A non-destructive detector for the strength of lightweight aggregate concrete

Abstract

The application discloses a kind of light aggregate concrete strength nondestructive detector, belong to concrete strength detector field, including body, the inside sliding connection of the body has top rod, the left side of the body is provided with self-checking mechanism, the surface of the middle part of the body is provided with reading mechanism;Self-checking mechanism is used to measure the impact of top rod, whether the spring elasticity coefficient for measurement inside body is decreased, self-checking mechanism is resisted when measurement light aggregate concrete surface, the moving direction of top rod is kept perpendicular to light aggregate concrete.By using installation disc and light aggregate concrete surface is pasted, the angle between top rod and light aggregate concrete is ninety degrees, so that top rod will not be offset, by the detection of spring elasticity coefficient and make top rod hit light aggregate concrete, the angle between light aggregate concrete and top rod is ninety degrees, so that detection is more accurate, avoid the deviation between detection result and actual result, lead to building unqualified.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete strength detector, more particularly, to a light aggregate concrete strength nondestructive detector. BACKGROUND

[0002] It is known that the strength quality of concrete is related to the safety and service life of the overall building structure, therefore, it is particularly important to do well in the quality control, quality supervision and quality detection of concrete throughout the life cycle of the building. The rebound method is widely used in construction engineering because of its simple operation, convenience, economy, rapidness and considerable detection accuracy. The rebound energy (nominal energy (0.50J±0.1000J)) of the rebound detector during the rebound process of the rebound detector hitting the surface of the concrete is mainly composed of three parts: the energy absorbed by the plastic deformation of the concrete; the work of the elastic deformation of the concrete, the rebound rod and the rebound hammer; and the rebound energy, which measures the strength of the concrete by measuring the rebound energy.

[0003] A light aggregate concrete strength nondestructive detector is disclosed in Chinese Patent No. CN112881156B. By installing a protrusion on the outer side wall of the rebound hammer, when it is necessary to reset the position of the rebound hammer, only the protrusion needs to be moved upward, and the limiting rod needs to be pulled away from the center guide rod. When the position of the rebound hammer rises to a certain height, the fixed block is loosened to drive the limiting rod to limit the rebound hammer by the elastic potential energy of the limiting spring a. There is no need to press the rebound rod into the shell to reset the rebound hammer in the detector, and the adjustment mode is simple.

[0004] Although the above-mentioned patent solves the problem of complex structure of the strength nondestructive detector and the difficulty in resetting the rebound hammer, the strength nondestructive detector detects by rebounding the spring. The spring constant decreases due to time and the number of uses of the strength nondestructive detector, but it is difficult for the staff to judge, resulting in a deviation between the detection result and the actual result each time the strength nondestructive detector is used for detection, leading to unqualified buildings. SUMMARY

[0005] In view of the problems in the prior art, the purpose of the present application is to provide a light aggregate concrete strength nondestructive detector. By using the installation disc to adhere to the surface of the light aggregate concrete and the angle between the top rod and the light aggregate concrete being ninety degrees, the top rod will not be offset. By detecting the spring constant and making the angle between the light aggregate concrete and the top rod ninety degrees when the top rod hits the light aggregate concrete, the detection is more accurate, and deviation between the detection result and the actual result is avoided, leading to unqualified buildings.

[0006] To solve the above problems, the present application adopts the following technical solutions.

[0007] The utility model provides a kind of light aggregate concrete strength nondestructive detector, including body, the inside sliding connection of the body is top rod, the left side of the body is equipped with self-checking mechanism, the surface of the middle part of the body is equipped with reading mechanism;

[0008] Self-checking mechanism is used to measure the impact of top rod, to obtain whether the spring constant of spring inside the body for measurement is reduced, and self-checking mechanism is against the surface of light aggregate concrete when measuring, so that the moving direction of top rod remains perpendicular to light aggregate concrete;

[0009] The self-checking mechanism includes a first circular ring rotatably connected to the left side of the body, a first rotating rod fixedly connected to the top left side of the first circular ring, an installation disc provided on the left side of the first rotating rod, two fixed rods fixedly connected to the right side of the installation disc and having an included angle of 120° with respect to the line connecting the center of the installation disc and the first rotating rod, the body surface being welded to the side of the two fixed rods away from the installation disc, and a measuring disc rotatably connected to the inside of the installation disc.

