 9 fixed on the slide base 10 is measured by a dial gauge 8 fixed on the fixed base 7 and taken out as an electric signal.
[0013]
In the present invention, the reason why the shot peening process can be used not only for improving fatigue strength but also for fine adjustment of the peripheral length of the endless metal belt 6 will be described.
In general, endless metal belts that require strength are subjected to surface hardening treatment such as nitriding, soft nitriding, and the like, but there are variations in the circumferential length, which is ± 0.02 with respect to the average circumferential length. It is extremely difficult to suppress the variation to% or less (± 0.144 mm or less with respect to the average circumference length of 720 mm).
In order to suppress this variation, if a process capable of adjusting the accuracy such as a normal tensile elongation process is performed after the surface is hardened, the surface hardened layer is cracked, the compression residual stress is released, and the strength is greatly reduced.
[0014]
The peripheral length change due to shot peening is about 0.1 to 0.2%, but if the processing is continued under a certain condition, the increasing rate shows a gradual decreasing tendency as shown in FIG. By adjusting this, fine adjustment of the circumference of 0.02% or less became possible. Specifically, the peripheral length change of the endless metal belt 6 with a peripheral length of 720 mm accompanying the shot peening process is about 1 to 3 mm, and the peripheral length increases with the projection time as shown in FIG. The increase rate shows a gradual decrease trend, and the increase rate of the circumference is relatively small after about 9 seconds from the start of projection, and is an order that can be used for fine adjustment of the circumference of 0.02% or less.
[0015]
On the other hand, as shown in FIG. 3, the compressive residual stress applied to the surface of the endless metal belt 6 is early with respect to the projection time, and the residual stress is saturated after about 9 seconds from the start of projection. It was found that the fatigue strength having a very strong correlation with can be secured by a relatively short treatment. In FIG. 3, minus indicates that the residual stress is a compressive stress. Moreover, the compressive residual stress of 200 kg / mm ² is a sufficient stress for improving the fatigue strength.
[0016]
If the shot peening process is considered only from the viewpoint of improving fatigue strength, which is a conventional purpose, it is reasonable to set the projection time to the lowest level that can ensure the fatigue strength. However, in the present invention, the tendency of FIG. 3 is utilized, that is, by performing shot peening in a region where the peripheral length increase rate is smaller than the projection time necessary for securing the fatigue strength, without reducing the fatigue strength, The circumference of the endless metal belt 6 was finely adjusted.
FIG. 4 shows that the projection characteristics are 9 seconds, 18 seconds, and 36 seconds, and the fatigue characteristic curve hardly changes. It can be seen that when the projection time is about 9 seconds or more, the fatigue strength is hardly affected by the magnitude of the projection time. That is, no change is observed in the fatigue strength after the compressive residual stress is saturated.
[0017]
By applying surface compressive residual stress by shot peening, both improvement in fatigue strength and circumferential elongation can be stably obtained.
Generally, when a material is strengthened by surface hardening such as nitriding or soft nitriding, embrittlement occurs at the same time as hardening, especially for tensile deformation, cracks occur from slight irregularities on the surface or embrittled grain boundaries. However, even a small strain is destroyed at the weakest part. On the other hand, such surface defects are relatively insensitive to compressive strain as compared with tension, and the material inherent strength is often obtained.
Circumferential elongation caused by shot grain projection is caused as a Poisson effect on compression plastic deformation, and local and uniform compression plastic deformation is continuously generated by shot peening treatment, thereby generating cracks. Stable circumferential expansion is possible without any problems.
[0018]
Next, parts specific to each embodiment of the present invention will be described.
In Example 1 of the present invention, the circumference of the endless metal belt 6 before the shot peening treatment was measured, and the circumference of the endless metal belt was adjusted by setting the conditions for the shot peening treatment based on the measurement result.
[0019]
Thirty endless metal belts 6 of maraging steel having a circumferential length of 720 mm, a thickness of about 0.2 mm, and a width of about 12 mm were prepared. The endless metal belt 6 has a variation of about ± 150 μm in circumference (0.021% relative to a circumference value of 720 mm, standard deviation of 50 μm) due to nitriding (the thickness of the nitrided layer is about 25 μm) before shot peening. Had. From the value measured in advance, it can be seen how many millimeters the circumference should be lengthened, and the required projection time is set to 18 seconds from the relationship between the circumference change amount and the projection time obtained in advance (graph in FIG. 3). It calculated | required in 36 seconds, the shot peening was given only for the time, and the circumference of the endless metal belt was finely adjusted. The shot peening treatment conditions were a preload radius of curvature R = 20 mm, a projected air pressure of 0.3 MPa, a projected particle diameter of Φ70 μm, a shot grain hardness HV700, and the same inner and outer circumference conditions.
