Continuous kiln apparatus for producing warp-free lumber
United States Patent 1191 Koch [ CONTINUOUS KILN APPARATUS FOR PRODUCING WARP-FREE LUMBER [76] Inventor: Peter Koch, hi5 Kimball A\&#39;c..  
 Alexandria. La. 7l3()l 22 Filed: July 23. 1974 21 Appl No.: 491.471  
 [52] US. Cl. 34/236; 34/95: 34/118;  
  34/DIG. l9; 2l4/l8 R [51) Int. Cl. F26!) 19/00 [58] Field of Search 34/).5. I34. 13.8. lit).  
  34/l20. ill, 20], 206. 208. 236, 239. 240. DIG. l9. 2l52l8&#39;. 432/66. l26. I87; 2l4/l8 (56] References Cited UNITED STATES PATENTS LSWLUZU 3/[926 Elmendorf 34/l3.ii 3.49L989 l/l)7(l Fritz et al. 34/95 3,680,219 8/]972 Koch 34/l3.4  
 [45] Apr. 8, 1975 1757328 9/l973 Runciman 34/DlG. l9  
 FOREIGN PATENTS OR APPLICATIONS 7,699 6/l927 Australia 34/95 Primary Eruminer-Kenneth W4 Sprague Assistant E.\&#39;umincr-James C. Yeung [57] ABSTRACT This invention relates to an apparatus for producing dried lumber that is free from crook, bow. and twist. The claimed apparatus functions as a continuous kiln accessary which employs paired arrays of rolls in combination with rigid lumber guiding and warp restraining bars interposed intermediate the paired roll arrays. supplies controlled. directed. uniform motion and provides total restraint against the forces of warping for sized. individual pieces of lumber undergoing kilning operations and passing serially in an end-to-end sequence through the apparatus.  
 2 Claims, 3 Drawing Figures CONTINUOUS KILN APPARATUS FOR PRODUCING WARP-FREE LUMBER A non-exclusive. irrevocable. royalty-free license in the invention herein described. throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes. is hereby granted to the Government of the United States of America.  
 OBJECTIVES OF THE INVENTION The objective of the instant invention is to provide a mechanical apparatus that functions as an adjunct accessory to a lumber kiln. The apparatus is adapted to be spatially accommodated within a selected lumber kiln and capable, performancewise. of moving. as a continuous operation, individual. thickness sized pieces of lumber through the selected kiln while at the same time providing to the pieces of lumber, throughout kilning, a total restraint against the forces of warping.  
  It will be understood by those to whom this disclosure is directed that the term kilning is inclusive broadly of all those operations central to the artificial seasoning of lumber and more specifically the term refers to the removal of moisture usually with heat, steam straightening, the relief of case hardening induced by heating and ultimately the cooling down of the lumber following the requisite heat treatments.  
  In general, the apparatus comprises a pair of mu]- timembered roller roll arrays aligned juxtaposed and parallel, adjustably spaced apart and biasable one toward the other via adjustable and resilient linking means.  
  Located intermediate the juxtaposed roll arrays and extended directionally normal the axes of roller members of the roll arrays is a series of parallel spaced fixed and rigid bar-like members. Thickness of the bar-like members can approximate, but must be kept less than, the finished thickness dimension of the lumber being kilned. The lateral spacing between adjacent bar-like members can approximate, but must be maintained slightly in excess of, the finished width dimension of the lumber being kilned. The spaces between adjacent barlike members serve as a pathway for lumber pieces passing through the apparatus and in addition, the spaces provide pathways restricted relative any warping forces in the width dimension for lumber pieces being kilned.  
  At least some of the roller members of both the roll arrays are driven rotationally with suitable roller driving means. Rotational driving of the rollers has the purpose of urging lumber pieces through the apparatus with positive and with uniform motion.  
