Roll Cladding Process for Industrial Rolling Mills

Introduction to Roll Cladding Technology

Roll cladding is a specialized weld overlay technology applied to the working surfaces of rolls used in metal rolling mills. The purpose is to restore worn rolls to their original dimensions and to provide enhanced surface properties such as wear resistance, thermal fatigue resistance, and improved surface finish. Compared to full replacement of worn rolls, cladding offers significant cost savings and reduces production downtime.

The study of roll cladding processes encompasses the selection of overlay materials, welding process parameters, heat treatment procedures, and quality control methods specific to the demanding requirements of rolling mill applications.

Cladding Process Classification and Selection

Process Comparison for Roll Applications

Process	Heat Input	Dilution Control	Productivity	Surface Quality	Typical Application
Submerged Arc Welding (SAW)	High (5–15 kJ/mm)	Moderate	High	Requires grinding	Bulk restoration of worn rolls
Electroslag Welding (ESW)	Very High (10–30 kJ/mm)	Low-Moderate	Very High	Requires grinding	Large diameter rolls, thick buildup
Plasma Transferred Arc (PTA)	Low-Moderate (1–5 kJ/mm)	Low	Moderate	Excellent	Precision cladding, thin layers
Laser Cladding	Low (0.5–3 kJ/mm)	Very Low	Moderate	Excellent	Thin precision layers, special alloys
Hot-Wire TIG	Moderate (2–8 kJ/mm)	Low	High	Good	Large area coverage with controlled dilution
GMAW (MIG)	Moderate (2–10 kJ/mm)	Moderate	High	Requires grinding	General purpose cladding

Material Selection for Roll Cladding

The selection of cladding material depends on the type of rolling operation and the material being rolled:

Rolling Type	Base Roll Material	Cladding Material	Required Properties
Hot strip finishing	H13 tool steel	H13 / M2 equivalent	Thermal fatigue resistance, wear resistance
Cold strip	Hardened steel	18CrNiMo7 / M50	Hardness >60 HRC, surface finish
Plate rolling	Alloy steel	Cr-Mo-B hardfacing	Abrasion resistance
Wire rod rolling	H13	H13 / VAD-remelted H13	Thermal shock resistance
Aluminum rolling	Steel	Nickel-based alloy	Anti-galling, corrosion resistance

Process Parameters and Quality Control

Submerged Arc Welding Parameters for Roll Cladding

Parameter	Typical Range	Critical Control Point
Current (A)	400–800	Must be sufficient for penetration but not excessive
Arc voltage (V)	28–40	Controls bead width and deposition rate
Travel speed (cm/min)	10–30	Balances deposition rate with solidification quality
Wire feed speed (m/min)	8–20	Must match arc voltage for stable arc
Flux coverage thickness (mm)	3–5	Ensures proper arc shielding
Preheat temperature (°C)	150–250	Reduces thermal stress and cracking risk
Interpass temperature (°C)	≤250	Prevents excessive grain growth
Post-weld heat treatment	820–850°C × 2h × 2 cycles	Restores hardness and eliminates residual stress

Quality Control Requirements

Dimensional accuracy: The final cladding layer must be machined to the specified roll diameter with a tolerance of ±0.02 mm.
Hardness uniformity: The cladding layer hardness must be uniform within ±5 HRC across the entire working surface.
Bond strength: The interface between the cladding layer and the base roll must withstand a minimum tensile strength of 600 MPa.
Crack-free: No cracks or lack of fusion at the bond line, verified by magnetic particle testing (MT) or ultrasonic testing (UT).
Thermal fatigue resistance: The cladding layer must withstand at least 10,000 thermal cycles between 20°C and 1000°C without surface cracking.

Common Defects and Remediation

Defect	Root Cause	Prevention and Remediation
Surface cracks	High cooling rate, thermal stress	Increase preheat, reduce travel speed, apply post-weld heat treatment
Lack of fusion at bond line	Insufficient penetration, surface contamination	Increase current, clean surface thoroughly, use first pass with higher heat input
Hardness below specification	Excessive dilution, inadequate heat treatment	Control dilution through process parameters; verify heat treatment parameters
Hardness variation	Uneven wire composition, variable heat input	Use certified wire with tight composition control; maintain stable welding parameters
Crater cracks	Inadequate crater filling	Use proper crater filling technique; avoid abrupt arc termination

Engineering Practice and Optimization

In a hot strip finishing mill application, a roll with 8 mm of wear was restored using submerged arc welding with H13 electrode wire and a basic flux. The process involved:

Preheating the roll to 200°C using induction heating.
Applying three layers of cladding with a total buildup of 12 mm (accounting for 4 mm of machining allowance).
Maintaining interpass temperature below 250°C.
Performing double-cycle heat treatment at 840°C for 2 hours each cycle, followed by oil quenching.
Final grinding to achieve a surface roughness of Ra 0.4 μm and dimensional accuracy of ±0.01 mm.

The resulting roll achieved a hardness of 48–52 HRC in the cladding layer with excellent thermal fatigue resistance, demonstrating a service life equivalent to a new roll.

Study Insights and Implications

The cladding of rolls requires a deep understanding of the interaction between welding process parameters, material properties, and the specific service conditions of the rolling mill. The key challenge is achieving a balance between productivity (high deposition rate) and quality (controlled dilution, crack-free interface, uniform hardness). The selection of the appropriate welding process depends on the roll size, required cladding thickness, and the specific performance requirements of the rolling operation. Engineers must recognize that roll cladding is not a simple repair operation but a precision manufacturing process that demands rigorous process control and quality verification at every stage.