THE STRENGTH OF WOOD CHIPS ATTACHMENT TO STORAGE WALLS CAUSED BY FREEZING

In cold climates, wet comminuted wood fuels sometimes freeze to walls and other surfaces during cold storage. This is well known. However, f ew studies have examined the relationship between the strength of atta chment caused by freezing and factors such as temperature, fuel moistu re content (MC), and surface type. The freezing of wood chips to three different surfaces (smoothed concrete, urethane rubber, and coated pl ywood) was studied on a laboratory scale with equipment designed for t he study. Six plastic pipes embedded in thick insulation and filled wi th wood chips (15% to 155% MC, dry basis) were kept in direct contact with the surfaces that were mounted on a cold wall (-25 degrees C). Th is allowed the freezing of wood chips to six circular sections of the wall surfaces. The strength of the attachment caused by freezing was d efined as the force parallel to the wall needed to loosen the wood chi ps. The force needed to loosen the wood chips was exponentially relate d to the MC of the chips. It was 4.3, 17.6, and 40.4 kN per m(2) of co ntact area at MCs of 50, 100, and 150 percent, respectively. There was no significant difference in attachment between the three wall surfac es. The strength of attachment caused by freezing was influenced by th e way the wall was kept cold. Because the study only included three su rfaces and used wood chips with a very low proportion of fines and ove rsized particles, more surfaces and kinds of comminuted wood fuel ough t to be studied.