US2720231A

US2720231A - Continuous press for plywood, fiberboard and the like

Info

Publication number: US2720231A
Application number: US296138A
Authority: US
Inventors: Herbert E Hessler; Orville W Rice; Robert F Johnson
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-06-28
Filing date: 1952-06-28
Publication date: 1955-10-11
Anticipated expiration: 1972-10-11

Description

Oct. 11, 1955 H. E. HEssLl-:R ETAL .CONTINUOUS PRESS FOR PLYWOOD, FIBERBOARD AND THE LIKE 4 Sheets-Sheet l Filed June 28, 1952 w JM .mwe $.57 N .RJ m A bww www@

,f f ,f ,f 7,. ,f, g E E i l E ,i E E m 224 226 74 Oct. l1, 1955 H. E -HESSLER ETAL 2,720,231

CONTINUOUS PRESS FOR PLYWOOD, FIBERBOARD AND THE LIKE I N VEN TORS Herbert E. Hess/er Orville W Rice Robert F rmSOr Oct. 1l, 1955 H. E. HESSLER ETAL CONTINUOUS PRESS FOR PLYWOOD, FIBERBOARD AND THE LIKE 4 Sheets-Sheet 3,

Filed June 28, 1952 Fig. 4

f m Mmes# N E J wmmf M Oct. 11, 1955 H. E. Hl-:ssLER ET Al.

CONTINUOUS PRESS FOR PLYWOOD, F'IBERBOARD AND THE LIKE Filed June 28, 1952 4 Sheets-Sheet 4 0 8` \\|\6 L M Z ID Z WMU 0 0 m w w w 2 2 2 m m4 a m Z 2 n m 0 0L. n Mn 6 0 2 m nu El/x INVENTOR Herbert E'. Hess/er Orville IM Rice n mw w m T m United States Patent O CONTINUOUS PRESS FOR PLYWOOD, FIBERBOARD AND THE LIKE Herbert E. Hessler, Newberg, Oreg., Orville W. Rice, Vancouver, Wash., and Robert F. Johnson, Portland, Oreg.

Application June 28, 1952, Serial No. 296,138

3 Claims. (Cl. 144-281) This invention relates to a continuous press of the class employed for pressing wood veneers in the manufacture of plywood, for consolidating librous mixtures in the manufacture of fberboard and in similar applications.

Although a large number of continuous presses heretofore have been devised for use in the manufacture of plywood and berboard, few, if any, have experienced commercial success. The failure `of these `devices is attributable to numerous factors, predominant among which is the diiiculty of constructing a continuous press which is free from friction and capable of exerting adequate pressure over a large working area without excessive strain on the bearings, and excessive torque on the shafts. It is also difficult to supply apparatus of this class wherein pressures may be applied uniformly over a large area and wherein uniform thickness adjustment may be secured over large areas. As a result, the continuous presses of the prior art have been subject to mechanical failure and have produced non-uniform products.

Included among the objects of the present invention therefore are the following:

First, to provide appress for the continuous production of plywood, fiberboard, veneer surfaced hardboard, hardboard surfaced plywood, and like products.

Second, to provide a continuous press having a very large press area without imposing excessive strain on bearings and shafts. j

Third, to provide a press wherein the material to be pressed may be passed continuously between the press members without excessive friction. p

Fourth, to provide a continuous press having opposed, synchronously moving press members.

Fifth, to provide a continuous press having pressing members including continuous caul belts which may be centered accurately and placed under uniform tension by the supporting members.

Sixth, to provide a continuous press having opposed press members which may be set accurately to produce pressed products of preselected `thicknesses and density and which may be adjusted to compensate `for pressing deection of the press members.

Seventh, to provide a continuous press which is easy to assemble and operate, and easy to clean.

Eighth, to provide a continuous press which is versatile and adaptable to the pressing of a variety of products, using a variety of dilferent classes of adhesive materials.

