JP2012233541A - Sliding surface structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sliding surface structure capable of coping with sliding in many directions, and contributing to improving a fluid lubrication characteristic and a mixing lubrication characteristic.SOLUTION: This sliding surface structure is provided for relatively sliding a sliding surface 1a of a first member 1 and a sliding surface 2a of a second member 2 under a lubricant. A periodic structure part 3 of a grating-shaped recess-projection is arranged on at least any one sliding surface of the first member 1 and the second member 2. This periodic structure part is formed in a line symmetry shape to the expected sliding direction, and pulls the lubricant in a sliding surface central part by relative sliding of the sliding surfaces 1a and 2a.

Description

  The present invention relates to a sliding surface structure.

  It is known that a grating-like periodic structure with a submicron periodic pitch and groove depth has high load capacity and rigidity. For this reason, such a grating-like periodic structure has been used for a reciprocating sliding structure and a rotating sliding structure. However, what uses a grating-like periodic structure has been limited to reciprocation in one axis direction and rotational movement around one axis.

  By the way, there are many sliding directions in an artificial hip joint or the like, and a static load state occurs irregularly. Therefore, even if ringing (contact) occurs and the static load state is released, the contact state may continue and the fluid lubricating film may not recover. Moreover, the ringing causes squeak noise and wear. For this reason, creation of a functional surface having a fluid lubricating film forming function with a minute clearance is desired.

  Conventionally, a sliding surface structure used for a sliding contact surface structure in an artificial hip joint has been proposed (Patent Document 1). In this sliding surface structure, there is one in which a concave and convex pattern is formed by providing a plurality of concave portions on a sliding surface of a base material that is in sliding contact with other members. In this case, the arrangement pitch of the recesses, the depth of the recesses, the area ratio of the recesses to the entire sliding surface, the diameter in terms of a circle, the material, and the like are limited.

  By limiting these various parameters, the effects such as "the supply of lubricant from the recesses and the prevention of abrasive wear due to the escape of wear powder into the recesses will improve the wear resistance and seizure resistance", etc. It is supposed to play.

Japanese Patent No. 3590992

  When configured as described in Patent Document 1, the concave portion (dimple) generates equal pressure in a narrow region. At this time, only the positive pressure part contributes to the load capacity due to the occurrence of cavitation. However, since the positive pressure generation region is narrow, only a slight pressure increase can be obtained. For this reason, the dynamic pressure generation effect is small, and the oil sump effect contributes to the mixed lubrication characteristics, but hardly contributes to the fluid lubrication characteristics.

  In view of the above problems, the present invention provides a sliding surface structure that can cope with multi-directional sliding and contributes to improvement of fluid lubrication characteristics and mixed lubrication characteristics.

  The sliding surface structure of the present invention is a sliding surface structure in which the sliding surface of the first member and the sliding surface of the second member slide relative to each other under a lubricant. At least one of the sliding surfaces of the member has a shape symmetrical with respect to a predetermined sliding direction, and the lubricant is drawn into the center of the sliding surface by relative sliding of the sliding surface. A periodic structure having grating-like irregularities is provided.

According to the sliding surface structure of the present invention, since the periodic structure portion has a line-symmetric shape with respect to the planned sliding direction, it can perform a sliding motion in all the planned sliding directions. Such a periodic structure has high load capacity and rigidity. In addition, the load capacity can be increased by obtaining the fluid introduction effect of drawing the lubricant into the center of the sliding surface. That is, the increase in load capacity due to the fluid introduction effect is larger than the decrease in the Rayleigh step effect.
For this reason, it is possible to improve the fluid lubrication characteristics and the mixed lubrication characteristics, and it is possible to obtain a large dynamic pressure without causing rolling in all planned sliding directions. Here, the planned sliding direction may be a uniaxial direction in a plan view or two or more multiaxial directions.

