KR102338130B1 - Scorll compressor - Google Patents

Abstract

A scroll compressor according to the present invention comprises: a first scroll; a second scroll having a boss; a rotation shaft provided with a boss coupling groove so that the boss portion of the second scroll is inserted and coupled; and a bush bearing press-fitted to and coupled to the outer circumferential surface of the boss, the bush bearing having an outer lubricating layer such that the outer circumferential surface forms a bearing surface with the inner circumferential surface of the boss coupling groove, wherein the bush bearing is formed in a cylindrical shape to form the boss portion a base member press-fitted to the outer circumferential surface; and a lubricating member integrally provided on the outer circumferential surface of the base member to form a lubricating layer, wherein, based on the initial state in which the bush bearing is press-fitted into the boss, the outer circumferential cylindricity of the bush bearing is It is formed to satisfy within 0.4% of the average thickness of the bush bearing.

Description

Scroll Compressor {SCORLL COMPRESSOR}

The present invention relates to a scroll compressor, and more particularly, to a scroll compressor in which a boss portion of an orbiting scroll is inserted into a rotation shaft to receive rotational force.

In the scroll compressor, a non-orbiting scroll or a fixed scroll (hereinafter, referred to as a first scroll) is coupled to the inner space of a casing, and an orbiting scroll (hereinafter, a second scroll) having a rotating shaft coupled to the first scroll is engaged to turn with respect to the first scroll It is a compressor that forms a pair of compression spaces composed of a suction chamber, an intermediate pressure chamber, and a discharge chamber between the first scroll and the first scroll during movement.

These scroll compressors are widely used for refrigerant compression in air conditioners, etc. because of their advantages in that they can obtain a relatively high compression ratio compared to other types of compressors and obtain a stable torque by smoothly connecting refrigerant suction, compression, and discharge strokes.

In a conventional scroll compressor, an eccentric portion of a rotating shaft is inserted into a boss provided in the second scroll to transmit the rotational force of the driving motor to the second scroll. In this case, the rotation shaft is inserted into the shaft hole of the main frame supporting the second scroll and supported in the radial direction, while the first wrap provided in the first scroll and the second wrap provided in the second scroll engage with each other and the two A pair of compression chambers are formed.

In such a scroll compressor, when power is applied to a driving motor and rotational force is generated, the second scroll rotates with respect to the first scroll by a rotating shaft to form a pair of compression chambers to suck, compress, and discharge refrigerant. will make it

At this time, the second scroll may receive a centrifugal force generated during a revolving motion, a gas force generated while compressing the refrigerant, and a gas repulsion force in the opposite direction to the centrifugal force, so that its behavior may be unstable, but the rotation shaft is rotated in the opposite direction by the main frame As it is supported by the motor, it is properly adjusted and the turning motion is continued.

In the conventional scroll compressor as described above, while the middle portion of the rotating shaft is supported by the main frame, the eccentric part provided at the upper end of the rotating shaft is coupled to the orbiting scroll, so that the supporting point at which the rotating shaft is supported by the main frame and the rotating shaft are the second scroll There is a large difference in height between the action points that apply the rotational force to the Accordingly, the rotating shaft is subjected to a large eccentric load, and as the bearing load due to the gas force increases, the compression efficiency due to friction loss may decrease. In addition, there are problems in that the compressor noise is increased, reliability is lowered, and the length of the main frame is increased to increase the size of the compressor.

Accordingly, conventionally, a method has been proposed in which a boss coupling groove is formed eccentrically with respect to the center of the shaft at the upper end of the rotation shaft, and the boss portion of the second scroll is inserted into the boss coupling groove to be coupled thereto.

In this case, since the supporting point supporting the rotating shaft and the point of applying the rotational force to the second scroll are located at the same height, the eccentric load received by the rotating shaft is reduced, thereby reducing friction loss and compressor noise in the bearing supporting the rotating shaft, and reliability. can be increased and the compressor can be miniaturized.

In the conventional scroll compressor as described above, a bush bearing must be provided between the outer circumferential surface of the boss portion and the inner circumferential surface of the boss coupling groove, and this bush bearing is usually press-fitted into the inner circumferential surface of the boss coupling groove to be coupled. This is because, when the bush bearing is press-fitted into the inner circumferential surface of the boss coupling groove, it is possible to effectively suppress separation or idle rotation even if the bush bearing thermally expands due to the operation heat of the compressor. If the bush bearing is press-fitted into the outer circumferential surface of the boss, plastic deformation occurs during the press-fitting process depending on the press-fitting zone, weakening the bonding force, or the bush bearing may be detached from the boss or idle due to thermal expansion due to the heat of operation.

However, in the conventional scroll compressor as described above, when the bush bearing is press-fitted into the boss coupling groove and coupled, the inner circumferential surface of the bush bearing forms the bearing surface, but the bearing surface is rubbed intensively at one point, and eventually the bearing There was a problem of shortening the lifespan.

Accordingly, prior patents registered in Korea on August 28, 2015 [Korean Patent No. 101549868 (Aug. 28, 2015), "Bush bearings for compressors and scroll compressors having the same"] have a bush bearing inserted into the outer circumferential surface of the boss. An example is given.

In the prior patent, a single bush bearing in which a bush bearing is formed only with a lubricating material or a double bush bearing in which a lubricating member made of a lubricating material is provided on an outer circumferential surface of a base member made of a methyl material has been introduced. In addition, in the prior patent, the physical properties or structure of the lubricating member are limited so that a single bush bearing or a double bush bearing is stably press-fitted or inserted into the boss portion of the orbiting scroll to be fixed. Accordingly, in the prior patent, there is no mention of a manufacturing method for dimensional control of a bush bearing, particularly a lubricating member.

However, the bush bearing provided in the conventional scroll compressor as described above only limits the physical properties of the lubricating member as described above, and during the manufacturing process, the lubricating member deviates from the original design value and increases the outer diameter. There was a problem in that the life of the bush bearing was shortened as a part of the lubricating member was worn out as well as friction loss on the surface.

In addition, in the conventional scroll compressor, the thickness of the lubricating member in the bush bearing is not constant, and as a result, the degree of thermal expansion of the lubricating member is different for each position due to operating heat generated during operation of the compressor, resulting in more severe friction loss or There was a problem that abrasion occurred.

