Design and Use of Novel Roll Hardfacing Heating Furnace

Literature Overview and Background

The preheating of large rolls prior to hardfacing is a critical step that directly influences weld quality, residual stress levels, and the risk of cracking. Traditional induction heating methods often suffer from non-uniform temperature distribution, particularly for large-diameter rolls. This literature presents the design and operational experience of a novel heating furnace specifically developed for roll hardfacing preheating. The furnace employs a combination of resistance heating elements and convective heat transfer to achieve uniform temperature distribution across the entire roll surface.

Core Technical Content

The furnace design incorporates a cylindrical heating chamber with adjustable temperature zones along the axial direction. The heating elements are arranged in a helical pattern to ensure radial uniformity, while axial temperature control is achieved through independently controlled heating zones. The furnace is equipped with thermocouple monitoring at multiple positions and an automated temperature control system.

Design Parameter	Specification
Maximum roll diameter	800 mm
Maximum roll length	3500 mm
Maximum operating temperature	800 °C
Temperature uniformity (±)	±15 °C across surface
Heating rate	50–80 °C/h
Cooling rate (controlled)	30–60 °C/h
Power consumption	120–180 kW
Heating time (to 300 °C)	2.5–4.0 hours

The furnace is designed to accommodate rolls in both horizontal and vertical orientations. The horizontal configuration is preferred for large-diameter rolls to ensure even heating of the full circumference. A rotating mechanism is integrated to slowly turn the roll during heating, further improving temperature uniformity.

Operational Procedure and Quality Control

The operational procedure follows a strict sequence: roll loading, positioning, furnace closure, gradual heating to target temperature, temperature holding (soaking) for thermal equilibration, and controlled cooling to welding temperature. The soaking time is typically 1.5–2.0 hours at the target temperature to ensure through-thickness temperature uniformity.

Temperature uniformity is verified using surface thermocouples placed at the roll barrel, roll neck, and roll end positions. The acceptance criterion is that the maximum temperature difference between any two measurement points does not exceed 20 °C. This is significantly better than the ±50–80 °C variation typically observed with induction heating alone.

The PDCA cycle is applied to furnace operation:

Phase	Activity	Key Metric
Plan	Set target temperature and heating profile	Target: 280–320 °C
Do	Execute heating cycle with monitoring	Uniformity: ±15 °C
Check	Measure temperature at multiple points	Max ΔT ≤ 20 °C
Act	Adjust zone heating if non-uniformity detected	Correction within 30 min

Engineering Practice Insights

A significant finding from this literature is that the controlled cooling capability of the furnace is as important as the heating capability. After hardfacing is complete, the roll can be placed back in the furnace for controlled cooling, which dramatically reduces residual stress in the overlay and base metal. This post-weld stress relief integrated into the furnace operation eliminates the need for a separate stress relief furnace, improving production efficiency.

The literature also documents that the use of this furnace reduced the incidence of hardfacing-related cracks by approximately 70% compared to preheating with portable induction heaters. The economic analysis shows that despite the higher capital cost of the furnace, the reduction in rework and roll failures results in a payback period of 12–18 months for high-volume operations.

Study Insights and Implications

This literature highlights an often-overlooked aspect of hardfacing quality — the importance of uniform preheating and controlled cooling. For engineers managing roll hardfacing operations, the investment in a purpose-built heating furnace is justified by the improvement in weld quality and reduction in failure rates. The integration of heating, preheating, and stress relief functions into a single piece of equipment represents a practical solution for production efficiency. The key design principle is that temperature uniformity must be achieved across both the radial and axial directions, and this requires careful engineering of the heating element layout and control system.