Two-way oil supply structure for piston crank pin in reciprocating compressor

Abstract

The utility model discloses a two-way oil supply structure for a piston crank pin in a reciprocating compressor, belongs to the technical field of piston compressor lubrication, and aims to solve the problems that when a piston crank pin is lubricated by a single oil way in the prior art, the oil supply amount of the crank pin is sharply reduced and the oil consumption amount of a crosshead is increased as the running time of a crosshead slideway is too long, the abrasion is increased and the oil consumption amount of the crosshead is increased. And accidents are easily caused. The double-way oil supply structure comprises a crosshead sliding rail, a crosshead, a connecting rod, a crosshead pin, a crank pin bearing bush, a crank pin, a crank arm, a main journal, a main bearing bush, a crosshead oil supply pipe and a main journal oil supply pipe, a first oil supply hole is machined in the connecting rod, and a second oil supply hole is machined in the crank arm. One path of lubricating oil enters the lubricating oil groove 16 through the oil passing groove 1, the cross head pin oil groove 6 and the first oil supply hole 7 to lubricate the crank pin 9, and the other path of lubricating oil enters the main shaft oil groove 17 through the main shaft neck oil supply pipe 15.

Description

Technical Field

[0001] The utility model belongs to the technical field of piston compressor lubrication, and in particular relates to a double-path oil supply structure for a piston crank pin in a reciprocating compressor. Background Art

[0002] The lubrication method for the piston crank pin in the existing reciprocating compressor is usually to divert the lubricating oil of the cross block pin. On the basis of ensuring that the cross block pin can achieve a stable lubrication effect, the excess oil is introduced into the lubricating oil groove of the piston crank pin and the crank pin is lubricated. The disadvantage of this lubrication method is that the amount of lubricating oil for the piston crank pin is the amount of oil inlet into the oil supply pipe minus the amount of lubricating oil for the cross block pin. As the crosshead slideway runs for too long, the wear increases, the contact gap increases from the original 0.2mm to 0.4mm, and the amount of oil consumed by the crosshead increases in a square exponential manner, which can cause a sharp decrease in the oil supply to the crank pin, which is easy to cause accidents. Therefore, in order to ensure that the lubricating oil amount of the piston crank pin is sufficient, it is very in line with practical needs to develop a dual-path oil supply structure for the piston crank pin in a reciprocating compressor. Utility Model Content

[0003] The utility model aims to solve the problem that when the traditional single oil circuit is used to lubricate the piston crank pin, as the crosshead slideway runs for too long, the wear increases, the oil consumption of the crosshead increases, resulting in a sharp decrease in the oil supply to the crank pin, which is easy to cause accidents. Thus, a dual-circuit oil supply structure for the piston crank pin in a reciprocating compressor is provided;

[0004] A dual-way oil supply structure for a piston crank pin in a reciprocating compressor, the dual-way oil supply structure comprising a crosshead slide rail, a crosshead, a connecting rod, a crosshead pin, a crankpin bearing, a crankpin, a crank arm, a main journal, a main bearing, a crosshead oil supply pipe and a main journal oil supply pipe, the crosshead is arranged in the crosshead slide rail, and the crosshead is slidably connected to the crosshead slide rail, the crosshead pin is inserted in the crosshead, and a crosshead pin oil groove is processed between the crosshead pin and the crosshead, and the crosshead slide rail is provided with a crosshead pin oil groove. An oil groove is machined in the rail, a crosshead oil supply pipe is inserted on the crosshead slide rail, and the oil inlet end of the crosshead oil supply pipe is connected with the oil tank through a pipeline, and the oil outlet end of the crosshead oil supply pipe is connected with the oil groove, a plurality of oil holes are machined at the bottom of the oil groove, and the oil groove is connected with the oil inlet end of the crosshead pin oil groove through the plurality of oil holes, one end of the connecting rod is hinged to the crosshead, and the other end of the connecting rod is sleeved on the crank pin, and the other end of the connecting rod is hinged to the crank pin, and the crank pin is connected to the connecting rod. A crankpin bearing is provided between the connecting rods, and a lubricating oil groove is formed between the crankpin bearing and the crankpin, a No. 1 oil supply hole is processed in the connecting rod, the oil inlet end of the No. 1 oil supply hole is connected to the crosshead pin oil groove, the oil outlet end of the No. 1 oil supply hole is connected to the oil inlet end of the lubricating oil groove, one end of the crank arm is fixedly connected to the crankpin as a whole, the other end of the crank arm is sleeved on the main shaft neck, and the crank arm and the main shaft neck are fixedly connected as a whole, the main shaft bearing is sleeved on the main shaft neck, and the main shaft bearing A main shaft oil groove is formed between the main shaft journal and the crank arm, and a No. 2 oil supply hole is processed on the crank arm. The oil inlet end of the No. 2 oil supply hole extends into the main shaft journal and is connected with the oil outlet end of the main shaft oil groove. The oil outlet end of the No. 2 oil supply hole extends into the crank pin and is connected with the oil inlet end of the lubricating oil groove. The main shaft journal oil supply pipe is inserted on the main shaft bearing, and the oil inlet end of the main shaft journal oil supply pipe is connected with the oil pump outlet pipe through a pipeline, and the oil outlet end of the main shaft journal oil supply pipe is connected with the oil inlet end of the main shaft oil groove.

