Dovetail type connection sleeve for standard section of crane

Abstract

The present invention provides a dovetail type connecting sleeve for a standard section of a crane, the back of the connecting sleeve forms a chord holding surface for holding the main chord of the standard section, the chord holding surface extends from the first end of the connecting sleeve to the second end and is recessed inward, and the orthographic projection of the chord holding surface includes a first straight section, an arc section and a second straight section connected in sequence. The dovetail type connecting sleeve in the present invention adopts an arc section + two straight sections to form the chord holding surface, which increases the chord holding area, facilitates welding and positioning, and improves the fatigue life of the weld. At the same time, the connection strength of this scheme is better. In addition, the connecting sleeve includes a connecting portion and a dovetail portion arranged at the outer edge of the end of the connecting portion, the front of the dovetail portion is a gradient portion formed by connecting a plurality of gradient surfaces in sequence, the gradient portion is connected to the connecting portion in an arc transition, which can avoid stress concentration and is easy to manufacture, and the gradient portion and the connecting portion adopt an arc transition, so that the stress transfer is more uniform.

Description

Technical Field

[0001] The invention belongs to the field of tower crane standard accessories, and in particular relates to a dovetail type connecting sleeve of a crane standard section. Background Art

[0002] The standard section of a tower crane is an important component of a tower crane. A good standard section can not only improve the stability of the entire tower crane, but also improve the fatigue durability of the entire machine. Therefore, it occupies a very important position in the entire tower crane. Similarly, the standard section connecting sleeve also occupies a very important position in the entire tower crane, which can ensure the stable connection between standard sections and improve the stability of the tower crane.

[0003] When the existing standard section connecting sleeve is in use, it is affected by the deadweight of the whole tower crane and the lifting operation, and the connecting sleeve will be subjected to a tension and compression cycle load. Therefore, in the prior art, a dovetail structure is added to the connecting sleeve to reduce stress concentration and increase the overall fatigue life of the connecting sleeve. However, the traditional tower crane dovetail type connecting sleeve has a small chord surface, a large sleeve height, a small dovetail height, and a long length of connecting bolts, and the fatigue life of the weld between it and the standard section is low. Summary of the invention

[0004] In view of the above-mentioned defects or shortcomings of the prior art, the present invention provides a dovetail type connecting sleeve for a standard section of a crane, which increases the chord area and improves the fatigue life of the weld.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a dovetail type connecting sleeve of a standard section of a crane, the back side of the connecting sleeve forms a chord-holding surface for holding the main chord of the standard section, the connecting sleeve comprises a connecting portion and a dovetail portion arranged at the outer edge of the end of the connecting portion, the front side of the dovetail portion is a gradient portion formed by connecting a plurality of gradient surfaces in sequence, and the gradient portion is connected to the connecting portion in an arc-shaped transition.

[0006] In an embodiment of the present invention, the string-embracing surface extends from the first end to the second end of the connecting sleeve and is recessed inwardly, and the orthographic projection of the string-embracing surface includes a first straight segment, an arc segment, and a second straight segment connected in sequence.

[0007] In the embodiment of the present invention, the extension line of the first straight segment is perpendicular to the extension line of the second straight segment, the intersection of the extension line of the first straight segment and the extension line of the second straight segment is the center point, the distance from the end of the first straight segment away from the arc segment to the center point is L1, and the distance from the end of the second straight segment away from the arc segment to the center point is L2;

[0008] Among them, L1 is equal to L2, and both L1 and L2 are 1 / 4 to 1 / 2 of the cross-sectional length of the main chord.

[0009] In an embodiment of the present invention, concave arc surfaces are formed on both sides of the connecting sleeve, and the edge line of the concave arc surface is tangent to the edge line of the chord-embracing surface.

[0010] In an embodiment of the present invention, the gradient portion includes a first gradient portion and second gradient portions located on both sides of the first gradient portion, and the first gradient portion and the two second gradient portions are arranged side by side;

[0011] Among them, the first gradient portion includes a first gradient surface, a second gradient surface and a third gradient surface connected in sequence from top to bottom, the first gradient surface and the second gradient surface are both inclined surfaces, the third gradient surface is an arc-shaped concave surface, and the height ratio of the first gradient surface, the second gradient surface and the third gradient surface ranges from 1:2:2 to 1:2:3.

[0012] In an embodiment of the present invention, the connection angle between any two adjacent gradual change surfaces in the second gradual change portion increases first and then decreases from top to bottom, and each gradual change surface in the second gradual change portion is inclined.

