A range of fasteners are available with several O-ring materials to improve the sealing of enclosures exposed to contaminants, such as salt spray in offshore turbines.
Similar O-ring arrangements and materials are available for nuts.
The University of Maine launched the U.S. offshore wind industry when it recently lowered the floating Volturnus 1:8 in the Penobscot River. (WPE&D, August 2013, pg 34) Well aware of the corrosive nature of sea water, University researchers designed the floating platform of a concrete composite. No mention was made of what is protecting the power generation unit that sits on a 65-ft tower also made of composites.
Corrosion protection will get a lot of attention before the next wind turbine is mounted onto either a floating tower or one planted firmly into the sea bed. Their nacelles may well be sealed but if not, internal components, power and control electronics on printed circuit boards, will need some protection against salt spray. One way would be to seal the electrical enclosures with special fasteners fitted with O-rings, such as those from Zago Manufacturing (www.zago.com).
The company says fasteners face severe strain when exposed to pressure, precipitation, and contaminants. The chances of exposure to contaminants when using generic screws increases considerably, adds the manufacturer, because there is nothing to block intrusive substances. Using regular screws, or simply using standalone O-rings and washers still leaves equipment vulnerable.
Affixing a rubber O-ring onto the fastener provides one way to seal the fastener’s opening, a potential channel for salt air. The O-ring’s shape transforms so as to create a wall of protection against a spectrum of dangers such as salt spray and oil. The self-sealing screws block hazards and keep equipment functioning for long periods.
The self-sealing screws, bolts, and rivets provide effective seals while allowing metal-on-metal contact. The fasteners require no messy prep, cleanup, or maintenance and they can be reused.
When choosing an O-ring material, consider these factors, says Zago: the application, the material to seal, size of the fastener, and the temperature and pressure to which the O-ring will be subjected. After considering each and selecting an O-ring, engineering calculations should be checked manually or with O-ring selection software.
Engineers most often choose from six basic O-ring materials which range from 60 to 70 durometer hardness depending on material. Zago says that although other materials and temperature ranges are available on request, those used most often include:
• EPDM compounds. These are commonly used outdoors and are excellent for weather and water resistant. The material has excellent resistance to ozone, steam, and chemicals. Its standard temperature range: –65 to 225°F.
• Buna-N (Nitrile) is the most common seal material chosen for contact with petroleum-based substances, water, and alcohols. Its standard temperature range: -40 to 225°F.
• Neoprene (Chloroprene) compounds are often used in the refrigeration industry for their resistance to ammonia and Freon. Neoprene is also used for numerous applications in the automotive industry because of its excellent resistance to oil. Resistance to ozone, sunlight, and oxygen also make it a great choice for products exposed to adverse weather conditions. Its standard temperature range: –40 to 225°F.
• Silicone rubber has a wide temperature range and withstands low temperatures without becoming brittle. However, it is usually not recommended for dynamic seals because it does not have optimal solvent or oil resistance. Its standard temperature range: -80 to 400°F.
• Fluorosilicone compounds are commonly used in the automotive and aerospace industries because of their resistance to fuel, oil, and solvents. Its standard temperature range: –67 to 350°F.
• Fluorocarbone (Viton) compounds are preferred when seals are required for aircraft engines and automotive fuel handling because of its resistance to high temperatures and harsh chemicals. Its standard temperature range: –20 to 400°F. WPE
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