JPH05148651A - Plated metallic material low in microwave damping factor and its manufacture - Google Patents

Abstract

PURPOSE:To provide a plated metallic material low in a microwave damping factor and useful as the part material having such required properties as being less in microwave damping and being capable of securing high energy utilizing efficiency to a microwave such as the waveguide and inner compartment of a microwave oven, and its manufacturing method. CONSTITUTION:The objective plated metallic material low in a microwave damping factor is constituted in such a manner that a pure Al plated layer having >=1.0mum thickness is formed on the topmost surface layer, preferably, its surface roughness is limited to Ra<=1.0mum and the levelling rate on the surface of the plated layer is increased to >=50%. This plated metallic material is obtd. by applying pure Al plating to a belt-like metallic material by an evaporation plating method and thereafter executing skin pass rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable as a material for parts, such as a waveguide of a microwave oven or an inner box, which requires high energy utilization efficiency against microwave irradiation from a magnetron, that is, The present invention relates to a plated metal material having a small microwave attenuation factor and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a component used for transmitting or containing microwaves, a stainless steel plate or a Zn-plated steel plate which has been bent and coated has been used.

From the viewpoint of microwave attenuating property, Cu, Al, etc., which have high electric conductivity and are not a ferromagnetic material, should be most suitable as such a component material.
Since it produces a highly toxic corrosion product such as patina, it can be used by painting, but it is difficult to use as an inner box of a microwave oven that may come into contact with food. Not used because it is much more expensive than it is. Al is also rarely used because its cost is higher than that of a steel plate and the workability and heat resistance are poor.

According to the theory of microwaves, it is only the outermost metal layer of several μm called the skin depth (SkinDepth) that is involved in the attenuation of microwaves, and the microwaves penetrate into this layer and the current flows. , Microwave energy is consumed. Therefore, if a metal substrate is plated with Cu or Al with a thickness of several μm, its microwave attenuation property should be the same as that produced by using Cu or Al. However, Cu plating not only causes the toxicity problem as described above, but also does not exert the effect of preventing microwave attenuation in a place not covered with the copper plating layer such as the end face and the processed portion, and also cannot prevent the corrosion of the base material. ..

Further, in the conventional hot dip Al plating method for Al plating, in order to prevent the fragile Fe--Al alloy layer from developing at the interface between the steel sheet and the plating layer,
The plating may contain a few% of Si, so that the electric conductivity is lower than that of pure Al plating, and the microwave attenuation rate is higher than that of pure Al. On the other hand, in hot-dip Al plating that does not contain Si, plating peeling occurs during bending and drawing, and therefore a method of plating and then processing into a waveguide or an inner box cannot be adopted.

For this reason, Zn-based plated steel sheets and stainless steel sheets, which are low in cost and excellent in corrosion resistance and heat resistance, have been used. However, they are not as good in electric conductivity as Cu and Al, and the steel sheets and Since the ferritic stainless steel sheet is ferromagnetic, the attenuation of microwave becomes more significant than that of Cu or Al.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its purpose is to obtain required characteristics as a component material such as a waveguide and an inner box of a microwave oven,
That is, the microwave attenuation factor is small, there is no problem in food hygiene, and excellent corrosion resistance and workability are provided.
Moreover, it is an object of the present invention to provide a plated material that can be obtained at low cost and a method for manufacturing the same.

[0008]

The structure of the plated metal material having a small microwave attenuation rate according to the present invention, which has been capable of solving the above problems, has a pure A having a thickness of 1.0 μm or more in the outermost layer.
The surface roughness of this plating layer is _Ra ≤ 1.0 μm (where _Ra is the center line average roughness specified in JIS B0601: the same applies hereinafter). Is particularly preferable, and a steel plate or a stainless steel plate is the most common material.

Further, the manufacturing method according to the present invention is characterized in that a strip-shaped metal base material is plated with pure Al to a thickness of 1.0 μm or more by a vapor deposition plating method, and then skin-pass rolling is performed, whereby the surface of the belt is 50. % Or more, and the above-mentioned plated metal material having _a surface roughness _Ra ≦ 1.0 μm is obtained.

