Background of the Invention
Field of the Invention
The present invention relates to an improved furnace for heating heat sensitive materials
and a method and an heating element thereof.
Description of the Related Art
Conventionally, in high pressure die casting process has a melting system which is an
integral part of the machine. The furnace for melting is attached to the machine which is
operated through either fuel (such as diesel, gas or furnace oil) fired or electrical heating.
In fuel fired type furnace, the fuel along with air is injected into the furnace and ignited
through a burner, which generates a flame, which heats up a pot, in which there is an alloy,
which subjected to heating which is melted by conduction (heat transfer from cast iron pot to the
metal or metal alloy). This system provides quick heating, which is important for process as
delayed heating results in quality defects. In this process, high temperature flue gases are
generated, which are exhausted through the chimney and therefore, lot of heat loss takes place,
from furnace body (referred to as skin losses). Both these contribute for high heat losses. The
temperature of molten metal is controlled through a temperature controller and thermocouple,
which operates the burner relay and starts the burner, as soon as temperature goes below the set
temperature. Since, burner has certain minimum firing rate (GPH—Gallons per hour), the heat
supplied is quite high, which changes the temperature beyond set value. As the flame is directly
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touching the pot, the life of pot is less. Although quick heating is achieved, but heat loss is more
and maintaining constant temperature is difficult and life of the melting pot is very low.
There are other heating furnace like the electrical furnaces, in which “u-type” coil heaters
are placed around the furnace, which transfers heat to the Pot by convection and radiation.
Subsequently, heat is transferred to the metal alloy by conduction. Since, heaters takes time to
raise temperature, the process of melting is slow moreover the losses are there from furnace body
and partly from the air which escapes from the space between furnace body and pot. As heating
of pot takes place without direct contact of any heat source, the life of pot is much more. Hence
the system is good for low energy consumption, fairly constant temperature and high pot life but
have disadvantage in respect of quick heating.
Therefore, the inventors have felt the need for a furnace system whereby quick heating
and uniform heating can be achieved for alloys or and heat sensitive materials such as zinc or
zamak.
Objects of the Invention
Accordingly, the present invention is directed to an improved heating system for a
furnace, whereby the furnace is used to melt or heat the metal alloys or materials of such nature,
which obviates the disadvantages associated with prior art.
It is another object of present invention to provide an improved furnave by which better
temperature control is possible with quick heating.
Other objects and features of the present invention will be apparent from the following
detailed description of the preferred embodiment.
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Summary of the Invention
The present invention is directed to an improved furnace for heating heat sensitive
materials that substantially obviates one or more problems due to the limitations and
disadvantages of the related art.
The present invention relates to an improved furnace for heating heat sensitive materials
for uniform heating, while maintaining accurate temperature which has both burner and emersion
type electric heaters. The emersion heating elements are fully submerged in the melting pot and
are in electrical communication with the thermocouple and temperature controllers. The
switching from burner to heater and vice versa is achieved through a circuit which has these said
temperature controllers and said thermocouple.
Quick heating is achieved through firing of fuel through burner and holding of molten
metal at set temperature is achieved through emersion type of dip heaters.
Additional advantages, objects, and features of the invention will be set forth in part in
the description which follows and in part will become apparent to those having ordinary skill in
the art upon examination of the following or may be learned from practice of the invention may
be realized and attained by the structure particularly pointed out in the written description as well
as in the accompanying drawings.
Brief Description of the Accompanying Drawings
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The invention will be described in conjunction with the accompanying drawings, in
which:
Figs. 1 and 2 illustrate the schematic view of arrangement of various components of
conventional heating system;
Fig. 3 illustrates the sectional view of furnace along with key elements, according to the
present invention;
Fig. 4(a) illustrates a view of heat transfer in a furnace where a burner is used in the
convention system;
Fig. 4(b) illustrates a view of heat transfer in a furnace where heating coils are used in the
conventional system;
Fig. 5 illustrates a view of heat transfer in a furnace, according to the present invention.
Skilled artisans will appreciate that elements in the drawings are illustrated for simplicity
and have not necessarily been drawn to scale. For example, the dimensions of some of the
elements in the drawings may be exaggerated relative to other elements to help to improve
understanding of embodiment of the present invention.
