Metal spraying, or thermal spraying, involves applying a metallic coating to a surface by spraying molten particles. This process enhances the surface properties of materials, providing increased durability, wear resistance, and protection against corrosion and extreme temperatures. Metal spraying is versatile and can be applied to various substrates, including metals, ceramics, and plastics.

Several techniques are used in metal spraying, including flame spraying, wire arc spraying, plasma spraying, detonation spraying, and high-velocity oxy-fuel (HVOF) spraying. Each technique involves heating the coating material to a molten state and propelling it onto the target surface using compressed gas. The molten particles flatten upon impact, forming a robust and cohesive layer.

Metal spraying is employed across numerous industries, including aerospace, automotive, manufacturing, and marine, due to its ability to provide cost-effective, high-performance coatings that extend the life and functionality of components.

How Does Metal Spraying Work?

Metal spraying, or thermal spraying, involves several stages to ensure the practical application of a metallic coating. These stages include surface preparation, the selection of metallising coating materials, the selection of the best metallising process for the type and use of component, and the evaluation of the characteristics of the finished coating.

Surface Preparation

Surface preparation is a critical step in the metal spraying process. The quality of the surface preparation directly affects the adhesion and performance of the sprayed coating. The surface must be thoroughly cleaned and roughened to create a bonding surface for the coating. Any contaminants, such as oil, grease, or dirt, must be removed, as these will prevent the coating from adhering firmly. Standard methods for surface preparation include:

  • Abrasive Blasting: This involves propelling abrasive materials, such as crushed steel grit or aluminium oxide, against the surface using compressed air. This method provides the necessary roughness for the coating to adhere effectively.
  • Machining: For vital bond components, surfaces may be machined to create grooves or undercuts. Again, this will help the coating adhere effectively.
  • Bond Coating: In some cases, a thin layer of bonding material, such as nickel-chromium alloy or molybdenum, is applied to improve adhesion. This bond coat creates a better foundation for subsequent layers of the primary coating material.

Metallising Materials and Selection

The choice of metallising materials depends on the desired properties of the final coating, such as hardness, wear resistance, corrosion resistance, and thermal stability. This will be determined given the environment in which the component will be used and the forces to which it will be subjected. Common materials used in metal spraying include:

  • Metals: Aluminium, zinc, stainless steel, copper, and nickel are frequently used for their corrosion resistance and mechanical properties.
  • Alloys: Materials like tungsten carbide, molybdenum, and various stainless steel and nickel-based alloys are chosen for their wear resistance and strength.
  • Ceramics: Aluminium oxide, chromium oxide, and zirconium oxide are used for their high hardness and resistance to heat and wear.
  • Composites: These materials combine metals and ceramics to achieve properties that would be impossible with single materials. For example, tungsten carbide-cobalt composites are commonly used for wear-resistant coatings.

Selection of Metallising Processes

Several processes are available for metal spraying, each suited to different applications and materials:

  • Flame Spraying: An oxy-acetylene flame melts the coating material, then sprayed onto the surface using compressed air. This method is suitable for various materials, including metals and ceramics.
  • Wire Arc Spraying involves feeding two consumable wires into an electric arc. The arc melts the cables, and compressed air atomises and propels the molten material onto the substrate. It is efficient for large-scale applications and high deposition rates.
  • Plasma Spraying: Utilises a plasma torch to melt powdered coating materials. The high temperatures produced by the plasma torch allow for the spraying of refractory materials like ceramics.
  • High-velocity oxy-fuel (HVOF) Spraying combines oxygen and fuel to produce a high-velocity jet. The coating material is injected into the plane, melted, and sprayed onto the surface. HVOF produces coatings with high density and strong adhesion.
  • Detonation Spraying: Involves the detonation of a mixture of oxygen and fuel gas to melt and accelerate the coating material. This process produces high-quality coatings with excellent bond strength.