[0010]

First, the reason why the outermost layer is set to pure Al plating will be described. This is because Al has the smallest microwave attenuation rate next to Cu among practical metals, and can be safely used in a microwave oven such as Cu that is not toxic even if ionized and may come into contact with food. This is because it has an advantage that it has a sacrificial anticorrosive action on Fe, though it is not as high as that of Fe.

Further, the higher the purity of Al plating, the higher the electric conductivity, and therefore the smaller the microwave attenuation rate. Therefore, although the expression of pure Al plating is adopted in the present invention, what the present inventors intend is that
This means that additional elements are not intentionally included in the plating layer for a specific purpose, such as hot-dip Al plating, etc., and it is an impurity element that is unavoidably mixed in the Al base metal, or it is mixed in the plating process. It is permissible that a small amount of an impurity element is contained in the Al plating layer, and the Al plating containing such unavoidable impurities is also included in the pure Al plating in the present invention.

Next, this pure Al plating can be carried out by a wet method such as a hot dip plating method or a molten salt electrolysis method, but a vapor deposition plating method is particularly preferable. The reason for this is that if the vapor deposition plating method is used, it is possible to easily apply pure Al plating with good adhesion to not only ordinary steel plates but also stainless steel plates, titanium plates, etc. This is because a high-purity Al plating layer can be easily obtained if the purity is set sufficiently high.

In order to suppress the microwave attenuation rate to a low level equivalent to that of an Al plate, the thickness of the pure Al plating layer of the outermost layer is set.
It must be 1.0 μm or more. This is because, as described above, microwaves penetrate and are attenuated only in the outermost layer, which is substantially called the skin thickness, but trial production of pure Al-plated steel sheets with various plating thicknesses is performed. As a result of an experiment, if the thickness of the pure Al plating layer is set to 1.0 μm or more, the microwave attenuation rate can be suppressed to be equal to that of the pure Al plate.

Therefore, in the present invention, it is essential that the pure Al plating thickness of the outermost layer is 1.0 μm or more, and as long as these requirements are satisfied, the corrosion resistance and workability of the lower layer of the uppermost layer plating are reduced. Zn, N for improving the property
It does not depart from the gist of the present invention even if it is plated with various undercoatings such as i, Co, Cr and Ti. When performing Al-based alloy plating by vapor deposition,
The plating layer may not be uniform but may be divided into several layers having different compositions. Even in such a case, the uppermost layer may be substantially a pure Al layer. For example, as shown in FIG. 2 described later, when two crucibles are arranged in the longitudinal direction of the vapor deposition chamber and Cr and Al are vaporized separately from each crucible to perform Al-Cr alloy vapor deposition plating, the plating layer is substantially the surface. The three-layer structure includes a pure Al layer, a θ-phase Al—Cr alloy layer, and a pure Cr layer in this order. Even in such a case, the top layer has a thickness of 1.0
If it is made of pure Al plating having a thickness of μm or more, its microwave attenuation rate shows the same value as that of the pure Al plate, and thus a plating layer having such a multi-layer structure is naturally included in the scope of the present invention.

Although there is no upper limit on the thickness of the pure Al plating layer from the viewpoint of the microwave attenuation factor, it is better not too thick from the viewpoint of the workability and adhesion of the plating layer, and corrosion resistance and the like are also taken into consideration. The thickness of the pure Al plating layer is preferably 20 μm or less, more preferably 10 μm or less.

In the present invention, the purpose can be met for the time being by defining the pure Al plating thickness of the outermost surface layer as described above, but the surface roughness of the pure Al plating layer is R _a ≤
The thickness of 1.0 μm is preferable because the microwave attenuation factor can be further suppressed. That is, the surface roughness of pure Al plating also affects the microwave attenuation characteristics, and _Ra (JISB0
When the surface roughness represented by the center line average roughness defined in 601) exceeds 1.0 μm, the microwave attenuation factor tends to increase. It is considered that this is because the lower limit of the skin thickness of pure Al is 1.0 μm, so that if the surface roughness is larger than this skin thickness, the path length of the current flows substantially due to the penetration of microwaves. Further, as a method of ensuring such surface roughness, it is effective to use a plated substrate having a fine surface roughness by bright rolling, fine dull rolling, hairline finishing, etc., but more preferable is a skin pass after vapor deposition plating. This is a method in which 50% or more of the surface is smoothed by rolling and the surface roughness _Ra is 1.0 μm or less.