The manner in which the foregoing and other objects of this invention are accomplished will be apparent from the accompanying specification and claims considered together with the drawings wherein like numerals of reference indicate like parts and wherein:

Fig. 1 is a View in side elevation of the presently described press;

Fig. 2 is a fragmentary plan view illustrating the prepress mechanism of the` presently described press;

Fig. 3 is a sectional view taken along the lines 3 3 fFig. 1; y y

Fig. 4 is a schematic view of the straining and centering ICC mechanism employed in operating the press members of the presently described press;

Figures 5 and 6 are sectional views taken along the line 5--5 of Fig. 4;

Fig. 7 is a partial sectional View taken along the line 7-7 of Fig. 1; and

Fig. 8 is a fragmentary perspective view illustrating the adjusting means for adjusting the position of one of the press members relative to the other. Generally stated, the continuous press of the present invention comprises prepressing means for applying preliminary pressure to the material to be pressed. After having been subjected to a preliminary pressure the material is introduced between a pair of endless caul belts each mounted on a pair of spaced apart drums driven synchronously from a common source of power. Means are provided for keeping the belts under uniform tension and for centering them on their respective drums. Each of the caul belts is supported by an endless roller assembly, the working stretches of which are reenforced by longitudinal tracks. Means are provided for adjusting the position of one of the tracks relative to the other, thereby determining the thickness and density of the pressed product. Means also are provided for adjusting the other of the tracks to compensate for any deflection which might occur during pressing, thereby insuring that a uniformly pressed product is obtained.

Considering the foregoing in greater detail and with particular reference to the drawings:

The prepress unit The prepress unit has for its primary purpose the preliminary consolidation of the material to be pressed, thus relieving the pressing load within the main press. In the production of iberboard, it also serves the function of consolidating a fibrous mat or felt to self-sustaining form, thereby facilitating its introduction into the press. Hence it is designed to prepress the material as nearly as possible to the iinal thickness.

The prepress unit includes a feed table 10 for receiving the press charge which may comprise laid-up wood veneer assemblies for the production of plywood; fibrous mats or felts of wood fibers, sawdust, chips, shavings, etc. for the production of insulation board or hardboard; assemblies for the production of cement or gypsum board and the like. The feed table is positioned to feed the charge between a pair of prepress rollers 12, 14. These are axially aligned with each other, spaced apart the desired distance and rotatably mounted on the frame of the unit.

Thus prepress roller 12 is rotatably mounted in bearings 16, 18 while roller 14 is rotatably mounted in similar fashion in bearings, one of which is indicated at 20. Both rollers are driven through peripheral internally directed spur gears 22, 24, thereby relieving strain and torque on the bearings and shafts supporting the rollers.

Gear 24 on the lower roller meshes with a spur gear 26 keyed to a common rotatable shaft 28 with a sprocket 30. Similarly, gear 22 on the upper roller meshes with a gear (not shown) keyed to a common rotatable shaft 32 with a sprocket 34. Sprockets 30 and 34 are driven respectively through chains 36, 38, the ratio of the gears and sprockets in these assemblies being such as to impart to rollers 12, 14 peripheral speeds which are substantially equal to the rate of travel of the charge through the main press unit. Chains 36, 38 in turn are connected to'the driving mechanism of the press in a manner to be described hereinafter.

The pressure exerted by the prepress rollers is relieved by suitably positioned back-up rollers which are axially aligned with the prepress rollers and in peripheral pressure contact therewith. In the illustrated embodiment prepress roller 12 has behind it two such back-up rollers indicated generally at 40, 42. The construction of these two assemblies is substantially identical, back-up roller comprising a shaft 44, having rigidly aixed thereto a pair of spaced apart pressure wheels 46, 48 and being rotatably mounted in bearings 50., 52.. Prepress roller 14 is provided with a similarly positioned pair of back-up rollers 54, 56, the construction-of which .is not illustrated, but which is similar to that indicated for roller 40.

