Split type heat treatment furnace plate for oriented silicon steel and bell-type furnace

Abstract

The utility model discloses a split type heat treatment furnace plate of oriented silicon steel, which comprises an annular furnace plate, a circulating through hole is arranged on the annular furnace plate, an air inlet flow channel is distributed on the annular furnace plate along the circumferential direction of the annular furnace plate, and the air inlet end and the air outlet end of the air inlet flow channel respectively extend to the circumferential outer edge and the circumferential inner wall of the annular furnace plate. The air inlet flow channel comprises a vent groove formed in the bearing surface of the annular furnace plate; the annular furnace plate comprises a plurality of fan-shaped plates which are sequentially and detachably connected end to end in the circumferential direction of the annular furnace plate, a circulating through hole is defined by the multiple fan-shaped plates, and the air inlet flow channel is defined by every two adjacent fan-shaped plates. The utility model further discloses a bell-type furnace of the oriented silicon steel. According to the split type heat treatment furnace plate for oriented silicon steel and the bell-type furnace, the annular furnace plate is of a split type structure and is formed by detachably connecting the multiple fan-shaped plates end to end in sequence in the circumferential direction, the air inlet flow channel is defined by every two adjacent fan-shaped plates, impurities in the air inlet flow channels can be conveniently cleaned, and the maintenance and replacement cost is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of silicon steel heat treatment equipment, in particular to a split heat treatment furnace plate and a bell-type furnace for oriented silicon steel. Background Art

[0002] High temperature annealing is a key process that determines the surface quality of oriented silicon steel. The high temperature annealing process of oriented silicon steel is mainly completed in a trolley annealing furnace or a bell annealing furnace.

[0003] The silicon steel coil obtained by the bell-type furnace heat treatment has a local watermark on the side that contacts the furnace plate. The reason is that the silicon steel coil is pressed on the surface of the furnace plate due to its own weight, and there is almost no air circulation between the two, which causes water vapor to be retained in the silicon steel coil and even causes problems such as crystal dew.

[0004] Based on the above phenomenon, a Chinese utility model patent with announcement number CN215757530U discloses a heat treatment furnace plate for thin strip oriented electrical steel. The heat treatment furnace plate for thin strip oriented electrical steel is further provided with air inlet holes on the basis of vent grooves. By introducing air flow into the air inlet holes, the air intake of the vent grooves is increased, which helps to timely discharge water vapor at the side of the silicon steel coil and the furnace plate being crimped, and further improves the heat treatment quality of the silicon steel in the coil.

[0005] However, the above-mentioned heat treatment furnace plate is an integrated structure, and the cross-section of the air inlet holes on the furnace plate is small. When impurities accumulate in the air inlet holes, they are easily blocked, resulting in the air inlet holes being unable to pass the protective gas, affecting the heat treatment effect of the silicon steel, and the impurities blocked in the air inlet holes are not easy to clean, and usually the entire heat treatment furnace plate needs to be replaced, which leads to an increase in the replacement and maintenance costs of the heat treatment furnace plate; in addition, due to the thin thickness of the silicon steel sheet, the silicon steel sheet is in a softened state during high-temperature treatment, the notch and groove depth of the ventilation groove are 2-5mm, and the gas entering the silicon steel coil through the ventilation groove in the hood furnace is limited, affecting the heat treatment quality of the silicon steel in the coil.

[0006] Therefore, it is necessary to improve the heat treatment furnace plate and bell-type furnace in the prior art. Utility Model Content

[0007] The purpose of the utility model is to overcome the defects in the prior art and provide a split heat treatment furnace plate and bell-type furnace for oriented silicon steel which are easy to clean, reduce maintenance and replacement costs and improve heat treatment quality.

[0008] In order to solve the above technical problems, the utility model provides a split heat treatment furnace plate for oriented silicon steel, comprising an annular furnace plate, on which a circulation through hole coaxial with the annular furnace plate is arranged, and the annular furnace plate is provided with an inlet flow channel distributed along its circumference, and the inlet end and the outlet end of the inlet flow channel extend to the circumferential outer edge and the circumferential inner wall of the annular furnace plate respectively, and the inlet flow channel comprises a ventilation groove arranged on the bearing surface of the annular furnace plate;

[0009] The annular furnace plate comprises a plurality of sector plates which are detachably connected in sequence along the circumference of the annular furnace plate. The plurality of sector plates are enclosed to form a circulation through hole. The inlet air channel is formed by enclosing two adjacent sector plates.

