JPS587912B2 - Low frequency melting and holding induction furnace for non-ferrous metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a melt-holding induction furnace for non-ferrous metals.

Generally, reverberatory furnaces are often used for melting non-ferrous metals, and melting and holding furnaces often use gas or heavy oil burners.

FIG. 1 explains a conventional example of heating with a burner. In the figure, the reference numeral 1 indicates an iron crucible or a graphite crucible, and a metal to be melted 2 is placed inside.

A gas or heavy oil burner 3 is arranged below the crucible 1, and its flame 4 hits the lower surface of the crucible 1.

When such a heating method using a burner is adopted, the flame directly hits the peripheral wall of the crucible, which causes rapid oxidation of the crucible, and the life of the crucible becomes extremely short.

Furthermore, although the outer periphery is usually surrounded by a refractory material to prevent flames from escaping to the outside, it has the drawback of extremely low thermal efficiency due to its structure.

Figure 2 shows a structure in which a heating element 5 such as a nichrome wire or an Elema heating element is placed outside the crucible 1 made of iron or graphite. Because it is exposed to a high-temperature heating element and exposed to air, oxidation is rapid and the life of the crucible is short.

Furthermore, since the heat of the heating element was transmitted to the metal to be melted 2 through the crucible 1, the thermal efficiency was also extremely poor.

Furthermore, in the method shown in Figures 1 and 2, the crucible is locally overheated, causing local peeling of the internal coating material, especially in aluminum melting and holding furnaces, and causing iron to be immersed in the melted material. This resulted in a shortened coating life and a shortened crucible life.

In the example shown in FIG. 3, the crucible 1 is a refractory cement or graphite crucible, and an induction heating coil 6 using a commercial frequency is arranged around the crucible.

In the case of a graphite crucible, backsand exists between the heating coil 6 and the crucible 1.

■ Hearth bricks or cement in case the crucible ■ cracks and molten metal leaks ■ indicates the furnace frame, and ■ indicates the iron core.

If such a structure is adopted, an induced current flows through the metal 2 to be melted and generates heat, resulting in poor heating efficiency and power factor.Therefore, the electrical capacity also becomes large. It has drawbacks such as being expensive due to its structure, and being unable to avoid stirring the molten metal.

Furthermore, in the case of such a melting and holding furnace, it is necessary to empty the molten metal in the crucible, so a tilting device is also required, and a water cooling cable is required to supply power to the tilting furnace, which requires improvements such as power factor improvement. Ancillary equipment becomes expensive and complicated due to the need for multiple capacitors and transformers with taps.

The present invention eliminates the above-mentioned drawbacks of the conventional method, and prevents oxidation and local overheating of the iron crucible, uses commercial frequency current to heat the crucible, and prevents the crucible from reaching extreme temperatures even in the event of a temperature control system failure. The present invention provides a low-frequency melt-resistant holding induction furnace for non-ferrous metals, which can prevent excessive heating, and allows convenient replacement of iron crucibles, particularly for melting and holding non-ferrous metals such as aluminum and zinc.

Hereinafter, details of the present invention will be explained in conjunction with embodiments shown in the drawings.

FIG. 4 explains one embodiment of the present invention. In the figure, what is designated by reference numeral 1 is an iron roof, the outer periphery of which is covered with a heat insulating material 3. FIG.

2 is molten metal.

Ceramic fibers, asbestos processed materials, etc. are suitable as the heat insulating material.

This heat insulating material is pre-formed and has a certain degree of mechanical strength.

An induction heating coil 6 is disposed outside the heat insulating material 39, and a current at a commercial frequency of 50 Hz or 60 Hz is supplied to the induction heating coil 6.

Crucible 1 is equipped with a hanging bolt to facilitate replacement.

4 is an effective guide when replacing the crucible 1, and is fixed to the furnace with bolts, for example, so that it can be attached and detached.
7 is a furnace frame, 7 is a coil support plate, and 8 is a structure made of heat-resistant nonmetallic material such as asbestos that holds a heat insulating material.

The crucible and insulation material should be able to be hung from the top.

By the way, the wall thickness of the iron crucible is detailed below.

Generally, if the penetration depth of current due to induction heating is P (cm), it can be expressed as follows.

