Zhuojin Pipe Fitting Co., LtdDetailed Technical Considerations for Surfacing Repair of Cement Grinding Equipment Components
Literature Overview
This paper by Huang Zhiquan, Yang Wei, and Li Junwei (Zhengzhou Machinery Research Institute, 2014) provides a comprehensive discussion of the technical details that determine the success of surfacing repair operations for cement grinding equipment, including vertical mill rollers, roller press rolls, and related components. The authors emphasize three critical aspects: base material characterization and defect treatment, transition layer (base layer) consumable selection, and welding consumable quality indicators.
The Three Pillars of Successful Surfacing Repair
1. Base Material Characterization and Treatment
The base material is the foundation of any successful surfacing repair. Key considerations include:
| Base Material Property | Impact on Surfacing | Treatment Requirement |
|---|---|---|
| Carbon equivalent (CE) | Determines crack susceptibility | Preheating and interpass temperature control |
| Existing defects (cracks, porosity) | Can propagate into new weld | NDT inspection and repair welding before surfacing |
| Hardness and microstructure | Affects fusion zone composition | Machining to sound material; possible pre-heat treatment |
| Residual stress from prior service | Increases cracking risk | Stress-relief annealing before surfacing |
| Surface condition | Affects fusion quality | Thorough grinding and cleaning |
The authors stress that surface cracks, even hairline cracks, must be identified through magnetic particle testing (MT) or dye penetrant testing (PT) before any surfacing operation begins. If cracks are found, they must be ground out to a smooth, rounded groove and repaired with a compatible low-hydrogen process before the surfacing layers are applied.
2. Transition Layer (Base Layer) Selection
The transition layer is the critical interface between the base material and the hard wear layer. Its function is to:
- Prevent cracking at the fusion boundary by diluting the high-carbon wear alloy with lower-carbon metal.
- Provide a metallurgically compatible bridge between dissimilar materials.
- Reduce the hardness gradient between the base and the wear layer.
| Transition Layer Type | Typical Composition | Application |
|---|---|---|
| Low-carbon steel | C < 0.20%, Mn 1.0–1.5% | General purpose, low CE base materials |
| Nickel-based | Ni 40–50%, Cr 5–10% | High-CE base materials, crack-sensitive applications |
| Austenitic stainless | Cr 18–25%, Ni 8–12%, C < 0.05% | Where corrosion resistance is also required |
| Low-alloy steel | Cr 1–2%, Mo 0.5–1% | Moderate carbon base materials |
The authors emphasize that the transition layer wire must be carefully selected based on the base material's carbon equivalent and the service conditions. A mismatched transition layer can lead to cracking, poor fusion, or reduced wear life.
3. Consumable Quality Indicators
The welding consumable itself must meet specific quality criteria for reliable surfacing:
- Arc stability: The wire must produce a steady, consistent arc without excessive spatter or arc wandering. Arc instability leads to uneven bead profiles and porosity.
- Porosity resistance: Self-shielded wires are inherently more susceptible to porosity than gas-shielded wires. The flux composition must be optimized to minimize hydrogen and nitrogen pickup.
- Slag distribution and removal: The slag must cover the weld bead uniformly and be easily removable. Incomplete slag coverage exposes the weld to atmospheric contamination.
- Spatter rate: High spatter rates reduce deposition efficiency and can cause surface irregularities. A spatter rate below 5% is generally acceptable for surfacing applications.
Engineering Practice Integration
In practice, the authors recommend a systematic approach using a PDCA (Plan-Do-Check-Act) framework:
- Plan: Conduct thorough base material assessment (NDT, hardness mapping, CE calculation); select appropriate consumables; develop a welding procedure specification (WPS).
- Do: Execute the surfacing operation according to the WPS, maintaining strict control of preheat, interpass temperature, and travel speed.
- Check: Perform post-weld NDT (MT/PT for surface defects, UT for subsurface defects), hardness mapping, and microstructural examination.
- Act: If defects are found, analyze root cause and revise the WPS accordingly.
Key Reflection
This paper's greatest contribution is its emphasis on the "details" that are often overlooked in field repair operations. In my experience, many surfacing failures in cement plants are not due to the wrong wear layer composition but rather due to inadequate base material preparation, poor transition layer selection, or consumable quality issues. The three-pillar framework presented here—base material, transition layer, and consumable quality—provides a practical checklist that can be used by field engineers to systematically evaluate and improve surfacing repair operations. The paper effectively bridges the gap between laboratory metallurgy and field practice.