﻿KILN DRYING HANDBOOK. 61 



perature will undoubtedly be higher there than in the upper and 

 lower passages. 



PLACING OF SAMPLES. 



The placing of samples is of prime importance, and a large num- 

 ber, 10 or 12, should be used for each run until the behavior of the 

 kiln is well determined. Samples should be so placed in the piles of 

 lumber that they will receive exactly the same drying treatment 

 as the lumber itself. They should be located on both entering-air 

 and leaving-air sides of the piles, high, low, and halfway up, so that 

 the relative drying effects can be determined. In case of erratic 

 circulation or trouble from uneven drying, samples can also be placed 

 in the middle of the piles; on these there will be no intermediate 

 weighings possible. In progressive kilns, or any type operating at 

 high temperatures, the obtaining of intermediate weights on any of 

 the samples is often a difficult matter. When the kiln has been 

 loaded steaming can start immediately. A full supply of high- 

 pressure steam should be available, so that the steaming temperature 

 may be reached quickly and full saturation of the air assured. 

 Care must be used to prevent possible injury to the instruments as 

 the kiln is heated ; the steaming temperature will probably be higher 

 than that for which the regulators are set, and if these are of the 

 liquid-filled type the excessive pressure developed may strain the 

 bulbs or diaphragms or cause the valve to stick on its seat. 



After the drying conditions have been established a study should 

 be made of the circulation. This study can well be supplemented 

 by the use of a number of wet and dry bulb hygrometers scattered 

 throughout the kiln, preferably near the various samples. The read- 

 ings of these will give a good idea of the relative drying conditions 

 at these points. The readings should be tabulated and the relative 

 humidity determined. The variations in the relative humidity are 

 a good indicator of the variations to be expected in the drying rate 

 throughout the kiln. In progressive kilns the matter is more diffi- 

 cult, and more reliance must be placed upon circulation tests and 

 upon the moisture content of the samples in the dry stock. If wet 

 and dry bulb hygrometers are used in progressive kilns to determine 

 uniformity of drying, they should all be placed on a single truck at 

 a time, since variations from end to end are to be expected. 



The samples should be weighed frequently enough so that there 

 will be at least 5 determinations for the kiln run; in the case of 

 runs extending over more than 10 days, the samples should be 

 weighed every day. The moisture per cent should be calculated 

 immediately, and a chart should be maintained, showing graphically 

 the loss of moisture day by day. On this same chart may be plotted 

 the daily temperatures and humidities. This can then be compared 

 with the drying schedule and differences noted and corrected. If 

 preferred, the temperature and humidity of the schedule may be 

 plotted on the same sheet, thus giving a useful comparison between 

 the schedule and the actual run. (See Fig. 12.) 



KILN RECORDS. 



In addition to this chart, it is desirable to keep a permanent 

 record of the details of each run. Forms for this purpose are 

 provided by some of the kiln companies and can well be used wher- 



