Process for reducing the difference between the inner diameters of the upper and lower ends of an asymmetric outer double-groove machine ring forging

Abstract

The application discloses a process method for reducing the inner diameter difference between upper and lower ends of an asymmetric outer double-groove machine case ring forging, taper compensation is performed on the inner surface of a ring blank for rolling to obtain an inner tapered cross-section ring blank, and the size of the inner tapered cross-section ring blank is calculated according to the principle that the volume is unchanged before and after rolling, so as to reduce the inner diameter difference between upper and lower ends generated in rolling of the asymmetric outer double-groove machine case ring forging from the rectangular ring blank, and a combined driving roller and a core roller for closed rolling are designed to prevent the upper and lower ends from moving up and down during the rolling of the ring piece and to ensure the rolling stability, the inner tapered cross-section ring blank is rolled into the asymmetric outer double-groove machine case ring forging by using the combined driving roller and the core roller for closed rolling, and the core roller rolling speed curve and the driving roller rotating speed are designed according to the volume change trend of each region during the rolling process. The method can ensure that the inner diameter difference between upper and lower ends of the asymmetric outer double-groove machine case ring forging is within a reasonable range without increasing the volume of the ring blank.

Description

Technical Field

[0001] This invention belongs to the field of aerospace manufacturing technology, and specifically relates to a process method for reducing the difference in inner diameter between the upper and lower ends of an asymmetric external double-groove casing ring forging. Background Technology

[0002] Aero engines are the core power source of modern aircraft, and their performance and reliability directly affect the safety and stability of the aircraft. The casing is one of the main components of an aero engine. The manufacturing process of the asymmetric external double-groove casing ring includes rolling and machining of the casing ring forging. The rolled casing ring forging must not only meet the performance requirements of the asymmetric external double-groove casing component base but also encompass the final external contour of the asymmetric external double-groove casing component. To reduce material costs and machining cycles, the external dimensions of the asymmetric external double-groove casing ring forging that encompasses the final external contour of the asymmetric external double-groove casing component must be as small as possible.

[0003] To ensure the successful machining of the final asymmetric double-groove casing part, a machining allowance of 8-10mm is typically added to each side of the outer contour. However, due to factors such as die design and material flow distribution during rolling, a 10mm difference in inner diameter occurs between the upper and lower ends of the asymmetric double-groove casing ring forging. Based on existing ring rolling processes, an additional allowance for this inner diameter difference needs to be added to the existing 8-10mm machining allowance, increasing the total machining allowance, resulting in a longer machining cycle and higher material costs.

[0004] As can be seen from the above, existing rolling processes for asymmetric double-groove casing ring forgings only increase the dimensions of the enveloping part's outline, failing to address the issue of inner diameter difference between the upper and lower ends of the asymmetric double-groove casing ring forgings, and thus making it difficult to meet the high-precision requirements of asymmetric double-groove casing ring forgings. Therefore, reducing the inner diameter difference between the upper and lower ends of asymmetric double-groove casing ring forgings is a key issue that urgently needs to be addressed in the precision forming and manufacturing of aero-engine casing ring forgings. Summary of the Invention

[0005] The purpose of this invention is to provide a process method for reducing the difference in inner diameter between the upper and lower ends of an asymmetric external double groove casing ring forging, which can ensure that the difference in inner diameter between the upper and lower ends of the asymmetric external double groove casing ring forging is within a reasonable range without increasing the volume of the ring blank.

[0006] The technical solution adopted in this invention is: A process for reducing the difference in inner diameter between the upper and lower ends of an asymmetric double-groove casing ring forging involves taper compensation of the inner surface of the rolling ring billet to obtain an inner tapered cross-section ring billet. The dimensions of the inner tapered cross-section ring billet are calculated based on the principle of constant volume before and after rolling, thereby reducing the difference in inner diameter between the upper and lower ends of the asymmetric double-groove casing ring forging produced by rolling a rectangular ring billet. A closed-loop rolling combination drive roll and mandrel are designed to prevent vertical movement of the ring during rolling and ensure rolling stability. The inner tapered cross-section ring billet is rolled into an asymmetric double-groove casing ring forging using the closed-loop rolling combination drive roll and mandrel. Based on the volume change trend of each region during rolling, the mandrel rolling speed curve and drive roll rotation speed are designed, thus ensuring that the difference in inner diameter between the upper and lower ends of the asymmetric double-groove casing ring forging remains within a reasonable range without increasing the volume of the ring billet.

