TECHNICAL FIELD

The invention relates to a production method for coated tubes, particularly to providing coated tubes by using chemical materials.

PRIOR ART

There are various coating methods available for producing coated tubes. Generally, the galfan coating process is carried out by galvanization in galfan pots. There is an adhesion problem of the new coatings applied upon the galfan coating when there is an additional coating process. The adhesion of other coatings onto the galfan coating is strengthened via an additional chemical material. It is dried by heating in order to prevent formation of defects on the surface of the chemical material.

The use of chemical materials to produce coated metal tubes is known in the technical field. CN106808775A publication describes a galvanized steel tube manufacturing process. The galvanized steel tube manufacturing process comprises the steps of: A, coating the outer surface of a steel tube with a hot-melt metal; B, C, coating the surface of the steel tube by being heated inductively and being placed in the galfan pot. According to the galvanized steel tube manufacturing process mentioned in the invention, a galfan coated steel tube is achieved which has an easy manufacturing process, low manufacturing costs and long service life thanks to the metal chemical hot-melt in the galvanize pot and the steel tube after the outer surface of the tube is heated.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is to enhance the adhesion strength of the polyamide material to the outer surface within the coated metal tube production.

In order to achieve the above mentioned object, the invention relates to a tube coating method comprising the process steps of providing a copper-brazed, double layered steel tube made of a copper coated sheet; heating the outer surface of the tube to a predetermined temperature; coating the heated outer surface of the tube with galfan; cooling the galfan coated outer surface; applying a chemical agent onto the cooled and galfan coated outer surface and obtaining a chemical agent coated outer surface; drying the applied chemical agent; applying primer coating onto the chemical agent coated outer surface by providing a primer solution and obtaining a primer coated outer surface; obtaining a polyamide coated outer surface by applying a polyamide coating onto the primer coated outer surface. The tube coating method comprises the process step of scraping the undried chemical agent off the chemical agent coated outer surface via the scraping device after drying the chemical agent. After the galfan coating process of the tube outer surface, a chemical agent is applied thereupon. Thereby, the coating strength of the primer solution used for the primer coating onto the galfan coated outer surface is enhanced. The galfan coated outer surface on which the chemical agent is applied is also dried and undried chemical agent is scraped off the outer surface via the scraping device in order to prevent the defects on the surface. As the undried chemical agent on the outer surface prevents an efficient adhesion of the primer, the primer easily peels off the outer surface due to the inadequate adhesion although the polyamide exhibits an efficient adhesion onto the primer due to the polyamide coating application. Therefore, the undried part of the chemical agent is scraped off the outer surface of the tube via the scraping device.

In a preferred embodiment of the invention, the chemical agent on the outer surface on which the chemical agent is applied is dried via an inductive heating process. Therefore, the tube is heated without any contact and defects such as stains and deformations on the surface are prevented. Besides, energy efficiency is high as the heat is produced on the surface of the substance via inductive heating.

In a preferred embodiment of the invention, the chemical agent on the outer surface on which the chemical agent is applied is dried between 50 °C and 80 °C via an inductive heating process. Therefore, the chemical content of the chemical agent is not spoiled.

In a preferred embodiment of the invention, inductive heating process is applied onto the chemical agent on the outer surface on which the chemical agent is applied between 0.5 and 1.5 seconds. Therefore, it is prevented that the temperature value of the chemical agent exceeds the desired temperature value while applying the inductive heating process.

In a preferred embodiment of the invention, the galfan coated outer surface is cooled by being passed through a water-filled tank. Thus, the galfan coated tube is cooled to the desired temperature value. In a preferred embodiment of the invention, the galfan coated outer surface is cooled by being passed through a water-filled tank for 2 to 3 seconds. By this means, a temperature value lower than the desired temperature value is prevented.

In a preferred embodiment of the invention, a polyamide coating is applied onto the primer coated outer surface via an extrusion process. Thus, the strength and the surface quality of the tubes are improved.

In a preferred embodiment of the invention, the polyamide coated outer surface is cooled to room temperature with cold water. Therefore, the polymerization is completed and the superficial defects to be formed on the final coating during the cooling process are prevented.

In a preferred embodiment of the invention, nitrogen is sprayed onto the heated outer surface of the tube and/or galfan coated outer surface in order to provide a galfan coating of desired thickness and homogeneity. Thus, the thickness of the galfan coating on the tube’s outer surface can be adjusted homogeneously.

In a preferred embodiment of the invention, application of chemical agent onto the galfan coated outer surface is carried out by being immersed in a liquid comprising a chemical agent. Thus, a surface with a desired thickness can be provided by coating the chemical agent homogeneously onto the galfan coated outer surface via a chemical reaction.

In a preferred embodiment of the invention, the galfan coated outer surface is immersed in the liquid comprising a chemical agent for 0.05 to 0.25 seconds. Thus, the required time is allowed for the chemical agent applied onto the galfan coated outer surface to be coated onto the surface of the tube.

