The demand for high quality
foundry products and their cost effective production places high
demands for furnace charging equipments in melting plants. Though
much of the initial head way made in foundry automation was with
the mould making process, more important is the meltshop automation.
This includes remote furnace charging systems. Automation is mainly
thought of as a solution to high labour cost and it certainly
can increase workers productivity. However, much more important
today is the effect of automation on quality. Another important
advantage that automation provides in foundry environment is enhanced
safety. For example automation allows foundrymen to work at a
safe distance from molten metal or do their jobs behind protective
barriers thus reducing injuries from metal splash or furnace eruption.
Also where automation exercises monitoring & control functions,
it helps prevent accidents related to in-attention or judgement
errors.
Today's most technologically
advanced induction furnaces provide high power densities and are
able to run to full power throughout the charging process. These
furnace require rapid charging to keep pace with the melting power
of the system. In many foundries, however, charging the furnace
can be a labour-intensive.Moreover, manual operation is too slow
which does not allow maximum utilization of the melting system.
Charge materials are simply dumped into the furnace with wheel
barrows or dropped in by hand essentially the same way as it has
been done for centuries. Besides the inefficient use of time and
manpower, manual charging can damage furnace lining if heavy charge
materials are dropped into the furnace, thus gouging or cracking
the wall or bottom refractory. In induction Furnaces improper
manual charging can also lead to dangerous bridging situation
in which tangled pieces of scrap from a layer above and apart
from the molten bath. If unrecognised by the furnace operator,
bridging can lead to superheating of the bath, failure of the
furnace lining and runout.
Manual charging also directly
exposes melt deck workers to the dangers of metal splash from
charge materials hitting the molten bath and of furnace eruption
or exoplosion caused by wet or damp chargematerials. Metal splash
is one of the most common melt deck hazards & ideally, melt deck
worker should be away from the furnace or behind protective barriers
during charging which can only be accomplished with remote systems.
Remote charging systems enhance safety not only by allowing melt
deck worker to be away from the furnace during charging, but by
reducing the chances of damage to the furnace lining & the likelihood
of bridging situtation.
Vibratory Furnace Charger
consists of a vibrating feeder mounted on a moving trolley with
a storage hopper mounted above the feeder. The metallic components
like scrap, bales, pig iron and foundry retains are stored in
the hopper. The hopper shape is specially designed to enable bulky
and irregular scrap pieces to be extracted without problem. The
withdrawal of the scrap from the hopper is carried out by a specially
built vibrating feeder. The feeder design is such that the materials
conveyed are spread out into individual pieces as they flow toward
the feeder discharge.
This technique brings
about a greater accuracy of dispensing. The metallic components
are dosed either into a weigh hopper or directly into the charge
bucket whicch stands on loadcells or by lifiting magnet on crane
hook with digital weigh scale.
The charging car on the
vibrating furnace charger comprises a discharge chute with vibratory
feeder for the metallic components and s hopper all mounted on
the travelling framework with drive gear. The discharge snout
is inclined and formed of a rounded trough to bring about a good
charge distribution and enable irregular or bulky pieces of scrap
or returns to be discharged. The feeder is driven by unbalancedmotors.
The vibration frequency can be altered by an A. C. Inverter, thereby
regulating the feed velocity and also influencing the noise emission.
The batch hopper as well as the charging feeder is built in sandwich
construction which reduces the noise generated by contact between
the charge materials and the hopper walls or feeder deck. However,
this does not eliminate the noise produced by contact between
the charge pieces themselves.
Once the charge is prepared
it is put into the storage hopper of the travelling charger. The
charger drives from the loading point onto the furnace platform
in front of the induction furnace. The furnace hood is arranged
in such a way that it can be fitted for charging pouring. The
furnace lid itself hangs from a chain inside the hood. The hood
is raised and the charging machine drives upto the charging point
and than the vibrating feeder is energised, The furnace is filled
and as the contents are melted down the furnace is kept full.
Various logic circuits
can be designed depending on the customers requirements so as
to charge multiple furnaces using a single furnace charging device.The
system can also be designed so as to achieve a completely automatic
cycle with time lags provided for energising and de-energising
the vibrating feeder and also for providing time lag for the reversing
cycle.
