US 3576349 A
Description (OCR text may contain errors)
United States Patent APPARATUS FOR THE MANUFACTURE OF WOOD FIBER PANELS 6 Claims, 6 Drawing Figs.
US. Cl 302/12, l9/l56.3, 156/370, 156/377 Int. B653 53/04 FieldotSearch 302/ll,12, I
Primary Examiner-Andres 1'1. Nielsen Attorney-Alexander and Dowell ABSTRACT: In an apparatus for the fonnation on a pervious conveyor band of a cushion of wood fibers entrained by an aiistream, the regular distribution of the fibers across the width of the band is effected by a series of longitudinal streamlined depending blades which define adjustable intermediate passages above the band within a vibrating distribution box. The air chest on the perforated upper side of which the band circulates, has its inner space divided into a number of separate chambers connected with at least one suction line through individual valves which permit of distributing the negative pressure below the band in the longitudinal and/or in the transverse direction.
PATENTEU m 1 l97l APPARATUS FOR THE MANUFACTURE OF WOOD FIBER PANELS BACKGROUND OF THE INVENTION The present invention refers to the manufacture of hard plates or panels of wood fibers by the so-called dry" process.
The dry process consists in realizing on an appropriate conveyor band one or several superposed layers of wood fibers which have been previously impregnated with a polymerizable resin and in compressing between heated platens the fibrous cushion thus obtained in order to cure the resin which acts as a binder. The panels thus obtained are extremely strong and rigid.
In such a process the characteristics of the panels are largely dependent on the homogeneity of the fibrous cushion and on the uniformity of its thickness. Experience however demonstrates that it is quite difficult to realize these conditions. The fibers .are very generally conveyed pneumatically, the conveyor band being realized in the form of a wire gauze slidably supported by the perforated upper side of an air chest. The disadvantage of this arrangement is that the edges of the con veyor band are underfed, the fibrous cushion being less dense and less thick in the corresponding zones. It has been proposed to separate the defective marginal portions of the fibrous cushion,'the fibers thus eliminated being recycled, but this results in a quite intricate apparatus and increases the consumption of power. It has also been suggested to combine the pneumatic feed of the fibers with a mechanical distribution across the width of the conveyor band, but without satisfactory results in actual practice.
Another problem in the dry process resides in the distribution of the negative pressure along the length of the conveyor band on the air chest. The thickness of the fibrous cushion above the air chest increases in the advancing direction of the band and therefore the pressure drop in the airstream which passes through this cushion increases correspondingly. The airflow decreases and therefore the quantity of fibers which settle on the cushion also decreases. It has been proposed to regularize the airflow along the length of the conveyor band by calibrating the perforations of the upper side of the air chest so as to increase their cross section where the fibrous cushion is relatively thick and to reduce it where this cushion is relatively thin, but the smaller perforations are easily clogged by fine fibers and moreover the calibrating operation is only effective for the type of panel for which it has been effected, another type requiring a different calibration.
It is an object of the present invention to provide an ap paratus for the manufacture of wood fiber panels by the dry process, wherein the thickness of the fibrous cushion to be pressed into a panel, may be controlled as desired across the width of the cushion, so as to be perfectly uniform, or even reinforced along the edges thereof.
A further object of this invention is to provide an apparatus of the kind above referred to, wherein" the negative pressure which realizes the fibrous cushion on the conveyor band may be adjusted as desired along the length of this cushion, and also across the width thereof, if required.
SUMMARY OF THE INVENTION In accordance with the present invention in an apparatus for the manufacture of wood fiber panels by the dry process, of the kind comprising a pervious conveyor band supported by the perforated upper side of an air chest in which a negative pressure is maintained, and pneumatic conveying means to The air chest may be internally divided into a number of chambers in the longitudinal and/or in the transverse direction with respect to the advance of the conveyor band, means being provided whereby the negative pressure may be adjusted as desired in each chamber.