In equation (1), μ is the effective magnetic permeability of the crucible, ρ is the specific resistance of the crucible (μΩ·cm), and f is the frequency Hz.

Therefore, for example, if P=1 cm and crucible temperature of 700° C. is targeted, μ≈47.

Various formulas regarding μ have been proposed, but for example, if μ=25800/Hm is adopted, Hm≈617.

Hm is Ersted.

By the way, this Hm is expressed by the following formula.

Hm=K・0.4πrrv'7 I ・・・・・・・・・
......(2) In equation (2), K is a coefficient related to the length of the coil, the distance from the center of the coil, and the air gap, K≦1, and n is the filter per 1 cm of coil length. The number of coils, ■ is the current A flowing through the coil.

Now, if we assume K-1, nI≒348.

Here, input power Pa・(w/
i) is Pa = 0.1 9 9 (nI)” (p completion x 1
Since it can be expressed as 0'...{3), Pa≒1
It becomes 1w/cm2.

In this way, a crucible of dimensions that allows the required input power to be input from the surface area of the crucible corresponding to the coil may be adopted.

By the way, if the wall thickness of the crucible is taken as 1 (α), most of the current induced by the coil will flow inside the crucible, and 1 of the current will flow to the metal to be melted inside the crucible on the side facing the coil. Only a current of less than /4 will flow.

As a result, the stirring force of the molten metal caused by the induced current is suppressed to a large extent by the thin crucible wall thickness.

On the other hand, if an accident occurs where the current is not cut off when it should be cut off due to a malfunction in the temperature control system, for example, and the crucible temperature exceeds the Curie point, μ = 1, so simply use equation (3) above. Even if calculated, Paf: 1.6 w/
criL, and extreme heating of the crucible no longer occurs.

However, in aluminum melting and holding furnaces, the normal melting and holding temperature is relatively high at 650°C to 730°C, close to the Curie point, and sometimes even higher than 750°C to 730°C.
Since it is also necessary to maintain melting at around 70°C, it is better to increase the wall thickness of the crucible to take into account (a) wear due to reaction with aluminum from the inner surface of the crucible, wear due to slight oxidation from the outer surface, etc.

(b) In case a relatively high melting and holding temperature is required, it is preferable to use a wall thickness that allows the crucible temperature to be below the Curie point.

(c) When melting the cold material, it is better to raise the temperature of the crucible for rapid melting.

For these reasons, it is preferable that the wall thickness of the iron crucible be approximately 20 to 25 mm.

In this case as well, the structure and features are the same except that the temperature of the crucible will rise slowly if the temperature control system fails.

Furthermore, the good heating efficiency according to the present invention will be explained here.

In general, metals such as aluminum, lead, and zinc have extremely low electrical resistance and have a resistance value that is approximately the same as that of copper, which is normally used in heating coils.

Here, for (nI)2 to obtain Pa≒11w/cm2 in equation (3), if power is directly applied to the metal to be melted, ρ is one tenth of that of iron, so μ=1 Therefore, (n■)2 is approximately 20 times larger.

This (nI)2 is related to the copper loss generated in the heating coil,
The coil loss will be about 20 times that of putting it into an iron crucible.

For example, when heating copper by induction, a phenomenon similar to the well-known fact that approximately the same amount of power is dissipated by the coil as is applied to the copper occurs.

In contrast, in the present invention, 1/1 of the power to be input is
A coil loss of 10 to 1/20 is sufficient, and in the case of ordinary induction heating, a considerable amount of heat is lost from the heat applied to the material to be melted through the monolithic refractory cement, the crucible, and the back sand.

However, by using an iron crucible, there is no need to worry about hot water leaking, high-performance insulation can be used, this loss can be reduced, and electricity can be saved by approximately 40%.

In addition, the melting and holding furnace according to the present invention has a much simpler structure as shown in the figure and is much cheaper than the conventional low frequency melting and holding furnace.

That is, (a) the crucible itself is a strong structure because it is made of iron and is not heated excessively.

Therefore, it is not necessary to arrange the coil almost entirely outside the crucible as in conventional furnaces, firmly hold the coil with an iron core from the outside, and surround the iron core with a strong furnace frame.

