Medium-speed coal mill

Abstract

The invention discloses a medium-speed coal mill applied to the technical field of coal mills, which is characterized in that the air inlet position of primary air is dynamically changed through the matched arrangement of an air equalizing frame capable of periodically rotating and a circumferential air equalizing unit, so that the circumferential abrasion of a millstone is homogenized, the problem of serious local abrasion caused by fixed air inlet is effectively solved, and the service life of the millstone is prolonged. The service life of key components is obviously prolonged; furthermore, an air inlet mode is changed into a multi-point air inlet mode, so that the problem caused by an uneven wind field is further weakened, and the homogenization control effect of abrasion is better. In addition, the deviation monitoring unit integrated on the air uniformizing frame can early warn rotation accumulated deviation in real time, a maintenance signal is provided before air leakage of the air inlet possibly occurs, and the long-term operation reliability and stability of the air uniformizing system are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of coal mill technology, and particularly to medium-speed coal mills. Background Technology

[0002] Medium-speed coal mills are crucial equipment in pulverized coal boilers of thermal power units, accounting for over 80% of all coal-fired units. Their primary function is to dry and grind raw coal into pulverized coal, which is then fed into the furnace for combustion. The mill's output is determined by the amount of pulverized coal it can produce while maintaining the required fineness. The mill's design output is calculated based on the type of coal being designed for operation. To save costs, thermal power plants commonly use lower-calorific-value coals, deviating from their design specifications. This results in the unit requiring more coal to operate under the same load, making the mill's original design output insufficient for the unit's load requirements and impacting boiler safety. Therefore, there is a widespread need to improve the adaptability of medium-speed coal mills to different coal types.

[0003] In use, air is generally introduced from the bottom and overflows circumferentially along the edge of the grinding disc, thereby carrying up the fine powder after grinding. The fine powder is then discharged from the top of the equipment, such as the medium-speed coal mill disclosed in Chinese Patent 2022111230035 and a coal mill disclosed in Chinese Patent CN118491619B.

[0004] However, the primary air intake below the mill disc is generally a single-point intake, which then diffuses within the primary air chamber and overflows upwards along the air ring at the edge of the mill disc. However, the single-point intake method results in severe uneven air velocity in the circumferential direction at the outlet of the air ring (nozzle ring). In areas with high air velocity, the coal dust is fully lifted and transported to the separator, while in areas with low air velocity, the coal dust (especially heavier particles) cannot be effectively lifted and will fall back or directly into the stone coal chamber, causing abnormally increased stone coal discharge, uneven output of the coal mill, and severe wear on one side of the mill disc. Summary of the Invention

[0005] The core of this invention lies in continuously adjusting the air outlet along the circumference so that the air outlet is not fixed on one side, thereby uniformizing the wear on the air inlet side (which is less than the wear on the air outlet side) in the circumference, thus solving the problem of severe local wear in coal mills in the prior art.

[0006] To solve the above problems, the present invention adopts the following technical solution.

[0007] A medium-speed coal mill includes a base, a primary air chamber fixedly connected to the upper end of the base, a grinding disc fixedly mounted on the upper end of the primary air chamber, an equipment shell fixedly connected to the upper edge of the grinding disc, three evenly distributed grinding rollers mounted on the inner wall of the equipment shell via an annular bracket, the lower ends of the three grinding rollers abutting against the upper end of the grinding disc, a feed pipe in the middle of the equipment shell, the lower end of the feed pipe passing through the annular bracket and extending between the three grinding rollers, a primary return cone and a secondary return cone fixedly connected to the outer end of the feed pipe, the primary return cone being located inside the equipment shell, and the secondary return cone fixedly penetrating the top of the equipment shell and extending above the equipment shell, two powder outlet pipes fixedly connected to the upper end of the secondary return cone, and multiple separation inclined plates arranged in an annular array fixedly connected to the top of the inner wall of the equipment shell, the ends of the multiple separation inclined plates away from the axis of the base contacting each other with the inner wall above the primary return cone; An air inlet pipe is fixedly connected to the outer end of the primary air chamber. An upper guide pipe is fixedly connected between the upper end of the air inlet pipe and the top of the equipment casing. The upper end of the upper guide pipe is directly opposite the separation inclined plate. A circumferential air distribution unit is fixedly connected to the inner wall of the primary air chamber. The air inlet pipe is connected to the circumferential air distribution unit. The circumferential air distribution unit includes a hollow ring and an air distribution frame installed on the inner wall of the primary air chamber via an electric slide rail. Multiple air inlets are cut into the hollow ring. The air distribution frame matches the air inlets. An angle sensor is installed on the air distribution frame.

