Swash Plate of Swash Plate Compressor and Combination of Swash Plate With Shoes

The present invention relates to a swash plate of a swash-plate type compressor and to a combination of a swash plate and shoes. More particularly, the present invention relates to a surface-treating technique for outstandingly improving, in a single-side compression--type swash-plate compressor, the sliding properties of a swash-plate which consists of an iron-based or aluminum-based material.

In the swash-plate type compressor, a swash-plate is rigidly secured obliquely to a rotary shaft or is secured obliquely to a rotary shaft in such a manner that its slanting angle is variable. The compression and expansion are carried out by means of rotating the swash-plate which increases or decreases the volume of a partition space within a compressor, depending upon the rotation of the rotary shaft. Such swash plate is caused to slide on a sliding member referred to as a shoe, and reciprocates a piston via the shoe. The cooling medium can therefore be compressed and expanded in the stated space.

A salient point in the sliding conditions of a swash-plate is that, during the initial operational period of a compressor, the cooling medium reaches the sliding part prior to the lubricating oil reaching the sliding part; thus the cooling medium has a rinsing effect on the lubricating oil which remains on the sliding part, with the result that the sliding condition is in a dry condition free of lubricating oil. The requirements for the sliding condition of the swash plate are therefore very severe.

The sliding properties, which are required for a swash-plate used under the condition described above, are seizure resistance, wear resistance, and the like. Proposals have thus been made to add hard matters into the aluminum material for enhancing the wear resistance, to improve the material of the swash plate, and to subject an iron-based swash-plate to heat treatment or surface treatment for enhancing the hardness and hence wear-resistance.

One of the present applicants proposed in Japanese Unexamined Patent Publication No. Sho 51-36611 to bond sintered Cu material on the shoe in the case of an iron-based swash plate. That is, an iron-based swash plate was heretofore subjected to hardening treatment. However, when the material of the opposed member, i.e., the shoe, is an iron-based material, the sliding takes place between identical kinds of materials thereby incurring a problem that a seizure is liable to occur. Sintered copper alloy is used for the opposing material (shoe) opposed to an iron-base swash plate, so as to avoid the above mentioned problem.

In addition, it was also proposed to apply tin plating on the iron-based swash-plate so as to avoid the sliding between identical kinds of materials and hence to enhance the seizure resistance.

In the ordinary swash-plate type compressor, the cooling medium is sucked into and compressed in the cylinder bores at both sides of a piston. In a recently produced single-side compression type swash-plate compressor, the compression and suction are carried out usually only in the rear (R) side. This swash plate compressor is described with reference to an example of the variable volume type compressor disclosed in Japanese Unexamined Patent Publication No. 6-288,347 filed by one of the applicants.

As shown in FIG. 13, the front housing 2 is secured to one side of the cylinder block 1, while the rear housing 3 is secured to the other side via the valve sheet 4. The driving shaft 6 is included in the crank space 5 formed by the cylinder block 1 and the front housing 2 and is rotatably supported by the bearings 7a and 7b. A plurality of the cylinder bores 9 are formed in the cylinder block 1 at a location where they surround the driving shaft 6. A piston 10 is inserted in each cylinder bore 9.

A rotor 16 is synchronous rotatably supported by the driving shaft 6 in the crank space. In addition, a sleeve 12 having a spherical surface is slidably supported by the driving shaft 6. A compression spring 13 is provided between the rotor 16 and the sleeve 12 having a spherical surface and forces the sleeve having a spherical surface in the direction toward the rear housing 3. A rotary swash plate 14 is rotatably supported on the outer peripheral surface of the sleeve 12 having a spherical surface. In the condition of the compression spring 13, which is at the maximum shrinkage condition as shown in FIG. 13, the contact surface 14, which is formed aslant on the lower back surface of the rotary swash plate 14, abuts on the rotor 16. Therefore, a further inclination of the rotary swash plate 14 to increase its inclination angle is restrained. Although not shown in the drawing, a further inclination to decrease the inclination angle of the swash plate may be restrained.

Semi-spherical shoes 15a, 15b abut on the outer peripheral parts of the rotary swash plate 14. The outer peripheral surface of these shoes 15a, 15b are engaged with the ball-bearing surfaces of the piston 10. Therefore, a plurality of the pistons 10 are coupled with the rotary swash-plate 14 via the shoes 15a, 15b and are capable of reciprocating in each cylinder bore 9, in which the pistons are mounted.

The rear housing 3 is divided into the suction space 20 and the exhaustion space 21. The suction port 22 and the exhaustion port 23 are formed through the valve sheet 4 and these ports are opened through the respective cylinder bores 9. The compression space formed between the bearing plate 4 and the piston 10 is communicated with the suction space 20 and the exhaustion space 21 via the suction port 22 and the exhaustion port 23, respectively. That is, the compression is carried out only in the single side of the swash plate, i.e., the rear (R) side.

A suction valve is provided in each suction port 22 and opens or shuts the suction port 22 in accordance with the reciprocating movement of the pistons 10. An exhaust valve is provided in each exhaustion port 22 and opens or shuts the exhaustion port 22 in accordance with the reciprocating movement of the pistons 10, while the exhaust valve is restrained by the retainer 24. A control valve (not shown) is provided in the rear housing 3 to adjust the pressure in the crank space 5.