[0005] Furthermore, the second oil supply hole is a straight hole structure;

[0006] Furthermore, the diameter of the second oil supply hole ranges from 18 mm to 26 mm;

[0007] Furthermore, the connection between the second oil supply hole and the outer circular wall of the crank pin is processed with a fillet with a radius of 3mm to 5mm;

[0008] Furthermore, the second oil supply hole is a curved hole structure;

[0009] Further, the No. 2 oil supply hole includes a first hole segment, a second hole segment and a third hole segment, the No. 2 oil supply hole includes a first hole segment, a second hole segment and a third hole segment, the first hole segment is located in the crank pin and the first hole segment is led to the crank arm, the second hole segment is located in the crank arm, the third hole segment is located in the main journal and the third hole segment is led to the crank arm, one end of the first hole segment is connected to the outer circular wall of the crank pin, the other end of the first hole segment passes through the end wall of the crank pin and is connected to the second hole segment, one end of the third hole segment is connected to the outer circular wall of the main journal, the other end of the third hole segment passes through the end wall of the main journal and is connected to the second hole segment, and the first hole segment intersects with the second hole segment at an obtuse angle, and the second hole segment intersects with the third hole segment at an obtuse angle;

[0010] Furthermore, the connection between the first hole segment and the second hole segment is processed with a fillet having a radius of 3 mm to 5 mm, and the connection between the second hole segment and the third hole segment is processed with a fillet having a radius of R3 to R5;

[0011] Furthermore, the connection between the first hole segment and the outer circular wall of the crank pin is processed with a fillet having a radius of 3 mm to 5 mm, and the connection between the third hole segment and the outer circular wall of the main journal is processed with a fillet having a radius of 3 mm to 5 mm;

[0012] Furthermore, the apertures of the first hole segment, the second hole segment and the third hole segment are the same, and the apertures of the three are all in the range of 18 mm to 26 mm;

[0013] The beneficial effects of this application compared to the prior art are as follows:

[0014] The present application proposes a dual-path oil supply structure for a piston crank pin in a reciprocating compressor. Compared with the traditional piston crank pin oil supply and lubrication structure, an oil supply pipeline is added, and the original one-way oil supply and lubrication is optimized to two-way oil supply and lubrication. Such a setting can effectively avoid the increase in the capacity of the crosshead pin oil groove due to the increase in working time, which affects the intake of oil in the lubricating oil groove and causes the piston crank pin to have a poor lubrication effect. After verification in actual application, after the piston crank pin is supplied with oil using the optimized oil supply structure of the present application, the crank neck oil supply effect is significantly improved, the service life is extended and the failure rate is greatly reduced. After verification by static operation inspection, when the compressor is stationary, the amount of lubricating oil overflowing outward along the periphery of the crank neck bearing (big head bearing 8) after the improved oil supply method is significantly increased compared with the oil supply method before the improvement. After dynamic low-load operation state test comparison test, the amount of lubricating oil overflowing outward along the periphery of the crank neck bearing (big head bearing 8) after the improved oil supply method is doubled compared with the oil supply method before the improvement.

