Molten Particle Temperature

[powerman]

hi, how can the substrate dissipate the heat from molten particle so fast by using air jet cooling only? Said the melting point of ceramic is 2k~3k degree C, but the substrate is able to maintain around 100 degree C. Wont the substrate oxidise due to high temperature, forming an oxide layer in between coating and substrate?

[Gordon]

Hi Powerman

The substrate dissipates heat relatively slowly compared to heat transfer from a molten particle to the substrate on impact and splatting. The particle mass and heat content is minuscule compared to that of relatively massive substrate that acts as a heat sink. Thermal spray relies on fast movement between spray gun and substrate so that only a very thin coating build up occurs on each pass of the gun, giving chance for the substrate to dissipate this heat input. A bit like quickly passing your hand through a candle flame and not getting burnt not that I recommend doing this.

Air jet cooling is not responsible for the high cooling rates of the particles, it is just used to provide extra cooling for coating and substrate. In fact air jet cooling in some applications is not used at all.

[powerman]

hi Gordon,

Thanks for your reply.

[Intel55]

LEHIGH VALLEY, Pa., April 14, 2008 /PRNewswire-FirstCall/ -- Air Products' new Thermal Spray Cooling Technology -- which uses cryogenic nitrogen vapor (-320 degrees Fahrenheit) to maintain part temperature during thermal spray coating applications -- is enabling Delta Air Lines, Inc. to apply quality coatings on critical aircraft parts more effectively and economically than with traditional methods. Additionally, the success of this technological collaboration assisted Air Products in winning a contract to supply Delta's Technical Operations Facility in Atlanta, Ga. with all of its bulk nitrogen, argon, oxygen and hydrogen needs.

"Delta gave us parameters on how they wanted the machine to think and act, and we designed a thermal spray cooling system to meet their specifications," said Matt Thayer, senior principal engineer, Commercial Technology at Air Products.

Air Products' Thermal Spray Cooling Technology is an automated cryogenic gas cooling system that is being used by Delta's HVOF (high velocity oxygen fuel) thermal spray department to coat critical wear parts, such as rotating engine parts and landing gear. By eliminating the need for inter-pass cooling breaks, the Air Products cooling system has enabled Delta to reduce by as much as 50 percent the spray-coating time, amount of feed powder sprayed, and the volume of gases consumed in the coating of its landing gear axles.

Air Products' U.S. patent-pending cooling technology also offers environmental and product quality improvements. The technology has enabled a tungsten carbide cobalt coating to be more cost-effectively substituted for traditional chrome plating, which can generate a potential carcinogen at high temperatures. In addition, the new technology minimizes the undesired thermal softening of coated parts by reducing the temperature fluctuations and the duration of the coating process.

"This is another great example of what Air Products does best," said Thayer. "We listen carefully to our customers so we can understand their challenges and needs, and then work closely with them to find a solution. We look forward to working with Delta on this emerging technology by continuing to improve it and expand its use within their facility."

Air Products serves customers in industrial, energy, technology and healthcare markets worldwide with a unique portfolio of atmospheric gases, process and specialty gases, performance materials, and equipment and services. Founded in 1940, Air Products has built leading positions in key growth markets such as semiconductor materials, refinery hydrogen, home healthcare services, natural gas liquefaction, and advanced coatings and adhesives. The company is recognized for its innovative culture, operational excellence and commitment to safety and the environment. Air Products has annual revenues of $10 billion, operations in over 40 countries, and 22,000 employees around the globe. For more information, visit http://www.airproducts.com/.