Water spray quenching – a new process option for intensive quenching of serial parts

Heuer Volker - ALD Vacuum Technologies GmbH (Germany)

The technology of Water Spray Quenching has been established in industry for many years, e.g. in steel production for the quenching of strips or for semi-finished products. When using this process, water-mist is formed in nozzles and accelerated with high velocities towards the components to be quenched. Water spray quenching provides very high cooling rates. Additionally, by variation of the rate of water-flow and air-flow, the quench intensity can be varied in a wide range.

However, for the heat treatment of complex shaped serial parts, such as gear-wheels, this process could yet not be applied successfully. So far this was not possible, since the water spray could not reach into the center of the heat treat loads consisting of multiple layers since the outer parts of the load shield the inner parts from the effect of the water spray.

With a new combination of vacuum heat treatment in single layers with subsequent Water Spray Quenching, it is now possible to apply Water Spray Quenching for serial parts.

An industrial-scale test rig has been developed and used to investigate the following topics:

• cooling curves,
• heat transfer coefficients,
• core hardness – values,
• CHD – values,
• surface quality after quenching and
• the effect of a variation of quench intensity.

It was demonstrated that the process offers a wide range of quench intensities up to very high cooling rates. Even when using low alloyed case hardening steels, high core hardness values were successfully reached.