Notes to the procedure of preheating

Pre-heating and cutting

• reduced cooling rate

             → reduction of the hardness at the flame cut edge (microstructure)

             → reduction of local stress due to balancing of the temperature gradient

• min.-preheating temperature shall be reached over the entire plate thickness   

             ← heating from lower subsurface, control at upper subsurface

• min.-preheating temperature shall be maintained during the entire cutting process
• measuring of temperature can be done with:

            - thermo couple

            - thermo chalk

            - pyrometer

• covering of the upper plate surface during pre-heating for isolation

Experiences concerning pre-heating and avoiding of crackoccurence

• slow flame cutting speed approves lower preheating temperature
• if so a loss in hardness will be induced
• if the cutting speed is too slow, deep cut drag lines will occur

Attention: preheating-temperature and time for heat-up will increase with increasing plate thickness.

Post-heating

• subsequent heating or/and holding at elevated temperature is usefull/recommended (<= 250 °C), especially for thicker plates (>75mm)
• e.g. holding at elevated temperature may be done through piling of the hot uniform flame cut pieces or by post-heating of the flame cut pieces
• e.g. when preheating temperature can not be maintained during the entire cutting process (e.g. for lager flame cut size)