Prior Patent: [Korea Patent No. 101549868 (2015.08.28), "Bush bearing for compressor and scroll compressor having same"]

It is an object of the present invention, when a bush bearing is press-fitted into a boss portion of an orbiting scroll that is inserted into and coupled to a boss engaging groove of a rotating shaft, and the outer peripheral surface of the bush bearing forms a bearing surface, the outer peripheral surface of the bush bearing and the boss engaging groove An object of the present invention is to provide a scroll compressor capable of maintaining a uniform spacing between inner peripheral surfaces.

In addition, another object of the present invention is to keep the outer diameter of the bush bearing uniform for this purpose, so that even if high operating heat is generated during operation of the compressor, the outer diameter of the bush bearing can be prevented from becoming more non-uniform, and thereby An object of the present invention is to provide a scroll compressor capable of minimizing friction loss between the boss coupling groove and the boss portion of the orbiting scroll and the wear of the bush bearing.

In order to achieve the object of the present invention, a lubricating member made of a lubricating material is injection-molded on the outer circumferential surface of the base member having a cylindrical shape, and a bush bearing having an external lubrication layer, characterized in that cut surfaces are formed at both ends of the lubricating member can be provided.

In addition, in order to achieve the object of the present invention, the base member is formed in a cylindrical shape, the base member is put in a mold, an injection product is injected to form an injection product, and the injection product manufactured in the mold is taken out from the mold, A bush bearing having an external lubrication layer obtained by primary processing the outer diameter of the injection-molded product, annealing the first-processed injection product for a predetermined temperature and time, and secondary processing the outer diameter of the heat-treated injection product A manufacturing method may be provided.

Here, when injecting the injection-molded material into the mold, the injection-molded material is injected in the longitudinal direction, and overmolding is performed so that the injection-molded material is further molded outwardly than the end of the base member on the opposite side of the mold entrance into which the injection material is injected, the overmolding The finished part can be removed by cutting during the first processing.

In addition, the processing thickness of the primary processing may be greater than the processing thickness during the secondary processing.

In addition, in order to achieve the object of the present invention, a first scroll in which a first wrap is formed on one side of the first end plate; a second scroll in which a second wrap is formed on one side of the second end plate, the second wrap is engaged with the first wrap to form a compression chamber, and a boss is formed on the other side of the second end plate; a rotation shaft provided with a boss coupling groove so that the boss portion of the second scroll is inserted and coupled; and a bush bearing press-fitted to and coupled to the outer circumferential surface of the boss, the bush bearing having an outer lubricating layer such that the outer circumferential surface forms a bearing surface with the inner circumferential surface of the boss coupling groove, wherein the bush bearing is formed in a cylindrical shape to form the boss portion a base member press-fitted to the outer circumferential surface; and a lubricating member integrally provided on the outer circumferential surface of the base member to form a lubricating layer, wherein, based on the initial state in which the bush bearing is press-fitted into the boss, the outer circumferential cylindricity of the bush bearing is A scroll compressor may be provided, characterized in that it is formed to satisfy within 0.4% of the average thickness of the bush bearing.

In addition, in order to achieve the object of the present invention, a first scroll in which a first wrap is formed on one side of the first end plate; a second scroll in which a second wrap is formed on one side of the second end plate, the second wrap is engaged with the first wrap to form a compression chamber, and a boss is formed on the other side of the second end plate; a rotation shaft provided with a boss coupling groove so that the boss portion of the second scroll is inserted and coupled; and a bush bearing press-fitted to and coupled to the outer circumferential surface of the boss, the bush bearing having an outer lubricating layer such that the outer circumferential surface forms a bearing surface with the inner circumferential surface of the boss coupling groove, wherein the bush bearing is formed in a cylindrical shape to form the boss portion a base member press-fitted to the outer circumferential surface; and a lubricating member integrally provided on the outer circumferential surface of the base member to form a lubricating layer; A scroll compressor can be provided, characterized in that it is formed so that an outer peripheral cylindricity of the bush bearing is within 0.5% of the average thickness of the bush bearing.

Here, the rate of change of the interval between the outer circumferential surface of the bush bearing and the inner circumferential surface of the boss coupling groove may be formed to satisfy within 0.4% of the average thickness of the bush bearing.

In addition, the base member may be formed of a material having the same heat transfer coefficient as that of the boss of the second scroll.

In addition, the base member may be formed of a material having the same material properties as that of the boss of the second scroll.

In addition, the lubricating member may contain carbon fibers in a resin series.

In addition, cut surfaces of the carbon fiber may be exposed at both ends of the lubricating member.

In addition, cut surfaces may be formed at both ends of the lubricating member.

And, the resin series may be formed of a PEEK material.

In addition, the carbon fibers may be arranged in a longitudinal direction of the base member.

In addition, cut surfaces of the carbon fiber may be exposed at both ends of the lubricating member.

In addition, the base member and the lubricating member may be formed in a shape without a cut surface along the circumferential direction.

In addition, a knurling portion may be formed on the outer circumferential surface of the base member so that a contact area with the inner circumferential surface of the lubricating member is enlarged.

In addition, when a is the thickness of the base member, b is the thickness of the lubricating member, and c is the depth of the knurling part, the following range may be satisfied. b/a = 1.09 to 1.15, c/a = 0.3 to 0.5

In addition, in order to achieve the object of the present invention, a first scroll in which a first wrap is formed on one side of the first end plate; a second scroll in which a second wrap is formed on one side of the second end plate, the second wrap is engaged with the first wrap to form a compression chamber, and a boss is formed on the other side of the second end plate; a rotation shaft provided with a boss coupling groove so that the boss portion of the second scroll is inserted and coupled; and a bush bearing press-fitted to and coupled to the outer circumferential surface of the boss, the bush bearing having an outer lubricating layer such that the outer circumferential surface forms a bearing surface with the inner circumferential surface of the boss coupling groove, wherein the bush bearing is formed in a cylindrical shape to form the boss portion a base member press-fitted to the outer circumferential surface; and a lubricating member integrally provided on the outer circumferential surface of the base member to form a lubricating layer, wherein the lubricating member contains a resin-based carbon fiber, and the carbon fiber has cut surfaces exposed at both ends of the lubricating member A scroll compressor characterized in that it may be provided.

In the scroll compressor according to the present invention, since the outer diameter of the bush bearing is maintained almost constant along the longitudinal direction, friction loss or wear between the boss portion of the orbiting scroll and the boss coupling groove of the rotating shaft can be suppressed, and through this It can improve compressor performance and extend lifespan.

