The M/S Suokki has transported people between mainland Finland and the Suomenlinna islands since 1952. Now owned by Sun Lines, the vessel carries both foot passengers and vehicles, and averages around 5,000 hours of use per year. M/S Suokki is a double-ended motor ferry and so has a controllable pitch propeller at each end. When the blade seals in these needed to be replaced, technical director Teemu Tassberg found them nearly impossible to source.
Seal searching: on the hunt for spare parts
The propellers were made in 1951 by Swedish manufacturing company Kamewa, who has since been taken over. The blade seals used were a specialist product, not available off the shelf. Little information about replacement parts and modern alternatives was available for the customer – even from Kamewa’s acquirer, Rolls-Royce.
Initial attempts to replace the seals with a modern alternative were unsuccessful. In one attempt, transition fittings located under the propeller blades were designed and sealed with O-ring gaskets. The solution failed when the rings leaked and began to disintegrate. Sun Lines needed an innovative solution that could be installed quickly and have the durability of the original seals.
Collaboration and innovation
Sun Lines contacted Tiivistekeskus Oy, Finland’s a leading supplier of seals and gaskets in Finland, and an SKF partner. The company has experience with hydroelectric turbines and therefore knowledge of rotary motion and tilted blades similar to those found in ships. Working from the customer’s drawings, Tiivistekeskus designed the blade seals and then produced them through the method of turning. In turning, a component is formed by rotating a material on a lathe against a cutting tool. Materials suitable for turning include metal, wood, and plastic polymers – such as polyurethane, which was selected for this project.
Polyurethane is a versatile thermoplastic polymer with excellent wear resistance and high performance over a wide temperature range. It is suitable for turning and can be joined with other pieces using heat when components are needed for large-scale installations. SKF’s H-ECOPUR® polyurethane withstands wear underwater and is therefore ideal for ship components.
The production method was ideal in this customer case as producing a mold for such a small batch size would be both costly and time-consuming. In turning, there is no need for a mold or cast, and the customer also saved tooling costs due to an on-site machining facility.[/row]
Solutions tailored to the customer
Sun Lines was pleased with the partner service provided by Tiivistekeskus and SKF. Teemu Tassberg praised the Finnish supplier for the way it handled the very specific problem with all the seriousness and time urgency of a large-scale project. Combining customer drawings with supplier expertise and SKF technology produced a great solution. M/S Suokki received polyurethane seals that are hard-wearing, cost-effective, and the perfect modern counterpart to the original propeller components.
TECHNICAL DESCRIPTION OF SOLUTION:
- SKF SEAL JET seal manufacturing method.
- SKF’s H-ECOPUR® polyurethane used as the seal material.
- Seal design produced from customer’s drawings.
- Delivery time of just over a week for the seal.