JP5943317B2 - Soft metal mixed shot peening powder - Google Patents

Description

The present invention relates to a mixed powder for shot peening in which soft metal powder and steel ball powder are mixed.

  In general, sliding parts are often lubricated using liquid lubricants such as oil, but liquid lubricants cannot be used for design reasons, or are used in vacuum. If there is a restriction in the usage environment, a solid lubricant is used. In recent years, as the social demand for energy problems increases, further reduction of friction of sliding members used in automobile engines and transmissions has been demanded.

  Therefore, in order to reduce the frictional resistance of the liquid lubricant used in the sliding part, a material having low viscosity tends to be used, and the thickness of the lubricant in the sliding part becomes thin, and the sliding members come into contact with each other. As the number of bearings used in possible boundary lubrication environments is increasing, it is necessary to develop members with high slidability and long stripping life even in boundary lubrication environments. The sliding part is covered.

  As a method for coating the sliding member with the solid lubricant, for example, as disclosed in JP-A-2002-161371 (Patent Document 1) and JP-A-2004-255522 (Patent Document 2), zinc or tin is used. A method is disclosed in which shot peening is performed on a sintered body using a mixed powder of a soft metal powder such as a solid lubricant powder such as molybdenum disulfide or a mixed powder of a steel ball and a molybdenum disulfide powder that is a solid lubricant.

  In patent document 1, the adhesiveness of the coating film of a single solid lubricant having a low adhesion strength is improved by forming a coating film in which a solid lubricant powder such as molybdenum disulfide is dispersed in a soft metal. Therefore, a highly durable coating can be formed while maintaining the lubricity of the solid lubricant. In Patent Document 2, solid lubricant powder such as molybdenum disulfide can be more penetrated into the sintered body by the collision energy of steel balls.

  JP 2007-10059 (Patent Document 3) discloses a film forming technique for shot peening a soft metal powder or a solid lubricant powder alone, and covers a coating area formed on a sliding surface, By controlling the thickness and surface roughness, it is said that a sliding member having a small friction coefficient and excellent sliding performance can be obtained.

Furthermore, as described in [Tribology Conference 2007 Spring Proceedings, pages 123-124, “Longer Life of Rolling Bearing by Solid Lubricant Shot Coating”] (Non-Patent Document 1), a soft metal powder of tin or zinc is used. A technique for reducing the coefficient of friction of a sliding member by shot peening on the sliding member to form a soft metal film is disclosed.
JP 2002-161371 A JP 2004-255522 A JP 2007-10059 A [Tribology Conference Spring 2007, Proceedings, pages 123-124 "Extending the life of rolling bearings by shot coating with solid lubricant"]

  However, in the technique described in Patent Document 1 described above, it is very difficult to mix homogeneously a soft metal powder such as tin or zinc and particles of a solid lubricant such as molybdenum disulfide or graphite. It is difficult to obtain a film in which the solid lubricant is uniformly dispersed on the sliding surface, and sufficient sliding properties may not be obtained due to poor film adhesion and adhesion efficiency.

  Also in the technique described in Patent Document 2, it is very difficult to uniformly mix the particles of a solid lubricant such as a steel ball and molybdenum disulfide because their densities are very different from each other. It is difficult to obtain the material penetration effect. With the technique described in Patent Document 3, the softness of the solid lubricant film on the sliding surface is low, such as tin or zinc, so the adhesion and wear resistance are low, and the film cannot withstand long-term use. There is sex.

Results We has proceeded intensive development in order to solve the problems as described above, after mixing soft metal powder consisting of S n alloy steel balls powder used to impart compressive residual stress, By performing shot peening using this mixed powder, the soft metal powder can be efficiently attached as a soft metal film having excellent slidability, and at the same time, adhesion to the base material forming the sliding surface can be improved. .

The gist of the invention is that
(1) A mixed powder for shot peening, characterized in that a steel ball powder and a soft metal powder made of an Sn alloy are mixed, and the mixing ratio of the soft metal powder is 20 to 40% by mass.

As mentioned above, after mixing soft metal powder consisting of high hardness shot peening powder and S n alloys such as spherical according to the invention, after mixing the soft metal powder by performing shot peening in this mixed powder, By performing shot peening using this mixed powder, it is possible to efficiently attach the soft metal powder as a soft metal film having excellent slidability, and at the same time, it is possible to improve the adhesion with the substrate forming the sliding surface, and further compress Residual stress can be applied to the sliding surface, and an extremely excellent effect is achieved.

Hereinafter, the present invention will be described in detail.
In the present invention, steel ball powder and soft metal powder are mixed, and the mixing ratio of the soft metal powder is 20 to 40% by mass. That is, since both of the present invention are metal, shot lubrication is performed under severe boundary lubrication environment by shot peening a mixed powder in which a soft metal powder is mixed in a ratio of 20 to 40% by mass with a steel ball powder having a specific gravity close to each other. It is possible to efficiently form a sliding coating that exhibits slidability in an environment and to improve the adhesion. However, if the mixing ratio is less than 20% by mass, it is difficult to obtain a sufficient soft metal film because the amount of the soft metal powder is too small, and conversely if it exceeds 40% by mass, the pressure-bonding effect by the steel ball decreases. Since the adhesiveness of the film is lowered, the range is set to 20 to 40% by mass. Preferably, the upper limit is 40% by mass. In addition, the steel ball powder and soft metal powder whose particle sizes are substantially equal are mixed in such a ratio that the soft metal powder is 20 to 40% by mass. The mixed powder of the present invention can be produced by manual mixing or using a mixer. It is preferable to perform mixing for 30 minutes to 1.5 hours using a mixer such as a V-type mixer.

