Multi-directional positioning welding tool for high-frequency welded pipe

Abstract

The utility model discloses a multidirectional positioning welding tool for a high-frequency welded pipe. The multidirectional positioning welding tool comprises a base, a linear guide rail, two groups of horizontal clamping components, a supporting seat component, a circular chuck, an end part pressing component and a vertical pressing component, the horizontal clamping assembly buffers and lowers the pipe body to a V-shaped clamping block through a floating lifting mechanism; the height of the supporting seat assembly is adjustable through a wedge-shaped block; the circular chuck is positioned by adopting three-jaw nylon; the end pressing assembly is hinged to the pressure head self-adaptive pipe end. The transverse position of the vertical pressing assembly is adjustable, and the vertical pressing assembly is pressed through a V-shaped connector. According to the tool, multidirectional cooperative positioning and flexible clamping are achieved, the straightness and concentricity of the welded pipe are guaranteed, surface damage is avoided, the tool is suitable for different pipe diameters and welding requirements, and the welding quality and efficiency are remarkably improved.

Description

Technical Field

[0001] This utility model relates to the field of high-frequency welded pipe production technology, and in particular to a multi-directional positioning welding fixture for high-frequency welded pipes. Background Technology

[0002] High-frequency welded pipe is made by bending metal plates into a tubular shape and then welding them using high-frequency resistance. The weld seam is formed by melting the base material of the steel strip, resulting in better mechanical strength than ordinary welded pipe. High-frequency welded pipe features high welding speed, a small heat-affected zone, no need for workpiece cleaning after welding, and the ability to weld thin-walled pipes and metal pipes. In the high-frequency welded pipe welding process, precise positioning and stable clamping of the pipe are crucial to ensuring welding quality (such as weld straightness, concentricity, and absence of indentation damage).

[0003] Traditional welded pipe positioning fixtures often suffer from the following problems: 1. Insufficient positioning accuracy and cumulative errors: Clamping mechanisms often use single or limited positioning reference points. When handling long welded pipes, it is difficult to guarantee the straightness and concentricity of the pipe body along the axial direction. Small radial and axial deviations between different sections of the pipe body can easily accumulate over long strokes, leading to welding eccentricity or even twisting. 2. High risk of pipe surface damage: Traditional clamping elements (such as fixed V-blocks and hard claws) directly and rigidly contact the pipe surface, which is prone to indentation or scratches, especially under high-pressure clamping, affecting the appearance and quality of the welded pipe. 3. Poor adaptability and cumbersome adjustment: Traditional fixtures are difficult to adjust for welded pipes of different diameters and welding positions. Replacing V-blocks, shims, or moving heavy components is time-consuming and laborious. The lack of efficient and precise axial, lateral, and height adjustment methods affects production efficiency and changeover speed. 4. Uneven or insufficient circumferential clamping force: Simply relying on end face clamping or bottom V-block support cannot effectively resist circumferential deformation force during welding, which can easily cause the pipe to roll or shift when under pressure or heat, affecting welding accuracy.

[0004] Therefore, there is an urgent need for a high-frequency welding fixture that can achieve multi-directional high-precision positioning, provide stable and reliable clamping force, effectively protect the pipe surface, and has rapid adjustment capability to adapt to welded pipes of different specifications. Utility Model Content

[0005] The technical problem to be solved by this utility model is to overcome the defects of the prior art and provide a multi-directional positioning welding fixture for high-frequency welded pipes.

[0006] To solve the above-mentioned technical problems, this utility model provides the following technical solution:

[0007] This utility model discloses a multi-directional positioning welding fixture for high-frequency welded pipes, comprising a base, on which a linear guide rail is provided along the axial direction of the welded pipe; two sets of horizontal clamping assemblies and at least one set of support base assemblies are slidably mounted on the linear guide rail, with an axially adjustable position; a circular chuck for radial positioning of the welded pipe is fixed at one end of the linear guide rail, and an axially movable end clamping assembly is provided at the other end; the base has multiple vertical clamping assemblies on the side of the linear guide rail; wherein: the horizontal clamping assembly includes: a horizontal slide table slidably connected to the linear guide rail; a V-shaped clamping block fixed to the top of the horizontal slide table; and an elastic lifting mechanism for elastically supporting the pipe body disposed on the horizontal slide table; the support base assembly includes: a support slider slidably mounted on the linear guide rail; and a wedge-shaped height adjusting block mounted on the top of the support slider; the end clamping assembly includes: an axially movable horizontal clamping cylinder; and an adaptive rotary clamping block connected to the end of the piston rod of the horizontal clamping cylinder; the vertical clamping assembly includes a vertical clamping cylinder with a laterally adjustable position.

