JPH10217217A - Manufacture of conical wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain a low specific gravity conical wave absorber with a high productivity by a method wherein molded articles, each of which is obtained by filtered water molding and drying silicate slurry containing carbon fibers cut short into the longitudinally bisect shape of a truncated hollow cone, are assembled into a truncated cone, to which an apex part made of the same material as that of the truncated cone and produced separately is mounted so as to obtain cone. SOLUTION: Carbon fiber chopped stands are added to a calcium silicate slurry and agitated and dispersed therein. The resultant slurry is molded with filtered water with a mold into a shape, which is obtained at least by longitudinally bisecting a truncated hollow cone. Next, calcium silicate formed bodies after being dried are assembled and bonded with each other so as to obtain a truncated cone, to which a separately formed apex part is bonded so as to obtain a cone. Thus, a lightweight and incombustible wave absorber can be easily manufactured at good production efficiency and, in addition, the breakage of the apex part, which mostly tends to break, can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a quadrangular pyramid or cone-shaped radio wave absorber used in an anechoic chamber. In particular, the present invention relates to a method for manufacturing a light-weight and nonflammable radio wave absorber.

[0002]

2. Description of the Related Art A cone-shaped radio wave absorber such as a quadrangular pyramid or a cone is used on a wall surface of an anechoic chamber. Conventionally, as this cone-shaped radio wave absorber,
A foamed plastic such as polyurethane foam mixed with graphite or other carbon powder is mainly used.
This is excellent in that it is lightweight and easy to manufacture, but has the disadvantage that it is easily deformed at high temperatures and easily burns.

As a lightweight and non-combustible material that can replace foamed plastic, there is calcium silicate having a low specific gravity used as a heat insulating material. However, a calcium silicate molded body for a heat insulating material is manufactured through a process of injecting a slurry of calcium silicate or a precursor thereof into a molding die and performing dehydration molding into a simple shape such as a thick plate or a semi-cylindrical shape. In order to form a shape like a cone used in a radio wave absorber, it is necessary to develop a molding technique suitable for the shape. Further, since the calcium silicate molded body having a low specific gravity has a low strength, even when molded into a conical body, it is feared that the top is damaged and the product yield is reduced. Accordingly, the present invention provides a cone-shaped radio wave absorber made of low specific gravity calcium silicate,
It is an object of the present invention to provide a method of easily producing a product with high productivity.

[0004]

According to the present invention, a cone-shaped radio wave absorber made of calcium silicate is constituted by a combination of at least three members, and the existing technology is utilized to improve productivity. Can be manufactured. That is, according to the present invention, a silicic acid slurry containing a carbon fiber cut into a short length was drained and formed into a shape obtained by cutting a hollow cone having a top portion cut off at least in a longitudinal direction, followed by drying. Combining the molded products to form a hollow cone with the top cut off, and attaching the separately manufactured top made of calcium silicate containing short-cut carbon fibers to form a cone, Can be manufactured with high productivity.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in more detail. First, a calcium silicate slurry containing short-cut carbon fibers is prepared. Normally, chopped strands of carbon fibers may be added to a calcium silicate slurry produced by a conventional method, and the mixture may be stirred and dispersed. Stirring is preferably performed until the chopped strands are opened into individual single fibers. The carbon fiber may be PAN-based or pitch-based, and has an average length of 30 mm or less, particularly 15 mm or less.
mm or less.

[0006] The calcium silicate slurry containing carbon fibers is then subjected to drainage molding using a molding die by a conventional method, and the shape is a shape obtained by vertically dividing the hollow cone having at least the top part into at least two parts. . Usually, it is divided into two, but if desired, it may be divided into three or four. However, further division usually increases the assembling labor and has no advantage. For example, in the case of a quadrangular pyramid-shaped radio wave absorber, it is preferable to divide into two along a diagonal line as shown in the figure. By adopting such a shape, drainage molding can be performed by directly applying the manufacturing technology of a conventional thick plate-like calcium silicate molded product or semi-cylindrical calcium silicate molded product. The thickness of the molded article varies depending on the size of the electromagnetic wave absorber to be manufactured.
It is 5 to 50 mm, preferably 20 to 40 mm, and may have the same thickness as a whole, or may have a thickness that gradually decreases toward the top of the cone.

[0007] The molded product is then dried by a conventional method to obtain a calcium silicate molded product. If desired, the molded article may be steam-cured to further grow the calcium silicate crystals or to convert the crystal form before drying. In this way, a calcium silicate molded body having a strength generally higher than that of simply drying can be obtained. The drainage molding is usually performed such that the bulk density of the obtained molded body is 0.1 to 0.5 g / cm ³ . The bulk density is preferably smaller, but generally 0.1 g
It is difficult to produce a calcium silicate molded body having a bulk density of less than / cm ³ . Preferably 0.1 to 0.35 g / c
The drainage molding is performed so as to obtain a m ³ calcium silicate molded body. Further, the content of the carbon fiber in the calcium silicate molded product is 0.01 to 50 g / l, particularly 0.05 to 5 g / l.
It is preferred that The preferred content of the carbon fiber depends on its average length. Generally, the longer the average length, the better the radio wave absorption at a smaller content.However, it is possible to obtain a molded article in which carbon fibers are uniformly dispersed. Becomes difficult.