In addition, in the scroll compressor according to the present invention, since the thickness of the lubricating member constituting the outer circumferential surface of the bush bearing is maintained substantially constant along the longitudinal direction, a portion of the lubricating member is greatly thermally deformed even when high operating heat is generated during the operation of the compressor. This can be suppressed in advance, and through this, friction loss or abrasion between the boss portion of the orbiting scroll and the boss coupling groove of the rotating shaft can be more effectively suppressed, thereby increasing compressor performance and extending life.

1 is a longitudinal cross-sectional view showing a scroll compressor according to the present invention;
2 is a perspective view showing the orbiting scroll separated from the rotation shaft in the scroll compressor of FIG. 1;
3 is a perspective view showing a part of the bush bearing according to FIG.
Figure 4 is a half cross-sectional view showing the bush bearing according to Figure 3,
Figure 5 is a block diagram for explaining the method ① for manufacturing the bush bearing according to Figure 3;
6 is a longitudinal cross-sectional view showing a bush bearing manufactured according to method ①;
7 is a perspective view illustrating secondary processing performed in a state in which the bush bearing manufactured according to method ① is press-fitted into the boss part of the orbiting scroll;
8 is a block diagram for explaining a method ② of manufacturing the bush bearing according to FIG. 3;
9a and 9b are longitudinal cross-sectional views showing a bush bearing manufactured according to method ②;
Figure 10 is a "VI-VI" front sectional view in Figure 9b,
11 is a perspective view illustrating secondary processing performed in a state in which the bush bearing manufactured according to method ② is press-fitted into the boss part of the orbiting scroll;
12 is a graph showing a comparison of changes in the outer diameter of the lubricating member according to the manufacturing method of the bush bearing;
13 is a graph showing a comparison of the cylindricity of the lubricating member according to the manufacturing method of the bush bearing;
14 and 15 are graphs comparing the change in the outer diameter and the difference in cylindricity of the bush bearing under the operating conditions of the scroll compressor according to FIG. 1 .

Hereinafter, a bush bearing having an external lubrication layer and a manufacturing method thereof according to the present invention will be described in detail based on an embodiment shown in the accompanying drawings.

The bush bearing according to the present invention can be applied even when manufactured only by a lubricating member having lubricity. However, as in the present embodiment, the lubricating member may be applied or laminated on the outer circumferential surface of the metal base member. Hereinafter, the latter case will be considered as a representative example.

1 is a longitudinal cross-sectional view showing a scroll compressor according to the present invention, and FIG. 2 is a perspective view showing the orbiting scroll separated from the rotation shaft in the scroll compressor of FIG. 1 .

As shown in this figure, in the scroll compressor according to the present embodiment, a driving motor 120 generating rotational force is installed in the inner space of the casing 110 , and the main frame 130 is disposed above the driving motor 120 . Can be fixedly installed. The fixed scroll 140 is fixedly installed on the upper surface of the main frame 130 , the orbiting scroll 150 is installed between the main frame 130 and the fixed scroll 140 , and the orbiting scroll 150 is the fixed scroll 140 . ) and may be eccentrically coupled to the rotation shaft 123 of the drive motor 120 to form a pair of compression spaces P that move continuously together. And an Oldham ring 160 for preventing rotation of the orbiting scroll 150 may be installed between the fixed scroll 140 and the orbiting scroll 150 .

The main frame 130 is welded to the inner circumferential surface of the casing 110 , and a bearing hole 131 may be formed through the center thereof. The shaft hole 131 may be formed with the same diameter from the top to the bottom.

The fixed scroll 140 protrudes from the bottom surface of the head plate 141 and the fixed lap 142 is formed so as to form a compression space P together with the orbiting lap 152 of the orbiting scroll 150 to be described later, and the fixed scroll A suction port 143 may be formed in the head plate portion 141 of 140 so that the suction pipe 111 and the compression space P communicate with each other.

And at the center of the head plate 141 of the fixed scroll 140, a discharge port 144 is formed so that the compression space P and the inner space of the casing 110 communicate with each other, and at the end of the discharge port 144, the normal operation of the compressor A check valve (not shown) that opens the discharge port 144 during wartime and closes the discharge port 144 when the compressor is stopped to prevent the discharged refrigerant from flowing back into the compression space P through the discharge port 144 can be installed.

The orbiting scroll 150 protrudes from the upper surface of the head plate portion 151 and engages with the fixed lap 142 of the fixed scroll 140 to form two pairs of compression spaces P, and the orbiting lap 152 is formed. , a boss portion 153 may be formed on the bottom surface of the head plate portion 151 of the orbiting scroll 150 to be inserted into the boss coupling groove 123d of the rotation shaft 123 to be described later to receive rotational force.

The boss part 153 may be formed in the geometric center of the orbiting scroll 150 . In addition, the boss portion 153 may be formed in a hollow cylindrical shape, but in order to reduce the weight of the orbiting scroll 150 , it may be formed in a hollow cylindrical shape.

The rotating shaft 123 includes a shaft portion 123a that is press-fitted into the rotor 122 of the driving motor 120 , and is provided on both upper and lower sides of the shaft portion 123a and is supported by the main frame 130 and the subframe 170 . The bearing part 123b and the sub bearing part 123c, and the boss coupling groove 123d formed eccentrically on the upper end of the main bearing part 123b and into which the boss part 153 of the orbiting scroll 150 is inserted and coupled. can An eccentric mass 180 for offsetting an eccentric load generated while the orbiting scroll 150 is pivoting may be coupled to the main bearing part 123b or the shaft part 123a.

In the drawings, unexplained reference numeral 112 denotes a discharge pipe, and 121 denotes a stator.

The scroll compressor according to the present embodiment as described above has the following effects.

That is, when power is applied to the driving motor 120 and rotational force is generated, the orbiting scroll 150 eccentrically coupled to the rotation shaft 123 performs a pivoting motion while continuously moving between the fixed scroll 140 and the two A pair of compression spaces (P) are formed.

Then, the compression space (P) is formed in several stages in succession of the compression space (P) whose volume is gradually narrowed in the direction from the suction port (or suction chamber) 143 to the discharge port (or discharge chamber) 144 .

Then, the refrigerant provided from the outside of the casing 110 flows in through the suction port 143 of the fixed scroll 140 through the suction pipe 111 , and the refrigerant moves toward the final compression space by the orbiting scroll 150 . compressed while And a series of processes of being discharged into the inner space of the casing 110 through the discharge port 144 of the fixed scroll 140 in the final compression space is repeated.

