JPS6330526B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a self-lubricating sliding material, particularly a fiber sintered type self-lubricating sliding material. Wear-resistant materials For example, sliding bearings are used on the relative sliding surfaces of various machine tools and motion mechanisms, and various lubricants are selected depending on the application. Supply may become impossible. As a countermeasure to this problem, bearings with self-lubricating properties have been developed. Specifically, bearings with a porous matrix material impregnated with oil and those with carbon or molybdenum disulfide contained in the matrix material have been developed. There are solid lubricants dispersed in the latter type of solid lubricant, but if the purpose is to avoid oil scattering and to withstand high compressive loads, the latter solid lubricant is preferable. Sliding materials in which this solid lubricant is dispersed have a low coefficient of friction (high solid lubricant content), good compressive load resistance and tensile strength, and are easy and inexpensive to manufacture. However, it has been difficult to fully achieve these objectives in the past. That is, as a method for dispersing a solid lubricant in a matrix material, a conventional method has generally been adopted in which a bush-shaped solid lubricant is press-fitted into a base material made of molten material. In this method, the base material is made from melted lumber, and the solid lubricant produced separately is drilled into this material. Therefore, there is a limit to the improvement of the coefficient of friction due to restrictions on hole spacing, etc. It cannot form a lubricated surface. In addition, there is a drawback that the manufacturing cost is high because it requires a large number of man-hours and complicated machining. Powder metallurgy is another method for dispersing solid lubricants, but conventionally, when a large amount of solid lubricant is included, formability, sinterability, and strength are significantly reduced, and even under good conditions, the powder metallurgy method %,
Practically speaking, a limit of about 10 ^wt % is not sufficient;
Therefore, the former method of press-fitting solid lubricant in the form of a bush has generally been used. The present invention was developed through research to solve the above-mentioned problems, and its purpose is to uniformly disperse solid lubricant at a high content of 20 to 50 wt%, and to improve strength. It is an object of the present invention to provide a method for mass-producing a self-lubricating sliding material having good properties and a high degree of freedom in shape through a simple process and at low cost. In order to achieve this object, the present invention uses fine short metal fibers with an aspect ratio of approximately 4 to 70, which are produced by vibration cutting of a base material, as a matrix material, and converts these fine metal short fibers into powder-like solids. It is mixed with a lubricant and press-molded to create a structure in which the solid lubricant is dispersed and encapsulated in a multilayer network-like skeleton of fine short fibers, and then sintered to embed and fix the solid lubricant. Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an example of a fiber sintered self-lubricating sliding material obtained by the present invention, which has the shape of a sleeve, plate or disc, ring, rail, or any other shape, and has a shaft on at least one surface. A contact surface 11 is formed. FIG. 2 shows an enlarged cross-section of the sliding material shown in FIG. As shown in the figure, it consists of short fine fibers 1 whose surfaces are welded to each other and a solid lubricant 2 trapped in interconnected pores 3 formed in the short fine fibers 1 welded to each other. Therefore, in order to obtain a self-lubricating sliding material, the present invention does not use powder as a matrix material, but uses fine short fibers, in particular, directly separated from the base metal by a chatter vibration cutting method, and has an aspect ratio of about 4.
~70 short fibers are used. As the base metal, any base metal can be used depending on the purpose, such as iron-based gold-copper such as cast iron, copper alloys such as brass and bronze, and aluminum alloys such as duralumin. When metal powder is used as a matrix material, it has an almost spherical shape (particles), so it requires high molding pressure, and when compacting with a mold etc., it is difficult to The porosity of the compact is low even at the minimum pressure. Therefore, if a large amount of solid lubricant is mixed, contact between the matrix powders will be hindered and the solid lubricant will segregate. Therefore, the present invention uses fine short fibers as the matrix material, but if the fine short fibers are simply crushed chips generated by machining, the roundness will be lost due to contact during crushing. This results in a cloudy powder, making it impossible to obtain a product with uniform dimensions and physical properties, and the intended purpose cannot be achieved. It is also possible to cut and use ultra-fine wires obtained by drawing methods, but ultra-fine wires that meet the purpose are extremely expensive, and it is also difficult to cut them uniformly to a predetermined length. be. As a result of repeated research and experiments by the present inventors, it was found that specific short fibers produced by chatter vibration cutting were particularly effective as fine short fibers. That is,
