JP4840109B2 - Sliding member and manufacturing method thereof - Google Patents

Description

    The present invention relates to a sliding member in which a Cr plating film is formed on an inner surface of an ellipse in which a seal member slides in the circumferential direction, and a manufacturing method thereof.

    For example, a rotor housing in which an apex seal of a rotary piston engine slides is known as a sliding member in which a Cr plating film is formed on an oval inner peripheral surface. Such a Cr plating (hard Cr plating) film has a feature that, for example, the hardness is as high as about Hv 1000, so that the wear is small, and the surface is protected by a Cr oxide film, and seizure hardly occurs.

In addition to the above-mentioned wear resistance, the sliding member is required to have low friction characteristics, but regarding Fe plating, a proposal to obtain low friction characteristics is known from the viewpoint of crystal orientation (Patent Document 1). reference). That is, the area ratio of the hexagonal metal crystal on the sliding surface is set to 60% or more so that (hhh) oriented crystals with the (hhh) surface facing the sliding surface side increase.
JP-A-6-316785

    However, regarding the sliding member in which the Cr plating film is formed on the inner surface of the ellipse, there has not yet been sufficiently studied to improve the characteristics from the viewpoint of crystal orientation. That is, although Cr plating has the characteristics as described above, the Cr oxide film formed on the surface of the Cr plating film has, for example, high hardness (Hv 1100 to 1400) with respect to an iron-based seal member (Hv 580 to about 600), and Since the Cr plating film is firmly bonded to the main body, the Cr oxide film acts on the counterpart material in an abrasive manner (so as to be polished), and the friction coefficient is high.

    Further, in such a sliding member having an elliptical inner peripheral surface, the sliding speed of the seal member is usually not constant, for example, from an elliptical short-axis-side inner peripheral surface to a long-axis-side inner peripheral surface. The sliding speed changes gradually depending on the location, for example, the sliding speed gradually increases when transitioning, and the sliding speed gradually decreases when transitioning from the major axis side inner circumferential surface to the minor axis side inner circumferential surface. There are many. Therefore, a stick-slip phenomenon occurs, and abnormal wear such as stepped wear is likely to occur on the sliding member and the seal member.

    Therefore, the present invention has an object to improve the Cr plated sliding member from the viewpoint of the crystal orientation and the speed dependency of the friction coefficient to reduce friction and prevent abnormal wear.

    In order to solve such problems, the present invention increases the ratio of (222) -oriented crystals in the Cr plating film, and the speed dependence of the friction coefficient exhibits a positive gradient characteristic.

The invention according to claim 1 is a sliding member including an oval inner peripheral surface having a Cr plating film formed on a surface thereof, and a seal member sliding in the circumferential direction on the inner peripheral surface,
The inner peripheral surface has a region A where the sliding speed of the seal member gradually increases and a region B where the sliding speed of the seal member gradually decreases,
In the Cr plating film, the (222) plane (the crystal plane of the Miller index (222)) specified by X-ray diffraction analysis is directed to the surface side, and the abundance of oriented crystals is the other crystal plane. Higher than the abundance of crystals oriented to the side,
The Cr plating film in the region A shows a characteristic that the speed dependency of the friction coefficient with respect to the change in the sliding speed of the seal member is a negative gradient (the characteristic that the friction coefficient decreases as the sliding speed increases),
The Cr plating film in the region B is characterized in that the speed dependency of the friction coefficient with respect to the change in the sliding speed of the seal member exhibits a positive gradient characteristic (characteristic that the friction coefficient increases as the sliding speed increases). To do.

    That is, the (222) plane is a crystal plane in which atoms of Cr crystal (BCC) are closely packed, and the crystal lattice spacing is the narrowest. Accordingly, the crystal distortion generated when an external force is applied to the Cr plating film by sliding of the seal member increases. For this reason, the Cr plating film having a high presence ratio of (222) oriented crystals originally has a high compressive residual stress, but the degree of increase of the internal compressive stress by an external force is large.

    Thus, the oxidation of the Cr crystal is caused by the diffusion of oxygen from the surface of the Cr plating film, and as a result, a Cr oxide film is formed on the surface of the Cr plating film. However, in the Cr plating film having a high compressive stress as described above, since the crystal lattice spacing is narrowed, it is difficult for oxygen diffusion to occur. For this reason, the Cr oxide film produced in a normal use environment becomes thin, and the gradient of internal stress from the surface of the film toward the inside becomes steep.

