TECHNICAL REPORT

Development of Hybrid Melting Furnace
for Aluminum Die Casting
K. KUMANO Y. MATSUURA

H. URUSHIDANI

We have developed a hybrid melting furnace for the purpose of raising fuel efficiency and reducing CO2 within
the melting process of aluminum die casting. Conventional melting furnaces used a gas burner to supply thenecessary heat for the melting, temperature raising and holding processes, however the newly developed hybrid
melting furnace uses a gas burner for the melting process which requires heating over a short period of time, andan electric heater, which is heat-efficient, for all other processes. In addition, the new furnace cuts heat radiation by
downsizing the furnace body, achieving a much higher fuel efficiency and reduced CO2. This has resulted in a 50%
decrease in CO2 emissions and 71% decrease lowering molten metal consumption rate.
Key Words: Aluminum die casting, melting furnace, hybrid, electric heater, CO2

1. Introduction
Aluminum die casting is a type of metal casting
whereby molten aluminum alloy is injected into a moldand turned into a casting with high dimensional accuracy
in a short period of time. Generally, melting furnaces areused to melt aluminum alloy.
In the automotive industry, initiatives to reduce CO2
emissions are accelerating as part of addressing global
warming and this need has been growing stronger
every year, even in relation to the aluminum die castingprocess. As such, this report introduces the developmentof a hybrid melting furnace (the developed furnace) andthe effects this has had on reducing the volume of CO2
emissions generated in the melting process of aluminum
die casting.

In conventional melting furnaces (conventional
furnaces), a gas burner was used as the sole heat sourcefor heat required by the melting, temperature raising andholding processes. Melting in a melting furnace involves
loading an aluminum alloy ingot (aluminum alloy) into
the melting chamber and melting this using a gas burnerat around 580℃. Afterwards, the ingot is placed in thetemperature-raising chamber where it is heated to a set
temperature ranging from 680℃ to 700℃ or more usinga gas burner then supplied to a die cast machine as molten
metal from the pumping port of the holding chamber via
a molten metal supply unit (Fig. 1).

Gas burner for melting(only operates during melting)Material
injection

Gas burner for holding(constantly in operation)

2. Development Aims
In order to reduce the volume of CO 2 emissions
generated by a melting furnace, there is a need to reduce
the energy consumption of the respective processes;
melting, temperature raising and holding, or in otherwords, improve the fuel efficiency of the melting furnace.
As such, first, JTEKT devised its own method to measure
the amount of heat radiated by a melting furnace, which
had been left up to the equipment manufacturer until now.
Next, using this method, we compared efficiency and CO2
emissions for each type of energy and determined the
optimal energy to use for each melting process based on
the amount of heat needed.

JTEKT ENGINEERING JOURNAL English Edition No. 1015E (2018)Material injection

Pumping port
To die cast machine

PreheatMelting

Temperature
raising

Holding

Fig. 1 Process of melting furnace67

−Development of Hybrid Melting Furnace for Aluminum Die Casting−

The largest amount of heat radiation is due to exhaust gas
No. 1

No. 3

No. 4

No. 5

412?

No. 2

The holding chamber supplies molten metalfrom the pumping port therefore the layout
cannot be changed due to requirements ofthe supply unit and the casting machine

Processing point measurement results
・No. 1455℃ 100 416 kJ
・No. 2412℃ 96 232 kJ
・No. 3 〜 No. 5
108℃, 239℃, 150℃ 87 864 kJ

Fig. 2 Results of measurement of heat radiation from conventional furnace

The feature of this conventional furnace layout wasthat the heat of the gas burner as the heat source, directly
heated material and molten metal and, as such, part of
the heat radiated reflected on the ceiling or walls of
the furnace, becoming reflective heat and heating themolten metal further. In other words, this is a typical
reverberatory furnace. From the perspective of fuelefficiency, reverberatory furnaces raise two issues, heatradiation due to discharged gas and heat radiation of thefurnace itself.
It would be desirable to trap the exhaust gas emitted by
the gas burner in the furnace and increase heat efficiency,
however, if the holding chamber is sealed, the exhaustgas will eventually pressurize the molten metal and it
will start to overflow from the pumping port. Therefore,
there is a need for a ventilation port to allow the exhaustgas to be dispelled from the furnace and prevent it frompressurizing the holding chamber and, due to this, theincrease in exhaust gas-derived heat radiation in facecauses fuel efficiency to decrease.
In order to increase efficiency as a reverberatory
furnace, it is possible to transmit the reflective heatefficiently to the molten aluminum metal by shaping thefurnace body like a boat (wide and shallow), for example.
However, if the furnace body was made a wide, shallow
shape would increase in overall size, which would in turnincrease heat radiation from the furnace itself and cause
fuel efficiency to decrease.
Here, we used a processing point measurement method
to take actual measurements of the exhaust gas-derived
heat radiation and furnace body-derived heat radiation ina conventional furnace (Fig. 2) and made a comparative
verification of the theoretical values and the actual values
obtained through such a measurement (Table 1 and 2).
As a result, we ascertained from Fig. 3 and Fig. 4 that68

