JPH11151509A - Sleeve roll for rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the number of renewal of a roll sleeve by regrinding by reducing the diameter of a shaft by improding the fatigue strength of the shaft thereby increasing the thickness of the roll sleeve. SOLUTION: The nitride layer 6 of the base material of the shaft is provided on the surface of the roll sleeve attaching part of a steel shaft 2. It is preferable to form the nitride layer 6 by ionic nitriding treatment and it is preferable to remove the brittle compound produced on the surface at the time of finish grinding. The roll sleeve 1 is fit on the outer periphery of the shaft 2 and roll sleeve is fixed onto shaft by adding side pressure with a nut 4 and spacer rings 3. The fixing of the roll sleeve may be executed by internal pressure fixation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling sleeve roll and a roll shaft formed by fixing a roll sleeve made of a hard material such as cemented carbide or ceramics and having excellent wear resistance to the outer periphery of a shaft. And a method for producing the same.

[0002]

2. Description of the Related Art In a shaft used for a sleeve roll for rolling, stress is already generated inside when a roll sleeve is fixed. For example, as shown in JP-B-52-26227 and JP-B-60-20084, when a roll sleeve is fixed by applying pressure from the side (hereinafter, this is referred to as lateral pressure fixing). , An axial tensile stress is generated inside the shaft due to the tightening reaction force,
In internal pressure fixing (fixing method such as a method disclosed in Japanese Patent Publication No. 56-53441 or shrink fitting or press-fit fixing), compressive stress is generated in a shaft radial direction, and tensile stress and compressive stress are generated in a shaft axial direction. Occurs in distribution. In this state, the shaft receives a rolling load, which is a variable load. Therefore, as a material of the shaft, alloy steel for machine structure (SCM material or SNCM material) having excellent fatigue strength and toughness is generally used. Nevertheless, since the internal stress generated by fixing the roll sleeve contributes to the reduction in fatigue strength, it is necessary to take measures such as increasing the shaft diameter in consideration of the reduction in fatigue strength due to internal stress. It is a fact.

In the case of fixing the internal pressure, 10 to 10
Since a very large contact surface pressure of about 40 MPa acts, the fitting surface on the shaft side having a lower hardness than the roll sleeve is plastically deformed or worn. When a plastically deformed portion is generated on the surface, a crack is easily generated, and the shaft may be broken. Further, when the fitting portion of the shaft is worn, the interference is reduced to cause the roll sleeve to idle, or stress is concentrated on the worn portion to cause the shaft to break.

[0004] Therefore, with regard to the sleeve roll of the internal pressure fixing type, a method of applying hard chromium plating to the surface of the roll sleeve mounting portion of the shaft to prevent wear and plastic deformation of the surface and simultaneously improve corrosion resistance has been adopted. Have been.

[0005]

When the shaft diameter is increased by increasing the diameter of the shaft, the thickness of the roll sleeve is reduced by the increased diameter of the shaft, and the effective diameter of the roll is reduced.
Roll life is shortened. When the rolling groove (calibur) on the outer periphery becomes rough or unevenly worn, the outer periphery of the roll sleeve is re-sharpened and regenerated as a roll having a diameter smaller than the original diameter. Since the roll rework allowance is determined by the thickness of the roll sleeve, increasing the shaft diameter shortens the roll life and is economically disadvantageous.

[0006] Since the shaft of the sleeve roll is not a mass-produced part, it is necessary to newly develop a dedicated shaft steel material having higher fatigue strength than the conventional material in view of development costs and manufacturing costs. Not a good idea.

Therefore, an object of the present invention is to make it possible to increase the fatigue strength of a shaft by using a commonly available steel material.

Further, the coating of the roll sleeve mounting portion of the shaft by hard chrome plating performed by the internal pressure fixing type sleeve roll does not contribute to the improvement of the fatigue strength of the shaft. Reduces fatigue strength due to the effects of internal cracks. This is already known and appears in the experimental data of FIG.

Further, the steel material is liable to be hydrogen embrittled by absorbing hydrogen generated at the time of chromium plating, and the toughness is often lowered to be brittle.

[0010] Further, in the case of internal pressure fixing, 10 to 40
The contact surface pressure of MPa is acting, and in this state, the contact surface pressure locally fluctuates due to the rotation of the roll during rolling, and fine dynamic friction occurs. May occur, making it impossible to remove the roll sleeve from the shaft. If it is forcibly removed, the plating layer will peel off, and if the shaft is reused, it will need to be repaired, losing the economic advantage of reusing the shaft.

