Abstract:
The present invention relates to an apparatus and processing method for drying lumber, for example two-by-four studs in an environment in a kiln in a manner to avoid warping, including crook, bow, cup and twist. The lumber pieces are stacked in a normal manner with stickers for providing air flow between courses of the lumber pieces, and the stack is dried while a horizontal force is provided to the respective courses of lumber in the stack to hold the individual pieces of lumber in edge to edge contact throughout the drying, equalizing, conditioning and cooling process for first drying of lumber, redrying of lumber or in a treatment process for removing warp from previously dried lumber. A vertical force comprising a weight or other force generating device can be also applied to the stack of lumber to augment the overall reduction in warpage if so evidenced.

Description:
[0001]     This application refers to and claims priority from U.S. Provisional Application Ser. No. 60/561,424, filed Apr. 12, 2004, the entire content of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a restraining and force applying device that is used during a drying process for lumber pieces to reduce warp, that is, reducing the amount of crook, twist, bow and cup, of the dried lumber pieces. The device applies horizontal force to clamp together the edge surfaces of the individual lumber pieces placed edge to edge in courses of lumber pieces, and maintains these clamping forces throughout the drying process and, if required, while the lumber cools. The horizontal force is parallel to the width face of the lumber, and thus to the plane of the course of lumber as opposed to vertical forces parallel to the narrower edge surfaces of lumber pieces and perpendicular to the plane of the lumber courses. A vertical force also can be applied during drying, if desired. The horizontal clamping force applied to the courses of stacked lumber pieces keeps the individual lumber pieces securely restrained and in tight edge to edge contact throughout the drying process. Under the forces applied, the lumber pieces are held straight so that the amount of warp (crook, twist, bow and cup) is significantly reduced or eliminated.  
         [0003]     In the prior art, it has been known to vertically restrain stacks of lumber as the lumber is dried in a kiln, or by other means of drying, through the use of weights on the top of the stack, which provides a vertical downward force on the stack. The lumber is generally stacked in layers or courses with each course separated from the next overlying layer or course by spacers called “stickers”. The stickers create passageways for air movement through the stack of lumber between the courses.  
         [0004]     The vertical load now applied on a stack of dimension lumber, such as for two-by-four studs of eight-foot length, is an attempt to reduce the warp in the individual lumber pieces as the lumber is dried. However, the effectiveness of vertical loads has been less than satisfactory, with a great deal of crook and twist of the dimension lumber occurring both during drying and after release from the lumber stack. The application of dead weight on top of the lumber stacks during drying is usually in the form of concrete blocks or a panel of steel. Also, it has been known to apply loads using hydraulic rams, again, in a vertical direction.  
         [0005]     The most serious and degrading forms of warp in dimension lumber are crook and twist. Crook is a deviation of the narrow edges of a piece of lumber from a straight line, while twist is the rise of a corner of the piece out of a horizontal plane from one end to the other. Grading rules for each size and grade of lumber mandate specified maximum amounts of crook and twist. Straighter lumber has the potential for meeting higher grades and thus increased value. Upgrading the lumber pieces to higher grades via warp reduction produces a substantial increase in both profitability of a mill and the assurance of better performance in subsequent use of the lumber.  
         [0006]     Presently, any resistance to crook development in individual dimension lumber pieces, such as studs, relies upon the ability of top loading to increase the frictional resistance to movement between the lumber pieces in each of the courses of lumber and the stickers used to separate the courses. The effect on reducing crook with only vertical forces is marginal, particularly for those individual lumber pieces with lower than average thickness.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention provides apparatus to maintain a lateral or horizontal force on a stack of lumber that keeps lumber pieces in unyielding edge to edge contact as the lumber is dried.  
         [0008]     A restraint device is provided that corrects the problem of excessive warping, especially crook, of dimension lumber as the lumber is dried. Lumber pieces are placed side by side to create horizontal courses which are then loaded and held clamped edge to edge with a horizontal force, that is, a force parallel to the wide faces (width) of the lumber pieces. The force thus is perpendicular to the edge (narrow side) of each course and is sufficiently large to hold the pieces of lumber warp free as they are dried. Courses (horizontal layers) of individual lumber pieces are laid down, and the courses are separated vertically by stickers to provide a space for air flow between the courses. The space between courses has a plane and the clamping force is parallel to the plane of the air flow space and parallel to the lumber courses. The horizontal load is of a magnitude to provide a side or edge force resisting any crooking or slippage of the lumber pieces one upon another. The restraint system takes up or prevents the spaces between the edges of adjacent lumber pieces that occur in contemporary drying as a consequence of the unavoidable width shrinkage of individual lumber pieces.  
