Abstract:
A platen press for pressing loose wood-based material into structural panels at high temperature while exhausting steam generated in the process through vents distributed across the face of a platen to thereby produce an improved product. The vents are periodically cleaned to remove elements of the panel material that have been deposited into the vents with steam flow or mechanical pressure by pins carried within the platen. The pins are positively extended into respective vents by actuating elements housed within the thickness of the body of the platen.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to improvements in press platens for manufacture of structural panels. 
   PRIOR ART 
   It is known, for example, from U.S. Pat. No. 6,668,714 to manufacture plywood, chipboard, particle board, oriented strand board and like panels by pressing layers, chips, particles and/or strands in loose, matte or cake-like form with adhesive binder resin between flat platens. Commercial production typically involves a multi-stage platen press in which numerous horizontally oriented platens are arranged one above another and are simultaneously pressed together to form a plurality of boards in a single pressing cycle. This referenced publication recognizes the problem of particles of the board material clogging vent holes in the faces of the platens and proposes the technique of exhausting high pressure steam or other gas through the vents to purge them of residual board material. Such a technique has limited effectiveness because the gas pressure/flow may not be sufficient to dislodge the particles or resin. Successive deposits of resin each with sufficient adherence to the preceding layer to stay in place when impinged by gas pressure/flow can accumulate to eventually plug a vent. 
   SUMMARY OF THE INVENTION 
   The invention provides a platen suitable for a multistage press that has vents distributed across its surface for exhausting steam and other vapors, expelled from wood-based material being pressed and heated, and mechanical elements for self-cleaning the vents. The mechanical elements include a pin associated with each vent hole in the pressing surface. The pins and elements that operate the pins within the boundary of the pressing surface are contained exclusively within the body of the platen. 
   In the disclosed embodiments, the platen pressing surfaces are rectangular and the vent holes and associated cleaning pins are spaced from one another along parallel spaced lines perpendicular to the major edges of the platen. The pins are movable from a retracted position where they allow free flow of vapor into the associated vent holes and an extended position where they occupy the space of the vent holes so as to positively displace any foreign material from the vent holes. The pins are forcibly mechanically extended from retracted positions by cam elements disposed in a passage common to all of the vents lying along the same perpendicular or transverse line. The cam elements in a common passage are all actuated simultaneously by mechanical forces transmitted along the passage. The pins are each returned to their retracted position by an associated compression spring. The common passage housing the cam elements also serves as a manifold for collecting and discharging vapor received by the individual vent holes. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a somewhat simplified plan view of a platen constructed in accordance with a first embodiment of the present invention; 
       FIG. 2  is an enlarged fragmentary cross-sectional view of the platen of  FIG. 1  taken in the plane  2 — 2  indicated in  FIG. 1 ; 
       FIG. 3  is a view similar to  FIG. 2  except on a larger scale showing details of a typical vent cartridge assembly and associated operating elements 
       FIG. 4  is a plan view of a platen constructed in accordance with a second embodiment of the invention; 
       FIG. 5  is an enlarged fragmentary cross-sectional view of the platen of  FIG. 4  taken along the plane of lines  5 — 5  in  FIG. 4 ; 
       FIG. 6  is a fragmentary cross-sectional view, similar to  FIG. 5 , of a vent cartridge assembly and associated operating elements; and 
       FIG. 7  is an enlarged fragmentary plan view, partially in section, of the platen of  FIGS. 4–6 ; 
       FIG. 8  is a schematic perspective view of a platen constructed in accordance with a third embodiment of the invention; 
       FIG. 9  is a fragmentary cross-sectional isometric view of an area of a typical vent hole taken in the plane indicated by the lines  9 — 9  in  FIG. 8 ; 
       FIG. 10  is a fragmentary cross-sectional view of the platen of  FIG. 8  taken in a plane indicated by the lines  10 — 10  in  FIG. 8 ; and 
       FIG. 11  schematically illustrates an example of a multi-opening press in elevational view, looking downstream. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIGS. 1–3  of the drawings, there is shown a first embodiment of a platen  10  constructed in accordance with the invention. The platen  10 , which customarily is rectangular in plan view, can range in size from about 4′×4′ to about 14′×30′. The platen  10 , as is customary, is machined from a solid flat slab of steel. The platen  10  has opposed faces that are ground flat and parallel to one another. One of the faces  11  is shown and typically the opposite face has the same vent hole and self-cleaning pin construction that is described below; the top and bottom plates in a multistage press ordinarily will not have vent holes or cleaning pins at their outside (top and bottom, respectively) faces. 
