High-protection front-end protection module of main shaft

Abstract

The present application relates to a kind of machine tool parts, provide a kind of high protection main shaft front end protection module, comprising: the front sealing cover and front bearing gland of being sequentially sleeved on the shaft core, the front sealing cover is placed in the front bearing gland inner ring;Sealing ring one is equipped between the front sealing cover and installation interface, sealing ring two is equipped between the front bearing gland and machine body installation cooperation position;Front sealing cover and the front bearing gland between the third protection gap passage, the upper portion of the front bearing gland is equipped with the gas seal passage leading to the third protection gap passage, to allow gas pressure to be discharged from inside to outside.The present application can completely solve the main shaft failure problem caused by the main shaft front end into cutting fluid.

Description

TECHNICAL FIELD

[0001] The present application relates to a machine tool part, in particular to a high-protection front-end protection module of a spindle. BACKGROUND

[0002] The invasion of cutting fluid leading to spindle failure has been one of the common problems of numerical control machine tool spindle. At present, for the spindle in working state, there are three places where the cutting fluid invades into the interior of the spindle:

[0003] As shown in Figure 3 , the first invasion point is the gap formed by the inner hole of the front sealing cover and the outer circle of the shaft core; the second invasion point is the gap formed by the front sealing cover and the front bearing gland, that is, the gap of the air curtain channel shown in Figure 1 , wherein the front sealing cover rotates at high speed with the spindle during work, the front bearing gland is a fixed part, and the air curtain channel has a "Fang" trend. Although the airflow is sprayed from inside to outside in the air curtain channel to hinder the invasion of cutting fluid, a small amount of cutting fluid still enters the air curtain channel after being splashed by contact with the workpiece during processing. The cutting fluid accumulated for a long time is enough to affect the equipment; as shown in Figure 7 , the third invasion point is the joint surface of the front bearing gland and the machine body after locking, which theoretically cannot enter oil due to the close fit of the two planes, but due to the influence of part processing accuracy and surface knife marks, there is a small gap between the actual fit surfaces. The cutting fluid will slowly penetrate into the interior of the spindle during long-term work of the spindle, thereby affecting the use of the spindle. SUMMARY

[0004] The present application aims to solve the technical problems existing in the prior art, and provides a high-protection front-end protection module of a spindle.

[0005] To achieve the above purpose, the present application provides a high-protection front-end protection module of a spindle, which comprises: a front sealing cover and a front bearing gland which are sequentially sleeved on a shaft core, the front sealing cover is arranged in the inner ring of the front bearing gland; a sealing ring one is arranged between the front sealing cover and the mounting joint surface, a sealing ring two is arranged between the front bearing gland and the mounting and cooperation position of the machine body; a three-stage protection gap channel is arranged between the front sealing cover and the front bearing gland, and an air seal channel is arranged on the upper part of the front bearing gland to lead to the three-stage protection gap channel, so that the air pressure is discharged from inside to outside.

[0006] As a further improvement to the solution, the first-level structure of the three-level protective gap channel is an oblique flare formed by the gap fit between the bottom ends of the front sealing cover and the front bearing cover. The second-level structure is a pressure-reducing zone arranged above the oblique flare. The third-level structure is a labyrinth zone arranged above the pressure-reducing zone. The labyrinth zone is connected to the air-sealing channel. The pressure of the air-sealing channel is required to be 0.1 to 0.2 MPa. The air pressure enters the pressure-reducing zone from top to bottom and then exits from the oblique flare. It also includes: a first intercepting tooth group and a second intercepting tooth group. The first intercepting tooth group is located in the pressure-reducing zone, and the second intercepting tooth group is located at the entrance of the oblique flare.

[0007] As a further improvement to the design, the maze area, the decompression area, and finally the oblique flare extend outwards in a stepped manner from top to bottom.

[0008] As a further improvement to the solution, it also includes: the sealing ring one and the sealing ring two are made of nitrile rubber.