Table 1 Amount of heat radiation from conventional furnace

Upwards heat radiation

Heat radiation
amount, kJ
18 828

Vertical heat radiation

47 279Downwards heat radiation
Heat radiation from molten
metal surface
Overall heat radiation (total)

14 644Heat radiation portion

39 116
119 867

Table 2 Comparative results
Heat radiation amount, kJ
Theoretical
Actualvalue
value
Furnace body-derived
heat radiation

119 867

100 416 kJ
24%Exhaustgas-derived heatradiation

Furn

ace
hea body-det radiatio rivedn

87 864 kJ
20%

87 864435 136 kJ
100%
Hol

ding
inpu heatt

96 232 kJ
22%
Pumping portheat radiation% indicates the breakdown of 435136 kJ＊

Fig. 3 Schematic diagram of melting furnace heat radiation

JTEKT ENGINEERING JOURNAL English Edition No. 1015E (2018)

−Development of Hybrid Melting Furnace for Aluminum Die Casting−Holding energy
435 136 kJ

Furnacebody,
87 864 kJ,(20%)

Exhaust gas-derived heatradiation
Molten aluminum holding
calorific value

118 136

120 000

Preheat,
117 152 kJ,(26%)

100 000
Calorific value, kJ

66%

Exhaustgas,
100 416 kJ,(24%)

Temperature-raising,
33 472 kJ,, (8%)

Pumping port,
96 232 kJ,(22%)

80 000Drops by 95 986 kJ

100 41660 00040 00022 14920 0000：Temperature-raising, preheat energy：Loss energy＊
The percentages shown in parentheses are thebreakdown of 435136 kJ

4 430

17 71917 719Gas burner

Immersion-type electric heater[Conditions]・Gas burner efficiency: 15%
・Immersion-type electric heater efficiency: 80%
・Exhaust gas-type heat radiation (from Fig. 4): 100 416 kJ
・Calorific value necessary for holding molten aluminum:(100 416 ÷ 85%)×15% = 17 719 kJ
・Exhaust gas-derived heat radiation from an immersion-type electric heater:(17 719 ÷ 80%) − 17 719 = 4 430 kJ

Fig. 4 Breakdown of energy efficiency

the energy loss of exhaust gas-derived and furnace bodyderived heat radiation accounted for approximately 66%of the overall loss. Moreover, energy efficiency of thegas burner is poor, averaging at around 15% (Fig. 5).
Therefore, when developing our hybrid melting furnace,
our aim was to reduce both of the above-mentioned formsof heat radiation in order to improve fuel efficiency andreduce CO2 emissions.
Furthermore, we made a comparison of the melting
methods in the melting chamber and decided to melt thealuminum alloy using a gas burner for the developed
furnace, in the same way as the conventional furnace(Table 3).

CO2, t･CO2/month

Fig. 5 Comparison of exhaust gas heat radiation withdifferent heat source

100
90
80
70
60
50
40
30
20
10
0

Immersion-type electric heaterGas burner

CO2 emissions 21.8 t･CO2/month
CO2 emissions 11.3 t･CO2/month

0

0.2

0.4

0.6

0.8

1

1.2

Thermal efficiency, %3. Specifications and Design of theDeveloped Furnace

Fig. 6 Efficiency and CO2 emissions of gas
burner/immersion-type electric heater

3. 1 Reduction of exhaust gas-derived heatradiation
One way to reduce exhaust gas-derived heat radiation
would be to change the gas burner, which has poor
efficiency, into a new heat source, and significantly
decrease the amount of exhaust gas. In light of this, we
examined using an immersion-type electric heater as a
new heat source for the temperature-raising and holding
processes on the developed furnace. As seen in Fig. 5, bychanging the heat source to an immersion-type electricheater, it was possible to reduce heat by 95 986 kJ − thedifference between the exhaust gas-derived heat radiationof the gas burner (100 416 kJ) and the exhaust gas-derived
heat radiation of the immersion-type electric heater(4 430 kJ). In terms of CO2 emissions, as Fig. 6 shows,with the 80% efficiency of the immersion-type electricheater, a reduction of 10.5 (21.8 - 11.3) t·CO2/month ispossible. Moreover, by changing the heat source to an
immersion-type electric heater, the furnace body size
is made compact thus fuel efficiency can be improved.

