Electron beam welding apparatus for square tubes

Abstract

The application discloses an electron beam welding device for building square pipes and belongs to the technical field of welding. Symmetrical fixing bases are fixedly arranged on the top of an operation table, and a semicylindrical rotating inner cylinder is rotatably arranged in a rotating outer cylinder. A sliding frame is slidably arranged in a clamping cavity, and a plurality of roller shafts are movably arranged in the sliding frame. A clamping plate for fixing square pipes to be welded is fixedly arranged on the inner side of a connecting rod, and an outer magnetic plate is fixedly arranged on the outer side of the connecting rod. A lifting frame is fixedly arranged at the output end of a swing cylinder, welding rails are fixedly arranged on the two sides of the lifting frame and are sleeved on the outer sides of square pipes to be welded, and a welding device capable of being adjusted in multiple directions is arranged on the bottom of a moving frame. The sliding frame and the notch are used for conveniently positioning the square pipe and rapidly discharging finished products after welding. When the lifting frame drives the rotating inner cylinder and the rotating outer cylinder to deflect, the welding rails and the welding device also synchronously descend, so that the notch is always located at the central position of the welding rails, and the welding effect is improved.

Description

Technical Field

[0001] This invention relates to the field of welding technology, specifically to an electron beam welding device for building square tubes. Background Technology

[0002] Square tubing is a common building material, named for its rectangular shape. It is lightweight, high-strength, and corrosion-resistant, making it widely used in construction. Square tubing can be cut and welded into various shapes, such as latticework and railings, for architectural decoration. Laser welding is a highly efficient and precise welding method that uses a high-energy-density laser beam as a heat source. It is an important application of laser material processing technology. During laser welding, the laser beam is focused on the workpiece surface, heating it to melting point through heat conduction, forming a specific molten pool, and finally solidifying into a weld. Laser welding features low heat input, minimal welding deformation, and is unaffected by electromagnetic fields.

[0003] Chinese patent application CN118287804A discloses an electron beam welding device for seam welding of vehicle shock absorbers, relating to the technical field of welding equipment. It solves the problem that the heat generated during seam welding of vehicle shock absorbers can easily cause hand injuries to workers, posing a safety hazard and affecting welding efficiency. This electron beam welding device includes an equipment box, a shock absorber positioning and rotating mechanism, an electron beam seam welding assembly, and an integrated control console. The shock absorber positioning and rotating mechanism is installed on one side of the top of the equipment box. The side of the shock absorber body is gripped and fixed by the side of the shock absorber positioning and rotating mechanism. The side of the support assembly is installed on the bottom of the shock absorber body, and the support assembly is installed on the other side of the top of the equipment box by screws. In this invention, the vehicle shock absorber rotates uniformly, achieving seam welding while automatically performing air cooling to dissipate heat from the shock absorber during the seam welding process, thus improving the efficiency of the vehicle shock absorber during seam welding.

[0004] However, the processing efficiency and automation level of the electron beam welding equipment disclosed above are generally low. It cannot simultaneously weld multiple sets of raw materials, and its degree of freedom is also limited. During use, it cannot freely adjust the clamping angle and welding angle of the parts on both sides according to actual needs, so as to meet the welding of various different specifications of cuts. Summary of the Invention

[0005] The purpose of this invention is to address the problems of existing electron beam welding equipment, such as low processing efficiency and automation, inability to simultaneously weld multiple sets of raw materials, limited freedom of use, and inability to freely adjust the clamping and welding angles of parts on both sides according to actual needs, thereby meeting the welding requirements of various different specifications of cuts. This invention provides an electron beam welding device for building square tubes.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: an electron beam welding device for building square tubes, comprising an operating table, a symmetrical fixed base fixedly mounted on the top of the operating table, a symmetrical rotating outer cylinder oscillatingly mounted on the top of the fixed base, and a semi-cylindrical rotating inner cylinder rotatably mounted inside the rotating outer cylinder; a clamping cavity is formed in the middle of the rotating inner cylinder, a sliding frame is slidably mounted in the clamping cavity, and multiple sets of rollers are movably mounted inside the sliding frame; a connecting rod is movably mounted on the inner wall of the rotating inner cylinder, a clamping plate for fixing the square tube to be welded is fixedly mounted on the inner side of the connecting rod, and an outer magnetic plate is fixedly mounted on the outer side of the connecting rod; a swing cylinder is also mounted on the top of the operating table, a lifting frame is fixedly mounted on the output end of the swing cylinder, welding rails fitted around the outside of the square tube to be welded are fixedly mounted on both sides of the lifting frame, a moving frame is movably mounted on the welding rails, and a multi-directional adjustable welding device is mounted on the bottom of the moving frame; when the rotating outer cylinder swings inward, welding operations can be performed on the square tube with cuts.