  Although the utility of the apparatus herein disclosed is not limited to the kilning of pine lumber, all of the data of the examples as set forth and the specific apparatus as depicted and described relate to southern pine lumber and in particular relate to the kilning of 2 4 studs 8 feet long. Accordingly, the following set of facts that relate to southern pine lumber will be helpful for an understanding of the utility of the apparatus claimed.  
  1. Southern pine lumber can be bent-and will retain its bend-if it is first steamed for a short time. Conversely, a bent piece of lumber can be steam straightened.  
  2. Moisture leaves southern pine readily at temperatures above the boiling point of water.  
 3. High temperatures and large wet-bulb depressions accelerate drying. If exposure time is short, strength loss in the wood is minor up to temperatures of 240F.  
  4. During the early stages of drying, water leaves the wood at a rate approximately proportional to the velocity of the circulating air.  
  5. In kiln-drying, energy costs are proportional to total drying time.  
  6. Case hardening and internal stresses in kilndried coniferous wood can be eliminated by several hours of steaming at dry-bulb temperatures just below the boiling point.  
  7. It is established that S-foot southern pine studs measuring 4 inches wide and 1.9 inches thick can be dried from the green condition to 9 percent moisture content in 2l hours in a kiln providing a crosscirculation velocity of 1.000 feet per minute at drybulb and wet-bulb temperatures of 240F. and l6UF. Case-hardening in such dried studs can be relieved by 3 hours at 195F. dry-bulb and 185F. wet-bulb temperatures.  
  The above related facts together with kilning schedules (i.e. times, temperatures. air velocities. and the like) all are well established in the lumber seasoning art. As such, they do not constitute a part of this inven tion. They will be included in the instant disclosure only to the extent that particular values arise as experimentally derived data from the operation of the claimed apparatus.  
  The claimed apparatus quite simply functions to convey lumber through a kiln in a continuous operation and at the same time functions to retain the individual pieces of lumber being kilned under total lateral restraint to the end that the finished kilned lumber will be free from any kilning warp distortions such as crook. bow, or twist.  
  Sized pieces of unkilned lumber and severally and serially fed into one end of the apparatus. The individual lumber pieces enter one of several ingress openings bounded top and bottom by the positionally paired roller members of the juxtaposed roll arrays and bounded on either side by the rigid bar-like warp restraining lumber guides.  
  Movement of the lumber pieces through the apparatus during the several stages of kilning is effected by driven roller members of the juxtaposed roll arrays. It may be found to be desirable in the case of certain lumber types to introduce into the roll arrays driven rollers the surfaces of which are not machined perfectly smooth but are in fact slightly rugose.  
  Driven rollers exhibiting a slight surface rugosity are useful in some instances for insuring positive driving friction viz-a-viz lumber pieces and rollers. However, smooth surfaced rollers have been found to be satisfactory for most applications.  
  Collaterally, the loading of the roller members of the roll arrays in the direction normal to the roller azis and normal also the plane of the roll array should be adjusted serially along the array with due consideration being given by the apparatus operator to the fact that a heavy roller loading at the lumber ingress where the lumber pieces are wet and relatively soft will tend to flatten and undesirably deform the lumber whereas an increasingly heavier loading may be required for those roller members further along in the apparatus at kilning locations where the lumber pieces are drier and not subject to easy deformation and where lumber surfaces may indeed even be case-hardened to a degree that lessened roller-lumber friction tends to impair positive. uniform movement of the lumber pieces. As a general proposition. roller loading at any particular location within the apparatus need never exceed by much that loading required to insure positive. uniform movement of the lumber pieces passing through the apparatus and that loading necessary to prevent kilning deformations such as twist, bow. and crook.  
  Roller loading is. in the main. a judgment for the operator of the apparatus. The judicious use of roller pressure in the early stages of kilning if not excessive can, for example. be used to smooth out minor surface defects on the lumber facings.  