[0007] Preferably, the method for obtaining an inner tapered cross-section ring blank by tapering the inner surface of the rolling ring blank is as follows: Let the maximum outer diameter of the asymmetric double-groove casing ring forging be... Inner diameter is Height is The groove depth is The rounded corners of the groove are The width of the large groove is The width of the small groove is The volume of the groove is The volume after filling the groove is Its own volume is V; The maximum outer diameter of the asymmetric double-groove casing ring forging Based on this, determine the outer diameter of the inner tapered cross-section ring blank. k is the equivalent rolling ratio; Height of inner conical cross section ring blank

[0008] Inner tapered cross section ring blank inner surface slope

[0009] Taper of the inner surface of the inner tapered cross section ring blank

[0010] Volume of inner conical cross section ring blank

[0011] in, The inner diameter of the small end of the inner tapered cross-section ring blank, The inner diameter of the large end of the ring blank with an inner conical cross section; In order to seek , First, the asymmetric external double-groove casing ring forging is divided into 5 regions along the axial direction from the small end to the large end. The volumes corresponding to the 5 regions are as follows: , , , , The inner diameters corresponding to the 5 regions are respectively , , , , The volume and inner diameter of regions 2 and 4 are determined by the following formula.

[0012]

[0013]

[0014]

[0015] Then, the slope of the inner surface of the inner tapered cross-section ring blank is obtained by the difference in inner diameter between the second and fourth regions. ,in The vertical distance between regions 2 and 4; the taper of the inner surface of the inner tapered cross-section ring blank. ; Using the above formula, given the outer diameter of the inner tapered cross-section ring blank... Taper of the inner surface of the inner tapered cross-section ring blank , Inner surface slope of the inner tapered cross section ring blank Height of the inner conical cross-section ring blank Based on this, and by adhering to the principle of equal volume before and after rolling, the inner diameter of the small end of the inner tapered cross-section ring is obtained. Inner diameter of the large end of the inner conical cross-section ring blank ; Among them, the volume of the asymmetric outer double groove casing ring forging Volume of the grooved portion of the asymmetric outer double groove casing ring forging The volume of the asymmetric outer double groove casing ring forging after filling the groove portion .

[0016] Preferably, the equivalent rolling ratio k is 1.3 to 2.

[0017] The method for designing the combined drive roll and core roll for closed-circuit rolling is as follows: Because the shape of the drive roller must correspond to the cross-sectional shape of the asymmetric double-groove casing ring forging when rolling an inner tapered cross-section ring into an asymmetric double-groove casing ring forging, the maximum diameter of the working surface of the drive roller is therefore... , minimum diameter and the diameter of the core roller working surface Determined by the following formula

[0018]

[0019]

[0020]

[0021] To prevent axial movement of the ring, the upper and lower baffles of the drive roller are increased, and the height of the drive roller cavity is increased. = + Core roller height mm, This is the axial displacement value. The height of the asymmetric outer double groove casing ring forging; Cavity width when the drive roller and core roller are closed ; in, Taper of the inner surface of the inner tapered cross-section ring blank. The maximum outer diameter of the asymmetric double-groove casing ring forging The inner diameter of the asymmetric external double groove casing ring forging The groove depth of the asymmetric outer double groove casing ring forging; Let be the friction angle. , The coefficient of friction; and These are the maximum and minimum allowable closed center distances for the ring rolling mill, respectively.

[0022] Preferably, the draft angle of the upper and lower baffles of the drive roller is 1-2°.

[0023] Preferably, the coefficient of friction The value is 0.1 to 0.4.