[0013] In an embodiment of the present invention, the connecting portion includes a sleeve body and an extension body extending from the outer side of the sleeve body, the dovetail portion is located above the extension body, and both sides of the extension body and the dovetail portion form an integral concave arc surface, and the two ends of the concave arc surface are respectively tangent to the edge line of the chord-holding surface and the edge line of the sleeve body.

[0014] In an embodiment of the present invention, a through connection hole is provided on the sleeve body, and the connection hole is provided along the height direction of the sleeve body.

[0015] In an embodiment of the present invention, the ratio of the height of the connecting portion to the height of the dovetail portion is 11:12.

[0016] In an embodiment of the present invention, the connecting portion and the dovetail portion are integrally formed.

[0017] Through the above technical solution, the crane standard section dovetail type connecting sleeve provided by the embodiment of the present invention has the following beneficial effects:

[0018] A chord-holding surface for holding the main chord is formed on the back of the connecting sleeve, and the chord-holding surface can hold along the outer periphery of the main chord. The chord-holding surface with this structure can increase the chord-holding area between the connecting sleeve and the main chord. When the chord-holding area between the connecting sleeve and the main chord is larger, the stress borne by the chord-holding surface will be more dispersed, and the welding between the connecting sleeve and the main chord will be easier and stronger, thereby improving the fatigue life of the weld. Since the back of the dovetail is a plane, stress concentration is likely to occur when the connecting sleeve holds the main chord. Therefore, the front side of the dovetail is set as a gradient portion composed of multiple gradient surfaces, so that the front side of the dovetail forms a gradient inclined surface structure. The dovetail with this gradient structure eliminates the stress concentration phenomenon in this area.

[0019] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide an understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 is a schematic structural diagram of a connecting sleeve according to an embodiment of the present invention;

[0022] Figure 2 is a schematic top view of a connecting sleeve according to an embodiment of the present invention;

[0023] Figure 3 is a front view schematic diagram of a connecting sleeve according to an embodiment of the present invention;

[0024] Figure 4 for Figure 3 Schematic cross-sectional view of the middle AA part;

[0025] Figure 5 It is a schematic diagram of the structure when the connecting sleeve and the main chord of the standard section are tightly embraced according to an embodiment of the present invention;

[0026] Figure 6 is a schematic structural diagram of a connecting sleeve according to a second embodiment of the present invention;

[0027] Figure 7 FIG. 4 is a schematic structural diagram of a connecting sleeve according to a third embodiment of the present invention.

[0028] Description of Reference Numerals

[0029] 1 Connection portion 213 Third gradient surface

[0030] 11 sleeve body 22 second gradient portion

[0031] 12 Extension 3 String holding surface

[0032] 13 Connection hole 31 First straight section

[0033] 2 Dovetail 32 arc segment

[0034] 21 First gradient section 33 Second straight section

[0035] 211 first gradient surface 4 concave arc surface

[0036] 212 Second gradient surface 5 Main chord DETAILED DESCRIPTION

[0037] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0038] The dovetail type connecting sleeve of the crane standard section according to the present invention is described with reference to the accompanying drawings.

[0039] See also Figure 1 In an embodiment of the present invention, a dovetail type connecting sleeve of a crane standard section is provided, and a chord holding surface 3 for holding the main chord 5 of the standard section is formed on the back of the connecting sleeve, and the chord holding surface 3 can hold along the outer periphery of the main chord 5, and the chord holding surface 3 of this structure can increase the chord holding area between the connecting sleeve and the main chord 5. When the chord holding area between the connecting sleeve and the main chord 5 is larger, the stress borne by the chord holding surface 3 will be dispersed more, and the welding between the connecting sleeve and the main chord 5 will be easier and firmer, thereby improving the fatigue life of the weld. The connecting sleeve includes a connecting portion 1 and a dovetail portion 2 arranged at the outer edge of the end of the connecting portion 1, and the chord holding surface 3 is formed on the back of the dovetail portion 2, and the front of the dovetail portion 2 is a gradient portion formed by connecting a plurality of gradient surfaces in sequence, and the gradient portion is connected to the connecting portion 1 in an arc transition.

