JPH031477A - Low frequency electromagnetic induction heater - Google Patents

Abstract

PURPOSE:To prevent electromagnetic vibration by forming a heater from six induction coils, allowing any pair of adjoining coils to receive supply of the power from either of three-phase AC power supplies, and feeding the current to induction coils in substantially symmetrical positions. CONSTITUTION:An induction heater is formed from at least six induction coils, which are arranged cylindrically. If they are designated as A1 thru A6, the A1 and A2 as adjoining are wired to the U phase of the three-phase power supply, the A3 and A4 to the V-phase, and the A5 and A6 to the W-phase. The wiring shall be made so that current flow occurs to the induction coils in substantially symmetrical positions. That is, the A1 and A4 are wired together, the A2 and A5, and also A3 and A6. This causes continuous generation of electromagnetic attraction force to allow pulling of the object to be heated continuously, which should prevent generation of vibratory sound even though a low frequency AC power supply is used.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a heater using low frequency induction heating.

[Prior Art] In power plants, factories, etc., petroleum, coal, natural gas, or the like is generally used as a heat source for steam or hot water, and combustion thereof is generally performed.

In addition, electrical resistance heaters are used in production processes such as manufacturing plants where heating by burning oil, coal, natural gas, etc. is not possible. For example, in the combination of axles and wheels of railway cars and electric trains, inner cases of bearings, etc., a hollow metal disc body is fitted onto a round rod that serves as the shaft. At this time, the hollow disc body is heated. , the hollow part is thermally expanded and fitted into a round bar. Such heating requires the use of electricity.

As yet another heating method, a low-frequency electromagnetic induction heater is known (see Utility Model Application Publication No. 56-86789, Japanese Patent Publication No. 58-39525, etc.).

[Problems to be Solved by the Invention] However, since resistance-type heaters use resistance-heated nichrome wire heaters or sheathed heaters, there is a large increase in electric capacity and thermal distortion due to local heating of the heater, making them impractical. It is difficult to convert. That is, even if the electric capacity is considerably large, it takes time to heat the object to be heated, the power loss is large, the cost is high, and the object to be heated is likely to be distorted due to local heating.

Furthermore, low-frequency electromagnetic induction heaters such as those disclosed in Japanese Utility Model Application Publication No. 56-86789 and Japanese Patent Publication No. 58-39525, which are other heating methods, generate loud noises due to electromagnetic vibrations or break the device due to electromagnetic vibrations. It had the essential problem of Another example is one that uses a transformer, but it has poor heating efficiency, requires several tens of minutes of heating time, and has many practical problems because it is difficult to attach and remove the heated object. .

The present invention uses a three-phase AC power supply to use a specific wiring method, and by constantly attracting the heated object to the coil side, electromagnetic vibration can be prevented from occurring, and the heating object can be attached and It is an object of the present invention to provide a low frequency induction heater that is easy to remove, can be operated stably and safely, and has excellent thermal efficiency.

[Means to solve the problem] In order to achieve the above object, the present invention consists of the following configuration.

That is, the present invention is an electromagnetic induction heater for heating an object to be heated in a state of contact, and the heater is formed of at least six induction coils, and the induction coils are arranged in a circumferential manner. At the same time, a pair of adjacent induction coils receives power from one of the three-phase AC power sources,
This is a low frequency electromagnetic induction heater characterized by a connection that allows current to flow through induction coils located at substantially symmetrical positions.

Preferably, there are six electromagnetic induction coils, and the connection method is three-phase double delta connection.

A characteristic feature of the present invention is that the heater has at least 6
The induction coils are arranged in a circumferential manner, and each adjacent pair of induction coils receives power from one of the three-phase AC power sources, and is substantially symmetrical. The wire connection is such that current flows to the induction coil located at the position. By using this unique wiring method, the object to be heated can be heated while being constantly electromagnetically attracted, making it possible to significantly increase the magnetic flux density.Moreover, it does not generate electromagnetic vibration noise, and achieves extremely high heating efficiency. can be achieved.