The reason for this is as follows. That is, the vapor-deposited pure Al plating layer is usually composed of Al crystal grains having a grain size of about 1 μm, and it is considered that the crystal grain size also affects the path length of the current, but the surface thereof is rolled. It is considered that the smoothing by means also smoothes the crystal grains, further shortens the path length of the current, and decreases the microwave attenuation rate. Although the attenuation rate decreases as the degree of smoothing increases, the effect saturates at about 50%, so it is useless to increase the smoothing rate further. The smoothing rate means the area rate of the portion where the plated crystal grains as Al plated are not smoothed by rolling when the surface is observed with an SEM or an optical microscope.

The thus-obtained plated metal material having the pure Al plating applied to the outermost layer has a microwave attenuation rate suppressed by the plating characteristics of the outermost layer, and therefore can be used as it is for the above-mentioned applications. it can. However, depending on the use environment, the pure Al plating layer may be corroded and the effect of suppressing microwave attenuation may be impaired.
Alternatively, after processing into the final product shape, it is also effective to further perform an inorganic film formation such as a chromate treatment, a resin coating, and a coating on the pure Al plating layer, which is more preferable from the viewpoint of corrosion. preferable. In short, in the present invention, pure A
As long as a metal coating is not further formed on the 1-plating, the microwave attenuation suppressing effect is not impaired even when another inorganic coating or organic coating is formed.

There is no limitation on the kind of the base material on which the pure Al plating as described above is applied. For example, titanium, high alloy steel such as 4-2 alloy (high Ni alloy steel), Ni such as Hastelloy, etc. Although any metal such as an alloy or an Al alloy such as duralumin can be applied, a steel plate and a stainless steel plate are the most common in consideration of workability and cost. Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples.

[0020]

[Example] Al-killed cold-rolled steel strip having a thickness of 0.5 mm and a width of 780 mm, or a SU having a thickness of 0.5 mm and a width of 780 mm
Using S304 stainless steel strip as a substrate, pure Al plating or Al-Cr alloy plating was performed by the continuous vapor deposition plating equipment shown in FIG. 1 or 2 (both are schematic diagrams). Further, some of the test materials were subjected to skin pass rolling with a skin pass rolling machine after vapor deposition plating to perform surface smoothing treatment.

In FIG. 1, 1 is a feeding roll, 2 is a shear, 3 is a welder, 4 is a pretreatment chamber, 5 is an inlet side vacuum lock system, 6 and 8 are electron guns, 7 is a first vapor deposition chamber, 9 is a second vapor deposition chamber, 10 is an outlet side vacuum lock system, 11 is a skin pass rolling mill, 12 is a shear, 13 is a take-up roll, 1
4 represents steel strips, respectively. In FIG. 2, 15 is a vapor deposition chamber, 16 is an electron gun, 17 is a steel strip, 18 is an electron beam, 1
9 indicates a crucible for Cr, and 20 indicates a crucible for Al.

Therefore, according to the method of FIG. 1, both surfaces of the steel strip 14 can be plated with pure Al. Further, in FIG. 2, a vapor-deposited plating layer of Cr-Al or the like is formed on one surface of the steel strip 17, but in this method, a single vapor of Cr is first deposited on the surface of the steel strip 17, and then a mixed vapor of Cr and Al is formed. Since vapor deposition is performed and pure Al vapor is finally vapor deposited, the vapor deposition plating layer has a three-layer structure including pure Al, Al—Cr alloy, and Cr when viewed from the outermost layer side. Therefore, the pure Al plating thickness of the outermost layer can be adjusted by controlling the running speed of the steel strip 17 and the evaporation speed of Al and Cr.