[0040] The string-embracing surface 3 may be concave or flat. Figure 7 As shown, when the back side of the connecting sleeve is a plane, that is, the chord-holding surface 3 is a plane, stress concentration is likely to occur when the connecting sleeve holds the main chord 5. Therefore, the front side of the dovetail portion 2 is set as a gradient portion composed of multiple gradient surfaces, so that the front side of the dovetail portion 2 forms a gradient inclined surface structure. The dovetail portion 2 with this gradient structure eliminates the stress concentration phenomenon in this area. In addition, the thickness of the tip of the upper end of the dovetail portion 2 is thinned. After the welding of the connecting sleeve and the main chord 5 is completed, there is no large step between the weld and the base material, and there is no stress concentration phenomenon. An arc-shaped transition connection is used between the gradient portion and the connecting portion 1, so that the overall transition is more uniform, and the transition radius between the gradient portion and the connecting portion 1 is increased, eliminating the stress concentration phenomenon in this area. Among them, as Figure 5 As shown, the main chord 5 is a rectangular tube, and when the connecting sleeve holds the main chord 5 of the standard section, the chord holding surfaces 3 of the three connecting sleeves respectively correspond to the three corners of the main chord 5, thereby achieving the holding and fixing of the main chord 5. In other embodiments, the depth of the arc segment 32 in the chord holding surface 3 can be reduced, which is conducive to the overall processing and forming.

[0041] In one embodiment of the present invention, the string-holding surface 3 extends from the first end of the connecting sleeve to the second end and is recessed inwardly. The orthographic projection of the string-holding surface 3 includes a first straight section 31, an arc section 32 and a second straight section 33 connected in sequence. The dovetail type connecting sleeve of the present invention adopts an arc section 32 + two straight sections to form the string-holding surface 3, which increases the string-holding area and facilitates welding and positioning. At the same time, this scheme has better connection strength.

[0042] In an embodiment of the present invention, Figure 2 As shown, the extension line of the first straight section 31 is perpendicular to the extension line of the second straight section 33, the intersection of the extension line of the first straight section 31 and the extension line of the second straight section 33 is the center point, the distance from the end of the first straight section 31 away from the arc section 32 to the center point is L1, and the distance from the end of the second straight section 33 away from the arc section 32 to the center point is L2; ​​wherein, L1 is equal to L2, and L1 and L2 are both 1 / 4 to 1 / 2 of the cross-sectional length of the main chord 5. And the first straight section 31, the second straight section 33 and the arc section 32 are all connected by arc-shaped smooth transition. In order to ensure that the roller has enough travel space on the surface of the main chord 5 during the jacking process, the plane length L1 and L2 of the connecting sleeve chord surface 3 are 1 / 4-1 / 2 of the cross-sectional length of the main chord 5. Within this range, the stress concentration of the connecting sleeve is small, and the optimal value is 1 / 2. Furthermore, in the chord-embracing surface 3, the edge line of the first straight segment 31 and the edge line of the second straight segment 33 are ensured to be tangent to the arc surface line, thereby determining that the curvature of the arc segment 32 is 90 degrees.

[0043] In addition, the protection scope of the present invention is not limited to the technical solution in this embodiment. In the third embodiment, Figure 6 As shown, when the angle between the extension line of the first straight section 31 and the extension line of the second straight section 33 is not 90 degrees, as long as an inwardly concave string-holding surface 3 structure is formed between the first straight section 31, the arc section 32 and the second straight section 33, the string-holding area between the connecting sleeve and the main chord rod 5 can be increased. This solution is also within the protection scope of the present invention. At this time, the inwardly concave depth of the string-holding surface 3 is relatively small.

[0044] In an embodiment of the present invention, Figure 2 As shown, both sides of the connecting sleeve are formed with an inner concave arc surface 4, and the edge line of the inner concave arc surface 4 is tangent to the edge line of the chord holding surface 3. By changing the two sides of the dovetail type connecting sleeve from flat surfaces to inner concave arc surfaces 4, through simulation analysis, it is concluded that this solution can reduce the use of materials and reduce the weight of the connecting sleeve without reducing the structural strength.

[0045] In an embodiment of the present invention, Figure 3As shown, the gradient portion includes a first gradient portion 21 and a second gradient portion 22 located on both sides of the first gradient portion 21, and the first gradient portion 21 and the two second gradient portions 22 are arranged side by side; wherein the first gradient portion 21 includes a first gradient surface 211, a second gradient surface 212 and a third gradient surface 213 connected in sequence from top to bottom, the first gradient surface 211 and the second gradient surface 212 are both inclined surfaces, the third gradient surface 213 is an arc-shaped concave surface, and the height ratio range of the first gradient surface 211, the second gradient surface 212 and the third gradient surface 213 is 1:2:2 to 1:2:3.

