US 2678897 A
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Ma m, 1954 J. w. MANN ETAL ,6 ,8
SPLIT POLE PARALLEL BONDING PROCESS Filed Jan. 30, 1951 2 Sheets-Sheet 1 INVENTOR. JUL/US 14/. jV/mw May 18, 1954 J, w. MANN ETAL SPLIT POLE PARALLEL BONDING PROCESS 2 Sheets-Sheet 2 Filed Jan. 30, 1951 INVENTOR. 2/01. 1115 W/ZUV/Vg y 550F615 173053544.
ATTOF/VEKS Patented May 18, 1954 SPLIT POLE PARALLEL BONDING PROCESS Julius W. Mann and George F. Russell, Tacoma, Wash.
Application January 30, 1951, Serial No. 208,626
An object of our invention is substantially to improve upon methods currently being employed to apply the principles of parallel bonding to the setting of resin and other adhesive glue lines in wood and other dielectric assemblies. A fur ther object of our invention is to apply the principles of parallel bonding in the easiest and most eiiective ways to accomplish quick setting of resin adhesive and to overcome some of the diificulties currently being experienced in its use.
The fundamentals of applying a high frequency electric field of force to an adhesive line so that the dominant field lines of force parallel the said adhesive line plane rather than extend across it has been set forth in our Patent No. 2,434,573, on Radio Frequency Parallel Bonding, issued January 13, 1948, and further, in our Patent No. 2,457,498, on Radio Frequency Parallel Bonding, issued December 28, 1948, we have described a process of applying a high frequency electric field of force to an adhesive line by parallel bonding so as to secure a truss, saw tooth, or 2 pattern set along and across the adhesive plane by a unique and novel arrangement of the electrodes between which is established the radio frequency field of force.
When the electrodes, attached to the source of high frequency energy, contact the adhesive line directly, as is the practice of many using parallel bonding, glue squeeze-out from the pieces being bonded, tends to remain unset and wet even after the glue plane inside the assembly has been completely cured. Unset or wet squeeze-out ad hesive necessitates a stack of glued or bonded assemblies being piled with sticks being placed between to prevent one assembly from adhering to another when left for some time one piled upon another. The process of putting sticks between finished panels, such as furniture core stock for example, is costly, objectionable and time consuming. Also, the wet squeeze-out of an adhesive causes a gumming up of the electrode members which results in waste due to the cleaning time requiredv Moreover, the glue build up on the electrodes causes an uneven contact between the electrodes and the material.
Our present invention overcomes the wet squeeze-out objection heretofore mentioned, by accomplishing What, up to this time, has been found impossible either with the use of simple parallel bonding, or Z pattern parallel bonding described and claimed in our two previous disclosures of the art in Patents 2,434,573 and 2,457,498. This invention is a distinct step forward in the use of parallel bonding and is useful,
advantageous and novel. Our invention consists of a method of gluing wood and other dielectric assemblies together by the application thereto of dielectric high frequency heating in connection with the polymerizing of synthetic resin and other adhesives used as the adhesive means in such assemblies.
In order fully to appreciate the unique character of this invention, it is desirable to explain that in setting an adhesive line or plane between dielectric materials for bonding them together, an alternating current high frequency field of force has been so applied that the adhesive plane (or at least part of it), is exposed in the field so the action of the alternating current electric field creates heat therein. Usually alternately charged electrodes are placed on opposite sides of the adhesive line or plane and the alternating current field of force established between the electrodes raises the temperature of the adhesive line to the critical setting temperature of the adhesive. Many methods of applying the field of force to a glue line have been used, and novel electrode arrangements have been employed, among which is our 2 pattern process, developed and invented among other things to minimize the glue or other adhesive squeeze-out problem. In Patent No. 2,457,498, column 4, line 58, we said: The use of corrugated electrodes or pipe or bar electrodes made into an assembly to simulate a corrugated sheet has a distinct advantage over flat plates in that glue squeezeout is caught in the valleys of the lower corrugations and does not build up on top of the edges used for the concentration of the field of force. Still, while Z pattern helped materially in the squeeze-out difiiculties over fiat parallel electrodes, it did not set the squeeze-out solid. Herein lies one of the distinct advantages of the present described process. In our invention, the glue squeeze-out is set so solid during the time the high frequency field of force is being applied to the adhesive plane, that it is unnecessary to separate core stock panels after edge gluing by sticks as described above.