[0010] Preferably, in order to facilitate assembly, the structural dimensions of each sector plate are the same.

[0011] Preferably, in order to facilitate connecting and combining multiple fan-shaped plates in sequence to form an annular furnace plate, the annular furnace plate also includes a concentric ring that is sleeved outside the fan-shaped plate and is coaxial with itself, and the circumferential inner wall of the concentric ring is sealed to the fan-shaped plate.

[0012] Preferably, in order to strengthen the connection between the concentric ring and the sector plate, the concentric ring and the sector plate are connected by fasteners.

[0013] Preferably, in order to facilitate fixing the furnace plate on the furnace platform, the fastener is a fastening bolt that passes through the fan-shaped plate, and the axis of the fastening bolt is parallel to the axial direction of the annular furnace plate.

[0014] Preferably, in order to increase ventilation volume and improve heat treatment quality of silicon steel coil, the space inside the ventilation groove includes a first space and a second space adjacent to the groove opening and the groove bottom respectively, and the width of the first space is smaller than that of the second space.

[0015] Preferably, in order to facilitate assembly, air intake recesses are provided on both sides of the fan-shaped plate, and the air intake recesses facing each other of two adjacent fan-shaped plates are combined to form the air intake flow channel.

[0016] Preferably, in order to increase the gas flow through the ventilation groove, the air inlet recess includes a first groove, a second groove and a third groove which are connected in sequence, and the ends of the first groove and the third groove which are away from each other extend to the inner wall and the outer wall of the fan plate respectively, and the first grooves facing each other of two adjacent fan plates are combined to form a ventilation groove.

[0017] In order to solve the above technical problems, the utility model also discloses a bell-type furnace for oriented silicon steel, comprising:

[0018] A furnace platform, wherein the furnace platform is provided with a central through hole extending in a vertical direction and an air guide channel communicating with the central through hole;

[0019] A heating element, wherein the heating element is fixed in the air guide channel;

[0020] A furnace cover, the furnace cover is arranged on the furnace platform and encloses the furnace platform to form a furnace cavity;

[0021] A sand sealing layer, wherein the sand sealing layer is arranged between the furnace cover and the furnace platform;

[0022] The annular furnace plate described in any one of the above technical solutions, wherein the annular furnace plate is coaxially sleeved on the furnace platform;

[0023] An air inlet pipe is passed through the central through hole and the inner side of the annular furnace plate and is communicated with the furnace cavity.

[0024] Preferably, in order to make full use of the protective gas, the air inlet pipe includes a sealing section and a gap section which are connected in sequence along its own axial direction. The sealing section is located below the air guide channel and is sealed and connected to the circumferential inner wall of the central through hole. There is a ventilation gap between the gap section and the circumferential inner wall of the central through hole and the circumferential inner wall of the circulation through hole.

[0025] In summary, compared with the prior art, the split heat treatment furnace plate and hood-type furnace for oriented silicon steel of the utility model adopt a split structure in which the annular furnace plate is formed by a plurality of fan-shaped plates that are detachably connected end to end in sequence along the circumferential direction, and an inlet air flow passage is formed by two adjacent fan-shaped plates, which facilitates the cleaning of impurities in the inlet air flow passage and reduces the cost of maintenance and replacement. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 2 is a schematic structural diagram of a split heat treatment furnace plate according to the first embodiment;

[0027] Figure 2 yes Figure 1 Explosion diagram of

[0028] Figure 3 yes Figure 1 A top view of

[0029] Figure 4 yes Figure 3 AA section view;

[0030] Figure 5 is a schematic structural diagram of a sector plate of the first embodiment;

[0031] Figure 6 2 is a schematic structural diagram of a split heat treatment furnace plate according to a second embodiment;

[0032] Figure 7 yes Figure 6 Explosion diagram of

[0033] Figure 8 is a schematic structural diagram of a bell-type furnace according to a third embodiment;

