KR100435436B1 - A Steel Material for Shielding Low Frequency having Magnetic Property - Google Patents

Abstract

The present invention relates to a low frequency shielding steel having magnetic properties, and to provide a steel that can shield the low frequency having magnetic properties more economically and more reliably by appropriately controlling the carbon content and the grain size of the steel. There is this.

The present invention has a low-frequency shielding steel having a magnetic property of less than 0.07% by weight and a grain size of ASTM number 11 or less.

Description

A steel material for shielding low frequency having magnetic property

The present invention relates to low frequency shielding steels having magnetic properties, and more particularly, to harmful low frequency shielding steels having magnetic properties that affect the human body or cause malfunction of other equipment.

As the hazards of magnetic waves become known, methods and materials to block them are emerging.

It is a wave having a magnetic field of blue magnetic field (WAVE). A wave that affects the human body or causes a malfunction of another device is called a harmful para.

In particular, in recent years, low-frequency harmonics with magnetic properties have been highlighted.

Representative examples of the harmful low frequency having the above magnetic properties include low frequency electromagnetic waves and so-called water waves.

For example, when the human body is exposed to low frequency electromagnetic waves having magnetic properties for a long time, an induced current is generated in the human body, resulting in an imbalance of various ions such as Na ⁺ , K ⁺ , and Cl ^- in the cell membrane, thereby releasing hormones and immune cells. It is known to affect.

On the other hand, the water wave is known to have a magnetic property of less than 10Hz generated by the modulation of the geomagnetic field in the place of the water vein, which is known to affect the human body because the frequency and frequency bands of humans at rest are similar. have.

Building flooring materials are widely used to block low frequencies having magnetic properties such as the above-mentioned water wave.

Copper plates (Korean Utility Model Publication No. 95-14481) and aluminum plates (Korean Patent Publication No. 94-19465) are mainly used as flooring materials for construction.

However, in the case of the above-described conventional shielding material, there is a problem that the autism ability to low frequency having magnetic properties is not only poor, but also limited in application in economical efficiency.

MEANS TO SOLVE THE PROBLEM The present inventors carried out research and experiment in order to solve the above-mentioned problems of the prior art, and based on the results, the present invention proposes the present invention, and the present invention provides magnetic properties by appropriately controlling the carbon content and the grain size of the steel. It is an object of the present invention to provide a steel material that can more reliably shield a low frequency having a lower cost.

1 is a schematic diagram for explaining a low frequency shielding mechanism having magnetic properties

2 is an example of a method for evaluating low frequency shielding ability having magnetic properties;

Figure 3 shows the magnetic field line distribution in the case of using the copper plate and the steel of the present invention as a shielding material,

(a) shows the case where a copper plate is used, and (b) shows the case where the steel material of this invention is used.

Figure 4 shows the leakage magnetic flux density distribution in the case of using the copper plate and the steel of the present invention as a shielding material,

(a) shows the case where a copper plate is used, and (b) shows the case where the steel material of this invention is used.

Explanation of symbols on the main parts of the drawings

One . . . Inner space of shielding material

2 . . . Shielding material

3. . . Outer space of shielding material

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention relates to a low-frequency shielding steel having a magnetic property of less than 0.07% by weight and a grain size of less than ASTM No. 11.

The present invention also relates to a low frequency shielding steel having a magnetic property having a carbon content of 0.002-0.07% by weight and a grain size of ASTM No. 6.5-11.

The shielding mechanism for the low frequency having magnetic properties will be described below with the shielding mechanism for electromagnetic waves as an example.

Mechanisms in which electromagnetic waves are shielded by metallic materials are classified into reflection shielding and absorption shielding.

Reflective shielding is applied when the electromagnetic waves are high frequency, and absorption shielding is applied when the electromagnetic waves are extremely cursed.

For example, as shown in FIG. 1, when the magnet is repeatedly moved at very low frequency (7-8 times per second) to the metal sheet, the magnetic flux of the metal sheet is changed with time.