The press unit Material leaving the prepress unit passes over a .transfer table 58 into the press uri-it wherein the final consolidation and setting of any adhesive which may :be present is accomplished. rlhe press unit preferably is heated by suitable means toa temperature level .sufficient to set the particular adhesive employed. Thus yit may be heated by hot gases, steam, radio frequency, or other suitable methods. In tlh-e illustrated form it is enclosed in a chamber 60 provided with a duct 62 through which hot air may be introduced. The elements of the press and the press charge thus are heated to the `desired level and maintained at that level during the operating period of the press.

The press assembly includes a pair of

endless caul belts

64, 66 made of stainless steel or other material capable of withstanding elevated temperatures and contact with corrosive materials. They may be of substantial size, for example, as much as inches in width and suiciently long 4to insure the necessary dwell time within the press.

The forward end of upper caul belt 64 is mounted on a rotatable drum 68 suitably mounted on the frame of the unit through bearings 70. In a similar manner the forward end of the lower caul belt 66 is carried by an idler drum 72 rotatably mounted on the frame by means of bearings 74.

Drums

68 and 72 are used to drive the prepress rollers. To this end `they are provided with internally directed peripheral spur gears 76, 78 respectively. Gear 76 meshes with a gear 89 keyed to a common shaft 82 with a sprocket 84. Gear 78 in turn meshes with another gear (not shown) keyed to a common shaft 86 with a sprocket 88. Sprockets 84 and 88 respectively engage chains 38 and 36 driving the prepress rollers, idler sprockets 90, 92 also being included in the assembly. In this manner .the prepress rollers are driven by the idler drums at a rate commensurate with the speed of the caul belts.

The rearward ends of

caul belts

64 and 66 are mounted on and carried by a pair of .driving

drums

94, 96. These are rotatably mounted on the frame by means of bearings 98, 100.

Synchronous driving of

drums

94, 96 is achieved by A providing them with peripheral internally directed spur gears 102 and 104, gear 102 being on the upper drum and gear 104 on the lower drum. Gear 102 meshes with spur gear 106 which is rigidly affixed to a common shaft 108 with gear 110.

Similarly, gear 104 meshes with a spur gear (not shown) keyed to a common shaft 112 with gear 114. Gears 110, 114 mesh respectively with worm gears 116, 118 mounted at spaced intervals on a common shaft 120. Shaft 120 is rotatably mounted in bearings 122, 124. It is driven through gear box 126 vby motor 128. In this manner there is afforded means for synchronously driving

caul belts

64 and 66 and prepress rollers 12, 14 connected thereto.

Since hard, gummy materials may be deposited on the caul belt, when pressing charges such as wood veneer assemblies and fibrous mats containing substantial quantities of adhesive, means are provided for cleaning the belts and for polishing them before they enter the working portion of the press. For this purpose there may be provided the motor driven brushes, 130 working on

belt

64, and 132 working on belt 66. Also, at the same or adjacent stations means may be provided for applying to the belts suitable lubricants or mold release cornpounds for inhibiting sticking of the charge to the belts.

The caul belt tensioning and centering means In the presently disclosed continuous press means are provided for straining or tensioning the caul belts to maintain them taut and center them on the drums upon which they are mounted. The tensioning means comprise a plurality of single-acting fiuid operated rams, preferably hydraulic rams, which act against the idler drum assemblies and exert a continuous and uniform pressure thereon. Thus in the idler drum assembly, including upper caul belt 64 and idler drum 68 there are provided a pair of slides 134, each slidably mounting one of bearings 70 which supports the drum on the frame of the unit. Acting upon bearings 70 are a pair of hydraulic rams 136, 136', one connected to each bearing and positioned for stretching the caul belt.

Similarly in the idler drum assembly, including caul belt 66 and drum 72, there are a pair of slides 138, each slidably mounting one of bearings 74 on lopposite sides of the drum. There also is provided a pair of hydraulic rams 140 each operating against yone of bearings 74 in a direction calculated to tension belt 66. Thus by uniform application of hydraulic pressure through

rams

136 and 140, a uniform tensioning or straining of both caul belts is achieved.

