PROCESSING | SMALL BATCHES
side feeder. Some of these feeders can be dedi- cated to frequently repeating recipe components to reduce the frequency of feeder changeovers. When this feeding concept is combined with
Feddem’s kneading-block-free screw geometries, the need for replacing screw geometries between recipes is drastically reduced, according to Hojer. “For example, with a given base polymer employing Feddem FME mixing elements in place of kneading blocks allows for producing powder filled products and fibre reinforced compounds on the same screw geometry in excellent quality,” he says.
Figure 1: Graphical representations make it easy to see process drift, according to Luis Roca, Leader of Compounding at Aimplas. In this example, the dark blue and yellow lines show a progressive decrease in torque and pressure due to a side feeder flooding. This was obviously affecting the final formula of a mineral-filled compound, and causing the material to be rejected Source: Aimplas
Graphical gains Roca recommends running the compounding extruder control display in graphical mode to help detect deviations faster. “Without knowing the compounding details, everybody should know that when the graph is not constant, you have a quality/ safety problem,” he says (see example in Figure 1) At compounding extruder maker Feddem, Business Development/Account Manager Klaus Hojer says the company has put a lot of thought into optimising its lines for heavy-duty production with frequently changing recipes and efficiently processing smaller batches. Hojer highlights the company’s Innovative
Compounding and Extrusion (ICX) technology concept. This was jointly developed with sister company Akro-Plastic, which is one of the largest producers of technical compounds in Germany. “Generating a substantial share of their business from toll compounding, Akro-Plastic may have several product changes per extrusion line daily, depending on the constellation of orders,” he says. To minimise changeover times between recipes,
the ICX concept provides for up to eight gravimet- ric feeders above the main feed throat of the extruder and up to two gravimetric feeders per FSB
Figure 2: There is a balance to be found between line output and run size in terms of quality and efficiency, according to Feddem. A larger extrusion line (left) will offer a short production time but a lot of material can be wasted reaching stable running conditions. A smaller line (right) reduces material waste but even small jobs can tie up capacity for long periods Source: Feddem
54 COMPOUNDING WORLD | April 2022 Consider the basics
When assigning lot sizes to individual extruders, Hojer says a compounder needs to consider basic performance and production time relations. “When employing a larger extrusion line for processing a relatively small lot size the run will be short. However, the challenge is that the processing parameters barely have time to reach stable running conditions. This, in turn, may lead to shortcomings in the repeatability of the product quality when the job is run on a production line with a smaller capacity the next time,” he says. Using a larger extruder also means more potential for wasted materials. “Start-up and shut-down waste is proportional to the extruder size. Larger extruders need more feed stocks to fill the cavities during start-up of the line and will hold more product that goes to waste when the production run is finished. Employing a small extrusion line for processing a relatively large lot size will lead to a long duration of the production run and will block this line for more appropriate job assignments,” he says. “Decades of experience in production planning have shown that it is far more important to focus on having the lines running per se rather than striving for utilising the individual extrusion lines to their highest throughput capacities,” Hojer adds. For flexible production with frequent product
changes, strand pelletising is the technology of choice for Feddem. The company’s FSK-series die heads have a low-volume melt channel for efficient distribution of the melt to the die holes, Hojer says, and are available with an oval breaker plate that can carry screens or — for small batches — with a
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