JP4584101B2 - Resin-based sliding member and manufacturing method thereof - Google Patents

Description

The present invention relates to a resin-based sliding member and a method for producing the same, and more specifically, a solid lubricant such as polytetrafluoroethylene (PTFE) and MoS ₂ on a copper alloy layer sintered on a back metal. The present invention relates to a resin-based sliding member impregnated and fired with a sliding material having a main component of and a manufacturing method thereof.

PTFE is a typical low-friction tribo material, but has the following physical properties in addition to the friction characteristics.
(1) Melting point: Research has been published that the melting point is constant at 327 ° C or has a width.
(2) Melt viscosity: Melt viscosity is very high at 10 ¹¹ to 10 ¹² Poise at 327 ° C., and commercially available PTFE hardly flows even above the melting point. For this reason, voids are likely to remain after firing.
(3) Crystallinity: Classified as crystalline resin, high molecular weight.
(4) PTFE before firing is easily fibrillated when sheared.

Patent Document 1, according to JP-A-2002-20568, as a sliding material component is impregnated in sintered copper alloy,. 1 to 30 vol% of barium sulfate, 5 ~40vol% of MoS _2, solid lubricants such as graphite The remainder is PTFE. According to this sliding member manufacturing method, an aqueous dispersion of spherical hydrophobic colloid resin obtained by emulsion polymerization is used as PTFE, and PTFE into the sintered pores of the sintered copper alloy layer on the back metal The impregnation of the sliding material mainly composed of a solid lubricant is carried out by placing the composition aggregated by gently stirring the PTFE dispersion, adding a flocculant, etc. on the copper alloy sintered layer and rolling the impregnated material. ing.
Patent Document 1 deals with the problem of PTFE that fluidity is low by this method and that voids are easily generated after firing. Here, the above-described fibrillation of PTFE occurs when the sliding material is impregnated with a roll.

In Patent Document 1, baking is performed once by heating to 370 to 420 ° C. after roll impregnation. Since the barium sulfate added to the sliding material has a conforming action equivalent to that of Pb, performance equivalent to that of the Pb-containing material is realized with a Pb-free composition under non-lubricated thrust sliding conditions. Of the test conditions, the speed (V) is 41.7 m / min and the pressure (P) is 75 kg / cm ² .
Japanese Patent Laid-Open No. 2002-20568

  For example, the bush that supports the rotating shaft of the compressor is designed to withstand the rotational speed and load within a certain range, but it is not sufficiently assumed that the constant rotational speed and load slightly fluctuate. However, in reality, as the refrigerant of the compressor is sucked and discharged in a pulsating manner, the shaft slightly vibrates in the orthogonal direction, so the load (P) fluctuates sharply and the shaft rotation speed (V) also sharpens. It has fluctuated. Therefore, the PV value fluctuated drastically even under conventional compressor operating conditions. Conventionally, although the improvement of sliding characteristics was achieved under conditions where the PV value was high, the PV value fluctuation due to the above-mentioned fine vibrations was taken into consideration. There wasn't. In particular, when the PV value becomes high and the fluctuation is added, the sliding condition becomes very severe. Therefore, it is necessary to sufficiently consider the fluctuation of the PV value.

  Similarly, in shock absorber bushes in which a resin-impregnated sintered copper alloy is conventionally used, the PV value fluctuates due to the pulsation of the hydraulic medium in addition to the normal vibration.

  Among the PV values that fluctuate violently, P causes a slight collision between the sliding members and causes impact wear. According to the theory of impact wear, (1) the wear of soft materials among sliding members is the same as normal adhesive wear; (2) fatigue wear occurs on the surface of soft materials; (3) surface fracture occurs on hard materials (Surface fracture) occurs; (4) When there is a large difference in hardness between hard and soft materials among sliding members, a mechanism has been proposed in which mild wear occurs in soft materials and fracture wear occurs in hard materials. Yes.

  In the conventional theory, the V value which fluctuates drastically is considered based on the friction force and friction coefficient fluctuation in stick-slip wear. In order to reduce the coefficient of friction in stick-slip wear, it has been proposed to form a lubricating film on the sliding portion.

