JPH08128512A - Solid lubricated ball screw - Google Patents

Abstract

PURPOSE: To prevent the lubricating film on the surface of a ball from wearing in the early stage by constituting a ball circulating mechanism part out of fluororesin or its composite, in a solid lubricated ball screw used by treating a screw shaft groove and a nut groove with solid lubricant. CONSTITUTION: A solid lubricated ball screw 11 in which balls are interposed between a screw shaft groove 12a formed on a screw shaft 12 and a nut groove 13a formed in a nut 13, is provided with a ball circulating mechanism part 15, and this ball screw is used at least by treating the screw shaft groove 12a and the nut groove 13a with solid lubricant. The ball circulating mechanism part 15 is constituted by full machining out of a block of fluororesin, its composite polytetrafluoroethylene, or polytetrafluoroethylene material containing fiber. Hereby, fitness with the solid lubricant becomes favorable, further because of low friction coefficient, bearing pressure generated on the ball is low, and hence wear of the film is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a ball interposed between a screw shaft groove formed in a screw shaft and a nut groove formed in a nut and has a ball circulation mechanism, and at least the screw shaft groove and the nut groove are provided. Regarding the improvement of the ball circulation mechanism in a ball screw used with a solid lubricant, more specifically, in the case of using the ball screw in outer space or in vacuum, the solid lubrication that further improves the durability of the ball circulation mechanism. It relates to ball screws.

[0002]

2. Description of the Related Art A ball is interposed between a screw shaft groove formed in a screw shaft and a nut groove formed in a nut, and a ball circulation mechanism is provided, and at least the screw shaft groove and the nut groove are provided with a solid lubricant. The ball screw used has been adopted in various fields as a special feed screw in which a large number of balls (balls) are inserted between the screw shaft and the nut as described above in order to improve the efficiency of the feed screw. ("Mechanical Engineering Handbook", Japan Society of Mechanical Engineers, May 15, 1988, First Edition, 2nd edition, B2-173).

In particular, the ball screw having such a structure has the following excellent features and is therefore widely used for automobile steering, machine tools and industrial machines.

(1) In general, the efficiency is as high as 92 to 97%, which is 3 to 4 times higher than that of a conventional feed screw having a surface contact.

(2) Not only can rotary motion be converted into linear motion, but linear motion can be easily converted into rotary motion.

(3) Most rolling friction occurs, and the stick-slip phenomenon is less likely to occur as compared with the surface contact feed screw and hydraulic drive.

(4) The life is longer than that of a normal feed screw.

Since the ball screw has the above-mentioned excellent characteristics, its use in outer space and vacuum has been expanded in recent years. Therefore, when a ball screw is used in outer space or in vacuum, oil lubrication cannot be performed, and thus solid lubricants such as Pb, MoS ₂ and WS ₂ are often applied and used instead of oil.

However, it has not been used in space or in vacuum yet, and it is almost used only by applying a solid lubricant to a conventional ball screw used under oil lubrication. As for the design guideline for the case of use, it is the actual situation that there is no particular design item in detail except the method of determining the processing target value corresponding to the film thickness increase by the solid lubricant.

Therefore, regarding a ball screw to which a solid lubricant is applied, an application regarding a method for preventing friction powder (actual plan 2)
(-150452, Japanese Utility Model Laid-Open No. 4-22638, etc.) are observed only in a few cases, and the present situation is that they have not been studied much.

As a conventional ball screw, for example, FIG.
There are a return piece type ball screw shown in Fig. 2 and a ball tube type ball screw shown in Fig. 2.

Of these, the return piece type ball screw 11 shown in FIG. 1 has a screw shaft groove 12 formed in a screw shaft 12.
The ball tube type ball screw 21 shown in FIG. 2 has a structure in which a ball 14 is interposed between a and a nut groove 13a formed in the nut 13 and a ball circulation mechanism portion (return piece) 15 is provided. A ball is interposed between the screw shaft groove 22a formed in the shaft 22 and the ball groove formed in the tube 23.

