Inclined Screw Feeders for Metering Dolomitic Limestone at Nucor Steel Plymouth, UT

General Description

Operating more than twenty facilities and several divisions across the United States, Nucor Steel is a leading North American producer of merchant bar & rebar, engineered bar, structural steel, carbon steel plate, and sheet steel products. Along with being the largest steel producer in the United States, Nucor is also one of the largest scrap recyclers in North America. Nucor Steel – Utah is one of Nucor’s 13 bar mills which produce a wide usage of bar products for the agricultural, automotive, construction, energy, machinery, railroad, shipbuilding, and heavy truck market segments. The capacity of Nucor’s bar mills is approximately 8,830,000 tons per year.

In the iron and steel industry, limestone and dolomite are used both in ironmaking and steelmaking. Dolomite is often preferred over limestone because it has a harder composition, is less absorbent and more resistant to freeze-thaw cycles and has a higher resilience to acidic erosion. Limestone is used as a slag former, while dolomite is used as a slag former, slag modifier, and refractory material. Nucor Steel – Utah needed a reliable method of discharging dolomite from storage silos into the production process. They contacted KWS to design and supply two inclined screw feeders that would meter dolomite from the silo through a bar magnet to a vibratory screener where it could be separated by size before entering the remainder of the process.

Design Parameters

1. Product Type: Dolomitic Limestone
2. Material Density: 60 to 70 Lbs. per Cubic Foot
3. Capacity: 155 Cubic Feet per Hour
4. Duty: Intermittent

KWS Advantages

The local KWS representative, Annik Engineering, performed equipment integration using drawings and design information provided by KWS, the vibratory screener manufacturer, and bar magnet manufacturer. KWS and Annik Engineering ensured interfaces and connections between various pieces of equipment would be seamless. Verifying equipment stack-up height was critical in confirming the incline angle and length of the screw feeder.

KWS Special Features

The KWS inclined screw feeders were designed with split tubular housings and abrasion resistant AR400 liners to enhance performance and service life. Liners improve efficiency when conveying very free-flowing and fluidizing limestone on the steep 35-degree incline by reducing the clearance between the screw and housing. The combination of the tubular housing and trough liners improves efficiency by reducing the amount of material that can fall back toward the inlet end due to gravity.

To remove a maintenance component, the screw was designed to span the full length of the screw feeder without the use of an intermediate support/hanger bearing. The center pipe was oversized to minimize screw deflection and increase torque rating. The same abrasion resistant AR400 plate was used for the screw flights for enhanced abrasion resistance to eliminate frequent maintenance, shortened equipment life, and higher overall operating cost. KWS also utilized hard surfacing to combat the negative effects of handling the abrasive material. Hard surfacing is the application of a layer of abrasion-resistant material over the carrying side and periphery of the AR400 flights to improve component longevity.