CN109514055B - A low-plate longitudinal beam assembly welding process - Google Patents

Abstract

The invention belongs to the technical field of aluminum alloy welding, and relates to a welding process for a low-plate longitudinal beam assembly. The web patch between the rear sections of the beam, the blocking plate welded to the front section of the longitudinal beam and the outer side of the web patch, and the lower flange of the longitudinal beam welded to the front section of the longitudinal beam and the lower end of the rear section of the longitudinal beam, are divided into four stages during welding. The specific steps are as follows: welding the front section of the longitudinal beam and the web patch, welding the front section of the longitudinal beam and the blocking plate, welding the web patch and the rear section of the longitudinal beam, and welding the lower flange of the longitudinal beam. Through the analysis of the factors, the welding sequence to prevent the welding deformation of the aluminum alloy longitudinal beams is proposed. By arranging the welding sequence reasonably, the welding deformation of the aluminum alloy longitudinal beams can be prevented, and the welded aluminum alloy longitudinal beams can meet the production requirements and reduce the The amount of adjustment after welding saves man-hours and speeds up the production progress.

Description

A low-plate longitudinal beam assembly welding process

technical field

The invention belongs to the technical field of aluminum alloy welding, and relates to a welding process for a low-plate longitudinal beam assembly.

Background technique

The density of aluminum alloy is 2.7g/cm ³ , which is only 1/3 of that of steel. Aluminum alloy has good corrosion resistance and can maintain a smooth surface for a long time without any protective measures. In addition, aluminum alloy also has good welding and plastic processing performance. In order to meet the requirements of energy saving and emission reduction, the lightweight of automobiles has become the consensus of the automobile industry, and the extensive use of aluminum alloy components is the most feasible way to realize the lightweight of automobiles.

The low-bed semi-trailer is a widely used heavy-duty transportation vehicle. In order to meet the strength requirements, the current low-bed semi-trailer mostly uses steel components; although all-aluminum low-bed semi-trailer products have also been reported, they mainly stay in the tank type. At the level of cars and vans, it cannot be extended to skeleton container semi-trailers, mainly because the skeleton container semi-trailer does not have a top assembly, and the frame assembly does not have ring beams, floors and side beams. The strength of the whole vehicle is completely borne by the longitudinal beams, and the strength requirements for the longitudinal beams of the low-plate semi-trailer are greatly improved, and the aluminum alloy longitudinal beams of ordinary structures cannot meet the strength requirements. The main reason is that the aluminum alloy low-plate semi-trailer longitudinal beams currently on the market often undergo deformation during the welding process, which reduces the accuracy of the welding component pairing, and the mechanical properties of the final welded low-plate semi-trailer longitudinal beam cannot meet the requirements. Production requirements.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a low-plate longitudinal beam assembly in order to solve the problems of low production quality and production efficiency of the low-plate longitudinal beam after welding by the welding method in the prior art, and the mechanical properties after welding cannot meet the production requirements. welding process.

In order to achieve the above object, the present invention provides a welding process for a low-plate longitudinal beam assembly. The low-plate longitudinal beam includes a longitudinal beam front section, a longitudinal beam rear section located on the lower right side of the longitudinal beam front section, and welded on the longitudinal beam front section and the longitudinal beam rear section. The web patch between the sections, the blocking plate welded on the front section of the longitudinal beam and the outer side of the web patch, and the lower flange of the longitudinal beam welded on the front section of the longitudinal beam and the lower end of the rear section of the longitudinal beam, are divided into four stages during welding, and the specific steps are as follows:

A. Welding the front section of the longitudinal beam and the web patch: leave a 1.5mm weld in the middle of the front section of the longitudinal beam and the arc section of the web patch, and open a 55° groove on both sides; the front section of the longitudinal beam and the sides of the web patch are Two-layer two-pass symmetrical welding, in which the welding current of each layer of welding seam is 180-200A, the welding voltage is 23.2-23.4V, the welding speed is 8-10mm/s, the shielding gas is high-purity inert gas, protective The gas flow rate is 18~22L/min, and the inclination angle between the welding torch and the vertical direction is 5~20°; after welding, the front section of the longitudinal beam and the flatness of the web patch are adjusted by orthopedic adjustment to ensure that the flatness is less than or equal to 1mm;

