FIELD OF TIIE INVENTION

The disclosed invention relates generally to a fastening device useful in facilitating the

assembly of associated materials by employing an assembly element such as a dowel or a disc constructed to include a target material and a solid substance which will exhibit adhesive

properties on exposure to heat. The heat will be generated in the target material by exposing the target material to electromagnetic waves.

DESCRIPTION OF THE PRIOR ART

United States Patent 4,038, 120 to Russell describes the use of an energized heating

element or wire to heat a hot melt glue resulting in adhesion between contiguously assembled panels. The reference method involves heating a glue- coated wire to liquify the glue

producing a cohesive state and facilitating the assembly of panels. This method is particularly

useful for introducing a cohesive material (glue) to an area of limited accessibility (groove), but

the heating element (wire) requires the direct application of energy (electricity) to provide the

heat to melt the glue.

United States Patent 3,996,402 to Sindt relates to the assembly of sheet materials by the use of a fastening device utilizing an apertured sheet of eddy current-conducting material

sandwiched between coatings of hot-melt glue. An induction heating system is activated

causing eddy current heating in the EC-conducting material with consequent melting of the hot-melt glue thus resulting in fusion and, ultimately, bonding of the sheet materials in

accordance with the desired construction.

United States Patent 3,574,031 to Heller et al. describes a method and material for

welding thermoplastic bodies by using a susceptor sealant between the bodies to be joined, The susceptor sealant is characterized by having particles, heatable by induction, dielectric or

radiant energy, dispersed in a thermoplastic carrier compatible with the thermoplastic sheets to

be welded. The welding of the thermoplastic sheets is effected by applying and exposing the susceptor sealant to heat energy, softening the carrier material and joining all thermoplastic

materials.

United States Patent 3,612,803 to Klaas discloses a fastening device, which, in its most relevant embodiment, consists of a quantity of heat-activatable adhesive containing a closed

electronically conductive loop and a ferromagnetic material insulated from said closed loop. In

operation, the fastening device is activated by a solenoid coil energized with alternating electrical current. The current emitted from the solenoid is transferred to the fastening device

where a current of large amperage and low voltage is generated in the loop enveloped by the heat-activatable adhesive. The current produces heat that causes the adhesive to become

sticky. The efficiency, and apparently the usefulness, of the disclosed device is improved by

fitting it with a ferromagnetic core enclosed within the closed loop.

SUMMARY OF THE INVENTION

The instantly disclosed fastening device is distinguished from, and goes beyond, the

prior art by describing an assembly element which will provide structure, strength and stability

to an assembled product while serving as a vehicle for introducing an adhesive material in a neat, non-messy form to internal and inaccessible areas of the pieces to be assembled. The

disclosed device will also provide a target material for absorbing and converting

electromagnetic waves to heat, for conducting heat energy to the adhesive material so that it

can be activated to provide an adhesive bond between the associated pieces.

This disclosure also relates to an improved and expeditious method for the assembly

and adherence of associated pieces of various materials which are, for the most part, transparent to electromagnetic waves. The improved method, adaptable to automated procedures, utilizes a device which comprises at least an assembly element which includes a

conductive target material for absorbing electromagnetic waves and a solid adhesive material, contiguous with the conductive target material, which will become physically or chemically adhesive by heat energy resulting from electromagnetic waves absorbed and conducted by the

target material. This disclosure also relates, of course, to the assembled products produced

according to the method utilizing the disclosed fastening device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the fastening device fashioned into the shape of a dowel.

FIG. 2 is a sectional view of the fastening device in the form of a dowel situated and

"hidden" within associated pieces.

FIG. 3 is a sectional view of the fastening device situated as in fig. 2 and being adhesively activated by electromagnetic waves emanating from a generator.

FIG. 4 is a partial sectional plan view of the fastening device in the shape of a disc

depicting repositories of adhesive material.

FIG. 4a is a sectional view of the fastening device, taken along section line a:a of fig. 4,

fashioned into the shape of a disc which is similar to the dowel of fig. 1 except that it has an

enhanced longitudinal aspect.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disclosed device 10, in its simplest form, will feature an assembly element 13 fashioned into a target material 12 coated with a solid adhesive material 1 1. As configured, the

device is designed to be placed, in a generally hidden relationship, between or within associated parts to be adhesively joined. When desirably situated, such as in holes 21 drilled to accommodate a dowel or in grooves cut to accommodate a disc, the device can be exposed to

electromagnetic waves 22, generally emanating from a generator 15 by passing the wand of the generator in the general area of the "hidden" device. The electromagnetic waves will penetrate the aligned associated pieces 20, to be adhesively joined, said parts, of course, must be substantially transparent to electromagnetic waves to allow the waves to contact the target material. The target material, for the most part, must be fashioned from substances that are not transparent to electromagnetic waves, that will absorb the electromagnetic waves; and as a

result of magnetic hysteresis and eddy currents, create heat which will be conducted to the solid adhesive material.

To elaborate, somewhat, heat is produced in the conductive target material by two

mechanisms: eddy current resistive heating and magnetic hysteresis. Eddy current resistive healing applies to all conductive materials and is produced in the target material by the electromagnetic waves emanating from the generator (induction coil). The generator is

energized by a traditional source of alternating current. The heat from magnetic hysteresis is

observed only in magnetic materials. As the electromagnetic field produced by the generator (induction coil) reverses polarity, the magnetic crystals in the target material also reverse.

