Double-flow-ring sealing tile structure with circumferential non-equal-depth distributed dynamic pressure grooves in stator surface

Abstract

The double-flow-ring sealing tile structure is characterized in that an air side stator surface and a hydrogen side stator surface are provided with a plurality of groups of dynamic pressure grooves which are distributed in the circumferential direction in a non-equal-depth mode, sealing weirs are arranged between the circumferential directions of the adjacent dynamic pressure grooves, the dynamic pressure groove formed in the upper portion of the stator surface is an upper dynamic pressure groove, and the dynamic pressure groove formed in the lower portion of the stator surface is a lower dynamic pressure groove; an upper dynamic pressure groove is formed in the lower portion of the stator face, a dynamic pressure groove formed in the lower portion of the stator face is a lower dynamic pressure groove, the depth of the upper dynamic pressure groove is larger than that of the lower dynamic pressure groove, and the depth of the dynamic pressure groove is gradually decreased from the upper dynamic pressure groove to the lower dynamic pressure groove in the circumferential direction. A fluid film pressure peak value generated by the upper dynamic pressure groove under a given sealing gap is higher than a fluid film pressure peak value generated by the lower dynamic pressure groove, buoyancy force can be generated under the concentric condition, or the eccentricity rate can be reduced during eccentric operation, the problem of circumferential non-uniform temperature rise caused by eccentric operation of the sealing tile is solved, and the sealing performance of the sealing tile is improved. The problems of thermal deformation of the sealing tile and thermal bending of the rotating shaft are solved.

Description

Technical Field

[0001] The invention relates to the technical field of cylindrical non-contact fluid sealing, and in particular to a double-flow ring sealing shoe structure with circumferential non-uniform depth dynamic pressure grooves distributed on a stator surface. Background Art

[0002] Thermal power generation using steam turbines to drive generators is the main power generation method in my country. Pressurized hydrogen is mostly used for cooling the generator cavity. Avoiding hydrogen leakage in the cavity and preventing excessive air from entering are the key to ensuring the economic and safe operation of the unit. Oil-lubricated floating ring seals represented by double-flow ring seals are currently a common sealing form for hydrogen-cooled generators, used to prevent the medium from flowing between the hydrogen-cooled cavity of the motor and the lubricating oil cavity of the bearing. The double-flow ring seal forms an oil film with a certain rigidity in the tiny gap between the seal and the shaft to achieve sealing by cooperating with the external sealing oil system. At present, the non-uniform temperature rise caused by the circumferential non-uniform gap caused by eccentricity, which in turn causes excessive thermal deformation, black gold layer debonding and thermal cracking, is one of the main reasons for the failure of the seal. How to generate sufficient buoyancy to balance the gravity of the seal under small eccentricity or even zero eccentricity conditions and support the normal operation of the floating ring seal is an urgent problem to be solved.

[0003] Some scholars have proposed some structures to improve the buoyancy of floating ring seals, such as opening equal-depth grooves on the circumference of the cylindrical sealing surface of the floating ring seal, such as opening rectangular grooves, spiral grooves, circular textures, etc. However, the opening of circumferential equal-depth grooves has a small effect on improving the buoyancy because the pressure is evenly distributed along the circumference, especially in the case of heavy floating ring seals. Therefore, it is necessary to propose a new double-flow ring seal tile structure with circumferential non-equal-depth dynamic pressure grooves, which can improve the buoyancy to a greater extent by changing the circumferential pressure distribution, thereby solving the problem of circumferential non-uniform temperature rise caused by eccentricity of oil-lubricated double-flow ring seal tiles. Summary of the invention

[0004] In order to enhance the buoyancy of the fluid film of the oil-lubricated double-flow ring sealing shoe to a greater extent and realize operation under low eccentricity or even zero eccentricity conditions, the present invention proposes a double-flow ring sealing shoe structure with circumferential non-uniform depth dynamic pressure grooves on the stator surface, which is suitable for shaft end and interstage sealing devices of large turbine machinery such as various compressors, steam turbines, gas turbines, etc.