[0008] Furthermore, both the secondary and primary powder return cones have a conical structure, and the outer wall of the primary powder return cone does not contact the inner wall of the equipment casing.

[0009] Furthermore, the air distribution frame includes a sliding frame connected to an electric slide rail, multiple connecting rods fixedly connected to the inner wall of the sliding frame, and variable air vanes fixedly connected to the ends of the multiple connecting rods away from the inner wall of the hollow ring. The variable air vanes correspond to the air inlet, and the length and width dimensions of the upper surface of the variable air vanes are larger than the length and width dimensions of the air inlet.

[0010] Furthermore, the variable wind vane includes an electromagnetic layer fixedly connected to the connecting rod, multiple guide rods fixedly connected to the upper end of the electromagnetic layer, and a plugging layer movably inserted into the upper end of the multiple guide rods. The upper end of the plugging layer is made of elastic material, and the bottom end of the plugging layer is made of magnetic material.

[0011] Furthermore, when not subjected to external force, the lower end of the plugging layer is in contact with the upper surface of the electromagnetic layer, and the upper end of the plugging layer is not in contact with the top of the hollow ring body.

[0012] Optionally, the number of air fins is one less than the number of air inlets, and during operation, multiple air fins cover and seal the lower ends of multiple air inlets respectively.

[0013] Optionally, the air inlets are divided into multiple groups, and the multiple air inlets in each group are arranged in a ring array around the central axis of the hollow ring body. The variable air vanes are also divided into multiple groups, and the number of variable air vanes in each group is one less than the number of air inlets in each group.

[0014] Optionally, the air distribution frame is equipped with a offset monitoring unit, which includes a laser rangefinder installed on the top of one of the air distribution vanes, multiple flat-top conical holes drilled in the top of the hollow ring body, and multiple alignment grooves drilled in the middle of the top of the flat-top conical holes, with the multiple flat-top conical holes corresponding to the middle of the multiple air inlets.

[0015] Furthermore, the radial distance between the center of the laser rangefinder and the center of the flat-top conical hole and the inner wall of the primary air chamber is the same. When the variable air vane is facing the air inlet, the distance between the edge of the alignment top groove and the top edge of the flat-top conical hole is not greater than the distance difference between the edge of the upper surface of the variable air vane and the edge of the air inlet.

[0016] Compared with the prior art, the advantages of this invention are: (1) This solution continuously adjusts the air outlet along the circumference so that the air outlet is not fixed on one side, thereby uniformizing the problem of less wear on the air inlet side and greater wear on the air outlet side in the circumference, so as to solve the problem of severe local wear of coal mill in the prior art.

[0017] (2) The air intake of the primary air chamber can also be set to multi-point air intake, and the positions of the multiple air intake points also change continuously in the circumferential direction, thereby further improving the uniformity of wear in the circumferential direction and further reducing the local wear of the coal mill.

[0018] (3) The offset monitoring unit integrated on the air distribution frame can provide real-time warning of cumulative rotational deviation and provide maintenance signals before air leakage at the air inlet, ensuring the long-term reliability and stability of the air distribution system. Attached Figure Description

[0019] Figure 1 This is a perspective view of the present invention; Figure 2 This is a perspective view of the invention with the device casing removed; Figure 3 This is a cross-sectional schematic diagram of the present invention; Figure 4 This is a schematic cross-sectional view of the grinding disc and the primary air chamber of the present invention; Figure 5 This is a cross-sectional schematic diagram of the air inlet of the primary air chamber of the present invention; Figure 6 This is a top view of the circumferential air distribution unit of the present invention; Figure 7 This is a top view of the air distribution frame of the present invention; Figure 8 This is a cross-sectional schematic diagram of the variable air vane of the present invention; Figure 9 This is a schematic cross-sectional view of the variable air vane of the present invention when it is used to seal the air outlet. Figure 10 This is a cross-sectional schematic diagram of the circumferential air distribution unit in the multi-point air intake configuration of the present invention; Figure 11 This is a top view of the air distribution frame for multi-point air intake according to the present invention; Figure 12 This is a schematic diagram of the vertical cross-section at the air inlet of the primary air chamber when the offset monitoring unit is added in this invention; Figure 13 This is a top-view cross-sectional diagram of the air inlet when the offset monitoring unit is added to the present invention.