[0010] The reading mechanism is used to measure the distance of rebound after the impact of top rod on the surface of light aggregate concrete, and the reading mechanism can more clearly see the reading.

[0011] The reading mechanism includes a reading disc slidingly connected to the middle part of the body, the reading disc being fixedly connected to the top rod, an installation groove being formed in the front side of the reading disc, and a convex lens fixedly connected to the inside of the installation groove.

[0012] Further, an arc-shaped tooth groove is fixedly connected to the bottom left side of the first rotating rod, the center of the installation disc is on the axis of the top rod, and a second extension block is fixedly connected to the inside top end of the installation disc.

[0013] Further, a gear is fixedly connected to the right top of the measuring disc and extends through the second extension block, the gear is engaged with the arc-shaped tooth groove, and a rotating groove is formed in the inside of the installation disc to accommodate the rotation of the measuring disc.

[0014] Further, a first sliding groove is formed in the inside bottom of the first circular ring, a first extension block is formed in the bottom of the body corresponding to the position of the first sliding groove, and a first spring is arranged in the inside of the first sliding groove and welded to the first extension block.

[0015] Further, an adjusting mechanism is arranged in the inside middle part of the body, the adjusting mechanism includes a fixed disc fixedly connected to the left side of the reading disc, a plurality of restriction rods arranged in a ring array are fixedly connected to the left side of the fixed disc, a first driving disc is slidingly connected to the left surface of the plurality of restriction rods, and a second driving disc is slidingly connected to the left inside surface of the plurality of restriction rods.

[0016] Further, the right side of the second driving disc is provided with a second measuring spring fixedly connected with the fixed disc, the right side of the first driving disc is provided with a first measuring spring fixedly welded with the fixed disc, and the elastic coefficients of the first measuring spring and the second measuring spring are different.

[0017] Further, a second rotating rod penetrating through the fixed disc and the reading disc in sequence and being rotationally connected with the reading disc is arranged at the gap between the first driving disc and the second driving disc, the left side of the second rotating rod is fixedly connected with an L-shaped block, and the cross-sectional shape of the L-shaped block is L-shaped.

[0018] Further, the left side of each of the plurality of limiting rods is fixedly connected with a baffle, and the outer surface and the inner surface of each of the plurality of limiting rods extend in opposite directions to form a protrusion, and the protrusion extends into the interior of the corresponding first driving disc and second driving disc.

[0019] Further, the left top of the reading disc is fixedly connected with a limiting plate, and the longitudinal cross-sectional shape of the limiting plate is fan-shaped.

[0020] Further, the top of the first annular ring is provided with two extension grooves, and the longitudinal cross-sectional shape of each of the two extension grooves is the same as that of the limiting plate.

[0021] Compared with the prior art, the beneficial effects of the present application are:

[0022] 1、The present application is characterized in that the mounting disc is attached to the surface of the lightweight aggregate concrete, the angle between the ejector rod and the lightweight aggregate concrete is ninety degrees, the ejector rod will not deviate, the elastic coefficient of the spring is detected, and when the ejector rod hits the lightweight aggregate concrete, the angle between the lightweight aggregate concrete and the ejector rod is ninety degrees, so that the detection is more accurate, and the deviation between the detection result and the actual result is avoided, so that the building is unqualified.

[0023] 2、The present application is characterized in that the first annular ring is rotated to drive the gear to rotate, and the measuring disc rotates around the gear, and the measuring disc is more convenient to move away from the inside of the mounting disc.

[0024] 3、The present application is characterized in that the first annular ring is rotated, the first extension block moves relatively in the first sliding groove at the same time, the first extension block extrudes the first spring while moving, and after the first annular ring is loosened, the first annular ring returns to the original position under the elastic potential energy of the first spring, so that the spring inside the body for measurement is conveniently detected.

[0025] 4、This scheme, can according to need to pull the corresponding first measuring spring and second measuring spring, and the elastic coefficient of first measuring spring and second measuring spring is different, can detect lightweight aggregate concrete and concrete, and also can be changed into first measuring spring with second measuring spring, when the elastic coefficient of one first measuring spring changes, another first measuring spring can be directly used to detect lightweight aggregate concrete, more convenient to use.