         [0009]     Vertical forces from top loading are optional. Preventing crook on dimension lumber, for example two-by-fours, with the four inch or side dimension laid horizontally, for drying, and formed into courses with the edge surfaces (2 inch nominal) of adjacent lumber pieces in contact, requires restraining the boards from separating, as well as taking up the shrinkage by providing a substantial uniform, and continuous adequate level clamping force for edge loading as drying proceeds.  
         [0010]     Various devices and designs can be utilized for providing an edge, generally horizontal load, which is defined as a load that acts substantially parallel to a wide side surface, or in other words, loads the courses with a force perpendicular to its narrowest dimension. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is an end view of a four sided, openable frame for receiving a stack of lumber and applying a horizontal clamping force for preventing warp in accordance with the present invention;  
         [0012]      FIG. 2  is an illustrative side view of the first form of the present invention and illustrating placement of the four sided, openable frames of  FIG. 1 ;  
         [0013]      FIG. 3  is a sectional view of a load applying side of the frame of  FIG. 1  taken on line  3 - 3  in  FIG. 1 ;  
         [0014]      FIG. 4  is a fragmentary enlarged exploded view of a removable reaction bar coupling to a base member to the openable frame shown in  FIGS. 1 and 2 ;  
         [0015]      FIG. 5  is a schematic view of an alternative force generating device capable of use in openable frames similar to those shown in  FIG. 1 ;  
         [0016]      FIG. 6  is a modified form of a load applying linkage arrangement for applying horizontal clamping force to a stack of lumber in a kiln; and  
         [0017]      FIG. 7  is a further modified form of the invention showing a weight actuated wedge that is loaded in a direction for generating horizontal restraint force on a lumber stack. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     The general concept of the present invention is set forth in  FIG. 1 , wherein a unit or stack of lumber  12  in a view is contained within a plurality of quadrangle (four sided) restraining frames or devices  10 . Each quadrangle frame  10  is designed to employ a selected one of a variety of force applicators to provide continuous, edge wise pressure or force on the individual horizontal courses  11  (horizontal layers) of individual lumber pieces  13  that make up the stacked unit  12 . The individual lumber pieces  13  of each course are laid edge to edge so that the wide face or width  13 A is horizontal. The courses are separated by stickers or spaces  15  to form an air flow space of channel  15 A between and parallel to the plane of the course of lumber pieces. The quadrangle frame  10  consists of vertical and horizontal steel components, including a horizontal base, comprising a base channel  16  that has an upright channel or member  18  fixed to one end to form a lumber unit support. The quadrangle frame  10  has a removable force reaction bar or channel  20  opposite the upright channel  18 . The upper ends of channels  18  and  20  are joined with a top tie rod  22 . The tie rod  22  can be secured in any suitable manner. As shown, the threaded nuts are used at the ends for securing it in place.  
         [0019]     The junction between the base channel  16  and upright channel  18  can be a permanent connection such as welding, or a bolted or otherwise rigid or semi-rigid connection that affords the ability to disassemble.  
         [0020]     The force reaction bar or channel  20  is removable and has a body end projection or shaft  24  ( FIG. 4 ) for insertion into a selected one of a sequence or series of openings  26  near the end of base channel  16  opposite the end supporting the upright channel  18 . The top tie rod  22  is a tie rod or other form of steel tension member between the top ends of upright channel  18  and reaction bar  20 . The members of the quadrangle frame are selected to be non-deformable during application of the horizontal clamping force generated by a pressure loading assembly  28  that is supported on and extends along the upright channel  18 .  
         [0021]     The loading assembly  28  comprises a pressure expandable, full vertical height, two section chamber. A base chamber  30  ( FIG. 3 ) has a base wall  30 A and side walls  30 B that are closed with end walls at the top and bottom of the chamber. It thus forms an open sided box. The base chamber  30  extends to the desired height of the unit  12  of the courses  11  of lumber pieces  13 . The upright channel or bar  18  extends upwardly beyond the base chamber  30  so that the cross tie rod  22  can be installed.  