Detailed Description of Invention
While the invention is susceptible to various modifications and alternative forms, specific
embodiment thereof has been shown by way of example in the drawings and will be described in
detail below. It should be understood, however that it is not intended to limit the invention to the
particular forms disclosed, but on the contrary, the invention is to cover all modifications,
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equivalents, and alternative falling within the spirit and the scope of the invention, as defined by
the appended claims.
Accordingly, the drawings are showing only those specific details that are pertinent to
understanding the embodiments of the present invention, so as not to obscure the disclosure with
details that will be readily apparent to those of ordinary skill in the art having benefit of the
description herein.
The terms “comprises”, “comprising”, or any other variations thereof, are intended to
cover a non-exclusive inclusion, such that a system, setup, device that comprises a list of
components does not include only those components but may include other components not
expressly listed or inherent to such setup or device. In other words, one or more elements in a
system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude
the existence of other elements or additional elements in the apparatus. The following paragraphs
explain present invention with respect to a Heating system for High pressure Die casting
machines. The invention in respect of the same may be deduced accordingly.
Accordingly, the present invention provides an improved furnace for heating heat
sensitive materials comprising: at least one burner; a melting pot; at least one thermocouple
partially immersed in the melting pot being used to sense the temperature of the heat sensitive
material; an emersion type heating element fully submerged in the melting pot and being in
electrical communication with said thermocouple and the first and second temperature
controllers; a flue gas exhaust line comprising a valve that opens and closes depending upon the
burner switch ON and OFF conditions; whereby the said furnace operating on burner up to a predetermined
temperature and subsequently operates on emerson type heating element to maintain
said pre-determined temperature, the said furnace being capable of switching ON and OFF from
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burner to heating element and vice versa in order to maintain predetermined temperature in the
melting pot.
In a first aspect of the present invention, the emerson heating element is having
submerged end, in shape and configuration, so as to cover wide area of melting pot.
Yet another aspect of the present invention, the submerged end is selected having shape
circular, oval, rectangular, square, U-shaped, triangular and preferably E-shaped or combinations
thereof.
Still another aspect of the present invention, the predetermined temperature is selected in
accordance with heat sensitive material.
Yet another aspect of the present invention, the heat sensitive material is selected from
the group containing Al, Zinc, Magnesium and Copper alloys.
Yet another aspect of the present invention, the heat sensitive material is selected from
the group containing zinc alloys and preferably zamak.
Still another aspect of the present invention, the first controller is connected to the burner
and thermocouple.
Yet another aspect of the present invention, the second controller is connected to the
heating element and thermocouple.
Still another aspect of the present invention, the method for heating of heat sensitive
materials in a furnace, comprising the steps of:
(a) placing one or more heat sensitive materials in the melting pot of furnace;
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(b) heating the said heat sensitive materials up to a predetermined temperature with
the at least one burner and obtaining a uniform mixture of molten materials;
(c) measuring the temperature of the said molten material by one or more
thermocouple and displaying / indicator on a first temperature controller (A);
(d) controlling the temperature of molten material of step (c), by a first temperature
controller (A) in the melting pot by switching OFF the burner, while desired temperature is
achieved;
(e) continuosly maintaining the predetermined temperature of molten material of step
(c) by turning ON the heating element;
(f) measuring and controlling the temperature in melting pot by second temperature
controller (B) and comparing with predetermined temperature set out in first temperature
controller (A), so as to switch ON and OFF burner to heating element and vice versa in order to
maintain the predetermined temperature in the melting pot.
Yet another aspect of the present invention, the heat sensitive materials or mixtures
thereof is placed in the melting pot in solid form or semi-solid or liquid form.
Still another aspect of the present invention, the melting pot is preferably made from cast
iron.
Yet another aspect of the present invention, in step (a) heat sensitive material is selected
from a alloy of zinc, aluminum, or any metal alloy.
Still another aspect of the present invention, the heat sensitive material is preferably zinc
alloys namely zamak.
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Yet another aspect of the present invention, the heating element is made of SS-316,
titanium or Incoloy.
Still another aspect of the present invention, the in step (b) predetermined temperature is
slightly higher than the melting point of heat sensitive material.
Yet another aspect of the present invention, the in step (c) the first temperature controller
(7) is set to a predetermined temperature.
Still another aspect of the present invention, the in step (c) the first and second
temperature controllers (7 & 8) comprise a circuit containing a logic for monitoring the
temperature in the melting pot together with the thermocouple.
Yet another aspect of the present invention, the first and second temperature controllers
(7 & 8) are set at a predetermined temperature having a difference of 10 to 30ºC.
