BIZOMAT MAKEOS · Materials
Energy and Time to Melt Metal
How much energy and time does it take to melt and superheat this charge of metal?
Energy to heat a metal charge to its melting point, melt it and superheat the liquid to the pouring temperature, and the melting time and energy cost at a furnace power and efficiency.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Charge mass | kg | Mass of metal charged. |
| Starting temperature | °C | Temperature of the charge when loaded. |
| Melting point | °C | Melting point (or liquidus) of the alloy. |
| Pouring temperature | °C | Temperature to which the liquid is superheated before pouring. |
| Specific heat of solid | kJ/(kg·K) | Average specific heat of the solid over the range (aluminium about 0.9, steel about 0.65, copper about 0.39 kJ/kg·K). |
| Latent heat of fusion | kJ/kg | Latent heat of fusion (aluminium 397, iron about 270, copper about 205 kJ/kg). |
| Specific heat of liquid | kJ/(kg·K) | Specific heat of the liquid metal. |
| Furnace power | kW | Furnace rated power. |
| Furnace efficiency | % | Share of furnace energy that reaches the metal (induction about 55–75%, fuel-fired lower). |
| Energy price | AUD/kWh | Energy price per kWh (or equivalent fuel cost). |
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 mass
- What it is
- The total mass of metal loaded into the furnace for one melt, including returns and scrap in the charge.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000000 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, time and cost all rise in direct proportion to the charge mass.
What this means: Starting temperature
- What it is
- The temperature of the charge when it goes into the furnace, usually the shop or storage temperature unless it is preheated.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -50 °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.
- Get it right
- Preheated or hot-returned charge needs less energy; use its real temperature.
What this means: Melting point
- What it is
- The temperature at which the alloy becomes fully liquid (the liquidus for alloys that melt over a range), from the alloy data sheet.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts 0 °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 starting and pouring temperatures, or the tool rejects the inputs.
What this means: Pouring temperature
- What it is
- The temperature the liquid metal is raised to before it is poured, set by the foundry practice for the casting.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts 0 °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.
- Get it right
- Superheat costs energy; it must be at or above the melting point.
What this means: Specific heat of solid
- What it is
- The average heat needed to raise one kilogram of the solid metal by one degree, over the range from the starting temperature to the melting point, from 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 10 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
- Enter kJ per kg per kelvin, not J; a value given in J/(kg·K) must be divided by 1000.
What this means: Latent heat of fusion
- What it is
- The heat needed to turn one kilogram of the alloy from solid to liquid at its melting point without changing its temperature, from 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
- Use the latent heat for the actual alloy; tables for pure metals may differ.
What this means: Specific heat of liquid
- What it is
- The average heat needed to raise one kilogram of the liquid metal by one degree, used for the superheat from the melting point to the 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 10 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; take it from the same alloy data source.
What this means: Furnace power
- What it is
- The power the furnace draws from its supply while melting, normally its rated input power.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 1000000 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
- Melting time is inversely proportional to furnace power; energy used is not affected.
What this means: Furnace efficiency
- What it is
- The share of the energy drawn by the furnace that actually ends up as heat in the metal; the rest is lost through walls, lid, cooling water and flue gas.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 1% 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, time and cost are inversely proportional to efficiency.
- Get it right
- Measure it from your own meter readings and melt records where possible.
What this means: Energy price
- What it is
- What you pay for one kilowatt-hour of energy delivered to the furnace, or the equivalent cost of fuel per kilowatt-hour.
- Units and format
- Enter a number in AUD/kWh: Australian dollars per kilowatt-hour. The form accepts 0 AUD/kWh to 100 AUD/kWh. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.25 AUD/kWh as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cost per melt rises in direct proportion to the price.
- Get it right
- Include network and demand charges if you want the true cost of each melt.
Method and formulas
- Q = m [cs (Tm − T₀) + L + cl (Tp − Tm)].
- Energy drawn = Q ÷ efficiency; time = energy drawn ÷ power.
- Cost = energy drawn × price.
- Example: 500 kg of aluminium to 720 °C needs 144.97 kWh in the metal, about 0.96648 h at 250 kW.
Limitations
- Average property values; alloys melt over a range and properties vary with temperature.
- Holding losses while waiting to pour are not included.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Estimate furnace time and energy per melt
- Compare melting costs of alloys
- Size a furnace for a production rate
Who it is for
- Foundry engineers
- Process engineers
- Estimators
What you get
- Energy to heat, melt and superheat
- Melting time
- Energy drawn and cost per melt
Interpreting the result
- Keep superheat to what the casting needs; each degree costs energy and increases gas pick-up and oxidation.
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
From liquid to solid
In Metal Casting by the Numbers
What it covers: What a foundry has to control when metal freezes in a mould: latent heat, freezing range, the three stages of shrinkage, and why most casting defects are decided by how the metal solidifies.
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.