JP6428180B2 - Oil-impregnated bearing manufacturing method, oil-impregnated bearing - Google Patents

Description

  The present invention relates to a method of manufacturing an oil-impregnated bearing that rotatably supports a rotating shaft of a rotating body, and an oil-impregnated bearing manufactured by the manufacturing method.

  Conventionally, a motor device including a rotor including a commutator, a shaft, and an armature, and an oil-impregnated bearing that rotatably supports the shaft (rotary shaft of the rotor) has been widely used. The motor includes a rotor including a commutator, a shaft, and an armature, and an oil-impregnated bearing that rotatably supports the shaft (rotary shaft of the rotor).

  For example, Patent Document 1 discloses an oil-impregnated bearing obtained by sintering CuNi alloy powder, copper powder, and tin powder, and a method for producing the oil-impregnated bearing.

  The manufacturing method of Patent Document 1 includes a mixing process, a compacting process, a sintering process, an oiling process, a sizing process, a cleaning process, and an oil immersion process in this order. In the mixing step, the raw material powders are mixed so that the whole is uniform.

  In the compacting step, the mixture is put into a mold and compression molded into a predetermined shape. In the sintering step, CuNi alloy powder, copper powder and tin powder are sintered at a temperature of 700 ° C. to 800 ° C. in order to sufficiently diffuse tin. In the oiling process, oil is applied to the surface of the sintered body to prevent rust. In the sizing step, the sintered body is sized into a predetermined shape. In the cleaning step, the sintered body is cleaned.

  Thereafter, in the oil immersion step, an oil immersion process is performed in which the sintered body is immersed in the lubricating oil and heated under vacuum. Thus, the manufacturing method of patent document 1 manufactures the oil-impregnated bearing (sintered body) impregnated with the lubricating oil.

Japanese Patent Laid-Open No. 11-256206

  However, the manufacturing method disclosed in Patent Document 1 is complicated because of a large number of steps. Therefore, the manufacturing method of Patent Document 1 has a problem that it takes a long time to manufacture the oil-impregnated bearing (sintered body) and the manufacturing cost is high.

  Accordingly, an object of the present invention is to provide an oil-impregnated bearing manufacturing method and an oil-impregnated bearing capable of manufacturing an oil-impregnated bearing with fewer steps than conventional manufacturing methods.

  The present invention relates to a method for manufacturing an oil-impregnated bearing that rotatably supports a rotating shaft of a rotating body. The manufacturing method of the present invention includes a charging step and a sintering step.

  In the charging step, a mixture of a granular material containing CuNi alloy powder or CuMn alloy powder and Sn powder and lubricating oil is charged into a container.

  In the sintering step, the mixture is sintered while being compressed at a temperature not higher than the boiling point of the lubricating oil. Thereby, a sintering process forms the sintered compact which makes the main phase the intermetallic compound produced | generated by reaction of CuNi alloy powder or CuMn alloy powder, and Sn powder. This sintered body is impregnated with lubricating oil.

  In this manufacturing method, since the sintering process sinters below the boiling point of the lubricating oil, the lubricating oil remains even after the sintering process and is impregnated inside the sintered body. The boiling point of the lubricating oil is, for example, 300 ° C. or less. An intermetallic compound is produced | generated at the temperature within the range of 200-300 degreeC, for example. The intermetallic compound is a SnCuNi alloy or a SnCuMn alloy. The intermetallic compound has a melting point of 300 ° C. or higher.

  In the sintering process of this manufacturing method, since the mixture obtained by mixing the powder and lubricating oil is sintered while being compressed, the compacting process, the sintering process, and the oil immersion process in the manufacturing method of Patent Document 1 Can be done at once.

  Therefore, this manufacturing method can reduce the number of steps compared to the conventional manufacturing method. Therefore, this manufacturing method can reduce the time and manufacturing cost which manufacture an oil-impregnated bearing.

  Moreover, in the manufacturing method of this invention, it is preferable that the weight ratio of the component element in a CuNi alloy exists in the range from Cu: Ni = 95: 5 to 75:25. That is, in the CuNi alloy, the ratio of the weight of Ni to the weight of Cu is preferably in the range of 5/95 or more and 25/75 or less.