In the compressor as constructed hereinabove, when the rotary swash-plate 14 is rotated along with the driving of the driving shaft 6, each piston 10 is reciprocated via the shoes 15a, 15b in the cylinder bore 9, thereby sucking the cooling-medium gas through the suction port 20 into the compression space, compressing the cooling-medium gas and then exhausting it into the exhaustion space 21. Here, the amount of the cooling-medium gas, which is exhausted into the exhaustion space 21, is controlled by means of adjusting the pressure in the crank space 5.

In addition, the compressor is provided with the mechanisms K, 17 through 19 which enable the exhaustion amount to be adjusted.

With reference to FIG. 14, which shows the essential parts of the above described, single-side compression type swash-plate compressor, the problems of wear in the single-side compression type swash plate compressor are explained.

In the compressing process, the compression reaction-force in the cylinder bore is transmitted via the single-head piston 10 and the shoes 15 to the rotary swash plate 14. The shoe 15a at the side of the compression space is subjected to the compression reaction force, with the result that great sliding resistance is generated between the shoe 15a and the rotary 14. Since such sliding resistance results not only in the power loss but also in the wear of the swash plate, countermeasures against such results become necessary.

Meanwhile, since the shoe 15b at the opposite side of the compression space is also brought into contact with the rotary swash plate 14, sliding resistance generates due to the relative displacement between them. However, the rotary swash plate 14 is not subjected via the shoe 15b to the compressing reaction-force, and the sliding contact between the shoe 15b and the rotary swash-plate 14 occurs only during the suction process, where the single-head piston 10 moves from the top dead center to the bottom dead center. In the suction process, the piston 10 is accompanied by the rotary swash-plate 10 via the shoe 15b, and, the force necessary for accompanying the swash-plate 10 is less than the force required in the compression process. The sliding resistance between the shoe 15b and the rotary swash-plate 14 is accordingly slight.

Since the tin plating applied on an iron-based swash-plate of the single-side compression type swash-plate compressor is soft, a problem that arises is insufficient wear-resistance. Furthermore, although a hard element added to an aluminum alloy enhances wear resistance, a problem that arises is insufficient seizure resistance of the swash plate at the compression-space side.

It is therefore an object of the present invention to enhance the performance and reliability of a single-side compression type swash-plate compressor by means of providing on the surface of an iron-based or aluminum-based swash plate a surface layer which exhibits improved both seizure resistance and wear resistance.

The present inventors extensively considered and experimented on a surface treating method, which can solve the above mentioned problems and discovered the following. The flame-sprayed copper alloy has, as compared with the sintered alloy, (a) fine structure, and (b) high hardness provided for the identical composition. Furthermore, (c) it is possible to adjust the structure, by means of adjusting the spraying condition, from a completely melted structure to a structure in which the shape of the atomized powder or the structure is partly retained, thereby making it possible to change the sliding properties in conformity with the usage conditions. It was discovered that improved seizure resistance and wear resistance are provided, with regard to the sliding between the shoes of compression-space side and a swash-plate, when these properties are utilized.

The invention, which is completed based on such discoveries, is related to a swash plate used in the single-side compression type swash plate compressor, which consists of an iron-based or aluminum-based material and is used in a swash-plate type compressor, and is characterized in that a flame-sprayed layer of a copper-based alloy, which contains, by weight percentage, not less than 0.5% in total, preferably not less than 1% and not more than 50%, one or more kinds selected from a group consisting of not more than 40% of lead, not more than 30% of tin, not more than 0.5% of phosphorus, not more than 15% of aluminum, not more than 10% of silver, not more than 5% of silicon, not more than 5% of manganese, not more than 5% of chromium, not more than 20% of nickel, and not more than 30% of zinc, is formed on at least the sliding surface with respect to the shoe, preferably an iron-based shoe at the compression space side, and, further electrolytic plating, electroless plating, lubricant coating, phosphatizing or hardening is applied on the shoe at the side opposite to the compression space.

The percentage in the present invention is weight percentage unless otherwise specified.

In the above mentioned copper-based alloy, which is applied as the flame-sprayed layer on the swash-plate at the compressing side, a part of the lead element is present as lead particles and provides compatibility and low-friction property. The other part of the lead element is solid-dissolved to strengthen the copper matrix and provides wear resistance and seizure resistance. Lead is the most preferred element for enhancing the sliding properties under a dry condition. However, when the lead content exceeds 40%, the strength of the copper alloy decreases. It is, therefore, necessary that the maximum limit is 40%. A preferred lead content is from 1 to 30%. A more preferred lead content is from 2 to 15%.

