CLADDING TECHNOLOGY SHANXI CO., LTDCladding of Spiral Shaft for Fiber Carbon Forming Machine
Literature Overview
This 1993 publication by Li Jixian from the General Machinery Factory in Hanzhong, Shaanxi Province, addresses the weld overlay repair and hardening of the spiral shaft used in fiber carbon forming machines. The spiral shaft (helical screw) is a critical component in fiber forming operations where continuous material feeding and precise extrusion are required. The document represents early Chinese industrial practice in applying cladding techniques to high-wear rotating components in specialized machinery, published at a time when domestic hardfacing expertise was still developing rapidly.
Core Technical Content
The spiral shaft in a fiber carbon forming machine operates under extreme conditions: continuous abrasive contact with carbon fiber precursor material, elevated temperatures from the forming process, and significant torsional and bending loads. The base steel of the shaft, typically a medium carbon steel such as 45# steel or 40Cr, suffers from rapid wear at the flight surfaces where material friction is highest. The cladding approach described here applies a hardfacing overlay to the flight surfaces to extend service life while maintaining dimensional accuracy.
Key Technical Parameters
| Parameter | Typical Value | Notes |
|---|---|---|
| Base material | 45# steel or 40Cr | Medium carbon / low-alloy steel |
| Cladding material | High-carbon martensitic hardfacing (Cr-C type) | E.g., D256 or equivalent |
| Overlay thickness | 1.5–3.0 mm | Minimum 1.5 mm for effective protection |
| Preheating temperature | 250–350 °C | Reduces HAZ hardness and cracking risk |
| Interpass temperature | ≤ 300 °C | Controls residual stress |
| Post-weld heat treatment | 560–600 °C, 2 h | Stress relief and tempering of overlay |
| Hardness requirement | HV 800–1000 (as-welded); HV 500–600 (after T/T) | Balances wear resistance and toughness |
| Bond strength | ≥ 200 MPa (shear) | Per NB/T 47014 qualification |
Process Analysis and Engineering Insights
The spiral geometry presents unique challenges for cladding operations. Unlike flat or cylindrical surfaces, the helical flight surface requires either:
- Manual welding with continuous rotation of the shaft, maintaining consistent travel speed and heat input along the helix.
- Machine welding with a programmed torch head that follows the helical path while the workpiece rotates at a controlled rate.
The critical process variable is maintaining a uniform overlay thickness along the entire helical length. Variations in thickness lead to eccentricity after grinding, which introduces vibration during operation. The recommended approach involves applying the overlay with a generous build-up (2–3 mm excess), followed by precision grinding to the final helical profile using a CBN or diamond tool on a specialized lathe.
Common Defects and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking in overlay | High carbon equivalent, rapid cooling | Preheat to 300 °C; use low-hydrogen consumable; post-weld stress relief |
| Poor bond at interface | Insufficient base metal melting | Increase heat input; ensure proper bevel preparation (30° V-groove) |
| Thickness variation | Inconsistent travel speed or torch height | Use CNC-guided welding head; monitor with in-process sensors |
| Porosity | Flux contamination or moisture | Bake flux at 300 °C for 2 h; maintain clean shielding gas |
Reflections on Engineering Practice
This publication, while modest in scope, reflects the practical engineering mindset of the early 1990s in Chinese manufacturing — solving immediate production problems through proven welding technology rather than exotic materials. The choice of Cr-C type hardfacing is well-suited to the abrasive wear regime of fiber forming, where sliding contact with carbon precursors demands high hardness and good cold cracking resistance.
From a modern perspective, the process parameters described would benefit from additional considerations: hydrogen-induced cracking susceptibility of high-carbon martensitic overlays, the potential for micro-cracking in the overlay itself (which may be acceptable for abrasive wear but not for corrosive environments), and the importance of metallurgical compatibility between the overlay and base metal. The transition zone hardness gradient should be monitored to ensure no brittle intermetallics form at the bond line.
This work remains relevant for engineers dealing with similar wear-critical rotating components in polymer processing, plastic extrusion, and composite forming applications where hardfacing of screw elements is a standard maintenance practice.
Study Value and Outlook
The document serves as a historical reference for the evolution of hardfacing applications in Chinese industrial machinery. Modern equivalents would incorporate laser cladding or PTA for superior dilution control, but the fundamental principles of preheating, interpass temperature control, and post-weld heat treatment remain unchanged. Engineers today should recognize that the spiral geometry constraint still demands careful process planning, and the choice between manual and automated approaches depends on production volume and quality requirements. The work underscores the enduring value of adapting established welding metallurgy to specialized geometric configurations.