Extrusion Rate vs Fiber Characteristics in Melt Blown Nonwoven

What “extrusion rate” means on a Melt blown nonwoven fabric machine

On a Melt blown nonwoven fabric machine, the extrusion rate is the polymer melt throughput delivered to the die. In day-to-day production, it is most useful to express this as:

• Per-hole throughput (g/min/hole): best for comparing dies with different hole counts.
• Throughput per die width (kg/h/m): practical for line-level planning and basis weight control.
• Total extruder output (kg/h): convenient, but it hides die geometry effects.

The keyword intent “How the extrusion rate impacts the fiber characteristics” is fundamentally a mass-balance question: when you push more polymer mass through the same attenuation system (hot air + die geometry + DCD), the fiber formation physics must shift unless you proportionally increase drawing energy.

Why extrusion rate changes fiber formation

1) Mass flow vs. available drawing energy

Meltblown fibers are attenuated by high-velocity hot air. If air velocity/temperature is unchanged and you raise extrusion rate, the air must stretch more mass per unit time. The typical outcome is larger average fiber diameter and a wider diameter distribution unless you also increase air energy (temperature, pressure/flow) or modify the die/airknife settings.

2) Residence time and melt temperature stability

At higher rates, the melt spends less time in the extruder and melt pump. That can reduce thermal equilibration and raise temperature gradients. If the melt temperature varies across the die, fiber diameter and web uniformity will vary across the width.

3) Viscosity and elasticity effects

For common PP meltblown grades (high melt flow), small viscosity changes translate into noticeable diameter shifts. Higher extrusion rate can increase shear heating in the die and change apparent viscosity, which can help or hurt attenuation depending on how stable the temperature control is. Practically: if the line’s temperature control is tight, higher shear can slightly assist flow; if not, it amplifies variability.

Fiber characteristics most sensitive to extrusion rate

Fiber diameter and distribution

In most meltblown setups, increasing extrusion rate at constant air conditions increases fiber diameter. A practical example often seen in filtration-grade PP lines:

• At a “balanced” condition, fibers may average ~2–4 μm.
• After a throughput increase without increasing air draw, averages can drift to ~4–7 μm, with more coarse fibers and fewer ultrafines.

The exact shift depends on polymer rheology, die hole diameter/spacing, air slot gap, air pressure/flow, and die-to-collector distance (DCD), but the direction is consistent: more mass with the same draw tends to produce thicker fibers.

Shot, beads, and “ropey” fibers

When extrusion rate rises beyond the attenuation capacity, the melt stream may not fully fibrillate. Symptoms include beads/shot (polymer droplets), ribbon-like fibers, and local fiber bundling. A useful operational rule is that the onset of shot typically coincides with either:

• Insufficient air momentum for the new mass flow (air pressure/flow too low for the rate), or
• Overly low melt temperature at the higher output (melt too viscous to attenuate smoothly).

Web uniformity and basis-weight profile

Higher throughput raises the risk of cross-direction (CD) basis-weight streaks if die pressure drop and temperature distribution are not uniform. In practice, if the die temperature varies by only a few degrees, the higher-rate condition often makes the profile defects more visible because the process window narrows.

Pore size and surface area

Coarser fibers reduce specific surface area and typically increase effective pore size. That can be beneficial for airflow media, but it can degrade barrier efficiency if the product depends on fine fibers to intercept particles.

Impact on filtration and barrier performance

For filtration (mask media, HVAC, industrial filters), fiber diameter distribution is a primary driver of capture efficiency and pressure drop. When extrusion rate increases and fiber diameter becomes larger (without compensating air draw), typical changes are:

• Lower efficiency at the same basis weight (fewer ultrafines, lower surface area).
• Lower pressure drop can occur (larger pores), but this is not always a win if efficiency falls too much.
• More variability batch-to-batch if temperature/pressure control is marginal, because higher-rate operation often tightens the stable window.

If electret charging is used, fiber diameter still matters: even with charging, shifting from predominantly ~2–4 μm fibers to ~5–8 μm fibers can reduce mechanical capture contribution, forcing higher charge levels or higher basis weight to maintain the same filtration rating.

Practical process windows and what to expect at low vs. high extrusion rate

A practical way to define a “safe” window is to set a fiber target (for example, filtration media often prioritizes a high fraction of ultrafines) and then find the highest extrusion rate that still meets the diameter/shot limits when air temperature/pressure, DCD, and collector speed are at sustainable setpoints.

How to tune extrusion rate without losing fiber quality

When you increase extrusion rate, treat it as a coordinated change across the meltblown “draw package.” The goal is to keep attenuation capacity proportional to mass flow so fiber characteristics remain stable.

Step-by-step tuning workflow

1. Lock your quality metrics first: target fiber diameter range, maximum allowed shot count, basis weight tolerance, and filtration/air-permeability limits.
2. Increase extrusion rate in small increments (for example, 2–5% steps) while holding collector speed and air settings constant to observe the natural direction of change.
3. If fibers coarsen, compensate by increasing draw energy: raise primary air flow/pressure and/or air temperature within equipment limits, then re-check diameter distribution.
4. If shot appears, address it immediately: either reduce rate or increase air momentum/temperature; also verify melt temperature stability at the die zones.
5. Re-balance basis weight: once fiber quality is recovered, adjust collector speed to hit gsm while maintaining the new stable fiber condition.

Which machine settings usually move with extrusion rate

• Primary air temperature and air flow/pressure (adds drawing power).
• Die-to-collector distance (DCD) and suction (affects fiber cooling, laydown, and web openness).
• Melt temperature profile and melt pump stability (reduces CD variation as output rises).

Operational takeaway: raising extrusion rate alone rarely increases output “for free.” In most cases, maintaining the same fiber characteristics requires additional air/thermal capacity or acceptance of a coarser fiber structure.

Troubleshooting checklist when higher extrusion rate causes defects

Common symptoms and likely causes

• Shot/beads increase: attenuation capacity exceeded; air momentum too low; melt too cool/viscous at the die.
• Fiber diameter shifts upward: throughput increase without proportional air energy increase; temperature drift changing viscosity.
• CD streaks or heavy bands: die temperature non-uniformity amplified at higher flow; contamination/partial plugging; melt pump ripple.
• Fused spots / film-like areas: too-hot laydown, short DCD, or excessive local mass flux causing fibers to land before solidifying.

Fast corrective actions (most effective first)

1. Reduce extrusion rate to the last stable point and confirm defects disappear (proves capacity limit vs. random upset).
2. Increase air draw (flow/pressure first, then temperature) while monitoring fiber diameter and shot.
3. Stabilize die temperature profile (verify zone control, insulation, and sensor accuracy across width).
4. Check melt filtration, screen pack condition, and die cleanliness if streaks or intermittent shot persists.

What to document to control fiber characteristics long-term

To consistently manage how the extrusion rate impacts the fiber characteristics on a melt blown nonwoven fabric machine, capture a concise “process fingerprint” for each product grade:

• Extrusion rate expressed as g/min/hole (or kg/h/m) plus melt pump rpm and die pressure.
• Primary air temperature and air pressure/flow setting.
• DCD, suction, collector speed, and basis weight target.
• Measured outcomes: fiber diameter (average and spread), shot count (or qualitative rating), air permeability/pressure drop, and (if relevant) filtration efficiency.

When those inputs are tracked together, extrusion rate changes become predictable: if a higher rate is required, you can pre-plan the matching air/thermal adjustments instead of reacting to quality losses after the fact.