Zhuojin Pipe Fitting Co., LtdSurfacing Technology Application on Hydraulic Cylinder Barrel
Literature Overview
This paper by Chen Zaiming, published in Coal Mine Machinery (Vol. 26, No. 5, 2005, pp. 87-88), describes the application of surfacing technology for the manufacture of hydraulic cylinder barrels (中缸) used in mining equipment. The work addresses a practical manufacturing challenge: producing cost-effective, high-performance cylinder barrels by applying a wear-resistant overlay layer onto a lower-cost base tube, rather than using expensive alloy tubes throughout.
Technical Approach and Feasibility Analysis
Base Material Selection
The study focuses on 27SiMn steel tube as the base material. 27SiMn is a low-alloy structural steel widely used in hydraulic cylinder applications due to its favorable combination of strength, toughness, and weldability. The key parameters of 27SiMn are:
| Parameter | Typical Value |
|---|---|
| Tensile strength (Rm) | 490-630 MPa |
| Yield strength (Re) | ≥345 MPa |
| Elongation (A) | ≥12% |
| Carbon equivalent (Ceq) | 0.42-0.48% |
| Hardness (HBW) | 130-200 |
The relatively high carbon equivalent (approximately 0.45%) places 27SiMn in the category requiring preheating and post-weld heat treatment to avoid hydrogen-induced cold cracking, a critical consideration for the surfacing process design.
Surfacing Methodology
The paper proposes a systematic approach to surfacing the cylinder barrel:
- Surface preparation: Mechanical grinding to remove surface oxide and contamination, ensuring adequate metallurgical bond between the base and overlay.
- Preheating: Applied at 150-250°C to reduce thermal gradient and mitigate residual stress.
- Surfacing process: Multi-pass surfacing using appropriate welding consumables to achieve the required overlay thickness and hardness profile.
- Post-weld heat treatment: Stress relief annealing to reduce residual stresses and prevent delayed cracking.
Welding Consumable Selection
The choice of surfacing consumable is critical for achieving the desired surface properties. For hydraulic cylinder barrels subjected to sliding contact with seals, the overlay should provide:
- Hardness in the range of HV 300-450 for adequate wear resistance without excessive abrasion of seals.
- Smooth surface finish to minimize friction and seal wear.
- Adequate toughness to resist impact loading during cylinder operation.
Common consumable options include austenitic stainless steel electrodes (e.g., E309L, E316L) for corrosion resistance, or martensitic stainless steel electrodes (e.g., E410, E414) for higher hardness and wear resistance. The selection depends on the specific service environment—mining applications may require enhanced wear resistance, while general hydraulic applications may prioritize corrosion resistance and seal compatibility.
Process Parameters and Quality Control
Welding Process Selection
The paper recommends SMAW (Shielded Metal Arc Welding) or SAW (Submerged Arc Welding) for the surfacing operation. SAW is preferred for thicker overlays due to its higher deposition rate and lower dilution, while SMAW offers greater flexibility for smaller or irregular geometries.
| Parameter | SMAW | SAW |
|---|---|---|
| Deposition rate | 1-3 kg/h | 5-15 kg/h |
| Dilution rate | 20-40% | 10-25% |
| Surface quality | Requires grinding | Requires grinding |
| Equipment cost | Low | Moderate |
| Flexibility | High | Moderate |
Post-Weld Heat Treatment
Given the carbon equivalent of the 27SiMn base material, post-weld stress relief is essential. The recommended treatment involves:
- Heating to 550-650°C at a rate of 200°C/h.
- Holding for 2 hours per 25 mm of wall thickness.
- Cooling in furnace at a rate of 100°C/h to below 200°C, then air cooling.
This treatment reduces residual stresses by 60-80% and transforms any martensitic microstructure in the heat-affected zone to a more ductile tempered condition.
Engineering Practice Considerations
From a production standpoint, the surfacing approach to cylinder barrel manufacture offers significant cost advantages over using solid alloy tubes. A typical comparison:
- Solid 40Cr or 42CrMo cylinder barrel: cost index 100
- 27SiMn tube with surfacing overlay: cost index 55-70
The savings are achieved while maintaining functional performance, as the overlay provides the required surface properties while the base tube provides structural integrity. However, engineers must ensure that the overlay thickness is adequate for the expected service life. For mining hydraulic cylinders, an overlay thickness of 3-5 mm per side is typically specified, with a minimum remaining thickness after wear of 1.5 mm.
Key Reflections
This paper exemplifies the practical application of surfacing technology in reducing manufacturing costs without compromising performance. The approach is directly transferable to other cylindrical components in mining and hydraulic equipment, including ram cylinders, accumulator housings, and hydraulic pump barrels. The key insight is that the surfacing process must be designed as an integrated system—base material selection, consumable choice, welding parameters, and heat treatment must all be optimized together rather than treated as independent decisions.