Views: 0 Author: Site Editor Publish Time: 2026-09-07 Origin: Site
A complete car dumper can weigh several hundred tons, with overturning torque exceeding several thousand ton-meters. Each working cycle subjects the structure to alternating loads, impact stresses, and fatigue cycles. Its steel structure serves as the mechanical skeleton, and any weld defect may lead to structural failure after tens of thousands of working cycles. This paper elaborates on the key technical points of steel structure welding for car dumpers from three dimensions: structure, process, and quality.
The core load-bearing members of the car dumper steel structure include:
Main girders typically adopt box-section beams with plate thicknesses of 20 mm to 60 mm, made of Q345B/Q345C steel, resisting bending moments and shear forces during overturning.
End girders connect the ends of the main girders. The butt welds between end girders and main girders are full-penetration Class I welds, requiring 100% UT acceptance.
The turntable (overturning platform) directly carries the weight of railway cars. Its structure is mostly a circular box girder or truss-type composite structure. The connection areas with the drive system have high stress concentrations, with weld design rated as Class I, requiring control of post-weld residual stress.
Roller support brackets bear the total dead weight and dynamic loads. The base plate thickness ranges from 80 mm to 120 mm, falling into ultra-thick plate welding, which requires preheating, interpass temperature control, and post-weld heat treatment (PWHT).
Components such as holding arms and backing plates endure dynamic impact from railway cars during each overturn. They often involve dissimilar steel welding between high-strength steel and wear-resistant steel (e.g., Q345 + NM400). The matching of welding consumables and the welding procedure qualification must be verified separately.
The hinge point supports of the hydraulic drive system are typical high-stress concentration areas. Welds must meet fatigue strength design requirements, generally assessed per BS 7608 or IIW (International Institute of Welding) fatigue design standards, corresponding to F2 or G class in S-N curves.
For each type of joint configuration, welding procedure qualification tests (PQR) must be completed prior to production welding to verify that the mechanical properties of the weld metal meet design requirements. Core assessment indicators include:
Test Item | Typical Requirement (Q345B/C) |
Tensile Strength | ≥ 490 MPa |
Yield Strength | ≥ 345 MPa |
Elongation after Fracture | ≥ 21% |
Impact energy (KV₂) at -20℃/-40℃ | ≥ 34J / ≥ 27J (depending on thickness and design temperature) |
Bend Test | Face bend / root bend 180°, no cracks |
For thick plates (≥40 mm) and steels used in low-temperature conditions, additional Z-direction tensile testing is required to evaluate the lamellar tearing susceptibility of the base metal. The Z-direction reduction of area ψz ≥ 35% is required for critical load-bearing members.
Base Metal Mechanical Properties (GB/T 1591 Q345 Series)
Property | Q345B | Q345C | Q345D |
Yield Strength ReL (MPa) | ≥ 345 | ≥ 345 | ≥ 345 |
Tensile Strength Rm (MPa) | 470–630 | 470–630 | 470–630 |
Elongation A (%) | ≥ 21 | ≥ 22 | ≥ 22 |
Impact Test Temperature (℃) | +20 | 0 | -20 |
Impact Energy KV₂ (J) | ≥ 34 | ≥ 34 | ≥ 34 |
Carbon Equivalent CEV (typical) | 0.40–0.44 | 0.38–0.42 | 0.36–0.40 |
Welding Consumable Matching Parameters
Base Metal | Welding Method | Wire/Electrode | Flux/Gas | Applicable Standard |
Q345B/C | SAW | H08MnA / H10Mn2 | SJ101 | GB/T 5293 |
Q345B/C | FCAW | E71T-1 / E71T-11 | 80%Ar+20%CO₂ | AWS A5.20 |
Q345B/C | GMAW | ER70S-6 | 80%Ar+20%CO₂ | AWS A5.18 |
Q345B/C | SMAW | E5015 / E5016 | — | GB/T 5117 |
Q345+NM400 | FCAW | E110T1-K3 | 80%Ar+20%CO₂ | AWS A5.29 |
Welding Method Application Matrix
Welding Method | Abbreviation | Applicable Welds | Thickness Range (mm) | Positions | Heat Input (kJ/cm) | Efficiency |
Submerged Arc Welding | SAW | Main girder longitudinal seams, circumferential seams | 20–60 | PA/PB | 25–40 | High |
Gas Shielded Welding | GMAW/FCAW | Short seams, fillet welds | 12–40 | All positions | 12–28 | Medium |
Shielded Metal Arc Welding | SMAW | Tack welding, repair welding | 6–40 | All positions | 8–30 | Low |
The car dumper steel structure welding adopts a combination of multiple welding methods:
Submerged Arc Welding (SAW): Used for long straight seams such as main girder longitudinal and circumferential seams, with H08MnA/H10Mn2 wire and SJ101 sintered flux. Welding current 600 A–1000 A, arc voltage 30 V–38 V.
