Where a Steel Re-Rolling Mill Loses Money: Scale, Fuel, Misrolls and the Hot Idle Furnace (₹ per Tonne, India)
Where does a steel re-rolling mill lose money? Mostly in steel, not minutes. A 2007 UNDP/GEF review for the Government of India put scale loss in conventional furnaces at 2–2.5% and fuel at 42–45 litres per tonne. On an illustrative 150-tonne-a-day TMT mill, avoidable leaks total about ₹1,200 per finished tonne (as of 17 Oct 2026).
By the Mama Editorial Team. Last checked: 17 Oct 2026. This is an owner's map for mid-size re-rolling mills that buy billets or ingots and roll TMT bars, rounds, angles or flats, the kind found around Mandi Gobindgarh, Raipur and Jalna. Every ₹ figure in the worked example is either sourced or labelled as an assumption you should replace with your own invoice.
Key takeaways
- Scale is the biggest leak, and it is steel you paid for. The 2007 UNDP/GEF review recorded scale loss of 2–2.5% in conventional pusher furnaces, and said a new energy-efficient pusher furnace reduced it by 1–1.5%. At an assumed ₹45,000 per tonne of billet, one point of scale is about ₹450 on every tonne you sell.
- Fuel per tonne is the second leak. The same review put conventional furnaces at 42–45 litres of fuel oil per tonne, and said a full revamp of an existing pusher furnace saves 4–5 litres per tonne. Your own litres per tonne, read every week, matters more than any brochure.
- A hot furnace with a stopped mill burns money twice. It burns fuel with nothing rolled, and the billets soaking inside grow more scale. Cobbles, roll changes and power trips all create this state.
- Misrolls and end cuts turn billet into scrap. Each kilogram of misroll or crop goes back at scrap value after you paid billet price and reheating for it.
- A camera sees time, not kilograms. It shows whether billets are leaving the furnace, when a cobble stopped the stands, and how long a roll change really took. Scale, fuel and bar weight belong to the weighbridge, the fuel meter and the energy meter.
Why re-rollers feel every rupee
India's induction-furnace steel route is growing fast. Per JPC data in the Ministry of Steel's Annual Report 2025-26, induction furnaces made 38.2% of India's crude steel in 2024-25 (58.08 million tonnes), up from 28.1% in 2020-21. The Ministry lists re-rolling mills as a segment of the secondary sector alongside induction and arc furnaces (Rajya Sabha reply, 28 March 2022).
The UNDP/GEF mid-term review of "Energy Efficiency in Steel Re-Rolling Mills" (8 August 2007) estimated energy at 15–25% of a re-roller's production cost. That review is nearly two decades old, so treat it as the shape of the problem, not today's price.
Leak 1: Scale loss in the reheating furnace
Every billet comes out of the furnace lighter: the surface oxidises into mill scale. You bought that steel at billet price.
The 2007 UNDP/GEF review recorded scale loss "around 2–2.5%" in conventional fuel-oil pusher furnaces and 2–4% in lump-coal-fired systems, where furnace temperature is harder to control. It said a new energy-efficient pusher furnace brings a scale-loss reduction of 1–1.5%, and walking-hearth furnaces run at 0.6–0.8%.
Scale grows with time and temperature. Billets that sit in the hot zone while the mill waits for a roll change or clears a cobble keep oxidising. That is why scale and mill stoppages are the same problem seen from two ends.
You measure scale with a weighbridge, not by eye. Weigh billets charged and bars dispatched for a week, add misroll, crop and short lengths, and the gap is your burning loss. Most owners know their "yield %"; fewer split it into scale, misroll and crop, which is where the fixes differ.
Leak 2: Furnace fuel per tonne
The same 2007 review put conventional furnaces at 42–45 litres of fuel oil per tonne. It listed recuperators, automatic zone-temperature and furnace-pressure control (3–4 litres per tonne) and better lining among the fixes, and said a complete revamp of an existing pusher furnace saves 4–5 litres per tonne.
Coal and producer-gas furnaces have their own numbers, but the useful measure is the same: fuel issued to the furnace divided by good tonnes rolled, every week.
Fuel per tonne rises when throughput falls, because burners hold temperature either way. Price your own trend with the energy per unit calculator.