Here, as shown in FIG. 1 , as the boss portion 153 of the orbiting scroll 150 is inserted into and coupled to the boss coupling groove 123d of the rotation shaft 123 , the rotation shaft 123 is supported by the main frame 130 . The height difference (Δh=0) between the supporting point A and the action point B at which the rotating shaft 123 acts on the orbiting scroll 150 can be eliminated. Accordingly, the eccentric load received by the rotating shaft 123 may be reduced, and through this, the friction loss in the main bearing part 123b may be reduced, and thus the compression efficiency may be improved. In addition, it is possible to reduce compressor noise and improve reliability by lowering the operating force at the welding points C and D between the casing 110 and the main frame 130 .

In addition, by reducing the eccentric load received by the rotating shaft 123, the weight and material cost of the eccentric mass 180 installed on the rotating shaft 123 can be reduced, and the compression efficiency can be improved by reducing the amount of deformation of the rotating shaft 123. In addition, the operating force at the welding point (C) (D) between the casing 110 and the main frame 130 due to the centrifugal force of the eccentric mass 180 is also lowered, thereby reducing compressor noise and improving reliability.

In addition, since there is no need for a separate pocket groove in the main frame 130, the material cost is reduced by reducing the axial length and diameter of the main frame 130, and at the same time, the axial length of the compressor is reduced to reduce the size of the compressor compared to the same capacity . In addition, it is possible to improve the compressor performance by increasing the stacking height of the motor within the limited axial length of the compressor.

Meanwhile, between the boss part 153 of the orbiting scroll 150 and the boss coupling groove 123d of the rotation shaft 123, a bush bearing 200 for lubricating between the boss part 153 and the boss coupling groove 123d is provided. can be installed.

In addition to the bush bearing 200 , a needle bearing, a roller bearing, a ball bearing, etc. may be applied. However, since these bearings are large in size, the bearing hole 131 of the main bearing becomes large, and thus friction loss may increase, it may be preferable to apply a bush bearing as in the present embodiment.

The bush bearing 200 according to the present embodiment may be more preferably coupled to the boss portion 153 of the orbiting scroll 150 than coupled to the inner circumferential surface of the boss coupling groove 123d. That is, when the bush bearing 200 is coupled to the boss part 153 , the outer circumferential surface of the bush bearing 200 comes into full periphery contact with the inner circumferential surface of the boss coupling groove 123d, and thus the bush bearing It is possible to significantly reduce damage to the bush bearing 200 due to wear by suppressing abrasion of the bush bearing that may occur when any one point of 200 is in intensive contact.

For example, when the boss portion 153 of the orbiting scroll 150 is inserted into the boss coupling groove 123d of the rotation shaft 123, the center of the rotation shaft 123 is the boss portion ( Since the rotation is performed in a state coincident with the center of the 153), the inner circumferential surface of the boss coupling groove 123d comes into contact with the entire outer circumferential surface of the boss portion 153 at one point. That is, the entire outer peripheral surface of the boss portion 153 comes into contact with one point on the inner peripheral surface of the boss coupling groove (123d).

Therefore, the outer peripheral surface of the boss part 153 is not in intensive contact with the inner peripheral surface of the boss coupling groove 123d at any one point, but the entire outer peripheral surface is in contact evenly. It is possible to prevent intensive contact of any one point with the boss coupling groove.

On the other hand, the bush bearing as described above may consist of a single bush bearing entirely made of a lubricating material, and as in this embodiment, a lubricating member made of a lubricating material is applied to the outer peripheral surface of the base member made of a steel material through insert injection or the like. It can also consist of stacked double bush bearings. Hereinafter, it will be described based on the double bush bearing. However, the present invention is to keep the outer diameter of the lubricating member almost uniform to suppress friction loss and wear between the boss portion and the boss coupling groove, or more precisely, between the outer circumferential surface of the bush bearing and the inner circumferential surface of the boss coupling groove, In addition to bush bearings, the same can be applied to single bush bearings.

FIG. 3 is a perspective view showing a part of the bush bearing according to FIG. 1 after being broken, and FIG. 4 is a half cross-sectional view showing the bush bearing according to FIG. 3 .

As shown in this figure, the bush bearing 200 according to the present embodiment includes a base member 210 that is press-fitted to the boss of the scroll compressor, and a lubricating member coated or laminated on the outer peripheral surface of the base member 210 to form a lubricating layer. (220).

The base member 210 may be formed of the same metal material as the boss of the orbiting scroll into which the bush bearing of this embodiment is to be press-fitted, or may be formed of a metal material having similar physical properties. Accordingly, the base member 210 may be formed of a material having the same heat transfer coefficient or the same material characteristics as that of the boss portion 153 . However, the base member 210 is not limited to a metal material, and at least a material having greater rigidity than the lubricating member 220 may be sufficient. Accordingly, the bush bearing according to the present embodiment may be firmly press-fitted to the member to be press-fitted and fixed.

And, since the base member 210 has to be press-fitted into a member such as a boss, it is formed in an annular cross-sectional shape, but the inner circumferential surface is not limited to a perfect circle, and may be formed in various ways depending on the shape of the member to be press-fitted. In addition, the outer peripheral surface of the base member 210 is a non-circular cross-sectional shape so that the lubricating member 220 does not rotate in vain as the lubricating member 220 provided on the outer peripheral surface of the base member 210 is insert-injected and applied or laminated. can also be formed.

For example, a knurling portion 211 may be formed on the outer circumferential surface of the base member 210 to enlarge a contact area with the inner circumferential surface of the lubricating member 220 . The knurling part 211 may be formed in a rhombus shape as shown in FIG. 3 to prevent the lubricating member 220 from being separated from the base member 210 in the longitudinal direction.

Here, as the depth of the knurling part 211 increases, the contact area with the lubricating member 220 may be increased, thereby increasing adhesive force. However, if the depth of the knurling portion is too deep, the rigidity of the base member 210 may be lowered, so that the coupling force of the bush bearing 200 with the member to be press-fitted may be lowered.