In the Linquist Patent No. 2,317,281, a method was described of spot gluing at various points using electrodes of alternate charges placed on opposite sides of the adhesive plane in edge gluing work, and allowing the interspanning portions to cold set afterwards. In our Patent No. 2,434,573, full set parallel bonding disclosed the use of electrodes of opposite charge being placed the entire length of a glue line and thereby setting the entire space of spread glue in the edge or plywood process. In our Patent No. 2,457,498, 2 pattern bonding was disclosed, but here again the electrodes on opposite sides of the adhesive planes were oppositely charged. In each case above described, the electrodes on one side of the assembly whether a single piece or a network of electrodes are all of one charge instantaneously.
This invention utilizes the principle that selectivity of the field of force will seek out a line which is more conductive than some other path 1 and this is shown in our parallel bonding Patent No. 2,434,573. The parallel bonding principle has been developed and improved because in thick assemblies, the so called stray field bcnding is limited-and because in 2 pattern bonding, the adhesive plane is only set and leaves unset the squeeze-out adhesive that lies between electrodes of the same instantaneous charge. Both of these disadvantages are overcome in our present invention.
A further advantage of this invention is its practical elimination of the arcing danger when oppositely charged electrodes applying the principles of parallel bonding are placed close together and tend to concentrate a heavy field of radio frequency force in a small glue plane area. In stray field bonding, if wide bar electrodes are employed, wide areas below the electrodes and within the adhesive plane are shielded from the effect of the high frequency field and are left unset to dry later. Shadows, i. e., areas of unset adhesive, appear under certain conditions. In 2 pattern bonding, the setting of the adhesive takes place in a truss shaped pattern with large areas left unset at both the top and the bottom of the glue plane.
It is an object of this invention to set a larger adhesive area by radio frequency heating than can be accomplished by spot or Z pattern bonding and to solid set the squeeze-out adhesive leaving, if any, only a small shadow area within the adhesive plane, and solid setting the outer edges of the glue plane.
In a continuous process where stock moves through a radio frequency field set up in the pattern herein described, the entire squeeze-out and all of the internal area of the adhesive line can be solid set. This is a distinct advantage over any other types of parallel bonding which often leave unset adhesive portions in one place or another on the material being treated, either on the surface or in the shadow areas internal on the adhesive plane.
The gist of our invention constitutes a means of setting adhesive planes and squeeze-out adhesive by a novel and useful arrangement of electrodes so instantaneously charged relative to each other as to accomplish this result.
Other objects and advantages will appear in the following specification, and the novel features of the method will be particularly pointed out in the appended claims.
Our invention is illustrated in the accompanying drawings forming a part of this application in which:
Figure 1 is a cross section of a pair of oppositely charged high frequency parallel rod type electrodes, illustrating the approximate dominant distribution of the high frequency field of force therebetween when energized.
Figure 2 is a similar cross section to that of Figure '1, and shows an adhesive plane in corn tact with both electrodes and extending at right angles to the axes of the electrodes, and showing an application of stray field parallel bonding;
Figure 3 illustrates the electrodes of Figure 2 split by an infinitely thin adhesive line passing through the centers of both electrodes;
Figure 4 shows the same illustration as in Figure 3, but with the split electrodes enclosing a wider adhesive plane;
Figure 5 shows round electrodes placed on both sides of a still wider adhesive plane, these electrodes being instantaneously charged as are the split electrodes of Figures 3 and 4;
Figure 6 illustrates fiat electrode elements placed on both sides of an adhesive plane;
Figure 7 is an isometric view of a package consisting of wood pieces with glue planes therebetween and placed in readiness for bonding together by the use of split pole parallel bonding to produce solid set adhesive planes and squeezeout portions and reduce arcing as well as radiation tendencies; and
Figure 8 is a section taken along the line VIII-VIII of Figure 7.
While we have shown only several forms of our invention, it should be understood that various changes and modifications may be made within the scope of the principles herein outlined and claimed without departing from the spirit of the invention.