[0026] 5、This scheme through the restriction of the first drive disc by limiting rod, make the first drive disc move more convenient, and the surface of the limiting rod can make the movement more stable, and the baffle can be used to limit the first drive disc again, so that the detection can be reused, prevent the first drive disc from leaving the surface of the limiting rod.

[0027] 6、This scheme through pulling the reading disc, then rotating the first ring, the limiting plate can reach the inside of the other side of the extension slot, convenient to make the reading disc move more convenient copper wire, the limiting plate extends into the extension slot, and keeps the first ring fixed, and the limiting plate slides in the other extension slot again, so that the reading disc moves more stably, and the detection is more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is the structural schematic diagram of the strength nondestructive detector of the present application;

[0029] Figure 2 It is the structural schematic diagram of the self-checking mechanism of the present application;

[0030] Figure 3 It is the structural schematic diagram of the first ring of the present application;

[0031] Figure 4 It is the structural schematic diagram of the installation disc and the measuring disc of the present application;

[0032] Figure 5 It is the internal structure schematic diagram of the installation disc of the present application;

[0033] Figure 6 It is the structural schematic diagram of the installation disc of the present application;

[0034] Figure 7 It is the structural schematic diagram of the reading mechanism of the present application;

[0035] Figure 8 It is the structural schematic diagram of the adjusting mechanism of the present application;

[0036] Figure 9 It is the half cut view of the adjusting mechanism of the present application;

[0037] Figure 10 It is the internal structure schematic diagram of the adjusting mechanism of the present application.

[0038] Explanation of reference numerals in the drawings:

[0039] 1, body; 11, first extension block; 12, first spring; 2, self-checking mechanism; 21, first ring; 211, first sliding groove; 212, extension groove; 22, first rotating rod; 221, arc-shaped tooth groove; 23, fixed rod; 24, mounting disc; 241, rotating groove; 242, second extension block; 25, measuring disc; 251, gear; 3, reading mechanism; 31, reading disc; 311, mounting groove; 312, convex lens; 313, limiting plate; 4, top rod; 5, adjusting mechanism; 51, first driving disc; 52, limiting rod; 521, baffle; 53, second rotating rod; 531, L-shaped block; 54, first measuring spring; 55, second measuring spring; 56, fixed disc; 57, second driving disc. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0041] Embodiment 1

[0042] Please refer to Figures 1 to 7The utility model provides a kind of light aggregate concrete strength nondestructive detector, including body 1, the inside sliding connection of the body 1 is provided with top rod 4, the left side of the body 1 is provided with self-checking mechanism 2, the middle surface of the body 1 is provided with reading mechanism 3;Self-checking mechanism 2 is used to measure the impact of top rod 4, whether the elastic coefficient of spring inside the body 1 for measurement is reduced is obtained, self-checking mechanism 2 is against light aggregate concrete surface when measuring, so that the moving direction of top rod 4 remains perpendicular to light aggregate concrete;The self-checking mechanism 2 includes the first ring 21 that is rotatably connected to the left side of the body 1, the left side top of the first ring 21 is fixedly connected with the first rotating rod 22, the left side of the first rotating rod 22 is provided with mounting disc 24, the right side of the mounting disc 24 is fixedly connected with two fixed rods 23, and the included angle of the two fixed rods 23 relative to the fixed rod 22 center line of mounting disc 24 is 120 °, the side of the two fixed rods 23 away from mounting disc 24 is welded with the surface of the body 1, and the inside rotatably connected of the mounting disc 24 has measuring disc 25;Reading mechanism 3 is used to measure the distance of rebound after top rod 4 impacts light aggregate concrete surface, and reading mechanism 3 can more clearly see reading;The reading mechanism 3 includes reading disc 31 that is slidingly connected to the middle part of the body 1, the reading disc 31 is fixedly connected with top rod 4, the positive side of the reading disc 31 is provided with mounting groove 311, and the inside fixedly connected of the mounting groove 311 has convex lens 312.