[0007] As a further embodiment of the present invention: a swing shaft is fixedly provided between the two rotating outer cylinders, and a swing hoop that cooperates with the swing shaft is fixedly provided on the top of the fixed seat; a swing fan is installed in the middle of the swing shaft, and toothed plates that mesh with the swing fan are installed on both sides of the lifting frame.

[0008] As a further embodiment of the present invention: a traveling gear ring is installed on the inner wall of the welding rail, a traveling motor is installed on the outer wall of the motion frame, a welding cylinder is installed at the bottom of the motion frame, and the welding equipment is installed at the output end of the welding cylinder.

[0009] As a further embodiment of the present invention: a control panel is also provided on the operating table, and collection boxes located below the welding rail are provided on both sides of the operating table.

[0010] As a further embodiment of the present invention: a limiting rail is fixedly provided on the inner wall of the rotating outer cylinder, a limiting groove that cooperates with the limiting rail is provided on the outer wall of the rotating inner cylinder, and a notch is provided on the top of the rotating outer cylinder to facilitate material removal.

[0011] As a further embodiment of the present invention: symmetrical sliders are provided on the outer walls of both sides of the sliding frame, sliding grooves that cooperate with the sliders are provided on the inner walls of both sides of the clamping cavity, and handles are also provided on the outer walls of the sliding frame.

[0012] As a further embodiment of the present invention: a first storage cavity is provided on the inner wall of the rotating inner cylinder, a second storage cavity is provided on the outer wall of the rotating inner cylinder, a through hole is provided between the first storage cavity and the second storage cavity, the connecting rod is movably disposed in the through hole, and multiple sets of return springs are connected to the inner wall of the clamping plate, the bottom of the return springs being connected to the inner wall of the first storage cavity.

[0013] As a further embodiment of the present invention: a mounting bracket is fixedly provided at the bottom of the rotating outer cylinder, a locking cylinder is installed on the inner side of the mounting bracket, and an inner magnetic plate that cooperates with the outer magnetic plate is installed at the output end of the locking cylinder.

[0014] As a further embodiment of the present invention: a rotating gear ring is fixedly installed on the outer wall of the rotating inner cylinder, and a rotating motor is also installed on the mounting bracket. The output end of the rotating motor is equipped with a drive gear that meshes with the rotating gear ring.

[0015] As a further aspect of the present invention, the angle of the notch is less than 180 degrees.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. This invention utilizes a swingable rotating outer cylinder and a rotating inner cylinder to weld square tubes with different types of cuts. When the cuts of the square tubes on both sides are perpendicular, the cuts of the two square tubes abut against each other under the transport of the sliding frames on both sides. At this time, with the cooperation of the drive gear and the rotating gear ring, the rotating inner cylinder rotates freely relative to the rotating outer cylinder and cooperates with the welding equipment on the welding rail to perform all-round welding on the cuts. When the cut of the square tube is in an inclined state, the cuts of the two square tubes on both sides are first aligned, and then the lifting frame is driven downward by the swing cylinder. At this time, with the cooperation of the gear plate and the swing fan, the rotating inner cylinder and the rotating outer cylinder on both sides deflect inward, and the cuts of the square tubes are now in contact. Then, the rotating inner cylinder and the rotating outer cylinder remain fixed and drive the welding equipment to move along the welding rail to perform all-round welding on the cuts. This design improves the degree of freedom of this electron beam welding device for building square tubes.