  In this manufacturing method, molten Sn diffuses rapidly during sintering. Therefore, this manufacturing method can quickly form a sintered body having high heat resistance at a temperature lower than the boiling point of the lubricating oil.

  Moreover, in the manufacturing method of this invention, it is preferable that a sintering process performs sintering in the state which contacted the housing | casing which accommodates a rotary body, and a mixture.

  In this manufacturing method, since the mixture is sintered together with the casing, there is no need to size the sintered body into a predetermined shape after sintering. That is, in the sintering process of this manufacturing method, the compacting process, the sintering process, the oil immersion process, and the sizing process in the manufacturing method of Patent Document 1 can be performed at a time.

  Therefore, this manufacturing method can further reduce the number of steps. Therefore, this manufacturing method can further reduce the time and manufacturing cost required for manufacturing the oil-impregnated bearing.

  Moreover, in the manufacturing method of this invention, it is preferable that at least the surface of a housing | casing is comprised with Cu or Ni.

  In this manufacturing method, an alloy layer is generated by a reaction between Cu or Ni covering the surface of the housing and the mixture. Therefore, this manufacturing method can improve the joint strength between the sintered body and the casing.

  Moreover, in the manufacturing method of this invention, it is preferable that a granular material further contains Cu powder and Fe powder.

  In this manufacturing method, since the Cu powder and the Fe powder are present in the sintered body, the wear resistance of the oil-impregnated bearing with respect to the rotating rotating shaft can be improved.

  The present invention also relates to an oil-impregnated bearing that rotatably supports a rotating shaft of a rotating body.

The oil-impregnated bearing of the present invention includes a porous sintered body mainly composed of an intermetallic compound produced by a reaction between CuNi alloy powder or CuMn alloy powder and Sn powder,
A lubricating oil impregnated in the porous interior of the sintered body;
Have

  The oil-impregnated bearing of the present invention is manufactured by the above-described manufacturing method of the present invention. Therefore, the oil-impregnated bearing of the present invention has the same effect as the manufacturing method of the present invention described above.

  Note that the above-described rotating body is provided in a rotating machine that converts electrical energy and rotational energy, for example.

  According to the present invention, an oil-impregnated bearing can be manufactured with fewer steps than the conventional manufacturing method.

It is an external appearance perspective view of the motor apparatus 100 provided with the oil-impregnated bearing 8 which concerns on embodiment of this invention. FIG. 2 is an external perspective view of the motor device 100 shown in FIG. 1. It is principal part sectional drawing of the SS line | wire shown in FIG. It is a flowchart which shows the manufacturing method of the oil-impregnated bearing 8 which concerns on embodiment of this invention. It is sectional drawing of the metal mold | die 80 used with the manufacturing method of the oil-impregnated bearing 8 shown in FIG. It is sectional drawing which shows the insertion process shown in FIG. It is sectional drawing which shows the injection | throwing-in process shown in FIG. It is sectional drawing which shows the sintering process shown in FIG. It is sectional drawing which shows the mode after passing through the sintering process shown in FIG. It is sectional drawing which shows the mode after passing through the taking-out process shown in FIG.

<< Embodiment of the Present Invention >>
A motor device including an oil-impregnated bearing according to an embodiment of the present invention will be described below.

  FIG. 1 is an external perspective view of a motor device 100 including an oil-impregnated bearing 8 according to an embodiment of the present invention. FIG. 2 is an external perspective view of the motor apparatus 100 shown in FIG. FIG. 3 is a cross-sectional view of an essential part taken along line SS shown in FIG.

  As shown in FIGS. 1 and 2, the motor device 100 includes a permanent magnet 2, a rotor 3, a brush 7, oil-impregnated bearings 8 and 18, and a housing 9. The motor device 100 converts electrical energy into rotational energy (rotational force) by the rotation of the rotor 3.

  The housing 9 has an annular upper plate 9A and a disc-shaped bottom plate 9B. The bottom plate 9B is fitted on the bottom surface of the housing 9. The housing 9 stores the permanent magnet 2, the rotor 3, and the brush 7. The permanent magnet 2 is fixed to the inner peripheral surface of the housing 9. The housing 9 is made of an iron-based material. At least the surface of the housing 9 is plated and covered with a Cu film.