[0015] The present application has a simple structure, low improvement cost, strong practical applicability, and relatively high stability. No failures or safety hazards occurred during the 12-month simulation verification process, and is suitable for promotion and use in this field. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the layout of the dual-path oil supply structure described in this application;

[0017] Figure 2 This is a schematic diagram of the state when the No. 2 oil supply hole in the dual-path oil supply structure of the present application is a curved hole;

[0018] In the figure, 1 is an oil groove, 2 is a crosshead slide rail, 3 is a crosshead, 4 is a connecting rod, 5 is a crosshead pin, 6 is a crosshead pin oil groove, 7 is a No. 1 oil supply hole, 8 is a crankpin bearing, 9 is a crankpin, 10 is a crank arm, 11 is a main journal, 12 is a main bearing, 13 is a No. 2 oil supply hole, 14 is a crosshead oil supply pipe, 15 is a main journal oil supply pipe, 16 is a lubricating oil groove and 17 is a main shaft oil groove. DETAILED DESCRIPTION

[0019] Specific implementation method 1: Combination Figure 1 to Figure 2The present embodiment is described. In the present embodiment, a dual-way oil supply structure for a piston crank pin in a reciprocating compressor is provided. The dual-way oil supply structure includes a crosshead slide rail 2, a crosshead 3, a connecting rod 4, a crosshead pin 5, a crankpin bearing 8, a crankpin 9, a crank arm 10, a main journal 11, a main bearing 12, a crosshead oil supply pipe 14 and a main journal oil supply pipe 15. The crosshead 3 is arranged in the crosshead slide rail 2, and the crosshead 3 is slidably connected to the crosshead slide rail 2. The crosshead pin 5 is inserted in the crosshead 3, and a crosshead pin 5 and the crosshead 3 are processed with a The crosshead pin oil groove 6, the crosshead slide rail 2 is processed with an oil groove 1, the crosshead oil supply pipe 14 is inserted on the crosshead slide rail 2, and the oil inlet end of the crosshead oil supply pipe 14 is connected to the oil tank through a pipeline, the oil outlet end of the crosshead oil supply pipe 14 is connected to the oil groove 1, the bottom of the oil groove 1 is processed with a plurality of oil holes, and the oil groove 1 is connected to the oil inlet end of the crosshead pin oil groove 6 through a plurality of oil holes, one end of the connecting rod 4 is hinged to the crosshead 3, the other end of the connecting rod 4 is sleeved on the crank pin 9, and the other end of the connecting rod 4 is hinged to the crank pin 9, the crank pin 9 A crankpin bearing 8 is provided between the crankpin bearing 8 and the connecting rod 4, and a lubricating oil groove 16 is formed between the crankpin bearing 8 and the crankpin 9. A No. 1 oil supply hole 7 is processed in the connecting rod 4, and the oil inlet end of the No. 1 oil supply hole 7 is connected to the crosshead pin oil groove 6, and the oil outlet end of the No. 1 oil supply hole 7 is connected to the oil inlet end of the lubricating oil groove 16. One end of the crank arm 10 is fixedly connected to the crankpin 9 as a whole, and the other end of the crank arm 10 is sleeved on the main journal 11, and the crank arm 10 is fixedly connected to the main journal 11 as a whole, and the main shaft bearing 12 is sleeved on the main journal 11, and the main shaft bearing A spindle oil groove 17 is formed between 12 and the main shaft journal 11, and a No. 2 oil supply hole 13 is processed on the crank arm 10. The oil inlet end of the No. 2 oil supply hole 13 extends into the main shaft journal 11 and is connected with the oil outlet end of the spindle oil groove 17. The oil outlet end of the No. 2 oil supply hole 13 extends into the crank pin 9 and is connected with the oil inlet end of the lubricating oil groove 16. The main shaft journal oil supply pipe 15 is inserted into the spindle bearing 12, and the oil inlet end of the main shaft journal oil supply pipe 15 is connected with the oil pump outlet pipe through a pipeline, and the oil outlet end of the main shaft journal oil supply pipe 15 is connected with the oil inlet end of the spindle oil groove 17.

[0020] Specific implementation method 2: Combination Figure 1 to Figure 2 The present embodiment is described, and the difference between the present embodiment and the first embodiment is that the second oil supply hole 13 is a straight hole structure. The other components and connection methods are the same as those of the first embodiment.

