As explained above, the controlled cooling of the wheels is
the most important heat treatment step. It mainly defines
microstructure and mechanical properties and therefore the
quality of the product. Figure 4 shows a modern cooling unit
(Gröne 2005) for the programmed quenching of wheels according
to cooling curves displayed in figure 2.
The actual cooling rate at the wheel is analysed online and
the temperature measurements are compared with the
desired cooling rate according to figure 2. If for example a
pearlitic-ferritic microstructure is desired, a possible cooling
schedule may consist of
the prevention of wheel unroundnesses. Additionally, wheel
damages such as rolling contact fatigue failures will be minimised.
It should be noted here, that a typical wheel with a
diameter of 920 mm reaches 107 rolling load cycles already
after 30.000 km in service.
4. REQUIREMENTS ON THE HEAT TREATMENT FACILITY
Figure 3 sketches the layout of a heat treatment facility for
wheels. A bogie hearth pusher furnace concept has been proven
to fit very flexibly to the demands of the customers. The
key elements of the facility are wheel magazines, hardening
and annealing furnaces, the cooling units, the transportation
system for the hearth bogies, the portal robots for the
handling of the wheels and an operating stand.
The concept allows for a very compact but also flexible
design to adjust to the most different structural conditions
at the customer’s site. Wheels of varying diameter (up to
1.300 mm), different weight (up to 1.200 kg) and changing
chemical composition are heat treated individually with
production rates of up to 100 wheels per hour. To assure
highest product quality, every single wheel is registered by
a material tracking system which comprises and links all
units of the facility. Time saving maintainability as well as
easy and safe accessibility are two of the aspects of operator
convenience. Of course the above described and widely automated
production process requires operators with a high
degree of competence and proficiency.
5
region untouched.
units of the facility. Time saving maintainability as well as
easy and safe accessibility are two of the aspects of operator
convenience. Of course the above described and widely automated
production process requires operators with a high
degree of competence and proficiency.
5.