Melt Pump Modes: For Single to Twin Screw Operation

The Quick Guide to Keeping Your Extrusion Line Flowing

Because nobody has time for pressure fluctuations and throughput headaches

For over 35 years, gear pumps with control systems have been the Extrusion industry standard  for stabilizing extrusion output. But here's what surprised me: after years running single-screw lines, I only knew one operating mode. It wasn't until I got into twin-screw extrusion that I discovered there were other options. Here's the breakdown of the main modes and what they actually do:

Constant Suction Pressure Mode (The Single-Screw Workhorse)

The pump speed adjusts to maintain steady pressure on the inlet side. The controller measures inlet pressure and regulates the extruder screw speed to maintain the setpoint

Why 95% of single-screw operations use this: Stabilizing the die discharge, lowering the extruder's head pressure boosts output per screw RPM by at least 10%, drops melt temperature (roughly 6-7°F per 1,000 psi reduction), and doubles the life of thrust bearings and screws. Translation: stable output, more output, cooler melt, longer equipment life.

The downside : You're stabilizing the extruder side, but discharge pressure can still vary.

Best for: Single-screw lines where maximizing stability and output of extruders with multiple resins and a single screw design.

This was the mode for years in my single-screw world. Simple, effective, and it just worked,

until I entered the Twin Screw Extrusion world.

I initially assumed that constant pressure mode would apply to twin screw systems but it took me some time to realize this isn't the case.

The Melt Pump mode Primer from PSI Polymer Systems Inc was instrumental in helping me understand the three modes used in twin screw melt pump operation. I've included it here for your reference.

Don't blame the Extrusion Operator for an unreliable production line you haven't got under control.

Throughout the years I've witnessed numerous frustrated supervisors and production managers blaming the operators when things go wrong and production requirements aren't being met. Upon reviewing the process, it becomes clear that the process itself is the real issue. Even today, despite all the Six Sigma and Lean methodologies, management can overlook the true problem under the pressure of a poorly designed process and blame the operators instead. It is the process however that always dictates the output, and even the most skilled operators can't be expected to consistently deliver positive results.

After years of troubleshooting, problem-solving and standardizing to enhance suboptimal extrusion processes, I found myself contemplating a systematic approach to the task. After some reflection, I was able to outline what I believe are the foundational principles for optimizing extrusion processes. Below are the critical points that should be relied upon and implemented for optimal results.

THE SEVEN PRINCIPLES OF PROCESS EXCELLENCE

A Framework for Operational Excellence and Continuous Improvement

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1. Process Drives the Output

"If you can't describe what you are doing as a process, you don't know what you're doing." — W. Edwards Deming

Output quality is determined by process quality, not by inspection or effort alone.

The fundamental principle of process management recognizes that consistent, high-quality outputs are the natural result of well-designed and controlled processes. Attempting to inspect quality into products or relying solely on individual effort cannot compensate for poorly designed or inconsistent processes. Focus on process excellence rather than output inspection.

2. A Process Not Documented Isn't Standardized

"If it isn't written down, it doesn't exist." — Philippe Kahn

Before you can standardize, you must clearly define and document what the process actually is.

Documentation is the foundation of standardization. Without clear, written procedures that define each step, input, output, and decision point, there is no common reference for what the "standard" should be. Documentation creates the baseline from which all improvement efforts begin and ensures knowledge transfer across the organization.

3. A Process Not Standardized Can't Be Controlled

"Without standards, there can be no improvement." — Taiichi Ohno

Without a defined standard, there is no baseline to maintain or reference point for consistency.

Control requires a target state—a standard to maintain. Standardization establishes the "right way" to execute a process, creating the reference point against which actual performance can be compared. Without this standard, there is no meaningful way to determine if a process is in control or out of control. Control is the act of maintaining adherence to the established

standard.

4. A Process Not Measured Can't Be Controlled and Improved

"In God we trust; all others must bring data." — W. Edwards Deming

You need data to maintain control within standards and to identify improvement opportunities.

Measurement serves two critical functions: First, it provides the feedback necessary to know whether a process is operating within its defined standards (control). Second, it generates the data required to understand current performance levels and verify that changes actually result in improvements. Without measurement, both control and improvement become guesswork rather than data-driven management.

5. A Process Not Standardized, Measured, and Improved Will Be Dominated by Variation

"Every system is perfectly designed to get the results it gets." — Paul Batalden

Without all three elements working together, inconsistency becomes the defining characteristic.

Variation is the natural state of unmanaged processes. Only through the combination of standardization (defining the target), measurement (monitoring performance), and improvement (reducing capability gaps) can variation be minimized. When any of these elements is missing, the process will exhibit unpredictable and inconsistent results, making it unreliable.

6. Variation Erodes Quality, Productivity, and Efficiency

"Uncontrolled variation is the enemy of quality." — W. Edwards Deming

Inconsistency wastes resources, creates defects, and reduces predictability.

Process variation is the enemy of operational excellence. It leads to defects and rework (quality loss), unpredictable throughput and scheduling difficulties (productivity loss), and wasted materials, time, and effort (efficiency loss). Variation also undermines customer confidence and increases costs throughout the value chain. Reducing variation is essential to achieving competitive advantage.

7. A Process Not Maintained Can't Be Sustained

"Sustaining gains is as important as making them in the first place." — John Kotter

Even improved processes degrade without ongoing attention, training, and reinforcement.

Process entropy is real—without continuous maintenance, even the best processes will degrade over time. Maintenance includes regular audits, refresher training, standard work updates, and management reinforcement. Sustainability requires building a culture of adherence and creating systems that make it easier to follow the standard than to deviate from it. Continuous improvement must be matched by continuous maintenance.

THE SEQUENTIAL LOGIC: Document → Standardize → Control → Measure → Improve → Maintain