Therefore, it is better not to have chrome plating,
If this is eliminated, the hardness of the mating surface becomes insufficient, and plastic deformation and wear of the surface occur, and the corrosion resistance also deteriorates.

It is an object of the present invention to improve the surface hardness and improve corrosion resistance without chromium plating.

[0013]

In order to solve the above-mentioned problems, according to the present invention, a nitride layer of a shaft base material is provided on a surface of a roll sleeve mounting portion of a steel shaft, and an outer periphery of the nitride layer forming portion is provided. Secure the roll sleeve to the.

The fixing of the roll sleeve may be performed by either lateral pressure fixing or internal pressure fixing. When applying the present invention,
No hard chrome plating is required.

The above-mentioned nitride layer may be provided on the surface of the bearing mounting portion (journal portion) of the shaft or the surface of the drive portion.

The material of the shaft is JIS SNC
M630 is particularly suitable.

Next, in the present invention, in order to form the above-mentioned nitrided layer, a steel material for a shaft having a surface hardness of HR _C 30 to 40, which has been tempered at a temperature of 560 ° C. to 650 ° C., is placed in a nitriding furnace. A method of vertically disposing them and performing an ion nitriding treatment at a temperature of 550 ° C. to 600 ° C. lower than the tempering temperature for 5 to 20 hours in this state is adopted. After the ion nitriding treatment by this method, if the surface layer portion of the nitrided layer formed on the surface of the steel material for the shaft is further removed to a depth of 0.02 mm to 0.15 mm, a shaft with better performance can be obtained.

[0018]

The shaft having a base material nitrided layer on its surface has improved fatigue strength. Therefore, it is possible to reduce the shaft diameter while maintaining the strength as compared with an untreated shaft or a chrome-plated shaft, and it is possible to increase the thickness of the roll sleeve by an amount corresponding to the diameter reduction. It can be increased to extend the life of the roll.

Further, the nitrided layer of steel is also excellent in wear resistance and corrosion resistance. Thus, in the internal pressure fixed type sleeve roll, the hard chromium plating layer provided on the shaft surface becomes unnecessary. The problem of seizure and peeling of the plating layer is eliminated, and the shaft can be reused without repair, thereby reducing the labor and cost of repair. Further, the fatigue strength does not decrease due to the application of chrome plating, which is further advantageous in extending the life of the shaft.

Incidentally, the bearing mounting portion of the shaft is damaged or worn by the attachment / detachment of the inner race of the bearing. Since the drive portion of the shaft also receives a strong surface pressure, fatigue and wear are likely to occur. Therefore, it can be said that providing a nitride layer on the surface of the bearing mounting portion or the driving portion to improve the fatigue strength and wear resistance of the portion is also effective in extending the life of the shaft.

Next, the operation of the method of the present invention and the reasons for limiting the conditions will be described.

JIS SNCM439, SNCM630
It is a common practice to increase the fatigue strength and surface hardness by nitriding an alloy steel such as that described in JP-A-2-29.
Related technology is disclosed in 4463 and JP-A-4-66646.

As the nitriding method, a tuff-ride method,
There are methods such as gas soft nitriding, ion nitriding, and gas nitriding, and any of these methods can generate the above-described nitrided layer.
This nitriding treatment is performed at a relatively low temperature, and it is known that distortion of a product after nitriding is small. Above all, ion nitriding has the smallest processing strain, and has a strong ion penetration, so that the processing time is short, and it is easy to suppress deterioration of mechanical properties due to heat of the steel material.

Therefore, the shaft manufacturing method of the present invention
The ion nitriding method is adopted.

The general nitriding temperature is 500 ° C.
Although it is said to be about 600 ° C., a temperature of about 500 ° C. is a temperature range of tempering embrittlement of a steel material, and if the temperature is maintained for a long time, the impact value of the steel material is reduced. The ion nitriding is performed in a region of 550 ° C. to 600 ° C.

The shorter the treatment time, the better from the viewpoint of cost and mechanical properties of the steel material. However, if the treatment time is less than 5 hours, the thickness of the nitrided layer formed is not sufficient. The thickness was increased, but the base material hardness was lowered, and the required mechanical properties of the shaft could not be obtained.