[0043] By rotating measuring disc 25 before examination, the result of the strength detection of measuring disc 25 is known, so that measuring disc 25 blocks mounting disc 24, then the spring inside the body 1 is used to push top rod 4 to move, so that top rod 4 impacts measuring disc 25, after top rod 4 impacts measuring disc 25, rebound occurs, and during rebound, top rod 4 moves with reading disc 31, by the scale pointed to the surface of the body 1 when reading disc 31 moves and stops, by convex lens 312 inside reading disc 31 to interpret scale, the result of the strength detection of measuring disc 25 at this time is obtained, and by comparing the detection result of measuring disc 25 through the body 1 with the known detection result, whether the spring inside the body 1 can detect the strength of light aggregate concrete can be known, then rotating measuring disc 25 again, so that measuring disc 25 is separated from the inside of mounting disc 24, then mounting disc 24 is attached to light aggregate concrete surface, so that top rod 4 is separated from the inside of the body 1 and reaches light aggregate concrete surface, the included angle between top rod 4 and light aggregate concrete is ninety degrees, so that top rod 4 does not deviate, by detecting the elastic coefficient of spring and making the included angle between light aggregate concrete and top rod 4 ninety degrees when top rod 4 impacts light aggregate concrete, the detection is more accurate, and deviation between detection result and actual result is avoided, so that building is unqualified.

[0044] As Figures 1 to 7As shown, the first rotating rod 22 is fixedly connected with an arc-shaped tooth groove 221 at the bottom of the left side, the arc-shaped tooth groove 221 is on the axis of the top rod 4 at the center of the mounting disc 24, the inner top of the mounting disc 24 is fixedly connected with a second extension block 242, the right top of the measuring disc 25 extends through the second extension block 242 and is fixedly connected with a gear 251, the gear 251 is engaged with the arc-shaped tooth groove 221, and the inner part of the mounting disc 24 is provided with a rotating groove 241 for accommodating the rotation of the measuring disc 25.

[0045] By rotating the first circular ring 21, the first circular ring 21 rotates with the first rotating rod 22, the first rotating rod 22 rotates with the arc-shaped tooth groove 221, the arc-shaped tooth groove 221 is engaged with the gear 251, one side of the gear 251 extends through the second extension block 242 and is fixedly connected with the measuring disc 25, the measuring disc 25 is rotated by driving the gear 251 to rotate, and the measuring disc 25 rotates around the gear 251. It is more convenient for the measuring disc 25 to move away from the inside of the mounting disc 24.

[0046] As shown in the figure, Figures 1 to 7 The inner bottom of the first circular ring 21 is provided with a first sliding groove 211, the bottom of the body 1 is extended to form a first extension block 11 at the position corresponding to the first sliding groove 211, and the inner part of the first sliding groove 211 is provided with a first spring 12 welded with the first extension block 11.

[0047] By rotating the first circular ring 21, the first extension block 11 moves relatively in the inner part of the first sliding groove 211 while the first circular ring 21 rotates, and the first extension block 11 extrudes the first spring 12 while moving. After the first circular ring 21 is loosened, the first circular ring 21 returns to the original position under the elastic potential of the first spring 12, which is convenient for spring detection for measuring the inside of the body 1.

[0048] As shown in the figure, Figures 8 to 10As shown, the middle part of the interior of the body 1 is provided with an adjusting mechanism 5, the adjusting mechanism 5 comprises a fixed disc 56 fixedly connected with the left side of the reading disc 31, a plurality of limit rods 52 in annular array are fixedly connected to the left side of the fixed disc 56, a first driving disc 51 is slidably connected to the left side surface of the plurality of limit rods 52, a second driving disc 57 is slidably connected to the inner surface left side of the plurality of limit rods 52, a second measuring spring 55 fixedly connected with the fixed disc 56 is arranged on the right side of the second driving disc 57, a first measuring spring 54 fixedly welded with the fixed disc 56 is arranged on the right side of the first driving disc 51, the elastic coefficients of the first measuring spring 54 and the second measuring spring 55 are different, a second rotating rod 53 penetrating through the fixed disc 56 and the reading disc 31 in sequence and rotationally connected with the reading disc 31 is arranged at the gap between the first driving disc 51 and the second driving disc 57, an L-shaped block 531 is fixedly connected to the left side of the second rotating rod 53, and the cross-sectional shape of the L-shaped block 531 is L-shaped.

