US 3905329 A
Foamed liquid mixtures are applied to substrates, in particular foamed plywood glues are spread on traveling wood veneers in the manufacture of plywood, by a method comprising the following steps: The liquid is withdrawn from a source of the same and foamed. The foam is continuously extruded or otherwise spread on an intermittently moving substrate during the periods of motion of the substrate. The foamed liquid is continuously diverted from the substrate during the periods of rest of the substrate. The diverted foamed liquid then is defoamed and cycled back to the liquid source where it is mixed with fresh liquid. This makes possible applying a uniform spread of the foamed liquid on the substrate even though the motion of the substrate is started and stopped at frequent intervals.
Description (OCR text may contain errors)
United States Patent Cone et al. Sept. 16, 1975 54 APPARATUS F T UNIFORM 3,402,695 9/1968 Baker et al. 118/315 x 3,825,435 7/1974 Hunt 118/612 x APPLICATION OF FOAMED LIQUID MIXTURES TO SUBSTRATES  Inventors: Charles N. Cone, Portland; Julius M. Steinberg, Hillsboro, both of Oreg.
1731 Assignee: Pacific Adhesives Company, Inc.,
 Filed: Mar. 30, 1973 [21 1 Appl. No.: 346,630
 US. Cl. 118/602; 118/612; 118/411; 259/50 R  Int. C13". B05C 11/10  Field of Search 118/410, 411, 602, 603, 118/8, 315, 610, 612; 156/78; 259/50 R  References Cited UNITED STATES PATENTS 2,649,758 8/1953 Cowgill 118/602 3,347,206 10/1967 Schmidt-Salzmann 118/8 Primary Examiner-John P. McIntosh Attorney, Agent, or F irmEugene D. Farley 1 5 7 ABSTRACT Foamed liquid mixtures are applied to substrates, in particular foamed plywood glues are spread on travel ing wood veneers in the manufacture of plywood, by a method comprising the following steps: The liquid is withdrawn from a source of the same and foamed. The
I foam is continuously extruded or otherwise spread on an intermittently moving substrate during the periods of motion of the substrate. The foamed liquid is continuously diverted from the substrate during the periods of rest of the substrate. The diverted foamed liquid then is defoamed and cycled back to the liquid source where it is mixed with fresh liquid. This makes possible applying a uniform spread of the foamed liquid on the substrate even though the motion of the substrate is started and stopped at frequent intervals.
6 Claims, 5 Drawing Figures APPARATUS FOR THE UNIFORM APPLICATION OI FOAMED LIQUII) MIXTURES TO SUBSTRATES This invention relates to apparatus for the uniform application of foamed aqueous mixtures to substrates. it pertains particularly to apparatus for spreading foamed plywood glues on intermittently moving wood veneers in the manufacture ofplywood and is described herein with particular reference to this application. No limitation thereby is intended, however. since the apparatus is applicable with equal facility to other situations in which foamed liquid is applied to a substrate.
in the US. Pat. application of Charles N. Cone and Julius M. Steinberg, Ser. No. 80,961 filed Oct. 15, 1970 for PLYWOOD MANUFACTURE USING FOAMED GLUES, now abandoned, there is disclosed method and apparatus for making plywood by continuously propelling a liquid plywood glue in unfoamed condition at a predetermined flow rate, continuously foaming the glue as it is propelled, and continuously extruding or otherwise applying the foamed glue to the surface of wood veneers as they travel along a conveying system in the plywood mill assembly line.
This is accomplished by passing the unfoamed glue through an in-line foamer while maintaining the flow rate of the unfoamed and foamed glue substantially the same, on a unit weight of liquid glue per unit time basis. The veneers to which the foamed glue has been applied then are laid up into plywood assemblies and pressed into plywood panels.
This method has many advantages, including economy of glue use and uniformity of plywood product. In executing the method, however, it is important that the foamed glue be applied uniformly on the plywood veneers. Otherwise the strength and other properties of the finished plywood will be non-uniform and unpredictable.
Achieving a uniform spread of foamed glue on the surfaces of wood veneers traveling along a plywood production line is a result difficult of achievement. This is for the reason that the operation of the line, and of the mechanical veneer lay-up machines included in it, is intermittent. It is necessary to shut down the line from time to time for various reasons, including mechanical failures, interruption of veneer supply, disarrangement of veneers in the machine etc. The total down time of the line in a 24 hour period usually amounts to about 12%, or a little less than three hours. However, the interruptions are frequent. Each one lasts only a few minutes.