The resin-based sliding material proposed in Patent Document 1 has a problem that cracks occur in the PTFE layer or the resin layer peels off at the interface with the sintered layer when subjected to fluctuating load under severe PV conditions. I understood that. Such a boundary layer is generated in a direction parallel to the impregnation performed in the continuous line direction, but may be generated in a direction perpendicular to the impregnation direction depending on the impregnation method. For example, when the sliding material is impregnated and dried in a liquid state, it is a mud crack caused by the drying of the liquid.
The theory introduced in the previous two paragraphs explains the various wear phenomena that occur under varying PV value conditions, assuming that the material is initially free of defects.
With reference to such conventional research, the present inventors conducted research to develop a fluororesin-based sliding material that can withstand sliding conditions in which the PV value fluctuates drastically. The fibrillated PTFE was conventionally thought to return to its original state by a single firing that has been conventionally performed. However, the coarse or long residual structure of fibers produces fine pseudo-cracks, and the above-mentioned sliding Attention was paid to the possibility of peeling in the resin layer or between the resin layer and the sintered layer under dynamic conditions. Although this pseudo-crack cannot be confirmed with an electron microscope, a clear relationship is observed between the quality of the sliding characteristics and the fiber formation under the PV value fluctuation condition.

The present invention relates to a backing metal, a copper alloy layer sintered on the backing metal, a sliding material mainly composed of PTFE and a solid lubricant, which are baked at a melting point of PTFE or higher and the fibrous structure of PTFE crystal disappears. A resin-based sliding member having a portion in which the sliding material is impregnated in the sintered voids of the copper alloy layer and a film forming portion on the copper alloy layer , the copper alloy layer and the film forming portion The electron microscope structure in the cross-sectional direction is characterized in that no streak structure exists at the boundary between the impregnated part and the film forming part or at the film forming part. Hereinafter, the resin-based sliding material of the present invention will be described in detail.

First, the structure which applied the well-known matter in the resin-type sliding member of this invention is demonstrated.
The backing metal is a thin metal plate usually used such as mild steel, and the thickness is not particularly limited but is 0.5 to 3.0 mm. If necessary, the surface of the back metal may be subjected to roughening treatment such as shot blasting or sanding, or adhesion improving means such as electroless Cu-P plating.
The copper alloy sintered layer is a porous material obtained by sintering phosphor bronze, a Cu—Sn alloy, a Cu—Sn—Pb alloy, or the like, and fine sliding voids are impregnated with the sliding material. Although the thickness of a sintered layer is not specifically limited, 250-350 micrometers is preferable. Sintering of the sintered layer is generally performed at 800 to 950 ° C. for the first time, and after the intermediate pressure, the second time sintering is performed at the above temperature range.

Examples of PTFE resins include dispersions (aqueous suspensions of spherical hydrophobic colloidal resin particles obtained by emulsion polymerization), such as “Teflon Dispersion 38-J” (trade name) manufactured by Mitsui DuPont Fluorochemicals, Daikin Industries, Ltd. “Polyfluorocarbon Dispersion D (trade name)” manufactured by the company can be used.
As the solid lubricant constituting the sliding layer together with PTFE, MoS ₂ , graphite, BaSO ₄ or the like can be used. PTFE and these solid lubricants occupy 90-100 mass% of the sliding layer. As this balance, at least one selected from Fe ₃ P, spherical carbon, glass sphere, carbon fiber, graphite fiber, glass fiber, metal powder, and metal fiber can be used.

Although the component ratio of the above-mentioned sliding material is not particularly limited, it is preferably vol%, PTFE of 73 to 91%, and the remaining solid lubricant. When the ratio of the solid lubricant in the sliding material is increased within these ratio ranges, the wear resistance is improved, but the low friction property and the adhesive strength of the film tend to be decreased. In this way, in the present invention, cracks are likely to occur in the PTFE material under the PV value fluctuation condition when there is a streak structure (also referred to as a “boundary layer”) although there is a change in the characteristics as described above. As described in the paragraph, the structure does not generate streak . The proportion of solid lubricant, for the entire sliding material, in vol%, MoS _2: 3-9%, graphite: 3 to 9%, BaSO _4: is preferably 3-9%. These solid lubricants may be added alone, but it is preferable to add them all in terms of wear resistance. As described above, a difference in wear resistance occurs depending on the form of addition of the solid lubricant, but a structure in which a streak structure does not exist is employed. As for the particle size of these solid lubricants, BaSO ₄ preferably has an average particle size of 0.1 to 10 μm, MoS ₂ preferably has an average particle size of 0.3 to 10 μm, and graphite preferably has an average particle size of 1 to 1 μm. 10 μm