B. Welding between the front section of the longitudinal beam and the blocking plate: Fix the blocking plate on the front section of the longitudinal beam and the outer side of the web patch, and weld the weld between the upper end of the web patch and the front section of the longitudinal beam by two layers and two symmetrical welding methods. The welding method of two layers and two passes welds the welds between the two sides of the web patch, the front section of the longitudinal beam, and the web patch. The welding current is 260-270A, the welding voltage is 24.4-24.5V, and the welding speed is both. It is 8～10mm/s, the shielding gas is high-purity inert gas, the shielding gas flow rate is 18～22L/min, and the inclination angle between the welding torch and the vertical direction is 5～20°;

C. Welding the web patch and the rear section of the longitudinal beam: Put the entire longitudinal beam vertically on the tooling, lift and fix the front section of the longitudinal beam, keep the front section of the longitudinal beam and the rear section of the longitudinal beam in the same horizontal direction, and place the blocking plate A single V-shaped groove is made at the connection with the rear section of the longitudinal beam, and the V-shaped groove and the side of the rear plate of the longitudinal beam are welded by two layers and two symmetrical welding methods. The welding current of the inner layer is 260~270A, and the welding voltage is 24.4~24.5 V, the welding current of the outer layer is 220~230A, and the welding voltage is 23.8~24.0V; the V-shaped groove and the upper surface of the rear panel of the longitudinal beam are welded by two layers and two symmetrical welding methods, and the welding current of the inner layer is 235~245A, The welding voltage is 24.1~24.2V, the outer welding current is 210~220A, and the welding voltage is 23.7~23.8V; the welding speed is 8~10mm/s, the shielding gas is high-purity inert gas, and the shielding gas flow rate is 18 ～22L/min, the inclination angle of welding torch and vertical direction is 5～20°;

D. Welding of the lower wing plate of the longitudinal beam: Flip the longitudinal beam and fix it on the tooling, and weld the lower wing plate of the longitudinal beam to the lower end of the entire longitudinal beam, in which the single-layer single-pass welding method is used to weld the lower wing plate of the longitudinal beam and the front section of the longitudinal beam. The welding current is 180~190A, and the welding voltage is 24.2~24.4V; the welding method of the lower wing plate of the longitudinal beam and the arc corner of the entire longitudinal beam is three-layer four-pass welding. The welding parameters from the inside to the outside are as follows: first Layer welding current is 265~275A, welding voltage is 24.5~24.6V, second layer welding current is 245~255A, welding voltage is 24.2~24.3V, third layer welding current is 220~230A, welding voltage is 23.8~24.0 V; the welding method of the lower wing plate of the longitudinal beam and the rear section of the longitudinal beam is two-layer three-pass welding, the welding current of the inner layer is 260-270A, the welding voltage is 24.4-24.5V, the welding current of the outer layer is 220-230A, and the welding voltage It is 23.8~24.0V, the welding speed is 8~10mm/s, the shielding gas is high-purity inert gas, the shielding gas flow rate is 18~22L/min, and the inclination angle between the welding torch and the vertical direction is 5~20°.

Further, in step A, the protective gas is 99.999% Ar.

Further, in step B, the two-layer two-pass symmetrical welding method between the upper end of the web patch and the front section of the longitudinal beam is to first weld the bottom and then cover the surface, and grind the weld after welding.

Further, in step C, the entire longitudinal beam is vertically placed on the tooling, and the front section of the longitudinal beam is supported and fixed with a brace.

Further, step D adopts the welding method of circular hole girder welding to point-fix the straight part of the rear end of the longitudinal beam lower wing plate and the longitudinal beam lower wing reinforcement plate; The gap between the plate and the lower wing reinforcement plate of the longitudinal beam is less than or equal to 3mm.

Further, perform reverse deformation before welding in step D, fix the rear section of the longitudinal beam on the tooling platform, and lift the front end with a jack, so that the front end of the front section of the longitudinal beam is about 30-40mm higher than the vertical height of the rear end, and the specific height difference is based on the actual production. The gap size of the weld seam is adjusted accordingly.

Further, grinding and preheating should be performed before the welding seams in steps A to D, and the welding seams should be smoothed after welding.

