US 3478791 A
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1969 A. ELMENDORF 3,478,791
METHOD OF FILLING OPEN DEFECTS IN VENEER Filed Aug. 21, 1967 2 Sheets-Sheet 1 INVENTOR.
ARMIN ELMENDORF m n W ATTORNEYS 1969 A. ELMENDORF 3, 78,791
METHOD OF FILLING OPEN DEFECTS IN VENEER Filed Aug. 21, 1967 2 Sheets-Sheet P FIG.2
ARMIN ELMENDORF zmwof w ATTORNEYS United States Patent O 3,478,791 METHOD OF FILLING OPEN DEFECTS IN VENEER Armin Elmendorf, 56 Granada Court, Portola Valley, Calif. 94025 Filed Aug. 21, 1967, Ser. No. 662,104 Int. Cl. B27d 5/00; B05c 3/132 US. Cl. 144310 Claims ABSTRACT OF THE DISCLOSURE A method of filling open defects in veneer in which veneer strips are stress-relieved and assembled into a continuous band, the width of the band being equal to the length of the strips, moving the b and in- 'a direction across the grain of the veneer, forming discrete particles composed of a filler and a binder having tack, assembling the coated particles in a loose mass, bringing the veneer into contact with this mass, withdrawing part of the mass into the open defects by suction, and shearing this part out of the parent mass while maintaining suction. The problem of sliding friction between two foraminous surfaces is eliminated by use of a single foraminous surface in the form of a rotating cylinder, and holding the veneer on the cylinder by suction. The filler portion of the particles can be mineral granules or comminuted ligno-cellulosic particles. Particles are removed from the surface of the veneer between the holes as the veneer emerges from the loose mass. The contents of the holes are then compacted under heat and pressure in a continuous operation.
Due to the fact that the large trees of virgin timber of the softwood plywood industry have been substantially depleted there has been a progressive reduction in the quality of the logs now being peeled into veneer. The second growth timber which must now be used is relatively small and numerous branches extend out from the bole of the tree. These result in many knots in the veneer of which a large part falls out in drying the veneer. Many splits develop that must be clipped out and the resultant narrow strips of veneer must then be reassembled into larger sheets. This procedure is not only costly in labor but it results in a large loss of veneer. Knot holes are objectionable in the faces of plywood as well as in the inner plies. In the inner plies the holes may be seen on the edges of the panel where they must be filled by the user or they must be filled with veneer patches before the veneer goes through the glue spreader to receive the adhesive. A large part of the manufacturing cost of plywood consists in the cost of clipping out splits and then reassembling the veneer, and in patching knot holes with veneer patches after the veneer has been dried.
Knot holes that appear in the outer plies of plywood are sometimes filled with putty-like pastes spread on manually. The resultant filling must then be dried. All of this is time-consuming and costly. Filling large knot holes in veneer manually with putty-pastes is not practical because the pastes sag and fall out. The purpose of the present invention is to fill all open defects such as knot holes and splits mechanically in a matter of seconds, while the veneer is moving, and in such a manner that upon emerging from the filling machine the veneers may be coated with adhesive immediately. The filling must furthermore be done in such a manner that the fill is firm and hard at the end of the process, so firm that it will not compress or soften when subjected to pressure in the plywood press, yet not so hard that it cannot be readily cut with a saw. A clean veneer surface free of all extraneous materials must be provided between the filled defects. The filling must be flush with the surface 3,478,791 Patented Nov. 18, 1969 of the veneer, and should not require sanding. These requirements are all met by the present invention.
The edges of the rotary-cut veneers used in the plywood industry must first be clipped or jointed so that they are parallel. It is customary in the industry to apply the adhesive to both sides of individual strips of the veneer of various widths and to assemble the freshly coated veneers manually in combination with the uncoated veneers, the assembly being then transferred to the plywood press. Assembling the separate strips of veneer in this manner results in many gaps between the veneer edges. These are objectionable and unsightly as they show as holes on the edges of the completed panel. A further purpose of the present invention is to eliminate such gaps. By filling all open defects in the veneers used for the inner plies and eliminating gaps, a completely sound panel is obtained. Such a goal is highly desired by the plywood industry, and the resultant upgrading has long been sought.