[0024] The method for designing the mandrel rolling speed curve and drive roll speed is as follows: During the rolling of an asymmetric double-groove casing ring forging from an inner conical ring billet, the volumes of regions 2 and 4 decrease sharply as the outer diameter of the ring is rolled from D0 to D1. The volume of region 2 compensates for the volume of regions 1 and 3, and the volume of region 4 supplements the volume of regions 3 and 5. This results in region 3 having the largest volume. Therefore, in the early rolling stage (0-t1)s, the feed speed of the mandrel can be linearly increased as the outer diameter of the ring is rolled from D1 to D2. k At that time, the volume of all regions reaches its maximum when the ring is rolled to D3. Therefore, during the rolling stage from D1 to D3, i.e., (t2-t3)s, the feed speed of the mandrel is set to a constant value to ensure smooth rolling of the ring. k During the (t3-t4)s stage, the core roll feed speed is reduced, and rolling gradually ends. Drive roller speed , This represents the maximum linear velocity of the drive roller; Core roller feed speed satisfy

[0025]

[0026]

[0027]

[0028] in The outer diameter of the ring is Wall thickness at that time; The outer diameter of the ring is Wall thickness at that time; The outer diameter of the ring is The wall thickness at that time.

[0029] Preferably, the maximum linear speed of the drive roller Take a value of 0.7~1.4 m / s.

[0030] The beneficial effects of this invention are: This method can reduce the difference in inner diameter between the upper and lower ends of the asymmetric external double groove casing ring forging, and can ensure that the difference in inner diameter between the upper and lower ends of the final asymmetric external double groove casing ring forging is within a reasonable range without increasing the ring billet volume. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the asymmetric external double groove casing ring forging in this invention. The red dashed line in the diagram represents the difference in inner diameter between the upper and lower ends caused by the prior art.

[0032] Figure 2 This is a schematic diagram of the volume distribution after determining the outer diameter of the ring billet for rolling in this invention.

[0033] Figure 3 This is a schematic diagram of the inner conical cross-section ring blank in this invention.

[0034] Figure 4 This is a schematic diagram of the combined drive rollers for closed-circuit rolling in this invention.

[0035] Figure 5 This is a curve showing the volume change of each region during the rolling process of the ring part of the present invention.

[0036] Figure 6 This is a schematic diagram of the core roll feed speed during the ring rolling process of the present invention.

[0037] Figure 7 This is a dimensional drawing of the asymmetric outer double groove casing ring forging in an embodiment of the present invention.

[0038] Figure 8 This is a dimensional diagram of the inner tapered cross-section ring blank in an embodiment of the present invention.

[0039] Figure 9 This is a schematic diagram of the assembly during rolling in an embodiment of the present invention.

[0040] Figure 10 This is a simulation result diagram of the asymmetric external double groove casing ring forging in an embodiment of the present invention.

[0041] Figure 11 This is a finished product drawing of the asymmetric external double groove casing ring forging in an embodiment of the present invention.

[0042] In the diagram: 1-Drive roller; 2-Left guide roller; 3-Core roller; 4-Upper conical roller; 5-Lower conical roller; 6-Right guide roller. Detailed Implementation

[0043] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0044] This application discloses a process method for reducing the difference in inner diameter between the upper and lower ends of an asymmetric double-groove casing ring forging. The purpose is to ensure that the difference in inner diameter between the upper and lower ends of the asymmetric double-groove casing ring forging remains within a reasonable range without increasing the volume of the ring billet. The principle is as follows: Taper compensation is applied to the inner surface of the rolling ring billet to obtain an inner tapered cross-section ring billet. The dimensions of the inner tapered cross-section ring billet are calculated based on the principle of unchanged volume before and after rolling, thereby reducing the difference in inner diameter between the upper and lower ends generated when rolling an asymmetric double-groove casing ring forging from a rectangular ring billet. A closed-loop rolling combination drive roll and mandrel are designed to prevent vertical movement of the ring during rolling and to ensure rolling stability. The inner tapered cross-section ring billet is rolled into an asymmetric double-groove casing ring forging using the closed-loop rolling combination drive roll and mandrel. Based on the volume change trend of each region during rolling, the mandrel rolling speed curve and drive roll rotation speed are designed, thus ensuring that the difference in inner diameter between the upper and lower ends of the asymmetric double-groove casing ring forging remains within a reasonable range without increasing the volume of the ring billet.

