Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Temples
Reexamination Certificate
1999-11-24
2002-07-16
Mai, Huy (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Temples
C351S041000, C351S126000
Reexamination Certificate
active
06419358
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the fabrication of eyeglasses, and, more particularly, to the making of eyeglass frames and parts thereof from a nickel-free titanium shape memory alloy.
BACKGROUND OF INVENTION
Eyeglasses
Alloys used in conventional eyeglass frames include stainless steel, copper based alloys and nickel-silver.
Shape Memory Effect and Pseudo-elasticity
The concept of using shape memory alloys for eyeglass components has been suggested in numerous articles and patents. Y. Suzuki, at that time head of shape memory alloy research at Furukawa Electric in Japan, published in Kinzoku Journal, vol. 31, No. 11, p115, 1981, the advantages of pseudoelastic shape memory alloy wire for fixing a lens into a frame. These findings were incorporated in one of the earliest patents on shape memory alloy applications for eyeglasses, Kokai Patent 56-89715, (Publication Date: Jul. 21, 1981) whose applications date back to 1979. Since these earlier studies, many other patents have issued claiming the advantages of using shape memory alloys for eyeglass components.
The driving force for making metal eyeglass frames from shape memory alloys lies in their great resistance to permanent deformation as compared to conventional alloys employed in this application.
Shape memory alloys belong to a class which exhibit what is termed thermoelastic martensite transformation. The term martensite refers to the crystalline phase which is produced in steels when quenched from a high temperature. The phase which exists at the elevated temperature is referred to as austenite; these terms have been carried over to describe the transformations which occur in shape memory alloys. When a steel has been quenched from the austenitic temperature to martensite, to again form austenite requires heating the structure to quite high temperatures, usually in excess of 1400° F. By contrast, the thermoelastic shape memory alloys can change from martensite to austenite and back again on heating and cooling over a very small temperature range, typically from 18 to 55° F. The transformation of a shape memory alloy is usually described by its hysteresis curve.
Materials which undergo martensite transformation may exhibit “Shape Memory Effect” and “Pseudo-elasticity.” During the transformation on cooling, the high temperature phase known as “austenite” changes its crystalline structure through a diffusionless shear process adopting a less symmetrical structure called “martensite”, and, on heating, the reverse transformation occurs. The starting temperature of the cooling transformation is referred to as the M
s
temperature and the finishing temperature, M
f
. The starting and finishing temperatures of the reverse transformation on heating are referred to as A
s
and A
f
respectively.
Materials exhibiting Shape Memory Effect can be deformed in their martensitic phase and upon heating recover their original shapes. These materials can also be deformed in their austenitic phase above the A
f
temperature through stress-induced martensitic transformation and recover their original shapes upon unloading. This strain recovery, referred to as “pseudo-elasticity” [sometimes referred to herein as “PE”] is associated with the reversion of stress-induced martensite back to austenite. A well known shape memory alloy is nitinol, a near-stoichiometric alloy of nickel and titanium.
The Alloy Material
Pure titanium has an isomorphous transformation at 882° C. The body centered cubic (bcc) structure, so called &bgr;-Ti, is stable above the isomorphous point and the hexagonal close packed (hcp) structure, so called &agr;-Ti, is stable below. When alloyed with elements such as vanadium, molybdenum, or niobium, the resulting alloys have an extended &bgr; phase stability below 882° C. On the contrary, when alloyed with elements such as Al or oxygen, the temperature range of stable &agr; phase extends above the isomorphous point. Elements which have the effect of extending the &bgr; phase temperature range are called the &bgr; stabilizers while those capable of extending the &agr; phase temperature range are called the &agr; stabilizers.
For alloys with. a high enough concentration of &bgr; stabilizer elements, the material would be sufficiently stabilized to obtain a meta-stable &bgr; phase structure at room temperature. The alloys showing such a property are called &bgr; titanium alloys. Martensite transformations are commonly found among &bgr; titanium alloys. The M
S
temperatures in &bgr;-Ti alloys decrease with increasing amount of &bgr; stabilizer in the alloys, while increasing amount of &agr; stabilizer raises the M
S
. The dependence of M
S
on the concentration of some transition metals in binary titanium alloys is shown in
FIG. 14
[‘The Martensite Transformation Temperature in Titanium Binary Alloys’, Paul Duwez, Trans. ASM, vol. 45, pp.934-940, 1953]. Therefore, depending on the extent of stabilization, &bgr;-Ti alloys may exhibit martensitic transformation when cooled very quickly from temperatures above the &bgr; transus, the temperatures above which &bgr; is the single phase at equilibrium.
To exhibit PE at room temperature, the alloys must be sufficiently &bgr; stabilized to have the A
f
point suppressed to below the ambient, but still allow the formation of stress-induced martensite before plastic deformation occurs. That is, the stress level for the martensite to form must be lower than that of plastic deformation. Shape memory effect, on the other hand, is observed when an alloy has an A
s
point higher than and M
S
temperature slightly below room temperature. Stress-induced martensite transformations have also been observed in &bgr; titanium alloys [‘Formation and Reversion of Stress Induced Martensite in Ti—10V—2Fe—3Al’, T.W. Duerig, J Albrecht, D. Richter and P. Fischer, Acta Metall., vol. 30, pp.2161-2172, 1982].
Both shape memory effect and pseudo-elasticity have been observed in certain Ti—Mo—Al &bgr; titanium alloys [‘Shape Memory Effect in Ti—Mo—Al Alloys’, Hisaoki Sasano and Toshiyuki Suzuki, Proc. 5th Int. Conf. on Titanium, Munich, Germany, pp.1667-1674, 1984]. In order to obtain SME or PE at room temperature the material has to be properly heat treated to produce the uniform &bgr; phase structure. The heat treatment to achieve that goal is called a solution treatment in which the test sample is heated to temperatures slightly above the &bgr; transus for a period of time long enough to allow for full austenization and then immediately cooled to room temperature.
Some &bgr;-Ti alloys, for example, TMA (Registered trade mark of Ormco, Glendora, Calif.), has been successfully commercialized for orthodontic arch wire application. The detailed description of the applications and properties of &bgr; titanium wires can be found in U.S. Pat. No. 4,197,643. The TMA wires show a unique balance of low stiffness, high spring-back, good formability [‘Beta titanium: A new orthodontic alloy’, C. Burstone and A. Jon Goldberg, American Journal of orthodontics, pp.121-132, February 1980], and weldability. [‘Optimal welding of beta titanium orthodontic wires’, Kenneth R. Nelson et al, American Journal of Orthodontics and Dentofacial Orthopedics, pp.213-219, September 1987]. The nickel-free chemistry of the alloy makes it more tolerable to some eyeglass wearers. However, TMA wires utilize the inherent mechanical properties of the material through thermo-mechanical processing. The material does not exhibit PE due to the occurrence and reversion of stress-induced martensite in the material.
Eyeglass frames fabricated from shape memory alloys are known to possess the advantages of wearer comfort and great resistance to accidental damage. The alloy traditionally used for this purpose is an equiatomic nickel-titanium alloy which exhibits pseudoelastic properties. These alloys are difficult to form, and require very exacting heat treatment to yield the properties required for eyeglass components; in addition they cannot be readily fusion
Lei Chi-Yuan
Schetky L. McDonald
Wu Ming H.
Cohen Jerry
Kaye Harvey
Mai Huy
Memry Corporation
Pekins, Smith, Cohen
LandOfFree
Pseudoelastic &bgr; titanium eyeglass components does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pseudoelastic &bgr; titanium eyeglass components, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pseudoelastic &bgr; titanium eyeglass components will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2872388