JP6248426B2 - Ball screw manufacturing method - Google Patents

Description

The present invention relates to a method of manufacturing a ball screw, more particularly to a method of manufacturing a high-load bearing or ball screws high rigidity is required.

Conventionally, a high-load ball screw used in an injection molding machine or a press is usually used with a large load for the purpose of use.
For example, as disclosed in Patent Document 1, such a ball screw for high load uses a dimension of the groove R portion (a radius of curvature of the rolling groove in a cross section along the axial direction) as close as possible to the diameter of the ball. Therefore, it is designed to increase the load capacity.

However, such a ball screw naturally has a large differential slip, and a spin slip due to having a lead unique to the ball screw, and further complicated in a three-point contact state because it is used under a heavy load. Sometimes skewed.
Also, such a ball screw is usually used for grease lubrication. It is known that when such a ball screw is used for grease lubrication, hydrogen separation in the grease is caused by a heavy load and slippage, hydrogen enters the steel, and damage occurs early.

Thus, as a measure to prevent such damage from occurring, a lubricant that does not easily cause hydrogen separation is being developed, but it is not general and may have been a factor in increasing costs.
Therefore, in Patent Document 2, for the purpose of preventing separation hydrogen intrusion in grease, at least one of a screw shaft, a nut, and a ball is coated with a triiron tetroxide film to prevent invasion of separation hydrogen in the grease into steel. Technology is disclosed.
Patent Document 3 discloses a technique in which, as in Patent Document 2, at least one of a screw shaft and a nut is provided with a triiron tetroxide film to prevent separated hydrogen from entering into the steel.

JP 2007-002976 A Japanese Patent Laid-Open No. 2004-257502 JP 2004-345317 A

However, unlike a bearing, a ball screw has a solid structure of a screw shaft, and a nut has a hollow structure. For this reason, even if the separated hydrogen in the grease intrudes into the steel material, the screw shaft has a solid structure, so the intrusion hydrogen is difficult to diffuse and diverge, and the nut has a hollow structure, so the intrusion hydrogen Is easy to spread and diverge.
The contact between the rolling groove of the nut and the ball is a contact between the concave member and the convex member, whereas the contact between the screw shaft and the ball is a contact between the convex member and the convex member. For this reason, the latter has a higher contact surface pressure.

  In addition, the ball screw differs from the bearing in that the screw shaft and the nut have complicated shapes. For example, the screw shaft is generally processed with a center hole, a tapped hole, a through hole for attaching to the machine base, a spline portion, a bearing fitting portion, and the like. On the other hand, a through hole for attaching a circulating part, a tapped hole, a through hole for attaching to a machine base, a tapped hole, and the like are processed in the nut.

Here, a strong alkaline solution at a constant temperature is used for the treatment of the iron trioxide film disclosed in Patent Document 2 and Patent Document 3. Then, the sludge (impurities) contained in this processing liquid enters the above-mentioned center hole, tap hole, through-hole or spline part for mounting on the machine base, etc., and the processing liquid is simply washed after processing. Could remain in the place. As a result, an unnecessary and strong oxide film is formed, which may cause a problem that the mounting accuracy is affected or the appearance is deteriorated. In order to solve these problems, not only simple cleaning but also brushing, ultrasonic cleaning, and the like are required, and there is a problem that costs increase due to cleaning.
Accordingly, the present invention has been made paying attention to the above-mentioned problems, and its purpose is to manufacture a ball screw that can reduce the peeling caused by hydrogen penetration of the screw shaft (so-called white peeling) at low cost. It is to provide a method .

In order to solve the above-mentioned problems, the present inventors have conducted intensive studies, and as a result, only the screw shaft of the ball screw is treated with the iron trioxide film, which is sufficient for peeling due to hydrogen penetration of the screw shaft. It was found that there was an effect.
The present invention is based on the above findings by the present inventors, and an aspect of the present invention for solving the above problems includes a screw shaft having a spiral rolling groove on the outer peripheral surface, and the screw shaft. The screw shaft via a plurality of balls having a rolling groove facing the rolling groove on the inner peripheral surface and rotatably loaded in a spiral load rolling path formed by the both rolling grooves. A ball screw having a nut screwed to and a ferric oxide film formed only on the screw shaft, a center hole, a tap hole, a through hole formed on the screw shaft, The screw shaft is immersed in a caustic soda solution in a state where at least one of the spline portion or the bearing fitting portion excluding the rolling groove is sealed with a sealing member, and the iron trioxide film is applied to the screw shaft. Are selectively formed.