Still another aspect of the present invention, the in step (b) the heat required to maintain
the predetermined temperature in the melting pot is based on the specific heat of the metal in
solid and liquid state as well as the latent heat of fusion.
Yet another aspect of the present invention, the improved heating element for a furnace
whereby heat sensitive materials are uniformly heated while maintaining accurate temperature,
said heating element comprises: a dip type heating element being fully submerged in the melting
pot and is in electrical communication with one or more thermocouples and temperature
controllers.
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Accordingly, the present invention relates to an improved heating system for a furnace
whereby heat sensitive materials can be uniformly heated, while maintaining accurate
temperature uniformly.
Referring to Fig. 1, a fuel fired furnace is illustrated. The said furnace has a melting pot
(1) and an open space around the melting pot (1) and a proper exhaust mechanism (6) helps in
exhausting the flue gases. A thermocouple (1) is placed in the melting pot (1) to measure the
temperature of the molten material in the melting pot (1). A burner (5) using fuel as Diesel,
Furnace oil or Gas is used to fire the furnace. A temperature Controller (7) is used to control and
monitor the temperature in the melting pot (1).
Referring to Fig. 2, a furnace with electrical heating is illustrated. The electrical heating
element (9) is close to the melting pot (1) and furnace wall to avoid any loss to the environment.
There is no exhaust system in this furnace. Two temperature Controllers (7 & 8) are electrically
connected to the thermocouple (2) through a circuit to control the temperature in the melting pot.
Referring to Fig. 3, the heating system automatically accommodates the mechanical
design of fuel fired (5) and electrical heating (9). The said fuel fired furnace has an exhaust pipe
(6) and space between the melting pot and furnace. The melting pot (1) is trapezoidal in shape
and is preferably made of cast iron. A thermocouple (2) and emersion type heating element (9) is
disposed in the melting pot (1). The emersion type heating elements are also known as dip type
heating elements. The said heating elements (9) provide maximum heat to the molten metal and
have long life. The thermocouple (2) measures the temperature of the molten material in the
melting pot (1). Two temperature controllers (7 & 8) are electrically connected through a circuit
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which enables switching from burner to heating element and vice versa. Quick heating is
achieved through firing of fuel through the burner (5) and the holding of molten metal at the
predetermined temperature is achieved through the emersion type heating element (9).
The furnace is initially fired with Burner (5) with diesel as fuel and temperature is
measured with thermocouple (2). The temperature is set to a predetermined temperature with the
help of a temperature Controller 7) initially to melt the metal alloy. When the temperature is
reached to a desired temperature pre-fixed for a particular metal or alloy the emersion type
heating elements (9) are switched ON. The value of temperature Controller (7) is reset to the
predetermined temperature and value of temperature controller (8) is set to the desired
temperature. Both the controllers (7, 8) are connected to same thermocouple (2).
When the temperature of molten metal goes below the predetermined temperature, the
controller (8) operates the dip type of heating elements (9) and maintains the temperature. As
soon as the temperature goes below predetermined temperature, the Temperature controller (7)
operates and the burner (5) is switched ON. The burner (5) then provides the extra heat to
maintain the temperature above the pre-determined temperature.
For example in the case of Zinc or Zamak, the temperature is set to 420ºC with the help
of the temperature Controller (7) to melt the Zamak. When the temperature of 420ºC is reached
the Dip type heating elements (9) are switched ON. Now the temperature Controller (7) A is
reset to 400ºC and the temperature Controller (8) is reset to 420ºC.
When the temperature of molten metal is between 420ºC and 400ºC, the controller (8)
operates the dip type of heating elements (9) and maintains the temperature. As soon as the
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temperature goes below 400ºC, the Temperature controller (7) operates and switch ON the
burner. The burner (5) then provides the extra heat to maintain the temperature above 400ºC.
As in the whole process cycle the quick heating required time is only 5~10% (while
adding fresh raw material and sudden drop in molten metal level).
This set up reduces the energy consumption and also provide quick heating whenever
necessary.
The heat loss is also controlled by providing an automatic damper on Flue gas exhaust (6)
line which become open only when burner is operational, otherwise it remain shut off.
As shown in figures-4(a) and (b) illustrate the heat loss pattern from completely external
heating system (only burner or only external heating elements) from the conventional system
wherein only burners are used or where only electrical coils are used. As clearly evident from the
said figures, the temperature taken from the various points like the top portion of the furnace and
the side portion are comparatively on the higher side than the heat loss pattern observed in Figure
5 according to the present invention. The heat loss from furnace surface is much less in case of
dual heating system and around 30ºC less temperature can be achieved on furnace outer surface.
