MACHINERY | BULK MATERIALS HANDLING
Right: Internal view of the Coperion K-Tron materials handling test facility at Salina in the US
70°. This means that the material would not exhibit mass flow, where all particles move in the hopper during discharge. Instead, funnel or stagnant flow occurs.” Piping and erratic flow behaviour are very common for funnel flow situations so aids such as vibrators, fluidisers and impactors are used to encourage flow in the hopper, Lawrence explains. “However, uniformity of material flow rate is hard to achieve for these materials. For example, if the expected flow rate was 5,000 lb/h [2,268 kg/h], only a flow rate of 3,000-4,000 lb/hr [1,361-1,814 kg/h] will be achieved, significantly reducing product production rates. There are various factors that affect this reduced flow. These include higher pick-up velocity, high speed rotary valves of a smaller size, vacuum probe feeding, shallow hopper slope and smaller outlet dimensions, temperature and relative humidity. Determining the optimum pick-up velocity and rotary valve speed will minimise these low flow rates.” Lawrence says these parameters can only be obtained by carrying out detailed material testing in a full scale laboratory. Equipment manufacturing companies have test facilities to study this and it is also a service that the Bulk Solids Innovation Center at Kansas State University can provide. Hopper slope and outlet dimensions need to be
ascertained at different temperatures and relative humidity through shear testing, Lawrence says. “Different wall friction materials can be tested to find the best hopper material for uniform flow. Hoppers may have already been purchased at a particular hopper angle, 70° for example. However, if the hopper angle for that material resulting from the test is 80°, then we need to retrofit the hopper with a different bin-insert to minimise the arching dimension.” Lawrence adds that probe feeding using vacuum pneumatic conveying, which is very common for pellets, may not provide a consistent flow rate when applied to powders. The vent in the probe will typically block, which affects the flow rate. This inconsistent feeding can be greatly
reduced by switching from probe to rotary valve feeding.
Flexibility While material handling systems can be designed to work highly effectively with a specific material, a major priority for many compounders is to have a level of flexibility enabling them to respond quickly to changing customer requirements. This is a key consideration for manufacturers of materials handling equipment. “Due to frequent product changes and ever smaller lot sizes, a state-of-the- art compounding line has to be built for quick product change and easy cleaning in-between different products. This allows a reduction in downtime for cleaning and improves the product quality by excluding contamination. At the same time, operational safety can be improved by better cleanability, easy access and facilitated housekeep- ing,” says Matt Burt, General Sales Manager at Coperion K-Tron in the US. “In addition, with more stringent NFPA (National
Fire Protection Association) regulations and height- ened awareness of dust explosion, material handling equipment requires more options to meet these needs. What was once considered a low risk factor, such as plastic resin pellets and the dust generated from handling, has now become a concern and requires special considerations like explosion venting or suppression systems. Many additives used in plastic compounding are also explosive.” Coperion K-Tron’s materials handling laboratory
The Bulk Solids Innovation Center of Kansas State University in the US 32 COMPOUNDING WORLD | February 2018
at Salina in the US allows it to conduct full-scale tests with actual bulk materials and determine the
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PHOTO: KANSAS STATE UNIVERSITY
PHOTO: COPERION K-TRON
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