Further, the tempering temperature needs to be higher than the nitriding temperature in order to suppress distortion and softening of the steel material after the nitriding treatment. However, if the tempering temperature is too high, the hardness of the steel material after the tempering becomes too high. When the HR _{C is} 30 or less, the tensile strength required for the sleeve roll shaft cannot be satisfied.
To secure the necessary strength, HR _C 30-4 after tempering
A surface hardness of 0 is required. If the tempering temperature is too low,
The surface hardness after tempering exceeds HR _C 40, the toughness is reduced, and the strength balance is deteriorated. Therefore, the tempering temperature is 5
60 ° C. to 650 ° C.

Further, in the method of the present invention, the following becomes particularly important. Nitriding is applied to relatively small parts such as crankshafts and camshafts of automobiles. Although such small parts can be processed without special measures, the shaft for the sleeve roll is very large,
Because of its heavy weight, the long shaft is particularly susceptible to the influence of its own weight during the ion nitriding process, which tends to increase the processing strain. Total length is 1
In the case of a long shaft exceeding 000 mm, a slight distortion appears as a large bend or warpage, so if the processing distortion is not kept as small as possible, the finish grinding allowance for correcting the bend and warp becomes large. . If an attempt is made to obtain a thicker nitrided layer in consideration of this, the treatment time of ion nitriding becomes longer, and the mechanical properties of the steel material deteriorate and the productivity decreases. Also, if the shaft bends or warps greatly,
The thickness of the nitrided layer remaining after the grinding finish becomes non-uniform in each part, and the variation in surface hardness increases.

Therefore, in the present invention, ion nitriding is performed by vertically disposing the shaft steel material in the nitriding furnace. As a result, the distortion due to its own weight is suppressed, and the absolute value of the distortion is reduced, so that the above-described problem is solved.

Further, the surface grinding of the nitrided layer has been performed only for the purpose of ensuring the dimensional accuracy, but in the present invention, the embrittlement on the surface layer is removed by limiting the grinding depth. The hard and brittle Fe _2-3 N compound or Fe ₄
N compounds and the like are generated. Since it was confirmed that these compounds were generated to a depth of about 0.015 mm, the surface layer was ground at least 0.02 mm in depth to remove embrittlement with a margin.

The upper limit of the grinding amount is 0.15 m since the nitriding treatment is meaningless if the nitrided layer is lost by grinding.
m is the upper limit. As a result, the toughness of the shaft is improved, and the remaining nitrided layer maintains the fatigue strength, increases the hardness of the surface, and secures the corrosion resistance, thereby obtaining a well-balanced shaft.

Although SACM645 is defined in JIS as a mechanical structural steel suitable for nitriding, a higher strength shaft can be realized by subjecting SNCM630, which has better mechanical properties, to nitriding. .

[0033]

2 to 6 show a rolling sleeve roll according to an embodiment of the present invention.

The sleeve roll shown in FIG. 2 is a roll sleeve 1 made of cemented carbide, hard alloy, ceramics or the like.
Is fitted to the outer periphery of the steel shaft 2 and a nut 4 screwed to the shaft 2 is tightened to apply a clamping pressure to both side surfaces of the roll sleeve 1 by the spacer ring 3, but the structure is limited to this structure. Not something. 5 is a fillet ring. The sleeve roll shown in FIG. 2 has a shaft 2 having a maximum bending moment when subjected to a rolling load.
Is provided with a nitrided layer 6 of base steel (portion which is finely dotted in the figure) on the surface of the roll sleeve mounting portion at the center of the above. Since high fitting accuracy is required for this portion, the surface of the nitrided layer generated after the ion nitriding treatment is ground and finished as necessary. As described above, since the hard and brittle Fe _2-3 N compound or Fe ₄ N compound is generated in the surface layer portion of the nitride layer, the grinding finish is preferably performed at a depth at which the brittle material is removed.

FIG. 3 shows an example of application to a sleeve roll for internal pressure fixed type hot wire rolling. In this sleeve roll, a hydraulic pressure is introduced into a taper fitting portion between the roll sleeve 1 and the shaft 2, and the diameter of the roll sleeve 1 is expanded by the hydraulic pressure to attach and detach the roll sleeve. When the hydraulic pressure at the fitting portion is removed, the roll sleeve 1 contracts, and the roll sleeve 1 is fixed on the shaft 2 in an interference fit state. In this sleeve roll, since a complicated stress is applied to the roll sleeve mounting portion (taper fitting portion) of the shaft, the nitride layer 6 is provided on the surface of that portion. Also in this case, if necessary, the finish grinding is performed after the nitriding treatment. Conventionally, a chrome plating layer for improving abrasion resistance and corrosion resistance was generally applied to this portion, but the chrome plating layer does not exist in the sleeve roll of FIG. Therefore, the problem of the roll sleeve not being removable due to the welding of chrome plating, the problem of repair when the shaft is reused due to the peeling of plating,
The problem of hydrogen embrittlement of the shaft does not occur. In fact, as a result of dismantling the roll sleeve 1 after the roll diameter reached the disposal diameter, the roll sleeve 1 could be removed without any trouble, and the shaft 2 could be reused without repair by attaching a new roll sleeve.