The hydraulic rams employed in tensioning the caul belts also are employed in keeping the belts centered on the drums. In so doing, advantage is taken of the basic principle that a belt will tend to climb toward the high (or extended) side of a pulley on which it runs. Thus it will be apparent that if a differential pressure is exerted on opposite sides of the unit by rams 136, or by rams 140, the corresponding caul belt will move toward the side on which the greatest pressure is exerted.

The application of this principle to the operation of the presently described press is particularly apparent in Figs. 1, 4, 5 and 6. Considering first the upper caul belt unit, rams 136, 136' on opposite sides thereof are supplied with hydraulic fluid through a system comprising a fiuid reservoir 142, a pump 144, a valve 146 for dividing the fluid into a high pressure stream which passes through a first conduit 148 and a low pressure stream which passes through a second conduit 150. vThe high pressure and low pressure streams are introduced into opposite sides of a four-way, spring centered distributing valve 152 and return to the vreservoir through the pressure relief valve 154 and conduit 156.

The design and adjustment of distributing valve 152 is such that the high pressure stream normally is connected to

rams

136, 136 through third conduit means 158, 160 respectively. The manner in lwhich this is accomplished is particularly apparent from Figs. 5 and 6, illustrating valve 152 in both of its operating positions. Within the valve is a perforated hollow Vcore member 162. Slidable within the core member longitudinally thereof there is a valve stem 164 provided with a pair of spaced apart

spool members

166, 168. A pair of

springs

170, 172 are positioned for maintaining the stern normally in the position of Fig. 5 wherein `the high pressure line 148 normaliy is connected to

rams

136, 136 through

conduits

158 and 160 respectively.

Stem 164 of valve 152 has associated with one of its ends a solenoid 174 and to the other of its ends a solenoid 176, the solenoids being positioned for shifting the position of the stem in a direction determined by which solenoid is energized. Solenoid 174 is in an electric circuit with an electric limit switch 178, positioned adjacent one side of the upper caul belt. Similarly solenoid 176 is in an electric circuit with a limit switch 180 stationed adjacent the other side of the upper caul belt.

When the caul belt is in its normal running position, illustrated in Fig. 4, it is centrally positioned on drum 68 and out of contact with

limit switches

178, 180. In this running position distributing valve 152 is adjusted to the position of iFig. 5 wherein the high pressure stream armoe-31 is connected to both of the rams which exert equal pressures on opposite sides of the belt. However, if dur ing the operation of the press it becomes displaced toward one side or the other of the drum, it contacts one or the other of the limit switches.

If limit switch 178 has thus been contacted, solenoid 174 acts upon valve stem 164 to shift the valve to the position illustrated in Fig. 6 in which the low pressure stream 150 is connected to ram 136 through conduit 158. This retracts the ram slightly so that a pressure differential exists between rams 136 and 136', the latter exerting the greater pressure. As a result the moving caul belt will shift its position in the direction of ram 136.

This motion will continue until the belt is out of contact with limit switch 178, whereupon springs 170 and 172 will return the valve to the position of Fig. 5 wherein the high pressure stream again is connected to ram 136 and the two rams exert the same pressure. If the belt should move to the other side of the drum, it would contact limit switch 180. This would energize solenoid 176 so that the valve would be adjusted to connect cylinder 136 to the low pressure stream and cause the belt to shift again toward the center of the drum. In this way the belt is maintained accurately centered while at the same time it is kept under a constant and uniform tension.

In a manner similar to the above the lower caul belt 66 is maintained under tension and properly centered, rams 140 being connected through conduits 182 with a valve system not illustrated but identical with that described above with reference to the upper belt assembly. Thus conduits 182 are connected to a distributing valve which in turn is connected on one of its sides to a high pressure stream 184 and a low pressure stream 186 (Fig. 4). The distributing valve is operated by a pair of solenoids which in turn are in an electric circuit with a pair of limit switches 188 stationed on opposite sides of the lower caul belt. Upon actuation of one or the other of these limit switches the system operates to shift the position of the belt as has already been described.

