CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Submerged Arc Welding Overlay Technology in Hydraulic Cylinder Production
Literature Overview
This study by Liu Tiejun, Liu Guiqiang, Yuan Guang, Liu Jiuliang, and Han Wenda from Sany Heavy Equipment Co., Ltd. (2012) examines the application of submerged arc welding (SAW) overlay technology in the production of hydraulic cylinders for mining machinery. Published in the journal Coal Mine Machinery, this paper addresses a practical manufacturing challenge: how to produce long, large-diameter hydraulic cylinder barrels with wear-resistant overlay layers at a reasonable cost and with acceptable quality.
Hydraulic cylinders used in mining equipment (excavators, loaders, mining trucks) are subjected to severe abrasive wear from coal, rock, and debris. The cylinder barrel must therefore have a hard, wear-resistant surface while maintaining sufficient toughness in the base material. SAW overlay offers a cost-effective method to deposit a wear-resistant layer on the interior surface of the cylinder barrel.
Core Technical Content
The authors investigated the use of SAW overlay with flux-cored wire or solid wire to deposit a wear-resistant layer on the inner surface of hydraulic cylinder barrels. The typical cylinder barrel dimensions studied are 100–400 mm in diameter and 2000–6000 mm in length, made from medium-carbon steel or low-alloy steel (e.g., 45 steel or 35CrMo).
The SAW overlay process involves the following key elements:
| Parameter | Typical Value |
|---|---|
| Wire type | Solid wire (e.g., H08Mn2SiA) or flux-cored wire |
| Wire diameter | 1.6–2.4 mm |
| Flux type | HJ431 or similar cored flux |
| Welding current | 300–500 A |
| Welding voltage | 28–35 V |
| Travel speed | 200–400 mm/min |
| Number of overlay passes | 1–3 |
| Overlay thickness | 2–5 mm |
| Preheat temperature | 100–150 °C |
The key challenge in SAW overlay for hydraulic cylinders is the geometric constraint: the overlay must be applied to the interior surface of a long, hollow cylinder, which requires specialized equipment such as a rotating fixture with a multi-wire SAW head or a single-wire head with a rotating workpiece.
Process Analysis and Technical Challenges
The primary technical challenges identified in this study include:
- Uniformity of overlay thickness: Achieving uniform overlay thickness along the entire length of the cylinder is critical. Variation in overlay thickness can lead to uneven wear and premature failure. The authors achieved thickness uniformity within ±0.5 mm by carefully controlling the travel speed and the rotation speed of the workpiece.
- Bond strength: The bond between the overlay layer and the base metal must be strong enough to withstand the cyclic loading in hydraulic cylinder service. The authors verified bond strength through tensile testing per ASTM A263, confirming that the fracture occurred in the base metal rather than at the interface.
- Residual stress control: The high heat input of SAW overlay introduces significant residual stresses, which can lead to distortion of the cylinder barrel. The authors addressed this by controlling the interpass temperature and by performing a stress-relief annealing after overlay welding.
- Surface quality: The overlay surface must be smooth enough to accommodate the cylinder piston seal. The authors found that a single-pass SAW overlay with optimized parameters produced a surface roughness (Ra) of 6.3–12.5 μm, which is acceptable for hydraulic cylinder service.
Engineering Practice and Defect Analysis
The following defects were identified and analyzed:
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Lack of fusion | Low current, high travel speed | Increase current, reduce travel speed |
| Porosity | Wet flux, gas porosity | Dry flux thoroughly, ensure proper flux coverage |
| Undercut | Excessive current, improper electrode angle | Reduce current, adjust electrode angle |
| Cracking | High carbon equivalent, insufficient preheat | Increase preheat, reduce heat input |
| Excessive dilution | Too few passes, high current | Increase number of passes, reduce current |
The authors also discussed the importance of post-overlay machining. After the SAW overlay, the cylinder barrel interior must be honed or ground to achieve the required surface finish and dimensional accuracy. This machining step removes the surface irregularities left by the welding process and ensures proper seal performance.
Study Insights and Implications
This paper demonstrates that SAW overlay is a viable and cost-effective method for producing wear-resistant hydraulic cylinder barrels. The key insight is that the process parameters must be carefully optimized for the specific geometry of the cylinder barrel, and that quality control must include both metallurgical and geometric assessments.
From a broader perspective, this study highlights the importance of process selection in manufacturing engineering. While laser cladding and plasma transferred arc (PTA) cladding offer superior surface quality and lower dilution, they are significantly more expensive. For hydraulic cylinders used in mining equipment, where cost is a major consideration and the service environment is not extremely demanding, SAW overlay provides an excellent balance of performance and cost.
The study also underscores the value of process optimization through systematic experimentation. The authors conducted a series of welding trials with varying parameters to identify the optimal process window, which is a fundamental approach to welding process development.