  The periodic structure portion can be set to have a fine groove structure composed of a plurality of fine grooves extending radially from the center of the sliding surface. By setting in this way, the fluid introduction function to the center part of the sliding surface can be exhibited stably.

  The central portion of the sliding surface can be a non-grooved portion that does not constitute the periodic structure portion, and the central portion of the sliding surface can be a line-symmetric shape with respect to a predetermined sliding direction line. .

  The periodic pitch of the periodic structure portion is preferably 10 μm or less, and the depth of the concave portion of the periodic structure portion is preferably 1 μm or less.

  The periodic structure portion is preferably formed in a self-organized manner by irradiating a linearly polarized laser beam with an irradiation intensity in the vicinity of the processing threshold, and scanning while overlapping the irradiated portion.

  With the sliding surface structure of the present invention, it is possible to obtain a large dynamic pressure without causing rolling in all planned sliding directions, exhibiting a fluid introduction effect against multi-directional sliding, and low friction. Can be obtained. For this reason, such a sliding surface structure can be used for an artificial hip joint, for example. That is, the cup of the artificial hip joint can be used as the first member of the present invention, and the bone head of the artificial hip joint can be used as the second member. In such a case, the inner diameter surface of the cup and the outer diameter surface of the bone head are pressed, and the inner diameter surface of the cup portion becomes the sliding surface, and the outer diameter surface of the bone head becomes the sliding surface. Therefore, if the sliding surface structure of the present invention is used for an artificial hip joint, it has a fluid lubrication film forming function with a minute clearance, so that the occurrence of ringing can be suppressed and the occurrence of squeak noise based on ringing or Wear can be effectively prevented. For this reason, a stable hip joint can be formed as an artificial hip joint over a long period of time.

  If the fine groove structure is composed of a plurality of fine grooves extending radially from the center of the sliding surface, a large dynamic pressure can be obtained efficiently and the lubricity is excellent. Moreover, if the center part of the sliding surface is a groove-unformed part, the load capacity can be further increased, and excellent lubricity can be exhibited stably.

  If the central part of the sliding surface is symmetrical with respect to the planned sliding direction line, a large dynamic pressure can be stably obtained without causing rolling in all the planned sliding directions. it can.

  When the concavo-convex pitch of the periodic structure portion is 10 μm or less, the leakage of the lubricant (side leakage) can be suppressed redundantly, and the dynamic pressure can be obtained efficiently. When the depth of the concave portion of the periodic structure portion is 1 μm or less, variation in the flying height when dynamic pressure is generated can be reduced, which contributes to improvement in rigidity.

  The periodic structure is irradiated with a linearly polarized laser beam with an irradiation intensity in the vicinity of the processing threshold, scanned while overlapping the irradiated part, and formed by self-organization. Those having a pitch and a depth of unevenness can be easily formed. By adopting such a submicron periodic structure, the fluid lubrication effect is effectively exhibited up to a narrow part of the gap in the mixed lubrication.

It is a simplified diagram of a sliding surface structure showing an embodiment of the present invention. The sliding surface of the 2nd member of the sliding surface structure shown in the said FIG. 1 is shown, (a) is a simplified view of the sliding surface which has a 1st periodic structure part, (b) is a 2nd periodic structure. It is a simplification figure of the sliding surface which has a part. It is an enlarged view of the periodic structure part formed in the said sliding surface. It is a simplification of the sliding surface of the other 2nd member of a sliding surface structure. It is a simplified view of the sliding surface of another second member having a sliding surface structure. It is a simplification figure of the laser surface processing apparatus for forming the said periodic structure part. The sliding surface of the 2nd member of the sliding surface structure used in Example 1 is shown, (a) is a simplified diagram in the case of having a periodic structure portion, and (b) is the case of having no periodic structure portion. It is a simplified diagram. It is a graph which shows the relationship between the load obtained in Example 1, and a friction coefficient. 6 is a simplified diagram of a sliding surface of a second member having a sliding surface structure used in Example 2. FIG. The comparative piece used in Example 2 is shown, (a) is a bottom view, (b) is a front view. It is a graph which shows the relationship between the smooth part length obtained in Example 2, and load capacity.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the sliding surface structure slides relatively under a lubricant taken by the sliding surface 1 a of the first member 1 and the sliding surface 2 a of the second member 2. The first member 1 is a flat plate, and the second member 2 is a flat plate. In this case, the first member 1 and the second member 2 may be carbon steel, copper, aluminum, platinum, cemented carbide, silicon ceramics such as silicon carbide or silicon nitride, engineer plastic, etc. It may be. Also, the lubricant may be water or alcohol, or may be a lubricating oil such as engine oil. That is, various lubricants can be used depending on the material of the first and second members 1 and 2 and the environment in which they are used.

