Date of Award

8-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Engineering Science

Major Professor

Robert D. vonBernuth

Committee Members

Bobby L. Bledsoe, Fred D. Tompkins, Paul M. Winistorfer

Abstract

The objective of this research was to design, fabricate and evaluate a device for in situ measurement of horizontal density of a wood particle mat during pressing. Requirements of the device were to maintain selected relative fixed positions, with reference to the press opening distance, during press closure.

A mechanical device was designed to .accommodate the requirements of the press environment, and to incorporate existing radiation based measurement equipment already in use in the laboratory. A system of stainless steel gears and racks was designed to maintain proportional velocity among three source and detector holders across the 24 inch opening of the existing hot press. Three individual positions selected for simultaneous radiation monitoring were 25%, 50% and 75% of mat height at any time during the press cycle. Aluminum yoke and source/detector holders were fabricated and attached to the press through a series of linear bearings. Aluminum plate stock was used to fabricate a frame to which all racks, gears and yokes were attached. A teflon insulating pad was placed between all surfaces of the mechanical device and the press to minimize heat transfer to the device.

After installation of the device on the press, an adjustment and calibration procedure was done to ensure positioning and collimation of the source and detector.

Evaluation of the performance of the device included employment of two linear variable displacement transformers to monitor the source and detector positions during press closure. The average relative difference in position of the source and detector holders was 0.003 inches during evaluation of a normal press cycle.

An Americium241 source, with a photon energy of 60 KeV, coupled to a sodium iodide crystal detector was used for initial measurements of density during pressing. Calibration samples (oak blocks) were used to determine the linear attenuation coefficient during experimentation. A constant linear attenuation coefficient of 0.21 cm2/g was found for different width calibration samples.

42 lb/ft3 laboratory panels were manufactured for initial measurement of density during pressing. Mats were cut to 2, 4, 6, 8, and 12 inches in width to evaluate attenuation distance influence on density measurement. Plots were developed depicting density change with time, during the press cycle. These plots revealed changing density during pressing; most notable is the dynamic change in density after the press has reached final position. These are the first recorded in situ measurements of density of a wood particle mat during pressing.

The system of gears and racks provided an accurate method for maintaining desired positions of the radiation source and detector during pressing. The application of a radiation-based measurement technique to measuring density proved successful during initial experimentation.

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