The heating elements (9) of the present invention play a pivotal role and are an important
part of the system, as it requires a heat source, which energy efficient and that is only possible if
it heats the metal by complete fluid communication. The heating element (9) is fully immersed in
the melting pot (1).
The development of immersion heating elements depends on the following parameters:
A) Molten metal temperature
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B) Reaction of heater material with molten metal
C) Shape of heater
D) Heating energy
Selection of Material of the Heating Elements
The temperature of molten metal goes up to 500ºC, hence suitable material is required
which can sustain this temperature and does not melt or elongate. The choice is SS-316 titanium
or Incoloy.
Properties of Titanum like Low density, high strength, corrosion resistance and melting
point of 1650ºC (close to heater element temperature) make it suitable but it is hard, difficult to
machine with low welding strength make it non preferred material for designing the heater for
requirement mentioned above.
Properties of SS-316 like good corrosion resistance, pitting resistance, high malleability
and ductility, high melting point of 2500ºC make it suitable material for heater construction.
Moreover SS-316 is available at 1/3rd rate which make it feasible for construction and
replacement.
Properties of Incoloy (mostly nickel-based) are excellent corrosion resistance as well as
high strength at high temperatures. Some specific alloys are resistant to particular chemical
attacks. But it is difficult to weld and needs to be heated to 200ºC for cold-forming processes.
Hence the material selected is SS-316.
Constructional features of the Heating Element
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The purpose of the heating element is to provide uniform heating in minimum time,
whereby heat sensitive materials can be uniformly heated, while maintaining accurate
temperature.
Heating energy
The heat required to achieve the desired temperature is based on the specific heat of the
metal in solid and liquid state as well as the latent heat of fusion.
One more important factor is the consumption of material and the time available to
achieve the desired temperature.
The same is shown with the help of an example:
In case of Zinc:
The specific heat at 20°C is: 0.093 Kcal/kg°C: Cp
The latent heat of fusion is: 27 Kcal/Kg : Cf
The melting point of Zinc is: 420°C.
Total heat required to melt one Kg of Zinc and keep it at temperature of 430ºC is:
mCpΔt1 + mCf+ mCpΔt2
wherein:
M= mass of metal
Δt1 = rise in temperature of solid metal i.e 420ºC -20ºC = 400ºC
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Δt2= rise in temperature of liquid metal i.e 430ºC – 420ºC = 10ºC
1 x 0.093 x 400 + 1 x27 + 1 x 0.093 x 10 = 37.2 + 27 +.93 = 65.13 Kcal
1 calorie = 4.18 joule
Hence, 65.13 Kcal=272.24 Kjoule.
If we talk in terms of electric energy:
1 unit = 1 kwh = 3600 K joule
Hence, one kg Zinc requires: 272.24/3600 units of electricity = 0.0756 units.
Now if the molten metal pot is of 100 Kg capacity and per hour output is 15 kg, the heat
required per hour is: 100 X 0.093 x 10 + (15 x 65.13) Kcal
93 + 976.95 = 1069.95 ≈1067 Kcal = 4460 kjoule = 1.24 units
This is the idle case when there is no loss of energy.
But practically there are various losses like convection losses from top surface,
conduction losses from pot to furnace body, skin losses etc.
The designing of emersion heaters are based on minimizing the losses and uniform
heating. This is achieved by coil type design which increases the surface area. Moreover the coil
is broad at the bottom which provides uniform heating all over the pot from lower part of the
molten metal.
Advantages of the present invention
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It is an advantage of present invention to provide an energy efficient heating system by the
furnace of the present invention.
The first advantage is to provide better temperature control by quick heating and
reduction of the skin temperature of furnace, so that better working environment can be provided
to workforce.
The second advantage of the present invention is the ability by which the whole system is
easy to handle and maintain.
The third advantage is that conservation of heat energy takes place as heat losses to the
atmosphere has been considerably reduced compared to the conventional systems of the prior art.
The advantages of the disclosed invention are thus attained in an economical, practical,
and facile manner. While preferred aspects and example configurations have been shown and
described, it is to be understood that various further modifications and additional configurations
will be apparent to those skilled in the art. It is intended that the specific embodiments and
configurations herein disclosed are illustrative of the preferred nature and best mode of
practicing the invention, and should not be interpreted as limitations on the scope of the
invention.