[0045] This process specifically employs the following steps: S1. Taper compensation is performed on the inner surface of the rolling ring blank to obtain an inner tapered cross-section ring blank. Asymmetric external double groove casing ring forging dimensions as follows Figure 1 As shown, where, The maximum outer diameter of the asymmetric double-groove casing ring forging The inner diameter of the asymmetric external double groove casing ring forging The height of the asymmetric outer double groove casing ring forging. The groove depth of the asymmetric outer double groove casing ring forging. The groove fillet of the asymmetric outer double groove casing ring forging is rounded. , These represent the widths of the large and small grooves in the asymmetric external double-groove casing ring forging, respectively. The volume of the grooved portion of the asymmetric outer double-groove casing ring forging. V represents the volume of the asymmetric external double groove casing ring forging after filling the groove portion.

[0046] The maximum outer diameter of the asymmetric double-groove casing ring forging Based on this, determine the outer diameter of the inner tapered cross-section ring blank. k is the equivalent rolling ratio, which is taken as 1.3~2.

[0047] Height of inner conical cross section ring blank

[0048] Inner tapered cross section ring blank inner surface slope

[0049] Taper of the inner surface of the inner tapered cross section ring blank

[0050] Volume of inner conical cross section ring blank

[0051] in, The inner diameter of the small end of the inner tapered cross-section ring blank, The inner diameter of the large end of the inner conical cross-section ring blank.

[0052] In order to obtain , First, the asymmetric external double-groove casing ring forging is divided into 5 regions along the axial direction from the small end to the large end. The volumes corresponding to the 5 regions are as follows: , , , , The outer diameter of the inner conical cross-section ring blank was determined. The inner diameters of the last 5 regions are respectively , , , , ,like Figure 2 As shown, the volume and inner diameter of regions ② and ④ are determined by the following formulas:

[0053]

[0054]

[0055]

[0056] Then, the slope of the inner surface of the inner conical cross-section ring blank is obtained by the difference in the inner diameters of regions ② and ④. ,in The vertical distance between regions ② and ④; the taper of the inner surface of the inner tapered cross-section ring blank. .

[0057] Using the above formula, given the outer diameter of the inner tapered cross-section ring blank... Taper of the inner surface of the inner tapered cross-section ring blank , Inner surface slope of the inner tapered cross section ring blank Height of the inner conical cross-section ring blank Based on this, and by adhering to the principle of equal volume before and after rolling, the inner diameter of the small end of the inner tapered cross-section ring can be obtained. Inner diameter of the large end of the inner conical cross-section ring blank The volume of the asymmetric outer double groove casing ring forging Volume of the grooved portion of the asymmetric outer double groove casing ring forging The volume of the outer cylindrical part of the asymmetric double-groove casing ring forging .

[0058] In this embodiment, the dimensions of the asymmetric outer double groove casing ring forging are as follows: Figure 7 As shown, mm, mm, mm, mm, 22.5mm, mm mm, ensuring the equivalent rolling ratio is between 1.3 and 2. After extensive simulation verification, a rolling ratio K of 1.3 was selected. The outer diameter of the inner tapered cross-section ring billet was determined using the above formula. mm, divide it into 5 regions as follows Figure 3 Obtain the region volume , The volume distribution of the ring billet is performed in different regions to obtain the inner diameter value of each region of the ring billet. , Through obtaining , Determine the taper of the inner surface of the inner tapered cross-section ring blank. mm, inner tapered cross-section ring blank inner surface slope °, and by applying the principle of equal volume, the volume of the groove portion can be obtained.

[0059] Volume of outer cylindrical body

[0060] Asymmetric external double groove casing ring forging volume V= =39325440.8

[0061] The inner diameter of the small end of the inner tapered cross-section ring blank was finally determined. mm, inner diameter of the large end of the inner tapered cross-section ring blank mm, the final schematic diagram of the inner conical cross-section ring blank is as follows Figure 8 As shown.

[0062] S2, Design of the combined drive roll and core roll for closed-loop rolling When rolling an inner tapered cross-section ring into an asymmetric outer double groove casing ring forging, the shape of the drive roller must correspond to the cross-sectional shape of the asymmetric outer double groove casing ring forging, and the maximum diameter of the working surface of the drive roller must be... , minimum diameter and the diameter of the core roller working surface Determined by the following formula:

[0063]

[0064]

[0065]

[0066] To prevent axial movement of the ring, upper and lower baffles are added to the drive roller, with a draft angle between 1-2°. The height of the drive roller cavity is [not specified]. = + Core roller height mm, This is the axial displacement value. The height of the asymmetric outer double groove casing ring forging.