The object to be heated of the present invention may be any material as long as it can come into contact with the induction coil surface and allows magnetic flux to pass through, such as a metal material. More specifically, if the end face of the induction coil is flat, it can be of any type as long as the contact surface of the object to be heated is flat. Therefore, when heating the object, it is sufficient to simply place it on the coil and then remove it. It can also be removed very easily.

[Operation] Next, one embodiment of the present invention will be described in more detail using the drawings.

FIG. 1 shows a wiring diagram which is the main part of the present invention. If six induction coils are arranged circumferentially and numbered A1 to A6, then adjacent A1 and A2 are connected to U of the three-phase power supply.
Connect adjacent A3 and A4 to V of the three-phase power supply.
Similarly, adjacent A5 and A6 are connected to the W phase of the three-phase power supply. Then, connections are made to allow current to flow to the induction coils located at substantially symmetrical positions. That is, A1 and A
4, A2 and A5, and A3 and A6.

In this way, as shown in Figure 8 (A), an attractive force due to electromagnetic force is generated continuously and continues to pull the object to be heated (for example, an iron plate), so even if a low-frequency AC power source is used, vibrations will be generated. can be prevented from occurring. The 0 point in FIG. 8(A) indicates the point where the suction force becomes zero. FIG. 8(B) shows the waveform of three-phase alternating current. That is, U, V at a certain moment of time
, W shows the current waveform of each phase. Here, Figure 8 (A) and Figure 8
To explain the relationship with FIG. 8(B), the waveform of the attraction force in FIG. 8(A) is drawn on an extension of the same time axis as the waveform in FIG. 8(B). Then, the suction force of the device due to the specific wiring connection of the present invention is such that the waveform on one side centering on the 0 point in Figure 8 (B) is combined with the waveform on the + side, and as a result, as shown in Figure 8 (A). It becomes an attractive force.

Note that in the present invention, since an AC power source is used, the induction coil may be wound in any direction.

FIG. 2 is a diagram showing the principle of the present invention. An induction coil is wound around the leg core 3 and placed on the yoke core 4. When an iron plate is used as the object to be heated, a magnetic flux path is formed in the iron plate 1, and an eddy current is generated around this in the thickness direction, so that the iron plate 1 is heated from the center. And if there is no center,
For example, even in the case of the heated object shown in FIG. 6, since the magnetic flux passes through the metal part, it is heated from around the hollow part. Note that FIG. 6 will be explained in an embodiment.

FIG. 3 is a side view of the heater of the present invention, viewed from the direction of the terminal 6. This CC sectional view is shown in FIG. terminal 6 is 3
The reason why there are two is to draw current from the three-phase power supply as mentioned above. FIG. 5 is a sectional view taken along the line AA in FIG. 3. Leg iron core 3
An induction coil is wound around and placed on the yoke core 4. This is then filled with a resin mold. FIG. 7 is a sectional view taken along line BB in FIG. 5. A hollow inner race 1 is used as the object to be heated.

In the device of the present invention, for example, 200 Hz of commercial frequency of 50 Hz or 60 Hz is applied to the induction coil on the negative side.
When an alternating current of 25 A is applied, a current of, for example, 0.5 V and 10.0 OOA flows through the iron plate on the secondary side due to the principle of a transformer. Low voltage, high current is most important for heating, and the present invention applies this principle to its brother. Further, since only an extremely low voltage flows through the iron plate 1, an electric shock will not occur even if it comes into contact with a human body.

In the present invention, preferably, the electromagnetic induction coil is composed of six pieces and has a three-phase double delta connection. This is because, as shown in FIG. 8, this is the wiring method that most easily exerts the suction force.

In the present invention, the iron plate 1, which is an example of the object to be heated, may have any thickness as long as the magnetic flux passes through it.

For example, the length is about 1 to 10 cm, but it is not limited to this. At least six induction coils 2 wound on leg iron cores 3 are arranged below the iron plate 1. The number of induction coils may be any number such as 9 or 12 as long as it is 6 or more, but 6 is preferable in terms of ease of wiring. Although it is preferable to arrange the six in a substantially circumferential manner, the method of arrangement is not limited to this. In short, any arrangement may be used as long as the magnetic flux passes over the iron plate 1.

The object to be heated is placed in close proximity to the induction coil 2.

