Poking off the charge assists in the decent of the semi-plastic mass of charge to from a pool in the bottom of the furnace, thus increasing the melt rate and prevents from bridging. Poking also prevents from uneven wear of the lining.
It is essential especially when there is no heal of liquid metal in the furnace and when the opening of the furnace crucible is smaller in diameter. Poking is a peculiar feature of medium frequency furnace and the furnaces with smaller batch quantities.
Effective poking largely depends upon the skills of the charge men. Poking can effectively be done with thick MS rods by using the lining top as a fulcrum.
The de-slagging should be done as fast as possible. This operation can be done simultaneously along with the superheating of the metal. The use of proper flux for coagulation of the slag is recommended. A dish type slag racker can be used for de-slagging.
Superheating of the metal should be avoided as it leads to
- Lower metallurgical qualities.
- Higher oxidation losses.
- Excessive lining losses.
- Lower utilization factor.
The temperature should be checked on reaching the taping temperature. Frequent temperature checking should also be avoided as it increases the consumption of the thermocouple tips and also reduces the utilization factor. For the given capacity furnace power input required for increasing a known temperature can be determined. On checking the temperature once, the calculated power can be supplied to the melt and tapped off. This gives fairly accurate temperature control.
The following are some of the figures of power input for a given rise in temperature.
|160 kW – 250 kg|
Medium Frequency (without lid)
|Rate of temperature rise on full load power input required to maintain the furnace||400 C per min 45 kWh (at 15000 C)|
|Approx. time taken to achieve this will be||58 seconds|
Similar observation should be made for individual furnaces as the operating conditions, such as design, radiation losses, etc. The following figures indicate the effect of the operating conditions on the power input figures.
|160 kW – 250 kg (without lid)||160 kW – 250 kg (with lid)|
|Rate of temperature rise on full load||400/min||460 C|
|Rate of fall of temperature||16.50/min||80/min|