Gas Shielded Welding (GMAW/FCAW): Used for short seams, fillet welds, and field installation welds. Flux-cored wires E71T-1 or E71T-11, all-position welding, low spatter, and easy slag removal.
Shielded Metal Arc Welding (SMAW): Used for tack welding, repair welding, and confined-space welding. Low-hydrogen electrodes E5015/E5016, baked at 350℃–400℃ for 2 hours before use.
The key to thick-plate welding lies in thermal cycle control, which requires a management system comprising preheating, interpass temperature, and post-weld heat treatment:
Preheating
When plate thickness ≥ 25 mm or carbon equivalent CEV ≥ 0.45%, preheating temperature ≥ 100℃.
When plate thickness ≥ 40 mm, preheating temperature 120℃–150℃.
When plate thickness ≥ 60 mm or for highly restrained T-joints, preheating temperature 150℃–200℃.
Preheating zone: at least ≥ 75 mm on both sides of the weld. Use electric heating pads or flame heating, with real-time monitoring by infrared thermometers.
Joint Type | Thickness (mm) | Wire Dia. (mm) | Welding Current (A) | Arc Voltage (V) | Welding Speed (cm/min) | Heat Input (kJ/cm) | Layers/Passes | Groove Angle | Gap (mm) |
Butt (main girder long. seam) | 20–30 | φ4.0 | 550–650 | 30–34 | 40–50 | 20–30 | 2 layers, 2 passes | 60° | 0–2 |
Butt (main girder long. seam) | 30–40 | φ4.0 | 600–750 | 32–36 | 35–45 | 28–38 | 3 layers, 4 passes | 60° | 0–2 |
Butt (end girder butt) | 40–60 | φ5.0 | 700–900 | 34–38 | 30–40 | 35–50 | 4 layers, 6 passes | 50° | 0–3 |
T-joint (web-flange) | 20–30 | φ4.0 | 500–600 | 28–32 | 45–55 | 16–24 | 1 layer, 1 pass | — | — |
T-joint (web-flange) | 30–40 | φ4.0 | 600–700 | 30–34 | 35–45 | 24–36 | 2 layers, 2 passes | — | — |
Interpass Temperature Control
During multi-layer and multi-pass welding, interpass temperature shall be strictly controlled between the preheating temperature and 250℃.
Designate dedicated temperature monitoring personnel, with at least 3 interpass temperature records per weld pass.
In case of overtemperature, stop welding and allow cooling to prevent grain coarsening in the heat-affected zone.
Post-Weld Heat Treatment (PWHT)
For critical load-bearing welds with plate thickness ≥ 40 mm, perform stress-relief heat treatment at 580℃–620℃ after welding.
Holding time calculated as 2.5 min/mm, with a minimum of 2 hours.
Heating rate ≤ 200℃/h, cooling rate ≤ 260℃/h; air cool below 300℃.
For large components that cannot be furnace-treated as a whole, use local heat treatment or vibratory stress relief (VSR) as alternatives.
The main girder of a car dumper is over 20m in length, and welding deformation control directly affects assembly accuracy. Deformation control strategies are as follows:
Design aspect: Welds shall be arranged symmetrically about the neutral axis of the section to reduce eccentric shrinkage.