[0049] When other quality of concrete is to be measured, the second rotating rod 53 can be rotated, the second rotating rod 53 rotates with the L-shaped block 531, the L-shaped block 531 changes from abutting against the first driving disc 51 to abutting against the second driving disc 57, when the top rod 4 moves, the top rod 4 moves with the reading disc 31, the body 1 is fixedly connected with the fixed disc 56, the movement of the reading disc 31 moves with the L-shaped block 531, the movement of the L-shaped block 531 extrudes the second driving disc 57 to move, the second driving disc 57 extrudes the second measuring spring 55, the fixed disc 56 remains fixed, the rotation angle of the L-shaped block 531 can be changed to control extrusion of one of the first measuring spring 54 and the second measuring spring 55, the elastic coefficients of the first measuring spring 54 and the second measuring spring 55 are different, the light aggregate concrete and the concrete can be detected, and the second measuring spring 55 can be replaced by the first measuring spring 54, when the elastic coefficient of one of the first measuring spring 54 changes, the other first measuring spring 54 can be directly used to detect the light aggregate concrete, which is more convenient to use.

[0050] As shown in the figure, Figures 8 to 10 The left side of each of the plurality of limit rods 52 is fixedly connected with a baffle 521, and the outer surface and the inner surface of each of the plurality of limit rods 52 extend in opposite directions to form a protrusion, and the protrusion extends into the interior of the corresponding first driving disc 51 and second driving disc 57.

[0051] Through the first drive disc 51 moves on the surface of the limiting rod 52, the first drive disc 51 is limited by the limiting rod 52, so that the first drive disc 51 is more convenient to move, and the surface of the limiting rod 52 is provided with a convex part, so that the movement is more stable, and the baffle 521 can limit the first drive disc 51 again, so that the detection can be reused, and the first drive disc 51 is prevented from moving away from the surface of the limiting rod 52.

[0052] As shown in Figures 8 to 10 The left top of the reading disc 31 is fixedly connected with a limiting plate 313, the longitudinal section of the limiting plate 313 is a fan shape, and the top of the first ring 21 is provided with two extension grooves 212, and the longitudinal sections of the two extension grooves 212 are the same as the limiting plate 313.

[0053] By pulling the reading disc 31, the limiting plate 313 on one side of the reading disc 31 is separated from the extension groove 212, and then the first ring 21 is rotated to make the limiting plate 313 reach the inside of the extension groove 212 on the other side, so that the copper wire is convenient to move, the limiting plate 313 is kept fixed in the extension groove 212, and the limiting plate 313 is slid in the other extension groove 212 again, so that the reading disc 31 moves more stably, and the detection is more accurate.

[0054] The use method is that the reading disc 31 is pulled, then the first ring 21 is rotated, and finally the reading disc 31 is loosened, the reading disc 31 moves under the elasticity of the first measuring spring 54, the reading disc 31 hits the measuring disc 25 with the top rod 4, then the first measuring spring 54 is detected, then the mounting disc 24 is pressed against the lightweight aggregate concrete, the first ring 21 is rotated again, the measuring disc 25 is separated from the mounting disc 24, then the top rod 4 is used to detect the lightweight aggregate concrete, and the ordinary concrete is detected only by rotating the second rotating rod 53, so that when the reading disc 31 is pulled, the reading disc 31 moves with the L-shaped block 531, the L-shaped block 531 moves with the second drive disc 57, the second drive disc 57 is pressed against the second measuring spring 55, and the elastic potential energy of the second measuring spring 55 is used to detect the strength of the ordinary concrete.

