JPS6137753B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to impeders, and more particularly to their core cases.

One example of the use of impeders is in the manufacture of steel pipes.
This will be explained with reference to FIG. In Figure 1, 1
0 represents a ferrite core, 12 represents a core case, 14 represents a steel plate, and 16 represents a high frequency coil. As shown in the figure, when the steel plate 14 is rolled up and pulled out in the direction of arrow A through the high-frequency electromagnetic field generated by the coil 16, the steel plate 14 is heated and becomes red hot due to the eddy current loss generated in the steel plate 14, and the edges 14a and 14b of the steel plate become red hot. Welded to obtain a steel pipe. Here, the impeder consists of a cylindrical ferrite rod 10 and a core case made of synthetic resin surrounding it, and serves to concentrate current at the welding point in the steel plate.

Figure 2 is a structural diagram of an impeder, with ferrite rod 1
0 and a cylindrical synthetic resin core case 12 that surrounds this with a gap 18 in between.
One end 12a of 2 is slightly tapered. This end portion 12a is connected to a water pipe, and cooling water is passed through the gap 18, thereby cooling the ferrite rod 10 and the case 12. From the viewpoint of electromagnetic properties, it is preferable that the ferrite rod be as thick as possible and close to the inner diameter of the steel plate 14. However, in reality, a non-magnetic portion formed by the core case 12 and the air gap 18 is unavoidable due to cooling and other needs. The magnetic flux generated by this is subject to large magnetic resistance. A large magnetic resistance results in an increase in high-frequency power for heating, which is undesirable from the standpoint of energy saving.

Therefore, various techniques were investigated to make the core case magnetic.

As a technique for imparting magnetism to a non-magnetic material, rubber ferrite, in which ferrite powder is mixed into natural rubber or artificial rubber, has been known for a long time. However, since rubber ferrite is mechanically soft and susceptible to high heat, it is unsuitable for use as an impeder core case for high-frequency heating processing.

Therefore, an object of the present invention is to provide an impeder core case that makes it possible to reduce heating power in a high-frequency heating process.The main feature of the present invention is that the synthetic resin constituting the core case is made of reinforced plastic mixed with glass fiber. The purpose is to mix ferrite powder into this. The impeder according to the present invention has a core made of a cylindrical ferrite rod, and a hollow cylindrical core case disposed substantially coaxially with the ferrite rod, which receives the ferrite rod through a gap through which water can pass. The core case is composed of a reinforced plastic made of plastic and glass fiber mixed with ferrite powder, and the volume ratio of the components of the core case is ferrite: 25vol% to 50vol%, plastic: 35vol% to 55vol%, glass fiber: 10vol% to It is composed in a range of 40vol%.

The plastics can be, for example, epoxy resins, unsaturated polyester resins or phenolic resins, and other plastics that can withstand high temperatures of 80° C. or higher can also be used.

Ferrite powder mixed into plastic is Mn.
- Zn-based ferrite is suitable, and experiments have shown that the volume ratios of each of the ferrite, plastic, and glass cloth are preferably within the above-mentioned ranges. Note that the total of each component is, of course, 100%.

When the ferrite content exceeds the above ratio, the viscosity of the plastic increases, causing manufacturing problems, and when the ferrite content is below the above ratio, the magnetic properties of the impeder are insufficiently improved. If the proportion of plastic is too large, the magnetic properties will deteriorate and the mechanical strength will be weakened, and the problem of resin flowing out during production will occur, and if the proportion of plastic is too small, the adhesiveness of the prepreg will deteriorate. If the ratio of glass cloth is too large, the magnetic properties of the impeder will deteriorate, and if the ratio is too small, the mechanical strength will be weakened, and the processability will be deteriorated due to resin flowing out during manufacturing. Therefore, the ratio of each component is preferably within the above range.

FIG. 3 shows the manufacturing process of the core case according to the present invention, in which a liquid resin 20 mixed with ferrite powder is placed in a case 32, a glass cloth 24 is passed through the resin along the roller 22, and the resin adheres. A sheet 26 is obtained. At this time, the thickness and passing speed of the glass cloth shall be controlled so that the component ratio satisfies the above values. The sheet 26 is pulled by rollers 28 and 34 and heated and dried by a heating means 30 in the middle to obtain a partially dried prepreg 36. A hollow cylindrical core case is obtained by wrapping the prepreg 36 around a cylindrical mold and adhering both ends with its own adhesive force. Note that one end of the core case is formed to be slightly thin in order to be connected to cooling water.

(The outer diameter, inner diameter of the core case, and the diameter of the ferrite rod) are, for example, (13 mm, 11 mm, 9 mm), or (15 mm, 13 mm, 11 mm), or (19 mm, 16 mm, 14 mm).
The length of the ferrite rod can be approximately 23cm.

According to the present invention, 31vol of Mn-Zn ferrite
%, plastic 17vol%, glass cloth
A core case with 17 vol% was made, and an impeder with a ferrite core inserted into it was tested at 200 oersted, and a magnetic flux density of 5900 Gauss was obtained. The test result for a conventional core case without ferrite powder mixed under the same conditions was 5600 Gauss, so the adoption of the core case according to the present invention increased the magnetic flux density by about 5.4%.

In another experiment, 47vol of Mn-Zn ferrite was
%, plastic 39vol%, glass cloth
When a core case with 14 vol% was made and a ferrite core was inserted into the impeder and tested at 200 oersted, a magnetic flux density of 6120 Gauss was obtained, which was 5689 Gauss when using a conventional core case under the same conditions. On the other hand, an improvement of 7.6% was observed.

In addition, in the above experiment, the applied high frequency was 200 to 400 KHz.
It is.

Radiofrequency heating using the impeder according to the invention reduces the magnetic reluctance of the circuit, thus reducing the required radiofrequency power and increasing the magnetic flux density by 5.4-7.6% using the core case used in the above-mentioned experiments. It has been confirmed that the high-frequency power required to manufacture steel pipes is reduced by 3% to 10% compared to conventional methods.

As described above, according to the present invention, since the core case of the impeder is made of FRP mixed with ferrite powder, the required high frequency power is reduced, contributing to energy saving.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the manufacturing process of a steel pipe, FIGS. 2A and 2B are structural examples of an impeder, and FIG. 3 is a diagram showing a manufacturing process of an impeder core case. 10...Ferrite core, 12...Core case, 18...Void.

Claims (1)

[Claims] 1. In an impeder having a core made of a cylindrical ferrite rod, and a hollow cylindrical core case disposed substantially coaxially with the ferrite rod, which receives the ferrite rod through a gap through which water can pass through. , the core case is composed of reinforced plastic made of plastic and glass fiber mixed with ferrite powder, and the volume ratio of the components of the core case is ferrite: 25vol% to 50vol% plastic: 35vol% to 55vol% glass fiber: 10vol % to 40vol%.