[0020] Explanation of the labels in the diagram: 1. Base, 21. Grinding roller, 22. Grinding disc, 23. Primary air chamber, 201. Annular support, 3. Equipment shell, 31. Feed pipe, 41. Primary powder return cone, 42. Secondary powder return cone, 43. Powder outlet pipe, 44. Separation inclined plate, 51. Air inlet pipe, 52. Upper guide pipe, 6. Circumferential air distribution unit, 61. Hollow ring, 62. Air inlet, 63. Air variable vane, 601. Sliding frame, 602. Connecting rod, 631. Electromagnetic layer, 632. Blocking layer, 633. Guide rod, 71. Flat top conical hole, 72. Alignment top groove, 73. Laser rangefinder. Detailed Implementation

[0021] The technical solutions will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0022] First implementation method: like Figures 1-3 A medium-speed coal mill includes a base 1. A primary air chamber 23 is fixedly connected to the upper end of the base 1. A grinding disc 22 is fixedly mounted on the upper end of the primary air chamber 23. An equipment shell 3 is fixedly connected to the upper edge of the grinding disc 22. Three evenly distributed grinding rollers 21 are installed on the inner wall of the equipment shell 3 via an annular bracket 201. The lower ends of the three grinding rollers 21 abut against the upper end of the grinding disc 22. A feed pipe 31 is provided in the middle of the equipment shell 3. The lower end of the feed pipe 31 passes through the annular bracket 201 and extends between the three grinding rollers 21. The outer end is fixedly connected to a primary powder return cone 41 and a secondary powder return cone 42. The primary powder return cone 41 is located inside the equipment housing 3, and the secondary powder return cone 42 is fixedly connected through the top of the equipment housing 3 and extends to the top of the equipment housing 3. Two powder outlet pipes 43 are fixedly connected to the upper end of the secondary powder return cone 42. Multiple separation inclined plates 44 arranged in a ring array are fixedly connected to the top of the inner end of the equipment housing 3. The ends of the multiple separation inclined plates 44 away from the axis of the base 1 are in contact with the inner wall above the primary powder return cone 41. When this coal mill is working, the coal material is fed onto the grinding disc 22 through the feed pipe 31. Then, the grinding disc 22 is rotated so that the grinding roller 21 crushes the coal material on the grinding disc 22. At the same time, primary air is introduced into the primary air chamber 23 through the air inlet pipe 51. The primary air diffuses in the primary air chamber 23 and overflows upward along the air ring around the grinding disc 22, thereby driving the small particles of powder to move upward. The primary air carries the powder over the periphery of the primary return powder cone 41 and enters the primary return powder cone 41 along the space of multiple separation inclined plates 44. Under the action of gravity and inertia, the coarse powder is deposited downward along the primary return powder cone 41, and the fine powder enters the secondary return powder cone 42 and is then discharged through the powder outlet pipe 43.

[0023] like Figures 3-4 An air inlet pipe 51 is fixedly connected to the outer end of the primary air chamber 23. An upper guide pipe 52 is fixedly connected between the upper end of the air inlet pipe 51 and the top of the equipment shell 3. The upper guide pipe 52 can intake air towards the separation inclined plate 44 and the primary return powder cone 41, thereby effectively disturbing the powder entering the primary return powder cone 41, thus raising the fine powder, facilitating the separation of coarse and fine powder, and improving the quality of coal powder. The upper end of the upper guide pipe 52 is directly opposite the separation inclined plate 44. A circumferential air equalization unit 6 is fixedly connected to the inner wall of the primary air chamber 23. The air inlet pipe 51 is connected to the circumferential air equalization unit 6. The circumferential air equalization unit 6 includes a hollow ring 61. The air distribution frame is installed on the inner wall of the primary air chamber 23 via an electric slide rail. Multiple air inlets 62 are cut into the hollow ring 61. The air distribution frame and the air inlets 62 are matched with each other. The primary air enters the circumferential air distribution unit 6 through the air inlet pipe 51, and then enters the primary air chamber 23. By setting the circumferential air distribution unit 6, the opening and closing of the multiple air inlets 62 on it can be changed periodically. Thus, the air inlet of the primary air chamber 23 is no longer fixed at the air inlet pipe 51, but changes continuously in the circumferential direction. This achieves circumferential homogenization of uneven wear caused by the fixed air inlet, thereby effectively protecting the grinding disc 22.

