Tim Donofrio, Vice President of Sales, Can-Eng Furnaces, highlights recent advancements in continuous mesh belt austempering technology, focusing on high-volume production of system-critical components for maximum energy efficiency.
The heat treatment of high-volume, high-integrity metal components has increasingly demanded improvements in product quality, process efficiency, and system reliability. These components—including high-strength, safety-critical fasteners, bearings, drive components, stampings, blanks, springs and precision-machined or cold-formed parts require consistent mechanical properties and dimensional stability.
Over the past several decades, various furnace designs have supported these requirements, including shaker hearth, rotary retort and mesh belt conveying systems. Among these, continuous mesh belt atmosphere furnaces have become the preferred choice for many manufacturers due to their high throughput and flexibility in handling diverse part geometries and sizes.
Historically, mesh belt systems integrated hot oil quenching followed by post-quench tempering to achieve desired material properties. As demands for system-critical components intensified, particularly in automotive and precision mechanical applications, manufacturers increasingly sought alternative processing techniques with enhanced performance. This led to a renewed focus on austempering using continuous mesh belt furnaces.
Austempering process overview
The austempering heat treatment process, first commercialised in the 1950s and adapted for continuous production in the 1960s, involves heating steel components above the austenitizing temperature, followed by rapid quenching in a molten salt bath maintained above the martensite start (Ms) temperature. The parts are held isothermally to promote a bainitic transformation. As can be seen in the following TTT curve provides a general graphical overview of the process.
Key factors influencing the process include:
• Alloy composition (typically high-carbon or medium-carbon steels).
• Soak time required for complete bainite formation.
• Uniformity and stability of salt bath temperature.
The resulting bainitic microstructure offers a balance of toughness, strength and wear resistance superior to conventional quench-and-temper methods, particularly for components subjected to high cyclic loading.
Austempering quench baths typically use molten salts composed of sodium and potassium nitrites/nitrates, operating between 500°F and 750°F. These media offer excellent heat extraction characteristics with minimal vapor formation, ensuring uni-form quenching and reduced part distortion.
Recent developments
Recent advances in furnace design and process integration have enabled broader industrial adoption of continuous austempering systems. These improvements include:
• Improved product performance: Components exhibit higher ductility, strength, and toughness at equivalent hardness levels, along with reduced dimensional variability.
• Minimised post-processing: Enhanced process control reduces the need for secondary operations such as re-threading or finish machining.
• Lower scrap rates: Reduced part distortion and soft handling designs contribute to improved yields.
System enhancements considerations
1. Furnace efficiency and emissions control
Recent furnace designs have focused on:
• Integration of auto-recuperative burners and high-velocity recirculating radiant tube heaters for improved thermal efficiency.
• Up to 50% reduction in NOₓ emissions compared to conventional burners.
• Lower CO₂ output through optimised combustion and heat transfer.
2. Atmosphere control
Endothermic protective atmospheres are commonly used to prevent decarburisation during processing. Since these gases are derived from methane, reducing consumption has both economic and environmental benefits.
Can-Eng’s Energy Reduction System
(ERS) demonstrates measurable reductions in:
• Endothermic gas usage: Up to 40%
• reduction via improved atmosphere management.
• Natural gas consumption: 15% reduction through waste heat recovery systems.
3. Electrification and hybrid heating
In response to variability in natural gas availability and carbon-related regulations, there is increasing adoption of electrically heated or hybrid electric/natural gas systems. These configurations allow for improved alignment with regional sustainability goals, optimisation of lifecycle operational costs and greater flexibility in meeting carbon tax or emissions targets.
4. Salt reclamation and waste minimisation
To minimise quench salt consumption and reduce environmental discharge, integrated salt recovery systems have been developed. These systems reclaim salt from the post-quench wash stage via brine evaporation, recover usable salt for reintroduction into the process, discharge clean water to maintain wash system balance, and reduce contamination from carbonate buildup and mitigate disposal costs.
Performance considerations
Modern continuous mesh belt austempering systems have demonstrated:
• Consistent metallurgical results for high-cycle, system-critical components.
• High operational reliability.
• Soft handling designs that minimise part damage and preserve dimensional tolerance.
• Compatibility with Industry 4.0 and CQI-9 compliance standards.
• Scalable throughput: From 250 lb/hr to 4,000 lb/hr, accommodating diverse production needs.
Conclusion
The evolution of continuous mesh belt austempering systems reflects a convergence of metallurgical science, mechanical engineering and sustainability-focused innovation. With enhanced process control, material performance and system efficiency, austempering has emerged as an alternative to hardening methods for demanding, high-cycle applications.
Ongoing developments in electrification, atmosphere management, and waste reduction continue to position this technology for expanded use across automotive, aerospace and precision manufacturing sectors.