[0009] As a further improvement to the solution, it also includes: a second vertical wall is provided at the lower part of the outer edge of the front sealing cover, the second vertical wall is a second inclined wall that slopes upward toward the center, the top of the second inclined wall is a flat platform step, the lower part of the inner edge of the front bearing cover adjacent to the second vertical wall is provided with an outer inclined side that slopes away from the center, the top of the outer inclined side is provided with a flat rounded buffer step, there is a gap between the rounded buffer step and the platform step, the second vertical wall, the second inclined wall and the outer inclined side together constitute the first-level structure of the three-level protective gap channel, which is a trumpet-shaped oblique flare.

[0010] As a further improvement to the solution, it also includes: the gap between the outer inclined edge and the second vertical wall is between 0.1 mm and 0.25 mm, and the outward inclination angle of the outer inclined edge is between 10 and 15 degrees.

[0011] As a further improvement to the solution, it also includes: a first vertical wall extending vertically upwards from the platform step, the first vertical wall having a first inclined wall sloping towards the center, and a first chamfered groove in the shape of a barb above the rounded corner buffer step, the first inclined wall and the first chamfered groove forming the second-level structural decompression zone in the three-level protective gap channel.

[0012] As a further improvement to the solution, it also includes: the first inclined wall has a vertically upward-facing apex, the side of the apex facing the center of the front sealing cover is an outwardly inclined edge away from the center, the top of the apex is a flat plane, a second chamfered groove is provided above the first chamfered groove, the apex extends into the second chamfered groove, a vertical third vertical wall is provided in the second chamfered groove, a vertical gap channel is left between the third vertical wall and the apex, an inclined inner inclined edge is provided in the second chamfered groove, the outer inclined edge and the inner inclined edge are parallel and have a gap to form an inclined channel, and a gap is left between the plane and the top of the second chamfered groove, this gap constitutes the labyrinth area of ​​the third level structure in the three-level protective gap channel.

[0013] As a further improvement to the solution, the first intercepting tooth group includes an upper oblique tooth and a lower oblique tooth. The upper oblique tooth is disposed on the first oblique wall and tilts upward, while the lower oblique tooth is disposed in the first chamfered groove and tilts downward. The lower oblique tooth and the upper oblique tooth cooperate with each other to form a "Z"-shaped passage in the space within the decompression zone. The second intercepting tooth group includes a crescent tooth and a curved inverted tooth. The crescent tooth is flush with the bottom edge of the front sealing cover and protrudes. The bottom of the crescent tooth is a concave curved surface. The curved inverted tooth is disposed on the outer oblique side and is located above the crescent tooth. The lower part of the curved inverted tooth facing the crescent tooth is a concave curved surface.

[0014] The present invention brings the following effects:

[0015] 1. This invention solves the problem of cutting fluid intrusion at intrusion points one and three by filling the gaps formed between the front sealing cover, the shaft core, and the machine body with sealing ring one and sealing ring two respectively. As for the gap between the rotating and non-rotating parts between the front bearing cap and the front sealing cover at intrusion point two, an air-sealed channel with a three-level protective gap channel is set between the front bearing cap and the front sealing cover to solve the problem of cutting fluid intrusion, thereby effectively protecting the inside of the spindle.

[0016] 2. The first-stage flared structure in the three-stage protective gap channel is trumpet-shaped. Its characteristic is that the gaps are distributed vertically but with a slight inclination, which can prevent cutting fluid splashed at a non-parallel angle from entering. In addition, the centrifugal force and air seal pressure generated by the high-speed rotation of the spindle can prevent most of the cutting fluid from entering.

[0017] 3. The second-level decompression zone in the three-level protection gap channel is a cavity that accommodates the cutting fluid to continue to invade after breaking through the first-level flared structure. This is to prevent the cutting fluid from continuing to invade upwards due to the siphon effect caused by the small gap between the front bearing cap and the front sealing cap and the combined effect of air pressure.

[0018] 4. The third-level labyrinth zone in the three-level protective gap channel can prevent the cutting fluid that has entered from the decompression zone from continuing to invade upwards, so that the cutting fluid that has entered this area can only stay here, and under the action of airflow pressure, centrifugal force and its own gravity, it is discharged along the original path. Attached Figure Description

[0019] Figure 1 This is a cross-sectional view of the existing technology.

[0020] Figure 2 This is a complete cross-sectional view of the present invention.

