Are DLC coatings no longer cutting it?
By Sara Worley on 03/27/23
Figure 1: Rollers from a main shaft bearing with DLC wearing away and large spalls.
Diamond-like carbon (DLC) is a hard film that is used to coat main bearing rollers to reduce failures from problems like contaminated lubrication. The coating itself is carbon based and due to the structure of its bonds has a mix of diamond and graphite characteristics (1). One of the advantages this coating offers is an increase in roller surface hardness. This benefit gives the rollers an increase in wear resistance while also generating lower friction (2).
DLC rollers have been used as a main bearing upgrade for years and is a standard that many operators adopted. DLC coatings have seen success on 1 MW and smaller platforms with minimal roller failures. However, many in the after-market are finding that the DLC coating on their rollers is being pushed beyond its limit on the large 2 MW platforms. The delamination of the DLC that has been seen has caused rollers to spall, as seen in figure 1, and even split in half during operation.
Just like paint can peel off your walls once damaged, DLC coated rollers are seeing a similar effect. Even with the merits DLC has, there is always a chance it can flake off the roller. There is still debate as to what factors are causing DLC coatings to fail and why it’s being seen primarily on larger platforms. Either way, with roller failures a contributing factor to extremely short main bearing service life, a different solution is needed.
DLC was introduced for main bearings because of its wear resistance properties in poor lubrication. Lubrication failures are the root cause of main bearing surface failures (see Peeling Damage article for more information). Rather than relying on a coating, a change in material offers benefits that won’t flake off. This is where the Super Tough main bearing comes in. Super Tough material is a combination of a different steel alloy and heat treatment that gives bearings the increased wear resistance that DLC offered with the addition of debris resistance, white etching cracking resistance, and an advanced raceway surface finish.
An additional factor of the Super Tough material is that the wear resistance and other benefits are baked into the steel itself. This makes it impossible to delaminate like a coating would. Additionally, improving lubrication through increased amount of manual lubrication, grease flushes, and/or installing an auto-luber will help maximize main bearing life.
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