Heavy-Duty Mass-Flow Twin Screw Feeders and Bucket Elevators for Ground Rubber

General Description

Cemex is a global building materials company that provides high quality products and services to customers all over the world. Their US network includes 13 cement plants, 46 strategically located distribution terminals, more than 100 aggregate quarries and more than 450 ready-mix concrete plants. For this capital project, the Cemex USA required mass-flow screw feeders to meter ground rubber material from hoppers that were fed by front end loaders. The mass-flow screw feeders metered the material to bucket elevators. The bucket elevators conveyed the material vertically to storage in silos. Cemex makes rubberized asphalt concrete (RAC), which uses ground rubber from recycled tires mixed with regular asphalt concrete. RAC is widely used because of its high durability and ability to reduce road noise. Since this was a design-build project, KWS was the perfect choice for this solution.

Design Parameters

KWS Advantages

KWS interfaced directly with Hoover Conveyor, the system supplier on this project, a manufacturer of specialty equipment for heavy industries located in Pennsylvania. Hoover Conveyor had worked with KWS on previous projects and was very comfortable with the engineering capabilities and quality workmanship. Basic layout dimensions and capacity requirements were given to the KWS engineering team. KWS has the experience to design the equipment to perfectly suit an application without the need of a third-party engineering firm or detailed specifications. The project needed to be designed and built on a quick timeline and KWS was up to the challenge. The design and manufacture of mass-flow screw feeders requires engineering knowledge and manufacturing capability. KWS has built thousands of mass-flow screw feeders with success. Screw flight pitch and tolerances are very important to achieve true mass-flow from a hopper.

Special Features

KWS designed and manufactured twin mass-flow screw feeders to match hoppers supplied by Hoover Conveyor. The screw feeders were 23-feet in length. The mass-flow screws were mounted on oversized heavy-duty pipe to reduce deflection under load. KWS understands difficult applications and designs heavy-duty systems to meet demanding operating conditions. Each screw feeder was equipped with two low-rpm, high torque gear reducers to feed the material under packed, upset conditions. The gear reducers were too large to put side-by-side on the screw feeders. KWS created a special design and located the gear reducers on opposite ends so there would be plenty of room for maintenance. KWS engineers selected a centrifugal discharge bucket elevator to elevate the material quickly and efficiently. Since the ground rubber was not a tremendously harsh product, KWS provide a belt-style elevator with nylon buckets. Iron digger buckets were implemented every seven buckets to dig material out of the boot section and to protect the nylon buckets. KWS also provided split gland seals on all bucket elevator shafts to provide superior leakage protection. The complete system was modeled in 3D Inventor, making design revisions during the engineering phase much easier and less time consuming. KWS also provided all of the equipment painted special Cemex USA green for their plant.