Supersonic metal coatings applied at the speed of robotics

2013-11-13 - As demands from the thermal spray industry have become more exacting and diverse, TAFA Incorporated, a Praxair Surface Technologies company has stayed at the cutting edge of innovation by eliminating guesswork.
In the late 1950s, when NASA needed to find a way to get their fledgling spacecraft back through the searing heat of reentry into Earth’s atmosphere they turned to Merle Thorpe, who was researching high temperature arc flame technology using an early DC plasma system he developed in Concord, New Hampshire. Thorpe helped solve the heat shield problem by creating a bond-coat layer that allowed the ceramic heat shield to stick to the capsule material.

Thorpe's efforts in DC and Induction Plasma, along with the development of high temperature corrosion resistant coatings, led to the creation of one of the world’s most influential thermal spray equipment companies: TAFA Incorporated.

Since that time the surface coatings industry and its demands have changed substantially, but through it all the basic purpose for applying high temperature metal, carbide or ceramic coatings to a substrate to make it tougher, more heat resistant, less susceptible to corrosion, and extend its lifespan has remained constant.

Global yet approachable
“In its present form, TAFA started in the late 1970s as a distributor for arc spray equipment,” says Richard Thorpe, son of company founder Merle Thorpe and Praxair Surface Technologies Global Thermal Spray TAFA-Brand Equipment Manager. “In the 1980s we started developing our own spray equipment and applications in the aerospace industry. At that time we also pioneered high pressure high velocity oxygen fuel technology, high energy plasma technology, thermal spray applications with standardized cells, and we were one of the first to introduce robots into the thermal spray market.”

Today, TAFA-brand equipment is used in more than 50 countries and has representation in all the major world regions.

“Even though we are part of a much larger organization, the TAFA portion of Praxair Surface Technologies is still very much a family atmosphere,” says Thorpe. “We’re easy to talk to yet we are on the leading edge of spray coating solutions.”


Labor intensive meets robotically efficient
While the thermal spray process has been around since the early 1900s, up until recently it was a labor intensive endeavor. Every part was hand sprayed and quality largely depended on the skills of the operator—something Thorpe refers to as a “black art.”

“At some point, when growth in the aircraft industry really started to take off and thermal spray coatings and technologies were being used to protect aircraft engines, landing gear and other essential parts, the industry demanded more repeatability and higher quality coatings,” says Thorpe. “Even so, it wasn’t until the late 1990s that robots really began to be accepted and used in the thermal spray industry.”

These days, parts for the aerospace industry are so exacting and complicated that the only way they can be thermal spray coated accurately is through robotics. A coating less than a millimeter thick significantly increases the engine life and temperature limits and, in some cases, engine efficiency.

“As robot prices started to come down we realized we could use them much more cost effectively than any other solution for accuracy and high quality,” says Thorpe. Today you’ll also find surface coatings in petrochemical, industrial gas turbine and other general industry applications.

Safety is imperative
On top of increasing the quality and affordability of the thermal spray process, robots have helped with a matter of critical importance: safety.

“Thermal spray is a nasty process,” says Thorpe. “It produces a lot of overspray heat and radiation, so getting the operator out of the spray booth is the right thing to do.”

“After Praxair Surface Technologies bought TAFA in 1989, we adopted Praxair’s rigorous safety and quality standards and culture,” says Richard Luding, Praxair’s TAFA-Brand Arc Spray Product Manager. “It was that mantra of quality and safety in tandem—creating a safe working environment and delivering a quality product - that was unparalleled in the rest of the industry, so it was a win-win for us.”

In-house innovation driven by the customer
The introduction of robots to the process of thermal spraying has allowed the industry to coat much more complicated parts on a more consistent basis than ever before.

“It always comes down to the coating and the application our customers want to solve,” says Thorpe. “Whether it’s corrosion, wear protection, thermal cycling, or the combination of several factors, Praxair listens to its customers and tries to solve their issues with innovative research.”