[0034] Fig. 9 yes Figure 8 Explosion diagram of

[0035] Fig.10 is an exploded schematic diagram of a furnace in the third embodiment;

[0036] Fig.11 yes Figure 8 A schematic diagram of the cross-sectional structure of;

[0037] In the figure: 1, annular furnace plate; 11, circulation through hole; 12, inlet air channel; 121, ventilation groove; 2, fan-shaped plate; 21, air intake recess; 211, first groove; 212, second groove; 213, third groove; 3, concentric ring; 31, fastening bolt; 4, furnace table; 41, central through hole; 42, air guide channel; 43, upper platform; 44, lower platform; 5, heating element; 6, furnace hood; 7, sand sealing layer; 8, air intake pipe; 81, sealing section; 82, gap section; 9, silicon steel workpiece. DETAILED DESCRIPTION

[0038] The following is a further description of the specific implementation of the present invention in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0039] First embodiment

[0040] like Figure 1-Figure 5 As shown, the split heat treatment furnace plate of oriented silicon steel in the first embodiment of the utility model comprises an annular furnace plate 1, on which a circulation through hole 11 coaxial with the annular furnace plate 1 is arranged, and an inlet flow channel 12 is distributed along the circumference of the annular furnace plate 1, and the air inlet end and the air outlet end of the inlet flow channel 12 extend to the circumferential outer edge and the circumferential inner wall of the annular furnace plate 1 respectively, and the inlet flow channel 12 comprises a ventilation groove 121 arranged on the bearing surface of the annular furnace plate 1; the annular furnace plate 1 comprises a plurality of fan-shaped plates 2 which are detachably connected in sequence head to tail along the circumference of the annular furnace plate 1, and the plurality of fan-shaped plates 2 enclose the circulation through hole 11, and the inlet flow channel 12 is formed by enclosing two adjacent fan-shaped plates 2.

[0041] Compared with the prior art, the annular furnace plate 1 of the present embodiment adopts a split structure, which is formed by connecting a plurality of fan-shaped plates 2 end to end in sequence along the circumferential direction, and two adjacent fan-shaped plates 2 enclose to form an inlet air flow channel 12. Specifically, there are a total of six fan-shaped plates 2 in the present embodiment, which enclose to form six inlet air flow channels 12. Of course, the number of fan-shaped plates 2 can also be another plurality, and the number of inlet air flow channels 12 on the annular furnace plate 1 formed after being connected in sequence is consistent with the number of fan-shaped plates 2.

[0042] Since the fan-shaped plates 2 are detachably connected, the fan-shaped plates 2 can be separated after the inlet air duct 12 is blocked, thereby facilitating the cleaning of impurities blocked in the inlet air duct 12. Moreover, when part of the fan-shaped plates 2 is damaged, the damaged part can be replaced and then spliced ​​with other fan-shaped plates 2 without replacing the entire furnace plate, thereby reducing the maintenance and replacement costs.

[0043] On the annular furnace plate 1, the air inlet end of the air inlet duct 12 extends to the circumferential outer edge of the annular furnace plate 1, and the air outlet end extends to the circumferential inner wall of the annular furnace plate 1 and is formed at one end of the ventilation groove 121. Therefore, during heat treatment, the protective gas can be introduced from the air inlet end and then enter the ventilation groove 121. In the process of flowing along the ventilation groove 121, the water vapor at the bottom of the silicon steel workpiece 9 is entrained, which facilitates the timely discharge of the water vapor to improve the heat treatment quality of the silicon steel workpiece 9.

[0044] A further improvement is that the structural dimensions of each sector plate 2 are the same.

[0045] After adopting the above design, the annular furnace plate 1 is convenient to assemble and splice. When splicing, there is no need to install in a specific order. The fan-shaped plates 2 can be connected in sequence to form an annular furnace plate 1. At the same time, it is convenient for maintenance and replacement. When any fan-shaped plate 2 is damaged, since the structural dimensions of the fan-shaped plates 2 are the same, only the fan-shaped plates 2 of a single structural dimension need to be prepared, and only the damaged part needs to be replaced.