[0021] Figure 3 This is a schematic diagram of intrusion point one and intrusion point two of the present invention.

[0022] Figure 4 This is a schematic cross-sectional view of the front sealing cover of the present invention.

[0023] Figure 5 This is a schematic diagram of the cross-section of the front bearing cap of the present invention.

[0024] Figure 6 This is a schematic diagram of the front sealing cover and the front bearing cover combined according to the present invention.

[0025] Figure 7 This is a schematic diagram of the air-sealing channel of the present invention.

[0026] Figure 8 This is a three-dimensional structural diagram of the front sealing cover and the front bearing cover of the present invention.

[0027] Figure 9 This is a schematic diagram of the first and second intercepting tooth groups of the present invention.

[0028] The correspondence between the reference numerals and the names of the components in the attached drawings is as follows:

[0029] 32-Air curtain channel, 33-Motor, 34-Broaching mechanism, 35-Tool holder, 21-Intrusion point one, 22-Intrusion point two, 23-Intrusion point three, 1-Shaft core, 2-Front sealing cover, 3-Sealing ring one, 4-Front bearing cover, 5-Locking nut, 6-Sealing ring two, 8-Body, 9-Air seal channel, 10-Air seal ring groove, 11-Maze area, 12-Decompression area, 41-Peak angle, 42-Outer inclined edge, 43-Plane, 44-First inclined wall, 45-First vertical wall, 46-Platform step, 47-Second inclined wall, 48-Second vertical wall, 51-Outer inclined edge, 52-Rounded corner buffer step, 53-First chamfered groove, 54-Third vertical wall, 55-Second chamfered groove, 56-Inner inclined edge, 61-Upper helical tooth, 62-Lower helical tooth, 63-Crescent tooth, 64-Curved surface chamfered tooth. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It is understood that the specific embodiments described herein are only for explaining this application and not for limiting it. Furthermore, it should be noted that, for ease of description, only the parts related to this application are shown in the accompanying drawings, not all structures. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0031] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0032] This invention specifically discloses a highly protective spindle front-end protection module, such as... Figures 1-8 As shown, it includes: a front sealing cover 2 and a front bearing cover 4 sequentially fitted onto the shaft core 1. The front sealing cover 2 is placed inside the front bearing cover 4. (Refer to...) Figure 8 As shown, the front sealing cover 2 is fixedly mounted on the locking nut 5 by bolts, and the locking nut 5 is screwed onto the shaft core 1 in a ring shape. The front bearing cover 4 is fixed to the machine body 8 by bolts. A sealing ring 3 is provided between the mounting surfaces of the front sealing cover 2 and the locking nut 5. The sealing ring 3 acts between the front sealing cover 2 and the locking nut 5 to prevent cutting fluid from entering the spindle from intrusion point 21 and causing spindle failure. A sealing ring 6 is provided between the mounting position of the front bearing cover 4 and the machine body 8. The sealing ring 6 acts at the gap between the front bearing cover 4 and the machine body 8 to prevent cutting fluid from entering the spindle from intrusion point 23 and causing spindle failure. The sealing ring 1 (3) and sealing ring 2 (6) are made of nitrile rubber. The sealing principle is mainly based on its elastic deformation characteristics and material properties. For intrusion point 22, a three-level protective gap channel is provided between the front sealing cover 2 and the front bearing cover 4. The upper part of the front bearing cover 4 is provided with an air seal channel 9 leading to the three-level protective gap channel, so that the air pressure is discharged from the inside to the outside. Intrusion point 22 is the gap between the front sealing cover 2 and the front bearing cover 4, that is, the gap between the rotating part and the non-rotating part. Therefore, through this three-level protective structure design, combined with the air pressure in the air seal channel 9, the direction is from top to bottom, so as to prevent the cutting fluid from entering the spindle from intrusion point 22.

[0033] By filling the gap between the front sealing cover 2 and the shaft core 1 with sealing ring 1 3, and filling the gap between the front bearing cover 4 and the machine body 8 with sealing ring 2 6, the problem of cutting fluid intrusion at intrusion point 1 21 and intrusion point 3 23 can be solved. As for intrusion point 2 22 (the gap between the front bearing cover 4 and the front sealing cover 2), an air seal channel 9 with a three-level protective gap channel is set between the front bearing cover 4 and the front sealing cover 2 to solve the problem of cutting fluid intrusion, thereby forming effective protection for the inside of the spindle.