[0005] The technical solution of the present invention is:

[0006] A double-flow ring sealing shoe structure with circumferential non-uniform depth dynamic pressure grooves on the stator surface, a sealing gap for lubricating oil to flow is formed between the inner surface of the sealing shoe and the outer surface of the horizontally placed rotating shaft, and an air-side oil inlet channel and a hydrogen-side oil inlet channel axially divide the inner surface of the sealing shoe into an air-side stator surface, an air-hydrogen stator surface, and a hydrogen-side stator surface;

[0007] The air side stator surface and the hydrogen side stator surface are provided with a plurality of groups of dynamic pressure grooves distributed in non-equal depths along the circumferential direction, and there are sealing weirs between adjacent dynamic pressure grooves in the circumferential direction. The inlet of the dynamic pressure groove of the air side stator surface is connected with the air side oil inlet channel, and there is an air side sealing dam between the outlet of the dynamic pressure groove of the air side stator surface and the air side lubricating oil cavity. The inlet of the dynamic pressure groove of the hydrogen side stator surface is connected with the hydrogen side oil inlet channel, and there is a hydrogen side sealing dam between the outlet of the dynamic pressure groove of the hydrogen side stator surface and the hydrogen side motor cavity. The dynamic pressure grooves provided at the upper part of the stator surface are upper dynamic pressure grooves, and the dynamic pressure grooves provided at the lower part of the stator surface are lower dynamic pressure grooves. The depth of the upper dynamic pressure grooves is greater than that of the lower dynamic pressure grooves, and the depth of the dynamic pressure grooves decreases step by step from the upper dynamic pressure grooves to the lower dynamic pressure grooves along the circumferential direction. When the shaft rotates, the peak value of the fluid film pressure generated by the upper dynamic pressure grooves under a given sealing gap is higher than the peak value of the fluid film pressure generated by the lower dynamic pressure grooves.

[0008] Furthermore, the depth of the single dynamic pressure groove is consistent along the circumferential direction, the axial cross-section of the dynamic pressure groove is fan-shaped, and the depth of the upper dynamic pressure groove is h u , the depth of the lower dynamic pressure groove is h d The average value of the sealing gap is h0, and the average value of the depth of each group of dynamic pressure grooves is h av The depth of the upper dynamic pressure groove is H u is the depth of the upper dynamic pressure groove h u The ratio of the sealing gap average h0 is preferably in the range of 2 to 4. The depth ratio t is the depth difference between the upper dynamic pressure groove and the lower dynamic pressure groove (h u -h d ) and the average depth h of the dynamic pressure groove 4 av The ratio ranges from 0 to 2, with a preferred range of 0.5 to 1.5.

[0009] Furthermore, the axial width of the air side dynamic pressure groove and the hydrogen side dynamic pressure groove is a, the axial width of the air side sealing shoe and the hydrogen side sealing shoe is l, and the axial width ratio L of the dynamic pressure groove is the ratio of the axial width a of the dynamic pressure groove to the axial width l of the sealing shoe 1, and the preferred value is 0.4 to 0.8.

[0010] Furthermore, the profile of the side wall of the dynamic pressure groove 4 is a spiral line, the spiral angle of the spiral line is β, and the preferred value range is 10° to 50°. The spiral direction of the side wall of the dynamic pressure groove 4 is consistent with the rotation direction of the shaft.

[0011] Alternatively, the side wall profile of the dynamic pressure groove is a straight line, and the side wall profile of the dynamic pressure groove is perpendicular to the end faces of the air-side oil inlet channel and the hydrogen-side oil inlet channel.

[0012] Furthermore, the depth of the single dynamic pressure groove gradually decreases along the circumferential direction, the axial cross-section of the dynamic pressure groove is a circular segment shape, and the dynamic pressure groove can be efficiently processed by grinding or turning with an internal cylindrical grinder.

[0013] Working principle:

[0014] Double-flow ring sealing pads are used between the hydrogen-cooled motor cavity and the bearing lubricating oil cavity of hydrogen-cooled generators to seal hydrogen with lubricating oil whose pressure is higher than the hydrogen pressure in the hydrogen-cooled motor cavity. Through the force analysis of the double-flow ring sealing pads, it can be found that when the unit is shut down, the sealing pads will be suspended on the rotor due to the gravity of the sealing pads themselves; when the unit is started, the sealing oil is injected into the annular gap between the sealing pads and the rotor to form an oil film, which will generate buoyancy. When the buoyancy generated by the lubricating oil film overcomes its own gravity, the sealing pads begin to float up. When the speed is stable, the sealing pads operate stably at a certain eccentricity.