The additive elements other than lead are mainly solid-dissolved in copper and enhance the wear resistance and seizure resistance. Among them, silver outstandingly enhances the sliding properties under a condition of a slight amount of lubricating oil. With regard to the amount of addition, tin precipitate at an amount of not less than 10%, silicon and manganese precipitate at an amount of not less than 1%, and the precipitates enhance the wear resistance. Heat conductivity, good sliding property with respect to an iron-based or aluminum-based opposing material, wear resistance and seizure resistance, which are inherent properties of copper, are lost when tin exceeds 30%, phosphorus exceeds 0.5%, aluminum exceeds 15%, silver exceeds 10%, silicon exceeds 5%, manganese exceeds 5%, chromium exceeds 5%, nickel exceeds 20%, and zinc exceeds 30%. These elements must, therefore, not exceed the above-mentioned maximum limits. Preferred contents are: from 0.1 to 20% for tin; from 0.2 to 0.5% for phosphorus; from 0.5 to 10% of aluminum; from 0.1 to 3% for silicon; from 0.1 to 8% for silver; from 0.5 to 4% for manganese; from 0.5 to 3% of chromium, from 0.5 to 15% for nickel; and, from 5 to 25% for zinc. More preferred contents are: from 0.1 to 15% for tin; from 1 to 8% of aluminum; from 0.5 to 1.5% for silicon; from 0.2 to 5% for silver; from 0.5 to 3% for manganese; from 1 to 2% for chromium; from 1 to 10% for nickel; and, from 10 to 20% for zinc. The total amount of the additive elements should be within a range of from 0.5 to 50% for the reasons described above.

The shoe per se is known. A shoe, which can be used, is disclosed, for example, in Japanese Unexamined Patent Publication No. Sho. 51-36611 filed by one of the present applicants, and has a sliding surface consisting mainly of iron. Bearing steel is preferred. Methods for producing a shoe are not at all limited. Such techniques as rolling, forging, powder-metallurgy and surface hardening can be optionally employed for the production of a shoe. The shoe at the side opposite to the compression space is preferably boronized or nitried on the sliding surface.

The surface of a shoe at the side opposite to the compression space must be subjected to electrolytic plating, electroless plating, lubricant coating, phosphatizing or hardening so as to improve the sliding properties of the shoe sliding on the steel or aluminum. Although the sliding properties attained by these treatments are inferior to those attained by the flame-sprayed copper-based material, these treatments are sufficient because the wear condition in the side opposite to the compression space is relatively moderate. Here, the electrolytic plating is preferably carried out by plating tin-, lead- or copper-based metal (alloy) to a thickness of from 0.5 to 3 .mu.m. Next, the electroless plating is preferably carried out by plating tin-based metal (alloy) to a thickness of from 0.5 to 3 .mu.m. Furthermore, the lubricant coating is preferably carried out by applying PTFE, or molybdenum disulfide powder bonded by resin binder, e.g., Defric (trade name), to a thickness of from 1 to 20 .mu.m. Subsequently, the phosphatizing is preferably carried out by applying manganese phosphate to a thickness of from 1 to 20 .mu.m. Finally, the hardening is preferably carried out by subjecting a steel swash-plate to carburizing, nitriding, soft-nitriding, boronizing or the like, and subjecting an aluminum swash-plate to anodizing.

FIG. 1 is a metal-structure photograph of a Cu--Al alloy flame-sprayed layer at its cross section (magnified 320 times).

FIG. 2 is a schematic drawing of the metal-structure of a Cu--Al alloy flame-sprayed layer at its cross section and distribution of Al amount.

FIG. 3 is a metal-structure photograph of an atomized Cu--Pb alloy powder (magnified 1000 times).

FIG. 4 is a metal-structure photograph of an atomized Cu--Pb alloy powder (magnified 1000 times).

FIG. 5 is a metal-structure photograph of a flame-sprayed layer, in which the atomized structure and the forcedly solid-dissolved flame-sprayed structure are mixed.

FIG. 6 is an electron-microscope photograph of a forcedly solid-dissolved flame-sprayed structure depicting an EPMA analysis chart (magnified 3000 times).

FIG. 7 is a metal microscope photograph of flame-sprayed structure having a lead-free melted structure (magnified 3 20 times).

FIG. 8 is a graph showing the properties of a flame-sprayed layer with the graphite additive.

FIG. 9 is a graph showing the effect of peening in preventing cross cracks.

FIG. 10 is a graph showing amount of deformation due to peening by iron balls.

FIG. 11 is a graph showing amount of deformation due to peening by zinc balls.

FIG. 12 is a drawing describing a test for the adhesive force.

FIG. 13 is a cross sectional view of a single-side compression type swash-plate compressor.

FIG. 14 is a schematic drawing for illustrating the sliding circumstance between the swash-plate and shoe in a single-side compression type swash-plate compressor.

The copper-based flame spraying applied on the surface of a swash-plate at the compression-space side is hereinafter described in detail.

A characteristic point of the metal structure of the flame-sprayed layer is that the atomized copper-powder is melted. More specifically, the droplets, which have been melted and hence formed in the flame of flame-spraying, are impinged upon the surface of the swash plate and then deformed. As seen in the cross section of the layer, portions in laminar form, flaky form or in a flat plate are laminated on one another. As seen on the flat plane, the small discs, fish scales, and the like are laminated on one another. The flame-sprayed layer according to the present invention may have such a structure as a whole.