[0024] Both the secondary return cone 42 and the primary return cone 41 have a conical structure, which facilitates the fall of coarse powder carried in the primary air and enables the screening of fine powder, thereby effectively ensuring the quality of the finished coal powder. In addition, the outer wall of the primary return cone 41 does not contact the inner wall of the equipment shell 3, providing a sufficiently long path for small particles of powder carried by the primary air to enter the primary return cone 41.

[0025] like Figures 5-7An angle sensor is installed on the air distribution frame. Specifically, the angle sensor can be installed on one of the variable air vanes 63. The air distribution frame includes a sliding frame 601 connected to an electric slide rail, multiple connecting rods 602 fixedly connected to the inner wall of the sliding frame 601, and variable air vanes 63 respectively fixedly connected to the ends of the multiple connecting rods 602 away from the inner wall of the hollow ring 61. The number of variable air vanes 63 is one less than the number of air inlets 62, so that there is always one air inlet 62 on the hollow ring 61 in the open state, for supplying air to the air distribution frame. Air enters the primary air chamber 23, and during operation, multiple variable air vanes 63 cover and seal the lower ends of multiple air inlets 62 respectively. The variable air vanes 63 correspond to the air inlets 62, and the length and width of the upper surface of the variable air vanes 63 are larger than the length and width of the air inlets 62. This effectively ensures that when the variable air vanes 63 and the air inlets 62 are in opposite positions, the variable air vanes 63 can completely block the corresponding air inlets 62, thereby making the actual air intake of the primary air chamber 23 controllable and preventing air leakage from some air inlets 62.

[0026] In this system, based on the angle sensor on the air equalization frame, when the air inlet 62 is changed, the air equalization frame can be controlled to rotate by the same angle each time, and this angle is the included angle between two adjacent air inlets 62. This ensures that after each rotation, a different air inlet 62 is opened, thereby achieving the effect of the air inlet of the primary air chamber 23 changing continuously in the circumference. This allows the uneven wear caused by the difference in wind speed between the air inlet side and the air outlet side of the grinding mill to be uniform in the circumference, thus effectively avoiding the impact on the quality of the finished coal powder caused by unevenness on one side.

[0027] like Figure 8 The variable air vane 63 includes an electromagnetic layer 631 fixedly connected to the connecting rod 602, multiple guide rods 633 fixedly connected to the upper end of the electromagnetic layer 631, and a blocking layer 632 movably inserted into the upper end of the multiple guide rods 633. The upper end of the blocking layer 632 is made of elastic material, and the bottom end of the blocking layer 632 is made of magnetic material. When there is no external force, the lower end of the blocking layer 632 is in contact with the upper surface of the electromagnetic layer 631, and the upper end of the blocking layer 632 is not in contact with the top of the hollow ring 61. This ensures that there is no frictional resistance between the variable air vane 63 and the top of the hollow ring 61 when the air distribution frame rotates, thereby effectively ensuring its stable and smooth position change. At the same time, it effectively protects the variable air vane 63 from wear due to rotation, so that it is not easy for air leakage to occur when it blocks the corresponding air inlet 62.

[0028] like Figure 9 When the angle sensor detects a predetermined rotation angle, the control system of the coal mill controls the electromagnetic layer 631 to be energized, thereby generating a magnetic repulsion force on the bottom of the blocking layer 632, causing it to move upward until it contacts the lower part of the air inlet 62, thus blocking the corresponding air inlet 62.

[0029] In summary, this solution continuously adjusts the air outlet along the circumference, preventing it from being fixed on one side. This uniformizes the wear on the inlet side (where wear is less) and the wear on the outlet side (where wear is greater) along the circumference, thus solving the problem of severe localized wear in existing coal mills.