[0046] In order to avoid stress concentration and facilitate manufacturing, the number of gradient surfaces in the first gradient portion 21 and the second gradient portion 22 in the front part of the dovetail portion 2 is the same, and the number of gradient surfaces used is in the range of 3 to 6. It is best to use 3 surfaces. In addition, multiple gradient surfaces in the first gradient portion 21 or the second gradient portion 22 are connected by arc transition to improve the structural strength.

[0047] Compared with the existing scheme, the front side of the dovetail portion 2 of the present invention adopts a multi-faceted gradual change structure, which is obtained through multiple rounds of static strength simulation analysis, fatigue life analysis and optimization and improvement processes. Combined with the processing cost of the dovetail portion 2 of the connecting sleeve, the complexity of the process and other factors, it is concluded through simulation analysis that the use of multiple gradual change surface structures can ensure that when the load is transferred from the sleeve portion through the dovetail portion 2 to the main chord section, the stress transfer is more uniform. This embodiment is explained below using the gradual change portion number analysis table in the first gradual change portion 21 as an example. Table 1 is a comparison of the stress and fatigue life of the connecting sleeve with different numbers of gradual change surfaces in the first gradual change portion 21.

[0048] Table 1 Comparison of different numbers of gradient surfaces in the first gradient portion 21

[0049] Gradient Solution Maximum stress (MPa) Fatigue life (times) 2 gradient surfaces 467 2e4 3 gradient surfaces 214 5.1e4 4 gradient surfaces 210 5.2e4 5 gradient surfaces 207 5.5e4 6 gradient surfaces 203 5.51e4

[0050] From the analysis structure comparison in Table 1 above, it can be seen that as the number of gradient surfaces increases, the maximum stress gradually decreases and the fatigue life number gradually increases. When the number of gradient surfaces is 3, the processing cost of the dovetail part, the complexity of the process and other factors are comprehensively considered. Therefore, in this embodiment, when the number of gradient surfaces in the first gradient portion 21 is 3, the comprehensive performance of the connecting sleeve is optimal.

[0051] In addition, when the number of gradient surfaces is 3, it is necessary to determine the ratio of the vertical interval length of each surface in the dovetail portion 2, and define the names of the gradient surfaces in the first gradient portion 21 as follows from top to bottom: the first gradient surface 211, the second gradient surface 212, and the third gradient surface 213, and define the height of the first gradient surface 211 as H1, the height of the second gradient surface 212 as H2, and the height of the third gradient surface 213 as H3. Then, the five gradient surface heights H1, H2, and H3 are compared respectively, and the stress and fatigue life times of each scheme are shown in Table 2.

[0052] Table 2 Comparison of gradient surface interval ratios

[0053]

[0054] According to the comparison of static strength and fatigue life strength analysis results, it is concluded that when the height ratio of the three gradient surfaces is between 1:2:2 and 1:2:3, the overall stress of the connecting sleeve is small and the fatigue life times are high. Among them, the optimal value is 1:2:2.2.

[0055] In an embodiment of the present invention, the connection angle between any two adjacent gradient surfaces in the second gradient portion 22 increases first and then decreases from top to bottom, and each gradient surface in the second gradient portion 22 is inclined, and the inclination direction of each gradient surface is consistent. Among them, the number of gradient surfaces in the second gradient portion 22 is also three, and the height ratio between the three gradient surfaces is the same as the height ratio of the three gradient surfaces in the first gradient portion 21, that is, the three gradient surfaces in the second gradient portion 22 and the three gradient surfaces in the first gradient portion 21 are arranged correspondingly, and the corresponding heights are the same. In order to ensure the optimal transmission path of stress, the dovetail portion 2 is also provided with a second gradient portion 22 located on both sides of the first gradient portion 21 to achieve the transition from the connecting portion 1 to the tower body. The number of gradient surfaces in the second gradient portion 22 is the same as the number of gradient surfaces in the first gradient portion 21. According to simulation and test results, the optimal number of gradient surfaces is three, and the angles and sizes between the three gradient surfaces have undergone multiple structural optimizations to ensure uniform stress transmission. Among them, the optimized structure is as follows:

