KR20190070042A - Method for coating a metal tube with enamel and Equipment for carrying out the method - Google Patents

Abstract

The present invention relates to an enamel-coating method for a metal tube and an enamel-coating apparatus used therefor and, more specifically, to a method for enamel-coating a metal tube for a heat exchanger of which a surface has a heat transfer fin while rotating and moving the metal tube. The method comprises the following steps of: (a) coating a surface of the metal tube with enamel glaze; (b) sintering the coated metal tube at temperature of 750-1000°C; (c) additionally coating the end portion of the heat transfer fin of the sintered metal tube with enamel glaze; and (d) resintering the additionally coated metal tube at temperature of 800-1100°C.

Description

(5) Method for coating a metal tube with enamel and equipment for carrying out the method

The present invention relates to an enamel coating method of a metal tube for a heat exchanger having heat conductive fins formed on a surface thereof, and an enamel coating apparatus used therefor.

Japanese Patent No. 10-1474277, No. 10-1474278 and No. 10-1074438 disclose the applicants' prior patents relating to enamel coating method and enamel coating apparatus of a metal tube for a heat exchanger in which heat transfer fins are formed.

However, according to the conventional enamel coating method, when the metal tube having the heat conductive fins formed thereon is coated with enamel, the heat conductive fin ends of the metal tube before the enamel glaze is applied and completely fired There is a problem that the enamel coating of the end portion of the heat conductive fin of the metal tube is damaged.

Since the enamel coating at the end of the heat transfer fin is damaged, there is a problem that corrosion occurs from the end portion when the metal tube is used. Therefore, a method of preventing the enamel coating damage at the end of the metal tube heat transfer pin needs to be considered.

Korean Patent No. 10-1474277 Korean Patent No. 10-1474278 Korean Patent No. 10-1074438

According to the present invention,

And an object of the present invention is to provide an enamel coating method and an enamel coating apparatus which can prevent the enamel coating on the side of the heat-transfer fin of the metal tube from being damaged during the firing process so as to improve the quality thereof.

It is also an object of the present invention to provide an enamel coating method and an enamel coating apparatus that prevent damage to the coating film on the heat transfer fin side of a metal tube, but do not significantly reduce production efficiency.

The enamel layer formed on the outer surface of the metal tube should have a certain range of thickness in order to maintain durability. It is an object of the present invention to provide a method of forming a thickness of an enamel layer in a predetermined range.

According to the present invention,

In a method of enameling a metal tube for a heat exchanger having heat conductive fins formed on its surface while rotating and moving

(a) coating the surface of the metal tube with an enamel glaze;

(b) firing the coated metal tube at a temperature of 750 ° C to 1000 ° C;

(c) further coating an enamel glaze on the end of the fins of the fired metal tube; And

(d) re-firing the further coated metal tube at a temperature of 800 ° C to 1100 ° C.

Further, according to the present invention,

Means for rotating and moving a metal tube for a heat exchanger having heat conductive fins on its surface; A coating chamber for coating the metal tube with an enamel glaze; A firing chamber for firing the coated metal tube at a temperature of 750 ° C to 1000 ° C; An additional coating chamber for further coating an enamel glaze on the end of the fins of the fired metal tube; And a re-burning chamber for re-firing the further coated metal tube at a temperature of 800 ° C to 1100 ° C.

According to the enamel coating method of the present invention,

Unlike the conventional method in which a coating film of a sufficient thickness can not be formed due to the damage of the enamel coating on the side of the heat-transfer fin end of the metal tube in the firing process, additional coating and re-firing are performed, A coating film can be formed, so that an enamel coated metal tube having excellent quality can be provided.

Further, since the additional coating and re-firing step can be performed by a continuous process after the firing step, the effect of improving the quality without reducing the production efficiency of the enamel coated metal tube is exhibited.

The present invention can also provide a metal tube having improved durability by forming the thickness of the enamel layer in a predetermined range.

