JPH0698453B2 - Insulation and heat retention coating material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a heat-insulating and heat-retaining coating material, and its purpose is to improve molten metal running around thin-walled parts of cast products in metal casting. It was done.

[Prior art and its problems]

Generally, in metal casting, a coating material is used for the purpose of smoothing the skin of a cast product, preventing seizure with the mold, and smoothing the release. These coating materials are mainly ZrO ₂
・ SiO ₂ , Al ₂ O ₃ , clay, bentonite,
Based on refractory fine powder such as natural mica, organic binders such as phenol resin and furan resin, inorganic binders such as water glass, phosphate, colloidal silica and ethyl silicate are used as binders. In applications where importance is placed on formability, aqueous dispersions of solid lubricants such as graphite, MoS ₂ and BN are used.

However, although these mold coating materials have the effects of smoothing the casting surface, preventing seizure, and smoothing the mold release, the cooling rate of the molten metal is delayed to improve the hot water flow to the thin-walled part of the cast product. Has little heat insulation and heat retention effect. That is, since the coating structure of these coating materials has not been devised, its heat insulation and heat retention tend to be largely controlled by the thermal conductivity of the refractory fine powder itself which is the base material. Yes, the thermal conductivity of the base material itself is graphite, which is a good conductor of heat,
Aside from MoS ₂ and BN, for example, ZrO ₂・ SiO ₂ 5.0 Kcal / m ・ h
r ・ ° C, 26.0Kcal / m ・ hr ・ ° C for Al ₂ O ₃ (100 ° C for all)
(Edited by Yoichi Mogi, published by Gihodo "Ceramics Notebook" P.48
4,485). On the other hand, the heat insulating and heat insulating materials that are usually used are not governed by the thermal conductivity of the base material itself, but are due to the multi-foam heat insulating property or air layer heat insulating property of the tissue. Closed-cell urethane foam with 0.016 Kcal / m ・ hr ・ ℃ at room temperature (by Masami Tanaka,
Yokendo Publishing "Research on Machines" November 1968 P.1443-1448)
Therefore, it can be said that the refractory fine powder described above can easily transfer heat of several tens to several hundreds of times as high as those of the heat insulating and heat insulating materials, and the heat insulating and heat insulating effects can hardly be expected with the conventional coating material.

[Means for solving problems]

The present invention has been made to improve these points,
A mold coating material that has excellent heat insulation and heat retention properties that conventional mold coating materials do not have, and that has the general necessary characteristics such as the smoothing of the casting surface, the prevention of seizure, and the smooth release that are necessary for mold coating materials. Is proposed.

The coating material of the present invention comprises an aqueous colloid of a swellable synthetic fluorine layered mineral and heat-expandable micro hollow spheres in an unexpanded state having heat insulation and heat retention after swelling by heating. Here, the swellable synthetic fluorine layered minerals are teniolite, tetrasilicic mica, and synthetic hectorite, which are types of synthetic fluoromica, and are represented by the following chemical formulas.

Na-Teniolite Na ・ Mg ₂ Li (SiO ₄ O ₁₀ ) F ₂ Li-Teniolite Li ・ Mg ₂ Li (SiO ₄ O ₁₀ ) F ₂ Ca-Teniolite Ca1 / 2 ・ Mg ₂ Li (SiO ₄ O ₁₀ ) F ₂ Na-tetrasilicic mica Na ・ Mg ₂ 1/2 (SiO ₄ O ₁₀ ) F ₂ Na-hectorite Na1 / 3 ・ Mg ₂ 2 / 3Li1 / 3 (SiO ₄ O ₁₀ ) F ₂ Li-hectorite Li1 / 3 ・ Mg ₂ 2 / 3Li1 / 3 (SiO ₄ O ₁₀ ) F _{2 The} above swelling synthetic fluorine layered minerals are all 1350〜14
Although it is a heat-resistant layered mineral that is artificially synthesized at a high temperature of 00 ° C, its characteristic is that it easily swells and peels off in water between layers, and finally has a thickness of 50 Å or less. The goal is to form a flake-shaped ultrafine particle colloid with a high aspect ratio of 500 to 5000Å.

As described above, these colloids are in the shape of flakes with a high aspect ratio, and are ultrafine particles close to the molecular unit, so they form a smooth film without a binder due to intermolecular cohesive force (van der Waals force). In addition, since the above synthetic fluorine layered minerals are heat-resistant ultrafine particles each having a melting point of 1000 ° C or higher, they have excellent effects in smoothing the casting surface and preventing seizure as a mold coating material. Can be done. These swellable synthetic fluorine layered minerals are graphite and Mo.
Similar to S ₂ and BN, the bond strength between layers is extremely weak, and it peels off easily with a small force, so it has an excellent releasability.

Thermally expandable micro hollow spheres are micro hollow spheres containing a foaming agent and have the property of forming a hollow body whose volume expands several tens of times by heating. For example, isobutane etc. are included as a foaming agent. Vinylidene chloride / acrylonitrile copolymer etc. This copolymer softens the shell of a thermoplastic vinylidene chloride / acrylonitrile copolymer (trade name: Expancel, manufactured by Expancel Co., Sweden) by heating, and at the same time increases the pressure due to vaporization of the foaming agent, resulting in hollow spheres. Expands. Their physical properties are shown in Table 1 below.
Is the street.