In consideration of this, the depth of the knurling portion may be defined as follows. That is, when a is the thickness of the base member with reference to FIG. 2, b is the thickness of the lubricating member, and c is the depth of the knurling part, it may be formed to satisfy the following range.

b/a = 1.09 to 1.15

c/a = 0.3 to 0.5

Accordingly, in the case of a bush bearing having an outer diameter of 29.9 mm, when the thickness of the bearing member is 0.8 to 1.5 mm and the thickness of the lubricating member is 0.45 to 1.15 mm, the depth of the knurling part can be formed to be about 0.24 to 0.75 mm. .

On the other hand, when the knurling part 211 is formed in a rhombus shape, it is not only difficult to injection-form the base member 210 by extrusion, but also to injection-form the lubricating member 220, which may somewhat interfere with the smooth flow of the injected material, which may become an obstacle. have.

Accordingly, the knurling portion 211 may be formed of at least one or more protrusions that are elongated along the longitudinal direction on the outer circumferential surface of the base member 210 . In this case, injection molding of the base member 210 may be facilitated, and the lubricating member 220 may be suppressed from spinning with respect to the base member 210 , which may be advantageous over a rhombus shape. Also, in this case, a plurality of knurling portions 211 may be formed along the circumferential direction as well as in the longitudinal direction.

When the plurality of knurling parts 211 are formed on the outer circumferential surface of the base member 210 as described above, the lubricating member 220 is inserted between the knurling parts 211 and coupled therebetween, so that the base member 210 and the lubricating member. The bonding area between the 220 is enlarged, so that the lubricating member 220 may be firmly coupled to the base member 210 . In addition, it is possible to suppress the lubricating member 220 from being separated in the longitudinal direction with respect to the base member 210 by the knurling portion 211 and also from rotating in the circumferential direction.

On the other hand, as described above, the lubricating member 220 is insert-injected to the outer circumferential surface of the base member 210 to form a lubricating layer. Accordingly, the lubricating member 220 may be preferably formed of a material having good oil-free properties, that is, a polyether ether ketone (PEEK) material, which is a plastic material having an ether ketone bond. In this case, as shown in FIG. 4 , it may be preferable to mix and form carbon fibers 222 together with the peaks 221 to increase durability.

Of course, the lubricating member 220 may be coupled to the outer peripheral surface of the base member 210 by press-fitting without insert injection as described above. However, in this case, since the lubricating member 220 is of the same resin type as the peak, the thermal expansion coefficient of the lubricating member 220, the maximum indentation zone or the minimum indentation zone, etc. must be appropriately taken into consideration in order for the lubricating member 220 to respond to the operating heat. Therefore, it can smoothly serve as a bearing without being separated from the base member 210 .

To this end, the lubricating member 220 may be attached to the outer peripheral surface of the base member 210 using an adhesive. However, the method using the adhesive has a relatively complicated manufacturing process. Therefore, it is preferable in terms of reliability or mass productivity to insert-inject the lubricating member 220 onto the outer circumferential surface of the base member 210 using a mold.

In fact, when the bush bearing 200 is applied to a compressor, the bush bearing 200 should be able to maintain a stable coupling force even at a high operating temperature of the compressor, and also the dimensional change of the bush bearing 200 should be kept to a minimum. Friction loss between members can be reduced. However, when the lubricating member 220 is press-fitted to the outer circumferential surface of the base member 210 , the press-fitting band and the like must be accurately calculated as described above, but in practice, it may be difficult to accurately calculate this. Then, the lubricating member 220 may be deformed during the press-fitting process so that the press-in force may not be sufficient, and thus the lubricating member 220 may be detached from the base member 210 . This is also true of the method of using the bonding agent. In addition, these methods are not advantageous compared to the injection method in terms of mass production. Therefore, a method of insert-injecting the lubricating member 220 may be preferable.

However, in the method in which the lubricating member 220 is applied or laminated on the outer circumferential surface of the base member 210 by insert injection as described above, the lubricating member 220 may be deformed during the manufacturing process, and thus the outer diameter of the bush bearing is It may be formed larger than the design value.

For example, the manufacturing process by insert-injecting the lubricating member into the base member is as follows. This is divided into method ① and will be described together with FIGS. 5 to 7 .

As shown in FIG. 5, first, the base member 210 is put into the injection space of the mold, the injection product such as a peak is injected, and the injection molded product is taken out from the mold through a general curing process. (S11)

Next, the annealing heat treatment is performed by heating the injection product, and after maintaining it at approximately 270°C for about 4 hours, it is cooled at room temperature for about 2 hours. Through this, the stress of the peak due to thermal contraction after injection is relieved (S12).

Next, the length, inner diameter, and outer diameter of the heat-treated injection product are first cut and manufactured for the bush bearing. (S13)

A bush bearing manufactured through the above process is disclosed in FIG. 6 . However, as described above, the final outer diameter of the bush bearing manufactured by proceeding in the order of <injection → heat treatment → primary processing> may be manufactured to be larger than the designed outer diameter. That is, it was recognized that, after the injection stage, the heat treatment stage and the primary processing were performed, the various dimensions of the bush bearing could be managed precisely.

However, the researchers who propose this embodiment have made it more difficult to manage the dimensions of the bush bearings due to the conventional manufacturing method that proceeds in the order of <injection → heat treatment → primary processing> described above through a lot of trial and error, experiments, and analysis. found that it would be This will be described later while comparing the circularity of the bush bearing according to the present embodiment.

That is, when the lubricating member 220 made of a lubricating material is injection-molded on the outer peripheral surface of the base member 210 made of a metal material, the lubricating member 220 having a heat-sensitive characteristic will be significantly deformed during the injection process and heat treatment process. has been However, according to the research results of the researchers who proposed this embodiment, it was found that, when the injection conditions are the same, the lubricating member 220 is thermally deformed to a greater extent during the cutting process rather than the extent to which it is deformed during the heat treatment process.

For example, if the amount of deformation of the lubricating member 220 during the heat treatment process is about 1 μm, the amount of deformation during the cutting process is about 7 μm. This can also be seen through the experimental graph of FIG. 10, which will be described later. Moreover, when cutting is performed through heat treatment after injection, the lubricating member 220 swells more during the heat treatment process, thereby increasing the thickness of the lubricating member 220, and thus the amount to be cut is further increased. Due to this, the cutting resistance generated during the cutting process increases and the cutting heat is greatly increased. Consequently, the thickness of the final lubricating member 220 is designed in spite of cutting the lubricating member 220 according to the design value. thicker than the value.

Accordingly, when the circularity of the bush bearing is measured after completing the primary cutting, the lubricating member 220 is finally cut to reach the desired design value for the outer diameter of the lubricating member 220 . It can be seen that the outer diameter of is deformed larger than the desired design value.

