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The steel industry involves a wide range of components and processes that are subject to various forms of degradation such as corrosion, wear, and high – temperature damage. Thermal spray technology offers effective solutions to enhance the performance and lifespan of steel components.

thermal spray technologies applicable to the steel industry

Arc Spray

    • Working Principle:

Two continuously fed metal wires are used as consumable electrodes. An electric arc is generated at their ends as a heat source to melt the metal wires. Then, the molten metal is atomized by high-speed airflow and sprayed onto the surface of the steel workpiece to form a coating.

    • Advantages:


High Efficiency and Cost-Effectiveness:

Arc spraying has relatively high production efficiency and can form relatively thick coatings in a short period of time. It is suitable for large-area protection and steel components with high requirements for production efficiency. For example, in the anti-corrosion protection of large structural components in steel mills and steel structures of bridges, arc spraying of aluminum or zinc coatings can complete the construction quickly and improve production efficiency.

Strong Bonding Force:

The bonding between the coating and the steel substrate is mainly mechanical bonding and metallurgical bonding, with a relatively good bonding force. It can withstand certain external forces and impacts and is not easy to fall off. For some steel components that need to bear large loads and friction, such as rolls and conveyor rolls, arc spraying of metal coatings can provide good wear resistance and impact resistance.

Diverse Material Selection:

Various metal wire materials can be used as spraying materials, such as aluminum, zinc, stainless steel, nickel-chromium alloys, etc. Appropriate materials can be selected according to the different usage environments and requirements of steel components. For example, for steel structures used in marine environments or humid environments, arc spraying of aluminum or zinc coatings can be selected to provide long-term and effective anti-corrosion protection.

Plasma Spray

    • Working Principle:

A plasma arc is used as a heat source to heat the powdered spraying materials to a molten or semi-molten state, and then they are sprayed onto the surface of the steel workpiece to form a coating.

    • Advantages:


High-Quality Coatings:

It can prepare high-quality, high-performance coatings with good coating compactness, low porosity, and relatively high hardness and strength. In the steel industry, for some components with extremely high requirements for surface quality and performance, such as high-precision rolls and molds, plasma spraying of ceramic coatings or cermet coatings can significantly improve the wear resistance, corrosion resistance and thermal stability of the components and extend their service life.

Wide Material Adaptability:

It can handle various high-melting-point, high-performance materials, including ceramics, cermets, carbides, etc. For some special needs in the steel production process, such as high temperature resistance, wear resistance, and corrosion resistance, plasma spraying can select corresponding materials to prepare coatings that meet the requirements. For example, spraying a zirconia coating on the surface of the continuous casting mold in the steel industry can improve the service life of the mold and the quality of the casting billet.

Precise Control of Coating Properties:

By precisely controlling the process parameters of plasma spraying, such as power, gas flow rate, powder feeding speed, etc., the properties of the coating, such as thickness, porosity, hardness, roughness, etc., can be finely adjusted to meet the individualized needs of different steel components. For example, according to the rolling process and requirements of different rolls, the hardness and roughness of the coating can be adjusted to achieve the best rolling effect and product quality.

Flame Spray

    • Working Principle:

The high-temperature flame generated by the combustion of fuel gas (such as acetylene, propane, etc.) mixed with oxygen is used to heat the spraying materials to a molten or semi-molten state. Then, the materials are atomized by compressed air and sprayed onto the surface of the steel workpiece to form a coating.

    • Advantages:

Simple and Flexible Equipment:

Flame spraying equipment is relatively simple, easy to operate, has a relatively low cost, and is convenient for movement and on-site construction. For the local repair and on-site maintenance of some large steel equipment, flame spraying has great advantages. For example, on the production line of a steel mill, when some components are worn or corroded, flame spraying equipment can be used for quick repair to reduce equipment downtime.

Wide Material Selection:

It can spray a variety of materials, including metals, alloys, ceramics, polymer materials, etc. In the steel industry, flame spraying can be used to prepare anti-corrosion coatings, wear-resistant coatings, anti-slip coatings, etc. For example, spraying an anti-slip coating on steel stairs, platforms and other parts can improve the safety of people walking; spraying ceramic coatings inside some steel pipes can improve the wear resistance and corrosion resistance of the pipes.

Multiple Functions:

Besides preparing conventional protective coatings, flame spraying can also be used for the size restoration and surface modification of steel components. For example, when the size of steel shaft components becomes smaller due to wear, metal coatings can be sprayed by flame spraying to restore their size while improving the surface hardness and wear resistance.

How to choose thermal spraying technology for applications in the steel industry?

Consider the Usage Environment of Components

    • Corrosion Environment

Severe Corrosion Environment (such as Marine Environment, Chemical Industry Environment):

If steel components are exposed to high humidity, salt fog, or environments containing strongly corrosive chemical substances for a long time, such as the steel structures of offshore platforms and reactors in chemical equipment, thermal spray technologies with excellent corrosion resistance should be prioritized. Plasma spraying is a good choice as it can prepare dense ceramic coatings, such as alumina-titania composite coatings. This kind of coating has good chemical stability and can effectively block the intrusion of corrosive media. In addition, arc spraying of aluminum or zinc coatings is also quite suitable because aluminum and zinc coatings can form a dense oxide film in a corrosive environment, protecting the steel substrate by the sacrificial anode method and providing protection for as long as 10 – 20 years or even longer in a marine environment.

