EP4012063A1

EP4012063A1 - Method for coating of metalic materials with single side coating

Info

Publication number: EP4012063A1
Application number: EP21020630.6A
Authority: EP
Inventors: Oguz Gunduz; Yasemin Kilic; Mehmet Bulut Ozyigit
Original assignee: Eregli Demir Ve Celik Fabrikalari T A S
Current assignee: Eregli Demir Ve Celik Fabrikalari T A S
Priority date: 2020-12-09
Filing date: 2021-12-09
Publication date: 2022-06-15
Also published as: TR202020089A2

Abstract

The invention related to a single-surface coating production method that enables the application of a thin-film coating that will reduce the strip/piece surface energy before the hot-dip step and obtaining a single-surface coated material, in processes where metallic coatings are carried out on metals with the hot-dip method. Cost savings will be achieved by reducing the use and consumption of unnecessary coatings, as well as reducing the energy consumed for melting, making it a more environmentally friendly coating method.

Description

Technical Area

The invention related to a single-surface coating production method that enables the application of a thin-film coating that will reduce the strip/piece surface energy before the hot-dip step and obtaining a single-surface coated material, in processes where metallic coatings are carried out on metals with the hot-dip method.

State of The Art

In the automotive industry, which is one of the biggest markets where zinc-coated materials are used, although corrosion resistance is needed on one surface for most parts, since there is no single side coated material, both surfaces are coated materials are used. Thus, unnecessary zinc consumption occurs.
Single side coated strip production can be achieved in different ways with very high initial investment cost. Summaries of these methods are given below. In this context, the method to be developed within the scope of the invention is uncomplicated, practical, fast and easy to implement, and the initial investment cost is low.
In the literature search, the application with the publication number US4254158A was found.
This patent document is about galvanizing a single side by spraying molten zinc on the bottom surface of the strip. This method can also be applied with different strip, ladle and spray angles. Since the bath mobility is high in the method, the zinc bath is made independent from the air environment in order to minimize the oxide formation and to reduce the surface defects.
Another application encountered in the patent research of the previous technique is the patent with the publication number US4120997A .
In this invention, firstly, the coating is made as in the current hot-dip production process, and then the galvanized coating is removed from one surface of the strip with scraper brushes. In this process, the formation of Fe-Zn intermetallic phases is encouraged in order to obtain a strip surface suitable for the respective mechanical lifting process. Similar to the galvanneal production after the dipping, the surface to be decoated is kept at 500-800°C for about 10 seconds to form brittle and abrasive Fe-Zn intermetallics, while the other surface is rapidly cooled to 150°C to obtain zinc coating.
In the literature search of the prior art, the Kawasaki Steel article named "Manufacturing of One-side Galvanized and Galvannealed Steel Sheet by Masking Coat" was found. In this article, one surface of the strip is coated with ceramic-based coatings with the help of a roll coater before galvanizing. Non-oxidizing furnace and reducing furnace environments are required to cure this coating. By applying heating to the ceramic coated surface of the strip coming out of the galvanizing bath, the viscosity of the zinc is reduced, and it is easily scraped with an air knife and returned to the galvanized bath. In the next step, the ceramic film on the strip surface is mechanically broken with rollers and removed from the final product.

Technical Problems That The Invention Aims to Solve

The current invention related to a single-surface coating production method that enables the application of a thin-film coating that will reduce the strip/piece surface energy before the hot-dip step and obtaining a single-surface coated material, in processes where metallic coatings are carried out on metals with the hot-dip method.
It is aimed to provide a more advantageous new product that is not in the market for users who need corrosion resistance on a single side, such as the automotive industry, the construction industry or general application area.
One of the problems that the invention aims to solve is the coating of the surface that is not needed. Because of this problem, the weight also increases. Since the invention will not use coating on the surface that is not needed in the industry, a total weight advantage is provided with a single side coating.
Another problem that the invention aims to solve; increase in consumption with unnecessary coating, unnecessary consumption of energy resources and environmental awareness. The application of the method to be developed thanks to the invention is simple and the initial investment cost is low. In addition, since it reduces unnecessary coating consumption, it provides cost savings as well as reducing the energy consumed for melting and increasing environmental awareness.

