Furnace fix: 5 ways foundries can cut gas consumption quickly

25% of the total cost of die cast parts is associated with energy consumption, with as much as 77% of that consumption attributable to melting returns and ingots and keeping molten metal at the right temperature.

That was before the current cost of energy crisis. And with further price hikes on the horizon for this autumn and winter, lowering the amount of gas furnaces consume is a major win.

The good news is that ‘win’ doesn’t have to take time. Here, Dr Theodoor van der Hoeven - VP Product Development at StrikoWestofen - suggests some quick changes foundries can make to lower their energy bills.  

 

1) Shaft savings: fill better, save more

In a melting furnace shaft, wasted space is wasted energy so reviewing filling processes is a natural first port-of-call for any die caster looking to cut costs.

Firstly, it is always better to fill the shaft before starting melting burners as this will put gas to good use right from the start. Charge mix is also important. A 50:50 charge mix ratio of returns and ingots will optimize filling conditions and material distribution within the shaft. Use of smaller ingots is preferable as this will achieve higher surface-to-volume-ratio which benefits heat transfer. Stacking ingots in the same direction within the ingot block can also reduce energy consumption by generating a more homogenous material distribution.

If a 50:50 ratio isn’t possible, for instance if foundries are focused on re-melting bulky returns in line with giant casting trends (bulky parts mean bigger voids), a hot gas baffle to cover the shaft will reduce heat loss considerably. Foundries not already using this feature should do so. We’ve had customers cut their energy consumption by up to 15%.

If a hot gas baffle is not already in place, our StrikoWestofen engineers can retrofit one in only 5 days.

2) Melting periods: avoid stop/start heat loss

Melting furnaces are most efficient when used at 100% capacity. The problem is that’s often not realistic.

Whether due to maintenance, production changes or simply shifting market conditions, many aluminium die casters may regularly experience furnace utilization as low as 30%, resulting in stop/start production and energy disappearing during the intervening gaps. But there is a fix for this. By continually switching between melting and holding modes according to utilization this avoids energy-intense re-heating. Savings of up to 20% are possible. Closing the shaft cover during holding is also advisable to save precious energy.

 

This can be done manually but it’s more efficient to automate the process. Our Part Load Efficiency Control can be fitted in just 2 or 3 days.

 

3) Rapid furnace reline: up to 50% savings

Wear to furnace linings is unavoidable: all melting, and dosing furnaces require regular relining to maintain correct operation and maximize energy efficiency. If you have unexplained energy loss, this could be the culprit – especially if your furnace is over 10 years old.

What’s more, when it’s time to reline, foundries should expect their supplier to commit to a specific target for gas consumption per ton of molten metal and provide validation data from onsite testing. We’ve seen savings of more than 50% delivered with melting furnaces tested, relined, re-installed and re-tested in just 4 weeks. Turnaround for dosing furnaces, using prefabricated parts, can be as quick as 5 working days.

Choosing OEM replacement linings is advisable. A poorly fitted replacement lining not designed to exactly match original furnace specifications can increase total energy consumption by as much as 30%.

4) Avoid burning money: check air-to-gas ratio

Foundries that don’t carry out a periodic review of burner calibration in their melting furnaces may regret it. Why? Because excess air is one of the most common contributors to increased gas consumption by melting furnaces, often caused by unbalanced air-to-gas ratios.

The ideal goal for any foundry is to ensure gas burns with minimum excess air – this level is known as a "near-stoichiometric air-to-gas ratio". As well as reducing gas costs (up to 2% compared to a burner with too much air surplus), maintaining a near-stoichiometric air-to-fuel ratio will help reduce metal oxidation that can lead to scrap (which ultimately also results in increased energy consumption).

 

Checking burner calibration takes relatively little time yet doing so could potentially result in using approximately seven kilowatt hours less energy per ton of metal.

5) Porous plugs: cut post-treatment time

Integrating porous plugs into melting and/or dosing furnaces is a well-known measure for improving the metallurgical quality of melt. Purge gas (usually nitrogen N2) releases hydrogen dissolved in the liquid aluminium, thus reducing the density index of the melt to improve quality.

What might be less obvious is that this is another great way to cut gas consumption quickly. Improving the melt quality within the furnace can strongly reduce the time required for a separate treatment stage for the melt. Reducing treatment time means reducing energy loss, due to which the temperature in the melting furnace can be lowered (as melt does not need to be heated to a higher temperature to compensate for cooling).

 

There may well be other opportunities for reducing furnace/melt temperature. For instance, it is worth looking at lower temperature settings for weekend holding periods as this could result in significant gas savings.

These are just a few relatively ‘quick fix’ solutions for minimizing gas consumption. For a more detailed look at potential opportunities, download our energy saving guide.

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