[0034] Reference Figure 3 As shown, the first-level structure of the three-level protective gap channel is an oblique flare formed by the lower part of the front sealing cover 2 and the front bearing cover 4. The second-level structure is a pressure-reducing zone 12 arranged above the oblique flare. The third-level structure is a labyrinth zone 11 arranged above the pressure-reducing zone 12. The labyrinth zone 11 is connected to the air-sealing channel 9. The pressure of the air-sealing channel 9 is required to be 0.1 to 0.2 MPa, preferably 0.2 MPa. The air pressure enters the pressure-reducing zone 12 from the labyrinth zone 11 from top to bottom and then exits from the oblique flare. The labyrinth zone 11 to the pressure-reducing zone 12 and finally to the oblique flare are distributed outward in a stepped manner from top to bottom.

[0035] Specifically, the cutting fluid enters upwards from the inclined flare. After being blocked by the inclined flare, only a small portion of the cutting fluid can enter the decompression zone 12. The decompression zone 12 is used to accommodate the cutting fluid that enters from the inclined flare below, so as to prevent the cutting fluid from continuing to enter upwards. If the cutting fluid continues to enter upwards, it will reach the labyrinth zone 11. The cutting fluid that enters the labyrinth zone 11 no longer has the driving force to continue upwards. It can only stay in this area for a short time and then be discharged along the original path under the air pressure of the air seal channel 9 and the centrifugal force of the rotation of the spindle and the front sealing cover 2.

[0036] Reference Figures 3-6 As shown, the main structure constituting the flared opening includes: a vertical second vertical wall 48 at the lower part of the outer edge of the front sealing cover 2; a second inclined wall 47 sloping upwards from the second vertical wall 48 towards the center of the front sealing cover 2; a flat platform step 46 at the top of the second inclined wall 47; an outer inclined edge 51 sloping away from the center at the lower part of the inner edge of the front bearing cover 4 adjacent to the second vertical wall 48; a flat rounded buffer step 52 at the top of the outer inclined edge 51; and a gap between the rounded buffer step 52 and the platform step 46. The second vertical wall 48, the second inclined wall 47, and the outer inclined edge 51 constitute the flared opening in the three-level protective gap channel. The gap between the outer inclined edge 51 and the second vertical wall 48 is between 0.1 mm and 0.25 mm, and the outward inclination angle of the outer inclined edge 51 is between 10 and 15 degrees.

[0037] The first-stage structure (slanted flare) is characterized by vertically distributed but slightly slanted slits, which can prevent cutting fluid splashed at non-parallel angles from entering. In addition, the centrifugal force and air seal pressure generated by the high-speed rotation of the spindle can prevent most cutting fluid from entering.

[0038] Reference Figures 3-6 As shown, the main structure constituting the decompression zone 12 includes: a first vertical wall 45 extending vertically upward from the platform step 46; a first inclined wall 44 inclined towards the center of the forward sealing cover 2 on the first vertical wall 45; and a first chamfered groove 53 in the shape of a barb above the rounded corner buffer step 52. The first inclined wall 44 and the first chamfered groove 53 together constitute the decompression zone 12 in the three-level protective gap channel.

[0039] If the cutting fluid breaks through the first-stage flared structure, it will enter the second-stage decompression zone 12. The cutting fluid entering here has a large retention space to prevent the siphon effect caused by the small gap between the front bearing cap 4 and the front sealing cap 2 and the combined effect of air pressure from causing the cutting fluid to continue to invade upwards.