[0015] The purpose of the present invention is to provide a novel double-flow ring sealing shoe structure that can change the circumferential pressure distribution of the fluid film, thereby greatly improving the buoyancy of the fluid film of the oil-lubricated double-flow ring sealing shoe, and realizing low eccentricity or even zero eccentricity operation, thereby solving the problem of circumferential non-uniform temperature rise of the oil-lubricated double-flow ring sealing shoe caused by eccentricity. Non-uniform depth dynamic pressure grooves are provided on the inner surface of the sealing surface of the air side and the hydrogen side of the sealing shoe, and the dynamic pressure grooves are connected to the air-hydrogen oil inlet channel. The sealing medium can be pumped into the grooves, which are gradually compressed in the grooves, causing the fluid film pressure to continue to rise. Since the depth of the dynamic pressure grooves decreases step by step from the upper dynamic pressure groove to the lower dynamic pressure groove along the circumferential direction, a non-uniformly distributed pressure is generated in the circumferential direction. When the shaft rotates, the peak value of the fluid film pressure generated by the upper deeper dynamic pressure groove under a given sealing gap is higher than the peak value of the fluid film pressure generated by the lower shallower dynamic pressure groove. This non-uniform distribution of pressure also makes the fluid film have an upward buoyancy F. The design of this circumferential non-uniform depth dynamic pressure groove has the buoyancy characteristic of the upward buoyancy generated by the eccentricity, which can be combined with the double flow ring sealing pad in the eccentric state to achieve the effect of reducing the eccentricity or even achieving zero eccentricity operation. Furthermore, while reducing the eccentricity, the circumferential non-uniform temperature rise caused by the eccentricity can also be reduced.

[0016] The advantages and beneficial effects of the present invention are:

[0017] 1) By opening circumferential non-uniform depth dynamic pressure grooves on the air side sealing surface and hydrogen side sealing surface of the double flow ring sealing shoe, buoyancy can be generated under concentric conditions when the shaft rotates, or the eccentricity can be reduced during eccentric operation, thereby improving the circumferential non-uniform temperature rise problem caused by the eccentric operation of the sealing shoe, thereby improving the thermal deformation of the sealing shoe and the thermal bending of the shaft;

[0018] 2) The spiral or rectangular dynamic pressure groove on the inner surface of the double-flow ring sealing shoe can be milled by a multi-axis machine tool. When its axial cross-section is a circular segment, it can be ground by an internal cylindrical grinder. The processing is convenient and the overall structure of the sealing shoe is slightly changed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 12. It is a cross-sectional schematic diagram of a double-flow ring sealing shoe structure with circumferentially unequal depth dynamic pressure grooves distributed on the stator surface according to Example 1 of the present invention;

[0020] Figure 2 It is a three-dimensional structural diagram of the hydrogen side sealing shoe with circumferentially non-uniformly distributed spiral grooves on the stator surface of Example 1 of the present invention;

[0021] Figure 3 This is a diagram defining the structural parameters of the end face of the sealing shoe with circumferentially non-uniformly distributed spiral grooves on the stator surface of Example 1 of the present invention;

[0022] Figure 4 This is a diagram defining the structural parameters of the inner surface of the sealing shoe with circumferentially non-uniformly distributed spiral grooves on the stator surface in Example 1 of the present invention;

[0023] Figure 5 This is the fluid film pressure distribution diagram of the classic double-flow ring seal pad under eccentric state;

[0024] Figure 6 This is the fluid film pressure distribution diagram of the classic double flow ring seal pad under the concentric state;

[0025] Figure 7 This is the distribution diagram of the fluid film pressure of the sealing pad with circumferential non-uniform depth dynamic pressure grooves on the stator surface under the concentric state;

[0026] Figure 8 This is a three-dimensional structural diagram of the sealing pad of the stator surface with circumferentially non-uniformly distributed rectangular dynamic pressure grooves in Example 2 of the present invention;

[0027] Fig. 9 It is a three-dimensional structural diagram of the sealing shoe of the circular dynamic pressure groove with non-uniform depth distribution on the stator surface in the implementation case 3 of the present invention;

[0028] Fig.10 It is a schematic diagram of the inner grinding process of the circular-segment type dynamic pressure groove sealing shoe of implementation example 3 of the present invention. DETAILED DESCRIPTION

[0029] The implementation of the present invention is further described below in conjunction with the accompanying drawings.