FIG. 4 shows a third embodiment. In this sleeve roll, a nitride layer 6 is also provided on the surface of a bearing mounting portion (journal portion) 2 a of the shaft 2. After nitriding, this part is also subjected to finish grinding as necessary. Other configurations are the same as those of the sleeve roll of FIG. The sleeve roll of FIG. 4 could be used without repairing the bearing mounting portion while the roll sleeve 1 was discarded twice (about 6 years).

FIG. 5 shows an example in which a nitride layer 6 is also provided on the surface of the drive section 2b of the shaft 2. This sleeve roll could also be used without repairing the shaft drive for about 6 years when the roll sleeve was scrapped twice.

FIG. 6 shows a structure in which a nitride layer is provided on the entire surface of the shaft 2. This is advantageous in terms of productivity because a step of covering unnecessary portions with a coating of a nitriding agent during the nitriding treatment is omitted. Further, since the nitrided layer 6 is provided on the entire area of the shaft 2 including the slack portion 2c on the outer periphery of the shaft where stress tends to be concentrated, the fatigue strength of the entire area is improved.

The nitride layer 6 of the exemplary sleeve roll
Were produced by ion nitriding.

This ion nitriding is a treatment method having the highest effect of suppressing strain. However, a long sleeve roll shaft has a slight distortion during nitriding treatment that appears as a large bend or warp. The following experiment was tried beforehand in order to establish the technique suitable for.

In the experiment, a shaft having the shape shown in FIG. 7 was used. The dimensions of the shaft are D = φ200m
m, d = φ150 mm, L = 1200 mm, L ₁ = 60
0 mm and L ₂ = 300 mm. The shaft material is SNCM439 which has been conventionally used for sleeve rolls.
And SNCM630. The two types of shaft steel materials were each tempered at 630 ° C., leaving a margin of 5 mm / diameter. At this time, the surface hardness of SNCM630 was H
Rc34 and SNCM439 were HRc31. After that, 1 at 580 ° C, leaving the grinding finish allowance of 0.2mm / diameter.
Under the condition of 0 hours, the entire shaft was subjected to ion nitriding treatment. This treatment was performed while the shaft was held vertically in a nitriding furnace to suppress distortion.

As a result, both shafts of the obtained shafts had a run-out of 0.02 mm or less based on both centers, and a nitrided layer was left on the surface even after grinding.

FIG. 8 shows the surface hardness distribution of the prototype shaft after nitriding. According to this, in both shafts, the nitride layer is formed at a depth of about 0.5 mm (1 mm / diameter), but the surface hardness of the two is significantly different. S
The surface hardness of the shaft of NCM630 is Hv900, and even after removing the finish grinding allowance of 0.2 mm / diameter, the shaft hardness is Hv.
A surface hardness of 750 or more is maintained. On the other hand, SN
The shaft of CM439 has a surface hardness of Hv540, and the surface hardness of the shaft after grinding is Hv49.
It becomes 0 or more. This difference is due to the Cr content. Therefore, nickel-chromium molybdenum steel (SN
When using CM material), the SNC with the highest Cr content
When M630 is selected, the effect of the nitriding treatment is maximized.

When the cross section of the nitrided layer was observed with a microscope, the white F
Compound layers of e _2-3 N and Fe ₄ N were confirmed. These brittle materials are susceptible to cracks on the surface when impacted, triggering shaft breakage. Therefore, for a practically used shaft, the surface layer portion of the nitrided layer has a depth of 0.02 mm or more.
It is desirable to remove 0.15 mm.

Next, the change of the fatigue strength was compared between the nitrified and untreated SNCM630. The evaluation of the fatigue strength was performed by the Ono-type rotary bending fatigue test. The nitriding conditions of the nitrided product were the same as those of the aforementioned prototype shaft, and the surface was ground by 0.2 mm / diameter (depth: 0.1 mm) after nitriding. FIG. 9 shows the result. From this figure, the effect of improving the fatigue limit by the nitriding treatment can be confirmed.

