JP2015224662A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw for allowing quick determination of whether abnormality occurs inside or not without the need for installing other components than indispensable components for the ball screw, and wirings.SOLUTION: A ball screw 10 includes a screw shaft 1, a nut 2, a plurality of balls 3, and a seal 5. A spiral groove 11 of the screw shaft 1 and a spiral groove 21 of the nut 2 form a rolling path where the balls 3 roll in loaded conditions. The nut 2 has a ball return path 45 to return the balls 3 from the end point to the start point of the rolling path. The balls 3 are arranged in the rolling path and in the ball return path 45. A contact part 52 of the seal 5 with the screw shaft 1 is formed of an elastomer composition containing inorganic pigment whose color is reversibly changed with temperature, and elastomer.

Description

  The present invention relates to a ball screw.

The ball screw has a screw shaft, a nut, and a plurality of balls. In the ball screw, the axial dimension of the screw shaft is longer than the axial dimension of the nut, and the screw shaft passes through the nut. A rolling path on which the ball rolls in a loaded state is formed by the spiral groove of the screw shaft and the spiral groove of the nut. The nut has a ball return path for returning the ball from the end point of the rolling path to the start point. The balls are disposed in the rolling path and the ball return path. The nut and the screw shaft move relative to each other via a ball that rolls in a rolling state in the rolling path.
Examples of the part (circulation part) that forms the ball return path in the nut include a part that has a main body and a leg part and is used by inserting the leg part into a hole that penetrates the nut in the radial direction. Specifically, a synthetic resin circulating part composed of a metal return tube and two divided bodies divided along a line indicating the moving direction of the ball can be mentioned. Moreover, the part which comprises a ball | bowl return path with the hole penetrated to the axial direction of a nut can also be illustrated. Specifically, an end deflector and an end cap are mentioned.

Each of the circulating parts has a tongue for lifting the ball from the rolling path into the ball return path at the end of the rolling path and for guiding the ball from the ball return path to the rolling path at the start point. A tongue is arrange | positioned in a rolling path, and the front-end | tip part of a tongue is arrange | positioned in the spiral groove of a screw shaft. The ball in the rolling path is picked up on the ball return path after colliding with the tongue.
Seals that close the gap between the screw shaft and the nut are attached to both ends of the ball screw nut in the axial direction. Examples of the ball screw seal include a wiper seal and a lip seal. The wiper seal is a substantially cylindrical member made of synthetic resin or rubber, and has an outer peripheral portion which is a fixed portion fixed to the nut, and an inner peripheral portion which is a contact portion in contact with the spiral groove of the screw shaft. The lip seal is a disc-shaped base (fixed part) having a center hole, and a lip part (contact part) made of an elastomer (rubber or thermoplastic elastomer) that contacts the outer peripheral surface of the screw shaft and the spiral groove in an elastically deformed state. Have The lip portion is formed by integrally molding an elastomer on a metal base.

With respect to such a ball screw, methods for detecting abnormalities such as seizure, wear, and damage have been proposed. For example, Patent Document 1 describes that a strain gauge is provided in a circulating part, and vibrations and collision forces generated when a rolling element collides with the circulating part are measured to detect an abnormality in the ball screw.
Patent Document 2 discloses a conventional thermolabel for detecting the temperature of an inner ring, an outer ring, a tapered roller or the like (bearing part) in order to prevent damage to a tapered roller or the like of a sealed rolling bearing device for a railway vehicle axle. Is attached to a front lid, a cage or a bearing box, and an abnormal temperature rise inside the rolling bearing is detected due to discoloration of the thermo label.

Also, because the thermo label is affixed at a position away from the bearing parts and because the thermo label is exposed to the outside, it is cooled while the vehicle is running. It is described that it cannot be said that the temperature rise can be detected sufficiently.
Therefore, in the invention described in Patent Document 2, “temperature detection means for detecting the temperature inside the rolling bearing filled with lubricant and transferring heat toward the outside of the rolling bearing” and “the temperature detection means” And a display means for displaying the temperature of the heat transmitted from the temperature detecting means is provided in the sealed type rolling bearing device.
Thereby, in the invention described in Patent Document 2, the filled lubricant becomes substantially equal to the temperature of the inner ring, the temperature of this lubricant is detected by the temperature detecting means, and the detected temperature is installed outside. Since it is displayed on the displayed display means, it is described that an abnormal temperature rise inside the rolling bearing can be reliably detected and seizure can be prevented.