[0056] like Figure 4As shown, when looking at the front of the dovetail portion 2 from the side, only the inclined relationship between the three gradient surfaces in the second gradient portion 22 can be seen. The gradient surface located at the top of the second gradient portion 22 is named the upper gradient surface, the gradient surface located in the middle of the second gradient portion 22 is named the middle gradient surface, and the gradient surface located at the bottom of the second gradient portion 22 is named the lower gradient surface. The connection angles between the left sides of the three gradient surfaces in the second gradient portion 22 are 163 degrees, 178 degrees, and 102 degrees from top to bottom, respectively, while the connection angles between the right sides of the three gradient surfaces in the second gradient portion 22 are 172 degrees, 176 degrees, and 96 degrees from top to bottom. The dovetail portion 2 formed by the second gradient portion 22 under this structure has a more uniform stress transfer from the connection portion 1 to the tower body, eliminating stress concentration.

[0057] In the embodiment of the present invention, the connection part 1 includes a sleeve body 11 and an extension body 12 extending from the outside of the sleeve body 11, the dovetail part 2 is located above the extension body 12, and the two sides of the extension body 12 and the dovetail part 2 form an integral concave arc surface 4, and the two ends of the concave arc surface 4 are tangent to the edge line of the string-holding surface 3 and the edge line of the sleeve body 11 respectively. The connection part 1 includes a cylindrical sleeve body 11 located below, an extension body 12 extends outward from one side of the sleeve body 11, the height of the extension body 12 is the same as the height of the sleeve body 11, the dovetail part 2 is arranged above the extension body 12, and the back structures of the dovetail part 2 and the extension body 12 are the same, both forming a concave string-holding surface 3, and the string-holding surface 3 extends from the top of the dovetail part 2 to the bottom of the extension body 12. In addition, both sides of the extension body 12 and the dovetail portion 2 are concave arc surfaces 4, and the concave arc surfaces 4 on both sides of the extension body 12 are integrally formed with the concave arc surfaces 4 on both sides of the dovetail portion 2 to form the same concave arc surface 4 that runs through from top to bottom. The side surface of the connecting sleeve of the present invention is a concave arc surface 4, and the edge line of the chord holding surface 3 and the edge line of the sleeve body 11 are tangent to the edge line of the concave arc surface 4, so that the position and angle of the concave arc surface 4 can be determined.

[0058] In the embodiment of the present invention, a through connection hole 13 is provided on the sleeve body 11, and the connection hole 13 is provided along the height direction of the sleeve body 11. The connection hole 13 is provided in the middle of the sleeve body 11. When the upper and lower standard sections are butt-jointed, the two connection sleeves respectively hold the corresponding main chord 5. A through connection hole 13 is provided on each sleeve body 11, and a connection bolt is used to pass through the connection holes 13 in the upper and lower connection sleeves respectively, so that the upper and lower connection sleeves can be connected, thereby realizing the connection and fastening between the upper and lower standard sections.

[0059] In an embodiment of the present invention, the ratio of the height of the connection part 1 to the height of the dovetail part 2 is 11:12. Through multiple simulations and test comparisons, the ratio between the height of the connection part 1 and the height of the dovetail part 2 is adjusted, and it is found that when the height of the connection part 1 is lower than the height of the dovetail part 2, the stiffness mutation is reduced, the stress concentration is reduced, and the fatigue life times are increased. Since the ratio of the dovetail part 2 to the connection part 1 affects the load transfer, thereby affecting the stress concentration degree and the fatigue life times, this embodiment simultaneously determines the ratio of the height of the connection part 1 to the height of the dovetail part 2, and a total of 6 schemes are compared, as shown in Table 3.

[0060] Table 3 Comparison of the height ratio of the connecting part 1 and the dovetail part 2

[0061] Proportional Scheme Maximum stress (MPa) Fatigue life (times) 11:6 236 4.1e4 11:8 224 4.5e4 11:10 218 4.9e4 11:12 214 5.1e4 11:14 211 5.1e4 11:16 210 5.2e4

[0062] Through simulation experiment analysis, it is concluded that as the height ratio of the dovetail 2 increases, the maximum stress gradually decreases and the fatigue life gradually increases. However, considering the maximum stress and fatigue life times, when the ratio of the height of the connection part 1 to the height of the dovetail 2 is less than 11:10, the static strength and fatigue life are better, that is, the longer the dovetail 2 is, the lower the stress concentration is. Considering the cost factor, the optimal ratio is 11:12, and the height of the connection part 1 is slightly lower than the height of the dovetail 2. Compared with the connecting sleeve in the prior art, the height of the connection part 1 in this embodiment is reduced, and the required length of the connecting bolt is correspondingly reduced, which can further reduce the weight and processing cost.