[0018] 2. The present invention can facilitate the rapid positioning of square tubes and the quick unloading of finished products after welding by the design of sliding frame and notch. When the lifting frame drives the rotating inner cylinder and rotating outer cylinder on both sides to deflect, the welding rails and welding equipment on both sides will also be lifted or lowered synchronously, so that the cut is always located in the center position of the welding rail. This design improves the welding effect of the electron beam welding device for building square tubes. Attached Figure Description

[0019] The present invention will be further explained below with reference to the accompanying drawings and embodiments:

[0020] Figure 1This is a three-dimensional structural diagram of the present invention;

[0021] Figure 2 This is a three-dimensional structural diagram of the operating table in this invention;

[0022] Figure 3 This is a three-dimensional structural diagram of the rotating outer cylinder and the rotating inner cylinder in this invention;

[0023] Figure 4 This is a three-dimensional structural diagram of the rotating outer cylinder in this invention;

[0024] Figure 5 This is a three-dimensional structural diagram of the rotating inner cylinder in this invention;

[0025] Figure 6 This is a cross-sectional view of the rotating inner cylinder in this invention;

[0026] Figure 7 This is a three-dimensional structural diagram of the sliding frame in this invention.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1. Operating table; 2. Control panel; 3. Collection box; 4. Swing cylinder; 5. Lifting frame; 6. Gear plate; 7. Welding rail; 8. Traveling gear ring; 9. Movement frame; 10. Travel motor; 11. Welding cylinder; 12. Welding equipment; 13. Fixed seat; 14. Swing hoop; 15. Swing shaft; 16. Swing fan; 17. Rotating outer cylinder; 18. Limiting rail; 19. Rotating inner cylinder; 20. Limiting groove; 21. Clamping cavity; 22. Sliding frame; 23. Slider; 24. Sliding groove; 25. Roller shaft; 26. Handle; 27. First storage cavity; 28. Through hole; 29. ​​Connecting rod; 30. Clamping plate; 31. Outer magnetic plate; 32. Return spring; 33. Mounting frame; 34. Flipping gear ring; 35. Flipping motor; 36. Drive gear; 37. Locking cylinder; 38. Inner magnetic plate; 39. Notch; 40. Second storage cavity. Detailed Implementation

[0029] The following will be combined with the appendix Figures 1 to 7 The technical solutions of the present invention have been clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides, through improvements, an electron beam welding apparatus for building square tubes, such as... Figures 1-7As shown, the system includes an operating platform 1. A symmetrical fixed base 13 is fixedly mounted on the top of the operating platform 1. A symmetrical rotating outer cylinder 17 is oscillatingly mounted on the top of the fixed base 13. A semi-cylindrical rotating inner cylinder 19 is rotatably mounted inside the rotating outer cylinder 17. A clamping cavity 21 is formed in the middle of the rotating inner cylinder 19. A sliding frame 22 is slidably mounted inside the clamping cavity 21. Multiple sets of rollers 25 are movably mounted inside the sliding frame 22. A connecting rod 29 is movably mounted on the inner wall of the rotating inner cylinder 19. A fixed inner side of the connecting rod 29 is provided with… There is a clamping plate 30 for fixing the square tube to be welded, and an outer magnetic plate 31 is fixedly installed on the outside of the connecting rod 29; a swing cylinder 4 is also installed on the top of the operating table 1, a lifting frame 5 is fixedly installed at the output end of the swing cylinder 4, and welding rails 7 are fixedly installed on both sides of the lifting frame 5 and sleeved on the outside of the square tube to be welded. A motion frame 9 is movably installed on the welding rail 7, and a multi-directional adjustable welding device 12 is installed at the bottom of the motion frame 9; when the outer cylinder 17 is rotated and swung inward, welding operations can be performed on the square tube with cuts.

