Technology Brief

Bale Quality Sampling: Coring Technology

Introduction

The intent of this project was to develop, manufacture, and evaluate core-sampling equipment for cost-effective inspection of baled recycled materials, including paper grades, and rigid and film plastics. Core sampling allows extraction of one or more cylindrical core samples from a bale of material so that representative sample(s) from the bale, including material from the bale interior, can be inspected without breaking the bale apart.

The CWC collaborated with the US EPA (the funding agent), Pacific Testing Laboratories/Professional Service Industries, Dynamark Engineering, Jefferson Smurfit Corporation, Re-Sourcing Associates, Inc., and the University of Washington Industrial Engineering Program to develop the prototype core sampling equipment and evaluate its performance in the field.

The initial objectives for the project were to:
· Design and manufacture bale coring equipment;
· Sort and evaluate bale core samples for contaminant and moisture levels;
· Correlate cored sample results to actual full bale sorts, to statistically compare contaminant levels in the bale versus core sample(s) from the same bale;
· Compare the cost savings of core sampling as a quality control measure to the alternative of breaking bales for inspection.

Equipment Development and Testing

Due to the prohibitive cost of licensing or purchasing off-the-shelf equipment (e.g., two international bale coring systems were identified), a local contractor was selected to design and manufacture the equipment.

Experimentation was conducted with a number of different equipment configurations, such as the advance mechanism, motor speeds and power, cutting bits, torque and other parameters to attempt to maximize penetration depth into the bale. For example, off-the-shelf hole saws, custom high-speed steel bit with scalloped edges, and custom carbide-tipped bits were tested for cutting performance on different recycled materials.

The equipment was designed for portability, on a wheeled cart, to facilitate testing at various field locations. Other features on the original version of the equipment included interchangeable cutting tips, an air cylinder ram, a jaw clamping system to hold the bale in place during drilling, and a 1 hp motor to rotate the coring bar as it penetrated into the bale. The design goal was to drill a minimum of 24" into the bale. It operated on a 110V, single-phase power supply, since higher volt/phase lines were not readily available at the first test facility.

The equipment was initially installed and tested at a recycling facility that generates large, dense bales (~35 pounds per cubic foot - pcf) of recycled paper grades and other commodities.

It was found that the design torque and advance thrust of this original design were too weak to core deep enough into the dense fiber bales. Due to limited power (1 hp motor) and the resistance within the bale itself, the average penetration depth into the bale was only about 8". A number of design changes were implemented and tested in an attempt to optimize penetration, however, it was deemed infeasible to extract core samples of adequate depth with this power-limited situation (110V).

A second test facility was found, that produces polyethylene film bales, ranging in bale density from 18 to 25 pcf. Because this facility had a 220V, 3-phase power supply, the new configuration of the equipment supported a 3 hp motor. The equipment was modified with the new motor, the air cylinder was replaced with a threaded-screw advance, and the clamping jaws were replaced with a simple winch and cable. Again, equipment functionality was tested on actual production bales, both rigid and film plastic.

Although the new equipment now possessed adequate power to achieve design penetration depth into the bale, and several film samples were extracted (up to about 16" depth), one of the final design changes caused a problem that hindered progress in field testing. Replacement of the clamping jaws, with a winch and cable system to hold the bale in place, did not provide enough strength to prevent movement of the bale with respect to the equipment, despite brakes on the coring unit wheels. This resulted in misalignment and arching of the coring tube which could not be repaired for the final testing. Thus, the final tests to extract and analyze sample for moisture and contamination, then correlate of the sample data with data from the sorted bale, were not conducted.

Results and Recommendations

The samples that were extracted during the course of field testing were measured for moisture content, and sorted and weighed for contaminant levels. Moisture was measured immediately after removal from the bale, with a moisture meter. Data was recorded in an Excel spreadsheet and graph.

Two examples of the utility of core sampling follow:

¨ A film plastic bale appeared to be LDPE from an exterior visual examination. Sortation of a sample from the bale showed that the majority of the film was HDPE, not LDPE, and that much of the film was covered with clear adhesive tape (about 24% of the sample by weight).
¨ During one extraction, a piece of upholstery textile inside a film bale wrapped itself around the coring tube. Upon removal from the bale, the textile contaminant was found to be a few inches wide and over 12' long. The sampling resulted in detection of a contaminant problem not visible from the exterior of the bale.

Although the final testing phase was not conducted, the project determined the important design parameters for core drilling of recycled bales, including:

· cutter tip design for specific materials;
· minimization of heat generation during coring (to avoid moisture evaporation, or degradation/melting of the sample);
· advance (thrust) and torque power requirements;
· convenient data collection and reporting.

Potential applications for quality control through bale coring technology include:

· Recycling facility or MRF to sample outgoing baled material and send sample analysis results to the customer.
· Recycled bale purchasers, such as pulp mills, who want to track incoming bale quality and be able to reject shipments before running low quality product through the plant.

Future Development

Some additional development and testing work is required for: full validation of this bale coring technology; statistical correlation of cored bale samples to bale contents or whole shipments; and labor and cost savings of coring compared to more labor-intensive quality control and inspection measures on broken bales.

Acknowledgments

This technology brief was prepared by CWC, the Managing Partner of the Recycling Technology Assistance Partnership (ReTAP). ReTAP is an affiliate of the national Manufacturing Extension Partnership (MEP), a program of the U.S. Commerce Department's National Institute of Standards and Technology. ReTAP is also funded by the U.S. Environmental Protection Agency.

Fact Sheet Issue Date: February 1999