In the unexpanded state at room temperature, the particle size is 5 to 30 μ, but when heated at 80 ° C. or higher for several tens of seconds, a hollow body that expands to a particle size of 10 to 100 μ and a volume of about 70 times is formed. This hollow body has a true specific gravity of 0.04 or less and is mostly composed of air containing hydrocarbons. This hollow body forms a closed multi-cellular body in the coating film, and exhibits excellent heat insulation and heat retention.

The coating material of the present invention can be obtained by adding and mixing unexpanded heat-expandable micro hollow spheres to an aqueous colloid of swellable synthetic fluorine layered mineral. Since the true specific gravity of the expanded hollow body is about 0.04, its true specific gravity is about 1.3, so that a stable uniform aqueous dispersion can be maintained without floating separation under normal stirring.

When this uniform water dispersion is sprayed or applied to a mold, a large number of unexpanded thermally expandable micro hollow spheres enter between the layers of the flakes of synthetic fluorine layered mineral ultrafine particles (orientation), and these micro hollow spheres are formed. A large number of swellable synthetic fluorine layered mineral coatings are formed in each orientation layer of the coating. This film is 80
Due to the volume expansion of about 70 times that of the hollow microspheres caused by heating above ℃, the orientation layers in the film are expanded, forming an air-layered adiabatic structure, and the expanded hollow bodies themselves are independent. Since it forms a foam insulation structure, it has an extremely excellent heat insulation and heat retention film.

The compounding ratio of the heat-expandable micro hollow spheres in an unexpanded state to the swellable synthetic fluorine layered mineral of the present invention is determined by the result of actually casting a metal by applying a mold material having the compounding ratio to the mold. According to it, the blending ratio is preferably in the range of 30 to 2% by weight based on the solid weight of the layered mineral.
If it exceeds 5% by weight, the thickness of the coating mold becomes excessively thick and the dimensional accuracy of the cast product deteriorates, and the cast gas may be carburized by the combustion gas of the hollow sphere during casting, which is not preferable. As shown in Fig. 2, no significant heat insulation effect corresponding to the additional amount of the small hollow spheres added was obtained, and 2
When the content is less than 10% by weight, heat insulation and heat retention effects cannot be obtained, and defective molten metal tends to occur in the thin wall portion of the cast product. In the present invention, the swellable synthetic fluorine layered mineral and the unexpanded thermally expandable micro hollow spheres are mainly used, but ZrOiSi is used for the purpose of improving the adhesion of other coatings to the mold and increasing the heat resistance.
Refractory fine powders such as O ₂ , Al ₂ O ₃ , clay, bentonite, and natural mica, and metal powders such as Al, Cu, and Fe can be added as appropriate.

〔The invention's effect〕

The coating material of the present invention comprising an aqueous colloid of a swellable synthetic fluorine layered mineral and heat-expandable micro hollow spheres in an unexpanded state,
Since this coating material forms a film having the above-described air-layered heat insulating structure and independent multi-foam heat insulating structure, it has excellent heat insulation and heat retention during casting, and the casting surface of the cast product is smooth with no seizure. Good releasability.

〔Example〕

 Examples of the present invention will be shown below.

Example 1 5% of Na-tetrasilicic mica NaMg ₂ 1/2 (Si ₄ O ₁₀ ) F ₂
1000g of aqueous colloid, DU-551 ”, product of Sweden, Expancel Co., with shell of vinylidene chloride / acrylonitrile copolymer. As a foaming agent, 5 g (10% by weight based on Na-tetrasilicic mica) of thermally expandable micro hollow spheres encapsulating and encapsulating isobutane was added and sufficiently stirred with a high-speed stirrer to obtain a uniform water dispersion. As a test of heat insulation and heat retention, an iron cylinder with a bottom of 50 mm, an inner height of 80 mm, and a thickness of 0.5 mm was heated to 150 ° C in a heating furnace, and immediately after taking out from the furnace, the water dispersion was attached to the outer surface of the cylinder. And sprayed uniformly on the outer bottom surface to form a film with a thickness of approximately 0.2 mm. Similarly, for comparison, a film of only Na-tetrasilicic mica and a commercially available coating material (base material ZrO ₂ · SiO ₂ and binder resin phenol) were formed to the same thickness. After holding the cylinder with the film formed on the outer and bottom surfaces of the cylinder at 80 ° C in a heating furnace, 120 cc of boiling water was added immediately after taking it out, and the open part on the cylinder was closed with a cork stopper with a thermometer. And the decrease in temperature was measured. The measured values are shown in Table 2. From this, it is clear that the mold coating material of the present invention is excellent in heat insulation and heat retention.

Example 2 An Al casting die having a thin-walled portion having a thickness of 2 mm × a width of 20 mm × a length of 50 mm was heated to 200 ° C., and the water dispersion of the present invention of Example 1 was diluted with water to an equal size. The mold was sprayed and an aluminum alloy (AC-4, melt temperature 720 ° C) was gravity cast. The product was well bathed, had a smooth casting surface, and had no defects.
On the other hand, when a commercially available graphite water dispersion was spray-coated and cast in the same manner, defective running around the thin portion occurred.

Claims (1)

[Claims] 1. A heat-insulating and heat-retaining coating material comprising an aqueous colloid of a swellable synthetic fluorine layered mineral and heat-expandable micro hollow spheres in an unexpanded state having heat insulation and heat retention after expansion by heating.