         [0022]     The pressure loading assembly  28  includes a telescoping outer chamber  32  that has an outer wall  32 A that extends vertically, and a pair of side walls  32 B that slide along the outside of the walls  30 B of the base chamber  30 , and the outer chamber  32  also has top and bottom walls to form an open sided box that slips over the base chamber  30 .  
         [0023]     A flexible membrane  34  closes the open side of the base chamber  30  and is sealed airtight to the side walls and the top and bottom walls of the base chamber to form a pressure tight internal chamber  37 . A pressure fitting  36  is provided in the base wall  30 A, and through the upright channel  18  and connected to a suitable, preferably controlled, fluid pressure source  38 . When fluid under pressure is provided to chamber  37 , the flexible sealing member  34  expands out pushing the outer chamber  32  against the lumber unit  12  of courses  11  of lumber pieces  13  with a horizontal force that is parallel to the wide face or width of the pieces of lumber and parallel to the plane of the lumber courses. Thus, the pressure loading assembly comprises a gaseous fluid actuator.  
         [0024]     The quadrangle frame  10  as illustrated is one of a chosen or of a selected number of frames spaced along the length of the unit of lumber. For example, if the unit  12  consists of 100 inch long by 2 inch by 4 inch studs, a recommended number of quadrangle frames  10  is three, as shown in  FIG. 2 , one near each end of the unit and one at mid-length. The quadrangle frames  10  can be fully assembled piece by piece around a pre-existing unit of stickered lumber, if desired, or when base channel  16  and upright channel  18  are an L-shaped subframe, with the tie rod  22  and reaction bar  20  removed, stickered units of lumber can be set in place on the base channel  16 . A forklift can be used to put the lumber unit in place. The vertical reaction bar  20  and tie rod  22  are then installed to complete the quadrangle frame assembly  10 . A third alternative is by placing a layer of lumber pieces on the channel bases  16  of the three frames with the vertical bars in place, and then putting stickers  15  on the first course and building the courses  11  piece by piece. Repetitive placement of complete courses of lumber can also be done with a mechanical stacker, and stickers  15  placed between the courses as the unit is formed, as currently done in many commercial operations.  
         [0025]     Prior to the application of clamping force edgewise to each course of lumber pieces, the individual pieces in each course can be in modest edge to edge contact. The initial application of force will remove any possible length wise deviations of the narrow edges from a straight line, i.e., remove any pre-existing crook traceable back to growth stresses present in the tree. This converts each course during the drying process to an integrated slab similar to a flitch, forced to give up its moisture through the horizontal wide surfaces or width of each lumber piece into the air travel space provided by the stickers. The continuous edgewise clamping force from the loading assembly  28  on the upright bar  18  eliminates the opportunity for shrinkage-caused openings to develop between the individual lumber pieces, as in contemporary conventional drying. The edge to edge contact of the lumber pieces, accomplished under adequate force, also prevents any possible inherent differences in longitudinal shrinkage for the two narrow edges of each of the lumber pieces being translated into crook. With the lumber pieces held straight during drying, especially in the context of high temperature kiln drying that plasticizes the wood and promotes stress relief, the lumber pieces remain straight when the clamping force is removed at the end of drying.  
         [0026]     Since the percent shrinkage values for commercial woods as a function of average moisture content are well known, the desired end point of drying is readily determinable by measuring the overall shrinkage of one or more courses  11  contained in the unit of restrained lumber by direct ruler type measurement or an automated device that registers readings at a remote location.  
         [0027]     The magnitude of the continuous force applied to the unit of lumber during its drying depends on the initial air pressure in the chamber  37  and the changes in volume, pressure and temperature that the air undergoes during the overall drying process. The basic air pressure chamber  37  consists of the two enclosed telescoping members analogous to the two box sections employed for containing a two-pound block of brick formed cheese. The movable “box”  32  of the two sections that make up the pressure loading assembly  28  illustrated in  FIGS. 1 and 3 . The open face of the fixed chamber  30  is rendered air tight by a rubber (flexible) membrane or diaphragm section or base chamber securely sealed to the inside perimeter of the fixed box near its open face. The securement of a rubber membrane of the required physical properties to the walls of the fixed base chamber or box section, which is preferably fabricated of steel, results in a closed chamber  37  that is capable of withstanding different levels of air pressure. When the membrane  34  expands it provides a force to the movable chamber  32  and the base wall  32 A bears against the individual courses of lumber that make up the unit of lumber and the clamping force is parallel to the planes of the individual courses.  