[0031] In this embodiment, the electron beam welding device for building square tubes mainly consists of three parts: an operating table 1, a rotating outer cylinder 17, and a welding device 12. When in use, the locking cylinder 37 is first activated, extending the inner magnetic plate 38 to both sides. The outer magnetic plate 31 drives the clamping plate 30 towards the center, compressing the return spring 32. Then, the sliding frame 22 is pulled outwards via the handle 26, placing the square tube to be welded onto the sliding frame 22. The sliding frames 22 on both sides are then brought closer together. When the cut surfaces meet, the locking cylinder 37 is closed, and the inner magnetic plate 38 retracts towards the center. At this time, under the action of the return spring 32, the clamping plate 30 clamps and fixes the square tube. When the cut surfaces of the square tubes on both sides are perpendicular, the rotating inner cylinder 19 rotates freely relative to the rotating outer cylinder 17 under the cooperation of the drive gear 36 and the rotating gear ring 34, cooperating with the welding device 12 on the welding rail 7 to perform omnidirectional welding at the cut surfaces. When the cut of the square tube is in an inclined state, the lifting frame 5 is driven to move downward by the swing cylinder 4. At this time, with the cooperation of the toothed plate 6 and the swing fan 16, the rotating inner cylinder 19 and the rotating outer cylinder 17 on both sides deflect inward. At this time, the cut of the square tube is completely fitted, and then the welding equipment 12 is driven to move along the welding rail 7 and perform all-round welding on the cut.

[0032] See appendix Figure 1 - Appendix Figure 2 A swing shaft 15 is fixedly installed between the two rotating outer cylinders 17. A swing clamp 14 that cooperates with the swing shaft 15 is fixedly installed on the top of the fixed seat 13. A swing fan 16 is installed in the middle of the swing shaft 15. Tooth plates 6 that mesh with the swing fan 16 are installed on both sides of the lifting frame 5.

[0033] In this embodiment: to ensure that the rotating outer cylinders 17 on both sides swing inward relative to the top of the fixed base 13, thereby satisfying the welding operation of square tubes with various different cuts, a swing hoop 14 structure is designed. When the lifting frame 5 drives the rotating inner cylinders 19 and rotating outer cylinders 17 on both sides to deflect, the welding rails 7 on both sides and the welding equipment 12 will also be lifted or lowered synchronously, so that the cut is always located at the center position of the welding rail 7.

[0034] See appendix Figure 1 - Appendix Figure 2 A traveling gear ring 8 is installed on the inner wall of the welding rail 7, a traveling motor 10 is installed on the outer wall of the motion frame 9, a welding cylinder 11 is installed at the bottom of the motion frame 9, and the welding equipment 12 is installed at the output end of the welding cylinder 11.

[0035] In this embodiment: when the cut of the square tube is an inclined cut, in order to perform 360-degree all-round welding operation at the cut joint, a welding cylinder 11 structure is designed to adjust the distance between the welding equipment 12 and the square tube.

[0036] See appendix Figure 1 - Appendix Figure 2 The control panel 1 is also equipped with a control panel 2, and collection boxes 3 located below the welding rail 7 are set on both sides of the control panel 1.

[0037] In this embodiment: a control panel 2 is designed to control the operation of the equipment. During welding operations, a symmetrical collection box 3 is designed to collect the welding slag.

[0038] See appendix Figure 4 - Appendix Figure 5 A limiting rail 18 is fixedly installed on the inner wall of the rotating outer cylinder 17, and a limiting groove 20 that cooperates with the limiting rail 18 is opened on the outer wall of the rotating inner cylinder 19. A notch 39 for easy material removal is opened on the top of the rotating outer cylinder 17.

[0039] In this embodiment: In order to ensure that the inner cylinder 19 can rotate freely relative to the outer cylinder 17 so as to perform 360-degree welding at the cut, a mutually cooperating limiting rail 18 and limiting groove 20 structure is designed.

[0040] See appendix Figure 6 - Appendix Figure 7 Symmetrical sliders 23 are provided on the outer walls of both sides of the sliding frame 22, and sliding grooves 24 that cooperate with the sliders 23 are provided on the inner walls of both sides of the clamping cavity 21. A handle 26 is also provided on the outer wall of the sliding frame 22.

[0041] In this embodiment: during loading, the sliding frame 22 is first pulled outward using the handle 26, and the square tube to be welded is placed on the sliding frame 22. Then, the sliding frame 22 is slid inward. Since multiple sets of rollers 25 are movably installed inside the sliding frame 22, the friction is small, so the square tube can freely adjust its position relative to the sliding frame 22, thereby further adjusting the contact position of the cut edges of the square tubes on both sides.