T he pressure applying means In presses of the class described it is a particular problem to move caul belts of great area and extent through the press under high pressure without increasing the friction between the belts and the charge to such an extent that the belts will bind, or move erratically. It also is a particular problem to adjust the spacing between the Working stretches of the caul belts, thereby determining the thickness of the pressed product. Still further, it is a serious problem to adjust the spacing between the working stretches of the caul belts so that it is uniform over the entire width and length of the belts, thereby insuring the production of a product of accurate and uniform dimensions.

The manner in which the above difficulties have been solved in the presently described press is particularly apparent from Figs. l, 3 and 7. Within each caul belt there is stationed an endless roller assembly backed up by a longitudinal track. The two roller assemblies are geared together with the rollers stationed diametrically opposite each other. Along the working surfaces of the assemblies, the rollers engage the caul belts on one side and longitudinal tracks on the other and this engagement causes the two assemblies to traverse the press synchronously and with a minimum of friction.

Thus the roller assembly associated with the upper caul belt 64 comprises a pair of parallel

endless chains

190, 192 having at spaced intervals a plurality of inwardly extending

pins

194, 196. The pins are employed for rotatably mounting a plurality of spaced apart rollers 200, which extend between the chains transversely of the caul belt. The assembly is rotatably mounted on a plurality of sprocket pairs 202, 204, 206 and 208. One of the sprocket pairs, for example sprocket pair 204, is mounted on a shaft 210 which in turn is mounted in bearings 212, 214. The latter are mounted upon

slides

216, 218 adjustable by means of screws 220. This affords a means of maintaining the roller assembly under proper tension. The working stretch of rollers 200 works against track means comprising a plurality of substantial beams 222 arranged longitudinally of the press and in parallel side by side relationship across its width.

The construction of the roller assembly associated with the lower caul belt is similar to that described in connection with the upper belt. It comprises a pair of parallel spaced apart

endless chains

224, 226 on opposite sides of the belt. These are interconnected by a plurality of rollers 230 extending transversely of the belt and contacting the same at spaced intervals. Rollers 230 are rotatably mounted between the chains by means of a plurality of inwardly extending

pins

232, 234 atixed respectively to

chains

224 and 226, and penetrating openings within the rollers.

Chains

224 and 226 are mounted on a plurality of rotatably mounted sprocket pairs. These include sprocket pairs 238, 240, 242 and 244. The sprockets comprising sprocket pair 240 are keyed to a common shaft 246 which is rotatably mounted on the frame of the unit and which carries at its outer end a spur gear 248. Gear 248 meshes with a gear 250 keyed to shaft 251 mounting sprockets 206 of the upper roller assembly.

By proper keying of sprocket 240 and gear 248 to shaft 246, and of sprocket 206 and gear 250 to shaft 251,

rollers

200 and 230 in the working stretches of the roller assemblies may be positioned diametrically opposite each other. This is an important feature of the present invention since it insures uniform and balanced application of pressure to the caul belt, eliminating strain and wear. Also, it insures that the caul belts will not be forced into a wavy or irregular outline which would in turn be imparted to the material being pressed.

As in the upper roller assembly, means are provided for tensioning the lower roller assembly. Such means include slide means on which are mounted bearings 252 supporting the shaft on which sprocket pair 242 is mounted. Associated with the bearing and slide means are a pair of screws, one of which is indicated at 254, which may be operated to adjust the roller assembly to the proper tension.

