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30 / September 2020 powderbulk.com SOLIDS WEIGHING AND BATCHING OVERVIEW — PART I Whether you're manufacturing cement or seasonings, if you're in the powder and bulk solids industry, you're going to need to weigh and batch ingredients to come up with a consistent end product. This two-part article describes how to weigh and batch ingredients in an accurate and cost-effective manner. Part I explains the different ways that materials can be measured while Part II, which will appear in the November issue of PBE, explains how to incorporate the weighing and batching methods into your process. Todd Smith, K-State Bulk Solids Innovation Center B ulk solids are a critical ingredient in most of the products we all buy and use. In manufacturing processes, dry ingredients are combined accord- ing to a recipe in the correct proportions with the other ingredients. But how are bulk solids measured? And what are the best methods for weighing and batching? This article describes the various techniques for weigh- ing and batching solid ingredients into your process. The methods are listed in general order from those that are the least expensive and have the least accuracy to those that are more expensive and have better accuracy. Volumetric feeding The simplest method of dispensing and dosing ingre- dients involves a feeding device without weighing capabilities but with the ability to control the volume of dry solids being dispensed. This device is typically a volumetric feeder such as a screw conveyor or rotary valve, as shown in Figure 1 and Figure 2, respectively. The volumetric feeder uses mechanical means to create a repeating void space at the feeding device's top. In other words, material ingredients fall into the empty void space at the feeder's top. Then the volumetric feeder's rotation carries material from the feeder's top to the bottom discharge end. This process continues as long as the volumetric feeder is turning and there's a supply of material falling into the device's top. The dispensing rate of a volumetric feeder is deter- mined by the machine's size and rotation speed. These mechanical volumetric methods are simple and low cost. They don't require any controls other than a variable- frequency drive to adjust the rotation speed of the drive motor. Volumetric feeders can be calibrated by catching a sample of material for a measured amount of time, then weighing the amount of dispensed material. These feeders can be reliable and consistent as long as the material properties, especially bulk density, are FIGURE 1 Volumetric screw feeder Hopper holding material Screw auger rotates inside housing Material outlet Courtesy of Coperion K-Tron. FIGURE 2 Airlock rotary valve Courtesy of Schenck Process. Material inlet Shaft with vanes rotates inside housing Material outlet