In extrusion and injection molding production, stability is everything. When the melt pressure keeps fluctuating, output becomes unstable, and product quality starts drifting, manufacturers often face:

• Frequent scrap and customer complaints
• Inconsistent dimensions and weight
• Poor surface finish (lines, roughness, gels)
• Production stops to adjust settings again and again
• Higher energy consumption and lower efficiency

If you are dealing with these issues, it is not just “machine tuning.” In many cases, the real root cause is related to screw & barrel condition, screw design, material feeding stability, and melt flow control.

Let’s break down the main reasons and the most effective solutions.

Why Melt Pressure Fluctuates in Extrusion and Injection

1) Inconsistent feeding or material bridging

One of the most common reasons is unstable feeding. When the hopper feeding is not consistent, the screw cannot maintain a stable melt supply, leading to pressure waves.

Typical causes include:

• Material bridging in the hopper
• Poor bulk density consistency (especially recycled materials)
• Moisture problems (wet resin causes steam and slip)
• Uneven regrind ratio

External link: Learn more about melt pressure behavior in polymer processing
https://www.sciencedirect.com/topics/engineering/melt-pressure

2) Worn screw & barrel causing leakage and backflow

When the barrel inner diameter is worn, or screw flights are worn down, the clearance increases. This creates:

• Melt leakage
• Reduced pumping efficiency
• Unstable pressure build-up
• Lower and unstable output

Even if you increase RPM, the output may not increase proportionally—because the melt is slipping backward.

Solution: Inspect screw OD and barrel ID regularly, especially in high-load production lines.

Internal link (product): Screw & Barrel for Extrusion and Injection
https://juyuan-machinery.com/screw-barrel/

3) Wrong screw design for your material or output target

A screw that is not optimized for your formulation can cause unstable melting and mixing, leading to:

• Temperature inconsistency
• Melt surging
• Pressure fluctuation at the die
• Poor dispersion (especially with fillers, pigments, additives)

For example, high output production often requires a better balance between:

• Solid conveying
• Melting efficiency
• Mixing uniformity
• Stable metering section

Internal link (service): Custom Screw Design & Manufacturing
https://juyuan-machinery.com/custom-screw-barrel/

4) Die head flow restriction or uneven flow channels

If the die head has wear, contamination, or flow channel imbalance, it can create unstable pressure and unstable product shape.

Common symptoms:

• Thickness fluctuation in pipe/profile/sheet
• “Breathing” effect (product size changes periodically)
• Unstable surface gloss and roughness

Internal link (product): Extrusion Die Head & Components
https://juyuan-machinery.com/extrusion-die-head/

The Hidden Cost: Quality Drift Is More Expensive Than You Think

Many factories focus on output only, but unstable pressure often leads to quality drift such as:

• Pipe OD/ID fluctuation
• Profile dimension instability
• Sheet thickness variation
• Injection molded part weight inconsistency
• Weak mechanical strength due to poor mixing

These problems increase:

• Scrap rate
• Rework cost
• Customer rejection risk
• Long-term damage to your brand reputation

Stability means profit.

Proven Solutions to Improve Pressure Stability and Product Consistency

1) Upgrade to a wear-resistant screw & barrel solution

If your production uses abrasive compounds (CaCO₃, glass fiber, recycled materials), wear will happen faster, causing unstable pressure earlier than expected.

A bimetallic barrel and wear-resistant screw can significantly improve:

• Pumping efficiency
• Pressure stability
• Service life

Internal link (product): Bimetallic Screw Barrel
https://juyuan-machinery.com/bimetallic-screw-barrel/

2) Optimize screw structure for stable melt flow

A stable process requires a stable melt supply. A well-designed screw can reduce surging by improving:

• Melting uniformity
• Mixing consistency
• Metering stability

For high-performance extrusion, screw design details matter more than most people think.

3) Maintain correct screw-barrel clearance

Even the best screw design cannot work well if clearance is too large.

Recommended actions:

• Measure wear periodically
• Check screw flights and barrel inner diameter
• Replace or refurbish before the process becomes unstable

4) Improve temperature and filtration control

Pressure fluctuation can also be related to:

• Heater band failure
• Incorrect temperature profile
• Blocked screen pack / filter change delays

A stable melt temperature and clean melt flow are essential for stable pressure.

How We Support Your Stable Production

At Zhoushan Juyuan Machinery Co., Ltd, we help extrusion and injection manufacturers solve process instability by providing:

✅ High-precision screw & barrel manufacturing
✅ Wear-resistant bimetallic solutions
✅ Customized screw design based on material and output
✅ Support for die head components and matching solutions

To recommend the best solution, we only need a few details:

• Machine brand/model
• Screw diameter and L/D
• Material type and filler ratio
• Current output (kg/h) and RPM
• Product type (pipe/profile/sheet/pelletizing/injection)

Contact Us for a Fast Technical Suggestion

Chen Xiujiang
Zhoushan Juyuan Machinery Co., Ltd
🌐 Website: https://juyuan-machinery.com/
📧 Email: cxj.job@gmail.com
📱 Phone/WhatsApp/WeChat: +86 13905808474

If you are facing unstable pressure, unstable output, or drifting product quality, contact us today. We will help you find a reliable screw & barrel solution to stabilize your production and reduce scrap.