JPS62107086A - Production of heat insulating metallic member - Google Patents

Abstract

PURPOSE:To produce a heat insulating metallic member having a heat insulating and water resistant coating layer without cracking and exfoliation by sticking refractory heat insulating material powder to the inside surface of the metallic member and subjecting the powder to a heat treatment, then sticking protective material powder thereon and subjecting the same to a heat treatment. CONSTITUTION:An inorg. binder soln. of sodium silicate, etc. is coated on the inside surface of the metallic member and immediately thereafter, about 10-500mum powder of the refractory heat insulating material such as SHIRASU balloon is stuck onto said soln. layer and is dried and solidified by the heat treatment to heat gradually the same up to about 300 deg.C. The inorg. binder soln. is then coated on the surface of the refractory heat insulating layer and about <=20mum powder of the protective material such as zirconia is stuck on such soln. layer and is dried and solidified by the heat treatment. The above- mentioned stage is executed at least once to form the protective layer to preferably about <=0.5mm. The member formed with the coating layer consisting of the above-mentioned tow layers is heat-treated at about 800-1,000 deg.C by which the heat insulating metallic member is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a heat insulating metal member having excellent heat insulation properties and water resistance.

[Conventional technology]

The internal combustion engine exhaust system equipment, especially the manifold, has the disadvantage that its inner surface is in contact with the high-temperature, high-pressure combustion gas discharged from the cylinder, so it is strongly affected by it and cannot be used for a long time, and it also has poor insulation properties. was there.

Japanese Patent Application Laid-Open No. 58-99180 discloses a method for applying a fire-resistant and heat-insulating coating to the inner surface of exhaust gas system equipment for an internal combustion engine, such as an exhaust manifold. In this method, a heat-resistant coating layer is formed by attaching a slurry made of a mixture of refractory raw material particles, an inorganic binder, and a frit to the inner surface of a metal device body that is in contact with high-temperature exhaust gas, and then the heat-resistant coating layer is formed. While the layer is in a wet state, refractory insulation material particles are attached to the surface thereof to form a refractory insulation layer, and then the heat resistant coating layer is solidified, and refractory raw material particles and inorganic materials are applied to the surface of the refractory insulation layer. A heat-resistant coating layer is formed by adhering a slurry made of a mixture of a binder and a frit, and if necessary, a fire-resistant heat-insulating layer of the same thickness as the fire-resistant heat-insulating layer and the above-mentioned The heat-resistant coating layer and the heat-resistant coating layer of the same village are sequentially repeated to form the required layer. With this method,
A coating is formed by integrating and laminating three layers: a heat-resistant coating layer, a fire-resistant heat insulating layer, and a heat-resistant coating layer.

[Problem that the invention seeks to solve]

However, in the above method, since the coating material is coated in the form of a slurry, the amount of rI! The moisture content in the layer must be relatively large, cracks occur during drying, and shrinkage is large during heat treatment, resulting in peeling and breakage. Furthermore, there is a high possibility that cracks will occur due to thermal shock when the material is rapidly heated by high-temperature exhaust gas.

[Means for solving the problems] [The inventors of the present invention have conducted various studies in view of these drawbacks, and have found that
We have discovered that by forming a fire-resistant heat-insulating layer and a protective layer on the inner surface of exhaust system equipment and performing heat treatment, it is possible to form a heat-insulating and water-resistant coating that does not crack or peel, leading to the completion of the present invention.

That is, the method for manufacturing a heat insulating metal member of the present invention includes (a) applying an inorganic binder solution to the inner surface of the metal member;

(b) Immediately adhering a refractory insulation powder to the layer of the inorganic binder solution, and (c) forming a refractory insulation layer by performing the first step at least once, including a step of drying and solidifying by heat treatment; Next, (d) applying an inorganic binder solution to the surface of the fireproof heat insulating layer.

(e) A protective material powder is immediately attached to the layer of the inorganic binder solution, and (f) a second step including a step of drying and solidifying by heat treatment is performed at least once to form a protective layer. .

The inorganic binder used to impart adhesiveness in the method for producing a heat insulating metal member of the present invention includes sodium silicate,
Silicate binders such as potassium silicate and lithium silicate, monobasic aluminum phosphate, monobasic calcium phosphate, monobasic magnesium phosphate, condensed sodium phosphate, phosphoric acid binders such as phosphoric acid, colloidal silica, colloidal alumina, colloidal Sol binders such as zirconia and ethyl silicate are suitable.