[0013]

However, in all such conventional ball screws, oil lubrication and grease lubrication are taken into consideration. Therefore, the material of the ball lubrication portion is the material of the nut portion. The processing of the end portion of the joint with the nut portion was at the level of C1 chamfering or thread chamfering at most.

Therefore, when the ball screw is coated with a solid lubricant and used, the lubricating films on the groove surfaces of both the screw portion and the nut portion are not so worn, but only the lubricating film on the ball surface is worn early. There was a problem of doing.

The cause of this is that the solid lubricant on the ball surface is scraped off by a slight step which is inevitably present at the end of the nut portion and the ball circulation mechanism portion, and at the same time, the ball (steel ball) inside the ball circulation mechanism portion is scraped off. ) Is for rolling to move the ball circulation mechanism part while being forcedly pushed by the ball in the rear and not being rolled, while being forcedly pushed.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and a ball is interposed between a screw shaft groove formed in a screw shaft and a nut groove formed in a nut. In addition to the conventional ball screw that has a ball circulation mechanism and uses a solid lubricant in at least the screw shaft groove and nut groove, the problem that only the lubricant film on the ball surface is worn out early is eliminated. The purpose of the present invention is to make it possible to greatly improve the durability of the ball screw because the lubricating film on the surface of the ball is unlikely to wear quickly.

[0017]

A solid lubricating ball screw according to the present invention, as set forth in claim 1, has a ball between a screw shaft groove formed in a screw shaft and a nut groove formed in a nut. And a ball circulation mechanism part is provided, and in a ball screw used by applying a solid lubricant to at least the screw shaft groove and the nut groove, the ball circulation mechanism part is made of a fluororesin or a composite material thereof. I am trying.

In the embodiment of the solid lubricated ball screw according to the present invention, as described in claim 2, the nut groove of the nut to which the solid lubricant is applied and the ball groove of the ball circulation mechanism portion are formed. 20% or more of the ball diameter at both ends of the groove on the mating surface
% Or less, and the composite material may be a fiber reinforced fluororesin, as described in claim 3.
As described in claim 4, the fluororesin or its composite material is polytetrafluoroethylene (PTF).
E) or a composite material thereof.

[0019]

The solid lubricated ball screw according to the present invention comprises:
As described in claim 1, balls are interposed between the screw shaft groove formed in the screw shaft and the nut groove formed in the nut, and a ball circulating mechanism is provided, and at least the screw shaft groove and the nut groove are provided. In a ball screw used with a solid lubricant applied to the ball circulation mechanism, the ball circulation mechanism is made of fluororesin or a composite material thereof, and the ball circulation mechanism is made of fluororesin (PTFE, PFA, FE).
(P, PCTFE, ETFE, ECTFE, etc.) or a composite material thereof to produce Mo as a solid lubricant.
Familiarity such as S ₂ and WS ₂ becomes extremely better than that of SUS material. Further, since the friction coefficient is low, the surface pressure generated on the ball is low, and the wear of the coating is reduced, so that the durability of the ball circulation mechanism portion is improved and therefore the durability of the ball screw is improved.

Further, as described in claim 2,
20% or more and 35% or more of the ball diameter at the groove ends of both the nut and the ball circulation mechanism on the mating surface of the nut groove of the nut with solid lubricant and the ball groove of the ball circulation mechanism
By adopting the following rounded processing, the ball can move in the original moving direction without being caught. In this case, if the rounded shape is less than 20% of the ball diameter, the life of the ball screw will be shortened.
In the case of a rounding with a large excess of%, the balls entangle with each other at the ball circulation mechanism and the end of the nut groove.

Then, as described in claim 3,
By using a fiber reinforced fluororesin for the composite material,
The strength of the ball circulation mechanism is improved, and fluororesin (PTFE, PFA, FEP, PCTFE, ETF
E, ECTFE, etc.), the use of PTFE (polytetrafluoroethylene), which belongs to the one having the lowest friction coefficient, further reduces the surface pressure generated on the ball, Premature wear of the lubricating film on the surface will be more effectively avoided.

[0022]

EXAMPLES The present invention will be described below based on examples.

