What is a tempering furnace?

A tempering furnace is a type of industrial heating equipment specifically used to temper metal workpieces. Tempering is a crucial step in the heat treatment process, occurring immediately after quenching.
The tempering process reduces some hardness but significantly improves toughness and ductility, eliminating internal stresses.
A tempering furnace is the equipment that completes this "tempering" process. It precisely controls the heating temperature, holding time, and cooling rate to achieve the desired final mechanical properties of the workpiece.

A tempering furnace primarily serves three functions:

1. Adjusting mechanical properties to achieve the optimal balance between strength and toughness

Although quenched valves are hard, they are also too brittle and prone to fracture under the high-speed reciprocating impact of an engine.
A tempering furnace uses precise heating (usually at several hundred degrees Celsius) to transform unstable microstructures within the metal (such as martensite) into more stable structures (such as tempered troostite). Result: The material's brittleness is optimally reduced, its toughness and ductility are enhanced, while maintaining sufficient strength and hardness, making the valve both impact-resistant and wear-resistant.

2. Eliminate Internal Stress and Prevent Deformation and Cracking

During the quenching process, the extremely rapid cooling rate generates significant internal stress within the workpiece. This stress is the primary cause of deformation and even cracking after processing or during use.
The heating process in the tempering furnace acts as a "massage" within the metal, allowing the atoms to rearrange and relax, effectively eliminating these residual stresses.
Result: Ensures long-term valve dimensional stability, preventing deformation caused by stress release in high-temperature and high-pressure environments, and ensuring the sealing and operational reliability of the engine valve.

3. Stabilize Microstructure and Dimensions to Ensure Reliability

Tempering stabilizes unstable microstructures, preventing significant dimensional changes during use.
Result: For valves, this means their shape and dimensions remain stable throughout the engine's lifecycle, ensuring a tight seal with the valve seat and preventing failures caused by microstructural changes. Process Characteristics: For high-precision, high-volume production of critical components such as intake and exhaust valves, mesh-belt tempering furnaces or vacuum tempering furnaces are typically used.

Mesh-belt furnaces: They enable continuous production, with valve components placed on a moving mesh belt and moving through the furnace at a constant speed, resulting in high production efficiency.
Vacuum furnaces: Heating in a sealed vacuum environment effectively prevents oxidation and decarburization of the valve surface at high temperatures, maintaining the metal's surface finish and composition, eliminating the need for subsequent cleaning and ensuring optimal product quality.