Roller Press Roll Surface Spalling Cladding Repair Technology

Literature Overview

The reference by Gui Xujun (2006), published in China Cement and associated with Jidong Heidelberg (Jingyang) Cement Co., Ltd., documents a systematic approach to repairing roller press rolls that have suffered surface spalling. Roller presses are critical equipment in modern cement grinding circuits, where two counter-rotating rolls compress clinker and raw materials under pressures exceeding 100 MPa. The roll surfaces are subjected to extreme contact stresses, abrasive wear, and thermal cycling from hot feed material, leading to progressive degradation manifested as surface spalling, pitting, and material loss. This reference presents a field-proven cladding repair methodology that restores roll geometry and surface integrity.

Core Technical Content

The spalling phenomenon on roller press rolls typically initiates at micro-defects in the original hardfacing layer or at the interface between the overlay and base material. As spalling progresses, it creates subsurface voids that act as stress concentrators, accelerating material loss in a cascading manner. The repair approach involves complete removal of the damaged zone, substrate preparation, and multi-layer hardfacing cladding with optimized material properties.

Damage Assessment and Removal Strategy

The repair begins with a comprehensive assessment of the spalled area using ultrasonic testing (UT) to determine the depth of subsurface damage. The damaged material is removed using a combination of milling, grinding, and in severe cases, plasma arc gouging. The removal depth must extend beyond the affected zone to ensure sound base material is exposed. A minimum overlap of 5–10 mm beyond the visible damage boundary is recommended to ensure complete removal of micro-cracked material.

Cladding Material System

The following table presents the material system employed for roller press roll repair:

Layer	Material	Hardness (HV)	Function
Base	45 steel or 40Cr (quenched and tempered)	200–250	Structural support
Transition layer	E309L or E310L stainless steel	200–250	Thermal expansion matching
Intermediate layer	Ni-Cr-Mo alloy (E309Mo equivalent)	300–350	Toughness buffer
Working layer	Cr-Cr₂C₃ hardfacing (E51700 or equivalent)	600–700	Wear resistance

The multi-layer approach addresses the fundamental challenge of matching thermal expansion coefficients between the base steel and the hard, brittle working layer. A single-layer hardfacing deposit on a carbon steel substrate would inevitably crack under thermal cycling due to the large coefficient mismatch.

Welding Process Parameters

Process Parameter	Value	Rationale
Process	SMAW (manual) + SAW (mechanized)	Flexibility for geometry
Preheat temperature	250–300 °C	Prevent cold cracking in HAZ
Interpass temperature	≤ 250 °C	Control grain growth
Heat input per pass	12–18 kJ/cm	Balance penetration and dilution
Pass thickness	3–5 mm	Control solidification rate
Post-weld treatment	Stress relief 580 °C × 2 h	Reduce residual stress
Final grinding	To original diameter ± 0.5 mm	Restore geometry

Process Optimization and Quality Control

The critical quality control points in this repair process include:

Pre-weld cleaning: The substrate surface must be cleaned to remove all oxide, scale, and contaminated material. Surface preparation to near-white metal finish ensures proper metallurgical bonding.
Bond strength verification: A tensile bond test per ASTM A743/A743M should be performed on a coupon welded under identical conditions. Acceptable bond strength is ≥ 220 MPa for hardfacing applications.
Hardness profiling: After repair, hardness should be measured at multiple points across the overlay thickness to verify uniformity and confirm adequate dilution control at the transition layer.
Visual and MT inspection: 100% visual examination of all welds, followed by MT of the final ground surface to detect any surface-breaking defects.

Common Defects and Engineering Countermeasures

Defect	Mechanism	Prevention
Overlay cracking (interpass)	Thermal stress from high CTE mismatch	Lower heat input; thinner passes; higher preheat
Delamination at base-overlay interface	Insufficient wetting; contamination	Thorough surface prep; transition layer
Porosity in overlay	Gas entrapment from flux	Controlled flux moisture; adequate shielding
Uneven hardness	Variable dilution	Consistent travel speed; proper wire feed
Residual spalling after repair	Subsurface damage not fully removed	Deeper material removal; UT verification

Study Insights and Practical Implications

This reference is particularly valuable for its practical orientation toward field repair conditions. Unlike laboratory studies that focus on material properties in isolation, this work demonstrates the integration of metallurgical knowledge with field logistics. The multi-layer approach with a transition layer is a critical insight—many practitioners attempt single-layer hardfacing repairs that inevitably fail within weeks due to thermal fatigue at the interface. The economic argument is compelling: a properly executed multi-layer cladding repair can extend roll life by 6–12 months, far exceeding the cost of consumables and labor. Furthermore, the repair eliminates the need for complete roll replacement, saving the substantial cost and lead time associated with new roll procurement. Engineers should note that the transition layer, while adding process complexity, is the single most important factor in long-term repair success.