Example 1 Return piece type SUS6 having the structure shown in FIG.
A ball screw 11 made of 30 (precipitation hardened stainless steel) material having the specifications shown in Table 1 was prepared, and an inorganic binder-bonded MoS ₂ baked film was used as a solid lubricant, and a screw shaft groove 12a,
The nut groove 13a, the ball groove 15 of the ball circulation mechanism portion 15
a and the surface of the ball 14 were each applied in a thickness of 10 μm.

At the same time, only the return piece constituting the ball circulation mechanism 15 is made by shaving all the same from a block of PTFE (polytetrafluoroethylene) material, and only the return piece is replaced with a PTFE material, and a ball screw is used. Was assembled by a double nut method to obtain a ball screw of Example 1.

In the inspection after assembly, both the axial clearance and the lateral clearance were 12 μm.

Next, a vacuum sliding test was conducted under the conditions shown in Table 2. At this time, in this embodiment, N = 4 (that is,
No. shown in FIG. 1 to No. 4).

[0027]

[Table 1]

[0028]

[Table 2]

Example 2 As in Example 1, a ball screw 11 made of a return piece type SUS630 material having the structure shown in FIG. 1 and having the specifications shown in Table 1 was prepared, and a solid lubricant was used to bond an inorganic binder. The MoS ₂ baked film was applied to the surface of the screw shaft groove 12a, the nut groove 13a, the ball groove 15a of the ball circulation mechanism portion 15 and the ball 14 in a thickness of 10 μm, respectively.

At the same time, only the return piece constituting the ball circulating mechanism 15 contains PT containing 10% by weight of glass short fibers.
The same block was manufactured by shaving out of a block of FE material, the ball groove ends were subjected to a 0.8R rounding, and only the return piece was replaced with the PTFE material. At the same time, a ball screw of Example 2 was obtained by combining the nut groove end portion with a 0.8R rounded one and assembling the ball screw by the double nut method.

Then, this ball screw was subjected to the same sliding test as in Example 1.

Example 3 PTF containing 10% by weight of glass short fiber as a return piece
Example 2 Except that, as a condition for rounding the ball groove end, the groove was machined from a block of E composite material and the groove end was 1.2R rounded, and at the same time, the nut groove end was 1.2R rounded. A ball screw of Example 3 was obtained in exactly the same manner as in Example 1, and the same sliding test as in Example 1 was performed.

[0033] In Comparative Example 1 Example 1, except that no replacing the return piece and PTFE materials, in the same manner as in Example 1, the ball screw of Comparative Example 1, subjected to the same sliding test as in Example 1 did.
In this comparative example, N = 5 (that is, Nos. 1 to N in FIG.
o. 5) was carried out.

Comparative Example 2 In Example 2, as a rounding condition for the ball groove end, 0.4R are rounded for the ball groove end of the return piece, and 0.4R are rounded for the nut groove end at the same time. Except for the above, the ball screw of Comparative Example 2 was prepared in the same manner as in Example 2 and subjected to the same sliding test as in Example 1.

Comparative Example 3 In Example 2, as a rounding condition for the ball groove end portion, the return groove ball groove end portion was rounded to 1.5R, and at the same time, the nut groove end portion was rounded to 1.5R. Except for the above, the ball screw of Comparative Example 3 was prepared in the same manner as in Example 2 and subjected to the same sliding test as in Example 1.

Comparative Example 4 In Example 2, as a rounding condition for the ball groove end portion, the ball groove end portion of the return piece was rounded to 2.0R, and at the same time, the nut groove end portion was rounded to 2.0R. Except for the above, the ball screw of Comparative Example 4 was prepared in the same manner as in Example 2 and subjected to the same sliding test as in Example 1.

Reference Example As a reference example, the rolling bearing was treated with the solid lubricant (MoS ₂ ) used in Example 1 to a thickness of 10 μm and subjected to the same sliding test as in Example 1. In this reference example, N = 2
(That is, No. 1 and No. 2 shown in FIG. 4).

Evaluation by Sliding Test In the sliding test, the cumulative number of times of sliding until the coating as the solid lubricant broke and the friction coefficient exceeded 0.3 was measured. The sliding life was evaluated from the cumulative number of sliding times of the ball circulation mechanism portion of the ball screw of each example and comparative example.