The flame-sprayed structure has, in addition to the above mentioned characteristic, the following characteristics. That is, when the atomized powder is forcedly supplied under pressure of gas into the flame, the atomized powder maintains the form of isolated particles, the particles being scattered. The atomized powder seems to be melted as it is, although a part of the particles may be incorporated into one another. Molten droplets impinge upon the swash plate and solidify. When the thickness of the flame-sprayed layer is decreased to accelerate the cooling speed, one droplet or a few droplets are not incorporated into the other numerous droplets but solidify as independent particles. The droplets, which are relatively small, collapse and are laminated on one another in the form of numerous fine laminar pieces, as described above. The droplets as a whole form the flame-sprayed layer. An example of such flame-sprayed layer is illustrated in FIG. 1 showing a microscopic photograph of a Cu- 8% Al alloy. In the flame-sprayed structure as shown in this drawing, the components are distributed in the entire flame-sprayed structure as schematically shown in FIG. 2(b). That is, the solidification segregation is repeated in the fine laminar pieces and the number of repeated solidifications segregations is the same as that of these pieces. Macroscopically observed, the distribution of components is uniform. Such uniformity in the components is believed to stabilize the sliding properties and is desirable particularly in the light of stabilizing the friction force. Incidentally, when the flame-sprayed layer was subjected to heat treatment at an appropriate temperature below the melting point so as to lessen the solidification segregation and to attain uniformity of the components even in the fine laminar pieces (FIG. (c)), the sliding properties attained further uniformity of the components even in the fine laminar pieces (FIG. (c)), and the sliding properties were further improved. However, when the material was considerably softened by the heat treatment, a tendency towards deterioration of the sliding properties arose.

In addition, it is preferred in the present invention that a part of the atomized powder does not melt but remains in the flame-sprayed layer.

Hereinafter are described the features of the mixed structure of the melted structure and the unmelted structure of atomized powder with regard to a Cu--Pb alloy.

The unmelted structure of lead-bronze atomized powder (hereinafter referred to as "the atomized structure"), of which the above mentioned structure is comprised, is the rapidly cooled structure of atomized lead-bronze powder, which structure does not disappear while the powder is in the flame but is left in the flame-sprayed layer. In the structure of this atomized powder, the phases mainly composed of lead disperse, as a minority phase, in a fine particulate form or distributes around the copper powder in the laminar form as is typically shown in FIG. 3 showing a microscopic structure of a Cu- 24% Pb alloy. This structure is one type of cast structure, but is characterized by: (1) the predominant cooling direction is from the periphery to the interior of a particle; (b) more rapidly cooled structure than the ordinary ingot casting or continuous casting, and the lead is fine particles, whose diameter is typically 10 microns or less; or, (c) lead distributes along the copper boundaries in the form of a network. Incidentally, the structure of FIG. 3 is a case of uniform cooling, while in the case of FIG. 4, a part of the periphery of the particles is so intensively cooled as to form fine-sized particles in this part, and the lead particles are coarse where the cooling is weak.

According to one form of the present invention, i.e., the mixed structure, the lead is forcedly solid-dissolved in the copper alloy. The so-formed structure in the flame-sprayed structure is hereinafter referred to as "the forcedly solid-dissolved flame-sprayed structure". In this mixed structure, the lead is forcedly solid-dissolved in the laminar structure, which is produced by melting the droplets within the flame of the flame spray, impinging the droplets on the substrate of a swash plate, and compressing them flat.

As shown in FIG. 5, the atomized structure, which is said to be an equilibrium structure (white lead phases are observed), and a forcedly solid-dissolved flame-sprayed structure, which is said to be a non-equilibrium structure (no white lead phases are observed) are mixed in these mixed structures.

FIG. 5 shows an example of the flame-sprayed structure according to the present invention (the white particles or pattern correspond to the lead) and elucidates the following points.

The atomized structure corresponds to approximately 13% by area in this structure, while the laminar portions, where no lead phases are recognized, comprise the remaining 87% by area. In these laminar portions, lead is forcedly solid-dissolved. Since the atomized powder collapses, when it impinges upon the backing metal, or since the outer side of the atomized powder may be probably melted, the remaining atomized structure has an outer configuration which is quite different from that of the powder. However, the lead morphology in the powder is maintained even after the flame spraying.

FIG. 6 is an EPMA photograph of the flame-sprayed Cu- 10% Pb-10% Sn layer and shows the forcedly solid-dissolved flame-sprayed structure by the cross section of the layer. This photograph shows that Pb and Sn are present, although the presence of particles is not identified. Incidentally, since the solubility of Pb in Cu is slight, Pb is forcedly solid-dissolved. Since Sn is solid-dissolved under ordinary casting conditions, its solid-solution is not forced. The sliding properties of the respective components of the flame-sprayed layer are described below.

Since numerous fine lead particles are present in the atomized structure, its compatibility, low-friction property, and lubricating property are excellent. In addition, the atomized powder has usually 100 .mu.m or less of the particle diameter, and the structure of the respective particles is virtually identical. There is, therefore, uniformity in the structure of the particles. Therefore, the lead particles disperse uniformly in the sliding material, when such atomized structure is maintained in the sliding material, so that the sliding properties are stabilized.

The forcedly solid-dissolved flame-sprayed structure has a high hardness amounting to approximately Hv 200 or more, because lead is forcedly solid-dissolved. The forcedly solid-dissolved flame-sprayed structure has thus excellent wear resistance. In addition, as the powder is once melted on the backing metal after the flame spraying, this structure can enhance the bonding strength with the backing metal.

