Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Producing multilayer work or article
Reexamination Certificate
1999-01-20
2001-07-24
Hurley, Kevin (Department: 3619)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Producing multilayer work or article
C264S314000, C280S281100
Reexamination Certificate
active
06264878
ABSTRACT:
STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT
(Not Applicable)
BACKGROUND OF THE INVENTION
The present invention relates generally to bicycles, and more particularly to a method of manufacturing a hollow, monocoque carbon fiber bicycle frame which is lightweight, durable, and relatively inexpensive to manufacture and finish.
The fabrication of bicycle frames from fiber reinforced polymer composites is well known in the prior art. According to prior art fabrication methodology, these composite bicycle frames are typically constructed by first pre-forming the elongate, composite members thereof, and then interconnecting these members with composite joints. For example, in one commonly practiced prior art composite bicycle frame fabrication process, separate top tube, down tube, and seat tube members are initially formed from fiber reinforced polymer composites, and subsequently placed into a common fixture. The placement of these members into the fixture maintains their desired orientations while they are connected to each other by forming interconnecting joints therebetween with additional fiber reinforced polymer composite material.
As will be appreciated by those skilled in the art, though this particular prior art fabrication methodology provides a bicycle frame which is lightweight and durable, it is extremely time consuming and expensive. The high amount of labor and resultant expense is attributable to each of the interconnecting joints having to be individually fabricated by hand, and the need to conduct extensive finishing operations upon the frame to provide the same with the desired smooth, properly contoured outer surface. Thus, although the prior art has recognized to a limited extent the benefits of providing a lightweight and durable bicycle frame, the known fabrication methodologies for such frames have been time consuming and cost ineffective.
In recognition of the deficiencies of prior art fabrication methodologies which employ the use of fiber reinforced polymer composite materials, Applicant has developed the composite bicycle frames and associated manufacturing methodologies described and claimed in the above-listed parent applications. These improved methodologies facilitate the minimization or elimination of the prior art steps needed to provide the interconnection of the various frame members or components to each other, and provided the desired smooth overall finish to the bicycle frame, thus substantially reducing the amount of labor involved in the manufacturing process and hence reducing the associated costs.
More particularly, Applicant's previous methodologies involve the placement of an elongate, flexible and expandable bladder covered with a polymer impregnated fiber material into a first mold section, and subsequently mating a second mold section to the first mold section so as to define a cavity having a desired frame shape through which the bladder covered with the polymer impregnated fiber material is extended. The polymer impregnated fiber material is then heated, with the bladder being inflated so as to cause the material to substantially conform to the shape of the cavity. The frame tube fabricated from this process includes at least a top tube portion and a down tube portion, and is formed entirely from a single, continuous section of the fiber reinforced polymer composite.
Though this methodology provides the aforementioned advantages over the prior art, the use of a non-rigid bladder therein gives rise to a susceptibility for the material to flow into unknown folds and/or wrinkles in the bladder during the pressurization thereof. As will be recognized, the flow of material into any such folds and/or wrinkles during the fabrication process results in undesirable inconsistencies in the wall thickness of the completed frame tube. The present invention addresses this particular shortcoming by providing a similar fabrication methodology which employs the use of a semi-rigid core or bladder to allow for better control of the internal wall surface texture and wall thickness of the resultant frame tube due to the absence of any unknown folds and/or wrinkles in the core for the material to flow into during the process of pressurizing the core. As in Applicant's previous fabrication methodologies, the present method also provides an absolutely continuous layer of fiber material about the entire frame tube where needed as opposed to a simple overlap of material as described in many prior art fabrication methodologies. These and other advantages attendant to the present invention will be discussed in more detail below.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a method for forming a bicycle frame. The method comprises the initial step of forming a hollow core or bladder from a semi-rigid material in a shape generally conforming to a desired frame shape for the bicycle frame. In the present application, a semi-rigid material is one which possesses selective phase change properties and is in a solid, rigid phase of a first hardness at room temperature, and transitions to a plastically deformable, expandable phase of a second hardness substantially less than the first hardness when subjected to elevated temperatures of a prescribed level.
Subsequent to the formation of the core, a layer of a polymer impregnated carbon fiber material is applied thereto. The polymer impregnated carbon fiber material is preferably provided in the form of an elongate strip which is wrapped about the core to substantially cover the same. Thereafter, the core having the polymer impregnated carbon fiber material applied thereto is placed into a first mold section, with a second mold section then being mated to the first mold section such that a cavity having the desired frame shape is defined therebetween.
After the second mold section has been mated to the first mold section, the core and the polymer impregnated carbon fiber material applied thereto are heated to an elevated temperature level sufficient to make the core pliable. The now semi-fluid core is internally pressurized and inflated so as to cause the polymer impregnated carbon fiber material applied thereto to substantially conform to the shape of the cavity. The heating of the core and the polymer impregnated carbon fiber material is preferably accomplished by heating the first and/or second mold sections, with the inflation of the core occurring as the same is being heated and reaches the prescribed temperature level at which is transitions from its solid, rigid phase to its plastically deformable, expandable phase. Subsequent to the inflation of the core, the first and second mold sections are cooled to form a continuous bicycle frame tube.
In the present method, the core is preferably formed from a semi-rigid material which becomes pliable or semi-fluid at approximately the same temperature level needed to facilitate the curing of the polymer impregnated carbon fiber material applied thereto. It is contemplated that the core may be formed from a plastic material via an injection molding process or a vacuum forming process. Additionally, the core is preferably formed to define at least one opening which is placeable into fluid communication with a pressurized fluid source for purposes of allowing the core to be internally pressurized as is needed to facilitate the inflation thereof after becoming pliable.
Further in accordance with the present invention, there is provided a bicycle frame formed in accordance with the above-described manufacturing methodology. The bicycle frame comprises a frame tube which defines at least a top tube portion and a down tube portion, and further preferably defines a seat tube portion. In view of the aforementioned fabrication process, the frame tube includes an outer layer which is formed entirely from a single, continuous section of the carbon fiber reinforced polymer composite material, and an inner layer which is integrally connected to the outer layer and formed from a single, continuous section of the semi-ri
Hurley Kevin
Stetina Brunda Garred & Brucker
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