Thermal Spray Welding (metalizing) or thermal spraying represents a sophisticated amalgamation of science and engineering. It is a formidable technique, that offers a versatile and efficient means of fortifying surfaces with a myriad of materials. In this article, read the intricacies of thermal spray welding, elucidating its principles, methodologies, applications, and manifold benefits. Industries ranging from aerospace to automotive, from oil and gas to electronics employ it.
Post Highlights:
- What is Thermal Spray Welding?
- Thermal Spray Welding Principle
- Thermal Spray Welding Courses
- Thermal Spray Welding Diagram
- Thermal Spray Welding Symbols
- Thermal Spray Welding Standards
- Thermal Spray Welding Types/ Thermal Spray Techniques
- Thermal Spray Welding Equipment
- Thermal Spray Welding Schools
- Thermal Spray Welding Certification
- Thermal Spray Welding Handbooks
- Applications of Thermal Spray Welding
- Advantages of Thermal Spray Welding
- Disadvantages of Thermal Spray Welding
- Thermal Spray Welding Safety Measures
- Thermal Spray Welding Employment Areas
- Thermal Spray Welding Job Types
- Thermal Spray Welding Salary
- Future Trends in Thermal Spray Welding
What is Thermal Spray Welding?
Thermal spray welding (thermal spraying or metalizing) is a coating process used to apply materials onto a substrate. It improves or modifies its surface properties. Thermal spray welding involves spraying molten or semi-molten materials onto a prepared surface, not like traditional welding processes where materials are fused at high temperatures. These materials can include ceramics, polymers, metals, and composites.
The working of thermal spray welding revolves around the controlled application of heat to a material. This transforms it into a molten or semi-molten state and then projects it onto a prepared surface. This process creates a coating that adheres to the substrate, imparting desired properties such as improved wear resistance, thermal insulation, corrosion protection, or electrical conductivity.
Thermal Spray Welding Principle
The key elements of the principle include-
1. Material Preparation – Typically, the material to be sprayed is in the form of powder, wire, or rod. It undergoes meticulous preparation, which may involve melting and blending with other materials for desired properties. Sometimes, it alloys to achieve specific characteristics.
2. Surface Preparation – Ensure good adhesion of the sprayed material to the substrate. This may involve roughening, cleaning, and sometimes applying a bond coat or primer to enhance adhesion.
3. Heat Source – Thermal spray welding utilizes various heat sources to melt the spraying material. These may include electric arcs, plasma arcs, oxy-fuel flames, or high-velocity combustion gases. The choice of heat source depends on factors such as the material type being sprayed, the desired coating properties, and the substrate material.
4. Spraying Technique – After the material is heated to a molten or semi-molten state, it is propelled toward the substrate using a spraying technique. The common spraying methods include plasma spraying, flame spraying, arc spraying, and high-velocity oxygen fuel (HVOF) spraying. Each technique offers unique advantages for different materials and applications.
5. Coating Formation – As the molten or semi-molten material is propelled towards the substrate. Then, it rapidly cools and solidifies upon contact, and forms a dense and adherent coating. Multiple layers of sprayed material may be applied to achieve the desired coating thickness.
6. Post-Coating Treatment – After the coating has been applied, it may undergo additional processes such as polishing, grinding, or machining. This is done to achieve the desired surface finish and dimensional accuracy. In some cases, heat treatment may also be employed.
Thermal Spray Welding Courses
Some common course types include-
1. Introductory Course – This provides a foundational understanding of thermal spray welding principles, processes, and applications.
2. Advanced Techniques Course – The program delves deeper into specific thermal spray welding techniques such as plasma spraying, flame spraying, arc spraying, or high-velocity oxygen fuel (HVOF) spraying.
3. Applications-Specific Course – This focuses on thermal spray welding applications in specific industries or sectors, such as automotive, aerospace, marine, oil and gas, electronics, and construction.
4. Hands-on Workshops/Training Program – These programs provide participants with practical experience in operating thermal spray equipment, performing coating applications, and troubleshooting common issues.
