BIZOMAT MAKEOS · Materials
Melting Furnace Batch Plan (Energy, Melt Time, Melts per Shift, Cost)
How long does each melt take in this furnace, how many melts and how much metal can I get per shift, and what does the energy cost per kilogram?
Plan of a batch melting furnace: heat to raise the charge to its melting point, melt it and superheat to pouring temperature, energy drawn at the furnace efficiency and melt time at its power (as the melting energy tool), the cycle with charging and tapping time, melts and metal per shift against the demand, energy per tonne and energy cost per kilogram.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Charge per melt | kg | Mass of metal charged per melt. |
| Charge temperature | °C | Temperature of the charge. |
| Melting point | °C | Melting point (or liquidus) of the alloy. |
| Pouring temperature | °C | Temperature at which the metal is tapped and poured. |
| Solid specific heat | kJ/kg·K | Mean specific heat of the solid. |
| Latent heat of fusion | kJ/kg | Latent heat of fusion of the alloy. |
| Liquid specific heat | kJ/kg·K | Specific heat of the liquid. |
| Furnace power | kW | Power input of the furnace. |
| Furnace efficiency | % | Share of input energy that goes into the metal. |
| Energy price | $/kWh | Price of the energy. |
| Charging and tapping time per melt | min | Time per melt for charging, skimming, sampling and tapping. |
| Hours per shift | h | Length of a shift. |
| Metal needed per shift | kg | Molten metal the moulding line needs per shift. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Charge per melt
- What it is
- The mass of solid metal (ingot, returns and scrap) loaded into the furnace for one melt and tapped as one batch.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 1000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 500 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Energy and melt time per melt rise in proportion to it; energy per tonne and cost per kilogram do not change.
- Get it right
- Weigh the actual charge; a furnace often runs below its rated capacity.
What this means: Charge temperature
- What it is
- The temperature of the charge as it goes into the furnace: workshop temperature for cold scrap and ingot, or higher if the charge is preheated.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -30 °C to 2000 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A warmer charge needs less heat to reach the melting point, so melt time and cost fall.
- Get it right
- It must not be above the melting point, or the tool stops.
What this means: Melting point
- What it is
- The temperature at which the alloy becomes fully liquid. For an alloy that melts over a range, use the liquidus from the material data.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts 0.000001 °C to 3500 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 660 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It must lie between the charge temperature and the pouring temperature.
What this means: Pouring temperature
- What it is
- The temperature the metal is heated to before tapping and pouring. The rise above the melting point is the superheat, heated at the liquid specific heat.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts 0.000001 °C to 3500 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 720 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher pouring temperature adds superheat energy, so each melt takes longer and costs more.
- Get it right
- Use the tapping temperature in the furnace, not the lower temperature measured in the mould.
What this means: Solid specific heat
- What it is
- The average heat needed to warm one kilogram of the solid alloy by one degree, between the charge temperature and the melting point. Take it from the alloy data.
- Units and format
- Enter a number in kJ/kg·K: kilojoules per kilogram per kelvin. The form accepts 0.000001 kJ/kg·K to 5 kJ/kg·K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.9 kJ/kg·K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Data in J/kg·K must be divided by 1000 to give kJ/kg·K.
What this means: Latent heat of fusion
- What it is
- The heat absorbed by one kilogram of the alloy as it changes from solid to liquid at the melting point, with no rise in temperature. Take it from the alloy data.
- Units and format
- Enter a number in kJ/kg: kJ/kg. The form accepts 0.000001 kJ/kg to 5000 kJ/kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 397 kJ/kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Data in J/kg must be divided by 1000 to give kJ/kg.
What this means: Liquid specific heat
- What it is
- The average heat needed to warm one kilogram of the molten alloy by one degree. The tool uses it for the superheat from melting point to pouring temperature.
- Units and format
- Enter a number in kJ/kg·K: kilojoules per kilogram per kelvin. The form accepts 0.000001 kJ/kg·K to 5 kJ/kg·K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.18 kJ/kg·K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- It differs from the solid value; do not reuse the solid specific heat.
What this means: Furnace power
- What it is
- The power the furnace draws from its supply while melting. Together with efficiency it sets how fast heat reaches the metal.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 100000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Melt time is inversely proportional to power; energy per melt does not change.
- Get it right
- If the furnace runs below its nameplate rating, use the power it actually draws.
What this means: Furnace efficiency
- What it is
- The share of the energy drawn by the furnace that ends up as heat in the metal; the rest is lost through the lining, cooling water, lid and off-gas.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 5% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Energy drawn is the heat needed divided by efficiency, so a lower efficiency raises energy, melt time and cost.
- Get it right
- Type the percentage itself, not a fraction. Measured meter readings over several melts give the best value.
What this means: Energy price
- What it is
- What you pay for each kilowatt-hour of energy delivered to the furnace, including any usage-based charges on your bill.
- Units and format
- Enter a number in $/kWh: money per kilowatt-hour. The form accepts $0/kWh to $10/kWh. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with $0.25/kWh as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Energy cost per kilogram rises in direct proportion to the price.
What this means: Charging and tapping time per melt
- What it is
- The time in each cycle when the furnace is not melting: charging, skimming, sampling and tapping. It is added to the melt time to give the cycle.
- Units and format
- Enter a number in min: minutes. The form accepts 0 min to 600 min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer handling time lengthens each cycle and can reduce the number of melts per shift.
- Get it right
- Type minutes, not hours.
What this means: Hours per shift
- What it is
- The length of the shift the furnace runs in. The tool counts only the complete melt cycles that fit into it.
- Units and format
- Enter a number in h: hours. The form accepts 0.000001 h to 24 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Melts per shift are the whole number of cycles that fit, so the result rises in steps.
- Get it right
- If the furnace stops for breaks or start-up, use only the hours it actually melts.
What this means: Metal needed per shift
- What it is
- The mass of molten metal the moulding or casting line needs from the furnace in one shift. It is compared with the metal the furnace can deliver.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0 kg to 10000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Include the metal for runners, risers and losses, not just the casting weight.
Method and formulas
- Q = m [c_s (T_m − T₀) + L + c_l (T_p − T_m)]; energy drawn = Q ÷ efficiency; melt time = drawn ÷ power (as the melting energy tool).
- Cycle = melt time + charge and tap time; melts per shift = ⌊shift ÷ cycle⌋; metal per shift = melts × charge.
- Energy per tonne = drawn ÷ mass × 1000; cost per kilogram = drawn × price ÷ mass.
- Example: each 500 kg melt takes 57.989 min; 6 melts give 3,000 kg a shift at 0.12081 per kg.
Limitations
- Average properties; holding losses between melts and slag are not included.
- Furnace efficiency varies with lining condition and charge make-up.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Plan a foundry’s daily melting
- Check whether a furnace can meet a casting schedule
- Estimate melting energy cost per kilogram
Who it is for
- Foundry engineers
- Production planners
- Energy managers
What you get
- Energy into the metal and drawn from the supply
- Melt time, cycle and melts per shift
- Metal per shift, energy per tonne and cost per kilogram
Interpreting the result
- Charging and tapping time often limits output more than melting power: keep it short.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 371–374, 1404–1420. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Melting: energy, time and cost
In Metal Casting by the Numbers
What it covers: How much energy, time and money each melt takes: the heat balance of a charge, furnace efficiency, the melting cycle with charging and tapping, metal per shift, and energy per casting.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Melting Furnace Batch Plan (Energy, Melt Time, Melts per Shift, Cost) calculator