Thermal barrier coating from Zircotec takes heat off of heavy-duty diesels

  • 07-Jun-2011 08:23 EDT
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The new Performance Diesel coating is applied using plasma spraying. It can be applied to most metals as well as many plastics and composites, in the latter preventing delamination.

A new ceramic coating developed by Zircotec reportedly can reduce surface temperatures by 125°C (225°F) in diesel engine applications, an attribute that the U.K.-based coatings specialist believes will attract truck and bus manufacturers challenged by higher temperatures stemming from new Euro VI emissions regulations and testing methods scheduled for late-2013 introduction.

“From our discussions with engine manufacturers and OEMs, heat management is more crucial with Euro VI,” said Zircotec’s Sales Director Peter Whyman. “Whether this is for SCR [selective catalytic reduction] engines where getting the catalyst warm is key, or in general terms, the engines are running hotter with heat soak to other components under the engine bay, risking poor reliability.”

The operating range for the new ceramic is up to 1400°C (2550°F), the same limit as for other zirconia-based ceramics that the company offers.

“There are also changes to the test cycle including cold start and soak test,” Whyman said. “During running, engines are running hotter and in these conditions improved thermal management is likely to help the manufacturers improve performance and overall engine reliability. This is particularly relevant for some aftertreatment systems.”

The new Performance Diesel coating is also applicable for heavy-duty diesel engines used in off-highway equipment, in Europe and elsewhere, including the U.S. According to Tom Prentice, Development Manager at Zircotec, the first Performance Diesel coating is now in service on an exhaust system diesel gen-set in a mine in Australia. And another trial was conducted with an off-highway vehicle manufacturer.

The coating can be applied to exhausts, turbochargers, and on plastic heat shields to manage heat and protect other components. It is described by Zircotec as a “fit and forget” ceramic formulation because it does not require reapplication, maintaining its reliability throughout the life of the vehicle, according to Whyman.

Zircotec believes its new Performance Diesel formulation, together with changes to the manufacturing process, can offer OEMs a 50% cost reduction compared to other coatings.

“We achieved the cost reduction by changing the composition of the ceramic,” Prentice explained. “The heat-reduction capability is marginally lower than the standard zirconia ‘Performance’ coating but still offers surface temperature reductions of 125°C. This reduction has been sufficient for most commercial-vehicle applications.”

He also noted that the coating does not have the same aesthetic appearance mandated by automotive OEMs for use on tailpipes: “The more functional appearance has enabled a further contribution to the cost reduction.”

“Use of our Performance Diesel coating can enable engineers to solve existing heat issues without a major redesign of the engine bay as well as offering the opportunity to delete heat shields,” Whyman added. “As a fit-and-forget solution, whole life costs are lower too.”

The coating is applied using a patent-pending plasma spray process, firing molten ceramic powder at the workpiece. The product uses a proprietary nickel-based bond coat and zirconia-based top coat composition. It can be applied to most metals as well as many plastics and composites, in the latter preventing delamination.

The only details that Prentice would reveal about process changes are that the parameters of flow rate, temperature, and the gas composition have been adjusted to spray this ceramic.

“The new patent relates to the process for applying metals and ceramics onto plastics,” said Prentice. “This development is to deliver a further improvement in adherence to cope with differential expansion and higher resistance to vibration for very harsh applications. The patent refers to the surface preparation, what is applied, and how it is applied.

“It also refers to the coating of composites with metals to improve other aspects. For example, we could offer a conductive coating or a coating that enhances EMC [electromagnetic compatibility] performance of a composite housing of an electronic component. This is an area we want to look at in the future and have some experience from aerospace and motorsport applications.”

The coating can be applied to sintered nylon, glass fiber, and some stereolithography (SLA) parts, but there are limitations. “The issues come with fiberglass and SLA where the temperature restrictions—anything that can’t withstand 100°C—of the substrate prevent the use of the plasma spraying. These can crack and damage during the process,” Prentice explained.

Materials with higher levels of plasticizer also pose a problem. Zircotec has developed cooling methods, however, that enable “a growing number of composites” to be coated via this method.

The coating was in trials with several OEMs. Testing has been completed in the past six months, according to Prentice, and the first production parts were delivered to Australia about two months ago. The company has been talking with OEMs and engine manufacturers about the technology for the past three to four months.

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