JPS61117265A - Thermal sprayed film - Google Patents

Abstract

PURPOSE:To obtain black film having superior acid resistance and no exfoliation and pinhole, by combining Cr oxide and alumina under a specified ratio, and forming thermal sprayed film made of the mixture. CONSTITUTION:On the surface of cooler, etc., used in manufacturing glass plate by Colburn method, thermal sprayed film is formed so that component main body is composed of CR oxide and alumina, and weight ratio of CR oxide to alumina becomes 6:4-9:1. Zr oxide can be incorporated by <= about 10wt% as the third component. By this way, black film having acid resistance under used atmosphere temp. of >= about 700 deg.C, causing no exfoliation and pinhole by taking in and out between room temp. and used atmosphere is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal spray coating used to prevent surface corrosion of heat exchangers, coolers, etc. used in high-temperature atmospheres containing acidic gases such as SOX, NOX, and halogens.

[Prior art]

For example, in the plate glass forming method known for a long time as the Colburn method, as shown in Figure 1, molten glass is pulled up from a molten glass reservoir (1) into a plate shape with a constant width, and then horizontally moved by bending rolls (2). It is bent and further cooled and solidified to become sheet glass.

During the pulling process, the plate-shaped molten glass is cooled by a cooler (3) (3/)K so that the viscosity is suitable for drawing the plate glass to a desired thickness.

In addition to the vertical drawing method such as the full pan method, the Pittsburgh method, and the flow-down method as seen in U.S. Pat. A cooler is used to cool the molten glass sheet.

The atmosphere in the forming section of such a plate glass manufacturing apparatus contains sulfur oxides released from the molten glass or contained in the combustion gas that heats the molten glass.

On the other hand, since cooling water is passed through the cooler to increase its cooling efficiency, there is a problem in that sulfur oxides and moisture in the atmosphere condense on the surface of the cooler, resulting in sulfuric acid corrosion on the surface of the cooler.

Various coating methods have been proposed for the purpose of preventing acid corrosion of such internally cooled coolers. For example, a paint containing -C black pigment mixed with epoxy resin, silicone resin, or fluoro rubber resin forms a strong coating film at relatively low temperatures, but in a plate glass molding atmosphere < 7
Under humid conditions that reach 00"C, the organic resin decomposes and the paint film becomes porous, blisters, pinholes and cracks, resulting in insufficient corrosion resistance and poor adhesion. Peeling and falling occurs, and the fallen pieces get mixed into the four products, lowering the product yield.

The purpose of using black pigment in the paint is to increase the efficiency of radiant heat transfer.

In addition, there is a type of inorganic heat-resistant paint that combines black pigment with a glassy substance and fuses it to the surface of the base material, but because the coating film is glassy, it is susceptible to heat shock and cracks when it is put in and out of sheet glass forming equipment. It is also known to thermally spray heat-resistant materials such as alumina or chromium oxide as a heat-resistant coating. Alumina thermal spray coatings have excellent heat resistance and acid resistance, but because the coating is white, it has a high reflectance, and radiant heat transfer at temperatures above 700°C is more than 20% lower than that of black paint. On the other hand, chromium oxide sprayed coatings have excellent heat and acid resistance, and are black in color, so they are also excellent in radiation heat transfer, but they have the disadvantage of being dense and prone to penetrating cracks due to thermal shock.

In general, there is a tendency that the denser the ceramic material, the more susceptible it is to heat shock. The reason for this is that in non-dense materials, even if cracks occur due to thermal shock, the cracks are stopped or dispersed by the presence of pores and coarse grain boundaries, whereas in dense materials, cracks that occur are stopped midway through. This is thought to be due to the strong tendency to run straight and penetrate the material.

For the above reasons, the thermal spray coating of chromium oxide is at best! There was a drawback that the ambient temperature for use was limited to below jO″C.

[Problem that the invention seeks to solve]

A black film is obtained which has acid resistance under an atmospheric temperature of 700'C and which does not cause peeling or pinholes when placed in and out of the working atmosphere from room temperature.

[Means for solving problems]

The coating is a thermally sprayed coating, and the coating components are mainly composed of chromium oxide and alumina, and the weight ratio of chromium oxide and alumina is from 6 to 92 liters.

[For production]

The thermal spray coating of the present invention has improved thermal shock resistance by adding alumina to chromium oxide, which has excellent heat resistance, acid resistance, and radiant heat absorption.

The chromium oxide spray coating usually has a porosity of 3 to t%.

A coating obtained by plasma spraying a mixture of chromium oxide powder and alumina powder of 70 to 0% by weight has a porosity of g to 10%. The reason for this difference in porosity is not clear, but the melting point of chromium oxide (Cr203) is /990'C, while the melting point of alumina is 20!;0'C. It is thought that the porosity increases because the material is not completely molten or has high viscosity and is difficult to deform.