         [0028]     Each pressure chamber  37  of the three quadrangle frames  10  can be pressurized at a different level from the others, or all chambers  37  can be connected to a common pressure source and carry the same pressure.  
         [0029]     The kiln drying of softwood dimension lumber is generally accomplished with the dry bulb temperature of the kiln atmosphere increasing steadily over a period of time to eventually arrive at a desired steady-state temperature that is maintained to the end of the drying process. Since the air pressure force applying assembly  28  is constructed primarily of steel, the temperature of the air it contains will come to and remain in close equilibrium with the dry bulb temperature of the kiln atmosphere in which it resides. In this context, there occurs an expansion or compression of the gas that conforms to the General Gas Law. According to this law, “the pressure of any given quantity of gas is proportional to the absolute temperature and inversely proportional to the volume”. In practical application of the law, the following equations are instructive:  
             P   1     ⁢     V   1         T   1       =           P   2     ⁢     V   2         T   2       =           P   3     ⁢     V   3         T   3       ⁢           ⁢     etc   .             
 
 in which: 
        P=pressure; V=volume and T is absolute temperature, and the absolute temperature=T° C.+273=° Kelvin.        
 
         [0031]     It is thus informative to illustrate performance of the General Gas Law in kiln drying a unit of green lumber to some final desired average moisture content. This illustration is in the context of defining the dimensions of the fixed box of  28  as having sidewall dimensions of 10 in. wide and 50 in. in height and the dimensions of its wall fixed to upright  18  being of 50 in. high and 3 in. wide.  
         [0032]     With a lumber unit  12  in place and a given number of quadrangle frames  10  surrounding it, assume the chamber containing the rubber membrane is inflated to 20 psi at an ambient air temperature of 20° C. This forces the individual lumber pieces of the courses  11  tightly edge to edge and into uniformly straight pieces. As the temperature of the kiln atmosphere increases during continued operation, the temperature of the pressurized air maintains equilibrium with the dry bulb temperature of the kiln atmosphere. The steady increase in dry bulb temperature accompanied by a steady increase in the wet bulb depression produces an in-kiln air atmosphere conducive to rapid drying of the lumber. As the lumber pieces dry, the width of the lumber unit decreases due to shrinkage and in keeping the volume of the air contained in the diaphragm sided chamber  30  increases in accordance with the amount of lumber shrinkage.  
         [0033]     At the initial 20° C. temperature and a pressure of 20 psi, the air chamber  37  volume is approximately 1500 cubic in., i.e., a chamber of 3×10×50 in. At a kiln air temperature of 50° C., the volume of 1500 cubic in. will increase to 1654 cubic in. if the initial air pressure of 20 psi remains constant.  
         [0034]     In keeping with the General Gas Law,  
             V   1     ⁢     P   1         T   1       =         V   2     ⁢     P   1         T   2           
 
 and thus:  
           V   2     =       V   1     ⁢       T   2       T   1           ,       
 
 in which 
        T 1 =20° C.+273=293° Kelvin     T 2 =50° C.+273=323° Kelvin 
 
 from which  
         V   2     =       1500   ⁢           ⁢     in   3     ×       323   ⁢   °       293   ⁢   °         =     1654   ⁢           ⁢     in   3             
       
 
         [0037]     However, in order for the pressure to remain constant, the increase in air volume due to shrinkage of the lumber must equal 154 in. If we assume the width of the lumber unit has decreased by 1 inch, the air volume will have increased by approximately the amount of 154 cubic in. (in 3 ). This is shown as follows:  
         [0038]     The original 1500 in 3 +(3 in.×50 in.×1 in.)=1500 in 3 +150 in 3 =1650 in 3 .  
         [0039]     The increase in air volume thus depends upon the inherent shrinkage for the specific type and species of lumber and the fraction of that shrinkage being realized at the specific level of average MC of the lumber.  