Subsequently, the features of the resin-based sliding member of the present invention will be described.
Under the conditions where the PV value of the conventional resin-based sliding material fluctuates violently, the reason why the sliding characteristics are not excellent was considered as follows, focusing on the impregnation conditions.
The impregnation of PTFE and solid lubricant is performed by roll impregnation in a continuous line for continuously treating the back metal with a sintered layer. The following phenomena (1) to (3) are considered to occur during the impregnation process. (1) Aggregated PTFE stays in layers before the impregnating roll, and is fluidized by the impregnating roll and press-fitted into the sintered pores. (2) The layered coagulated PTFE slightly enters the sintered pores before the impregnating roll, and thereafter, the above-described press-fitting occurs. (3) When agglomerated PTFE enters the sintered pores to some extent, it acts to push back the subsequently infiltrated agglomerated PTFE, so that part of the agglomerated composition is not impregnated into the sintered pores over time. Further, the agglomerated composition that has been pushed back and retained is impregnated with a new agglomerated composition. At this time, since the staying composition is fluidized before the impregnating roll, fibrillation proceeds. As a result, the sliding layer is likely to have a layered boundary between the staying aggregate composition whose fibrillation has progressed in the impregnation direction and the new aggregate composition. Generally the resin material is the boundary surface by firing is extinguished by fusing, because in the case of PTFE is very large melt viscosity, without fusing the boundary surface, the influence of shrinkage due to melting, streaky tissue There is a tendency to not disappear or spread in reverse. This phenomenon becomes more prominent as the fibrillation of the retained composition and the progress of fibrillation by impregnation increase, and a streak structure is likely to occur. Furthermore, if the stirring during PTFE dispersion aggregation is vigorous, coarse and long fiber structures are generated, and a streak structure is likely to be generated at the interface with the copper alloy layer .

In this streak tissue , it can be observed with a scanning electron microscope or the like that the fibrillated portion and the non-fibrillated portion are in contact with each other. However, since the fibrillated fiber structure almost disappears by firing as described above, the object observed with a scanning electron microscope or the like is a trace of a tissue having a history of fibrillation detected. It is. Similarly, the crystal structure of muscle streaky tissue, can not be identified, such as molecular structure, has a clearly influence the sliding properties in the PV value variation conditions.

FIG. 1 is a sketch of this observation result, where 1 is a back metal, 2 is a sintered copper alloy layer, 3 is a sliding layer, and 4 is a streak structure denoted as “boundary layer”. Although this boundary layer 4 was not considered as a problem under normal friction conditions, peeling wear tends to occur starting from the boundary layer 4 at the site where the PV value fluctuates severely. When the boundary layer 4a exists in the vicinity of the interface between 2 and the sliding layer 3, peeling wear becomes more likely. Therefore, the present invention is characterized in that no streak tissue exists . That is, the boundary layer 4 is not found by observation with an electron microscope in the sliding layer above the copper alloy sintered layer 2 or at the boundary between the copper alloy sintered layer 2 and the sliding layer 4 by the observation method described above. And If a streaky structure is generated inside the copper alloy sintered layer, there will be no significant effect on sliding, but if it occurs in the surface layer of the sintered layer or in the sliding layer above the sintered layer, the sliding will occur during sliding. The shearing of the dynamic layer is likely to occur. In particular, when a streak structure is generated in the vicinity of the boundary between the sintered layer surface layer portion and the sliding layer portion, which are different materials, shearing during sliding occurs, and cracks tend to occur.

When the resin-based sliding material of the present invention is compared with the conventional sliding material, there is a difference in the presence or absence of the above-mentioned streak structure , but the difference is not visually recognized immediately after manufacturing, such as a crack. . However, if the sliding is continued under the condition where the PV value fluctuates violently, a crack is generated at a portion where the streak structure is present in the sliding material having the streak structure . This crack can be observed with an electron microscope (SEM).

  Furthermore, the hardness shown in the following table is one in which a significant difference was recognized by measuring other properties. As shown in this table, the material of the present invention has a high hardness, but since the boundary layer is a kind of defect, it is shown that the apparent hardness is low if there is a defect.

The manufacturing method of the above-described resin-based sliding part material will be described below.
In the production method according to the present invention, a certain amount of an agglomerated composition mixed with a solid lubricant or the like is placed on a back metal provided with a porous copper alloy sintered layer and impregnated with an impregnation roll. After the impregnation, drying is performed under appropriate conditions or setting is performed, and after the impregnated state of the sliding material is stabilized, the first baking is performed by melting. As a result, bonding of PTFE and copper alloy particles and fluidization of PTFE particles are realized in the sliding material. However, if the aggregate composition stays during impregnation of the aggregate composition, fiberization (fibrillation) proceeds and new When mixed with the agglomerated composition, a streak is generated between the old and new agglomerated compositions. There is no tendency as to where this streak occurs in the impregnated layer.

