﻿KILN DRYING HANDBOOK. 



43 



record is the drying of 1 by 4 inch Douglas fir flooring strips in 24 

 hours; the slowest, the drying of some southern oak wagon bolsters, 

 which were in the kiln almost a year, and then were not drier than 15 

 per cent. 



The average periods required to dry several common hardwoods 

 are presented in Table 14. While these drying rates can readily be 

 secured in kilns with high velocity of circulation, it does not neces- 

 sarily follow that they can be duplicated under all conditions. 



Table 14. — Average drying time for 1-inch stock, green from the saiv to 5 per 



cent moisture. 



Species. 



Sfellow birch. 

 Red gum 



Sugar maple. 

 Mahogany... 

 Black walnut 



Original 

 moisture 

 content. 



Drying 

 time. 



Per cent. 

 80 

 100 

 80 

 80 

 80 



Days. 

 21 

 26 

 23 



22 

 30 



Species. 



k, red and white: 1 

 Northern highland stock . . , 

 Northern lowland stock. _ . 

 Southern highland stock. . 

 Southern lowland stock 



Original 

 moisture 

 content. 



Per cent. 



SO 



[■ 80 



80- 



Drying 

 time. 



Days. 



1 Plain sawed only; quartered takes about one-third longer with the same schedule. 



Maple last blocks can be dried in about 60 days, and walnut gun- 

 stock blanks in about the same length of time. Heavy oak wagon 

 stock takes from one and one-half to two months per inch of thick- 

 ness to dry down to 15 per cent moisture. The common drying times 

 for 1-inch softwoods, such as Douglas fir, the southern yellow pines, 

 and the white pines, run from two to four days, there being excep- 

 tions in both directions. Quartered stock may usually take a higher 

 schedule, and thus make up for some of its natural slowness in dry- 

 ing. It has already been mentioned that certain woods, like red- 

 wood, western red cedar, and cypress, are subject to collapse at high 

 moisture and temperatures. The hardwoods, as a rule, are more 

 plastic when hot and moist than the conifers, and in consequence are 

 more easily bent. This fact is taken advantage of in the drying of 

 red gum, for instance, which has a natural tendency to warp, but 

 seems plastic enough at high temperatures to overcome this tendency, 

 drying with but little trouble if properly " stickered.'' 



FINAL MOISTURE CONTENT. 



As has been stated, the "final moisture content should be slightly 

 lower than that which the finished product would naturally have 

 after it had been in service for some time. The first thing to con- 

 sider, therefore, is the ultimate use to which the finished product is 

 to be put and the climatic conditions at the point of use. Whether 

 the product is for use indoors or outdoors also is a determining 

 factor. Sometimes it is desired to have the stock swell after it is 

 put in service, and in these cases it is dried lower than it otherwise 

 would be. 



A study of the weather reports for various parts of the country 

 shows that the average atmospheric temperature and humidity con- 

 ditions vary greatly in the different regions and that they also have 

 important seasonal variations in each place. The relative humidities 

 for a number of cities are given in Table 15 to show these variations. 