  The upper surface of the first member 1 becomes the sliding surface 1a, and the lower surface of the second member 2 becomes the sliding surface 2a. A grating-like irregular periodic structure 3 as shown in FIG. 2 is provided on the sliding surface 2 a of the second member 2. This periodic structure portion 3 is provided in a rectangular ring range on the outer peripheral side, leaving a square land portion (groove-unformed portion) 4 of the sliding surface 2a.

  As shown in FIG. 3, the periodic structure portion 3 is formed by alternately arranging minute concave portions 5 and minute convex portions 6 at a predetermined pitch. It is preferable that the irregular pitch of the periodic structure portion 3 is 10 μm or less and the depth of the concave portion 5 is 1 μm or less. In this case, the concave portion 5 of the periodic structure portion 3 is opened at the outer peripheral edge of the sliding surface 2 a of the second member 2.

  The periodic structure part 3 is formed so as to have a line-symmetric shape with respect to a predetermined sliding direction. That is, the periodic structure portion 3 shown in FIG. 2 (a) has a fine groove structure constituted by a plurality of fine grooves (recess portions 5) extending radially from the center portion of the sliding surface, excluding the land portion 4. Consists of. In FIG. 2A, since the groove-unformed portion 4 is square, it is optimal for sliding in two directions in the X and Y axis directions orthogonal to each other. In such two-direction sliding in the X-axis direction and the Y-axis direction, the periodic structure may be as shown in FIG. That is, in FIG. 2B, the grooves are arranged so as to be orthogonal to the outer side from the respective sides of the groove-unformed portion 4, and are arranged radially from the corner portion of the groove-unformed portion 4.

  The periodic structure portion 3 is formed in a self-organized manner by irradiating a linearly polarized laser beam with an irradiation intensity in the vicinity of the processing threshold and scanning the overlapping portions in an overlapping manner. Specifically, the femtosecond laser surface processing apparatus shown in FIG. 6 is used. A laser (eg, pulse width: 120 fs, center wavelength: 800 nm, repetition frequency: 1 kHz, pulse energy: 0.25 to 400 μJ / pulse) generated by a laser generator 11 (titanium sapphire femtosecond laser generator) is reflected by a mirror 12. It is folded back toward the work material W and guided to the mechanical shutter 13. At the time of laser irradiation, the mechanical shutter 13 is opened, the laser irradiation intensity can be adjusted by the half-wave plate 14 and the polarization beam splitter 16, the polarization direction is adjusted by the half-wave plate 15, and the condenser lens (focal length) : 150 mm) 17, the surface of the work material W on the XYθ stage 19 is condensed and irradiated. A femtosecond laser is a light source that compresses energy in an extremely short time unit of 1/1000 trillion seconds.

  That is, when a workpiece (working material) W is irradiated with a linearly polarized laser beam at a fluence near the ablation threshold, the pitch and grooves on the order of wavelengths are caused by interference between incident light and scattered light or plasma waves along the surface of the processing material W. A grating-like periodic structure having a depth is formed in a self-organizing manner perpendicular to the polarization direction. At this time, the periodic structure can be expanded over a wide range by scanning the femtosecond lasers while overlapping them.

