MACHINERY | MATERIALS HANDLING
Right: Coperion’s Mix-a-Lot weighs and mixes compo- nents to
simplify plant feeder configuration
damage or heating of the product. “Up to now it has generally been standard
practice to feed each individual component to the extruder through a separate differential loss-in-weight feeder with a buffer hopper,” the company says. “However, using this technique, the new Mix-A-Lot first produces the specific pellet mixture, for which one single loss-in-weight feeder is then sufficient.” The weighing function of the mixer ensures accurate recording of the weight of each component fed in. The unit is vacuum and pressure-resistant, making direct pneumatic feeding possible without the need for a separate reception bin for pneumatic conveying. “This simplified plant concept allows the
reduction of investment and maintenance costs compared to conventional systems,” according to Coperion. “The cleaning effort during changes of product has been greatly reduced, and much less space is required above the extruder.”
Below: Mini Cori-Flow mass flow meters from Bronk- horst provide improved fluid dosing control over displace- ment pumps
Measuring fluids Bronkhorst, a specialist provider of low-flow fluidics handling equipment, was one of several suppliers from the sector exhibiting at the Com- pounding World Expo in Essen, Germany, last year. Its offering encompasses standard and customised mass flow and pressure meters, as well as a broad range of controllers for gas and low-flow liquid applications. Angela Puls, responsible for sales and technical
service at the company, says there are several reasons for using one of its Coriolis instruments to provide precise additive dosing. “Additives are frequently added by use of needle valves, which is inexpensive but always has a risk of malfunction because of fluctuations within the process – pres- sure and temperature for example,” she says. “With its Cori-Fill dosing technology, Bronkhorst offers an
easy-to-use setup to ensure the required accuracy and reproducibility.” A Coriolis flow meter contains a tube which is
energised by a fixed vibration. When a fluid passes through the tube, it produces a change in the vibra- tion, and the tube twists, resulting in a measurable phase shift. From this measurement, a linear output can be derived that is proportional to the flow. As well as measuring the phase shift in frequency between inlet and outlet, the Bronkhorst meters can also measure changes in natural frequency, which are directly proportional to the density of the fluid. Measurements of mass flow rate and density can then be used to calculate the volume flow rate. As the measurements are independent of what is within the tube, the Coriolis principle can be applied to any fluid, irrespective of whether it is a liquid or a gas. This differentiates the Bronkhorst meters from thermal mass flow meters, which are dependent on the physical properties of the fluid. Combining a small Cori-Flow mass flow meter with a pump or a suitable valve, allows fluids to be dosed continuously or in batch mode with high reproducibility. “These systems can be integrated or used as an add-on in already existing processes and production lines,” says Puls.
Dosing accuracy Her colleague James Walton explains that a Coriolis mass flow meter may still be a useful addition when using a dosing or metering pump. “Traditionally, and in most cases we see, dosing or metering pumps are believed to be accurate because the theory is that a known pump head displacement will move a known volume over a known time, giving a known delivered volume,” he says. “In practice however, it will never achieve a high level of accuracy, with deviations of 10-15% being normal.” Inaccuracies are caused by changes in numer-
ous process conditions, such as temperature and pressure variation, air entrapment, and component
54 COMPOUNDING WORLD | February 2019
www.compoundingworld.com
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PHOTO: BRONKHORST
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