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The example above shows that weight is important to establish your basis, but the actual micro-feeder volume output design (feeding three pellets) will have a greater impact on your true product consistency at low rates. This is the major reason material consistency is so crucial for feeding low rates. FEEDING INTO THE PROCESS Once the material type, expected rate, and the process have been defined, you can now establish a building block for the feeder type that will feed into the process. Most low-rate applications are being fed into small-tonnage molding machines and small extruders of 0.75-in. to 2-in. diam. Incorporation of the feeder into the extruder requires some general review and consideration. Testing has shown that feeding the pellet or powdered materials as close to the feedscrew as possible will provide the best results. Avoid feeding additives into the stream of virgin material, as this may result in delays in getting the color started into the process and result in possible dispersion inconsistencies. An additional advantage of feeding the material as close to the extruder screw as possible is that this makes it easier to accomplish material changeovers with minimal downtime. WHAT TYPE OF FEEDER SHOULD I USE? When considering feeding at such low rates it is important to understand that precise volumetric feeding is required. Today's equipment suppliers offer different types and options of feeders. Most offer both gravimetric and volumetric versions. When considering a gravimetric type of feeder at these low rates, the measurement of weight loss can be difficult. You will have to evaluate the pros and cons of using gravimetric or volumetric systems. Typically, when considering feeding below 150 g/hr, gravimetric control may not be feasible due to longer weight recording times. This should be evaluated with your equipment supplier. If consid- ering powder feeding, it will be important to look at the feeding equipment and how well it is sealed to prevent leaks. In some operations, small amounts of additives are hand mixed into a single feeder. If considering automated loading instead, be sure the loader and feeder are compatible and will not interfere with the Testing has shown that feeding the pellet or powdered materials as close to the feedscrew as possible will provide the processor with the best results. www.rjginc.com INVEST IN YOUR COMPANY, INVEST IN YOUR EMPLOYEES Training & Technology for Injection Molders Studies suggest that strategically managing employee training can result in two times the revenue per employee. RJG training can partner with you to close your companies skills gap. 46 JULY 2017 Plastics Technology PTonline.com T ips & Technique s