In late 2023, I received a call from a die casting plant manager in Hai Phong, Vietnam. His plant supplies aluminium components to Japanese and Korean automotive customers. His energy bill had risen 35% in two years. He told me: “Our customers will not accept a price increase. We need to cut energy, but we cannot afford new furnaces.”
I spent four days on site. We did not buy new furnaces. We optimised what was already there. By the end of the following month, their energy consumption per tonne had dropped by 27%. The total investment was less than $9,000. The payback period was just over three weeks.
This is how we did it.
The Starting Point: Energy Consumption at 1,080 kWh/t
The plant operates two gas-fired reverberatory furnaces, each with a capacity of 2.5 tonnes. They melt around 14 tonnes per day of ADC12 for die casting. The furnaces run two shifts per day, six days per week.
When I arrived, the furnaces were consuming an average of 1,080 kWh per tonne of aluminium melted. That is typical for a legacy gas-fired reverb furnace, but well above the modern benchmark of 550–650 kWh/t.
I measured four things first:
| Measurement | Reading | Normal Range |
|---|---|---|
| Flue gas oxygen | 8.4% | 2–4% |
| Flue gas temperature | 910°C | 300–400°C after recuperator |
| Furnace shell temperature | 175°C (hot spots) | Below 120°C |
| Door seal condition | Worn flat | Sealed |
The plant manager admitted they had no maintenance schedule. The burners had not been tuned in over two years. The recuperator had never been cleaned. The door seals were original — 7 years old.
I told him: “Your furnaces are not broken. They are neglected. We can fix this without buying new equipment.”
Step 1: Burner Tuning — The Biggest Single Win
The burners were running with 8.4% oxygen. The ideal range is 2–4%. Too much excess air means you are heating nitrogen instead of aluminium. Every 1% reduction in O₂ saves roughly 2–3% of fuel.
We borrowed a portable flue gas analyser and spent a full day tuning both burners. We:
Cleaned the burner nozzles (they were partially clogged with carbon)
Adjusted the air dampers
Re-set the gas pressure regulators
Checked the flame shape and colour
The result: O₂ dropped to 3.1%. CO stayed below 25 ppm. Flame colour changed from yellow to a crisp blue.
That single change reduced gas consumption by 13%.
I have written a detailed guide on how to optimise burner efficiency. The principles are simple: measure, adjust, verify.
Step 2: Clean the Recuperator — The Forgotten Asset
The flue gas was leaving the recuperator at 910°C. That is money going up the stack.
We inspected the recuperator. It was partially blocked with soot and dust. The foundry had never cleaned it. We removed the access panels and cleaned the tubes with a brush and compressed air.
We also found a leaking gasket on the recuperator inlet. We replaced it for $60.
After cleaning, the combustion air preheat temperature rose from 170°C to 350°C. Every 100°C of preheat improves efficiency by about 5%. That gave us another 8% energy saving.
The total cost for this step: $60 for the gasket, plus one day of maintenance labour.
I have written about heat recovery in my guide on burner efficiency. It is often overlooked. Do not overlook it.
Step 3: Fix Door Seals and Lining Hot Spots
The furnaces had two main heat leaks:
Door seals: Worn flat. We could feel hot air escaping. Replacing them cost $320 per furnace.
Refractory hot spots: The shell was 175°C in two areas. We applied a refractory coating to the affected zones. Cost: $850 total.
These fixes reduced heat loss by another 3%. They also made the working environment safer.
A thermal camera is invaluable for this. If you do not have one, borrow one. The hot spots you find will pay for the effort.
Step 4: Change Operating Practice — Free Savings
The operators were making three mistakes:
Charging wet scrap. They stored scrap outdoors. After rain, they charged it wet. Moisture absorbs heat and increases oxidation.
Overcharging. They filled the furnace to 95% capacity. The burner could not melt efficiently.
Holding metal overnight at 750°C. They melted on Friday and held until Monday.
We changed these practices:
Built a simple drying rack under a roof. Scrap dries before charging.
Reduced charge to 80% of capacity. Melt time dropped, and oxidation loss fell.
Adjusted the schedule: melt on Sunday evening for Monday start. Holding temperature reduced to 700°C.
These changes cost almost nothing. They saved another 3% in energy and reduced metal loss by 0.7%.
I have written about reducing oxidation loss. It is often the hidden cost that nobody measures.
Step 5: Install Simple Monitoring
We installed a gas flow meter and a temperature logger on each furnace. The cost was $500 per furnace.
Now the plant manager can see daily gas consumption per tonne. If it rises, he knows something is wrong. He can call me before the problem gets worse.
Data is not a luxury. It is the foundation of control.
The Results After One Month
| Metric | Before | After | Improvement |
|---|---|---|---|
| Energy consumption | 1,080 kWh/t | 788 kWh/t | 27% reduction |
| Flue gas O₂ | 8.4% | 3.1% | Optimised |
| Metal oxidation loss | 3.3% | 2.4% | 0.9% reduction |
| Annual energy cost (14 t/day) | $498,000 | $364,000 | $134,000 saved |
| Investment | — | $8,700 | Payback: 3.3 weeks |
The plant manager was shocked. He had been told he needed new furnaces. He didn’t. He needed someone to look at the details.
What I Learned — And What You Can Apply
This case is not unique. I have seen similar results in China, Malaysia, Thailand, India, and the UK. The pattern is always the same:
Most furnaces are running with too much excess air. Tune the burner first. It is the cheapest and biggest win.
Waste heat is free money. Clean the recuperator. It pays for itself in weeks.
Small leaks add up. Door seals, lining cracks, and open doors waste more than you think.
Operating habits matter. Wet scrap, overcharging, and unnecessary holding are common and costly.
Measure everything. You cannot improve what you do not measure.
I wrote a detailed guide on how to optimise burner efficiency and a furnace maintenance checklist. If you follow those, you will capture most of these savings yourself.
When to Call an Expert
You can do much of this work yourself. But sometimes an experienced eye finds things you miss. The plant in Vietnam had a maintenance team. They were competent. But they had never been trained on combustion analysis or thermal imaging.
I spent four days on site. The fee was less than 7% of the annual savings. That is a good return.
If your energy bills are rising, and you have not tuned your burners in the last six months, call someone. Or buy a flue gas analyser and learn to do it yourself. Either way, do not wait.
Final Thoughts
Cutting energy costs by 27% did not require new furnaces. It required attention to detail, a few inexpensive parts, and a willingness to change habits.
In my 25 years, I have seen this pattern repeat in foundries across the world. The biggest savings are often hiding in plain sight — in the burner, in the flue, in the door seal, in the charging practice.
If you run a die casting plant, start with the burner. Then clean the recuperator. Then fix the leaks. Then train the operators. You will see the difference in your first gas bill.
Internal links: How to Optimize Burner Efficiency in Gas-Fired Aluminium Furnaces, Furnace Maintenance Checklist, How to Reduce Oxidation Loss in Aluminium Melting Operations, Why Is My Furnace Consuming More Gas than Usual?, Case Study – How a Chinese Expert Cut Energy Costs by 22% in a Shanghai Foundry.
About the Author: Hu Shenyue is a veteran aluminium melting furnace expert with 25 years of hands-on experience in China, Southeast Asia, India, the UK, and Europe. He writes practical, experience-based content on furnace selection, maintenance, and optimisation at SmeltPro.