5. Material Science/Selection Course – These courses focus on the selection of suitable materials for thermal spray welding applications, considering factors such as desired coating properties, environmental conditions, substrate material, and performance requirements.
6. Quality Control/Inspection Course – This course explores non-destructive testing methods, quality assurance protocols, and inspection techniques for evaluating coating thickness, porosity, adhesion, and other key properties.
7. Safety/Environmental Compliance Course – These courses educate participants on best practices for handling equipment, materials, and waste disposal to mitigate risks and ensure regulatory compliance.
8. Surface Preparation/Pre-Treatment Course – These courses cover techniques for cleaning, roughening, and applying bond coats or primers to enhance substrate-coating adhesion.
Thermal Spray Welding Diagram
The components of the diagram are as follows-
1. Control Systems – This regulates parameters such as spray velocity, temperature, and feed rate to ensure optimal coating quality and consistency.
2. Gas Supply – This represents the gas supply system and provides the necessary gases for combustion or plasma generation in certain thermal spray processes.
3. Heat Source – This is used to melt the spraying material, such as oxy-fuel flame, plasma arc, electric arc, or HVOF combustion gases.
4. Material Feed System – This is the mechanism for feeding the spraying material into the thermal spray gun. This may include powder feeders, wire feeders, or rod feeders.
5. Spray Gun – It serves as the primary tool for projecting the molten or semi-molten material onto the substrate.
6. Substrate – This visualizes the substrate onto which the sprayed material is deposited. This may include various materials such as ceramics, metals, polymers, or composites.
Thermal Spray Welding Symbols
Some common symbols include-
1. Bond Coat Symbol – This is used where a bond coat is required to improve adhesion between the substrate and the thermal spray coating.
2. Coating Thickness Symbol – This indicates the desired thickness of the thermal spray coating. It typically includes a line with an arrow pointing towards the coated surface, accompanied by a numerical value indicating the thickness in micrometers (µm) or millimeters (mm).
3. Flame Spraying Symbol – This typically includes a flame icon next to the welding symbol. This denotes that flame spraying is the specific thermal spray process being employed.
4. HVOF Spraying Symbol – This indicates high-velocity oxygen fuel (HVOF) spraying and may include a representation of a high-pressure nozzle emitting a supersonic stream of particles onto the substrate.
5. Material Specification Symbol – This represents the material specification for the thermal spray coating material. It indicates the type of material to be used and any relevant standards or specifications.
6. Plasma Spraying Symbol – This includes a depiction of a plasma arc next to the welding symbol. It signifies that plasma spraying is being utilized.
7. Surface Finish Symbol – This denotes the desired surface finish of the thermal spray coating. It may include specifications such as roughness average (Ra) or surface texture.
8. Surface Preparation Symbol – This indicates the required level of surface cleanliness or roughness before thermal spray welding. Common surface preparation symbols include “SSPC-SP” codes or equivalent standards.
9. Thermal Spray Process Symbol – This is often depicted as a spray gun emitting material onto a substrate. This symbol indicates the presence of a thermal spray coating without specifying the exact process used.
Thermal Spray Welding Standards
Some prominent standards include-
1. AWS C2.18/C2.18M: Recommended Practice for Thermal Spraying of Zirconia (ZrO2) – This document provides guidelines for the thermal spraying of zirconia coatings, including surface preparation, spraying techniques, material selection, and quality control measures.
2. ISO 14917: Thermal spraying – Terminology – This standard provides a comprehensive list of terms and definitions related to thermal spraying processes, equipment, and materials.
3. ISO 14918: Thermal spraying – Approval Testing of Thermal Sprayers – This standard specifies procedures for the approval testing of thermal spray equipment and operators. It ensures that thermal sprayers meet specified performance criteria and that operators demonstrate proficiency in operating the equipment and producing quality coatings.