[0046] A further improvement is that air intake recesses 21 are provided on both sides of the fan-shaped plate 2, and the air intake recesses 21 facing each other of two adjacent fan-shaped plates 2 are combined to form an intake flow channel 12; specifically, the air intake recess 21 includes a first groove 211, a second groove 212 and a third groove 213 which are connected in sequence, and the ends of the first groove 211 and the third groove 213 which are away from each other extend to the inner wall and the outer wall of the fan-shaped plate 2 respectively, and the first grooves 211 facing each other of two adjacent fan-shaped plates 2 are combined to form a ventilation groove 121.

[0047] Through the above design, the structures on both sides of the fan-shaped plate 2 are the same. When two adjacent fan-shaped plates 2 are spliced, the two fan-shaped plates 2 have two mating surfaces that are sealed and fitted with each other, and the air inlet recess 21 is arranged on the mating surface. The two air inlet recesses 21 are arranged opposite to each other, and the combination forms an inlet flow channel 12, which is convenient for the assembly and splicing of the annular furnace plate 1; in the air inlet recess 21, the third groove 213 is arranged on the outer wall of the fan-shaped plate 2, and two second grooves 212 are arranged. The cross-sectional area of ​​the third groove 213 is greater than the sum of the cross-sectional areas of the two second grooves 212. By increasing the number of the second grooves 212, the flow rate of the protective gas passing through the inlet flow channel 12 is increased, and by using the third groove 213, it is convenient to introduce more protective gas into the second groove 212, so that more protective gas passes through the first groove 211, that is, through the ventilation groove 121, and then the water vapor between the annular furnace plate 1 and the silicon steel workpiece 9 is discharged, which is beneficial to improve the annealing quality of the silicon steel workpiece 9.

[0048] A further improvement is that the space inside the vent groove 121 includes a first space and a second space respectively adjacent to the groove opening and the groove bottom thereof, and the width of the first space is smaller than the width of the second space.

[0049] Specifically, the cross-sectional shape of the space inside the ventilation groove 121 is an inverted T-shape. This structural design reduces the slot size of the ventilation groove 121, which is beneficial to increasing the bearing area of ​​the annular furnace plate 1 and avoiding the slot being too wide. Under high-temperature annealing, the softening of the silicon steel workpiece 9 affects the molding quality. In this way, the support area of ​​the annular furnace plate 1 is guaranteed, and the width of the part close to the bottom of the ventilation groove 121 is increased, so as to facilitate the introduction of more protective gas to take away water vapor and improve the heat treatment quality of the silicon steel workpiece 9.

[0050] Of course, the structure of the ventilation groove 121 can also be in other forms. For example, the cross-section of the ventilation groove 121 is L-shaped, an isosceles trapezoid, or the ventilation groove 121 is a dovetail groove. The above technical effect can be achieved by simply ensuring that the first space width near the groove mouth is smaller than the second space width near the groove bottom.

[0051] A further improvement is that the annular furnace plate 1 further comprises a concentric ring 3 which is sleeved outside the sector plate 2 and is coaxial with the annular furnace plate 1 , and the circumferential inner wall of the concentric ring 3 is sealedly connected to the sector plate 2 .

[0052] The above design makes it convenient to splice each fan-shaped plate 2 in sequence, and then connect multiple fan-shaped plates 2 using concentric rings 3 to prevent radial displacement of the fan-shaped plates 2, ensuring that all fan-shaped plates 2 are enclosed to form a circulation through hole 11, while the intake recesses 21 facing two adjacent fan-shaped plates 2 form an intake flow channel 12.

[0053] Specifically, the concentric ring 3 is connected to the sector plate 2 by a fastener. Specifically, the fastener is a fastening bolt 31, which is arranged between two adjacent sector plates 2 and is threadedly connected to the concentric ring 3. The fastening bolt 31 facilitates fixing the sector plate 2 to the inner side of the concentric ring 3 to prevent the sector plate 2 from rotating about the axis of the concentric ring 3.

[0054] Second embodiment

[0055] like Figure 6 and Figure 7 As shown, the split heat treatment furnace plate for oriented silicon steel of the second embodiment of the utility model is based on the first embodiment, with the difference that the fastener is a fastening bolt 31 penetrating the fan-shaped plate 2, and the axial center line of the fastening bolt 31 is parallel to the axial direction of the annular furnace plate 1.