That is, fluctualtion of magnetic flux occurs on the surface of the steel sheet, which is the same as the effect of the induction of the ultra-low magnetic field electromagnetic waves on the surface of the steel sheet.

That is, the physical fact that the current (eddy current, eddy current, or eddy current) is generated in the direction of reducing the magnetic flux on the plate surface by repeatedly moving the magnet to the metal plate as shown in FIG. have.

The generated current is absorbed and lost as thermal energy while flowing through the metal surface.

This is commonly called vortex loss.

Therefore, when low frequency electromagnetic waves are incident on the surface of the steel sheet, eddy currents are generated on the surface of the steel sheet in a direction to reduce the magnetic flux.

That is, the eddy current generated due to the low frequency of the incident magnetic property is absorbed and lost by thermal energy as it flows through the metal surface, and thus is blocked from passing through the steel sheet.

Therefore, the eddy current loss must be large for the shielding ability against the low frequency having magnetic properties to be large.

In the case of general soft magnetic materials, the eddy current loss causes a problem of lowering the energy efficiency. However, the eddy current loss must be large in order to become a material having high magnetic shielding ability against low frequency.

The eddy current loss value of the magnetic property material can be expressed by Equation 1 below.

K: proportional constant

σ: electrical conductivity

μ: permeability

f: frequency

As can be seen from the above equation, in order to improve the low frequency shielding ability having magnetic properties, a material having high electrical conductivity and permeability must be used.

Accordingly, the present inventors have conducted research and experiment on the production of a material having a high electric conductivity × permeability value in order to improve the low frequency magnetic field shielding ability having magnetic properties.

In particular, the steel of the present invention is highly economical.

More preferred steel materials of the present invention include hot rolled steel sheet or cold rolled steel sheet.

The inventors confirmed that controlling the carbon content and grain size of the steel greatly changed the conductivity and permeability, thereby bringing a remarkable change in the shielding capability of low frequency magnetic properties.

That is, the lower the carbon content and the larger the grain size of the steel (the lower the ASTM number), the higher the conductivity and permeability will be.

Therefore, in order to shield the low frequency magnetic properties, the carbon content and grain size of the steel must be properly controlled.

That is, the carbon content of the steel of the present invention is preferably limited to 0.07% by weight or less, and the grain size is preferably limited to ASTM No. 11 or less, for the following reason.

In the steel of the present invention, when the carbon content exceeds 0.07% by weight and the grain size exceeds ASTM 11, the grain size increases due to the increase in Fe ₃ C precipitation and grain refinement, resulting in a decrease in conductivity and permeability. This is because the low frequency shielding ability is lowered.

More preferred steel of the present invention has a shielding ability of 40dB or more against low frequency.

On the other hand, when the steel of the present invention is to be used as a structural material such as building flooring, it is preferable to limit the carbon content to 0.002-0.07% by weight and the grain size to ASTM No. 6.5-11, because the carbon content is 0.002% by weight. If less than%, the grain size is less than ASTM No. 6.5 is because the mechanical strength, such as yield strength is relatively low, it is not suitable for structural materials such as building flooring.

The steel of the present invention, which is more suitable for structural materials such as building flooring, has a shielding ability of at least 40 dB against low frequencies and a yield strength of at least 15 kg / mm ² .

On the other hand, in order to use the steel of the present invention as a structural material, it is preferable to plate various corrosion-resistant elements such as zinc, nickel, tin, aluminum, etc. on the steel having carbon content and grain size in accordance with the present invention in order to prevent corrosion. The same magnetic field shielding effect as above is obtained.

The frequency having magnetic properties that can be shielded by the steel of the present invention is a low frequency having a frequency of KHz band, more preferably the frequency that can be shielded is a low frequency having a frequency of 500KHz or less.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

The improvement of the shielding ability against the low frequency which has a magnetic property can be anticipated from the material with a high permeability x electrical conductivity value from Formula (1).

