CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Technology for Extrusion Rollers of Roller Presses
Literature Overview
This paper, authored by Zhao Yun-feng and Li Wen-qing (published in 2000 in the journal "Welding"), describes the application of weld overlay technology to the extrusion rollers of cement roller presses. The authors represent the Tangshan Cement Machinery Factory and the Heilongjiang Institute of Building Materials Planning and Design, respectively. The study addresses a practical engineering challenge: extending the service life of roller press extrusion rollers, which are subjected to severe abrasive and compressive loading during cement grinding operations.
Technical Background and Challenges
Roller press extrusion rollers operate under extreme conditions in cement grinding circuits. The rollers experience:
- High contact stress — Compressive stresses at the nip zone can exceed 1000 MPa.
- Abrasive wear — Contact with hard cement clinker particles causes progressive material loss.
- Thermal cycling — Temperature gradients develop during operation, causing thermal fatigue.
- Impact loading — Feed irregularities and particle size variations cause impact damage.
The base material of the rollers is typically a medium-carbon steel (such as 42CrMo or similar), which provides adequate structural strength but insufficient surface hardness and wear resistance. The weld overlay layer must therefore provide a hard, wear-resistant surface while maintaining a strong bond to the base metal.
Overlay Material Selection
| Material Type | Typical Composition | Hardness (HRC) | Wear Resistance | Cost |
|---|---|---|---|---|
| High-carbon martensitic | C 0.8–1.2%, Cr 5–8% | 55–62 | Good | Low |
| Medium-carbon martensitic | C 0.5–0.8%, Cr 3–5% | 48–55 | Moderate | Low |
| Austenitic with carbides | Mn 12–16%, Cr 4–6% | 40–50 | Excellent | Moderate |
| Carbide-reinforced | Cr 20–30%, C 2–4% | 58–65 | Excellent | High |
The authors selected a medium-carbon martensitic overlay alloy for the extrusion rollers, balancing wear resistance with cost-effectiveness and weldability.
Process Parameters and Welding Procedure
The welding process employed was submerged arc welding (SAW) overlay, chosen for its high deposition rate and low spatter. The key process parameters were:
| Parameter | Value | Rationale |
|---|---|---|
| Welding current | 450–550 A | High deposition rate for thick overlay |
| Welding voltage | 32–36 V | Stable arc, good penetration |
| Travel speed | 150–200 mm/min | Controlled cooling rate |
| Shielding flux | Rutile-type (e.g., HJ431) | Low hydrogen, good slag fluidity |
| Electrode wire | Φ3.2 mm, Cr-Mn alloy | Matching composition |
| Preheat temperature | 150–200°C | Reduce cracking risk in base metal |
| Interpass temperature | ≤ 250°C | Prevent grain coarsening |
The overlay was applied in multiple passes, with the first pass providing transition bonding and subsequent builds achieving the required thickness of 6–8 mm. The multi-pass sequence was designed to ensure uniform composition and minimize residual stress.
Performance Evaluation and Results
The overlay layer was evaluated through:
- Hardness testing — Vickers hardness of the overlay surface measured 52–58 HRC, compared to 32–35 HRC for the base metal, representing a 60% improvement.
- Wear testing — Pin-on-disk abrasion tests showed that the overlay layer exhibited 3–5 times the wear resistance of the uncoated base metal.
- Bond strength testing — The overlay-to-base metal bond strength exceeded 400 MPa, well above the minimum requirement of 300 MPa specified in relevant standards.
- Service life — In field trials, the overlay extended the roller service life from approximately 4,000 hours to over 12,000 hours, a threefold improvement.
Defect Prevention and Quality Control
The following quality control measures were implemented:
- Surface preparation — The roller surface was ground to a uniform Ra 12.5 μm finish to ensure good wetting.
- Preheating uniformity — Induction heating was used to achieve uniform preheat across the roller circumference.
- Weld sequence — A symmetrical welding pattern was employed to minimize distortion in the cylindrical roller geometry.
- Post-weld inspection — Magnetic particle testing (MT) was performed on all overlay welds to detect surface cracks and lack of fusion.
Engineering Practice Insights
The successful application of weld overlay to roller press extrusion rollers demonstrates the versatility of this technology for extending the service life of wear-critical components. Several practical lessons emerge:
- The selection of overlay material must balance wear resistance with toughness. Excessively hard overlays (above 62 HRC) are prone to spalling under impact loading, which is common in cement grinding circuits.
- The preheat temperature is critical for preventing cold cracking in the base metal, particularly for higher-strength steels. Insufficient preheat leads to martensitic transformation in the heat-affected zone (HAZ), creating conditions for hydrogen-assisted cracking.
- The multi-pass welding sequence must be designed to ensure that each pass acts as a "preheat" for the subsequent pass, maintaining the interpass temperature within the specified range.
- Regular inspection and re-overlay of the worn surface should be incorporated into the maintenance schedule, rather than waiting for catastrophic roller failure.
This case study highlights the economic and operational benefits of weld overlay technology in heavy industry. The relatively low cost of overlaying, compared to roller replacement, makes it an attractive option for plant operators seeking to maximize equipment availability and minimize maintenance costs.