Start From Takt Time, Not From the Equipment List
Takt time is the rhythm the plant has to hit. It is not the time a batch takes — it is the interval at which a finished batch has to leave. The two are different numbers, and confusing them is where most capacity plans go wrong.
The calculation is short. Take the operating minutes available in the period, divide by the batches required in that period, and the result is the takt time. A plant that needs twenty batches a week over a single shift of about 2,400 usable minutes has a takt time of roughly 120 minutes per batch. That 120 minutes is the budget every station has to fit inside.
| Input | How to get it | The trap |
|---|---|---|
| Available minutes | Shift length times shifts, minus planned breaks, changeovers and scheduled maintenance. | Using gross shift hours. A 480-minute shift rarely yields 480 productive minutes. |
| Batches required | Annual demand divided by the working periods, then adjusted for the batch size actually run. | Using nameplate capacity instead of the demand the sales plan supports. |
| Takt time | Available minutes divided by batches required. | Treating it as the time per batch rather than the interval between batches. |
| Station count | True cycle time divided by takt time, rounded up. | Dividing by the mixing time instead. This is the error that under-buys capacity. |
The last row is the whole article in one line. The rest of it is about measuring that cycle time honestly.
What Cycle Time Actually Contains
A station’s cycle runs from the moment a clean, empty vessel is available to the moment the next clean, empty vessel is available. On a high-viscosity product that is a much longer window than the mixing phase, and the phases that get forgotten are the ones that scale worst.
- Charging, powders go in slowly on a viscous base, because a fast charge either dusts out or forms lumps that the mixer then has to spend time breaking. On a sealed machine the charge often happens under vacuum through a hopper, which is safe but not fast
- Mixing and dispersion, the phase everyone measures. Its length is set by the product, not by the operator, so it is the least compressible part of the cycle
- Process holds, vacuum hold, heating or cooling to a set point, deaeration. These are dead time for the vessel even though nothing is being mixed
- Discharge, a high-viscosity product will not drain. Whether it leaves through a valve, a pump or a tilted trough changes this stage from minutes to tens of minutes
- Cleaning, the vessel and the head both have to be cleaned before the next batch, and on a multi-color or multi-product line this is a fixed cost per batch rather than per ton
Add those five and compare the total against the mixing time alone. On an adhesive or sealant line the difference is routinely a factor of two or more, and it is the reason a plant that looks over-equipped on paper turns out to be short of capacity in practice — or the reverse.
The Station Count, Worked Through
Two plants, same nominal output, different products. The numbers below are worked examples to show the method, not a benchmark for any particular product — the cycle times have to be measured on your own line.
| Plant A: low-viscosity coating | Plant B: high-viscosity sealant | |
|---|---|---|
| Available minutes per day | 900 (two shifts) | 900 (two shifts) |
| Batches required per day | 8 | 4 |
| Takt time | about 112 minutes | about 225 minutes |
| Charging | 25 minutes | 70 minutes |
| Mixing and dispersion | 45 minutes | 60 minutes |
| Holds (vacuum, cooling) | 10 minutes | 40 minutes |
| Discharge | 15 minutes | 55 minutes |
| Cleaning | 15 minutes | 30 minutes |
| True cycle time | about 110 minutes | about 255 minutes |
| Cycle divided by takt | about 1.0 | about 1.1 |
| Stations needed | 1 | 2 |
Read the last three rows together. Plant A carries one station with almost no margin, which means any upset — a slow discharge, a failed seal, a cleaning overrun — immediately becomes lost output. Plant B is nominally at one station by the arithmetic, but a ratio of 1.1 in practice means two, because there is no buffer anywhere in the cycle. The ratio has to be comfortably below one before a single station is a real answer.
That is the practical form of the rule: a computed ratio between about 0.8 and 1.0 is the danger zone. Below 0.8 the margin absorbs normal variation. Above 1.0 the line is short of capacity and the shortfall shows up as overtime rather than as an obvious bottleneck.