Further, after the welding in step D, the overall longitudinal beam rectification ensures that the levelness error between the front section of the longitudinal beam and the rear section of the longitudinal beam is less than 3 mm.

Further, in step D, a 50mm non-welded part is left at the end of the lower wing plate of the longitudinal beam at the lower end of the rear section of the longitudinal beam.

The beneficial effects of the present invention are:

Due to the good thermal conductivity and ductility of aluminum alloys, during the welding process of aluminum alloys, the heat generated will cause deformation of the aluminum alloys, which will cause difficulties in the accuracy of the welding parts, and cannot guarantee the welding process. The mechanical properties of the weld bead; and the use of a reasonable welding sequence can reduce the deformation of aluminum alloy profiles, which is a good and effective method in production practice. In actual aluminum alloy welding production, there are many structural sections with symmetrical shapes and symmetrical weld arrangements, but bending or twisting deformation occurs after welding, which is mainly caused by unreasonable welding sequence, that is, the deformation caused by each weld is not Can cancel each other, resulting in deformation.

对某些焊缝布置不对称的结构，应该先焊接焊缝少的一侧。

先焊短焊缝，后焊长焊缝；先焊横焊缝，后焊纵焊缝。

当存在焊接应力时，先焊拉应力区，后焊剪应力和压应力区。

位于构件刚性最大的部位最后焊接(尽可能使构件能够自由收缩)。The welding sequence is one of the main factors affecting the deformation of the welded structure. The following principles should be paid attention to when arranging the welding sequence: ① All welds must be welded (including covered welds). ②The welding seam that can be reached by the welding torch can be welded. ③ For workpieces with weld shrinkage, they should be welded into assemblies first, and the process volume should be marked on the drawing. ④Try to let the welding seam shrink without restraint, and the welding direction is from the inside to the outside, from the middle to the two ends. ⑤ Butt welds are welded before fillet welds. ⑥ Y-shaped grooves are not allowed to have gaps. First weld the Y-shaped grooves, and then weld the V-shaped grooves. ⑦For long welds, try to use symmetrical welding, and 2 welders perform symmetrical welding from both sides at the same time. In this way, the deformation caused by each weld can be partially offset, and the diagonal welding method or welding from the middle to both sides can also be used. ⑧ For double-sided welding, the welding sequence is based on the difficulty of root cleaning. ⑨ Try to avoid unnecessary multiple turnover of the workpiece. ⑩ Weld the weld with larger section first, and then weld the weld with smaller section.

For some structures with asymmetrical arrangement of welds, the side with less welds should be welded first.

Weld short welds first, then weld long welds; weld horizontal welds first, then longitudinal welds.

When there is welding stress, the tensile stress area is welded first, and then the shear stress and compressive stress areas are welded.

The most rigid part of the component is welded last (as much as possible to allow the component to shrink freely).

In the welding process of the low-plate longitudinal beam assembly disclosed in the present invention, through the analysis of the influencing factors of the welding deformation of the low-plate longitudinal beam, a welding sequence for preventing the welding deformation of the aluminum alloy longitudinal beam is proposed. The welding deformation of the alloy longitudinal beam ensures that the welded aluminum alloy longitudinal beam can meet the production requirements, and also reduces the amount of post-weld adjustment, saves man-hours, and speeds up the production progress.

Description of drawings

In order to make the purpose, technical solutions and beneficial effects of the present invention clearer, the present invention provides the following drawings for description:

1 is a schematic diagram of the welding structure of the front section of the longitudinal beam and the web patch panel of the present invention;

2 is a schematic diagram of the welding structure of the front section of the longitudinal beam and the blocking plate of the present invention;

Figure 3 is a schematic diagram 1 of the welding structure between the web patch and the rear section of the longitudinal beam according to the present invention;

Figure 4 is a second schematic diagram of the welding structure between the web patch and the rear section of the longitudinal beam according to the present invention;

FIG. 5 is a schematic diagram of the welding structure of the lower wing plate of the longitudinal beam of the present invention.

Detailed ways

The preferred embodiments of the present invention will be described in detail below.

Reference numerals in the accompanying drawings include:

The front section of the longitudinal beam 1, the web patch plate 2, the blocking plate 3, the rear section of the longitudinal beam 4, and the lower wing plate of the longitudinal beam 5.