JP 2013-200032 A JP 11-287251 A

Among the above-described background arts, the method using a thermo label and the method for detecting the temperature of a lubricant have room for improvement in that an abnormal temperature rise inside can be detected quickly. In the method using a strain gauge, there is a problem that it takes time to install the strain gauge and wiring.
An object of the present invention is to provide a ball screw that can quickly determine whether or not an abnormality has occurred inside without installing components or wiring other than components essential to the ball screw.

In order to solve the above problems, a ball screw according to one embodiment of the present invention is characterized by having the following configurations (1) to (3).
(1) It has a screw shaft, a nut, a plurality of balls, and a seal. The axial dimension of the screw shaft is longer than the axial dimension of the nut, and the screw shaft penetrates the nut. A rolling path on which the ball rolls in a loaded state is formed by the spiral groove of the screw shaft and the spiral groove of the nut. The nut has a ball return path for returning the ball from the end point of the rolling path to the start point. The balls are arranged in the rolling path and the ball return path. The seal is a component that closes the gap between the screw shaft and the nut at the axial end of the nut. The nut and the screw shaft move relative to each other via a ball that rolls in a rolling state in the rolling path.
(2) The seal has a fixed portion fixed to the nut and a contact portion in contact with the screw shaft. The contact portion is composed of an elastomer composition containing an inorganic pigment that changes color reversibly with temperature and an elastomer.

The ball screw of this aspect can have the following configuration (3).
(3) It has a heat insulating cover that covers the surface on the axial end side of the nut of the seal. The heat insulating cover is a cover made of a material having low thermal conductivity (for example, 0.20 W / mK or less), and has a transparency that allows the color of the seal to be identified.
With a ball screw, the ball rolls in a loaded state in the rolling path, enters the ball return path from the end of the rolling path, moves in the ball return path, and then returns to the starting point of the rolling path to roll. Repeatedly rolling in the road. Therefore, the ball is the part that has the largest momentum and the largest calorific value among the parts constituting the ball screw.

When an abnormality such as peeling occurs on the spiral groove of the screw shaft, the helical groove of the nut, or the surface of the ball, the momentum of the ball is larger than when no abnormality occurs. Accordingly, the temperature of the ball also becomes higher than when no abnormality has occurred. This temperature rise of the ball is transmitted to the screw shaft and the nut, and is also transmitted to the contact portion of the seal in contact with the screw shaft. In the ball screw of this aspect, since the contact portion of the seal is made of an elastomer composition containing an inorganic pigment that changes color reversibly with temperature and an elastomer, the contact portion of the seal is changed as the temperature of the contact portion of the seal changes. The color changes.
Therefore, in the ball screw of this aspect, it is possible to quickly determine whether or not an abnormality has occurred inside by looking at the color of the contact portion of the seal during operation.
In addition, when the ball screw of this aspect has the configuration (3), the color of the seal is prevented from being changed by the influence of the temperature outside the ball screw.

  ADVANTAGE OF THE INVENTION According to this invention, the ball screw which can determine immediately whether abnormality has generate | occur | produced is provided, without installing components and wiring other than a component essential to a ball screw.

It is a perspective view showing the ball screw of a 1st embodiment, and a ball circulation mechanism is shown by omitting a part of nut. It is sectional drawing which shows the ball screw of 1st Embodiment. It is sectional drawing which shows the ball screw of 2nd Embodiment.

Hereinafter, although embodiment of this invention is described, this invention is not limited to embodiment shown below.
[First Embodiment]
As shown in FIGS. 1 and 2, the ball screw 10 of the first embodiment includes a screw shaft 1, a nut 2, a ball 3, a return tube 4, a seal 5, and a tube presser 6. In FIG. 2, the tube presser 6 is omitted.
The axial dimension of the screw shaft 1 is longer than the axial dimension of the nut 2, and the screw shaft 1 passes through the nut 2. The spiral groove 11 of the screw shaft 1 and the spiral groove 21 of the nut 2 form a rolling path on which the ball 3 rolls in a loaded state. The return tube 4 is a part that forms a ball return path 45 in the nut 2, and includes a main body 41 and both leg portions 42. The ball 3 is disposed in the rolling path and the ball return path 45.