[0030] Example 1

[0031] Reference Figure 1 , 2, 3, 4, a double-flow ring sealing shoe structure with circumferential non-uniformly distributed dynamic pressure grooves on the stator surface, a sealing gap 3 for lubricating oil to flow is formed between the inner surface 15 of the sealing shoe and the outer surface 21 of the horizontally placed rotating shaft, the air side oil inlet channel 12 and the hydrogen side oil inlet channel 11 axially divide the inner surface of the sealing shoe into an air side stator surface 151, an air-hydrogen stator surface 152 and a hydrogen side stator surface 153, the air side stator surface 151 and the hydrogen side stator surface 153 are provided with a plurality of groups of dynamic pressure grooves 4 distributed in non-uniform depths along the circumferential direction, a sealing weir 18 is provided between adjacent dynamic pressure grooves 4 in the circumferential direction, and an inlet 421 of the dynamic pressure groove on the air side stator surface is connected to the air side oil inlet channel 1 2 is connected, an air side sealing dam 16 is provided between the dynamic pressure groove outlet 422 of the air side stator surface 151 and the air side lubricating oil chamber 52, the hydrogen side stator surface dynamic pressure groove inlet 411 is connected with the hydrogen side oil inlet channel 11, a hydrogen side sealing dam 17 is provided between the dynamic pressure groove outlet 412 of the hydrogen side stator surface 153 and the hydrogen side motor chamber 51, the dynamic pressure groove 4 opened at the upper part of the stator surface is the upper dynamic pressure groove 43, the dynamic pressure groove 4 opened at the lower part of the stator surface is the lower dynamic pressure groove 44, the depth of the upper dynamic pressure groove 43 is greater than that of the lower dynamic pressure groove 44, and the depth of the dynamic pressure groove 4 decreases step by step from the upper dynamic pressure groove 43 to the lower dynamic pressure groove 44 along the circumferential direction.

[0032] The inner and outer diameters of the sealing shoe end face are r i and r o , inner diameter r i The circumferential groove angles of the dynamic pressure groove 4 and the corresponding sealing weir 18 are θ1 and θ2 respectively. The depth of a single dynamic pressure groove 4 is consistent along the circumference, and the axial cross-section shape is fan-shaped. The depths of the upper dynamic pressure groove 43 and the lower dynamic pressure groove 44 are h u and h d The average depth of each group of dynamic pressure grooves is h av , the depth of the upper dynamic pressure groove 43 is greater than H u The depth h of the upper dynamic pressure groove 44 u The depth ratio t is the depth difference (h u -h d ) and the average depth h of the dynamic pressure groove 4 av The ratio of is in the range of 0 to 2, and the preferred range is 0.5 to 1.5. The axial width of the air side dynamic pressure groove 42 and the hydrogen side dynamic pressure groove 41 is a, the axial width of the air side sealing shoe 14 and the hydrogen side sealing shoe 13 is l, and the axial width ratio L of the dynamic pressure groove 4 is the ratio of the axial width a of the dynamic pressure groove 4 to the axial width l of the sealing shoe 1, and the preferred value is 0.4 to 0.8. The depth ratio t of the dynamic pressure groove 4 and the average depth h can be changed. av , the axial width ratio L of the dynamic pressure groove 4 and the sealing shoe 1, the circumferential groove angle θ1 and other parameters are adjusted to achieve the dynamic pressure enhancement effect of the non-equal depth distribution of the dynamic pressure groove 4.

[0033] The side wall profile of the dynamic pressure groove 4 is a spiral line, the spiral angle of the spiral line is β, and the preferred value range is 10 to 50 degrees. The spiral direction of the side wall of the dynamic pressure groove 4 is consistent with the rotation direction of the shaft 2.

