US3490974A

US3490974A - Method and means for forming plural elongated strips of veneer into an endless ribbon

Info

Publication number: US3490974A
Application number: US569999A
Authority: US
Inventors: Elmer H Jacobson
Original assignee: VANCOUVER PLYWOOD CO
Current assignee: VANCOUVER PLYWOOD CO
Priority date: 1966-08-03
Filing date: 1966-08-03
Publication date: 1970-01-20
Anticipated expiration: 1987-01-20

Description

E. H. JACOBSON AND MEANS FOR FORMING PLURAL ELONGATED STRIPS METHOD Jan; 20, 1970 OF VENEER INTO AN ENDLESS RIBBON 2 Sheets-Sheet 1 Filed Aug. 5, 1966 Elmefhicl'acobsbn INVENTOI? ,Jan. 20, 1970 E. H. JACOBSON 3,490,974

METHOD AND MEANS FOR FORMING PLURAL ELONQTATBD STRIPS OF VENEER INTO AN ENDLESS RIBBON Filed Aug. 5, 1966 2 Sheets-Sheet 2 h f ll:Il:1 5 &

Elm HJacobson INVENTOR United States Patent US. Cl. 156-166 6 Claims ABSTRACT OF THE DISCLOSURE Wood veneer core suitable for plywood panel layup is formed in a continuous web by joining narrow veneer strips together in tight edge-to-edge relationship with a plurality of spaced strings laid transversely of the strip lengths and secured with adhesive. The adhesive is of the water-dispersion type which, after being coated in dilute solution form on the string, is rendered plastic and tacky by heat applied through a roller drum at the point of application of the string to the veneer surface, and is thereafter set by drying. After the point of its application by the heated drum the string is subjected to an air stream for drying the adhesive and the string is compressed and flattened onto the veneer surface by a small roller wheel.

This invention relates to a method, and to a machine, for forming plural strips or pieces 'of veneer into an endless ribbon which is thereafter cut into predetermined lengths and placed between face and back veneer sheets to produce sheets of plywood. During the last several years the art of edge gluing pieces of veneer to form face and back sheets has progressed to such a degree that it is now more or less a standard practice. Thus the two external pieces of a sheet of plywood may be handled as units. The are has experienced great difliculty in forming pieces of veneer for core stock so that they may be thus handled and the common practice is to lay them manually side by side in a stack made up of plural plies and after they have had glue applied to their faces, to press-them together until the stacked sheets are adhesively bonded. The adhesive commonly used is some type of a synthetic resin.

The difliculty involved in forming core stock into an endless ribbon is partly mechanical and partly economic. Pieces of core stock contain knotholes, pitch seams and splits so that it results in a sheet that is quite fragile. If it is tied together or edge jointed, the amount of work involved prices plywood with sheet core stock out of the market. The plywood market is highly competitive.

I am familiar with US. Patent No. 1,977,199, that issued Oct. 16, 1934, to George H. Osgood and entitled Art of Making Crossing Sheets of Plywood Panels. This patent was directed to the art of making plywood panels for doors and other uses. Osgood teaches the use of tape or string as flexible tying material for binding sheets of veneer into a ribbon. If tape is used, it is of a type covererd with glue which must be moistened and then applied immediately in place in a sheet of plywood. If string is used, it was laid upon a narrow band of glue applied to a face of said piece of veneer making up the pieces into ribbon form. During the 30 odd years that has elapsed since the granting of the Osgood patent, many efforts have been made in the industry to use some type of flexible tying device of this character, but all efforts have been unsuccessful in commercial practice. During the last several years I have endeavored to provide a practical means of securing plural pieces of veneer into 3,490,974 Patented Jan. 20, 1970 a ribbon by the use of longitudinally arranged strings, tapes, monofilament lines or woven shoelacelike material.

If a length of thread, a cord or line is fed from a supply, usually comprising spindles, which then passes through a glue pot, or modifying container for monofilament lines, and a surface application is made, it transfers adhesive to the guides even though they are covered by Teflon (polyetrafluor-ethylene)-coated surfaces. If a resin-type of adhesive is used, it produced good initial bonding, but it produced a hard brittle external sheathing that fractures and mechanically breaks and thus loses its bond.

