In this guide 6 sections
Lost changeover hours hide in waiting, not in the swap itself. Time a die swap, a colour purge, a screen change and start up scrap as four separate steps, then log each one by line and shift. A month of entries shows which step eats the most.
A changeover is four jobs, not one
Production heads often quote a single changeover time. It hides everything useful. A film or pipe line loses hours across the die swap, the colour purge, the screen pack change and the climb back to good product.
Start by splitting the clock. Mark when the last good metre leaves the line. Then note when the die is out, when the new one is bolted on, when melt runs clean and when the first saleable length is taken.
Those five timestamps give four durations. The biggest is rarely where the crew thinks it is.
- Last good product to die removed
- Die fitted and heated to temperature
- Purge until colour or grade runs clear
- Start up scrap until first saleable length
Die swaps lose time before and after the spanners
The swap is usually quick when the crew has the die, the tooling and the crane ready. The delay is the heat. A large die can take a long time to come up evenly, and an operator who waits for the temperature to soak is not idle by choice.
Ask whether the next die is preheated while the current job runs. Ask whether bolts, gaskets and the lifting tackle sit on a cart at the line. Hunting for a torque wrench shows up as a long swap but is really a kitting problem.
Record who was on the crew. A swap that takes two people and a fitter is a different cost from one done by a single operator.
Colour purges and screen changes
A move from black to natural can burn through many kilos of purge compound and a long stretch of scrap. A move from natural to black costs much less. The order of jobs on the schedule matters more than the speed of the crew.
Log the colour pair every time. After a few weeks you can sequence light to dark and group similar grades. Some shops keep a simple matrix that shows the cost of each pair.
Screen changes follow the pressure rise across the pack. Note the pressure before and after, the mesh grade and the resin lot. If screens clog sooner on one lot or on heavy regrind, the log will show it.
- Colour from and to
- Purge compound used and time to clear
- Screen mesh and pressure before and after
- Resin lot and regrind share
Start up scrap is a trend, not a total
Weigh start up scrap on every changeover and write it against the die and the product. Gauge swings, die lip lines and melt fracture settle at a different pace on each tool.
A die that always needs twice the scrap of its twin points to wear, a blocked channel or a setpoint sheet that is out of date. Without the log, that die just feels unlucky.
Keep the final good settings with the job. The next crew should start from the temperatures, screw speed and line speed that last worked, not from memory.
What a month of the log tells you
After four weeks, sort entries by step and by line. The top item is your target. It might be waiting for a forklift, a heater band that fails on one die, or a colour order that doubles purge time.
Share the sorted list with the shift leaders before changing anything. They will often explain a pattern in a minute. Then pick one cause and fix it for a month.
Start tomorrow with a paper sheet at the line and five boxes. Keep it simple, and move it into software only once the crew trusts the numbers.
Extrusion changeover log sheet
Each changeover takes a row on this single-page log. Columns hold date, line, shift, from product and to product. Five timestamps follow, from last good product to first saleable length. Then come colour pair, purge weight, screen mesh, pressure, scrap weight and a delay reason. A footer row totals time by step.
Open a blank worksheet to printQuestions owners ask
What counts as the start of a changeover?
Count from the last good product, not from the stop button. Many crews run the line down on scrap first, and that time belongs to the changeover.
Do we need software to log changeovers?
No. A sheet at the line works well for the first month. Software helps later, when you want trends by die, colour pair or resin lot.
Why does the same changeover vary so much between shifts?
Usually from kitting, preheating and who is on the crew. Compare the five timestamps across shifts to see which step differs.
How do we cut colour purge time?
Sequence jobs from light to dark, group similar grades and record the purge for each colour pair. Then plan the schedule around the costly pairs.