[0034] Reference Figure 5 , 6 7. When the shaft rotates, when the classic double-flow ring sealing shoe 1 is in an eccentric state, the fluid film in the sealing gap 3 is non-uniformly distributed along the circumference to form a wedge-shaped gap. The pressure p generated by the non-uniformly distributed fluid film along the circumference gradually increases along the rotation direction of the shaft and reaches a peak near the entrance of the minimum gap, and then reaches a valley near the exit of the minimum gap. This non-uniform distribution of pressure p allows the fluid film to have a certain buoyancy F to balance the sealing shoe's deadweight G, so that the sealing shoe can reach a stable operating state. When the classic double-flow ring sealing shoe 1 is in a concentric state, the fluid film in the sealing gap 3 is evenly distributed along the circumference and has not yet formed a wedge-shaped gap. The fluid pressure p of the evenly distributed fluid film along the circumference is equal, and the buoyancy F that can be used to balance the deadweight G of the sealing shoe 1 cannot be generated, and the sealing shoe 1 cannot float and operate stably. When the double-flow ring sealing shoe of the present invention is provided with a non-uniformly distributed dynamic pressure groove 4 in the circumferential direction in a concentric state, due to the pumping action of the dynamic pressure groove 4, the fluid is gradually compressed in the spiral groove, causing the fluid film pressure p to continuously rise, forming a dynamic pressure effect, and due to the uneven distribution of the circumferential dynamic pressure groove 4, this dynamic pressure effect is also non-uniformly distributed along the circumference, and the peak value of the fluid film pressure generated in the upper dynamic pressure groove 43 is higher than the peak value of the fluid film pressure generated by the lower dynamic pressure groove 44. This non-uniform distribution of pressure p also makes the fluid film have an upward buoyancy F of the combined force. The design of this circumferential non-uniformly distributed dynamic pressure groove 4 has the upward buoyancy characteristic of the combined force generated by eccentricity, which can greatly improve the buoyancy of the fluid film of the oil-lubricated double-flow ring sealing shoe and realize operation under low eccentricity or even zero eccentricity, thereby solving the problem of circumferential non-uniform temperature rise caused by eccentricity of the oil-lubricated double-flow ring sealing shoe.

[0035] Example 2

[0036] Reference Figure 8 The difference between this embodiment and the first embodiment is that the side wall profile of the dynamic pressure groove 4 is a straight line, and the side wall profile of the dynamic pressure groove 4 is perpendicular to the end faces of the hydrogen side oil inlet channel 11 and the air side oil inlet channel 12.

[0037] Example 3

[0038] Reference Fig. 9 , 10 The present embodiment is different from the previous two embodiments in that the depth of a single dynamic pressure groove 4 varies along the circumferential direction, the axial cross-section of the dynamic pressure groove 4 is a circular segment, and the dynamic pressure groove 4 can be efficiently processed by internal grinding or turning.

[0039] The above embodiments are only preferred embodiments of the present invention and are not limitations of the technical solutions of the present invention. Any technical solution that can be implemented on the basis of the above embodiments without creative work should be deemed to fall within the scope of protection of the patent of the present invention.

Claims

1. A double-flow ring sealing shoe structure with circumferential non-uniform depth dynamic pressure grooves on the stator surface, comprising a sealing shoe (1), a hydrogen side oil inlet channel (11) and an air side oil inlet channel (12); characterized in that: The air side oil inlet channel (12) and the hydrogen side oil inlet channel (11) axially divide the inner surface of the sealing shoe into an air side stator surface (151), an air-hydrogen stator surface (152) and a hydrogen side stator surface (153); the air side stator surface (151) and the hydrogen side stator surface (153) have a plurality of groups of dynamic pressure grooves (4) distributed in a circumferential direction with non-uniform depths, and sealing weirs (18) are provided between adjacent dynamic pressure grooves (4) in the circumferential direction; the dynamic pressure grooves (4) at the upper part of the air side stator surface (151) and the hydrogen side stator surface (153) are upper dynamic pressure grooves. (43), the dynamic pressure groove (4) at the lower part of the air side stator surface (151) and the hydrogen side stator surface (153) is a lower dynamic pressure groove (44), the depth of the upper dynamic pressure groove (43) is greater than that of the lower dynamic pressure groove (44), the depth of the dynamic pressure groove (4) decreases step by step from the upper dynamic pressure groove (43) to the lower dynamic pressure groove (44) along the circumferential direction, and when the shaft rotates, the fluid film pressure peak value generated by the upper dynamic pressure groove (43) under a given sealing gap (3) is higher than the fluid film pressure peak value generated by the lower dynamic pressure groove (44).