In Figure 1, we show a pair of electrodes A and B in cross section and oppositely charged with radio frequency current. The dotted lines I in this figure illustrate the approximate dominant distribution of the high frequency field of force existing between the electrodes when they are energized.
In very thin veneers, such as that having a thickness corresponding to the heighth of the adhesive plane C, shown in Figure 2, the heating effect of the high frequency field of force established between the electrodes A and B will cause stray field parallel bonding in the portion of the adhesive plane lying between the electrodes. The adhesive plane C lies between adjacent pieces of veneer and the heating of this plane results in the edge bonding of the pieces. The adhesive plane C will be cured completely between the inner limits of the opposing electrodes.
If either of the electrodes A and B is spaced a slight distance from the veneer whose thickness corresponds to that of the glue plane C, then there will be an unbalance in the radio frequency circuit and a sharp tendency to create a flash are between the raised electrode and the work. The type of electrode shown in Figure 2 must be carefully employed and is susceptible of causing erratic bonding performances.
In a copending application on a radio fre quency edge gluing press and process, Ser. No. 208,627, filed January 30, 1951, we have shown this type of electrode arrangement. A machine has been built and we have found that extreme care must be exercised to balance the electrode components and to maintain pressure bearing against the wood so that the latter will maintain contact with the electrodes while the material is moved throughout the machine. An exact control of the frequency of the generator must also be maintained, lest undesirable shifts take place during the curing of the adhesive plane from electrode networks becoming unbalanced over a period of time. This type of electrode also tends to radiate spurious harmonics excessively. The dash line area 2 of the adhesive plane C in Figure 2, indicates the portion of the adhesive which will be cured by radio frequency lines of force extending between the electrodes A and B.
split poles Al era-evens? the line Ci in Figure-3, the electrodes Al and'Bl may be split the thin adhesive lineextend therebetween. By this arrangement for thin veneer sections, we can overcome the difiiculties of unstable characteristics possessed'by the electrodes shown in Figure 2.
In Figure the glue plane C2 is wider and the are spaced from each other a greater distance, and so are the split poles Bl. The dashed area'Za indicates :the portionof the adhesive plane, lying between the electrodes Al and Bi that is cured by the radio frequency lines of force.
lhe illustration of Figure shows the split electrodes A2 and B2 fully rounded in cross sectionrather'than half circular as in Figures 3 and 4. Where the cross sections of the electrodes are tangent to the work as in Figure 5, more of the adhesive plane C3 will be cured, as indicated by the area 2b, than will be curedin Figure 4. The fiat portions of the half circle electrodes vA! and B! in Figure 4 will prevent the adhesive lying between the split electrodes Al and Al and between the split electrodes Bi and :BI from ourin The non-cured portions of the adhesive plane C2 are indicated by the clear areas in Figure 4.
When fiat split electrodes A3 are used and contact the material which has a cross sectional area the same as the size of the adhesive plane C4 in Figure 6, this plane will have cured areas indicated by the dashed portions 20, and uncured areas indicated by the clear portions. These uncured portions have a length coextensive with the widths of the electrodes A3 and B3,
The round electrodes A2 and B2 of Figure 5 are shown applied to a package consisting of wood pieces 3 with adhesive planes Ci} therebetween in Figures '7 and 8. Pressure is applied against the two outermost pieces 3 and this pres- Sure is in the directions indicated by the arrows 4 and 5 in Figure 7. This pressure holds the pieces 3 in abutting relation during the curing of the adhesive planes C3. In case of a continuous bonding process being used as shown in our copending application, above referred to, the package of wood pieces 3 would be moved in the direction of the lengths of the electrodes A2 and B2, and new pieces would be added to the package and bonded to adjacent pieces as rapidly as space would provided between the upper and lower groups of electrodes.