  The rollers can be loaded using any conventional roll loading method. Spring loaded bearing yokes tensioned via adjustable threaded rod linkages to the roll-case support as is shown in certain of the drawings (FIGS. and 2) can be used. Pneumatic or hydraulic methods of loading the individual rollers or alternatively loading ofthe entire roll-case sub-support assembly also can be employed.  
  The specific apparatus herein disclosed utilized a pneumatic method of roll-array loading primarily for reasons of convenience and for ease of accomplishing rapid experimental loading variations.  
  This particular apparatus will now be described with reference being made to the accompanying drawings in which FIG. I is a perspective view of the apparatus.  
  FIG. 2 is a side elevation of the apparatus and shows particularly a method of driving the roller members of the juxtaposed roll arrays.  
  FIG. 3 is a perspective view limited to a portion (i.e. segment of side frame member and one roller member) of the upper roll-case sub-support assembly and shows a method of resiliently positioning and loading a single roller member. An obvious variant of the loading and linking scheme shown in FIG. 3 can be employed to load and link the roll-case sub-support assembly to the primary apparatus support (i.e. the bearing shaft of the roller becomes a stationary link pin integral the rollcase. sub-support assembly). Such a linkage at each corner of the apparatus can provide a mechanical linking positioning and loading method for the juxtaposed roll arrays.  
  Referring now to FIGS. I and 2 collectively, the apparatus components are supported and in general are confined within the primary apparatus support entity 1 which support is constructed from rigid elongated members that in the aggregate form an open supportive framework in the form of a rectangular parallelpiped. Rotatively mounted and journaled to side support member 2 and a counterpart side support member (not shown) with positionally fixed bearings 7 (one of 36, of which total eighteen are shown in FIG. 2) are rollers of othe first or bottom roll aray 4H (one of nine shown in FIG. I) and rollers of the second or top roll array 5 and 5H (two of nine shown in FIG. 1). The rollers are uniform. cylindrical shaped, and hard surfaced. The rollers are disposed uniformly spaced and axially parallel one to the others and the rollers collectively constitute what will hereinafter be referred to as the first (bottom) roll array and the second (top) roll array.  
  A horizontal, two dimensional. tangential projection of the, at any given moment. adjacent and vertically juxtaposed peripheral surface locations of the several roller members of the two roll arrays effectively define the planes (first roll array the base plane and the second roll array the cover plane) of moving but restrictive pathways for pieces of lumber traversing the apparatus. The individual roller members of the second (top) roll array are mounted and journaled rotatively within the roll-case, sub-support assembly of which assembly one of two counterpart side frame members 8 and one of two counterpart end frame members 88 are shown in FIG. 1.  
  As a matter of apparatus fabricator choice and depending upon the choice of method employed for loading the rollers. the individual roller members of the second (top) roll array can be journaled with positionally fixed bearings to the respective side frame members 8 (one of two counterpart members) of the roll-case, sub-support assembly. If positionally fixed bearings are employed for journaling of the individual roller members of the second (top) roll array to the roll-case. subsupport assembly, then the roll-case, sub-support assembly can be linked and loaded relative the primary apparatus support via pneumatic piston and cylinder assemblies 9, QA, 9B. and 9C as shown in FIG. 1.  
  Alternatively, the individual members of the second (top) roll array can be journaled to the two respective side frame members of the roll-case, sub-support assembly with positionally variable and load adjustable resilient mechanical mountings. The spring loaded yoke and threaded rod assembly depicted in FIG. 3 is one convenient method for loading and positioning vertically the individual roller members of the second (top) roll array.  
  In FIG. 3, the slot cut into frame side member 8 carries bearing block I2 into which is journaled roller shaft 35. Rod I5 is threaded to match counterpart threads in frame side member 8.  
  Item 14 is a coil spring compressively resilient and interposed between bearing block 12 and the lower tip of threaded rod I5. Threaded rod 15 in conjunction with spring 14 provides positioning and a resilient loading for roller shaft 35.  
  As noted above, an adaptation of this loading and linking method can be employed for linking the entire roll-case, sub-support assembly to the main apparatus support.  
