How do you calculate refractory heat-up schedule duration?

Divide the mass or thickness to cure by the controlled ramp rate for the base time, then apply the soak allowance. With 120 units of work at 12 units/hr and a 10% allowance, the base is 10 hours and the adjusted duration is 11 hours.

Why do you add a soak allowance to the ramp time?

A safe dry-out holds at temperature plateaus to drive off free and chemically-bound water without spalling. The allowance adds that hold time on top of the pure ramp; a 10% allowance turns a 10-hour ramp into an 11-hour schedule.

What happens if you heat a refractory lining too fast?

Trapped moisture flashes to steam, building pore pressure that spalls or explosively fractures the hot face. That is exactly why the ramp rate is capped and this calculator exists — to plan around the safe rate rather than beat it.

What is a typical soak allowance percentage?

It depends on lining thickness and cement content, but 10-25% over the pure ramp time is common for conventional castables; dense low-cement castables with more bound water need larger allowances. Use your material data sheet's schedule to set it.

How does lining thickness change the duration?

Thicker linings mean more mass to heat through, increasing the work input and therefore the base time proportionally. Thick sections also usually need longer soaks, so consider raising the allowance as well as the mass input.

Is this a substitute for the manufacturer's dry-out curve?

No. It sizes the outage window from an averaged ramp and allowance. The actual controller program must follow the manufacturer's stepped ramp-and-soak curve for that specific castable.

Refractories, Furnace Linings & Foundry Consumables calculator

Heat-Up Schedule Duration Calculator

Heat-Up Schedule Duration estimates how long a controlled refractory dry-out and cure will take, dividing the mass or thickness that must be heated through by the safe controlled ramp rate, then adding an allowance for the isothermal soak holds that a proper dry-out schedule requires. Furnace commissioning engineers and refractory installers use it to plan an outage window, because heating a fresh castable or monolithic lining too fast traps moisture, spalls the hot face, and can destroy a lining before first production. The soak allowance captures the mandatory hold periods at 110C, 315C, and similar plateaus where free and chemically-bound water is driven off. Getting the total right keeps a commissioning schedule honest and protects an expensive new lining.

What this calculator does

Heat-Up Schedule Duration estimates how long a controlled refractory dry-out and cure will take, dividing the mass or thickness that must be heated through by the safe controlled ramp rate, then adding an allowance for the isothermal soak holds that a proper dry-out schedule requires.
Use it when heat-up schedule duration in refractories, furnace linings and foundry consumables is changing rate or allowance and you want to see the impact.
It divides the work to be cured by the controlled ramp rate for a base time, then multiplies by an allowance factor to add soak-and-hold time.

Formula used

Base heat-up schedule duration time = required work ÷ processing rate
Adjusted time = base time × allowance factor

Inputs explained

Total refractory mass or thickness to cure:
Controlled ramp rate (cure throughput):
Soak and hold-time allowance:

How to use the result

Use it when planning the dry-out window for a new or repaired monolithic refractory lining before returning a furnace to service.
It models dry-out as a single averaged ramp plus a flat allowance; a real schedule has stepped ramps and multiple soak plateaus, so use this for outage planning, not as the controller setpoint program.

Current U.S. benchmarks

The producer price index for steel mill products stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. Quotes priced off last quarter's material cost miss this move.
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Common questions

How do you calculate refractory heat-up schedule duration? Divide the mass or thickness to cure by the controlled ramp rate for the base time, then apply the soak allowance. With 120 units of work at 12 units/hr and a 10% allowance, the base is 10 hours and the adjusted duration is 11 hours.
Why do you add a soak allowance to the ramp time? A safe dry-out holds at temperature plateaus to drive off free and chemically-bound water without spalling. The allowance adds that hold time on top of the pure ramp; a 10% allowance turns a 10-hour ramp into an 11-hour schedule.
What happens if you heat a refractory lining too fast? Trapped moisture flashes to steam, building pore pressure that spalls or explosively fractures the hot face. That is exactly why the ramp rate is capped and this calculator exists — to plan around the safe rate rather than beat it.
What is a typical soak allowance percentage? It depends on lining thickness and cement content, but 10-25% over the pure ramp time is common for conventional castables; dense low-cement castables with more bound water need larger allowances. Use your material data sheet's schedule to set it.
How does lining thickness change the duration? Thicker linings mean more mass to heat through, increasing the work input and therefore the base time proportionally. Thick sections also usually need longer soaks, so consider raising the allowance as well as the mass input.

Last reviewed 2026-05-12.