The results of the evaluation of the sliding life of the ball screw are shown in FIGS.

As is clear from FIG. 3 showing the results of Example 1, in the ball screws (No. 1 to No. 4) of Example 1, the ball circulation mechanism portion (return piece) was compatible with MoS _2. The durable life of the ball screw could be greatly improved by changing to a PTFE material that is good and resistant to pure slip. However, in the disassembly study after the sliding test, the return piece was replaced with a resin material with low rigidity, so SUS
It was also confirmed that the groove edge was larger than that when the material was used.

Further, as is clear from FIG. 4 showing the results of Comparative Example 1, the ball screw (No. 1 to No.
The life of the coating of 5) was considerably shorter than that of the rolling bearings (No. 1 and No. 2) shown as a reference example. About this cause, 2 × 10 ³
As a result of disassembling and examining each part of the ball screw by interrupting the sliding test at each rotation, the solid lubricating coating of the ball had already disappeared, but the solid of the screw shaft groove, nut groove, and ball groove of the ball circulation mechanism part It was found that the lubricating coating was still present.

As a result of the detailed examination of each part, according to the appearance observation of the ball circulation mechanism part, it seems that the solid lubricating coating remains on the surface of the ball groove of the ball circulation mechanism part. Cross-sectional observation revealed that surface plastic flow of the base metal was remarkably observed, and it was found that the balls did not roll in the ball circulation mechanism part, but moved by forcibly sliding. Further, according to the cross-section observation of the groove end, the plastic flow is more intense toward the end, and the settling (when the shape of the end is the level of the thread chamfering C0.1 at the time of processing,
It was found that deformation occurred to a level of 0.2), the surface pressure generated on the ball at the joint between the nut groove and the ball groove of the ball circulation mechanism was high, and the coating film was severely worn at this stage.

From the above, the disappearance of the early lubricating coating only on the balls is caused by the fact that the solid lubricant on the surface of the balls is scraped off at the same time as the solid lubricant on the balls is scraped off by a slight step which is inevitably present at the ends of the nut portion and the ball circulation mechanism portion. It is considered that this is because the ball does not roll in the ball circulation mechanism portion, and the ball circulation mechanism portion moves by forced sliding while being pushed by the rear ball forcibly afterward.

Further, as is clear from FIG. 5 showing the test results in which the rounding conditions applied to the ball groove end portions are changed, as in Comparative Example 4, the return piece groove end portion is rounded to 2.0R, and at the same time, the nut groove end portion is processed. In the case where the rounded part is also 2.0R, the balls are caught in the ball circulation mechanism part and the end of the nut groove, and if the radius is too large, the ball will not move in the original direction of movement. It has been found that the two balls are easily engaged with each other in the direction perpendicular to the moving direction of the balls.

The ball diameter used in this test is 3.9688 mm as shown in Table 1. In Example 2, the radius at the end of the nut groove and the radius at the end of the return piece groove are both 0.8R. It is 20.16% of the diameter, and that of Example 3 is both 1.2R and 3 of the ball diameter.
This was 0.23%, and a good result was obtained with the cumulative number of sliding times being about 10 ⁷ times.

However, the radiuses of Comparative Example 2 and Comparative Example 3 are 0.4R and 1.5R, respectively, and the ball diameter is 1 respectively.
The values were 0.09% and 37.79%, and the cumulative number of sliding times was 10 ⁶ or less, which was inferior to the above two examples.

In this embodiment, the rounding of the end portion of the nut groove and the rounding of the end portion of the return piece groove are performed as a combination of the rounding of the same radius. It has been confirmed that similarly long sliding life can be obtained with a combination of R-shaped R-shaped pieces having a size of% -35%.