The calcium silicate compacts in which the carbon fibers thus obtained are dispersed are then combined with each other and joined to form a cone having a truncated top. Bonding of the calcium silicate molded body can be easily performed using an adhesive such as water glass. Of course, nailing may be used if desired. In the present invention, a separately formed apex is joined to the conical body with the apex cut off in this manner to form a conical body. The top may be formed of a material different from the other parts of the cone, such as calcium silicate containing graphite or other carbon powder, but usually the same material, that is, a carbon fiber content of 0.01 -50 g / l, preferably 0.05-5 g / l, bulk density 0.1-0.5 g / cm
³ , preferably made of calcium silicate containing short cut carbon fibers of 0.1 to 0.35 g / cm ³ . This top, like the other parts, can be produced by drainage molding of a calcium silicate slurry containing short-cut carbon fibers, but because of its small size, it is filtered from a slurry containing short-cut carbon fibers. It is preferable to produce a thick plate by water forming and cut it into a small cone to form a top.

In a preferred embodiment of the present invention, a surface hardening agent is applied to the surface of the calcium silicate to strengthen the surface of the calcium silicate. Since calcium silicate having a low specific gravity has low strength, and particularly its surface is easily broken, it is very advantageous in handling and use to strengthen the surface and make it hard to be broken. As the surface hardening agent, an organic one such as rubber latex or a polyurethane-based paint can be used, but usually, an inorganic one such as a sodium sulfate aqueous solution, water glass, or methyl silicate solution is preferably used. For example, when a 10% aqueous solution of sodium sulfate is applied, the easiness of the surface collapse can be greatly suppressed. The application of the surface hardening agent may be performed on the steps of the member before assembling into a cone, or may be performed after assembling into a cone.

One example of a method for producing a quadrangular pyramid for a radio wave absorber having the shape shown in FIG. 1 according to the method of the present invention is as follows. A calcium silicate slurry produced by a conventional method is mixed with a chopped strand (length) of carbon fiber. 5 to 10 mm) and well stirred. This is formed by a drainage press material by a conventional method, and further subjected to steam curing and drying. The carbon fiber content is 0.6 g / l, the bulk density is 0.15 g / cm ³ , and the shape shown in FIG. Calcium silicate shaped body in the shape of a chevron obtained by bisecting the resected pyramid along the diagonal line (the size of each piece constituting the chevron is about 305 mm on the lower side and about 6 mm on the upper side)
0 mm, about 776 mm long and 30 mm thick). When two of the molded bodies are adhered with water glass, a square pyramid having a cut off top is obtained.

Separately, a calcium silicate slurry in which chopped strands (5 to 10 mm in length) of carbon fibers are dispersed in the same manner as described above is formed by a drainage press material by a conventional method, and is further subjected to steam curing and drying. Content 0.6g
/ L, a bulk density of 0.15 g / cm ³ and a 30 mm thick calcium silicate plate are produced. A triangular member 2 having a base length of 60 mm and a height of 190 mm from the calcium silicate plate 2
After cutting a piece, it is cut and then glued with water glass to produce a small square pyramid. When this small square pyramid is bonded to the above-obtained square pyramid lacking the top with water glass, a square pyramid having a base length of about 305 mm and a height of about 956 mm is obtained. When a 10% aqueous solution of sodium sulfate is applied to the surface of the quadrangular pyramid and dried, a quadrangular pyramid-shaped radio wave absorber made of calcium silicate having a low specific gravity and a reinforced surface is obtained.

[0012]

According to the present invention, a lightweight and nonflammable radio wave absorber can be easily manufactured. In the present invention, since the cone is divided into a base and a top, and the base is also manufactured by combining members manufactured by dividing the base in the vertical direction, the production efficiency is good and the damage to the top which is most easily broken is reduced. be able to.

[Brief description of the drawings]

FIG. 1 is an example of a quadrangular pyramid-shaped radio wave absorber manufactured by the method of the present invention.

FIG. 2 is a member for forming a base of the quadrangular pyramid-shaped radio wave absorber of FIG.

Claims (5)

[Claims] 1. A calcium silicate slurry containing short-cut carbon fibers, which is formed by filtering water into a shape obtained by cutting a hollow conical body having a top portion cut off at least in a longitudinal direction, and then drying. A hollow cone having a truncated top formed by combining the products, and a cone formed by attaching a separately manufactured top made of calcium silicate containing short cut carbon fibers to the cone. Manufacturing method of the electromagnetic wave absorber. 2. The molded product obtained by drainage molding and drying has a carbon fiber content of 0.01 to 50 g / l and a bulk density of 0.1 to 0.5 g / cm ^3. The method for producing a cone-shaped electromagnetic wave absorber according to claim 1, characterized in that: 3. The molded product obtained by drainage molding and drying has a carbon fiber content of 0.05 to 5 g / l and a bulk density of 0.1 to 0.35 g / cm ^3. The method for producing a cone-shaped electromagnetic wave absorber according to claim 1, characterized in that: 4. A top made of calcium silicate has a carbon fiber content of 0.01 to 50 g / l and a bulk density of 0.1 to 0.5 g.
The method for producing a cone-shaped electromagnetic wave absorber according to any one of claims 1 to 3, wherein the density is / cm ³ . 5. The method for producing a cone-shaped radio wave absorber according to claim 1, wherein the absorber is a quadrangular pyramid or a cone.