[0042] See appendix Figure 4 - Appendix Figure 7 A first storage cavity 27 is formed on the inner wall of the rotating inner cylinder 19, and a second storage cavity 40 is formed on the outer wall of the rotating inner cylinder 19. A through hole 28 is formed between the first storage cavity 27 and the second storage cavity 40. A connecting rod 29 is movably disposed in the through hole 28. Multiple sets of return springs 32 are connected to the inner wall of the clamping plate 30, and the bottom of the return springs 32 is connected to the inner wall of the first storage cavity 27. A mounting bracket 33 is fixedly provided at the bottom of the rotating outer cylinder 17. A locking cylinder 37 is installed on the inner side of the mounting bracket 33, and an inner magnetic plate 38 that cooperates with the outer magnetic plate 31 is installed at the output end of the locking cylinder 37.

[0043] In this embodiment: To improve automation and automatically lock and unlock the square tube, a locking cylinder 37 structure is designed. When the square tube is installed, the locking cylinder 37 is activated, and the inner magnetic plate 38 extends to both sides. Under the attraction of opposite poles, the outer magnetic plate 31 drives the clamping plate 30 to move towards the center and compresses the return spring 32. At this time, the square tube is installed towards the center under the action of the sliding frame 22. After the square tubes on both sides abut, the locking cylinder 37 is closed, and the inner magnetic plate 38 retracts towards the center. At this time, under the action of the return spring 32, the clamping plate 30 clamps and fixes the square tube.

[0044] See appendix Figure 1 and attached Figure 3 - Appendix Figure 4 A rotating gear ring 34 is fixedly installed on the outer wall of the rotating inner cylinder 19. A rotating motor 35 is also installed on the mounting bracket 33. The output end of the rotating motor 35 is equipped with a drive gear 36 that meshes with the rotating gear ring 34.

[0045] In this embodiment: when the cuts of the square tubes on both sides are perpendicular, in order to weld the cuts in all directions, the inner cylinder 19 rotates freely relative to the outer cylinder 17 under the cooperation of the flipping motor 35 and the flipping gear ring 34.

[0046] See appendix Figure 3 - Appendix Figure 4 The angle of the gap 39 is less than 180 degrees.

[0047] In this embodiment: Since the rotating inner cylinder 19 is rotatably disposed inside the rotating outer cylinder 17, and the rotating inner cylinder 19 is semi-cylindrical with an angle of 180 degrees, in order to install the rotating inner cylinder 19 and ensure its stable rotation and avoid accidental detachment, the opening angle of the notch 39 is made less than 180 degrees.

[0048] The working principle of this invention is as follows: When using the device, firstly, the locking cylinder 37 is activated, extending the inner magnetic plate 38 to both sides. The outer magnetic plate 31 drives the clamping plate 30 to move towards the center, compressing the return spring 32. Then, the sliding frame 22 is pulled outwards via the handle 26, placing the square tube to be welded onto the sliding frame 22. Next, the sliding frames 22 on both sides are brought closer together. When the cut surfaces meet, the locking cylinder 37 is closed, and the inner magnetic plate 38 retracts towards the center. At this time, under the action of the return spring 32, the clamping plate 30 clamps and fixes the square tube. When the cut surfaces of the square tubes on both sides are perpendicular, the inner cylinder 19 rotates freely relative to the outer cylinder 17 under the cooperation of the drive gear 36 and the rotating gear ring 34, cooperating with the welding equipment 12 on the welding rail 7 to perform all-around welding at the cut surfaces. When the cut surfaces of the square tubes are inclined, the lifting frame 5 is driven downwards by the swing cylinder 4. At this time, with the cooperation of the toothed plate 6 and the swing fan 16, the rotating inner cylinder 19 and the rotating outer cylinder 17 on both sides deflect inward. At this time, the cut of the square tube is completely fitted. Then, the welding equipment 12 is driven to move along the welding rail 7 and perform all-round welding on the cut.

[0049] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and inventive features disclosed herein.

