JP2015068330A - Slide member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slide member in which frictional loss is reduced by specifying the element of a dimple required for reduction in frictional loss.SOLUTION: In a slide member 1 including a first member 10 and a second member 20 arranged so as to slide to each other, countless dimples 13 are substantially evenly provided on a first slide surface 11 of the first member 10. A dimple area percentage to be the ratio of the total area of the opening parts of the dimples 13 is 5-50%, and an aspect ratio to be the ratio of a depth H to a diameter (opening diameter) D of the dimple 13 is 0.5-4.5%.

Description

  The present invention relates to a sliding member in which a plurality of fine depressions called micro dimples are formed on a sliding surface.

It has been studied to reduce the friction loss of equipment by forming a fine depression (hereinafter referred to as dimple) on the sliding surface. The technique for providing the dimples is mainly intended to hold the necessary lubricating oil between the opposed sliding surfaces.
For example, Patent Document 1 provides a dimple area ratio that is a ratio of a total area of dimple openings, and dimples are provided substantially uniformly over a whole area or a certain region of at least one sliding surface of a pair of sliding members. It is proposed to be in the range of 5-50%. According to this proposal, when a load is applied to the sliding surface, the lubricating oil held by the dimple under the surface pressure oozes out to a flat portion other than the dimple, thereby generating an oil film on the sliding surface. It is supposed to be promoted. In addition, by setting the depth of the dimple in the range of 0.5 to 3.0 μm, it is possible to maintain a good degree of oozing of the lubricating oil to the sliding surface and to promote the formation of an oil film. Says.

Patent Document 2 proposes that the sliding surface is divided into a first region and a second region, and the depth and the aperture ratio (area ratio) of each dimple are set as follows. The proposal of Patent Document 2 is intended to divide into areas where the lubrication conditions are severe depending on the sliding conditions and areas where the lubrication conditions are not, and to set the dimple specifications according to each area.
1st area | region: Depth; 1-3 micrometers area ratio; 10-25%
2nd area | region: Depth; 3-12 micrometers Area ratio; 20-50%

JP 2011-21597 A International Publication 2013-5394

Various proposals have been made for dimples, including Patent Document 1 and Patent Document 2, but the relationship between dimple specifications and friction loss is still unclear because it may depend on sliding conditions and lubrication conditions. Often not.
Therefore, an object of the present invention is to provide a sliding member in which the friction loss is reduced by specifying the dimple specifications necessary for reducing the friction loss.

For this purpose, the present inventors examined the specifications of the dimples, and found that in addition to the dimple opening area ratio, the aspect ratio defined by the ratio of the dimple depth and the opening diameter greatly affects the friction coefficient. I found out.
That is, the present invention is a sliding member in which a plurality of dimples are provided substantially uniformly in a predetermined region of the sliding surface, and the sum of the opening areas A _d of the plurality of dimples with respect to the area A ₀ of the predetermined region. The dimple area ratio as a ratio is 5 to 50%, and the aspect ratio as a ratio of the dimple depth H to the dimple opening diameter D is 1 to 4.5%.

In the sliding member of the present invention, the dimple depth is preferably 15 μm or less.
Depending on the method of forming the dimple, when the dimple is deepened, burr due to burrs and bulges is likely to occur around the dimple, and this burr acts to increase the frictional resistance. Although this burr can be removed by polishing, it may be required to use a sliding member without polishing. Therefore, the present invention preferably limits the depth of the dimple to 15 μm or less. According to the study by the present inventors, even when the depth of the dimple is 15 μm or less, the necessary lubricating oil can be held and the ability to supply the lubricating oil to the sliding surface can be secured.

In the sliding member of the present invention, one of the pair of sliding members may be stationary and the other may move. In this case, it is preferable to form dimples on the moving sliding member.
This is because it is advantageous for replacement of the lubricating oil contained in the dimple.

