5 ways to save energy when melting and transferring metal

Aluminium die-casting operations are notoriously energy intensive. In fact, approximately 25% of the total cost of die cast parts is associated with energy consumption. Identifying and tackling energy ‘hot spots’ can therefore make a huge difference to overall cost-efficiency and profitability.

Which is exactly why this guide takes a closer look at melting and transferring liquid aluminium. Energy intensive processes are by no means limited to this specific area, but a substantial amount of energy is required to melt scrap and ingots and keep the molten metal at the right temperature. So much so that evidence suggests the melt-shop alone can account for as much as 77% of the overall energy consumption in a die casting foundry.

To help you make savings that could make a big difference to your business - here are 5 things to consider when it comes to cutting energy consumption and carbon emissions in your aluminium foundry:

Most foundry equipment, including melting and dosing furnaces, now leaves the production line Industry 4.0 ready meaning machines are pre-equipped to collect and provide informative data on performance. For legacy equipment that doesn’t fall into the ‘4.0 ready’ category, so-called gateway technology exists - Norican’s NoriGate solution being one example - which can be retrofitted to any machine in order to leverage the same information. A data-driven view of the entire die casting line is now possible and practical to achieve.

Crucially data ready to be unlocked in this way – and, with tools like Monitizer, displayed and analysed in real time - includes production KPIs which can be matched against energy consumed in order to identify potential issues and/or technology not performing to its full efficiency potential.

Quick fact: With an energy consumption level of 540kWh/t, a StrikoMelter shaft melting furnaces with an annual melting capacity of about 14,000 t creates 860 t less CO₂ emissions every year than the melting furnace technology otherwise available on the European market.

But even shaft furnaces can be made more efficient. Particularly by looking at shaft fill and material distribution in the shaft. Wasted space is wasted energy. Here are 3 things you might want to look at to make sure your fill is as efficient as possible:

This often translates to shorter, interrupted melting periods that are very inefficient – energy is lost during the intervening gaps, and must be spent again to re-heat. In addition to seeing energy consumption go up, the process can also see metal quality go down due to oxidation and dross formation. A lose/lose situation.

And often, it’s not necessarily one big thing but rather an accumulation of small things than can add up to significant energy savings. For example:

• Maintaining the rope seal on furnace doors may seem a very small detail but even this can generate an energy saving of 1%. Together with the self-sealing cleaning door, the rope seal achieves perfect tightness. Having a tight seal in place saves energy by reducing heat loss during melting and holding, while also preventing air ingress which could result in oxidation and corundum formation.
• Burner efficiency means better efficiency. A well-adjusted burner with a stoichiometric air fuel ratio can save up to 2% of energy compared to a burner with too much air-surplus. This is because excess air i.e. air not necessary for the combustion process, will actually lower flame temperature and make heat transfer less efficient.

While they are pre-heated, most transfer ladles typically used to complete this task are uncovered resulting in heat loss and energy waste – melt often has to be over-heated to compensate, a solution which has the potential negative side effect of metal quality degradation.

Hot tip: In addition to being considerably safer, a closed metal transfer system like the Schnorkle mitigates this efficiency issue by keeping the molten aluminium at a constant temperature. Hermetically sealed transfer solutions also minimise contact with the atmosphere for optimal metal quality which in turn has implications for productivity - better quality metal in, better quality cast parts out, more efficient and effective use of energy.

Another cover up: As with transferring metal from the primary melting furnace, holding and dosing systems for liquid aluminium are also far more energy efficient as they eliminate the potential for wasteful temperature loss. Energy consumption for this process can be cut by around 2/3 as a result. Closed dosing systems can also have a dramatic impact on metal loss and quality.