[0021] Specific implementation method three: Combination Figure 1 to Figure 2 The present embodiment is described as follows: the present embodiment is different from the second embodiment in that the diameter of the second oil supply hole 13 is in the range of 18 mm to 26 mm. The other components and connection methods are the same as those of the second embodiment.

[0022] Specific implementation method four: Combination Figure 1 to Figure 2 This embodiment is described. The difference between this embodiment and the third embodiment is that the connection between the second oil supply hole 13 and the outer wall of the crank pin 9 is processed with a fillet with a radius of 3mm to 5mm, and the connection between the second oil supply hole 13 and the outer wall of the main journal 11 is processed with a fillet with a radius of 3mm to 5mm. The other components and connection methods are the same as those of the third embodiment.

[0023] In combination with the description of Specific Embodiments 2 to 4, a straight hole oil supply hole structure is provided in the present embodiment, and a straight hole is drilled through the crank pin 9, the crank arm 10 and the main journal 11. This processing method is relatively simple and convenient, but the size constraints on the crank pin 9, the crank arm 10 and the main journal 11 are relatively large, and it is necessary to ensure that there is sufficient processing space after the three are connected. The connection between the No. 2 oil supply hole 13 and the crank pin 9 and the main journal 11 is processed with a fillet to ensure the stability of the oil supply transition, which is beneficial to the diffusion of the oil in the oil tank, and is also beneficial to the subsequent assembly to avoid scratches or scratches on the staff during assembly. When using this embodiment, it is necessary to change the crank neck bearing structure so that there are oil grooves inside and outside the bearing to store oil and facilitate the circulation of lubricating oil.

[0024] Specific implementation method five: Combination Figure 1 to Figure 2 The present embodiment is described. The present embodiment is different from the fourth embodiment in that the second oil supply hole 13 is a curved hole structure. The other components and connection methods are the same as those of the fourth embodiment.

[0025] Specific implementation method six: Combination Figure 1 to Figure 2 This embodiment is described. The difference between this embodiment and the fifth embodiment is that the second oil supply hole 13 includes a first hole segment, a second hole segment and a third hole segment. The first hole segment is located in the crank pin 9 and the first hole segment is led to the crank arm 9. The second hole segment is located in the crank arm 10. The third hole segment is located in the main journal 11 and the third hole segment is led to the crank arm 9. One end of the first hole segment is connected to the outer circular wall of the crank pin 9, and the other end of the first hole segment passes through the end wall of the crank pin 9 and is connected to the second hole segment. One end of the third hole segment is connected to the outer circular wall of the main journal 11, and the other end of the third hole segment passes through the end wall of the main journal 11 and is connected to the second hole segment. The first hole segment intersects with the second hole segment at an obtuse angle, and the second hole segment intersects with the third hole segment at an obtuse angle. Other components and connection methods are the same as those of the fifth embodiment.

[0026] Specific implementation method seven: Combination Figure 1 to Figure 2This embodiment is described. The difference between this embodiment and the sixth embodiment is that the connection between the first hole segment and the second hole segment is processed with a fillet with a radius of 3mm to 5mm, and the connection between the second hole segment and the third hole segment is processed with a fillet with a radius of 3mm to 5mm. The other components and connection methods are the same as those of the sixth embodiment.

[0027] Specific implementation method eight: Combination Figure 1 to Figure 2 This embodiment is described. The difference between this embodiment and the seventh embodiment is that the apertures of the first hole segment, the second hole segment and the third hole segment are the same, and the apertures of the three are all in the range of 18 mm to 26 mm. The other components and connection methods are the same as those of the seventh embodiment.

[0028] Specific implementation method nine: Combination Figure 1 to Figure 2 This embodiment is described. The difference between this embodiment and the eighth embodiment is that the connection between the first hole segment and the outer wall of the crank pin 9 is processed with a fillet with a radius of 3mm to 5mm, and the connection between the third hole segment and the outer wall of the main journal 11 is processed with a fillet with a radius of 3mm to 5mm. The other components and connection methods are the same as those of the eighth embodiment.

