Casting method saves energy

A novel method of casting aluminium could save the UK's light-metal foundries up to one third of their energy costs while significantly improving casting quality.

Traditional foundry methods involve melting hundreds of kilograms of aluminium and keeping it hot while ladling out what is needed into a mould, a process that is energy inefficient and can cause defects.

The CRIMSON (Constrained Rapid Induction Melting Single Shot) process ensures that the exact amount of aluminium needed for a particular casting is melted rapidly in a crucible, using induction heating. It is then squeezed upwards into a cast using a device like a toothpaste pump dispenser. The fully liquid metal is pushed up with a piston controlled by hydraulic motors linked back to computers that accurately control filling of the casting.

Developed by

researchers and local SME

, CRIMSON has received £800,000 from the EPSRC and project partners to get it to the benchmarking stage.

Dr Mark Jolly, a senior lecturer at Birmingham University's department of mechanical engineering, is leading a project to compare the energy used in traditional foundry processes against CRIMSON and develop a model of the energy used at each stage. This will allow a like-for-like comparison of the energy used to create a certain part.

'It's not just the energy used for melting, we'll look at the energy costs across the entire casting process,' said Jolly. 'If you melt three tons of aluminium, you can't use it all at once: you have to hold it at that temperature for an entire shift, which could be eight hours of wasted energy.

'However efficient or well insulated the equipment is, you are always going to lose some heat through radiation and conduction through the furnaces and they are never more than 50 per cent efficient. It's like keeping a bath full of water boiling all day for whenever you want a cup of tea, rather than boiling a cupful.'

As well as energy lost in keeping it hot, if the aluminium is held at just over its melting point for a long period, it reacts with the atmosphere and some of it oxidises. The aluminium can be recovered from its oxide, but this is a process that requires more energy.

The hot aluminium also reduces atmospheric water to oxygen, which creates further oxide, and hydrogen, which dissolves into the aluminium and creates little bubbles in the metal as it solidifies, affecting the quality.

'The other benefit of our process is that as you're pushing against gravity, the liquid metal never falls and never becomes turbulent: it's always under control,' said Jolly. 'If you pour metal into a cast, the turbulence can cause defects in the casting. By controlling the flow into the casting cavity against gravity, you have complete control of the fluid flow up into that cast and you get higher quality.'

The method would also suit prototyping, because if a manufacturer wanted to compare two different alloys to make a component, there would be no need to clean out the furnace — a slug of the new material could just be melted as needed. The process would suit other metals such as magnesium and copper, but the temperature capabilities mean it is not yet suitable for iron or steel.

The energy used in each step of a variety of processes in different types of casting, such as permanent die casting, gravity die casting, low-pressure die casting, sand casting and investment casting, will be monitored using equipment such as Watt meters and thermocouples.

'Each of those processes has its own way of doing things, so it's important we identify the different stages and measure the energy used,' said Jolly. 'It's not something that's been done well in the industry before.'

He added that many foundries are on load-shedding plans where they only melt at certain times a day to avoid grid peak loading. 'They know what they use as a site, but they won't necessarily know how much each piece of equipment is using,' Jolly said.

To compare like-for-like, if a factory makes a cylinder head, the researchers will take the same mould and make exactly the same cylinder head back in the laboratory using CRIMSON. They will also measure the quality to ensure it is at least comparable if not better than traditional processes.

As well as on-site measuring, the model may incorporate CAD input, which can provide the geometry, volume and mass of the component, which can be used to calculate theoretical energies of melting. The model could include numerical analysis of solidification processes. All theoretical figures could be compared directly with experimental results, so if a manufacturer is considering a new product, the model can estimate the energy costs of making it.

Mass melting may still be appropriate for some time-dependant applications where simple components are moulded

. Initially, CRIMSON will be aimed at high-end specification components such as those used in the aerospace and automotive industries.

These applications are reflected in the project's industrial partners. Aeromet International uses a sand and investment casting (lost wax method) to supply aerospace and automotive sectors. Grainger & Worral is a high-end automotive supplier that is also prototyping for companies such as Jaguar. Both companies will provide materials and moulds for the researchers to perform casting at the university, and alongside Ford Motor Company, will learn if CRIMSON could save money on their casting processes and improve quality.

Cast Metals Federation, the body that supports the UK foundry industry, will provide a link to potential partners and help disseminate the results. The KTN for Resource Efficiency is interested in publicising potential energy savings online. Original project partners N-Tec will also be involved.

'I'm very interested in making sure we keep up the relationship between processing and energy usage,' said Jolly. 'It's important that people realise we can have an effect on climate change and sustainability and if you reduce energy, it's not just altruistic, you're also saving the company money.'