1 is an illustration of an enamel coating apparatus used in the enamel coating method of the present invention.
FIG. 2 is a simplified view of the coating section of the enamel coating apparatus used in the enamel coating method of the present invention.
FIG. 3 illustrates an enamel glaze part of an enamel coating apparatus used in the enamel coating method of the present invention.
4 illustrates an enamel glaze spray nozzle and a recipient of an enamel coating apparatus used in the enamel coating method of the present invention.
5 is a photograph of a metal tube for a heat exchanger in which heat conductive fins are formed on the surface of the enamel coating method according to the present invention.
6 schematically shows an enamel coating apparatus employing an elongated roller used in the enamel coating method of the present invention.
7 schematically shows a coating chamber conveyor 400, a firing chamber conveyor 500, an additional coating chamber conveyor 600 and a re-firing chamber conveyor 700 among the enamel coating apparatuses used in the enamel coating method of the present invention. It is.
8 is a photograph of a metal tube coated by a conventional enamel coating method.
9 is a photograph of a metal tube coated by an enamel coating method according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would unnecessarily obscure the gist of the present invention.

According to the prior art, a metal tube for a heat exchanger in which a heat transfer fin is formed on a surface,

(A) The surface of a metal tube is coated with an enamel glaze,

(B) firing the coated metal tube at a temperature of 750 ° C to 1000 ° C.

The metal tube used in the heat exchanger for a power plant usually has a length of 5 m to 30 m. In order to rotate and move the circular metal tube, an elongated roller is usually arranged at 1.5 m intervals.

The firing of (B) usually takes about 10 minutes. In the firing furnace used in the step (B), long rollers, which normally support six or seven metal tubes, are used.

In the process of rotating and advancing the metal tube 10 coated with the enamel glaze using the long roller 270 in the firing furnace, as the end of the heat transfer fin of the metal tube contacts the long roller 270 There is a problem that the enamel coating of the part is damaged.

8 is a photograph of a state in which enamel is not properly formed at the end portion of the heat transfer fin, that is, the outer edge portion, by a conventional method.

Disclosure of Invention Technical Problem [8] The present invention has been devised in order to solve the problems as described above, and is characterized by further coating the side of the heat conductive fin of the metal tube in which the enamel coating is damaged.

The enamel glaze powder is applied to the end of the heat conductive fin of the metal tube 10 after the firing process and the enamel coating of the damaged part is re-formed by re-firing the metal tube 10 with the enamel glaze powder attached to the end of the heat transfer fin .

As shown in FIGS. 2 and 3, the enamel glaze splitting 131 is disposed at a position where the end portion of the heat conductive fin of the metal tube 10 moves, and while the metal tube 10 is moving forward while rotating, The end of the heat conductive fin of the honeycomb structure 10 is buried in the enamel glaze powder 132 by about 1 mm to 5 mm, and the enamel glaze powder is coated.

The enamel glaze powder 131 is placed on the lower side of the metal tube so that the end portion of the heat transfer fin advancing and rotating is in contact with the enamel glaze powder 132 in a slightly pressing manner so that the application of the glaze powder is easy, The enamel layer on the end side of the heat conductive fins of the tube is damaged. However, since the enamel is thinly formed, the glaze powder easily adheres.

Further, the additional coating of the end of the heat conductive fin of the metal tube 10 may be performed by spraying an enamel glaze on the end of the heat conductive fin of the metal tube 10 after the sintering process.

4, an enamel glaze spray nozzle 133 is disposed in the additional coating chamber 130, and the enamel glaze spray nozzle 133 is disposed in the enameled glaze spray nozzle 133 in the direction of the heat conductive fin end of the metal tube 10, Spray glaze. At this time, when the injected enamel glaze reaches the end of the heat conductive fin of the metal tube 10, the water of the enamel glaze is evaporated by the hot heat of the surface of the metal tube and the enamel glaze powder is attached to the end of the heat transfer fin of the metal tube 10.

The enamel glaze spraying may be performed such that the enamel glaze spraying nozzle 133 reciprocates at a predetermined interval along the traveling direction of the metal tube 10. The gap between the enamel glaze spray nozzles 133 is preferably 400 mm to 500 mm. In this case, the metal glaze may be more uniformly coated on the heat transfer fin end of the metal tube 10.

Next, the additional coated metal tube 10 is re-fired at 800 ° C to 1100 ° C.

