KEVOS® MAKEOS · Materials
Quench Tank Temperature Check (Equilibrium Temperature per Load, Loads to the Limit, Cooling Duty)
When a hot load is quenched into my tank, what temperature does the bath settle at, how many loads can it take without cooling before it passes its limit, and is the cooler big enough for my load rate?
Heat balance of a quench: the mixture (equilibrium) temperature of a hot load and the bath from their heat capacities (mass × mean specific heat) and starting temperatures, the bath temperature rise and heat released per load, the entropy generated, the number of loads in a row the bath can take before it passes its highest allowed temperature with no cooling, and the average heat input at your loads per hour against the cooler capacity.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Load mass (parts plus basket or fixture) | kg | Mass of everything that goes into the bath hot: parts, basket, fixtures and grids. |
| Mean specific heat of the load over the quench | J/(kg·K) | Mean specific heat of the load between the quench-in and bath temperatures, from material data; for steel include the heat of transformation if your data give it separately. |
| Load temperature entering the quench | °C | Temperature of the load as it enters the bath (the furnace temperature less any cooling in transfer). |
| Quench bath | ||
| Quenchant volume | L | Volume of quenchant in the tank at its working level. |
| Quenchant density | kg/m³ | Density of the quenchant at its working temperature, from the supplier’s data sheet. |
| Quenchant specific heat | J/(kg·K) | Specific heat of the quenchant at its working temperature, from the supplier’s data sheet. |
| Bath temperature before the load | °C | Temperature of the bath just before the load goes in. |
| Highest allowed bath temperature | °C | Highest bath temperature allowed by the quenchant supplier, the process specification or the fire-safety margin below the flash point. |
| Load rate and cooling | ||
| Loads per hour | loads/h | Average number of loads quenched per hour. |
| Cooler capacity | kW | Heat the bath cooler can remove at the working bath temperature, from its data sheet (0 if there is no cooler). |
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: Load mass (parts plus basket or fixture)
- What it is
- The mass of everything that goes into the quench hot: the parts plus the basket, fixture or grid that carries them.
- 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 150 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The heat released per load and the bath rise grow almost in proportion.
- Get it right
- Baskets and fixtures often weigh as much as the parts; weigh a loaded basket.
What this means: Mean specific heat of the load over the quench
- What it is
- The average heat the load gives up per kilogram for each kelvin it cools between its entry and the bath temperature.
- Units and format
- Enter a number in J/(kg·K): J/(kg·K). The form accepts 1 J/(kg·K) to 10000 J/(kg·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 600 J/(kg·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The heat released per load and the bath rise grow almost in proportion.
- Get it right
- Steel’s specific heat rises steeply near its transformation range; use an average over the whole cooling range.
What this means: Load temperature entering the quench
- What it is
- The temperature of the load as it enters the bath, normally the furnace temperature less the cooling during transfer.
- 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 850 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A hotter load releases more heat and raises the bath further.
- Get it right
- A slow transfer can lose tens of kelvin, but use the furnace temperature for a cautious check.
Quench bath
What this means: Quenchant volume
- What it is
- The volume of quenchant in the tank at its normal working level, which together with density and specific heat sets the bath’s heat capacity.
- Units and format
- Enter a number in L: litres. The form accepts 0.000001 L to 10000000 L. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3000 L as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger bath rises less per load and takes more loads before its limit.
- Get it right
- Measure the working level, not the tank’s brim capacity; drag-out lowers it between top-ups.
What this means: Quenchant density
- What it is
- The mass of one cubic metre of the quenchant at its working temperature, used to find the mass of the bath.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 1 kg/m³ to 5000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 870 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A denser bath has more mass and so rises less per load.
- Get it right
- Oil density falls as it warms; take the value at the working temperature from the data sheet.
What this means: Quenchant specific heat
- What it is
- The heat one kilogram of quenchant absorbs for each kelvin it warms, at its working temperature.
- Units and format
- Enter a number in J/(kg·K): J/(kg·K). The form accepts 1 J/(kg·K) to 10000 J/(kg·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2000 J/(kg·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher specific heat lets the bath absorb more heat for the same rise.
- Get it right
- Quench oils are roughly half the value of water; polymer quenchants are close to water.
What this means: Bath temperature before the load
- What it is
- The temperature of the bath just before the load goes in, the starting point of the heat balance.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -50 °C to 500 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 60 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The bath temperature after the load rises almost one for one with it.
- Get it right
- Read it from the bath thermometer after the previous load has been taken out and the bath mixed.