In addition, as described above, in addition to the peak 221 , an additive such as carbon fiber 222 may be added to the injection-molded product to improve wear resistance or mechanical properties of the lubricating member 220 . However, in this case, while forming a kind of vortex at the opposite end (hereinafter, rear end) 202 of the side (hereinafter, the front end) 201 on which the injection is injected (hereinafter, the front end) 201 as the additive is injected with the peak, the additive bundle (222a) is formed, and the thickness of the rear end of the lubricating member 220 becomes thicker due to this additive bundle 222a, thereby further increasing the heat of cutting during cutting. Due to this, the difference between the front end outer diameter (D1) and the rear end outer diameter (D2) of the bush bearing 200 could be further increased.

Accordingly, in the present embodiment, a method for manufacturing a bush bearing capable of efficiently managing the dimensions of the bush bearing by minimizing thermal deformation of the lubricating member 220 is presented. This is referred to as a method according to the present embodiment. We will look at this in more detail later.

Meanwhile, as described above, the bush bearing manufactured as described above is press-fitted into the boss portion of the orbiting scroll and inserted into the boss coupling groove, thereby coupling the rotating shaft and the orbiting scroll. At this time, the outer diameter of the bush bearing is cut once again while being press-fitted into the boss.

This will be described with reference to FIGS. 5 and 7 as follows.

That is, the previously processed bush bearing 200 is press-fitted to the outer peripheral surface of the boss part 153 and fixed. (S14)

Next, the outer diameter of the bush bearing 200 is secondarily cut and processed so that the outer diameter of the bush bearing 200 corresponds to the outer diameter of the orbiting scroll 150 in a state of being press-fitted to the outer circumferential surface of the boss part 153 . Through this, the outer diameter of the bush bearing 200 can obtain a desired design value. (S15)

However, as described above, the final outer diameter of the bush bearing coupled to the boss by proceeding further in the order of <injection→heat treatment→primary machining> and then <press-fitting→secondary machining> may be deformed larger than the designed outer diameter. can

Therefore, as described above, in this embodiment, the heat treatment process is performed after the primary cutting processing (hereinafter, the primary processing) is performed on the insert-injected article, and the bush bearing after the heat treatment process is press-fitted into the boss part. By performing secondary cutting (hereinafter, referred to as secondary processing) again later, thermal deformation that may occur during cutting of the lubricating member 220 is minimized. That is, this embodiment proceeds in the order of <injection → primary processing → heat treatment → press-fitting → secondary processing>.

For example, as shown in FIG. 8 , an injection product in which the lubricating member 220 is applied to the outer circumferential surface of the base member 210 is manufactured through the insert injection process described in the above method ① (S21).

However, in the present embodiment, an overmolding part 225 is further formed at one end of the lubricating member 220 as shown in FIG. 9A . To this end, an over-molding space extending from the molding space is formed in the mold at the rear end of the injection-molded product among both ends of the base member 210 . This over-molding space is a space for over-molding so that the over-molding part 225 is formed at the rear end of the injection-molded product. Accordingly, the overmolded part 225 is formed to extend longer than the end of the base member 210 on the opposite side to which the injection-molded product is injected.

In addition, the carbon fibers 22 are injected together with the peak 221 into the injection-molded product, and the carbon fibers 222 are elongated in a direction in which the injection-molded product is injected. However, the opposite side of the injection molding inlet side, that is, the rear end 202, into which the injection product is injected, is in a blocked form, so as described above, on this blocked side, the peak 221, the injection product, and the carbon fiber 222, an additive, by the flow pressure of the injection product, as described above. ) forms a kind of vortex. As a result, the carbon fibers 222 having a grain among the peaks 221 and the carbon fibers 222 are aggregated to form a fiber bundle 222a, which is an additive bundle.

However, in the present embodiment, as the over-molding space extending from the molding space is further formed outside the rear end of the base member 210, the fiber bundle 222a is formed in the over-molding space instead of in the molding space. This forms the over-molding part 225 in the injection-molded product. In addition, the overmolded part 225 does not exist in the range of the base member 210 and is formed of a material constituting the lubrication member 220 only outside the range of the base member 210 .

Next, the injection product is taken out from the mold, and the outer diameter is subjected to primary processing. (S22)

For example, if the final outer diameter of the desired bush bearing is 29.9mm, and the outer diameter of the injection product removed from the mold is about 30.6mm, cut about 0.5~0.6mm through primary processing.

In addition, in the primary processing step, the inner diameter of the base member 210 forming the inner circumferential surface of the bush bearing 200 is cut, and the length of the lubricating member 220 forming the outer circumferential surface is also cut. At this time, as shown in FIG. 9B , not only the front end 201 constituting the molding inlet is cut, but also the over-molding part 225 of the rear end 202 opposite to that is cut and removed. Then, the injection product forms a cylindrical shape having the final length of the bush bearing 200 . Accordingly, as shown in FIG. 10 , the cut surface of the carbon fiber 225 may be exposed to the outside on the front surface 220a and the rear surface 220b of the lubricating member 220 , respectively.

Next, annealing heat treatment is performed on the first processed injection product under the conditions described in Method ① to form a bush bearing. (S23)

Through this, the internal stress of the peak material constituting the lubricating member 220 is relieved. In this process, the lubricating member 220 may slightly swell, but this is only negligible compared to the deformation caused by the cutting heat in the primary machining.

Next, as shown in FIG. 11 , the bush bearing 200 after the heat treatment process is press-fitted to the outer peripheral surface of the boss part 153 and coupled. (S24) And, the bush bearing 200 is press-fitted into the boss part 153 . Secondary cutting is performed to cut the outer diameter of (S25)

For example, if about 0.5~0.6mm is machined in the first machining step, by machining about 0.1~0.2mm in the second machining step, the outer diameter of the bush bearing can reach the initial design value of 29.9mm .

Through this, a relatively high cutting heat is generated while cutting a relatively large amount in the primary machining process, and thus the lubricating member 220 may be additionally deformed. As a result, additional deformation of the lubricating member 220 may be minimized. Accordingly, as the remaining part is cut and removed through secondary processing, the original design value for the outer diameter of the bush bearing can be satisfied.