Where the Time Actually Goes
Before adding a station, measure the five phases separately for a week. The distribution is almost always a surprise, and it usually points at the same two stages.
- Charging dominates on viscous products, powder into a thick base is slow because it must be added at a rate the mixer can wet out. Feeding through a vacuum induction system rather than a hopper is the usual fix, because it wets the powder into the liquid stream rather than dropping it on top of the batch
- Discharge dominates on high-solids products, a paste with a high filler load will not flow out of a bottom valve at a useful rate. A discharge pump sized for the viscosity, or a tilting arrangement, changes the phase from a wait to an operation
- Cleaning dominates on multi-color lines, the cost is per batch, not per ton, so it hits short runs hardest. Reducing the wetted surface that has to be cleaned — one vessel per batch rather than a transfer circuit — is often worth more than a faster mixer
- Holds hide in the schedule, a cooling hold is invisible in a batch record but it occupies the vessel. If the jacket is undersized for the heat the mixing step puts in, the hold lengthens every batch for the life of the plant
Each of these is cheaper to fix than a second station, and fixing two of them will usually recover more capacity than the extra machine would have added — without adding floor space, operators or cleaning load.
Mobile Vessels Change the Arithmetic
If the vessel can move and the head cannot, the head becomes the constrained resource and the vessels become buffers. That is the arrangement in the photographs: several mobile jacketed vessels, one lift head per station, and a docking position where the vessel is clamped and the head lowered into it.
The effect on the calculation is that the station’s cycle no longer has to contain discharge and cleaning, because the vessel leaves with the batch in it and the next vessel is already in position. What remains at the station is charge, mix and the process holds — roughly half the original cycle. A single station can then serve a takt time it could not have met before, and the extra cost is vessels and handling rather than drives.
Two costs come with it, and both should be in the calculation. Vessels are not free, and each one needs a jacketed body if temperature control matters. Handling equipment and floor space are needed, and the vessels have to be tracked so a batch is not lost in the plant. The arrangement only pays when the cycle time is dominated by phases the vessel can carry away with it. Our guide to concentric dual shaft mixing kettles covers the vessel side, and the high viscosity mixer range covers the head side.
Four Ways the Calculation Goes Wrong
| The mistake | What it produces | The correction |
|---|---|---|
| Counting mixing time as cycle time | A station count that is too low, and a plant that needs overtime from the first month. | Time the full cycle for a week: charge, mix, holds, discharge, clean. |
| Averaging the product mix | A station count that fits the average batch and fails on the slowest one, which is the one that sets the schedule. | Size the count on the worst-case product, then check the average still fits. |
| Ignoring changeover | Capacity that exists on paper and disappears as the number of colors or products grows. | Treat cleaning and changeover as a per-batch cost, then look at what a mobile vessel would remove. |
| Assuming a bigger mixer solves it | A larger vessel that takes longer to charge and discharge, with the same number of stations and less flexibility. | Redo the arithmetic at the new batch size before ordering, including the limits on vessel size. |
All four share a root cause: the plan was made from an equipment list rather than from a measured cycle. The arithmetic is simple enough to do in a spreadsheet, and it is worth doing before the layout is fixed, because the vessel count is what the layout is built around.
Send Us the Batch, the Cycle and the Target
Tell us the product, the batch size, the viscosity and the output you need to reach. Our engineers will work through the cycle time with you, confirm the station count and the vessel arrangement, and quote directly from the factory.
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Where These Mixers Are Built
Vessel shells, planetary frames, lift columns and the hydraulic assemblies are machined and built in the same plant, so a station count agreed on paper corresponds to equipment that can actually be laid out and serviced as drawn.
It is worth walking that boundary before fixing the vessel count. The station count determines how much finished product arrives at the packaging stage and how unevenly it arrives. A line that is perfectly balanced inside the mixing hall and produces four batches at the same hour is not balanced at all. An adhesives and sealants production line is normally planned around that arrival pattern.