    As a result, when the seal member is slid, the Cr oxide film is easily peeled off, or the Cr oxide film is cleaved and partially cracked, and the frictional force, in other words, the sliding resistance is reduced. . That is, the Cr oxide film and the counterpart material partially adhere during sliding, and the shearing force necessary to peel the adhesion part from the Cr oxide film or Cr plating film becomes the frictional force. Since the Cr oxide film is thin and easily peels or cleaves, it acts as a solid lubricant and reduces the frictional force.

    Thus, whether or not stick slip occurs is affected by the change of the friction coefficient with respect to the change of the sliding speed. According to the present invention, the Cr in the region A in which the sliding speed of the seal member gradually increases. Since the plating film has a negative slope characteristic of the speed dependency of the friction coefficient, stick-slip is suppressed. Further, in the region B where the sliding speed of the seal member gradually decreases, the speed dependency of the friction coefficient exhibits a positive gradient characteristic, which means that the friction coefficient gradually decreases as the seal member moves. Is to go. For this reason, generation | occurrence | production of a stick slip is suppressed.

    In order to form a Cr oxide film that is likely to cause thin peeling or internal cleavage as described above, the compressive residual stress of the Cr plating film is preferably 20 MPa or more, and more preferably 40 MPa or more.

    The thickness of the Cr oxide film is preferably smaller than the average crystallite diameter of the (222) oriented crystal. That is, when the thickness of the Cr oxide film is approximately the same as or larger than the size of the (222) oriented crystallite, it means that the entire (222) oriented crystallite is oxidized. It is none other than. If so, the crystallites easily fall off during sliding, which causes excessive wear.

    However, the case where the thickness of the Cr oxide film is too thin as compared with the crystallite diameter is not preferable. This case occurs when the crystallite diameter is excessively large, which means that the Cr oxide film is bonded to a single crystallite in a wide area, and the Cr oxide film It becomes difficult to peel from the Cr plating film, that is, the friction coefficient increases. Therefore, the Cr oxide film preferably has a thickness of, for example, 1/5 or more and less than 1/1 of the crystallite diameter.

    Further, the Cr plating film may be formed by CrMo alloy plating containing Cr as a main component, in addition to the Cr polycrystal. Addition of Mo makes it possible to refine the crystal of the plating film, improve strength, and improve heat resistance, and is advantageous for improving lubricity, reducing friction (reducing the friction coefficient), and preventing seizure. The amount of Mo eutectoid is preferably 0.3% or more and 1.0% or less.

The invention according to claim 2 is the invention according to claim 1,
The Cr plating film in the region A is characterized in that the abundance of the (222) oriented crystals is smaller than the Cr plating film in the region B.

    That is, as the abundance of the (222) oriented crystal increases, the speed dependency of the friction coefficient tends to become a positive gradient characteristic. Therefore, according to the present invention, in the region A where the presence rate of the (222) oriented crystals is small, the speed dependence of the friction coefficient becomes a negative gradient characteristic, and in the region B where the presence rate of the (222) oriented crystals is large, the friction coefficient is reduced. This is advantageous in making the speed dependence positive slope.

    In this case, in the region A, the abundance ratio of (222) oriented crystals is preferably less than 70%, particularly 65% or less. The lower limit may be 50% to 55% or 60% as a guide. In the region B, it is preferable that the abundance ratio of (222) oriented crystals is 70% or more, particularly 80% or more. The upper limit may be about 85% to 90%.

The invention according to claim 3 is provided with an oval inner peripheral surface formed with a Cr plating film on which the seal member slides in the circumferential direction, and the sliding speed of the seal member is gradually increased on the inner peripheral surface. A method for manufacturing a sliding member in which there is a rising region A and a region B where the sliding speed of the sealing member gradually decreases,
The sliding member workpiece is placed in a plating bath, and the positive electrode treatment is performed to positively treat the inner peripheral surface of the workpiece with the (222) plane specified by X-ray diffraction analysis facing the surface side. Is provided with a step of forming a Cr plating film higher than the abundance of crystals in which other crystal faces are oriented on the surface side
In the step, the current density for forming the Cr plating film is made smaller in the region A than in the region B, whereby the speed dependency of the friction coefficient with respect to the change in the sliding speed of the seal member is The Cr plating film in the region A has a negative gradient characteristic, and the Cr plating film in the region B has a positive gradient characteristic.