Leak 3: The furnace is hot and the mill is stopped
This is the leak an owner can see: burners firing, discharge door shut, nothing moving at the stands.
Common causes are a cobble being cut out, a roll or guide change, a bearing failure, a busy crane, billets not ready at the charging end, and a grid trip. Each is logged as "mill down". Few registers show how long the furnace held temperature, or how much billet was soaking inside.
Grid trips matter more in some months than others. In April 2026, PSPCL imposed 8 to 10-hour outages in parts of Punjab, with power off from 9 am to 5 pm in many areas of Ludhiana (ETV Bharat, 22 Apr 2026). Our power cuts and DG set guide prices what idle hours cost a Punjab plant.
Leak 4: Misrolls and cobbles
A cobble is a bar that leaves the pass line and jams the mill. It is cut out and sold as scrap while the furnace holds.
IspatGuru, a trade reference site, ties misroll generation in re-rolling mills to power failures and to a drop in bar temperature (IspatGuru, 1 June 2017). That puts most misrolls at the joint between the furnace and the mill, not in the stands alone.
Each misroll costs billet price minus scrap value, the reheating already spent, and the minutes of a stopped mill.
Leak 5: End cuts, crop and short lengths
Every bar is cropped at the head and tail, and every customer length leaves an off-cut. The 2007 UNDP/GEF review listed crop-length optimisation (better roller guides, spindles and couplings, roller and tilting tables) and computerised roll pass design among the mill-side fixes, with a payback of around half a year.
Short lengths sell at a discount or go back as scrap. Count the crop bin and the short-length rack per shift; they tell you more than the month-end yield figure.
Leak 6: Roll and size changes
A size change on a TMT mill means changing rolls, guides and sometimes stands, then rolling trial bars until the section is right. The register says "size change, 1 hour 15 minutes". It rarely says how much of that was waiting for the roll shop, the crane or the fitter.
Keep the next rolls and guides ready at the stand, and time the change from the last good bar of the old size to the first good bar of the new one. Price the minutes with your own downtime cost.
Leak 7: Mill electricity per tonne
Mill motors, cooling pumps and compressors draw power whether or not steel moves. For FY 2026-27, PSERC set Punjab's tariffs from 1 April 2026 and reported an average cost of supply of ₹6.15/kWh (Mercom, 10 March 2026). PTI reported industrial rates cut by up to 74 paise per unit, with energy charges not raised (The Federal, 6 March 2026).
In Chhattisgarh, the CSERC tariff order for FY 2026-27 was passed on 15 June 2026. Mercom reported an average increase of 6.23% across categories (Mercom, 16 June 2026). Steel plants there are billed under a separate "HV-4 Steel Industries" category (SolarQuarter on CSERC Petition No. 55 of 2025, 27 Feb 2026). Read your category's rate off your own bill; how one demand spike raises the cost of every tonne is in power bill up, output flat.
The ₹ map: an illustrative 150-tonne-a-day TMT mill
Assume a mill rolling 150 tonnes of finished bar a day over 20 rolling hours (7.5 t/h), 26 days a month, so 3,900 t a month, from bought billets in a fuel-oil pusher furnace.
Assume billet costs ₹45,000/t landed, misroll and crop sell at ₹30,000/t, mill scale fetches nothing worth counting, furnace oil costs ₹55/litre, power costs ₹7.50/kWh all-in, and a fully loaded mill crew costs ₹4,000 per mill-hour. Replace each with your own invoice. For wages, use your state's current minimum-wage notification for your trade; most states revise the DA part twice a year, and our crew figure is illustrative.
