New Continuous Gravimetric Blender from Conair Accurately Mixes Up To Six Dissimilar Materials

The cascade mixing technology used in the new TrueWeigh™ continuous blender from Conair results in a more homogeneous blend, even when additives need to be dosed in very small quantities. This makes the unit ideal for extrusion applicationshighly-accurate blend of sometimes-dissimilar ingredients is critical. The new continuous blender made its NPE debut in booth 3643 in the West Hall at NPE 2012 held April 1-5 in Orlando, FL.

The new blenders can be configured to handle two, three, four, five or six different components in total throughput ranges of up to 700 lb/hr (320 kg/hr) or up to 3000 lb/hr (1365 kg/hr). Ingredient hoppers and dispensing augers can be sized to deliver any amount up to the maximum or as little as ¼ lb/hr (115 gm/hr) with metering accuracy within half a percent of setpoint, depending on the material.

“What makes this gravimetric continuous blender different from batch blenders is that all ingredients are dispensed simultaneously at the desired rate,” explains Alan Landers, Product Manager. “Different materials flow together out of the blender and into the extruder or a holding bin. In batch blenders, ingredients are dispensed one at a time into a mixing chamber where they are combined by mechanical agitation before being dumped from the blender. This works quite well in applications involving similar materials (virgin pellets and masterbatch pellets, for instance) and relatively large quantities of minor ingredients. However, when materials of different particle sizes and bulk densities are involved, there is a limit to the uniformity achievable with mechanical agitation. With continuous cascade mixing, if there is supposed to be just a few pellets of color or additive in a pound of virgin, then that’s exactly what you get.”

The new continuous Conair blender is part of a growing family of products aimed at meeting the special requirements of extrusion processors making film and sheet, pipe and profiles, wire and cable, and the like. It makes use of weighing and control technology developed as part of the TrueWeigh gravimetric extrusion line control system Conair introduced in 2009.

Two standard configurations are available: a stand-mounted unit that dispenses blended material into a holding bin, or a machine-mounted version. The latter includes an integral TrueWeigh hopper to control and maintain the desired weight per hour or weight per length extruded regardless of changes in process conditions. Up to six ingredient hoppers are available and each is mounted on a load cell that reads the loss-in-weight of material as it is dispensed. An inclined auger moves each ingredient from the individual hoppers into a central TrueWeigh hopper above the machine feedthroat. As material flows into the extruder, the TrueWeigh hopper measures the loss in weight. Its control unit can be linked to the extruder screw drive to maintain a specified weight/time throughput. The same control system also governs the speed of the dispensing augers under each ingredient hopper so that the exact blend ratio, in the required quantities, is consistently delivered to the weigh hopper.

The flow rate of each ingredient is controlled by the diameter and rotational speed of the inclined auger under each material hopper. Major changes in metering volume – through the range from near zero to maximum throughput – are made by changing auger screws, which are available in diameters from 0.5 to 2 inches (1.25 to 5 cm). Fine adjustments to output are made by the blender control and a motor that drives the auger at a variable speed. Because the motor speed is variable, it is not necessary to change both the motor and the auger when making adjustments to dispensing rates. Unlike competitive continuous blenders, in which both the motor and the auger need to be changed frequently to achieve rate adjustments, the Conair unit only needs a single variable-speed motor. This technique allows for a speed range of a single auger to be 200:1.   

PLC-Based Control

The TWB continuous blender uses the same kind of PLC-based control as other Conair extrusion control units. It features a 5.7-inch LCD touch-screen operator interface with color graphics. To enter a blend recipe, the user only needs to enter a number of each ingredient representing the percentage of the total recipe and the control automatically sets and maintains the proper ratio regardless of changes in throughput. It can store the set-up parameters for up to 250 named recipes.  

Remote interface capabilities allow the system to be integrated into a complete extrusion line or plant supervisor control system. Communication may be accomplished through either serial or Ethernet links. Optional interface protocols, including Ethernet IP, Modbus TCP, Modbus serial, Profibus, Allen-Bradley^® DH+™, Canbus and DeviceNet™, are available. The system can be monitored and/or controlled remotely via these interfaces.

Conair Group

The Conair Group (www.conairgroup.com) is the world’s leading supplier of auxiliary equipment for plastics processors, including resin drying systems, blenders, feeders and material-conveying systems, temperature-control equipment and granulators. Extrusion solutions include line-control systems, film and sheet scrap-reclaim systems and downstream equipment for pipe and profile extrusion. Over 450 individual products solve problems, save energy, cut waste and are easy to use. Conair is also an international company, with long-standing operations in Europe, Asia and South America. The industry’s most complete product line, top-flight engineering and unbeatable service, all combine to give processors the confidence they need to succeed in today’s competitive global marketplace.