I have now determined that it is necessary to apply the adhesive or modifying agency while it is in a very liquid state so that it will impregnate the surface of a cord or thread or will soften the surface of a monofilament line. In this state of fluidity it will not transfer to and build up upon the guides, but it has insuflicient adhesive power to serve the purpose of tying the sheets of veneer together into a ribbon of core stock. For example, if a water-soluble glue is used, the concentration of adhesive is thinned out with excess water to a point where it produces good penetration and transfer from the glue pot to the string but produces insufficient adhesive deposit upon the surface of the string.

I have discovered that if this dilute adhesive is applied at a point distant from the point of application and if it is thereafter heated to temperature substantially above room temperature, it will become dehydrated and be rendered quite tacky. Then when adhesive, as thus modified and rendered viscous and tacky, is immediately applied to the surface of the abutting veneer sheets, it will be bonded with suflicient adhesive power to serve its intended purpose.

I have also determined that rollers of small diameter must be used for stripping the adhesively coated lines from the heating roller and applying said lines under high compression to the surfaces of the sheets of core stock making up the ribbon. This pressure must be of sufficient intensity to flatten substantially the coated flexible tying member so that it appears as a tape rather than a string of circular section, if viewed under magnification.

My invention thus is embodied in a new method, and a new machine, in which lengths of veneer are formed into an endless ribbon which is produced by feeding a plurality of elongated strips of veneer cross-wise of the path of flow and in edge-to-edge contact to form a ribbon of indeterminate length while it passes through a conveyor-type press. While it is in said press, plural spaced courses of flexible tying material are applied over the upper face or the two opposed faces of a ribbon of veneer strips cross-Wise of the veneer and lengthwise of said ribbon. Somewhat in advance of said application of flexible material to a ribbon of veneer thus being constructed, the tying materials have applied thereto a dilute solution of adhesive sufficient to coat and impregnate the external surface of said tying material. Immediately prior to the point of application, heat at temperatures substantially above room temperatures is employed to dehydrate the dilute adhesive and cause it to be concentrated into a tacky plastic consistency. While at said elevated temperatures and at said consistency, it is applied by the heated rollers to the surface or surfaces of the ribbon thus being made. Due to such tackiness, I have discovered that said tying material will tend to adhere to the heated rollers to some degree, and thus make an imperfect bond with the surface or surfaces of the plywood. To perfect said bond, I arranged one, or a plurality of, small diameter rollers which strip the string from the heated roller and apply it under substantial pressure to the surface or surfaces of the ribbon thus being constructed. Immediately after said final bonding I preferably direct a fluid such as a jet of air which cools the adhesive and improves the bond as it is being discharged from the press and before the ribbon is clipped into predetermined lengths.

Further details of my invention and the method or machine by which it is practiced are hereinafter described in greater detail with reference to the accompanying drawings in which:

FIG. 1 is a schematic section through a machine involving ribbon-forming conveyors, the thread coating and guiding mechanisms, the heating rollers, the small diameter stripping rollers that give the string its final bond to the sheet of core stock thus being formed, and two cooling jets for cooling and hardening the bonding for the flexible tying members in advance of the clipping operation;

FIG. 2 is an enlarged elevation of a glue pot and guides therefor by which adhesive in dilute form is applied to the flexible tying element some distance in advance of the point of application of a flexible tying member to the panels, portions of the pot are shown broken away to disclose details which would otherwise be concealed, and arrows are applied to said figure to show the direction of movement of the flexible tying member therethrough;

FIG. 3 is an elevation view of the mechanism illustrated in FIG. 2;

FIG. 4 is an end view of said pot with guide rollers shown by breaking away a portion of the pot to illustrate their arrangement and construction;

FIG. 5 is a plan view of a sheet of core stock made by my invention, showing the arrangement of the pieces of veneer with relation to each other in a sheet and tied by longitudinal cords of flexible tying material;

FIG. 6 is a greatly enlarged view illustrating, in somewhat schematic detail, the point of application of the flexible material to the upper and lower faces of a sheet of plywood by a pair of superimposed heated rollers of large diameter and followed successively thereafter by a pair of stripping rollers which lay the flexible tying members onto the face, or faces, of a ribbon of core stock under relatively high compression and over a restricted area of application, arrows indicating the direction of movement of the flexible tying material and the ribbon of core stock;

FIG. 7 is a still greater enlarged view showing the point of application beneath a stripping roller and the degree of compression is indicated to show how adhesive is forced into minute hairlike cracks in the surface of a sheet of core stock produced previously during the peeling operation; and

FIG. 8 is a schematic sectional view, taken on the line 8-8 in FIG. 7, showing how the tying material is flattened into a ribbon form and adhesive applied to the edge surfaces thereof so that the tying material resembles a tape rather than a cord or thread of circular section as it would appear under magnification before application to the plywood.