  Laser scanning may be performed by moving the XYθ stage 19 that supports the processing material W while fixing the laser, or may move the laser while fixing the XYθ stage 19. Alternatively, the laser and the XYθ stage 19 may be moved simultaneously. In addition, the said FIG. 3 is the figure which imaged the periodic structure part 3 formed with the said femtosecond laser surface processing apparatus with the electron microscope.

  In the sliding surface structure of the present invention, the periodic structure part 3 has a line-symmetric shape with respect to the planned sliding direction, so that it can perform a sliding motion in all the planned sliding directions, Such a periodic structure part 3 has high load capability and rigidity. Moreover, the load capacity can be increased by obtaining the fluid introduction effect of drawing the lubricant into the sliding surface central portion 4. For this reason, it is possible to improve the fluid lubrication characteristics and the mixed lubrication characteristics, and it is possible to obtain a large dynamic pressure without causing rolling in all planned sliding directions. In the example shown in FIG. 1, the first member 1 is fixed and the second member 2 is reciprocated with respect to the first member 1 as indicated by an arrow X.

  For this reason, such a sliding surface structure can be used for an artificial hip joint, for example. That is, the cup of the artificial hip joint can be used as the first member 1 of the present invention, and the bone head of the artificial hip joint can be used as the second member 2. In such a case, the inner diameter surface of the cup and the outer diameter surface of the bone head are in pressure contact, the inner diameter surface of the cup portion becomes the sliding surface 1a, and the outer diameter surface of the bone head defines the periodic structure portion 3. It becomes the sliding surface 2a which has. Therefore, if the sliding surface structure of the present invention is used for an artificial hip joint, it has a fluid lubrication film forming function with a minute clearance, so that the occurrence of ringing can be suppressed and the occurrence of squeak noise based on ringing or Wear can be effectively prevented. For this reason, a stable hip joint can be formed as an artificial hip joint over a long period of time.

  If the fine groove structure is composed of a plurality of fine grooves (recesses 5) extending radially from the center of the sliding surface, a large dynamic pressure can be obtained efficiently and the lubricity is excellent. Further, if the central portion of the sliding surface is the groove-unformed portion 4, the load capacity can be further increased, and excellent lubricity can be exhibited stably.

  If the central part of the sliding surface is symmetrical with respect to the planned sliding direction line, a large dynamic pressure can be stably obtained without causing rolling in all the planned sliding directions. it can.

  When the concavo-convex pitch of the periodic structure portion 3 is set to 10 μm or less, the leakage of the lubricant (side leakage) can be suppressed redundantly, and the dynamic pressure can be obtained efficiently. When the depth of the concave portion 5 of the periodic structure portion 3 is 1 μm or less, variation in the flying height when dynamic pressure is generated can be reduced, which contributes to improvement in rigidity. In particular, even in the mixed lubrication state, the fluid lubrication effect can be exhibited in a partly narrow (1 μm or less) gap region.

  The periodic structure unit 3 is irradiated with a linearly polarized laser beam with an irradiation intensity in the vicinity of the processing threshold, scanned while overlapping the irradiation part, and formed by self-organization. Those having a periodic pitch and uneven depth can be easily formed. By adopting such a submicron periodic structure, the fluid lubrication effect is effectively exhibited up to a narrow part of the gap in the mixed lubrication.

  In the sliding surface 2 a shown in FIG. 4, the land portion (the central portion of the sliding surface and not forming the periodic structure portion) 4 has a circular shape. Moreover, in FIG. 5, it is set as the short cylindrical body of the 2nd member 2, and the land part 4 is made into circular shape.

  For this reason, even if it is the sliding surface 2a of the 2nd member 2 shown in FIG.4 and FIG.5, there exists an effect similar to the sliding surface 2a of the 2nd member 2 shown in the said FIG. In particular, as shown in FIG. 4 and FIG. 5 and the like, if the groove-unformed portion 4 is circular and the periodic direction of the periodic structure portion 4 is arranged radially, it is not limited to the biaxial direction, It can cope with sliding in multiple directions.