As is clear from the results shown in FIGS. 3 and 5, the ball circulation mechanism portion of the ball screw made of fluororesin, particularly preferably PTFE material or its composite material, has a friction coefficient of 0.3. In all cases, the cumulative number of sliding movements before exceeded 10 ⁶ or more, a long sliding life was obtained. At the same time, in the mating surface of the nut groove of the ball screw and the ball groove of the ball circulation mechanism part, both ends of the groove are rounded to have a size of 20% to 35% of the ball diameter. Even better durability was obtained, with the number of sliding times being about 10 ⁷ times.

[0049]

As described above, according to the solid lubricating ball screw of the present invention, as described in claim 1, the screw shaft groove formed in the screw shaft and the nut groove formed in the nut are formed. In a ball screw in which a ball is interposed between the balls, a ball circulation mechanism is provided, and at least a screw shaft groove and a nut groove are provided with a solid lubricant, the ball circulation mechanism is made of a fluororesin or a composite material thereof. As a result, solid lubricants such as MoS ₂ and WS ₂
The conformability to the SUS material is remarkably better than that of the SUS material, and since the friction coefficient is low, the surface pressure generated on the ball is low and the abrasion of the coating is reduced,
The excellent effect is that the durability of the ball screw is greatly improved.

Further, as described in claim 2,
20% or more and 35% or more of the ball diameter at the groove ends of both the nut and the ball circulation mechanism on the mating surface of the nut groove of the nut with solid lubricant and the ball groove of the ball circulation mechanism
Even better durability can be obtained by using a solid-lubricated ball screw with the following sizes that have been rounded, and a long life with a sliding life equivalent to that of a rolling bearing was obtained in the evaluation of surface pressure. The remarkable effect of obtaining a solid-lubricated ball screw with a long life is provided.

And, as described in claim 3,
By using a fiber-reinforced fluororesin as the composite material, the strength of the ball circulation mechanism portion is improved, and it is possible to compensate for the lack of strength when resin is used instead of metal.

Further, as described in claim 4,
PT belonging to the one with the lowest friction coefficient among fluororesins
By using FE, the surface pressure generated on the ball can be further lowered, and the remarkably excellent effect that the durable life of the ball screw can be extended is brought about.

[Brief description of drawings]

1 is a side crushing explanatory view ((A) of FIG. 1) and a front explanatory view (FIG. 1) showing a structure of a return piece type ball screw.
(B)).

FIG. 2 is an explanatory view showing the structure of a ball tube type ball screw.

FIG. 3 is a ball screw (No. 1 to No. 4) of Example 1 of the present invention in which only the return piece is replaced with a PTFE material.
It is explanatory drawing which shows the evaluation result of sliding life.

FIG. 4 is a ball screw of Comparative Example 1 (No. 1 to No. 5).
3 is an explanatory diagram showing evaluation results of sliding life of rolling bearings (No. 1 and No. 2) of Reference Example.

FIG. 5 is an explanatory diagram showing the evaluation results of the sliding life of the ball screws of Examples 2 and 3 of the present invention and Comparative Examples 2, 3 and 4 in which only the return piece was replaced with the PTFE composite material.

[Explanation of symbols]

 11 Return Piece Type Ball Screw 12 Screw Shaft 12a Screw Shaft Groove 13 Nut 13a Nut Groove 14 Ball 15 Ball Circulation Mechanism (Return Piece) 15a Ball Groove (Return Piece Groove)

Claims (4)

[Claims] 1. A ball is interposed between a screw shaft groove formed in a screw shaft and a nut groove formed in a nut, and a ball circulating mechanism is provided, and at least the screw shaft groove and the nut groove are provided with a solid lubricant. A solid lubricating ball screw, wherein the ball circulation mechanism portion is made of fluororesin or a composite material thereof. 2. A ball having a diameter of 20 at both groove ends of the nut and the ball circulation mechanism on the mating surface of the nut groove of the nut to which the solid lubricant is applied and the ball groove of the ball circulation mechanism.
%. The solid lubricating ball screw according to claim 1, which is rounded to have a size of not less than 35% and not more than 35%. 3. The solid lubricating ball screw according to claim 1, wherein the composite material is a fiber reinforced fluororesin. 4. The solid lubricating ball screw according to claim 1, wherein the fluororesin or its composite material is made of polytetrafluoroethylene or its composite material.