Case Study – How a Chinese Expert Helped a European Recycler Reduce Melt Loss

How a Chinese expert helped a European aluminium recycler cut melt loss from 9.2% to 4.6%. Temperature, salt flux, skimming, burner tuning, and training.

In late 2023, I received an email from a recycling plant manager in northern Spain. His company processes mixed aluminium scrap into ADC12 ingots for European die casters. His melt loss had risen to 9.2%. That meant 9.2% of every tonne of scrap was going to dross, salt slag, or oxidation. With 8,000 tonnes per year of throughput, he was losing 736 tonnes of metal. At €2,200 per tonne, that was €1.6 million per year.

He told me: “We have tried changing the salt. We have tried new skimming tools. We have tried training the operators. Nothing works. Our energy costs are rising. Our carbon footprint is under scrutiny. We need help.”

I flew to Spain the following week. I spent five days on site. We did not buy a new furnace. We optimised the process. By the end of the following month, melt loss had dropped to 4.6%. Metal recovery improved from 86% to 93.2%. Energy consumption fell by 16%. The annual saving was over €950,000.

This is how we did it.

The Starting Point: 9.2% Melt Loss

The plant operates two tilting rotary furnaces, each with a capacity of 5 tonnes. They feed a central holding furnace and an ingot casting line. They melt around 8,000 tonnes per year of mixed scrap — UBC, extrusion offcuts, turnings, and post-consumer material. The plant runs two shifts per day, five days per week.

The problems were visible from the first day:

The plant manager admitted they had no formal maintenance schedule. The burners had not been tuned in over two years. The recuperator had never been cleaned. The door seals were original — 8 years old.

I told him: “Your furnaces are not broken. They are neglected. We can fix this without buying new equipment.”

Step 1: Diagnosing the Root Cause

I started with a full process audit. The findings were revealing.

Temperature. The furnaces were set to 790°C. For ADC12, the recommended melt temperature is 700–730°C. Every 10°C above 750°C increases oxidation loss by 5–10%. Running 60°C too hot was the single biggest cause of melt loss.

Salt flux. The salt factor was 1.4. For a tilting rotary furnace, the salt factor can be as low as 0.4–0.8. They were using more than double the necessary salt. That increased slag volume and metal entrapment.

Skimming. Operators were skimming every 20 minutes. Each skim removed a thick layer of dross, and that dross contained 48% metal. They were literally throwing away metal with every skim.

Burner and heat recovery. The burners were running at 8.6% oxygen. Too much excess air. The flame was lazy and yellow. The recuperator was partially blocked with soot and dust. Flue gas was leaving at 920°C.

Atmosphere. The furnace door seals were worn flat. We could feel hot air escaping. Cold air was entering, causing thermal shock and increasing oxidation.

Scrap storage. Scrap was stored outdoors. After rain, it was charged wet. Moisture causes steam explosions, thermal shock, and hydrogen pickup. It also increases oxidation loss.

The root cause was clear: the furnaces were running too hot, skimming too often, using too much salt, and charging wet scrap. All four could be fixed without new equipment.

Step 2: Lower Melt Temperature

We lowered the furnace setpoint from 790°C to 720°C. The operators were sceptical. They thought melt time would increase.

It did not. Because we also tuned the burner. The burner was running with 8.6% oxygen. We adjusted it to 3.1%. The flame became shorter and more intense. Melt time actually decreased by 10 minutes per cycle.

The lower temperature reduced oxidation loss immediately. The dross metal content began to fall.

I have written about how to reduce metal loss in secondary aluminium melting for ingot production. The principles apply to every furnace and every alloy.

Step 3: Optimise Salt Flux

We reduced the salt factor from 1.4 to 0.7. The tilting rotary furnace can handle a lower salt factor because the tilting action mixes the salt and metal more efficiently.

We also changed the flux composition

The higher cryolite content helps strip oxides from the metal surface and reduces the viscosity of the slag. The lower NaCl and KCl content reduces chemical attack on the refractory.

The result: salt consumption dropped by 50%. Salt slag volume dropped by 35%. Metal recovery improved because less metal was trapped in the slag.

Step 4: Change Skimming Practice

We changed the skimming frequency from every 20 minutes to every 45 minutes. We also changed the skimming tool. Instead of a solid rake, we used a perforated skimming tool that drains metal back into the furnace.

The operators were resistant at first. They thought more dross would build up. But the dross layer stabilised. The furnace ran cleaner. And the metal content in the dross dropped from 48% to 26%.

