Ball screw with lubricating grease and seal member of solid...

Machine element or mechanism – Gearing – Teeth

Reexamination Certificate

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C074S089100, C074S424830

Reexamination Certificate

active

06178839

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a ball screw used in an environment in which intrusion of foreign matter into the ball nut or the lubricant being washed away from the ball not is liable to cause an insufficiency of lubrication.
Many sealing devices for ball screws are of a type in which a non-contact seal made of rubber or the like is mounted on the end of the ball nut. In this case, however, since there is a clearance between the inner periphery of the seal member and the groove surface of the screw shaft, the effect of suppressing foreign matter intrusion and sealed grease wash-away is decreased depending on the service conditions, sometimes leading to a lowering in the functional capability or the life of the ball screw. Under severe lubricating conditions as in the case where the surrounding environmental temperature is high or the travel stroke or the travel speed of the ball nut (rpm of the screw shaft) is large, the use of the lubricating oil supplied by the sealed grease alone is likely to result in an insufficient amount of lubrication available in the areas of contact between the balls and the screw groove surface.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to improve sealability and lubrication performance simultaneously, to thereby provide a ball screw which has a long life under severe conditions as described above.
According to the invention, to achieve the above object, lubricating grease is sealed in a ball nut and a seal member is made of a solid lubricating composition containing a lubricating oil as a component which is of the same kind as the base oil of the lubricating grease or which does not lower the lubricability by interaction therewith, the seal member being mounted on each end of the ball nut with its inner periphery placed in slide contact with the groove surface of the screw shaft. The “lubricating composition” is in solid form, retaining lubricating oil as a component in the structure of the base material such as synthetic resin, and has an oily surface in that the lubricating oil component retained in the base material gradually continuously seeps onto the surface thereof. The wording “containing lubricating oil as a component” refers to a manner in which it is dispersed and retained in the state of lubricating oil in the matrix of the base material and also a manner in which it is dispersed and retained in the state of lubricating grease in the matrix of the base material. As lubricating compositions, it is possible to use, for example, the compositions described in Japanese Patent Publication Kokoku Sho 63-23239 and Sho 47 -3455.
A seal member made of such lubricating composition is placed in slide contact with the groove surface of the ball screw to seal off the ball nut, whereby a high degree of sealability is obtained and the lubricating oil component (the retained lubricating oil or the base oil of the retained lubricating grease) is gradually continuously fed from the lubricating composition to the portion in slide contact with the screw groove surface, reducing the friction force in said slide contact portion. Further, the lubricating oil component fed to said slide contact portion is fed to the portion in contact with the balls as the screw groove surface travels with the operation of the ball screw, thereby assisting the lubricating function of the lubricating grease (sealed grease) in the ball nut. That is, in the case where the amount of sealed grease in maintained at a suitable value necessary for lubrication of the interior of the ball nut, a satisfactory lubricating function provided by the sealed grease can be expected; however, the amount of sealed grease inevitably decreases with the passage of the operating time, even in which case, the amount by which the function is lowered by the decrease in the amount of sealed grease is compensated by the lubricating function of the lubricating oil component supplied from the lubricating composition, so that the lubricating function which is satisfactory on the whole is maintained for a long time.
As described above, since the lubricating oil component supplied from the lubricating composition assists the lubricating function of the sealed grease while reducing the friction force in the seal slide contact portion, it is desirable that the lubricating oil component of the lubricating composition and the base oil component of the sealed grease be of the same kind or be such that their interaction will not cause a lowering of lubricability. The wording “same kind” means that the lubricating oil component of the lubricating composition and the base oil component of the sealed grease are identical or similar. Further, the wording “interaction does not cause a lowering of lubricability” means that the lubricating oil component of the lubricating composition and the base oil component of the sealed grease do not undergo a physical or chemical interaction which leads to a lowering of lubricability. That is, as considered from the standpoint of lubricating function, the two components are compatible.
The present invention has the following effects.
(1) In the case where the amount of sealed grease is maintained at a proper value necessary for the lubrication of the interior of the ball nut, a satisfactory lubricating function by the sealed grease can be obtained. Further, even if the amount of sealed grease decreases with the passage of operating time, the lowering of the function attending the decrease in the amount of sealed grease is compensated by the lubricating function of the lubricating oil component fed from the seal member; thus, the lubricating function which is satisfactory on the whole is maintained for a long time. Therefore, the ball screw of the present invention has a high service life even under severe lubricating conditions.
(2) Since the inner periphery of the seal member formed of solid lubricating composition is in slide contact with the screw groove surface of the screw shaft, the lubricating grease sealed in the ball nut can hardly leak out and foreign matter can hardly intrude from outside.
(3) The lubricating oil component retained in the structure of the base material of the seal member gradually continuously seeps out to the portion which is in contact with the screw groove surface of the screw shaft, reducing the friction force in the slide contact portion, so that there is little wear of the seal member and the torque is low.


REFERENCES:
patent: 3729415 (1973-04-01), Davis et al.
patent: 5178029 (1993-01-01), Klinkenberg
patent: 5555771 (1996-09-01), Kuroiwa et al.
patent: 5722294 (1998-03-01), Kobayashi et al.
patent: 5749266 (1998-05-01), Tsukada
patent: 5782135 (1998-07-01), Kondo et al.
patent: 5809838 (1998-09-01), Miyaguchi et al.
patent: 5832776 (1998-11-01), Kuo
patent: 5906136 (1999-05-01), Yabe et al.
patent: 47-3455 (1965-09-01), None
patent: 63-23239 (1988-05-01), None

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