The microwave attenuation rate of each of the obtained test materials was examined by the following method. That is, the test material has a diameter of 110 m.
m is punched into a disk shape, the punched material A is attached to one end face of a copper cavity resonator B shown in FIG. 3 and fixed with a bolt C (D is an antenna), and cavity resonance is performed under the following conditions. Measure the Q value of the vessel. The Q value decreases as the microwave attenuation rate of the test material increases. <Q value measurement conditions> ・ Frequency: 2.45 GHz ・ Measurement mode: H ₁₁₁ mode ・ Measuring device: HEWLETT-PACKARD 8510B NETWORK ANALYZER

Further, as comparative materials, hot-dip Al-plated steel sheet, hot-dip Zn-plated steel sheet, alloyed hot-dip Zn-plated steel sheet, pure Al
The Q value was measured in the same manner using a plated plate, a SUS304 steel plate, and an Al-killed cold rolled steel plate. The configurations of the test materials and the Q value measurement results are summarized in Tables 1 and 2.

[0025]

[Table 1]

[0026]

[Table 2]

As is clear from Tables 1 and 2, the plated steel sheets of Examples (Nos. 1 to 17) all have a Q value of 190.
00 or more and using a pure Al plate (comparison of Table 2
The Q value is comparable to that of No. 8), and the microwave attenuation rate is small. On the other hand, Si-containing hot-dip Al-plated steel sheet (Comparative N
o.3), hot-dip galvanized steel sheet (comparative No. 4), alloyed hot-dip galvanized steel sheet (comparative No. 5), Al-killed cold-rolled steel sheet (comparative No. 6), SUS304 steel sheet (comparative No. 7). The used Q values are all small, and the microwave attenuation rate is large as compared with the examples. In addition, even if pure Al plating is applied, the thickness is less than 1.0 μm (Comparative No.
The Q value of 1 and 2) is small and the effect of suppressing microwave attenuation is insufficient.

In addition, comparing Example No. 6 in Table 1 with Example Nos. 7, 8 and 9 in which this was subjected to skin pass rolling after plating, the skin pass reduction rate was increased and the surface smoothness rate was increased to 5.
It can be seen that when the content is 0% or more, the Q value is further increased and the microwave attenuation rate is decreased as compared with the case where the skin pass is not reduced.

[0029]

EFFECTS OF THE INVENTION The present invention is constructed as described above. By forming a pure Al plating layer having a specific thickness on the outermost surface, the microwave attenuation factor is small, and the corrosion resistance and workability are excellent and the cost is low. The plated metal material is provided, and can be widely used as a constituent material of parts such as an inner box of a microwave oven and a waveguide that need to contain microwaves.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a vapor deposition plating method used in Examples.

FIG. 2 is a conceptual diagram showing another vapor deposition plating method adopted in Examples.

FIG. 3 is a schematic diagram of a cavity resonator used for measuring a Q value. 1 Feeding reel 6,8,16 Electron gun 7 First evaporation chamber 9 Second evaporation chamber 11 Rolling machine 13 Take-up reel 14,17 Steel strip 18 Electron beam

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shoji Miyake 212-5 Nakano, Hiraoka-cho, Kakogawa-shi (72) Inventor Akemi Itasaka 97-21 Nagasuna, Noguchi-cho, Kakogawa-shi (72) Inventor Junji Kawafuku, Higashinada-ku, Kobe-shi 1-1-24 Uozaki Nakamachi

Claims (4)

[Claims] 1. A pure Al layer having a thickness of 1.0 μm or more on the outermost layer.
A plated metal material having a small microwave attenuation rate, which is characterized in that a plated layer is formed. 2. Surface roughness R _a ≦ 1.0 μm (provided that R a
_The plated metal material having a small microwave attenuation rate according to claim 1, wherein a is a center line average roughness specified in JIS B0601). 3. The plated metal material having a small microwave attenuation rate according to claim 1, wherein the smoothing rate of the plated surface is 50% or more. 4. The microwave attenuation factor according to claim 1, wherein pure aluminum plating is applied on the surface of the strip-shaped metal base material by vapor deposition plating and then skin pass rolling is performed. Method for producing small plated metal material.