BRIEF DESCRIPTION OF THE DRAWINGS In the annexed drawings:
FIG. 1 is a transverse section of an apparatus according to the invention for the manufacture of panels of wood fibers.
FIG. 2 is a longitudinal section taken through line II-II of FIG. I. the plane of section of FIG. 1 being indicated by line H.
FIG. 3 reproduces to an enlarged scale a detail of FIG. 2.
FIG. 4 is a section taken along line lV-IV of FIG. 3.
FIG. 5 is a view similar to FIG. 3, but illustrating a slightly modified arrangement.
FIG. 6 is a horizontal section taken along line Vl-VI of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus illustrated in FIGS. l and 2 comprises a downwardly-diverging pyramidal inlet chamber or hood I the upper end of which is connected with the conveying conduit 2 through which the airstream loaded with wood fibers is supplied to the apparatus. The lower end of chamber 1 opens into a distributing box 3 of substantially rectangular cross section, a highly flexible seal 4 being interposed between box 3 and chamber 1 in order to permit the former to vibrate substantially freely. An air chest 5 is disposed below the lower end of box 3, the horizontal upper side of this air chest being formed with perforations 5a. A pervious conveyor band 6, as for instance made of wire gauze, slides on this perforated upper side. For the cleamess of the drawing conveyor band 6 has been illustrated in FIGS. l and 2 as slightly spaced from the upper side of chest 5 while it is actually in contact therewith so as to be slidably supported thereby. Band 6 moves from right to left in FIG. 2. As shown the vertical walls of air chest 5 extend upwardly above the perforated upper side thereof and they are connected in an airtight manner with the lower edge of the distributing box 3 by means of another highly flexible seal 7 similar to the above-mentioned seal 4.
Each of the vertical walls of box 3 which extend transversely with respect to conveyor band 6 is formed with an elongated horizontal slot 3a (FIGS. 1 and 3).
A number of vertical streamlined air-guiding blades 8 are disposed within box 3, each being carried by a longitudinal rod 9 the protruding ends of which are passed through slots 3a and carry blocks 10 which are secured thereto in any appropriate manner, not indicated in FIGS. 2 and 3. Each of the transverse walls of box 3 carries a guide formed of two parallel U-shaped sheet iron members 11 which define a gutter in which blocks 10 are slidably retained. This gutter is closed by a flat lateral cover 12 which forms a substantially tight seal.
With this arrangement blocks 10, and therefore blades 8, may be disposed at any position desired across the width of the perforated band 6 in order to determine intermediate air passages of variable cross section. By disposing blades 8 closer to each other above the central portion of he band than above the edges thereof, as illustrated in FIG. 1, it is possible to obtain a uniform distribution of the fibers in the fibrous cushion which issues from the apparatus.
Blocks It) may be fixed at the desired position in any appropriate manner. In FIGS. 3 and 4 the upper U-shaped member 11 has a series of holes lla which may selectively receive a screw 13 screwed into each block 10. Holes 11a are quite close to each other and those which are not used may be plugged.
In the modification of FIG. 5 blocks 10 are slidably mounted on a rod 14 and each has a setscrew 15, cover 12 being easily removable to permit access to screws 15. The ends of rod 14 are appropriately secured to U-shaped members 11.
The air chest 5 is provided with a narrow horizontal inlet 5b (FIG. 2) for the conveyor band 6 and with a corresponding outlet 50 in the form of a rectangular nozzle. The upper side of this nozzle, which has been illustrated as rigidly secured to the remainder of the air chest is preferably hingedly supported and may be adjusted at will in accordance with the thickness of the fibrous cushion A formed of the conveyor band.
Vibrators 16 are secured against the outer side of the lateral walls of box 3.
The inner space of the air chest 5 below the perforated upper side 5a thereof is divided into eight individual chambers by a transverse partition 5d and by three longitudinal partitions 5e. These chambers are individually connected to one of two suction lines 17 by valves 18, each line 17 being in turn connected with a suction fan 19. By appropriately adjusting valves 18 it is thus possible to control at will the negative pressure within each chamber and to obtain a uniform fibrous cushion issuing from the apparatus.