4. ISO 14919 Series: Thermal spraying – Procedures for the Application of Thermal Spray Coatings – This series of standards outlines procedures for various aspects of thermal spray coating application, including coating material selection, surface preparation, spraying techniques, quality assurance, and post-coating treatment.
5. ISO 14921: Thermal Spraying – Pre-treatment of Surfaces of Metallic Parts before Thermal Spraying – This standard specifies procedures for the pre-treatment of metallic surfaces before thermal spraying. It includes methods for cleaning, roughening, and applying bond coats to improve adhesion between the substrate and the thermal spray coating.
6. ASTM B883: Standard Specification for Metal Injection Moulding (MIM) Materials – While not specific to thermal spray welding, it provides specifications for metal powders used in metal injection molding (MIM) processes.
7. NACE SP0214: Design, Fabrication, and Inspection of Tanks for the Storage of Concentrated Sulfuric Acid and Oleum at Ambient Temperatures – While not specific to thermal spray welding, this includes recommendations for the use of thermal spray coatings in the protection of tanks storing corrosive substances such as sulfuric acid.
Thermal Spray Welding Types
Some common types include-
1. Flame Spraying (Oxy-Acetylene Spraying) – During this process, a mixture of oxygen and a fuel gas (typically acetylene or propane) is combusted to produce a high-temperature flame. The material is to be sprayed in the form of wire or powder and is fed into the flame. There it melts and is propelled onto the substrate. Flame spraying is versatile and suitable for a wide range of materials.
2. Plasma Spraying – This involves the generation of a high-temperature plasma arc using an inert gas (argon or nitrogen) and a high-frequency electric arc. The material to be sprayed (typically in powder form) is injected into the plasma. There it melts and is accelerated towards the substrate by the gas flow. Plasma spraying offers high coating quality, density, and bond strength.
3. High-Velocity Oxy-Fuel (HVOF) Spraying – It utilizes a high-velocity combustion process to propel the spraying material onto the substrate at supersonic speeds. A mixture of oxygen and a fuel gas (hydrogen or kerosene) is combusted in a combustion chamber. Then, it generates a high-pressure, high-velocity jet of combustion gases. The material to be sprayed is typically in powder form and is injected into the jet. There it undergoes rapid acceleration and impacts the substrate with high kinetic energy. HVOF spraying produces dense, low-porosity coatings with excellent adhesion and mechanical properties.
4. Arc Spraying (twin wire arc spraying) – This involves the generation of an electric arc between two consumable metal wires. The heat from the arc melts the wire tips, and forms molten droplets that are propelled towards the substrate by compressed air or inert gas. Arc spraying is particularly suited for applying thick coatings of metals.
5. Detonation Spraying – This utilizes the rapid expansion of a detonation wave to propel molten particles onto the substrate. The spraying material (powder form) is introduced into a combustion chamber, where it undergoes detonation and forms a high-velocity gas jet. The gas jet accelerates the molten particles towards the substrate, creating dense coatings with high bond strength. Detonation spraying is commonly used for applying ceramic coatings.
Thermal Spray Welding Equipment
Some common equipment include-
1. Control System – This regulates various parameters of the thermal spray process such as feed rate, spray velocity, temperature, and gas flow rates. These systems ensure optimal coating quality, consistency, and adherence to specifications.
2. Cooling System – This cooling system maintains optimal operating temperatures and prevents overheating of components.
3. Gas Supply System – A gas supply system provides the necessary gases for combustion or plasma generation. These gases may include oxygen, fuel gases (such as acetylene or propane), inert gases (such as argon or nitrogen), or high-pressure gases for HVOF spraying.
4. Heat Source – The heat source may include oxy-fuel flames, electric arcs, plasma arcs, or high-velocity combustion gases.
5. Material Feed System – This delivers the spraying material to the thermal spray gun. The system may include powder feeders, wire feeders, or rod feeders, depending on the form of the spraying material used (wire, powder, or rod).
6. Power Supply – In arc spraying and plasma spraying processes, a power supply is required to generate the electric arcs or plasma arcs used for melting the spraying material.
