New Whitford Piston Coatings Improve Engine Performance
The newest piston coatings by Whitford Worldwide provide improved engine performance, while addressing ever-more-demanding engine efficiency requirements. Test data show Whitford’s new Xylan® 16-000 Series low-friction coatings increase engine efficiency, mileage and torque by approximately 3% in all three categories.
Date: 4th October 2018
Whitford has been manufacturing low-friction, wear-resistant coatings for more than 50 years at its facilities worldwide and formulating automotive coatings for more than 40 years.
“We are producing low-friction coatings, which also result in higher durability than the coatings currently on the market,” says Stephen Butler, global business director for Whitford. “Furthermore, these coatings also address a number of important engine design issues.”
While the key driver in the development of the new Xylan formulations is reducing friction, the quest for new efficiencies in engine performance has placed greater demands on improving the lifespan of the coatings, as well, according to Butler.
“The increased emphasis on efficiencies in engine performance by utilizing oil with very low viscosity has created a level of nervousness about dry engine starts, resulting from the oil settling away from the pistons overnight, particularly on cold mornings,” he explains. “That, in turn, places greater demand on a coating’s friction-reduction capabilities, while at the same time requiring the coating to have increased durability. In the past, you’ve always had this oil layer that would act as a kind of primary lubrication boundary. Now, the primary lubrication layer might well be the coating because the oil has drained away from the piston and cylinder wall.”
New Formulations Improve Adhesion
“The longevity of a coating is a combination of toughness, durability and adhesion,” Butler explains. “The importance of adhesion is a factor often overlooked and seldom evaluated. Without adhesion, chipping or flaking are often the cause of failure for otherwise well-engineered materials.”
Adhesion is principally governed by how well the coating liquid spreads across the substrate metal being coated. This spreading is largely a function of surface tension, or how well the surface to be coated accepts the coating itself.
“To determine how well a liquid is likely to spread, we perform a drop test,” Butler explains. “This measures the contact angle of the drop, expressed as its theta designation. If the drop is really well-defined, i.e. it has a high theta number, it is unlikely to spread on the surface to be coated, as the contact area is arbitrarily limited. On the other hand, a flat drop, with a low theta number, signifies more surface contact for the same amount of coating, or a greater surface to adhere to. Our new Xylan Series coatings have significantly lower theta numbers than the competition.”
Looming Problems with Solvents
Although the ongoing priority for manufacturers, which provide piston coatings, is to create coatings that reduce friction, improve wear resistance and increase the longevity of pistons, new regulations proposed for solvents widely used in coating formulations, may become a limiting factor concerning their usage.
Among those identified as problematic or on watch lists in parts of the world, are NMP (N-Methyl-2-pyrrolidone), NEP (N-Ethylpyrrolidone), DMSO (Dimethyl sulfoxide). Among the reasons given are mutagenic or narcotic effects and the transdermal ability to create harmful reactions in the human body. Therefore, while a coating formulation has well-established beneficial effects on engine performance, if the solvent used in creating it is banned, the coating won’t make it out the door.
“We’ve developed new coatings utilizing proprietary solvents that adhere to stricter government regulations,” Butler says. “Our laboratories around the world have devoted substantial time and resources to the solvent issue. Our new solvent formulations are cleaner, more useful products. They dissolve the resins, which form the foundations of our coatings, and they do it more completely. Further, they allow higher solids to be formulated, have lower surface tensions, permit better dispersion of pigments and fillers and make it easier to achieve thicker films with less effort than previous formulae.”
In addition to all the other attributes of the new Xylan coatings, Butler says the coatings can be applied more efficiently.
“Almost everyone we are working with now is doing screen printing,” he says. “So, we are formulating screen printing products, which allow applicators to use the product far more efficiently.”
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