A stripe pattern is noticeable in FIG. 6. The solid-solution amount of Pb and Sn is large in the white portions of the stripe pattern. It is presumed from the stripe pattern that the flame-spraying deposited amount of material per unit time changes periodically or in a pulsatory manner, and, further, the cooling speed increases or decreases corresponding to the above change. Such interesting structure is formed. However, it is needless to say that this fact does not limit the forcedly solid-dissolved flame-sprayed structure according to the present invention.

It is not preferred that either one of the atomized structure or forcedly solid-dissolved flame-sprayed structure predominates excessively. It is, therefore, desirable that the atomized structure is preferably from 2 to 70% by area, more preferably from 2 to 50% by area. It is necessary here that the flame-sprayed layer essentially totally consists of the atomized structure and the forcedly solid-dissolved flame-sprayed structure. Any structure other than the above mentioned one, for example, a precipitated lead structure, in which lead is not forcedly dissolved in the flame-sprayed lead-bronze alloy but precipitates, may be mixed, provided that its amount is minimal. However, the targeted upper limit of such structure is 10% by area.

The present inventors conducted research to control the structure of flame-sprayed sliding layer from a point of view different from the point of view of constructing the layer structure and the forcedly solid-dissolved flame-sprayed structure. As a result, the sliding performance could be further enhanced as is described hereinafter.

Lead has mainly a lubricating effect in the bronze (the bronze means in the present invention a copper alloy, in which tin is not an essential element). The lead phases in the atomized structure implement this effect in the flame-sprayed bronze. Lead is solid-dissolved in the copper matrix when the forcedly solid-dissolved flame-sprayed structure is formed by the flame spraying. Although a part of the lead phases may be in a laminar form, since copper, tin and the like are solid-dissolved in the lead phases, the lubricating effect is not expected to be realized.

Meanwhile, when the particles of atomized powder are melted during flame spraying, they solidify around the non-melted atomized powder and on the substrate surface and enhance the adhesion properties of the flame-sprayed layer during solidification and strengthen the flame-sprayed layer. However, the lead of the forcedly solid-dissolved flame-sprayed structure may precipitate in the grain boundaries due to heat generated in the sliding. In addition, the segregated parts in a long laminar form are of low strength and may therefore exert a detrimental effect upon the adhesion of the flame-sprayed layer and its strengthening.

When the sliding material is covered with a flame-sprayed bronze layer which contains network or granular lead-phases in the atomized structure and is subjected to stress parallel to the plane, since the strength of lead is lower than that of copper, cracks run along the laminar lead-phases, and, hence the cracking occurs under a relatively low stress. Contrary to this, the fine particulate lead-phases have a high resistance against the cracking.

It is preferred that lead is completely absent or is contained 3% at the most in the melted structure, i.e., a region in which the atomized powder, which has been melted during flame-spraying transportation or on the backing metal, is caused to solidify on the backing metal in a different fluid form from the one before spraying, without retaining such as laminar form, flaky form or the like before flame-spraying. This melted structure is hereinafter referred to as "the lead-free melted structure". Lead present in the melted structure in an amount exceeding 3% based on such structure not only fails to exhibit any lubricating effect, but also becomes a cause for impairment of the properties of the entire lubricating layer except for the wear resistance. Lead is, therefore, preferably present in the starting powder of flame spraying, which does not undergo any melting in the process from the flame-spraying transportation until the layer formation by spraying, i.e., in the unmelted structure. The flame-sprayed structure consisting of the lead-free melted structure and such lead-containing unmelted structure is hereinafter referred to as the "lead-segregated melted structure".

The powder may be crushed powder, but atomized powder is preferably used because it is appropriate for flame spraying. The lead-free melted structure, which is a characteristic of the present invention, is hereinafter described. An example of the atomized powder, which forms such structure, is described.

FIG. 7 is an optical microscope photograph of the flame-sprayed layer obtained in the later described Example 4. In this drawing, a few parts appearing mainly as white nodules are the unmelted structure of the atomized bronze powder (copper-tin-lead). What appears mainly black is the melted structure of bronze powder (copper-tin). A number of white small parts are either the nodular, unmelted structure, whose cut cross section is shown, or atomized powder which has been finely divided into fine fragments during the transportation of flame-spraying. Fine white points in the white nodular, unmelted structure are lead phases which precipitate or crystalize in the atomized powder.

It is undesirable in the lead-segregated structure that either atomized structure or lead-free melted structure predominates excessively. It is, therefore, desirable that the unmelted atomized structure is from 2 to 70% by area, more preferably from 2 to 50% by area.

The lead phases in the atomized structure may be in the form of a network but is preferably in a particulate form, because the cracking does not propagate along the lead layer during sliding, when the lead phases are in the particulate form, so that the crack resistance is enhanced. In order for the lead phases in the atomized structure to be in a particulate form, it is necessary that: the atomized powder, whose lead phases are in the particulate form, is selected as starting material; and, further, the impinging pressure upon the blank material should not be so excessively high as to collapse the unmelted powder to such an extent that its lead phases are converted to laminar form. When the particle diameter of particulate lead-phases is too large, the strength is lowered. On the other hand, when the particle diameter is too small, the lubricating property is lowered. Desirably, the diameter is within a range of 0.5 to 20 .mu.m, assuming that each lead phase is converted to a circle having the identical area.