My invention is adapted to be practiced in a press through which a ribbon of veneer is to be made up of horizontal pieces arranged in more or less abutting edgeto-edge contact. Such a machine has a frame 10 defining a path of travel 11 therethrough. The path permits the ribbon to be formed while it lies flatwise and it is fed in from the lefthand side of FIG. I, and discharged off the righthand side thereof. The path of travel is defined by the opposed faces of conveyor chains 13-14 in which the lower infeed chain 13 extends to the left farther than the upper feed chain 14. This provides an exposed upper face on the lower chain which permits the feeder to watch the pieces of core stock being thus arranged. The pair of infeed chains 13-14 lead the ribbon thus formed between the opposed faces of an upper compression chain 15 and a lower compression chain 16. Infeed chains and the compression chains overlap, as is shown in FIG. 1, so.

that there is no tendency of the pieces of veneer to shift or move about or to move into overlapping relation with an adjacent one.

The compression chains feed the ribbons thus arranged between a pair of opposed guide plates 17-18 in which plate 17 is the uppermost plate. The infeed side of these plates preferably is flared somewhat to serve as a guide to ensure that the pieces of veneer stock move smoothly from the compression chains to between the guide plates 17-18. The guide plates 17-18 move the sheets of core stock between a pair of mated rollers in which the upper compression roller 19 and the lower compression roller 20 define a nip 21 between them. It is at this nip that flexible material is adhesively bonded to the core stock.

At the discharge side of a compression roller, and the nip between, are arranged related pairs of initial stripping rollers 22-23, of which 22 is uppermost of the related pair. Each of these stripper rollers is freely rotatable and is supported by a flexible arm in which the upper arm 24 carries the stripper roller 22 and the lower arm 25 carries roller 23.

Means are provided (not shown) for inducing a predetermined flexure in said arms 24-25 so as to cause the rollers to be pressed towards each other for a purpose later defined and with which my invention is particularly concerned. Secondary stripper rollers 27-28 are downstream, considered in connection with flow path 11, and these rollers are also freely rotatable and spring-biased towards each other similarly to the manner in which stripping rollers 22-23 are mounted. I usually provide greater spring-bias between the rollers 27-28, than between the rollers 22-23.

After the ribbon 37 passes the stripper rollers 27, the flexible strips of material are securely bonded to the opposed faces of the ribbon formed of strips of core stock 12. The ribbon is directed to the flared inlets edge of upper and lower outfeed guide plates 29 and 30, respec tively. A pair of mated feed rollers 31-32 engage the opposed faces of the ribbon 37 thus formed, and guide them between secondary outfeed guide plates 33-34, in which 33 is the upper guide plate and 34 is the lower guide plate. The ribbon then is fed under a clipper 35 to cut it into predetermined lengths and prior thereto the side margins are trimmed by a related pair of cutoff saws 35a. Each sheet of veneer, constituting core stock, is discharged from the clipper onto a discharge conveyor 36 in rectangular pieces of predetermined length and width so that they can thereafter be laid up in a sheet of plywood.

All of the foregoing is relatively old in the art except for the stripper rollers and no specific claim is made for the old construction.

As has been pointed out heretofore, flexible strips of tying material have been secured to the opposed faces of a ribbon of plywood in the past, but these efforts have been unsuccessful as far as I am advised. The causes of failure are many. The principal defect is that the strings are not bonded tightly to the opposed faces of the ribbon of core stock. In some cases the adhesive bond has been imperfect, either through lack of adhesion, or by reason of an adhesive bond that was brittle and fracturable under reverse flexure of the sheets thus tied together. One of the serious mechanical faults of prior art techniques is that precoating of the string (or similar flexible tying material) involves too much expense. On the other hand, if the string material is covered with fresh adhesive of proper consistency, loss by contact results.

The following is definitive of the advance that I have made in this art:

To be eflective and useful, it is necessary that sheets of core stock thus tied together must be relatively stiff so that they can be handled as sheets, rather than as plural pieces of core stock that are tied together by string. By making the core stock in sheets, as the face and backs are presently made, these can be laid up by being sandwiched between face and back pieces by mechanical stacking devices rather than by hand or manual lay-up.