  As will be evident to those to whom this disclosure is directed, combinations and variations of the depicted resilient and adjustable linkages are possible. For example, both the roll-case and the individual roller members can be loaded and adjustably linked. The method of loading can be via bearing yoke, spring and threaded rod, or via hydraulic or pneumatic piston and cylinder actuated means. The experimental data set forth below was obtained with an apparatus wherein the adjustably resilient linkages were of the pneumatic piston and cylinder actuated means as per FIG. 1 and all of the individual roller members of each roll array were journaled to their associated frame work structures with positionally fixed bearings.  
  In FIG. 1, lumber pieces 10 (one of six shown) are located intermediate the bar-like lumber guides 11 (one of seven shown) which guides are smooth surfaced, rigid, rectangular cross-sectioned bars fixedly secured to the primary apparatus support via through bolts 19 (one of eleven shown). The lumber guides are disposed lengthwise through the. apparatus in spaced parallel array, intermediate the two juxtaposed roll arrays and normal the roller axis thereof.  
  The lumber guide bars can approximate but must always have a lesser thickness (vertical dimension) than the thickness of the lumber pieces that pass among them. otherwise the loaded roll array and the individual roller members thereof would ride upon the lumber guide bars rather than the lumber pieces. Lateral spacing of the lumber guide bars is operator established in accordance with the width dimensions of the lumber pieces undergoing kilning.  
  The roller members of the two juxtaposed roll arrays can be driven by any suitable means for imparting positive and uniform rotation to the particular roller members selected to be driven.  
  The specific apparatus depicted in the drawings (FIGS. I and 2) was driven for reasons of experimental convenience with a powerful hydraulic motor 30 that operated through shaft l8 and toothed gear to rotate the driven rollers via roller chain 33. Toothed gears 34, 3M (two of several shown) are fixed to their associated roller shafts 35. 351 (two of several shown) and transfer the rotational forces to the driven rollers.  
  The requirements of the roller driving means are that the drive be controllable and both positive and of uniform speed to the end that residence time of the lumber pieces passing through the apparatus and undergoing kilning can be controlled with precision.  
  Item 42 in FIG. I represents a pneumatic accumulator employed to actuate the loading cylinders 9, 9A. 9B. and 9C via pneumatic lines 43 (FIGS. 1 and 2) one line supplying each cylinder.  
  Set forth below as an operational example is a kilning experiment that employed the apparatus as described and for purposes of comparison employed a conventional stacking and drying operation carried out con current therewith.  
  The specific apparatus was equipped with nine pairs of 4-inch-diameter, 34-inchlong. smooth rollers spaced 12 inches apart. Four pneumatic piston and cylinder assemblies located at the corners of the roll-case. sub-support assembly applied the resilient loading force between the roll arrays. Air pressure of about 80 pounds per square inch was applied to the 5-inchdiameter pneumatic cylinders.  
  The lumber guides were rigid and fixed steel bars approximately r inch thick and about 1% inches wide. The guides were spaced 4.02 inches apart.  
 PROCEDURE To make this comparison eight kilnloads were dried;  
 each load contained six 8-foot 2 by 4&#39;s held by the rollfeed mechanism. and another six-dried (in a single layer) conventionally stacked with a top load of IS pounds per square foot.  
 Factors were as follows:  
 A. Treatment 1. Mechanically restrained while moving in rolls (roll dried). 2. No restraint (conventionally stickered). B. Replications within load: 6 boards/treatment C. Load replications: 8  
  The 96 studs required were purchased from a commercial source in two separate lots of 48 (widely separated in time). The studs were rough-sawn from veneer cores. Studs from cores were used in the experiment because of the propensity of such wood to warp.  
  The 96 green studs were trimmed to 96.0-inch length. surfaced to 1.75-inch thickness and 3.84-ineh width. randomly assigned to treatment and replication. and then stored under water pending use.  
