Continuous Rapid Tempering of an Induction hardened Crank shaft

The case file describes the introduction of a Pyromaitre Continuous Conveyor Oven to temper Induction hardened Forged Steel Crank shafts rapidly in less than an hour (cycle time -In to Out).  This replaces the existing Batch Process using Pit Retort Type and Box Ovens. The process time -Tempering /Stress Relieving in a batch Oven is usually 3-4 Hours from Load to Un load. The introduction of Continuous Conveyor Pyromaitre Ovens allowed the process to be straight line integrated with a Robotic “Pick and Place” system via an Overhead gantry. The cam shaft transport between the Induction harden, Temper and Grind Line were synchronized and automated. The savings by replacing the Batch Furnaces with the continuous Pyromaitre Stress Relieving Oven was not only in space, and Time but also reduction in in Process and Energy Cost . 

Reported benefits by an Indian Forging Company manufacturing Automotive and Industrial Crank shafts are described below with specific examples of Energy and Cost savings. 


Forged Steel Crankshaft





  • (Maximum Length of Crankshaft: 1300 mm)
  • (Maximum Crankshaft Swing Diameter: 320mm)
  • (Maximum Weight: 170 kg each.)
Rapid Heating
Rapid Heating

Conventional Tempering Process: (In Vertical Retort Batch Furnace)

  • 240-300 minutes cycle time at 210-350 °C including heat up, soaking at temperature (120 minutes) and cooling before unload
  • 10-20 crankshafts of 65-170kg each part in process (~1300-1700 kg batch load)
  • Output approximately 350 kg/hr.
  • Batch Process
  • Number of Vertical Retort Furnaces in Underground Pits used with necessity for overhead loading and unloading manual systems.


Pyro Tempering Process: (In continuous conveyor Pyro ovens)

  • 45-60 minutes cycle time In to Out including cooling to room temperature.
  • 8 crankshafts/hr. with 650kg/hr. output in a PYRO-P-4412 Oven @ 210-350 °C
  • 8 crankshafts/hr. with 1360kg/hr. output in PYRO-P-4422E/P6011E and P6411E @ 210-350 °C
  • Continuous Process allowing an integration with Robotic pick and place overhead gantry transfer of crankshaft from Induction Machine to Pyro Tempering Oven to final grind machine in an Inline Lean manufacturing layout
  • Less parts in process
  • Savings in Space


Energy and cost reduction on tempering of induction hardened cam shafts in a Pyro continuous electrically heated stress relieving furnaces.

The Company used the following methodology to measure the impact of Energy and Cost reduction by introducing a PYRO Continuous rapid tempering Furnace to replace the batch Pit type retort and Box furnaces.

  1. Measurement of specific Energy consumption.
  2. Identity heat Loss areas
  3. Study of hot air convection system.
  4. Implementation of corrective measurers
  5. Monitor heat consumption after installation of the Pyro Ovens.


Benefits derived were:

  • Power saving of 6 Kw per Cam shaft Tempered
  • Surrounding temperature reduced and normalized
  • Monthly Power Saving (2013) is 25,200 kWh @ Rs. 200,000
  •  Annual Power savings (2013) is 302,400 kWh @Rs 2,449,000
  • Specific energy consumption reduced from 13.5kWh/crankshaft to 7.5kWh/crankshaft
  • Heat losses reduced by 5,160 kCal/crankshaft
  • Energy consumption reduced by 44.4%
  • Improved Air circulation by variable blower directions
  • Installed vestibules at Intel and outlets of Oven to reduce heat losses
  • Installed heat barrier plates to restrict heat emissions to outside areas (Shop floor environment impact).

Four models of Seven numbers (7) Pyro Conveyor Continuous tempering were supplied for different size crank shafts in two (2) Plants and three (3) Divisions to the Indian Forged Crank shaft manufacturer.

Pyro P4412E oven with cooler

The PYRO P-4412E Oven was designed for Sizes of Crank Shaft up to 1000 mm Long with swing Diameter 275 mm and an average weight 65 kg/ pc. The design output was 10 pieces per hour (650 kg/hour) with cycle times between 45-75 minutes.


Rapid Heating

Pyro P-4422E oven with cooler

The PYRO P-4422E Oven was designed for Sizes of Crank Shaft up to 1000 mm Long, and an average weight of 160 kg/pc. The design output was 8 pieces per hour (1300 kg/hour) with cycle times between 45-75 minutes



Pyro P-6011E and P-6411E oven with cooler

The PYRO P-6011E AND P-6411E Oven were designed for Sizes of Crank Shaft up to 1300 mm Long with swing Diameter 320 mm and an average weight 170 kg/ pc. The design output was 8 pieces per hour (1360kg/hour) with cycle times between 45-75 minutes.



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