JP2004076754A - Ball screw apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw apparatus, which can prevent the damage on the surfaces of helicoidal grooves for a long time, and can improve the smoothness of its operation. <P>SOLUTION: A screw shaft 1 and a nut 2 are made of a case hardening steel treated by carburizing and quenching. The hardness of their surfaces is set to be Rockwell C (HRC) 62-67, and the residual austenite at these surfaces is set to be 15-25 volume %. Thus, even when contaminated lubricant is used, the surfaces of the helicoidal grooves 1a, 2a of the screw shaft 1 and the nut 2 are hardly damaged for a long time. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ball screw device.
[0002]
[Prior art]
As a ball screw device, for example, as disclosed in Japanese Patent Application Laid-Open No. 2000-346162, a circulator that communicates an opposing space between spiral grooves provided to face a screw shaft and a nut, respectively, and one end and the other end of the opposing space. A number of balls are rolled and circulated between the tubes.
[0003]
In addition, an end cap may be used instead of the circulator tube.
[0004]
[Problems to be solved by the invention]
In the above-described conventional example, the screw shaft and the nut are formed of metal. However, when minute wear powder called contamination is mixed in the lubricating oil, the wear powder is generated between the ball and each spiral groove. You will be bitten. In particular, when the wear powder bites into the spiral groove serving as the raceway surface of the ball, a small dent is formed on the surface of the spiral groove with the bite of the wear powder, and a bulge is formed at the edge of the dent. Is done. In particular, the raised portions are turned up and easily peeled off, which causes the surface of the spiral groove to become rough. As a result, the rolling characteristics of the ball are reduced and the operation smoothness is reduced, leading to a shortened life.
[0005]
[Means for Solving the Problems]
A ball screw device according to the present invention includes a screw shaft having a spiral groove formed on an outer peripheral surface thereof, and a return passage having a spiral groove formed on an inner peripheral surface thereof, the spiral groove being opposed to the spiral groove of the screw shaft, and having an outer diameter portion extending along an axial direction. And a number of balls interposed in opposing spaces of the opposed spiral grooves. At least one of the nut and the screw shaft is carburized and quenched using steel for carburizing, and has a surface hardness of 62 to 67 in Rockwell hardness (HRC), preferably 64 to 67, and The amount of retained austenite is set to 15 to 25% by volume, preferably 20 to 25% by volume.
[0006]
In this case, for at least one of the screw shaft and the nut, since the surface of the spiral groove is sufficiently hardened, when using lubricating oil in which abrasion powder is mixed, the abrasion powder in the lubricating oil contains the helical groove and the ball. Even if the spiral groove is engaged, the surface of the spiral groove is unlikely to be dented as in the conventional example, and a raised portion is not easily formed around the depression. Further, by optimizing the retained austenite, appropriate toughness and early disappearance of the raised portion can be expected. Therefore, the surface of the spiral groove is less likely to be damaged for a long time. If the amount of retained austenite is less than 15% by volume, toughness cannot be expected, and if it exceeds 25% by volume, the swelled portion undergoes work hardening, and early disappearance cannot be expected.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
1 and 2 show an embodiment of the present invention. The illustrated ball screw device includes a screw shaft 1, a nut 2, a pair of end caps 3, 3, and a number of balls 4.
[0008]
The screw shaft 1 is formed by forming one spiral groove 1a on the outer peripheral surface of a solid shaft body. The nut 2 has a single spiral groove 2a formed on the inner wall surface of the center hole of the cylindrical member, the spiral groove 2a facing the spiral groove 1a of the screw shaft 1. Each of the pair of end caps 3 and 3 is formed of an annular body having the same shape, and is attached to both ends of the nut 2 in the axial direction using a coupling tool such as a bolt (not shown).
[0009]
The opposing space between the helical groove 1a of the screw shaft 1 and the helical groove 2a of the nut 2 is the main passage 10 in which the ball 4 rolls. In other words, it can be said that the opposing spiral groove 1a of the screw shaft 1 and the spiral groove 2a of the nut 2 form the main passage 10 in which the ball 4 rolls. The balls 4 rolling in the main passage 10 guide relative rotation between the screw shaft 1 and the nut 2.
[0010]
A return passage 2b is provided at the outer diameter of the center hole of the nut 2. The return passage 2 b is formed of a through-hole penetrating the entire length of the nut 2 in the axial direction.
[0011]
Further, the end caps 3, 3 are provided with direction change paths 3a, 3a for communicating the main path 10 with the return path 2b. The direction changing path 3 a is formed of a groove having a substantially hemispherical cross section formed on the inner surface of the end cap 3.
[0012]
In the above-mentioned ball screw device, a large number of balls 4 rolling in the main passage 10 are turned by the turning path 3a of one end cap 3 with the rotation of the screw shaft 1 or the nut 2, and the return path of the nut 2 is returned. The ball 4 that is introduced into the return passage 2 b and exits from the return passage 2 b is turned in the direction change passage 3 a of the other end cap 3 and is introduced into the main passage 10. Thus, the ball 4 is circulated in the main passage 10, the direction change passages 3a, 3a, and the return passage 2a.