  As mentioned above, although it demonstrated per embodiment of this invention, this invention is not limited to the said embodiment, A various deformation | transformation is possible, for example, in the said embodiment, the periodic structure part 3 is the 1st member 1 side. It may be formed on both sides of the first member 1 and the second member 2. Further, the shape of the groove-unformed portion 4 at the center of the sliding surface is not limited to the square as shown in FIG. 2 or the circle as shown in FIG. For example, it may be a regular hexagon or a regular octagon. The shapes of the first member 1 and the second member 2 are not limited to those shown in the drawings, and may be configured in other various shapes.

  The size, arrangement pitch, and the like of the periodic structure portion 3 can be variously changed according to the size, material, lubricant type, sliding speed, and the like of the first and second members to be used.

  In the above embodiment, the relative sliding movement of the first member 1 and the second member 2 is such that the first member 1 is fixed and the second member 2 is reciprocated, that is, the periodic structure portion 3 is formed. However, the second member 2 side may be fixed and the first member side may be slid. That is, you may slide the direction in which the periodic structure part 3 is not formed. Further, both the first member 1 and the second member 2 may be slid.

  According to the sliding surface structure of the present invention, a low friction can be obtained by exhibiting a fluid introduction effect against multi-directional sliding. For this reason, the sliding surface structure of the present invention is not limited to an artificial hip joint, but can be used for various devices such as a spherical bearing, various micromachines, optical components, and a micro object trap.

  Using the second member 2 (test piece A) having the sliding surface 2a as shown in FIG. 7A, the relationship between the load and the friction coefficient was examined. As the test piece A, the material is SUS440C, the sliding surface diameter D is 5 mm, and the outer peripheral side of the sliding surface 2a is a grating-like shape having a periodic interval of about 700 nm and an unevenness depth (recessed portion depth) of about 200 nm. The periodic structure part 3 was formed. The width (radial width) E of the periodic structure portion 3 was set to about 0.5 mm. (Since the periodic structure forming portion is φ4 mm to φ5 mm, E is 0.5 mm.) Further, as the first member 1 to be used, a flat plate body as shown in FIG. 1 is used. The flat plate body as the first member 1 is made of SUS440C as is the material of the test piece. The surface roughness of the sliding surface 1a of the first member 1 and the sliding surface 2a of the test piece A was Ra 0.02 μm. As the lubricant, PAO6 having no polarity and being thermally and chemically stable was used.

  Further, a comparative piece A1 (see FIG. 7B) having no periodic structure portion 3 on the sliding surface 2a was manufactured. This comparison piece A1 was also SUS440C, its outer diameter D1 was 5 mm, and the surface roughness of the sliding surface 2a1 was Ra 0.02 μm. The periodic structure portion 3 of the test piece A was formed using the femtosecond laser surface processing apparatus shown in FIG. That is, it is formed in a self-organized manner by irradiating the material surface with a linearly polarized femtosecond laser at an energy density near the processing threshold. And the direction of a periodic structure is made radial so that it can respond to multi-directional slip.

  And as a test, as shown in FIG. 1, the test piece A (2nd member 2) and the comparison piece A1 were reciprocated in the arrow X direction in the range of 6 mm in 1 linear direction, respectively. At this time, the sliding speed was 4 mm / s, and the load was increased stepwise from 1N to 50N.

  The test results are shown in the graph of FIG. In FIG. 8, the horizontal axis is the load (N), and the vertical axis is the friction coefficient. A black circle in FIG. 8 indicates the test piece A having a periodic structure portion, and a white circle in FIG. 8 indicates the comparison piece A1 having no periodic structure. In FIG. 8, in the test piece A, this test piece is called a periodic structure, and this comparison piece A1 is called a mirror surface.

