Open-Arc Self-Shielded Automatic Cladding of HRC48-30 Roller Press Rollers

Literature Overview

This 2003 technical report by Lin Zhong from Wuxi Hade Rui Welding Technology Co., Ltd. describes the application of open-arc self-shielded automatic cladding to achieve a hardness of HRC 48-50 on roller press rollers. Roller presses are critical equipment in mining and mineral processing, where two counter-rotating rollers crush material through compression. The rollers experience extreme contact stresses, abrasive wear from mineral particles, and cyclic loading, making surface hardening through cladding an essential maintenance strategy.

Technical Context and Material Requirements

Roller press rollers typically have diameters ranging from 800 mm to 2000 mm and lengths of 1000-3000 mm. They are manufactured from high-chromium white cast iron, medium-carbon steel, or alloy steel, with the working surface requiring:

Hardness: HRC 48-55 for wear resistance
Toughness: Sufficient to resist spalling under impact loading from oversized material
Wear resistance: 3-5 times that of the base material
Fatigue strength: Adequate to withstand cyclic contact stresses of 2000-3000 MPa

The open-arc self-shielded cladding process (also known as flux-cored arc welding without external gas shielding) offers several advantages for roller press applications:

Outdoor and field applicability: No external shielding gas required, making it suitable for remote mining locations and outdoor work
High deposition rate: Typically 3-8 kg/h, significantly higher than GTAW or PTA processes
Cost efficiency: Eliminates shielding gas costs and associated equipment
Wind resistance: Self-shielded flux provides protection against wind and air movement

Process Parameters and Equipment

Parameter	Typical Value	Notes
Wire type	Self-shielded flux-cored wire (e.g., SFS-6 or equivalent)	Contains alloying elements for hardfacing
Wire diameter	1.2-1.6 mm	Larger diameter for higher deposition rate
Welding current	200-350 A	DCEN polarity for stable arc
Welding voltage	24-32 V	Adjusted for wire diameter and speed
Travel speed	200-500 mm/min	Depends on desired bead profile
Nozzle height	15-20 mm	Longer nozzle for self-shielded process
Wire feed speed	5000-8000 mm/min	Matched to current setting
Preheat temperature	100-200 °C	For thick sections; reduces cracking risk
Interpass temperature	≤ 250 °C	Control HAZ hardness and residual stress

Cladding Layer Composition and Properties

The self-shielded flux-cored wire used for HRC 48-50 cladding typically contains:

Element	Content (%)	Function
C	0.8-1.2	Solid solution strengthening; carbide formation
Cr	8-12	Carbide formation; wear resistance
Mo	1-3	Carbide formation; high-temperature strength
Mn	1.5-2.5	Deoxidizer; solid solution strengthening
Si	0.3-0.8	Deoxidizer
Fe	Balance	Base matrix

The resulting microstructure consists of a martensitic or bainitic matrix with dispersed carbides (Cr7C3, Mo2C, Fe3C), which provides the combination of hardness and toughness required for roller press applications.

Defect Analysis and Quality Control

Open-arc self-shielded cladding introduces specific defect risks that must be managed:

Defect	Cause	Prevention
Inclusion of flux residue	Incomplete slag removal between passes	Thorough slag removal with wire brush; ensure adequate slag fluidity
Cracking	High carbon equivalent; rapid cooling	Preheat to 150-200 °C; use low-carbon filler; post-weld stress relief
Porosity	Moisture in wire or flux	Store wire in dry conditions; bake wire at 100-150 °C before use
Excessive dilution	High heat input; narrow groove	Reduce current; increase travel speed; use wider groove preparation
Uneven bead profile	Wind disturbance; parameter drift	Use wind screens; monitor parameters continuously

Quality Assurance Protocol

For roller press cladding, the following quality assurance measures are essential:

Surface preparation: Remove all rust, paint, scale, and contaminants from the roller surface by grinding to bare metal.
Preheat verification: Measure preheat temperature at multiple locations to ensure uniform heating.
In-process monitoring: Record current, voltage, and travel speed for each pass; inspect each pass visually for defects.
Post-weld inspection: Perform MT or PT examination of the entire cladding surface; measure hardness at standardized positions; verify dimensional accuracy.
Functional testing: Before returning to service, perform a load test at 50% operating load for 2 hours, followed by inspection for any new defects.

Engineering Practice and Economic Analysis

The economic advantages of open-arc self-shielded cladding for roller press rollers are significant:

Equipment cost: Self-shielded cladding equipment costs 40-60% less than gas-shielded systems, as it eliminates the need for gas cylinders, regulators, and flow meters.
Operating cost: No shielding gas consumption reduces per-meter cladding cost by approximately 15-25%.
Productivity: Higher deposition rates (3-8 kg/h vs. 1-3 kg/h for GTAW) reduce repair time by 50-70%.
Field applicability: The ability to work outdoors and in remote locations eliminates the need to transport rollers to a workshop for repair.

However, the trade-offs must be acknowledged: self-shielded cladding typically produces slightly lower surface quality than gas-shielded processes, with more flux residue and potentially higher porosity rates. For critical applications where surface finish is paramount, gas-shielded processes may be preferable.

Study Insights and Reflections

This study demonstrates the practical value of process selection tailored to application requirements. Open-arc self-shielded cladding is not a compromise—it is a purpose-built solution for large-scale, field-applicable cladding of heavy equipment. The key insight for engineers is that process selection should be driven by the total cost of ownership and the specific constraints of the application, not by a default preference for the most advanced technology. For roller press cladding in mining environments, where outdoor work, large component sizes, and cost sensitivity are dominant factors, self-shielded automatic cladding offers an optimal balance of performance, productivity, and economics. The HRC 48-50 target hardness, while not as high as some specialized hardfacing alloys (HRC 60-65), provides the critical balance of wear resistance and toughness that roller press applications demand. Engineers should always validate cladding performance through field trials before committing to a new process, and should maintain open communication with equipment manufacturers regarding the expected service life of cladded rollers under specific operating conditions.