JP2939911B2 - Cementitious arc resistant material and its manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cementitious arc-resistant material containing no asbestos and a method for producing the same.

[Conventional technology]

Cement boards for electrical insulation (commonly known as hemits and lumbers) specified in JIS C2210 are made by molding asbestos using Portland cement as a binder, and can be cut, heat-resistant and arc-resistant. Is a good material, so it is used for arc-resistant materials (for example, arc-extinguishing plates, arc shooters) and electric insulation (for example, induction furnace casings), as well as for heat-insulating materials that require high strength (for example, heat insulation for heat presses). Plate), heat-resistant members (for example, a hot plate of a baking machine) and the like.

However, since the above JIS standard product contains about 40% asbestos, a large amount of asbestos dust is generated during cutting,
Since this is harmful to health, there is a need for an alternative that does not contain asbestos.

As an alternative material to cementum containing no asbestos, a heat-resistant material having a density of 1.6 to 2.0 obtained by combining talc powder and valp with Portland cement has been proposed. (JP-A-61-109205). However, since this material has a low melting point, the arc resistance is not sufficient, and there is a problem that a decrease in mechanical strength and dimensional shrinkage due to heating are large, and furthermore, a pulp burning odor is generated when heated. Having no asbestos at all has its advantages,
It has not been widely used in place of hemits.

[Problems to be solved by the invention]

Accordingly, an object of the present invention is to provide an asbestos-free, cementitious arc-resistant material that is comparable to a hemit or a river in arc resistance and heat resistance and is excellent in workability and usability.

[Means for solving the problem]

The present invention contains 15 to 45% by weight of mica particles, the matrix portion is composed of boehmite and calcium aluminate hydrate in a weight ratio of 1: 1 to 1: 2, and has a density of 1.9 to 2.46 g / c.
cementitious arc resistant material, characterized in that the m ^3,
And a method for producing the arc resistant material, that is, a weight ratio of 1:
15 to 45% by weight of mica powder based on the weight of the final product is mixed with alumina cement having a composition capable of producing 1 to 1: 2 boehmite and calcium aluminate hydrate, and the resulting mixture is mixed with alumina cement. The required amount of water for hydration is added and mixed, and the resulting mixture finally has a density of 1.9-2.4 g / cm
⁽³⁾ Molding is performed while heating at a molding pressure sufficient to obtain a molded body, and the obtained molded body is heat-treated in an autoclave to obtain boehmite and calcium aluminate water from the alumina cement hydration reaction product in the molded body. It is intended to provide a method for producing a cementitious arc resistant material characterized by forming a hydrate.

In the arc-resistant material of the present invention as described above, the boehmite constituting the matrix is dehydrated and decomposed to high melting point γ-alumina when heated to about 500 ° C. or higher, but the dimensional change and strength decrease at this time are However, it is much smaller than gibsite contained in Portland cement hydrate or alumina cement hydrate at room temperature and calcium aluminate hydrate formed by autoclave treatment. Further, the matrix portion composed of boehmite and calcium aluminate hydrate in a weight ratio of 1: 1 to 2 is dense,
Excellent in physical properties. As a result, the arc resistant material of the present invention exhibits little deterioration when exposed to a high temperature such as an electric arc, and shows good arc resistance and heat resistance. If the amount of boehmite is smaller than the above range, the arc resistance and heat resistance become insufficient, and if it is too large, a dense molded body cannot be obtained.

Further, the mica particles combined with the matrix, based on their cleaving properties, keep the cracks generated during the cutting process at the sites where they occur, and prevent them from becoming large cracks and propagating. Mica not only improves the machinability but also improves the mechanical strength of the arc resistant material and reduces dimensional shrinkage during heating. However, if it is less than 15% by weight, the machinability cannot be sufficiently improved, and if it exceeds 45% by weight, the melting point is lowered and the arc resistance is deteriorated. A particularly preferred amount of mica is 25 to 35% by weight.

