JP2016109180A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw in which a shearing force acting on a bottom of a rolling groove is reduced, and durability is improved.SOLUTION: A ball screw comprises: a screw shaft in which a spiral shaft rolling groove is formed at an external peripheral face; a nut in which a nut rolling groove opposing the shaft rolling groove is formed at an internal peripheral face; a communication route for connecting the nut rolling grooves; and a plurality of rolling balls which roll in a circulation rolling route constituted of the shaft rolling groove, the nut rolling groove and the communication route. The shaft rolling groove and the nut rolling groove are formed into Gothic arc shapes which are formed by connecting two arcs by a continuous curved line at bottoms of the rolling grooves, hardened layers having substantially the same hardness are formed at an outside diameter face of the screw shaft and the shaft rolling groove, and the hardness of the hardened layer of the shaft rolling groove is made harder than the hardness of the hardened layer of the shaft outside diameter face.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ball screw used for a feed mechanism or a positioning mechanism of a moving body such as a machine tool or a precision machine.

  Conventional ball screws have a uniform hardened layer formed on the surface of the axial rolling groove of the screw shaft by quenching such as carburizing and induction hardening, thereby improving the rolling fatigue life (for example, Patent Documents). 1). In addition, the screw groove of the nut and screw shaft has a Gothic arch shape, the curvature and contact angle of each arc are in the optimal range, and when a large axial load is applied to the ball screw, the ball is the shoulder of the shaft rolling groove The load resistance is improved by preventing the vehicle from climbing on (see, for example, Patent Document 2).

JP 2005-337414 A JP 2010-112399 A

  In recent years, the use of a ball screw with a high load and a high speed is expanding, and a ball screw with a large lead angle is used to operate the ball screw at a high speed. As the lead angle increases, the torsional stress generated in the screw shaft increases, and the shear stress generated in the bottom of the rolling groove also increases. Since the Gothic arc-shaped rolling groove formed on the screw shaft has a very small groove at the bottom, a large lead ball screw has a large shear stress on the very small groove at the bottom of the rolling groove. May occur, which may cause deformation and breakage of the screw shaft.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a ball screw that has a reduced shear stress acting on the bottom of a rolling groove and has improved durability.

  In order to solve the above problems, the present invention provides a screw shaft in which a spiral shaft rolling groove is formed on the outer peripheral surface, and a nut in which a nut rolling groove facing the shaft rolling groove is formed on the inner peripheral surface. A ball screw comprising: a connecting path that connects the nut rolling grooves; and a plurality of rolling balls that roll on a circulating rolling path composed of the shaft rolling groove, the nut rolling groove, and the connecting path. The shaft rolling groove and the nut rolling groove have a Gothic arc shape in which two arcs are connected by a continuous curve at the bottom of the rolling groove, and the outer diameter surface of the screw shaft and the shaft rolling groove are A hardened layer having substantially the same hardness is formed in the moving groove, and the hardened layer of the shaft rolling groove is harder than the hardened layer on the outer surface of the shaft.

  Thereby, even if an excessive axial load acts, this invention can prevent the deformation | transformation and damage of a screw shaft, and can exhibit the outstanding durability and reliability.

Sectional drawing which shows the cross-sectional shape and quenching part of the screw shaft of an Example The perspective view which shows the ball screw of an Example

  Embodiments of a ball screw according to the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing a rolling groove shape and a quenching state of a screw shaft of an embodiment, and FIG. 2 is a perspective view showing a ball screw of the embodiment.
In FIG. 2, 1 is a ball screw.
Reference numeral 2 denotes a screw shaft of the ball screw 1, which is made of a steel material such as alloy steel or carbon steel, and has a substantially semicircular arc-shaped shaft rolling groove 3 formed with a hardened layer 11 to be described later at an equal pitch on the outer peripheral surface 2 a. It is formed in a spiral shape.

Reference numeral 4 denotes a nut of the ball screw 1, which is made of a steel material such as alloy steel or carbon steel, and has a substantially half of which an inner peripheral surface 4 a is formed with a later-described hardened layer 11 having a plurality of pitches facing the shaft rolling groove 3. An arc-shaped nut rolling groove 5 is formed.
Further, the nut 4 is provided with a flat surface 4b cut in parallel with the axial direction thereof, and an outer diameter portion of an end portion of a return tube 7 described later is fitted into a bottom portion of a hole 4c provided in the flat surface 4b. A fitting hole 4d is provided.