[0067] Cavity width when the drive roller and core roller are closed .

[0068] in, Taper of the inner surface of the inner tapered cross-section ring blank. The maximum outer diameter of the asymmetric double-groove casing ring forging The inner diameter of the asymmetric external double groove casing ring forging The groove depth of the asymmetric outer double groove casing ring forging; Let be the friction angle. The coefficient of friction is between 0.1 and 0.4. and These are the maximum and minimum allowable closed center distances of the ring rolling mill, respectively; In this example, the maximum diameter of the driving roll working surface is measured during the rolling process of an asymmetric external double groove casing ring forging. mm, minimum diameter mm, drive roller cavity height mm and core roller diameter mm, core roller height mm. A schematic diagram of the assembly process for rolling an asymmetric outer double-groove casing ring forging is shown below. Figure 9 As shown.

[0069] S3. Design the mandrel rolling speed curve and drive roll speed. Because the volume of each region changes during the rolling of an asymmetric double-groove casing ring forging from an inner conical ring billet, the volumes of regions ② and ④ decrease sharply as the outer diameter of the ring is rolled from D0 to D1. The volume of region ② compensates for regions ① and ③, and the volume of region ④ supplements regions ③ and ⑤, resulting in the largest volume in the middle region ③. Therefore, in the early stage of rolling (0-t1)s, the feed speed of the mandrel can be linearly increased, and the outer diameter of the ring can be rolled from D1 to D2. k At that time, the volume of all regions reaches its maximum when the ring is rolled to D3. Therefore, during the rolling stage from D1 to D3, i.e., (t2-t3)s, the feed speed of the mandrel can be set to a constant value to ensure smooth rolling of the ring. When rolling from D3 to D... k During the stage (t3-t4)s, the core roll feed speed is reduced, and the rolling gradually ends, resulting in the core roll feed curve.

[0070] Drive roller speed , The maximum linear velocity of the drive roller is taken as 0.7~1.4 m / s; Core roller feed speed satisfy

[0071]

[0072]

[0073]

[0074] in The outer diameter of the ring is Wall thickness at that time; The outer diameter of the ring is Wall thickness at that time; The outer diameter of the ring is The wall thickness at that time.

[0075] In this example, the linear velocity of the drive roller is taken as 0.7 m / s, then the rotational speed of the drive roller n = 0.2 rad / s, and the feed speed of the core roller is... The outer diameter of the ring blank with an inner conical cross section mm rolled to When mm, it can be obtained that When the core roller feed speed is mm, the volume of regions ② and ④ decreases significantly, and the excess volume is transferred to other regions. It takes 9.5 seconds to reach 0.5 mm / s, and then uses that as a plateau speed to reach... Rolled to the outer diameter of the ring mm, then Outer diameter of rolled ring mm.

[0076] The final forming effect of the asymmetric outer double groove casing ring forging is as follows: Figure 10 As shown, the axial taper is 1.5mm, which greatly improves the accuracy of the ring.

[0077] This method involves volume distribution of the rolling blank during the rolling forming process of asymmetric double-groove casing ring forgings. This prevents excessive differences in the inner diameter of the upper and lower ends of the forgings due to factors such as die design and material flow distribution during rolling. Furthermore, specific die and parameter designs are implemented for the rolling forming process to prevent issues such as roller climbing and wobbling that could cause the asymmetric double-groove casing ring forgings to fail to meet the performance requirements of the asymmetric double-groove casing component substrate. This method successfully produces asymmetric double-groove casing ring forgings with an inner diameter difference of less than 1.5 mm between the upper and lower ends. Experimental results are shown in the figure below. Figure 11 This solved the problem of large inner diameter difference after rolling of asymmetric double-groove casing ring forgings.