WE CLAIM:
1. An improved furnace for heating heat sensitive materials comprising:
at least one burner;
a melting pot;
at least one thermocouple partially immersed in the melting pot being used to sense the
temperature of the heat sensitive material;
an emersion type heating element fully submerged in the melting pot and being in
electrical communication with said thermocouple and the first and second temperature
controllers;
a flue gas exhaust line comprising a valve that opens and closes depending upon the
burner switch ON and OFF conditions;
whereby the said furnace operating on burner up to a pre-determined temperature and
subsequently operates on emersion type heating element to maintain said pre-determined
temperature, the said furnace being capable of switching ON and OFF from burner to heating
element and vice versa in order to maintain predetermined temperature in the melting pot.
2. The improved furnace as claimed in claim 1, wherein the emersion heating element is
having submerged end, in shape and configuration, so as to cover wide area of melting pot.
3. The improved furnace as claimed in claim 2, wherein the submerged end is selected
having shape circular, oval, rectangular, square, U-shaped, triangular and preferably E-shaped or
combinations thereof.
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4. The improved furnace as claimed in claim 1, wherein the predetermined temperature is
selected in accordance with heat sensitive material.
5. The improved furnace as claimed in claim 1, wherein the heat sensitive material is
selected from the group containing Al, Zinc, Magnesium and Copper alloys.
6. The improved furnace as claimed in claim 5, wherein the heat sensitive material is
selected from the group containing zinc alloys and preferably zamak.
7. The improved furnace as claimed in claim 1, wherein the first controller is connected to
the burner and thermocouple.
8. The improved furnace as claimed in claim 1, wherein the second controller is connected
to the heating element and thermocouple.
9. A method for heating of heat sensitive materials in a furnace as claimed in claims 1 to 8,
comprising the steps of:
(a) placing one or more heat sensitive materials in the melting pot of furnace;
(b) heating the said heat sensitive materials up to a predetermined temperature with
the at least one burner and obtaining a uniform mixture of molten materials;
(c) measuring the temperature of the said molten material by one or more
thermocouple and displaying / indicator on a first temperature controller (7);
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(d) controlling the temperature of molten material of step (c), by a first temperature
controller (7) in the melting pot by switching OFF the burner, while desired temperature is
achieved;
(e) continuosly maintaining the predetermined temperature of molten material of step
(c) by turning ON the heating element;
(f) measuring and controlling the temperature in melting pot by second temperature
controller (8) and comparing with predetermined temperature set out in first temperature
controller (7), so as to switch ON and OFF burner to heating element and vice versa in order to
maintain the predetermined temperature in the melting pot.
10. The method as claimed in claim 9, wherein in step (a) the heat sensitive materials or
mixtures thereof is placed in the melting pot in solid form or semi-solid or liquid form.
11. The method as claimed in claim 9, wherein in step (a) the melting pot is preferably made
from cast iron.
12. The method as claimed in claim 9, wherein in step (a) heat sensitive material is selected
from a alloy of zinc, aluminum, or any metal alloy.
13. The method as claimed in claim 11, wherein the heat sensitive material is preferably zinc
alloys namely zamak.
14. The method as claimed in claim 9, wherein the heating element is made of SS-316,
titanium or Incoloy.
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15. The method as claimed in claim 9, wherein in step (b) predetermined temperature is
slightly higher than the melting point of heat sensitive material.
16. The method as claimed in claim 9, wherein in step (c) the first temperature controller (7)
is set to a predetermined temperature.
17. The method as claimed in claim 9, wherein in step (c) the first and second temperature
controllers (7 & 8) comprise a circuit containing a logic for monitoring the temperature in the
melting pot together with the thermocouple.
18. The method as claimed in claim 9, wherein first and second temperature controllers (7 &
8) are set at a predetermined temperature having a difference of 10 to 30ºC.
19. The method as claimed in claim 9, wherein in step (b) the heat required to maintain the
predetermined temperature in the melting pot is based on the specific heat of the metal in solid
and liquid state as well as the latent heat of fusion.
20. An improved heating element for a furnace whereby heat sensitive materials are
uniformly heated while maintaining accurate temperature, said heating element comprising:
a dip type heating element being fully submerged in the melting pot and is in electrical
communication with one or more thermocouples and temperature controllers.