Figures 7 and illustrate how the upper and lower electrodes A2 and B2 are connected in pairs to a radio frequency coil-6 or a radio frequency generator, notshown, so as toset up an electrical net work known as split pole parallel bonding. For example, the pair of electrodes A2 and P 2 at the left hand side of Figures 7 and 8 are electrically connected to the side I of the coil 5. next of electrodes A2 and B2 are electrically connected to the side 8 of the coil. The third pair of electrodes A2 and B2, counting from the left, are electrically connected to the side i of the coilt, and the fourth pair are electrically connected to the side 8. The radio frequency generator used of which the coil 6 is a part, is preferably the one disclosed and claimed in our patent on a Single Standing Wave Radio Circuit, llo. 2,596,158, issued May 2, 1950,
Figure 8 illustrates the instantaneous charges on the electrode network and it will be noted that electrodes of like instantaneous.charge,..directly oppose each other on opposite sides of the adhe- :sive ;plane;C3 being cured. We 'feelffirm'in our belief that this new and novel arrangement .of
anielectrode network has been the cause of great- 1y reduced radiation of spurious harmonics and signal strength on the fundamental when measured for radiation around a gluing installation employing split pole parallel bonding. The entire field is so confined vithin the bounds of the adhesive plane that radiation from the network is greatly reduced compared to the types having an entire network of oppositely charged electrodes on opposing sides of the glue plane.
The dotted lines 9 in Figure 8 illustrate the radio frequency lines of force that travel between adjacent electrodes A2 in the upper group and the dotted lines ill illustrate the radio frequency lines of force that travel between adjacent electrodes in the lower group. The adhesive portions in the plane C3, bordering and extending along the upper and lower edges of the plane, will he cured and thus seal up any uncured portions, indicated the dotted circles H in Figure 8. Moreover, any squeezc-out adhesive from the plane C3- will also be cured and there will therefore be no need to separate the bonded packages from each other by spacing members. The uncured adhesive areas I I, known as shadow areas, will cure in time, and the uncured adhesive in these areas will be entirely surrounded by the cured adhesive portions of the adhesive plane. Th efore can be no drainage of any uncure-d adhesive from the package after the adhesive planes have once been subjected to the split pole radio frequency parallel bonding. The dotted lines El and ii in Figure 8 represent the dominant field lines of force within the area of opposite instantaneous charge between the electrode elements of opposite charge.
A principle or the high frequency field is that between poles or electrodes of like charge, there is no effective field line concentration, but instead a repelling effect. Between electrodes of unlike charge, there is an effective concentration of the field lines of force or an attractive relationship.
The electrode arrangement in Figure 8, shows its unique character if it is imagined that the adhesive plane C3 moves from left to right as in a continuous process. This will expose the shadowed circular areas i l to the field effect between the electrodes in upper bank as well as the field effect between the electrodes in the lower bank. The adhesive in the shadowed circular areas will he cured. -f the adhesive plane C3 advances in a direction an angle to its own plane and at an angle to the lengths of the electrodes A2 and B2, all of the shadow areas i I will set solid and the squeerewut adhesive will also set solid.
In Figure 8, the adhesive plane 03 is represented as a plane of adhesive between the abutting edges of dielectric materials to be bonded. The placement of the electrodes A2 and B2 in each pair, above and below the adhesive plane is such that the spacing is approximately equal to the height of the adhesive plane. A straight vertical line connecting any two vertically separated electrodes having the instantaneous charge, will approximate the width of the adhesive plane.
The spacing of one pair of electrodes A2 and A2 from adjacent pairs may vary widely, but would not be ordinarily closer than the approximate width of the adhesive plane C3 for the best and most effective results. Three or four times the width of the plane C3 where the plane is one inch high has been found desirable. In the case where the adhesive lane is one tenth of an inch high, the pairs of electrodes are spaced apart about thirty times the height of the plane. It might be said that the spacing of the electrode elements of opposite instantaneous charge on the same side of the adhesive plane should be at least equal to the height of the plane, and in most cases greater than the spacing, of the elements in each pair and of the same instantaneous charge, from each other.
If the spacing of unlike electrodes on the same side of the plane is less than the width of the adhesive plane, depth of penetration suilers. If the spacing is increased, depth of penetration increases. lhe depth of penetration desired whether a full or a partial cure inwardly toward the middle of the adhesive plane, determines the spacing to be employed between the pairs of electrodes A2 and B2. Either factors which need consideration are the power applied, the speed of travel of the material if a continuous process is used, the length of time the adhesive plane is subjected to heating by the radio frequency lines of force, the thickness of the layer of adhesive and other variables.
