A sudden or gradual drop in melt pressure on extrusion lines is a common problem that directly affects product quality and dimensional consistency. In this article, we systematically examine the most common causes of pressure drop.
1. Screw-Barrel Wear
An increase in the clearance between the screw and the barrel causes part of the melt to flow backward (backflow) instead of moving forward. This is one of the most common causes that directly reduces pressure-building capacity. This is the first point to check when in doubt.
2. Insufficient Material Flow in the Feed Zone
Bridging in the hopper, moisture, or inconsistent pellet size can cause irregular material intake into the screw feed zone, leading to pressure fluctuation.
3. An Unsuitable Temperature Profile
Setting barrel temperatures lower than required can prevent the melt from fully plasticizing, while setting them higher than required can excessively lower viscosity and weaken pressure buildup. The temperature profile needs to be optimized for the raw material.
4. Change in Die Resistance
Material residue accumulating in the die flow channels or die wear can change flow resistance and affect pressure readings. Regular die cleaning and inspection reduces this risk.
5. Filter (Screen Pack) Clogging
Contamination buildup in melt filters can initially raise pressure, but over time it can make flow irregular and cause fluctuations. Tracking filter replacement intervals is important.
6. Check Ring Wear — A Common Point with Injection
Similar to injection applications, wear of the check ring mechanisms used in some extrusion systems can also be an additional source of pressure loss.
How to Correctly Diagnose the Problem
Pressure drop is usually not due to a single cause but a combination of multiple factors. For a systematic check, it is recommended to first measure the screw-barrel clearance, then examine the temperature profile, feed arrangement and die condition in turn.
We can evaluate the screw-barrel condition together for the line where you are experiencing a pressure problem.
View Our Screw-Barrel Products Get Technical SupportOther Articles
- How to Tell It Is Time to Replace Your Screw and Barrel? 8 Signs of Wear
- What Dimensions and Information Are Needed to Get a Screw-Barrel Quote?
- Differences Between Bimetal Screw-Barrels and Nitrided Screw-Barrels
- How to Measure Barrel Inner Diameter and Screw Outer Diameter? How to Check Wear Clearance?
- How Does Screw-Barrel Wear Affect Capacity, Pressure and Energy Consumption?
- Which Screw-Barrel Material Should Be Chosen for Machines Processing Glass Fiber, Calcium Carbonate and Mineral Filler?
- 38CrMoAlA, Bimetal and Tool Steel: How to Choose a Screw-Barrel Material?
- Differences Between Parallel Twin Screws and Conical Twin Screws
- Can a Screw-Barrel Be Manufactured Without Knowing the Machine Brand and Model?
