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Get Started TodaySpecific energy consumption, or SEC, is the energy the line puts into the material divided by the mass of material it produces, expressed in kWh/kg or kWh/lb. Compared against a baseline for each recipe, it shows when the extruder is working harder to make the same product, often before anyone sees it in dimensions or surface finish. That makes SEC a diagnostic, not just a utility report number.
The core of SEC is specific mechanical energy, or SME: the shaft power delivered to the screw divided by mass throughput. If the drive is putting a given number of kilowatts into the screw and the line is producing a given number of kilograms per hour, the ratio is kWh/kg.
SME is the most informative part of the calculation because it reflects what is happening inside the barrel. Melt viscosity, screw geometry and clearances all affect the torque needed to push a given rate through the die.
Barrel and die heaters add thermal energy on top of the mechanical input. Total SEC is drive energy plus heater energy, minus whatever the barrel cooling removes, all divided by throughput. On many single-screw lines at steady state, the drive supplies most of the melting energy and heaters mainly hold zone temperatures and cover losses.
Tracking the two components separately is more useful than tracking only the total. A rise in mechanical energy paired with heater zones spending more time in cooling points to excess shear. A rise in heater energy with flat mechanical energy points somewhere else, such as a failed heater band or missing insulation.
Pick one unit and use it everywhere: kWh/kg or kWh/lb. One kWh/kg equals about 0.454 kWh/lb, so mixing them in the same report is an easy way to produce a false trend. Also fix whether drive power means drive input, motor output or estimated shaft power after the gearbox. Consistency matters more than the absolute value.
Modern AC drives report motor speed, torque, current and calculated power as parameters that the PLC can read over an industrial network such as EtherNet/IP or PROFINET. Reading power directly from the drive is far better than inferring it from an analog load meter or amps on the HMI.
Older DC drives are harder. Armature voltage and current give a usable power estimate, but the signals are often only available as analog outputs with limited resolution and calibration drift. This is one of the practical reasons plants pursuing process data end up converting DC drives to AC.
The denominator is just as important as the numerator. A gravimetric feeder or blender with loss-in-weight control gives a direct, continuous mass rate. Without it, throughput is estimated from line speed and weight per length, which works but adds lag and error. Pulling feeder rate into the extruder PLC over the network makes real-time SEC possible. The integration details are covered in integrating gravimetric feeders with extruder controls.
Watch for refill periods on loss-in-weight feeders, where the controller holds rate based on a model rather than measuring it. Those intervals should be flagged or excluded from the calculation.
Heater energy can come from dedicated power meters on the heater circuits or be estimated from each zone's output percentage multiplied by its rated heater wattage. The estimate is adequate for trending as long as the heater ratings in the PLC are correct and updated when bands are replaced. Sample all inputs at the same rate, average over a meaningful window such as one to five minutes, and timestamp them together so drive power and throughput line up.
As the flight clearance between screw and barrel grows, more melt leaks back over the flights instead of moving forward. The screw delivers less output per revolution, so to hold rate, operators or the rate control loop increase screw speed. The material sees more shear and SME climbs. A related signal is specific output, mass throughput divided by screw rpm. A gradual decline in kg/h per rpm on a stable recipe is one of the clearest wear indicators available without pulling the screw.
Resin with a higher melt flow index has lower viscosity and generally needs less torque at the same rate, so SME drops. A lower melt flow lot, a change in regrind ratio, higher filler loading or a different supplier grade can all shift SME. When SEC steps up or down abruptly at a lot change, check material records before assuming an equipment problem. A step change usually means material; a slow drift usually means equipment.
Raising barrel setpoints lowers melt viscosity, which reduces mechanical energy but increases heater energy, so the total may change less than either component. A screen pack that is loading up raises head pressure and drive load. Logging setpoint changes alongside SEC makes these causes easy to separate from drift. Stable zone temperature control is a prerequisite for meaningful comparison.
SEC only means something compared against a baseline for the same product, material and die. Store the recipe or product code with every SEC sample so the data can be grouped correctly. Establish the baseline after a known good condition, such as a new or rebuilt screw, a fresh barrel measurement or a validated process window. Cross-recipe comparisons are useful for understanding product differences, not as a wear signal.
SEC is not constant across throughput. Fixed losses such as heater standby, gearbox losses and drive overhead are spread over more kilograms at higher rates, and shear behavior changes with screw speed. The simplest approach is to bin data by rate band and compare only within a band. A more thorough approach is to fit a baseline curve of SEC against throughput or screw speed for each recipe and trend the deviation from that curve.
Startups, purges, product transitions, screen changes and feeder refills all produce SEC values that do not represent normal running. Use simple state logic in the PLC or historian: only accept samples when the line is in run mode, throughput is above a minimum, setpoints have been stable for a defined time and no alarms are active.
Motor load alone rises and falls with rate, material and temperature, so it is a poor wear indicator in isolation. The useful view is load and screw speed plotted against throughput for one recipe over months. A worn screw shows higher rpm for the same rate, a drifting SME and often a rise in melt temperature as the extra shear turns into heat.
Once a baseline exists, define a deviation that prompts investigation, such as a sustained rise in normalized SEC or a decline in specific output beyond the normal scatter for that recipe. Use a rolling average over shifts or days rather than single samples. The goal is a maintenance flag, not an alarm that stops the line. That gives time to plan a screw and barrel measurement during scheduled downtime instead of discovering wear through scrap or lost rate. This fits naturally into the approach in predictive maintenance tips for extruders.
Summarize SEC, specific output and throughput by shift and by product code in a regular report from the historian or HMI. Shift reports can reveal practice differences, such as one crew running hotter profiles or higher screw speeds than others for the same product. Product reports show which recipes consume the most energy per kilogram and how that changes over time. Show the baseline next to the current value so the deviation stands out.
Start by checking whether your current system can supply the inputs: networked drive power or torque, a mass rate from gravimetric feeding, heater output data and a way to tag each sample with a recipe and line state. On many older lines these signals sit in separate controllers and paper logs. A control system that brings drive, feeder and temperature data into one PLC and historian makes it a standard trend. ICT designs extruder control systems that integrate these signals, and a review of what your existing line already provides is a reasonable first step before deciding what to add.
Specific mechanical energy covers only drive power divided by throughput. Specific energy consumption adds heater energy, and sometimes auxiliary loads, to give total energy per unit mass. SME is usually the more sensitive diagnostic for screw condition and material changes.
Yes, by estimating throughput from line speed and measured weight per length, which is common on pipe and profile lines. The result is less immediate and depends on how often weight checks are taken. A gravimetric mass rate gives a cleaner, continuous calculation.
It depends on how often each recipe runs and how much rates vary. A baseline needs enough steady-state data across the normal rate range to see the typical scatter. Recipes that run frequently reach a usable baseline sooner than occasional products.
No. Material lot changes, regrind ratio, moisture, setpoint changes, screen pack loading and die changes can all raise SEC. Wear typically appears as a gradual drift together with declining output per rpm on a stable recipe, while most other causes appear as step changes tied to a specific event.