Coating Characteristics and Evaluation

The performance of the sprayed coating depends on several characteristics, which must be evaluated to ensure quality:

  • Porosity: Voids in the coating can affect its strength and corrosion resistance. Lower porosity generally indicates a higher-quality coating.
  • Oxide Content: High levels of oxides can reduce the coating’s flexibility and adhesion. The process parameters should be controlled to minimise oxide formation.
  • Hardness: The hardness of the coating material is critical for wear resistance. It is measured using standard hardness testing methods.
  • Bond Strength: The adhesion between the coating and the substrate is vital for durability. Bond strength is assessed through tensile testing or other appropriate methods.
  • Surface Roughness: The coating’s surface finish affects its performance in applications such as bearings and seals. Surface roughness is measured and controlled to meet specific requirements.

The metal spraying process offers a versatile and effective solution for enhancing the properties of various components across many industries.

What Materials Are Used For Metal Spray Coating?

Metal spray coatings use various materials tailored to meet specific application requirements. Commonly used materials include:

  • Metals: Aluminium, zinc, stainless steel, copper, and nickel are frequently used due to their corrosion resistance and mechanical properties.
  • Alloys: Tungsten carbide, molybdenum, and various stainless steel and nickel-based alloys are selected for their wear resistance and strength.
  • Ceramics: Aluminium oxide, chromium oxide, and zirconium oxide are applied for their high hardness and resistance to heat and wear.
  • Composites: Composites combining metals and ceramics, such as tungsten carbide-cobalt, achieve enhanced wear resistance.

 Each material is chosen based on its ability to provide specific benefits, including increased durability, thermal resistance, and protection against corrosion and wear. It is essential that you select the best coating for your component’s location and usage. A component used in an offshore rig will be subjected to very different forces than a component in a furnace.

The Advantages of Metal Spraying

Metal spraying offers numerous advantages, making it a preferred method for enhancing the performance and lifespan of components. Key benefits include:

  • Increased Durability: Coatings provide robust protection against wear, extending the service life of components.
  • Corrosion Resistance: Metal spraying effectively shields surfaces from corrosive environments, preventing degradation.
  • Heat Resistance: Coatings can withstand high temperatures, making them suitable for applications in extreme conditions.
  • Enhanced Surface Properties: Metal spraying can modify electrical conductivity, friction levels, and hardness to meet specific application needs.
  • Repair and Reclamation: Damaged or worn parts can be restored to their original dimensions and functionality.
  • Cost-Effective: The process is often more economical than replacing parts, offering significant cost savings.
  • Fast Application: High deposition rates make metal spraying a quick solution for applying protective coatings.

These advantages contribute to the widespread use of metal spraying across various industries and show why thermal spraying is a popular and economical choice for many scenarios.

IRS Thermal Spraying Systems and Processes

IRS Surfacing Technologies Ltd offers a comprehensive range of advanced thermal spraying systems to cater to diverse industrial requirements. These include arc spraying, plasma spraying, flame spraying, high-velocity oxy-fuel (HVOF) coating, fusion spraying, and hypersonic arc spraying. Each method has unique advantages, making them suitable for various applications.

Arc Spraying

Arc spraying involves feeding two consumable wires into an electric arc. The arc melts the cables, and compressed air atomises and propels the molten material onto the substrate. This method is known for its efficiency and high deposition rates, making it ideal for large-scale applications. Commonly used materials include zinc, aluminium, and stainless steel. Arc spraying is particularly effective for corrosion protection and component restoration. The process produces coatings with good adhesion and low porosity, which are suitable for industrial machinery and infrastructure.

Plasma Spraying

Plasma spraying utilises a plasma torch to melt powdered coating materials. The torch generates a high-temperature plasma jet, which can exceed 10,000°C, allowing the spraying of refractory materials such as ceramics. Plasma spraying produces coatings with excellent wear resistance, thermal barriers, and electrical insulation properties. It is commonly used in aerospace, automotive, and industrial applications where high-performance coatings are essential.

