Joints and connections – Member ends joined by inserted section – Fluted or splined section
Reexamination Certificate
1999-01-29
2001-07-03
Browne, Lynne H. (Department: 3629)
Joints and connections
Member ends joined by inserted section
Fluted or splined section
C403S266000, C403S292000, C411S908000
Reexamination Certificate
active
06254301
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to dowels used in the woodworking industry to secure two pieces of wood or wood-like material together. In particular, the present invention relates to novel dowels made of a thermosetting resin, a process for making such dowels, and methods of using such dowels.
2. Background of Related Art
In manufacturing cabinets, furniture, and other articles from wood or wood-like material, adjoining pieces of wood are often held securely together with dowels and an adhesive, such as woodworking glue. Conventionally, dowels have been made of wood. Wood costs have increased substantially in recent years and, in turn, the cost of wooden dowels has increased.
In conventional woodworking practice, receiving cavities are formed in each of the respective pieces of wood or wood-like material that are to be adjoined. When the pieces of wood or wood-like material are assembled, glue is typically injected into the dowel receiving cavities. Dowels are then inserted into the cavities and held there by the glue. Alternatively, pre-glued dowels may be employed. Water is typically applied to the dowel cavities and the dowels are moistened to activate the glue as the dowels are inserted into the cavities. U.S. Pat. No. 5,338,569 (Hatch).
It has been suggested to make dowels from thermoforming plastic materials, but such dowels are typically incapable of adhering to the glues used in the woodworking industry. Thus, plastic dowels have heretofore required surface features that create a frictional engagement with the wood into which the dowels are inserted. This frictional engagement may not result in nearly as much bonding strength as is obtained with wood dowels that are glued in the cavities. Thus, thermoplastic dowels have not been widely used in the commercial manufacture of furniture and other articles from wood.
Materials such as fiberboard are able to adhere to glues that have conventionally been employed in the woodworking industry.
Medium density fiberboard (“MDF” or “MDFB”) and high-density fiberboard (“HDF” or “HDFB”), which have been conventionally referred to as particle board, include wood chips and, thus, conserve wood by employing wood scraps that are by-products of other wood processing or recycled wood. Typically, particle board has a density of about 45 lbs/ft
3
to about 55 lbs/ft
3
. Due to high wood or cellulose content, fiber boards have similar properties to those of wood. While the densities of these materials are about the same or even greater than those of some types of woods, the strengths of these materials and, thus, the strength with which a dowel made from these materials secures two pieces of wood or wood-like material together is typically lower than that of some types of wood.
Fiberboard, including MDF and HDF, may be fabricated from particles, pieces or chunks of wood of mixed characteristics, and a resinous binder material. U.S. Pat. No. 4,857,252 (hereinafter “the '252 Patent”), issued to Melchior et al. on Aug. 15, 1989, discloses an exemplary process for fabricating fiber board. The process disclosed in the '252 Patent includes processing a wet mixture of thermosetting resin and paper, cardboard, or kraft fibers under caustic conditions through a paper machine to provide a sheet of the mixture including 95-98% solids, then subjecting the mixture to a high temperature to dry the mixture and cure the thermosetting resin. The process of the '252 Patent is time-consuming, requires expensive equipment, and is not useful for fabricating relatively thick layers of dense composite material and, in turn, is not useful for making dowels.
Accordingly, there is a need for a dowel that has comparable strength and comparable adherence to adhesives as wood dowels. There is also a need for a process of fabricating dense composite products with these properties suitable for use as a dowel.
SUMMARY OF THE INVENTION
The dowels of the present invention are fabricated from a composite material including thermosetting resin and a fibrous filler material. The composite dowel will adhere to adhesives, such as the glues conventionally used in the woodworking industry. When glued into a cavity of a piece of wood or wood-like material, such as medium density fiberboard or high density fiberboard, the composite dowel of the present invention will bond to the wood or wood-like material with a bonding strength comparable to that of a wooden dowel that is glued into an identical cavity in the piece of wood or wood-like material with substantially the same amount of the same type of glue.
The composite material from which the composite dowel of the present invention is fabricated preferably includes about 4% to about 90% by weight thermosetting resin, or an amount of thermosetting resin sufficient to flow throughout and bind the fibrous filler material together, and about 10% to about 96% by weight fibrous filler material, or an amount of fibrous filler material sufficient to impart the composite material with the desired properties.
The thermosetting resin and the fibrous filler material are mixed together, and then subjected to a high pressure and, preferably, an elevated temperature, to set the thermosetting resin and form a dense mass of composite material. Preferably, the mixture of thermosetting resin and fibrous filler material is subjected to a specific pressure of at least about 3500 pounds per square inch, or a pressure sufficient to cause the thermosetting resin to flow or set, or a pressure sufficient to form a dense mass of composite material. The mixture of thermosetting resin and fibrous filler material is preferably subjected to elevated pressure for at least about 60 seconds, or a time that permits the resin to begin flowing and to set, to form the mass of composite material. A preferred elevated temperature is from about 95° C., or a temperature that will cause the thermosetting resin to flow and set, to about 230° C., or a temperature at which a fibrous filler material such as paper begins to combust. The thermosetting resin preferably sets, or cures, while the mixture of thermosetting resin and fibrous filler material is subjected to pressure to facilitate the fabrication of a composite material having a desired density.
The density and strength of the composite material increase when greater pressures are employed to form the composite material. Accordingly, the strength of the composite materials of the present invention may be tailored by applying a specific amount of force to the mixture of thermosetting resin and fibrous filler material for a specific duration of time. Preferably, a mass of composite material according to the present invention has a density of at least about 75 pounds per cubic foot.
A preferred temperature for setting the mixture is about 90 degrees C., although ambient and other temperatures may be employed. Of course, the optimal temperatures at which the composite material may be formed depend upon the type of thermosetting resin employed in the composite material and the amount of pressure employed to fabricate the composite material.
The degree to which the thermosetting resin flows through the fibers of the fibrous filler material during the formation of the composite material also increases with an increase in the amount of pressure applied to the mixture of thermosetting resin and fibrous filler material. The fibrous filler material imparts the composite material with surface porosity.
The composite material of the present invention adheres to adhesives employed in woodworking, such as water-based adhesives, resinous adhesives, animal-based glues (e.g., horse-hide glues), and chemically manufactured glues. Thus, the composite material of the present invention is useful in woodworking applications where adhesion of an article of the composite material to a piece of wood or wood-like material is desired. For example, the mass of composite material may be formed into the cylindrical shape of a dowel. The mass of composite material may be molded substan
Browne Lynne H.
Cottingham John R.
TraskBritt
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