Tips for Troubleshooting the Degassing Zone

The degassing zone, also known as the vacuum zone, is a critical component located just before the pressure build-up zone of the extruder. Its main function is to effectively release gases, moisture, or residual materials that may promote the formation of voids within the pellets. Co-rotating twin-screw extruders typically have at least one vacuum zone for effective degassing, thereby achieving very high product quality.

Although degassing is generally a reliable part of extrusion, issues may arise over time. When operators encounter problems, the root cause is often related to blockages or a vacuum level that is too low.

Issue: Blockage of the Vacuum Vent

If the material starts to swell from the die, you are likely facing a blockage in the degassing zone. To troubleshoot this blockage, several steps are usually followed. First, operators should check whether the melt has changed compared to previous states (e.g., is the viscosity of the product lower?). If so, you should adjust your parameters: either decrease the die pressure by adding more die holes or lower the inlet pressure of the gear pump, if applicable. However, changes in the viscosity of your raw materials may also be responsible for the blockage.

If you find no changes regarding the properties of the mass, you may be using the vacuum vent incorrectly. Ensure you are using the correct type of vacuum vent for your application, as this is crucial to successfully prevent material build-up. There are various types of vents for different materials, such as sticky polymers or hot melts.

If you are confident that the problems are not related to the vacuum vent, the next step is to take a closer look at the die. As a first step, you should clean the die holes or replace the screen if applicable. In this context, it makes sense to compare pressure levels before and after cleaning to evaluate its effectiveness.

If none of the above measures resolve your issues, it is likely that the blockage is caused by the vacuum design itself. If you have recently changed the screws, ensure that no kneading elements are located below the vacuum. Additionally, check the screw elements for wear. Abrasion is usually an indicator that you are not using adequate materials for your application. Corrosion or adhesion may indicate there is still room for optimization concerning the screw profile.

Issue: Vacuum Level Cannot Be Reached

If you regularly experience problems with your degassing zone, it may make sense to upgrade your system with a side devolatilization unit. Monomex's twin-screw side devolatilization unit is an add-on solution that keeps the material reliably in the processing section. Even at maximum torque, the product will not leak. Furthermore, if you find yourself having to clean your vacuum vent regularly to avoid problems, it may be beneficial to upgrade to a twin-screw side devolatilization unit, especially with a simpler design. Cleaning can be done much faster, making operations more efficient and economical.