The binder is used in the form of an aqueous solution, and its concentration is between 20 and 6
0 wt% is preferred. If it is lower than 20%, the adhesive strength is low and it is easy to peel off. Moreover, if it is higher than 60%, the coating operation becomes difficult. More preferably, it is 25 to 55 wt%.

Appropriate amounts of curing agents can also be added to the binder solution. Although the curing agent differs depending on the type of binder, any known curing agent can be used. For example, silicate binders include sodium silicate, calcined aluminum phosphate, dicalcium silicate, carbon dioxide, and the like. For primary aluminum phosphate, there are basic oxides such as magnesia and lime, calcium aluminate, ammonium fluoride, and the like.

The fireproof heat insulating material used to provide heat insulation properties is an inorganic heat insulating material such as glass balloon, foamed silica, and perlite. The particle size of the powder is suitably in the range of 10 to 500 μm. When it is smaller than 10 μm, cracking and peeling occur due to shrinkage, and when it is larger than 500 μm, it is difficult to form a smooth film layer.

A more preferable particle size range is 20 to 200 μm.

Protective materials include chamotte, heat-resistant glass (Pyrex glass), fused silica, and cordierite.

Commonly used materials such as mullite, alumina, zircon, and zirconia may be used, but zirconia is particularly preferred because of its low thermal conductivity.

The particle size of the protective material is suitably 20 μm or less.

A small amount of frit may be added to further strengthen the water resistance of the protective material.

The method for manufacturing a heat insulating metal member of the present invention includes a step of forming a fireproof heat insulating layer and a step of forming a protective layer.

When forming a fireproof heat insulating layer, an inorganic binder solution is first applied to the inner surface of a metal member. As a result, the inner surface of the metal part is evenly wetted with the binder solution. A fireproof insulation material powder is attached to this. As a method of attachment, there are methods such as scattering powder on the binder-applied surface or filling the metal member with powder and leaving it for a certain period of time. In the case of the latter method, the interior of the metal member is filled with refractory insulation powder and, when left for a certain period of time, the binder solution penetrates between the powder particles and a sufficient amount of the powder is wetted. Some pressure may be applied throughout the powder to facilitate this process. Next, the powder is taken out from inside the metal member, and the powder that is insufficiently adhered is blown away by an air flow and removed.

In this way, a layer of refractory insulation powder fully impregnated with binder solution is formed. The thickness of this layer varies depending on the concentration and thickness of the binder solution, but is generally between 0.1 and 1.5
It is mm.

The binder solution-impregnated refractory insulation powder layer formed by the above method has a significantly lower moisture content than a layer applied in the form of a slurry. This is a significant feature of the invention. Due to this feature, the layer does not crack or peel during the subsequent drying and solidification process by heat treatment.

The heat treatment of the layer is carried out by gradually heating it to about 300°C. Rapid heating should be avoided as this may cause cracking and delamination of the layers. Preferably, the layer is allowed to air dry at room temperature, with subsequent increases in temperature. For example, after air drying, hold at 50℃ for 1 hour, then 100℃
Hold for 1 hour. To further improve stability, 30
It is desirable to heat to 0°C.

Next, if necessary, a binder solution is further applied on the above-mentioned fireproof insulation layer by the same method.

A fireproof insulation material powder is attached and dried and solidified by heat treatment. This cycle is repeated several times to obtain a relatively thick refractory insulation layer. In order to ensure sufficient heat insulation properties, the fireproof heat insulation layer needs to be 1.5 mm or more.

A protective layer is formed on top of this fireproof insulation layer,
A protective layer is formed by a method including the steps of applying an inorganic binder solution on the fireproof heat insulating layer, immediately adhering a protective material powder to the layer of the inorganic binder solution, and drying and solidifying it by heat treatment. If necessary, the cycle consisting of the above steps may be repeated, but the thickness of the retaining layer is preferably Q, 5 mm or less.

If it exceeds 0.5 mm, the protective layer may crack or peel due to thermal stress.

The exhaust system equipment on which the coating layer consisting of the fireproof heat insulating layer and the protective layer has been formed is heated to 800 to 1,000°C in a furnace.
The coating process is completed by heat treatment for 5 to 120 minutes.

In this case, if the temperature is lower than 800°C, the water glass will not vitrify, so a complete protective layer will not be formed, and if the temperature exceeds 1,000°C, no effect can be expected and it is disadvantageous in terms of thermal energy.

The most preferred temperature is 850-970°C.

This heat treatment may be performed by heating in a furnace or by passing hot air through a port.

〔Example〕

The present invention will be explained in further detail by the following examples.

