What Is Thermal Spraying?
Thermal spraying is a method of melting and heating materials using high-temperature plasma or flame and spraying them onto the surface of a substrate.
Through this technique, protective and strengthening layers are formed on the surface of the substrate, enhancing the wear resistance of mechanical components and industrial products, and ultimately extending their durability and lifespan. The formation of corrosion-resistant coatings also protects against chemical corrosion. Moreover, it allows for precise control and efficient, economical coating application, as coatings can be selectively applied to specific areas.
However, effective substrate preparation is crucial for coating formation on the substrate surface. Insufficient cleaning or pretreatment of the surface may lead to reduced adhesion and lower coating quality.
Uses of Thermal Spraying
Thermal spraying finds widespread application across various industrial fields due to its diverse advantages.
1. Improved Wear Resistance of Mechanical Components
Internal combustion engines often experience wear-related degradation of components such as pistons and cylinders. By applying thermal spraying technology, it is possible to extend the lifespan of these components by coating their surfaces with wear-resistant coatings.
Moreover, coatings are often applied to bearings used in the rotating and moving parts of mechanical components to enhance wear resistance. This leads to an extended bearing lifespan and longer maintenance intervals.
2. Repair
By repairing the surfaces of worn-out parts or equipment with thermal spray coatings, it becomes economically viable to address the issue compared to purchasing new parts. Repairing aged or damaged components for reuse results in cost savings. Thermal spraying is frequently employed for repairs, especially in cases where the fit of components in large, aging motors has deteriorated.
3. Improved Corrosion Resistance
Coatings with corrosion resistance are applied to components and equipment exposed to corrosion and erosion in environments such as chemical plants or seawater. This helps extend the lifespan of components and reduces the frequency of maintenance.
Principles of Thermal Spraying
Thermal spraying involves melting and heating materials using high-temperature plasma or flame and then forming coatings by spraying the melted particles onto the surface of the substrate.
Materials used are often provided in the form of powder or wire. These materials are heated to high temperatures using a special heat source, causing them to melt. The melted materials transition to a liquid or molten state.
The molten materials are accelerated by a high-speed gas flow generated by plasma or flame and sprayed toward the surface of the substrate. This mechanism involves the spray-coated materials adhering to the substrate surface. The sprayed and melted materials are rapidly cooled on the substrate surface, solidifying and adhering as a coating. The thickness of the coating can be adjusted based on conditions such as the amount of sprayed material and time.
Types of Thermal Spraying
There are several major types of thermal spraying, each differing based on the heat source used and the state of the material being sprayed. The following are representative types of thermal spraying:
1. Plasma Spraying
Plasma spraying involves ionizing gas using high-frequency energy, creating plasma to melt and heat materials. The melted material is sprayed onto the substrate using high-speed plasma gas. This method is mainly used for coating metals and ceramic materials.
2. High-Velocity Oxygen Fuel (HVOF) Process
HVOF involves mixing high-pressure oxygen and fuel gas to generate combustion, producing high-speed flames. The melted material is sprayed onto the substrate using these high-speed flames. This process forms coatings with strong adhesion, exhibiting excellent wear resistance and corrosion resistance.
3. High-Velocity Air Fuel (HVAF) Process
HVAF involves mixing high-pressure air and fuel to generate high-speed flames, which are used to spray melted material onto the substrate. It allows for coating formation at lower temperatures compared to HVOF. Notable features include high adhesion and coating quality.