   Spaced parallel passages or bores (not shown) are gun drilled from one long edge  16  to the other edge  17  along lines perpendicular to these edges. Where the platen  10  is square, either pair of opposed edges can be considered the long sides or edges. The ends of the passages are interconnected to create a serpentine path for hot oil flow in a known manner to allow the hot oil to heat the platen to an elevated temperature of, for example, 350° F. 
   In accordance with the invention, an array of spaced vent holes  21  is provided across the area of at least one and, more typically, both faces or pressing surfaces  11  of the platen  10 . In the preferred arrangement, vents or holes  21  are arranged in sets with the vents of each set being spaced generally uniformly from one another along a respective common line perpendicular or transverse to the long edges  16 ,  17  and with these lines being generally uniformly spaced along the length of the platen  10 . 
     FIGS. 2 and 3  show cross-sections of the platen  10  at a typical transverse line of vent holes  21 . Each vent hole  21  in a platen surface  11  is formed as a cylindrical hole in the center of a circular plug  22  of a cartridge or assembly  23 . The cartridge  23 , which is received in a circular bore  24  in the body of the platen  10  perpendicular to the platen surface  11  includes, besides the plug  22 , a pin unit  26  and a compression spring  27  disposed between the plug  22  and pin unit  26 . The pin unit  26  is a circular body sized to freely move axially in the cylindrical bore  24 . An annular peripheral groove  28  on the pin unit  26  receives a linear ball bearing assembly  29  that reduces friction between the wall surface of the bore  24  and the pin unit  26  thereby facilitating axial motion of the pin unit in the bore. An annular groove  31 , formed in the pin unit  26  on a side facing the plug  22 , receives a portion of the length of the compression spring  27  such that the end of the spring abuts the bottom of the groove. The opposite end of the spring  27  abuts an inner face of the plug  22 . A cylindrical pin  32  sized to move in and out of the vent hole  21  is formed as a central axially extending projection of the main body of the pin unit  26 . The length of the pin  32  is preferably at least as great as the length of the vent hole  21 . 
   An inner end of the pin unit  26  has a convex, preferably hemispherical portion  33  proportioned, when a radial face  34  of the unit abuts an end wall  36  of the bore  24  to extend into a passage in the form of a round bore  37  machined or otherwise formed in the body of the platen  10 . A pair of diametrally opposed axially oriented holes  38  extend through the body of the pin unit  26  from the bottom of the annular groove  31  to the exterior of the projection  33 . 
   The cartridge assembly  23  is assembled in the circular bore  24  by first dropping in the pin unit  26 , including the bearing assembly  29 , and spring  27 . The plug  22  is thereafter installed in the bore  24 . One preferable method of locking the plug  22  in position is to size it to have an interference fit with the bore and chill it with liquid nitrogen before installing it in the bore. Normally, the surface  11  of the platen is smooth and it is important that the plug  22  fits flush with this surface so that the products being formed by the platen  10  are smooth. Various other methods of securing the plug  22  of the cartridge  23  in place are contemplated. Where the plug is welded in place, the platen and plug can be ground flat after welding. A bore  37  is formed by gun drilling or other suitable process along a line that is parallel to the face  11  and intersects all of the cartridge receiving bores  24  and is thereby common to the vent holes  21  lying on the same transverse line of the vent array. 
