Threaded – headed fastener – or washer making: process and apparat – Process – Making externally threaded fastener – e.g. – screw or bolt
Reexamination Certificate
1994-12-06
2002-07-30
Larson, Lowell A. (Department: 3725)
Threaded, headed fastener, or washer making: process and apparat
Process
Making externally threaded fastener, e.g., screw or bolt
C411S909000
Reexamination Certificate
active
06425829
ABSTRACT:
This invention relates to a threaded load transferring attachment for a device having high strength, high elastic elongation, and high damping characteristics. More particularly, this invention relates to an apparatus and method for threaded attachment of a device made of shape-memory effect alloy, such as Nitinol, to another member for transferring loads between the device and the other member.
BACKGROUND OF THE INVENTION
Shape memory effect alloys are intermetallic compounds that have some characteristics that would make them good candidates for many types of load transferring devices. Type 55 Nitinol, an intermetallic compound of approximately 55% nickel and 45% titanium, is one such alloy. In certain metallic states, its yield strength increases as work is applied, and it has a remarkable ability to absorb and dampen vibration. In certain metallic states, the alloy can undergo elongation of as much as 60% exerting an increasing resistance and elastic restoring force which would make it ideal for a self-locking, strain indicating fastener. When the alloy is strained in its Martensitic state and then heated to its Austenitic transition temperature, it spontaneously exerts a restoring force on the order of 100 KSI to restore the material to its pre-strained shape. This shape-memory effect of Nitinol makes its use in actuators particularly attractive because such actuators can be made with no moving parts such as electric motors, and without pyrotechnic gas generators or hydraulic systems.
Despite this potential, shape memory effect alloys have not been widely used in load transferring applications, primarily because of the difficulty in attaching the load transferring device to the load bearing member. Threading, the simplest and most widely used fastening technique for connecting a load transferring device to a load bearing member, has not been used for Nitinol because it is very difficult to cut, apparently because of its characteristic of increasing yield strength as cold work is applied. Even the hardest threading tools are quickly dulled or broken when attempting to cut Nitinol. Thread grinding of Nitinol would be slow and cause rapid wear of the grinding wheels, hence it would be uneconomical and unsuited to high volume production.
There are other techniques for connecting a Nitinol load transferring device to a load bearing member, but they are usually time consuming, inconvenient, expensive, not removable, and/or prone to failure. They include welding, clamping, crimping and separate fasteners. The use of fasteners is difficult because it usually requires drilling a hole in the Nitinol element, but there have been no known practical methods for production drilling of Nitinol; its increasing strength as cold work is applied quickly ruins ordinary drills. Clamping and crimping are difficult processes to control for consistent quality, and they tend to loosen over time because of vibration and thermal expansion. Welding produces a permanent connection which is often undesirable, and it creates a heat affected zone in the Nitinol that can change the desirable metallurgical characteristics of the material. These methods are used occasionally because there have been no known processes for threading Nitinol material. It would be a significant advance in the art to have available a fast, inexpensive and precision process for making threads in Nitinol and other shape memory effect alloy elements for making a fast, convenient and secure attachment for the element to a load.
When strained up to 8% in its Martensitic state and then heated to its transition temperature, Nitinol spontaneously exerts a restoring force equivalent to about 100 KSI to return to its pre-strained shape. This shape memory effect of Nitinol has been utilized to make Nitinol actuators, used for example to deploy missile fins after launch from a launch tube. Such an actuator includes a Nitinol element, such as a wire or ribbon, strained in its Martensitic state by as much as 8% and connected between the movable member (such as the missile fin) and a fixed member. A source of heat is provided for the Nitinol element to raise its temperature to the Austenitic transition temperature, whereupon it will exert a substantial force to return to its pre-strained shape. The source of heat can be a pyrotechnic or a resistance heating element surrounding the Nitinol element, or more typically, can be a source of electric power for passing a current through the Nitinol element itself, thereby raising its temperature by resistive heating.
A need exists for a blind-side capture device that is reliable, simple, light weight, inexpensive and remotely operable. One application for such a device is in spacecraft wherein a deployable structure, such as a pivoted arm or boom, must be secured permanently in its deployed position after it is deployed. Spacecraft and many other systems need reliable mechanisms, especially when the consequences of failure of the mechanism could be failure of the entire system. Reliability is often inversely proportional to complexity, so simplicity is a virtue in such systems, especially when it also saves weight and cost. The actuation of the latch in such fasteners is conventionally done by an electric motor or by a pyrotechnic device. Motors are heavy, expensive and failure prone. Pyrotechnics are usually fairly light weight, but produce undesirable shock and fumes that can be damaging to sensitive instruments, and the speed of actuation is difficult to control. If a blind side fastener could be actuated by a Nitinol actuator element instead of motors or pyrotechnics to secure a deployable structure in its deployed position, it would provide the needed capability and reliability without shock or fumes while reducing the cost and the weight of the mechanism to do the job.
Another actuator with many actual and potential uses in aerospace and other applications is the pin puller. A pin puller is a device having a pin supported at its two ends, releasably supporting a load on the middle section of the pin between the two supports. The load can be remotely released by axially withdrawing the pin from one of the supports and into the other support. Conventional pin pullers use pyrotechnics to pull the pin, but pyrotechnics have come into disfavor because of the risk to personnel installing the pyrotechnics, and also because of the shock and fumes produced when the pyrotechnic is initiated. However, they are used anyway because heretofore there have been no alternatives that matched the simplicity and reliability of the pyrotechnic pin puller. A pin puller that could use a Nitinol actuator element to withdraw the pin would provide the same or superior simplicity and reliability without the danger, shock, and fumes produced by pyrotechnic pin pullers.
Equipment and machinery mounts are widely used throughout industry and in consumer products to support machinery and equipment, and to isolate it from vibration, or isolate the structures on which they are mounted from vibration which the equipment or machinery produce. Motors and compressors are common examples of machinery that produces vibration, and this machinery is often mounted on vibration isolating mounts. The mount is often a resilient device, such as spring feet for mounting a compressor, and sometimes includes a damping device, combined sometimes in a single element such as an elastomeric pad. These devices usually perform adequately when they are new, but are subject to fatigue and deterioration with age and gradually lose their vibration isolating qualities as they age.
Nitinol functions well as a spring because of its high elastic elongation capability in the “superelastic” form, and because, in both its Martensitic binary state and the superelastic form, it also has a damping capability that enables it to absorb a large percentage of the energy in vibrations. Moreover, it is virtually inert and unaffected by very high temperatures, so it can withstand environments that would quickly destroy an elastomeric mount. It can be easily tuned to pr
Larson Lowell A.
Neary J. Michael
Nitinol Technologies, Inc.
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