Therefore, the magnetic permeability of copper sheet, aluminum sheet, zinc sheet and 0.044 wt% of carbon content according to the present invention and cold rolled steel sheet having ASTM number = 10 according to the present invention are currently used as shielding materials for low frequency with magnetic properties such as water wave. (Gauss / Oersted) and electrical conductivity (Sm ⁻¹ ) were measured, and the results are shown in Table 1 below.

Electrical Conductivity (Sm ^-1 ) Permeability (Gauss / Oersted) Permeability × Electric Conductivity Remarks Conventional Example 1 5.98 × 10 ⁷ One 5.98 × 10 ⁷ 99.99% copper plate Conventional Example 2 3.77 × 10 ⁷ One 3.77 × 10 ⁷ 99.98% Al Conventional Example 3 1.69 × 10 ⁷ One 1.69 × 10 ⁷ 99.9% zinc plate Inventive Example 1 1.05 × 10 ⁷ 1520 1.58 × 10 ⁹ Cold rolled steel sheet

As can be seen in Table 1, compared to non-ferrous materials such as Cu, Al, Zn, the cold-rolled steel sheet of the present invention exhibits a significantly higher permeability × electrical conductivity value, which is a low-frequency shielding material having magnetic properties. It means to be suitable.

Example 2

In order to compare the low frequency shielding ability with magnetic properties with respect to the copper plate (conventional example 1) and the cold rolled steel sheet (invention example 1) of the present invention, a low frequency shielding ability having a magnetic property of 7.5 Hz, which can be referred to as the frequency of the water wave Was compared.

As a method of comparing the shielding ability, a sealed box method used for the evaluation of the electromagnetic shielding performance was used.

That is, after forming a box-shaped space with the shielding material 2 as shown in FIG. 2, the magnetic field generating source is put into the shielding inner space 1, and the strength of the magnetic field leaked from the shielding inner space 1 to the outer shielding material 3 with the shielding material. The distribution of magnetic field lines was analyzed.

Simulated evaluation was used to measure the strength of the magnetic field flowing from the inside of the shield box to the outside.

That is, after measuring the magnetic permeability and electrical conductivity of the material and using a magnetic analysis program called OPERA Series of Vector Field of England, as well as the distribution of magnetic lines in a space as shown in FIG. 3, the magnetic flux density in one space as shown in FIG. The strength of the magnetic field can also be determined accurately.

Figure 3 is a magnetic field distribution of the magnetic field of 7.5Hz when using a copper plate and the cold-rolled steel sheet of the present invention as a shielding material, Figure 4 schematically shows a distribution of leakage magnetic flux density.

As shown in FIGS. 3 (b) and 4 (b), the cold rolled steel sheet of the present invention having a high permeability prevents leakage of magnetic fields to the outside by connecting a low frequency magnetic field in a shielding material. As shown in (a), simulation results show that low-permeability materials such as copper have low frequency magnetic fields.

On the other hand, the shielding effect of the low frequency having magnetic properties is usually defined as follows.

Shielding Effect [dB] = 20log (∑ H _{out, shield} / ∑H _{out, blank} )

H _{out, shield} : Sum of the strength of the magnetic field leaking outside the _shield ("3" in Figure 2) when there is a _shield

H _{out, blank} : Sum of the strengths of the magnetic fields leaking outside the shield ("3" in Figure 2) when there is no shield

Therefore, 20 dB is generated when magnetic flux shielding occurs by 1/10, and 40 dB when magnetic flux shielding occurs by 1/100.

As a result of analyzing the shielding ability of the cold rolled steel sheet according to the magnetic properties of the present invention, the cold rolled steel sheet showed a shielding ability of 53.3 dB, while the non-ferrous shielding materials such as copper showed a poor shielding ability of 10 dB or less. It was.

Therefore, it could be confirmed that the cold rolled steel sheet according to the present invention is an excellent material in shielding ability against low frequencies having magnetic properties.

Example 3

In order to analyze the shielding ability against the low frequency having magnetic properties, the components were adjusted to have a carbon content of 0.002-0.09% by weight in the steelmaking process during the production of cold rolled steel sheet.