         [0040]     At a kiln air temperature of 50° C., it is likely that the absolute width shrinkage of an original 48 in. wide lumber unit is less than the 1.0 inch employed in the above calculation. Thus, the volume of the air is not increasing in accordance with a constant pressure and thereby the pressure at 50° C. is slightly higher than the central starting pressure of 20 psi. Further, in keeping with the well known relationships of wood shrinkage to average moisture content of the wood, it is probable that the air pressure in the chamber will remain slightly above its initial temperature during all or at least most of the kiln residence time of the restrained lumber. Maximum lumber shrinkage for the overall drying process is reached at the end of drying. Thus, it is of interest and need to evaluate the overall situation at the end point of the process. If the unit of lumber  12  illustrated in  FIG. 1  is 48 in. wide and the final average moisture content of the lumber is near 10 percent, the average width shrinkage at that moisture content will perhaps be in the range of 4-5 percent. Using the 5 percent value, this equates to an absolute change in width for the lumber unit of 2.4 in., i.e., 48 in.×0.05=2.4 in. As a consequence, the volume of the air contained in the chamber has increased from its original 1500 in 3  to 1860 in 3 . The increase of 360 in 3  is derived from multiplying the total horizontal movement of the outer chamber  32  times its approximate cross sectional area, i.e., (2.4 in.×3.0 in.×50 in.) equals 360 in 3 . A common dry bulb air temperature in the kiln at the end of drying for nominal 2 in. thick softwood dimension lumber is 240° F., which equates to 116° C. The air volume in the chamber  37  near to and at the end of drying becomes nearly constant since the average moisture content of the lumber is near equilibrium with the drying potential of the kiln&#39;s atmosphere and thereby wood shrinkage is inactive. Thus, the following calculation can be performed:  
             P   1     ⁢     V   1         T   1       =             P   2     ⁢     V   2         T   2       ⁢           ⁢   and   ⁢           ⁢         (     20   ⁢           ⁢   psi     )     ⁢     (     1500   ⁢           ⁢     in   3       )       293       =         (     P   2     )     ⁢     (     1860   ⁢           ⁢     in   3       )       389           
         from   ⁢           ⁢   which     ⁢               
         P   2     =         389   293     ×       30000   ⁢     (   psi   )     ⁢     (     in   3     )         1860   ⁢           ⁢     in   3           =       1.328   ×   16.129     =     21.4   ⁢           ⁢   psi             
 
         [0041]     Therefore, with a 48 in. width unit of lumber, a width shrinkage for the lumber unit of 5 percent, an assumed final average moisture content of 10 percent and the dimension of the pressurized air chamber as employed, the final air chamber pressure is nearly 1.5 psi greater than the initial pressure.  
         [0042]     For units  12  of lumber wider than 4 feet, and especially in the context of high shrinkage values for the wood, the initial volume of pressurized air can be increased to accommodate its magnified increase in volume and thereby maintain at least constant or preferably somewhat increasing force on the lumber unit  12  throughout the drying process. For example, the volume of the air chamber  37  in  FIGS. 1 and 2  could be doubled to accommodate an 8-foot unit width of the same lumber to produce the same outcomes as those calculated for the 4 foot wide lumber unit.  
         [0043]     The required volumes of pressurized air are perhaps best obtained by employing a pressurized steel storage tank connected to the fixed chamber by appropriate hose connections and valves. The added pressurized storage capability should be designed and situated in the most efficient manner possible with respect to the unit of lumber under restraint.  
         [0044]     A sequence of the right angle (L-shaped) subframes created by the joining of base channel  16  and upright channel  18 , as shown in  FIG. 1  can be fixed to a pair of supporting rails  42  running parallel to the length of the lumber unit. Spacing of the L-shaped assemblies is in keeping with the length of the lumber unit and the propensity of warp for the species being dried. As an example, for southern yellow pine nominal 2 in. by 4 in. lumber 100 in. long, three of the L-shaped frames would be affixed to a parallel pair of properly spaced 8 foot long steel rails, with one L-shaped frame near each end of the rails and the third at mid-length of the rails. With a lumber unit in place on the sequence of horizontal steel base channels  16 , the perimeter of the quadrangle frames or restraining device is completed by installation of members  20  and  22 . The entire assembly of restraint quadrangle frames, steel rails and units of lumber then becomes a portable assembly to be handled by a forklift or other means into a conventional heated kiln shown schematically at 40. These individual assemblies of lumber unit and quadrangle frames can then be placed on kiln cars for transport into the drying kiln or elsewhere by the same means currently used for separate units of stickered lumber. Since the individual pieces of lumber and the stickers  15  are held firm during subsequent transport and overall handling, the opportunity for unfavorable misalignment of stickers is and lumber pieces  13 , or actual fallout of each from the unit, is avoided. These portable assemblies can also be placed one upon another in the same format currently employed for separate unrestrained units of stickered lumber.  