[0008] As a preferred technical solution of this utility model, the elastic lifting mechanism includes a floating support cylinder that vertically penetrates the horizontal slide table, and an arc-shaped support plate disposed on the top of the floating support cylinder. The curvature of the arc-shaped support plate matches the outer diameter of the welded pipe and elastically supports the pipe body under the action of floating support.

[0009] As a preferred embodiment of the present invention, the adaptive rotary clamping block comprises: a base detachably connected to the piston rod of the horizontal clamping cylinder; an arc-shaped hinged pressure head embedded in the base; and an elastic buffer layer disposed on the bottom end face of the hinged pressure head.

[0010] As a preferred technical solution of this utility model, the end clamping assembly is further provided with a transverse adjustment slide that is fixedly connected to the base. The cylinder body of the horizontal clamping cylinder is slidably connected to the transverse adjustment slide through a slider, and one end of the slide is provided with an adjustment handwheel that drives the cylinder to move along the slide.

[0011] As a preferred embodiment of this utility model, the vertical pressing assembly is mounted on the base via a lateral displacement mechanism. The lateral displacement mechanism includes: a lateral guide rail fixed to the base; a lateral slider mounted on the lateral guide rail; a fine-tuning screw that drives the lateral slider to move along the guide rail; and an adjustment knob located at the end of the fine-tuning screw for locking the position.

[0012] As a preferred technical solution of this utility model, the end of the clamping rod of the vertical clamping cylinder is provided with a quick-change connector, and the contact surface between the quick-change connector and the welded pipe is a V-shaped structure with an included angle greater than 90°.

[0013] As a preferred embodiment of this utility model, the circular chuck includes three radially locating claws evenly distributed along the circumference, and each radially locating claw has a nylon pad at its end to protect the surface of the welded pipe.

[0014] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0015] 1. Multi-directional collaborative positioning for improved accuracy: Through the combined action of two sets of axially movable horizontal clamping assemblies on the linear guide rail, the support base assembly, and the circular chuck and end clamping assembly at the end, precise axial positioning and support of the welded pipe are achieved. The radial positioning claws of the circular chuck provide the initial radial reference, the V-shaped clamping blocks of the horizontal clamping assembly coordinate radial positioning, the vertical clamping assembly applies downward clamping force, and the axial clamping of the end clamping assembly forms a multi-directional, multi-degree-of-freedom constraint system in the axial, radial, and circumferential directions. This effectively ensures the straightness and concentricity of the pipe body throughout its entire length, significantly reducing the cumulative error of welding eccentricity.

[0016] 2. Effective protection of the pipe surface and prevention of damage: The elastic lifting mechanism in the horizontal clamping assembly can elastically lift the pipe before clamping, reducing impact damage caused by rough placement; during clamping, the floating support provides cushioning to prevent rigid impact between the pipe and the V-shaped clamping block. The adaptive rotating clamping block at the end of the end clamping assembly can automatically adapt to the curved surface of the pipe end, apply force evenly, and prevent end crushing. The radial positioning claws of the circular chuck are equipped with nylon pads at their ends to directly avoid hard contact between the positioning claw metal and the pipe surface. The quick-change connector at the end of the vertical clamping cylinder is designed with a V-shaped contact surface to increase the contact area, disperse pressure, and reduce the risk of indentation.