   A cam  41  in the form of a spherical ball, is associated with each of the vent hole cartridges  23 . An elongated force transmitting member in the form of a chain  42 , such as a conventional roller chain, extends along a respective bore  37  and is fixed to each of the cam balls  41 . A force actuator  43 , such as a hydraulic pancake cylinder, is connected to one end of the chain  42  and an opposing force actuator  44  such as spring pack or a hydraulic pancake cylinder is connected to the opposite end of the chain on the opposite edge of the platen  10 . Each row or transverse line of vent holes  21  has the same construction including cartridge assemblies  23 , bores  37 , cams  41  and chains  42 , and force actuators  43 ,  44 . 
   The platen  10  is typically used with other identical platens in a multi-stage press where the platens are arranged in a horizontal orientation, one overlying another. Material, in particle, chip, strand, layer or like form and an accompanying thermally responsive binder is laid out on each intermediate upper face of a platen. The press is then closed by forcing the platens together to thereby compress the material into a rigid board. As mentioned, the platens  10  are conventionally heated to an elevated temperature in the range of, for example, about 350° F. with circulating hot oil through the passages  13 . The material being pressed, which ordinarily is wood or cellulose-based, typically contains moisture which is converted into steam during the heating and pressing process. The vents  21  allow this steam to escape from the pressing space as it is generated and this exhaust of steam ultimately results in an improved board product. Steam passes through a vent  21  over a pin  32  into the bore  24  and through the axial passages  38  into the transverse bore  37 . The cam balls  41  are slightly smaller in diameter than the bore  37  so that steam can flow around the cam balls and along the bore and exhaust through passage  46  at the ends of the bore. Prior attempts to vent a platen surface have had limited success because elements of the board materials driven by steam flow and mechanical pressure would find their way into the vents and through accumulation would plug the vents and render them ineffective. The pins  32  of the cartridge assemblies  23  are arranged to positively mechanically clean out the vent holes  21  and displace any accumulation of board material from these openings. To purge the vents  21  of any accumulation of board material, the pin units  26  are moved from their retracted positions illustrated in  FIGS. 2 and 3  where the pins  32  are displaced from the vents  21  to extended positions where the pins project through the associated vents with their outer end faces flush or projecting slightly from the plane of the platen face  11 . The pins  32  are forcibly extended by pressuring the associated hydraulic actuator  43  to tension and move the chain  42 . Limited chain motion (to the left in  FIGS. 2 and 3 ) causes the cam balls  41  through contact with the projecting hemispherical portions  33  to actuate and cam the respective pin units  26  outwardly such that the pins  32  extend into their associated vent holes  21 . The opposing force actuator  44  maintains a level of tension in the chain  42  to avoid any slack so that the cams  41  are registered with the hemispherical cam following portion  33  and returns the chain and cams to the illustrated position when the actuator  43  is depressurized at the end of a vent cleaning cycle. The actuators  43  can be energized when the press is open to clean the vents  21  as frequently as conditions warrant. 
   Referring now to  FIGS. 4–7  another embodiment of the invention is shown. An elongated rigid segmented rod  51  replaces the chain  42  of the first embodiment. A typical rod segment  51  is illustrated in  FIG. 5  and comprises a round steel tube machined from seamless tubing or otherwise formed into the illustrated round form. At one end, the rod segment  52  has external threads  53  and at the opposite end an enlarged bulb or head  54  with internal threads that are complementary to the external threads  53 . Diametral cross holes  56  in the segment  52  communicate with a central bore  57  running through the rod segment  52 . Each end of the head  54  is sloped with a conical camming surface  58 ,  59 . The head  54  is sized to slide freely in a transverse passage or round bore  61  (corresponding to the common passage or bore  37  of the earlier described embodiment of  FIGS. 1–3 ). The rod segments  52  are threaded into one another as indicated in  FIG. 5 . The length of a rod segment  52  is determined so that when it is assembled with the other segments, the heads  54  of adjacent segments are spaced longitudinally from one another by a distance equal to the spacing between the vents  22  along their respective transverse lines. 
