Kerke, a Wanplas factory with more than 12 years of dedicated experience in co-rotating parallel twin-screw compounding extruders, builds complete high-fill compounding lines for masterbatch and modified plastic producers in more than 70 countries. A high-fill twin-screw compound line is only as reliable as the machines that feed it and the machines that cut the melt into uniform pellets. The extruder barrel and screw do the mixing, but feeding and pelletizing decide whether the line runs for days without stopping, whether the filler disperses without agglomerates, and whether the final pellet ships as a saleable product.
This article explains the supporting feeding and pelletizing machines that determine the real-world performance of a high-fill twin-screw compound line. You will learn how loss-in-weight feeding, side feeding, and crammer feeding handle low-bulk-density fillers such as calcium carbonate, talc, and glass fiber; how liquid feeding introduces oils, peroxides, and coupling agents without streaking; and how die-face hot cutting and underwater pelletizing solve the strand-breakage problem that appears once filler loading climbs past 40 percent. We then show how Kerke configures these machines around the KTE series twin-screw extruder so the whole line is balanced instead of a collection of units that fight each other.
Why a High-Fill Compound Line Lives or Dies on Its Support Machines
A high-fill formulation is defined by a large mass fraction of solid additive inside a polymer matrix. Typical high-fill compounds carry 40 to 80 percent mineral filler, flame retardant, or fiber. The polymer may be a commodity resin such as polypropylene or polyethylene, an engineering plastic such as polyamide or polybutylene terephthalate, or a recycled stream such as regrind and flakes. The high solid fraction changes every handling step before and after the extruder barrel.
Before the barrel, the filler is usually a fine powder with very low bulk density. Calcium carbonate and talc often sit below 0.6 grams per cubic centimeter in loose bulk density. Such powders bridge in a plain hopper, flush through a volumetric screw, and surge into the throat. The result is an unstable feed rate that the screw cannot correct. Because the screw meters on volume, not mass, a surging feeder makes the compound recipe wander from lot to lot even when the operator changes nothing.
After the barrel, the melt is stiff and abrasive. High filler raises melt viscosity, increases die pressure, and accelerates wear on the die plate and cutting edges. Long strands of a 60 percent filler masterbatch snap under tension, clog the water bath, and force a line stop. Choosing the wrong pelletizing method turns a capable extruder into a stop-start liability. Supporting machines are therefore not accessories. They are the difference between a line that compounds continuously and a line that needs an operator standing by the water bath with scissors.
The engineering answer is to treat feeding and pelletizing as part of the same mass-balance problem. Material enters by mass, mixes by shear, and leaves as a counted pellet. Kerke designs the KTE twin-screw extruder, the feeder skid, and the pelletizer as one matched system, so the throughput of the feeder, the output of the screw, and the cut rate of the pelletizer are specified together rather than bought separately.
Two physical effects grow with filler loading and shape the supporting machine choice. The first is wear. Mineral filler and glass fiber act like grinding paste inside the barrel, so the screw and liner life fall as filler rises. Feeding abrasive filler through a side port limits that wear to a short barrel section and protects the expensive main screw. The second is thermal load. Filling a polymer raises the energy needed to melt and pump the mix, and the melt holds more heat per unit of polymer. The pelletizing step must remove that heat fast enough that pellets do not agglomerate in the conveyor, which is why die-face and underwater methods with active cooling outperform a passive water bath at high fill. Both effects argue for designing the feeder and pelletizer with the screw, not after it.
Feeding Technology for Low-Bulk-Density Fillers
Feeding is the first control point for recipe accuracy. Five feeder types cover the filler and additive families found in high-fill compounding. Each solves a different flow problem, and most production lines use two or three together because a single recipe rarely contains only free-flowing pellets.