This characteristic of the operation of the plywood production line in turn means that the extruder or other foamed glue spreading device must be timed to stop and start with the line. At first sight it would appear that this might be accomplished through the agency of a simple control valve actuated by a limit switch or other agency associated with the production line. In fact, it is a matter which is quite difficult of accomplishment.
The control of the flow of foamed glue must be highly accurate. When the line stops, the flow of foamed glue must stop. When the line resumes, the flow of foamed glue must resume and continue at the same rate as when it stopped. Otherwise the spread rate will change.
Foamed liquids do not share the easily controlled flow characteristics of ordinary liquids. The rate of flow from the extruder is a function of the pressure within the extruder head. Therefore, in order to insure a constant spread rate, the pressure within the head must be maintained the same at all times.
Simply shutting off the flow to the extruder when the line stops and resuming flow when it starts does not achieve the desired result. Foamed liquids, and particularly foamed phenolic resin glue, have two characteristies that make it necessary to take special precautions if the same flow is to be secured instantaneously after flow cut off as existed before cut off. These are first, a high degree of resistance to flow and second, a high degree of compressibility.
Because of its high resistance to flow, a considerable amount of pressure is required to make the foamed glue move from the foaming unit where it is produced down the line and into the extrude r.
For example, in normal operation of such a unit, the pressure in the line at the discharge port of the foaming unit will be in the neighborhood of 70 pounds per square inch. However, because of the high resistance to flow of the foamed liquid, the pressure in the extruder will be only 510 pounds per square inch. This steep pressure gradient is maintained during operation of the line by the force exerted by the unfoamed glue being pumped into the foaming unit. I
If the foamed discharge from the extruder head is cut off and simultaneously the flow of unfoamed glue into the system also is cut off, the pressure gradient will disappear.
This occurrence is explained by the fact that at the instant of cut off the foam in the line near the foaming unit is more highly compressed than it is in the extruder head. It consequently will expand until the pressure is equalized. This means that after cut off the pressure inside the extruder head is higher than it was and the pressure in the foaming unit is lower than it was before cut off.
Because of this, when the operation of the line is resumed, the initial rate of flow of foamed glue from the extruder head will be much greater than normal. This then will be followed by a period of diminished rate of flow until the normal pressure gradient has been reestablished. This variation in flow in turn will be reflected in uneven application of the glue to the traveling veneers in the plywood production line.
Two solutions to the foregoing problem seem selfevident.
One is to shunt the non-uniform flow of foamed glue away from the extruder after cut off and discard it. This is not feasible first, because it is wasteful and costly and second, because there is no place to put the discarded glue except in the sewer, and this leads to serious ecology problems.
The other apparent solution is to recycle the nonuniform portion of the glue flow back to the storage vessel which feeds the foamer, and combine it therewith the raw feed. This expedient is unsatisfactory be cause mixing the foamed glue with the unfoamed glue changes the density of the latter so that the density of the mixture varies with time. This in turn makes nonuniform the amount of glue discharged from the extruder since the amount of foamed glue dispensed by the extruder on a weight basis per unit time is a direct function of the amount of glue pumped to it from the system. The latter amount in turn is a direct function of the glue density.
It accordingly is the general purpose of the present invention to provide apparatus for overcoming the foregoing problem and for applying foamed liquids uniformly to substrates, in particular foamed aqueous phenolic resin glues to traveling plywood veneers in a plywood mill production line.
It is a further object of the present invention to provide apparatus of the class described which is simple in concept and construction, easily included in the plywood line, easily and accurately operated and controlled, and relatively maintenance free.
In its broad concept, the present invention comprises an apparatus for accomplishing a method for the uniform application of foamed liquids to substrates which comprises the following steps:
First a source of foamable liquid is provided. The liquid is withdrawn from the source and foamed. The foamed liquid is spread continuously on an intermittently and relatively moving substrate during the periods of motion of the substrate relative to the foaming means employed.
The foamed liquid is diverted from the substrate during the periods of rest of the latter. The diverted foamed liquid then is defoamed and cycled back to the liquid in the original source of liquid.
Defoaming the diverted foamed liquid restores it to substantially its original density, i.e. the density of the unfoamed liquid in the source. As a consequence, the recycled defoamed liquid may be mixed with the raw liquid without adversely affecting its density and hence without adversely affecting the amount of liquid, on a weight basis, spread on the substrate.
In the drawings:
FIG. 1 is a schematic view in side elevation of a plywood production line including provision for applying foamed liquid glue uniformly to moving plywood veneers.
FIG. 2 is a schematic view in elevation, partly in section, of apparatus employed in the application of foamed liquids to substrates adaptable for inclusion in the production line of FIG. 1.