To support the idling stretch of the lower roller assembly and to facilitate its movement there are provided a plurality of rollers 256 rotatably mounted on appropriately positioned frame members. The working stretch of the rollers is supported by and works against track means comprising a plurality of longitudinal beams 260 spaced parallel to each other across the width of the press. The

track members are axed to a plurality of transverse beams 262, 264, 266, 268 and 270. The latter extend outwardly from the press and are interconnected in pairs by the cross pieces or keepers 272, 274. Also, a keeper 276 associated with transverse beam 262 has on its forward end an inwardly directed hook 278 which engages a flange 280 on a vertical frame member. In this way there is provided a track assembly for the lower roller assembly which is adjustable vertically to vary the opening of the press and hence determine the width of the pressed product.

To guide material into the press the lower track assembly is provided with a forward extension comprising a plurality of parallel longitudinal members 282 spaced apart across the width of the press. The inner ends of members 282 are pivoally attached to the track members 260 through pins 284. Their forward ends rest on a pad 286 which has an arcuate outer surface to facilitate sliding movement of the track extension. The outer surface of pad 286 normally is positioned somewhat below the level of track members 260 thereby forming an opening into which material may be introduced into the press and quickly brought to final compression. It then is maintained at final compression during the rest of its dwell time within the press until the adhesive has set and it has become dimensionally stable.

The press opening adjustment As has been indicated above, the track means including the longitudinal track members 260 supporting the lower roller assembly floats on the press frame and hence may be adjusted vertically for increasing or decreasing the press opening. Although various means may be provided for efectuating this result, preferred means are indicated in Figures l, 3 and 8. Thus as is seen from Fig. l there is provided a plurality of wedges series disposed at i-ntervals transversely of the press, these being indicated generally at 290, 292, 294, 296 and 298. It will be apparent, however, that the number of such wedge series incorporated in a given press will be determined by the press length.

As is shown in Fig. 3 each series of wedges includes a plurality of

individual wedge members

300, 302 and 304. These are arranged end to end across the width of the press and each works against an appropriately positioned angle block indicated at 306, 308 and 310 respectively.

'The construction and manner of mounting of the wedge members is readily observable in Fig. 8. Thus the wedge members preferably are arranged in pairs, the pair illustrated comprising

members

302 and 312. These are mounted respectively in housings or frames 314, 316. The latter in turn are tied together by a connecting member 318 having a threaded bore longitudinally thereof.

Adjustable mounting of the wedges within the frame is secured by means of

bolts

320, 322, and 324, and 320', 322', and 324', respectively extending through the wedges and through appropriately placed slots in the frame. Releasing the bolts enables longitudinal adjustment of the wedges by means of the

screws

326, 328. After the adjustment has been made,

bolts

320, 322 and 324 then are tightened to lock the wedges securely in place.

Each of the wedges is mounted on a guide block, that for wedge 302 being indicated at 330, and that for wedge 312 at 332. The latter in turn are afiixed to the

transverse beams

334, 336.

Before operating the press, the wedges are adjusted as described above until the track comprising members 260 is perfectly aligned. As the press is used, however, the `opening may be adjusted by the contemporaneous adjustment of the wedges as a group. This is accomplished by motor driven screw means comprising a plurality of transverse threaded shafts, one of which is indicated at 340 in Fig. 8. These penetrate the internally threaded openings in 4the connecting members 318. Keyed to one end of each of them is a gear 342. Gear 342 engages a worm gear 344 on a longitudinal shaft 346 extending substantially the length of the press. Shaft 346 is provided with a sprocket 348 which is interconnected through chain 350 with a sprocket 352 on the shaft of a reversible electric motor 354. Hence operation of motor 354 will effect the transverse adjustment of the wedges which in turn will adjust the opening of the press to the preselected degree.

The adjustment for working deflection The track members 260 supporting the lower roller assembly may be adjusted for deflection caused by the developed working pressure by individual adjustment of the wedges in the manner indicated above. Means also are provided, however, for adjusting the track members 222 against which the rollers 200 of the upper roller assembly work. This enables maintaining a wide sheet of material of uniform thickness across its width.