[0055] The above is only the preferred specific embodiment of the present application; however, the protection scope of the present application is not limited to this. Any person skilled in the art can make equivalent replacement or change according to the technical scheme and the improvement concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A non-destructive testing device for lightweight aggregate concrete strength, comprising a body (1), a top rod (4) is slidably connected inside the body (1), characterized in that: The left side of the body (1) is provided with a self-checking mechanism (2), and the middle surface of the body (1) is provided with a reading mechanism (3); The self-checking mechanism (2) is used for measuring the impact of the ejector rod (4), and the spring elastic coefficient inside the body (1) for measurement is obtained whether it is decreased, and the self-checking mechanism (2) is abutted against the lightweight aggregate concrete surface during measurement, so that the moving direction of the ejector rod (4) is perpendicular to the lightweight aggregate concrete; The self-checking mechanism (2) comprises a first circular ring (21) rotatably connected to the left side of the body (1), a first rotating rod (22) fixedly connected to the left top of the first circular ring (21), an installation disc (24) arranged on the left side of the first rotating rod (22), two fixed rods (23) fixedly connected to the right side of the installation disc (24) and having an included angle of 120° with the center line of the installation disc (24), the two fixed rods (23) being welded to the surface of the body (1) away from the installation disc (24), and a measuring disc (25) rotatably connected to the inside of the installation disc (24). The reading mechanism (3) is used for measuring the rebound distance of the lightweight aggregate concrete surface after the impact of the ejector rod (4). The reading mechanism (3) comprises a reading disc (31) slidably connected to the middle part of the body (1), the reading disc (31) is fixedly connected with the ejector rod (4), and an installation groove (311) is formed in the front side of the reading disc (31). The inside of the body (1) is provided with an adjusting mechanism (5), the adjusting mechanism (5) comprises a fixed disc (56) fixedly connected to the left side of the reading disc (31), a plurality of limiting rods (52) arranged in an annular array and fixedly connected to the left side of the fixed disc (56), a first driving disc (51) slidably connected to the left surface of the plurality of limiting rods (52), and a second driving disc (57) slidably connected to the left inner surface of the plurality of limiting rods (52). The right side of the second driving disc (57) is provided with a second measuring spring (55) fixedly connected with the fixed disc (56), the right side of the first driving disc (51) is provided with a first measuring spring (54) fixedly welded with the fixed disc (56), and the elastic coefficients of the first measuring spring (54) and the second measuring spring (55) are different. A second rotating rod (53) penetrating through the fixed disc (56) and the reading disc (31) in sequence and rotatably connected with the reading disc (31) is arranged at the gap between the first driving disc (51) and the second driving disc (57), the left side of the second rotating rod (53) is fixedly connected with an L-shaped block (531), and the cross-sectional shape of the L-shaped block (531) is L-shaped.

2. The non-destructive strength detector for lightweight aggregate concrete according to claim 1, characterized in that: The left bottom of the first rotating rod (22) is fixedly connected with an arc-shaped tooth groove (221), the center of the arc-shaped tooth groove (221) and the center of the installation disc (24) are on the axis of the ejector rod (4), and the inside top of the installation disc (24) is fixedly connected with a second extension block (242).

3. A non-destructive strength detector for lightweight aggregate concrete according to claim 2, characterized in that: The right top of the measuring disc (25) extends through the second extension block (242) and is fixedly connected with a gear (251), the gear (251) is engaged with the arc-shaped tooth groove (221), the inside of the mounting disc (24) is provided with a rotating groove (241) for accommodating the rotation of the measuring disc (25).

4. The non-destructive strength detector for lightweight aggregate concrete according to claim 1, characterized in that: The inside bottom of the first circular ring (21) is provided with a first sliding groove (211), the bottom of the body (1) is extended to form a first extension block (11) corresponding to the position of the first sliding groove (211), and the inside of the first sliding groove (211) is provided with a first spring (12) welded with the first extension block (11).

5. The non-destructive strength detector for lightweight aggregate concrete according to claim 1, characterized in that: The left side of each of the plurality of limiting rods (52) is fixedly connected with a baffle (521), and the outer surface and the inner surface of each of the plurality of limiting rods (52) are extended to form protrusions which extend into the interiors of the corresponding first driving disc (51) and the second driving disc (57).

6. The non-destructive strength detector for lightweight aggregate concrete according to claim 1, characterized in that: The left top of the reading disc (31) is fixedly connected with a limiting plate (313), and the longitudinal section of the limiting plate (313) is fan-shaped.

7. A non-destructive strength detector for lightweight aggregate concrete according to claim 6, characterized in that: The top of the first circular ring (21) is provided with two extension grooves (212), and the longitudinal sections of the two extension grooves (212) are all same as the limiting plate (313).

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