machinery feature | Laboratory compounders
of tie rods inside the barrel has been increased from two to four, allowing several side feeders to be mounted. In addition, the number of cartridge heaters per barrel has also been doubled to four, enabling the processing of high temperature materials, such as PEEK. Researchers at the
Georg-Simon-Ohm
Hochschule in Nuremberg have been comparing the residence time distribution of the Leistritz ZSE 18 Maxx with a production-scale ZSE 40 Maxx.
This was achieved by adding fine powdered chalk as a tracer material into the input stream and monitoring its concentration in the output
stream by weighing the chalk obtained after incinerating the polymer strands. Two different screw geometries were run
Coperion’s ZSK 18 Megalab has an OD/ID ratio of 1.55 to match produc- tion extruders
on the lab-scale machine and then the same two configurations were run on the production extruder. Following a detailed analysis of the results for the
two screw designs at different throughput rates, the researchers concluded that “the ZSE 18 Maxx is excellently suitable for scaling up to the ZSE 40 Maxx”. They added that the comparable specific energy input levels and Bodenstein numbers of the ZSE Maxx series allow reliable scale-up and a large processing window. Coperion is targeting laboratory work and small
production runs with its smallest ZSK twin-screw extruders, an 18 mm and a 26 mm model. The quick- clean features of these extruders are important in such applications, where users want to reduce downtime and have easy changeovers between recipes. For example, the die-head and screws have a quick-release feature, in which only two retaining bolts need to be unscrewed. Easily removing the screws allows researchers to see
how the melt is progressing within the barrel, or to thoroughly clean the machine between runs, explains Peter von Hoffmann, head of the Compounding Machines business unit at Coperion. Some customers purchase a second die-head so that they can remove one die-head for cleaning and have another die-head cleaned, pre- heated, and ready-to-go to minimize downtime. In addition to easy cleaning features, Coperion
agrees that scalability to production equipment is critical. Coperion’s lab extruders have a OD/ID ratio of 1.55, which is the same as its production extruders. In addition, the screw profile of the lab and production extruder can be matched. For example, if the production extruder is to have two kneading blocks, the lab-scale extruder should have two kneading blocks with an appropriately scaled length-to-diameter ratio (L/D) to ensure reliable scale-up. While laboratories often pre-mix and feed all
ingredients at once, scale-up is more accurate if feeding also mimics production scale, and Coperion’s laboratory extruders have side-feeding capability if desired. For the lab extruders, Coperion offers a variety of materials of construction similar to those of production machines, because lab extruders may also need wear and corrosion resistance, says von Hoffmann. Pharmaceutical or hot-melt extrusion applications
have stringent requirements for materials of construc- tion and also for temperature control. Coperion recently redesigned the barrel heating and cooling system of its 18-mm extruder used in this market to give it the ability to more quickly change zone temperature as well as to improve temperature control to +/- 1°C. “In pharmaceu- tical extrusion, raw materials are expensive. Enabling quicker temperature changes allows labs to run experiments more quickly and minimize material quantities,” explains von Hoffmann. KraussMaffei Berstorff launched its ZE 30 UTX twin-
screw extruder earlier this year at the Chinaplas exhibi- tion, filling a gap between the ZE 25 UTX laboratory
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