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A synthetic substitute

Plastic increasingly replaces metal in shaft components

Rough seas exert enormous force on ships. As a result, it is absolutely vital that ship components are robust—but, typically, this also means they are heavier. Shipping companies are urgently seeking new ways to reduce weight, and they are open to using alternative materials. Are plastics about to take over?

It was more than a prestige project that SKF presented to the public a few years ago. With support from Germany’s Federal Ministry of Education and Research, the company developed the first stabilizer fin made of glass-fiber reinforced plastic (GRP).

The project proved that special plastics can withstand the forces of the ocean. Although the fin itself was only a prototype, it sparked a debate about the use of plastics in the shipping industry.

Stabilizer fin made from GRP: a pioneering prototype

Background

What is GRP?

The composite material combines and enhances the advantages of traditional materials while reducing their downsides. Like muscle fibers, the fiber reinforcements in plastics strengthen their structure. Today, there are GRPs that are stronger than steel and more flexible than aluminum. Only through sophisticated research and development can such composites be manufactured—opening up new opportunities to create lighter products.

Lightweight for heavy duty

Today, every gram of weight saved has a noticeable impact on costs and resource consumption—even for the largest cruise ships. That is why research and development now focuses more heavily on new methods of manufacturing lightweight products. In the last few years significant advances have been made in shaft components.

Over this period, SKF engineers have researched countless plastic compounds and test scenarios. They developed seals that are considerably lighter than their bronze, cast iron, or stainless steel counterparts—and work just as well.

Benefits of plastic shaft components

  • High strength at lower weight
  • Weatherproof, with no risk of corrosion
  • Compatible with all seal housing and hull materials

 

In use from Trinidad to New York

The first vessel to be retrofitted with Simplan seals made from GRP was a catamaran passenger ferry carries up to 765 passengers and 200 vehicles on the Caribbean Sea. Since then, several newly constructed vessels have been completely fitted with GRP-based seals. Over the next few years, 30 modern ferries will be built for Hornblower Cruises featuring the new SKF products.

“If I’m building a modern vessel, then I also want to use state-of-the-art components.” – An SKF customer

Specialized Materials

But not all plastics are the same. While GRP is a well-known and well-suited material for seal housing parts, the demands on materials for plain bearing applications are more complex. For this reason, SKF is developing and testing modified polyurethane, which is envisaged for use in plain bearings. The aim is to create plastics that are highly resistant to wear, even when exposed to high friction. Such a material could significantly extend the lifespan of water-lubricated plain bearings, for example.

This is an important benefit for many ship owners in light of increasingly strict environmental regulations. Depending on their purpose, plastic plain bearings can therefore prove to be more cost-effective than metal bearings in the long term. This is especially true considering the high demands set by the 2013 Vessel General Permit concerning the effectiveness of shaft seals at oil-to-sea Interfaces.

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A useful alternative

“Plastics won’t completely replace metals. For components that are exposed to extremely high stress, metal or bronze remain important,” says Patrick Arand, Senior product manager Simplex shaft components at SKF. “However, during research we keep finding new potential applications where the advantages of GRP, polyurethane, and other materials could pay off.”

 

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