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Home / Wide material compatibility: Screw Dosers are suitable for virgin, regrind materials, and masterbatch

Wide material compatibility: Screw Dosers are suitable for virgin, regrind materials, and masterbatch

2026/02/07 By le zhan

Screw Dosers are suitable for virgin, regrind materials, and masterbatch

For modern processors requiring precise and repeatable metering of various raw materials, Screw dosers offer a practical solution. Whether the production line is conveying virgin granules, screened regrind, masterbatch, or functional additives, a well-configured screw feeder can achieve proportional mixing with minimal operator intervention. Simply put, the device transforms the variability of the raw material flow into a stable input required by injection molding machines or extrusion lines. This guide will explain why Topstar’s screw dosers are widely compatible with different polymer compounds, how microcomputer control and dual operating modes provide accuracy and flexibility, and which operating practices maximize performance.

The Versatility of Screw Dosers

The superior performance of screw dosers stems from the inherent adaptability of their physical metering mechanism. The core component of the device is the metering screw, which conveys material at a rate proportional to its rotational speed and the volumetric displacement per revolution. Unlike gravity feeders or paddle systems that rely on the overall flow characteristics of the material, the positive displacement nature of screw dosers makes them less sensitive to particle shape, bulk density, or flowability. Therefore, as long as the screw geometry and drive settings are matched to the material type, a screw doser can meter virgin polymer granules, recycled flakes, and masterbatch powders or granules using the same hardware platform.

However, not all materials behave the same. Filled compounds and fiber-reinforced resins may be more abrasive and have greater variations in bulk density, while fluffy masterbatches and powdered additives may require controlled agitation to prevent bridging. To address these situations, the Topstar screw doser is equipped with configurable feed chambers, interchangeable screws, and agitators within the hopper. These enhancements ensure stable material flow into the metering screw and prevent pulsation at the injection molding machine.

TSM-Screw- Doser 1

Precise Automatic Proportional Metering and Microcomputer Control of Screw Dosers

Screw dosers equipped with microcomputer controllers achieve automatic proportional metering by continuously adjusting the screw speed to maintain the target additive ratio, even when the main material flow changes. The controller receives input data—target percentage, measured feed rate, and sometimes feedback from a gravimetric blender or in-line scale—and calculates the appropriate setpoint for the metering screw. This tight closed-loop control method eliminates operator guesswork, reduces color drift, and maintains consistency in the mechanical and aesthetic properties of molded parts.

First, it supports recipe storage and recall, allowing for instant loading of color and additive ratios for specific parts or customers. Secondly, the controller enables gradual acceleration and deceleration, preventing under- or over-feeding of the hopper, thus protecting the injection molding machine and downstream quality control systems.

Another advantage is automatic compensation. When the injection molding machine temporarily slows down, the controller senses the reduced demand for the primary material and proportionally reduces the screw feeding speed to maintain a constant mixing ratio. This proportional control can be achieved through volumetric or gravimetric control, with the latter offering higher accuracy. Regardless of the mode, the microcomputer-controlled screw metering device translates process fluctuations into stable, predictable ratios, helping manufacturers improve first-pass yield.

Two Operating Modes: Injection Molding and Extrusion

The screw doser is carefully designed to serve both injection molding and extrusion processes, offering two operating modes to match the metering behavior to the target process. In injection molding applications, metering typically responds to the demand of each injection or cycle, requiring precise timing to coincide with the plasticizing phase for short bursts of material. In contrast, extrusion requires continuous and stable material delivery at a preset kg/h rate. The efficient screw metering device meets the needs of both applications through flexible control logic and mechanical design.

For injection molding machines, the controller typically integrates with the machine’s cycle signal, utilizing proportional pulses or machine status inputs to coordinate metering intervals. The screw metering device then meters colorants or regrind in sync with the injection molding machine’s output, preventing hopper shortages or material surges, thus preventing variations in injection weight. For extruders, it operates in continuous mode, maintaining a constant screw speed and delivering the required weight percentage over long production runs. The device’s screw geometry and feed port design ensure uninterrupted feeding, avoiding pulsations that could lead to variations in the quality of the extrudate.

Injection Molding and Extrusion

Processing Virgin Materials, Recycled Materials, and Masterbatches

The practical advantages of Topstar screw dosers are evident when mixing materials with different characteristics, such as virgin polymer granules, recycled flakes, and concentrated masterbatches. Each material requires a tailored processing method to ensure dosing accuracy and product quality. Virgin granules typically have good flow properties, resulting in stable and repeatable dosing. Recycled flakes often have uneven bulk density and irregular shapes; these characteristics require robust agitation and anti-bridging hopper designs to ensure smooth material flow into the screw. Masterbatches, especially high-concentration colorants, may be dense and abrasive, or fluffy and electrostatic; reliable dosing depends on the appropriate screw pitch and controllable feeding energy.

virgin, regrind materials, and masterbatch

Integration with Injection Molding Machines and Other Auxiliary Equipment

The successful implementation of screw dosers depends not only on the metering unit itself but also on system integration. Integration points include machine status signals, gravimetric feedback loops, network communication, and safety interlocks. When the screw-type metering device communicates with the injection molding machine, it can anticipate production demands and adjust the metering speed in advance, reducing transient errors and making mixing smoother during cycle transitions. For applications requiring higher precision, connecting it to a gravimetric blender creates a closed-loop control system that corrects deviations in real time. This method measures the actual output mixture and automatically adjusts the screw speed to restore the target ratio.

Providing Broad Material Compatibility

Broad material compatibility is a significant advantage of modern screw dosers and a key reason why they are indispensable in today’s injection molding processes. Screw dosers can accurately and proportionally meter virgin materials, recycled materials, masterbatches, and additives, transforming various raw materials into a stable and controllable feedstock for the injection molding machine. With microcomputer control and dual injection/extrusion modes, they achieve consistent mixing ratios, reduce material waste, and improve product repeatability.

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