In the sliding member of the present invention, the wear-resistant coating may be applied only to one sliding surface. In this case, the wear-resistant coating is applied only to the sliding surface on which no dimple is formed. Preferably it is applied.
When coating is applied to the sliding member not provided with dimples, the burr around the dimple of the mating sliding member can be eliminated relatively quickly due to friction, and the familiarity between the sliding surfaces is improved.

  According to the present invention, a sliding member that can keep the coefficient of friction low is provided by setting the dimple area ratio to 5 to 50% and the aspect ratio to 1 to 4.5%.

It is a figure which shows the structure of the sliding member in this embodiment. It is a figure which shows the various examples of the dimple in this embodiment. In this embodiment, it is a figure which shows the example which provides a dimple in the moving sliding member. In this embodiment, it is a figure for demonstrating the effect which gives a coating. It is a table which shows the specification of the rotation test piece used in the Example. It is the evaluation result obtained in the Example, and is a graph showing the coefficient of friction by the size of the bubble on the coordinates with the dimple area ratio on the horizontal axis and the aspect ratio on the vertical axis. It is the evaluation result obtained in the Example, (a) is a graph which shows the relationship between the dimple area ratio of a dimple, and a friction coefficient, (b) is a graph which shows the relationship between an aspect ratio and a friction coefficient.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
The sliding member 1 according to the present embodiment includes a first member 10 and a second member 20.
The sliding member 1 is applied to sliding portions existing in various machine elements. Therefore, although the sliding member 1 having a simple shape is shown here, the sliding member has a shape corresponding to a machine element actually used.
The first member 10 and the second member 20 include a first sliding surface 11 and a second sliding surface 21, respectively. The first member 10 and the second member 20 move relatively with the first sliding surface 11 and the second sliding surface 21 in contact with each other. Lubricating oil is interposed between the first sliding surface 11 and the second sliding surface 21. The relative movement here means that the first member 10 moves while the second member 20 remains stationary, the first member 10 moves while the second member 20 remains stationary, and the first It includes three forms of both the member 10 and the second member moving. The movement here is not limited to a linear movement but includes, for example, a curved movement and a rotational movement.

The sliding member 1 according to the present embodiment has a plurality of dimples 13 formed in the entire region of the first sliding surface 11 of the first member 10. In the present embodiment, the plurality of dimples 13 have the same shape and dimensions within a range described later. It has been studied that texturing is performed on the sliding surface, not limited to the plurality of dimples 13, to bring out the function of the lubricating oil present on the sliding surface. In this embodiment, the friction coefficient between the first sliding surface 11 and the second sliding surface 21 is kept low by setting the dimple area ratio and the aspect ratio of the dimple 13 within a specific range.
First, the dimple area ratio will be described with reference to FIG.
The sliding member 1 of the present embodiment has a dimple area ratio R1 of 5 to 50%. This is because the coefficient of friction can be kept low in this range as shown in the examples described later. The reason why the coefficient of friction is small when the dimple area ratio R1 is in the range of 5 to 50% is not clear, but if it is less than 5%, the amount of the dimple 13 is insufficient and the effect of forming the dimple 13 is insufficient. On the other hand, when the dimple area ratio R1 exceeds 50%, the area of the sliding surface 11 excluding the dimple 13 is reduced, and the contact pressure with the sliding surface 21 is increased accordingly, and the frictional force is increased. . The dimple area ratio R1 is preferably 10 to 45%, more preferably 15 to 40%. The dimple area ratio A can be adjusted when the dimple 13 is formed. This adjustment method will be described together with the adjustment of the aspect ratio R2 in the description of the method for forming the dimple 13 described later.

