Black Spots in Extrusion: Causes Related to Flow Dead Zones and Effective Prevention
Black spots and burnt plastic particles in the extrudate are among the most common and costly quality issues in extrusion. The cause is often hidden within the extrusion die: in what are known as flow dead zones. But how do these deposits form, and how can you sustainably avoid costly downtime through the preventive use of cleaning pellets?
How do deposits form in the extrusion die?
Until the final profile is formed (as it exits the extrusion die), the molten plastic must be redirected within the die. At these redirections, the flow velocity of the molten plastic is nearly 0. These areas are referred to as dead zones.
In these areas where the process is slowed down, the plastic remains exposed to high temperatures for too long. As a result, the plastic suffers thermal damage and gradually burns.
The consequences of thermal deposits:
- Layered buildup: The burned plastic adheres to the mold walls, forming multiple layers of deposits.
- Particle Entrainment: When the deposit reaches a critical mass, the flowing plastic melt carries fragments along with it.
- Impurities in the extrudate: This results in visible black specks or even burnt plastic chunks the size of a penny in the final product.
Prevention and Removal: How to Effectively Prevent Black Spots
Once multiple layers of burnt plastic have built up on the metal surfaces, the only effective solution is often to completely disassemble the extruder and the extrusion die. Mechanical cleaning requires days of downtime and results in immense production losses and labor costs.
The solution lies in regular, preventive cleaning and preventing the buildup of deposits.
- Continuous Prevention with Cleaning Granules
By regularly using special cleaning granules, you can prevent multiple layers of burnt plastic from building up on top of each other right from the start. New deposits are removed immediately after they form. - Targeted Rinsing with Cleaning Concentrates
With our highly effective cleaning concentrates, per-tas and syn-tas, you can quickly and thoroughly clean affected areas during material or color changes.
Conclusion: Prevention saves on high disassembly costs
Avoid costly tool disassembly and ensure the quality of your extruded products. By systematically cleaning with ver-rus cleaning agents, you can keep dead zones clean and effectively prevent the formation of black spots.
Would you like to reduce scrap costs? Then schedule a personal consultation today to learn more about our per-tas and syn-tas cleaning solutions.