The general operation is as follows:
The previous conveyor band 6 advancing in the direction of the arrow in F*G. 2, the air loaded with impregnated wood fibers issuing from the conveying conduit 2 is distributed across the width of suction box 3 by blades 8. If the latter are appropriately adjusted (FIG. 1) the tendency of the airstream to flow preferentially in the central portion of the width of the box may be obviated. if a finer adjustment is required, it may be'obtained by acting on the valves 18 corresponding to the lateral chambers of the air chest 5. The vibrations imparted to the section box 3 prevent the formation of fibrous plugs between the successive blades 8 or between the outer' blades 8 and the walls of box 3. As to the distribution of the wood fibers along the length of the cushion, it may be controlled by acting on valves 18 so as to increase the negative pressure in the four chambers of air chest 5 which are situated at the left of transverse partition 5d. The thickness of fibrous cushion A may thus increase regularly between inlet 5b and outlet 5c as this is desirable for obtaining good results.
As this is conventional in the dry process the cushion formed on conveyor band 6 is thereafter pressed between heated platens.
1. An apparatus for use in the manufacture of panels from fibers impregnated with a binder, comprising:
a longitudinally movable pervious conveyor band;
an air chest having a perforated horizontal upper side in sliding contact with said conveyor band;
means to maintain a negative pressure within said air chest;
means on said air chest to define above said perforated upper side thereof a closed space having an inlet and an outlet for said conveyor band;
a plurality of substantially vertical and parallel spaced airguiding blades disposed side-by-side within said closed space at a distance above said conveyor band, said blades extending substantially longitudinally with respect to said conveyor band and said blades defining a plurality of intermediate passages; and means connected to said closed space above said blades to supply to said space an airstream loaded with fibers impregnated with a binder, said airstream being uniformly distributed by said blades across the width of said conveyor band within said closed space and passing through said band and through the perforated upper side of said air chest, while the fibers entrained by said airstream are retained by said pervious band to form thereon a fibrous cushion which may thereafter be pressed into a panel. 2. In an apparatus as claimed in claim 1, said blades being adjustable in position across the width of saidconveyor band.
3. In an apparatus as claimed in claim 1, said blades having a streamlined cross-sectional profile.
4. In an apparatus as claimed in claim 1, each of said blades having two ends and having at each end a longitudinally protruding rodlike extension, said means to define a closed space above the perforated upper side of said air chest comprising two substantially vertical walls extending transversel with respect to said conveyor band and being each forme with an elongated horizontal slot, each of said extensions being passed through one of said slots, and said apparatus further comprising means exterior to said closed space to adjustably retain said extensions in position along said slots.
5. In an apparatus as claimed in claim 1, said means to define a closed space above the perforated horizontal upper side of said air chest comprising:
longitudinal and transverse walls extending upwardly around said upper side, with said inlet and said outlet being formed in said transverse walls;
an open-ended rectangular distribution box disposed above said longitudinal and transverse walls, with said blades being supported by said distribution box;
a first flexible seal interposed between said distribution box and said longitudinal and transverse walls;
a downwardly diverging hood above said distributing box, said hood having an upper end and a lower end, with said means to supply an airstream loaded with fibers being connected with the upper end of said hood;
a second flexible seal interposed between said distribution box and the lower end of said hood;
and vibrating means acting on said distribution box to vibrate same together with said blades.
6. In an apparatus as claimed in claim 5, said distribution box having transverse walls each formed with a horizontal elongated slot, each of said blades having two ends and having at each end a longitudinally protruding rodlike extension, each of said extensions being passed through one of said slots, and said apparatus further comprising on each of said transverse walls of said distribution box means exterior to said box to adjustably secure said extensions in position across the width of said box and means to substantially prevent airflow through each of said slots.