Plasma Transfer Arc Welding for Abrasion Resistant Coating
In the thermal spray world there are two types of coatings; mechanical bond and metallic bond. These two differentiate how the coating material interacts with the surface material of the component. Mechanically bonded coatings, such as HVOF and plasma, rely on the friction of the coating material and substrate particles to adhere to the surface. These application processes typically involve grinding or blasting the component to ensure good particle adhesion. Metallic bonding, also known as metallurgical bonding, occurs when the coating material and the substrate material adhere at the chemical level. This means that their metallic structures are altered where they combine. This is usually facilitated using heat during or after the coating is applied. Spray and fuse coating is a metallic bond that is achieved by adding heat to the component after thermal spray has occurred. Another type of metallic bond coating is plasma transfer arc (PTA) welding. PTA welding is a form of hardface welding in which a powdered metal alloy is adhered to the surface of a component.
Less Metal Dilution Means Better Coating
PTA welding uses a specialized welding torch to introduce powdered metal, via an additional carrier gas, to the arc and apply it to a surface. Since it achieves a higher arc temperature than TIG and MIG welding, it creates less base metal dilution. Metal dilution is a term used in welding that refers to how much the intended properties of the filler metal is diluted during the welding process. Diluted metals result in softer coatings and a higher likelihood of corrosion. PTA welding is typically faster than MIG and TIG and is easily automated using robotic controls. Common PTA weld coatings are cobalt based alloys (such as Stellite® 6), stainless material alloys and tungsten carbide. These types of metals, along with the metallic bonding, offer benefits such as better corrosion resistance, thermal shock resistance and abrasion resistance.
When to Use PTA Hardface Welding
PTA welded coatings are one of the best solutions for components in highly abrasive environments such as direct impact cutting tools and rotating bearing components. It also lengthens the service life of components used in highly corrosive environments such as the petrochemical and mining industries. It works well for mud rotor repair and some pump component repairs. PTA welding can be used for Stellite® 6 welding on steam inlets for steam turbine component repair; as well as for valve seats. With a variety of applications, PTA welding can be used in a variety of harsh environments to extend the life of components, as well as to repair components damaged by wear and corrosion.
Extreme Abrasion and Impact Resistant Coating
In most environments a mechanically bonded coating will suffice, but when the environment is too harsh, a metallic bond is well worth the investment. The coatings are typically harder, impact and abrasion resistant and even more corrosion resistant than a mechanically bonded coating. PTA weld coatings offer a more uniform hardness over spray and fuse coatings and often take less time to apply. Overall, PTA welding is the way to go when you need an extreme abrasion and impact resistant coating or when the component comes in direct contact with water or other corrosive materials. HTS Coatings has the experience and expertise to help you engineer the correct coating and material for the repair or enhancement of your components.
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