A better class of feeder
K-Tron’s accurate solids feeders simplify the compounding and pelletizing of high-value products

High-performance solids feeders from K-Tron help plastics manufacturers, processors and users make the most of modern compounding systems. Such installations are suitable to produce a wide range of polymers, but especially for highend engineering plastics such as polyacetal, ABS, polyurethane, polycarbonate or Peek.

With high-performance compounding technology, the time-consuming step of fine grinding of pellets and premixing in batch quantities can be eliminated. Instead, pigments and additives are fed directly into the melt by gravimetric feeders. Pigment concentrations up to 70 percent are possible.
Compared with the old premix feeding method, high-performance compounding allows formulations with reduced wax content or no wax at all. The result is higher productivity, higher quality and lower raw material costs. However, high-performance compounding does require feeders of equally high performance.
A key requirement in high-speed compounding is to ensure a continuous, uniform feed with very tight short-term accuracy and repeatability. The figure below shows a typical layout for filling, reinforcing, alloying and coloring. The base polymer and the additive masterbatch are fed very accurately into the main inlet of the compounder using a single-screw feeder such as the K-Tron K2G or K2-MLS60/ S100, or the K2-MLKV2/3 vibratory feeder. Feed rates for screw feeders are in the range 0.2–15,000 l/h, and for vibratory feeders 2–5,000 l/h. Other additives are fed to the main inlet of the compounder using loss-in-weight screw feeders such as the K-Tron K2-ML-T20/T35 at rates of 0.2–200 kg/h. Chopped fiberglass is fed via a K2-ML-KV2F loss-in-weight vibratory feeder into the side feeder of the second inlet of the extruder.
Advanced feeding for high accuracy
For free-flowing products, K-Tron Hurricane vacuum loaders or receivers can be used to keep the feeders well supplied. Thanks to the Hurricane’s patented dual-cyclone technology, most materials can be fed without needing a filter. Sticky additives such as Irganox, Tinuvin and calcium carbonate need refill hoppers, extraction systems and shutoff valves or bag dumping stations.
All recipe handling and line monitoring is done by the factory’s DCS system. Ratio control is handled by the Smart Line (KSL) control unit and operator interface, which in turn controls a series of Smart Control Modules (SCM or KSH) mounted locally on each feeder. These units combine the function of motor drive and feeder control in a compact package.

A single KSL unit provides a single user interface for up to eight feeders. An integrated communications function known as K-Link allows communication with the host DCS system via Modbus, Allen Bradley or Siemens protocols. A larger version of the KSL, the Smart Commander, can control up to 30 feeders and eight lines. Plastics compounding systems are typically classified as IP55/NEMA12, and
some require nitrogen blanketing. To facilitate nitrogen blanketing, K-Tron feeders are fitted with a proven pressure compensation system at inlet and outlet. Hazardous area approval may also be required. K-Tron’s XP equipment series meets the new Atex 95 requirements. Loss-in-weight feeders with Smart Force Transducer weighing technology provide advanced gravimetric control with high sampling rates and resolutions, allowing the feeder to track even large or rapid setpoint changes closely. The upper diagram on this page compares the performance of K-Tron feeders against competing designs in response to a step change in the setpoint.
The lower diagram compares the performance on free-flowing and poorly-flowing materials. The good performance of the K-Tron feeders is achieved through the use of a sampling frequency (here 112 samples/s) effective digital filtering and a fast control algorithm, that is faster than the response time of the controled elements.
The feeders feature very few parts subject to wear, smooth surfaces that avoid contamination, effective digital control and a feed mechanism that does not cause weight fluctuations. Competing technologies include feeders with flexible walls, which have the drawbacks that the polyurethane liner can become contaminated by the additive powders and needs regular replacement, which results in much higher running cost for the customer. Paddles whose vibration can also upset the weighing accuracy. Old-fashioned heavy-duty screw feeders also suffer from vibration and use relatively unsophisticated weighing technology. They also tend to use lower-grade stainless steel with a pickled finish, whose roughness can restrict flow and create contamination.
Several thousand customers worldwide are successfully using modular feeders in their compounding processes. The company is always happy to supply references and to carry out trials on customers’ own materials.