Several methods have been proposed for filling knot holes and splits in veneer but each of these has inherent liabilities or objections. One of the purposes of the present invention is to overcome the difficulties experienced in the prior art of filling open defects in veneer.
One of the early methods resorted to for filling knot holes and splits is to apply l3. paste-like putty such as plastic wood to the openings using a blade for spreading the putty. As low-grade veneers generally containg many open defects, manual filling with putty-like compositions is not practical. Such compositions also involve some kind of a solvent which must be allowed to evaporate and this, in turn, results in shrinkage, necessitating the reapplication of the filler to obtain a surface that is flush with the veneer surface. Paste-like compositions may therefore require subsequent sanding to remove the paste unavoidably spread on the veneer surface around the opening.
Several methods have been proposed for drawing lignocellulosic particles and a binder into open defects in veneer by means of suction. One such method is suggested in US. Patent 2,774,556 in which comminuted particles and powdered resin are used. The powdery mixture of particles and binder is carried in an air stream over the surface of the veneer and some of'the particles are drawn into the holes from the air stream. In this system the deposition of the filler tends to build up a rim around the edges of many holes which impairs the quality of the filling and may require subsequent sanding or scraping of the veneer surface. Due to unavoidable w aviness or distortions in the veneer, the veneer will bulge away from the support and dry fines of the mixture will drift into the gaps so formed. This accumulation also aggravates the problem of cleaning the wire screen used to support the veneer. The present invention eliminates this problem.
Another method proposed for filling open defects in veneer by suction is that illustrated in US. Patent 3,155,- 55 8. In this method a crust is formed by heat on the plug of particles in the defect while the veneer is suspended. A thermo-plastic resin and a suitable extender such as Douglas fir bark powder are preferred. The extender and the resin are first fused together and then ground to form particles similar to ground coffee. The thermo-active particles of this method are propelled upwardly from beneath the veneer to be drawn into the holes by suction and are held there by suction. As resins that soften in the presence of heat became sticky they rapidly accumulate on the surface upon which the freshly filled veneers are deposited. Paper faces are introduced to solve this problem. These keep the sticky veneers from contacting the supports. One of the purposes of the present invention is to eliminate the need for paper faces. Paper layers cannot be tolerated between veneers in a plywood panel.
Another serious problem encountered in both of the methods described for filling knot holes by suction lies in the fact that the veneers must be transported on a wire screen, and the screen, in turn, must move over a foraminous surface. If any appreciable suction is introduced, friction is generated between the wire screen and the foraminous surface. This limits the intensity of the suction. Unless the suction is low, excessive pulls are required to draw the screen over the foraminous surface. One important purpose of the present invention is to eliminate such friction thereby making possible much more intense suction. Only one foraminous surface is required in the present invention and the veneer remains in contact with this surface. There are no sliding surfaces.
Another purpose of the present invention is to facilitate the mechanization of glue spreading by standardizing the size of the sheets that go through the glue spreader. The usual narrow strips of veneer are held together edge to edge by an adhesive or by means of fiat strings, and the band of veneer so formed, with the defects filled is clipped to a standard width. Veneers of a fixed size can be handled mechanically through the glue spreader. Filling of the openings while the veneer moves in a direction across the grain as a continuous connected band of strips therefore facilitates mechanization at the glue spreader.
The filler of the present invention may be made of ligno-cellulosic particles such as sawdust, or it may consist of fine mineral granules derived from a soft stone such as limestone, bonded together with a binder that is activated by heat. Sand may not be used because its presence in the filler quickly dulls the saw when the filled veneer is made into plywood and the plywood is cut with a power saw. With sand, dangerous sparks are thrown out by the saw. The hardness of the stone from which the comminuted particles are derived should be less than 6 on the Mohs scale.