In a preferred embodiment of the invention, an eddy current test is carried out which detects the defects on the outer surface on which the chemical agent is applied after the drying process of the chemical agent. Thanks to the eddy current test, the defects on the tube’s outer surface can be detected and they can be cleaned out.

In a preferred embodiment of the invention, the scraping device is made of a special rubber material. Therefore, any superficial defects to be formed on the outer surface on which the chemical agent is applied can be prevented during the scraping process. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view of the coatings on the tube’s outer surface of the present invention.

Fig. 2 is a schematic view of the tube coating process steps.

Fig. 3 is a cross-sectional view of the scraping device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In this detailed description, the embodiment of the present invention is described in a nonlimiting way and with reference to the examples with the aim of better clarifying.

Fig. 1 shows a schematic view of the coatings on the tube’s outer surface. Firstly, an outer surface (12) of an elongated, copper-brazed, double layered, steel tube (10) is heated via inductive heating, then sent to a galfan pot for galfan coating, and passed through a molten metal of zinc+aluminum having a temperature value of 475-550 °C. The outer surface (12) of the tube (10) is coated with galfan having an average thickness of about 10 microns within the galfan pot. At the outlet of the galfan pot, a galfan coated outer surface (14) is achieved. The thickness of the galfan coated outer surface (14) is adjusted by spraying nitrogen thereon at the outlet of the galfan pot. The galfan coated outer surface (14) is cooled at the outlet of the galfan pot via a quenching process. After the cooling process, the galfan coated outer surface (14) is immersed into a special solution comprising a chemical agent. A chemical agent coated outer surface (16) is achieved by applying a chemical agent onto the galfan coated outer surface (14) via the immersing process. The chemical agent coated outer surface (16) is dried at a temperature between 50 °C and 80 °C via an inductive heating method. After the completion of the drying process, it is passed through a scraping device (20) in order to scrape the undried chemical agent off the chemical agent coated outer surface (16). After being passed through the scraping device (20), a primer coated outer surface (18) is achieved by applying a primer solution onto the chemical agent coated outer surface (16). A polyamide coated outer surface (19) is achieved by applying a polyamide coating onto the primer coated outer surface (18) via an extrusion method. An embodiment of a polyamide coated metal tube (10) is provided by cooling the polyamide coated outer surface (19) to the room temperature by cooling with water. Fig. 2 shows a schematic view of the tube coating process steps. The outer surface (12) of the tube (10) provided is heated (1 ) up to a predetermined temperature. The galfan coated outer surface (14) is obtained by applying a galfan coating (2) onto the outer surface (12) of the tube (10) along with a heating process by being passed through a galfan pot (molten zinc+aluminum bar of max 550 °C). The galfan coated outer surface (14) is cooled (3) via a quenching process. The cooling process is carried out by passing through cold water having a temperature of 10 °C to 15 °C. The quenching process is applied onto the galfan coated outer surface (14) between 2 and 3 seconds. A chemical agent is applied (4) onto the cooled galfan coated outer surface (14). The chemical agent application (4) is carried out by passing the galfan coated outer surface (14) through a liquid filled with the chemical agent. The galfan coated outer surface (14) is exposed to the liquid filled with the chemical agent for 0.15 seconds and thus, a chemical agent coated outer surface (16) is obtained. The chemical agent is dried (5) between the temperature value between 50 °C and 80 °C via an inductive heating process on the chemical agent coated outer surface (16). After the chemical agent is dried (5), the undried chemical agent is scraped off (6) the chemical agent coated outer surface (16) via a scraping device (20). The primer coating is applied (7) by adding a primer solution onto the chemical agent coated outer surface (16) and the primer coated outer surface (18) is obtained. A polyamide coated outer surface (19) is achieved by applying a polyamide coating (8) onto the primer coated outer surface (18) via an extrusion method. The primer coating is an intermediate layer used to provide the adhesion of the polyamide coating which is the final coating. The chemical agent application facilitates an easier adhesion of the primer coating and prevents peeling off the tube (10). Therefore, the peeling of the coatings off the tube (10) is prevented by achieving the desired adhesion criteria.

Fig. 3 shows a cross-sectional view of the scraping device. The scraping device (20) comprises an opening (22) equal to the external diameter of the tube (10) in the center. The tube (10) having a chemical agent coated outer surface (14) is passed through the opening (22) and the undried chemical agents on the tube (10) is scraped off. The scraping device (20) is rectangular or have a similar form in any kind of geometric shape, and is made of a rubber material. REFERENCE NUMERALS

1 Heating the outer surface of the tube 14 Galfan coated outer surface

2 Galfan coating of the tube’s outer 16 Chemical agent coated outer surface surface

3 Cooling the outer surface with water 18 Primer coated outer surface

4 Chemical agent application 19 Polyamide coated outer surface

5 Drying of the chemical agent 20 Scraping device

6 Scraping off the chemical agent 22 Opening

7 Primer coating application

8 Polyamide coating application

9 Cooling with water

10 Tube

12 Outer surface