[0063] In the embodiment of the present invention, the connecting portion 1 and the dovetail portion 2 are integrally formed. In order to save the manufacturing cost of the connecting sleeve and reduce the manufacturing process flow, the connecting portion 1 and the dovetail portion 2 are integrally formed and manufactured.

[0064] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0065] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0066] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0067] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A dovetail type connecting sleeve for a standard section of a crane, characterized in that: The back side of the connecting sleeve forms a chord-holding surface (3) for holding the main chord rod (5) of the standard section tightly; The connecting sleeve comprises a connecting portion (1) and a dovetail portion (2) arranged at the outer edge of the end of the connecting portion (1); the front side of the dovetail portion (2) is a gradient portion formed by sequentially connecting a plurality of gradient surfaces; the gradient portion is connected to the connecting portion (1) in an arc-shaped transition; the gradient portion comprises a first gradient portion (21) and a second gradient portion (22) located on both sides of the first gradient portion (21); the first gradient portion (21) and the two second gradient portions (22) are arranged side by side; the number of gradient surfaces in the first gradient portion (21) and the second gradient portion (22) is the same and the number ranges from 3 to 6; The first gradient portion (21) comprises a first gradient surface (211), a second gradient surface (212) and a third gradient surface (213) which are sequentially connected from top to bottom, the first gradient surface (211) and the second gradient surface (212) are both inclined surfaces, the third gradient surface (213) is an arc-shaped concave surface, and the height ratio of the first gradient surface (211), the second gradient surface (212) and the third gradient surface (213) is in the range of 1:2:2 to 1:2:

3.

2. The crane standard section dovetail type connecting sleeve as claimed in claim 1, characterized in that: The string-embracing surface (3) extends from the first end to the second end of the connecting sleeve and is recessed inwardly, and the orthographic projection of the string-embracing surface (3) comprises a first straight section (31), an arc section (32), and a second straight section (33) which are connected in sequence.

3. The crane standard section dovetail type connecting sleeve as claimed in claim 2, characterized in that: The extension line of the first straight section (31) and the extension line of the second straight section (33) are perpendicular, the intersection of the extension line of the first straight section (31) and the extension line of the second straight section (33) is the center point, the distance from the end of the first straight section (31) away from the arc section (32) to the center point is L1, and the distance from the end of the second straight section (33) away from the arc section (32) to the center point is L2; Wherein, L1 is equal to L2, and both L1 and L2 are 1 / 4 to 1 / 2 of the cross-sectional length of the main chord (5).

4. The crane standard section dovetail type connecting sleeve as claimed in claim 2, characterized in that: Both sides of the connecting sleeve are formed with an inwardly concave arc surface (4), and the edge line of the inwardly concave arc surface (4) is tangent to the edge line of the chord-embracing surface (3).

5. The crane standard section dovetail type connecting sleeve as claimed in claim 1, characterized in that: The connection angle between any two adjacent gradual change surfaces in the second gradual change portion (22) increases first and then decreases from top to bottom, and each of the gradual change surfaces in the second gradual change portion (22) is arranged obliquely.

6. The crane standard section dovetail type connecting sleeve as claimed in claim 4, characterized in that: The connecting portion (1) comprises a sleeve body (11) and an extension body (12) extending from the outer side of the sleeve body (11); the dovetail portion (2) is located above the extension body (12); the extension body (12) and the two sides of the dovetail portion (2) form an integral concave arc surface (4); the two ends of the concave arc surface (4) are respectively tangent to the edge line of the chord-embracing surface (3) and the edge line of the sleeve body (11).

7. The crane standard section dovetail type connecting sleeve as claimed in claim 6, characterized in that: The sleeve body (11) is provided with a through connection hole (13), and the connection hole (13) is opened along the height direction of the sleeve body (11).

8. The crane standard section dovetail type connecting sleeve according to any one of claims 1 to 7, characterized in that: The ratio of the height of the connecting portion (1) to the height of the dovetail portion (2) is 11:

12.

9. The crane standard section dovetail type connecting sleeve according to any one of claims 1 to 7, characterized in that: The connecting portion (1) and the dovetail portion (2) are integrally formed.

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