20 



HARDWOOD RECORD 



May 10, lyiO 



signal. A simple statement that temperature and humidity conditions 

 are flexible and under the immediate control of the operator would 

 inspire more confidence. 



The most satisfactory types of kilns yet developed are those with 

 features of automatic temperature and humidity control which make 

 the operator a complete master of his kilns in that any conditions 

 which he regards beneficial to the lumber may bo maintained hour 

 after hour, or day after day, until he considers it desirable to change 

 such conditions. 



The kiln operation itself can never become automatic altliough the 

 control of drying" conditions may well be that, and efforts to bring 

 about automatic control of such phases are most decidedly on the right 

 track. A brief and general discussion of some of the features of 

 kiln operation which are of utmost importance may throw additional 

 light on the importance of the skilled operator as apart from the kihi. 



Relation Between Method op Piling and Uniformity or Drying 



The first opportunity for an cxhiliition of skill in kilu operation is 

 in the adoption of 

 the proper system 

 of piling the lum- 

 ber in the kiln. It 

 may be safely said 

 that comparatively 

 few kilns ^rc op- 

 erated with any 

 thought as to 

 whether the piling 

 suits the kiln or 

 not. Because of the 

 very definite rela- 

 tion that exists be- 

 tween method of 

 piling and the cir- 

 culation of air in 

 the kiln, this sub- 

 ject is to be as 

 .strongly emphasized 

 as careful temjiera- 

 ture control and rog- 

 u 1 a t i n of the 

 humidity. 



First and fore- 

 most, lumber is piled 

 in the dry kiln so 

 as to dry uniformly 

 and as quickly as 

 possible. There Is 

 no more effective 

 way of bottling up 

 the circulation in a kiln and slowing up the drying rate than 

 by piling in lumber across the path of the moving air. The piling 

 should be such as to offer the least obstruction to a free and 

 positive circulation of air within the kiln. Methods of piling which 

 lead to complete utilization of all space and in greatest economy of 

 handling the lumber through the kiln arc important features to be 

 sure, but entirely secondary and subordinate to the method that con- 

 forms to the circulation system of the kiln. The method of piling 

 must be such as will throw the "stickers" parallel to the predominant 

 air currents and never perpendicular to and obstructing it. 



End piling in a progressive type of kiln, which depends for its 

 circulation on the passage of air from the hot, dry end to the green, 

 cool end jdaces great obstruction to free and uniform passage of air 

 and is obviously wrong. Cross-piling in a tyjie of kiln in which the 

 circulation is vertical-lateral as in many tj-pes of ventilated and con- 

 denser kilns is just as serious in that the normal air currents are 

 obstructed. 



This point is illustrated clearly by a case of practical experience. 

 Some 4/4 green maple was loaded into a dry-kiln having vertical- 



"fiH 



£)ayj /n Dry/n^ Per/od 



lateral circulation. Part of the stock was end piled and part of it 

 cross piled. Temperature readings were taken daily at different 

 parts of both piles. After the run was well started the difference 

 between the hottest and coolest portion of the end jiiled stock was 

 10° while the difference in the cross-piled stock was 58°. This had a 

 marked effect on the uniformity of drying. The end piled stock dried 

 from 30 per cent to a maximum moisture content of 6 per cent in 

 10 days, while it took 13 days for the stock piled crosswise to dry 

 from 30 per cent down to 12 per cent. This shows that there is a 

 right and wrong way for lumber to be piled in every type of kiln. 

 (See cuts on page 19.1 



To those interested in even, rapid drying, this point is of great 

 practical significance. 



Knowledge of Actual Conditions in Kiln Prevents Losses in 



Stock 



After the lumber is properly piled in the kiln and the heat turned 

 on the competency of the operator again comes into play. It is essen- 

 tial that the opera- 

 !|!|iii|;!!'|!!i!l|!!!|l!i!|!!l!U:w'-:|l| tor know accurately 

 the drying condi- 

 tions in every part 

 of the kiln. The de- 

 termination of the 

 conditions to which 

 the lumber is actu- 

 ally subjected is a 

 critical phase of 

 kiln operation. With 

 that knowledge 

 available to the op- 

 erator no lumber 

 need be ruined in 

 any dry-kiln. If 

 one part of the kiln 

 is warmer than an- 

 other, that fact 

 should be known by 

 the operator, and 

 allowances made 

 therefor. If one end 

 of the kiln runs at 

 lower humidity 

 than the other, that 

 fact should be 

 known and reckoned 

 with. When meas- 

 urements of tem- 

 perature and humid- 

 ity are taken they 

 are too often taken by sticking an instrument through a hole in the big 

 door and assuming that all parts of the kiln read the same as near the 

 door. The temperature and humidity taken at any one part of the kiln 

 are no criterion of the condition in other parts of the kiln unless the 

 circulation is more perfect than in most kilns. (See cut on this page.) 



The kiln operator should know the behavior of his kiln when lumber 

 is being dried in it as an engineer knows the correlated workings of 

 his gas engine. 



Regulation op Kiln Should be Based Entirely on Moisture 

 Condition op Lumber 



The fundamental basis of kiln regulation is the actual condition 

 of the lumber in the kUn. This statement ought to be as easily and 

 broadly recognized by kiln operators as the fact that the amount of 

 fire under a boiler is the measure of the amount of heat produced, 

 and yet there is a most flagrant disregard of this fundamental truth 

 in many kiln-drying oj)erations. Ordinary practice involves kiln 

 operation based on the number of days that the lumber has been in the 

 kiln. The variation in the original condition of the lumber is so great, 



.Vn actual record of temperature conditions during the kiln drying of heavy, green oak at an 

 nuto body plant in Oliio. Note the great difTcronce in temperature readings obtained from the record- 

 ing instr'uraont in oiu' part of the Iciln and from a staudanl thcrmonietor in another part. The oper- 

 ator ot tlir lain dill nut know under what condition the lumber was actually being dried. Result 

 was a loss ol 70 per cent. 



