Published by the EPRl Center for Metals Production
A low cost, efficient method for the melting
metals.
# Z K T X i ! of aluminum and c
""
Introduction
Types of Resistance
Furnaces
Conduction through the walls of the
Melting using electric resistance
Electric resistance melting of low
crucible ultimately melts its contents.
heating can be the low-cost choice,
temperature metals such as zinc,
Efficiency is very high because using
as well asproviding complete freedom aluminum, and magnesium, is done
from the noise and excessive heat of using either crucible or reverberatory this construction, there is little heat
loss due to convection or radiation.
combustion processes. This simplistic furnaces. Crucible furnaces are so
Using resistance elements for heating
heating method also results in a high called because melting takes place
results in greater uniformity
and control
qualtity melt with low
oxidation losses.
either in a silicon carbide or graphite
than is often possible with gas burResistancefurnaces are often suitable crucible or in aniron or steel crucibleners. The result islonger crucible life.
shaped pot. The type of production,
for smaller melting facilities, where
and the purity of the melt will determine
investment funds are limited and high
the type of crucible that is to be used.
Larger heats and heavier production
production rates are not necessary.
If iron contamination
is a problem, such schedules can be handled with
Production electric resistance melting
as inthe case of melting aluminum, then reverberatory furnaces. These are
furnaces are available in a range of
similar in construction to gas-fired
graphite or silicon carbide crucibles
sizes from250 Ib.capacity to custom
counterparts with refractory hearths
are required.The crucible is supported
designed furnaces in excess of 20
and are heated by elements suspended
tons. Crucible furnaces are generally at the bottom, and heated from the
over thecharge and/or melt. Radiation
outside, See Figure 1.
used in the 250 to 2500 Ib. range,
from silicon carbide, graphite, or
while reverberatory furnaces are suited
metal resistance elements combine
for higher production requirements.
Photo courtesy of lnductotherm
-1
~ F u m a c e
.:
e .
.
Moveable Resistance Heatini
Door
Elements ,
:,!i The rincipaladvantageofthis
is the extremely low energy
for holding. For example, to
Ib. of aluminum at 1380°F
ontv 4 to 5 kW comDared to
l~&UkWfbconventionalfurnaces.
When highcapacityfurnacesare
used, m&mg can be during off-peak
psriods and pouring canbe during
I'
ctow
I
L
m&m
~
~~~.
,A
fn
M ,electric
curt"S of4OOO to 5OOO amperes are
wmmcady used to heat graphite or
bilicism-crrclJide mistance elements
w h i mdiat~tothe
furnace load and
walls, see Fi.5.
These furnaces are made to oscillate,
thereby facilitating conduction totfm
melt from the furnace walls. Radiant
require relatively Icw
mwm@ne@costs, but are primarily
bei#gussdasRolding furnaces.While
not reportedly used for melting in this
country,theyarebeingusedforthis
I
Europe.
purpose
in
CIIYI, Radiant rod timace.
Klsl:fwmaxs
,
'
&t
Rad
Radiant Rod
EcoL....~
Electric R
Furnaces
1
i
f
. .I j
Comparisons in thistable are for heating aluminum alloys f m ambient temperature to furnace
will vary depending
temperatures prior to pouring; metal losses and energy required>for melting
on the meltinQtemperatuepnd &by group. Losses shown for naturalgas arefor luminous fiameb
u
m
.R-rtedly,
reapt& developed radiant tub gas- fired units reduce
metal loss.
t y ~
e,,?
lccs a comparisonof
\
I
-
I ,
I
I
.,;#
YI using aluminum as an
?he energy values listed in
llllbe are presented for comconverting from Btu's per
a.
to €heequivalentinelectrical
e f m g y , kwh per Ib., or vice vew
Efficiency values arenow being
reported as high as 75% for electric
resistance furnaces.
a.
GAS
Cost:
Fuel
LUMINOUS
,:*'by
-:'
t
FLAMETYPE 1.5cuFHbAL
X loooE'u/C~Ft X
$4.59/10 6 8 t u X 1OOO'bAh
X
4000Vyr
= $
27,54
MetalLoss:
1OOO'bAYhr
X
40OO'Vyr
X
$l/lb
X
4% *
=
$160,00
Total Cost: $187,54
i
InstaHation costs of electric resistanceELECTRICPowerCost(On-Peak):
and fo$sil-fuel-fired furnaces are
wmpmable. It is not practical to
hypdbsize a specific example as
tlmwmmm many possibilitiesto take
'
,WBECOUnt. In general, fossil-fuel-
0.23kWh%x 10001bAhr
x $0.0667/kWhr x 40OOhVyr
I
= $ 61,361
Metal Loss:
10001bAfir
x 4000hr/vr x $l/lb x (1% max)
= $
40,001
TotalCost: S101,36r
Difference: S 86,174
I
'~costsmtajnthemost
&dbg~whichWuenw
final ~ s i o n sAn
. OPbMtingGaet
.
.:
higher quality staridards maybe the
final persuader in selecting electric
resistance melting, as these furnaces
have a decided edge in producing
molten metal free of unwanted gases,
oxides, and other impurities. The
absence of fluing creates a situation
where the melt can be isolated from
convection heat losses and where the
usualnoise levelassociated with fossilfurHiredfumaces is virtually eliminated.
R.@mr, since electric furnaces do not
require fluing, enviromental
6. Furnace downtime is reduced,
:
minimized.
cutting down on labor costs.
7
m
Daily furnace cleaqhg can be
s and relatively low
substantially minirnized.bcause
where initial capital
ladles and tundishes.
of lower maintenance, thereby
dominant factor, the
,
on
labor
costs.
cutting
down
might be the logical
8. Long term problems of pollution
naces offer a high
both inside and outside the plant
of flexibility
changing
in
from
are dramatically reduced, paving l m “Fossil Fuels or Electric - Ho
m e alby to another, as crucibles can
the way for better relations with
Should You Melt” by Scott F
be quickly removed and replaced to
environmental authorities.
Kennedy-Courtesy of Frank
accommodate jobbing demands. +.
Schaefer, Inc.
Larger castings or higher production 9. Increased worker comfort can
requirements may dictate the need for lead to greater employee satis- 2 “Electric Process Heating” by .
faction with fewr comphints.
Maurice Orfeuil.
a reverberatory furnace utilizing the
1
0
.
Melts can be produced at any
advantages of continuous melting.
deaar
ierj loprd M,i.e., it.@not
necessary to
fill the furr#csto a
minimum level as isc required by
other electric meltingmethods.
-
(slc43). TIroat amy are*memJ.
casrhg,rdilhpprsd~,and
”
’)
. a
:;
+
”
EPRt
lyel?
Jeff-
”
\ I .
This Techcommentary
prepared
was
by
Robert L. Kirchner, Special Consultant to
JoaphE.ooQkrQl
,,
CMP. Technical and editorial review were
provided by Robert J. Schmitt, Manager
of Technical Projects and John Kollar,
Manager of Communications.
r
~1988~farMe?alsprodudion
okrdor
c.nkrkr”
Mellon Institute
4400 Fifth Avenue
Pittsburgh,PA 1521 3-2683
412-268-3243
CMP-
<:
. .
,
.
. .