[0030] Second implementation method: This embodiment changes the arrangement of the air inlet 62 and the air variable vane 63 based on the first embodiment, while the rest remains the same as the first embodiment.

[0031] like Figures 10-11 The air inlets 62 are divided into multiple groups, and the multiple air inlets 62 in each group are arranged in a ring array around the central axis of the hollow ring body 61. The variable air vanes 63 are also divided into multiple groups, and the number of variable air vanes 63 in each group is one less than the number of air inlets 62 in each group, so that there is always one air inlet 62 in each group in the open state. When the primary air from the air inlet pipe 51 enters the hollow ring body 61, it can enter the primary air chamber 23 through multiple air inlets 62 evenly distributed around the axis of the hollow ring body 61, and then overflow along the air ring at the edge of the grinding disc 22, realizing multi-point air intake of the primary air chamber 23, thereby effectively weakening the wind speed difference between the near wind side and the far wind side, and thus making the circumferential uniformity of wear better.

[0032] In this embodiment, the air intake of the primary air chamber is set to multi-point air intake, and the positions of the multiple air intake points also change continuously in the circumferential direction, thereby further improving the uniformity of wear in the circumferential direction and further reducing the local wear of the coal mill.

[0033] The third implementation method: This embodiment adds an offset monitoring unit based on the first or second embodiment, while the rest remains the same as the first embodiment.

[0034] like Figures 12-13 The air distribution frame is equipped with a deviation monitoring unit, which includes a laser rangefinder 73 installed on the top of one of the air distribution vanes 63, multiple flat-top conical holes 71 drilled in the top of the hollow ring 61, and multiple alignment top grooves 72 drilled in the middle of the top of the flat-top conical holes 71 respectively. The multiple flat-top conical holes 71 correspond to the middle of the multiple air inlets 62 respectively.

[0035] The radial distance between the center of the laser rangefinder 73 and the center of the flat-top conical hole 71 and the inner wall of the primary air chamber 23 is the same. When the variable air vane 63 is directly opposite the air inlet 62, the distance between the edge of the alignment top groove 72 and the inner top edge of the flat-top conical hole 71 is not greater than the distance difference between the upper surface edge of the variable air vane 63 and the edge of the air inlet 62. When the air distribution frame experiences cumulative deviation, the laser emitted by the laser rangefinder 73 will shift from the center of the alignment top groove 72 to the top flat surface of the flat-top conical hole 71. At this time, the laser rangefinder... The data on 73 will decrease, and the decrease will be equal to the depth of the top groove 72. When the cumulative deviation further increases, the laser emitted by the laser rangefinder 73 will fall on the conical surface of the flat-top conical hole 71. Due to the setting of the edge distance difference between the variable air vane 63 and the air inlet 62, the variable air vane 63 can still completely cover the air inlet 62 at this time. That is, the cumulative deviation has not yet caused the corresponding air inlet 62 to leak air, so it is not easy to affect the normal coal grinding of the current coal mill, and it can provide the staff with enough time for maintenance.

[0036] With prolonged use, the offset monitoring unit can effectively monitor the position of the variable air vane 63 relative to the air inlet 62. When the rotation of the air distribution frame accumulates deviation, the deviation can be detected in time, thereby effectively preventing air leakage between multiple variable air vanes 63 and their corresponding air inlets 62.

[0037] The above description is merely a preferred embodiment of the present invention; it encompasses all the protection scope of the present invention. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solutions and improved concepts of the present invention, should be covered within the protection scope of the present invention.

