JPS5857388B2 - Manufacturing method of lightweight heat-resistant ceramic - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a lightweight heat-resistant ceramic material useful as a mold material from a siliceous glass hollow sphere-aluminum composite material.

Conventionally, sand molds using foundry sand have been the mainstream in the casting method, which is an important metal forming technology, but recently, sand molds have been subject to factory regulations due to browning of sand resources, waste sand, dust noise generation, and other pollution sources. With this trend, the use of metal molds, or metal molds, is increasing, mainly for casting various metals with melting points lower than copper alloys.

This mold has approximately the following advantages compared to a sand mold.

(1) It is a so-called permanent mold that can be used repeatedly with one mold.

(2) The product has high dimensional accuracy.

(3) High productivity. (4) Environmental improvements such as reduction of noise and dust.

(5) Pressure casting can be performed, improving the mechanical properties of the product.

On the other hand, the following points can be cited as drawbacks of molds.

(1) It takes many days to manufacture the mold and is expensive. (2) A brittle chill layer tends to form in the part of the cast product that comes into contact with the mold.

(3) The mold itself is heavy and inconvenient to handle.

(4) It is difficult to respond to design changes. (5) It is uneconomical if the number of units manufactured using the same mold is small.

Therefore, it is desirable that the ideal mold material has the advantages of a mold, is easy to manufacture, has low thermal conductivity so as not to penetrate the chill layer, is as lightweight as possible, and is inexpensive.

The present inventors have a strong interest in the problem of mold materials and have conducted various studies, resulting in the completion of the present invention.

The present inventors have previously developed a siliceous glass hollow sphere-aluminum composite material (Patent Nos. 847310 and 847352).
It has been revealed that a lightweight fire-resistant insulation material (Patent No. 9910125) can be obtained by heat-treating the material in air. However, if the conditions for the ideal shape material described above are applied to this material, the composite The material is extremely easy to manufacture and process, and if this composite material is made into a ceramic material through heat treatment, heat resistance can be obtained. It is thought that it has characteristics that are satisfactory as a permanent molding material in place of a mold in many respects, such as being small and having little thermal deformation, as well as the lightness that is a characteristic of the composite material.

However, materials obtained by conventional heat treatment of composite materials often have small blisters or minute cracks on their surfaces, and when they suddenly come into contact with high-temperature molten metal, minute cracks appear from the contact surface. It was also found that thermal shock resistance, which is an important property for molds, was low.

Therefore, the inventors of the present invention believe that such drawbacks can be eliminated by strictly controlling the heating process during heat treatment of the composite material, and as a result of various studies, by using the following heat treatment conditions. It was discovered that an ideal mold material could be obtained.

In other words, the 8008C required for ceramicizing the composite material
When performing heat treatment at a temperature higher than 600°C, 70°C
The temperature increase rate when passing through the temperature range to 0℃ is 20℃/
It is important to keep it below H.

In the first place, the heat treatment of the composite material is carried out using silica glass (S s Aluminum oxide (
The main purpose is to convert into alumina).

Of these, a particularly important reaction is the redox reaction between silica and aluminum.

3 S t02 + 4 AI= 38 t + 2
Al2O3(1) This reaction occurs at relatively low temperatures (e.g. A
It is recognized that even at 500'C, when I is in a solid state, the reaction proceeds at a very slow rate with a long induction period (precursor phenomenon of the reaction), but as the temperature gradually increases, the reaction rate decreases. The substance rises, causing a rapid reaction with exotherm.

In the case of heat treatment of the aluminum composite material using Shirasu balloons, which are typical silica glass hollow spheres, as a lightweight filling material, the outer periphery of each Shirasu balloon is in contact with aluminum, and depending on the heating temperature, formula (1) is obtained. Reactions such as occur at the contact point.

Of course, the oxidation reaction of aluminum due to oxygen in the air also proceeds from the outer periphery of the composite material.

4Al+302=2Al□03 (2) In this case, when heating to a predetermined temperature under conventional heat treatment conditions, for example, at a temperature increase rate of 5°C/M or more, mainly (1), (2)
A lightweight alumina heat insulating material (sometimes accompanied by dripping of molten aluminum) can be obtained by the reaction of the formula, but in this case, it is not necessary to maintain a precise shape like mold material, so it is difficult to heat it under such heat treatment conditions. It is enough.