12 is a graph showing a comparison of changes in outer diameter of a lubricating member according to a method of manufacturing a bush bearing. In this comparison, the outer diameter of the bearing was compared and analyzed by manufacturing an injection-molded product by inserting a lubricating member made of a peak and carbon fiber on the outer circumferential surface of the base member by the insert injection method, and then proceeding with the machining process by the two methods described above.

As shown in this figure, in the case of manufacturing a bush bearing by the method ① in which heat treatment is performed after injection and the outer diameter of the injected product is cut, approximately the same outer diameter is maintained from the front end, which is the molding entrance, to the vicinity of the rear end, which is the opposite side. However, it can be seen that the outer diameter rapidly increases as it approaches the rear end. This can be seen that the outer diameter of the lubricating member 220 made of the peak material is greatly deformed as the cutting resistance generated during the cutting process is greatly increased at the rear end of the bearing.

In particular, in the case of method ①, since the overmolding space is not formed in the mold, the overmolding part is not formed in the injection product, so an additive bundle (fiber bundle) is formed near the rear end of the bearing. Not only does the amount to be cut increases by the bundle of additives, but also the cutting resistance increases, resulting in increased cutting heat. It can be seen that the value increased significantly at the rear end compared to the front end.

On the other hand, in the case of manufacturing a bush bearing by the method according to this embodiment (hereinafter, method ②) in which primary processing is performed after injection, heat treatment is performed, and secondary processing is performed again, the opposite side from the front end of the molding entrance It can be seen that the outer diameter of the bearing is maintained almost constant all the way to the end of the rear end. Of course, the outer diameter of the bearing at the rear end increased slightly, but this is negligible compared to the method ①. In the case of forming the lubricating member 220 of the bush bearing according to method ② in this way, as the outer diameter is processed by dividing the injection product into primary processing and secondary processing, the generation of cutting heat can be lowered compared to deep processing at once. It can be understood that this is because it is possible to minimize deformation of the lubricating member 220 made of the peak material due to the cutting heat through this. Furthermore, in method ②, an overmolding space is formed in the mold to form an overmolding part 225 in the injection product, and a fiber bundle 222a is formed in this overmolding part 225, and then cut and removed. It is possible to prevent in advance that the bundle (222a) is concentrated on the rear end and aggravates the cutting heat. Through this, it is possible to suppress the rapid increase in the outer diameter of the bearing at the rear end as in the method ①.

On the other hand, this can be seen by comparing the cylindric diagram shown in FIG. 13 . That is, the result shown in FIG. 13 is a comparison of the outer circumferential cylindricity for each bush bearing manufactured according to method ① and method ②. it will be saved Here, the outer peripheral cylindricity value is a value obtained by measuring the outer diameter for a plurality of positions in the range from the front end to the rear end for each bush bearing, and averaging the outer diameter change values for the plurality of positions.

As shown in this figure, it can be seen that the average cylindricity (hereinafter, cylindricity) is about 12 μm in Method ①, whereas the cylindricity is about 4 μm in Method ②. That is, when the average thickness of the bush bearing applied to this embodiment is about 1.95 mm, the cylindricity in method ① is about 0.62% compared to the average thickness of the bush bearing, but in method ②, the cylindricity is about 0.2% becomes Therefore, considering the measurement error, the cylindricity can be within 0.3 to 0.4%. However, as seen above, in Method ①, the cylindricity can be at least 0.62% or more, and it can be seen that in Method ②, the cylindricity is greatly improved by approximately 1/2 compared to Method ①.

This is because the cylindricity is improved while suppressing the deformation of the outer diameter at one end (rear end) of the bush bearing in the case of method ② compared to the case of method ①. can be reduced. This can be seen with reference to FIG. 10 again. That is, in the case of method ②, the difference in the outer diameter of both ends of the lubricating member is about 1 to 2 μm, and even if processing errors are taken into consideration, it can be within about 3% of the average thickness of the lubricating member. On the other hand, in method ①, it can be seen that the difference between the outer diameters of both ends of the lubricating member is about 7 to 8 μm.

As described above, the small cylindricity means that the change in the outer diameter of the bush bearing is not that large. It is possible to increase the reliability of the bearing.

On the other hand, when the bush bearing 200 is previously applied to the scroll compressor as described above, the change in the outer diameter of the bush bearing 200 greatly affects the performance or reliability of the product.

For example, as described above, the bush bearing 200 is press-fitted into the boss portion 153 of the orbiting scroll 150 to serve as a bearing between the boss coupling groove 123d of the rotating shaft 123 and have.

In this case, in the bush bearing according to method ①, the outer diameter of the lubricating member 220 is not uniform and increases significantly toward the rear end (lower end) 202, so that the outer diameter of the bush bearing 200 is uniformly managed. becomes very difficult. That is, when the outer diameter of the bush bearing 200 is uniformly changed, the outer diameter of the bush bearing 200 may be deep machined as a whole to match the final outer diameter to the original design value. However, if only a portion of the outer diameter of the bush bearing 200 is abnormally deformed, it becomes difficult to process the entirety and uniformly manage it.

Then, while the outer peripheral surface of the bush bearing 200 is excessively closely contacted with the inner peripheral surface of the boss coupling groove 123d, friction loss may occur and uneven wear of the bush bearing 200 may occur. As a result, the inclination of the orbiting scroll 150 is increased, and refrigerant leakage from the compression chamber may occur, and the compression efficiency may also decrease.

On the other hand, in the bush bearing 200 according to method ②, as the outer diameter of the lubricating member 220 is maintained uniformly, even if the bush bearing 200 is press-fitted into the boss part 153 , the outer peripheral surface of the bush bearing 200 and the boss It is possible to suppress friction loss with the inner circumferential surface of the coupling groove 123d and uneven wear of the bush bearing. In addition, it is possible to suppress the leakage of the compression chamber by suppressing the inclination of the orbiting scroll 150 .

In particular, when the bush bearing 200 is applied to a scroll compressor, the problems mentioned above may be further exacerbated as the lubricating member 220 thermally expands even by heat generated during operation of the compressor. This may increase the degree of thermal expansion as the thickness of the lubricating member 220 increases.

However, in the bush bearing 200 according to the method ② of this embodiment, as the thickness of the lubricating member 220 is maintained almost constant from the front end (upper end) 201 to the rear end (lower end) 202, the bush bearing ( 200) may be such that the outer diameter D2 of the rear end (lower end) hardly increases compared to the outer diameter D1 of the front end (upper end). Accordingly, the degree of thermal expansion of the lubricating member 220 may be maintained relatively small even by heat generated during operation of the compressor.

