Plain sailing for castings experts as they meet marine sector’s Titanium challenge

Castings Technology International (Cti) is pursuing new opportunities in the luxury and performance yacht market after helping a top marine propulsion specialist create what is believed to be the first four blade folding propeller made from Titanium.

Bruntons Propellers’ Varifold designs are used on luxury motor yachts and have blades that fold inwards, to reduce drag when the yachts are under sail, rather than engine power.

The propellers are usually made from Aluminium Bronze, so when a client asked if Titanium could be used to save weight on a high performance superyacht, Bruntons approached Cti, operators of the UK’s only commercial Titanium casting facility.

“Titanium offers a number of advantages,” says Cti’s Anthony Kenney.

“There are considerable weight savings over Aluminium Bronze. Titanium has superior resistance to corrosion in salt water and sea organisms, including creatures like barnacles, are repelled by the metal, so maintenance costs are lower.

The advantages don’t end there.

Expensive wooden patterns have to be made to create the sand mould for an Aluminium Bronze propeller blade casting and castings have to be made over sized to avoid problems associated with traditional casting processes, which means up to eight millimetres of excess metal has to be machined off all of a blade’s surfaces and features.

Cti’s technology uses data taken directly from Computer Aided Design drawings to make ‘Quickcast®’ patterns on a 3D printer and produces a near net shape casting, with only minimal post cast processing necessary to enable the end user achieve the correct component geometry.

“There are no initial tooling costs, which is particularly advantageous if you are making just one or only a few castings and hard tooling can be made later if demand subsequently increases,” says Kenney.

Titanium’s high strength to weight ratio and corrosion resistance means it is widely used in the aerospace and oil and gas sectors, however, Kenney believes there could be increasing applications for using the metal to make a range of components for higher value luxury and performance marine markets.

Making castings from Titanium isn’t without its challenges. The metal is highly reactive when liquid which means melting and casting must take place under vacuum and special expertise is needed when designing the moulds for the casting and choosing the refractory materials they are made from.

Cti has built that expertise up over a number of years and is currently developing the capability to melt and pour up to 1,000 kg of Titanium at a time.

Based on the knowledge the company obtained during the initial manufacture of the propeller blades for Bruntons, Anthony Kenney believes Cti should be able to cut lead times for Titanium marine components by up to 30 per cent in future for similar products, further increasing its capability to compete with producers in continental Europe.

Bruntons’ product manager, David Sheppard, said: “Bruntons is often asked to design and manufacture propellers or complete propulsion systems for yachts where the currently available options just will not do.

“Our collaboration with Cti was very successful and resulted in a weight saving of between 40 and 50 kilos on a 36 inch Varifold propeller. All our range of two, three and four bladed Varifold propellers will now be available in Titanium, giving any racing sailing yacht an additional competitive edge.”

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