[0017] 3. Convenient axial position adjustment: Both the horizontal clamping assembly and the support base assembly are slidably fixed on the linear guide rail, facilitating quick adjustment of the axial position according to the welded pipe length and clamping / support requirements; Convenient height adjustment: The wedge-shaped height adjustment block on the top of the support base assembly allows for fine-tuning of the pipe height at the fulcrum to adapt to different support or welding requirements; Precise lateral adjustment: The vertical clamping assembly can accurately position its lateral position through the lateral displacement mechanism, ensuring that the pressure point is in the optimal position, and has good adaptability to different pipe diameters. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings:

[0019] Figure 1 This is a schematic diagram of the overall structure of this utility model;

[0020] Figure 2 This is the front view of this utility model;

[0021] Figure 3 This is a partially enlarged view A of the present invention;

[0022] Figure 4 This is a side view of the present invention;

[0023] Figure 5 This is a schematic diagram of the horizontal clamping assembly of this utility model;

[0024] In the diagram: 1. Base; 2. Linear guide rail; 3. Horizontal clamping assembly; 4. Support base assembly; 5. Circular chuck; 6. End clamping assembly; 7. Vertical clamping assembly; 31. Horizontal slide; 32. V-shaped clamping block; 33. Elastic lifting mechanism; 41. Support slider; 42. Wedge height adjustment block; 51. Radial positioning claw; 52. Nylon pad; 61. Horizontal clamping cylinder; 62. Adaptive rotary clamping block; 63. Lateral adjustment slide; 64. Adjusting handwheel; 71. Vertical clamping cylinder; 72. Quick-change connector; 73. Lateral displacement mechanism; 331. Floating support cylinder; 332. Arc-shaped support plate; 621. Base; 622. Hinge pressure head; 623. Elastic buffer layer; 731. Lateral guide rail; 732. Lateral slider; 733. Fine-tuning screw; 734. Adjustment knob. Detailed Implementation

[0025] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0026] In the attached diagram, all identical reference numerals refer to the same components.

[0027] Example 1: Basic Structure and Core Positioning Functions

[0028] like Figure 1-5 As shown, this utility model provides a multi-directional positioning welding fixture for high-frequency welded pipes, mainly comprising:

[0029] Base 1: Serving as the base of the entire fixture, it is typically made of thick steel plate by welding or casting, providing stable support. Its upper surface is machined with mounting reference surfaces.

[0030] Linear guide rail 2: Fixedly mounted on the upper surface of base 1, extending precisely along the axial direction of the welded pipe. Typically, two parallel high-precision linear guide rails are used, with their length determined based on the typical length of the welded pipe. The grooves or sliders of guide rail 2 provide guidance for subsequent movable components.

[0031] Horizontal clamping assembly 3 (two sets): Two sets are provided to meet basic radial positioning requirements. Each set of horizontal clamping assembly 3 includes: Horizontal slide 31: A slider at the bottom that matches the linear guide rail 2, which can be manually or locked to any axial position on the guide rail 2 by a locating pin. The slide 31 body is generally made of cast iron or welded steel. V-shaped clamping block 32: Rigidly fixed to the top of the horizontal slide 31. The angle of the V-shaped opening is usually 90 degrees or designed to be replaceable according to common pipe diameter series. Its function is to clamp and position the bottom and sides of the welded pipe in the horizontal direction (see appendix). Figure 5 ).

[0032] Elastic lifting mechanism 33: Located on a horizontal slide table 31. Specifically, it consists of one or more vertically mounted floating support cylinders 331, with the cylinder body fixedly embedded in the slide table 31. An arc-shaped support plate 332 is mounted on the top of the piston rod of the cylinder 331. The support plate 332 is made of 5-8mm thick aluminum alloy or engineering plastic, with its upper surface machined into an arc shape matching the outer diameter of the target welded pipe, and lined with a rubber or polyurethane buffer layer. Its function is to elastically lift the welded pipe before clamping to avoid direct collision; during clamping, the floating cylinders 331 provide cushioning and floating support to prevent damage to the pipe body.

[0033] Support assembly 4 (at least one set): slidably mounted on the same linear guide rail 2. Each set includes: a support slider 41: structurally similar to a horizontal slide 31, its bottom slidably connected to and locked to the linear guide rail 2; and a wedge-shaped height adjustment block 42: fixedly mounted on top of the support slider 41. The upper surface of this block is an inclined plane on which standard pads of different thicknesses can be placed, or it may have a movable wedge-shaped slider, whose height at the top of the wedge 42 can be changed by moving the slider. Its function is to finely adjust the height of the welded pipe relative to the V-shaped clamping block 32 at the support point, compensating for straightness errors or meeting special process requirements.