This is to make it easier for magnetic flux to pass through. Note that a heat-resistant film such as a polyimide film may be used as a cushioning material between the iron plate 1 and the leg iron core 3 as long as the magnetic flux is allowed to pass therethrough. The leg cores 3 and the yoke cores 4 may be of any type as long as they can easily pass magnetic flux. A preferred specific example is a yoke core wrapped with a silicon steel plate. The thickness of the leg core and yoke core is such that the magnetic flux density can be maintained at a level that does not reach magnetic saturation, and preferably has a cross-sectional area that can be maintained at 20,000 Gauss or less.

Next, in the present invention, it is preferable that the three-phase AC power source has a commercial frequency. This is because it is economically easiest to use. Although the commercial frequency differs from country to country, in Japan it is 50Hz or 60Hz. Furthermore, the reason why a three-phase AC power source is used is that it is possible to continuously generate and maintain suction force.

In the present invention, the temperature can be easily controlled by the current value (ampere). In other words, since the current value and temperature have a constant relationship, control is extremely easy. Furthermore, it is easy to control the temperature of the heated object, and the temperature can be set according to the settings.

The reason for this is that the object to be heated itself becomes a heat source. This is different from the conventional concept of heating, which requires a temperature difference between the heating body and the heated body.

Note that the heater of the present invention includes a temperature detector, an overheat preventer,
A limit switch or the like can be provided as appropriate.

[Example] The following will be described in detail with reference to Examples. However, the present invention is not limited to the examples.

Example 1 Bearing inner race shown in Fig. 6 (outer diameter 290 m)
(m, inner diameter 130 mm, thickness 35 mm, made of iron) were arranged as shown in Fig. 7, and the temperature was raised from 25°C to 100°C. The power was 200V, three-phase, and 14A. As a result, the 9th
As shown in the figure, the temperature exceeded 100° C. in about 160 seconds at the central inner diameter peripheral portion pi. The reason why the temperature curve is flat at the 160 second point is because the thermistor is activated and the electrical input is cut off at this point. The temperature also reached 100° C. in about 200 seconds at the intermediate portion P2 and the outer diameter peripheral portion P3. The reason why the temperature rise curve of the inner diameter peripheral part PI is higher than that of the intermediate part P2 and the outer diameter peripheral part P3 is thought to be because the magnetic flux density is higher in the center part.

In addition, in the case of iron, the coefficient of linear thermal expansion α = 1.2X10', so if the temperature difference is 75°C
) inflate.

Therefore, due to this expansion, the object to be heated could be fitted into the shaft core.

Induction heating using a conventional transformer took more than 30 minutes, but the heater of the present invention takes about one-tenth the time.
This means that it was heated in a time of .

The present invention can also be applied to objects to be heated other than those mentioned above, such as boilers,
It can be effectively used to heat steamers, pots, cauldrons, etc., or other metal items.

[Effects of the Invention] The present invention uses a three-phase AC power supply and employs a special wiring method, so that the object to be heated is always continuously attracted to the coil side.
Prevents the generation of electromagnetic vibrations, and also makes it easy to attach and
Easy to remove and operate stably and safely.
We were able to provide a low-frequency induction heater with extremely high thermal efficiency.

[Brief explanation of drawings]

1 to 7 show one embodiment of the heater of the present invention. 8th
Figures (A) and (B) show the electromagnetic attraction force of the heater of the present invention. FIG. 9 shows a temperature rise curve of an example of the present invention. 1: Heated object 2: Electromagnetic induction coil 3: Leg core
4: Yoke core 5: Resin mold 6: Terminal

Claims (2)

[Claims] (1) An electromagnetic induction heater for heating an object to be heated in contact with the object, the heater being formed of at least six induction coils, the induction coils being arranged in a circumferential manner, and A low-frequency electromagnetic device characterized in that a pair of adjacent induction coils receives power from one of three-phase AC power sources, and the wiring is such that current flows to the induction coils located at substantially symmetrical positions. induction heater. (2) The low frequency electromagnetic induction heater according to claim 1, wherein the electromagnetic induction coil is comprised of six pieces and the wiring system is a three-phase double delta connection.