How many trains does a roving transport system need?

What a train has to do

A train is a rake of full roving bobbins that the system carries from a speed frame to a ring frame. The question every mill asks is simple. How many of them do we actually need on the floor?

It is easy to get this wrong by treating it as a throughput sum, dividing daily production by train size. That undercounts, because it ignores how long each train sits at a machine before it runs empty. The honest way to size it is to count where the trains actually have to be at any moment.

The simple idea

There is a well known rule for any system where things arrive, wait, and leave. The number of items sitting in the system at any moment equals how fast they arrive multiplied by how long each one stays.

For a roving transport system that turns into something you can picture on the floor. A train sits at a ring frame and slowly empties as the operator replaces run out bobbins from it. Because a roving bobbin lasts a long time, that train stays there for the best part of a day. So at any moment there is a train standing at each place one is needed. Counting the trains becomes counting the places.

That gives us four places to add up, and then one safety check.

What you need to know

• R, the number of ring frames
• s_RF, the spindles on each ring frame
• S, the number of speed frames
• s_SF, the spindles on each speed frame. One doff fills one train, so this is also the train length.
• P, one shift of production in kilograms
• B, the weight of one full roving bobbin in kilograms

Step 1: bobbins in a shift

Every kilogram of yarn spun uses a kilogram of roving, so the bobbins used in a shift is just the shift production divided by the bobbin weight.

Bobbins per shift = P ÷ B

Step 2: trains at the ring frames

The operator keeps a working stock of full bobbins on each side of the ring frame and swaps them into the creel as bobbins run out. That is one train on each side, so two per frame.

Trains at the ring frames = 2 × R

This is the largest of the numbers, and it does not depend on your production rate at all. It is simply how many frame sides you have.

Step 3: trains at the speed frames

Each speed frame has one train being filled and exchanged at any time as it doffs.

Trains at the speed frames = S

Step 4: a buffer for count changes

Normal creeling is already covered by the reserve at the frames. A count change is different. To move a ring frame to a new count you stage a whole fresh creel of the new roving first, then change it in one go. A full creel is s_RF bobbins, which is ⌈s_RF ÷ s_SF⌉ trains.

You plan for a handful of frames changing at once. A safe allowance is one for every fifteen ring frames.

Buffer trains = ⌈R ÷ 15⌉ × ⌈s_RF ÷ s_SF⌉

This material waits in the parking area until the frames are ready for it. There is more on the different parking arrangements here.

Step 5: a few on the move

At any moment some trains are travelling between the speed frames and the ring frames. Adding about ten percent covers them.

In transit ≈ 10% of (2R + S)

Adding it up

Trains from occupancy = 2R + S + buffer + transit

The safety check: one shift of storage

There is one more thing to confirm. The trains on the floor should be able to hold at least one full shift of production. That way, if creeling pauses or a group of ring frames stops for a shift, the roving already made has somewhere to sit and the speed frames do not have to stop.

One shift of production is P ÷ B bobbins. Divide that by the train length to put it in trains.

Storage floor = P ÷ (B × s_SF) trains

If the number from the steps above is smaller than this floor, we raise it to the floor.

Final number = the larger of the occupancy total and the storage floor

A worked example

Take a mill with 20 ring frames of 1440 spindles, fed by 3 speed frames of 240 spindles. The train length is 240. Say a shift produces about 5,760 kg and a full roving bobbin weighs 2 kg.

Those 59 trains carry 59 × 240 = 14,160 bobbins, close to five shifts of production. That is comfortable head room for a bad day.

What this means for your mill

The count is driven far more by how many frames you run than by how many tonnes you make. A mill with many frames spinning fine counts needs more trains than a throughput sum would ever suggest, because every frame still keeps its own reserve. Our configuration portal runs exactly these steps from your own figures, so you see the number and the reasoning side by side.

Run the Innospin RTS Configuration Portal

Our free portal takes your Speed Frame and Ring Frame parameters and gives you a Fixed-flow vs. Flexi-flow recommendation backed by your own production data.