JPS59169642A - Mold coating material for metallic mold - Google Patents

Abstract

PURPOSE:To form a stable mold coat having a high grade by using an aq. slurry prepd. by compounding a binder with diatomaceous earth having water absorptivity in a specific range in forming the mold coat on the inside wall surface of a metallic mold. CONSTITUTION:Diatomaceous earth having water absorptivity ranging 115-135 is used and the chemical component compsn. thereof is adjusted to about 90- 94% SiO2, about 2-6% Al2O3, about 0.4-0.5 bulk specific gravity and grain size of about <=1% residue on 325 mesh. An aq. slurry is prepd. by using such diatomaceous earth and a binder (bentonite, etc.) to the compsn. of about diatomaceous earth : binder : water =23-27:1-3:70-76. Such aq. slurry is coated on the inside wall surface of a metallic mold to form a mold coat to about 1.0- 2.5mm. layer thickness. A product having a smooth and beautiful casting surface is thus cast.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a mold coating agent made of diatomaceous earth for forming a coating mold on the inner wall surface of a mold.

It is widely known that quartzite is used as a coating agent for metal molds in casting steel and other metals (centrifugal casting, etc.). The coating mold is formed by mixing diatomaceous earth with a binder and usually applying this as an aqueous slurry to the inner surface of the mold. The purpose of the coating mold is to completely prevent the metal to be cast from seizing on the inner wall surface of the mold, and to form a smooth and beautiful casting surface on the resulting cast body. Therefore, the diatomaceous earth used for this must be of a quality that allows the entire coating mold to be formed. Conventionally, 1. Its dignity.

Chemical composition, specific gravity, particle size, and color are used as characteristics for evaluation and management.

However, even though the coating mold is formed using diatomaceous earth, which satisfies all of the above characteristics and is evaluated to have no quality problems, the cast surface of the resulting cast body often has some Otherwise, problems such as roughness of the casting surface over the entire surface, peeling of the coating mold, accompanying penetration and seizure of molten metal, and biting of foreign objects often occur.

As a result of intensive research to solve the above problem, the present inventors discovered that the water absorption rate should be noted as a characteristic of diatomaceous earth that completely affects the quality of the coating mold.The water absorption rate is within a certain range. The present invention has been made based on the knowledge that by using a certain diatomaceous earth, the quality and stability of the formed coating mold can be improved and the above-mentioned casting defects can be eliminated.

The present invention provides a mold coating agent that uses diatomaceous earth with a water absorption rate of 115 to 135, blends a binder with it, and applies it to the inner wall surface of the mold as an aqueous slurry to form the entire coated mold. .

The water absorption rate of diatomaceous earth is calculated by the following formula [A].

Wk [In the formula, Wk: weight of diatom raw sample (!li'),
Ww: water absorption amount (P) of raw diatom sample].

In order to measure the water absorption rate, an appropriate amount of diatomaceous earth aggregate is used as a sample, water is added to it, and the sample is allowed to absorb water.

The amount of liquid that can be absorbed by a sample reaches saturation at a certain level, and no more liquid is absorbed, or even if it is absorbed once, it separates again. Based on the water absorption amount and sample weight at that time,
The water absorption rate can be obtained using the A3 formula.

It is generally called liquid absorption rate, but in the present invention, water is used as the liquid, so it is called water absorption rate. Note that the sample weight in the above measurement is suitably about 2.00y from the viewpoint of accuracy of measurement values, simplicity of measurement operation, etc.

The water absorption rate of diatomaceous earth varies depending on the lot, and even for diatomaceous earth that satisfies each of the above properties and is used as a coating agent, its water absorption rate varies over a wide range of about 60 to 200. There are variations. The mold coating agent of the present invention is
The requirement is to use silica raw metal with a water absorption rate of 115 to 135. If the water absorption rate is lower than 115, even if there are no problems with the chemical composition, specific gravity, particle size, etc., the quality and stability of the coating mold will be poor, and the resulting cast body will have rough casting surfaces. On the other hand, if the water absorption rate exceeds 135, unevenness will occur on the casting surface, and in extreme cases, the coating will peel off, and the molten metal will infiltrate into the area, causing seizing on the mold wall and chewing of peeled pieces. This is because it causes problems such as

Table 1 shows hollow cylindrical cast bodies (external) obtained by centrifugally casting SM material (carbon steel for welded structures) into fully coated molds made of diatomaceous earth with various water absorption rates. Diameter: 400
mm, wall thickness: 45 mm, length = 4050 mm). The characteristics of diatomaceous earth in each fragrance other than the water absorption rate are substantially the same, and are common as mold coating agents.