General Corrosion Environment (such as Outdoor Atmospheric Environment):

For outdoor steel facilities, such as steel structures for construction and bridges, flame spraying of zinc or aluminum coatings can meet the basic anti-corrosion requirements. Flame spraying equipment is simple, easy to operate, and has relatively low costs. It can form a protective layer on the surface of steel to prevent the corrosion of steel by moisture and oxygen in the atmosphere, and the protection life is generally about 10 – 15 years.

    • Wear Environment

High Wear Environment (such as Rolls, Crusher Components):

In the steel processing process, components that bear huge pressure and friction, such as rolls, require thermal spray technologies that can form coatings with high hardness and high wear resistance. High-Velocity Oxygen-Fuel Spray (HVOF) is an ideal choice as it can spray hard materials such as tungsten carbide-cobalt (WC-Co) onto the surface of rolls at high speed to form dense and firmly bonded wear-resistant coatings. The hardness of this kind of coating can reach 1200 – 1600HV, which can effectively resist the wear between rolls and steel materials, greatly extending the service life of rolls. Usually, the maintenance cycle of rolls can be extended by 2 – 3 times.

Moderate Wear Environment (such as Conveyor Equipment Components):

For conveyor equipment components in steel mills, such as conveyor rolls and conveyor belt idler rolls, arc spraying of metal alloy coatings (such as nickel-chromium alloys) can provide sufficient wear resistance. The bonding force of the arc spraying coating is relatively strong, and the alloy coating can withstand a certain degree of friction and also has a certain degree of corrosion resistance, making it suitable for use in such moderately worn and possibly slightly corroded environments.

    • High Temperature Environment (such as Components of Blast Furnaces, Heat Treatment Furnaces):

For high-temperature equipment in steel production, such as the linings of blast furnaces, heating elements and furnace walls of heat treatment furnaces, thermal spray technologies that can prepare coatings with high temperature resistance and oxidation resistance are needed. Plasma spraying is one of the preferred technologies as it can use high-temperature-resistant ceramic materials such as zirconia to prepare thermal barrier coatings. For example, spraying a zirconia coating on the surface of the heating element of a heat treatment furnace can effectively reduce the temperature of the element substrate, improve its high-temperature resistance, enable the heating element to work stably in a high-temperature environment of 1000 – 1200 °C, and also prevent oxidation and extend the service life.

Consider the Shape and Size of Components

    • Large Components (such as Large Steel Structures, Oil Storage Tanks)

For the protection of large steel structures, arc spraying is a relatively suitable technology. Arc spraying equipment can quickly spray on the surface of a large area of steel, and it has high efficiency and can complete the preparation of a large-area coating in a relatively short time. For example, for the anti-corrosion of the outer surface of a large oil storage tank, arc spraying can take advantage of its high efficiency to quickly spray zinc or aluminum coatings, and the equipment has good mobility and can operate around the large tank, effectively reducing construction costs and time.
Flame spraying can also be used for the local repair of large components or some large components that do not have high requirements for coating precision. For example, for the local corrosion areas of large steel structures, flame spraying equipment can be conveniently moved to the site for repair, and flame spraying has a wide range of material adaptability, so appropriate materials can be selected for repair according to needs.

    • Small or Complex-Shaped Components (such as Molds, Precision Mechanical Parts)

For small and complex-shaped steel components, such as steel molds and precision mechanical parts, plasma spraying is a better choice. Plasma spraying can precisely control the direction and speed of sprayed particles, enabling the coating to evenly cover the surface of complex-shaped components. For example, on the cavity surface of a steel mold, plasma spraying can adjust the angle of the spray gun and spraying parameters to prepare high-quality coatings, improve the demolding performance, wear resistance and corrosion resistance of the mold, and also precisely control the thickness and surface roughness of the coating to meet the requirements of precision components.

Consider Cost Factors

    • Equipment Cost

Flame spraying equipment is relatively simple and has a relatively low price. For some small steel enterprises or application scenarios where the requirements for coating performance are not particularly high, flame spraying equipment is an affordable choice. For example, in some small steel processing workshops where the requirements for the anti-corrosion or wear resistance of steel parts are not extremely high, flame spraying equipment can meet the basic needs, and the equipment purchase cost is relatively low and easy to be accepted by enterprises.
Plasma spraying equipment and High-Velocity Oxygen-Fuel Spray equipment are relatively complex and have relatively high prices. However, they can prepare high-performance coatings. For some key components and application scenarios with extremely high requirements for coating quality, the investment in such equipment is worthwhile. For example, in the high-end mold manufacturing and precision component production in the steel industry, in order to ensure the quality and performance of products, it is necessary to use plasma spraying equipment to prepare high-quality coatings. Although the equipment cost is high, it can be balanced by increasing the added value of products.

    • Operating Cost

The operating costs of flame spraying and arc spraying mainly include the costs of fuel, electrode materials, and compressed air. The operating costs of these processes are relatively low. In some large-scale projects that are relatively sensitive to costs, such as the anti-corrosion protection of large steel structures, the operating cost advantage of arc spraying is relatively obvious. For example, in the anti-corrosion construction of steel structures for construction, the operating cost of arc spraying zinc coatings is relatively low, and a large area of spraying can be completed in a short time, which is an economical and efficient anti-corrosion method.
Plasma spraying and High-Velocity Oxygen-Fuel Spray need to consume a large amount of electrical energy and expensive spraying powder materials, so the operating costs are relatively high. However, considering that they can prepare high-quality coatings, for some components with extremely high performance requirements, such as high-precision rolls and high-end molds in the steel industry, the high cost investment can be compensated by extending the service life of components and improving product quality.

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