Mixing Screw Conveyor for Polyethylene Powder & Additives

General Description

Polyethylene and polypropylene are the most common forms of plastic and used in thousands of consumer and industrial goods ranging from plastic bags and bottles to N95 medical masks and face shields. The demand for polyethylene and polypropylene has increased significantly during the COVID-19 crisis.

One of the world’s largest suppliers of high-density polyethylene and polypropylene was undergoing an expansion of an extrusion line requiring new loss-in-weight additive feeders and a mixing screw conveyor. The feed stream from the additive feeders would be distributed along the length of the mixing screw conveyor. The conveyor would be used to smooth out feed variations from the upstream feeders and mix the powdered polyethylene with various pure additives before accurately discharging into an extruder.

Design Parameters

1. Product Type: High Density Polyethylene (HDPE) Powders & Pure Additives
2. Material Density: 21.2 to 35 Lbs. per Cubic Foot
3. Conveyor System Capacity: 7,747 Cubic feet per Hour
4. Design Pressures: 0.75 psig internal; 60 psig jacket
5. Design Temperature: 212-degrees F
6. Duty: Continuous

KWS Advantages

The end user contracted KBR to oversee the project, create detailed specifications, and select equipment manufacturers. Coperion K-Tron, an industry leader in volumetric feeding solutions, was selected to provide the mechanical conveying equipment for the project. Over many years, Coperion K-Tron and KWS have worked as successful partners on several similar projects. KWS supplied the mixing screw conveyor with water-cooled jacket for collection from the Coperion K-Tron feeders.

KWS and Coperion K-Tron sales and engineering teams collaborated to ensure the extrusion line expansion would be successful. KWS engineers interpreted the complex specifications and provided an accurate design. Engineers from both companies exchanged 3D parametric models to ensure the equipment would fit together in the field seamlessly. In addition to standard ISO quality procedures, KWS provided raw material traceably, material test reports, and positive material identification testing services for enhanced quality assurance.

Special Features

The KWS mixing screw conveyor was designed as a single piece screw to span the length of over 28-feet without the use of an intermediate support/hanger bearing. The screw was mounted on oversized pipe to prevent excessive screw deflection. The screw flights were cut-flight with notches every 90-degrees to promote mixing and agitation as the materials were conveyed. At the tail end of the screw, double flighting was added to provide even discharge to the extruder.

KWS utilized a drive pedestal to protect the gear reducer and motor from heat and shock loads. The gear reducer and motor are located away from the heat source and operate at ambient temperature. The KWS drive pedestal is a compact design that houses the motor, gear reducer, bearings, low-speed coupling, seals and shafts. All rotating parts are guarded with OSHA compliant guards.

The screw conveyor trough was designed with an external jacket. Cooling water runs through the jacket and cools the material as it is conveyed. The jacketed trough and inlets were custom designed and manufactured in accordance with the ASME Boiler and Pressure Vessel Code for years of long, safe and reliable operation.