I have determined that the string must be impregnated to a substantial degree with adhesive at a point somewhat in advance of its point of application upon the faces of the ribbon of core stock passing through the press. String should thus be relatively absorbent, and adhesive being applied thereto should be more fluid than tacky so that it can be absorbed by the string. Such string is normally purchased and used while it is in frusto-conic spindles 41. These are supported upon vertically supported pins 42 at the inlet side of a pan or container filled with adhesive. The string is fed from the spindle and guided by guide plates 43. The string is led obliquely downwardly, as is illustrated in FIG. 2, from the guide 43, beneath serrated guide roller 45, and is then led upwardly through a pair of mated guide rollers 46, preferably mounted on the upper edge of the pan or container 44. At this stage the adhesive is quite fluid and dilute. It then passes under guide rollers 47-48, respectively, to

compression rollers

19 and 20, respectively. These compression rollers are modified by having heating elements housed therein. Heating elements may be supplied with a combustible fuel such as air-fuel intermixture or a combustible gas, or may be heated by electrical resistance elements. In any event, heat is applied to the rollers 19-20 which are hollow, and the peripheral surfaces of the rollers are heated. The string with diluted adhesive carried thereby makes a partial turn about these rollers of about 270 of rotation, as is illustrated in FIG. 1. It leaves the rollers, respectively, at or slightly beyond the nip 21 where the upper and lower surfaces of the ribbon 37 are contacted.

During the passage of said adhesively-coated string from guide rollers 47-48, respectively, about their related compression and heating rollers, the moisture content of water soluble glue becomes dehydrated and the adhesive is quite tacky and of proper consistency and strength to bond the strings to the faces, respectively, of veneer.

This degree of tackiness is necessary to produce a good adhesive bond with the ribbon of veneer, but is disadvantageous because the string tends to adhere to the peripheral surface of the

rollers

19 and 20, respectively, past the nip 21, as is illustrated in FIG. 6. I have found that a pair of mated

stripper rollers

22 and 23 will strip the coated string from the rollers and press it tightly against the faces of the ribbon of veneer constituting the core stock. A first set of nozzles 50 is arranged to eject a blast of air over the strings thus pressed upon the opposed faces of ribbon of core stock and to dissipate the heat of the glue so that it will harden to some degree. Thereafter, another pair of stripper rollers 27-28, under greater bias force, roll the strings downwardly in the manner illustrated in FIG. 7. The compression thus exerted not only flattens the strings, as shown in FIG. 8, but tends to cause some of the adhesive to fill and thus bridge the gaps in the minute cracks of core stock produced when the wood is peeled from a log in a veneer lathe. This is illustrated, and exaggerated to some degree, in FIG. 7.

A second set of air nozzles 51 direct a cooling blast of air over the strings thus adhesively bonded. At this point the ribbon is a continuous sheet in that, in passage through successive pairs of

outfeed guide plates

29 and 30, and 33 and 34, under the action of the feed rollers 31 and 32,

it has gained suflicient strength to perform as a sheet. I

Thereafter it is trimmed by saw 35a that define the width of the ribbon and is clipped by transverse cuts 35 which define the overall length of the sheets cut from said ribbon.

Referring now to FIG. 5:

A sheet of core stock 37 preferably has applied to both upper and lower faces continuous lengths of tying material 38. This typing material must be flexible, be of minimal thickness or diameter and be inexpensive, but must also be capable of effecting a firm tie across the abutting edges of the strips of core stock 12 so that the edge-toedge abutment of the pieces is maintained. Some tension is developed in the cords constituting the tying material as applied to the ribbon of veneer stock, as is illustrated in FIG. 6. This is not of sufliciently high amplitude to tend to produce rupture, but is suflicient to maintain the edges of the strips in abutment when a sheet lies flatwise, at rest. Because the tying material is applied to both faces of the sheet of core stock, it is subject to tension if the sheet is flexed convexly as when it is not supported upon a plane horizontal surface; that is, the pieces of tying material upon the convex face of a flexed sheet are tensed and the tying material on the concave face is relaxed.

I have practiced my invention with various types of flexible tying material such as tight and loosely wound string or thread, woven or flattened tapes, lengths of monofilament synthetic resin and various vegetable fibers. Unfortunately, those that have better mechanical properties are the most expensive.