  In the rotor 3, an armature 5 and a commutator 6 electrically connected to a coil (not shown) of the armature 5 are provided on a shaft (rotary shaft) 4 rotatably supported in the housing 9. Is. The armature 5 includes an iron core and a coil that is not shown. Each commutator 6 is a member in which three cylindrical piece-shaped metal plates are integrally molded or bonded with an adhesive to a cylindrical insulator.

  The brush 7 is fixed to the inner peripheral surface of the housing 9. The brush 7 is always in sliding contact with the commutator 6 and has a role of flowing current through the coil of the armature 5.

  The oil-impregnated bearing 8 and the oil-impregnated bearing 18 rotatably support the shaft (rotary shaft) 4 of the rotor 3. The oil-impregnated bearing 8 has an annular shape. The oil-impregnated bearing 8 is provided on the upper plate 9 </ b> A of the housing 9. The oil-impregnated bearing 18 is provided on the bottom plate 9 </ b> B of the housing 9. The oil-impregnated bearing 8 and the oil-impregnated bearing 18 have the same configuration.

  As shown in FIG. 3, the oil-impregnated bearing 8 includes a porous sintered body 12 and a lubricating oil 40 impregnated inside the porous body of the sintered body 12. The sintered body 12 has a large number of fine open pores, and a lubricating oil 40 is held in the open pores. A minute gap is formed between the sintered body 12 and the shaft 4, and the lubricating oil 40 is interposed in this gap.

  The oil-impregnated bearing 8 sinters the mixture 70 of the granular material 30 containing the Sn powder 11 and the CuNi alloy powder 21 and the lubricating oil 40 shown in FIG. 7 described later while compressing the mixture 70 at a temperature equal to or lower than the boiling point of the lubricating oil 40. Is generated.

  Hereinafter, the manufacturing method of the oil-impregnated bearing 8 will be described in detail.

  FIG. 4 is a flowchart showing a method for manufacturing the oil-impregnated bearing 8 according to the embodiment of the present invention. FIG. 5 is a cross-sectional view of a mold 80 used in the method for manufacturing the oil-impregnated bearing 8 shown in FIG. 6 is a cross-sectional view showing the insertion step shown in FIG. FIG. 7 is a cross-sectional view showing the charging process shown in FIG. FIG. 8 is a cross-sectional view showing the sintering step shown in FIG. FIG. 9 is a cross-sectional view showing a state after the sintering step shown in FIG. FIG. 10 is a cross-sectional view showing a state after the extraction step shown in FIG. 5 to 10 correspond to the cross section taken along the line S-S shown in FIG.

  First, the housing 9 in a state where the bottom plate 9B is not mounted and the mold 80 are prepared. As shown in FIG. 5, the mold 80 includes a lower plate 81, an annular middle plate 82, and an annular upper plate 83. The lower plate 81 has a columnar center portion protruding upward and an annular outer frame portion protruding upward.

  The mold 80 corresponds to an example of the container of the present invention.

  Then, as shown in FIG. 6, the housing 9 is inserted between the lower plate 81 and the middle plate 82, and the upper plate 9A of the housing 9 is sandwiched between the lower plate 81 and the middle plate 82 (FIG. 4: S1). As described above, the housing 9 is made of an iron-based material. At least the surface of the housing 9 is plated and covered with a Cu film.

  Next, as shown in FIG. 7, the mixture 70 containing the granular material 30, the lubricating oil 40, and rosin is put into the lower plate 81 and the middle plate 82 (FIG. 4: S2). As a result, the tip of the upper plate 9A of the housing 9 is inserted into the mixture 70. The powder body 30 is composed of Sn powder 11, CuNi alloy powder 21, and additive powder 27.

  In the mixture 70 of this embodiment, the content of the Sn powder 11 is 5 parts by weight, the content of the CuNi alloy powder 21 is 60 parts by weight, the content of the additive powder 27 is 35 parts by weight, and the lubricating oil The content of 40 is 5 parts by weight, and the content of rosin is 1 part by weight. Rosin is a flux component. In addition to rosin, organic acids, acrylic resins, epoxy resins, and the like can be used for the flux. As the mixture 70, a mixture that has been agitated in advance so that the powder 30 is uniform over the entire lubricating oil 40 is used.