On the other hand, the mold material that is the object of the present invention is made of an aluminum composite material that has been processed into a mold shape and then made into a ceramic material through heat treatment. This is a fatal flaw.

Conventional heating conditions often result in these defects as described above.

Although it has already been known from experience that defects such as deformation are reduced when the heating rate is slowed, the present invention was achieved through a detailed study of the causes thereof.

That is, when the composite material was heat-treated by changing the heating rate from 600°C to 700°C between 50°C and 1/6°C (10°C/H), the above defects were removed. As the temperature increase rate decreases, it decreases to 1/3°C/
Upon acclimatization (20° C./H), a ceramic material completely free of defects was obtained.

In the differential heat measurement carried out at the same time, the temperature of the composite material rises due to rapid generation of reaction heat according to equation (1) between 6000C and 7008C due to the large temperature increase rate, and a so-called differential heat peak is observed.

However, the temperature increase rate is 1/3°C/min.
Below, few differential thermal peaks are observed, (1)
It was observed that the reaction of the formula was proceeding slowly.

If the heating rate is such that a differential thermal peak clearly occurs,
Inside the composite material, not only the reaction of formula (1) but also the reaction of formula (2) is accelerated by the partial temperature rise.

Further, silicon produced by the reaction of formula (1) is dissolved in aluminum, and as formula (2) progresses, an oxidation reaction of silicon in the aluminum also occurs.

These exothermic reactions occur rapidly at each contact point between the glass balloon wall and aluminum of the composite material, resulting in thermal strain in the material as a whole and local temperature rises in the ceramic part (
Distortion due to the difference in thermal expansion between the glass part and the alumina part (which is a reaction product) and the remaining metal part increases,
This is thought to eventually lead to material deformation and crack generation.

In addition, during heat treatment, temperatures from room temperature to 600°C and 700°C
If the temperature increase rate at temperatures above ℃ is extremely high, it may cause distortion and defects such as deformation.
It is usually desirable to use a temperature increase rate of about 10'C/m to 30'C/m.

On the other hand, with regard to thermal shock resistance, which is important for mold materials, those that were heat treated at a temperature increase rate that causes differential thermal peaks may be due to already existing fine cracks or internal strain, or when they come into contact with high-temperature molten metal. Immediately a sound was emitted and the crack was observed to progress.

However, as seen in the examples, no cracks were observed in the heat-treated materials at a heating rate of 20°C/H or less.

Next, a specific example according to the present invention will be described. Example 1 A composite material of 50 x 50 x 10 dimensions consisting of 60 volumes of silica glass hollow spheres with an average particle size of 300μ and 40 volumes of aluminum alloy (Al-12% 5i) The processed material was heated in a tubular electric furnace to 600'C at a heating rate of 100C/M, and then to 700°C at a heating rate of 500.20/min.
°, 100.5°, 2゜1°, 1/3°, 1/6
When the cutting edge was heated under various conditions of °C, then heated to 825 °C at a temperature increase rate to'c/=, and then cooled in the furnace, the temperature increase rate between 600 °C and 7000 °C was 1 °C. /M or more, deformation, cracking, blistering, etc. were observed, and this tendency became more pronounced as the temperature increase rate increased.

On the other hand, in the samples whose heating rate was 1/3° C./heating (20° C./H) or less, the above deformation, cracking, blistering, etc. were not observed at all, and extremely sound ceramic materials were obtained.

Example 2 Lightweight heat-resistant ceramics of various sizes heat-treated using the heat treatment method of Example 1 at a heating rate of 20'C/H between 600° and 700°C were used as molds. Where molten metals such as tin, aluminum, copper, and cast iron were cast, no burning or thermal shock cracking of the mold was observed.

For those with a temperature increase rate of 1 °C/min or more,
Cracks were observed to occur with a slight sound during casting.

Claims (1)

[Claims] 1 Silica glass hollow sphere-aluminum composite material 80
When producing heat-resistant ceramics by heating to 00'C or more, the heating rate is controlled to 20C/H or less when passing through the thermal temperature between 600C and 700C. A method for manufacturing lightweight heat-resistant ceramic.