Table 3 Comparison of melting methods
Gas burner
Heating
methodDirect heating

Eﬃciency

Direct heating withgood eﬃciency

Electric heater
Evaluation

Indirect heating○

Indirect heating withpoor eﬃciency (air haspoor heat transfer)

Electromagnetic induction heating (IH)

Evaluation

Direct heating

Evaluation△

・Aluminum alloy has low permeability,and depth of penetration becomes deeper
・If frequency is high, the depth is shallow
and eﬃciency is poor×

JTEKT ENGINEERING JOURNAL English Edition No. 1015E (2018)69

−Development of Hybrid Melting Furnace for Aluminum Die Casting−

3. 2 Reduction of furnace body-derived heatradiation
Two options for reducing furnace body-derived heatradiation are (1) making the furnace body size compactand (2) improving thermal insulation performance.
Moreover, the determining factor of furnace size is not
the aluminum alloy melting capacity, but rather the heatsource.
Here, as discussed in Section 3. 1, it is possible to
make the furnace body size compact by changing theheat source of the temperature-raising chamber andholding chamber to an immersion-type electric heater,thus improving fuel efficiency. Here, specifications wererevised to reduce the gas burner combustion space anduse highly-insulating, thin thermal insulation material
for the furnace, the molten metal height was determinedfrom the heat generation length of the immersion-type
electric heater, and we decided upon a molten metal
holding capacity of 700 kg and furnace size of 2 950mm
×2 271mm ×1 800mm. In order to verify this result,
we calculated heat radiation and obtained the amount of
furnace body-derived heat radiation (Table 4).
Table 4 Amount of heat radiation from developed furnace

Upwards heat radiation

Heat radiation
amount, kJ
11 966

Vertical heat radiation

18 728Downwards heat radiation
Heat radiation from molten
metal surface
Overall heat radiation (total)

6 673

Heat radiation portion

39 116Heat-resistant silver ⇒ thermo resin
Conductive
heat transfer loss
HeatsourceinsidefurnaceConvective
heat transfer loss

Radiation
heat transfer loss

[Heat radiation types]
・Conductive heat transfer:
Heat that is transferred toparts (furnace body)・Convective heat transfer:
Heat taken by the air
・Radiation heat transfer:
Heat released as infrared[About thermo resin]
A thermal insulating coatingwith a ceramic hollow balloon
added
Radiation heat loss is reduced
due to the high emissivity of e
Heat resistant temperature:
600℃
Reduction of radiation heat loss
Furnace body-derived
heat radiation canbe reduced by 24 008 kJ

Fig. 7 Heat-insulated coating

76 484

The result of these changes, as Table 1 and 4 show,
was a reduction in furnace body-derived heat radiation of
43 383 (119 867 - 76 484) kJ. Furthermore, consideringthat the melting mechanism is the same with a molten
metal holding capacity of 700 kg, the melting chamber
supplies aluminum alloy melted at approximately 580℃
to the temperature-raising chamber. The temperatureraising chamber ranges from 680 to 700℃, and there is
no heat source in the holding chamber. Therefore, whenmolten metal is supplied from the temperature-raisingchamber to the holding chamber, the temperature of themolten metal drops. With consideration to this point,
we installed immersion-type electric heaters in both thetemperature-raising chamber and the holding chamber
to secure a heat source in the holding chamber also, thus

70

preventing the temperature of the molten metal fromdropping.
In terms of improving the thermal insulation
performance, the insulation coating (heat-resistantsilver) of a general melting furnace has a heat resistanttemperature of 250℃ or less, and peels away if used in
conditions which exceed this temperature. Moreover, thefurnace temperature is higher, the more portions there
are which radiate heat and these portions exceed the heat
resistant temperature, therefore this insulation coating is
not suitable for the melting furnaces used in aluminum die
casting. In light of this, we decided to adopt thermo resin
as an insulation coating with a heat resistant temperatureof 600℃ for the developed furnace (Fig. 7). In relation to
the results of a furnace heat radiation measurement shownin Table 4, we calculated the furnace heat radiation whenthermo resin was used on the furnace’s exterior wall
(Table 5).

Furnace exterior

Consequently, we decided to use an immersion-type
electric heater as the heat source for the temperature
raising and holding processes.