  Moreover, in the granular material 30, the content of the Sn powder 11 is in the range of 5 parts by weight or more and 60 parts by weight or less, and the content of the CuNi alloy powder 21 is in the range of 40 parts by weight or more and 95 parts by weight or less. The content of the additive powder 27 is preferably in the range of 0 to 35 parts by weight.

  This is because if the content of the Sn powder 11 is less than 5 parts by weight or the content of the CuNi alloy powder 21 is more than 95 parts by weight, the strength of the oil-impregnated bearing 8 cannot be maintained without being completely sintered. On the other hand, if the content of the Sn powder 11 exceeds 60 parts by weight or the content of the CuNi alloy powder 21 is less than 40 parts by weight, Sn remains without reacting.

  The average particle diameter of the Sn powder 11 is preferably in the range of 5 μm to 30 μm, and the average particle diameter 21 of the CuNi powder is preferably in the range of 1 μm to 10 μm. The melting point of Sn is 231.93 ° C. The melting point of the CuNi alloy is higher than the melting point of Sn, for example, 1000 ° C. or higher.

  Here, the CuNi alloy powder 21 may remain in the sintered body 12 (see FIG. 9) generated in the sintering step. However, it is preferable that the Sn powder 11 does not remain in the sintered body 12 after sintering.

  This is because if the unreacted Sn powder 11 remains in the sintered body 12, the heat resistance of the remaining Sn portion is lowered. Further, when the unreacted Sn powder 11 remains in the sintered body 12, the oil-impregnated bearing 8 is likely to be seized due to wear with the rotating shaft 4.

  Next, the weight ratio of the component elements in the CuNi alloy constituting the CuNi alloy powder 21 is preferably in the range of Cu: Ni = 95: 5 to 75:25. That is, in the CuNi alloy, the ratio of the weight of Ni to the weight of Cu is preferably in the range of 5/95 or more and 25/75 or less. An alloy satisfying this ratio is, for example, a Cu10Ni alloy or a Cu6Ni alloy. In this embodiment, a Cu10Ni alloy is used.

  If the weight ratio of the component elements in the CuNi alloy is within this range, even if the heating temperature in the sintering process is 300 ° C. or less, the diffusion of the molten Sn proceeds rapidly, and the molten Sn and the CuNi alloy powder 21 The reaction rate becomes extremely high.

  However, if the Cu ratio is less than 75 or more than 95, the reaction rate between the melted Sn and the CuNi alloy powder 21 decreases in the sintering process, or the reaction does not occur at 300 ° C. or lower.

  The additive powder 27 is an additive powder added to improve the wear resistance of the oil-impregnated bearing 8 with respect to the rotating shaft 4. The additive powder 27 is, for example, Cu powder, Fe powder, C powder, or the like. The average particle size of the additive powder 27 is preferably in the range of 1 μm to 10 μm.

  Next, as the lubricating oil 40, for example, a hydrocarbon-based, fluorine-based, ester-based, or ether-based synthetic oil, liquid grease, or mineral oil can be used. The boiling point of the lubricating oil 40 is 300 ° C., for example.

  The blending amount of the lubricating oil 40 with respect to the powder body 30 is preferably in the range of 5 volume% or more and 25 volume% or less. If the blending amount of the lubricating oil 40 with respect to the granular material 30 exceeds 25% by volume, the strength of the oil-impregnated bearing 8 tends to decrease. On the other hand, when the blending amount of the lubricating oil 40 with respect to the granular material 30 is less than 5% by volume, the oil-impregnated bearing 8 tends to be seized due to wear with the rotating shaft 4.

  Next, as shown in FIG. 8, the mixture 70 is sintered at a predetermined temperature while applying pressure in the direction of the arrow P (that is, while being compression-molded) (FIG. 4: S3). The predetermined temperature is a temperature within the range of 200 ° C. or higher and the boiling point of the lubricating oil 40 (300 ° C. in this embodiment) or lower. The predetermined temperature is preferably a temperature within a range from the melting point of the Sn powder 11 to the boiling point of the lubricating oil 40.

  Further, the pressure of S3 is applied to the mixture 70 by moving the upper plate 83 in the direction of arrow P. The pressure of S3 is preferably in the range of 10 MPa to 40 MPa. By performing the sintering step under high pressure, the reaction rate between the molten Sn and the CuNi alloy powder 21 is increased. The heating time is also preferably from 1 minute to 10 minutes.