Dimple area ratio R1 as the ratio of the sum _{A d} of the opening areas of the dimples 13 to the surface area _{A o} of the first sliding surface 11 is defined by the following equation (1). The surface area A _o is the surface area of the entire area of the first sliding surface 11, and the opening area _Ad is the area of the opening portion connected to the first sliding surface 11 of each dimple 13 by the number of all the dimples 13. The total area. This embodiment, since all of the dimples 13 has the same size, shape, the opening area of one dimple 13 and ad, when the number of the dimples 13, n, A _d is represented by ad × n The
R1 = Ad / Ao × 100 (1)

Next, the aspect ratio R2 will be described with reference to FIG.
The sliding member 1 has an aspect ratio R2 of 1.0 to 4.5%. This is because, similarly to the dimple area ratio R1, the friction coefficient can be kept low in this range. The aspect ratio R2 is preferably 1.0 to 3.0%, more preferably 1.0 to 2.5%.
The aspect ratio R2 is defined by the following formula (2) as the ratio of the depth H of the dimple 13 to the diameter (opening diameter) D of the dimple 13. This embodiment is based on the premise that all the dimples 13 have the same shape and dimensions. However, since the dimples 13 obtained in the actual forming process may have slight differences in shape and dimensions, the aspect ratio R2 is 1. Whether it is included in the range of 0 to 4.5% may need to be determined by determining the aspect ratio R2 for the plurality of dimples 13 in some cases.
R2 = H / D × 100 (2)

Next, various forms of the dimple 13 will be described with reference to FIGS. 1 and 2.
The dimples 13 are formed uniformly distributed on the first sliding surface 11. Uniformity here refers to allowing an error that occurs when the dimple 13 is formed on an industrial production scale, and includes a category called substantially uniform.

In the example of FIG. 1, the dimple 13 is formed over the entire area of the first sliding surface 11, but as shown in FIG. 2A, the dimple 13 is surrounded by a specific part (broken line). ) Only. For example, when only a specific part has a severe load condition due to friction, the dimple 13 is provided only in the specific part in order to improve the lubricating performance of the specific part. When providing the dimples 13 only to a particular site, the area in the particular site is identified in accordance with equation (1) above as A _0.
The dimples 13 are arranged in a lattice pattern in the example of FIG. 1, but can also be arranged in a staggered pattern as shown in FIG.
The dimple 13 has the same size in the example of FIG. 1, but as shown in FIG. 2C, the dimple area ratio R1 and the aspect ratio R2 have different dimensions within the scope of the present invention. The dimples 13 can also be formed together.
Further, in the example of FIG. 1, the dimple 13 is drawn as a hemispherical shape for easy understanding, but the cross-sectional shape of the dimple 13 changes depending on the aspect ratio R2. Further, the opening shape of the dimple 13 is circular in the example of FIG. 1, but may be other shapes such as an ellipse or a polygon.

As described above, the sliding member 1 may have one of the first member 10 and the second member 20 moving and the other stationary. In addition, the sliding surfaces between the moving member and the stationary member partially coincide, but one member may not slide with the other member. In this case, it is preferable to form the dimple 13 on the moving member 10. The reason will be described with reference to FIG.
As shown in FIG. 3A, the stationary side is the first member 10, the moving (black arrow) side is the second member 20, and the dimple 13 is provided on the second member 20. The second member 20 has regions that do not slide with the first member 10 at both ends in the drawing. In the second member 20 provided with the dimples 13, the lubricating oil O is supplied from other than the sliding surface with the first member 10, so that cooling of the sliding surface is expected. In addition, the lubricating oil O that has been held in the dimple 13 until then is discharged from the sliding surface between the dimple 13 and the first member 10 and then discharged to the outside. This also is expected to cool the sliding surface. Further, along with the discharge of the lubricating oil O, the wear powder generated on the sliding surface can be discharged out of the sliding surface.
On the other hand, as shown in FIG. 3B, when the dimple 13 is formed on the stationary first member 10, the lubricating oil O tends to stay inside the dimple 13. Easy to rise.

  Next, the sliding member 1 can apply a wear-resistant coating to one or both of the first sliding surface 11 of the first member 10 and the second sliding surface 21 of the second member 20. In the sliding member 1, lubricating oil is interposed between the first sliding surface 11 and the second sliding surface 21, and the lubrication state in the sliding member 1 is a fluid lubrication region, a mixed lubrication region, and a boundary lubrication region. It is divided into three. In the fluid lubrication region, the first sliding surface 11 and the second sliding surface 21 are separated by a lubricating oil film. In the mixed lubrication region and the boundary lubrication region, particularly in the boundary lubrication region, the first sliding surface 11 and the second sliding surface 21 are separated. The two sliding surfaces 21 are in direct contact with each other. The wear-resistant coating is composed of a material having a hardness higher than that of the material constituting the first member 10 and the second member 20 in order to mainly correspond to the boundary lubrication region.