[0013]
The screw shaft 1 and the nut 2 were carburized and quenched using steel for carburizing, and had a surface hardness of 62 to 67 in Rockwell hardness (HRC) and a surface residual austenite amount of 15 to 67. It is set to 25% by volume. Examples of the carburizing steel include SAE standard 4150, SAE standard 8620H, SAE standard 4320H, JIS standard SCM415, JIS standard SCM420H, JIS standard SCR420H, and the like. Note that the present invention also includes one in which at least one of the screw shaft 1 and the nut 2 is set to have the above-described properties.
[0014]
The ball 4 is carburized and quenched using JIS standard SUJ2 as a material, and has a surface hardness of about 58 to 62 in Rockwell hardness (HRC).
[0015]
Further, the end cap 3 may be formed by compression molding using, for example, polyamide 66 reinforced by adding 20 to 40 wt% of fiber such as glass fiber. In addition, the end cap 3 is cast using a ferrous metal such as JIS standard SC450, JIS standard FC350, or JIS standard FCD450-10, or an aluminum metal such as JIS standard 2014 or JIS standard 2017. be able to.
[0016]
Specifically, a method for manufacturing the screw shaft 1 and the nut 2 will be described.
[0017]
After the outer shape of the screw shaft 1 and the nut 2 is formed using the above-described carburizing steel as a material, a carburizing quenching process, a preliminary tempering process, a sub-zero process, and a main tempering process are performed in this order.
[0018]
The carburizing and quenching treatment is performed by maintaining the temperature at 900 to 950 ° C. for a predetermined time. The surface hardness after carburizing and quenching is 55 to 65 in Rockwell hardness (HRC), and the amount of retained surface austenite is about 30 to 35% by volume.
[0019]
The preliminary tempering process is performed by holding at 110 to 130 ° C. for 30 minutes or more. The sub-zero treatment is performed by holding at -40 to -80 ° C for 10 minutes or more. The surface hardness after the sub-zero treatment is 63 to 68 in Rockwell hardness (HRC), and the amount of retained austenite is about 20 to 25% by volume. The main tempering process is performed by holding at 140 to 175 ° C. for 30 minutes or more.
[0020]
By appropriately adjusting the details in this manner, the surface hardness of the screw shaft 1 and the nut 2 is 62 to 67, preferably 64 to 67 in terms of Rockwell hardness (HRC), and the surface residual austenite amount is 15 ２５25% by volume, preferably 20-25% by volume. In addition, no carbide is recognized in the surface layer at a depth of 50 μm from the outermost surface of the steel.
[0021]
By the way, when the sub-zero treatment is performed without performing the preliminary tempering treatment, austenite is easily decomposed into martensite, and the amount of retained austenite is reduced. Unstable austenite is stabilized and becomes less likely to become martensite even when the sub-zero treatment is performed.
[0022]
In the above method, the preliminary tempering process can be omitted by appropriately adjusting the processing temperature of the sub-zero process. After the carburizing and quenching treatment, a secondary quenching treatment may be performed. This secondary quenching treatment is performed by heating and holding at 770 to 850 ° C. for 0.5 hour or more and then quenching by oil cooling.
[0023]
As described above, if the screw shaft 1 and the nut 2 are configured as described above, even when a lubricating oil containing minute wear powder called contamination is used, the lubricating oil in the lubricating oil may be used. When the abrasion powder gets stuck between the spiral grooves 1a, 2a and the ball 4, the surface of the spiral grooves 1a, 2a is suppressed or eliminated from being dented or bulging as in the conventional example. be able to. Therefore, the surfaces of the spiral grooves 1a and 2a are less likely to be damaged over a long period of time, which contributes to improvement in reliability and life.
[0024]
Note that the present invention is not limited to only the above-described embodiment, and various applications and modifications are conceivable. For example, the pitch of the spiral grooves 1a and 2a of the screw shaft 1 and the nut 2 is not particularly limited. In addition, the spiral grooves 1a and 2a of the screw shaft 1 and the nut 2 may be formed in a single row or in multiple rows.
[0025]
【The invention's effect】
In the ball screw device of the present invention, even when dirty lubricant is used, the surface of the spiral groove is hardly damaged for a long period of time, so that the reliability and the life can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a ball screw device according to an embodiment of the present invention. FIG. 2 is a view of the end cap of FIG. 1 viewed from the inside.
DESCRIPTION OF SYMBOLS 1 Screw shaft 2 Nut 3 End cap 4 Ball 1a Screw shaft spiral groove 2a Nut spiral groove 2b Nut return passage 3a End cap direction change passage 10 Main passage

Claims (1)

A screw shaft with a spiral groove formed on the outer peripheral surface,
A spiral groove formed on the inner peripheral surface of the screw shaft, the nut having a return passage along an axial direction in an outer diameter portion;
A number of balls interposed in the opposing space of the opposing spiral grooves,
At least one of the nut and the screw shaft is carburized and quenched using steel for carburizing, and has a surface hardness of 62 to 67 in Rockwell hardness (HRC) and a surface residual austenite amount of 15 to 67. Ball screw device set to 25% by volume.

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