How to Select a Masterbatch Feeder: Volumetric, Gravimetric, and Loss-in-Weight Types
Introduction
Color control in plastic products is a long-standing production management challenge for many factories. Too much masterbatch and the color is too deep — cost wasted. Too little and the color is too light — parts fail inspection. Color shifts every time there is a shift change or batch change — these problems all trace back to one root cause: insufficient precision in masterbatch addition.
A masterbatch feeder automatically and precisely controls the amount of masterbatch added, delivering consistent color from batch to batch while eliminating the random error of manual addition. Masterbatch feeders fall into three main categories — volumetric, gravimetric, and loss-in-weight — with significant differences in operating principle and accuracy. Matching the right type to the application saves money and stabilizes quality. The wrong choice spends money without solving the problem.
What a Masterbatch Feeder Does
A masterbatch feeder is installed above the forming machine's (injection machine, extruder, blown film line) material inlet. It automatically blends masterbatch pellets or powder into the main material at a set ratio.
Masterbatch addition ratios are typically 0.5–5%, depending on the desired depth of color and the masterbatch's tinting strength. This sounds small, but in large-volume production a 0.1% addition error can accumulate to produce visible color deviation or unexpected masterbatch cost overruns. The core value of a masterbatch feeder is making each addition accurate and repeatable — not dependent on operator experience or judgment.
Volumetric Masterbatch Feeder
Operating principle
A volumetric masterbatch feeder controls addition by counting screw rotations. Each revolution of the screw delivers a fixed volume of masterbatch. Setting the rotation count sets the addition quantity; the addition ratio is controlled by the ratio of screw speed to main material feed rate.
Advantages
Low equipment cost: volumetric feeders have a relatively simple structure and sell at much lower prices than gravimetric or loss-in-weight models — the most common entry-level choice for small-to-medium factories.
Simple setup: setting the ratio requires only adjusting the speed parameter. The control interface is intuitive and easy for general operators to learn quickly.
Suitable for stable production conditions: when feed rate is stable and masterbatch pellet size is uniform and consistent, volumetric feeders provide accuracy adequate for most standard color control needs.
Limitations
Cannot compensate for feed rate changes: if the main material feed rate changes for any reason, the actual masterbatch addition ratio drifts. The device cannot detect this change and self-correct.
Masterbatch density and pellet size affect accuracy: even small batch-to-batch differences in masterbatch pellet size or density mean the same speed setting delivers different actual weights — introducing addition ratio deviation.
Higher risk for high-color-consistency requirements: for products with strict color consistency requirements, volumetric accuracy may be insufficient. Batch-to-batch color differences may be visible to the naked eye.
Gravimetric Masterbatch Feeder
Operating principle
A gravimetric masterbatch feeder controls addition by actual weighing. The device has a built-in high-precision weight sensor that continuously monitors actual masterbatch addition weight, adjusting masterbatch output in real time based on actual main material feed volume — ensuring the addition ratio remains accurate at all times.
Advantages
High accuracy with automatic compensation: directly measuring actual weight, unaffected by masterbatch pellet size or density variation, and unaffected by main material feed rate fluctuations. Accuracy is typically within ±0.1–0.5%.
Suitable for high-requirement products: automotive interior components, premium appliance housings, medical device parts — products with strict color consistency requirements benefit from the batch-to-batch stability gravimetric feeders provide.
Strong data recording capability: typically logs complete material usage data — actual masterbatch addition per shift and per batch — facilitating cost accounting and quality traceability.
Limitations
Higher equipment cost: high-precision weighing systems place gravimetric feeder prices 3–5 times higher than volumetric models.
Higher maintenance requirements: weight sensors require periodic calibration with standard weights; maintenance complexity is higher than volumetric feeders.
Sensitive to environmental vibration: the weighing system is sensitive to external vibration. If there is a strong vibration source nearby, it may interfere with sensor readings.
Loss-in-Weight Masterbatch Feeder
Operating principle
The loss-in-weight feeder is the most technically advanced of the three types, using dynamic continuous metering. Each material component is precisely controlled by its own screw for flow rate and ratio. Mixed material falls into a lower hopper; the system automatically adjusts each material's supply speed based on the extruder's actual output — achieving precise ratios.
"Loss-in-weight" refers to the measurement method: the system continuously monitors the rate of material weight decrease (i.e., discharge rate) and adjusts screw speed accordingly in real time, ensuring each component's actual discharge strictly matches the set ratio. It is a dynamic closed-loop continuous metering method.
Advantages
Dynamic continuous metering — highest accuracy: loss-in-weight feeders can achieve ratio accuracy within ±0.3%, maintained continuously throughout production without batch correction. Best performance for color consistency control over long-duration continuous production runs.
Automatically follows extruder output: the core advantage is automatic adjustment of supply speed based on the extruder's actual output rate. No manual re-setting needed when output changes — particularly suited to extruder applications where output varies with production conditions.
Three external interface modes: configurable with analog signal, digital signal, or communication signal interfaces depending on customer requirements — easy integration with factory automation control systems or MES systems.
All-stainless-steel material contact parts: all components that contact material are manufactured from 304 stainless steel — meeting stricter hygiene and corrosion protection requirements for food-related or material-purity-sensitive production.