A low-plate longitudinal beam assembly welding process, the low-plate longitudinal beam comprises a longitudinal beam front section 1, a longitudinal beam rear section 4 located on the lower right side of the longitudinal beam front section 1, and welded between the longitudinal beam front section 1 and the longitudinal beam rear section 4 The web patch 2, the blocking plate 3 welded on the front section 1 of the longitudinal beam and the outer side of the web patch 2, and the lower flange 5 of the longitudinal beam welded on the lower end of the front section 1 of the longitudinal beam and the rear section 4 of the longitudinal beam, are divided into four parts during welding. stage, the specific steps are as follows:

A. Welding the front section 1 of the longitudinal beam and the web patch 2 as shown in Figure 1: leave a 1.5mm weld in the middle of the arc section of the longitudinal beam front section 1 and the web patch 2, and open a 55° bevel on both sides; The two sides of the front section 1 and the web patch 2 are welded with two layers and two passes. The welding current of each layer of welding seam is 180~200A, the welding voltage is 23.2~23.4V, and the welding speed is 8~10mm/ s. The shielding gas is 99.999% Ar, the shielding gas flow rate is 18~22L/min, the inclination angle between the welding torch and the vertical direction is 5~20°, the welding seam should be ground and preheated before welding, and the welding seam should be ground after welding. Flat; orthopedic adjust the flatness of the front section 1 of the longitudinal beam and the web patch 2 after welding to ensure that the flatness is less than or equal to 1mm;

B. Welding the front section 1 of the longitudinal beam and the blocking plate 3 as shown in Figure 2: Fix the blocking plate 3 on the outer side of the front section 1 of the longitudinal beam and the web patch 2, and weld the web patch by two layers and two symmetrical welding. 2 The welding seam between the upper end and the front section 1 of the longitudinal beam, the welding method is bottom welding and then cover welding, and the weld seam is ground after welding; the two sides of the web patch 2 are welded with the welding method of two layers and two passes. The welding seam between the front section 1 of the longitudinal beam and the web patch 2, the welding current is 260~270A, the welding voltage is 24.4~24.5V, the welding speed is 8~10mm/s, and the shielding gas is 99.999%Ar , The flow rate of the shielding gas is 18~22L/min, the inclination angle of the welding torch and the vertical direction is 5~20°, the welding seam should be ground and preheated before welding, and the welding seam should be smoothed after welding;

C. Weld the web patch 2 and the rear section 4 of the longitudinal beam as shown in Figures 3 to 4: place the entire longitudinal beam on the tooling, support and fix the front section 1 of the longitudinal beam with a brace, and keep the front section of the longitudinal beam. 1 and the rear section 4 of the longitudinal beam are in the same horizontal direction, a single V-shaped groove is made at the connection between the blocking plate 3 and the rear section 4 of the longitudinal beam, and the V-shaped groove and the rear plate of the longitudinal beam are welded by two layers and two symmetrical welding methods. On the side, the welding current of the inner layer is 260-270A, the welding voltage is 24.4-24.5V, the welding current of the outer layer is 220-230A, and the welding voltage is 23.8-24.0V; the V-shaped groove is welded by two layers and two symmetrical welding methods. With the upper surface of the rear panel of the longitudinal beam, the welding current of the inner layer is 235~245A, the welding voltage is 24.1~24.2V, the welding current of the outer layer is 210~220A, and the welding voltage is 23.7~23.8V; the welding speed is 8~10mm /s, the shielding gas is 99.999% Ar, the shielding gas flow rate is 18-22L/min, the inclination angle between the welding torch and the vertical direction is 5-20°, the welding seam should be ground and preheated before welding, and the welding should be carried out after welding. seam smooth;

