Technical and metallurgical criteria for installation of isothermal annealing station for car gearbox forgings

Zimmermann D. - Bosio (Germany)

Isothermal annealing of gearbox parts made of 18NiCr5-4, 16MnCr5 carburizing steel remains a necessary and compulsory operation in order to secure optimum workability by achieving clearly defined laminated pearlite and ferrite structures.
Its implementation in a modern installation requires very accurate technical data in terms of thermal and mechanical properties, which we managed to achieve based on the following criteria:
- A principle of type installation with rollers control which allows substantial flexibility with regard to the transport of parts loosely placed in the baskets on the conveyor and the flexibility of processing in the case of a change of production type or product.
- Filling baskets using an automatic loading system and weighing defined according to the part type.
- Quick and homogeneous reaching of austenitic structure with temperature accuracy of ±5 °C in the furnace fitted with burners with automatic recovery with high energy efficiency combined with thermal insulation by fibrous modules securing substantial energy yield.
- Cooling regulated and controllable in the unit equipped with additional heating to secure cooling rate irrespective of the degree of loading and the size of the parts and securing homogeneous temperature in the core and surface of the parts.
- Isothermal holding furnace with electric heating equipped with mixing turbines allowing homogeneous and full pearlite transformation of these types of steel.
- Terminal cooling at the outlet of the furnace to reduce the temperature of parts below 50 °C.
- Automatic emptying of baskets.
- Automatic transport of empty baskets back to the loading station.
- Full automation of the line with tracking of all parameters and diagnostics at all levels.
- It corresponds to the operating conditions of automotive manufacturers with continual production 7 days a week.
- Possibility to implement standard normalizing with slow cooling.
This installation with the processing capacity of 1,000 kg/h has been studied particularly as regards the cooling unit with additional heating and its processing flexibility due to which metallurgical results are achieved corresponding to the requirements of the end client.

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