Editor's Note: This is the first of a two-part story that begins by reviewing some history and fundamentals of coatings, including a look at where the technology stands today, sprinkled with bits of advice and a few observations from authorities in the coatings and racing community.
This wheel is as it came off...
This wheel is as it came off the track. You'll note that there is plenty of mud on the car but none on the wheel since it has a coating on it.
Historically speaking, what we'll call the "coatings industry" began to take root in the 1980s, according to current information sources, even though there was a modicum of activity prior to that period. At the time, there were two fundamental directions that began to emerge: plasma-spray coatings (initially applied to piston crowns and exhaust system components) and liquid coatings that focused on dry-film lubricants (both thermal barriers and thermal dispersants).
Plasma-sprays generally involved applying a "melted" coating material by spraying it onto a component or system to be protected. Liquid coatings are applied as such and then subjected to a curing process that then involves heating the coated part.
The piston with a hole is...
The piston with a hole is part of a test where half the piston was coated. A torch blew right through the uncoated part and you can see the line where the damage stopped with the coating. Only where the flame got under the coating was any loss experienced under the coating.
Much of the early coatings development occurred in the aerospace industry, while some products evolved from the commercial community, such as applications involving Teflon and various release coatings used in certain manufacturing processes. However, it wasn't long until enterprising people recognized that some of the technology had use in the automotive segment and growth in this area moved very quickly, particularly for the reduction of friction and heat found in engine bearings and valvesprings. Thermal dispersants were discovered to be particularly beneficial on these types of parts.
Then, moving into the late '80s and throughout the '90s, there was significant growth in the overall technology of motorsports. Interestingly, according to Leonard Warren (founder of Techline Coatings and a pioneer in that industry), the flow of new coatings development was turned around from how it began.
"Rather than being fed from the commercial and industrial side, the automotive community began to develop coatings technology that was flowing back into the commercial, industrial, and aerospace sectors. As an example, a coating Techline had developed for automotive mufflers became the coating specified for the exterior of a spacecraft to protect against re-entry temperatures. Essentially, we use that coating today as an air-drying thermal barrier for exhaust system components."
Coating piston skirts is intended...
Coating piston skirts is intended to reduce friction horsepower and aid in maintaining cylinder wall finish and ring seal.
It appears that as the automotive applications and needs have increased because of rapid technological advances in other areas (including those outside the powertrain envelope), the diversity between the needs of aerospace and motorsports has grown wider, resulting in coatings requirements that are more applicable to the automotive environment than in space programs.
Parts life, durability, performance, pressures, and temperatures are all demands placed on parts intended for racing, and the fact these conditions are applied simultaneously to components and systems further complicates the requirements placed upon coatings. The need for coatings specialization has evolved in direct proportion to the ever-advancing and changing conditions in motorsports.
Again, according to Warren, "Coatings that were developed to meet the needs of racing just a few years ago, in many instances, are not sufficient for the needs we see in motorsports today. The stress and loads placed on parts today are greater than in the past. We've also seen a need to develop new coatings, especially thermal barrier products, to avoid some of the problems associated with the plasma-sprayed coatings."
Of the difficulties that can be linked with the plasma-spray approach, one deals with differences in thermal expansion rates between the coatings and base materials on which they are applied.