  Here, when the heating / pressurizing conditions are below 200 ° C. and 10 MPa, unreacted Sn powder 11 and CuNi alloy powder 21 may remain. On the other hand, if the heating / pressurizing conditions exceed 300 ° C. and 40 MPa, the lubricating oil 40 evaporates, or the reaction between the Sn powder 11 and the CuNi alloy powder 21 proceeds excessively and the oil-impregnated bearing 8 becomes brittle. May end up.

  If the heating time is less than 1 minute, unreacted Sn powder 11 and CuNi alloy powder 21 may remain. On the other hand, if the heating time exceeds 10 minutes, the oil-impregnated bearing 8 may become brittle and crack, or the oil-impregnated bearing 8 may be easily chipped.

  FIG. 4: When the mixture 70 of the granular material 30 and the lubricating oil 40 shown in FIG. 8 is heated in the sintering step shown in S3, the oil-impregnated bearing 8 shown in FIG. 9 can be obtained. The oil-impregnated bearing 8 is composed of a sintered body 12, a lubricating oil 40 filled in pores, a CuSn alloy layer 25, and an additive powder 27.

  More specifically, when the mixture 70 is heated, an intermetallic compound is generated by a reaction between the Sn powder 11 and the CuNi alloy powder 21. This reaction is, for example, a reaction associated with liquid phase diffusion bonding (“TLP bonding: Transient Liquid Phase Diffusion Bonding”). The sintered body 12 is a phase composed of this intermetallic compound.

In this embodiment, the intermetallic compound is a SnCuNi alloy. Specifically, this intermetallic compound is, for example, (Cu, Ni) ₆ Sn ₅ , Ni ₃ Sn ₂ , Cu ₂ NiSn, or the like. The melting point of this intermetallic compound is 300 ° C. or higher, and further 400 ° C. or higher.

  In addition, since the sintering is performed at a temperature equal to or lower than the boiling point of the lubricating oil 40, the lubricating oil 40 remains even after the sintering process, and the porous body of the sintered body 12 is impregnated. That is, the oil-impregnated bearing 8 has a structure in which the main phase is the CuNiSn intermetallic compound phase, and the lubricating oil 40 and the additive powder 27 filled in the pores are dispersed in the main phase.

  Further, when the mixture 70 is heated, at the same time, the CuSn alloy layer 25 is generated by a chemical reaction between the Sn powder 11 and the Cu film covering the surface of the housing 9. Therefore, the sintered body 12 and the housing 9 are firmly joined.

  Next, after natural cooling, the housing 9 is removed from the mold 80 (FIG. 4: S4). Thereby, as shown in FIG. 10, the housing 9 in which the oil-impregnated bearing 8 is mounted on the upper plate 9A is completed.

  In addition, the manufacturing method of the oil-impregnated bearing 18 does not include an insertion step (FIG. 4: S1) for inserting the housing 9 into the mold 80 and a removal step (FIG. 4: S4) for removing the housing 9 from the mold 80. Thus, the manufacturing method of the oil-impregnated bearing 8 is different. Since other points are the same, description thereof is omitted.

  When the oil-impregnated bearing 18 is completed, the oil-impregnated bearing 18 is mounted on the bottom plate 9B of the housing 9. Then, the permanent magnet 2, the rotor 3, the brush 7, and the like are attached to the inside of the housing 9, and when the shaft 4 is inserted into the oil-impregnated bearings 8 and 18, the motor device 100 is completed (see FIGS. 1 and 3). .

  As described above, for example, a porous sintered body 12 having an intermetallic compound having a melting point of about 400 ° C. as a main phase can be formed by a heat treatment at about 200 to 300 ° C. In addition, since the sintering is performed below the boiling point of the lubricating oil 40, the lubricating oil 40 remains even after the sintering process and is impregnated into the porous interior of the sintered body 12. That is, the oil-impregnated bearings 8 and 18 having high heat resistance can be formed by heat treatment at a relatively low temperature.

  In the sintering process of the oil-impregnated bearings 8 and 18, since the mixture 70 obtained by mixing the granular material 30 and the lubricating oil 40 is sintered while being compressed, the compacting process and the sintering in the manufacturing method of Patent Document 1 are performed. The kneading step and the oil immersion step can be performed at a time.