  The coating can be provided on at least one of the first member 10 and the second member 20. However, in the sliding member 1 on which the dimple 13 is formed, it is preferable to form a wear-resistant coating on the second member 20 rather than the first member 10 on which the dimple 13 is formed. Hereinafter, this reason will be described with reference to FIG.

FIG. 4A shows an example (case A) in which a wear-resistant coating 25 is formed on the second member 20 where the dimples 13 are not formed. The dimple 13 is formed on the first member 10, and a burr 17 is generated around the dimple 13.
On the other hand, FIG. 4B shows an example (case B) in which the wear-resistant coating 15 is formed on the first member 10 on which the dimples 13 are formed. The coating 15 is also formed on the surface of the burr 17 and protrudes locally.

In case A, when the first member 10 and the second member 20 are in direct contact with each other in the boundary lubrication region, the coating 25 is harder than the burr 17 and therefore the coating 25 is not easily damaged. Conversely, since the burr 17 is polished by the coating 25, the burr 17 is removed.
On the other hand, in the case B, the protruding portion of the coating 15 hits the second member 20 having low hardness, so that the second sliding surface 21 is damaged. If the coating 15 is applied after removing the burr 17 by lapping or the like, this problem does not occur, but the number of steps is increased compared to the case A. Even if the burr 17 is removed, the coating 25 is easily peeled off due to a local force applied to the coating 25 at the peripheral portion of the dimple 13.
For the above reasons, when coating is performed, it is preferable to apply to the sliding member on the side where the dimples 13 are not formed.

  The wear-resistant coating is provided according to the sliding condition of the sliding member 1, the material constituting the sliding member 1, and the like. As a material for the coating, metal nitride, metal carbide, and metal carbonitride such as TiN, TiC, CrN, CrC, and DLC (diamond-like carbon) can be used.

  Here, the burr 17 is generated by the fact that the meat corresponding to the dimple 13 flows around the opening of the dimple 13. Accordingly, as the depth h of the dimple 13 increases, the protrusion amount of the burr 17 becomes more prominent. Therefore, in this embodiment, in order to suppress the burr 17 from occurring, it is recommended that the upper limit of the depth of the dimple 13 be 15 μm or less. The upper limit of the depth h of the dimple 13 is more preferably 12 μm, and even more preferably 10 μm. On the other hand, the dimple 13 preferably has a lower limit of 1 μm, more preferably 3 μm, from the viewpoint of retaining lubricating oil.

Next, a method for forming the dimple 13 will be described.
The present invention does not matter how the dimples 13 are formed as long as they can be formed in the required shape, number and arrangement. For example, a formation method by shot blasting (or shot peening) can be applied.
The formation method by shot blasting projects substantially spherical projection particles onto the first sliding surface 11 of the sliding member 1. In order to form innumerable dimples 13 uniformly, the first sliding surface 11 is masked. This masking is provided so that the projected particles pass only where the dimples 13 are to be formed and reach the first sliding surface 11. This method of forming the dimple 13 is referred to as microblast.

  In addition to the formation method using microblast, a method of pressing and transferring a hard mold having protrusions, formation of dimples 13 by a laser beam, formation of dimples 13 by etching, dimples by machining using a small diameter drill The formation of 13 can be applied.

The sliding member 1 of the present embodiment can be applied to sliding members of various machines and devices, and the dimple 13 is within the scope of the present embodiment depending on the material, operating conditions, lubricating oil conditions, and the like. May be formed.
A specific application is a compressor that compresses a refrigerant in a refrigeration cycle. As this compressor, there are a rotary compressor, a scroll compressor, and the like. Since each of them includes a plurality of sliding portions including a bearing portion, the present invention may be applied as appropriate.

