Inclined Screw Conveyor System Signode Plastic Recycling Plant in Florence, KY

General Description

Signode Packaging Systems in an international manufacturer of packaging materials. One of their largest product lines is plastic strapping that is commonly used to secure cardboard boxes and pallets. Using recycled materials in their products has been an initiative for Signode for some time. The recycling facility in Florence, KY has been in operation since 1997 and is responsible for keeping tons of plastic waste out of landfills during that time. Much of the plastic arrives in the form of used plastic beverage bottles, which will be shredded, washed, ground and remade into plastic strapping.

Part of the process requires conveying the clean PET flakes from ground level up into a tank. The existing screw conveyor was 33-foot-long and ran without hanger bearings. As a result, the screw sagged and was constantly in direct contact with the housing, wearing holes in the housing. Any material that leaked through these holes would have to go through the entire cleaning process again. Using an intermediate hanger bearing wasn’t an option as it would obstruct the flow of the material on the steep incline. After dealing with the problem for years using patches on the trough, Signode looked to KWS for a solution. Thankfully, KWS has been solving problems in the screw conveyor industry for over 45 years. A piggyback system utilizing two tubular screw conveyors in series was used to eliminate the need for a long single screw conveyor while still not requiring hanger bearings.

Design Parameters

1. Product Type – PET Flakes
2. Material Density – 15 Lbs. per Cubic Foot
3. Capacity – 16,000 Lbs. per Hour
4. Duty – 24 Hours per Day, 7 Days per Week

KWS Advantages

The root cause of Signode’s problem was the long single piece screw that sagged and wore holes in the housing. After careful review of the restrictions and requirements, KWS recommended a piggyback design using two separate tubular screw conveyors. One screw conveyor would convey the bulk material half of the distance and then discharge to another screw conveyor. By using two shorter screw conveyors, the long conveying distance could be spanned without issue. Each shorter screw conveyor was designed with minimal sag or deflection, so the screw would never touch the housing. Also, by shortening each screw conveyor, the horsepower requirements were reduced. KWS has extensive knowledge and experience in solving problems for many industries. The new design offered by KWS for Signode was simple and very effective.

Special Features

The new KWS tubular screw conveyors operate on a 38-degree incline and proper screw conveyor design is very important for successful operation. The screws are mounted on larger-than-standard pipe to minimize deflection over their length and eliminate the potential for rubbing the housing. The screw pitch was shortened to improve conveying efficiency and there is a close clearance between the screw and housing. The speed of each screw conveyor was carefully chosen based on testing the PET flakes and historical knowledge. Additionally, each screw was straightened in a lathe to within 0.015-inches TIR and dynamically balanced since the screws rotate at high speeds.