If mineral granules are used the particles consist of the granule, a binder, and moisture, the moisture being present in an amount of not less than about 3% nor more than about 12% of the weight of the granules, with resin binder of at least 10% of the dry weight of the granules. With ligno-cellulosic particles the moisture content of the binder may range from about 15% to 40%, when using at least 10% of thermo-setting resin based on the dry weight of the particles. It is the presence of moisture in the binder in about these amounts which gives the binder the desired tack and makes the process possible. The moisture results in giving the binder holding power to hold the particles together like damp sand squeezed in the hand. The term tack is here used to apply to similar holding of particle to particle under light pressure. When the particles have tack they may still be separated and assembled as a mass of discrete particles without sticking together as a solid lump. In no case shouldthe filler introduced into the holes be liquid or paste-like, nor may it be completely free of moisture.
The binder-coated particles must be discrete and when assembled as a mass they must be readily separated. Small nodules of mineral granules are readily obtained when the mixture of particles, binder, and moisture is forced through a sieve. For example, good results are achieved when limestone granules that pass through an 80-mesh screen are mixed with 10% phenolic resin, and moisture, based on weight of granules, and the mixture is forced through a flour sieve.
Either thermo-setting or thermo-plastic binders may be used, with either mineral granules or ligno-cellulosic particles such as sawdust or sanding dust, as long as the particles when assembled as a mass remain discrete. Care should be taken when using mineral granules that the nodules do not dry excessively while they are being formed. If a powder-like mass results with mineral granules due to drying, moisture must be added by humidifying the ambient air or by moistening with a fine spray. Danger of drying is less likely to be incurred with lignocellulosic particles because such particles are hygroscopic and retain moisture under normal atmospheric conditions.
The method of the invention will be readily understood by referring to the drawings in which:
FIGURE 1 shows an elevational sectional view of one form of apparatus in accordance with the present invention in which suction is provided on the inside of a rotating cylinder and the veneer is fed to and away from the cylinder from the same side of the machine.
FIGURE 2 shows an elevational sectional view of another embodiment of the invention in which suction is provided in part of the inside or concave area of a rotating cylinder and the veneer is fed to and taken away from the cylinder from the same side of the machine.
FIGURE 3 shows an elevational sectional view of another embodiment of the invention in which suction is provided in part of the area on the inside of a rotating cylinder and the veneer is fed to and taken away from the machine in the same direction.
Having produced discrete resin-coated tacky particles, the next step is to assemble such particles in a loose stationary mass and to bring the veneer into contact with this mass. One method for achieving the desired results is illustrated in FIGURE 1 in which the veneer 1 containing knot holes 2 is brought in contact with the curved foraminous surface of a rotating cylinder or drum 11. Suction is provided around half the perimeter of the concave surface of the cylinder 11, the other half being encased in a rigid chamber 12 from which the air is withdrawn so that the vacuum outside the cylinder in this half is about the same as that on the inside. The veneer 1 comes in contact with the cylindrical surface of the drum 11 and then moves with the cylindrical surface. The air pressure holding the veneer against the cylinder 11 starts at 3 and ends at 4. The stationary mass of discrete tacky particles is shown at 5 along the curved surface of the drum 11 and this mass is maintained at a constant level by any conventional means such as an electric eye, not shown. The means for feeding fresh particles into the trough 9 to replace those drawn 01f does not constitute part of the invention. The veneer 1 is brought into contact with the stationary mass of discrete particles 5 in the trough 9 as shown. As a hole in the veneer reaches the trough 9 containing the mass of discrete binder-coated particles it is instantly filled with particles carried into the hole by the air stream going through the hole. The air which is drawn through the openings in the veneer and through the perforations of the drum 11 carries with it some of the particles removed from this mass.