Reference numeral 6 denotes a rolling ball, which is a sphere made of a steel material such as an alloy steel or a ceramic material. When the sphere is made of a steel material, a hardened layer is formed on the surface thereof by quenching.
Reference numeral 7 denotes a return tube as a connecting path, which is made of a steel material, a resin material, or the like, and is a tube bent into a substantially U shape having an inner diameter that allows the rolling ball 6 to roll. The ends of the holes 4c are fitted into the fitting holes 4d at the bottom of the provided holes 4c, and the ends on both sides of the nut rolling groove 5 are connected.

Reference numeral 8 denotes a tube fixture, which is a fixture produced by bending a steel material, a resin material, or the like. The return tube 7 is fastened to the nut 4 by fastening the flat surface 4b of the nut 4 with fastening means such as a small screw 9 or the like. Fix it.
Reference numeral 10 denotes a flange portion which is integrally provided on the outer peripheral portion of the nut 4 and is fixed to a moving body (not shown) with a bolt or the like through a bolt hole 10a provided in the flange portion 10.

A circulation rolling path is formed by the shaft rolling groove 3 of the screw shaft 2, the nut rolling groove 5 of the nut 4 opposed to the shaft rolling groove 3, and the inner diameter surface of the return tube 7 connecting the nut rolling groove 5.
In addition, a predetermined amount of lubricant, such as grease, is sealed in the circulating rolling path together with a plurality of rolling balls 6, and the shaft rolling groove 3 and the nut rolling groove 5 are screwed together via the rolling ball 6. Then, by rotating the screw shaft 2 or the nut 4, the rolling ball 6 rolls while circulating through the circulating rolling path, and the nut 4 screwed into the screw shaft 2 is moved in the axial direction.

In FIG. 1, the shaft rolling groove 3 has a Gothic arc shape in which arc-shaped portions 3a and 3a are continuously connected by a curved bottom portion 3b. Reference numeral 11 denotes a hardened layer, which is a hardened layer having a predetermined hardness formed on the screw shaft 2 by induction hardening.
Reference numeral 12 denotes a rolling portion, which is formed on the spiral shaft rolling groove 3 including the contact point between the arcuate portion 3a of the shaft rolling groove 3 and the rolling ball 6 and the periphery thereof, which are contacted at a contact angle α by preload or the like. It is a band-like region along.
The hardened layer 11 is formed on the outer circumferential surface 2a of the screw shaft 2 and the shaft rolling groove 3, and the outer circumferential surface 2a has a hardness of about Hv400 so that the shaft rolling groove 3 has a hardness of about Hv500. The depth of the hardened layer 11 on the rolling part 3 nominal outer peripheral surface 2a is preferably the same thickness, and is 5% or more of the bottom diameter of the rolling groove of the screw shaft 2. Is more preferable.

The operation of the above configuration will be described.
When the screw shaft 2 is manufactured, the shaft material is formed by forming the shaft rolling groove 3 on a round bar made of a steel material such as alloy steel or carbon steel by processing means such as grinding or rolling.

The shaft material was inserted into a cylindrical high-frequency coil, and the high-frequency coil was energized for a predetermined time using a high-frequency power source. The outer peripheral surface 2a of the screw shaft 2 and the shaft rolling groove 3 were heated by induction heating to be red-hot. After that, quenching is performed by quenching with oil or water.
Thereby, as shown in FIG. 1, the hardened layer 11 of uniform hardened layer depth is formed in the shaft rolling groove 3 and the screw shaft outer peripheral surface 2a.

In this way, the screw shaft 2 is manufactured.
The same applies to the nut 4. In this case, a cylindrical high-frequency coil is inserted on the inner peripheral surface 4a side of the nut 4, the inner peripheral surface 4a and the nut rolling surface 5 are induction-heated in the same manner as described above, and subjected to quenching treatment, and the hardened layer 11 is formed. To form.