D. Welding of the longitudinal beam lower wing plate 5 as shown in Figure 5: Flip the longitudinal beam and fix it on the tooling, and use the welding method of circular hole ring welding to flatten the longitudinal beam lower wing plate 5 and the rear end of the longitudinal beam lower wing reinforcement plate. The straight part is point-fixed; the point-fixing length is 50mm, the adjacent point-fixing is 400mm intermittently, and the gap between the longitudinal beam lower wing plate 5 and the longitudinal beam lower wing reinforcement plate is ≤3mm. At the same time, do reverse deformation before welding, fix the rear section 4 of the longitudinal beam on the tooling platform, and lift the front end with a jack, so that the front end of the front section 1 of the longitudinal beam is about 30-40mm higher than the vertical height of the rear end, and the specific height difference is based on the actual production welding. Adjust the gap size accordingly. Weld the lower wing plate 5 of the longitudinal beam on the lower end of the entire longitudinal beam, wherein the lower wing plate 5 of the longitudinal beam and the front section 1 of the longitudinal beam are welded by a single-layer single-pass welding method, the welding current is 180-190A, and the welding voltage is 24.2-24.4V; The welding method of the lower wing plate 5 of the longitudinal beam and the arc corner of the entire longitudinal beam is three-layer four-pass welding. The welding parameters from the inside to the outside are: the welding current of the first layer is 265-275A, and the welding voltage is 24.5-24.6 V, the welding current of the second layer is 245-255A, the welding voltage is 24.2-24.3V, the welding current of the third layer is 220-230A, and the welding voltage is 23.8-24.0V; the lower wing plate 5 of the longitudinal beam and the rear section 4 of the longitudinal beam The welding method is two-layer three-pass welding, the inner welding current is 260~270A, the welding voltage is 24.4~24.5V, the outer welding current is 220~230A, the welding voltage is 23.8~24.0V, and the welding speed is 8~ 10mm/s, shielding gas is 99.999% Ar, shielding gas flow rate is 18~22L/min, welding torch and vertical inclination angle are 5~20°, grinding and preheating should be carried out before welding, and after welding Welds are ground.

Step D: A 50mm unwelded part is left at the end of the lower wing plate 5 of the longitudinal beam at the lower end of the rear section 4 of the longitudinal beam. After welding, the overall longitudinal beam orthopedic ensures that the level error between the front section 1 of the longitudinal beam and the rear section 4 of the longitudinal beam is less than 3mm.

Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should Various changes may be made in details without departing from the scope of the invention as defined by the claims.

Claims (9)

1. The utility model provides a low dull and stereotyped longeron assembly welding process, its characterized in that, low dull and stereotyped longeron include the longeron anterior segment, be located longeron rear segment of longeron anterior segment right side downside, the welding mends the board at the web between longeron anterior segment and longeron rear segment, welds the closure plate in longeron anterior segment and web mends the board outside and welds the longeron lower wing board at longeron anterior segment and longeron rear segment lower extreme, four stages during the welding, concrete step is:

A. welding the front section of the longitudinal beam and the web plate patch plate: reserving a 1.5mm welding line between the front section of the longitudinal beam and the arc line section of the web plate patch, and forming 55-degree bevels on two sides; two layers of two symmetrical welding are adopted for the front section of the longitudinal beam and two sides of the web plate patch, wherein the welding current of each layer of welding seam is 180-200A, the welding voltage is 23.2-23.4V, the welding speed is 8-10 mm/s, the shielding gas is high-purity inert gas, the flow of the shielding gas is 18-22L/min, and the inclination angle of a welding gun to the vertical direction is 5-20 degrees; the flatness of the front section of the longitudinal beam and the web plate patch plate is adjusted in a shape-righting manner after welding, and the flatness is guaranteed to be less than or equal to 1 mm;

B. the front section of the longitudinal beam is welded with the blocking plate: fixing a blocking plate on the front section of a longitudinal beam and the outer side of a web plate patch, welding a welding seam between the upper end of the web plate patch and the front section of the longitudinal beam by adopting a two-layer two-way symmetrical welding mode, and welding seams between two sides of the web plate patch and the front section of the longitudinal beam and between two sides of the web plate patch by adopting a two-layer two-way symmetrical welding mode, wherein the welding current is 260-270A, the welding voltage is 24.4-24.5V, the welding speed is 8-10 mm/s, the protective gas is high-purity inert gas, the flow of the protective gas is 18-22L/min, and the inclination angle of a welding gun to the;

