Kiln Drying of Southern Hardwood Cross Ties

The objectives of investigation were to obtain information on moisture content, moisture distribution, rate of water removal, and degrade when accelerated kiln schedules are employed to season cross ties. The effect of species and heartwood content, and the reaction of the species to preservative treatment after seasoning is also examined. The study extended over 2 years and included laboratory and commercial trials. The species considered were: red gum (Liquidambar styraciflua L), black gum (Nyssa sp.), red oak (Quercus sp.) , hickory Carya sp.), beech (Fagus Ehrh.), and elm (Ulmus sp.). Altogether 3,000 cross ties were studied. The collected data show that a fast, high temperature (230? F.) kiln schedule is more satisfactory for conditioning cross ties than are schedules which utilize lower temperatures over a longer period. Heat and power costs are less, water removal rates higher, and the size of seasoning checks smaller. Checks and splits are narrower and shorter than those normally found on air seasoned ties. The specimens were dried in a double track, cross circulation Moore dry kiln and subsequently pressure treated with 80/20 creosote coal tar solution. Creosote retention and penetration measurements indicate that the kiln-dried ties can be satisfactorily pressure treated. Some of the southern hardwood species, namely black gum, red gum, elm, and hickory responded well to accelerated kiln-drying. Further study and revised drying and treating schedules may lead to more acceptable results in the case of beach, red oak, and other species. The effects of percentage of heartwood volume and species were obscured by such factors as differences in initial moisture content, the uncontrollable differences in heartwood volume, and others.

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