The mass of particles in the hole is pulled out and sheared off the parent mass. When it emerges from the parent mass it is considerably thicker than the thickness of veneer. The excess above the optimum thickness is removed by a cut-off brush 6 which projects the excess particles back into the trough. The air pressure on the veneer continues while this takes place as it does while the filler in the opening is being subsequently compacted by a roller 8. While a rotating brush or a rotating series of radially mounted blades is preferred to remove the surface particles to obtain the desired thickness of filling, an oscillating brush may be used. A soft oscillating brush 7 may also follow a rotating cut-off brush as shown in FIGURE 1.
The veneer moves toward the machine on the infeed side and away from the machine at the out-feed end. The seal between the atmosphere and the vacuum in the chamber 12 is provided at 13'. The air may be pumped out by means of the fixed tube 14 at the center of the cylinder.
One of the unexpected features of the invention lies in the fact that the particles do not adhere to the surface of the veneer but rather readily slide off. As the particles removed by the brush 6 also fall down and into the loose stationary mass, the method eliminates the need of any mechanism for transferring the removed particles back into the system.
On account of the tack of the binder on the particles they pack together under suction and subsequently under the pressure of the compacting roll 8 and remain in place as a damp flat plug when the veneer leaves this suction zone. Due to the tendency to spread out laterally under the pressure of the compacting roll 8 the plug is held in place on the rim of the hole. It does not adhere to the roll. On leaving the compacting roll, the plug expands slightly so that its surface is above that of the veneer. The veneer with the openings filled in this manner then proceeds to the hot press, which may be a pair of steel belts moving between pressure rolls. There the plug is compacted under heat, and the binder is set sufficiently Well to be hard to the touch and hard enough to remain in place when the veneer goes through the glue spreader. The specific means for hot pressing the filler does not constitute part of the invention, as various means may be used.
The presence of moisture improves the packing under heat and pressure, and the clean surface of the veneer around the filled holes eliminates troublesome cleaning by mechanical means.
Both thermo-setting and thermo-plastic binders may be used as will be seen from the following examples:
Example I: Air-dry sawdust which has been screened to pass through a 10-mesh screen and of which about 50% is retained on 2'0-mesh is mixed with Amres resin No. 255-A using 40% resin on the dry basis and 25% moisture based on the dry weight of the particles. The resultant coating provides the desired tack on the particles, and the particles remain discrete.
Example II: Polyvinyl acetate adhesive, PVA resin 1287, 40% liquid basis is mixed with the particles screened out as in Example I. The coating provides the desired tack without destroying the discreteness.
Example III: Limestone, which has been crushed to pass through an 80-mesh screen, is mixed with 10% cascophen HP-403 based on the weight of the limestone, plus 6.5% water, also based on the weight of the limestone particles. When thoroughly mixed a damp-sand-like consistency is obtained.
FIGURE 2 shows means that are substantially similar to those of FIGURE 1. The air is withdrawn from the half of the cylinder 11 to the left of the partition 17 through the central tube. The seal 18 at the ends of the partition exerts very little pressure on the cylinder and results in very little friction. The oscillating brush 7 of FIGURE Imay be used in place of the rotating brush 19 or in addition to it. In addition, a soft oscillating br-ush may be used to remove loose particles from the plug and from the veneer at the edge of the plug.
The means of FIGURE 3 differs from that of FIGURE 2 in that the veneer entering the filling machine moves in the same direction as the veneer leaving the machine. The veneer is preferably stress-relieved by mechanical means such as shown in US. Patent No. 2,974,697 in order to make it more flexible so that it can be more readily bent around a cylinder 20 thereby greatly reducing the diameter of this roll as well as the diameter of the main cylinder 22. The lower edge of the trough 23 contacts the cylinder or roll 20 and effectively prevents escape of the particles.
I claim as my invention an improved method of upgrading veneer having open defects such as knot holes and splits by filling the openings as follows:
1. The method of filling open defects in veneer which includes the following steps,
assembling strips of veneer into a continuous connected band, the width of the band being equal to the length of the strips,
moving the band in the direction across the grain of the veneer,
bringing the veneer into contact with a stationary loose mass of discrete binder-coated particles having tack, withdrawing part of the mass into the openings by suction,
shearing this part from the parent mass while maintaining suction,
and compacting the filler in the openings under heat and pressure.