[0078] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A process for reducing the difference in inner diameter between the upper and lower ends of an asymmetric double-groove casing ring forging, characterized in that: Taper compensation is applied to the inner surface of the rolling ring billet to obtain an inner tapered cross-section ring billet. The dimensions of the inner tapered cross-section ring billet are calculated based on the principle of constant volume before and after rolling to reduce the difference in inner diameter between the upper and lower ends of the asymmetric outer double groove casing ring forging produced by rolling a rectangular ring billet. A combination drive roll and mandrel for closed rolling are designed to prevent vertical movement of the ring during rolling and to ensure rolling stability. The inner tapered cross-section ring billet is rolled into an asymmetric outer double groove casing ring forging using the combination drive roll and mandrel for closed rolling. Based on the volume change trend of each region during rolling, the mandrel rolling speed curve and drive roll speed are designed to ensure that the difference in inner diameter between the upper and lower ends of the asymmetric outer double groove casing ring forging is within a reasonable range without increasing the volume of the ring billet. The method for obtaining an inner tapered cross-section ring blank by taper compensation of the inner surface of the rolling ring blank is as follows: Let the maximum outer diameter of the asymmetric double-groove casing ring forging be... Inner diameter is Height is The groove depth is The rounded corners of the groove are The width of the large groove is The width of the small groove is The volume of the groove is The volume after filling the groove is Its own volume is V; The maximum outer diameter of the asymmetric double-groove casing ring forging Based on this, determine the outer diameter of the inner tapered cross-section ring blank. k is the equivalent rolling ratio; Height of inner conical cross section ring blank Inner tapered cross section ring blank inner surface slope Taper of the inner surface of the inner tapered cross section ring blank Volume of inner conical cross section ring blank in, The inner diameter of the small end of the inner tapered cross-section ring blank, The inner diameter of the large end of the ring blank with an inner conical cross section; In order to seek , First, the asymmetric external double-groove casing ring forging is divided into 5 regions along the axial direction from the small end to the large end. The volumes corresponding to the 5 regions are as follows: , , , , The inner diameters corresponding to the 5 regions are respectively , , , , The volume and inner diameter of regions 2 and 4 are determined by the following formula. Then, the slope of the inner surface of the inner tapered cross-section ring blank is obtained by the difference in inner diameter between the second and fourth regions. ,in The vertical distance between regions 2 and 4; the taper of the inner surface of the inner tapered cross-section ring blank. ; Using the above formula, given the outer diameter of the inner tapered cross-section ring blank... Taper of the inner surface of the inner tapered cross-section ring blank , Inner surface slope of the inner tapered cross section ring blank Height of the inner conical cross-section ring blank Based on this, and by adhering to the principle of equal volume before and after rolling, the inner diameter of the small end of the inner tapered cross-section ring is obtained. Inner diameter of the large end of the inner conical cross-section ring blank ; Among them, the volume of the asymmetric outer double groove casing ring forging Volume of the grooved portion of the asymmetric outer double groove casing ring forging The volume of the asymmetric outer double groove casing ring forging after filling the groove portion ; The method for designing the combined drive roll and core roll for closed-circuit rolling is as follows: Because the shape of the drive roller must correspond to the cross-sectional shape of the asymmetric double-groove casing ring forging when rolling an inner tapered cross-section ring into an asymmetric double-groove casing ring forging, the maximum diameter of the working surface of the drive roller is therefore... , minimum diameter and the diameter of the core roller working surface Determined by the following formula To prevent axial movement of the ring, the upper and lower baffles of the drive roller are increased, and the height of the drive roller cavity is increased. = + Core roller height mm, This is the axial displacement value. The height of the asymmetric outer double groove casing ring forging; Cavity width when the drive roller and core roller are closed ; in, Taper of the inner surface of the inner tapered cross-section ring blank. The maximum outer diameter of the asymmetric double-groove casing ring forging The inner diameter of the asymmetric external double groove casing ring forging The groove depth of the asymmetric outer double groove casing ring forging; Let be the friction angle. , The coefficient of friction; and These are the maximum and minimum allowable closed center distances for the ring rolling mill, respectively.

2. The process method for reducing the difference in inner diameter between the upper and lower ends of an asymmetric external double-groove casing ring forging as described in claim 1, characterized in that: The equivalent rolling ratio k is taken as 1.3~2.

3. The process method for reducing the difference in inner diameter between the upper and lower ends of an asymmetric external double-groove casing ring forging as described in claim 1, characterized in that: The draft angle of the upper and lower baffles of the drive roller is 1-2°.

4. The process method for reducing the difference in inner diameter between the upper and lower ends of an asymmetric external double-groove casing ring forging as described in claim 1, characterized in that: coefficient of friction The value is 0.1 to 0.4.

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