[Example]
Hereinafter, the results of experiments that are the basis of the present invention will be described as examples.
In this experiment, a ring-on-disk friction tester was used. This test apparatus is a pressure-resistant container in which a storage portion of a test piece is partitioned from the atmosphere, and can perform a friction test in a refrigerant atmosphere. A disk-shaped fixed test piece and a ring-shaped rotating test piece are arranged in the pressure vessel, and the rotating test piece is rotated by a drive motor provided outside. The fixed test piece can be moved back and forth in the axial direction by a hydraulic cylinder, and can be pressed against the rotating test piece. The frictional force generated on the sliding surface between the fixed test piece and the rotating test piece is measured by a strain gauge installed on a torsion bar provided between the hydraulic cylinder and the fixed test piece.

The fixed test piece was made of cast iron, and the rotating test piece was also made of cast iron. Further, dimples having the specifications shown in FIG. 6 were formed on the rotating test pieces. The sliding surface excluding the dimples has a surface roughness Ra of about 0.3 μm.
The inside of the pressure-resistant container was under the environment of the refrigerant R410A, and polyol ester refrigerating machine oil was used as the lubricating oil. The rotational speed of the rotating test piece was fixed at 1700 rpm, and the load was changed by increasing the pressure of the hydraulic cylinder at regular intervals. Each load was held for 10 minutes, and the coefficient of friction was evaluated by the average value for the last 1 minute.

The evaluation results are shown in FIGS.
As shown in FIG. 6, both the dimple area ratio and the aspect ratio are too large or too small, the value of the friction coefficient is large, and it can be seen that there is an optimum range for each.
If this optimum range is specified based on FIG. 7, if the friction coefficient is 0.02 or less, the dimple area ratio may be in the range of 5 to 50%, and the aspect ratio is 1.0 to 4 It may be in the range of 5%.
Regarding the dimple area ratio, the friction coefficient can be further reduced to a range of 10 to 45%, and the friction coefficient can be further decreased to a range of 15 to 40%. In the latter case, the friction coefficient can be made 0.01 or less.
With respect to the aspect ratio, the friction coefficient can be further reduced in the range of 1.0 to 3.0%, and the friction coefficient can be further decreased in the range of 1.0 to 2.5%. In the latter case, the friction coefficient can be made 0.01 or less.

The preferred embodiments of the present invention have been described above. However, the configurations described in the above embodiments can be selected or modified as appropriate to other configurations without departing from the gist of the present invention.
For example, although the sliding member 1 showed the example which forms a dimple in one member, it can also form a dimple in both of a pair of members.
Further, the sliding environment in the embodiment is merely an example assuming a compressor used in a refrigeration cycle, and the present invention can be applied to a sliding member used in an environment where no refrigerant exists. The lubricating oil used is not limited to the polyol ester type refrigerating machine oil, and other types of lubricating oil can be used.

DESCRIPTION OF SYMBOLS 1 Sliding member 10 1st member 11 1st sliding surface 13 Dimples 15 and 25 Coating 20 2nd member 21 2nd sliding surface O Lubricating oil

Claims (4)

Dimples are formed substantially uniformly in a predetermined region of the sliding surface of at least one of the pair of sliding members arranged to slide relative to each other,
The predetermined area ratio of the total area _{A d} of the opening of the dimples to the surface area _{A 0} of the _(A d / _{A 0)} is a dimple area ratio from 5 to 50%
The aspect ratio (H / D), which is the ratio of the depth H to the opening diameter D of the dimple, is 0.5 to 4.5%.
A sliding member characterized by that.   The sliding member according to claim 1, wherein a depth h of the dimple is 15 μm or less. A pair of the sliding members in which one of them is stationary and the other is moving;
The dimple is formed on the sliding member that moves.
The sliding member according to claim 1 or 2. In the sliding member where the wear-resistant coating is applied to the sliding surface,
The wear-resistant coating is applied only to the sliding surface on which the dimple is not formed.
The sliding member according to claim 3.

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