PROCESSING | SMALL BATCH COMPOUNDING
Right: Entek’s self-aligning screw shafts make for easier installation
purge method that works consistently. Avoid reverse convey elements in the screw design, if possible. These make purging more challenging and time consuming.” An HMI that has a user friendly and easy to
access recipe program where formula and run conditions can easily be located and downloaded on to the run screen is extremely helpful, according to Elliott, as operators often waste significant amounts of time trying to locate previous run sheets. “For start-up, software usually allows the operator to input a date, time and temperature profile, this is a good idea as the machine will start heating up ahead of time, so it is ready for the first shift. Also preheating of the gearbox oil in cold climates is helpful.” Fast product changeover was a priority in development of Entek’s latest QC3
(Quick-Change,
Quick-Clean, Quality Control) twin-screw extruders, according to Marketing and Business Development Manager Tammy Straw. She says the machines are designed so change-overs do not require mainte- nance staff, allowing the operators to quickly and easily perform them. Some of the specific QC3
features that facilitate
Below: A user-friendly control
interface with easy set-up and recipe storage can help speed job changes
changeovers include: self-aligning screw shafts for easy installation; a quick-change die with easily- replaceable flow channel parts; die heaters and sensors that stay in place while the inner assembly (breaker plate, die plate and die body) is removed to leave an easy-to-clean flat surface; a quick-clean feed chute that extends into the barrel opening so that only the chute needs to be cleaned and not the barrel inlet; and pivoting stuffers that are easy to clean and remove and can access four or five barrel locations.
The winning approach The car racing approach to fast changeover is also promoted by Adam Dreiblatt, Director of Process
Technology at CPM Extrusion Group. “The winner can be decided in the pit stop. The crew has a few seconds to replace tyres, refuel, etc. The vehicle is fitted with specialised features for rapid change and requires highly trained personnel armed with the correct tools to perform these tasks as efficient- ly as possible,” he says. Compounding extruder operators can learn
from that car racing approach. “Extruder compo- nents and related auxiliary equipment (feeders, side feeders, vent ports, die plates) that require removal and cleaning between lots can be fitted with captive fasteners allowing for easy disassem- bly and reassembly,” he says. If screw shafts are to be removed for cleaning or
replacement without disassembly, the use of two-piece screw tips will keep the screw elements compressed on the shafts while providing a means to attach the screw removal fixture, Dreiblatt says. “Removing standard screw tips to withdraw the shafts from the machine allows the melt to pen- etrate between the elements and makes disassem- bly more difficult. If the next lot requires a different screw configuration, having a second set of assembled screws (already cleaned offline) reduces the time required for disassembly and reassembly. This represents substantial investment which can be recovered quickly by maximising uptime,” he says. “Best practices for changeover between batches
where a different raw material is to be used in one or more gravimetric feeders includes re-calibration of the feeder to account for any differences in bulk density. This material calibration procedure is an automated function that allows the feeder to calculate the maximum output and is used to determine the start-up condition,” Dreiblatt says. “If this procedure is not done (for example, to save time), the feeder will start-up at a higher or lower feeding rate and take longer to reach setpoint. Off-spec material is produced until all feeders are running at setpoint and represents yield-loss. This is a critical point for small batch
16 COMPOUNDING WORLD | April 2020
www.compoundingworld.com
IMAGE: ENTEK
IMAGE: ENTEK
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