    That is, the abundance of (222) oriented crystals in the Cr plating film varies depending on the current density during Cr plating, and the abundance of (222) oriented crystals increases as the current density increases. Therefore, according to the present invention, the current density for forming the Cr plating film is set to be smaller in the region A than in the region B. Therefore, in the region A, the abundance of the (222) oriented crystals is larger than in the region B. The speed dependency of the coefficient of friction can be reduced, and a negative gradient characteristic can be obtained in the Cr plating film in the region A, and a positive gradient characteristic can be obtained in the Cr plating film in the region B.

    As described above, according to the first and second aspects of the present invention, the abundance of the (222) -oriented crystals in the Cr plating film is made higher than the abundance of crystals of other orientations, and the seal member slides. In the region A where the moving speed gradually increases, the speed dependency of the friction coefficient of the Cr plating film shows a negative gradient characteristic, and in the region B where the sliding speed of the seal member gradually decreases, the friction coefficient of the Cr plating film depends on the speed. Since it exhibits positive gradient characteristics, it is advantageous for reducing friction of the sliding characteristics, and it is possible to prevent abnormal wear by suppressing stick slip.

    According to the invention of claim 3, in forming a Cr plating film in which the abundance of (222) oriented crystals is higher than the abundance of crystals of other orientations, the current density is higher in region A than in region B. Since it is made smaller, the presence rate of (222) oriented crystals is smaller in the region A than in the region B, the speed dependency of the friction coefficient is made a negative gradient characteristic in the Cr plating film in the region A, and The Cr plating film can have positive gradient characteristics.

    Hereinafter, embodiments of the present invention will be described with reference to the drawings.

    FIG. 1 is a schematic view of a rotary piston engine according to an embodiment. In the figure, 1 is a rotor housing as a sliding member, and 2 is an apex seal as a fluid seal member for sealing an internal fluid (gas). The apex seal 2 mounted on each top of the rotor 5 that rotates the output shaft slides on the trochoidal inner peripheral surface (oval inner peripheral surface) 3 of the rotor housing 1. In this engine, fuel containing oil is sucked into the working chamber 7 together with air from the intake port 6, and the fuel moved in the direction of the arrow 8 while being compressed as the rotor 5 rotates is ignited by the spark plugs 9 </ b> A and 9 </ b> B. A series of steps of expanding and exhausting from the exhaust port 10 after the output shaft is rotated by the pressure of the combustion gas is repeated.

    As shown in FIG. 2, the rotor housing 1 is conspicuous on the back surface of a liner 11 made of, for example, a high-strength steel plate on which a trochoid inner peripheral surface 3 is formed, and the liner 11 is cast into an aluminum alloy housing body. Produced by turning. Since the apex seal 2 slides on the inner peripheral surface 3 of the liner 11, high heat resistance, wear resistance, and low friction are required. Therefore, the presence rate of (222) oriented Cr crystals in which the (222) plane specified by the X-ray diffraction analysis is directed to the surface side on the inner peripheral surface 3 is a crystal in which other crystal planes are oriented on the surface side. A Cr plating film or a CrMo alloy plating film higher than the abundance ratio is formed.

    FIG. 3 schematically shows a Cr plating film. In FIG. 3, 12 is a (222) -oriented Cr crystal, and 13 is another Cr crystal having a different crystal orientation. On the surface of this Cr plating film, a Cr oxide film 14 made of oxides 12a and 13a formed at the sites of (222) oriented Cr crystal 12 and other Cr crystal 13 is formed. This sliding member is characterized in that the abundance of (222) -oriented Cr crystals 12 on the surface of the Cr plating film is high. Therefore, the thickness of the Cr oxide film 14 is the average crystallite diameter of the (222) -oriented Cr crystals 12. Smaller, that is, thinner.

