CLADDING TECHNOLOGY SHANXI CO., LTDCrankshaft Regeneration Technology and Submerged Arc Welding Overlay Special Equipment
Literature Overview
This technical document addresses the regeneration of worn crankshafts through submerged arc welding (SAW) overlay and the development of dedicated welding equipment tailored to this application. Crankshafts in heavy-duty engines and industrial machinery are subject to severe wear, particularly at the journal surfaces and cam lobes. Conventional repair methods often involve grinding down the worn surfaces, which reduces the overall shaft diameter and may compromise structural integrity. SAW overlay offers a superior alternative by restoring dimensional accuracy while simultaneously improving surface hardness and wear resistance.
Core Technical Principles
The fundamental approach involves depositing a layer of alloy steel or high-carbon steel weld metal onto the worn crankshaft surface using submerged arc welding. The flux blanket protects the molten pool from atmospheric contamination while stabilizing the arc and providing controlled cooling. The key technical challenges lie in maintaining geometric accuracy on a cylindrical, often contoured, surface and ensuring metallurgical compatibility between the base material (typically 40CrNiMo or 42CrMo quenched and tempered steel) and the deposited overlay.
Process Parameters and Equipment Design
The dedicated SAW equipment must accommodate the following requirements:
| Parameter | Typical Value | Notes |
|---|---|---|
| Welding current | 300-500 A | Single wire SAW |
| Arc voltage | 24-32 V | Controlled by wire feed |
| Wire diameter | 2.0-3.2 mm | High-carbon or alloy wire |
| Flux type | Low-hydrogen rutilic | Must be low-spatter |
| Travel speed | 150-300 mm/min | Adjusted for layer thickness |
| Preheat temperature | 150-250 °C | Reduces residual stress |
| Interpass temperature | ≤250 °C | Prevents grain coarsening |
The special equipment incorporates a rotating fixture that indexes the crankshaft while the welding head traverses axially. Positioning accuracy of ±0.1 mm is critical to ensure uniform overlay thickness across the journal. The flux delivery system uses a gravity-fed hopper with a pneumatic return mechanism to minimize flux waste and contamination.
Engineering Practice and Defect Analysis
During field application, the most common defects observed include:
- Lack of fusion at the root: Caused by insufficient preheat or excessive travel speed. The countermeasure is to increase preheat to 200 °C and reduce travel speed by 20%.
- Cracking in the heat-affected zone: Occurs when welding thick overlay layers without adequate interpass temperature control. A post-weld stress relief treatment at 580-620 °C for 2 hours per 25 mm of thickness is recommended.
- Porosity from flux contamination: Moisture absorption in stored flux is the primary cause. Flux must be stored at 150-200 °C in a heated cabinet and used within 8 hours of removal.
- Surface irregularities: Result from improper wire stick-out length or oscillation frequency mismatch. Maintaining a constant stick-out of 12-15 mm and oscillation frequency of 2-4 Hz yields smooth surfaces.
Integration with Machining Operations
After overlay, the crankshaft journals are machined to final dimensions. The recommended sequence is: rough grinding to remove 0.5-1.0 mm of the overlay, followed by finish grinding to achieve surface roughness Ra ≤ 0.4 μm. The overlay material should provide a minimum build-up of 3.0 mm to allow for multiple grinding passes without exposing the base metal. Hardness after tempering should be 35-45 HRC to match the base material specification.
Study Insights
The development of dedicated SAW equipment for crankshaft regeneration represents a significant advancement over manual or semi-automatic approaches. The precision of automated wire tracking and flux delivery directly translates to consistent weld bead geometry, which reduces post-weld machining time by an estimated 30-40%. This study reinforces the principle that equipment design and process parameter optimization must be treated as an integrated system rather than independent variables. Engineers should always validate the proposed process through a full-scale trial weld on a sacrificial component before committing to production repair.