After manufacturing coil springs, internal stresses exist within the steel wire. These stresses can lead to defects and may impact the working lifespan of springs. Stress must be relieved to maximize the elastic properties of the spring alloys. Stress relief is a critical step during the manufacturing process, typically using large belt furnaces and convection ovens. The fluidized bed heat treatment system is an alternative for stress relief of small- and medium-sized coil springs. Springs are suspended in a parts basket and deposited into a fluidized bed furnace, consisting of fine aluminum oxide particles gently mixed by an upward air flow. With its high heat transfer coefficient, fluidized bed relieves the stress in coil springs in significantly less time than other conventional heat treatment methods. Bed temperature is accurately controlled using either electric heaters, with excellent thermal uniformity throughout the working area of the bed. Fluidized bed, with its advantages of uniformity and quick turnaround time, render it the best option for the rapid and efficient stress relief processing of coil springs and heat treatment of other metal components.

This paper compares and contrasts heat treat processes and equipment typically used to harden gears. It discusses the basic design and operation of vacuum, controlled atmosphere, and hybrid furnaces and process techniques such as carburizing, carbonitriding, nitriding, nitrocarburizing, and neutral hardening. It also includes information on operating and maintenance costs, using batch integral quench furnaces as the base case for comparison. A discussion on when to consider continuous furnace types is included as well.

The evolution of Low Pressure Vacuum Carburizing in the automotive industry is well embedded in assembly plants with continuous batch loading. This batch loading, which causes a need for high cost WIP (work in progress), can now be reduced with the Low Pressure Vacuum Carburizing furnace equipment being sized to fit into single piece flow line with small batches. This presentation will look into the recent integration of heat treatment for in-line machining cells and the overall influences for the customer to provide equipment for heat treating in-line. These details will be compared to batch or continuous batch heat treatment as we know it today in the automotive industry. High Pressure gas quenching will be illustrated in both in-line and continuous batch integration.

Advanced electrolysis hydrogen technology has demonstrated utility in providing hydrogen for brazing, annealing, MIM, P/M, flame spray and other thermal treatment techniques, in both continuous and batch modes. Advantages include low flammable inventory, elimination of pressure hazards, eliminating of the need to move cylinders and elimination of deliveries. By combining on-site hydrogen generation with a small amount of in-process hydrogen surge storage, on-site hydrogen generation can be used to meet the needs of batch process such as batch furnaces. By carefully choosing generation pressure and surge storage vessel volume, the process can provide maximum flexibility while minimizing the amount of hydrogen actually stored. As compared with dissociated ammonia, advanced electrolysis hydrogen generation provides drier gas, and the ability to vary furnace atmosphere from no hydrogen to 100% hydrogen, enhancing processing flexibility. Additionally, advanced electrolysis can be turned off when not in use saving power as compared with ammonia retorts.

Batch integral quench (BIQ) furnace technology, initially introduced in the 1950s, has undergone significant innovations in the 21st century. This paper examines modern sealed quench furnace designs that integrate quenching capabilities with carburizing hot zones to maximize throughput and ensure uniform material properties. Enhanced heating systems now deliver faster heating rates while maintaining excellent temperature uniformity. Quench tank designs have been optimized to provide consistent flow velocities with minimal variation, resulting in more predictable and uniform hardening results. Additionally, this paper discusses advances in furnace motion control systems and processing line automation that further improve operational efficiency and product consistency in contemporary heat treatment operations.