2. A double-flow ring sealing shoe structure with circumferential non-uniform depth dynamic pressure grooves on the stator surface according to claim 1, characterized in that: A dynamic pressure groove inlet A (421) of the dynamic pressure groove (4) on the air side stator surface (151) is connected to the air side oil inlet channel (12), and an air side sealing dam (16) is provided between a dynamic pressure groove outlet A (422) of the dynamic pressure groove (4) on the air side stator surface (151) and the air side lubricating oil chamber (52); The dynamic pressure groove inlet B (411) of the dynamic pressure groove (4) on the hydrogen side stator surface (153) is connected to the hydrogen side oil inlet channel (11), and a hydrogen side sealing dam (17) is provided between the dynamic pressure groove outlet B (412) of the dynamic pressure groove (4) on the hydrogen side stator surface (153) and the hydrogen side motor cavity (51).

3. According to claim 1, a double flow ring sealing shoe structure with non-uniform depth distribution dynamic pressure grooves on the stator surface is characterized by: The axial cross-section of the dynamic pressure groove (4) is fan-shaped, and the depth of a single dynamic pressure groove (4) remains consistent along the circumferential direction.

4. According to claim 1, a double flow ring sealing shoe structure with non-uniform depth distribution dynamic pressure grooves on the stator surface is characterized by: A sealing gap (3) for lubricating oil to flow is formed between the sealing shoe inner surface (15) of the sealing shoe (1) and the outer surface (21) of the horizontally placed rotating shaft (2), and the average value of the sealing gap (3) is h0; the depth of the upper dynamic pressure groove (43) is h u The depth of the lower dynamic pressure groove (44) is h d The average depth of the plurality of groups of dynamic pressure grooves (4) is h av , the depth of the upper dynamic pressure groove is H u is the depth h of the upper dynamic pressure groove (44) u The ratio of the average value h0 of the sealing gap (3) is in the range of 2 to 4. The depth ratio t is the depth difference h between the upper dynamic pressure groove (43) and the lower dynamic pressure groove (44). u -h d The average depth h of the dynamic pressure groove (4) av The ratio ranges from 0 to 2.

5. According to claim 1, a double flow ring sealing shoe structure with non-uniform depth distribution dynamic pressure grooves on the stator surface is characterized by: The sealing shoe (1) comprises a hydrogen side sealing shoe (13) and an air side sealing shoe (14); the dynamic pressure groove (4) on the hydrogen side sealing shoe (13) is a hydrogen side dynamic pressure groove (41), and the dynamic pressure groove (4) on the air side sealing shoe (14) is an air side dynamic pressure groove (42); the axial widths of the air side dynamic pressure groove (42) and the hydrogen side dynamic pressure groove (41) are both a, the axial widths of the air side sealing shoe (14) and the hydrogen side sealing shoe (13) are both l, and the axial width ratio L of the dynamic pressure groove is the ratio of the axial width a of the dynamic pressure groove (4) to the axial width l of the sealing shoe, and the preferred value is 0.4 to 0.

8.

6. The double flow ring sealing shoe structure with non-uniform depth distribution dynamic pressure grooves on the stator surface according to claim 1 is characterized by: The profile of the side wall of the dynamic pressure groove (4) is a spiral line, the spiral angle of the spiral line is β, and the preferred value range is 10° to 50°, and the rotation direction of the spiral line of the side wall of the dynamic pressure groove (4) is consistent with the rotation direction of the shaft (2).

7. The double flow ring sealing shoe structure with non-uniform depth distribution dynamic pressure grooves on the stator surface according to claim 1 is characterized by: The side wall profile of the dynamic pressure groove (4) is a straight line, and the side wall profile of the dynamic pressure groove (4) is perpendicular to the end faces of the hydrogen side oil inlet channel (11) and the air side oil inlet channel (12).

8. The double flow ring sealing shoe structure with non-uniform depth distribution dynamic pressure grooves on the stator surface according to claim 1 is characterized by: The axial cross section of the dynamic pressure groove (4) is in the shape of a circular segment, and the depth of a single dynamic pressure groove (4) decreases step by step from the upper dynamic pressure groove (43) to the lower dynamic pressure groove (44) along the circumferential direction.

9. The double flow ring sealing shoe structure with non-uniform depth distribution dynamic pressure grooves on the stator surface according to claim 8 is characterized by: The dynamic pressure groove (4) can be efficiently processed by grinding or turning with an internal grinding machine.

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