Zhuojin Pipe Fitting Co., LtdApplication of Surfacing Welding Technology on Hydraulic Cylinder Middle Barrel
Literature Overview
This paper by Chen Zaiming, published in Coal Mine Machinery (Volume 26, Issue 5, 2005, pp. 87–88), describes the application of surfacing welding technology for manufacturing the middle cylinder (barrel) of hydraulic support pillars used in underground coal mining. The author, representing Huaibei Mining Group Electromechanical Equipment Co., Ltd., addresses the practical challenges of producing wear-resistant cylinder barrels using 27SiMn steel tubing as the base material.
Technical Background
Hydraulic support pillars are critical equipment in mechanized coal mining, where the middle cylinder (or barrel) is subjected to severe wear from coal dust, rock fragments, and hydraulic fluid. The wear resistance of the cylinder inner surface directly affects the service life and reliability of the pillar. Traditional manufacturing approaches involve machining the inner surface to precise tolerances and applying surface treatments, but these methods may not provide sufficient wear resistance for harsh underground conditions.
Material Selection: 27SiMn Steel
27SiMn is a medium-carbon low-alloy steel widely used in China for hydraulic cylinder barrels due to its favorable combination of strength, toughness, and machinability. The key material properties relevant to surfacing welding are:
| Property | Typical Value | Relevance to Surfacing |
|---|---|---|
| Carbon equivalent (CE) | ~0.45–0.55% | Moderate crack susceptibility |
| Tensile strength | 630–760 MPa | Adequate substrate strength |
| Hardness | 200–250 HB | Requires compatible overlay |
| Preheat requirement | 100–200°C | To reduce crack risk |
Surfacing Method and Process Design
Surfacing Approach
The paper proposes a multi-pass surfacing scheme for the inner surface of the cylinder barrel. The process involves:
- Surface preparation: Grinding and cleaning of the inner surface to remove oxide scale and contamination.
- Preheating: Uniform preheating of the cylinder to 150–200°C to reduce thermal stress and hydrogen-induced cracking risk.
- Multi-pass surfacing: Application of multiple layers of wear-resistant weld metal using shielded metal arc welding (SMAW) or submerged arc welding (SAW), depending on accessibility.
- Post-weld heat treatment (PWHT): Stress relief annealing at 550–650°C followed by slow cooling in the furnace.
Welding Material Selection
The selection of welding consumables is critical for ensuring both wear resistance and metallurgical compatibility with the 27SiMn substrate. The recommended approach involves:
- Transition layer: A low-carbon steel or low-alloy steel electrode (e.g., E5015 or E5016) to reduce dilution and prevent cracking at the interface.
- Overlay layer: A high-carbon or high-alloy wear-resistant electrode (e.g., E50MoCr or E60MoCr) to provide the required hardness and abrasion resistance.
Post-Weld Heat Treatment
The PWHT is a critical step in this application. For 27SiMn steel components, the following considerations apply:
| PWHT Parameter | Recommended Range | Purpose |
|---|---|---|
| Temperature | 550–650°C | Stress relief without excessive grain growth |
| Holding time | 2–4 hours per 25 mm thickness | Uniform stress relief |
| Cooling rate | ≤50°C/h (furnace cooling) | Prevent re-introduction of residual stress |
| Maximum cooling rate | 100°C/h (below 300°C) | Avoid martensitic transformation |
Feasibility Analysis
The author provides a theoretical analysis of the feasibility of surfacing welding on 27SiMn tubes, considering:
- Weldability: 27SiMn has a moderate carbon equivalent, requiring preheat and controlled heat input to prevent cold cracking. The use of low-hydrogen electrodes and appropriate preheat effectively mitigates this risk.
- Dilution control: Multi-pass surfacing with a transition layer reduces the dilution rate to acceptable levels, ensuring the overlay layer achieves the target hardness.
- Dimensional control: The thermal distortion from surfacing welding can be managed by symmetric welding sequences and fixture support, maintaining the cylindrical geometry within tolerance.
Engineering Practice and Recommendations
Based on production experience, the paper offers the following practical recommendations:
- Use low-hydrogen, low-alloy electrodes with controlled hydrogen diffusion rate to minimize porosity and cracking.
- Maintain interpass temperature between 150–250°C to prevent excessive cooling and thermal shock.
- Apply a back-gas or backing strip during welding to prevent oxidation and undercut on the back side.
- Perform visual inspection and magnetic particle testing (MT) after each pass to detect defects early.
- Conduct hardness profiling across the overlay to verify the gradient from substrate to overlay surface.
Study Insights and Implications
This paper, though relatively concise, addresses a practical manufacturing challenge that is highly relevant to the coal mining and heavy equipment industries. The key insight is that surfacing welding can be successfully applied to 27SiMn cylinder barrels by carefully managing the welding sequence, consumable selection, and heat treatment. For engineers involved in the manufacturing or repair of hydraulic cylinder components, this work provides a validated process framework that balances wear resistance, metallurgical compatibility, and manufacturing feasibility. The emphasis on PWHT as a critical quality control step is particularly important, as residual stress from surfacing can lead to premature failure under cyclic hydraulic loading. Future improvements could include the use of automated surfacing systems for improved consistency and the development of low-dilution overlay consumables specifically designed for 27SiMn substrates.