PROCESSING | SMALL BATCH COMPOUNDING
Right: Aimplas uses carousel feeders to help speed up material changes
to maximise the output rate. They don’t want to stretch the campaign only to utilise the machine because they can also use the downtime for maintenance or people can clean up. This is a business decision. Roca: Equipment must be flexible enough (screw designs, side feeding, venting, etc) to allow working with different types of compounds and it is mandatory to have enough capacity to work with similar materials at the same time to avoid long lead times. Also, extruders must be similar in geometries (L/D and OD/ID ratios). This is certainly something to have in mind when buying new compounding machines and lines as brands used to have different geometries. Staff must be highly qualified to modify process- ing conditions and to work with different screw designs, and also to adapt them to work with different compounds in the same extruder or different extruders with the same compounds. Training and integration of the methodologies and quality procedures of the company are mandatory. This last part is probably less exploited but it can make a big difference.
CW: Are there specific management procedures or operational strategies you would recommend for cost effective small batch production? Lechner: You need a universal machine set-up, you need a universal screw design, you need to avoid screw changes, and you need all the quick-change features already mentioned. Then you don’t have to make compromises. Having high torque available is also perfect – you can take the 18 [Nm/cm³] or operate the line at 10, 12, 13 depending on the process you are running. This way you can always operate the line at its optimum; you can be flexible. Roca: Small batch compounding implies a lot of formula changing. Avoiding dead times leads to more productivity and less energy spend, which is especially important in this era of high costs. Scheduling and start-stops are key points, assum- ing that process control is already good. And, as stated before, the right methodology for extruder selection, finely tuned material changeovers, and parallel testing are more than mandatory. Lindsey: Operator training is essential to getting the most out of your extruder. Often HMI/control screens contain information that isn’t essential to the process. Having a simple and ‘lean’ operator platform that only references the required process parameters helps reduce confusion and stream- lines operator training. And don’t overfill feeders
34 COMPOUNDING WORLD | April 2023
when approaching the end of a lot. This will allow the operator to save time emptying the feeder and scrap less material.
CW: What advice can you offer in terms of optimis- ing production equipment selection? How can the right balance be found between achieving quick start-up with minimal off-spec production while still being able to complete a customer order in a short time? Roca: If the compounding process is robust (robustness is a mix of the right equipment selec- tion and process optimisation) and the line flexible enough, the process will arrive at the steady state sooner and bottlenecks will be detected and corrective actions put in action, for example modifying or repairing peripherals. Sometimes companies get used to working in conditions which are not optimal and in the long term that creates more problems than the modification itself. Side feeder flooding, voids and irregular pellet shape, die build up, fines generation, vacuum extraction of fibres, venting via side feeders, etc, are all problems that should be listed with solutions. The quality system plays a crucial role in parallel to testing to check that the process is running within specifications and, of course, achieves a steady state as quickly as possible. Quality results must be correlated with processing conditions and staff have to identify deviations in the response variables as quality failures. The range of variation in quality has to be defined in order to always work within the margins of confidence for each compound. Lindsey: Leverage operating conditions from previous production runs. This can be done by logging process parameters manually or electroni-
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IMAGE: AIMPLAS
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