   It will be noted that in this embodiment, the vent holes  21  are provided by cartridge assemblies  23  identical to those described above in connection with  FIGS. 1–3 . 
   The platen, designated  70 , is heated with hot oil circulating through passages as discussed in connection with the embodiment of  FIGS. 1–3 . Steam being exhausted through the vent holes  21  is allowed to pass through the cross holes  56  into the central bore  57  of the rod segments. Steam escapes axially through the central bore  57  out through a transverse hole  74  of a cam follower  73  at one end of the rod  51  and ultimately exhausts at the long edge  62  of the platen  70 . 
   The rods  51  are forcibly moved by a cam bar  62  ( FIG. 7 ) that extends along a long edge  66  of the platen  70 . The cam bar  62  is constrained by a mounting plate assembly  71  such that it can move only in the longitudinal direction of the platen edge  66 . The cam bar  62  includes a cam surface  72  at each of a plurality of locations along its length corresponding to locations of the transverse bores  61 . The rod segment  52  adjacent the cam bar  62  has the cam follower  73  fixed on its head  54 . The cam follower  73  provides the transverse hole  74  which communicates with a central bore that connects with the axial bore in the segments  52 . At the opposite end of each segmented rod  51  is a compression spring  77  that resiliently forcibly biases the rod towards the cam bar  62 . The piston rod  78  of an actuator cylinder  79  is connected to the cam bar  62  through a rigid extension  81 . When the actuator cylinder  79  is energized, the cam bar  62  is moved longitudinally a short distance (to the left in  FIG. 5 ). At an appropriate time when the press in which the platen  70  is employed is open, the actuator  79  is energized to simultaneously extend all of the vent cleaning pins  32  into their respective vent holes  21 . The cam surfaces  72  move their respective segmented rods  51  axially in the bores  61  overcoming the resistance of the springs  77  so that the conical camming surface  58  at each cartridge assembly is caused to actuate and cam the hemispherical portion  33  of the respective pin unit  26  outwardly to drive the hole cleaning pin  32  into its respective vent hole  21 . 
   Referring to  FIGS. 8–10 , there is shown a third embodiment of the invention that comprises a platen  90 . The platen  90  has a plurality of vent holes  91  distributed across its pressing surface  92 . The vent holes  91  are preferably formed in elongated T-shaped bars  93  received as inserts in open face T-slots  94  milled or otherwise formed in a main body  96  of the platen  90 . Preferably, the vent holes  91  are uniformly spaced along the length of a respective T-bar  93  and the slots or grooves  94  are parallel and uniformly spaced from one another across the pressing surface  92 . The bars  93  are closely fitted to the geometry of the slots  94  and have their outer surfaces  97  forming part of the pressing surface  92  and being coplanar with the major parts of the pressing surface  92  formed by the main body  96 . The bar  93  has a passage in the form of a slot  98  open at its broad face and extending along its full length. As shown, the slot  98  is centered on the plane of symmetry of the T-bar  93 . Associated with each vent hole  91  is a hole in the form of a counterbore  99  that extends from the slot  98  to an end wall  101  adjacent the outer pressing surface  97  of the T-bar  93 . 
   A pin unit, which can be identical to the pin unit described above in connection with the earlier discussed embodiments, is indicated by the same reference numeral  26 . The pin unit  26  and associated spring  27  are releasably retained in the counterbore  99  by an internal snap ring  102 . 
   Disposed in the passage or slot  98  of each T-bar  93  is an elongated cam bar  103  that extends the length of the T-bar. At regularly spaced locations along its length corresponding to the centers of the vent holes  91 , the cam bar  103  includes cam surfaces  104 . The cam surfaces  104  are milled or otherwise formed on the bar such that they are inclined at an angle relative to the longitudinal direction of the bar. The cam bar  103  is proportioned to slide freely longitudinally in the slot  98 . The linear ball bearing assembly  29  supports the pin unit  26  for axial movement in the counterbore  99 . 
