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Molders and extruders that need to feed tiny amounts of material to their process require precision in both the material being fed and the equipment doing the dosing. When a shot size consists of three pellets, there is no margin for error. Understanding Low-Rate Feeding for Continuous And Batch Processes Perhaps now more than ever, processors are being driven by their customers to maintain extremely tight color tolerances, use only a very specific amount of additives, and comply with additional requirements such as documentation. This has given rise to new feeding technology that can deliver material at extremely low rates. While low-rate feeding itself is not new, processors previously had asked their material suppliers to carry the burden of putting these components together, putting colors and certain additives into a single pellet. But as product requirements change, processors want the flexibility to add minor ingredients separately in order to make short runs, reduce cost to be more competitive, and customize the product to fit their customers' changing needs. A large part of this is being driven by the medical industry, which has made processors in both injection molding and extrusion look at new ways they can feed these minor ingre- dients at low rates and maintain consistency. When considering equipment for low-rate feeding in your injection molding or extrusion process, understanding your material (whether pellets or powder) and how it should be fed into your process is crucial. By reviewing the points below, you can determine whether your material is capable of being fed at the desired low rates to ensure consistent and repeatable feeding. For the purposes of this article, "micro feeding" is defined as dosing materials from 200 g/hr (0.44 lb/hr) down to 1 g/hr (0.0022 lb/hr). Many processors wonder why it is critical to understand the material when feeding at low rates. The simple answer is that your material varies in shapes and sizes, which can affect feeding accuracy and consistency. Let's start by reviewing the material considerations and define some basic points. In most molding applications we feed pellets; in extrusion applications we can feed both pellets and powder. WHAT IS YOUR MATERIAL TYPE? Some general information to know about your material would be its bulk density (lb/ft 3 ) ; flowability (free flowing, fairly free flowing, or poorly flowing); and particle size or sizes. Do you have an accuracy requirement for these properties, and can it be achieved? By Roger Hultquist Orbetron LLC WHAT YOU WILL LEARN 1. IMPORTANCE OF MATERIAL: Bulk density, flowability, and particle size(s) impact feed accuracy. 2. WHERE TO FEED: Deliver material as close as possible to the feedscrew. 3. FEEDER TYPES: Evaluate the pros and cons of using gravimetric or volumetric systems. 4. AUTOMATED LOADING?: Ensure loader/feeder compatability. This standard setup for feeding an additive into a molding or extrusion process requires no special mounting adapters. A clear tube allows for easy viewing of material that will deposit just above the feed screw. This setup can typically can be mounted on any existing material hopper. 44 JULY 2017 Plastics Technology PTonline.com Tips and Techniques