An elastic tool is applied to the surface of a base metal in the form of a column while rotating, and while giving a predetermined minute feed to this elastic tool, chatter vibration is actively generated, causing vibrations of the base metal with each cycle of chatter. The surface layer is forcibly divided into fibers, and fine and uniform dimensions are produced in large quantities. The fibers produced by chatter vibration cutting exhibit strength greater than the strength of the base material due to work hardening, and because they are created directly from the base material in a dry process, there are few surface oxides, and the cross section resembles a triangle consisting of a smooth surface, a fractured surface, and a rough surface. It has a large surface area and has good dispersibility due to the presence of a smooth surface. Furthermore, the activity for bonding is extremely high. However, it is not sufficient to simply use fibers produced by such chatter vibration cutting. This is because fibers generally have lower fluidity than particles, which causes problems when filling molds, etc., and tends to separate from the solid lubricant.To avoid this, reducing the size of the fibers causes , it becomes difficult to achieve strength and high content. According to the studies of the present inventors, when the aspect ratio of fine short fibers produced by chatter vibration cutting is approximately 4 to 70, all aspects such as fluidity, formability, and sinterability are satisfied, and solid lubricants are not used. Uniform containment was possible at a high content rate. When the aspect ratio (length (l)/thickness (d)) is less than 4, the solid lubricant cannot be dispersed in a large amount even if the molding pressure is increased because the particles become too close to particles and point contact occurs. On the other hand, if the aspect ratio exceeds 70, the mixture with the solid lubricant tends to become uneven, and lumps called fiber balls tend to form during mixing, making it difficult to obtain a sliding material of good quality. do not have. Some examples of fine short fibers including manufacturing conditions are shown in Table 1 below.

[Table] Therefore, in the present invention, the specific fine short fibers 1 as described above and a powder 2 of a solid lubricant such as graphite (scaly, lumpy), molybdenum disulfide, etc. are charged into a ball mill or other arbitrary container, Stir and mix manually or mechanically. Since the aspect ratio is appropriate, the fine short fibers 1 are appropriately entangled, and the solid lubricant 2 is uniformly dispersed despite having different specific gravity, and the third
The result is a mixed structure as shown in the figure. Next, the mixture 4 of the fine short fibers 1 and the solid lubricant 2 is filled into a molding means, for example a mold 5 as shown in FIG. 3, and pressed at a desired pressure. The pressing force at this time is lower than that when powder is used as the matrix material, so a small-capacity press is sufficient. After obtaining the compact in this manner, it is heated in a reducing atmosphere such as hydrogen or an inert atmosphere to perform sintering. This sintering is carried out quickly and at a much lower temperature than in the case of green compact sintering. The reason for this is not necessarily clear, but it is thought that this is because the surface of the fine short fibers is clean, has a high bonding activity, has a large surface area, and has a suitable aspect ratio that allows the fibers to intertwine moderately. The above steps result in a self-lubricating sliding material as shown in Figures 1 and 2, but if necessary, re-compression and/or re-sintering may be performed after sintering, thereby increasing the density. Strength can be improved. The self-lubricating sliding material according to the present invention is produced by adding and mixing a solid lubricant to fine short fibers with an aspect ratio of 4 to 70 produced by chatter vibration cutting, molding and sintering, and forming a sintered structure of the fine short fibers. Because the structure contains a solid lubricant, a multilayer network skeleton with extremely high porosity is formed at low molding pressure due to line contact and fiber entanglement, rather than point contact like powder, and the Since these are interconnected pores, a large amount of the blended solid lubricant is uniformly dispersed and encapsulated. In addition, since the aspect ratio is appropriate, it can be easily filled into the molding means without forming lumps.
Sintering after shaping is also carried out at a lower temperature than in the case of powdered matrices, despite the presence of a large amount of solid lubricant. In addition, it has excellent properties such as sufficient strength, strong solid lubricant retention, good impact resistance due to remaining metallic properties, and resistance to chipping. Next, examples of the present invention will be shown. EXAMPLE A self-lubricating sliding bearing was manufactured according to the present invention, and for comparison, the above-mentioned sliding bearing was also manufactured using powder as a matrix material. Cast iron having the components shown in Table 2 below was used as the metal base material, and fine short fibers of Samples 1 to 6 shown in Table 1 were created by a chatter vibration cutting method. On the other hand, as cast iron powder, FC15 grade casting chips shown in Table 2 were crushed and classified into #120 and above. Commercially available graphite powder was used as the solid lubricant.

[Table] Place the above matrix material in a container, add 10 to 50 wt% of graphite, stir mechanically for about 10 minutes, fill it into a mold, and then mold at a molding pressure of 60 kg/mm ² .
