JPS64461B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a thermal spraying method for forming various thermal spray coatings on metal surfaces.

<Conventional techniques and their problems> Thermal spraying technology uses metals or non-metals that have various properties such as heat resistance and abrasion resistance that are not possessed by the substrate to be thermally sprayed, on the surface of the substrate to be thermally sprayed, regardless of whether the substrate is metal or non-metallic. It is a means of surface treatment technology to form a material film, and flame spraying, plasma spraying, explosion spraying, etc. have been put into practical use, and improved methods such as those reported in Japanese Patent Publication No. 59-51860 are also known. There is.
However, in this thermal spraying method, there is almost no chemical bonding between the sprayed substrate and the sprayed particles, and they are only connected by mechanical or physical bonds, so the adhesion strength is limited. The problem is that it is not very large. A major reason for this is that the thermal spray particles in a molten state are rapidly cooled and solidified when they collide with the surface of the substrate to be thermally sprayed.

By the way, among these thermal spraying techniques, the technique of forming a ceramic sprayed layer on the surface of metal materials has recently attracted attention, and one method of obtaining a glossy glassy thermal sprayed layer with low air permeability on metal materials has been studied. However, it is difficult to obtain a homogeneous glassy sprayed layer.
The reason for this is due to the above-mentioned problems specific to the thermal spraying method. Because the temperature of the surface of the substrate to be thermally sprayed is low, when the thermal spray particles collide with the surface of the substrate to be thermally sprayed, they instantly solidify, causing the entire surface to melt. It does not become a uniformly molten glass. During thermal spraying, if you try to increase the temperature of the surface of the substrate to be thermally sprayed using the thermal spray nozzle or the thermal spray gun itself, the flame or plasma flame must be made longer, which changes the thermal spraying conditions. In such a method, since only a local part of the surface of the base material to be thermally sprayed is heated, the base material to be thermally sprayed may be thermally deformed. Furthermore, even if a separate heating burner or the like is used for heating, only local heating can be achieved, so thermal deformation of the base material to be thermally sprayed cannot be prevented.

<Means for Solving the Problems> The present invention aims to provide a thermal spraying method that solves the above-mentioned problems. This is a method for thermal spraying a metal surface, which is characterized by passing an electric current through the metal substrate and raising the temperature of the metal substrate to a predetermined temperature by the Joule heat, and then spraying a thermal spraying material.

The metal base material used as the material to be thermally sprayed in the method of the present invention is not further limited as long as it is a conductive metal, and the thermal spraying material may be either metal or non-metal such as ceramic. This is particularly effective in the case of nonmetals such as ceramics, and in this case, it is desirable to take into account the melting point of the nonmetallic material such as ceramics and heat the metal base material in advance to approximately the same temperature as the melting point.

<Examples and operations> The method of the present invention will be described in detail below with reference to the drawings illustrating the examples.

In this example, as shown in the drawing, a method was adopted in which a current was passed through the SS material 1 from the upper and lower ends to heat it, measuring 500 mm x 300 mm and having a thickness of 2 mm. The current passed in this case was converted into a voltage of 8V and a current of 2500A by the transformer 2, and by passing this for about 10 minutes, the overall temperature of the SS material 1 was raised to about 350°C. Next, thermal spray equipment 3
The balance is 75% by weight of SiO ₂ whose melting point is about 400℃.
Ceramic particles 4 consisting of Al ₂ O ₃ , CaO and Na ₂ O were sprayed. The thermal spraying device in this case is a device that uses oxygen-acetylene as a heat source, and oxygen and acetylene are supplied to oxygen cylinder 5 and acetylene cylinder 6, respectively.
The ceramic particles 4 are introduced into the thermal spraying apparatus 3 from a thermal spraying material supply pipe 7 using oxygen as a carrier gas. The combustion conditions of the burner of the thermal spraying device are acetylene 4Nm ³ /hr., oxygen 10Nm ³ /hr., and ceramic particles 4 are 0.4Nm ³ /hr. oxygen and 10Kg/hr.
It was supplied at a flow rate of

Ceramic particles sprayed under these conditions 4
is completely melted in the flame generated from the thermal spraying device 3 and adheres to the surface of the SS material 1 in a molten state,
After adhesion, it remains molten for a while, and the SS
The supply of electricity to the material 1 was stopped, and as the temperature of the SS material 1 itself decreased, it gradually solidified and a uniform and dense glassy sprayed layer 8 was formed.

For comparison, the same SS material as in the above example was used, and thermal spraying was carried out under the same spraying conditions as in the example except that the SS material was energized and heated. As a result, numerous microcracks were generated on the surface. Only a sprayed layer can be obtained,
Furthermore, the adhesive strength was low and it easily peeled off.

As can be seen from the above Examples and Comparative Examples, in the method of the present invention, the temperature of the metal base material is increased by passing an electric current through the metal base material and using the Joule heat generated at that time. Since the metal base material is heated substantially uniformly over the area, heating by the burner of the thermal spraying device itself or a separately provided heating burner does not cause thermal deformation of the metal base material compared to local heating.

When spraying material is sprayed onto the metal base material, which is maintained at a predetermined temperature in this way, using oxygen-acetylene, oxygen-propane, or plasma as a heat source, the spray material melted in the flame will spread onto the metal base material. Even if they collide with each other, they will not be rapidly cooled, and therefore the bond between them will be that much stronger, and the resulting sprayed layer will be homogeneous and dense.

<Effects of the Invention> As described above, according to the method of the present invention, since the thermal spraying material is sprayed after uniformly heating the entire substrate to be thermally sprayed, there is no deformation of the substrate to be thermally sprayed, and the thermal spraying material is are bonded with high adhesion, and particularly when glassy ceramic or the like is used as the thermal spraying material, the resulting thermal sprayed layer has the effect of being homogeneous and dense.

[Brief explanation of the drawing]

The drawing is an explanatory view showing one embodiment of the thermal spraying treatment method of the present invention. In the figure, 1: SS material, 2: transformer, 3: thermal spray equipment, 4: ceramic particles, 5: oxygen cylinder, 6:
Acetylene cylinder, 7: Thermal spray material supply pipe,
8: Sprayed layer.

[Claims]

1. After roughening the inner surface of the thin metal cylinder, which is the object to be thermally sprayed, to a surface roughness Rz of 20 μm or less, cooling water is injected from the outside over the entire length of the roughened cylinder, while centering on the cylinder axis. A method for thermal spraying onto the inner surface of a thin cylinder, characterized by applying thermal spraying to a cooling position on the inner surface of the cylinder using a thermal spray gun that rotates and travels along the cylinder axis inside the same rotating cylinder.