Teflon, or polytetrafluoroethylene (PTFE), is one of the most versatile industrial coatings available. Best known for its non-stick properties, it offers an extremely low coefficient of friction, chemical inertness, and excellent dielectric stability and can be used to solve a variety of design challenges. This includes preventing build-up of contaminants and corrosion; reducing friction or sticking between parts that come into contact; and even used as an ingredient in heavy wear, high-load applications.

“Teflon is the ultimate problem solver for design issues that can include sticking, release, wear, noise, and abrasion,” says George Osterhout, president of Teflon coatings applicator Orion Industries. “Engineers often seek assistance when they are experiencing problems, whether it’s a part that has no coating or a coating that isn’t performing as expected.”

According to Osterhout, Teflon can be applied to most substrates including carbon steel, aluminum, stainless steel, steel alloys, brass, titanium, magnesium, glass, fiberglass, silicone rubber, rubber, and plastics.

Precision application

Increasing investments in automation and precision equipment have expanded applications for Teflon and other functional coatings. Increasingly, as equipment gets more specialized and environmental regulations get stricter, specialty coaters are taking on Teflon work that used to be done in-house by their customers.

According to Osterhout, the difference in quality between applicators is usually defined by two primary factors:

  • Proper, thorough pretreatment of parts prior to coating
  • Ability to apply coatings as thin as 10µm with a tolerance of ±3µm

The industrial norm is 10µm to 20µm per side of coating. To assure that level of precision, applicators must design and build their own production lines, and these systems must be able to accommodate a wide range of parts in different sizes and geometries.

Orion uses a flexible cellular manufacturing approach to speed production for a wide variety of parts while controlling material cost and energy.

The stationary equipment or robotic cell moves into position and applies coatings, while conveyers and ovens perform flash and curing. Parts are coated in these cells with very little overspray or coating waste.

“In our process, we meter the coating material out of the gun so it is the same every single time,” Osterhout says. “There is very little overspray because we apply the coating where it needs to be, not all over the coating booth.”

Infrared ovens mixed with convection air ovens allow parts to be cured 3x faster than with traditional convection ovens.

Conformable coatings

For applications where tight clearances between parts are required, such as rotary screw compressors, Teflon-based conformable coatings can be used to narrow the gap without allowing metal-to-metal contact during operation.

Decreasing gaps reduces noise, stops air or fluid leakage, and creates a tighter hydrodynamic seal. With rotary screw compressors, conformable coatings can increase efficiency more than 10% without changing machining tolerances.

Ultra-thin conformable coatings, such as Orion’s DB L-908, contain a mixture of polyimide and other resins, nanometer-sized wear-resisting particles, and PTFE.

The coating is applied in thicknesses specified during initial design and testing, so the two coated surfaces initially contact each other while allowing the tips clearance to pass in a rotary screw application.

Small air pockets in the polymer allow the coating to compress under mechanical pressure. Once compressed, the air pockets remain crushed so the coating holds the new profile. The PTFE in the formulation prevents the surfaces from galling or sticking to each other during this initial contact. Conformable coatings must hold ±0.001" tolerance on all surfaces at a thickness of 0.002" to 0.006".

R&D laboratory

Osterhout says the variety of coating formulations and products that could benefit is daunting. In many cases engineers have a product with no coating, or a coating that isn’t performing as expected, and need a resource to explore the options.

“Engineers need to establish how the Teflon coating is going to function and they also need to know the thickness that will be applied to compensate for it to fit within their existing dimensions,” Osterhout says.

To assist in developing specialized materials and application methods, several applicators maintain in-house R&D laboratories to test coatings and research and develop customer-specific applications.

“We have access to baseline performance information from past research and experimentation so we can compare one coating to another that we have developed,” Osterhout says. “This allows us to know that we made substantial improvements in new coatings performance.”

Orion Industries

www.orioncoat.com