Kent Henry
Godfrey, IL
Thermal spray technologies, developed as early as 1910, have been continually refined to provide cost-effective means to repair and protect equipment. These technologies encompass processes used to apply metallic and nonmetallic coatings to machinery, characterized by the simultaneous melting or softening of powder or wire materials that are sprayed to coat surfaces. The broad range of materials that can be applied using thermal spray processes allows for diverse applications across various industries. This paper discusses the different thermal spray processes and their use in restoring machine surfaces, highlighting how these technologies can offer repair solutions without adversely affecting the original properties of the parts.
Thermal spray applications in service centers are primarily associated with addressing wear due to factors such as abrasion, adhesive wear, erosion, corrosion, impact, fatigue, and cavitation. Recognizing the types of wear and finding solutions that address all factors can improve reliability and provide a competitive advantage. Thermal spray coatings can enhance resistance to wear and extend the time between scheduled shutdowns, thereby increasing productivity. Common applications include rebuilding worn bearing and seal surfaces on shafts, bearing housings, and machined surfaces, as well as providing hard surfacing, corrosion resistance, or wear resistance for various components.
The paper defines thermal spray technologies as coating processes where wire or powder material is heated to a molten or plastic state by a flame or electric arc and then sprayed onto the workpiece. The kinetic energy of the particles causes them to flatten upon impact, forming a laminar coating. The two thermal modes used in thermal spray technologies are the cold process, which involves mechanical bonding without significantly affecting the base metal, and the hot process, which involves metallurgical bonding and can alter the base metal properties.
Basic thermal spray processes include flame spray, electric arc spray, high-velocity oxygen fuel (HVOF), plasma arc spray, cold spray, and spray fuse powders. Each process has its advantages and disadvantages, with variations in heat input, bond strength, coating porosity, and equipment costs. The choice of process depends on the specific application and desired coating properties.
Thermal spray coatings offer several benefits, including the ability to repair parts without changing their original properties, improved reliability, and reduced repair costs. The paper provides examples of how thermal spray can address issues such as shaft currents and worn seal surfaces, demonstrating the versatility and effectiveness of these technologies. The basic procedure for applying a thermal spray coating involves cleaning the surface, undercutting the repair area, roughening the surface, masking adjacent areas, preheating the part, applying the coating, and machining the part to the final dimension.
The paper also discusses conditions to avoid coating failure, such as wet, corrosive environments, high compressive forces, and improper surface preparation. It emphasizes the importance of protecting equipment from contamination during the thermal spray process and highlights safety considerations, including the use of personal protective equipment and proper ventilation.
Key Points Covered:
- Definition and history of thermal spray technologies
- Types of wear addressed by thermal spray coatings
- Applications of thermal spray in service centers
- Description of thermal spray processes and their advantages and disadvantages
- Benefits of thermal spray coatings
- Basic procedure for applying thermal spray coatings
- Conditions to avoid coating failure
- Equipment protection and safety considerations
Key Takeaways:
- Thermal spray technologies offer cost-effective repair solutions without altering original part properties.
- Recognizing and addressing different types of wear can improve reliability and provide a competitive advantage.
- Various thermal spray processes are available, each with specific advantages and applications.
- Proper application of thermal spray coatings involves several critical steps to ensure effectiveness and durability.
- Protecting equipment and ensuring safety during the thermal spray process are essential for successful outcomes.
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