In order to effectively re-form the enamel coating on the end of the heat conductive fin of the metal tube 10, the temperature of the surface of the metal tube 10 must be sufficiently raised so that the enamel glaze powder attached to the end of the heat conductive fin can be completely fired. However, since the re-plasticization chamber 140 in which the re-plasticization process is performed is shorter than the plasticization chamber 120, the time required for the metal tube 10 to pass therethrough is reduced. Therefore, in order to sufficiently increase the temperature of the surface of the metal tube 10, it is necessary to carry out a re-firing process at a temperature of 800 ° C to 1100 ° C higher than the temperature of the firing process.

The re-firing process of the metal tube is preferably performed for 1 minute to 3 minutes. In this case, the enamel coating can be effectively formed at the end of the heat conductive fin of the metal tube 10.

The re-burning chamber 140 is provided with a heating means. As the heating means, any of those commonly used in this field can be used without limitation. For example, an electric furnace, a plasma annealing furnace, a heavy oil furnace, a light oil furnace, a gas furnace, a hydrogen annealing furnace, and an induction heating furnace can be used.

The re-burning chamber 140 may further include a blower. In the course of the re-fired metal tube 10 moving to the outfeed conveyor 300, the enamel coating of the unheated heat transfer fin end may be damaged as it comes into contact with the rollers. Therefore, the temperature of the enamel portion re-formed at the end of the heat transfer fin can be lowered by allowing the metal tube 10 after the re-firing to pass through the blower before contacting the roller of the outfeed conveyor 300, It is possible to prevent damage to the enamel coating that has been re-formed at the end of the heat conductive fin of the heat sink.

FIG. 8 is a photograph of a metal tube coated by a conventional enamel coating method, and it can be seen that the end of the heat conductive fin of the metal tube exhibits a transparent color. FIG. 9 is a cross- The photograph of the metal tube shows that the end of the heat transfer pin shows a clear blue color.

As shown in FIGS. 8 and 9, in the case of the metal tube coated by the conventional enamel coating method, the enamel coating at the end of the fin is partially damaged to show a transparent color, whereas the enamel coating method according to the present invention In the case of the coated metal tube, the end of the heating pin also shows a vivid blue color, thus effectively forming an enamel coating.

Now, the formation of the enamel layer in a predetermined range will be described. Generally, the metal tube used as a generator heat exchanger is used in a harsh environment. Therefore, in order to prevent corrosion and maintain durability, it is preferable that the thickness of the coated enamel layer of the metal tube is 250 +/- 100 mu m.

However, when the viscosity of the enamel glaze is increased to increase the thickness of the enamel layer coated on the cylindrical metal tube, since the degree of the flow of the enamel glaze from the surface of the metal tube can be reduced, However, since the enamel glaze is not evenly applied due to the increased viscosity, it is difficult to form a uniform enamel layer.

In order to uniformly apply the glaze to the cylindrical metal tube, the viscosity of the glaze is preferably 9 to 13. The viscosity of the glaze is measured by immersing a 10 cm x 10 cm x 0.5 mm stainless steel plate in a glaze liquid, placing the iron plate with a forceps and vertically erecting the liquid to flow down, and then placing the glaze on the iron plate. That is, the weight of the iron plate after immersing in the glaze is measured in grams, and the viscosity of the glaze is measured.

When a glaze having a viscosity of 9 to 13 is coated on a cylindrical metal tube and then an enamel layer is formed by firing, the thickness of the enamel layer is formed to be thinner than 250 +/- 100 mu m.

In the present invention,

(a) coating the surface of the metal tube with an enamel glaze;

(b) firing the coated metal tube at a temperature of 750 ° C to 1000 ° C;

(c) further coating an enamel glaze on the end of the fins of the fired metal tube; And

(d) after the step of re-firing the further coated metal tube at a temperature of 800 ° C to 1100 ° C,

By repeating the above steps (a) to (d), a metal tube having an enamel layer thickness of 250 +/- 100 mu m was obtained. By this method, it is possible to obtain a metal tube for a heat exchanger of excellent quality in which a uniform enamel layer is formed without increasing the viscosity of the enamel glaze.

The present invention also relates to an enamel coating apparatus for a metal tube as shown in Figs.

In the enamel coating apparatus of the present invention,

Means for rotating and moving a metal tube for a heat exchanger having heat conductive fins on its surface; A coating chamber 110 for coating the metal tube with an enamel glaze; A firing chamber 120 for firing the coated metal tube at a temperature of 750 ° C to 1000 ° C; An additional coating chamber 130 for further coating an enamel glaze powder at the end of the fins of the fired metal tube; And a re-firing chamber (140) for re-firing the further coated metal tube at a temperature of 800 ° C to 1100 ° C.

