Hardening Steel Crankshafts
Most crankshafts are manufactured in cast steel; some high-end crankshafts are produced with forged steel. Hardening crankshafts involves consideration of 4 different heating zones - pins, journals, flanges, and shaft - with unique characteristics. The heating time for each zone depends on the material used.
Within the induction heating machine, open type inductors with flux concentrators
are often used for this hardening process. The flange and shaft are usually hardened with closed inductors, and it is sometimes possible to used a closed inductor for the outer journal.
We suggest a heating frequency around 10 kHz for pins and journals; higher frequencies are used for the flange and shaft because the required hardening
depth is lower. Installed power levels ranges from 100 to 400 kW.
Innovative Induction Heating
Independent vs Shared Inductors
Independent inductors can be used for each hardening zone of the crankshaft - one for each pin, journal, flange and shaft . This ensures maximum production rates.
Shared Inductors are often used for lower production rates when flexibility and economy are paramount. One or more servo-controlled shared inductors can be used to harden different zones. Shared inductors are also generally used for larger crankshafts.
Types of Installations
Manual Load - The crankshafts are manually loaded on a motorized carrier or an indexing device that takes them to the heating station. Manual load systems offer the lowest cost and can be automated at a later date if required.
Transfer Type - The delivery of the crankshafts to the heat station is automatically handled by a chain or walking beam. This type of installation often works best for automated production lines. Our CFW Automatic Crankshaft Hardening Machine
with walking beam can harden crankshafts in 40.5 seconds.
Drum Type - Medium-to-large size crankshafts are manually placed on a 4-position, rotating drum. Drum installations utilize shared inductors that harden multiple zones on the same crankshaft. Drum type installations offer flexibility with relatively high production rates.
Turning Type - These simple installations are used for hardening large parts. The crankshafts are loaded horizontally, then each zone is hardened individually or in groups by moving the inductors along the crankshaft.
Typical cycle times vary depending on the type of inductor and type of installation. In our experience, manual installations with independent inductors typically have a 91 second cycle times, whereas with a transfer type installation, cycle time can be reduced to 40.5 seconds. For transfer type installations with shared inductors, the typical cycle time increases to 109 seconds.
Tempering after Hardening
After the hardening process is complete, the crankshafts typically undergo a tempering process. This can be accomplished with either an induction-conduction tempering machine or a conventional recirculation hot air furnace.