    The abundance ratio of the (222) oriented Cr crystal is not uniform over the entire inner peripheral surface 3 and varies depending on the location. That is, the sliding speed of the apex seal 2 is fast on the long-axis-side inner peripheral surface 3a of the inner peripheral surface 3 and slow on the short-axis-side inner peripheral surface 3b. For this reason, as shown in FIG. 4, in the region A where the apex seal 2 slides from the short-axis-side inner peripheral surface 3b to the long-axis-side inner peripheral surface 3a, the sliding speed gradually increases, and the apex seal In the region B in which 2 slides from the long-axis-side inner peripheral surface 3a to the short-axis-side inner peripheral surface 3b, the sliding speed gradually decreases.

    In view of this point, the abundance ratio of the (222) oriented Cr crystal is made smaller in the region A where the sliding speed gradually increases than in the region B where the sliding speed gradually decreases. Thus, in region A, the speed dependency of the friction coefficient with respect to the change in the sliding speed of the apex seal 2 exhibits a negative gradient characteristic, and in region B, the speed dependency of the friction coefficient exhibits a positive gradient characteristic. Yes. The relationship between the abundance of the (222) -oriented Cr crystal and the speed dependency of the friction coefficient will be described later based on data.

<Production method>
A method for manufacturing the rotor housing 1 will be described.

(Production Example 1)
After forming the Cr plating film on the liner steel plate, the steel plate is processed into a long cylindrical shape having the trochoidal inner peripheral surface by laser welding. This long cylindrical liner 11 is cast in an aluminum alloy housing body. The rotor housing 1 is obtained by finishing the inner peripheral surface of the obtained rotor housing workpiece with a honing grinding wheel to a predetermined roughness.

    In forming the Cr plating film on the liner steel plate in such a manufacturing method, as shown in FIG. 5, in the portion A ′ corresponding to the region A of the liner steel plate 11A, the abundance of the (222) oriented Cr crystals is high. Cr plating treatment is performed so as to be 60% or more and 65% or less, and Cr plating treatment is performed so that the abundance ratio of the (222) oriented Cr crystals is 80% or more and 85% or less in the portion B ′ corresponding to the region B. To do.

    Hereinafter, a method for forming the Cr plating film will be specifically described. The basic Cr plating method is as follows.

    A steel plate for liner is put in a plating bath containing a Cr component, sulfuric acid, and an organic sulfonic acid as a catalyst, and if necessary, a Mo component, and preheated to a predetermined temperature, and the work surface is cleaned by a reverse electric treatment for several minutes. Then, a Cr plating film is formed by sequentially performing a strike plating process (positive electric process) for several minutes and a main plating process (positive electric process) for a predetermined time. “Strike plating” is short-time plating to increase the adhesion of the plating film to the workpiece surface.

As the Cr component, anhydrous chromic acid CrO ₃ is preferable, and Cr ₂ O ₃ is added as necessary. As the Mo component, sodium molybdate or ammonium molybdate can be employed. The organic sulfonic acid is represented by HSO ₃ R, and R has an aliphatic hydrocarbon group having 10 or less carbon atoms such as a methyl group and an ethyl group, toluene having a methyl group at the para position, and an unsaturated hydrocarbon group. An aromatic hydrocarbon group in which an acyclic hydrocarbon is bonded to one aromatic ring such as styrene is preferable. R may be another aromatic hydrocarbon group or a plurality of sulfonic acid groups (HSO ₃ ). Specific examples include methanesulfonic acid and methanesulfonic acid.

    The plating bath is, for example, 240 g / L or more and 280 g / L or less of anhydrous chromic acid, 2.5 g / L or more and 3.3 g / L or less of sulfate ion, 10 to 35 ml / L or less of organic sulfonic acid, The amount of sodium molybdate may be 50 g / L or more and 65 g / L or less. The plating bath temperature is adjusted to 45 ° C. or more and 60 ° C. or less, for example.

The current density of the cleaning reverse current treatment may be 50 A / dm ² or more and 60 A / dm ² or less, and the current density of the strike plating treatment may be 40 A / dm ² or more and 55 A / dm ² or less. The finish grinding is preferably performed by honing or the like so that the surface of the plating film is, for example, Ra 2.0 μm or less.

    The abundance of (222) oriented Cr crystals can be adjusted by the current density specific to the present plating treatment. That is, as the current density increases, the proportion of (222) oriented Cr crystals increases.

    When the Cr plating film is formed on the part A ′, the other part is masked, and the plating process is performed by reducing the current density of the main plating process. When forming the Cr plating film on the part B ', the other part is masked, and the current density of the main plating process is increased to perform the plating process. For the parts other than the parts A ′ and B ′, for example, the plating process may be performed at an intermediate current density between the parts A ′ and B ′.