  As can be seen from FIG. 8, it can be seen that the test piece A has a lower coefficient of friction than the comparative piece A1 under each load condition. That is, the test piece A slides more smoothly than the comparison piece A1.

  The relationship between the load capacity and the size of the land portion (groove-unformed portion) 4 was examined. As the test piece B in this case, as shown in FIG. 9, the sliding surface 2a is a square having a side S of 5 mm in length, and the periodic structure portion 3 along each side is provided on the outer periphery thereof. is there. Further, the non-grooved portion 4 is square, and the length L of one side of the non-grooved portion (smooth portion) 4 is changed from 0 mm to 5 mm as shown in the graph of FIG.

  Further, as the comparison piece B1, as shown in FIG. 10, the height from the sliding surface 2a1 to the position corresponding to the non-grooved portion (smooth portion) 4 is set on the sliding surface 2a having a side length S1 of 5 mm. A bulging portion 50 having a thickness T of 200 nm is formed. The length L1 of one side of the bulging portion 50 was changed from 0 to 5 mm.

  The load capacity of the test piece B was calculated according to the infinite groove number theory as an oil film thickness of 200 nm, a hill groove ratio of 0.5, a periodic structure depth of 200 nm, a viscosity of 31.28 cp, and a sliding speed of 50 mm / s. Further, the load capacity of the comparison piece B1 was calculated under the same conditions as the calculation of the load capacity of the test piece B.

  The calculation results are shown in the graph of FIG. In FIG. 11, a solid line shows the test piece B, and a broken line shows the comparison piece B1. In FIG. 11, the test piece B is called a periodic structure, and the comparison piece B1 is called a uniform step.

  As can be seen from FIG. 11, with the test piece B, a load capacity 1.4 times that of the comparison piece B1 was obtained. Although the Rayleigh step effect is reduced by providing the periodic structure portion 3 in the test piece B, a fluid introduction effect for drawing the fluid into the central portion is newly generated. That is, the load capacity of the test piece B is increased because the increase in the load capacity due to the fluid introduction effect is larger than the decrease in the Rayleigh step effect.

  By this test, as in the test piece B, the one in which the groove non-formed part 4 is formed in the center part of the sliding surface and the periodic structure part 3 is formed in the outer peripheral part can obtain a large load capacity. In particular, when one side has a square sliding surface 2a of 5 mm, the maximum load capacity can be obtained by making the groove-unformed portion (smooth part) 4 a square having a side of about 2 mm.

1a Sliding surface 1 First member 2a Sliding surface 2 Second member 3 Periodic structure portion 4 Groove not formed portion (land portion)
5 recess

Claims (7)

  A sliding surface structure in which the sliding surface of the first member and the sliding surface of the second member slide relative to each other under a lubricant, the sliding surface of at least one of the first member and the second member. The moving surface has a symmetrical structure with respect to the expected sliding direction and a periodic structure with grating-like irregularities that draws the lubricant into the center of the sliding surface by relative sliding of the sliding surface. A sliding surface structure characterized by that.   2. The sliding surface structure according to claim 1, wherein the periodic structure portion has a fine groove structure including a plurality of fine grooves extending radially around a central portion of the sliding surface.   The sliding surface structure according to claim 1 or 2, wherein a central portion of the sliding surface is a non-grooved portion that does not constitute a periodic structure portion.   The sliding surface structure according to any one of claims 1 to 3, wherein the central portion of the sliding surface has a line-symmetric shape with respect to a predetermined sliding direction line.   The sliding surface structure according to any one of claims 1 to 4, wherein a periodic pitch of the periodic structure portion is 10 µm or less.   The sliding surface structure according to any one of claims 1 to 5, wherein a depth of the concave portion of the periodic structure portion is 1 µm or less.   The periodic structure part is formed in a self-organized manner by irradiating a linearly polarized laser beam with an irradiation intensity in the vicinity of a processing threshold and scanning the overlapping part in an overlapping manner. The sliding surface structure according to claim 6.