         [0045]     Within the kiln atmosphere one or more steel storage tanks for providing additional air volume under pressure could be used to supplement the air volume capability inherent to the pressure creating assemblies  28  incorporated into each restraint quadrangle frame  10 . The master storage pressure source tank or tanks would be connected to each of the individual air pressure chambers via an optimized line design and any required valving.  
         [0046]     The pressure loading assembly  28  of  FIG. 1  is replaceable by any one of several alternative force generators such as air bags, air pressure springs or cylinders; steel springs, liquid hydraulic systems or leverage systems driven by gravity, etc. Each is employable and able in its individual design to provide continuous edge to edge clamping pressure onto the courses of lumber that make up a given lumber unit. These alternative force generators would likely not deliver force to the lumber by using the movable box form that is part of the pressure loading assembly  28 . Instead, a vertical pressure bar, driven by one of the alternative types of force generators, would deliver a force perpendicular to the planes of vertically orientated edges of the lumber courses.  
         [0047]     For example, an air cylinder or cylinders driven by an offsite air compressor, which is positioned between the vertically orientated channel  18  and a pressure bar resting on the full height of the vertical side face of the lumber unit. Again, a scissors-type of leveraged system, driven by gravity acting on a dead weight load or by an alternative force generator is also a candidate for impelling the above defined pressure bar.  
         [0048]     In  FIG. 5 , a modified quadrangle frame and pressure creating assembly is illustrated. The quadrangle frame  50  includes a base member or channel  52 , that can be essentially the same as that indicated before, with an upright channel or member that can be called a first reaction bar indicated at  54  rigidly attached to one end of the base member  52  and extending upwardly. A second or outer reaction bar  56  can be removably secured to the opposite end of the base channel  52 , as in the previous form of the invention, and the upper ends of the first reaction bar or upright member  54  and the second reaction bar or upright member  56 , which is removable, are tied together with a tie bar  58 .  
         [0049]     The individual courses  11  of lumber pieces  13  are numbered the same, and can be supported on the bottom or base member  52  in the normal manner and separated with stickers  15 . In this form of the invention, the pressure loading assemblies are indicated generally at  60 , and include a pair (more can be used) of conventional pneumatic air springs  62 , each of which is a fluid spring or actuator that is fixed at one end as at  64  to the upright member or first reaction bar  54 , and the expandable or outer end of the airbags  62  are affixed as at  66  to a push bar  68  that is spaced from and positioned between the base channel  52  and the tie bar  58 , but of sufficient length to engage all of the courses  11  of the lumber pieces  13 . A fluid pressure source or tank  70  can be provided on and secured on the first reaction bar, and connected with suitable hoses  72  to the respective air spring  62 . As shown, these are double chamber air springs, but other suitable fluid pressure cylinders could be substituted.  
         [0050]     The action in this form of the invention is the same as previously explained, wherein the unit of lumber pieces having the stickers  15  between them can be stacked onto the subframe when the second reaction bar  56  has been removed, and then the second reaction bar  56  can be put into place and fastened with a tie bar, through suitable fasteners that are shown generally at  58 A as bolts, and suitable fastening straps, so that the frame and lumber units are complete. The entire assembly can then be placed into a kiln with a forklift. Suitable spacers can be provided below the cross member  52  so that the forklift forks can be placed under the base channel or member  52 .  
         [0051]     It can be seen here that the use of the continuous pressure springs can be accomplished easily by using airbags and a movable push bar that provides a horizontal force that is parallel to the wide faces of lumber pieces for preventing crook and other distortions of the individual number of pieces.  
         [0052]      FIG. 6  shows a typical schematic representation of a scissor-type force generator for providing the edge to edge force F along the lateral sides of the lumber unit of stack, and the reaction force R as well. In  FIG. 6 , a kiln floor  69  is illustrated that supports rails  42 . A conventional kiln car can be used to support the lumber pieces  13  held edge-to-edge and arranged in horizontal courses  11 , and with spacers or stickers  15  between the courses. A kiln car is shown in  FIG. 7 .  
         [0053]     Only selected courses of lumber are shown for convenience, but a full stack of lumber courses would be dried at a time. A quadrangle frame  63  having a base support  65 , an upright reaction bar  65 A, a removable second reaction assembly  67  is shown. The removable second reaction assembly  67  is removably secured to a tie bar  67 A that connects to the top of reaction bar  65 A. The removal of reaction assembly  67  opens the frame for loading lumber pieces on to base support  65 . A full lumber unit is supported on the support  65 . A plurality of the frames  63  can be used along the longitudinal length of lumber stack or unit  12 .  
