Every extrusion plant has a wastage number. Usually it is one figure per month: material issued minus product dispatched. That number tells you how much you lost, but not where, when or why. To reduce wastage you first have to measure it where it happens.
The five places extrusion loses material
- Start-up and changeover. Material run to waste while the line comes up to temperature, size or colour after a start, a size change or a colour change.
- Running over-weight. Product that is heavier than the standard: pipe over the target weight per metre, tape above the target denier, sheet above the target thickness. It is shipped, but the extra material is given away.
- Trim and cut-offs. Edge trim, slitting trim, end cut-offs and samples.
- Rejects. Product that fails a dimension, appearance or test check.
- Unrecorded loss. Spillage, sweepings, material left in hoppers and dryers, and stock differences.
Measure each one separately
Book waste at the stage where it is created, with its type and the line and shift. A simple rule works well: anything that leaves the line and is not good product goes on a scale and into the system with a reason. Within a few weeks the pattern is clear: one line loses most at start-up, another runs over-weight on the night shift, a third has high trim on one product.
Over-weight is the hidden one
Start-up waste and rejects are visible because someone has to move them. Over-weight running is invisible because the product is shipped. In pipe extrusion, compare actual weight per metre with the standard for each size and class every shift. In tape lines, compare denier with the target. Small differences on every metre add up to more material than the scrap bin.
Give regrind a value
Clean waste that is ground and reused is not free: it costs energy and handling, and it can only replace virgin material up to the limit your recipe allows. Weigh regrind back into stock, record the regrind percentage used in each batch, and value it, so the real cost of waste is visible.
Turn the numbers into actions
- Review wastage by stage and line in the morning meeting, not at month end.
- Set targets per line for start-up loss and over-weight, not one plant-wide figure.
- Plan production to reduce size and colour changes, grouping similar orders.
- Link stoppages to start-up waste: every unplanned stop usually creates a new start-up.
A worked example of over-weight cost
Take an illustrative line producing 500 kg of pipe an hour that runs 2% above its standard weight per metre. That is 10 kg of extra material every hour, or 240 kg a day if the line runs around the clock, all shipped to customers without payment. Multiply by your own output and material price, and the case for checking weight every shift usually makes itself.
A start-up routine that cuts waste
- Prepare the next material, die and settings before stopping the previous run.
- Record the start time and the material run to waste until the product is in specification.
- Check size, weight and appearance before releasing the line to good production.
- Bring the weight back to target once the line is stable, not hours later.
Make someone own it
Wastage falls fastest when each line has an owner who sees its figures every day and is asked about them in the morning meeting. Plant-wide wastage targets rarely change behaviour; a line-wise figure with a name next to it does.
Formezy books wastage by stage, type, line and shift, compares actual weight per metre with the standard, and returns regrind to stock. See the plastic pipe process flows and the PVC pipe ERP page for how it works step by step.