[0056] By changing the axial angle of the fastening bolt 31, the fastening bolt 31 is axially parallel to the axial direction of the annular furnace plate 1, and the fastening bolt 31 passes through the fan-shaped plate 2, so that the concentric ring 3 and the fan-shaped plate 2 are fastened and connected, and the annular furnace plate 1 is fixed on the furnace table 4.

[0057] A further improvement is that an arc-shaped recess is provided on the outer side of the top surface of the sector plate 2, and the arc-shaped recesses of each sector plate 2 are connected end to end in sequence to form an annular recess that matches the concentric ring 3. In this way, the flatness of the surface of the annular furnace plate 1 is ensured, and it is convenient to fix the annular furnace plate 1 and the sector plate 2 with the tightening bolts 31.

[0058] Third embodiment

[0059] like Figure 8-Figure 11 As shown, the bell-type furnace for grain-oriented silicon steel of the third embodiment of the utility model comprises:

[0060] A furnace table 4, on which a central through hole 41 extending in a vertical direction and an air guide passage 42 communicating with the central through hole 41 are provided;

[0061] A heating element 5, the heating element 5 is fixed in the air guide channel 42;

[0062] A furnace cover 6, which is disposed on the furnace platform 4 and encloses the furnace platform 4 to form a furnace cavity;

[0063] A sand sealing layer 7, wherein the sand sealing layer 7 is arranged between the furnace cover 6 and the furnace platform 4;

[0064] The annular furnace plate 1 of the second embodiment is coaxially sleeved on the furnace table 4;

[0065] The air inlet pipe 8 is passed through the central through hole 41 and the inner side of the annular furnace plate 1 and is communicated with the furnace chamber.

[0066] Furthermore, the air intake pipe 8 includes a sealing section 81 and a gap section 82 which are connected in sequence along its own axial direction. The sealing section 81 is located below the air guide channel 42 and is sealed and connected to the circumferential inner wall of the central through hole 41. There is a ventilation gap between the gap section 82 and the circumferential inner wall of the central through hole 41 and the circumferential inner wall of the circulation through hole 11.

[0067] The furnace table 4 of this embodiment is a stepped structure, and the sand sealing layer 7 covers the top surface, the circumferential outer edge and the lower part of the circumferential outer edge of the lower layer. The sand sealing layer 7 is provided with a slot coaxial with the centerline thereof for the bottom of the furnace cover 6 to be inserted; the furnace table 4 includes a lower table 44 and an upper table 43 coaxially arranged directly above the lower table 44, the upper table 43 and the lower table 44 enclose an air guide channel 42, the heating element 5 is fixed between the upper table 43 and the lower table 44 and is located in the air guide channel 42; the silicon steel workpiece 9 is coaxially placed on the annular furnace plate 1.

[0068] The protective gas is introduced into the furnace chamber through the air inlet pipe 8, and the heating element 5 is started to heat the silicon steel workpiece 9. After the protective gas is introduced from the inner side of the silicon steel workpiece 9, it flows upward to the top of the silicon steel workpiece 9, diffuses to the outside, and then flows downward. A part of it is introduced from the air inlet end of the air inlet channel 12 of the annular furnace plate 1, and the water vapor on the bottom of the silicon steel workpiece 9 is taken away through the air inlet channel 12. A part of it is introduced from the air guide channel 42 and enters the central through hole 41. The two parts of the protective gas merge on the inner side of the silicon steel workpiece 9 and then flow upward. In this cycle, the silicon steel workpiece 9 is heat treated. The circulating hot gas discharges the water vapor to the outside through the sand seal layer 7.

[0069] Since the annular furnace plate 1 of the present embodiment adopts a connection structure in which multiple fan-shaped plates 2 are detachable in sequence head to tail, and two adjacent fan-shaped plates 2 are enclosed to form an inlet air flow channel 12, it is convenient to maintain the annular furnace plate 1. Impurities between the fan-shaped plates 2 can be cleaned only by separating the fan-shaped plates 2. When some fan-shaped plates 2 are damaged, only the damaged fan-shaped plates 2 need to be replaced, thereby reducing the maintenance and replacement costs. Moreover, since the ventilation groove 121 is an inverted T-shaped groove, the protective gas flow rate in the ventilation groove 121 is increased, which is beneficial to improving the heat treatment effect of the silicon steel workpiece 9.

