CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment and Application of Hardfacing Electrodes for Calender Rolls
Literature Overview
The paper by Huang Zhiquan, Wei Jianjun, Pan Jian, and Xu Jian from the Zhengzhou Machinery Research Institute addresses the development and industrial application of specialized hardfacing electrodes for calender rolls used in rubber, paper, and textile processing industries. Published in the journal "Welding" in 1997, this work represents a significant contribution to the field of tribological engineering and surface engineering, addressing the critical need for durable, wear-resistant surfaces on calender rolls that are subjected to extreme sliding contact conditions. The research combines materials development with process engineering to create a comprehensive solution for calender roll refurbishment and performance enhancement.
Core Technical Content
Calender rolls are cylindrical components used in the processing of rubber, paper, textiles, and other sheet materials. They are subjected to severe wear conditions characterized by high contact pressures (10–50 MPa), sliding velocities (0.5–5 m/s), and the presence of abrasive particles from the processed material. The traditional approach of replacing worn calender rolls is economically impractical due to the high cost of precision-machined roll blanks and the long lead times for manufacturing. Hardfacing welding provides an economical and effective solution for restoring worn rolls and enhancing their surface properties.
The hardfacing electrodes developed in this study are designed to produce overlay welds with specific microstructural characteristics that provide superior wear resistance under the sliding contact conditions encountered in calender roll service. The electrode composition is tailored to produce a weld metal with a combination of hard carbide phases dispersed in a tough matrix, providing both wear resistance and adequate toughness to resist cracking under impact loading.
| Electrode Parameter | Value | Description |
|---|---|---|
| Electrode type | Cellulose coated | E70T-1 equivalent |
| Electrode diameter | 3.2–4.0 mm | Standard sizes |
| Welding current | 100–180 A | DC or AC |
| Overlay thickness | 3–5 mm | Total build-up |
| Surface hardness | 55–65 HRC | Post-quench |
| Carbon content (weld) | 2.5–4.0% | High carbon for carbides |
| Chromium content (weld) | 10–15% | For carbide formation |
| Molybdenum content | 2–3% | Solid solution strengthening |
Electrode Design and Microstructural Engineering
The design of the hardfacing electrode involves careful selection of alloying elements to produce the desired microstructure in the weld metal. The high carbon content (2.5–4.0%) promotes the formation of hard carbide phases such as chromium carbides (Cr7C3, Cr23C6) and cementite (Fe3C), which provide the primary wear resistance mechanism. The chromium content (10–15%) is optimized to maximize carbide formation while maintaining adequate matrix toughness. Molybdenum (2–3%) provides solid solution strengthening of the matrix and improves hot hardness.
The microstructure of the hardfacing weld metal consists of a two-phase system: hard carbide particles (1–10 μm in size) dispersed in a tempered martensitic matrix. The carbide particles are typically Cr7C3 and Cr23C6, with hardness values of 1800–2200 HV and 1500–1800 HV, respectively. The martensitic matrix, after tempering, has a hardness of 45–55 HRC, providing adequate toughness to support the hard carbide particles. The volume fraction of carbides is typically 30–50%, which is sufficient to provide wear resistance without compromising the matrix integrity.
The welding process parameters are optimized to achieve the desired microstructure. The welding current is maintained at 100–180 A to ensure adequate penetration into the base metal while avoiding excessive dilution. The welding speed is controlled to maintain a consistent bead profile and prevent excessive heat input that could lead to coarse carbide formation. The interpass temperature is kept below 200°C to maintain the hardness of previously deposited layers.
Application Performance and Wear Testing
The performance of the hardfacing electrode is evaluated through laboratory wear testing and field trials on actual calender rolls. The laboratory wear testing employs the pin-on-disc method, which simulates the sliding contact conditions encountered in calender roll service. The wear rate is measured as the volume of material lost per unit sliding distance, expressed in mm³/N·m. The results show that the hardfacing weld metal exhibits a wear rate of 0.05–0.15 mm³/N·m, which is 3–5 times lower than that of the base steel and 2–3 times lower than conventional hardfacing materials.
| Test Condition | Wear Rate (mm³/N·m) | Relative Wear Life |
|---|---|---|
| Base steel (16Mn) | 0.5–0.8 | 1.0 |
| Conventional hardfacing | 0.2–0.3 | 2–3 |
| Developed electrode | 0.05–0.15 | 5–8 |
| Stellite 6 | 0.08–0.12 | 4–6 |
Field trials on calender rolls in rubber processing plants demonstrate that the hardfacing overlay extends the service life of the rolls by 4–6 times compared to unhardfaced rolls. The overlay thickness is typically 3–5 mm, which provides adequate material for multiple regrinding operations during the service life of the roll. The overlay surface is ground to a smooth finish (Ra ≤ 0.8 μm) after welding to ensure uniform contact with the processed material.
Defect Prevention and Quality Control
The hardfacing welding process is susceptible to several defects that can compromise the performance of the overlay. Cracking is the most critical defect, as it can lead to spalling of the overlay layer during service. Cracking is primarily caused by the high carbon content of the weld metal, which promotes the formation of brittle carbides and increases the susceptibility to hydrogen-induced cracking. The prevention of cracking requires careful control of the welding parameters, including preheat temperature (150–200°C), interpass temperature (<200°C), and post-weld cooling rate.
Porosity is another common defect, caused by inadequate flux coverage or contamination of the base metal surface. The prevention of porosity requires thorough surface preparation, including grinding to remove rust and scale, and the use of dry electrode storage. Lack of fusion between the overlay weld and the base metal is prevented by ensuring adequate penetration through proper current settings and electrode angle control.
Study Insights and Conclusions
This literature provides a comprehensive approach to the development and application of hardfacing electrodes for calender rolls, integrating materials design, process optimization, and performance evaluation. The key insight is that the performance of a hardfacing electrode is determined by the synergy between the weld metal composition, microstructure, and the welding process parameters. The development of a successful electrode requires iterative optimization of all three factors, guided by a thorough understanding of the wear mechanism and the operating conditions. For engineers, this work demonstrates that even relatively simple welding consumables can provide significant performance improvements when properly designed and applied, offering an economical solution for extending the service life of critical industrial components.