Therefore, the Rurobo, heat insulating material, and coil can each be fixed individually.

Manufacturing and assembly are also very easy.

(b) When it becomes necessary to empty the inside of the crucible, the crucible can be lifted out using a crane, forklift, etc. and emptied in a safe place, eliminating the need for a tilting device.

Fixed wiring is possible and water cooling cables are not required.

(c) There is very little risk of hot water leaking from the crucible, and even if hot water leaks, there is a hole in the bottom of the heat insulating material to drain the hot water, so it has good insulation performance with no risk of spilling over to the coil. Since heat insulating material can be used, this thickness can be reduced.

Since the material to be heated is iron rather than non-ferrous metals such as aluminum or zinc, the coil has a good power factor, the coil current is small compared to the required input power, and the thickness of the heat insulating material is thin. Since the coil and the object to be heated are close, there is little leakage magnetic field that heats the furnace frame, etc., so there is no need to use a time-consuming iron core.

Moreover, for the above-mentioned reasons, the voltage supplied to the coil can be of the 100V, 200V, or 400V class, which is commonly used in factories, so a transformer is often unnecessary.

Also, fewer capacitors are needed for power factor improvement.

Insulating the coil is easy and good.

(d) Coil copper loss is extremely low, so there is no problem with wind cooling, but to improve reliability, water cooling requires a very small amount of cooling water, making cooling water equipment very expensive. It can also be abbreviated.

(e) Installation, wiring, and piping work are extremely easy, and foundation work is also simple.

For these reasons, the price is 1/2 to 1/2 that of conventional furnaces.
It becomes 3.

As is clear from the above description, according to the present invention, since the iron crucible covered with the heat insulating material is heated by the induction coil, excellent effects as described below can be obtained.

(1) Since no burner is used, there is no smoke or noise, which improves the working environment and is safe.

(2) The outside of the iron crucible is covered with heat insulating material, and the inside is covered with molten metal, so oxidation does not occur, and a uniform current flows around the crucible facing the coil, preventing local overheating, which extends the life of the iron crucible. increase and maintenance costs decrease.

(3) Fuel costs can be reduced by dramatically improving heating and melting efficiency.

(4) It is much simpler and cheaper than conventional induction furnaces.

(5) Even if a failure occurs in the temperature control system, there is no extreme temperature rise and it is safe.

(6) Since the stirring movement of molten metal is suppressed, the chances of contact with air are reduced, unnecessary oxides are not produced, and quality is improved.

[Brief explanation of drawings]

Figures 1 to 3 are longitudinal sectional side views explaining the conventional structure;
The figure is a longitudinal sectional side view of one embodiment of the present invention. 1... Iron crucible, 2... Molten metal, 3... Heat insulation material, 4...
... Guide, 5 ... Furnace frame, 6 ... Induction heating coil, 7 ...
Coil support plate, 8...Insulating heat insulating material support structure.

Claims (1)

[Claims] 1. An iron crucible whose outside is covered with a heat-insulating material, and a low-frequency induction heating coil disposed outside the heat-insulating material, wherein the wall thickness of the iron crucible is set to a required value below the Curie point. 1. A low-frequency melting and holding induction furnace for non-ferrous metals, which is characterized by having a wall thickness that is so thin that the induced current does not cause harmful stirring motion to the materials to be melted. 2. In the low frequency melting, holding and induction furnace according to claim 1, the crucible for aluminum or its alloy is
A low frequency melting and holding induction furnace for nonferrous metals, characterized in that the wall thickness thereof is approximately 20 to 25 mm. 3. A low-frequency melting and holding induction furnace for non-ferrous metals, characterized in that the melting and holding induction furnace according to claim 1 or 2 is configured to hold the iron crucible, the heat insulating material, and the coil individually. induction furnace. 4. A low frequency melting, holding and holding induction furnace for non-ferrous metals, characterized in that a removable guide is attached to the furnace for replacing the iron crucible in the melting, holding and holding induction furnace according to claim 3. 5. A low-frequency melting, holding, and induction furnace for nonferrous metals as claimed in claim 4, wherein the iron crucible is configured to incorporate a preformed heat insulating material.