2. The method of filling open defects in veneer which includes the following steps,
forming discrete particles composed of a comminuted filler coated with a binder having tack,
assembling the coated particles in the form of a loose mass,
bringing the veneer into contact with this mass,
sucking part of the mass into the openings,
shearing this part from the parent mass, while maintaining suction, in such a volume that in leaving the parent mass it projects above the surface of the veneer,
compacting the mass in the openings under heat and pressure.
3. The method of filling open defects in veneer which includes the following steps,
providing suction on the concave side of a rotating foraminous cylindrical surface, bringing veneer containing open defects into contact with the convex side of the cylindrical surface, with the grain of the veneer parallel to the axis of the cylinder and holding it on the surface by suction,
bringing discrete binder-coated particles having tack into contact with the veneer, and drawing particles into the openings by suction.
4. The method of filling open defects in veneer which includes the following steps,
providing suction on the concave side of a rotating foraminous cylindrical surface,
bringing veneer containing open defects into contact with the convex side of the cylindrical surface, with the grain of the veneer parallel to the axis of the cylinder and moving it with that surface,
while being held on the rotating cylindrical surface moving the veneer into contact with a stationary mass of loose discrete particles coated with a binder having tack,
removing particles from the stationary mass into openings in the veneer by suction,
while the opening is submerged in the stationary mass,
shearing the mass of particles in the openings from the stationary mass, in sufficient volume so that a particle protrusion remains above the veneer on leaving the stationary mass,
removing particles from the surface of the mass in the openings by projecting them back into the stationary mass.
5. The method of claim 4 with the additional step of sliding particles from the surface of the veneer adjacent to the openings while the mass of particles in the openings is being withdrawn from the stationary mass and allowing the particles removed from the surface of the veneer to fall by gravity into the parent stationary mass.
6. The method of claim 4 wherein the suction is applied to only part of the inside surface of the cylinder,
and the veneer is removed from the cylindrical surface after leaving the zone of suction.
7. The method of claim 4 wherein the particles are removed from the surface of the mass of particles protruding above the veneer in the openings by brushing them in a direction at right angles to the tangential direction of the movement of the veneer and allowing the removed particles to fall back by gravity into the stationary mass.
8. Apparatus for filling open defects in veneer com prising:
a member having a foraminous cylindrical surface;
means for mounting said member for rotation;
means for producing suction within at least a portion of said member to draw air through said cylindrical surface;
means for directing veneer with open defects into contact with said cylindrical surface on the convex side thereof for movement of said veneer with said cylindrical surface; and
means for holding a plurality of binder-coated particles in the form of a loose mass with the holding means being positioned to place the particles in contact with the veneer when the latter moves with said cylindrical surface.
9. Apparatus for filling open defects in veneer comprising:
a drum having a foraminous cylindrical surface;
means for rotatably mounting said drum;
means for producing suction within one portion of said drum to draw air through at least a portion of said cylindrical surface;
means for directing veneer with open defects into contact with said portion of said cylindrical surface during rotation of said drum with the grain of the veneer parallel to the axis of the drum for movement of said veneer with said cylindrical surface;
means for positioning discrete binder-coated particles on the convex surface of the veneer when moving in contact with said cylindrical surface; and
means for removing at least certain excess particles projecting above the convex surface of the veneer.
References Cited UNITED STATES PATENTS 2,368,172 1/1945 Taber 117-2 XR 2,770,556 11/ 1956 Grangaard et a1 1172 2,860,597 l1/l958 Works et a1 117-2 XR 2,888,359 5/1959 Jorgensen et al 117-2 3,011,903 12/1961 Clock et a1. 15694 3,043,738 7/1962 Demeter et al l56-229 3,084,661 4/1963 Roberts l1850 3,155,558 11/1964 Clapp 15694 3,165,432 1/1965 Plaskett l56244 GERALD A. DOST, Primary Examiner US. Cl. X.R.