[0034] Please see the appendix Figure 4 The circular chuck 5 is fixedly mounted on the base 1, located at one end of the linear guide rail 2. It has three radial positioning claws 51, evenly distributed along the circumference at 120-degree angles. Each positioning claw 51 can synchronously extend and retract radially via an internal worm gear or lead screw mechanism. A nylon pad 52, made of PA66 or POM with medium hardness, is fixed to the extended end of each positioning claw 51. The function of the circular chuck 5 is to provide a precise initial radial reference point for the welded pipe, restrict the radial freedom of the pipe end, and protect its surface.

[0035] End clamping assembly 6: Located on the base 1 at the other end of the linear guide rail 2, its position is axially adjustable. This assembly includes: a horizontal clamping cylinder 61: for example, a standard double-acting cylinder with a stroke of 150-300 mm, the cylinder body of which is mounted in the end region of the base 1. An adaptive rotary clamping block 62: mounted on the end of the piston rod of the horizontal clamping cylinder 61 via a connector. Specifically, it includes a base 621, an arc-shaped hinged clamping head 622 embedded in the base 621, and an elastic buffer layer 623 adhered to the bottom surface of the hinged clamping head 622. This clamping block 62 can automatically adapt to any slight non-perpendicularity that may exist on the end face when axially clamping the welded pipe, ensuring uniform application of axial force and preventing end deformation or damage.

[0036] Please see the appendix Figure 2 Vertical clamping assemblies 7 (multiple): Arranged on the base 1, located on the side of the linear guide rail 2, and spaced apart along the length of the guide rail. The core of each vertical clamping assembly 7 is a vertical clamping cylinder 71. The position of this cylinder 71 is adjustable laterally. This is achieved through a lateral displacement mechanism 73, which includes a lateral guide rail 731 fixed to the base 1, a lateral slider 732 mounted on the guide rail 731, a fine-tuning screw 733 driving the slider 732 to move along the guide rail 731, and an adjustment knob 734 mounted at the end of the screw 733 for manual rotation and locking. A quick-change connector 72 is installed at the end of the piston rod of the vertical clamping cylinder 71. This connector 72 is used for quick replacement of different pressure heads; its bottom surface in contact with the welded pipe is designed with a V-groove structure with a V-angle of 100-120 degrees to increase the contact area, reduce pressure, and protect the upper surface of the pipe.

[0037] The method of using this utility model is as follows:

[0038] 1. Place the pipe body to be welded on the elastic lifting mechanism 33 of the two horizontal clamping components 3, with one end close to the nylon pad 52 of the circular chuck 5;

[0039] 2. Starting device: The elastic lifting mechanism 33 slowly descends, causing the tube to fall into the opening of the V-shaped clamping block 32, thus completing the radial positioning;

[0040] 3. The horizontal clamping cylinder 61 of the end clamping assembly 6 extends, driving the adaptive rotating clamping block 62 to press against the other end face of the tube body, completing axial positioning and clamping; the radial positioning claw 51 of the circular chuck 5 extends synchronously, and lightly abuts against the outer wall of the tube body through the nylon pad 52 to accurately determine the radial reference.

[0041] 4. When needed, the vertical clamping cylinders 71 of each vertical clamping assembly 7 press down, and through the quick-connect joints 72 at their ends, they press down on the upper surface of the tube body to provide additional circumferential constraint force to resist welding deformation.

[0042] Example 2: Enhanced Adjustment and Auxiliary Support

[0043] Based on Example 1, the tooling's adjustment flexibility, support capacity, and protective performance are further enhanced:

[0044] Position adjustment of end clamping assembly 6: A transverse adjustment slide 63 parallel to the linear guide rail 2 is additionally provided on the base 1 and fixedly installed. The cylinder body of the horizontal clamping cylinder 61 is slidably connected to the slide 63 via a matching slider. An adjusting handwheel 64 is installed at one end of the slide 63, which drives a mechanism that meshes with a lead screw inside the slide 63, so that rotating the handwheel 64 drives the entire end clamping assembly 6 to move precisely along the axial direction. The operator can easily adjust the position of the clamping force according to different welded pipe lengths or pipe end structures.