Table 5 Results of calculation of heat radiation fromdeveloped furnace/heat-insulated coating during
operation
Heat radiation portion
Upwards heat radiation

Heat radiation
amount, kJ
4 473

Vertical heat radiation

7 196

Downwards heat radiation
Heat radiation from molten
metal surface
Overall heat radiation (total)

1 515
39 29252 476

JTEKT ENGINEERING JOURNAL English Edition No. 1015E (2018)

−Development of Hybrid Melting Furnace for Aluminum Die Casting−Temperature-raising chamber:
Immersion-type electric heater
21 600 kJ×3 units

Melting
Temperature raising

Holding chamber:
Immersion-type electric heater
21 600 kJ×3 units

Holding

Fig. 8 Structure of developed furnace

Table 6 Comparison of specifications of conventional furnaceand developed furnace

Melting capability

Conventional
furnace
200 kg/h

Developed furnace
200 kg/hMelting chamber

Gas burner
836 800 kJ

Gas burner
836 800 kJ

Molten metal
holding capacity

1 000 kg

700 kgFurnace body size

3 870mm×
2 595mm×
3 311mm

2 950mm (▲23.8%)×2 271mm (▲12.5%)×
1 800mm (▲45.6%)

Holding capability

700℃±10℃

Temperatureraising chamber

Gas burner
502 080 kJ

Holding chamber─

700℃±3℃
Immersion-type
electric heater
64 800 kJ
Immersion-type
electric heater
64 800 kJ

JTEKT ENGINEERING JOURNAL English Edition No. 1015E (2018)

4. Results on an Actual Furnace
The developed furnace designed as described in
Section 3 was introduced to a production line and its
results verified for a duration of one year from May 2016
through April 2017.

4. 1 Effect on reducing CO2 emissions
The developed furnace was able to reduce CO 2
emissions by 50% compared to a conventional furnace.
Figure 9 shows the CO2 reduction effects.
1CO2 emissions

1.0

50% reduction

0.8
0.6

0.50

0.4
0.2
0

Conventional furnace

Developed furnace

Fig. 9 Results of reduction of CO2 emissions

4. 2 Effect on reducing the molten metal
consumption rate
The molten metal consumption rate of the developed
furnace was reduced by 71% compared to that of aconventional furnace. Figure 10 shows the effect on
reducing the molten metal consumption rate.
Molten metal consumption rate

The result of this change, as Table 4 and 5 show, wasa reduction in furnace body-derived heat radiation of
24 008 (76 484 - 52 476) kJ. As Table 4 and Fig. 5 shows,the necessary calorific value of the immersion-type
electric heater is 118 359 [(76 484 + 22 149) multiplied
by a safety ratio of 1.2] kJ or higher. As such, in order tosatisfy this requirement, three units of 21 600 kJ were set
up in the temperature-raising chamber and three units of
21 600 kJ were set up in the holding chamber, therefore
achieving a total of 129 600 kJ for all six.
As described in Section 3. 1 and 3. 2, we were able
to finalize the layout and specifications of the developed
furnace. For the developed furnace, a gas burner isused as a heat source for the melting chamber, while
immersion-type electric heaters are used as heat sources
for the temperature-raising chamber and holding chamber,consequently leading to the development of a hybrid(gas and electric) melting furnace. Figure 8 shows the
structure of the developed furnace while Table 6 shows acomparison of specifications for the conventional furnaceand developed furnace.

1

1.0
0.8

71% reduction

0.6
0.4

0.29

0.2
0

Conventional furnace

Developed furnace

Fig. 10 Results of lowering molten metal consumption rate

5. Conclusion
As a result of this development, we succeeded in
reducing exhaust gas-derived heat radiation by adopting
immersion-type electric heaters and reducing furnacebody-derived heat radiation by making the furnace bodysize compact and using insulation coating, thus reducing
CO2 emissions by 50% and the molten metal consumption
rate by 71%.
In order to design, fabricate and verify the results of thedeveloped furnace, there were many points that could not
be predicted with prior examination based on theoretical
calculations. However, by utilizing the processing point71

−Development of Hybrid Melting Furnace for Aluminum Die Casting−measurement technique devised independently by JTEKT,
it was possible to make a quantitative judgment andefficiently determined the optimal furnace body layout
and specifications.
The developed technologies described in this paper ofthe immersion-type electric heater and insulation coating(thermo resin) can be horizontally-deployed to existing
conventional-type furnaces, and all of the technologies
can be deployed to updated furnaces. Moving forward, wewould like to leverage this technology to help in solving
environmental issues which will continue to receive more
and more attention.

K. KUMANO**

72

Y. MATSUURA* H. URUSHIDANI*

Casting & Forging Production Engineering Dept.,
Production Engineering Headquarters

JTEKT ENGINEERING JOURNAL English Edition No. 1015E (2018)