Quick color-change and cleaning: the bin design allows fast, easy cleaning when changing formulations — shorter shutdown time for color changes compared to other types, suitable for production lines with frequent color changes.
Wide application range: applicable to plastic film, cable, pipe, sheet, and other continuous extrusion lines.
Limitations
Highest equipment cost: loss-in-weight feeders have the highest technical complexity and precision — and correspondingly the highest investment. Suited to factories with the strictest color and formulation accuracy requirements and larger production scale.
Primarily for continuous extrusion processes: the dynamic continuous metering advantage is most fully realized in continuous extrusion operations. For injection molding's intermittent process, gravimetric feeders are generally sufficient — loss-in-weight level is not always necessary.
Quick Comparison
Volumetric feeder: control method = screw rotations (volumetric); accuracy = ±1–3%; cost = low; auto-compensation = none; best process = injection, extrusion, blow molding; best products = standard color requirements.
Gravimetric feeder: control method = actual weighing; accuracy = ±0.1–0.3%; cost = medium to high; auto-compensation = yes (per batch); best process = injection, extrusion, blow molding; best products = high color consistency requirements.
Loss-in-weight feeder: control method = dynamic continuous metering; accuracy = within ±0.1% (continuous); cost = high; auto-compensation = yes (continuous and dynamic); external interfaces = three modes available; contact materials = 304 stainless steel; best process = continuous extrusion and blow film; best products = highest accuracy requirements.
Application and Selection Guidance
Choose volumetric when
Color requirements are not strict and color deviation tolerance is generous — industrial crates, agricultural products, construction fittings — volumetric accuracy is fully adequate. Stable production conditions with low changeover frequency, or budget-limited small-to-medium factories — volumetric is the practical entry-level choice balancing cost and quality.
Choose gravimetric when
High color consistency requirements — automotive parts, electronics housings, medical device components. Brand customers with documented color control requirements, or applications needing precise control of multiple additives simultaneously. High-unit-price specialty masterbatch (pearlescent, metallic effect, fluorescent) where precise metering quickly pays back the investment through material savings.
Choose loss-in-weight when
Primarily for continuous extrusion processes — film, cable, pipe, sheet — where long-duration continuous stable production makes loss-in-weight dynamic continuous metering most valuable. Applications requiring integration with factory automation systems where loss-in-weight three interface modes provide maximum flexibility. Processes with food safety or material purity standards where 304 stainless steel contact parts are a requirement. Production lines with frequent color changes needing to minimize changeover cleaning time.
Installation and Calibration
Installation position
Masterbatch feeders are installed above the forming machine's material inlet. For injection machines, adding at the hopper inlet typically gives the best mixing. For extruders, adding at the screw feed section is recommended so masterbatch and main material mix thoroughly in the screw. Loss-in-weight feeder integration settings must confirm compatibility with the extruder's control system interface mode. Confirm that the feeder's discharge outlet aligns securely with the hopper inlet to prevent masterbatch leaking from gaps.
Volumetric calibration
When changing masterbatch batches, re-calibrate the output rate. Run the feeder at the set speed for a fixed time, weigh the actual output with a scale, and adjust the speed setting based on this measurement. Any batch with noticeably different masterbatch brand or pellet size must be re-calibrated — previous batch settings cannot be carried over.
Gravimetric calibration
The weight sensor requires periodic calibration with standard weights. Generally recommended quarterly; monthly for high-accuracy applications. Perform calibration when the device is at rest and free from vibration.
Loss-in-weight calibration and integration
Loss-in-weight systems use dynamic continuous metering and continuously self-correct during normal operation — daily manual calibration like volumetric systems is not necessary. However, when changing material formulations or adjusting line parameters, re-confirm each component's set ratio. Interface mode settings (analog, digital, or communication signal) should be confirmed and integration tested during initial installation with supplier assistance.
Common Problems and Prevention
Masterbatch bridging causing uneven discharge: masterbatch pellets in the storage hopper jam against each other due to static or pellet shape, causing intermittent feed interruption — parts show alternating light and dark color. Prevention: confirm uniform masterbatch pellet size; install a vibrator or bridge-breaking device in the storage hopper.
Volumetric color shift after batch change: color shifts after switching to a new masterbatch batch but the set ratio was not changed. Prevention: always re-calibrate output rate after batch changes — never assume different batches have identical density and pellet size.
Gravimetric sensor readings unstable: weigh values continuously fluctuate causing unstable addition ratios — typically caused by a nearby vibration source or a sensor needing recalibration. Add vibration-isolation pads under the installation base and follow the manufacturer's recommended calibration schedule.
Masterbatch and main material separating in the hopper: density differences cause masterbatch to sink to the bottom and main material to float, resulting in uneven color at the beginning and end of production. Prevention: shorten masterbatch time in the hopper; position the feeder outlet near the hopper outlet rather than the top; or install a slow-speed stirrer inside the hopper to prevent density segregation.
Related articles: Why Do Plastic Raw Materials Need Drying? — raw material feed management basics; What Is a Vacuum Loader? — automatic loading equipment; What Is a Central Material Conveying System? — overall plant feeding automation planning.