The cut surface of the arc resistant material of the present invention becomes smoother as the particle size of the mica in the material is smaller, but if it is too fine, high density molding becomes difficult in the manufacturing process of this material, and the mechanical strength of the material is reduced. It is not preferred because it tends to lower. The most preferred mica particles have a particle size of about 100-400 μm
Things.

The density of 1.9 to 2.4 g / cm ³ is necessary for obtaining sufficient strength while ensuring machinability.

Next, a method for producing the arc resistant material according to the present invention will be described.

As raw material alumina cement, high alumina cement (Al ₂ O ₃ about 73% by weight, CaO about 26% by weight) or JIS No. 1 alumina cement (Al ₂ O ₃ about 54% by weight, CaO about 37% by weight)
Most can be used, but those with low alumina content, especially JIS No. 2 alumina cement with Al ₂ O ₃ content of about 49% by weight, are also blended with activated alumina such as alumina fume to achieve a weight ratio of 1: It can be used if the composition is adjusted so as to produce 1 to 1: 2 boehmite and calcium aluminate hydrate. Ultra-high alumina alumina cement having an Al ₂ O ₃ content of about 80% by weight has a too high Al ₂ O ₃ ratio and is difficult to use.

First, as described above, the mica powder of the particle size range and the alumina cement are mixed well in a weight ratio of about 15:85 to 45:55 (the exact mixing ratio is that the amount of mica in the final product is 15 to 45
The amount is adjusted in consideration of the amount of the materials to be mixed so as to obtain the weight%). At this time, a small amount of powder of zircon, cordierite, corundum or the like effective for improving arc resistance may be blended. Water is further added to the obtained mixture and stirred. The amount of water is set to the amount required for the hydration reaction of the alumina cement, or slightly larger. An appropriate amount of water is about 8 to 13 parts by weight based on 100 parts by weight of the raw material mixture. Care should be taken not to use an excessive amount of water, as this may cause delamination or deformation in the subsequent autoclave treatment.

The raw material mixture to which the appropriate amount of water has been added is in a wet powder state. This is press-formed into a desired shape such as a plate shape. Molding, preferably a principle mixture if Oyo press die is carried out applying a pressure of about 200~1000kgf / cm ² while heating to about 60-80 ° C., and causing hydration of alumina cement during pressing, Obtain a cured molded body. Therefore, the higher the heating temperature, the shorter the pressurization time. However, since the evaporation of water becomes more intense, it is about 10 times in normal molding performed under atmospheric pressure.
0 ° C is the upper limit. The higher the molding pressure, the higher the density and the strength of the molded body. However, the molding pressure is adjusted according to the molding raw material and the molding temperature so that a product of 1.9 to 2.4 g / cm ³ is finally obtained. When a small amount of a hardening accelerator such as lithium such as lithium carbonate is blended, the pressurizing time during molding can be shortened.

In the obtained molded body, calcium aluminate hydrate and gibbsite formed from alumina cement form a matrix together with a small amount of unhydrated alumina cement. The compact is then heat-treated in an autoclave to convert the matrix to one consisting of boehmite and calcium aluminate hydrate. The processing conditions required for this conversion are a temperature of about 120 to 200 ° C. and a heating time of about 3 to 7 hours. The higher the temperature, the shorter the heating time. When the conversion is complete, boehmite and calcium aluminate hydrate are formed in a weight ratio of 1: 1.5. Although the apparent volume change of the molded article due to the treatment is scarce, the change in composition causes densification.

The product is appropriately processed such as cutting, perforating, varnishing, etc., and is used as an arc resistant material.