         [0054]     The lateral or horizontal forces for clamping the narrow edges of the lumber pieces together are provided by loading push or force bars  71 A and  71 B. Scissor-type link force generators  73  are positioned on each of the lateral sides of the lumber stack  12  to actuate the push or force bars  71 A and  71 B.  
         [0055]     The push bars  71 A and  71 B, as shown, are positioned to movably engage the individual lumber courses  11 , to clamp the lumber pieces  13  edge to edge. The spacers or stickers  15  permit air circulation. The bars  71 A and  71 B have the scissor type force generators  73  pivotably connected thereto and spaced at desired vertical intervals, which can be selected according to the needs of the lumber and the force required.  
         [0056]     The scissor type force generators  73  are each made up of a pair of links or arms  74 A and  74 B that are pivoted together at  74 C, and the first art  74 A of each force generator is pivoted to the respective upright frame members  65 A and  67 B. Upright frame member  67 B is part of the removable reaction assembly  67 . The second arm  74 B of each force generator pivots on the respective force applying on push bar  71 A and  71 B.  
         [0057]     In order to apply the horizontal clamping load, using the scissor force generators, a load-applying link  76  is pivoted at each of the pivots  74 C, on all of the scissor force generators  73  utilized for applying the lateral forces on the lumber pieces. A suitable weight or mass  77  is attached to the interconnected links  76  on each side of the quadrangle frame  63  that will then apply a constant downward force tending to pivot the arms  74  and  74 B, to cause the outer ends of the arms  74 A and  74 B to separate. A mechanical device (hydraulic cylinder, or a winch-like device that loaded the center pivots for example) can substitute for the suitable weight or mass  77  in generating the required downward force.  
         [0058]     This force of separation of the ends of the links will apply a horizontal or lateral force onto the stack  12  of the lumber pieces  13  and the force will be substantially uniform as the lumber dries. The number of quadrangle frames  63  and push bars  71 A and  71 B used along the length of the stack or unit  20  of lumber can be selected as desired.  
         [0059]     Additionally, the weight or mass  77  is mounted so that it will not touch the kiln floor, so that the horizontal force will be maintained throughout the drying process. The bars  71 A and  71 B can move inwardly to continue to apply lateral or horizontal clamping force.  
         [0060]     By maintaining a lateral or horizontal clamping force on the unit of stickered lumber parallel to the plane of the courses of lumber, each of the individual lumber pieces  13  in each course is kept in edge to edge contact with the next adjacent lumber piece to prevent crook and other warp forms. A vertical force can be added to the lumber stack or unit by use of weight or other loading device to keep the wide side surfaces (width) in forced clamping contact with the stickers  15  as well, to further help prevent twisting and bowing. As the lumber pieces dry, the internal stresses that would tend to cause warping of some type are resisted by the lateral or horizontal forces, in particular, and thus warping is prevented.  
         [0061]      FIG. 7  is a schematic end view of a further modified form of the invention. It is to be understood that the application of force can be from a number of longitudinally spaced frames such as that shown in  FIG. 2 . In this form of the invention, a kiln car  80  is positioned inside a heated kiln, having walls  82  or separate members that are capable of withstanding reaction forces. The kiln car  80  has wheels  80 C supported on rails  80 A on the kiln floor  80 B and carries a lumber stack or unit  12  (the same number is used for the stack of lumber) comprising lumber pieces  13  arranged in courses  11 , with stickers or spacers  15  between the courses  11 . The kiln car  80  has pressure bars  84  on each side, that can be supported on the kiln car in a desired manner, but which are movable relative to the platform  86  of the kiln car  80 . The bars  84  are able to move inwardly laterally against the edges of the courses  12  of lumber pieces to apply lateral or horizontal clamping force.  