A volumetric feeder is the simplest option. It turns a metering screw at a set speed and assumes a fixed bulk density. It works for free-flowing pelletized additives where small rate drift is acceptable, but it fails on fluffy powder. A loss-in-weight feeder hangs the whole hopper and screw on load cells and controls screw speed from the measured loss of mass per unit time. This closes the loop on actual material flow, so bridging or flushing downstream of the hopper no longer ruins the rate. Accuracy near plus or minus 0.5 percent is normal for a well-tuned loss-in-weight feeder handling mineral powder.
A side feeder is a second, smaller twin-screw unit mounted on the barrel at a downstream port. It adds glass fiber, high-bulk-density minerals, or shear-sensitive additives after the main melting zone. Adding fiber downstream shortens the residence time in the high-shear zone, reduces fiber breakage, and lowers wear on the main screw because the abrasive filler never passes the full length. Side feeding is the standard answer for glass-fiber-reinforced compounds above 20 percent fiber.
A crammer feeder uses a fast-spinning screw inside a vertical tube to force material into the throat. It is the right tool for low-bulk-density, dusty, or fluffy material that a gravity hopper cannot move. Wood flour, recycled fluff, expanded perlite, and talc batches with poor flow all benefit from crammer assist. Without it, the operator watches the throat starve and the screw slip. A liquid feeder injects oils, peroxides, coupling agents, and pigment slurries through a pump and nozzle. Liquids must enter where they can be dispersed quickly, so the injection point is chosen with the screw configuration, not left to chance.
| Feeder type | Best for | Metering accuracy | Flow risk solved |
|---|---|---|---|
| Volumetric feeder | Free-flowing pellets, minor additives | Plus or minus 1 to 2 percent | None, assumes stable bulk density |
| Loss-in-weight feeder | Mineral powders, CaCO3, talc, TiO2 | Near plus or minus 0.5 percent | Bridging, flushing, surge |
| Side feeder | Glass fiber, downstream minerals | Matched to main screw | Fiber breakage, main screw wear |
| Crammer feeder | Fluffy, low-bulk-density fillers | Throughput controlled | Throat starvation, bridging |
| Liquid feeder | Oils, peroxides, coupling agents | Plus or minus 1 percent | Streaking, local overheating |
Recipe accuracy is only one benefit. A gravimetric line also gives the plant a mass balance. Because every feeder reports actual kilograms per hour, the control system can show total filler added versus resin consumed, flag a drift before it reaches the pellet, and store the whole recipe for repeat orders. This is why Kerke positions loss-in-weight feeding as the default for any high-fill masterbatch that must hold color or properties across campaigns.
Different fillers demand different feeder choices, and the table below maps the common high-fill additives to the feeding method that handles each one. Bulk density and particle shape drive the decision more than chemistry. A spherical bead flows differently from a platey talc, and both differ from a fibrous glass roving. Matching the feeder to the particle shape removes most of the starvation and surge problems that plague first-time high-fill lines.
| Common filler | Typical bulk density | Recommended feeder | Special note |
|---|---|---|---|
| Calcium carbonate | 0.4 to 0.9 g/cm3 | Loss-in-weight | Use hopper agitator |
| Talc | 0.3 to 0.7 g/cm3 | Loss-in-weight | Platey, needs anti-bridge |
| Glass fiber | Roving, bulk low | Side feeder | Chopper at inlet |
| Wood flour | 0.2 to 0.4 g/cm3 | Crammer feeder | Fluffy, must force feed |
| Flame retardant | 0.5 to 1.0 g/cm3 | Loss-in-weight | Often dusty, vent exhaust |
| Pigment slurry | Liquid | Liquid feeder | Heated line for viscosity |
A useful way to picture the balance is a simple mass check. If a line targets 1000 kilograms per hour of a 70 percent filler masterbatch, the feeder must deliver 700 kilograms per hour of solid and the resin side must deliver 300 kilograms per hour, while the screw mixes them and the pelletizer cuts 1000 kilograms per hour of melt into pellets. If the loss-in-weight feeder drifts to 660 kilograms per hour, the final product is 66 percent filler, not 70, and the customer’s coloring or stiffness spec fails. The control loop that ties feeder, screw, and pelletizer together is what keeps that 700 kilogram figure steady across an eight-hour shift and across the next campaign.