Examples of the steel balls according to the present invention described above include high-speed steel and Fe-Cr-B alloys. As the soft metal can be listed a S n alloy. In addition, the member to be treated is particularly suitable for a sliding member, where the sliding member is a member having a sliding surface that is in sliding contact with the counterpart member, and a specific example of such a sliding member. Is a mechanical part that performs contact movement on a cylindrical surface, spherical surface, flat surface, etc., for example, a cam and a cam follower that constitutes an automobile engine, a piston ring, a fuel injection device, a crack part, and a sliding member that constitutes a sliding bearing And retainers for rolling bearings and plain bearings.

  It is preferable to use a steel ball having a Vickers hardness of 800 to 1500 HV and an average particle size of 30 to 60 μm. It is preferable to use a soft metal powder having an average particle size of 30 to 60 μm. The shot peening condition is that a soft metal may be formed on the sliding surface by accelerating and jetting using a shot peening apparatus under conditions of a pressure of 0.4 to 1.0 MPa and an injection time of 5 to 20 minutes. preferable.

Hereinafter, the present invention will be specifically described with reference to examples.
A mixed powder was produced by a combination of soft metal powder and steel ball powder shown in Table 1 . The mixed powder is a steel ball powder having an average particle size of 44 μm and a soft metal powder (average particle size of 44 μm) weighed so that the mixing ratio of the soft metal powder is 20 to 40% by mass, and 1 hour using a V-type mixer. A total of 30 kg of mixed powder was prepared by mixing . Under the same conditions, the mixed powders shown in Table 1 were shot peened on the surface of a roller of a bearing having a diameter of 26 mm and a thickness of 28 mm with a SURC hardness of HRC60 and a surface roughness Ra of 0.1 μm. . The shot peening conditions were a gas pressure of 0.6 MPa and a shot time of 10 minutes.

  As a comparative example, a steel ball powder having an average particle size of 44 μm and a soft metal powder (average particle size 44 μm) are weighed so that the mixing ratio of the soft metal is 0 to 4% by mass and 51% by mass or more. 30 kg of mixed powders were produced by mixing for 1 hour using a machine. Shot peening was performed on the surface of the roller of a bearing having a diameter of 26 mm and a thickness of 28 mm, each having a hardness of SUJ2 of HRC60 and a surface roughness Ra of 0.1 μm, under the same conditions as the mixed powder shown as an example. The shot peening conditions were a gas pressure of 0.6 MPa and a shot time of 10 minutes.

As shown in Table 1, no. 1-3 are examples of the present invention. No. 4 to 6 are comparative examples.

  In order to evaluate film adhesion, a scanning electron microscope (SEM) was used to analyze the interface with the coating at the cross-section, and the diffusion of the soft metal into the bearing steel was measured. In the bearing steel shot with the corresponding mixed powder, the soft metal was detected at a point of 0.5 μm or less from the film interface under any condition, and therefore the film adhesion was evaluated as “◯”. This is due to the effect that the soft metal film is mechanically pressed by the collision energy of the steel ball.

On the other hand, since the soft metal was not detected below 0.5 μm in any case in the bearing steel shot with the soft metal simple substance and the mixed powder shown as the comparative example, the adhesion of the film was evaluated as “x”. This is because the soft metal shot was too little or the pressure-bonding effect by the steel ball was reduced .

Furthermore, it was recognized that the fatigue strength was improved as compared with the case of shot with the mixed powder shown in the examples. This is considered to be due to the synergistic application of the compressive residual stress and the effect of mechanically pressure-bonding the soft metal film by shot with a mixed powder of steel balls and soft metal.

  As described above, the mixed powder of the steel ball and the soft metal powder collides with the member to be treated at a high speed, and the soft metal powder surface adheres to the member to be treated at the time of the collision and is transferred to the soft member. By simultaneously applying the collision energy of the steel balls when the metal film is formed, it is possible to efficiently form the film and at the same time form a film with high adhesion. Furthermore, a compressive residual stress can be given to a to-be-processed member with the collision energy of a steel ball.

  As a result, when shot peening is performed with a mixed powder of steel balls and soft metal powder, the soft metal is stably coated on the processing member in a highly adhesive state, works as a lubricant, and maintains a low coefficient of friction for a long period of time. Thus, the sliding characteristics are stably maintained over a long period. Moreover, the surface hardness is increased by the projection of the steel ball powder, and a large compressive residual stress is applied to the surface, so that not only the wear resistance is sufficient, but also the fatigue strength is improved, and the effect of the present invention is great. .

Claims (1)

A mixed powder for shot peening, characterized in that a steel ball powder and a soft metal powder made of an Sn alloy are mixed, and the mixing ratio of the soft metal powder is 20 to 40% by mass.