Thickness of the flame-sprayed layer having the lead-segregated melted structure is preferably within a range of from 5 to 500 .mu.m. When the thickness is too great, the desired structure is not obtained but the unmelted atomized structure undergoes melting because heat is confined in the flame-sprayed layer, unless labor-consuming measures are employed such that the backing metal is subjected to forced cooling of the opposite side of flame spraying. Contrary to this, when the thickness is too small, the sliding properties are inferior. Considering both these aspects, the thickness needs to be determined appropriately.

Next, the structure of bronze, to which a solid-solution type element such as aluminum is added, is described. In this structure is mixed a structure, in which the original shape of atomized powder (namely, "the atomized structure") and a structure, in which the original shape of atomized powder is changed to a laminar form or the like (hereinafter referred to as "the flame-sprayed deformed structure"). This point is the same as that of the flame-sprayed structure of copper-lead alloy described above. Points of contrast between the atomized structure and the flame-sprayed deformed structure are described. Since the atomized structure is heated during the flame-spraying and after impinging upon the swash plate, the structure is a homogenized and annealed one. On the other hand, the flame-sprayed deformed structure is a cast structure, in which the atomized powder is re-melted and solidified. Therefore, the solid solution amount of aluminum is small in the atomized structure, and the aluminum is liable to precipitate uniformly and finely. The solid-solution amount of aluminum is large in the flame-sprayed deformed structure. In addition, when the addition amount of aluminum is much less than the solid-solution amount under the equilibrium state, aluminum segregates in the case of the flame-sprayed deformed structure, as seen in the cast structure, while the aluminum distribution is uniform in the atomized structure. Uniform distribution of the solute element, i.e., aluminum, always provides a contact with the surface of the opposing material, having microscopically uniform sliding properties, and is considered to be desirable in the light of sliding properties. To summarize the above description, the two aspects of the sliding properties as described in detail with respect to the copper-lead alloy are realized, although not distinctly.

Such elements as nickel, antimony, iron, aluminum, phosphorus, zinc and manganese are preferably contained in only either the melted structure or forcedly solid-dissolved flame-sprayed structure. Silver may be contained in any structure(s).

It is possible to add into copper alloys having the above mentioned various flame-sprayed structures not more than 10%, preferably from 1 to 10% of one or more compounds selected from a group consisting of Al.sub.2 O.sub.3, SiO.sub.2, SiC, ZrO.sub.2, Si.sub.3 N.sub.4, BN, AlN,TiN, TiC, B.sub.4 C, iron-phosphorus compound, iron-boron compound, and iron-nitrogen compound, as a component for enhancing the wear resistance. When the addition amount of these component(s) exceeds 10%, the lubricating properties and the compatibility become poor, and as a result, seizure becomes liable to occur.

Furthermore, in the present invention, the bronze can contain not more than 3% of graphite by weight percentage. Graphite is an additive agent which enhances the lubricating property and hence prevents cracks in the sliding layer of a swash plate. When the content of graphite exceeds 3%, the strength of bronze disadvantageously lowers. The preferred content of graphite is from 0.15 to 1.5%.

FIG. 8 is a graph showing the relationship between the amount of graphite, which is added to the flame-sprayed sliding layer (the flame-sprayed structure--lead-segregated flame-sprayed structure, thickness--200 .mu.m) of a Cu-6% Sn alloy, and the physical properties and seizure time.

The testing conditions are as follows.

Testing machine: a pin-disc testing machine

Sliding speed: 20 m/second

Load: 500N

Lubricating oil: ice-machine oil applied at the beginning

Opposing material: SUJ-2

It is apparent from FIG. 8 that: the hardness (Vickers hardness under 300 g of load) and the shear stress lowers along with the addition amount of graphite, thereby impairing the basic physical properties of the flame-sprayed layer; but, on the other hand, the seizure resistance, which is one of the sliding properties, is enhanced. Such an outstanding effect is attributable to the fact that the graphite decreases the coefficient of friction. The above-mentioned basic physical properties do not significantly influence the seizure under a condition which is infinitely close to the dry condition.

Since graphite, which is effective for decreasing coefficient of friction, is liable to burn during the flame-spraying, a measure against the oxidation, such as a copper coating, should be employed.

It is preferred in the present invention, in order to enhance the adhesion of the flame-sprayed layer, that an intermediate layer, which consists of one or more kinds of material selected from a group consisting of copper, nickel, aluminum, copper-nickel based alloy, nickel-aluminum based alloy, copper-aluminum based alloy, copper-tin based alloy, self-fluxing nickel alloy, and self-fluxing cobalt alloy, is formed between the flame-sprayed layer and the substrate of a swash plate by means of a method such as plating, sputtering, flame-spraying or the like. Any one of these materials is easily alloyed with the bronze and is, therefore, strongly bonded with the (un)melted layer during the flame spraying. The bonding strength between the flame-sprayed layer and the backing metal, is enhanced, when the surface of materials is rough. A preferred thickness of the intermediate layer is from 5 to 100 .mu.m. As the copper-tin based alloy, a Cu--Sn--P based alloy can be used. This alloy has good fluidity and does not oxidize easily and hence can provide improved performance when it is flame-sprayed to form an intermediate layer.