Kerke Feeding Machines Built Around the KTE Twin-Screw Extruder
Kerke supplies the full feeder family as modules that mount to the KTE series co-rotating parallel twin-screw extruder. The KTE range runs from the KTE-16B laboratory unit up to the KTE-135D production machine, with output from roughly 30 kilograms per hour to high capacity. The feeder skid scales with the barrel: a small KTE-25B pilot line uses single loss-in-weight feeders on a frame, while a KTE-75 or KTE-95 production line uses a multi-feeder platform with a side feeder and a liquid pump.
Kerke loss-in-weight feeders use a twin-screw or single-screw metering section driven by a servo motor, with the hopper suspended on high-resolution load cells. The controller reads mass loss each second and adjusts screw speed to hold the set rate. For dusty mineral powders Kerke fits a hopper agitator and a vertical agitator screw so the powder discharges evenly instead of rat-holing. The same controller talks to the main extruder over a common bus, so when the line speed changes, every feeder rescales together and the recipe ratio stays fixed.
The Kerke side feeder is a twin-screw unit with its own gearbox and drive, mounted on a barrel port through a standardized flange. It is sized so the added throughput matches the main screw at the chosen operating point. For glass-fiber reinforced compounds Kerke offers a fiber roving inlet with a chopper and a gentle metering zone that lays fiber into the melt with minimal attrition. The crammer feeder option bolts onto the main throat for fluffy filler, and the liquid feeder uses a positive-displacement pump with a heated line for peroxide or oil.
| Kerke module | Throughput range | Metering accuracy | Drive |
|---|---|---|---|
| Loss-in-weight feeder | 0.5 to 2000 kg/h | Near plus or minus 0.5 percent | Servo motor |
| Side feeder | 5 to 600 kg/h fiber or filler | Matched to main screw | Dedicated gearbox |
| Crammer feeder | 20 to 800 kg/h | Throughput controlled | AC motor with inverter |
| Volumetric feeder | 1 to 1500 kg/h | Plus or minus 1 to 2 percent | Inverter drive |
| Liquid feeder | 0.2 to 120 L/h | Plus or minus 1 percent | Positive pump |
Kerke screw design supports the feeding story. The KTE screw assembly is computer-aided designed with kneading and co-type elements that give excellent self-cleaning, so a high-filler recipe does not leave residue that degrades the next run. The elements are interchangeable, which lets Kerke tune the screw layout to the filler type: more conveying and gentle kneading for fiber, more high-shear kneading for agglomerated mineral. Good interchangeability also means a plant can reconfigure one barrel for several products instead of buying a separate line for each.
Wanplas, as the parent brand, shares the quality standards and service promises across its factory network, so a Kerke feeder and pelletizer package inherits the group’s testing, spare-parts, and open-factory policies described later. This matters for buyers who want one accountable supplier for the whole supporting system rather than a feeder from one source and a pelletizer from another.
Pelletizing Systems Downstream of the Compounding Extruder
Pelletizing converts the extruded melt strand or melt sheet into uniform pellets that a customer can dose, blend, and re-melt. For high-fill compounds the choice of cutting method decides whether the line runs unattended or needs constant attention. Kerke offers the full cutting range so the method matches the filler level and the pellet quality target.
Strand pelletizing pulls one or more melt strands through a water bath and a pelletizer. Water-cooled strand pelletizing is the lowest-cost route and suits low-fill and heat-sensitive grades. Air-cooled strand pelletizing skips the water bath for soft or water-sensitive compounds. The weakness at high fill is strand strength: a masterbatch at 60 percent pigment or a compound at 70 percent filler simply snaps, so strands break, wrap the puller, and stop the line. Strand pelletizing stays the right call when filler is low and capital must stay minimal, but it is fragile above roughly 40 percent filler.