All of the technical features described above in the enamel coating method can be applied to the enamel coating apparatus of the metal tube, and redundant descriptions thereof are omitted in this section.

The means for rotating the metal tube may include a motor 220 installed in an in-feed conveyor 200 and / or an out-feed conveyor 300, as shown in FIG. And may be a plurality of pairs of rotating rollers 230 that receive a power from the motor and form a bevel so that the metal tube can be rotated while being advanced.

6 and 7, a motor (not shown) installed in an in-feed conveyor 200 and / or an out-feed conveyor 300 and a motor And may be an elongated roller 270 capable of advancing while rotating the metal tube.

In the enamel coating apparatus of the present invention, the additional coating chamber 130 may include an enamel glaze fin 131 that receives the enamel glaze powder in a lower direction of the direction in which the metal tube advances.

In this case, it is preferable that the enamel glaze fin (131) is provided at a height at which the end of the heat conductive fins of the metal tube in the additional coating process can be rotated and moved by being buried in the enamel glaze powder by 1 mm to 5 mm.

In the enamel coating apparatus of the present invention, the additional coating chamber 130 may include an enamel glaze injection nozzle 133. The additional coating chamber 130 may further include a pair of reciprocators 135 for reciprocating the enamel glaze injection nozzle 133 at predetermined intervals along the traveling direction of the metal tube 10.

The reciprocating machine 135 has a connecting bar 134 connecting between the pair of reciprocating machines, and the enamel glaze jetting nozzle 133 is attached thereto. The connecting bar 134 may receive power from the reciprocating unit 135 and reciprocate back and forth along the traveling direction of the metal tube 10. The reciprocating distance may be 400 to 500 mm.

In the enamel coating apparatus of the present invention, the re-firing chamber 140 may include a blower between the re-firing chamber 140 and the out-feed conveyor 300.

10: metal tube 11: enamel coated metal tube
12: heat conductive fin 100: coated portion
110: coating chamber 120: firing chamber
130: additional coating chamber 131: enamel glaze minutes
132: enamel glaze powder 133: enamel glaze jet nozzle
134: Connection bar 135:
140: Re-firing chamber 200: In-feed conveyor
210: an in-feed conveyor die
220: motor 230: rotating roller
270: Long spherical roller 300: Out-feed conveyor
400: Coating chamber conveyor 500: Conveyor for plastic chamber
600: Additional coating chamber conveyor 700: Conveyor for re-plasticizing chamber
The foregoing description is merely illustrative of the technical idea of the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the essential characteristics thereof. Therefore, the technical idea of the present invention is not limited to the above embodiment.

Claims (7)

A method of enamelling a metal tube for a heat exchanger having a heat conductive fin on a surface thereof while moving while rotating,
(a) coating the surface of the metal tube with an enamel glaze;
(b) firing the coated metal tube at a temperature of 750 ° C to 1000 ° C;
(c) further coating an enamel glaze on the end of the fins of the fired metal tube; And
(d) re-firing the further coated metal tube at a temperature of 800 ° C to 1100 ° C. [6] The method of claim 1, wherein the step (c) is performed by rotating the end of the heat conductive fins of the metal tube with 1 to 5 mm of the enamel glaze powder. [6] The method of claim 1, wherein the step (c) comprises coating an enamel glaze on the end of the heat conductive fins of the metal tube. The method according to claim 1, wherein the steps (a) to (d) are performed again after the step (d). Means for rotating and moving a metal tube for a heat exchanger having heat conductive fins on its surface; A coating chamber for coating the metal tube with an enamel glaze; A firing chamber for firing the coated metal tube at a temperature of 750 ° C to 1000 ° C; An additional coating chamber for further coating an enamel glaze on the end of the fins of the fired metal tube; And a re-firing chamber for re-firing the further coated metal tube at a temperature of 800 ° C to 1100 ° C. The enamel coating apparatus of claim 5, wherein the additional coating chamber comprises an enamel glaze containing an enamel glaze powder in a direction below the direction in which the metal tube advances. 6. The enamel coating apparatus of claim 5, wherein the additional coating chamber comprises an enamel glaze spray nozzle.

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