Flame Spraying

Flame spraying uses an oxy-acetylene flame to melt the coating material, which can be a powder, wire, or rod. The molten material is then sprayed onto the substrate using compressed air. Flame spraying is suitable for various materials, including metals, alloys, and ceramics. It is a cost-effective method for corrosion protection, wear resistance, and rebuilding worn components. The process can be applied manually or automated for larger projects. Typical applications include coating pipelines, machinery parts, and structural components.

HVOF Coating

High-velocity oxy-fuel (HVOF) coating involves the combustion of oxygen and fuel to produce a high-velocity jet. The coating material, usually powdered, is injected into the plane, melted, and propelled onto the surface. HVOF produces high density, low porosity, and excellent bond strength coatings. Typical coating materials include tungsten carbide, chromium carbide, and various metallic alloys. HVOF coatings are renowned for their wear resistance, corrosion protection, and ability to withstand high temperatures. Aerospace, automotive, and power generation industries frequently use HVOF for critical component protection.

Fusion Spraying

Fusion spraying involves applying a thermal spray coating followed by a fusing process to achieve a dense, metallurgically bonded layer. The fusion process can be performed using a furnace, torch, or induction heating. This method ensures a strong bond between the coating and the substrate, enhancing durability and performance. Fusion spraying is suitable for materials that require high bond strength and low porosity, such as nickel-based, stainless steel, and cobalt-based alloys. Applications include wear-resistant coatings for industrial machinery, valves, and pump components.

Hypersonic Arc Spraying

Hypersonic arc spraying uses higher velocities to achieve superior coating properties. This process involves creating an electric arc between two wires, similar to standard arc spraying, but with the addition of a hypersonic gas stream to accelerate the molten particles. The result is a coating with higher density, improved bond strength, and reduced oxide content. Hypersonic arc spraying is ideal for applications requiring high-performance coatings with enhanced mechanical properties. Commonly used materials include stainless steel, nickel alloys, and tungsten carbide. This method mainly benefits oil and gas, chemical processing, and heavy machinery industries.

Main Steps in Thermal Spray Process

The thermal spray process involves several steps, including surface preparation, material selection, spraying, and post-processing.

Surface Preparation

Surface preparation is vital for a strong bond between the substrate and the coating. The surface must be thoroughly cleaned to remove contaminants like oil, grease, and dirt. Abrasive blasting is commonly used to roughen the surface, providing the necessary texture for adhesion. Machining sometimes creates grooves or undercuts that enhance the coating’s grip.

Material Selection

It is crucial to choose the best coating for your component. Coatings range from metals and alloys to ceramics and composites. Each coating offers unique properties such as hardness, wear resistance, corrosion protection, and thermal stability.

Spraying

Spraying involves heating the coating material to a molten or semi-molten state and propelling it onto the prepared surface. Different methods, such as flame spraying, arc spraying, plasma spraying, and HVOF spraying, can be used.

Post-Processing

After spraying, post-processing steps such as finishing and inspection are carried out. The coating may be ground or polished to achieve the desired surface finish and dimensions. Inspections are performed to evaluate the coating’s properties, including thickness, porosity, bond strength, and hardness.

Why Choose IRS Surfacing Technologies Ltd?

Choosing IRS Surfacing Technologies Ltd gives you 20 years of industry experience and a comprehensive range of advanced thermal spraying and overlay systems. Our state-of-the-art facility has the latest technology, including 8-axis robotics, ensuring consistent and high-quality coatings. We offer specialised services across various sectors, including aerospace, offshore, chemical, and manufacturing. 

Our commitment to quality is demonstrated through our meticulous surface preparation, coating selection, and precise application processes. We provide cost-effective solutions tailored to combat premature wear and tear, extending the life of your components. Our engineering and technical professionals are dedicated to delivering exceptional results and providing on-site procedural and technical support.

IRS Surfacing Technologies Ltd stands out for its innovative approach, high-performance solutions, and customer-focused service, making us a trusted partner for all your thermal spraying needs. Contact our dedicated team today by calling 01704 896332

 

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