Batch consistency of granules: why two bags of one grade should match

Sometimes two bags of the same grade do not behave alike on one production line: parts warp every other shot, the colour shifts slightly, or the injection pressure needs adjusting. Usually the grade is not at fault; the batch is.

What is a batch and why does it matter?

A batch is a quantity of granule made in one production run with one formulation. Two batches of one grade share a name, but there is no guarantee that MFI, filler dispersion, colour and moisture match exactly, unless the supplier measures and records every batch.

What differs between batches?

• MFI: the smallest shift changes injection pressure and cooling time.
• Filler percentage: affects density, part weight and stiffness (see ash and filler content).
• Colour and appearance: especially in white, visible parts.
• Moisture: damp granule affects surface and strength.
• Share of recycled material: in recycled and blended grades, changes in input are more visible from batch to batch.

A batch number on the datasheet means traceability

When the batch number is on both the bag and the datasheet, any production problem can be traced to one batch: what was measured, when it was made and which bags belong to it. Without it, a datasheet is only an approximate figure for “that grade”.

What to do on your line

• Record the batch number of every shipment and keep it with the first production part.
• Do not mix batches in an unmarked hopper; if you must, record the ratio.
• Keep a retained sample of every new batch to compare if parts change.
• When the batch changes, watch the first parts and compare the new datasheet with the old.

What to ask your supplier for

• The datasheet of each batch with its batch number, not one general datasheet for the grade;
• MFI with its test condition, density, and ash or filler percentage;
• production date and a retained sample of the batch.

For batch datasheets, orders or advice contact Epic Polymer: +98 919 212 4919 · WhatsApp.