   Each cam bar  103  with its cam surfaces serves like the cam balls  41  and chain  42  of the first embodiment, and the conical camming surfaces  58  and segmented rod  51  in the second embodiment to extend the pins  32  into their respective vent holes  91  at appropriate times in the operation of a press in which the platen  90  is used. A hydraulic or other known type of actuator, like the actuator  79 , can be used to simultaneously operate all of the cam bars  103  through a common drive analogous to the cam bar  62  or individual actuators can be connected to each of the cam bars  103  like the arrangement of the actuators  43  of the first described embodiment. In either case, the power actuator or actuators is/are mounted on the platen  90 . 
   As in the earlier described embodiments, steam generated by the pressing process is exhausted through the vent holes  91 , the pin unit bores  38  and along a clearance space  106  between the cam bar  103  and the passage or slot  98  to the edges of the platen body  96  where it is discharged to the atmosphere. Each of the T-bars  93  can be removed from the main body  96  by sliding it longitudinally out of its respective slot  94 . Removal of a T-bar  93  enables the pin unit  26  and parts associated with it to be maintained and/or replaced as needed. 
   Hot oil or steam circulates through passages  107  in the platen body to heat the platen  90  to an operating temperature. The vent holes, pin units and operating elements for the pin units, as described, are typically provided on both pressing surfaces of the platen  90 . 
     FIG. 11  illustrates a multi-opening or multi-platen press embodying the invention. The press includes a plurality of columns  111  that support the press through a bottom bolster  112 . Vertical tie rods  113  extend between the bottom bolster  112  and a crown  114 . A main platen  116  is moved upwardly by jack cylinders  117  in the initial closing movement of the press, and by hydraulic main ram cylinders  118  during high pressure compression operation of the press. The cylinders  117 ,  118 , are operated by hydraulic oil pressurized by electrically driven pumps  119  and supplied under pressure from the pumps through lines  121  and exhausted through lines  122 . Hydraulic oil is supplied from and received by reservoirs  123 . 
   A series of horizontal platens  126 ,  126   a,  and  126   b,  representing one of the styles of the platens  10 ,  70 , or  90  disclosed above, are arranged in a vertical stack one above the other. The top and bottom platens  126   a  and  126   b  typically will have vent holes as described hereinabove on their lower and upper pressing surfaces, respectively, while the remaining platens  126  are provided with vent holes on both pressing faces. Pipes  127  convey heated oil or steam to the platens  126  as described. Hydraulic lines, not shown, connect to the actuators  43  or  79  on the individual platens  126 . Pivotal closing arms  128  in a manner known in the art maintain the platens  126  in parallel horizontal alignment. 
   Loose material to be pressed into panels is conveyed onto the top surface of each of the platens  126 . The jack cylinders  117  are actuated with pressurized hydraulic fluid to raise the main platen  116  and close the openings between platens  126 . Thereafter, the main ram cylinders  118  are pressurized to compress the board material to the requisite pressure. The vent holes in the pressing surfaces of the platens  126  enable the press  110  to compress the board material without the need to decompress this material by backing off the platens  116 ,  126  to allow the steam being generated from moisture contained in the board material to escape without an explosive effect. By eliminating the need for decompression or backing off of the platens to allow steam to be released, the vent holes can reduce the molding cycle time by about 20% to thereby increase the productivity of the press. This decrease in cycle time is of great significance in the return on investment in the cost of the press  110 . Besides significantly improving productivity, the vent holes of the platens  126  enable the press  110  to produce an improved board product with greater uniformity and with far less rejected material that otherwise occurs when steam is not properly released in prior art presses. 
   While the invention has been shown and described with respect to particular embodiments thereof, this is for the purpose of illustration rather than limitation, and other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art all within the intended spirit and scope of the invention. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.