Study Note on Roller Press Roller Surface Spalling Weld Overlay Repair Technology

Literature Overview

This technical paper, published in China Cement in 2006 by Gui Xujun of Jidong Heidelberg (Jingyang) Cement Co., Ltd., addresses a critical maintenance challenge in cement grinding operations: the repair of spalled roller surfaces on roller presses. Roller presses are workhorse equipment in modern cement grinding circuits, operating under extreme compressive and abrasive conditions. The roller surface, which directly contacts the material being ground, undergoes progressive wear, fatigue cracking, and ultimately spalling — a catastrophic failure mode where chunks of the hardened surface layer detach from the substrate. This study note examines the weld overlay repair methodology proposed in this early literature, which was among the first systematic treatments of this problem in the Chinese cement industry.

Core Technical Problem — Spalling Mechanism

Spalling on roller press surfaces typically initiates at the interface between the hardened overlay layer and the base steel, or within the heat-affected zone (HAZ) of the overlay weld. The mechanism involves a combination of:

Thermal cycling fatigue: The roller surface experiences repeated heating from friction and cooling from material feed, creating cyclic thermal stresses.
Compressive fatigue: Sustained high contact pressure (typically 200–400 MPa in cement roller presses) drives subsurface crack initiation.
Hydrogen-assisted cracking: Hydrogen generated during welding operations can migrate into the HAZ, reducing local ductility and promoting delayed cracking.
Residual stress concentration: Inadequate preheating or improper welding sequence leads to high tensile residual stresses at the overlay-substrate interface.

The paper identifies that spalling depth typically ranges from 5 to 25 mm, with crack initiation often occurring at 2–5 mm below the surface. This subsurface crack location makes conventional surface inspection methods such as magnetic particle testing (MT) less effective, necessitating ultrasonic testing (UT) for reliable defect detection.

Weld Overlay Repair Process Parameters

The repair methodology described involves removing the spalled region and applying a new hardfacing overlay. Key process parameters extracted from the literature are summarized below:

Parameter	Specification	Rationale
Base material	42CrMo or 40CrNiMo steel	High-strength roller steel
Overlay material	Cr-Mo hardfacing alloy (e.g., D262, D256)	Wear resistance > 2000 HV
Welding method	Submerged arc welding (SAW) or multi-layer GTAW	High deposition rate for thick repairs
Preheat temperature	200–300 °C	Reduce cooling rate, minimize HAZ hardness
Interpass temperature	200–250 °C	Control thermal cycling
Post-weld treatment	Stress relief at 550–600 °C, 2 h	Reduce residual stresses
Final hardness target	45–55 HRC	Balance wear resistance and toughness
Dilution control	< 15%	Maintain overlay properties

Multi-Layer Weld Strategy

The repair employs a three-layer approach:

Bond layer (GTAW, 2–3 mm): A transition alloy with good weldability to the base steel, serving as a metallurgical buffer.
Transition layer (SAW, 5–8 mm): A medium-hardness alloy that reduces the property gradient between bond and cap layers.
Wear layer (SAW, 8–15 mm): High-carbon, high-chromium hardfacing providing the final wear-resistant surface.

This layered approach addresses the fundamental challenge of joining dissimilar materials with vastly different hardness levels while maintaining adequate toughness at each interface.

Defect Analysis and Countermeasures

Based on the spalling failure analysis presented in the literature, the following defect modes and preventive measures are identified:

Defect Mode	Root Cause	Detection Method	Countermeasure
Delamination at interface	Excessive dilution, poor wetting	UT (PAUT preferred)	Optimize bond layer composition
Cracks in HAZ	High cooling rate, hydrogen embrittlement	MT + UT	Increase preheat, use low-hydrogen consumables
Surface cracking	Thermal stress from high hardness	Visual + MT	Control carbon equivalent, stress relieve
Incomplete fusion	Poor surface preparation	UT	Thorough grinding to bright metal

Engineering Practice Insights

The Jingyang cement plant case demonstrates that proper weld overlay repair can extend roller press service life by 3–5 times compared to original factory conditions. However, several practical lessons emerge:

Roller press repair requires careful removal of the damaged zone with adequate depth (typically 5 mm beyond the deepest crack detected by UT) to ensure no residual defects remain.
Surface preparation is critical: the repair area must be ground to a flat, clean surface with a slight undercut (0.5–1 mm) to promote fusion.
The welding sequence should follow a symmetric pattern to minimize distortion, especially on rollers with diameters exceeding 1000 mm.
Post-weld grinding and profiling must restore the precise roller geometry (cylindricity tolerance typically ±0.1 mm) to maintain proper nip pressure distribution.

Study Reflections and Implications

This 2006 paper represents an important early contribution to the field of cement equipment repair welding in China. The systematic approach to spalling analysis and repair methodology established a framework that subsequent literature has built upon. One key insight is that the failure of roller press overlays is rarely a simple wear problem — it is fundamentally a metallurgical compatibility and residual stress management challenge. The emphasis on multi-layer weld design with controlled dilution reflects a mature understanding of weld metallurgy principles applied to a demanding industrial context. For modern practitioners, this literature provides the foundational understanding that remains relevant today, even as welding technologies have advanced to include plasma transferred arc (PTA) and laser cladding alternatives.