7. Safety Equipment – Safety equipment, such as personal protective gear (e.g., goggles, gloves, protective clothing), exhaust ventilation systems, and fire suppression systems.
8. Substrate Handling Equipment – This includes manipulators, fixtures, or robotic systems used to position and move the substrate relative to the thermal spray gun during the coating process.
9. Thermal Spray Gun – This is a primary tool used to apply the molten or semi-molten material onto the substrate. It consists of a nozzle where the spraying material is heated and propelled towards the substrate.
10. Auxiliary Equipment – This may include masking materials, preheating equipment, abrasive blasting equipment for surface preparation, and post-coating treatment equipment (e.g., grinding, polishing, machining).
Thermal Spray Welding Schools
A few notable schools include-
- Iowa State University (ISU)
- Montana Tech of the University of Montana
- National Center for Advanced Materials Performance (NCAMP) – University of Dayton Research Institute (UDRI)
- North Dakota State University (NDSU)
- The Center for Thermal Spray Research (CTSR) – Stony Brook University
- The Thermal Spray Society (TSS) – ASM International
- University of Cincinnati (UC)
Thermal Spray Welding Certification
Some common certification types include-
- Certified Thermal Spray Operator
- Certified Thermal Spray Inspector,
- Certified Thermal Spray Supervisor
- Certified Thermal Spray Engineer
NCAMP Certification-
- Thermal Spray Operator Certification
- Thermal Spray Inspector Certification
- Thermal Spray Supervisor Certification
NACE International Certification-
- Coating Inspector Certification program
Coating Society of the Houston Area (CSHA) Certification-
Manufacturer-Specific Training and Certification-
ISO 14917:2003 Certification-
Thermal Spray Welding Handbooks
Some well-known handbooks include-
- ASM Handbook, Volume 5A: Thermal Spray Technology edited by Robert C. Tucker and S.V. Nadendla
- Handbook of Thermal Spray Technology by J.R. Davis
- Thermal Spray Coating Applications in the Chemical Process Industries by Louis D. Vincent
- Thermal Spray Coatings: Properties, Processes, and Applications by C.C. Berndt
- Thermal Spray Fundamentals: From Powder to Part by Pierre L. Fauchais, Joachim V.R. Heberlein, and Maher I. Boulos
- Thermal Spray Surface Engineering by Pierre L. Fauchais, Joachim V.R. Heberlein, Maher I. Boulos, and Serge L. Guigon
- Thermal Spray Technology by C.J. Li and X.P. Zhang
Applications of Thermal Spray Welding
Some common applications include-
1. Aerospace Industry – Thermal spray coatings protect against high temperatures, abrasion, and corrosion. They are applied to engine components, combustion chambers, and turbine blades, other critical parts.
2. Automotive Industry – Thermal spray coatings enhance wear resistance, corrosion resistance, and thermal insulation. They are applied to engine components, brake components, exhaust systems, and suspension parts.
3. Electronics/Semiconductor Industry – Thermal spray coatings provide thermal management, electrical insulation, and corrosion protection. They are applied to circuit boards, heat sinks, semiconductor components, and electronic enclosures.
4. Industrial Manufacturing – Thermal spray coatings improve surface properties, enhance wear resistance, and increase productivity. They are applied to machine components, dies, molds, cutting tools, and wear parts.
5. Marine Industry – Thermal spray coatings protect offshore structures, ships, and marine equipment from corrosion, fouling, and cavitation. They are applied to hulls, propellers, shafts, and other components.
6. Medical Devices – Thermal spray coatings provide biocompatible coatings, thermal barriers, and wear-resistant surfaces. They are applied to prosthetics, implants, surgical instruments, and medical equipment.
7. Oil and Gas Industry – Thermal spray coatings protect equipment and infrastructure from corrosion, erosion, and abrasion. They are applied to pipes, valves, pumps, compressors, and offshore platforms.