As a result, the amount of variation was about ± 51 μm (about 0.007% with respect to the circumference value, standard deviation 17 μm), and the amount of variation could be suppressed to about 1/3 of the conventional amount.
As shot peening conditions, not only the shot time but also the shot pressure and shot grain amount may be adjusted. However, the peripheral length increase rate is small after 9 seconds from the start of the shot. In view of easy adjustment of the length, it is desirable to adjust by the shot time.
[0020]
In Example 2 of the present invention, the circumference of the endless metal belt 6 during the shot peening process was measured, and the circumference of the endless metal belt 6 was adjusted by ending the shot peening process based on the measurement result.
[0021]
In the fine adjustment of the circumference in the first embodiment, the circumference variation after shot peening is 1/3 of the conventional one, but exists. This is due to variations in the state of the product to be processed before shot peening processing and variations in shot conditions. Therefore, in order to further suppress the variation in the circumferential length, the circumferential length was continuously measured even during the shot peening process, and the processing was terminated when the target circumferential length was reached. Endless metal belt 6 conditions were the same as in Example 1, and the shot conditions were the same as in Example 1 except for continuous measurement of the circumference during the shot and stopping the shot when the target value was reached. The projection time was set to a minimum projection time of 9 seconds, and the processing was terminated when the target circumference was reached thereafter. The treatment was performed on 30 endless metal belts, and the circumference of the treated product was measured with a separate measuring instrument.
As a result, the variation in circumference is about ± 30 μm (about 0.004% with respect to the circumference value, standard deviation is 10 μm), and accuracy management with a variation amount of about 1/5 or less of the conventional one becomes possible.
[0022]
【The invention's effect】
According to the manufacturing method of the endless metal belt of claim 1, since the circumference of the endless metal belt is adjusted by adjusting the shot peening treatment, the endless metal belt can be adjusted by adjusting the shot peening conditions while maintaining the fatigue strength. The circumference of the metal belt can be adjusted, and an endless metal belt with high productivity and high circumference accuracy is available compared to the method of selecting and assembling a product that has been produced in large numbers and has a similar circumference. It can be manufactured.
According to the manufacturing method of the endless metal belt of claim 2, the circumference of the endless metal belt before the shot peening treatment is measured, the shot peening conditions are set based on the measurement result, and the circumference of the endless metal belt is finely defined. Since the adjustment is made, the circumference can be adjusted with high accuracy.
According to the manufacturing method of the endless metal belt of claim 3, the circumference of the endless metal belt during the shot peening process is measured, and the shot peening process is terminated based on the measurement result. It is not influenced by conditions such as the previous nitriding treatment or soft nitriding treatment, and the circumference can be adjusted with higher accuracy than the method of claim 2.
[Brief description of the drawings]
FIG. 1 is a plan view of an apparatus in which an endless metal belt manufacturing method of the present invention is being carried out.
FIG. 2 is a front view of the apparatus of FIG.
FIG. 3 is a graph showing changes in circumferential length and residual stress with respect to projection time in an endless metal belt manufacturing method of the present invention.
FIG. 4 is a stress amplitude-repetition number diagram (SN diagram) when the shot time is changed in the method of manufacturing an endless metal belt of the present invention.
FIG. 5 is a perspective view and a partial cross-sectional view of an endless metal belt manufactured by the method of manufacturing an endless metal belt of the present invention.
FIG. 6 is a stress distribution diagram in the plate thickness direction in each step of preload application, shot peening treatment, and preload release in the method of manufacturing an endless metal belt of the present invention.
[Explanation of symbols]
1, 2, 3 Roller 1 Drive roller 2 Second roller (driven roller)
3 First roller (driven roller)
4 Projection nozzle (outside projection)
5 Projection nozzle (inner projection)
6 Endless metal belt 7 Fixed base 8 Dial gauge 9 Arm 10 Slide base 11 Spring 12 Servo motor 13 Drive shaft 14 Drive shaft 15 Shot grain

Claims (3)

A method for manufacturing an endless metal belt having a shot peening process for performing shot peening on an endless metal belt, wherein the circumference of the endless metal belt is adjusted by adjusting the shot peening process. . 2. The endless metal belt according to claim 1, wherein a circumference of the endless metal belt is measured before the shot peening treatment, and the circumference of the endless metal belt is adjusted by setting conditions for the shot peening treatment based on the measurement result. Manufacturing method. The manufacture of an endless metal belt according to claim 1, wherein the circumference of the endless metal belt is measured during shot peening and the circumference of the endless metal belt is adjusted by ending the shot peening based on the measurement result. Method.

Images