[0029] In combination with the description of the fifth to ninth embodiments, the second oil supply hole 13 in this embodiment adopts a multi-stage curved hole structure. The curved hole structure is adopted considering that the sizes of the crank pin 9, the crank arm 10 and the main journal 11 are limited and insufficient to support the processing space of the straight hole. When performing the curved hole processing, the following method is generally used:

[0030] Step 1: Score and locate the crankshaft, and drill a φ12mm, 10mm deep hole on the main journal 11 for positioning;

[0031] Step 2: Rotate the crankshaft and slowly drill holes according to the marking positioning angle; if the hole cannot be drilled through, 2 to 3 holes can be crossed to achieve the pupil purpose (if three holes intersect, the middle hole should be blocked);

[0032] Step 3: Repair the curling, burrs, chamfering and polishing of the processed holes: After drilling the holes, repair the curling and burrs to a smooth level; chamfer the intersection of the hole and the journal by 3 to 5 mm, and polish the inner wall of the hole with 200-mesh and 400-mesh sandpaper to make a smooth transition without sharp contact angles.

[0033] The connection between the No. 2 oil supply hole 13 and the crank pin 9 and the main journal 11, as well as the connection between the various hole sections in the No. 2 oil supply hole 13, are all processed with rounded corners, which can ensure the stability of the oil supply transition, facilitate the diffusion of oil in the oil tank, and also facilitate subsequent assembly to avoid scratches or nicks on the staff during assembly. When using this embodiment, it is necessary to change the crank neck bearing structure so that there are oil grooves inside and outside the bearing to store oil and facilitate the circulation of lubricating oil.

[0034] The present invention has been disclosed as above with preferred implementation cases, but it is not used to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent implementation cases with equivalent changes by using the above-disclosed structures and technical contents without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above implementation cases based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

[0035] How it works

[0036] When the present application is in use, in the early stage of work, oil will be injected through the crosshead oil supply pipe 14 like the traditional oil supply lubrication method. The lubricating oil enters the lubricating oil groove 16 through the oil groove 1, the crosshead pin oil groove 6 and the No. 1 oil supply hole 7 to lubricate the crank pin 9. As the working time increases, the crosshead pin wears during work, resulting in an increase in the oil capacity of the crosshead pin oil groove 6, resulting in an increase in the oil storage in the crosshead pin oil groove 6, and at the same time, the amount of oil flowing into the lubricating oil groove 16 decreases, thereby affecting the lubrication effect of the crank pin 9. At this time, under the premise that the first oil supply circuit is guaranteed to be normal, the second oil circuit is opened. The second oil circuit enters the main shaft oil groove 17 through the main shaft neck oil supply pipe 15, and then enters the lubricating oil groove 16 through the No. 2 oil supply hole 13 to lubricate the crank pin 9. The dual-path oil supply can ensure the oil supply of the lubricating oil groove 16 and the lubrication effect on the crank pin 9, thereby improving the working stability of the crank pin 9 and extending the service life of the crank pin 9.