    Each steel plate for region A and region B is prepared separately, and the steel plate for region A is subjected to Cr plating treatment with a (222) orientation Cr crystal abundance ratio of 60% to 65%. 222) A long cylindrical liner 11 is manufactured by performing Cr plating treatment with an abundance of oriented Cr crystals of 80% or more and 85% or less, and joining the Cr plated steel sheets for region A and region B. It may be.

<Examples and Comparative Examples>
To form a CrMo plating film on the plating current density ^{25A / dm 2, 30A / dm} 2, 45A / dm 2 and the change is allowed by the test piece (steel). The plating bath composition is as shown in Table 1, and Heef25-R manufactured by Atotech was used as the catalyst, that is, the organic sulfonic acid.

    Then, the abundance ratio of each crystal face facing the surface side in the Cr plating film of each obtained test piece was measured by X-ray diffraction analysis. The measurement was performed under the conditions shown in Table 2 using an X-ray diffractometer RU-200 manufactured by Rigaku Corporation after honing the Cr plated surface of the test material. The results are shown in Table 3.

    According to Table 3, it can be seen that the abundance of (222) -oriented Cr crystals increases as the current density of the main plating process increases.

    About each said test piece, after the honing process, the friction test was done using the test device shown in FIG. 6, and the speed dependence of the friction coefficient was investigated. In the figure, 21 is a disk-shaped test piece, and 22 is a disk-shaped rotation support base to which a chilled iron sliding piece 23 is fixed. A Cr plating layer 24 is annularly provided on the lower surface of the test piece 21 so as to go around the periphery. An air supply hole 25 penetrating the test piece 21 is formed at the center of the test piece 21. In the vicinity of the periphery of the test piece 21, a lubricating oil supply hole 26 that penetrates the test piece 21 is formed at the site of the Cr plating layer 24. Three slide pieces 23 are fixed to the rotation support base 22 at an angular interval of 120 degrees in the circumferential direction, and the upper ends of the slide pieces 23 protrude upward from the support base 22. A test piece 21 is placed on the three sliding pieces 23.

The friction test was performed while supplying air at a pressure of 2.5 kg / cm ² from the air supply hole 25 and supplying lubricating oil at a temperature of 100 ° C. from the lubricating oil supply hole 26. As the lubricating oil, 0W-20 engine oil was used. And the peripheral speed of the sliding piece 23 was changed and the friction coefficient in each sliding speed was measured. The results are shown in FIG.

    In the same figure, A is Example A surface of Table 3, B is Example B surface, and a comparative example is each data of a comparative example. On the surface of Example A where the abundance of (222) oriented Cr crystals is small, the coefficient of friction decreases as the sliding speed increases. That is, the speed dependence of the friction coefficient shows a negative gradient characteristic. In Example B surface where the abundance of (222) -oriented Cr crystals is larger than that in Example A surface, the friction coefficient increases as the sliding speed increases. That is, the speed dependency of the friction coefficient indicates a positive gradient characteristic. In the comparative example, the abundance ratio of the (222) oriented Cr crystal is small, and the main orientation plane is changed from the (222) plane to the (211) plane. Therefore, like the surface of Example A, the speed dependency of the friction coefficient shows a negative gradient characteristic, but the friction coefficient is high.

<Production Example 2>
In this example, a rotor housing work is formed by casting a liner on the housing body, and then the work is subjected to Cr plating. After the workpiece is put in the plating bath, preheating, cleaning of the workpiece surface by reverse electric treatment, and strike plating treatment are performed, as shown in FIG. 8, the area 15 of the Cr plating electrode 15 and the rotor housing workpiece 1A A shielding plate 17 is disposed between the inner peripheral surface and the main plating process (positive electric process). The distance between the electrode 15 and the inner peripheral surface of the workpiece 1A is substantially the same over the entire circumference.