In the carrying out of our invention, we have embodied electrode arrangements circular in cross section, but other shapes and embodiments may be employed. Also, we have illustrated the instantaneous charges on the electrodes as positive and negative, but it should be understood that this condition would be effective in only one charged state when the electrodes of opposite charges as illustrated are connected in turn to opposite sides of a double ender source of high frequency alternating current, with the charges, as shown, reversed at the next instant.
It should be borne in mind that a high frequency source of alternating current using a single ender output as well be employed, in which event one of the charges shown in the illustrations would be grounded and its electrode of opposite charge would alternate between positive and negative on alternate instants.
Whatever the source of high frequency energy, therefore, if it delivered through a single radio frequency hot electrode network, working against other electrodes acting ground or if delivered through electrodes both radio frequency hot and alternately charged with relation to each other or other method of delivery, the principles of this invention are essentially the same.
The use of a single set of electrodes, or a network, or bars, rods, fiat plates, or other shapes which electrodes may take, this is not a factor limiting the scope of the invention. We have employed many forms of electrodes. For example, it may be desirable in the gluing of some laminated assemblies to shadow portions of the assembly so not to create heat and adhesive cure therein. In this event, wider electrode ele-- ments or plates or the same charge above and below adhesive plane will shadow the area enclosed therebetween as illustrated in Figure 6, in the manufacture of the veneer assembly used in making a hollow core for a door.
In edge glued assemblies, the mass of dielectric being glued together may vary widely in size, shape and material. To illustrate, we will discuss wood edge gluing. Thin veneers such as employed in the manufacture of plywood or surfacing core stock, when glued together will present to the adjacent veneer only a thin glue plane, for example of an inch in thickness or height and from four to twelve feet in length. Thicker solid wood boards, such as are employed in the manufacture of wide boards Or core stock panels when glued edge to edge together will present to the adjacent pieces varying thicknesses, but a typical illustration would show a. glue plane between these boards of one inch in thickness and from one to several feet in length.
In edge gluing door rails and stiles, the glue planes will normally be 1 /2 inches wide and from two to eight feet long. In the manufacture of laminated beams, a glue plane may be from two to twelve inches wide and up to several feet in length. A common laminated beam will run from thirty to fifty feet long. It should be pointed out that whether an adhesive line is thin as in veneers, medium as in edge glued boards or thick as in beams or barn rafters, distinct advantages accrue to one employing the split pole method of parallel bonding herein described in applying a high frequency alternating current field of force to the said adhesive lines for quick- 1y curing them by the internal heating effect of the said field.
1. The herein described process of setting relatively wide and vertically arranged adhesive plane disposed between abutting pieces of dielectric material that are to be joined, which comprises establishing high frequency lines of force flowing parallel with the plane and adjacent to the upper and lower edges thereof for quick setting portions of the adhesive to provide continuous barriers of set adhesive bordering the entire length of the upper and lower edges with these barriers trapping any unset adhesive lying therebetween; and in permitting the unset adhesive to cold set while still held in a trapped state by said barriers.
2. The herein described process of setting a relatively wide and vertically arranged adhesive plane disposed between abutting pieces of dielectric material that are to be joined, which comprises: establishing high frequency lines of force flowing parallel with the plane and adjacent to the lower edge thereof for quick setting portions of the adhesive to provide a continuous barrier of set adhesive bordering the entire length of the lower edge with the barrier trapping any unset adhesive lying thereabove; and in permitting the unset adhesive to cold set while still held in a trapped state by the barrier.
23. The herein described process of setting a relatively wide adhesive plane disposed between abutting pieces of dielectric material that are to be joined, which comprises: establishing high frequency lines of force flowing parallel with the plane and adjacent to opposed. edges thereof for quick setting portions of the adhesive to provide continuous barriers along the opposed edges with these barriers trapping any unset adhesive lying therebetween; and in permitting the unset adhesive to cold set while still held in a trapped state by said barriers.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,397,615 Mittellnann Apr. 2, 1946 2,457,498 Russell et a1 Dec. 28, 1948 FOREIGN PATENTS Number Country Date 555,054 Great Britain Aug. 3, 1943