Hardfacing is a process designed to extend the service life of equipment components. It can be used on both worn components and new components. Hardfacing consumables are hard materials selected to be deposited on components for protection, including rods, powders, grits, and pellets. By using different hardfacing methods or techniques, those consumables cover the surface of machine components that are subject to wear during operation. Today, we will explain these hardfacing methods in detail.
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Thermal spray is a hardfacing method that sprays heated materials, such as metals, ceramics, or polymers, onto a substrate to create a protective coating. Thermal spray consumables are typically in the form of powder or wire. To achieve a high deposition rate, this hardfacing method utilizes electrical or chemical heating to create several millimeters thick coatings covering large areas on the surface. Unlike other hardfacing methods, thermal spray minimizes the influence on the temperature of the underlying surface. Therefore, it is ideal for coating flammable materials.
Diode laser hardfacing is an advanced solution for improving longevity and minimizing wear in material handling components. This innovative technique uses a laser to weld a layer of thin metal infused with extremely hard and durable particles, forming a super wear-resistant coating. This method is capable of achieving an impressive hard particle density of up to 75%. By employing the diode laser hardfacing method, the service life of components can be greatly extended while guaranteeing optimized performance.
Individuals who are experienced in welding may find oxygen-acetylene hardfacing quite simple. This method is not suitable for large-sized components, but it has its advantages, such as precise control over the shape of the deposit. Thanks to its slower heating and cooling process, oxygen-acetylene hardfacing reduces the risk of thermal shock. By utilizing this hardfacing method, high precision and required durability can be achieved.
Several arc welding methods can be applied in hardfacing.
SAW is a highly effective welding technique that uses flux to integrate protective gases and slag within the welding pool. During the process, an arc is created between the flux and the workpiece by a wire electrode that is continuously fed. SAW hardfacing can offer outstanding deposition rates, achieve deep weld penetration, and impressive versatility for both indoor and outdoor applications. In addition, the remaining flux can be recycled through a recovery system, minimizing waste and promoting sustainability.
FCAW is a hardfacing method that requires a continuously fed tubular electrode filled with flux. It operates on a constant voltage system. FCAW is commonly used in construction applications thanks to its portability and efficiency. Although it is not suitable for all metals, the FCAW hardfacing method stands out for its advantages, including high penetration rates, exceptional penetration capability, and adaptability.
SMAW is a manual arc welding method and uses a consumable metal electrode covered with flux to shield the welding pool. It creates an electric arc between the substrate and the electrode, powered by an electric current. During the welding process, the flux coating disintegrates and creates a layer of slag and shielding gas that can safeguard the weld during the cooling process. Compared to other arc welding methods, SMAW has a lower deposition rate, but it stands out for its compatibility with a wide range of metals. Besides, the SMAW hardfacing method can be powered by diesel or gas, making it a popular choice in remote regions.
GMAW or MIG is a semi-automatic or automatic arc welding method, feeding a consumable wire electrode and a shielding gas through a welding gun. A constant voltage is required during the process. Due to its unsuitability for overhead or vertical welding positions, GMAW or MIG has limited flexibility. However, it offers several advantages like low cost of consumables and low slag generation.
GTAW or TIG forms an arc between the workpiece and a non-consumable electrode. During the welding process, a shielding gas is employed to protect the welding pool. GTAW or TIG has a relatively lower deposition rate, but it delivers a clean and refined finish without producing any slag. Besides, GTAW or TIG is extremely versatile because it is ideal for a wide range of metals. Moreover, it allows for automatic and manual welding in any position.
"Hard facing&#; and &#;cladding&#; are two terms that are often used synonymously, actually they are different applications. Hardfacing is a welding process that applies a high-wear surface to add protection and extend the life of the object. The material welded typically contains carbides and, in most cases, this is cemented carbide. It looks like a bunch of weld beads laid down side by side.
Cladding is the application of a dissimilar metal to the surface of another metal. Cladding will typically use overlay material that is similar to the base material but in many cases uses different material to give a beneficial property to just that portion of the component, such as high hardness, corrosion resistance, or just to meet a refurbishing function. As with cladding, laser hardfacing cannot be machined and must be ground.
Hardfacing VS. Cladding process
However hardfacing and cladding are surface overlay processes that are different in material characteristics that meet different requirements, they both can be achieved using similar processes:
&#; Lasers
&#; Thermal spray
&#; Flux-cored arc welding or FCAW
&#; Plasma Transfer Arc [PTA] welding
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The choice between hardfacing and cladding comes down to the characteristics you want to impart, the materials involved, and an understanding of the environment that the surface is subjected too. In hardfacing, the heavy, wear-resistant carbide/metal deposit can be applied by laser, thermal spraying, spray-fuse, or welding. Thermal spraying is best for items sensitive to heat distortion, as opposed to spray-fuse that requires flame spraying and fusion with a torch. Thermal spray is not a welding process; therefore, bond strength is very low as compared to a welded or brazed overlay. Traditional weld hardfacing can be used to apply a very thick layer (up to 10&#;s of mm) of wear-resistant material. Laser hardfacing has benefits over the other processes primarily because it is a welding process that has lower heat, lower dilution, and less dissolution of the carbide. This all enables the ability to achieve very thin hardfacing overlays.
Cladding is a weld overlay process yielding a totally new surface that can be used with a large variety of overlay materials in different forms such as powder, wire, or cored wire. What's more, traditional overlay processes can be used as listed above. Just like laser hardfacing, laser cladding has benefits over the other processes primarily because it is a welding process that has lower heat and lower dilution. This all enables the ability to achieve very thin clad overlays.
Laser hardfacing and cladding are used in almost every industry market with applications such as:
&#; Oil and gas
&#; Automotive
&#; Construction equipment
&#; Agriculture
&#; Mining
&#; Military
&#; Energy generation
&#; Repair and refurbishment of tools, turbine blades, and engines
Laser hard facing and laser cladding both provide the advantages of little thermal distortion, high productivity, and cost-effectiveness.
Lasers In Hardfacing And Cladding Processes
Using lasers as a heat source in hard facing and cladding provides precision and the lowest amount of chemical dilution to weld two materials. It provides a cost-effective way to use less expensive substrate materials by applying a weld overlay, which provides corrosion, oxidation, wears, and temperature resistance. The high production rate with which products can be completed combined with material cost advantages makes laser cladding and hard facing a popular choice for many industries.
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