[0040] Reference Figures 3-6 As shown, the main structure constituting the maze area 11 includes: a vertically upward-facing apex 41 above the first inclined wall 44; an outwardly inclined side 42 on the side of the apex 41 facing the center of the front sealing cover 2 away from the center; a flat plane 43 at the top of the apex 41; a second chamfered groove 55 above the first chamfered groove 53; the apex 41 extending into the second chamfered groove 55; a vertical third vertical wall 54 inside the second chamfered groove 55; a vertical gap channel between the third vertical wall 54 and the apex 41; an inclined inner side 56 inside the second chamfered groove 55; the outer inclined side 42 and the inner inclined side 56 are parallel and have a gap to form an inclined channel; and a gap between the plane 43 and the top of the second chamfered groove 55. This gap constitutes the third-level structure of the maze area 11 in the three-level protective gap channel.

[0041] The cutting fluid that breaks through the decompression zone 12 has no driving force to continue upwards to the labyrinth zone 11. It can only stay in the labyrinth zone 11 for a short time, and then it will be discharged along the original path under the action of airflow pressure, centrifugal force and its own gravity.

[0042] Reference Figure 9As shown, it also includes: a second intercepting tooth assembly disposed at the entrance of the oblique flare; the second intercepting tooth assembly includes crescent teeth 63 and curved teeth 64. The bottom of the crescent teeth 63 is flush with the bottom of the front sealing cover 2 and protrudes towards the edge away from the center of the front sealing cover 2. The bottom of the crescent teeth 63 is a concave curved surface. When cutting fluid splashes into the oblique flare, it will be blocked by the crescent teeth 63. Most of the cutting fluid will contact the curved surface at the bottom of the crescent teeth 63 and flow obliquely downward under the guidance of the curved surface, thereby reducing the cutting fluid flow. The amount of cutting fluid entering is controlled by the curved tooth 64, which is located on the outer bevel 51 and above the crescent tooth 63. The lower part of the curved tooth 64 facing the crescent tooth 63 is a concave curved surface. Even if some cutting fluid enters the flared opening from the end area of ​​the crescent tooth 63, the splashed cutting fluid will contact the curved surface at the bottom of the curved tooth 64. The splashed cutting fluid will weaken its kinetic energy after contacting the curved surface, thereby reducing the upward intrusion potential energy of the cutting fluid. This can prevent most of the cutting fluid from flowing into the decompression zone 12.

[0043] It also includes a first intercepting tooth assembly set in the decompression zone 12. The first intercepting tooth assembly includes two parts: an upper helical tooth 61 and a lower helical tooth 62. The upper helical tooth 61 and the lower helical tooth 62 are respectively set on the front sealing cover 2 and the front bearing cover. The upper helical tooth 61 is set on the first inclined wall 44 and tilts upward, while the lower helical tooth 62 is set in the first chamfered groove 53 and tilts downward. The lower helical tooth 62 and the upper helical tooth 61 cooperate with each other to form a "Z"-shaped passage in the space within the decompression zone 12. When the cutting fluid invades upward from the inclined flare and reaches the decompression zone 12, it will first be blocked by the lower helical tooth 62 and the upper helical tooth 61. Since the lower helical tooth 62 tilts downward, if the cutting fluid needs to continue upward, it needs to flow along the "Z"-shaped passage to enter the upper part of the decompression zone 12, which further increases the difficulty of the cutting fluid invading upward.

[0044] Reference Figure 2 , Figure 3 , Figure 7 and Figure 8 As shown, the upper part of the front bearing cover 4 is provided with a recessed air seal ring groove 10. The air seal ring groove 10 and the air seal channel 9 are connected and a pressure of 0.2 MPa is input. It should be noted that the air circuit must be kept open when the machine tool is powered on, whether the spindle is running or stationary, so as to achieve the expected protection effect.