FIG. 3 is a view in front elevation, partly broken away and partly in section, and illustrating a defoaming unit which is a component of the apparatus of FIG. 2.
FIG. 4 is a fragmentary, detail sectional view taken along line 44 of FIG. 3 and FIG. 5 is a fragmentary side elevation of the defoaming unit of FIG. 3.
The production line illustrated schematically in FIG. 1 basically comprises the veneer lay-up line of a plywood manufacturing plant. It contains a foamed phenolic resin glue extruding unit, such as is described in the aforesaid patent application of Charles N. Cone and Julius M. Steinberg Ser. No. 80,961.
As illustrated in FIG. 1, the production line includes two wood veneer pre-heating lines running at right angles to each other and meeting at a common assembly As they waver along'the conveyer system including conveyer units 10, I2, 14 the core, back and center veneers are preheated with suitable heating units 24. Preferably these comprise infared heating units capable of heating the veneers to a temperature of from 200 to 400F. during their time of passage through the heating unit.
As they travel along conveyer system I6, face veneers 22 are preheated to the same temperature level by means of heating elements 26.
Foamed glue is applied to core veneers I8 and back and center veneers 20. The application is made to the upper surfaces only of these veneers. It is made by means of a foamed glue extruder positioned downstream from heater 24 and indicated generally at 28. The extruder applies to the veneers a coating of foamed glue 30 in a pattern determined by the size and dimensions of its extruding orifices.
No adhesive whatsoever is applied to the surfaces of face veneers 22.
At the assembly station, the core, back. center and face veneers are composited into a plywood panel assembly 32. This is combined with other panel assemblies to form a press load which is transferred into a press 34 and consolidated into plywood panelsv The press may be either a single opening or multiple opening hot press, or a cold press.
The plywood lay-up 'line described above also includes an electric limit switch 36 positioned adjacent extruder 28 with its sensing element in contact with the moving veneers. As will appear hereinafter. the limit switch is in an electric circuit with a valve controlling the flow of foamed glue through the extruder and coordinates the discharge of glue by the extruder with the intermittent movement of the veneers.
The hereindescribed apparatus is adapted for inclusion in a plywood line such as that described above. It comprises in combination a reservoir or feed source 40, of unfoamed liquid phenolic resin glue; a resin glue foaming device 42', an electrically operated valve 48; a foamed glue applicator or extruder 28', one or more foamed glue defoamers 54 in series relation to each other; and a raw glue storage tank 58; all interconnected by suitable piping including pumps adequate to circulate the fluid through the various conduit systems.
Reservoir 40 which serves as a working source of unfoamed glue comprises a storage tank of adequate capacity. It contains a quantity of unfoamed glue 64 and is fitted with a float-operated switch 66 which is worked by alterations in level of the glue contents of the tank.
Immediately downstream from tank 40 is a foaming unit 42. This has for its function converting the unfoamed glue, which has a density, for example, of from 1.0 to 1.1 to a foam having a density of, for example, 0.1 to 0.5, preferably 0.15 to 0.3 grams per cc.
The foaming unit comprises means for vigorously agitating the liquid glue with air or other foaming gas and has a structure suitable to accomplish this purpose. A preferred structure is described and illustrated in detail in the aforesaid patent application of Cone and Steinberg, Ser. No. 80,961.
The foaming unit 42 is supplied with air under pressure through an air inlet 68. It is supplied with unfoamed liquid resin glue from tank 40 by means of conduit 44.
The conduit includes a pump 46 which supplies the liquid drive for the system. The pump is of the positive displacement type. such as a gear pump. and delivers accurately metered quantities of liquid glue to the foaming unit.
Immediately downstream from foaming unit 42 is an electrically operated valve 48. This is a threcway valve which is fed by conduit 50, leading from foaming unit 42. It transmits the flow of foamed glue either to extrudcr 28 via conduit 52 or diverts it to the dcfoaming unit 54 via conduit 56. As noted above. it is adjusted between its two positions by means of limit switch 36.
the sensing element of which is positioned in contact with the moving veneers in the plywood lay-up line.
The extraction unit 28 has for its function extruding the foamed glue in uniform streams onto the upper surfaces of the plywood veneers positioned on a conveyer immediately below. It may be of various types but preferably comprises a unit such as is described in detail in the aforesaid patent application of Cone and Steinberg. Ser. No. 80.96I. In accordance with this disclosure, the foamed glue is pressure extruded through nozzles 70 in the form of ribbons, which are laid down in laterally spaced relation lengthwise of the traveling veneers. As noted. it is essential for the production of a satisfactory plywood product that the glue be thus deposited in metered quantity at a uniform rate.
