CLADDING TECHNOLOGY SHANXI CO., LTDSintering Blower Blade Cladding Process Study Note
Literature Overview
This 1989 publication by Zhao Jiancang, published in the journal "Fan Technology," addresses the cladding process for sintering blower blades in iron and steel making plants. Sintering blowers operate in extremely harsh environments characterized by high temperatures (up to 250–350°C at the blade leading edge), abrasive dust laden with iron oxide particles, and continuous cyclic loading. The service life of unprotected blades is typically limited to 3–6 months, necessitating frequent maintenance shutdowns.
Core Technical Content
The fundamental problem addressed is the severe erosion wear at the blade leading edge and pressure face of sintering blower impellers. The particle-laden gas stream impacts the blade surface at velocities of 40–60 m/s, causing progressive material removal through micro-cutting and fatigue spalling mechanisms.
Wear Mechanism Analysis
| Wear Zone | Dominant Mechanism | Typical Life (Unclad) | Failure Mode |
|---|---|---|---|
| Blade leading edge | Micro-cutting erosion | 2–3 months | Progressive thinning |
| Blade pressure face | Abrasive sliding | 4–6 months | Surface roughening |
| Blade trailing edge | Erosion + fatigue | 3–5 months | Edge chipping |
| Blade root | Fatigue | 6–12 months | Crack initiation |
The cladding strategy focuses primarily on the leading edge and pressure face, where wear rates are highest. The overlay material must resist erosion by hard iron oxide particles (Fe₂O₃, Fe₃O₄) with Mohs hardness of 6–6.5.
Process Selection and Optimization
The study evaluated multiple cladding processes for application to blower blades:
| Process | Applicability | Deposit Thickness | Surface Quality | Equipment Cost |
|---|---|---|---|---|
| Oxy-acetylene | Simple geometries | 1–3 mm | Moderate | Low |
| Shielded metal arc (SMAW) | Field repair | 0.5–2 mm | Rough | Very low |
| Submerged arc (SAW) | Large flat areas | 2–5 mm | Smooth | Moderate |
| Plasma transferred arc (PTA) | Precision cladding | 0.5–2 mm | Excellent | High |
| Gas tungsten arc (GTAW) | Thin deposits | 0.3–1.5 mm | Fine | Moderate |
For sintering blower blades, the recommended approach combines SAW for building up the base overlay layer (2–3 mm) followed by GTAW or PTA for the final finishing pass (0.5–1 mm) to achieve surface smoothness critical for aerodynamic performance.
Recommended Overlay Material System
The optimal material system for sintering blower blade cladding is a high-chromium cast iron or high-carbon martensitic alloy with the following composition range:
- Carbon: 2.5–4.0%
- Chromium: 12–20%
- Molybdenum: 1–3%
- Vanadium: 0.5–2%
This composition produces a microstructure of primary M₇C₃ carbides in a martensitic matrix, providing excellent resistance to abrasive erosion. The hardness typically achieves 58–64 HRC.
Process Parameters and Quality Control
Critical Process Parameters
| Parameter | Recommended Range | Rationale |
|---|---|---|
| Preheat temperature | 200–300°C | Prevent cold cracking in high-C alloy |
| Interpass temperature | 200–250°C | Control cooling rate for fine microstructure |
| Heat input | 1.5–3.0 kJ/mm | Balance dilution and microstructure |
| Dilution control | <20% | Maintain overlay hardness |
| Post-weld stress relief | 550°C × 2h | Reduce residual stress without softening |
Defect Analysis and Countermeasures
| Defect Type | Root Cause | Detection Method | Countermeasure |
|---|---|---|---|
| Cracking | Excessive cooling rate | MT/PT | Increase preheat, reduce travel speed |
| Excessive dilution | High heat input | Hardness test | Reduce current, increase speed |
| Incomplete fusion | Poor surface preparation | UT | Clean oxide, improve fit-up |
| Porosity | Flux contamination | RT/UT | Dry flux, proper storage |
| Uneven thickness | Manual technique | Visual + UT | Use backing plate, robotic control |
Engineering Practice Integration
The practical implementation of blower blade cladding requires careful consideration of the impeller balance. After cladding, the impeller must be dynamically balanced to G6.3 or better (per ISO 21940-11) to prevent vibration-induced fatigue failure during operation.
A typical maintenance strategy involves:
- Initial cladding — Apply 3–4 mm overlay during original manufacture or first major overhaul.
- Periodic inspection — Measure remaining overlay thickness at 6-month intervals using ultrasonic thickness gauging.
- Rebuild welding — When overlay thickness drops below 1.5 mm, apply additional overlay material to restore the original thickness.
- Grinding and balancing — After rebuild, grind to aerodynamic profile and rebalance.
The economic benefit is substantial: with proper cladding, blade life extends from 4 months to 18–24 months, reducing maintenance frequency by 75–80%. For a large sintering plant with multiple blowers, this translates to significant savings in both material costs and production downtime.
Key Insights and Reflections
The most important insight from this research is that cladding for erosion-resistant applications requires a fundamentally different approach than cladding for corrosion resistance. The overlay material must possess both hardness and a certain degree of toughness to resist the combined effects of impact and sliding abrasion. Purely hard, brittle materials will spall rapidly under erosive conditions.
The study also highlights the importance of surface finish in aerodynamic applications. Unlike static components where surface roughness has minimal functional impact, blower blades require a smooth overlay surface to maintain aerodynamic efficiency. This constraint limits the choice of cladding process — processes producing rough surfaces (such as oxy-fuel or low-quality SAW) are unsuitable for the final layer.
The methodology presented can be extended to other rotating equipment in the iron and steel industry, including induced draft fans, forced draft fans, and dust collection system fans, where similar erosion wear conditions exist.