A recess 22 is formed in a part of the outer peripheral surface of the nut 2. A pair of circulation holes 23 that penetrate the nut 2 in the radial direction and a female screw for fastening the fixing bolt of the tube retainer 6 are formed on the outer flat surface 22 a of the nut 2 that is the bottom surface of the recess 22. Concave portions 24 for attaching the seal 5 are formed at both axial ends of the nut 2.
A main body 41 of the return tube 4 is disposed on the outer flat surface 22 a of the nut 2, and each leg portion 42 is inserted into each circulation hole 23. The return tube 4 is fixed to the nut 2 by the tube presser 6.

The seal 5 is a wiper seal formed in a substantially cylindrical shape, and is made of an elastomer composition containing vanadium zirconium yellow powder (an inorganic pigment reversibly discolored by temperature) and an elastomer. The seal 5 includes a fixed portion (outer peripheral portion of the cylindrical member) 51 that fits into the recess 24 of the nut 2, a contact portion (inner peripheral portion of the cylindrical member) 52 that contacts the spiral groove 21 of the screw shaft 2, and Have The gap between the screw shaft 1 and the nut 2 is closed by the seal 5 at both axial ends of the nut 2.
The seal 5 is manufactured by the following method, for example.
Fluororubber pellets, calcium carbonate powder and vanadium zirconium yellow powder are placed in a biaxial kneading extruder at a mass ratio of fluororubber: calcium carbonate: vanadium zirconium yellow = 100: 15: 10, and biaxial kneading extrusion. The machine is operated at a kneading and melting temperature of 210 to 230 ° C. to obtain compound pellets.

Next, the obtained compound pellets, nitrile rubber pellets, and a crosslinking agent (morpholidine sulfide) are compounded in a mass ratio into a compound: nitrile rubber: crosslinking agent = 90: 100: 10. The fluororubber and the nitrile rubber are cross-linked by holding for 30 minutes at a temperature of 120 to 170 ° C. and a pressure of 10.13 MPa to 30.4 MPa. Next, rubber obtained by crosslinking fluororubber and nitrile rubber is put into a granulation extruder to obtain crosslinked rubber pellets.
Next, the obtained pellet is put into a hopper of an injection molding machine to which a mold corresponding to the seal 5 is attached, and the material temperature is 210 to 230 ° C., the mold temperature is 45 to 50 ° C., and the injection pressure is 15 MPa to 20 MPa. Injection molding is performed under the following conditions.
Since the temperature of vanadium zirconium yellow changes in accordance with the change in the temperature of the seal 5, the temperature of the seal 5 at that time can be known from the color of the seal 5. The seal 5 manufactured by this method is white gray at less than 70 ° C. and becomes black gray at 70 ° C. or higher.

In the ball screw of the first embodiment, the temperature rise of the ball 3 is transmitted to the screw shaft 1 and also to the contact portion 52 of the seal 5 that is in contact with the screw shaft 1. The color of the seal 5 changes as described above according to the temperature at that time. When an abnormality occurs in the ball screw, the temperature of the ball 3 is 80 ° C. or higher, and the temperature of the seal 5 is 70 ° C. or higher. Along with this, the temperature of the seal 5 changes from white gray to black gray.
Therefore, according to the ball screw of the first embodiment, it is possible to quickly determine whether or not an abnormality has occurred inside by looking at the color of the seal 5 during operation.

[Second Embodiment]
As shown in FIG. 3, the ball screw 10 of the second embodiment is a transparent heat insulating cover that covers the end surface of the seal 5 (the surface on the axial end portion side of the nut) in the recesses 24 at both axial end portions of the nut 2. 7 is arranged. The rest is the same as the ball screw 10 of the first embodiment.
The heat insulating cover 7 is a disk-shaped member having a center hole 71, and the inner peripheral line of the center hole 71 is located on the radially outer side of the nut 2 with respect to the inner peripheral line of the contact portion 52 of the seal 5. That is, the heat insulating cover 7 does not contact the screw shaft 1.
The heat insulating cover 7 is obtained, for example, by injection molding a polyethylene terephthalate (PET) resin.

In the ball screw of the second embodiment, the temperature rise of the ball 3 is transmitted to the screw shaft 1 and also to the contact portion 52 of the seal 5 that is in contact with the screw shaft 1. The color of the seal 5 changes as described above according to the temperature at that time. When an abnormality occurs in the ball screw, the temperature of the ball 3 is 80 ° C. or higher, and the temperature of the seal 5 is 70 ° C. or higher. Along with this, the temperature of the seal 5 changes from white gray to black gray.
Further, since the seal 5 is covered with the heat insulating cover 7, the temperature of the seal 5 is less affected by the temperature outside the ball screw as compared with the case where the heat insulating cover 7 is not provided.

