44 



Hardwood Record — Veneer & Panel Section 



July 10, 1921 



TABLE GLU 



The Picture Sliozvs the Present Home of 



^ERKM^ 



TRADE MARK 



1 



(Re- 



U. S. Pat. Off.) 



Our proo-ress has been made possible because the majority of the glue using trade was 

 alive to the opportunity of PERKINS QUALITY and PERKINS SERVICE. 



Process and Product Patents covering Perkins Glue were granted Tiilv 2nd and March 19th, 1912, and have been held valid and 

 ulnuged by the United States Circuit Court of Appeals. Patents have also been granted in Canada, Great Britain, Germany, 

 !• ranee, Belgium, Italy and other foreign countries. 



PERKINS GLUE COMPANY 



Factory and Gen. Offices : LANSDALE, PA. 



Sales Office: SOUTH BEND, INDIANA 



{<'i>iitliiiti-(l jruiii iiiiifc 30) 



What occurs in drying and controlling moisture in veneers la 

 almost identical with lumber except as stated at the outset, the 

 time required is proportionately greater according to the thickness, 

 and no matter what specie of thickness of lumber you are drying 

 and regardless of conditions under which you are manufacturing, 

 there is no reason why any of the common ills should be tolerated. 



Casehardening, excessive warping, bowing, cupping and honey- 

 combing are all due to unequal drying. In other words, the atmos- 

 phere in the kiln is too dry in comparison to the moisture in the 

 stock and, therefore, the outer portions of the board shrink faster 

 than the inside, because the moisture can not be transfused out- 

 wardly fast enough to prevent this. When the outside portion of 

 a board is dried in this way, the fibres are drawn or stretched apart 

 over the wet interior and set rigidly in this condition. Surface 

 checking results frequently in this case, but more often this does 

 not occur. A board when warm and moist is somewhat plastic 

 and is not unlike papier mache. When the outside portions of 

 a board have taken a rigid position or formed a shell, it is known 

 to be "casehardened.*' 



Later on in the drying period when the inner portion gives up 

 moisture and consequently must shrink, it is prevented from doing 

 so by the set outer shell. When the internal stresses develop 

 beyond the strength of the fibres, numerous ruptures occur, which 

 we call "honeycombing." Practically all other drying ills can be 

 attributed to the same causes. 



Drying schedules should provide specifications of temperatures 

 and humidities for moisture content in the species you are drying 

 in five per cent reductions. As for example, drying conditions 

 for black walnut containing over 40 per cent moisture, which is 

 to be used for high grade furniture, can safely be started at a 

 temperature of 115° fahrenheit and 85 per cent Relative Humidity. 

 Tests of the lumber should be made to determine a change of these 

 conditions, as time is a very poor indicator. When the stock 



shows a reduction in moisture to 35 per cent, the temperature 

 should be increased to 120° and the humidity lowered to 80 per 

 cent. This procedure must be carried out by degrees in accordance 

 with frequent tests of the lumber to an ultimate condition of 150° 

 fahrenheit and 30 per cent relative humidity. It may be noted 

 that the first or initial drying condition is equal to an E. M. C. of 

 much less than 40 per cent moisture; in fact, it is between 16 per 

 cent and 1 8 per cent. It is, of course, necessary to maintain a 

 considerably lower E. M. C. than the moisture in lumber in order 

 to reduce it, and, in other words, these conditions indicate a safe 

 drying speed. Because walnut in drying is subject to fine surface 

 checking and other uncommon ills, and for the reason that in 

 this case the stock is to be used for high grade furniture, conditions 

 are controlled from 40 per cent moisture instead of 30 per cent, 

 which may be applied in less exacting circumstances, and, in fact, 

 conditions considerably more severe can be applied when the kiln 

 operator at all times is thoroughly familiar with what actually is 

 taking place in the lumber and the kiln. 



Tests should be made on two pieces — one to determine the 

 average moisture content and the other to determine distribution 

 of the moisture. The first is common, the second is made by cut- 

 ting away the outer shell to a line about Ya" ^'l around the section 

 and testing this and the remaining center piece separately. This 

 is very important, especially in all cases where considerable case- 

 hardening and other troubles exist which can only be eliminated 

 by correction of faulty kiln design. 



1 have attempted to outline in this discussion the fundamental 

 and known principles underlying the process of reducing and con- 

 trolling moisture in wood, and the logical deductions to aid in their 

 practical application in the manufacture of veneers and panels. 

 Discussion of the various details of operation and design of drying 

 equipment has been purposely avoided, my aim being rather to 

 ■establish the standards \vith which you can study and compare 

 your present methods and practices. 



