Pipes and tubular conduits – Reinforced
Reexamination Certificate
1997-09-03
2001-09-25
Scherbel, David A. (Department: 3752)
Pipes and tubular conduits
Reinforced
C138S125000, C138S142000
Reexamination Certificate
active
06293313
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to hollow stainless steel shafts or tubing, assemblies and methods of making same. More particularly, the present invention is directed to brazed, air hardenable stainless steel tubular shafts. In addition, the present invention is directed to reinforced stainless steel tubular shafts, the reinforcement member being brazed inside the tubular shaft. The present invention is also directed to producing unitary assemblies of air hardenable stainless steel tubing which may be reinforced at pre-selected locations.
The shafts or tubing of the present invention are brazed in a controlled atmosphere furnace. Brazing in a controlled atmosphere furnace allows for the hardening and brazing of air hardenable stainless steel in the same brazing temperature cycle. The shafts produced by this process are light, flexible and strong. In addition, the process of the present invention allows for the reinforcement of air hardenable hollow stainless steel shafts with stainless steel inserts of any pre-selected dimension. The inserts are brazed inside the hollow shafts, thereby providing tubular shafts with reinforcement at precise locations.
Hollow metallic shafts are ubiquitous in our society. They are used in products where lightness and strength are required. Products which require hollow shafts include esoteric goods, such as sporting goods, and utilitarian ones e.g. airplane fuselage supports, cantilever street light poles, ladders, furniture, tools, etc. With respect to sporting goods, hollow shafts are used for golf clubs, bicycle frames, ski poles, fishing poles and the vertical supporting members of volleyball nets. In addition to lightness and strength, hollow shafts used in sporting goods sometimes require precise flexibility. Golf clubs and bicycle frames also require torque resistance.
Materials presently used to construct hollow metallic shafts include aluminum, low and high carbon steels, coated steels, alloy steels and composites. These materials may be objectionable for numerous reasons, including, but not limited to, weight, weakness, rigidity, flexibility, torque resistance and price. A hollow shaft which is light, strong, flexible and inexpensive is needed.
With respect to hollow shafts presently used in sporting goods, these shafts comprise fiberglass, kevlar, metals, graphite and composites. While fiberglass, composite and graphite shafts are light and strong, their flexibility can be limited. This characteristic results in their snapping under loads in which a metal shaft would not. As for hollow metallic shafts, aluminum is light, but lacks the strength of steel. Titanium and formerly classified metals generally have very favorable characteristics, but are in limited supply and are therefore very expensive. Carbon steels are strong but oxidize easily. Prior art carbon and alloy steel tubular shafts are often inadequate because of their weight and their tendency to corrode.
In addition to the difficulties of weight and corrosion, welding, the joining technique of choice for metallic hollow shafts, weakens practically all metals adjacent the weld. Even the welding of austenitic stainless steel introduces impurities into the grain boundaries which often result in oxidation and failure of the weld. Since corrosion resistance, as well as lightness, strength and flexibility, is a desirable characteristic for hollow shafts, graphite and composites have become the materials of choice.
Despite the limitations of stainless steel to provide a completely corrosion resistant hollow shaft, it has been, and still is, used to manufacture hollow shafts. Austenitic stainless, as opposed to ferritic and martensitic, is the most widely used type of stainless steel for producing tubular shafts. Austenitic stainless is non-magnetic and is not air hardenable. Of the stainless steels, only martensitic is air hardenable.
In addition to austenitic, that is, 300 series, stainless steel's limitations vis-a-vis corrosion resistance, stainless steel cannot presently be fashioned to provide strength where needed at a competitive cost utilizing prior art methods. Austenitic steel can be drawn so it is butted and thereby provide reinforcement, however drawing requires a significant amount of labor, thereby increasing the cost. In addition, excessive drawing will introduce impurities into the grain boundaries of austenitic stainless steel.
BACKGROUND ART
The prior art suggests numerous, but unsatisfactory, methods for producing and/or reinforcing hollow metallic shafts. U.S. Pat. No. 1,944,069 describes a tubular metallic shaft closely simulating the wooden shaft used on a golf club reinforced within the tube by a convoluted material having reentrant portions extending longitudinally therefrom and separated by longitudinal ribs. U.S. Pat. No. 1,950,342 describes a hollow tubing metallic “steel” shaft with a core of sponge rubber. U.S. Pat. No. 3,762,707 describes the use of a material of a predetermined flexibility to a shaft which is used for a golf club. In addition, the interior of the shaft is partially filled from the point of attachment to the golf club head with a flexible plastic material. This plastic material is present within the tube from the point of attachment to a predetermined point.
Another unsatisfactory means of reinforcing hollow shafts is taught by U.S. Pat. No. 908,127 entitled Reinforcement for Metallic Tubing. This patent teaches tack brazing angle iron inside hollow shafts. This method provides shafts which are extremely heavy with reinforcement which has limited attachments to the hollow shaft it is reinforcing. Such an invention has no uses with the present demand for light, strong shafts demanded by present applications for hollow shafts.
The present invention provides an improved hollow shaft which can be reinforced in preselected locations. More particularly, the present invention solves the problems of the prior art by providing an air hardenable stainless steel tubing which can be reinforced or attached to other stainless steel tubing or steel without weakening the tubing or introducing impurities.
SUMMARY OF THE INVENTION
The present invention provides reinforced and hardened stainless steel tubing and methods for producing such tubing from an assembly of stainless steel tubing or pipe, a stainless steel reinforcement member and a brazing material. The method comprises introducing within the tubing a stainless reinforcement member, at least a portion of which contacts the internal surface of the tubing; contacting at least one confluence of the tubing and the member with a brazing material; introducing the assembly into a controlled atmosphere furnace; and brazing and hardening the assembly to form hardened and reinforced stainless steel tubing.
The present invention also provides a stainless steel tubular shaft, and methods of making same, made from air hardening stainless steel reinforced by a coil of stainless steel wire, said coil forming a tight fit between the outside diameter of the coil and the internal diameter of the shaft; and brazing material proximal to the loci of intersections of the coil with the tubular shaft.
The present invention also provides hardened stainless steel tubing and methods for producing such tubing from air hardenable stainless steel sheet and a brazing material, the method comprising selecting an annealed sheet of air hardenable stainless steel capable of being formed into tubing, the sheet characterized by a leading edge, two joining edges, a following edge, a top and a bottom; folding a portion of each of the joining edges; rolling the sheet in such a manner that it becomes tube-shaped; arranging the folded portions of the joining edges to form a seam; contacting the brazing material with a portion of the seam; introducing the assembly into a controlled atmosphere furnace; and brazing and hardening the assembly sufficiently to form hardened stainless steel tubing.
The present invention further provides methods for producing a unitary structural frame from an assembly of air
Hwu Davis
King Timothy J.
Scherbel David A.
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