[0045] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A high-protection spindle front-end protection module, comprising: A front sealing cover (2) and a front bearing cover (4) are sequentially fitted onto the shaft core (1). The front sealing cover (2) is placed inside the front bearing cover (4). A sealing ring 1 (3) is provided between the front sealing cover (2) and the mounting mating surface, and a sealing ring 2 (6) is provided between the front bearing cover (4) and the mounting mating position of the machine body (8). A three-level protective gap channel is provided between the front sealing cover (2) and the front bearing cover (4). An air seal channel (9) leading to the three-level protective gap channel is provided on the upper part of the front bearing cover (4) so ​​that the air pressure can be discharged from the inside to the outside. The first-level structure of the three-level protective gap channel is an oblique flare formed by the gap fit between the bottom ends of the front sealing cover (2) and the front bearing cover (4). The second-level structure is a pressure-reducing zone (12) arranged above the oblique flare. The third-level structure is a labyrinth zone (11) arranged above the pressure-reducing zone (12). The labyrinth zone (11) is connected to the air-sealing channel (9). The pressure of the air-sealing channel (9) is required to be 0.1 to 0.2 MPa. The air pressure enters the pressure-reducing zone (12) from top to bottom and then exits from the oblique flare. It also includes: a first intercepting tooth group and a second intercepting tooth group. The first intercepting tooth group is located in the pressure-reducing zone (12), and the second intercepting tooth group is located at the entrance of the oblique flare. The lower part of the outer edge of the front sealing cover (2) is provided with a vertical second vertical wall (48). The second vertical wall (48) is an inclined second wall (47) that slopes towards the center. The top of the second inclined wall (47) is a flat platform step (46). The lower part of the inner edge of the front bearing cover (4) adjacent to the second vertical wall (48) is provided with an outer inclined side (51) that slopes away from the center. The top of the outer inclined side (51) is provided with a flat rounded buffer step (52). There is a gap between the rounded buffer step (52) and the platform step (46). The second vertical wall (48), the second inclined wall (47) and the outer inclined side (51) together constitute the first-level structure of the three-level protective gap channel, which is a flared, trumpet-shaped opening. The first vertical wall (45) is vertically arranged from the platform step (46) upwards. The first vertical wall (45) is a first inclined wall (44) that slopes towards the center. A first chamfered groove (53) in the shape of a barb is provided above the rounded corner buffer step (52). The first inclined wall (44) and the first chamfered groove (53) together form the second-level structural pressure relief zone (12) in the three-level protective gap channel. The first intercepting tooth group includes an upper helical tooth (61) and a lower helical tooth (62). The upper helical tooth (61) is disposed on the first inclined wall (44) and tilts upward. The lower helical tooth (62) is disposed in the first chamfered groove (53) and tilts downward. The lower helical tooth (62) and the upper helical tooth (61) cooperate with each other to form a "Z" shaped passage in the space within the decompression zone (12). The second intercepting tooth group includes a crescent tooth (63) and a curved tooth (64). The crescent tooth (63) is flush with the bottom edge of the front sealing cover (2) and protrudes. The bottom of the crescent tooth (63) is a concave curved surface. The curved tooth (64) is disposed on the outer inclined side (51) and is above the crescent tooth (63). The lower part of the curved tooth (64) facing the crescent tooth (63) is a concave curved surface.

2. The high-protection spindle front-end protection module according to claim 1, characterized in that, The maze area (11) extends outward in a stepped manner from top to bottom to the decompression area (12) and finally to the oblique flare.

3. The high-protection spindle front-end protection module according to claim 1, characterized in that, Also includes: The sealing ring one (3) and the sealing ring two (6) are made of nitrile rubber.

4. The high-protection spindle front-end protection module according to claim 1, characterized in that, Also includes: The gap between the outer inclined edge (51) and the second vertical wall (48) is between 0.1 mm and 0.25 mm, and the outward inclination angle of the outer inclined edge (51) is between 10 and 15 degrees.

5. The high-protection spindle front-end protection module according to claim 1, characterized in that, Also includes: The first inclined wall (44) has a vertically upward-facing apex (41). The side of the apex (41) facing the center of the front sealing cover (2) is an outwardly inclined side (42) away from the center. The top of the apex (41) is a flat plane (43). A second chamfered groove (55) is provided above the first chamfered groove (53). The apex (41) extends into the second chamfered groove (55). A vertical third vertical wall (54) is provided in the second chamfered groove (55). A vertical gap channel is left between the third vertical wall (54) and the apex (41). An inclined inner inclined side (56) is provided in the second chamfered groove (55). The outer inclined side (42) and the inner inclined side (56) are parallel and have a gap to form an inclined channel. A gap is left between the plane (43) and the top of the second chamfered groove (55). This gap constitutes the labyrinth area (11) of the third level structure in the three-level protective gap channel.

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