Therefore, if the spraying temperature of chromium oxide is lowered, the porosity should be reduced, but this causes the problem that the adhesion of the film decreases and it becomes easier to peel off.

In the present invention, the blending ratio of chromium oxide and alumina is limited to a weight ratio of 6 to 9:/; however, if the blending ratio of chromium oxide is smaller than the lower limit, the blackness of the film will decrease, and the radioactivity will decrease. On the other hand, when the upper limit is exceeded, the porosity of the film decreases and the thermal shock resistance decreases.

Addition of a third component other than chromium oxide and alumina or impurities mixed in these raw materials may be considered.

For example, zirconium oxide has a high melting point of 260° C., and titanium oxide has a melting point lower than chromium oxide, so even if they are blended, no improvement in thermal shock resistance can be expected.

Iron oxide and copper oxide are conceivable substances that increase blackness, but both have lower melting points than chromium oxide and have poor acid resistance. For the reasons mentioned above, it is preferable that the amount of the third component added is 70% by weight or less of the entire film.

As for the thermal spraying method, it is preferable to plasma spray a mixture of chromium oxide powder and alumina powder, but each powder may be sprayed simultaneously using two thermal spray guns. Further, the method is not limited to powder spraying, and rod spraying in which a mixture of chromium oxide powder and alumina powder is solidified in advance into a rod shape and then applied may be used.

Furthermore, as a heat source, not only plasma but also oxyhydrogen flame, oxidized acetylene flame, etc. can be used.

C Example] (1) Metco Material &'l'l J was used as a base treatment on the surface of an aluminum box-type cooler through which cooling water was passed.
(Ni-Or-A1 alloy) was thermally sprayed to a thickness of 110 to 30 ttm, and chromium oxide powder (Meteco AP/
06F-#)) and alumina powder (Meteco &10!;)
and 100:0,9 respectively! ;:! ;, Wa 0:1
0. to:, 220.70 2 30゜O:≠o,
A mixed powder mixed in a weight ratio of so:so was plasma sprayed to obtain a film with a thickness of about 100 μm.

While passing cooling water inside this box-type cooler, so2 is J 00 ppm r Na2O is 10m/Nll+
After keeping it in a 00"C atmosphere for several months and then taking it out and observing the peeling of the film and the corrosion of the cooler metal surface, it was found that many Microscopic peeling was observed all over the cooler, and some of the peeled areas showed traces of corrosion on the metal layer of the cooler.Furthermore, no traces of corrosion were seen in the case of 95:S, but the coating Several peelings were observed.

No peeling of the film or corrosion of the metal surface was observed in any of the samples other than the above two samples.

(2) In order to apply the thermal spray coating of the present invention to the aluminum water-cooled cooler (31, (3/)) of the Colburn plate glass manufacturing equipment shown in FIG. Two sets of coolers with two types of thermal spray coatings were prepared and tested in sequence.The period of use was 1ψ days, and the atmospheric conditions were the same as in Example (1). After use, there was no peeling of the thermal spray coating or corrosion of the metal on either cooler, and after use, it was possible to reuse it by simply wiping off the Glauber's film adhering to the surface with a cloth.However, the blending ratio gaso:s
In the case of o, the pulling speed for pulling up a plate glass of the same thickness is 7% lower than in the case of 70:30, and if the pulling speed is forced to increase, the plate glass becomes too thin and the product standard is exceeded. Ta. This is thought to be due to insufficient cooling of the molten glass due to the low radiation activity of the sprayed coating. Mixing ratio 70
When the cooler with the sprayed coating of :30 was subsequently used for 70~/j days/times, partial peeling of the sprayed coating was observed for the first time after 2j~50 uses. Compared to the conventional coating film made of a mixture of black pigment and epoxy resin, which lasted only three times at most, the service life of the glass plate could be extended several times without reducing the pulling speed.

〔Effect of the invention〕

The thermal spray coating of the present invention has excellent heat resistance, acid resistance, and high radiation ability, as well as excellent thermal shock resistance.
It has a wide range of uses as an anti-corrosion coating for local cooling devices such as industrial kilns and incinerators, water-cooled furnace walls, and heat exchange devices such as boiler tubes and heat pipes.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the arrangement of coolers in a Colburn plate glass manufacturing apparatus.

Claims (2)

[Claims] (1) The main components of the film are chromium oxide and alumina, and the weight ratio of chromium oxide and alumina is 6:4 to 9.
: A thermal spray coating characterized by being 1. (2) The coating is thermally sprayed onto a metal material whose at least one side is in contact with a high temperature atmosphere containing acidic gas and the other side is in contact with a heat transfer medium, and the coating is in contact with a high temperature atmosphere. The thermal spray coating according to claim 1, which is provided on a surface that is coated.