The screw shaft 2 and / or the nut 4 manufactured in this way is provided with a hardened layer so that when the screw shaft 2 and the nut 4 are screwed together via the rolling ball 6, the preload or the nut 4 is provided. When the rolling ball 6 comes into contact with the shaft rolling groove 3 and the nut rolling groove 5 at a contact angle α due to the thrust force at the time of movement, the rolling ball 6 has sufficient hardness and depth to withstand rolling. Thus, the rolling fatigue life of the ball screw 1 can be maintained by withstanding the load applied to the rolling part 12 as the screw shaft 2 or the nut 4 rotates.
Further, since the shaft rolling groove 3 is a Gothic arc shape in which the arc-shaped portions 3a and 3a are continuously connected by the curved bottom portion 3b, the bottom portion 3b does not have a groove having a very small width as in the prior art. Even if a large torsional stress is generated on the screw shaft 2, it is difficult for stress concentration to occur on the bottom portion 3b, so that deformation and breakage of the screw shaft can be prevented, and load bearing performance can be improved.

  In the present embodiment, it has been described that the hardened layer 11 is formed on the outer peripheral surface 2a and the shaft rolling groove 3 by induction hardening. However, for example, the rolling part 12 is mainly heated by laser heating to perform the quenching process. You may make it perform. The same applies to the nut 4.

In addition, the gothic arc shape of the rolling groove of the present embodiment may be at least formed on the screw shaft, but both the shaft rolling groove 3 and the nut rolling groove 4a may be the gothic arc shape of the present embodiment. In addition, the hardened layer 11 of this embodiment may be formed only on one of the screw shaft 2 and the nut 4 or on both.
As described above, in this embodiment, the shaft rolling groove 3 has a gothic arc shape in which the arc-shaped portions 3a and 3a are continuously connected by the curved bottom portion 3b. Even if stress occurs, it is difficult for stress concentration to occur in the bottom portion 3b, so that deformation and breakage of the screw shaft can be prevented, and load bearing performance can be improved.
Further, in this embodiment, the hardened layer is formed by quenching mainly on the axial rolling groove and the outer peripheral surface portion of the screw shaft, so that the range affected by the heat can be narrowed, and the screw affected by the heat can be reduced. It is possible to prevent changes in the dimensions of the shaft and the occurrence of bending, and it is possible to reduce work steps such as confirmation of bending and correction of bending, thereby shortening the manufacturing time of the screw shaft.

The above effect is the same for the nut.
In this embodiment, the case where the present invention is applied to a ball screw using a tube-type circulation system that circulates rolling balls using a return tube as a connection path has been described as an example. However, the connection path is not limited to the above. Even if the present invention is applied to a circulation type ball screw having a connection path of a top type or an end cap type, the same effect can be obtained.

  Further, the case where the present invention is applied to a ball screw has been described as an example, but the present invention is applied to a rolling groove of a rolling ball of a linear motion guide bearing device that moves a moving table on a rail via a rolling ball. However, the same effect can be obtained.

DESCRIPTION OF SYMBOLS 1 Ball screw 2 Screw shaft 2a Outer peripheral surface 3 Axle rolling groove 3a Arc-shaped part 3b Bottom part 4 Nut 4a Inner peripheral face 4b Plane 4c Hole 4d Fitting hole 5 Nut rolling groove 6 Rolling ball 7 Return tube 8 Tube fixture 9 Small screw 10 Flange part 10a Bolt hole 11 Hardened layer 12 Rolling part 13 Groove bottom part

Claims (1)

  A screw shaft in which a spiral shaft rolling groove is formed on the outer peripheral surface; a nut in which a nut rolling groove facing the shaft rolling groove is formed on the inner peripheral surface; and a connecting path for connecting the nut rolling groove; A ball screw comprising a plurality of rolling balls that roll on a circulating rolling path constituted by the shaft rolling groove, the nut rolling groove, and a connecting path, wherein the shaft rolling groove and the nut rolling The groove has a Gothic arc shape in which two arcs are connected by a continuous curve at the bottom of the rolling groove, and a hardened layer having substantially the same hardness is formed on the outer diameter surface of the screw shaft and the shaft rolling groove. And the hardness of the said hardened layer of the said shaft rolling groove was made harder than the hardness of the hardened layer of the said shaft outer diameter surface, The ball screw characterized by the above-mentioned.

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