Claims

1. A medium-speed coal mill, comprising a base (1), characterized in that: A primary air chamber (23) is fixedly connected to the upper end of the base (1). A grinding disc (22) is fixedly mounted on the upper end of the primary air chamber (23). A device housing (3) is fixedly connected to the upper edge of the grinding disc (22). Three evenly distributed grinding rollers (21) are installed on the inner wall of the device housing (3) through an annular bracket (201). The lower ends of the three grinding rollers (21) abut against the upper end of the grinding disc (22). A feed pipe (31) is provided in the middle of the device housing (3). The lower end of the feed pipe (31) passes through the annular bracket (201) and extends between the three grinding rollers (21). The outer end is fixedly connected to a primary powder return cone (41) and a secondary powder return cone (42). The primary powder return cone (41) is located inside the equipment shell (3), and the secondary powder return cone (42) is fixedly connected through the top of the equipment shell (3) and extends to the top of the equipment shell (3). The upper end of the secondary powder return cone (42) is fixedly connected to two powder outlet pipes (43). The top end of the equipment shell (3) is fixedly connected to multiple separation inclined plates (44) arranged in a ring array. The ends of the multiple separation inclined plates (44) away from the axis of the base (1) are in contact with the inner wall above the primary powder return cone (41). An air inlet pipe (51) is fixedly connected to the outer end of the primary air chamber (23). An upper guide pipe (52) is fixedly connected between the upper end of the air inlet pipe (51) and the top of the equipment shell (3). The upper end of the upper guide pipe (52) is directly opposite the separation inclined plate (44). A circumferential air equalization unit (6) is fixedly connected to the inner wall of the primary air chamber (23). The air inlet pipe (51) is connected to the circumferential air equalization unit (6). The circumferential air equalization unit (6) includes a hollow ring (61) and an air equalization frame installed on the inner wall of the primary air chamber (23) via an electric slide rail. Multiple air inlets (62) are drilled on the hollow ring (61). The air equalization frame matches the air inlets (62). An angle sensor is installed on the air equalization frame.

2. The medium-speed coal mill according to claim 1, characterized in that: Both the secondary powder return cone (42) and the primary powder return cone (41) are conical structures, and the outer wall of the primary powder return cone (41) does not contact the inner wall of the equipment shell (3).

3. The medium-speed coal mill according to claim 1, characterized in that: The air distribution frame includes a sliding frame (601) connected to an electric slide rail, multiple connecting rods (602) fixedly connected to the inner wall of the sliding frame (601), and variable air vanes (63) fixedly connected to the ends of the multiple connecting rods (602) away from the inner wall of the hollow ring (61). The variable air vanes (63) correspond to the air inlet (62), and the length and width dimensions of the upper surface of the variable air vanes (63) are larger than the length and width dimensions of the air inlet (62).

4. The medium-speed coal mill according to claim 3, characterized in that: The variable air vane (63) includes an electromagnetic layer (631) fixedly connected to the connecting rod (602), a plurality of guide rods (633) fixedly connected to the upper end of the electromagnetic layer (631), and a plugging layer (632) movably inserted into the upper end of the plurality of guide rods (633). The upper end of the plugging layer (632) is made of an elastic material, and the bottom of the plugging layer (632) is made of a magnetic material.

5. The medium-speed coal mill according to claim 4, characterized in that: When not subjected to external force, the lower end of the plugging layer (632) is in contact with the upper surface of the electromagnetic layer (631), and the upper end of the plugging layer (632) is not in contact with the top of the hollow ring (61).

6. The medium-speed coal mill according to claim 5, characterized in that: The number of the variable air vanes (63) is one less than the number of the air inlets (62), and during operation, the multiple variable air vanes (63) respectively cover and seal the lower ends of the multiple air inlets (62).

7. The medium-speed coal mill according to claim 5, characterized in that: The air inlets (62) are divided into multiple groups, and the multiple air inlets (62) in each group are arranged in a ring array around the central axis of the hollow ring body (61). The variable air vanes (63) are divided into multiple groups accordingly, and the number of variable air vanes (63) in each group is one less than the number of air inlets (62) in each group.

8. The medium-speed coal mill according to claim 5, characterized in that: The air distribution frame is equipped with an offset monitoring unit, which includes a laser rangefinder (73) installed on the top of one of the air distribution vanes (63), multiple flat-top conical holes (71) drilled in the top of the hollow ring (61), and multiple alignment top grooves (72) drilled in the middle of the top of the flat-top conical holes (71). The multiple flat-top conical holes (71) correspond to the middle of the multiple air inlets (62).

9. The medium-speed coal mill according to claim 8, characterized in that: The radial distance between the center of the laser rangefinder (73) and the center of the flat-top conical hole (71) and the inner wall of the primary air chamber (23) is the same. When the variable air plate (63) is facing the air inlet (62), the distance between the edge of the alignment top groove (72) and the inner top edge of the flat-top conical hole (71) is not greater than the distance difference between the edge of the upper surface of the variable air plate (63) and the edge of the air inlet (62).

Images