KWS Manufacturing

Twin Mass Flow Screw Feeders and Material Shut-Off Gates

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Twin Mass Flow Screw Feeders and Material Shut-Off Gates: United States Steel CorporationPlant Name and Location

United States Steel Corporation
Gary, IN

Consulting Engineer

Carbonyx, Inc.
Plano, TX

General Description

A major steel producer was seeking an alternative to coke for the steel making process. The coke alternative was a blend of carbon based materials with coal being the base material. The various carbon based materials are stored in large 1,000 ton silos and metered into the process using special, mill-duty mass flow screw feeders. KWS designed and manufactured 28 twin mass-flow screw feeders and electrically actuated material shut-off gates, which proved to be the ideal solution.

Design Parameters

  1. Product Type: Calcined Coal and Dried Coal Blend
  2. Material Density: 45 Lbs. per Cubic Foot
  3. Conveyor System Capacity: 1,556 Cubic feet per Hour

KWS Advantages

KWS worked directly with engineers at Carbonyx to design mass flow screw feeders specifically for the harsh application. Screw feeder inlets and material shut-off gates were designed to match each silo and provide mass flow in the silos. Product bridging and ratholing were eliminated. KWS engineers provided 3D models and collaborated with Carbonyx engineers to ensure optimal performance and design requirements were met prior to the equipment’s arrival on-site. In doing so, we were able to minimize field installation time. The shut-off gates and mass flow screw feeders fit up perfectly with the silos.

Special Features

KWS utilized “twin” counter rotating, mass flow (cone) screws with variable pitch flighting for a uniform draw throughout the entire cross section of the silo discharge. The screw design is most critical in large silo/bin applications in which free flowing materials can bridge and/or rathole and possibly have catastrophic results on the structural integrity of the silo. The mass flow screw design ensured even discharge of bulk materials from the silos. KWS also incorporated an independent drive arrangement providing each screw with its own power supply. Maximum torque could then be generated for each screw and prevent motor stall.

The two drive units also provide redundancy in the system. This allows maintenance to be performed on one drive unit without completely shutting down production. Variable frequency drives (VFDs) accurately controlled the product feedrate with accuracy within 1-percent. Screw feeder speeds could be varied based on final product blend and Customer requirements. The material shut-off gates were designed to shear through the material head in the silos to shut-off material flow in case the screw feeders required maintenance. The electric gate actuators were capable of opening and closing the gates with up to 15,000 lbs. of force.


"KWS has been a pleasure to work with throughout the entire process. Their engineering expertise and manufacturing quality is the finest in the industry. We will be working with KWS on many future projects."

Vibha Bansal – Project Manager, Carbonyx, Inc.


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