Die-face hot cutting fixes the strand problem by cutting the melt at the die before it forms a long strand. In air-cooled die-face hot cutting, a rotating blade shears pellets at the die face and a stream of air conveys and cools them. It handles highly filled and pigmented compounds that would break as strands, and it needs less floor space than a water bath. Water ring die-face hot cutting uses a ring of water at the die to cool and convey pellets, raising the practical output. Underwater pelletizing cuts inside a pressurized water chamber, giving the most uniform, spherical pellet at the highest output and protecting heat-sensitive melt, but it carries the highest equipment and maintenance cost. Eccentric water mist hot cutting is a Kerke variant that balances cost and pellet quality for mid-range filled compounds.
| Kerke method | Output range | Pellet size | Filler level fit |
|---|---|---|---|
| Water-cooled strand | Low to medium | 2 to 4 mm | Up to 40 percent |
| Air-cooled strand | Low to medium | 2 to 4 mm | Heat-sensitive grades |
| Air-cooled die-face hot cut | Medium | 2 to 3 mm | High fill, masterbatch |
| Water ring die-face hot cut | Medium to high | 2 to 3 mm | High fill, high output |
| Underwater granulation | High | 1.5 to 3 mm | High output, uniform pellet |
Die selection ties feeding to pelletizing. The number and diameter of die holes set the melt velocity and the load on each cutting edge. A high-fill melt is more viscous, so Kerke engineers the die hole count and the blade speed together with the feeder rate so the pelletizer keeps up with the extruder without over-thinning the strand or overloading the blade. A balanced die also keeps pellet length uniform, which matters when the customer meters by count or volume rather than weight.
Ancillary machines complete the pelletizing cell. A dewatering screen and a centrifugal dryer remove surface water from water-ring or underwater cuts. A vibrating screen separates fines and longs. A central loader returns pellets to the silo. None of these are optional at production scale because fines raise dust, lower bulk density, and hurt the customer’s dosing accuracy. Kerke supplies these as part of the pelletizing package so the cell delivers a screened, dried pellet rather than a wet mixture.
The water used in water-ring and underwater cutting must be cleaned and cooled in a loop. A filter removes grit carried from the die face, and a heat exchanger pulls the heat picked up from the melt so the water returns to the cutting chamber below the temperature that would soften the pellet. Skipping the loop lets fine filler circulate, scratch the die, and raise water temperature until pellets stick together. Kerke sizes the filter and heat exchanger to the line output, and pairs them with the dryer so the finished pellet leaves the cell at a stable moisture level that passes the customer’s quality gate. Classification by the vibrating screen also protects the next process: removing longs and fines gives a uniform pellet that meters evenly in the customer’s dosing unit and avoids the bridge-and-surge problem that started this article at the feeder.
Configuring and Selecting a Balanced Supporting System
A balanced high-fill line matches three rates: feeder throughput, screw output, and pelletizer cut rate. When one lags, the line either starves or floods. Kerke configures the package from the recipe upward, starting with the filler type, the target filler percentage, the resin, and the required output. The selection table below maps common high-fill cases to a recommended Kerke configuration.
| Requirement | Recommended Kerke setup | Pelletizing | Note |
|---|---|---|---|
| Filler masterbatch 60 to 70 percent | KTE-65 with loss-in-weight feeder | Air-cooled die-face hot cut | Strand breaks at this fill |
| Glass-fiber compound 20 to 50 percent | KTE-75 with side feeder | Water ring die-face cut | Fiber added downstream |
| Filler compound 30 percent, low cost | KTE-50 with volumetric feeder | Water-cooled strand | Capital stays low |
| Wood-flour WPC, fluffy filler | KTE-72 with crammer feeder | Air-cooled die-face hot cut | No throat starvation |
| High output 1000 plus kg/h | KTE-95 or KTE-135D with multi-feeder | Underwater granulation | Uniform pellet at scale |
High-fill compounds made on Kerke lines reach many end industries. In masterbatch production, color masterbatch, filler masterbatch, additive masterbatch, black masterbatch, and textile masterbatch all rely on stable feeding and clean cutting. In plastic compounding, engineering plastics, biodegradable plastics, cable compounds, PVC compounds, thermoplastic elastomers, and wood-plastic composites use the same supporting machines with different screw and die layouts. Recycled PET flakes and similar streams also pass through Kerke feeding and pelletizing when a plant upgrades recovered material into a compound.
