Flame-Spray Industries Offers Three Key Thermal Spray Processes
• PTWA is a robust thermal spray process designed to coat the internal surface of bores with consistent, high quality coating
• Kinetic Spray is a new production-ready process running at multiple facilities with ability to repair difficult parts with unique material properties
• Flame-Spray has been providing two wire arc systems since 1964 as a low cost method for coating of flat surfaces PTWA Overview Plasma Transferred Wire Arc is a unique manufacturing process that can deposit a coating on the internal surface of a cylinder, or on the external surface of a part of any geometry. Any conductive wire can be used as the feedstock material, including “cored” wire. Refractory metals as well as low melt materials are easily deposited. The system is designed for easy start-stop operation, can be hand held or machine mounted and may be operated for up to 100 hours continuously without changing components. The PTWA process uses one wire, which makes it ideal for stable, trouble-free solid and cored wire applications. In general, PTWA is used to repair corroded or worn parts, to improve part life by adding a wear-resistant coating, to apply a coating to irregular surfaces, and to reduce part
cost.
Recently, engine manufacturers and remanufacturers as well as automotive companies have turned to PTWA to apply a wear resistant coating on the internal surface of engine block cylinder bores. For hypoeutectic aluminum silicon alloy blocks, PTWA provides a lower cost and lower weight alternative to cast iron liners, while delivering increased displacement in the same size engine package and a potential for better heat transfer.
PTWA coatings may also be applied directly to cast iron engine blocks for remanufacturing. PTWA coated test engines have been run for over 3 million combined miles of trouble free on-the-road performance, and the technology is currently in use at a number of major production facilities around the world.
How the System Works
The PTWA thermal spray process utilizes a single wire as the feedstock material. All conductive wires up to and including 0.0625″ (1.6mm) can be used as feedstock material, including “cored” wires. The wire is melted, atomized and propelled to the substrate by a supersonic plasma jet that is formed by a transferred arc between a non-consumable cathode and the tip of the wire.
After initial atomization, a large flow of forced air through the nozzle transports the stream of molten droplets onto the bore wall. The high kinetic energy causes the particles to flatten when they impinge on the surface of the substrate; the heat transfer between the flattened particles and the substrate causes a rapid solidification. Thus the coating is made up of these solidified droplets stacked one on top of another along the surface.
Application for New Product Aluminum Engines
An important goal for engine manufacturers is to reduce fuel consumption, which can be accomplished by decreasing overall vehicle weight and improving engine efficiency by reducing the internal friction losses. Substantial weight savings can be achieved with the use of aluminum engines. However, most aluminum engines require cast iron liners to be used as the wear surface.
Additional weight savings and potential friction reduction can be achieved by replacing these heavy cast iron liners with a low friction, wear resistant PTWA coating on the cylinder bores.
Additional benefits of PTWA in new production engines include improved heat transfer and decreased bore distortion, which reduces friction loss and oil consumption.
Application for Remanufacturing of Worn Engines
PTWA can be used to repair worn cylinder bores in both aluminum and cast iron engine blocks. This technology makes it possible to salvage engine blocks that would otherwise be scrapped. In addition, PTWA thermal spray can be used to reduce costs for engines that are already remanufactured using expensive over-sized pistons. With reduced costs and salvaging previously scrapped components, the use of PTWA technology can increase the amount of remanufacturing for critical engine components.
Additional Engine Applications
PTWA can be used to apply a coating to the wear surface of engine or transmission components to replace a bushing or bearing. For example, using PTWA to coat the bearing surface of a connecting rod offers a number of benefits including reductions in weight, cost, friction potential, and stress in the connecting rod.
Other Coating Applications
PTWA can deposit a coating on an internal or external surface of a cylinder. Internal diameters as small as 2″ (50mm) or as large as 14″ (360 mm) can be coated. Benefits for Aluminum Engines with PTWA Developed to replace cast iron liners in aluminum engines
• Weight savings
1.5kg / block for I4 engine, 3kg for V8
• Packaging
Allows for closer spacing than liners
• Improved heat transfer and fatigue life
Nissan published data states: “temperature of the entire bore can be reduced by 20-50º C”
• Reduced friction
Published data from Ford and other OEMs shows friction improvements
• Improved bore wear
Component testing and running engine testing data shows improved bore wear
• Decreased cost
• Potential for lower cost compared to liners