Therefore, according to the ball screw of the second embodiment, it is possible to quickly determine whether or not an abnormality has occurred inside by looking at the color of the seal 5 via the heat insulating cover 7 during operation. Moreover, the abnormality detection accuracy in a high-temperature usage environment is higher than that of the ball screw of the first embodiment.
The ball screws of the first and second embodiments have a wiper seal as the seal 5, but in the case of a ball screw having a lip seal, the lip portion (contact portion) of the lip seal is reversible depending on the temperature. It is formed of an elastomer composition containing an inorganic pigment that changes color and an elastomer.

[Materials for seals and insulation covers]
The contact portion of the seal constituting the ball screw of the present invention is made of an elastomer composition containing an inorganic pigment reversibly discolored by temperature and an elastomer.
Usable elastomers include synthetic rubbers and thermoplastic elastomers.
Examples of the synthetic rubber include nitrile rubber, hydrogen nitrile rubber, butadiene nitrile rubber, acrylic rubber, silicone rubber, and fluorine rubber.
Examples of the fluororubber include vinylidene fluoride, tetrafluoroethylene-propylene, tetrafluoroethylene-perfluoromethyl vinyl ether, perfluoroether, and fluorosilicone.
The elastomer composition preferably contains a filler or an acid acceptor.

As fillers, fused silica, crystalline silica, alumina, zircon, calcium silicate, calcium carbonate, potassium titanate, silicon carbide, silicon nitride, aluminum nitride, boron nitride, beryllia, zirconia, fosterite, steatite, spinel, mullite And powders such as titania, or beads, glass fibers and the like obtained by spheroidizing these. Examples of the inorganic filler having a flame retardant effect include aluminum hydroxide, magnesium hydroxide, zinc borate, and zinc molybdate.
Examples of inorganic pigments (temperature indicating materials) that reversibly discolor with temperature include vanadium tin yellow, vanadium zirconium yellow, praseodymium yellow, chromium titanium yellow, antimony yellow, and cadmium yellow.

  Examples of the material of the heat insulating cover that covers the seal include AS (acrylonitrile styrene) resin, PC (polycarbonate) resin, PET (polyethylene terephthalate) resin, PMMA (polymethyl methacrylate) resin, and PS (polystyrene) resin. The thermal conductivity of each resin is 0.15-0.16 W / mK for AS resin, 0.19 for PC resin, 0.14 W / mK for PET resin, 0.02-0.03 W / mK for PMMA resin, The PS resin is 0.10 to 0.14 W / mK.

DESCRIPTION OF SYMBOLS 1 Screw shaft 11 Spiral groove of screw shaft 2 Nut 21 Helical groove of nut 22 Recessed part provided in outer peripheral part of nut 22a Outer flat surface of nut 23 A set of two circulation holes penetrating nut in radial direction 24 Female thread 3 Ball 4 Return Tube 41 Return Tube Body 42 Return Tube Leg 45 Ball Return Path 5 Seal 51 Seal Fixing 52 Seal Contact 6 Tube Presser 7 Heat Insulation Cover 71 Center Hole in Heat Insulation Cover 10 Ball Screw

Claims (2)

A screw shaft, a nut, a plurality of balls, and a seal;
The axial dimension of the screw shaft is longer than the axial dimension of the nut,
The screw shaft passes through the nut;
A rolling path in which the ball rolls in a loaded state is formed by the spiral groove of the screw shaft and the spiral groove of the nut,
The nut has a ball return path for returning the ball from the end point of the rolling path to the start point,
The balls are arranged in the rolling path and the ball return path,
The seal is a part that closes a gap between the screw shaft and the nut at an axial end of the nut;
The nut and the screw shaft move relative to each other through the ball that rolls in a loaded state in the rolling path,
The seal has a fixed portion fixed to the nut, and a contact portion in contact with the screw shaft,
The contact portion is a ball screw made of an elastomer composition containing an inorganic pigment reversibly discolored by temperature and an elastomer.   The ball screw according to claim 1, further comprising a heat insulating cover that covers a surface of the seal on the end side in the axial direction of the nut.

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