〔Example〕

Example Alumina cement (trade name: Denka High Alumina Cement; a product of Denki Kagaku Kogyo Co., Ltd .; 73% by weight of Al ₂ O ₃ , CaO 2
6.0 weight%, SiO ₂ 0.3 weight%, Fe ₂ O ₃ 0.3 weight%) 70 weight parts,
30 parts by weight of mica powder (average particle size 300 μm) and 10 parts of water
Parts, temperature 74 ° C, molding pressure 230kgf / cm ² , pressurization time 15
In a minute, it was formed into a plate having a thickness of 6 mm. Next, the obtained molded body was transferred to an autoclave and treated at 180 ° C. for 7 hours.

As a result of the X-ray diffraction test, it was confirmed that the matrix portion of the product was composed of boehmite and calcium aluminate hydrate in a weight ratio of 1: 1.5.

Table 1 shows the results of examining the characteristics of the product in the dry state, together with the characteristics of the following comparative examples 1 and 2, which are conventional products. The test was conducted under the old Japanese national railway standard JRS15612-4D-15AR8E
The test was performed in accordance with "Vehicle asbestos insulating plate".

Comparative Example 1 (Conventional product using asbestos) 60 parts by weight of Portland cement and 40 parts by weight of chrysotile asbestos 5R were mixed with 150 parts by weight of water, dewatered and pressed, and then steam-cured at 9 kg / cm ² for 7 hours.

Comparative Example 2 (conventional asbestos-free product) Portland cement 50 parts by weight Silica powder 10 Silica flower 10 Pulp 3 Wollastonite 10 Mica 10 Talc 10 The above raw materials were mixed with 200 parts by weight of water, and subjected to dehydration press molding. Autoclaved at 9 kg / cm ² for 7 hours.

Examples 2, 3; Comparative Examples 3, 4 Mixing ratio (weight ratio) of alumina cement and mica powder
Were modified in the same manner as in Example 1 to produce four types of cementitious arc-resistant materials having a weight ratio of boehmite to calcium aluminate hydrate of 1: 1.5.

 Table 2 shows the results.

Example 4; Comparative Examples 5 and 6 A cementitious arc resistant material was produced in the same manner as in Example 1 except that the type of alumina cement was changed as follows. Table 3 shows the results.

Example 4: JIS No. 1 alumina cement (54% by weight of Al ₂ O ₃ , 37% by weight of CaO) Comparative Example 5: Ultra-high alumina alumina cement (80% by weight of Al ₂ O ₃ , 18% by weight of CaO) Comparative Example 6: JIS No. 2 Alumina cement (Al ₂ O ₃ 49% by weight, CaO 33% by weight) [Effects of the Invention] According to the present invention, JI
Materials with arc resistance and heat resistance equivalent to or higher than asbestos cement board for electrical insulation according to S standard are provided,
It solves the problems of the conventional arc-resistant cementitious material containing no asbestos, such as low arc resistance, insufficient heat resistance, and generation of odor during heating.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-48-40000 (JP, A) JP-A-61-149311 (JP, A) JP-B-53-43679 (JP, B2) JP-B-51- 111828 (JP, B2) (58) Field surveyed (Int. Cl. ⁶ , DB name) C04B 28/06

Claims (2)

(57) [Claims] (1) a matrix portion comprising boehmite and calcium aluminate hydrate in a weight ratio of 1: 1 to 1: 2 containing 15 to 45% by weight of mica particles, and having a density of 1.9 to 2.4 g / cm.
^3. A cementitious arc resistant material, characterized in that: 2. Mixing boehmite in a weight ratio of 1: 1 to 1: 2 and alumina-based cement having a composition capable of forming calcium aluminate hydrate with mica powder in an amount of 15 to 45% based on the weight of the final product. , the resulting mixture was added water in an amount necessary for hydration of the alumina cement is mixed in, sufficient to obtain finally a molded article of density 1.9~2.4g / cm ³ and the resulting mixture molded Pressure, molding while heating, the obtained molded body is heat-treated in an autoclave to produce boehmite and calcium aluminate hydrate from the alumina cement hydration reaction product in the molded body A method for producing cementitious arc resistant materials.