We also installed a dross press. The press squeezes residual metal from the dross. That metal goes back into the furnace. The dross press cost €18,000. It paid for itself in three weeks.

Step 5: Tune the Burner and Recover Heat

We tuned the burner to 3.1% oxygen. We cleaned the recuperator, which had not been cleaned in two years. Combustion air preheat rose from 160°C to 340°C.

The result: gas consumption dropped by 16%. The furnace reached setpoint faster. The lower oxygen level reduced oxidation.

We also installed a simple oxygen trim system. The cost was €6,500. The payback was under two months.

I have written about how to optimise burner efficiency in gas-fired aluminium furnaces. The principles are simple: measure, adjust, verify.

Step 6: Fix Door Seals and Atmosphere

The furnace door seals were worn flat. We replaced them with high-temperature ceramic fibre seals. Cost: €450 per furnace.

We also checked the furnace shell for hot spots. Thermal imaging showed two areas at 170°C. We applied a refractory coating to the affected zones. Cost: €1,200 total.

These fixes reduced heat loss by another 3%. They also made the working environment safer.

Step 7: Pre-Dry Scrap

We built a covered drying rack next to the furnace. Scrap is now stored under cover and pre-dried before charging. We also installed a simple scrap preheater using waste heat from the furnace exhaust. The preheater raises scrap temperature to 200–250°C, driving off moisture.

The result: no more wet charging. No more steam explosions. Less hydrogen pickup. Less oxidation.

I have written about how to improve heat transfer efficiency in a rotary furnace. The principles apply to preheating as well.

Step 8: Train Operators and Measure Everything

We trained all operators on the new procedures:

• Target melt temperature: 720°C
• Skimming frequency: every 45 minutes
• Salt factor: 0.7
• Scrap must be dry before charging
• Burner oxygen: 3.1%

We also started measuring metal recovery every day. We weigh the metal charged and the metal poured. We weigh the dross and estimate metal content. We track recovery per shift.

The operators now see the results of their work. When recovery goes up, they know why. When it goes down, they know what to check.

The Results After One Month

The plant manager was stunned. He had been ready to buy a new furnace. He didn’t need one. He needed to fix the process.

What Made the Difference

Three things drove the improvement:

1. Lower melt temperature. Reducing from 790°C to 720°C cut oxidation loss immediately. This was the single biggest win.

2. Better skimming practice. Skimming less often and using a dross press recovered metal that was previously thrown away.

3. Lower salt factor. Reducing salt consumption from 1.4 to 0.7 reduced slag volume and metal entrapment.

I have written about how to reduce metal loss in secondary aluminium melting and how to choose a secondary aluminium melting furnace. Both are directly relevant to this case.

What You Can Apply

If you operate an aluminium recycling plant, ask yourself these questions:

• What is your melt temperature? If it is above 730°C for ADC12, you are losing metal.
• How often do you skim? If it is more than every 30 minutes, you are losing metal.
• What is the metal content of your dross? If it is above 30%, you are losing money.
• What is your salt factor? If it is above 0.8 for a tilting rotary furnace, you are using too much salt.
• Is your scrap dry? If it is stored outdoors, it is wet.
• When did you last tune your burner? If it was more than six months ago, you are wasting gas.

These are not theoretical. They are the minimum requirements for efficient secondary aluminium melting. I have seen plants in China, Malaysia, Vietnam, and now Spain fail because they ignored one of these.

When to Call an Expert

You can measure these things yourself. A pyrometer, a scale, and a stopwatch will tell you most of what you need to know. But sometimes an experienced eye sees the system, not just the components.

The Spanish plant had a competent maintenance team. They had kept the furnaces running for years. But they had never been trained on metal balance or salt factor optimisation. They did not know what they did not know.

My fee for the five-day audit and commissioning support was €14,000. The annual saving was €955,000. That is a 68x return.

If your metal recovery is below 88%, or your dross metal content is above 30%, call someone. Or use the checklists on this blog. Either way, do not wait.

Final Thoughts

Improving metal recovery in a European aluminium recycling plant is not about buying a new furnace. It is about controlling temperature, skimming practice, salt flux, and charge moisture.

In my 25 years, I have seen plants recover millions by making small changes to their process. The furnace did not change. The people did.

If you run a recycling plant, start by measuring your metal recovery and dross metal content. If either is out of specification, fix it. You will see the difference in your profit.

Internal links: How to Reduce Metal Loss in Secondary Aluminium Melting for Ingot Production, How to Improve Heat Transfer Efficiency in a Rotary Furnace,  How to Optimize Burner Efficiency in Gas-Fired Aluminium Furnaces.