KWS Manufacturing

Limestone Conveying System

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Plant Name and Location

Duluth Minerals, LLC
St. Louis Park, MN

General Description of the Application

Duluth Minerals provides ground or pulverized limestone to the roofing industry. Ground or pulverized limestone is used extensively in asphalt roofing shingles, both fiberglass-reinforced and organic-mat-based, as well as in rolled roofing. Ground limestone has two primary functions. As fillers, ground limestone reduces the cost by replacing a portion of the asphalt. It also improves the physical performance properties of the shingles. Raw limestone is delivered by barge to the facility for processing. It is off-loaded, stored, crushed, ground and dried. Duluth Minerals needed to meter and convey both raw and finished limestone with particle sizes ranging from 2-inch down to 20-mesh. Their process required flood fed screw feeders as well as multiple screw conveyors.

Design Parameters of Application

  1. Product Type: Limestone
  2. Material Characteristics: Mixture of 2-inch minus Limestone and 20-mesh Limestone
  3. Material Density: 68 -90 Lbs. per Cubic Foot
  4. Conveyor Capacity: Multiple Capacities Ranging from 2353 to 3677 Cubic Feet per Hour
  5. Duty: 24 Hours per Day, 7 Days per Week

Advantages Provided by KWS

KWS engineers designed a system that could meter and convey the different capacities of raw and finished limestone needed by the Customer. 20-inch diameter screw feeders and conveyors were chosen for the application. Due to the varying size of the limestone, the equipment was designed to handle 2-inch rock down to fine 20-mesh powder. The screw feeders utilized variable pitch screw design to allow for even withdrawal of material from the silos. The screw conveyors were designed to convey the raw and finished limestone to multiple stages of the process. Screw conveyors were used to convey product to grinding, crushing, drying and storage.

Special Features of KWS Design

KWS provided our standard heavy-duty design and construction on all equipment. Due to the abrasiveness of the material and capacities required, hardened shafts, pedestal and bulkhead trough ends were implemented to improve the life of the equipment. The KWS screw feeders utilized high-torque drives to prevent stalling out under load. All of the screw conveyors were designed to start and operate under upset conditions. Also, the screw conveyors were designed with low rotational speeds and trough loading to reduce abrasive wear and increase the life of the system.

Testimonial

"The equipment provided by KWS worked very well and helped us achieve our goals."

David Dunning – Vice President of Operations

Limestone

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