Patent Application
20050028938
The invention relates to bonding of materials. In particular, an example of the invention involves application of rapid curing adhesive to bond wood components together.
In woodworking applications, it is often necessary to bond wood pieces together to produce a wood product. For example, recent environmental regulations and depletion of old-growth timber supplies have made it increasingly difficult and expensive for manufacturers to obtain high-grade lumber to use in wood products, for example including furniture, cabinets and millwork. One way of addressing the shortage and high cost of high quality lumber is the use of veneered stock. Typically, veneered wood products are created by laminating high quality veneer over a lower grade core material, such as medium density fiberboard (MDF), particle board, plywood or finger-jointed stock. Use of veneered wood members results in a substantially more efficient utilization of high quality wood, and therefore reduces raw material costs. Other examples of wood products produced by joining wood members together include door and window jambs, plywood, laminated veneer lumber, and other laminated wood products.
For most woodworking applications, a wood bond must be strong in order to provide structural strength and stability. For example, it is often desirable to form a “high-strength wood bond” that has a shear-strength exceeding the shear-strength of the wood itself. Generally, high strength wood bonding procedures require application of an adhesive to a wood surface, and subsequent pressing of the wood surface against another wood surface or against a polymeric material such as PVC, polyethylene, polystyrene, polypropylene, phenolic paper and wood fiber composites with any one of the above-listed polymers.
One significant limitation with prior wood bonding techniques is that the procedure required to produce a high-strength wood bond may take a long time, for example, several hours, to produce a cured product.
Other procedures can be performed more rapidly by using an adhesive that is activated to some extent during the pressing process. For example, adhesives may be activated by applying heat. These adhesives are referred to as “thermoset adhesives.” Presses may use heating platens or radio frequency mechanisms to activate and speed up significantly the cure time of a thermoset adhesive. Presses with heat activation mechanisms are generally complex, and expensive. These presses may also be limited in their ability to achieve uniform curing in some composite configurations.
Another way of activating an adhesive during pressing is to use a two-part adhesive system in which the two parts are substantially separate and unmixed until the pressing step, sometimes referred to as a “honeymooning” process. For example, see U.S. Pat. Nos. 5,944,938 and 5,626,705. However, a problem with this approach is that the pressing step may not adequately or reproducibly mix the two adhesive parts, thereby creating an inferior or inconsistent bond, or causing delays in the curing process. Another problem with a honeymooning process is that it is difficult to control the actual ratio of mixed adhesive components due to variable penetration or dilution of the components into the wood prior to mixing, particularly where the moisture content of the wood is variable.
There is a need for simplified wood bonding systems and procedures that can produce a rapidly-curing, high-strength wood bond between different types of wood pieces having a wide range of possible moisture contents, and between wood and polymeric materials such as vinyl, without requiring complicated adhesive activation steps while the wood pieces are being pressed.
The current inventor previously filed U.S. patent application Ser. No. 10/007,624 which discloses uses of rapid gelling two-part adhesive systems to quickly form high strength bonds between materials. This application is hereby incorporated by reference in it entirety, and is not in any way admitted to be prior art relative to the current invention.
One of the challenges with using rapid curing adhesives is that the fluid adhesive must be channeled, accurately metered, and uniformally dispensed over a short time window during which the fluidic properties of the adhesive change significantly as polymeric bonds are formed and the curing process moves rapidly toward completion. Various applicating systems are disclosed in the '624 application. Some of the previously disclosed systems involve spray techniques. However, some desirable adhesive formulations may not be conducive to spraying application.
Accordingly, an example of the invention involves use of a dispensing tube suspended across a material conveyor. The tube has a plurality of apertures for dispensing adhesive. Rapid gelling adhesive components are mixed and injected into both ends of the tube, and subsequently dispensed through the apertures onto material such as wood veneer being conveyed below the tube. The tube oscillates in a direction non-parallel to the direction of material travel so that the adhesive is deposited in a nonlinear pattern configured to result optimally in a uniform film of desired thickness when the adhesive is sandwiched and pressed between material components.