Praxair offers three different types of TAFA-brand thermal spray technology: twin-wire arc spray, plasma and high pressure/high velocity oxygen fuel (HP/HVOF). In twin-wire arc spray, two wires are fed into the front of a gun and then melted when an electric arc is created between the wire tips and the subsequent molten metal is propelled onto the substrate with compressed air. Plasma utilizes a powder of metal, ceramic or cermet that is injected into a plasma plume of ionized gas such as argon or nitrogen and then propelled onto the substrate.

The third process, HP/HVOF, is essentially a rocket motor producing supersonic gas speeds fueled by oxygen and liquid-fuel (kerosene) that is used to propel powdered feedstock materials such as metals and carbide cermets onto a substrate. In HP/HVOF, the higher kinetic energy released by the higher impact velocity of the particles, compared to gaseous-fueled HVOF devices, onto the surface is a major factor in the unique, extremely high quality coatings produced.

“What separates TAFA-brand products from those of other manufacturers of high velocity oxygen fuel equipment is that our products are high pressure,” says Luding. “The high pressure creates world class coatings with densities at or less than 1% porosity. These are very hard coatings that are difficult to duplicate with other processes. We also have a large range of plasma products, everything from low-power guns that can spray carbides or ceramics at very high quality all the way up to devices that can spray tremendous amounts of powdered feedstock at very high rates.”

“Our thermal spray technology moves to a new level when combined with robotic technology from ABB.”

Richard Luding, Praxair’s TAFA-Brand Arc Spray Product Manager

Praxair has spent a great deal of time and effort creating software solutions for TAFA-brand equipment that take the guesswork out of operating thermal spray equipment. “The software interface we’ve developed makes it easy to produce high quality coatings,” says Stephen Ford, Praxair’s Engineering Manager for TAFA-Brand Equipment. “You can run the entire process from the ABB robot and IRC5 robot controller, so operators only need operating knowledge of a robot and not thermal spray equipment. I believe we’re the only ones in the industry who can run all of our equipment through a plug-and-play standardized interface.”

According to Luding, many of Praxair’s TAFA equipment innovations are only possible through its intimate relationships with customers. “Many thermal spray and turnkey product developments have come about wholly through customer input,” he says. “Our turnkey robotic spray systems are designed to satisfy a customer’s complete needs by not just increasing operator safety, but providing output rates that justify the capital expenditure of purchasing such a system.”

Close partnership with ABB
“One thing that sets Praxair apart from other thermal spray equipment suppliers is the long standing relationship we’ve forged with ABB,” says Luding. “Our thermal spray technology moves to a new level when combined with robotic technology from ABB. It’s very important to maintain a particular position and angle when applying thermal-sprayed materials. ABB robots allow TAFA-brand coating systems to produce completely repeatable coatings, which is something that isn’t available with other automated systems. With coatings being applied at a thickness of between 1 and 15 thousandths of an inch, repeatability and accuracy are key to the coating process.”

TAFA-brand coating systems also rely heavily on ABB’s RobotStudio PC-based, 3D, virtual programming tool. “Some thermal spray processes can be incredibly intricate and time consuming to program,” says Luding. “If you were to do that kind of programming in the booth using point-to-point robot programming, you would be taking the booth offline for a considerable amount of time. But with RobotStudio the booth can be used for other purposes while these programs are being written.”

“We have customers around the globe, so ABB’s worldwide support network is also very important to us,” says Ford. “If a customer system is not in working order anywhere in the world we can call ABB and they’ll be there for us.”

ABB and TAFA have been working together for about 15 years and that close relationship has proven fruitful for both companies.

“We function, and have grown in the same markets together, therefore we’ve developed a close working relationship and understand each other’s needs fully,” says Luding. “The reliability of ABB’s products is excellent; they’re tireless, they’re robust and they communicate with TAFA thermal spray equipment at a very high degree of accuracy and repeatability. When a customer works with us they’re also working with ABB and vice versa. It’s a partnership that’s definitely transmitted right to our customer.”
Praxair offers three different types of TAFA-brand thermal spray technology: twin-wire arc spray, plasma and high pressure/high velocity oxygen fuel (HP/HVOF).