A 100-ton molten-steel ladle typically needs about 20–30 minutes under vacuum, while VD/VOD treatment commonly takes 30–70 minutes [S3][S5][S8].
Published data cover ladle-vacuum units from 10 to 330 tonnes, with the largest concentration in the 30–150 tonne range; treatment time is not a function of ladle capacity alone [S2].
Compare RH, VD, and VOD treatment windows
RH is a circulation-based vacuum process, while VD treats steel in the ladle under a vacuum lid or in a vacuum tank; VOD combines vacuum treatment with oxygen blowing [S2][S5][S7]. For an initial capacity-planning estimate, RH normally falls in a 20–30 minute cycle, whereas VD and VOD require a broader 30–70 minute treatment window [S3][S5][S8].
The comparison is process-specific, not a simple size multiplier:
For a 30–150 tonne ladle, start with 20 minutes for a straightforward RH cycle or 30 minutes for a routine VD cycle, then reserve 50 minutes for VOD. Actual plant recipes must then be checked against the target carbon level, pressure, temperature loss, and downstream casting window [S2][S3][S5].
Use ladle size to set the planning envelope
Published ladle-vacuum configurations cover melt weights of 10–330 tonnes, while the most common application range is 30–150 tonnes [S2]. A steel vacuum-degassing configuration with a molten-steel capacity of at least 30 tonnes lists a 20–30 minute degassing time, so 30 tonnes should not be treated as a universal minimum for every unit design [S8].
For planning, one 100-ton heat should be allocated about 30 minutes of RH treatment, 40 minutes of VD treatment, or 60–70 minutes of VOD treatment. Those figures are treatment windows, not equipment occupancy guarantees. Vacuum preparation, transfer, sampling, alloying, temperature measurement, and casting must be added separately. A casting ladle also has a casting window of roughly 40–70 minutes, constrained by casting speed and temperature decline, so degassing cannot be scheduled without checking heat loss and downstream capacity [S4].
Separate treatment time from total cycle time
The 20–25 minute figure reported for an RH route is the average vacuum-degassing process duration, with the result depending on the target carbon content [S1]. A separate RH account gives a normal cycle time of 20–30 minutes and notes that the unit can circulate up to 85 tonnes, although that circulation figure is equipment capacity rather than a universal ladle limit [S3].
Cycle planning must therefore include more than the vacuum hold. For a 30-tonne-plus degassing unit, use 20–30 minutes for the RH treatment stage itself, then add transfer, vacuum evacuation, alloying, sampling, temperature checks, and return to the casting position. If the total scheduled window is 45 minutes, only about 20 minutes remains for those auxiliary operations, which may be insufficient for a more elaborate grade recipe [S1][S3][S8].
Match the process to the steel objective
RH is suited to high-throughput production because circulation and mixing can support a short decarburization cycle, including a reported case of reaching carbon below 20 ppm in less than 15 minutes under the specified plant conditions [S3]. VD is more appropriate when a treatment must remain in the casting ladle, especially for alloying, inclusion control, and precise composition adjustment [S2][S5].
VOD is the longer option when oxygen blowing is required for deep decarburization, including low-carbon electric steel, stainless steel, and automotive sheet grades [S2][S5]. A 100-tonne ladle assigned a 50–70 minute VOD window must also preserve temperature and avoid excessive metal and slag overflow. Level rise is driven by vacuum depth, argon intensity, and metal oxidation, so the treatment recipe must be coordinated with freeboard and the casting ladle rim condition [S5].
This distinction matters because a 100-tonne ladle does not have one universal treatment time. A 20-minute RH cycle can be suitable for routine circulation-based refining, while the same ladle assigned to VOD may require 50–70 minutes. Target chemistry decides the process first; capacity then determines equipment feasibility and cycle allocation [S2][S5][S7].
Avoid extending vacuum time without a metallurgical target
Longer vacuum exposure is not automatically a better recipe. In the VD/VOD route, vacuum creation above the bath combined with argon stirring promotes frothing and raises metal and slag levels; excessive level growth can cause overflow across the ladle board [S2][S5]. Argon flow, vacuum pressure, bath depth, and oxidation state therefore have to be controlled as a set rather than treating time as the only control variable.
Typical failure modes include excessive metal or slag overflow, poor or nonuniform stirring, underfilled ladles, dirty vacuum-lid flanges, and temperature loss that leaves insufficient time for casting. Tank arrangements are common, but lid arrangements require clean, slag-free sealing surfaces, an operational constraint documented in steel vacuum-unit practice [S2][S5].
Do not add arbitrary minutes to compensate for an undersized unit. Confirm that the rated heat mass, lift-gas capacity, vacuum pumping performance, stirring system, and available freeboard match the intended steel grade. The holding furnace and ladle-furnace route also affect the thermal budget because the casting window remains only about 40–70 minutes [S4].
Build the schedule from verified cycle data
Use three numbers in the operating plan: 20–30 minutes for the RH treatment window, 30–40 minutes for VD, and 50–70 minutes for VOD or combined treatment [S3][S5][S8]. For a 100-tonne ladle, those become concrete baseline allocations of 20–30, 30–40, and 50–70 minutes before auxiliary operations are added.
Track the actual time to target carbon, actual vacuum pressure, argon consumption, treatment temperature, and elapsed time from degassing to casting. The degassing unit refractory box life: heats and years decision should also be checked because refractory condition, seal integrity, and repeatability affect available treatment time. A defensible ladle-size estimate begins with the published process window, then proves it against grade-specific production data.