  Furthermore, in the manufacturing method of the oil-impregnated bearing 8, since the sintering is performed in a state where the mixture 70 and the housing 9 are in contact with each other in the mold 80, it is not necessary to size the sintered body 12 into a predetermined shape after the sintering. . That is, in the sintering process of the manufacturing method of the oil-impregnated bearing 8, the compacting process, the sintering process, the oil immersion process, and the sizing process in the manufacturing method of Patent Document 1 can be performed at a time.

  Therefore, the manufacturing method of this embodiment can reduce the number of processes compared with the conventional manufacturing method. Therefore, the manufacturing method of the present embodiment can reduce the time and manufacturing cost required for manufacturing the oil-impregnated bearings 8 and 18.

  In the manufacturing method of the present embodiment, the alloy layer 25 is generated by the reaction between the Cu film formed on the surface of the housing 9 and the mixture 70. Therefore, the bonding strength between the sintered body 12 and the housing 9 can be improved.

  Moreover, in the manufacturing method of this embodiment, since Cu powder and Fe powder are added in the sintered compact 12, the abrasion resistance of the oil-impregnated bearings 8 and 18 with respect to the rotating shaft 4 can be improved.

<< Other Embodiments >>
In the above-described embodiment, the present invention is applied to a motor that converts electrical energy into rotational energy (rotational force). However, the present invention is not limited to this. In implementation, for example, the present invention may be applied to a dynamo that converts rotational energy (rotational force) into electrical energy, a wheel of an automobile, or the like.

  Moreover, in this embodiment, although the shape of the oil-impregnated bearings 8 and 18 is a cylindrical shape, it is not restricted to this. In implementation, the shape of the oil-impregnated bearing may be an arbitrary shape such as a rectangular parallelepiped shape.

  Further, at least the surface of the housing 9 is covered with a Cu film by plating, but the present invention is not limited to this. In implementation, for example, at least the surface of the housing 9 may be covered with a Ni film by plating. In this case, a NiSn alloy layer is formed instead of the CuSn alloy layer 25.

  Moreover, in this embodiment, although CuNi alloy powder is used, it is not restricted to this. In implementation, CuMn alloy powder may be used. In this case, Sn powder and CuMn alloy powder react to produce a SnCuMn alloy.

  Finally, the above description of the embodiments should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

2 ... Permanent magnet 3 ... Rotor 4 ... Shaft 5 ... Armature 6 ... Commutator 7 ... Brush 8 ... Oil-impregnated bearing 9 ... Housing 11 ... Sn powder 12 ... Sintered body 18 ... Oil-impregnated bearing 21 ... CuNi alloy powder 25 ... CuSn alloy layer 27 ... additive powder 30 ... granular material 40 ... lubricating oil 70 ... mixture 80 ... mold 81 ... lower plate 82 ... middle plate 83 ... upper plate 100 ... motor device

Claims (5)

In the manufacturing method of the oil-impregnated bearing that rotatably supports the rotating shaft of the rotating body,
A charging step of charging a mixture of a granular material containing CuNi alloy powder or CuMn alloy powder and Sn powder and a lubricating oil;
The mixture is sintered while being compressed at a temperature equal to or lower than the boiling point of the lubricating oil, and the main phase is an intermetallic compound produced by the reaction between the CuNi alloy powder or the CuMn alloy powder and the Sn powder. a sintering step of forming a sintered body impregnated with lubricating oil, only contains,
The method for producing an oil-impregnated bearing, wherein the CuNi alloy powder or the CuMn alloy powder is 40 parts by weight or more, and the Sn powder is 5 parts by weight or more .   2. The method of manufacturing an oil-impregnated bearing according to claim 1, wherein a weight ratio of the component elements in the CuNi alloy is in a range of Cu: Ni = 95: 5 to 75:25.   3. The method for manufacturing an oil-impregnated bearing according to claim 1, wherein the sintering step is performed in a state where the casing housing the rotating body and the mixture are in contact with each other.   The method for manufacturing an oil-impregnated bearing according to claim 3, wherein at least a surface of the housing is made of Cu or Ni.   The said granular material is a manufacturing method of the oil-impregnated bearing of any one of Claim 1 to 4 which contains Cu powder and Fe powder further.

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