Tandem Screw Conveyors for Conveying Wood Chips and Bark Biewer Sawmill in Prentice, WI

General Description

The John A. Biewer Company has been in operation almost 50 years. Biewer is a third generation, family-owned group of companies that is committed to the environment and sound forest practices. The Biewer sawmills are considered the largest-volume, random-length mills in the Midwest. Biewer has the capacity to produce more than 300 million board-feet of dimensional lumber and timber annually.

Most of the power used to operate the Biewer sawmills is supplied by boilers that utilize refuse wood chips and bark for fuel. The Prentice, WI sawmill needed to upgrade an existing screw conveyor between a bucket elevator and storage silo. The existing screw conveyor had internal hanger bearings to support the screw due to the distance the bulk material was being conveyed. During operation, wet and stringy wood chips and bark would interlock causing blockage at the hanger bearings, damaging the flights of the screw and shutting down the system. The screw conveyor is located approximately 100-feet above ground and made maintenance a major issue. KWS was contacted by one of our local distributor partners for a solution.

Design Parameters

1. Material – Wood Chips and Bark
2. Product Density – 8 to 16 Lbs. per Cubic Foot
3. Conveyor Capacity – 4,203 Cubic Feet per Hour
4. Duty – 24 Hours per Day, 7 Days per Week

KWS Advantages

Sales and engineering personnel from KWS met with the operations and maintenance staff at Biewer to resolve the conveyor performance issues. The existing screw conveyor was 46-feet long and had multiple internal hanger bearings. Completely eliminating the internal hanger bearings was the goal of the new design.

Utilizing Autodesk Inventor 3D Solid Modeling, KWS Project Managers proposed a solution with two screw conveyors in tandem or “piggy backed”. Each screw conveyor was approximately 25-feet long and would not have an internal hanger bearing. Special consideration was taken to design the conveyor screws for minimum deflection.

Special Features

Each conveyor screw was designed on large diameter pipe with a maximum deflection over the 25-foot length of 0.19-inches. The drive and end shafts were sized for infinite loading. With the expectation for extended life, abrasion resistant (AR235) flight material and AR235 bolted-in trough liners were chosen. AR235 is designed to last at least 4 times longer than carbon steel. The liners are field replaceable with tools instead of needing a grinder or cutting torch up on an elevated cat walk. KWS maximized the lengths of each new screw conveyor by using flush end discharges. Due to the harsh Wisconsin winters, KWS chose hip roof covers to help shed the heavy snow from the tops of the conveyors. KWS is staffed with 9 degreed Mechanical Engineers and three Professional Engineers. KWS met the challenge and solved the problems at Biewer.