C. welding a web plate patch plate and the rear section of the longitudinal beam: vertically placing the whole longitudinal beam on a tool, lifting and fixing the front section of the longitudinal beam, keeping the front section of the longitudinal beam and the rear section of the longitudinal beam in the same horizontal direction, forming a single V-shaped groove at the joint of the blocking plate and the rear section of the longitudinal beam, and welding the V-shaped groove and the side surface of the rear plate of the longitudinal beam by adopting a two-layer two-way symmetrical welding mode, wherein the inner layer welding current is 260-270A, the welding voltage is 24.4-24.5V, the outer layer welding current is 220-230A, and the welding voltage is 23.8-24.0V; welding the V-shaped groove and the upper end face of the longitudinal beam rear plate by adopting a two-layer two-way symmetrical welding mode, wherein the welding current of the inner layer is 235-245A, the welding voltage is 24.1-24.2V, the welding current of the outer layer is 210-220A, and the welding voltage is 23.7-23.8V; the welding speed is 8-10 mm/s, the shielding gas is high-purity inert gas, the flow rate of the shielding gas is 18-22L/min, and the inclination angle of a welding gun to the vertical direction is 5-20 degrees;

D. welding a lower wing plate of the longitudinal beam: the longitudinal beam is turned and fixed on a tool, and a lower wing plate of the longitudinal beam is welded at the lower end of the whole longitudinal beam, wherein a single-layer single-channel welding mode is adopted to weld the lower wing plate of the longitudinal beam and the front section of the longitudinal beam, the welding current is 180-190A, and the welding voltage is 24.2-24.4V; the welding mode of longeron lower wing board and whole longeron arc corner is four welds of three-layer, and welding parameter from inside to outside does in proper order: the welding current of the first layer is 265-275A, the welding voltage is 24.5-24.6V, the welding current of the second layer is 245-255A, the welding voltage is 24.2-24.3V, the welding current of the third layer is 220-230A, and the welding voltage is 23.8-24.0V; the welding mode of the lower wing plate of the longitudinal beam and the rear section of the longitudinal beam is two-layer three-pass welding, the welding current of the inner layer is 260-270A, the welding voltage is 24.4-24.5V, the welding current of the outer layer is 220-230A, the welding voltage is 23.8-24.0V, the welding speed is 8-10 mm/s, the protective gas is high-purity inert gas, the flow of the protective gas is 18-22L/min, and the inclination angle of a welding gun to the vertical direction is 5-20 degrees.

2. The low plate rail assembly welding process of claim 1, wherein the shielding gas in step a is 99.999% Ar.

3. The welding process of the low flat plate longitudinal beam assembly according to claim 1, wherein the two-layer symmetrical welding mode of welding the upper end of the web patch and the front section of the longitudinal beam in the step B is that backing welding is performed first and then cover surface welding is performed, and the welding seam is ground flat after welding.

4. The welding process of the low flat plate longitudinal beam assembly according to claim 1, wherein in the step C, the whole longitudinal beam is vertically placed on a tool, and the front section of the longitudinal beam is supported and fixed by a support.

5. The welding process of the low flat plate longitudinal beam assembly according to claim 1, wherein in the step D, the straight parts of the rear ends of the longitudinal beam lower wing plate and the longitudinal beam lower wing reinforcing plate are fixed in a spot mode through circular hole girth welding; the length of the point fixing is 50mm, the adjacent point fixing is interrupted by 400mm, and the gap between the lower wing plate of the longitudinal beam and the lower wing reinforcing plate of the longitudinal beam is less than or equal to 3 mm.

6. The welding process of the low flat plate longitudinal beam assembly according to claim 5, wherein the backward deformation is performed before the welding in the step D, the rear section of the longitudinal beam is fixed on a tool platform, the front end of the longitudinal beam is jacked up by a jack, the vertical height of the front end of the front section of the longitudinal beam is 30-40 mm higher than that of the rear end of the longitudinal beam, and the specific height difference is adjusted correspondingly according to the gap size of the welding line in actual production.

7. The welding process of the low flat plate longitudinal beam assembly according to any one of claims 1 to 6, wherein grinding and preheating are carried out before welding of the welding seams in the steps A to D, and the welding seams are ground flat after welding.

8. The welding process for the low flat plate longitudinal beam assembly according to claim 7, wherein the step D of the integral longitudinal beam reshaping after welding ensures that the levelness error of the front section of the longitudinal beam and the rear section of the longitudinal beam is less than 3 mm.

9. The low plate rail assembly welding process of claim 7, wherein step D leaves a 50mm unwelded portion at the end of the lower panel of the lower end rail of the rear section of the rail.

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