Inasmuch as core stock for veneer panels in jointed form must be competitive with those that are laid manually, economic limits must be observed. I thus have described my invention as used with a loosely Wound cotton string of such diameter and compressibility that it is readily absorptive of the adhesive material and of such bulk that it does not produce a major interruption of the glue line of the plies of panel laid up in a sheet of ply- Wood.

A string meeting these qualities is one somewhat more loosely woven than cotton grocery twine. It is normally procurable in spindles 41. There are used a number of spindles equalling the number of tying strips to be laid upon the face or faces of the piece of core stock. In FIG. 5 I have shown five courses. Two lie adjacent the edges of the sheet, one upon the longitudinal midline and one each intermediate the midline and the marginal courses.

In FIG. 1, I have shown but two spindles, but this is meant to be illustrative of a plurality.

One or more pairs of stripping rollers 2243 and 27-28 lay the cord tightly upon the faces of the ribbon of veneer 37. The small diameter of said stripper rollers 22-23 and 27-28 causes the tying material not only to be adhesively bonded to the opposed face of the ribbon of veneer 37, but also to have the adhesive coating forced into the veneer to a limited degree and to flatten the cord by mashing, as is illustrated in FIG. 8.

Link chains 52 in FIG. 1 show one means for mechanically driving the several parts and to keep them in synchronism.

I claim:

1. In the method for forming sheets of veneer into a continuous web of core stock for plywood panel layup comprising feeding a plurality of narrow strips of veneer While being held in tight edge-to-edge relationship to form a longitudinally-extending traveling web of crosswaysaligned strips and securing plural spaced courses of string material with adhesive to the major surfaces of said strips in direction parallel to said web travel, characterized by first applying to said string material a dilute solution of adhesive suflicient to coat and impregnate the external surface thereof, next heating said impregnated string material to an elevated temperature in order to dehydrate the dilute adhesive to a tacky plastic consistency, said heating step occurring immediately in advance of and at the point of application of said string to said web of veneer, and thereafter compressing said string material into a flattened band on the surface of said veneer web.

2. The method of claim 1 further characterized in that, after application of said string material to said veneer web surface, a stream of air is directed thereagainst in order to accelerate the drying of said adhesive.

3. The method set forth in claim 2 further characterized in that said impregnated string material is subjected to said airstream before there is any substantial flattening of said material by compression onto the surface of said veneer web.

4. In an apparatus for forming sheets of veneer into a continuous web of core stock for plywood panel layup comprising means for conveying a plurality of narrow strips of veneer while being held in tight edge-to-edge relationship to form a longitudinally-extending traveling web of crossways-aligned strips and securing plural spaced courses of string material with adhesive to the major surfaces of said strip in direction parallel to said Web travel, characterized by means for coating said string with a dilute solution of adhesive, a roller drum of relatively large diameter axially-aligned transversely to the direction of web travel and contacting a major surface of said web, said adhesively-coated string being Wound around said roller drum, said roller drum containing associated heating means for elevating the temperature of said adhesive coating in suflicient amount to dehydrate it to a tacky plastic consistency immediately in advance of and at the point of application of said string to said web'of veneer, and roller wheel means of relatively small diameter mounted transversely of said web travel direction and downstream from said roller drum, said roller wheel means contacting said web surface and said string carried thereon under heavy pressure for stripping said string away from said roller drum and onto said web surface and 8 for compressing said string into a flattened band thereon.

5. The apparatus in claim 4 further characterized in that means are provided for directing a stream of air against said string after its application to said web surface in order to accelerate the drying of said adhesive.

6. The apparatus of claim 5 further characterized in that said air stream means directs air against said string on said Web surface at a point on said Web travel prior to any substantial compression of said string into a flattened band by said roller wheel means.

References Cited UNITED STATES PATENTS 3,377,223 4/1968 Clausen et al. 156l66 1,977,199 10/1934 Osgood 156-466 2,290,761 7/1942 Miller 156304 2,772,717 12/1956 Ware 156-551 XR PHILIP DIER, Primary Examiner US. Cl. X.R.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,490,974 Dated January 20, 1970 Inventor(3) wimpy-J1 .Iarnhenn It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 40, "The are" should be The art Col. 2, line 9, "Teflon (polyetrafluor-ethylene)" should be Teflon (polytetrafluoroethylenl Col. 5, line 72, change "This typing material" to This tying material slam m QEMEP our 1 ED Edward H. Fletch, II

Gomissioner of Patents