A New EPS Pre-expander Machine Density Weighting Unit
Density is the number that decides whether an EPS block meets specification, and it is set long before the block reaches the mould — it is set by the EPS pre-expander machine. Years ago that was done by operator judgement. Today it is measured, cycle by cycle, by a density weighting unit.
How the unit works
The sequence runs automatically on every cycle:
- Pre-expanded beads are sucked into a holding tank
- Beads fill a measuring cup of fixed volume — the weighing unit
- An air cylinder pushes a scraper across the top, levelling the beads so every sample has exactly the same volume
- The load cell weighs that fixed volume
- The PLC divides weight by volume and calculates the density for that cycle
Because volume is held constant by the levelling scraper, the weight reading is a direct density reading. That is what makes the measurement repeatable rather than approximate.
What the unit reports
- Automatic density calculation — a density value for every batch, not a spot check once a shift
- Density record print — a printed or exported record per batch, which is what customers ask for when they audit a shipment
- Large deviation warning — an alarm when a batch falls outside the tolerance band, so the operator corrects it before the beads reach the silo
Why it pays for itself
The cost of density error is downstream and expensive. Beads that come out too heavy produce blocks that are overweight — you have given away raw material on every cubic metre. Beads that come out too light produce blocks that fail compressive strength and get rejected. Catching either at the pre-expander costs nothing; catching it after moulding costs a whole block.
Where it sits in the process
The weighting unit measures beads as they leave the pre-expander and before they enter the ageing silos. Pairing it with an EPS silo system means the beads measured are the beads actually used, with no chance of mixing between measurement and moulding.
Ask us about fitting a density weighting unit to an existing pre-expander, or specifying one on a new machine — contact our team.