The sliding layer according to the present invention can be produced by the ordinary flame-spraying method and under ordinary conditions. However, when the flame-sprayed structure with the mixed, melted and unmelted structures is to be formed, the flame-spraying conditions must be that: only part of the atomized bronze powder is melted during the transportation of flame-spraying; after impinging upon the backing metal, the whole lead-bronze is not remelted (a partial remelting may occur); and, the cooling speed of the melted alloy and solidified alloy is fast. More specifically, the high-speed fire-flame spraying method is employed, in which gas-pressure and gas-speed are made high, while the flame-spraying distance is set at approximately 180 mm, thereby providing a conditions for limiting the thickness of the flame-sprayed layer. More specified conditions are as follows.

Gas pressure: 10 kgf/cm.sup.2

Flame speed: 1200 m/sec

Thickness of flame-sprayed layer: 150 .mu.m

In order to increase the proportion of the atomized structure under the above-mentioned conditions, the proportion of powder to gas may be increased. Optional proportion of the structure can be revised by adjusting the spraying conditions.

Next, a method for producing a lead-segregated melted structure is described.

It is indicated in the metal (copper)/ceramics(Al.sub.2 O.sub.3) based flame-spraying that the latter is once melted, then separated from the former and is solidified (Bulletin of The Japan Institute of Metals. "Materia" Vol. 33 (1994), No.3, page 271, FIG. 5). Such separation and solidification is virtually impossible in the copper-lead based powder because of the low melting point of lead. On the other hand, the possibility of lead melting during flame spraying is higher than that of copper.

Consideration was given to the flame-spraying conditions, under which the above points are avoided, whereby the complete melting of the lead-containing powder with coarse grains does not occur but melting of the lead-free powder with fine grains occurs during the transportation of flame-spraying and the above-mentioned powder with coarse grains does not melt after impinging on the backing metal. As a result, it turned out that an advisable flame-spraying condition lies in the first powder with fine grains, which is fine powder essentially not containing lead and is mainly composed of copper, and, further in the second powder with coarse grains, which contains lead and is mainly composed of copper.

The coarse grains and fine grains here indicate that there is a difference of two or more grades in the average grain diameter according to JIS Z 8801 (amended in 1981, standard mesh opening). When the difference in grades is only one, the melting of lead is liable to occur. A difference in grade of eight or less is preferable from the viewpoint of the strength of bond of flame-sprayed layer.

The physical properties of the flame-sprayed layer are now described.

Hardness of the flame-sprayed layer is mainly dependent upon the amount of the additive element(s) and is in the range of Hv.sub.(0.3) 110-280 when the addition amount is in the range of 0.5 to 40%. This high hardness of the flame-sprayed layer is characteristic as compared with the hardness of sintered material and cast material.

Thickness of the flame-sprayed layer is preferably from 5 to 500 .mu.m. When the thickness exceeds 500 .mu.m, the amount of heat confined in the flame-sprayed layer becomes great. When the calorie exceeds a certain level, the copper alloy may be remelted, so that the hardness and density are lowered. As a result, the sliding properties are impaired. Preferred thickness of the flame-sprayed layer is from 5 to 300 .mu.m, particularly, from 20 to 200 .mu.m.

After flame-spraying, the surface of the flame-sprayed layer may be or may not be polished, and the above-mentioned thickness is attained to provide the sliding layer.

The surface of a swash plate may be subjected to roughening treatment, such as shot blasting, etching, chemical conversion treatment and the like, or may be subjected to plating for providing an adhesive layer. This treatment can be optionally applied.

In addition, in the present invention, the heat treatment may be carried out under a condition to attain the homogenization of the components in the flame-sprayed layer. More specifically, the copper-based alloy having the above-mentioned composition, if necessary together with the hard matters, is flame-sprayed, and, subsequently, to this flame-sprayed layer heat treatment can be applied in a temperature range from 100.degree. to 300.degree. C. for 30 to 240 minutes. When the temperature and time are less than these lower limits, the heat treatment is not effective to homogenize the components. On the other hand, when the temperature and time exceed the above upper limits, the flame-sprayed layer softens, or the crystal grains, of which the above-mentioned structures such as the atomized structure and the flame-sprayed deformed structure are comprised, the lead particles and a flaky structure are coarsened and, hence, the peculiar morphology of the flame-sprayed structure may be destroyed and the sliding properties are impaired. Preferred conditions for heat treatment are 150.degree.-300.degree. C. for 10 to 120 minutes, more preferably 150.degree.-250.degree. C. for 60-120 minutes.

In addition in the present invention, the flame-sprayed layer may be subjected to peening (which is occasionally referred to as shot blasting) so as to prevent the cross cracks from occurring on a swash plate. The peening may be preferably carried out such that the grains of steel, zinc or the like having a particle diameter of from approximately 0.05 to 1.0 mm are projected under a condition of 50-200 kg/m.sup.2 and speed of 10 to 80 m/second.

FIG. 9 is a graph showing the results of such tests where the resistance against the surface cracking is measured by a seizure-testing method. The number of surface cracks generated by this testing method is measured for each case of peening and without peening. The powder used was 30% by weight of the following (a) and 70% by weight of the following (b).