  The guide bars on the continuous dryer apparatus were spaced 4.02 inches apart. so a green stud width of 3.84 gave minimal clearance.  
  The unrestrained lumber had a top load of 250 pounds evenly distributed.  
  Before each load replication. studs were measured green for: weight. length. width. thickness. twist. bow. and crook.  
  For each load replication. the studs were charged into a cold kiln. the rolldryer apparatus made operational, the kiln heated to 240 F./l F. and held for 2l hours after startup; the load was then steamed for 3 hours at 195 F./l F. Finally. the load was discharged at the end of the 24-hour period and each stud measured immediately for weight. dimensions. and warp. One-inch cross-sectional slices were taken at quarter points of each stud to permit computation of ending moisture content and specific gravity.  
  Case-hardening specimens were cut from quarter points of three studs from each treatment.  
 RESULTS The green studs averaged 87.9 percent in moisture content and 20.1 pounds in weight. Crook. bow. and twist when green averaged 0.064. 0.094. and 0.065 inch. Specific gravity of the studs was 0.47 based on green volume and ovendry weight (table 1).  
  Dry studs averaged 8.3 percent in moisture content. 0.l26 inch in length shrinkage (0.13 percent), and 0.l28 inch in width shrinkage (3.33 percent). Moisture content range was from 4.9 to 16.4 percent with standard deviation of 2.5 percent. Average stud weight on discharge was ll.8 pounds (table I).  
 Table 1 Properties of green an dry studs dried at 240 F. with conventional stacking and with roll-feed restraint Table l (&#34;onlinued Properties of green an dry studs klllLLl at 240 F. with comentional stacking and with roll-feed restraint Standard Property Mean Deflation Maximum Minimum Dr moisture content. &#39;1 7.92 2.57 10.36 4.147 Dr} eight. lb. 11.74 1.65 17.2! 8.96 Dry length. inches 95.H2 .12 95.96 95.27 Dr lLllh. inches 3.70 .03 3.77 3.62 Dr thickness. inches l.h7 .03 1.73 1.02 Dry crook. inch .i7 .11) .54 .05 Dry him. inch .16 .12 .70 .05 Dr tnist. inch .14 .10 .50 .05 Specific grmity .47 .00 .04 .35 Length shrinkage. inch .l-l .12 v70 .01 Witlth shrinkage. inch -I3 .03 .19 .07 Thickness hrinkage. inch .01&#39;( .02 I2 .05  
 (ONYENTIONALLY S&#39;IICKERED (irccn moisture content. 1 .\(1.R3 34.98 109.92 36.48 (irccn eight. lb. 19.93 2.87 25.38 14.42 (ircen length. inches 95.9. .07 96.00 95.82 (ircen \\idth. inches 3.84 .01 3.86 3.82 (irecn thickness. inches 1.75 .02 1.78 1.71 (irccin crook. inch 07 .03 .20 .02 Green bo\\ inch .10 .(m .28 .04 (irccn tuisl. inch .07 .02 .1 1 .04 Dr moisture contcnt. W 8.08 2.38 15.06 5.25 Dr eight. &#34;&#39;1. l 1.77 1.66 17.77 9.87 Dr length. inches 95.83 .11 95.97 95.42 Dr idth. inches 3.71 .03 3.76 3.63 Dr thickness. inches 1.61% .03 1.72 1.63 Dr crook. inch .30 .18 .74 .05 Dr bu. inch .34 .17 .70 .10 Dr t\\l.sl. inch .32 v2 1.37 .04 Specific gnu it .47 .06 .67 .38 Length shrinkage. inch .12 .09 .55 .02 Width shrinkage. inch .13 .03 .19 .024 Thickness shrinkage. inch .07 .02 .12 .04  
 Ba is o1 grccn \ultmh: .rntl mentlr eight Thickness shrinkage was greater in studs dried between rolls (0.079 inch, 4.5 percent) than in those conventionally stickered (0.070 inch, 4.0 percent).  
