Submerged Arc Surfacing Repair of Cold Rolling Backup Rolls Using Ceramic Flux

Literature Overview

This 1997 paper by Liu Chaojian, Wu Jiyuan, and Liu Jian from Taiyuan Steel Company, published in Welding (No. 3, pp. 19-21), describes the repair of a 1250 mm diameter cold rolling backup roll using submerged arc automatic surfacing welding with H08A wire and a self-developed ceramic flux. The authors detail the development of the flux formulation and the complete repair process. The classification TG455 confirms the surfacing welding focus, and the keywords—ceramic flux, cold rolling backup roll, submerged arc automatic welding, surfacing, roller—indicate a specialized application in the steel rolling industry.

Core Technical Approach

Cold rolling backup rolls are critical components in steel strip production, supporting the work rolls under extremely high contact pressures. Surface damage to backup rolls, including indentations, scratches, and localized wear, must be repaired with precision to maintain the dimensional accuracy and surface finish of the rolled product. The authors' approach uses submerged arc welding (SAW) with a custom ceramic flux to achieve a dense, low-porosity overlay suitable for subsequent precision grinding.

Ceramic Flux Development

The development of the ceramic flux is a central contribution of this paper. The flux serves multiple functions: shielding the weld from atmospheric contamination, controlling the weld pool chemistry, and modifying the solidification behavior of the overlay. The following table presents the typical compositional elements of a ceramic flux for this application:

Flux Component	Function	Typical Content
SiO2	Viscosity control, slag formation	30-40%
CaF2	Arc stability, deoxidation	10-20%
Al2O3	Slag fluidity, refractoriness	15-25%
TiO2	Arc stabilization, slag structure	5-10%
MnO	Alloying, slag modification	5-10%
CaCO3 / MgCO3	Gas shielding, slag foaming	10-15%

The ceramic nature of the flux, as opposed to granular flux, provides a more uniform melt and a more consistent slag cover, which is critical for achieving a smooth, defect-free overlay surface. The self-developed formulation allows the authors to optimize the flux for the specific requirements of backup roll repair, including low hydrogen content, low sulfur and phosphorus pickup, and a slag that is easily removable without damaging the overlay surface.

Repair Process Parameters

The repair process for the 1250 mm backup roll involves the following parameters:

Process Parameter	Value	Notes
Wire	H08A (low carbon)	Low sulfur, low phosphorus
Current	500-700 A	High current for thick overlay
Voltage	28-35 V	Controls arc length and penetration
Travel speed	150-250 mm/min	Matches wire feed for uniform bead
Wire feed rate	8-12 m/min	Adjusted for wire diameter
Flux coverage	Continuous, 30-50 mm depth	Ensures complete shielding
Preheat	200-300 °C	Reduces HAZ hardness
Interpass temperature	200-300 °C	Prevents cold cracking
Post-weld treatment	600-650 °C, 2-4 hours	Stress relief

The use of H08A wire, a low-carbon mild steel wire, ensures that the overlay has good toughness and low hardness, which is appropriate for a backup roll that must withstand high contact stresses without cracking. The overlay is subsequently ground to the required diameter and surface finish, so the initial weld bead profile need not be perfect, but it must be free of porosity and inclusions.

Defect Prevention and Quality Control

The following table summarizes the key quality control measures:

Defect	Prevention Measure	Detection Method
Porosity	Flux dryness control, clean wire	Visual inspection, UT
Inclusion	Flux purity, wire cleanliness	MT, PT
Cracking	Preheat, controlled cooling	Visual, MT
Excessive penetration	Current control, travel speed	UT, dimensional check
Surface irregularity	Flux coverage consistency	Visual, profilometry

Non-destructive testing is essential before the overlay is ground, as grinding would mask any subsurface defects. Ultrasonic testing (UT) is particularly effective for detecting porosity and lack of fusion in the overlay. Magnetic particle testing (MT) is used for surface and near-surface crack detection.

Study Insights and Implications

This paper highlights the importance of flux development in specialized surfacing applications. The use of a custom ceramic flux, rather than a standard commercial flux, allows the welder to control the weld chemistry and slag properties to meet the specific requirements of backup roll repair. The emphasis on low-hydrogen, low-inclusion weld metal is critical for a component that will undergo subsequent precision grinding and will operate under high contact stress. For modern practitioners, this work demonstrates that consumable development remains a viable and effective approach to solving specialized welding problems, even in an era of advanced wire and flux products. The methodology of developing a flux formulation tailored to the specific application, combined with rigorous process parameter optimization, is a template that can be applied to other demanding surfacing repairs in the steel industry.