Process aspect: Welding sequence (symmetric welding, back-step welding, skip welding), SAW heat input 25 kJ/cm–40 kJ/cm.
Fixturing aspect: Use dedicated welding jigs and counter-deformation tooling; preset an upward camber of 3 mm/10 m–5 mm/10 m for the main girder.
The following parameter matrices are based on common joint types and thickness ranges used in car dumper steel structures, verified by procedure qualification, and may serve as references for WPS preparation.
Wire grades: H08MnA / H10Mn2; Flux: SJ101 (sintered type), baked at 350℃×2h; Polarity: DC reverse polarity (DCEP).
Joint Type | Thickness (mm) | Wire Dia. (mm) | Current (A) | Voltage (V) | Speed (cm/min) | Gas Flow (L/min) | Heat Input (kJ/cm) | Stick-out (mm) |
Butt (all positions) | 12–20 | φ1.2 | 220–280 | 24–28 | 25–35 | 15–20 | 12–20 | 15–20 |
Butt (flat) | 20–40 | φ1.6 | 280–360 | 26–32 | 20–30 | 18–25 | 18–28 | 18–25 |
Fillet (short seams) | 10–20 | φ1.2 | 200–260 | 22–26 | 30–40 | 15–20 | 8–16 | 15–20 |
Fillet (field welds) | 20–30 | φ1.6 | 260–320 | 26–30 | 20–30 | 18–25 | 16–24 | 18–22 |
FCAW wire grades: E71T-1 (all positions) / E71T-11 (vertical-down); Shielding gas: 80%Ar + 20%CO₂; Polarity: DCEP.
Electrode Dia. (mm) | Thickness (mm) | Current (A) | Voltage (V) | Speed (cm/min) | Heat Input (kJ/cm) | Typical Application |
φ3.2 | 6–12 | 100–130 | 22–26 | 12–18 | 8–14 | Tack welding, root pass |
φ4.0 | 10–20 | 150–180 | 24–28 | 10–16 | 14–22 | Filling, cover pass |
φ5.0 | 16–40 | 200–250 | 26–30 | 10–14 | 20–30 | Thick-plate filling |
Electrode grades: E5015 (J507) / E5016 (J506), low-hydrogen type; bake at 350℃–400℃ for 2h before use, keep in holding oven for on-demand use.
Parameter | Narrow-Gap GMAW | Narrow-Gap SAW | Conventional V-Groove (for comparison) |
Groove angle | 10°–15° | 8°–12° | 60° |
Groove depth | 60–100 mm | 60–100 mm | 60–100 mm |
Root gap | 2–4 mm | 2–4 mm | 0–3 mm |
Passes per layer | 1–2 | 1–2 | 3–5 |
Total fill volume | reduced 40%–60% | reduced 45%–65% | reference |
Welding heat input | 15–25 kJ/cm | 25–40 kJ/cm | 35–60 kJ/cm |
Interpass temperature | ≤ 200℃ | ≤ 250℃ | ≤ 250℃ |
Post-weld deformation | reduced 30%–50% | reduced 35%–55% | reference |
Heat treatment: Furnace treatment preferred for the whole component; if not feasible, use flexible ceramic electric heating pads for local heating, covering an area at least 3× plate thickness on both sides of the weld and no less than 300 mm, with thermocouple spacing ≤ 300 mm and temperature difference controlled within ±20℃.
Based on IIW formula: CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
CEV Value | Thickness < 25 mm | Thickness 25–40 mm | Thickness 40–60 mm | Thickness > 60 mm |
< 0.40 | No preheat | No preheat | ≥ 75℃ | ≥ 100℃ |
0.40–0.45 | No preheat | ≥ 75℃ | ≥ 100℃ | ≥ 125℃ |
0.45–0.50 | ≥ 50℃ | ≥ 100℃ | ≥ 125℃ | ≥ 150℃ |
> 0.50 | ≥ 75℃ | ≥ 125℃ | ≥ 150℃ | ≥ 175℃ |
Typical CEV for Q345B: ≈ 0.40–0.44; for Q345C: ≈ 0.38–0.42.