In the production method of the embodiment of the present invention, as described above, after the first firing, after cooling once, re-firing at a temperature equal to or higher than the melting point of PTFE is performed. As long as the re-firing is at or above the melting point of PTFE, the conditions are not particularly limited and the cooling conditions are not limited, but the same conditions as the first firing are preferable. However, PTFE is decomposed when the firing temperature is too high. The cooling after the completion of the first firing may be lowered to the melting point of PTFE or less, and cooling to near room temperature is not necessary. The reason why the fiber formation disappears by once firing again after cooling is considered to be due to melting and disappearing of the streak structure because there is almost no shrinkage of the resin layer after re-firing after cooling.
Further, after re-firing or simultaneously with re-firing, if the rolling is performed at the melting temperature or a temperature close to the melting temperature, the streak structure disappears completely.

As another means for preventing the generation of streak structure , it is only necessary to continuously infiltrate the aggregated PTFE at a constant rate so that the aggregated PTFE does not stay in the sintered pores. A method is conceivable. Or conversely, a method of increasing the impregnation rate and ending the impregnation at once can be considered. Further, the rolling is effective during the first firing (melting temperature range).
Subsequently, the embodiment of the present invention will be described in more detail.

Comparative Example A phosphor bronze sintered layer was laminated to a thickness of 0.3 mm on a low carbon steel (S15C) backing metal having a thickness of 0.7 mm. The following materials were used as the components of the sliding material.
PTFE (Mitsui DuPont Fluoro Chemical Co., Ltd .: Trade name Teflon dispersion 38-J)
MoS ₂ : average particle size 1.0μm (manufactured by Sumiko Lubricant: trade name PA powder)
Graphite: Average particle size 1.0μm (Nippon Graphite Co., Ltd .: Product name CSSP)
BaSO ₄ : Average particle size 10 μm (manufactured by Sakai Chemical Industry Co., Ltd .: trade name BMH-100)

  The above sliding material components were kneaded so as to have the composition of the comparative example in Table 2, and impregnated with a roll onto the sintered layer of the back metal moving on the continuous line. Thereafter, firing was performed once at 380 ° C. for 20 minutes.

In order to measure the peeling load, the reciprocating peeling test was performed by the following method.
Reciprocating peel test (Fig. 2, 10-specimen, 11-mating material)
Speed: 4Hz
Shaft (mating shaft): Cr plated round bar (diameter 10mm)
Oil type: Compressor oil stroke: ± 10mm
Load: Load gradually increased from 98N to 20N / 5min
The occurrence of peeling was detected by a change in friction torque.
The test results are shown in Table 2 together with the examples.

Example After firing under the same conditions as in the comparative example, it was cooled to room temperature and then fired again under the same conditions.

As is apparent from Table 2, it is clear that the sliding material of the present invention has a higher peel load than the material of the comparative example. Streaks (denoted as “boundary layer”) were observed in the comparative material, but not in the example material.

An actual compressor test was conducted for the examples and comparative examples in Table 2. The test conditions were as follows.
Test material: bush
Pd / Ps: 35 / 2.7 (kg / cm ² )
Td / Ts: 160/50 (℃)
Rotation speed: 2000rpm
Time: 100Hr
Evaporator tank temperature: 55 ° C
Condenser tank temperature: 95 ° C
The test results are shown in the graph of FIG.

From FIG. 3, it is apparent that peeling is extremely difficult to occur according to the present invention.
Further, when the appearance of the inner surface of the bush was observed, the sintered layer was exposed in the comparative material.

  As described above, the resin-based sliding member according to the present invention exhibits high sliding characteristics under conditions in which the PV value fluctuates violently and is not considered in conventional materials as well as conventional sliding conditions. It can also cope with sliding conditions that could not be handled.

It is a boundary layer image figure. It is principal part explanatory drawing of a reciprocation peeling tester. It is a graph which shows the result of an actual machine test.

Explanation of symbols

10 Specimen
11 Mating material (shaft)

Claims (2)

A backing metal, a copper alloy layer sintered on the backing metal, and a sliding material mainly composed of PTFE and solid lubricant, which are fired at a melting point of PTFE or higher and the fibrous structure of PTFE crystal disappeared , In a resin-based sliding member having a portion in which the sliding material is impregnated in the sintered pores of the copper alloy layer and a film forming portion on the copper alloy layer, a cross-sectional direction of the copper alloy layer and the film forming portion The resin-based sliding member is characterized in that a streak structure does not exist at the boundary between the impregnation part and the film forming part or at the film forming part. In the method of manufacturing a resin-based sliding member in which a copper alloy layer sintered on a back metal is impregnated with a sliding material mainly composed of PTFE and a solid lubricant and fired at a melting point of PTFE or higher, after the firing, A method for producing a resin-based sliding member, which is cooled once and refired at a temperature equal to or higher than the melting point of the PTFE.