         [0062]     In this form of the invention, the force reaction walls  82  as shown have tapered interior surface  82 A and  82 B, respectively, on opposite sides of the lumber stack or unit  12 . A weighted, wedge shaped, ram car  88 A or  88 B is provided on each side of the lumber stack or unit between the side walls surfaces  82 A and  82 B and the pressure bars  84 . The wedge ram cars  88 A and  88 B have wheels that are shown at  90 A and  90 B, respectively, that ride against the inwardly sloped surfaces  82 A and  82 B and also roll against the outer surfaces of the pressure bars  84 . The weight of the wedge ram cars  88 A and  88 B acting as a wedge provides a lateral or horizontal clamping force. By selecting the spacing between the surfaces  82 A and  82 B and the pressure bars  84 , and the angle of inclination of the surfaces  82 A and  82 B, the initial position of the ram cars in vertical direction can be controlled. The weighted wedge ram cars will move down as the lumber pieces dry and shrink to keep edge to edge contact of the lumber pieces  13  in each course  11  and resist any crook as the lumber pieces dry and cool. Mechanical advantage can be used to assist downward movement of the ram cars  88 A and  88 B and also for raising the ram cars when needed. The pressure bars  84  are selected so they will apply clamping pressure along their lengths. The ram bars can be elongated more than shown herein and can have several sets of which to apply the force at desired locations along the pressure bars.  
         [0063]     A top pressure panel or bar  94  can be provided as well, to exert a vertical load on the stack of lumber in a normal manner.  
         [0064]     The wedge ram cars  88 A and  88 B can be heavy enough to provide not only a lateral force because of the wedge-type wall surfaces  82 A and  82 B, but through optional elastic tension loading members  96 , provide a controlled weight that is transferred by the elastic tension members so it is applied to the top loading pressure bar  94  while permitting a needed portion of the weight from the wedge ram cars to continue to provide lateral or horizontal force.  
         [0065]     These forces in both horizontal and vertical directions can be selected as required. The tension members  96  can also be eliminated so that the wedge ram cars  88 A and  88 B only load the lumber stack in lateral or horizontal direction. The pressure panel  94  at the top can be loaded in a conventional manner using a dead weight or mechanical force.  
         [0066]     In order to provide the lateral or horizontal force, any suitable force generator for moving members against the outer sides of the lumber stack can be used in generally any lumber drying circumstance. The force generators can be air bags, pneumatic cylinders, hydraulic cylinders, mechanical (helical) springs or screw tacks. The wedge type rams shown in  FIG. 7  also can be used to apply a horizontal force against the edges of the lumber pieces  13 . The force generator is selected to continuously apply the restraining force as the lumber pieces dry.  
         [0067]     Concrete weighting as a top load also can be used to provide a vertical force to restrain the lumber pieces  13  from twisting, bowing and cupping during the drying process. Various other weights can be utilized. There can be one or several force applying bars, walls, panels or columns along the length of the stack. The stickers  15  (or spacers) form planar channels  15 A for air flow between the courses of lumber pieces. The air channels  15 A have planes parallel to the planes of the courses made up of the plurality of lumber pieces. The force applied is in direction parallel to the plane of the lumber courses and the plane of the air flow channel between courses. This means the clamping forces are parallel to the surfaces of the lumber that are exposed to the drying air.  
         [0068]     The individual quadrangle frames can be closed by bolt on brackets, or welded at selected joints to form an enclosure for conventionally stacked and stickered lumber. The load applying bars and reaction bars are directly opposite each other and offset laterally from the stickers.  
         [0069]     In all forms of the invention, the concept is to maintain a horizontal lateral force on the stack or unit of lumber parallel to the courses of lumber pieces to maintain unyielding edge to edge contact of the lumber pieces as the lumber is dried.  
         [0070]     The force applying mechanism ensures that the lumber pieces in each course are forced tightly, edge to edge to prevent warp, especially the manifestation of crook during the drying process and subsequent cooling or other post-drying treatment. Application of dead weight or other loading on the top of the lumber stack will assist the horizontal force provided by the horizontal pressure bar in eliminating twist and bow of the lumber pieces, but is not needed in all cases. The need for vertically oriented loading may be dependent upon the species of the lumber.  
         [0071]     The quadrangle frames with lumber in place for continuous restraint during drying and post-drying treatments can be used in a stand alone manner. However, the frames may be configured to rest one on top of another for two or more units of lumber stacked in a kiln or elsewhere. For vertical stacking of units in particular, all structural members must be correctly sized and designed to ably withstand the forces expressed in the context of the conditions used to dry the lumber and complete the overall processing. To maximize trouble free repetitious use of the quadrangle frames, all members are best made of suitable steel with properly welded joints wherever permissible and treated for rust resistance.  
         [0072]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.