When ambient temperature ≤ 5℃, add 25℃ to all preheating temperatures.
The quality inspection system for car dumper steel structure welds includes the following stages:
All welds shall be 100% visually inspected. Acceptance criteria:
Uniform weld appearance, reinforcement 0–3 mm, width deviation ≤ 2 mm.
No undercut, lack of fusion, surface porosity, crater cracks, or other surface defects.
Smooth weld toe transition without sharp notches (especially critical in fatigue-prone areas).
Weld Class | UT Ultrasonic Testing | MT Magnetic Particle | RT Radiographic Testing |
Class I | 100% (GB/T Grade II acceptable) | 100% | Spot check 10%–20% |
Class II | 20% (GB/T Grade III acceptable) | 100% on critical areas | — |
Class III | — | Spot check | — |
For full-penetration welds with thickness ≥ 40 mm, supplement with TOFD (Time-of-Flight Diffraction) or Phased Array Ultrasonic Testing (PAUT) to improve defect detection rate and quantification accuracy.
Product weld test plates shall be welded with the same furnace batch and same process as the product, and heat-treated together with the product.
Samples from the test plates shall undergo tensile, bend, and impact tests (full set of mechanical properties).
Impact test temperature shall be determined by the minimum design service temperature (typically -20℃ or -40℃).
Main girder camber / sweep: Measure with total station or laser tracker; deviation controlled within L/1000.
Flatness of critical mounting surfaces: ≤ 1 mm/m.
Coaxiality of hinge holes: ≤ φ0.5 mm.
Abrasive blast cleaning grade: Sa2.5 (per GB/T 8923).
Coating system: Zinc-rich epoxy primer (75 μm) + epoxy micaceous iron intermediate (100 μm) + polyurethane topcoat (50 μm); total dry film thickness ≥ 225 μm.
Adhesion test: Cross-cut method, Grade 0–1 acceptable.
The Welding Management System (WMS) enables:
Real-time acquisition and storage of welding parameters (current, voltage, speed, heat input).
Welder identification and qualification traceability.
Consumable batch traceability and baking records.
NDT report correspondence with weld locations, supporting digital delivery.
For complex joints and ultra-thick plate welding, finite element welding simulation techniques (e.g., Sysweld / Abaqus Welding Interface) are employed to:
Simulate temperature fields and optimize preheating schemes.
Predict residual stress and guide PWHT parameters.
Predict deformation and optimize welding sequence and counter-deformation amounts.
Narrow-Gap Welding: For full-penetration welds with thickness ≥ 60 mm, using narrow-gap GMAW or SAW with groove angle 10°–15°, reducing fill volume by 40%–60%.
Robotic Welding Workstation: 6-axis welding robot with positioner, repeat positioning accuracy ±0.1 mm.
Field Welding Technology: For on-site installation welding of large components, equipped with mobile weather-proof welding shelters and portable heat treatment equipment.
The welding of car dumper steel structures shall comply with the following standards:
GB/T 12469 – Quality assurance for welding – Classification and grading of defects for fusion welded joints in steel
GB 50661 – Code for welding of steel structures
NB/T 47014 – Welding procedure qualification for pressure equipment (reference)
AWS D1.1 – Structural Welding Code – Steel (for export projects)
EN 1090-2 – Execution of steel structures and aluminium structures (for CE-marked projects, EXC3/EXC4 level)
ISO 3834-2 – Quality requirements for welding – Comprehensive quality requirements (system certification)
Welder qualification: All welders shall hold qualification certificates for the corresponding welding methods (per GB/T 5185 or ISO 9606) through ISO 3834-2 certification, and shall undergo regular retraining and skill reassessment.
Car dumpers are widely used in bulk material unloading in port terminals, thermal power plants, steel and metallurgical industries, performing hundreds of turnovers per day with annual throughput measured in tens of millions of tons.
From consumable incoming inspection to weld delivery, from process simulation to non-destructive testing, this paper systematically presents the technical system for welding car dumper steel structures, for industry reference.
For further details on car dumper steel structure welding processes or technical consultation, please feel free to contact us.
