CLADDING TECHNOLOGY SHANXI CO., LTDWear-Resistant Cladding of Spiral Conveyor Screw Blades - A Study Note
Literature Overview
This 2018 publication by Ma Tiantian and Wang Bingjun from Tangshan Sanyou Chemical Engineering Design Co., Ltd. addresses a specific and highly practical engineering problem: the wear-resistant cladding of spiral conveyor screw blades used in the soda ash industry. Spiral conveyors are critical components in the soda ash production process, where they transport solid materials such as soda ash, intermediate products, and waste materials under abrasive and corrosive conditions. The screw blades are subjected to severe wear from the continuous contact with abrasive particles, and their failure leads to production downtime, increased maintenance costs, and reduced operational efficiency. The study investigates the application of weld overlay cladding to extend the service life of these critical components.
Core Technical Content
The wear mechanism in spiral conveyors is primarily abrasive wear, caused by the sliding contact between the screw blade surface and the solid material being transported. In the soda ash industry, the transported material may contain abrasive particles such as silica, alumina, and calcium carbonate, which cause progressive material removal from the blade surface. The base material of the screw blade is typically a carbon steel such as Q235 or 20# steel, which offers adequate structural strength but poor wear resistance. The application of a wear-resistant overlay layer is therefore essential for extending the service life of the blade.
| Overlay Material | Hardness (HV) | Wear Resistance (relative) | Cost (relative) | Application Suitability |
|---|---|---|---|---|
| Cr-Mo alloy steel (e.g., 40Cr) | 300-400 | 1.0 | 1.0 | Baseline reference |
| High-carbon martensitic steel (e.g., D2) | 600-800 | 2.5-3.5 | 1.5-2.0 | Moderate abrasion |
| Stellite 6 (Co-Cr-W) | 350-450 | 3.0-4.0 | 3.0-5.0 | High abrasion + corrosion |
| WC-Co composite | 800-1200 | 4.0-6.0 | 2.5-4.0 | Severe abrasion |
| High-chromium white cast iron | 600-900 | 3.0-5.0 | 1.5-2.5 | Abrasion + moderate corrosion |
The study evaluates several overlay materials and processes for application to spiral conveyor screw blades. The recommended approach involves a multi-layer cladding strategy: a first layer of a transition alloy (such as a Ni-Fe or Ni-Cr alloy) to ensure adequate bonding with the base steel, followed by one or more layers of the wear-resistant overlay material. The welding process selected depends on the geometry of the screw blade and the production environment. For small to medium-sized blades, SMAW or FCAW may be suitable, while for larger blades or higher production volumes, SAW or GTAW may be preferred.
Process Design and Engineering Considerations
The geometry of a spiral conveyor screw blade presents unique challenges for cladding. The blade surface is helical, with a continuously changing curvature and pitch, which complicates the welding process. The welder must maintain a consistent torch angle and travel speed as the blade rotates, or alternatively, the blade must be rotated during welding to ensure uniform coverage. For automated cladding, a CNC-controlled welding system with a rotating fixture is required to accommodate the helical geometry.
| Process Parameter | Recommended Value | Remarks |
|---|---|---|
| Preheat temperature | 100°C to 200°C | To prevent cracking in base metal |
| Interpass temperature | Below 250°C | To avoid grain coarsening |
| Weld bead overlap | 50% to 60% of bead width | To ensure uniform coverage |
| Layer thickness | 3 mm to 6 mm total | Depending on expected wear rate |
| Post-weld treatment | Stress relief at 550°C to 650°C | To relieve residual stresses |
The dilution rate is a critical factor in the cladding of spiral conveyor blades. The first layer of overlay is subject to significant dilution from the base metal, which can reduce the hardness and wear resistance of the overlay. To mitigate this, a high-dilution-resistant filler material is used for the first pass, followed by a matching composition filler for the subsequent passes. The total dilution rate for a multi-layer overlay is typically in the range of 10% to 20%, which is acceptable for most wear-resistant applications.
Defect Analysis and Quality Control
| Defect Type | Root Cause | Detection Method | Countermeasure |
|---|---|---|---|
| Porosity | Moisture in flux, contamination | Visual inspection, UT | Bake electrodes; clean base metal |
| Cracking | High carbon equivalent, excessive restraint | MT, PT | Preheat; reduce heat input |
| Incomplete fusion | Insufficient current, improper technique | UT, RT | Increase current; optimize torch angle |
| Excessive dilution | High heat input, thin first layer | Metallographic analysis | Use dilution-resistant filler; reduce heat input |
| Uneven thickness | Improper tracking, manual inconsistency | Visual inspection, measurement | Use CNC tracking; standardize technique |
Study Insights and Implications
The application of wear-resistant cladding to spiral conveyor screw blades is a straightforward yet impactful engineering solution that can significantly reduce maintenance costs and improve production reliability in the soda ash industry. The study demonstrates that through careful selection of overlay material, welding process, and process parameters, it is possible to extend the service life of the screw blade by a factor of 3 to 6 compared to the uncladded base material.
The economic analysis presented in the study is particularly valuable for engineers and plant managers who must justify the investment in cladding. The cost of cladding a single screw blade is typically 20% to 40% of the cost of a new blade, but the extended service life results in a net saving of 50% to 70% over the operational life of the conveyor system. This economic benefit is further enhanced by the reduction in production downtime associated with blade replacement.
However, the study also highlights the importance of proper maintenance and inspection of cladded components. The overlay layer is not immune to wear, and periodic inspection is required to monitor the remaining thickness of the overlay and to identify any signs of damage or degradation. When the overlay layer has been worn to a critical thickness, the component should be re-cladded or replaced to prevent damage to the base metal.
This publication is a practical and valuable resource for engineers working on wear-resistant cladding applications in the chemical industry. It provides a clear framework for selecting overlay materials, optimizing welding parameters, and implementing quality control measures for the cladding of spiral conveyor components. The findings are directly applicable to other industries where spiral conveyors are used, including mining, cement, and food processing, and the principles outlined in the study can be adapted to address the specific wear conditions encountered in each application.