  Warp was significantly less (0.01 level) in studs roll dried than in those conventionally stickered. as follows:  
 Method of Drying Warp Roll Dried Conventionally Stickered Inch Crook 0.17 0.30  
 How l (i .34  
 Twist l 4 .32  
  Planed 8-foot 2 by 4&#39;s in Stud grade (according to the Southern Pine inspection Bureau&#39;s rule book dated 1970) cannot exceed one-fourth inch in crook. onehalf inch in bow. or three-eighths inch in twist. Only seven (15 percent) of the roll-dried rough studs exceeded these limitations, whereas 32 (67 percent) of the conventionally stickered rough dry studs exceeded Stud grade limitations on warp (table 2).  
  Table 2 Amount of warp in those rough dry studs that exceeded the degree of warp permitted in Stud grade Warp In 48 roll- In 48 conventionally dried studs stickered studs Inch Crook .54. .43. .42. .74. .71. .70. .61. .60. .50. .35. .31. .26 .47. .46. .45. .45. .44, .42. .40. .38. .36. .35. .33. .32. .32. .31. .31. .30, .30. .30. .28 Bow .7()* .70. .57. .77. .53. .51, .67.  
  .64. .59&#34;. .55 Twist .50 .43. .39. 1.37&#34;. .76. .65.  
  Of the seven excessively warped roll-dried studs. all but one could be straightened suiiiciently in a crookreducing planer to get within Stud grade: with conventionally stickered studs. however, at least 11 would be expected to fall below Stud grade when graded after planing.  
  Studs that developed excessive crook during drying, typically contained compression wood and/or pitch.  
 1 claim:  
  1. An apparatus for maintaining upon individual pieces of lumber, total lateral restraint in both the horizontal and the vertical plane and simultaneously providing to said individual pieces of lumber. uniform directed motion throughout kilning operations, which apparatus includes in combination:  
 A primary apparatus support, a first roll array. a second roll array juxtaposed and parallel said first array and mounted within a roll-case. sub-support separate the primary apparatus support, adjustable resilient linking means joining the roll-case subsupport and associated second roll array assembly to the primary apparatus support, said linking means adapted to bias the juxtaposed first and second roll arrays one toward the other while maintaining the relative parallel and lateral positions of the roll arrays, lumber guiding and warp restraining means intermediate the juxtaposed roll arrays and roll driving means associated with at least one roll array:  
 Said primary apparatus support consisting of means defining a rigid, generally rectangular parallelipiped frame adapted, relative function, to support and to provide mounting locations for the roll arrays, the associated roll driving means, the ad- 9 justable resilient linking means. the lumber guiding and warp restraining means and adapted. relative overall dimensions. to permit operational accommodation within a preselected kiln. v  
 Said first roll array consisting of a plurality of uniform. cylindrical shaped. hard-surfaced rolls rotatably mounted in horizontally disposed. spaced and axially parallel array. each end of each roll journaled via fixed bearings to the primary apparatus support;  
 Said second roll array located juxtapositionally adjacent and parallel to said first roll array and carried with a rigid. generally rectangular roll-case. subsupport separate the primary apparatus support and adapted to provide mounting locations and support as a unit for the second roll array, said second roll array consisting of a plurality of uniform, cylindrically shaped. hard surfaced rollers. rotatably mounted in horizontally disposed, spaced and axially parallel array. each end of each roller journaled via fixed bearings to the roll-case subsupport. each roller locationally paired with a counterpart roller of the first roll array;  
 Said linking means consisting of adjustable. resilient members joining the roll-case, sub-support of the second roll array to the primary apparatus support and adapted to provide adjustable. resilient biasing of the juxtaposed roll arrays one toward the other while maintaining the relative parallelism and lateral location of the roll arrays, the roll arrays together with the linking means pre-set selectively and adapted to provide a thickness accommodating and positive warp restraining channel in the thickness dimension for pieces of lumber undergoing kilning and progressing serially in end to end sequence through the apparatus;  
 Said roll driving means consisting of a driving motor and requisite associated equipment adapted to provide controlled rotational motion to selected members of at least one roll-array thereby to provide directed uniform movement of the pieces of lumber undergoing kilning and progressing through the apparatus;  
 Said lumber guiding and warp restraining means consisting of a plurality of rigid. bar-like members disposed severally parallel intermediate the juxtaposed roll-arrays and positioned normal the roll axes, secured via the primary apparatus support to maintain substantial lateral inflexibility and selectively spaced to provided between any one individual bar-like member and an immediately adjacent counterpart a width accommodating and positive warp restraining channel for pieces of lumber undergoing kilning, the thickness dimension of the individual bar-like members of the lumber guiding and warp restraining means intermediate the roll arrays being less than the finished thickness dimension of the pieces of lumber undergoing kilning and passing serially in end to end sequence through the apparatus.  