In the annealing process in the production of cold rolled steel sheet was prepared by cold-rolled steel sheet having a grain size of ASTM No. 6-12 by controlling the annealing temperature.

On the other hand, the shielding ability against the low frequency having a magnetic property at 7.5Hz was evaluated in the same manner as in Example 2 for the sample having a different carbon content and grain size.

In addition, yield strength, which is an important factor of building flooring materials, was measured in a universal testing machine and is shown in Table 2 below.

Carbon content (wt%) ASTM Number Yield strength (kg / mm ² ) Low frequency shielding ability (dB) Invention 1 0.002 8 15 65 Invention Material 2 0.002 6 12 65 Invention 3 0.005 9 17 63 Invention 4 0.005 7 15 64 Invention 5 0.025 10 22 56 Invention Material 6 0.025 9 19 59 Invention Material 7 0.044 11 26 51 Invention Material 8 0.044 10 23 53 Invention Material 9 0.067 11 30 46 Invention Material 10 0.067 10 28 48 Comparative material 1 0.090 12 37 35 Comparative material 2 0.090 11 35 35

As can be seen in Table 2, the lower the carbon content and the lower the ASTM number, the higher the shielding ability against the low frequency magnetic properties.

However, when the carbon content is 0.002% and ASTM No. = 6 (Inventive Material 2), the shielding ability against low frequency with magnetic properties is excellent, but the yield strength is less than 15 kg / mm ² , which is not suitable for structural materials. It can be seen that.

On the other hand, as the carbon content increases and the ASTM number increases, the yield strength increases but the low frequency magnetic field shielding ability decreases rapidly.

When the carbon content is 0.09% and ASTM numbers 11 and 12 (Comparative Material 1) and (Comparative Material 2), it can be seen that the shielding ability against low frequencies having magnetic properties is significantly lowered to 40 dB or less.

Therefore, when using the steel of the present invention as a building flooring material it can be seen that it is preferable to control the carbon content to 0.002-0.07% by weight, and the ASTM number in the range of 6.5-11.

On the other hand, as a result of surface treatment of various corrosion resistance elements such as Zn, Ni, Cu, Sn, and Al in order to improve the corrosion resistance of the cold rolled steel sheet of Table 1, the shielding ability against low frequencies having magnetic properties was not significantly changed.

Example 4

In order to investigate the shielding ability of the water vein according to the characteristics of the cold rolled steel sheet, the cold-rolled steel sheet having 50cm × 50cm (width × vertical) having different carbon content and grain size was prepared, and then the shielding ability of the water vein was evaluated.

The shielding ability of the water veins was using the most commonly used el-lod (L-lod).

After measuring the position of the strongest vein in advance using the el rod, the prepared cold-rolled steel sheet and copper plate were placed in the strongest vein of the vein, and the change of the el rod was observed.

Evaluation of shielding ability was measured by the vibration angle of the elrod.

In other words, if it moves more than 90 degrees, the shielding capacity is 0% (if there is no shielding material), and when the two elrods are not moving at all and in parallel, the 100% shielding is determined and the vein shielding ability is evaluated for each sample. The results are shown in Table 3 below.

division Carbon content (wt%) ASTM Number L-lod vibration angle Shielding rate (%) Invention 4 0.005 7 0 100 Invention Material 8 0.044 10 20 80 Comparative material 1 0.090 12 45 55 Comparative material 3 Pure copper plate use 70 30 Vein strong place without shield over 90 0

As shown in Table 3, the L-lod vibrated at an angle of about 100 at the vein strong place without the shield.

In addition, it was found that the invention materials 4 and 8 having a low carbon content and large crystal grain size blocked almost all water veins due to the slight vibration at the water vein when measured by L-lod.

However, as the carbon content increases and the ASTM number increases, the shielding ability of the water veins decreases as in the shielding ability result for the low frequency having the magnetic properties of Table 2.

In addition, it was found that the cold rolled steel sheet having the carbon content and grain size in accordance with the present invention (invention materials 4 and 8) is much better shielding against water veins than the copper plate used as a vein shielding material in the market.