In this way, by performing the triiron tetroxide coating treatment only on the screw shaft, it is possible to prevent an unnecessary cost increase that the nut must be treated. In addition, it has the advantages of solving various problems such as poor aesthetics and influencing mounting accuracy due to the ingress of processing liquid during the treatment with iron tetroxide film, and simple post-cleaning (cost reduction). . As a result, it is possible to provide a ball screw that can reduce peeling due to hydrogen penetration of the screw shaft at low cost .

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the ball screw which can reduce the peeling resulting from hydrogen penetration of a screw shaft at low cost can be provided.

It is sectional drawing which follows the axial direction which shows the structure in 1st Embodiment of the ball screw which concerns on this invention. It is sectional drawing which follows the axial direction which shows the structure of the screw shaft in 2nd Embodiment of the ball screw which concerns on this invention. It is sectional drawing which follows the axial direction which shows the structure of the screw shaft in 3rd Embodiment of the ball screw which concerns on this invention.

Hereinafter, embodiments of a ball screw according to the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a cross-sectional view along the axial direction showing the configuration of the ball screw according to the first embodiment of the present invention.
<Configuration of ball screw>
As shown in FIG. 1, the ball screw 1 of the present embodiment includes a screw shaft 10 having a spirally continuous rolling groove 11 formed on the outer peripheral surface and a spirally continuous rolling groove 21 having an inner peripheral surface. And a cylindrical nut 20 formed in the above.

The screw shaft 10 is inserted through the nut 20, the rolling groove 11 of the screw shaft 10 and the rolling groove 21 of the nut 20 face each other, and a spiral load is formed in the space between the rolling grooves 11 and 21. A rolling path is formed. A plurality of balls (rolling elements) 30 are slidably loaded in the load rolling path, and the nut 20 is screwed onto the screw shaft 10 via the balls 30.
In this embodiment, a triiron tetroxide film is formed only on the surface of the screw shaft 10. Here, as a method for forming the triiron tetroxide film, for example, the coating object is applied by immersing the object in a caustic soda aqueous solution heated at a low temperature (130 ° C. to 160 ° C.).

Hereinafter, examples of the present embodiment will be described.
In the present example, durability evaluation was performed using a ball screw manufactured by NSK Ltd., BS6316-10.5 (nominal number: JIS B 119263 × 16 × 300-Ct7). The specifications of each ball screw are shown below. · Screw shaft outer diameter: φ63mm
・ Lead: 16mm
-Ball diameter: 12.7 mm
・ Test load: 300 [kN]
・ Maximum rotation speed: 3200min ⁻¹ (Dn200,000)
Grease and base oil used: mineral oil, thickener: lithium soap, base oil kinematic viscosity: 40 ° C. 138.8 mm ² / S, 100 ° C. 14.3 mm ² / S
-Holding piece: Available (NSK S1 series)

Only the screw shaft was subjected to a triiron tetroxide coating treatment (black dyeing treatment) as shown below.
・ Processing liquid: Caustic soda liquid ・ Processing temperature: 130-150 ° C
・ Immersion time: 20 to 120 minutes ・ Processed film thickness: 0.1 to 10 μm

  Durability tests were performed on the ball screws subjected to these treatments, and evaluations were made on the “screw shaft intrusion hydrogen amount”, “nut intrusion hydrogen amount”, and “structure damage (existence of peeling)”. . The results are shown in Table 1. In Table 1, “Intrusion hydrogen amount of screw shaft” and “Intrusion hydrogen amount of nut” are the results measured by the temperature programmed desorption gas analysis method, and “Damage form” shows the result of visual observation. It is. The “life ratio” in Table 1 is a durability evaluation in which the life until peeling occurs in any of the screw shaft, nut, and ball is measured by the above durability test. evaluated. Further, “Cost Evaluation” in Table 1 was evaluated with the cost of Comparative Example 1 as 1, regarding the cost required for the black dyeing process.

As shown in Table 1, Examples 1 to 3 were obtained by blackening only the screw shaft, but no damage was observed on the screw shaft or the nut.
On the other hand, in Comparative Example 1, neither the screw shaft nor the nut was subjected to the black dyeing process, but hydrogen penetration type peeling was observed on the screw shaft.
In Comparative Example 2, only the nut was subjected to black dyeing treatment, but hydrogen penetration type peeling was observed on the screw shaft.

In Comparative Example 3, the screw shaft and the nut were subjected to black dyeing treatment, but no damage was observed on the screw shaft and the nut. However, the production cost increased as much as the nut was black dyed.
Here, focusing on the amount of hydrogen penetrating the screw shaft, from Comparative Examples 1 and 2, about 1.3 ppm of penetrating hydrogen considered to be grease-separated hydrogen is observed, and hydrogen penetrating type peeling is observed on the screw shaft. When the iron trioxide film treatment is not performed, it can be said that hydrogen intrusion occurs and hydrogen intrusion-type peeling occurs.