The defiection adjusting means associated with the upper roller assembly comprises the transverse beams 360, 362, 364 and 366 rigid to the frame, reinforced by the

saddle members

368, 370, 372 and 374 and backing up 8 the longitudinal track members 222. Centrally located on beams 360, 362, 364 and 366 and extending substantially normal thereto area plurality of pairs of thrust beams 376, 378, 380 and 382 (Fig. 3). These bear against horizontal beams 384, 386, and 388.

Over the horizontal beams extend angular truss rods 390, 392, 394 and 396. The ends of the truss rods are threaded and penetrate openings in the web members 398, 400, 402 and 404, such web members being provided in pairs on opposite sides of the press, and each being reinforced by a strut member, e. g. strut member 406 associated with web member 402.

Truss rods 390, 392, 394 and 396 are provided respectively with

nuts

408, 410, 412, 414. It will be apparent that upon tightening nuts 412 on truss rod 394, for example, pressure will be applied to the thrust beams 380 and 380. This in turn will be transmitted to the transverse beam 364 and thence to the longitudinal track members 222. In this manner correction for working deflection of the track members may be obtained.

Operation The manner of Operation of the presently described continuous press is apparent from the foregoing description. Material to be pressed, comprising plywood assemblies, felted fibrous mats and the like are introduced between the prepress rollers 12, 14 if a prepressing operation is necessary. After having been substantially pressed by the same, the material passes over transfer table 58 and between the

endless caul belts

64, 66. These lead the material within heated chamber 60 where it is heated to a temperature calculated to set any adhesive which may be present. Depending upon thenature of the material to be pressed, the identity of the adhesive employed and other factors, the rate of travel of the material through the press is adjusted to give the desired dwell time.

Caul belts

64, 66 are driven synchronously from a common motor 128, the drive being applied peripherally to the driving

drums

94, 96 to lessen the strain and torque on the bearings and shafts on which these drums are mounted. The drive is transmitted to the idler drums 68 and '72 and thence via chains 36, 38 to the prepress rollers 12 and 14. The latter therefore may be driven at a surface speed identical with the rate of travel of the caul belts.

The caul belts are maintained taut uniformly over their substantial area by means of a plurality of hydraulic rams 136, operating upon the idler rollers. These same rams are employed to center the caul belts through a system of limit

switches including switches

178, 188, one such switch being stationed adjacent each edge of the caul belt. The limit switches operate solenoids which in turn operate distributing valves 152 supplying hydraulic uid to the respective rams. 'When one of the limit switches is vcontacted by an edge of the caul belt the distributing valve is adjusted to the position of Figure 6 so that the pressure of fiuid supplied to the corresponding ram is decreased. As a result of the resulting differential pressure applied to the belt, the latter will creep toward the high pressure side and thereby become centered out of contact with the limit switch. Thereupon the valve is automatically adjusted through

springs

170, 172 to the position of Fig. 5 wherein equal pressure is applied to the cylinders on both sides of the belt.

Within the press the material is subjected to pressure applied through two pairs of roller assemblies one associated with the upper caul belt and the other with the lower caul belt. The rollers of the working stretches of each of these assemblies work against longitudinal tracks comprising

heavy beams

222, 260 spaced apart across the width of the press. The rollers -are maintained opposite each other by gearing one of the roller assemblies tothe other so that they operate synchronously. Driving of the assemblies is accomplished by engagement of the press charge with the driven caul belts which, because of the developed pressure, carry the roller assemblies along with them but at a rate one-half the rate of the motion of the caul belts.

Finally, the opening of the press is determined by a plurality of wedges arranged in series transversely of the press and operated synchronously from a common motor. Thus

wedge assemblies

290, 292, 294 and 296 underlie the track members 200, which float on the frame, and raise or lower the same as required. In addition, the outer surfaces of the track beams may be set so that they are level and corrected for any working deflection by adjustment of the individual wedge assemblies through

bolts

320, 322 and 324.