Example 5

Evaluation of the shielding ability of the copper plate consisting of 0.025% carbon content, a cold rolled steel sheet having a grain size of ASTM No. 10 and 99.99% copper, and the results are shown in Table 4 below.

The shielding ability in Table 4 was evaluated in the same manner as the magnetic field shielding ability evaluation method of Example 3.

At this time, the frequency was measured while changing to 60Hz, 1000Hz, 1MHz.

Metal plate type, thickness Frequency (Hz) Shielding capacity (dB) Conventional Example 2 Copper Plate, 0.4mm 7.5 3 Inventive Example 5 Steel plate, 0.4mm 7.5 56 Conventional Example 3 Copper Plate, 0.4mm 60 4 Invention Material 10 Steel plate, 0.4mm 60 59 Conventional Example 4 Copper Plate, 0.4mm 1,000 7 Inventive Example 11 Steel plate, 0.4mm 1,000 62 Conventional Example 5 Copper Plate, 0.4mm 1,000,000 63 Inventive Example 12 Steel plate, 0.4mm 1,000,000 60

As shown in Table 4, the use of a cold rolled steel sheet according to the present invention shows similar shielding ability (invention example 12) in the MHz band, compared to the case in which the copper plate is used, but especially in the low frequency of the KHz band and below. It can be seen that it shows much higher shielding ability.

As described above, the present invention has an effect of more economically providing a steel material capable of more reliably shielding low frequencies having magnetic properties by appropriately controlling the carbon content and the grain size of the steel.

Claims (21)

Low-frequency shielding steel with magnetic properties, characterized in that the carbon content is 0.07% by weight or less, the grain size is ASTM number 11 or less, and has a shielding ability of 40 dB or more against low frequency magnetic properties. delete The low-frequency shielding steel according to claim 1, wherein the carbon content is 0.002-0.07 wt% and the grain size is ASTM No. 6.5-11. 4. The low frequency shielding steel having magnetic properties according to claim 3, wherein the yield strength of the steel is 15 kg / mm ² or more. 2. The low frequency shielding steel having magnetic properties according to claim 1, wherein at least one element of Zn, Cu, Al, and Ni is plated on the surface of the steel. 4. The low frequency shielding steel having magnetic properties according to claim 3, wherein at least one element of Zn, Cu, Al, and Ni is plated on the steel surface. 5. The low frequency shielding steel having magnetic properties according to claim 4, wherein at least one element of Zn, Cu, Al, and Ni is plated on the surface of the steel. The low frequency shielding steel material having magnetic properties according to claim 1, wherein the low frequency having magnetic properties is a water wave. 4. The low frequency shielding steel having magnetic properties according to claim 3, wherein the low frequency having magnetic properties is a water wave. The low frequency shielding steel material having magnetic properties according to claim 4, wherein the low frequency having magnetic properties is a water wave. The low-frequency shielding steel having magnetic properties according to claim 5, wherein the low frequency having magnetic properties is a water wave. The low-frequency shielding steel having magnetic properties according to claim 6, wherein the low frequency having magnetic properties is a water wave. The low frequency shielding steel material having magnetic properties according to claim 7, wherein the low frequency having magnetic properties is a water wave. 4. The low frequency shielding steel having magnetic properties according to claim 3, wherein the steel is a building material. 5. The low frequency shielding steel having magnetic properties according to claim 4, wherein the steel is a building material. The low frequency shielding steel having magnetic properties according to claim 6, wherein the steel is a building material. The low frequency shielding steel having magnetic properties according to claim 7, wherein the steel is a building material. 10. The low frequency shielding steel having magnetic properties according to claim 9, wherein the steel is a building material. 11. The low frequency shielding steel having magnetic properties according to claim 10, wherein the steel is a building material. 13. The low frequency shielding steel having magnetic properties according to claim 12, wherein the steel is a building material. 14. The low frequency shielding steel having magnetic properties according to claim 13, wherein the steel is a building material.