One of the most versatile processes used today is the Flame Spray. In this process the coating material is fed into an Oxyfuel gas flame where it is melted, and then compressed gas is used to atomize the coating material and propel it onto the substrate. With proper substrate preparation, the coating adheres to the roughened surface of the prepared substrate and is referred to as a mechanical bond. With the use of special self-fusing metallic powder and a post heat treatment of the coated area, a coating can become “fused” to the substrate and is referred to as a metallurgical bond.
Courtesy of Sulzer Metco. © Sulzer Metco
Materials and Applications.
From the extreme wear resistant characteristics of spray and fuse tungsten carbide coatings, to the repair of worn areas damaged in service, to the corrosion, insulating, and electrical properties associated with numerous coating materials, flame sprayed coatings deliver some of the most cost-effective options to extend, restore or upgrade the life of a component. Following are types of flame spray coatings and some of the industries that utilize them.
Wear Resistance: These coatings protect against fretting and adhesive wear, and are impact abrasion-, erosion-and cavitation-resistant. Nearly all industries can benefit from these coatings, and they are used in the most demanding applications. One common family of coatings consists of nickel/chrome brazing material containing boron and silicon along with tungsten carbide. Post processing after spraying of this coating requires a heat treat process at temperatures of approximately 1030 deg C (1890 deg F), which forms a hard, diffusion-bonded surface. This is commonly known as spray and fuse. This process is used extensively on agricultural knives and blades, combine threshing components, and ground engaging machinery.
Corrosion Resistance: Able to protect less noble materials, predominantly low-alloy steels, from chemical attack, these coatings are also used for protection against oxidation and galvanic corrosion. The chemical and petrochemical processing industries often make use of this type of flame spray coatings. Applications: Pump parts, storage tanks, food handling equipment. Coatings: Stainless steel, aluminum, Inconel and tungsten carbide.
Insulating: These coatings provide components with thermal and electrical resistance. Typical industries include electronics, aircraft and automotive. Applications: gas turbines, burners, exhaust ducts, mufflers and exhaust valve stems. Coatings: Aluminum, nickel/chrome, alloy and ceramics.
Dimensional Restoration: A wide variety of industries can benefit from these coatings, which are used for the buildup of worn and damaged areas on elemental machine components. Applications: Printing rolls and undersized bearings. Coatings: Carbon steel, stainless steel and bronze.
Electrical Conductance: These are coatings that make non-magnetic or nonconductive components magnetic and/or conductive. Industries that use this type of coating include electrical, packaging and printing. Applications: Electrical contacts, ground connectors. Coating: Copper, carbon steel.