CLADDING TECHNOLOGY SHANXI CO., LTDQuick Repair of Broken Spiral Feeder Shaft by Overlay Welding Method
Literature Overview
This 2002 technical paper by Liu Xinhua from Hunan Yueyang Paper Group Co., Ltd., published in "China Paper Making," describes a practical repair methodology for a broken spiral feeder shaft using overlay welding techniques. The paper exemplifies the application of weld overlay technology in industrial equipment maintenance and repair, demonstrating how proper consumable selection and process control can extend component service life while minimizing production downtime.
Failure Analysis and Repair Strategy
Component Description
The spiral feeder shaft is a critical component in paper manufacturing equipment, responsible for conveying pulp or paper stock through the production line. The shaft typically consists of:
- Material: 45# steel or 40Cr (medium carbon alloy steel)
- Diameter: 80–150 mm
- Length: 2–5 m
- Operating conditions: Continuous rotation under load, exposure to moisture and fibrous material
Failure Mode
The shaft fracture typically occurs due to:
- Fatigue failure: Cyclic loading from continuous operation leads to crack initiation and propagation
- Wear-induced stress concentration: Localized wear creates stress risers at the fracture site
- Corrosion fatigue: Moisture and chemical exposure from paper manufacturing processes accelerate crack growth
- Thermal cycling: Temperature fluctuations from hot pulp exposure create thermal stresses
Repair Approach Selection
| Repair Method | Feasibility | Cost | Downtime | Durability |
|---|---|---|---|---|
| Complete replacement | High | Very High | Long (ordering) | Excellent |
| Mechanical fastening (sleeve) | Moderate | Low | Short | Poor (stress concentration) |
| Overlay welding repair | High | Low-Medium | Short | Good (with proper technique) |
| Brazing | Moderate | Medium | Short | Moderate |
| Bushing + interference fit | High | Medium | Short | Good |
The overlay welding approach was selected because it offers the best combination of cost-effectiveness, minimal downtime, and adequate repair durability for a feeder shaft operating under moderate loads.
Repair Process Details
Surface Preparation
- Fracture assessment: Visual and MT examination to determine crack extent and propagation direction
- Crack removal: Grinding or machining to remove all cracked material with a minimum 5 mm undercut beyond visible fracture
- Surface cleaning: Grinding to bare metal (Ra < 6.3 μm), followed by solvent cleaning
- Preheating: 200–300°C applied to reduce HAZ hardness and hydrogen cracking risk
Welding Parameters
| Parameter | Value | Rationale |
|---|---|---|
| Process | SMAW (shielded metal arc welding) | Portability, suitability for field repair |
| Electrode | E5016 / D107 (low-hydrogen type) | Low hydrogen content, good weldability |
| Electrode diameter | 4.0 mm | Adequate penetration for shaft diameter |
| Current | 160–200 A | Balanced penetration and spatter |
| Arc voltage | 22–26 V | Stable arc, good bead profile |
| Preheat temperature | 200–300°C | Prevents cold cracking |
| Interpass temperature | ≤ 300°C | Controls cooling rate |
| Number of layers | 2–3 | Achieves full section restoration |
| Post-weld treatment | 600°C × 2h stress relief | Reduces residual stresses |
Welding Sequence
The repair welding sequence follows these principles:
- Start at the center of the repair area to minimize restraint
- Weld in multiple short passes (not exceeding 100 mm per pass) to control heat input
- Alternate sides to compensate for angular distortion
- Grind between layers to ensure proper fusion and remove surface defects
- Final grinding to restore original shaft diameter and surface finish (Ra < 3.2 μm)
- Post-weld stress relief to prevent delayed cracking and reduce residual stresses
Quality Verification
Inspection Protocol
| Inspection | Method | Acceptance Criteria |
|---|---|---|
| Surface quality | Visual + MT | No cracks, pores > 0.5 mm |
| Penetration | UT or sectioning | Full fusion, no lack of fusion |
| Hardness | Rockwell B scale | 200–250 HB (matching base metal) |
| Mechanical properties | Tensile test (coupons) | Tensile ≥ 500 MPa, elongation ≥ 20% |
| Dimensional accuracy | Micrometer/OD gauge | Within ±0.05 mm of original diameter |
| Surface finish | Roughness tester | Ra ≤ 3.2 μm |
Performance Verification and Service Life
After repair, the shaft underwent:
- Load testing: Verification under simulated operating loads confirming adequate strength
- Balancing: Dynamic balancing to ensure smooth rotation at operating speed
- Service monitoring: Periodic MT inspection at 3-month intervals during the first year
The repaired shaft achieved a service life of 18–24 months before requiring re-inspection, representing a significant extension compared to the pre-repair failure interval of 6–8 months. This demonstrates that properly executed overlay welding repair can restore component functionality to near-original levels.
Engineering Practice Reflections
This case study illustrates several fundamental principles of industrial repair welding:
- Root cause analysis is essential: Understanding the failure mechanism (fatigue vs. overload vs. corrosion) determines the appropriate repair strategy and whether repair is even feasible.
- Consumable selection governs repair success: Low-hydrogen electrodes (E5016/D107) are critical for medium-carbon alloy steel repairs to prevent delayed hydrogen cracking. The use of high-hydrogen electrodes would likely result in repair failure within days of return to service.
- Heat input control prevents new problems: Excessive heat input during repair can soften the HAZ of the original shaft, creating a new weakness. Controlled heat input (limited by short passes and interpass temperature control) preserves the base metal properties.
- Post-weld treatment is non-negotiable: Stress relief after repair welding reduces the risk of delayed cracking and improves fatigue resistance of the repair area.
- Economic justification: The repair cost (typically 5–10% of new shaft cost) and minimal downtime make overlay welding repair the preferred option for non-critical rotating equipment where component weight and shipping logistics make replacement impractical.
The broader implication for maintenance engineering is that weld overlay repair should be considered as a standard maintenance option for rotating shafts, rather than defaulting to complete replacement. With proper procedure development, consumable selection, and quality verification, repair welding can extend component life at a fraction of replacement cost while reducing production downtime and environmental impact from scrapped material.