Defoaming unit 54, which is immediately downstream from extrusion unit 28 and valve 48. receives foamed glue diverted be valve 48 from extrusion unit 28 and transmitted via conduit 56 into the deforming unit. It dcfoams the glue and returns it to reservoir 64.
The major portion of the make up of reservoir 64, however. is derived from a storage or holding tank 58. This communicates with feed tank or reservoir 64 via conduit 60. Conduit 60 includes a suitable pump 62 controlled by an electric circuit including float operated switch 66 in feed tank 64. It supplies fresh glue to tank 64, as required to meet the demands of the apparatus.
Although various types of defoaming units 54 may be included in the apparatus thus comprised, a novel and preferred type is illustrated in FIGS. 3, 4 and 5.
Basically the defoaming unit illustrated in these figures comprises a mill or beater having a design such that the foam is beaten under conditions which break up its component bubbles and separate the foam into a liquid phase and a gas phase. In viewv of the fact that under other conditions a beating action may be employed to create a foam, rather than to destroy it, it is of interest that defoaming, rather than foaming is accomplished by the special design of the hereindescribed defoaming unit.
Defoaming unit 54 includes a pear shaped case 72 having an arcuate upper portion and a restricted, open. lower portion which provides a discharge opening 74. (use 72 further is provided with a face plate 73 which is bolted to the case and provides access to the interior.
A pair of infeed ports 76. 78 communicate with the interior of the case at its upper, rounded end.
Port 76 is coupled to conduit 56 which delivers foamed glue diverted by valve 48 to a peripheral position at the upstream end of the flow generated within the defoamer.
(.onduit 56 is designed to have substantially the same resistance to flow as do conduits 52 and extrusion noz- LIBS 70. This insures that at the same driving pressure the rate of flow of the foamed glue will be substantially the same in the one as in the other.
Port 78 communicates with conduit 60 which deliversthe feed stock from storage tank 58, and charges it into the case in a location downstream from infeed port 76.
Rotary beating means is mounted in case 72 for beating the foam introduced into the case via infeed port 76 and thus separating into its liquid and gaseous phases.
The beating means comprises a shaft 80 journaled in bearings 82 which in turn are supported on a frame member 84. The shaft is driven at a suitable rotational speed of about 3,000 rpm by means ofa belt and pulley assembly 86 coupled to a motor, not illustrated. I
The end of shaft 80 opposite to that which mounts belt and pulley assembly 86 mounts a rotor indicated generally at 90. j
The rotor is arranged concentrically with the rounded upper end of the case and comprises a plurality of support plates 92 spaced longitudinally along the end of shaft 80 and positioned radially in substantial parallelism to each other. The plates are welded to the shaft.
A plurality of radial blades or arms 94 are interposed in staggered relation to each other in the spaces be tween support plates 92. They are secured releasably in place by means of bolts 96. The arms comprise flat plates of rectangular cross section and having a length sufficient to reach out into close proximity with the inner wall of the rounded portion of case 72.
Foamed glue introduced into the defoamer via infeed port 76 is driven around in the clockwise direction as viewed in FIG. 3 and subjected to the intense beating action of the leading edges of blades 94. This hammers the component bubbles of the foam and breaks the foam into liquid and gaseous phases.
The liquid phase is discharged through the open bottom discharge port 74 at the bottom of the unit and is returned to feed tank 40. The gas phase is dispersed into the atmosphere or conducted to a suitable venting I facility. Raw feed liquid introduced into the defoamer via conduit also passes in a short cycle through the rotor. However, it is adjusted to a level approximating that of the defoamed glue.
OPERATION A typical operation of the hereindescribed apparatus for applying foamed liquids to substrates is as follows:
The liquid employed in this example is an aqueous, alkaline, phenol-formaldehyde resinous plywood glue mixed with a foaming agent in suitable amount and having a viscosity of 3l0 poises and a density of about 1.1 grams per cc.
To start the operation with clean and empty equipment. pump 62 draws glue at a density of 1.1 from storage tank 58 and propels it through defoamer 54 into feed tank 40. Operation of the defoamer through some unknown mechanism reduduces the density of the glue to 0.93 grams per cc. When the level of glue in the feed tank is sufficient to actuate float switch 66, pump 62 shuts off.
Next pump 46 is started. It draws glue from tank 40 and propels it through foaming unit 42 to valve 48. The valve diverts the foamed glue, which has a density of about 0.2 g./cc.. back into defoamer 54, which delivers it in defoamed condition back into feed tank 40. It is delivered defoamed at a density of 0.93 g./cc..'the same density as it had when it left the tank.
