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FEATURE


BEARINGS BEARING


SOLUTIONS FOR SUSTAINABLE SHIPPING


LNG has long been regarded as a sustainable fuel and has gained significant traction as a viable alternative for a wide range


of commercial transport applications, including marine and shipping. But with bearings a vital component in LNG pumps, these need to be capable of coping with cryogenic temperatures. Carter Manufacturing explains how its bearings meet the demands


A


round 3% of global greenhouse gas emissions are generated by maritime traffic, so the International Maritime


Organisation (IMO) is increasingly looking to


reduce CO2 emissions. However, while LNG has long been regarded as a sustainable fuel, it presents significant challenges to fuel systems and pumps specifically dealing with extreme (cryogenic) temperatures. Bearings are a vital component in LNG pumps, but these need to withstand being fully submerged in Liquid Natural Gas at temperatures ranging from -196˚C, or in Liquid Hydrogen from -253˚C. Carter Manufacturing has decades of


experience in supplying proven bearing solutions for cryogenic applications.


BEARING CONSIDERATIONS As fuel systems approach operating temperatures of absolute zero (0˚K) the ability to utilise liquid lubrication becomes increasingly challenging, which means dry running bearings are mandatory. ‘Standard’ steel bearings (rated 52100 Chrome Steel) are simply ineffective. In addition to the challenges of


lubrication, the expansion and contraction of the different materials used in the bearing housings (as aligned with the coefficient of the required thermal expansion) becomes even more critical for bearing efficiency. Moreover, balancing the pump system, to account for the contraction of the materials, is essential. A bearing supplier who can offer the extensive specialised ‘cryogenic’ experience is therefore necessary. Special material selection and heat treatment processes are also essential to help ensure


20 DESIGN SOLUTIONS JUNE 2023


that warping or non-linear contraction of the bearing components doesn’t occur. This includes additional cryogenic heat treatment processes and other proprietary considerations to help achieve the best possible results. Bearing cage failure is a common


occurrence in cryogenic applications so material selection, in addition to cage design, is critical to performance. Many common engineering plastics become too brittle at cryogenic temperatures. To help, Carter offers bearing materials such as PEEK and PTFE with custom additives, or even Durafilm or PCTFE. The company has also developed a proprietary two-piece riveted cryo cage design for deep


contact and the resulting risks of micro-welding adhesion. This is not possible for bearings where cryogenic temperatures are involved, so Carter offers ceramic bearings, such as silicon nitride, which not only removes the need for liquid lubricants but also significantly reduces the mass and increases the bearings speed capabilities. This, in conjunction with the application of a dry film lubricant such as tungsten disulphide (rated AMS2530), are other important factors for cryogenic bearing success. To ensure the cryogenic bearings meet


application demands, Carter has developed proprietary cryogenic testing procedures to minimise the risks. The cryogenic bearings undergo a strict testing procedure where they are fully submerged in Liquid Nitrogen at -196˚C. The bearings also undergo performance torque and dimensional analysis, helping to ensure optimal performance for your application.


A GREEN SOLUTION Switching to ‘greener’ energy options and helping to reduce greenhouse gas emissions continues apace, as proven by Carter’s involvement in the significant expansion of LNG projects for the marine sector. LNG as a marine fuel meets all the current IMO and EU regulations, and switching to it means complete removal of Sox and particles, along with a reduction of Nox emissions of up to 85%. The result is a


groove ball bearings that has dramatically increased performance. Traditional bearings used in lower temperature


applications operate effectively with liquid lubricants, creating a thin film between the steel rolling elements which minimises metal-to-metal


reduction in CO2 emissions by at least 20%.


Carter Manufacturing T: 01865 821720 www.carterbearings.co.uk/bearings/ cryogenic-bearings


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