What this means: Highest allowed bath temperature
- What it is
- The highest temperature the bath may reach, set by the quenchant supplier, the process specification or a safe margin below the flash point.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts -50 °C to 500 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The decision fails if one load takes the bath above it, and it sets how many loads can follow in a row.
- Get it right
- For oil keep a margin below the flash point, because the oil next to the parts is much hotter than the bath average.
Load rate and cooling
What this means: Loads per hour
- What it is
- The average number of loads quenched each hour, which with the heat per load gives the average heat the cooler must remove.
- Units and format
- Enter a number in loads/h: loads/h. The form accepts 0.001 loads/h to 1000 loads/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 loads/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The average heat input to the bath rises in direct proportion.
- Get it right
- Use the busiest sustained hour of a shift, not the daily average.
What this means: Cooler capacity
- What it is
- The heat the bath cooler or heat exchanger can remove continuously at the working bath temperature.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0 kW to 100000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 45 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The decision fails if the average heat input from the loads is above this value.
- Get it right
- Cooler ratings fall as the cooling water or air warms; use the rating on the hottest day.
Method and formulas
- With no work and no heat loss, the heat given up by the load equals the heat taken by the bath: T_f = (C_L T_L + C_B T_B) ÷ (C_L + C_B), with C = mass × specific heat (Greiner Exercise 2.6, the “mixture temperature” of an irreversible process).
- Entropy generated = C_L ln(T_f ÷ T_L) + C_B ln(T_f ÷ T_B) in kelvin, always positive (Greiner Exercise 2.6); heat per load Q = C_L (T_L − T_f).
- Loads in a row: repeat the balance from each new bath temperature until it passes the limit; average heat input = Q × loads per hour ÷ 3600 against the cooler capacity.
- Example: the bath settles at 73.39 °C, a rise of 13.39 K; each load releases 69.895 MJ, an average 38.831 kW against a 45 kW cooler.
Limitations
- Uniform, well-mixed bath and no loss to the tank, air or evaporation, so the rise is slightly overstated; local temperatures near the load are much higher, which matters for flash point and vapour.
- The load is taken all the way to the bath temperature; with short quench times the parts leave warmer and less heat goes into the bath.
- Mean specific heats only: the specific heat of steel changes strongly with temperature and through transformation.
- Fire safety of oil quenching (flash point, lid, extinguishing, agitation) is governed by the quenchant supplier’s data and the applicable rules; this is a screening aid.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a quench tank or check an existing one for a heavier load
- Check whether the oil cooler keeps up with the load rate
- Plan how many loads can go in before the bath must cool
Who it is for
- Heat-treatment engineers and supervisors
- Maintenance engineers
- Manufacturing engineers
What you get
- Equilibrium bath temperature and rise per load
- Heat released and entropy generated per load
- Loads in a row before the limit with no cooling
- Average heat input against the cooler capacity
Interpreting the result
- A rise of more than a few kelvin per load means the bath is small for the load; a larger volume or a cooler sized from the average heat input keeps the quench repeatable.
- The entropy generated shows how irreversible the quench is; it is large because heat falls across hundreds of kelvin, the same reason the quench cools so fast.
References
- Greiner W., Neise L. and Stöcker H., Thermodynamics and Statistical Mechanics (Springer-Verlag, New York, 1995), pp. 55–56: mixture temperatures of two systems with constant heat capacities and the entropy changes of an irreversible mixing (Exercise 2.6). Method reference; no text, tables or worked examples are reproduced.
- ASM Handbook, Volume 4A: Steel Heat Treating Fundamentals and Processes (ASM International, 2013): quenching and quenchants.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Explains the concept · KEVOS® original book
Entropy generated by heat transfer
What it covers: Why heat crossing a temperature difference always generates entropy, how to calculate it for heat exchangers, kettles and heaters, and how matching temperatures and staging sources cut it.
Also in Throttling, mixing and friction
Method explained here · KEVOS® original book
Quenching the hot layer
In Induction Hardening by the Numbers
What it covers: Turning the heated layer into martensite: spray quenching and polymer quenchants, how fast is fast enough, the quench tank's heat balance per part and per hour, and a summer rush that warmed the bath.
Method explained here · KEVOS® original book
Heat treating castings
In Metal Casting by the Numbers
What it covers: Solution treating, quenching and ageing aluminium castings: what each step does, the furnace energy and cycle time per load, the quench tank's heat balance, and a tank too small for the load.
Useful alongside · KEVOS® original book
The surface condition: radiation, loads and quenchants
In Heating and Cooling Times by the Numbers
What it covers: Where surface coefficients come from in furnaces, loaded baskets, tempering ovens and oil quenches, and how a tempering cycle using the hardening coefficient ran half as long as needed.
KEVOS® 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.