The shaft of the sleeve roll shown in FIG.
In the case of 600 mm, the diameter of the roll sleeve mounting portion 210 mm, and the material SNCM630), the above-described processing has actually obtained a life longer than the life (about 6 years) in which the roll sleeve is discarded twice.

If nitriding treatment is premised, SACM645, which is a nitrided steel, is also an option. However, this is inferior to SNCM630 in terms of hardenability and mechanical properties. When used for a shaft, the strength is lower than that of the SNCM 630, and the price is higher than that of the SNCM 439, so that there is not much advantage in nitriding. In addition, the development of special materials on the premise of nitriding
It is not advisable to consider the development cost and productivity. Therefore, it is preferable to use a steel for machine structural use, which has a large amount of traffic specified by JIS, as the shaft material.

[0048]

As described above, in the rolling sleeve roll of the present invention, the fatigue strength of the steel shaft is increased by nitriding the surface, so that the diameter of the shaft can be reduced. It is possible to increase the rework allowance and to improve the life of the roll.

In particular, the internal pressure fixed type sleeve roll does not require the chrome plating conventionally provided on the shaft surface of the fitting portion, so that the plating layer is liable to seizure, peeling, and hydrogen embrittlement of the shaft during plating. The problem is eliminated and the shaft can be reused without repair.

Further, according to the shaft manufacturing method of the present invention,
Since the shaft steel material is placed vertically in the nitriding furnace to suppress the strain due to its own weight during nitriding, the bending and warping of the shaft after nitriding is reduced, the allowance in finish grinding is averaged, and the Variations in the surface hardness distribution are reduced.

Further, by averaging the allowance, it is not necessary to form the nitrided layer unnecessarily thick, and the mechanical properties of the shaft can be prevented from deteriorating due to shortening of the nitriding time, and the productivity can be improved.

Further, the material obtained by removing the embrittlement on the surface of the nitride layer at the time of finish grinding can suppress the reduction of the impact value of the shaft and enhance the effect of preventing breakage of the shaft.

[Brief description of the drawings]

FIG. 1 is a table showing the results of a fatigue test of an untreated SNCM447 product and a chrome-plated product.

FIG. 2 is a partially broken side view showing an embodiment of the sleeve roll of the present invention.

FIG. 3 is a partially cutaway side view of another embodiment.

FIG. 4 is a partially broken side view showing still another embodiment.

FIG. 5 is a partially broken side view showing still another embodiment.

FIG. 6 is a partially broken side view showing still another embodiment.

FIG. 7 is a side view of a shaft used in an experiment of ion nitriding treatment.

FIG. 8 is a chart showing a hardness distribution of a shaft after nitriding.

FIG. 9 is a table showing the results of a fatigue test of an untreated and a nitrided SNCM630 product.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Roll sleeve 2 Shaft 2a Bearing mounting part 2b Driving part 2c Sliding part 3 Spacer ring 4 Nut 5 Fillet ring 6 Nitride layer

Claims (8)

[Claims] 1. A rolling sleeve roll comprising a roll sleeve made of a hard material fixed to an outer periphery of a steel shaft having a nitride layer of a shaft base material provided on a surface of a roll sleeve mounting portion. 2. The rolling sleeve roll according to claim 1, wherein the fixing of the roll sleeve to the shaft is performed by internal pressure fixing. 3. The rolling sleeve roll according to claim 1, wherein the nitride layer is also provided on a surface of a bearing mounting portion of the shaft. 4. The rolling sleeve roll according to claim 1, wherein said nitrided layer is provided also on a surface of a driving portion of a shaft. 5. The material of the shaft is JIS SNCM63.
The rolling sleeve roll according to any one of claims 1 to 4, wherein the value is 0. 6. The rolling sleeve roll according to claim 1, wherein an embrittlement generated on the surface of the nitrided layer is removed. 7. A shaft steel material having a surface hardness of 30-40 HR _C tempered at a temperature of 560 ° C.-650 ° C.
6. The apparatus according to claim 1, which is vertically disposed in a nitriding furnace, and in this state, is subjected to ion nitriding at a temperature of 550 ° C. to 600 ° C. lower than the tempering temperature for 5 to 20 hours. Method for manufacturing a shaft of a sleeve roll for rolling. 8. The method according to claim 7, wherein the surface layer of the nitrided layer formed on the surface of the steel material for the shaft is further removed to a depth of 0.02 mm to 0.15 mm after the ion nitriding treatment. The method for producing a shaft of a sleeve roll for rolling according to claim 6.