14 and 15 show the change in outer diameter and cylinder of the bush bearing after exposure to the same operating conditions (210°C) when the bush bearing according to method ① is applied to the scroll compressor and when the bush bearing according to method ② is applied to the scroll compressor. It is a graph showing the difference in degrees.

As shown in FIG. 14 , when looking at the change in the outer diameter of the bush bearing after exposure to the same operating conditions described above, it can be seen that the method ① deforms about 22 μm, and the method ② deforms about 6 μm. It can be seen that this is because the thickness of the lubricating member 220 in the method ② is kept thinner than that of the method ①.

This can be seen by comparing the cylindric diagram shown in FIG. 15 . That is, looking at the change in the cylindricity of the outer circumference of the bush bearing after the compressor is operated under the previous operating conditions, when the average thickness of the design value of the bush bearing applied in this embodiment is approximately 1.95 mm, the Compared to the average thickness, the cylindricity of the outer circumferential surface in Method ① is about 1.13%, but in Method ②, the cylindricity is about 0.31%. Therefore, considering the measurement error and the like, the cylindricity of the outer peripheral surface of the bush bearing 200 according to the present embodiment may be within 0.5%. Accordingly, it can be seen that the difference in cylindricity is greatly improved in the method ② compared to the method ① by about 1/4 to 1/3.

In other words, if you look at the difference in cylindricity for each bush bearing manufactured according to method ① and method ② under the previous operating conditions, it can be seen that method ② has less thermal deformation than method ①. Considering that the interval between the bush bearing and the boss coupling groove is managed within 100 μm, it can be expected to exert a fairly large effect.

After all, in the case of method ②, the increase in the thickness of the lubricating member 220 is kept to a minimum by lowering the cutting heat generated during cutting, while thermal expansion due to the operating heat of the compressor can be kept to a minimum when applied to a compressor. . Accordingly, the change in the overall outer diameter of the bush bearing is significantly lower than in the case of method ①, so that the performance and reliability of the compressor to which the bush bearing is applied can be increased.

123: rotation shaft 123d: boss coupling groove
130: main frame 131: shaft hole
140: fixed scroll 142: end plate part
142: fixed lap 150: orbiting scroll
152: turning lap 153: boss part
200: bush bearing 201: front end of the injection product
202: rear end of the injection product 210: base member
211: knurling part 220: lubrication member
220a: front end of the lubricating member 220b: rear end of the lubricating member
221: peak 222: carbon fiber
222a: fiber bundle 225: overmolding part

Claims (15)

a first scroll in which a first wrap is formed on one side of the first end plate;
a second scroll in which a second wrap is formed on one side of the second end plate, the second wrap is engaged with the first wrap to form a compression chamber, and a boss portion is formed on the other side of the second end plate;
a rotation shaft provided with a boss coupling groove so that the boss portion of the second scroll is inserted and coupled; and
a bush bearing press-fitted to and coupled to the outer circumferential surface of the boss, the bush bearing having an outer lubricating layer so that the outer circumferential surface forms a bearing surface with the inner circumferential surface of the boss coupling groove;
The bush bearing is
a base member formed in a cylindrical shape and press-fitted to an outer circumferential surface of the boss; and
a lubricating member integrally provided on the outer circumferential surface of the base member to form a lubricating layer;
Based on the initial state in which the bush bearing is press-fitted into the boss, the cylindricality of the outer peripheral surface of the bush bearing is formed to satisfy within 0.4% of the average thickness of the bush bearing. a first scroll in which a first wrap is formed on one side of the first end plate;
a second scroll in which a second wrap is formed on one side of the second end plate, the second wrap is engaged with the first wrap to form a compression chamber, and a boss portion is formed on the other side of the second end plate;
a rotation shaft provided with a boss coupling groove so that the boss portion of the second scroll is inserted and coupled; and
a bush bearing press-fitted to and coupled to the outer circumferential surface of the boss, the bush bearing having an outer lubricating layer so that the outer circumferential surface forms a bearing surface with the inner circumferential surface of the boss coupling groove;
The bush bearing is
a base member formed in a cylindrical shape and press-fitted to an outer circumferential surface of the boss; and
a lubricating member integrally provided on the outer circumferential surface of the base member to form a lubricating layer;
Based on the state after the bush bearing is press-fitted into the boss part and operated at 210° C. for 2 hours, the outer peripheral surface cylindricity of the bush bearing is formed to satisfy within 0.5% of the average thickness of the bush bearing Scroll compressor, characterized in that. 3. The method of claim 1 or 2,
The scroll compressor according to claim 1, wherein a change rate of a gap between the outer peripheral surface of the bush bearing and the inner peripheral surface of the boss coupling groove is formed to satisfy within 0.4% of the average thickness of the bush bearing. 3. The method of claim 1 or 2,
The scroll compressor according to claim 1, wherein the base member is formed of a material having the same heat transfer coefficient as that of the boss of the second scroll. 5. The method of claim 4,
The scroll compressor according to claim 1, wherein the base member is formed of a material having the same material properties as that of the boss of the second scroll. 3. The method of claim 1 or 2,
The lubricating member is a scroll compressor, characterized in that the resin-based carbon fiber is contained. 7. The method of claim 6,
The carbon fiber scroll compressor, characterized in that cut surfaces are exposed at both ends of the lubricating member. 7. The method of claim 6,
The scroll compressor having an external lubrication layer, characterized in that the lubricating member has cut surfaces formed at both ends. 7. The method of claim 6,
The resin series is a scroll compressor, characterized in that the PEEK material. 7. The method of claim 6,
The scroll compressor, characterized in that the carbon fibers are arranged in the longitudinal direction of the base member. 11. The method of claim 10,
The carbon fiber scroll compressor, characterized in that cut surfaces are exposed at both ends of the lubricating member. 3. The method of claim 1 or 2,
The scroll compressor according to claim 1, wherein the base member and the lubricating member are formed in a shape without a cut surface along a circumferential direction. 13. The method of claim 12,
and a knurling portion formed on an outer circumferential surface of the base member so as to increase a contact area with an inner circumferential surface of the lubricating member. 14. The method of claim 13,
A scroll compressor satisfying the following range when a thickness of the base member is a, a thickness of the lubricating member is b, and a depth of the knurling part is c.
b/a = 1.09 to 1.15,
c/a = 0.3 to 0.5 delete

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