Assume the furnace holds temperature at about 150 litres an hour while the mill is stopped, roughly half its firing rate at full output. That too is an assumption; your fuel meter gives the real figure.
| Leak | Assumption | ₹ per finished tonne | ₹ per month (3,900 t) |
|---|---|---|---|
| Scale loss above achievable | 2.5% vs 1.5%: 10 kg/t × ₹45/kg | ₹450 | ₹17.55 lakh |
| Furnace fuel above achievable | 44 vs 39 L/t: 5 L × ₹55 | ₹275 | ₹10.73 lakh |
| Misrolls and cobbles | 1.5% vs 0.5%: 10 kg/t × (₹45 − ₹30)/kg | ₹150 | ₹5.85 lakh |
| Hot furnace, mill stopped | 1.5 h/day: 225 L × ₹55 + crew 1.5 h × ₹4,000 | ₹123 | ₹4.80 lakh |
| End cuts and short lengths | 2.0% vs 1.2%: 8 kg/t × ₹15/kg | ₹120 | ₹4.68 lakh |
| Slow roll and size changes | 1 change/day, 30 min over target: 75 L fuel + 0.5 h crew | ₹41 | ₹1.60 lakh |
| Mill power drift | 5 kWh/t above your best month × ₹7.50 | ₹38 | ₹1.48 lakh |
| Total, mill not sold out | ≈ ₹1,197 | ≈ ₹46.7 lakh | |
| Add if sold out: lost tonnes | 2 h/day of stops × 7.5 t/h × ₹3,000/t margin | ₹300 | ₹11.70 lakh |
| Total, mill sold out | ≈ ₹1,497 | ≈ ₹58.4 lakh |
Read the shape, not the total. Scale and fuel make up about 60% of the leak, and both are read on the weighbridge and the fuel meter, not on video. The hot-idle furnace and slow changes look small, but they also feed the scale line.
The ₹3,000 margin per tonne is an assumption for a mill that could have sold the extra tonnes. If your order book is thin, leave that row out; in that case the lost hours cost you fuel, power and crew, not sales.
A re-rolling mill on camera: what shows up and what does not
Can see, reliably enough to be useful:
- Whether billets are leaving the furnace. A camera on the discharge door gives true rolling time, every stop, and the hours the furnace was hot with nothing discharged.
- Cobbles at the stands. When the mill stopped, how long the cut-out took, how often by shift and size.
- Roll and size changes, end to end. Last good bar of the old size, crane and fitters arriving, first good bar of the new size.
- The crop bin and short-length rack. How fast they fill, by shift.
Out of a camera's reach, whatever a vendor claims:
- Scale loss and yield. That is the weighbridge: billets in, bars and scrap out.
- Fuel and kWh per tonne. Only the fuel meter and the energy meter measure them.
- Billet and bar temperature. That needs a pyrometer.
- Bar weight per metre and grade. That is the QC bench and the lab.
Two people points. Cameras in a mill should count what happens to the furnace and the stands, not rank operators. Footage of recognisable workers is personal data under s.2(t) of the DPDP Act, 2023; before installing, tell workers in writing what is recorded and why (see the worker CCTV notice under DPDP).
Our pipe extrusion plant leak map makes the same argument for another continuous process: material lost per tonne usually outweighs minutes lost.
Where Mama fits
Mama reads the cameras a mill already has, or a few added at the furnace discharge, the stands and the cooling bed, and every morning sends the owner a short note in plain language. The note says how long the furnace stood hot with no billet discharged, how many cobbles stopped the mill and for how long, and how yesterday's size change compared with the usual. It watches the furnace and the mill, not individual workers, and leaves kilograms and litres to your weighbridge and meters. Leave an email or phone in the form below.
FAQ
Is downtime the biggest loss in a steel re-rolling mill? Usually not: the bigger loss is steel lost as scale. The 2007 UNDP/GEF review put scale loss in conventional pusher furnaces at 2–2.5% and said a new energy-efficient furnace reduced it by 1–1.5%. In our illustrative model, avoidable scale is ₹450 of a ₹1,197 per-tonne leak.
How much fuel should a re-rolling furnace use per tonne? The 2007 UNDP/GEF review recorded 42–45 litres of fuel oil per tonne in conventional furnaces and savings of 4–5 litres per tonne from a full revamp of an existing pusher furnace. Track your own litres per good tonne weekly.
Can a camera measure yield or scale loss? No. Yield and scale come from the weighbridge. A camera helps with the time-based leaks: hot idle furnace, cobbles, slow size changes.
What causes most misrolls in a re-rolling mill? IspatGuru (1 June 2017) ties them to power failures and a drop in bar temperature, so the furnace and the grid matter as much as the stands. Count misrolls by shift and size first.