Each mold coating agent is made by mixing diatomaceous earth with bentonite as a binder, and spraying it as an aqueous slurry (mixing weight ratio of diatomaceous earth: binder: water = 25:2 near 3) onto the inner wall surface of the mold. It was applied all over. The coating thickness is 1.5m in each case.
It is m.

As shown in the test results in Table 1 above, the water absorption rate is 115-135.
In perfumes 3 to 5 using a coating agent made of diatomaceous earth,
It can be seen that a product with excellent coating mold stability, no peeling, no roughening of the casting surface, no unevenness, and a smooth and beautiful casting surface can be obtained.

The mold coating agent according to the present invention is prepared by blending diatomaceous earth with the above-mentioned water absorption rate with a suitable binder, such as bentonite, silica sol, water glass, etc., and adding water to the mixture to form an aqueous slurry, which can be prepared by spraying or other methods. It is applied to the inner wall surface of the mold. Of course, the properties of the diatomaceous earth used other than the water absorption rate may be those typical of those normally required as a mold coating agent. For example, the chemical composition may be approximately 90 to 94% SiO2.
, 112,032 to 6%, a specific gravity of about 0.4 to 0.5, and a particle size of 325 mesh with 1% or less remaining.

The aqueous slurry may be prepared according to a conventional method, and the mixing ratio is diatomaceous earth: binder: water = 23 to 27 by weight.
:1-3 near 0-76.

Moreover, the layer thickness of the coating mold is the same as that of a usual one, and may be, for example, 1.0 to 2.5 mm. In forming the layer thickness, layering thin film layers to the desired layer thickness by multilayer coating is also an effective method for improving coating performance.

The mold coating agent of the present invention can also be used in combination with other constituents used as a mold coating agent, such as zircon and rind. For combined use, diatomaceous earth and other components such as zircon may be mixed and integrated, but in order to fully utilize the material characteristics of each component, each component should be applied separately. It is desirable to layer it in multiple layers. For example, a first layer with a thickness of about 0.5 to 1.5 mm is formed on the inner wall surface of a metal mold using the mold coating agent of the present invention, and a layer thickness of 1.5 mm is further formed with an aqueous slurry containing zircon and a binder. 0～
If the entire coating mold is formed with a two-layer structure in which a second layer of about 1.5 mm is laminated, it will have both the heat insulation properties of the first layer (diatomaceous earth) and the fire resistance of the second layer (zircon). . The coating type is
While its excellent fire resistance reliably prevents the molten metal from seizing, its heat insulating effect ensures the same vortex flow of the molten metal in the mold and enables the formation of a uniform casting structure, even in horizontal centrifugal casting. It also provides a smooth and beautiful casting surface over the entire surface.

The mold coating agent of the present invention can be applied as a mold coating agent for molds used in casting of cast steel, cast iron, and various other metals and alloys, regardless of the casting method such as centrifugal force casting or stationary casting. C, which forms a stable, high-quality coating mold, guarantees the casting of products with a smooth and beautiful casting surface without causing casting problems such as peeling, metal seizure, and foreign matter biting. .

In addition, it goes without saying that the stability of the coating mold suppresses the progress of damage and deterioration of the inner wall surface of the mold, resulting in various effects such as improving the service life of the mold and reducing the unit cost.

Agent: Patent Attorney Shinhachibe Miyazaki

Claims (1)

[Claims] (1) A coating agent for forming a coating mold on the inner wall surface of a mold as an aqueous slurry by blending a binder with diatomaceous earth, and the diatomaceous earth has a total water absorption rate of 115 to 1'35. A coating agent for molds that is unique in its characteristics.