I. Introduction to the Large Base
The large base is a rigid structural platform that supports ultra-heavy equipment, such as 10,000-ton presses, steam turbine sets, and mining crushers. It bears static loads (including the equipment's own weight—up to several thousand tons)—as well as dynamic loads (such as impacts, vibrations, and torques—for example, the impact force of forging hammers can exceed 10,000 kN)—and environmental loads (including seismic forces, wind loads, and thermal deformations).
Core function: Supporting the equipment's own weight (ranging from hundreds to thousands of tons) and dynamic working loads (impact/vibration).
Maintain equipment installation accuracy (levelness ≤ 0.1 mm/m, parallelism ≤ 0.2 mm/m)
Distribute the load to the foundation to prevent settlement and deformation.
II. Common Materials for Large Bases
Component |
Commonly Used Materials |
Standard/Performance Requirements |
Primary Board Material |
Q355D/E (Chinese National Standard) |
Low-alloy high-strength steel, with an impact energy ≥47 J at -20°C |
A572 Gr.50 (U.S. Standard) |
Yield strength ≥ 345 MPa |
|
Critical weld zone |
Q355ND |
Anti-laminar tearing steel (Z-directional performance ≥ Z25) |
Foundation anchor bolts |
40CrNiMoA |
Alloy structural steel (tensile strength ≥980 MPa) |
III. Selection of Welding Methods
Weld Type |
Recommended Process |
Advantages |
Primary Board Splicing |
Submerged Arc Welding (SAW) |
Large penetration depth, high efficiency (plate thickness ≥30mm) |
Gusset Plate Fillet Weld |
Flux-Cored Arc Welding with Gas Shielding (FCAW) |
Flexible welding in all positions |
High-Requirement Sealed Welds |
Narrow-Gap GMAW |
Low heat input, controllable deformation |
4. Key Processes in Welding Technology
Pre-weld preparation: material cutting, forming, and beveling (with precision control).
Strict cleaning: Remove oil, rust, water, oxide scale, and other contaminants from the bevel and surrounding areas on both sides.
Assembly tack welding: Use the same welding materials and processes as for the final welds, ensuring high-quality tack welds with appropriate length and spacing. Also, inspect assembly gaps and misalignment.
Preheating (if required): Heat evenly to the specified temperature and monitor and record accordingly.
Welding process:
Weld strictly according to the WPS and welding sequence.
Control interlayer temperature (monitor and record).
When performing multi-pass, multi-arc welding, carefully clean away interlayer slag and spatter. Ensure proper fusion of the weld beads to prevent defects.
Monitor key parameters (current, voltage, speed, gas flow rate, etc.).
Key Process Control
Bevel Design: Thick Plate Butt Joint: Double-U Bevel (Reduces Weld Material by 30% and Minimizes Residual Stress)
Rib plate welding: Deep-penetration fillet welds (weld throat ≥ 0.7 × plate thickness)
Preheating and Interpass Temperature: Q355D (plate thickness ≥40mm): Preheat to 80–120°C, with an interpass temperature ≤250°C.
Welding sequence: Symmetrical skip welding method: First weld the vertical rib-to-bottom plate seam → then weld the vertical rib-to-top plate seam
Weld outward from the center to reduce concentrated shrinkage stress.
Post-weld treatment: Vibration Stress Relief (VSR): 30%–50% residual stress reduction (as an alternative to thermal stress relief)
Localized annealing: 600°C stress treatment in the anchor bolt area (preventing fatigue cracks)
Welding Process |
Application Scenarios |
Material preparation process |
Flame cutting (CNC cutting), plasma cutting, laser cutting, shearing, and sawing. High-precision bevel machining (such as edge milling and bevel cutting machines). |
Forming process adopted |
Rolling (cylindrical and conical shapes), bending (using a bending machine), pressure forming (with large-scale presses), and roll forming. |
Assembly and Alignment |
Using large-scale tooling fixtures and platforms—such as welding positioners and roller stands—ensures the precise positioning and dimensions of each component. This is a critical step in quality control. |
Common Welding Methods |
Application Scenarios |
Submerged Arc Welding |
Suitable for long straight welds and circumferential seams (such as longitudinal and circumferential seams of cylindrical shells). |
Gas-shielded welding |
MAG (CO2 or mixed gas), MIG (inert gas). Widely used and highly versatile (manual, semi-automatic, automatic), suitable for various positions and joint types. |
Shielded Metal Arc Welding |
Suitable for positions that are difficult to automate, short welds, and repair welding. It is less efficient and relies heavily on the welder's skill. |
Electroslag Welding |
Vertical welding for extra-thick plates (such as box-beam diaphragms). |
Narrow-Gap Welding |
Designed for butt joints of ultra-thick plates, it offers high efficiency with minimal deformation. |
Post-weld treatment |
|
Stress |
Large components generally require post-weld heat treatment—either overall or localized (typically stress relief annealing)—to remove weld slag and spatter, followed by grinding of the weld seam and its surrounding areas. This process helps relieve residual welding stresses, preventing deformation, cracking, and improving the material's toughness. |
Orthopedic |
Flame straightening, mechanical straightening (using a press), to control welding deformation. |
Mechanical Processing |
Perform precision machining operations such as milling, boring, and drilling on critical mating surfaces and hole locations. |
We will conduct non-destructive testing, inspection, and testing on the products:
| Project | Content |
Visual Inspection |
Surface defects (cracks, undercut appearance inspection (VT), porosity, arc craters, etc.). |
Ultrasonic Testing (UT) |
Detecting internal defects (such as lack of fusion, incomplete penetration, slag inclusions, and cracks) is especially critical for thick plates. |
Radiographic Testing (RT) |
Intuitively displays internal defects and is commonly used for critical butt joints. |
Magnetic Particle Testing (MT) |
Detection of Surface and Near-Surface Defects (Ferromagnetic Materials) |
Penetrant Testing (PT) |
Detecting surface opening defects (non-magnetic materials). |
Destructive Testing (Sampling) |
Such as tensile, bending, impact, hardness, and metallography tests (typically conducted during process qualification or random inspections). |
Dimensional Inspection |
Check whether the overall structural dimensions and dimensions of key components meet the drawing requirements. |
Pressure/Leak Test (if required) |
Such as hydraulic tests, pneumatic tests, and air-tightness tests. |
V. Specification Range
Typical scenario weight reference
Device Type |
Equipment self-weight |
Base weight |
Structural Features |
2000-ton press |
300t |
350–450 tons |
Box-type integral casting + welding |
300MW Steam Turbine Generator Unit |
450t |
550–700 tons |
Modular Steel Plate Welding (Modules ≤50 tons) |
Mining crusher |
80t |
100–120 tons |
Thick base plate + heavy-duty ribbed plate |
Ship Propeller Base |
- |
200–300 tons |
Double-layer grid structure (torsion-resistant design) |
Weight Composition Ratio
Component |
Weight Percentage |
Explanation |
Baseplate |
40% to 50% |
The thickest plate (often reaching 100mm+) |
Top cover plate |
20% to 25% |
Precision-finished surface (flatness ≤1 mm/m) |
Ribbed Plate |
25% to 35% |
Grid spacing ≤ 1.5 m |
Attachment |
5% to 10% |
Anchor bolt boxes, lifting lugs, and more |
Keywords
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