Example 1 The inner surface of a cast iron manifold having an oxide film that had been previously degreased with an alkaline solution of PHIO to 11 was baked as a hardening agent in a sodium silicate aqueous solution with a silica ratio of 2.9 and a concentration of 45 wt% as a first step. Aluminum phosphate (H, B hardener manufactured by Hoechst) was added in a spray form with 10 wt% of aluminum phosphate (H, B hardener manufactured by Hoechst) and was applied in the form of a spray with 5 kg/cm2 of air through a rotating feed pipe.
．． 2. Shirasu balloons with a particle size of 44 to 150 μm were sprayed.

After the Shirasu balloon was sufficiently attached, it was kept at room temperature for 1 hour, then raised to 50℃ and kept for 1 hour, and then heated to 50℃ for 1 hour.
The temperature was raised to 300°C and held for 1 hour, and finally to 300°C and held for 1 hour. This heat treatment completely solidified the fireproof heat insulating layer. Repeat this process two more times until thickness 3
A fireproof heat insulating layer of mm was formed.

In the second step, the same inorganic binder as above is applied on the fireproof heat insulating layer, and immediately alumina with a particle size of 2 to 6 μm is attached to the layer of the inorganic binder solution, and then dried and solidified by heat treatment. A protective layer of 0.2 mm was thereby formed.

The manifold on which the refractory heat insulating layer and protective layer were formed was heat-treated in a furnace at 950° C. for 1.5 hours to complete the coating process.

No cracks were observed in the coating layer of the obtained manifold, and even though the manifold was heated with combustion gas at 1,00°C and cooled with air 100 times, no cracks or peeling of the coating layer was observed. There wasn't.

Example 2 As a first step, calcined phosphorus was added as a hardening agent to a sodium silicate aqueous solution with a silicate ratio of 3.0 and a concentration of 40 wt% on the inner surface of a cast iron manifold having an oxide film that had been previously degreased with an alkaline solution of PHIO to 11. A coating containing 8 wt % of aluminum acid (H, B hardener manufactured by Hoechst) was applied. Bulk specific gravity 0.22, particle size 4 immediately as a heat insulating material
Perlite of 4 to 150 μm was sprinkled. Heat treatment was performed in the same manner as in Example 1 to completely solidify the fireproof heat insulating layer. Repeat this process two more times until the thickness is 3 mm.
A fireproof insulation layer was formed.

As a second step, the same inorganic binder as above is applied on the fireproof heat insulating layer, alumina with a particle size of 2 to 6 μm is immediately attached, and dried and solidified by heat treatment.
．． A protective layer of 2 mm was formed.

The manifold on which the fireproof heat insulating layer and protective layer were formed was heat treated in the same manner as in Example 1 to complete the coating process.

No cracks were observed in the coating layer of the obtained manifold, and even though the manifold was heated with combustion gas at 1,000°C and cooled with air 100 times, no cracks or peeling of the coating layer were observed. There wasn't.

Although this embodiment describes a heat insulating manifold, the present invention is not limited thereto, but can be applied to the formation of a fire-resistant heat insulating coating on metal members such as chemical equipment or heating equipment that handle high-temperature gas.

〔Effect of the invention〕

The method of the present invention forms a fire-resistant heat-insulating layer and a protective layer by attaching fire-resistant heat-insulating powder and protective material to the binder solution, so that cracks and peeling do not occur even after drying and solidification, and there is no risk of damage caused by high-temperature gas. No cracking or peeling occurs even after repeated heating and cooling cycles.

The final layer, the insulation layer, prevents water that is generated by decomposition when the fuel gasoline is combusted in cold regions from condensing and penetrating and destroying the fireproof insulation layer, and also smooths the inner surface of the manifold and prevents water from flowing. It has an excellent effect in reducing air resistance.

Further, since the concentration of the binder in the binder solution can be increased, work efficiency is improved. A coating layer of a desired thickness can be obtained by repeating the application of the binder solution and the powder deposition.

Claims (1)

[Claims] A method for manufacturing a heat insulating metal member, comprising: (a) applying an inorganic binder solution to the inner surface of the metal member;
b) Immediately depositing a refractory insulation powder on the layer of inorganic binder solution; (c) forming a refractory insulation layer by performing at least one first step comprising drying and solidifying by heat treatment; (d) applying an inorganic binder solution to the surface of the fireproof heat insulating layer; (e) immediately attaching a protective material powder to the layer of the inorganic binder solution; and (f) drying and solidifying by heat treatment. A method for producing a heat insulating metal member, characterized in that a protective layer is formed by performing two steps at least once.