8. Power Generation – Thermal spray coatings protect against high temperatures, erosion, corrosion, and fouling, improving efficiency and reliability in power plants.
Advantages of Thermal Spray Welding
Some key advantages include-
1. Complex Geometries Adaptability – Thermal spray welding can be applied to substrates with complex shapes, sizes, and geometries including irregular shapes, internal surfaces, and intricate features.
2. Cost-Effectiveness – The welding can extend the service life of components and machinery by protecting against wear, corrosion, and other forms of degradation.
3. Enhanced Surface Properties – Thermal spray coatings significantly improve surface properties such as corrosion resistance, wear resistance, thermal insulation, electrical conductivity, and thermal conductivity.
4. Environmental Benefits – Thermal spray welding is a relatively environmentally friendly process compared to traditional coating methods. It produces minimal waste and pollution with many thermal spray materials being non-toxic and recyclable.
5. Minimal Heat Distortion – Thermal spray welding operates at relatively lower temperatures. This minimizes distortion and heat-affected zones in the substrate material, preserving dimensional stability and integrity.
6. Tailored Coating Thickness – Thermal spray welding enables precise control over coating thickness, allowing for the application of thin or thick coatings as needed.
7. Versatility – Thermal spray welding can be applied to a wide range of materials onto various substrates including ceramics, metals, polymers, and composites.
8. Wide Range of Applications – Thermal spray welding finds applications across various industries including automotive, aerospace, oil and gas, power generation, marine, electronics, and medical devices.
Disadvantages of Thermal Spray Welding
Some common limitations include-
1. Cost – The welding can be cost-effective for certain applications. However, it may involve higher initial equipment and material costs compared to some other coating methods.
2. Environmental Concerns – Thermal spray welding is generally considered environmentally friendly compared to some other coating methods. It still involves the use of compressed gases, consumable materials, and energy-intensive processes.
3. Limited Adhesion Strength – Achieving strong adhesion can be challenging, particularly for certain materials and surface conditions. For this, proper surface preparation and selection of suitable bonding agents or bond coats are essential.
4. Limited Substrate Compatibility – Certain substrates may be prone to distortion or damage due to the heat generated during the process. Not all materials and substrates are suitable for thermal spray welding.
5. Limited Thickness – Thermal spray coatings are typically applied in thin layers. For applications requiring thicker coatings, multiple layers may be necessary.
6. Porosity – Thermal spray coatings may exhibit porosity, which can compromise their integrity and performance. Porosity can also make the coatings more susceptible to moisture ingress and degradation over time.
7. Process Complexity – It requires specialized equipment, materials, and expertise. This makes it a relatively complex process compared to some other coating methods.
8. Surface Roughness – Thermal spray coatings often have a rougher surface finish compared to other coating methods. The roughness may require additional post-coating machining or finishing processes.
Thermal Spray Welding Safety Measures
Some key safety measures include-
1. Electrical Safety – Electrical connections and cables should be inspected regularly for signs of damage or wear, and defective components should be repaired or replaced promptly.
2. Emergency Preparedness – There should be emergency response procedures, including evacuation plans, first aid protocols, and emergency contact information. Keep accessible emergency equipment such as eyewash stations, safety showers, and first aid kits.
3. Fire Prevention/Control – Implement fire prevention measures such as eliminating flammable materials from the work area, using flame-resistant barriers, and maintaining proper housekeeping practices. Keep at workplace equipment like fire extinguishers, fire blankets, and other firefighting equipment.
4. Gas Safety – Properly handle, store, and use compressed gases such as oxygen and fuel gases (e.g., acetylene, propane). Gas cylinders should be securely stored in well-ventilated areas, away from heat sources.
5. Material Handling/Storage – Thermal spray materials such as powders, wires, and rods, should be stored with due care. Material containers should be labeled properly, and incompatible materials should be stored separately.
6. Personal Protective Equipment (PPE) – Operators should wear appropriate PPE including face shields, safety goggles, gloves, flame-resistant clothing, and hearing protection.