[0045] Active application of support assembly 4: When welding long welded pipes, in addition to the two support points provided by the horizontal clamping assembly 3 in Embodiment 1, at least one more support assembly 4 is added. The welded pipe is placed on the top plane of the wedge-shaped height adjusting block 42. By finely adjusting the sliding part on the wedge block 42 or replacing the shims, the height of this fulcrum is precisely adjusted to ensure that the straightness of the welded pipe along its entire length meets the requirements of high-precision welding. The support assembly 4 itself has no clamping function, only providing auxiliary support.

[0046] Detailed Description of Flexible Lifting and Protection: The working process of the flexible lifting mechanism 33 is described in more detail. The floating support cylinder 331 typically operates at its lower limit position. When placing the welded pipe, the pipe body is first placed on the arc-shaped support plate 332. When clamping is required, the floating cylinder 331 is slowly vented or a controllable back pressure is applied via air circuit control, causing the pipe body to slowly and smoothly sink into the V-shaped clamping block 32 under gravity or a small force. The arc-shaped surface and buffer layer of the support plate 332 ensure flexible and adaptable contact, significantly reducing the risk of impact damage during placement.

[0047] Example 3: Integrated System Operation

[0048] Combining all the features of the foregoing embodiments, this paper describes the complete process of a welded pipe from placement to clamping, preparing it for welding. It particularly emphasizes the synergistic effect of multi-directional positioning and uses the aforementioned part numbers:

[0049] Axial position preset: Based on the designed length of the welded pipe, move and lock the positions of the two horizontal slides 31 on the linear guide rail 2. Move and lock the support slider 41 to below the middle of the welded pipe. Rotate the adjusting handwheel 64 to move the end clamping assembly 6 as a whole along the transverse adjusting slide 63 to the appropriate position. Rotate the adjusting knobs 734 of each vertical clamping assembly 7 to drive the transverse slider 732 to move on the transverse guide rail 731 through the fine-tuning screw 733, moving the vertical clamping cylinder 71 and quick-change connector 72 to the expected clamping position directly above the welded pipe. If necessary, manually adjust the wedge height adjusting block 42 to make its top surface height appropriate.

[0050] Placement and radial coarse positioning of the welded pipe: Place one end of the welded pipe onto the nylon pad 52 of the extended circular chuck 5 to restrict its radial movement. The entire welded pipe is placed on the arc-shaped support plates 332 of the two horizontal clamping assemblies 3. The middle part of the welded pipe is placed on the top surface of the wedge-shaped height adjustment block 42 of the support assembly 4.

[0051] Multi-directional Precise Positioning and Clamping: The horizontal radial clamping control system uses two sets of horizontal clamping components 3 with floating support cylinders 331 that slowly exhaust air / descend, allowing the welded pipe to smoothly fall into the groove of the V-shaped clamping block 32, achieving precise radial positioning. Simultaneously, the radial positioning claws 51 of the circular chuck 5 move synchronously, and the nylon pad 52 contacts the pipe wall, reinforcing the radial reference. Axial Positioning and Tightening: The piston rod of the horizontal clamping cylinder 61 extends, pushing the adaptive rotating clamping block 62 to contact the free end face of the welded pipe. During tightening, the hinged pressure head 622 adapts to the end face angle, and the buffer layer 623 evenly distributes pressure, completing axial positioning and clamping the welded pipe between the chuck 5 and the clamping block 62. A slight axial preload is applied simultaneously to eliminate gaps. Circumferential Constraint: One or more vertical clamping cylinders 71 extend their piston rods downwards, and the V-shaped surface of their end quick-connect fittings 72 presses against the upper surface of the welded pipe, providing stable downward pressure. This force not only prevents the pipe from sinking due to gravity or welding deformation, but more importantly, it provides the restraining torque required to resist circumferential deformation during the welding process.

[0052] Auxiliary support maintains straightness: The support base assembly 4 provides a stable intermediate support point, and its preset height is ensured by the wedge-shaped height adjustment block 42 to ensure that the tube body will not deflect significantly due to its own weight, thereby improving the overall straightness.