There is an energy loss in this reversal which is analogous to friction: This energy loss is

magnetic hysteresis. The "lost" energy is quickly converted to heat and conducted by the

target material to the heat-activatable adhesive material to initiate adhesion.

When heated to the necessary temperature, the adhesive material will liquify or become

heat-activated, attach itself to the adjacent associated parts, and, on cooling, create an adhesive

relationship between the associated parts.

Two adhesion mechanisms, hot-melt and heat-activated cure are proposed for use with

the disclosed device. Both mechanisms are initiated by heat emanating from the conductive target material. Hot-melt adhesives are solid at ambient temperatures, but melt or liquify when the temperature is elevated by, for instance, heat flowing from the conductive target material.

The melted adhesive wets the adherends and, in the case of porous or fibrous adherends,

penetrates the surface of the pieces to be bonded. As the adhesive cools, the adherends and adhesive are bonded by the electrostatic attraction of polar molecular groups. In the case of

porous or fibrous adherends, mechanical interlocking can contribute to bond strength. Note

that for the hot-melt mechanism, the bonding is reversible. Thus, by repeating the induction

heating procedure, the bond can be undone and the adherends separated. The ability to reverse

the adhesion and separate assembled pieces is not a trivial attribute. In addition to the obvious advantage of being able to re-assemble or repair misaligned pieces, it is also desirable to be

able to disassemble manufactured articles to facilitate serviceability and repair. And, when

working with associated pieces of different materials, it will frequently be beneficial to

disassociate assembled pieces to facilitate recycling.

Heat-activated curing adhesives are also solid and easy to manipulate materials at

ambient temperatures, but when the adhesive temperature is elevated by, for example, the heat

flow from the conductive target material, a chemical reaction is initiated. This reaction

involves a cure or crosslinked bonding either within the adhesive or between the adhesive and the adherends. Such bonds are typically irreversible. Frequently, a heat-activated curing

adhesive bond will demonstrate an electrostatic attraction between the adhesive and the

adherends and a crosslinked bond within itself.

In one form of a typical embodiment of the disclosed fastening device 10, the adhesive

coated target material can comprise or be affixed to, or incorporated into, an assembly element 13, such as a dowel or a disc. The assembly element can be comprised of almost any kind of material because its purpose is to support the adhesive-coated target material and provide

added structural integrity, in addition to the adhesive bond, to the assembled product. Frequently, the assembly element will be made of wood, metal, plastic, ceramic, composite and even paperboard materials. When fashioned into a dowel or disc, it should be constructed of a

material that is readily available, easy to form and work with. In one preferred embodiment of

the disclosed device, the assembly element is formed, molded, compressed or machined into a

dowel having an annular dam 14 or fitted diameter for containing or localizing the adhesive

after it has liquified and positioning barbs 16 to help the dowel remain in the desired alignment. The dowel is then wrapped, coated, surrounded, embedded or integrated with a metallic target material 12 fashioned from a readily available metal such as steel or aluminum. The solid

adhesive material is attached to the foil by a liquid coating or physical self-attachment in the

form of a film, encapsulants, granules or powder. The fully fabricated device is then inserted in pre-drilled holes 21, aligned between associated pieces 20 to be joined and the joined pieces

are then exposed to electromagnetic waves 22 from an electromagnetic wave generator 15.

The waves must penetrate the pieces to be joined, but this is a relatively minor consideration

because almost all materials, to some extent, are transparent to electromagnetic waves. Materials that are not as transparent, such as thicker materials or materials containing

significant amounts of metal, will simply require a longer or more intensive exposure to the electromagnetic wave generator and the emanating waves. And by way of reiteration, the target material will absorb the emanating waves, convert the waves to heat energy, conduct the

heat energy to the adhesive coating which is designed to liquify or become chemically activated and adhere to the adjacent associated piece.

The commercial applications of the disclosed device are only as limited as the

imagination. Immediate needs for the disclosed fastening device have been identified in the

furniture industry where neat, effective and efficient assembly methods can readily be exploited to manufacture affordable units in a fast, effective and clean manner. Furniture and cabinet

manufacturing applications will involve, primarily, the assembly of associated pieces of wood

and plastic, both of which are transparent to electromagnetic waves and receptive to adhesive

bonding. Other construction uses for the disclosed device include the fabrication of lattice

panels, the installation of trim molding and fence erection. Also envisioned is the assembly of plywood, gypsum board and combination boards to wall ceiling and floor framing materials. In

the packaging industry, there is a need to facilitate the the fast and effective construction of

containers made of wood, plastic, and especially containers made of inexpensive materials

made from engineered fiber base materials, which could all be readily assembled using the disclosed device.

In addition to the simplest configuration of the fastening device where the assembly element is a brad, disc, dowel or pin coated with an adhesive material, other configurations of the fastening device are also envisioned. One such configuration features a fastening device

comprising an assembly element providing alignment and support to assembled associated

pieces, a conductive target material integrated with the assembly element, for absorbing electromagnetic waves and an adhesive material, contiguous with the conductive target

material, becoming adhesively active by heat energy resulting from the electromagnetic waves absorbed and conducted by the target material.