    As shown in FIG. 9, the shielding plate 17 has a strip shape that is elongated in the axial direction of the rotor housing. As shown in FIG. 8, the shielding plate 17 is against the normal line of the arc-shaped inner peripheral surface on the long axis side of the workpiece 1A. Inclined. 9 schematically shows the case where the shielding plate 17 is arranged in the normal direction, and the right side of FIG. 9 schematically shows the case where the shielding plate 17 is inclined with respect to the normal direction. When the shielding plate 17 is arranged to be inclined with respect to the normal direction, the shielding plate 17 becomes an obstacle and the energization path becomes longer, so that the bath resistance is increased, and compared with the case where the shielding plate 17 is arranged in the normal direction. Thus, the current density is reduced.

    That is, according to the manufacturing method example 2, in the region A of the work 1A, the current density is smaller than that in the region B because the shielding plate 17 is disposed and the positive electric processing is performed. Accordingly, the positive current treatment is performed by adjusting the energization amount so that a Cr plating film having a presence ratio of (222) oriented Cr crystals of 80% or more and 85% or less is formed in the region B where the shielding plate 17 is not disposed. Thus, in the region A, a Cr plated film having an abundance of (222) -oriented Cr crystals of 60% to 65% can be formed.

    The current density in the region A can be set to an optimal value by appropriately adjusting the number of shielding plates 17, the height, the width, or the inclination angle with respect to the normal line.

    The present invention is not limited to a rotor housing of a rotary piston engine, and has an oval inner peripheral surface on which a seal member slides, and a sliding load is generated between a long axis side inner peripheral surface and a short axis side inner peripheral surface. It can also be applied to different hydraulic pumps and compressor housings.

1 is a schematic front view of a rotary piston engine according to an embodiment of the present invention. It is a perspective view of the rotor housing of the same engine. It is a figure which shows typically the structure of a Cr plating film surface part. It is a schematic front view of the said rotor housing. It is a perspective view which shows the steel plate for liners of the manufacturing method example 1. FIG. It is the front view made into the partial cross section which shows the test device for a friction characteristic test. It is a graph which shows the sliding speed dependence of a friction coefficient. It is a schematic front view which shows the relationship between the workpiece | work of the manufacturing method example 2, an electrode, and a shielding board. It is a perspective view which shows the relationship between the angle of the shielding board of manufacturing example 2, and current density.

Explanation of symbols

1 Rotor housing (sliding member)
1A Workpiece 2 Seal member 3 Inner peripheral surface 12 (222) oriented Cr crystal 12a Oxide produced in (222) oriented Cr crystal part 13 Other Cr crystal 13a Oxide produced in other Cr crystal part 14 Cr oxidation Film 15 Electrode 17 Shield plate

Claims (3)

A sliding member having an oval inner peripheral surface with a Cr plating film formed on the surface, the seal member sliding in the circumferential direction on the inner peripheral surface,
The inner peripheral surface has a region A where the sliding speed of the seal member gradually increases and a region B where the sliding speed of the seal member gradually decreases,
In the Cr plating film, the abundance of (222) oriented crystals with the (222) plane facing the surface side specified by X-ray diffraction analysis, and the abundance of crystals with other crystal planes oriented on the surface side Higher than
The Cr plating film in the region A shows a characteristic that the speed dependency of the friction coefficient with respect to the change in the sliding speed of the seal member has a negative gradient,
The Cr plating film in the region B is characterized in that the speed dependency of the friction coefficient with respect to the change in the sliding speed of the seal member exhibits a positive gradient characteristic. In claim 1,
The Cr plating film in the region A has a smaller abundance of the (222) oriented crystal than the Cr plating film in the region B. The seal member includes an oval inner peripheral surface formed with a Cr plating film on which the seal member slides in the circumferential direction. The inner peripheral surface includes a region A where the sliding speed of the seal member gradually increases, and the seal A method for manufacturing a sliding member having a region B where the sliding speed of the member gradually decreases,
The sliding member workpiece is placed in a plating bath, and the positive electrode treatment is performed to positively treat the inner peripheral surface of the workpiece with the (222) plane specified by X-ray diffraction analysis facing the surface side. Is provided with a step of forming a Cr plating film higher than the abundance of crystals in which other crystal faces are oriented on the surface side
In the step, the current density for forming the Cr plating film is made smaller in the region A than in the region B, whereby the speed dependency of the friction coefficient with respect to the change in the sliding speed of the seal member is A method for manufacturing a sliding member, wherein the Cr plating film in the region A has a negative gradient characteristic and the Cr plating film in the region B has a positive gradient characteristic.

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