  2. An apparatus for maintaining upon individual pieces of lumber, total lateral restraint in both the horizontal and the vertical plane and simultaneously providing to said individual pieces of lumber, uniform directed motion throughout kilning operations, which apparatus includes in combination:  
 A primary apparatus support. a first roll array. a second roll array juxtaposed and parallel said first array and mounted within a roll-case, sub-support separate the primary apparatus support. adjustable resilient linking means joining the roll-case subsupport and associated second roll array assembly to the primary apparatus support, said linking means adapted to bias the juxtaposed first and second roll arrays one toward the other while maintaining the relative parallel and lateral positions of the roll arrays. lumber guiding and warp restraining means intermediate the juxtaposed roll arrays and roll driving means associated with at least one roll array:  
 Said primary apparatus support consisting of means defining a rigid, generally rectangular parallelipiped frame adapted, relative function. to support and to provide mounting locations for the roll arrays. the associated roll driving means. the adjustable resilient linking means. the lumber guiding and warp restraining means and adapted. relative overall dimensions, to permit operational accommodation within a preselected kiln;  
 Said first roll array consisting of a plurality of uniform. cylindrical shaped. hard-surfaced rolls rotatably mounted in horizontally disposed. spaced and axially parallel array, each end of each roll jounaled via fixed bearings to the primary apparatus support;  
 Said second roll array located juxtapositionally adjacent and parallel to said first roll array and carried within a rigid, generally rectangular roll-case. subsupport separate the primary apparatus support and adapted to provide mounting locations and support as a unit for the second roll array. said second roll array consisting of a plurality of uniform, cylindrically shaped, hard surfaced rollers. rotatably mounted in horizontally disposed, spaced and axially parallel array, each end of each roller jou naled to the roll-case sub-support via resiliently loaded bearings said bearings adapted to bias the associated individual rolls downward in a direction normal to the plane of the roll array; each roller locationally paired with a counterpart roller of the first roll array;  
 Said linking means consisting of adjustable. resilient members joining the roll-case, sub-support of the second roll array to the primary apparatus support and adapted to provide adjustable, resilient biasing of the juxtaposed roll arrays one toward the other while maintaining the relative parallelisms and lateral location of the roll arrays, the roll arrays together with the linking means pre-set selectively and adapted to provide a thickness accommodating and positive warp restraining channel in the thickness dimension for pieces of lumber undergoing kilning and progressing serially in end to end sequence through the apparatus;  
 Said roll driving means consisting of a driving motor and requisite associated equipment adapted to provide controlled rotational motion to selected members of at least one roll-array thereby to provide directed uniform movement of the pieces of lumber undergoing kilning and progressing through the apparatus;  
 Said lumber guiding and warp restraining means consisting of a plurality of rigid, bar-like members disdergoing kilning. the thickness dimension of the individual bar-like members of the lumber guiding and warp restraining means intermediate the roll arrays being less than the finished thickness dimension of the pieces of lumber undergoing kilning and passing serially in end to end sequence through the apparatus.