[0053] This utility model is a multi-directional positioning welding fixture for high-frequency welded pipes. Through its ingenious multi-directional positioning clamping structure and flexible and efficient adjustment mechanism, it effectively solves the problems of low positioning accuracy, damage to pipe body, cumbersome adjustment, and poor adaptability of traditional welded pipe fixtures, and significantly improves the welding quality and production efficiency of high-frequency welded pipes.

[0054] Finally, it should be noted that the above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A multi-directional positioning welding fixture for high-frequency welded pipes, comprising a base (1), characterized in that: The base (1) is provided with a linear guide rail (2) along the axial direction of the welded pipe; two sets of horizontal clamping assemblies (3) and at least one set of support assemblies (4) are slidably mounted on the linear guide rail (2) with adjustable axial position; one end of the linear guide rail (2) is fixedly provided with a circular chuck (5) for radial positioning of the welded pipe, and the other end is provided with an end clamping assembly (6) that can move axially; the base (1) is provided with a plurality of vertical clamping assemblies (7) on the side of the linear guide rail (2); wherein: the horizontal clamping assembly (3) includes: a horizontal slide (31) slidably connected to the linear guide rail (2); a V-shaped clamping block (32) fixed to the top of the horizontal slide (31); an elastic lifting mechanism (33) for elastically supporting the pipe body is provided on the horizontal slide (31); the support assemblies (4) include: a support slider (41) slidably mounted on the linear guide rail (2); a wedge-shaped height adjusting block (42) mounted on the top of the support slider (41); the end clamping assembly (6) includes: A horizontally movable clamping cylinder (61); an adaptive rotating clamping block (62) connected to the end of the piston rod of the horizontal clamping cylinder (61); the vertical clamping assembly (7) includes a vertically adjustable clamping cylinder (71).

2. The high-frequency welded pipe multi-directional positioning welding fixture according to claim 1, characterized in that, The elastic lifting mechanism (33) includes a floating support cylinder (331) that runs vertically through the horizontal slide (31) and an arc-shaped support plate (332) located on the top of the floating support cylinder (331). The curvature of the arc-shaped support plate (332) matches the outer diameter of the welded pipe and elastically supports the pipe body under the action of floating support.

3. The high-frequency welded pipe multi-directional positioning welding fixture according to claim 1, characterized in that, The adaptive rotary clamping block (62) includes: a base (621) detachably connected to the piston rod of the horizontal clamping cylinder (61); an arc-shaped hinged clamping head (622) embedded in the base (621); and an elastic buffer layer (623) provided on the bottom end face of the hinged clamping head (622).

4. The high-frequency welded pipe multi-directional positioning welding fixture according to claim 1, characterized in that, The end clamping assembly (6) is also provided with a transverse adjustment slide (63) fixedly connected to the base (1). The cylinder body of the horizontal clamping cylinder (61) is slidably connected to the transverse adjustment slide (63) through a slider, and one end of the slide is provided with an adjustment handwheel (64) for driving the cylinder to move along the slide.

5. The high-frequency welded pipe multi-directional positioning welding fixture according to claim 1, characterized in that, The vertical clamping assembly (7) is mounted on the base (1) via a lateral displacement mechanism (73). The lateral displacement mechanism (73) includes: a lateral guide rail (731) fixed to the base (1); a lateral slider (732) mounted on the lateral guide rail (731); a fine-tuning screw (733) for driving the lateral slider (732) to move along the guide rail; and an adjustment knob (734) located at the end of the fine-tuning screw (733) for locking the position.

6. The high-frequency welded pipe multi-directional positioning welding fixture according to claim 1, characterized in that, The end of the clamping rod of the vertical clamping cylinder (71) is provided with a quick-change connector (72), and the contact surface between the quick-change connector (72) and the welded pipe is a V-shaped structure with an included angle greater than 90°.

7. The high-frequency welded pipe multi-directional positioning welding fixture according to claim 1, characterized in that, The circular chuck (5) includes three radial positioning claws (51) evenly distributed along the circumference, and each radial positioning claw (51) has a nylon pad (52) at its end to protect the surface of the welded pipe.

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