(a) Cu-10% Pb-10% Sn, average particle diameter of 63 .mu.m.

(b) Cu-6% Sn, average particle diameter of 19 .mu.m.

The flame-sprayed layer has a lead-segregated structure and a thickness of 200 .mu.m. As is apparent from FIG. 9, the peening is very effective for preventing the cross cracks.

Preferred peening conditions are described with reference to FIG. 10 and FIG. 11.

Flame-spraying of Cu-10% Pb-10% Sn alloy with 300 .mu.m thickness (structure as shown in FIG. 5) was applied on a substrate (SPCC) having 1.5 mm of thickness and 40 mm of width. After flame spraying, the samples were deflected so that the substrate side was concave. The deflection amount (d) was thus measured. Subsequently, the peening was carried out by the iron balls as shown in FIG. 10. The deformation amount in terms of deflection amount (d) is indicated in the graph of said drawing. As is apparent from this drawing, the peening effect is appreciable at approximately 10 seconds or later. Considering the size difference in an actual swash-plate and the samples, preferred peening on an actual swash-plate is believed to be approximately 50 secons or more.

FIG. 11 shows the result of the same flame-spraying and peening as in FIG. 10 except for 0.5 mm zinc balls and 2 kg/cm.sup.2 in peening. As is apparent from this drawing, the peening effect is appreciable from approximately 1 minute in the case of zinc balls. Time of zinc-ball peening on a swash plate is believed to be preferably 5 minutes or more.

In Table 1 is shown the change of stress in a flame-sprayed layer, in a case where the Cu-10% Pb-10% Sn alloy is flame-sprayed on an aluminum-substrate to a thickness of 200 .mu.m (the structure as shown in FIG. 5) and is subsequently subjected to heat treatment or peening.

As is apparent from this table, the tension stress is mitigated by applying peening on the flame-sprayed layer and is converted to compression stress. This is believed to make the surface cracking difficult to occur. Contrary to this, the heat treatment does not change the internal stress.

The present invention is hereinafter more specifically described with regard to the examples.

The water-atomized bronze powder having the following qualities were flame-sprayed on a swash-plate (FCD70, thickness 10 mm) to form a flame-sprayed layer having a thickness of from 20 to 200 .mu.m shown in Table 2 as "layer thickness".

(1) Copper-based atomized powder

Al content: 10%

Particle diameter: under 75 .mu.m

(2) Lead bronze atomized powder

Lead content: 10%

Tin content: 10%

Particle diameter: under 90 .mu.m

Structure: shown in FIG. 3

(3) Composite bronze atomized powder

Lead content: 10%

Tin content: 10%

Phosphorus content: 0.05%

Silver content: 3%

Hard matter (kind AlN): 5%

Particle diameter: under 75 .mu.m

Structure: shown in FIG. 3

(4) Bronze atomized powder

Tin content: 10%

Particle diameter: under 75 .mu.m

Structure: shown in FIG. 3

The flame-spraying was carried out by using a diamond-jet type gun produced by FIRST METECO Co., Ltd., and under the following conditions. The structure of the resultant flame-sprayed layer had the surface area percentage of the atomized structure (A) and the surface area percentage of the melted structure (M) shown in Table 2. The unit of thickness in this table is .mu.m.

Kind of gas: Mixed gases of propylene in 10 volume parts and oxygen, air in 90 volume parts.

Pressure of gas: 7 kgf/cm.sup.2

Flame speed: 1200 m/sec

Flame-spraying distance: 180 mm

Supplying amount of powder: 50 g/minute

Prior to the flame spraying, an intermediate layer was formed on the swash-plate by means of preliminarily flame-spraying 50 .mu.m thick Ni--Al alloy. The swash plate, on which the intermediate layer was applied, is indicated with "i" in the test number of Table 2.

The seizure resistance was tested under the following conditions.

Seizure Test

Testing machine: Pin-disc type testing machine

Sliding speed: 15 m/s

Lubricating condition: Ice-machine oil

Application method of load: 400 N/10 minutes, successive increase

The seizure load was measured, when the seizure occurred first in either the compression space side or the opposite side to the compression space. However, in every one of the present tests, the seizure occurred in the compression-space side.

Test of Adhesive Force

Bonding test by adhesive agent (shown in FIG. 12)

Adhesive agent: epoxy-based adhesive agent (the adhesive agent-layer 2 was bonded on the lower side of the sheet)

Flame-sprayed layer: thickness- 150 .mu.m (denoted as 101 in FIG. 12 )

Rod 103 was horizontally pulled off. The force required for pulling was obtained. As another method, the judgment was made that non-separation and partial separation were .smallcircle. and .DELTA., respectively.

The wear resistance was qualititavely evaluated by the wear amount obtained by the pin-disc tester. The three levels of judgment were; made good, small and great.

The results of the tests are shown in Table 2.

It is apparent from these results that the inventive examples are superior to the comparative example 16 in the wear resistance and seizure resistance.

Industrial Applicability

As is described hereinabove, the sliding properties, which are considerably superior to the conventional swash-plate compressor, are realized by combining the features of the copper-based material and the flame spraying. Therefore, the present invention enhances the durability and reliability of a swash plate which is exposed under a severe load and lubricating condition. The present invention attains a very advantageous industrial effect.