Service and support close the loop. Kerke runs pre-shipment testing on the full line, not just the extruder, so the feeder rates and pelletizer cut are proven together. Engineers handle installation and commissioning on site, train the operator team, and stay reachable through remote monitoring of the control system. The Wanplas group policy supplies USD 500 free spare parts per year and replaces damaged parts within warranty, and Kerke keeps an open-factory policy that welcomes customers to inspect the line and run their own material before purchase.
Planning the supporting machines early also simplifies the rest of the project. Once the feeder platform, screw size, and pelletizer type are fixed, the plant can size the feeding room, the water loop, and the power supply without rework. Kerke sends a layout drawing that places each module within reach of the barrel and the utility connections, so the line fits the building instead of the building being rebuilt around the line. That coordinated layout is the practical payoff of buying feeding, extrusion, and pelletizing as one Kerke system rather than three separate purchases.
Frequently Asked Questions
Why do high-fill formulations need gravimetric feeding instead of volumetric feeding?
High-fill recipes use low-bulk-density powders that bridge and flush. A loss-in-weight feeder weighs the actual material flow and holds recipe accuracy near plus or minus 0.5 percent, which keeps pellet properties consistent from lot to lot.
When should a side feeder be used on a twin-screw line?
Use a side feeder for glass fiber, high-bulk-density minerals, or shear-sensitive additives added downstream. Side feeding reduces screw wear, limits degradation, and improves dispersion because the material enters after the main melting zone.
Which pelletizing method suits highly filled compounds?
Die-face hot cutting and underwater pelletizing suit high filler loadings because strands with 40 to 80 percent filler break easily. Strand pelletizing stays attractive for low fill and heat-sensitive grades where capital cost must stay low.
Can Kerke feeders integrate with an existing twin-screw extruder?
Yes. Kerke supplies gravimetric feeders, side feeders, and liquid feeders as stand-alone modules with a common control bus, so they retrofit to most co-rotating twin-screw barrels through a standardized mount and recipe interface.
How does crammer feeding help fluffy or recycled fillers?
A crammer feeder uses a spinning screw to force low-bulk-density, dusty, or fluffy material into the throat without bridging. It is the standard solution for wood flour, recycled fluff, and talc batches with poor flow.
What service does Kerke provide for a complete feeding and pelletizing package?
Kerke runs pre-shipment line testing, provides installation and commissioning, training, remote support, and USD 500 free spare parts per year, plus an open-factory policy that welcomes customer visits before purchase.
Does high filler loading reduce output of the pelletizing system?
It can. High filler raises melt viscosity and lowers throughput per screw revolution. Selecting the right die-hole count and cutting method with Kerke engineering keeps pellet quality stable while matching the extruder output.
Conclusion
Feeding and pelletizing are not afterthoughts on a high-fill twin-screw compound line. They set the recipe accuracy at the front and the pellet quality at the back, and either one can cap the line if underspecified. Kerke, a Wanplas factory, matches loss-in-weight feeders, side feeders, crammer feeders, and liquid feeders to the KTE series twin-screw extruder, then pairs the barrel with the right cutting method from strand to underwater granulation. The result is a balanced system where the feeder, screw, and pelletizer speak the same control language and run at the same rate.
If you are planning a high-fill masterbatch or modified plastic line, send Kerke your recipe, target filler percentage, and required output. The engineering team will configure a matched feeding and pelletizing package, invite you to the factory to run your material, and prepare a sample trial so you can verify pellet quality before committing to the full line.