Explanation of Figures

Figure 1: Flow Chart of the Method

Description of the Invention

In this disclosure, the single-side coating method is explained only for a better understanding of the subject and without any limiting effect.
The invention relates to a method for single side coating.
Boron nitride is an oxide-free, synthetically produced ceramic material with the chemical formula BN. Due to its physical and chemical properties, it finds intensive use in the field of ceramics. The most important feature of boron nitride, which is used effectively in foundries, is that it does not wet metal melts such as aluminum, magnesium or copper. Boron nitride is in two modifications.
Hexagonal boron nitride (h-BN) is in graphite structure and is known to be obtained by nitriding boric oxide at high temperature. Cubic boron nitride is formed by processing hexagonal boron nitride at high pressure and temperature. Cubic boron nitride is very hard and has been defined as the material with the second highest hardness after diamond, and it is suitable for wear surfaces and special usage areas where hardness is demanded. The most prominent features of hexagonal boron nitride are its self-lubricating property, oxidation resistance, electrical and thermal stability, and non-wetting by metal melts.
In this study, the effect of hexagonal boron nitride on the material surface energy at high temperatures will be used and the surface adhesion of the liquid melt (Zn, Al, Mg, Si and alloys) will be prevented. Boron nitride solution can maintain its stability up to 900°C.
Hexagonal boron nitride reduces the wetting energy on the surface where it is applied against the melt of most metals. In other words, it causes a wetting angle of over 90° between the metal melt and the surface.
Boron nitride solution can also be used as a coating inhibitor in the plants that make part coating with the hot dip method in the method of the invention.
The hot-dip coating method canbe used in continuous lines as well as in facilities where piece coating is carried out. The continuous lines are consists of cleaning, oven, cooling and crucible sections where hot dipping takes place, respectively. In the furnace section, which has a controlled atmosphere environment, heating can be carried out by electricity, induction, radiant tube, direct combustion/burning methods. After the heating and/or cooling steps, the material whose heat treatment is completed is immersed in the molten metal bath by hot dipping method. There is a snout section that acts as a bridge in order to prevent the contact of the material with air during the transition from the furnace to the pot area and to minimize the formation of oxide and pollution. This area, which is a very important step for the coating process, directly affects the coating quality of the material after the hot dipping process. There are technologies in the snout area where a controlled atmosphere environment can be provided.
Alcohol-based boron nitride will be sprayed on the undesired surface (bottom or top) before the strip enters the liquid melt pot, inside the snout or between the furnace and the snout zone, and production can be achieved without a surface coating.
Boron nitride solution is applied at a rate of 0.1-10 g/cm2 to the surface of the part or strip that is not desired to be coated, between the furnace and the snout zone or in the snout zone for continuous lines where annealing and coating is made, before the dipping process for piece coatings.
In continuous annealing lines, after applying boron nitride to the surface that is not desired to be coated, by spray method, the strip is dipped into the molten metal bath in a controlled manner. Depending on the performance and capability of the continuous line, the strip stays in the molten metal bath for 4-16 seconds.
For part coatings, the parts coming out of the molten metal bath are allowed to air-cooling to complete the solidification of the coating part, while the targeted coating thickness is obtained by using air knives for coating thickness control on the coated surface of the strip at the exit of the coating bath in continuous lines. In both part coating and continuous strip coating processes, the material coming out of the molten metal bath is cooled in a controlled atmosphere or by free air-cooling.
Final surface treatments are carried out for part coatings. In continuous galvanizing lines, galvanized or galvanneal coated materials are applied to skin pass (temper rolling) process in accordance with the strip surface properties and mechanical properties. Temper rolling is applied in accordance with the mechanical and surface properties of the galvanized strip or the temper rolling in accordance with the mechanical and surface properties of the strip that is coated and annealed for alloying the coating with iron.
For zinc coatings, the application temperature of boron nitride spray may also vary for cases where the inlet temperature of the strip or part to the liquid zinc pot varies between 450-550°C. However, the fact that boron nitride does not react with the material to which it is applied or the liquid melt allows it to be applied in a very wide temperature band.
Boron nitride can be applied at the beginning of the snout zone or at the exit of the furnace zone between 400-650°C, or at a higher temperature (650-850°C) in the furnace zone, or after the furnace inlet cleaning section. It has been determined that the most suitable application within the scope of the invention is obtained at the exit of the furnace and the entrance of the snout zone.
The boron nitride solution prepared with alcohol-based solvents is applied to the strip surface at a rate of 0.1-10 g/cm². Alumina or silica-based binder can be used in the solution, and it should contain a minimum of 7% boron nitride.
In the method subject to the invention, boron nitride is applied to hot substrate materials with a large surface area by spraying with pressurized nitrogen or argon gas. Because in order to obtain the best coated surface properties in the hot dipping process, the material to be coated with the dipping method should be ±50 °C with the molten metal temperature in the pot. In this case, the strip temperature should vary between 350-600 °C for zinc coatings. Air pressurized spray application of the substrate material at high temperatures will increase the amount of oxidation on the surface. Pressurization should be done with nitrogen or argon gas to prevent unwanted oxide layers on the surface before final use.

Industrial Application of the Invention

Although this invention is based on the production of single-sided zinc-coated strip in the iron and steel industry, it can also be used in many hot-dip coating methods.

Claims

A method for coating a single side of the metal strip in processes where metallic coatings are carried out on metal materials by hot dipping, comprising the steps of;
application of boron nitride solution at 0.1-10 g/cm² on the strip/piece surface which is not desired to be coated, immersing the metal strip/part to be coated in the molten metal bath, waiting for solidification of the coating after the coating bath for part coatings or adjusting the thickness of the molten metal coating with nitrogen pressurized air knives at the pot outlet in continuous hot dip coating plants, cooling in controlled environment or by free cooling, performing final surface treatments for piece coatings, applying temper rolling in accordance with the mechanical and surface properties of the galvanized strip or applying the temper rolling in accordance with the mechanical and surface properties of the strip that is coated and annealed for alloying the coating with iron.
A method according to claim 1, wherein the solution is to contain a minimum of 7% hexagonal boron nitride.
A method according to claim 1 or 2, wherein the application of boron nitride solution to the metal strip surface at the beginning of the snout zone or at the exit of the furnace zone or in the furnace zone or after the cleaning section.
A method according to claim 1 to 3, wherein the application of boron nitride solution to the metal strip surface at a temperature of 350-850°C.
A method according to claim 1 to 4, wherein the application of boron nitride from at least one nozzle on the metal surface that is not desired to be coated on continuous lines coated with the hot dip method.
A method according to claim 1 to 5, wherein the method subject to the invention, boron nitride is applied to hot substrate materials with a large surface area by spraying with pressurized nitrogen or argon gas.
A method according to claim 1 to 6, wherein the coating of the undesired surface of the piece metal with a boron nitride solution by spraying pressurized with nitrogen or argon gas.
A method according to claim 1 to 7, wherein the immersion of the metal strip, desired to be coated, in the molten metal bath for 4-16 seconds.
A method according to claim 1 to 8, wherein the coating of a single side of the steel strip with zinc.