Also, the fixed track members 222 may be adjusted for working deflection by adjusting

nuts

408, 410 and 414 on truss rods 390, 392, 394 and 396. This adjusts the pressure exerted by

thrust beams

376, 378, 380 and 382 bearing centrally on the transverse beams 360, 362, 364 and 366. The latter, in turn, bear against track members 222 so that the pressure exerted by the truss rods is transmitted to the track members the position of which accordingly is adjusted as desired.

It thus is apparent that by the present invention I have provided a continuous press which is versatile and applicable to the fabrication of a variety of consolidated products of selected dimensions. Furthermore, the press may be operated continuously without binding due to friction. Still further, the pressing surfaces may be maintained precisely level even though they are of very substantial area. This in turn insures the production of a pressed product of uniform thickness and desirable surface properties.

It is to be understood that the form of our invention, herewith shown and described, is to be considered as a preferred example of the same, and that various changes in the shape, size and arrangement of parts may be resorted to, without departing from the spirit of our invention, or the scope of the subjoined claims.

Having thus described our invention, we claim:

l. A continuous press for pressing plywood, berboard and the like, which comprises first and second rotatably mounted endless caul belts stationed opposite each other for receiving material between their opposed working stretches, motor means connected to the caul belts for driving them synchronously, a plurality of fluid operated rams positioned on opposite sides of the caul belts for tensioning the same, a source of fluid under pressure, valve means for separating the iluid into a high pressure stream and a low pressure stream, a pair of distributing valves associated one with each of the caul belts, first conduit means for conveying the high pressure stream to one side of each of the distributing valves, second conduit means for conveying the low pressure stream to the other side of each of the distributing valves, third conduit means interconnecting the distributing valves and the fluid operated rams, adjusting means in each of the distributing valves for connecting the third conduit means alternately with the irst and second conduit means, means for maintaining the adjusting means normally in a position of connecting the rst and third conduit means and for returning the adjusting means to such position after each displacement, a plurality of electric limit switches stationed one adjacent each side of each of the caul belts, a plurality of solenoids operably connected two to each of the adjusting means and each in an electric circuit with one of the limit switches, each of the solenoids acting upon contact of its respective limit switch with the caul belt to operate the distributing valve with which it is associated for adjusting the adjusting means until the second conduit means is connected to the third conduit means, thereby disconnecting the corresponding ram from the high pressure stream and connecting it with the low pressure stream, retracting the ram and correspondingly shifting the position of the caul belt until it is centered and out of contact with the limit switch.

2. A continuous press for pressing plywood, iberboard and the like, which comprises rst and second rotatably mounted endless caul belts stationed opposite each other for receiving material between their opposed working stretches, motor means connected to the caul belts for driving them synchronously, a plurality of uid operated rams positioned on opposite sides of the caul belts for tensioning the same, a source of fluid under pressure, a pair of distributing valves associated one with each of the caul belts, conduit means interconnecting the distributing valves with the source of fluid under pressure and the uid operated rams, a plurality of electric limit switches stationed one adjacent each side of each of the caul belts, a plurality of solenoids operably connected to each of the distributing valves and each in an electric circuit with one of the limit switches, each of the solenoids acting upon contacts of its respective limit switch with the caul belt to operate the distributing valve with which it is associated, for retracting the corresponding ram and correspondingly shifting the position of the caul belt until it is centered and out of contact with the limit switch.

3. In a continuous press for pressing plywood, fiberboard and the like, wherein is included a rotatably mounted endless caul belt, means for maintaining said caul belt centered, comprising a plurality of fluid operated rams positioned on opposite sides of the caul belt for tensioning the same, a source of fluid under pressure, a distributing Valve associated with the caul belt, conduit means interconnecting the distributing valve with the source of fluid under pressure and the uid operated rams, a plurality of electric limit switches stationed adjacent each side of the caul belt, a plurality of solenoids operably connected to the distributing valve and each in an electric circuit with one of the limit switches, each of the solenoids acting upon contact of its respective limit switch with the caul belt to operate the distributing valve with which it is associated, for retracting the corresponding ram and correspondingly shifting the position of the caul belt until it is centered and out of contact with the limit switch.

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