Shape Memory Alloy Products
The Product
UniLok rings offer new ways to join and seal cylindrical components. These nickel-titanium rings shrink 4.5% in diameter when heated. Once shrunk, UniLok rings apply a uniform gripping pressure that is seamless, powerful, consistent and permanent. The gripping force can be set between 220N (50lbs) and 130kn (30,000lbs) by choice of the ring dimensions. UniLok rings can clamp to a holder to a delicate optical lens or swage a fitting onto a pipe to seal 400bar (6000 psi). No other fastener system provides seamless radial pressure over these force levels with comparable radial close up.
UniLok rings maintain their grip over an operating range of -65C to +300C. If the rings are cooled with liquid nitrogen they will relax their grip, allowing disassembly or repositioning.
How They Work
The unique action of UniLok rings is unrelated to conventional thermal expansion. Intrinsic makes its products from proprietary nickel-titanium alloys that have a property called shape memory. These alloys undergo a transformation from one crystal phase to another at a particular temperature. The low temperature phase can be deformed from its original memory, shape and will remain in this deformed shape indefinitely. When heated later, the material transforms to its high temperature phase and returns to its memory shape.
Intrinsic Fabricates UniLok rings and expands them in diameter. The rings are supplied in this expanded condition. Rings are installed by heating. Most UniLok rings are made from Heat-To-Recover material. These rings begin to shrink at 50C (122F) and develop clamping pressure at 165C (330F). To insure full heating, Heat-To-Recover rings are marked with temperature indication paint that changes colour at 165C.
Sizes and Materials
Standard UniLok rings are available in a variety of rectangular and circular cross sections with inside diameters ranging from 1.4 mm (0.054") to 150mm (6.0"). New rings of virtually any size can be produced for specific applications.
While heat-to-recover rings are normally the best choice, Intrinsic offers Cryogenic and High-Recovery-Temperature rings to meet the needs of special applications. Cryogenic rings are shipped, stored and handled in liquid nitrogen. They recover on warming to room temperature. This is a benefit when working with large assemblies or heat sensitive components. High-Recovery-Temperature rings shrink at temperatures between 80C (175F) and 120C (250F) but relax on cooling to room temperature. They are typically used in temporary clamping applications.
Benefits
UniLok rings produce highly reliable joints because the shrinkage and clamping pressure generated are fundamental properties of the ring material. Benefits over conventional techniques such as crimping, welding, adhesives, elastic assembly and threaded fasteners include:
• Operator insensitive assembly
• Low installation temperature
• Joins and seals dissimilar materials
• Repeatability
• Seamless 360 clamping pressure
• Immunity to vibration, shock and thermal cycling
• Chemical Resistance
• Rotary balance
• A unique product that enables efficient designs
Hermetic Sealing
UniLok rings swage thin-walled metal cups onto headers to seal hermetic assemblies. Rings can be used in the packaging of gyroscopes, sensors, fuses, and other electronic packages. This application illustrates the capability of the UniLok to join dissimilar materials such as aluminium canisters to Kovar Headers.
Braid Termination
UniLok rings are used to attach cable electromagnetic shielding braids to connectors or other devices. Metallic and polymeric braids serving mechanical functions can also be clamped. This termination method is especially advantageous for applications that subject joints to thermal cycling, heat aging, vibration, and mechanical shock.
Pipe and Tube Joints
UniLok rings offer the controlled strength and uniformity of clamping pressure to terminate anything from thin elastomeric tubing to heavy wall steel pipe.
Piezoelectric, Magnetic and Optical Cluster Assemblies
UniLok rings provide easier assembly, more consistent performance, and greater insensitivity to temperature extremes than thermal shrink-fit rings, press-fit rings or adhesive bonding.
Reliable Electrical Interconnections
UniLok rings are used to create zero insertion force, high retention strength connectors. The exceptionally high contact closure force generated by the ring produces a gas-tight seal between contact surfaces, resulting in a stable, low-resistance connection. The dependability of UniLok rings makes them ideally suited for high amperage electrical connections subjected to heat and vibration.
Shaft Mounted Components
UniLok rings can fix the location and angle of a component at any point on a shaft. If desired, a controlled axial preload force can be locked in. Benefits in this application include size, weight, balance, consistency and reliability.