Claims

1. A dual-path oil supply structure for a piston crank pin in a reciprocating compressor, characterized in that: The dual-path oil supply structure comprises a crosshead slide rail (2), a crosshead (3), a connecting rod (4), a crosshead pin (5), a crankpin bearing (8), a crankpin (9), a crank arm (10), a main journal (11), a main journal (12), a crosshead oil supply pipe (14) and a main journal oil supply pipe (15); the crosshead (3) is arranged in the crosshead slide rail (2), and the crosshead (3) is slidably connected to the crosshead slide rail (2); the crosshead pin (5) is inserted in the crosshead (3), and a crosshead pin oil groove (6) is processed between the crosshead pin (5) and the crosshead (3); and an oil run groove (12) is processed in the crosshead slide rail (2). ), a crosshead oil supply pipe (14) is inserted on the crosshead slide rail (2), and the oil inlet end of the crosshead oil supply pipe (14) is connected to the oil tank through a pipeline, and the oil outlet end of the crosshead oil supply pipe (14) is connected to the oil groove (1), the bottom of the oil groove (1) is processed with a plurality of oil holes, and the oil groove (1) is connected to the oil inlet end of the crosshead pin oil groove (6) through the plurality of oil holes, one end of the connecting rod (4) is hinged to the crosshead (3), the other end of the connecting rod (4) is sleeved on the crank pin (9), and the other end of the connecting rod (4) is hinged to the crank pin (9), and a crank pin bearing (8) is provided between the crank pin (9) and the connecting rod (4). ), and a lubricating oil groove (16) is formed between the crankpin bearing (8) and the crankpin (9), a No. 1 oil supply hole (7) is processed in the connecting rod (4), the oil inlet end of the No. 1 oil supply hole (7) is connected to the crosshead pin oil groove (6), the oil outlet end of the No. 1 oil supply hole (7) is connected to the oil inlet end of the lubricating oil groove (16), one end of the crank arm (10) is fixedly connected to the crankpin (9) to form a whole, the other end of the crank arm (10) is sleeved on the main journal (11), and the crank arm (10) and the main journal (11) are fixedly connected to form a whole, the main bearing (12) is sleeved on the main journal (11), and the main bearing (12) is connected to the main journal (11). A main shaft oil groove (17) is formed between the journals (11), a second oil supply hole (13) is processed on the crank arm (10), the oil inlet end of the second oil supply hole (13) extends into the main shaft journal (11) and is connected to the oil outlet end of the main shaft oil groove (17), the oil outlet end of the second oil supply hole (13) extends into the crank pin (9) and is connected to the oil inlet end of the lubricating oil groove (16), the main shaft journal oil supply pipe (15) is inserted into the main bearing (12), and the oil inlet end of the main shaft journal oil supply pipe (15) is connected to the oil pump outlet pipe through a pipeline, and the oil outlet end of the main shaft journal oil supply pipe (15) is connected to the oil inlet end of the main shaft oil groove (17).

2. A dual-path oil supply structure for a piston crank pin in a reciprocating compressor according to claim 1, characterized in that: The second oil supply hole (13) is a straight hole structure.

3. A dual-path oil supply structure for a piston crank pin in a reciprocating compressor according to claim 1, characterized in that: The diameter of the second oil supply hole (13) ranges from 18 mm to 26 mm.

4. A dual-path oil supply structure for a piston crank pin in a reciprocating compressor according to claim 3, characterized in that: The connection point between the second oil supply hole (13) and the outer circular wall of the crank pin (9) is processed with a fillet having a radius of 3 mm to 5 mm, and the connection point between the second oil supply hole (13) and the outer circular wall of the main journal (11) is processed with a fillet having a radius of 3 mm to 5 mm.

5. A dual-path oil supply structure for a piston crank pin in a reciprocating compressor according to claim 4, characterized in that: The second oil supply hole (13) is a curved hole structure.

6. A dual-path oil supply structure for a piston crank pin in a reciprocating compressor according to claim 5, characterized in that: The second oil supply hole (13) comprises a first hole section, a second hole section and a third hole section, wherein the first hole section is located in the crank pin (9) and the first hole section leads to the crank arm (10), the second hole section is located in the crank arm (10), the third hole section is located in the main journal (11) and the third hole section leads to the crank arm (10), one end of the first hole section is connected to the outer circular wall of the crank pin (9), the other end of the first hole section passes through the end wall of the crank pin (9) and is connected to the second hole section, one end of the third hole section is connected to the outer circular wall of the main journal (11), the other end of the third hole section passes through the end wall of the main journal (11) and is connected to the second hole section, and the first hole section and the second hole section intersect at an obtuse angle, and the second hole section and the third hole section intersect at an obtuse angle.

7. A dual-path oil supply structure for a piston crank pin in a reciprocating compressor according to claim 6, characterized in that: The connecting part between the first hole segment and the second hole segment is processed with a fillet with a radius of 3mm to 5mm, and the connecting part between the second hole segment and the third hole segment is processed with a fillet with a radius of 3mm to 5mm.

8. A dual-path oil supply structure for a piston crank pin in a reciprocating compressor according to claim 7, characterized in that: The connection between the first hole section and the outer circular wall of the crank pin (9) is processed with a fillet having a radius of 3 mm to 5 mm, and the connection between the third hole section and the outer circular wall of the main journal (11) is processed with a fillet having a radius of 3 mm to 5 mm.

9. A dual-path oil supply structure for a piston crank pin in a reciprocating compressor according to claim 8, characterized in that: The apertures of the first hole segment, the second hole segment and the third hole segment are the same, and the value range of the apertures of the three is 18 mm to 26 mm.

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