A foundry in Norway has successfully trialled a new method of manufacturing ship propeller blades that cuts the energy required by a third.
Oshaug Metall in Molde has collaborated with independent research organisation SINTEF to develop the energy-saving casting technology that reduces the amount of metal that needs to be melted for each blade as well as increasing production capacity.
The technology, devised by SINTEF senior scientist Arne Nordmark, has now successfully completed pilot trials at the foundry’s manufacturing centre, which creates propellers for vessels ranging from cruise ships to naval vessels. The foundry’s smelting furnaces consume as much electricity as 100 average Norwegian households – 1.5 million kilowatt hours a year.
“The results of the project so far indicate that we can reduce electricity consumption by half a million kilowatt hours a year, and in this way reduce both costs and negative impacts on the environment,” said Stein Berg Oshaug, managing director of Oshaug Metall.
The key to the energy saving has been an alteration to the design of feeders – the molten metal reservoirs attached to the mould that compensate for the fact that the casting shrinks in volume as it solidifies by supplying additional molten metal.
To prevent the metal in the feeder from solidifying before the casting is complete, foundries have traditionally made the feeders very large, on the basis that large volumes solidify more slowly than small ones. As a result, a blade weighing 1,000kg may require a feeder weighing as much as 800kg. But as shrinkage during solidification constitutes only about 10 per cent of the weight and volume of the propeller blade, as much as 700kg of the molten metal in the feeder will not be used in the final casting.
The new invention increases the efficiency of the process by surrounding the feeder with an induction coil that supplies heat to keep the metal from solidifying. This means that the feeders only have to be large enough to contain the small amount of molten metal needed to compensate for the shrinkage in the casting. This drastically reduces the amount of metal that needs to be melted for each casting, saving energy and allowing the foundry to cast more propeller blades in a given time, or to cast bigger blades, than its current production capacity permits.
“The pilots reveal that the method can save as much as 35 per cent of the electricity currently used to melt the metal we need to cast a propeller,” said Dr Nordmark.
“The new technology enables us to increase production capacity by as much as 50 per cent, and in cash terms this is even more than we save in electricity,” said Mr Oshaug.
The new process also means less post-casting work. After the casting process is complete and the metal has solidified, the feeder metal has to be cut from the casting for re-melting. This cutting process is very time-consuming for feeders of large diameter, but during the pilot trials of the new technology the diameter of the feeder was reduced by 60 per cent, so reducing the cutting work.
“Less post-casting work means lower costs. Moreover, the environment in the foundry is improved when cutting is reduced,” added Mr Oshaug.