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principle of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A split heat treatment furnace plate for grain-oriented silicon steel, comprising an annular furnace plate (1), wherein the annular furnace plate (1) is provided with a circulation through hole (11) coaxial with the annular furnace plate itself, wherein the annular furnace plate (1) is provided with an inlet flow channel (12) distributed along its circumference, wherein the inlet end and the outlet end of the inlet flow channel (12) extend to the circumferential outer edge and the circumferential inner wall of the annular furnace plate (1) respectively, and the inlet flow channel (12) comprises a ventilation groove (121) provided on the bearing surface of the annular furnace plate (1), characterized in that: The annular furnace plate (1) comprises a plurality of sector plates (2) which are detachably connected in sequence along the circumference of the annular furnace plate, the plurality of sector plates (2) enclosing a circulation through hole (11), and the inlet flow channel (12) is formed by enclosing two adjacent sector plates (2).

2. The split heat treatment furnace plate for oriented silicon steel according to claim 1, characterized in that: The structural dimensions of each sector plate (2) are the same.

3. The split heat treatment furnace plate for oriented silicon steel according to claim 1, characterized in that: The annular furnace plate (1) further comprises a concentric ring (3) which is sleeved outside the sector plate (2) and is coaxial with the concentric ring itself, and the circumferential inner wall of the concentric ring (3) is sealedly connected to the sector plate (2).

4. The split heat treatment furnace plate for oriented silicon steel according to claim 3, characterized in that: The concentric ring (3) and the sector plate (2) are connected via fasteners.

5. The split heat treatment furnace plate for oriented silicon steel according to claim 4, characterized in that: The fastener is a fastening bolt (31) that passes through the sector plate (2), and the axis of the fastening bolt (31) is parallel to the axial direction of the annular furnace plate (1).

6. The split heat treatment furnace plate for oriented silicon steel according to claim 1, characterized in that: The space inside the vent groove (121) comprises a first space and a second space respectively adjacent to the groove opening and the groove bottom thereof, and the width of the first space is smaller than the width of the second space.

7. The split heat treatment furnace plate for oriented silicon steel according to claim 1, characterized in that: Air intake recesses (21) are provided on both sides of the sector plate (2), and the air intake recesses (21) facing each other of two adjacent sector plates (2) are combined to form the air intake flow channel (12).

8. The split heat treatment furnace plate for oriented silicon steel according to claim 7, characterized in that: The air intake recess (21) comprises a first groove (211), a second groove (212) and a third groove (213) which are connected in sequence, and the ends of the first groove (211) and the third groove (213) which are away from each other extend to the inner wall and the outer wall of the fan-shaped plate (2) respectively, and the first grooves (211) facing two adjacent fan-shaped plates (2) are combined to form a ventilation groove (121).

9. A bell-type furnace for producing oriented silicon steel, characterized in that: include: A furnace table (4), wherein the furnace table (4) is provided with a central through hole (41) extending in a vertical direction and an air guide passage (42) communicating with the central through hole (41); A heating element (5), wherein the heating element (5) is fixed in the air guide channel (42); A furnace cover (6), the furnace cover (6) being arranged on the furnace platform (4) and enclosing the furnace platform (4) to form a furnace cavity; A sand sealing layer (7), wherein the sand sealing layer (7) is arranged between the furnace cover (6) and the furnace platform (4); The annular furnace plate (1) according to any one of claims 1 to 8, wherein the annular furnace plate (1) is coaxially sleeved on the furnace platform (4); An air intake pipe (8), the air intake pipe (8) is arranged through the central through hole (41) and the inner side of the annular furnace plate (1) and is communicated with the furnace chamber.

10. The bell-type furnace for producing oriented silicon steel according to claim 9, characterized in that: The air intake pipe (8) comprises a sealing section (81) and a gap section (82) which are connected in sequence along its own axial direction; the sealing section (81) is located below the air guide channel (42) and is sealed to the circumferential inner wall of the central through hole (41); and there is a ventilation gap between the gap section (82) and the circumferential inner wall of the central through hole (41) and the circumferential inner wall of the circulation through hole (11).

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