Large base
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  • Large base

1. Introduction to Large Bases

Large bases are rigid structural platforms that support ultra-heavy equipment (such as 10,000-ton presses, turbine units, mining crushers, etc.). They bear static loads (equipment self-weight up to several thousand tons), dynamic loads (impact, vibration, torque, e.g., forging hammer impact force >10,000 kN), and environmental loads (seismic forces, wind loads, temperature deformation).

Core function: To bear the equipment's self-weight (hundreds to thousands of tons) and dynamic working loads (impact/vibration).

Maintain equipment installation accuracy (levelness ≤0.1mm/m, parallelism ≤0.2mm/m).

Distribute loads to the foundation to prevent settlement and deformation.

2. Common Materials for Large Bases

Component

Common Materials

Standards/Performance Requirements

Main Plate Material

Q355D/E (Chinese Standard)

Low alloy high strength steel, impact energy ≥47J at -20°C.

 

A572 Gr.50 (American Standard)

Yield strength ≥345MPa.

Critical Weld Zones

Q355ND

Lamellar tear resistant steel (Z-direction performance ≥Z25).

Anchor Bolts

40CrNiMoA

Alloy structural steel (tensile strength ≥980MPa).

3. Selection of Welding Methods

Weld Type

Recommended Process

Advantages

Main Plate Splicing

Submerged Arc Welding (SAW)

Deep penetration, high efficiency (plate thickness ≥30mm).

Rib Plate Fillet Welds

Flux-Cored Arc Welding (FCAW)

Flexible welding in all positions.

High-demand sealing welds.

Narrow Gap Gas Metal Arc Welding (GMAW)

Low heat input, controllable deformation.

4. Key Welding Process Steps

Pre-welding preparation: material cutting, forming, groove processing (precision control).

Thorough cleaning: remove oil, rust, water, scale from groove and adjacent areas.

Assembly positioning weld: use the same welding materials and processes as formal welding to ensure positioning weld quality; length and spacing should be appropriate. Check assembly gaps and misalignment.

Preheating (if needed): uniformly heat to specified temperature and monitor/record.

Welding process:

Strictly follow WPS and welding sequence.

Control interpass temperature (monitor and record).

For multi-layer and multi-pass welding, carefully clean interpass slag and spatter. Ensure good fusion of weld beads and avoid defects.

Monitor key parameters (current, voltage, speed, gas flow, etc.).

Key process controls

Groove design: thick plate butt joint: double U-groove (reduces welding material by 30%, lowers residual stress).

Rib plate welding: deep penetration fillet weld (weld throat ≥0.7×plate thickness).

Preheat and interpass temperature: Q355D (plate thickness ≥40mm): preheat 80~120°C, interpass temperature ≤250°C.

Welding sequence: symmetrical skip welding: first weld rib to base plate weld → then weld rib to top plate weld.

Weld from center outward to reduce shrinkage stress concentration.

Post-weld treatment: vibration stress relief (VSR): 30%~50% residual stress (alternative to thermal stress relief).

Local annealing: anchor bolt area treated at 600°C (to prevent fatigue cracks).

Welding Processes

Application Scenarios

Cutting processes used

Flame cutting (CNC cutting), plasma cutting, laser cutting, shearing, sawing. High-precision groove processing (such as milling edges, groove cutting machines).

Forming processes used

Plate rolling (cylinders, cones), bending (press brakes), pressure forming (large presses), rolling.

Assembly and fitting

Use large tooling fixtures and platforms (such as welding positioners, roller racks) to ensure precise position and dimensions of components. This is a key quality control step.

Common Welding Methods

Application Scenarios

Submerged Arc Welding

Suitable for long straight welds and circumferential welds (such as cylinder longitudinal and circumferential seams).

Gas Shielded Welding

MAG (CO2 or mixed gas), MIG (inert gas). Most widely used, highly flexible (manual, semi-automatic, automatic), suitable for various positions and joint types.

Shielded Metal Arc Welding (SMAW)

Suitable for positions difficult to automate, short welds, and repair welding. Lower efficiency, depends on welder skill.

Electroslag Welding

Used for vertical welding of ultra-thick plates (such as box girder diaphragms).

Narrow Gap Welding

Used for butt welding of ultra-thick plates, high efficiency, low deformation.

Post-Weld Treatment

 

Stress

Large components generally require overall or partial post-weld heat treatment (usually stress relief annealing), removal of welding slag and spatter, grinding of weld seams and surrounding areas to release residual welding stress, prevent deformation and cracking, and improve toughness.

Straightening

Flame straightening, mechanical straightening (press, etc.) to control welding deformation.

Machining

Precision machining such as milling, boring, drilling on key mating surfaces and hole positions.

 

We conduct nondestructive testing and inspection of products:

Item Content

Visual Inspection

Surface defects (cracks, undercut appearance inspection (VT), porosity, arc pits, etc.).

Ultrasonic Testing (UT)

Detect internal defects (lack of fusion, incomplete penetration, slag inclusion, cracks, etc.), especially important for thick plates.

Radiographic Testing (RT)

Directly displays internal defects, commonly used for important butt joints.

Magnetic Particle Testing (MT)

Detect surface and near-surface defects (ferromagnetic materials).

Penetrant Testing (PT)

Detect surface open defects (non-ferromagnetic materials).

Destructive Testing (Sampling)

Such as tensile, bending, impact, hardness, metallographic tests (usually performed during process evaluation or sampling inspection).

Dimensional Inspection

Check whether overall structural dimensions and key part dimensions meet drawing requirements.

Pressure/Leakage Testing (if needed)

Such as hydraulic test, pneumatic test, airtightness test.

5. Specification Range

Typical Scenario Weight Reference

Equipment Type

Equipment Self-weight

Base Weight

Structural Features

2000t Press

300t

350~450t

Box-type integral casting + welding

300MW Steam Turbine Generator Set

450t

550~700t

Modular steel plate welding (module ≤50t)

Mining Crusher

80t

100~120t

Thick base plate + heavy rib plate

Ship Propeller Base

-

200~300t

Double-layer grid structure (torsion-resistant design)

Weight Composition Ratio

Component

Weight Proportion

Description

Base Plate

40%~50%

Thickest plate (often reaching 100mm+)

Top Cover Plate

20%~25%

Machined surface (flatness ≤1mm/m)

Rib Plate

25%~35%

Grid spacing ≤1.5m

Attachments

5%~10%

Anchor bolt boxes, lifting lugs, etc.

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Large base
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  • Large base

Large base

The large base is a rigid structural platform that supports super heavy equipment (such as 10,000-ton presses, turbine units, mining crushers, etc.) and bears static loads. Common materials used include Q355D/E (national standard), Q355ND, 40CrNiMoA, etc. It is applied in the chemical and mining equipment industries.

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