Study Notes on Weld Overlay Repair of Roller Mill Roller Surfaces

Literature Overview and Background

Roller mills are critical equipment in cement grinding, mineral processing, and power generation industries. The roller surfaces endure severe abrasive wear, impact loading, and thermal fatigue during continuous operation. When the working surface wears beyond the allowable dimensional tolerance, weld overlay repair offers a significantly more economical alternative to full roller replacement. The reviewed literature presents a systematic study of the weld overlay repair scheme for roller mill rollers, encompassing material selection, process parameter optimization, and quality control methodologies.

Core Technical Points

The fundamental challenge in roller surface overlay repair lies in achieving a hard, wear-resistant surface layer while preserving adequate toughness to resist impact and thermal shock. The selection of overlay material must be driven by the specific tribological conditions: grinding pressure, material hardness, operating temperature, and the presence of corrosive or abrasive media. Common overlay materials include high-chromium cast irons (Cr15, Cr20), martensitic stainless steels (410, 440C), and nickel-based alloys for severe service conditions.

Welding Process Selection and Parameters

Parameter	SAW (Build-up Layer)	GMAW (Finishing Layer)
Current	400–600 A	200–350 A
Voltage	30–38 V	22–28 V
Travel Speed	200–400 mm/min	300–600 mm/min
Wire Diameter	3.2–4.0 mm	1.2–1.6 mm
Shielding	Flux (rutile or acidic type)	CO₂ or Ar + 10–20% CO₂
Typical Layers	3–5 passes	1–2 passes
Preheat Temperature	150–250°C	—
Interpass Temperature	≤ 200°C	≤ 200°C

The submerged arc welding process is preferred for the build-up layer due to its high deposition rate and deep penetration, while GMAW is employed for the finishing layer to achieve superior surface quality and dimensional accuracy. The transition from SAW to GMAW requires careful management of the heat input to prevent cracking at the interface.

Defect Analysis and Countermeasures

Defect Type	Root Cause	Countermeasure
Cracking at fusion line	High carbon + alloy segregation in base metal	Apply Ni-based transition layer (e.g., Ni 625)
Porosity	Flux moisture absorption or base contamination	Bake flux at 300°C for 2 hours; clean base surface
Incomplete fusion	Insufficient heat input or excessive travel speed	Increase current by 10–15%; reduce travel speed
Overlay spalling	Excessive residual stress and thermal mismatch	Control interpass temperature ≤ 200°C; post-weld stress relief
Excessive dilution	Low heat input or thin layers	Increase wire diameter; use multi-pass technique

Engineering Practice Insights

In field repair operations, preheating is a critical step that is often underestimated. For carbon steel roller bases, preheating to 150–250°C is recommended to reduce the risk of hydrogen-induced cracking and to slow the cooling rate in the heat-affected zone. The interpass temperature must be maintained below 200°C to avoid excessive grain growth in the overlay layer, which would degrade both hardness and toughness. Post-weld stress relief at 550–600°C for a duration of 2 hours per 25 mm of total weld thickness is advisable for heavily loaded applications.

The geometric profile of the overlay layer must also be considered. A convex profile that matches the original roller curvature is essential to ensure uniform grinding pressure distribution. The engineer should use a combination of SAW for bulk build-up and GMAW or TIG for the final contouring to achieve the required surface finish and geometric accuracy.

Key Reflections

The literature emphasizes that the overlay repair scheme must be tailored to the specific service conditions. A common engineering mistake is selecting an overly hard material that cracks under impact loading during startup or material feed variations. The optimal approach balances hardness (typically 45–60 HRC for cement grinding rollers) with fracture toughness. Non-destructive testing via magnetic particle inspection (MT) and ultrasonic testing (UT) should be performed on every weld pass to detect surface and subsurface defects. In particular, UT is essential for detecting delamination at the fusion line, which is the most critical defect location for structural integrity.

Summary

The weld overlay repair of roller mill rollers is a well-established practice, but success depends on careful material selection, disciplined process control, and rigorous quality assurance. The engineer must understand the tribological demands of the service and translate them into appropriate metallurgical and geometric specifications. A systematic approach that considers material compatibility, process parameters, and defect prevention is essential to achieve a durable and reliable repair that restores the roller to its original functional performance.