7. Training/Education – Operators and personnel should receive comprehensive training on safety procedures, equipment operation, hazard recognition, and emergency response.
8. Ventilation/Exhaust Systems – Adequate ventilation systems should be in place to remove fumes, gases, and particulates generated during the operations. Local exhaust ventilation hoods can help capture contaminants.
Thermal Spray Welding Employment Areas
Some common employment areas include-
- Aerospace Industry
- Automotive Industry
- Defense/Military Sector
- Electronics/Semiconductor Industry
- Industrial Manufacturing
- Marine Industry
- Medical Device Industry
- Oil and Gas Industry
- Power Generation Industry
- Research/Development Institutions
Thermal Spray Welding Job Types
Some common job types include-
- Applications Engineer
- Materials Engineer
- Project Manager
- Research Scientist
- Quality Control Inspector
- Sales/Marketing Representative
- Thermal Spray Engineer
- Thermal Spray Operator
- Thermal Spray Technician
- Training/Education Specialist
Thermal Spray Welding Salary
The average hourly wage for a Thermal Spray Welder in the United States is $24. However, this figure can vary based on factors such as experience, certification, location, education level, industry type, and employer size.
However, the approximate salary range for a thermal spray welder includes.
- Hourly Wage – $15 to $40
- Monthly Salary – $2,500 to $6,500 or more
- Yearly Salary – $35,000 to $120,000 or more
These salary ranges are just estimates and can vary based on individual circumstances and market trends.
Future Trends in Thermal Spray Welding
Some potential future developments include-
1. Additive Manufacturing Integration – Integration of thermal spray welding with additive manufacturing (AM) processes (laser powder bed fusion, directed energy deposition) is expected to emerge. This integration will enable the deposition of near-net shape components with complex geometries and tailored properties.
2. Advanced Materials/Alloys – Continued research efforts are expected to yield new thermal spray materials with enhanced properties. These advanced materials will enable the development of innovative coatings tailored to specific application requirements.
3. Customization/Personalization – With advancements in manufacturing technologies, there will be an increased focus on the customization of thermal spray coatings to meet specific needs. Tailored coatings will offer unique functionalities and performances.
4. Digital Twin/Simulation Tools – The development of digital twin models and simulation tools will allow for virtual optimization. Digital twin technology will enable manufacturers to simulate process conditions and predict coating performance.
5. Environmental Sustainability – The use of eco-friendly materials, energy-efficient processes, and waste reduction strategies will become increasingly important in thermal spray welding. Innovations in green technologies will address environmental concerns.
6. Global Market Expansion – The global market for thermal spray coatings is expected to expand further in key industries such as automotive, aerospace, energy, oil and gas, and medical devices.
7. Industry 4.0 Integration – Integration of thermal spray welding with Industry 4.0 principles will drive digital transformation. Smart sensors, IoT devices, and cloud-based platforms will enable seamless integration of thermal spray processes into the digital manufacturing ecosystem.
8. In-situ Monitoring/Control – Advances in sensing technologies are likely to enable real-time monitoring of thermal spray processes. In-situ monitoring systems will provide insights into process parameters, coating quality, and defect detection.
9. Multi-material/Functionally Graded Coatings – Future trends may involve the use of multi-material and functionally graded coatings. In this process, different materials are combined in layers to achieve tailored properties and functionalities.
10. Robotics/Automation – The adoption of robotics in thermal spray welding is expected to increase in the future. This will lead to higher productivity, repeatability, and precision.
Conclusion
Thermal spray welding is a versatile and effective surface engineering technique. The properties such as wear resistance, corrosion protection, and thermal insulation make it indispensable in automotive, aerospace, and power generation. With the advancement of technology in thermal spray welding, we can expect further developments in processes, materials, automation, and digitalization. Welding remains a key player in the realm of surface engineering despite some potential challenges. Overall, thermal spray welding offers solutions for enhanced performance, durability, and sustainability in a rapidly changing world.