On the other hand, when paying attention to the intrusion hydrogen amount of the nut, from Examples 1 to 3 and Comparative Examples 1 to 3, when the iron tetroxide film treatment is performed, the intrusion hydrogen amount is about 0.4 ppm. If not, it is about 0.7 to 0.8 ppm. However, in any case, no peeling of the nut is observed.
In other words, it can be said that the effect on the hydrogen-penetrating type peeling is irrelevant whether or not the nut is subjected to the triiron tetroxide coating treatment.
From the above, it can be said that applying the triiron tetroxide coating only to the screw shaft is a preferred embodiment in that unnecessary cost increase does not occur.

(Second Embodiment)
FIG. 2 is a cross-sectional view along the axial direction showing the configuration of the screw shaft in the second embodiment of the ball screw according to the present invention. Note that this embodiment is different from the first embodiment described above only in that the screw shaft is provided with a portion not subjected to the triiron tetroxide coating treatment, and therefore, the same reference numerals as those of the first embodiment described above are attached. The description of the same configuration is omitted.
As shown in FIG. 2, the screw shaft 10 is provided with at least one center hole, tapped hole, through hole, spline part, and bearing fitting part. In the present embodiment, in addition to the rolling groove 11, a center hole 12, a through hole (not shown), a spline portion 14, and a bearing fitting portion 15 are provided on the screw shaft 10.

  In the present embodiment, the screw shaft 10 shown in FIG. 2 (a) is covered with a cover 50 (not shown), the spline portion 14, and the bearing fitting portion 15 with a cover 50 as shown in FIG. 2 (b). At the same time, a cap 51 in the form of a mounting screw is attached to the center hole 12 so as to close the center hole 12. The gap between the screw shaft 10 and the cover 50 and cap 51 may be sealed with an O-ring 52 or the like. Thereafter, the entire screw shaft 10 is immersed in a caustic soda aqueous solution heated at a low temperature (130 ° C. to 160 ° C.). At this time, since the through hole (not shown), the spline portion 14 and the bearing fitting portion 15 are sealed by the cover 50, the through hole (not shown), the spline portion 14 and the bearing fitting portion 15 are sealed. A triiron tetroxide film is not formed on the surface.

  Here, the material of the O-ring 52 that closes the gap between the screw shaft 10 and the cover 50 and the cap 51 and prevents the intrusion of the processing liquid such as caustic soda is highly resistant to corrosion by the processing liquid (= strong alkali). Is preferred. As a material of the O-ring 52, for example, a product made of perfluoroelastomer is preferable.

(Third embodiment)
Next, a third embodiment of the ball screw according to the present invention will be described with reference to the drawings. FIG. 3 is a cross-sectional view along the axial direction showing the configuration of the ball screw according to the third embodiment of the present invention. In addition, since this embodiment is different from the second embodiment described above only in that the rolling groove and the tap hole of the screw shaft are treated with the iron trioxide film, the same reference numerals as those of the second embodiment are used. A description of the same components attached is omitted.

As shown in FIG. 3, the ball screw 1 of the present embodiment has a screw shaft 10 shown in FIG. 3A and a support bolt 61 provided on each of support members 60 and 60 as shown in FIG. 3B. , 61 is immersed in a caustic soda solution heated at a low temperature (130 ° C. to 160 ° C.) in a state where the end surfaces of the screw shafts 10 are abutted against tap holes 13 and 13 provided at both ends of the screw shaft 10 and sealed. To do. The gap between the screw shaft 10 and the support bolt 61 may be sealed with the above-described O-ring (not shown) or the like. At this time, since the tap hole 13 is sealed with the support bolt 61, the iron trioxide film is not formed on the inner surface of the tap hole 13.
The ball screw according to the present invention has been described above. However, the ball screw according to the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Ball screw 10 Screw shaft 11 Rolling groove 12 Center hole 13 Tap hole 14 Spline part 15 Bearing fitting part 20 Nut 21 Rolling groove 30 Ball (rolling element)
40 Iron trioxide coating 50 Cover 51 Cap 52 O-ring

Claims (1)

A screw shaft having a spiral rolling groove on the outer peripheral surface;
Through a plurality of balls having a rolling groove facing the rolling groove of the screw shaft on the inner peripheral surface and rotatably loaded in a spiral load rolling path formed by the both rolling grooves. A nut screwed onto the screw shaft,
A triiron tetroxide film formed only on the screw shaft;
A method of manufacturing a ball screw having
Of the center hole, tap hole, through hole, spline portion, or bearing fitting portion formed in the screw shaft, the screw shaft is caustic soda in a state where at least one place excluding the rolling groove is sealed with a sealing member. A method for producing a ball screw, comprising dipping in an aqueous solution to selectively form the iron tetroxide film on the screw shaft.

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