In another example of the invention multiple dispenser heads are arranged across a conveyor path. Each conveyor head has a conduit defining a stream path for directing glue fluid toward a work piece being transported along the conveyor path, and a drive mechanism for causing the stream path to oscillate resulting in a repeating pattern of glue on the work piece.
In another example of the invention, a plurality of glue mixing and applicating mechanisms are suspended across a conveyor. Each applicating mechanism is equipped with a drive mechanism configured to reciprocate a dispenser so that glue is deposited in a repeating zigzag pattern on materials being conveyed along a processing path.
The invention includes numerous systems, devices, and methods for depositing glue on material. One aspect of the invention involves a method of mixing rapidly gelling glue systems and depositing the glue uniformly on a moving work piece. For example, the glue may be deposited in a pattern including multiple side-by-side zigzag lines.
Another aspect of the invention utilizes equipment including a tube suspended over a conveyor path. The tube has apertures for dispensing glue which flows into the tube from opposite ends. A drive mechanism causes the tube to oscillate back and forth along a direction non-parallel to the conveyor path, thereby producing multiple repeating adjacent zigzag patterns of glue on the work piece. The glue patterns may be completely separate or may overlap.
Still another aspect of the invention utilizes multiple dispenser heads, each having its own glue injector, mixing chamber, and drive mechanism for repeatably altering the dispense path of a glue mixture. Numerous variables can be tuned and controlled to achieve an infinite number of different glue application objectives. For example, the invention may be used to permit relatively fast glue flow rates compared to a relatively slow material transport rate which is sometimes necessary with glue systems formulated to gel and cure quickly.
Crowder outfeed 30 then becomes the conveyor infeed for glue applicator station 40. Workpieces 22 then translate through glue application station 40. Glue applicator station 40 is configured to dispense a mixture of a two-part rapid-curing adhesive system. Component A of the adhesive system is contained in reservoir 42a. Component B of the adhesive system is contained in reservoir 42b. For example, a glue system may be obtained for this purpose from Bordon. A resin blend of WS 749-002 and WS 749-010 has been used with catalyst number WS 730-139. The gel time for this system is approximately 5 minutes. Hoses 44a and 44b carry the adhesive components through pumps and temperature control equipment before entering a mixing chamber, and flowing through dispense tube 46. Purge hose 47 is provided to clean out and purge tube 46 when it is not being used to dispense glue. Water, air, or other appropriate fluids may be used for purging.
Tube 46 has multiple holes for dispensing glue onto workpieces 22. Tube 46 may, for example, have an outer diameter of {fraction (5/16)}-inch. The tube may be suspended by about three- to five-inches, or up to 20-inches or more for other applications. Both sides of tube 46 are equipped with an adhesive mixing and pumping system, as previously described, so that a gelling adhesive mixture is injected into the tube from both ends toward the center of tube 46. The holes or apertures in tube 46 may have uniform or varying diameters that increase somewhat towards the center of tube 46 to compensate for a drop in pressure as the glue flows through tube 46. For example, the diameters of the holes are in the approximate range of 30-40 thousandths-of-an-inch.
Tube 46 is connected to rail 52. A mechanism is provided to oscillate or reciprocate rail 52 and tube 46 resulting in deposition of zigzagging glue pattern 54. Any mechanism for oscillating tube 46 may be used. For example, a rotary reciprocator may be used. Alternatively, a hydraulic cylinder, pneumatic cylinder, hydraulic rotary actuator, or pneumatic rotary actuator may be used.
Numerous other deposition patterns may be achieved by, for example, using a tip device to alter the dispersion path of the glue. For example, a tip configuration may be used to generate a spray-like dispersion which may or may not be used in conjunction with an oscillating motion.
It is believed that the following claims particularly point out certain combinations and subcombinations that are directed to one of the disclosed inventions and are novel and non-obvious. Inventions embodied in other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether they are directed to a different invention or directed to the same invention, whether different, broader, narrower or equal in scope to the original claims, are also regarded as included within the subject matter of the inventions of the present disclosure.
