In injection and extrusion machines, the screw and barrel are the heart of the plastic processing process. Wear that develops over time disrupts the precise tolerances that enable molten plastic to be conveyed, mixed and pressurized. Catching wear early is the most effective way to prevent quality losses and unexpected downtime. Here are 8 key signs that it's time to replace your screw-barrel set.
1. Drop in Capacity (Flow Rate)
If you can no longer reach the production capacity you previously achieved at the same speed and temperature settings, this is usually caused by an increase in the clearance between the screw flights and the barrel inner surface. Worn clearance causes the melt to backflow where it should be conveyed forward, and output drops.
2. Fluctuation in Melt Pressure
If you observe sudden drops or fluctuations in melt pressure that should otherwise be stable, an increase in the screw-barrel clearance may be causing pressure loss. This especially turns into filling problems for thin-walled products.
3. Deterioration in Product Quality
Loss of surface gloss, longer color transitions, gas marks, or unmelted particles showing up in the product are signs that mixing and plasticizing performance has declined. Worn screw geometry makes it harder to achieve a homogeneous melt.
4. Increase in Energy Consumption
If you notice the motor consuming more power to produce the same product, increased friction and inefficient conveying may be the cause. Worn surfaces increase the energy required for the melt to advance.
5. Abnormal Behavior in Motor Amperage Values
Sudden increases or drops in motor amperage values that are normally stable can be an indicator of uneven wear or localized damage on the screw surface.
6. Increasing Backflow
Wear at the screw tip and check ring area causes the melt to flow backward instead of moving forward as intended. This disrupts shot repeatability and leads to deviations in part weight.
7. Visible Wear Marks Upon Disassembly
If you observe shine, scratches, pitting or discoloration on the screw flights during periodic maintenance, this is concrete evidence that wear has progressed. The screw tip and feed zone in particular should be examined carefully.
8. Measured Clearance Exceeding the Limit Value
If periodic measurements with calipers or an internal diameter micrometer show that the difference between the screw outer diameter and the barrel inner diameter has exceeded the manufacturer's tolerance, it is time for a replacement. This value varies by material and application but should be tracked regularly.
Conclusion
If you are observing several of these signs at the same time, we recommend having your screw-barrel set measured before production stops. At Milon, we offer screw-barrel manufacturing tailored to your existing machine's dimensions along with technical consulting support.
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