As pump 46 continues to operate and fills the lines. the pressure at the outlet of foamer 42 and at valve 48, which in practice may be located to advantage inside extruder 28, rises and finally stabilize at values of about 50 psi at the foamer and about 10 psi at the valve. When this gradient has become stabilized. extrusion is started by turning valve 48 so as to connect the foamer to the extruder and simultaneously divert the flow of foam away from the defoamer.
When this occurs, the pressure inside the extruder will not .change. This is for the reason that conduit 56 on the one hand. and the conduit system including discharge nozzles 70 on the other hand, are dimensioned to have the same resistance to flow. Accordingly, one path is as favorable as the other to the foamed liquid.
The foamed glue is discharged through extruder 28 as long as the moving veneers on the plywood production line activate switch 36. However, when the motion of the veneers is arrested, switch 36 shifts the position of valve 48 so that the foamed liquid is diverted to defoamer 54 and returned in defoamed condition to tank 40.
Since the glue is delivered to tank 64 at the same density (0.93 g./cc.) whether it comes from storage tank 58 through defoamer 54, or from the extruder 28 through the same defoamer, the rate at which pump 46 propels glue into the system remains constant.
Since pump 46 delivers glue into the system at a constant rate and the pressure at the extruder remains the same whether the foamed glue is'being extruded or not, the pressure gradient in the line will remain constant. The rate of flow to the extruder will remain the same at all times and the rate of flow through the extrusion nozzles will be unaffected when the flow in the nozzles is stopped and startedagain.
The system thus may be stopped and started as often as required by the demands of the plywood assembly line without disadvantage to the uniformity of foamed glue spread on the veneers. Furthermore, this is accomplished without loss of glue and without incurring a pol lution problem resulting from the discharge of waste glue into facilities wherein it is detrimental.
Having thus described our invention in preferred embodiments, we claim:
1. Apparatus for the uniform application of foamed liquid mixtures to substrates which comprise:
a. a reservoir for holding a quantity of foamable liquid,
b. liquid foaming means,
c. first conduit means interconnecting the reservoir and the liquid foaming means,
d. foam spreading means downstream from the liquid foaming means,
e. second conduit means interconnecting the liquid foaming means and the foam spreading means,
f. foamed liquid defoaming means downstream from the foam spreading means.
g. third conduit means interconnecting the liquid foaming means and the foamed liquid defoaming means.
h. the foamed liquid defoaming means communicating with the reservoir means for discharging defoamed liquid into the same,
i. valve means in the second and third conduit means and operable to direct the flow of foam selectively are proportioned and arranged to develop substantially equal pressures of foamed liquid therein.
3. The apparatus of claim 1 including a storagetank, fourth conduit means communicating with the storage tank and also with the foamed liquid defoaming means for discharging stored liquid into the same.
4. Apparatus for the uniform application of foamed liquid mixtures to substrates comprising a. a reservoir for containing a quantityof foamable liquid, 1
b. withdrawing means positioned for withdrawing a predetermined quantity of the liquid from the reservoir,
c. continuous foaming means located for receiving andcontinuously foaming the withdrawn liquid,
d. spreading means,
e. means directing the foamed liquid from said foaming means to said spreading means, said spreading means being arranged for continuously spreading the foamed liquidon an intermittently and relatively moving substrate during its periods of motion,
f. said means directing the foamed liquid from said foaming means to said spreading means including diverting means for continuously diverting the foamed liquid away fromthe spreading means during the periods of the restof the substrate, g. defoaming means arranged for defoaming the diverted foamed liquid. h. means directing the-diverted foamed liquid from the diverting means to the defoaming means, and i. means directing the defoamed liquid from the defoamer to the reservoir. 5. The apparatus of claim 4, wherein the defoaming means'comprises a casehaving a first inlet, a second inlet, an outlet, a rotor mounted for rotation within said case, and a plurality of blades mounted radially on said rotor and extending into close proximity .to said inlets and the periphery of the case; and wherein said apparatus includes a supply means for unfoamed liquid. and first connecting means connecting said supply means to said first inlet for the introduction of unfoamed liquid into said case, saidmeans directing the diverted.
foamed liquid directing said diverted foamed liquid to said second inlet for introduction of the diverted foamed liquid into said case, said means directing the defoamed liquid from the defoamer including said outlet.
6. The apparatus of claim 5 wherein the rotor comprises a rotatably mounted shaft, motor means connected to the shaft for driving it at a high rotary speed, a plurality of spaced blade mounting plates fixed radially to the shaft in spaced relation to each other, said plurality of radially extending blades inserted in the spaces between the mounting plates and angularly spaced from each other, and fastening means securing the arms to the plates.