Claims

1. An apparatus for electron beam welding of square tubes for construction, comprising an operating table (1), characterized in that: The top of the operation table (1) is fixedly provided with symmetrical fixed seats (13), the top of the fixed seat (13) is swingingly installed with symmetrical rotating outer cylinders (17), the inside of the rotating outer cylinder (17) is rotatably provided with a semicylindrical rotating inner cylinder (19), the middle of the rotating inner cylinder (19) is provided with a clamping cavity (21), the clamping cavity (21) is slidably installed with a sliding frame (22), the inside of the sliding frame (22) is movably installed with a plurality of roller shafts (25), the inner wall of the rotating inner cylinder (19) is movably installed with a connecting rod (29), the inner side of the connecting rod (29) is fixedly provided with a clamping plate (30) for fixing the square tube to be welded, and the outer side of the connecting rod (29) is fixedly provided with an outer magnetic plate (31). The top of the operation table (1) is also installed with a swing cylinder (4), the output end of the swing cylinder (4) is fixedly provided with a lifting frame (5), the two sides of the lifting frame (5) are fixedly provided with welding rails (7) sleeved on the outside of the square tube to be welded, the welding rails (7) are movably installed with a moving frame (9), and the bottom of the moving frame (9) is installed with a welding device (12) which can be adjusted in multiple directions; when the rotating outer cylinder (17) swings inward, the square tube with a notch can be welded; The two rotating outer cylinders (17) are fixedly provided with a swing shaft (15), the top of the fixed seat (13) is fixedly provided with a swing hoop (14) matched with the swing shaft (15), and the middle of the swing shaft (15) is installed with a swing fan (16); the two sides of the lifting frame (5) are installed with toothed plates (6) engaged with the swing fan (16).

2. An electron beam welding apparatus for square tubes used in construction according to claim 1, characterized in that: The inner wall of the welding rail (7) is installed with a walking gear ring (8), the outer wall of the moving frame (9) is installed with a walking motor (10), the bottom of the moving frame (9) is installed with a welding cylinder (11), and the welding device (12) is installed at the output end of the welding cylinder (11).

3. An electron beam welding apparatus for square tubes used in construction as defined in claim 1, characterized in that: The operation table (1) is also provided with a control panel (2), and the two sides of the operation table (1) are provided with collection boxes (3) located below the welding rails (7).

4. An electron beam welding apparatus for square tubes used in construction as defined in claim 1, wherein: The inner wall of the rotating outer cylinder (17) is fixedly provided with a limiting rail (18), the outer wall of the rotating inner cylinder (19) is provided with a limiting groove (20) matched with the limiting rail (18), and the top of the rotating outer cylinder (17) is provided with a gap (39) facilitating material taking.

5. An electron beam welding apparatus for square tubes used in construction as defined in claim 1, wherein: The outer walls of the two sides of the sliding frame (22) are provided with symmetrical sliding blocks (23), the two inner walls of the clamping cavity (21) are provided with sliding grooves (24) matched with the sliding blocks (23), and the outer wall of the sliding frame (22) is also provided with a handle (26).

6. An apparatus for electron beam welding of square tubes for constructional purposes according to any one of claims 1-5, characterized in that: The inner wall of the rotating inner cylinder (19) is provided with a first receiving cavity (27), the outer wall of the rotating inner cylinder (19) is provided with a second receiving cavity (40), a through hole (28) is arranged between the first receiving cavity (27) and the second receiving cavity (40), the connecting rod (29) is movably arranged in the through hole (28), and the inner wall of the clamping plate (30) is connected with a plurality of reset springs (32).

7. An apparatus for electron beam welding of square tubes for constructional purposes according to any one of claims 1-5, characterized in that: The bottom of the rotating outer cylinder (17) is fixedly provided with a mounting frame (33), the inner side of the mounting frame (33) is provided with a locking cylinder (37), and the output end of the locking cylinder (37) is provided with an inner magnetic plate (38) matched with the outer magnetic plate (31).

8. An electron beam welding apparatus for square tubes used in construction according to claim 7, characterized in that: The outer wall of the rotating inner cylinder (19) is fixedly provided with a turnover gear ring (34), the mounting frame (33) is further provided with a turnover motor (35), and the output end of the turnover motor (35) is provided with a driving gear (36) engaged with the turnover gear ring (34).

9. An electron beam welding apparatus for square tubes used in construction as defined in claim 4, wherein: The angle of the notch (39) is less than 180 degrees.

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