Sintering was carried out in a hydrogen stream at a sintering temperature of 1140°C and a sintering time of 30 min. A tensile test piece was made from the obtained sliding bearing, and the results of the tensile test are shown in Fig. 5, and the present invention shows a tensile strength of about 3 Kg/mm ² even with the addition of 20 wt% graphite. 50wt%
Even with the addition of (77VoC%), a tensile strength of 0.5Kg/mm ² was obtained. On the other hand, when cast iron powder was used, even though it could be molded with an addition of 20 wt%, it was not sintered, and molding was impossible with an addition of 30 wt% or more. In the case of the present invention, fine short fibers with excellent properties obtained by chatter vibration cutting are used as the matrix material, and the aspect ratio is optimized, so even though the specific gravity differs by three times, it can be mixed uniformly and has good moldability. , good sinterability. To examine this, we looked at the relationship between sintering temperature and tensile strength when molded at a surface pressure of 80 kg/mm ² . As is clear from FIG. 6, cast iron powder must be sintered at a temperature of 1110° C. or higher, and its maximum tensile strength is about 42 Kg/mm ² . In contrast, the present invention achieves a strength of 25 to 30 Kg/mm ² even when sintered at 950°C, despite using matrix materials with the same components. Furthermore, Fig. 7 shows the effect on tensile strength when the sintering temperature was 1140°C, the sintering time was 30 min, and the molding pressure was 20 to 80 kg/mm ² . As ^is clear from FIG. 7, the present invention
A tensile strength of 20 kg/mm ² was obtained at such a low molding pressure. The sliding bearing of the present invention exhibits good lubricity and durability when used under load conditions of 300 kg/cm ² or higher, speeds exceeding 50 m/min, or when the sliding direction is sliding or rotating. Ta. Example 2 Fine short fibers of Samples 1 to 6 shown in Table 1 were made of bronze, mixed with graphite powder, then molded and sintered to obtain a plain bearing. When only the fibers were molded in advance, the porosity was 80% and 5000 kg/ ^cm2 at a molding pressure of 140 kg/cm2.
By adding 50% graphite powder and sintering it at 810°C in ^a hydrogen atmosphere, a plain bearing with a tensile strength of about 3 Kg/mm ² was obtained. Similar results were shown for brass and aluminum alloys. According to the present invention as described above, fine short fibers obtained by chatter vibration cutting of a base material, especially those with an aspect ratio in the range of approximately 4 to 70, are used as a matrix material, and these fine metal short fibers are processed into powdered short metal fibers. We mixed it with a solid lubricant and pressure-molded it to create a structure in which the solid lubricant was dispersed and encapsulated in a multilayer network skeleton of fine short fibers, and then sintered it to embed and fix the solid lubricant. Excellent effects can be obtained. Fine tertiary fibers with excellent characteristics are used, which have fine and uniform dimensions and good strength due to work hardening, and have a large surface area, low surface oxides, high activity, and an appropriate aspect ratio. Not only can an original network-like skeleton structure be formed, but also a large amount of solid lubricant can be uniformly dispersed and embedded in this fine skeleton without the presence of impurities. Therefore, a self-lubricating sliding material with uniform and fine lubricity over the entire surface and excellent strength can be obtained. Instead of filling a solid lubricant into a material with artificial pores formed in advance, mixing it with a solid lubricant,
Pressure molding forms a fine mesh skeleton and disperses and encapsulates solid lubricant, so the manufacturing process is simple and has a high degree of freedom in shape, and by setting the appropriate aspect ratio, low molding pressure and sintering can be achieved. Sliding materials in desired shapes can be mass-produced at a low temperature and in a short processing time, thereby reducing costs.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an example of a self-lubricating sliding material obtained by the method for manufacturing a fiber sintered self-lubricating sliding material according to the present invention, and Fig. 2 is a schematic diagram of a part of the structure. 2a is a partial view thereof, FIG. 3 is a sectional view showing the mixing state, FIG. 4 is a sectional view showing the molding process, and FIG. 5 is a solid lubricant blending ratio in an example of the present invention. FIG. 6 is a graph showing the relationship between sintering temperature and tensile strength, and FIG. 7 is a graph showing the relationship between molding pressure and tensile strength. 1...Fine short fibers, 2...Solid lubricant, 3...
Coupled vacancy.

Claims (1)

[Claims] 1. Fine short metal fibers with an aspect ratio in the range of approximately 4 to 70 are used as the matrix material by vibration-cutting the base material, and these fine short metal fibers are mixed with powdered solid lubricant and then pressure-molded. A fiber sintered self-lubricating sliding material characterized in that a structure is created in which a solid lubricant is dispersed and encapsulated in a multilayer network skeleton of fine short fibers, and then the solid lubricant is embedded and fixed by sintering. Production method.