I n t r i n s i c  D e v i c e s  I n c o r p o r a t e d

UniLok Applications

NiTi shape memory fastener rings for connectors, bellows, fuel duct, sensors, pipe couplings and accelerometers

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Braid terminations
Electrical connectors
Lens and window mounts
Magnet assemblies
Piezoelectric accelerometers
Shaft clamps
Axial preload
Threaded fastener preload
Threaded fastener locking
Hermetic sealing
Tube joints
Hose termination
Cylinder joints
Tamperproof fastening
Blind Assembly


Braid Terminations
Terminate metallic EMI shielding braids as well as Kevlar®, Tyvek®, steel and fiberglass mechanical braids.  Use for small diameter electrical cables, fiber optic cables, overbraided hoses, and towed array strength members.  UniLok is especially advantageous for applications with severe vibration, thermal cycling or high temperatures that lead to rapid deterioration of other braid termination types.

The UniLok ring produces a very high contact pressure between the braid and connector such that a "gas tight seal" is created. This means that oxygen is excluded from the contact area so the contact surfaces will not oxidize over time, whch would otherwise lead to increasing electrical contact resistance.

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Nitinol ring attaches emi emp shielding braid to connector adapter

Electrical Connectors
Zero insertion force combined with extreme retention strength and vibration resistance.  The exceptionally high contact closure force applied by the shape memory ring produces a gas-tight seal between contact surfaces, resulting in a stable, low-resistance connection.  Use for munitions, missiles, high amperage buss connections and bulkhead feedthroughs. The connector is de-mated by cooling with either liquid nitrogen or HFC spray refrigerant, depending on the alloy chosen.

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SMA ring actuated zero insertion force electrical connector

Lens and Window Mounts
UniLok rings apply even pressure to mount delicate lenses in holders. When a sealed mount is required, the ring compresses a non-slotted tubular fitting onto the lens or window. A soft metal plating may be applied to the fitting to enhance sealing. Use for sapphire, germanium, ferrite and calcium fluoride lenses and windows.

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memory metal ring clamps mounting fixture onto lens

Magnet Assemblies
Bind magnet assemblies where extreme temperatures, rpm or shock loading render other assembly techniques inadequate. 

UniLok shape memory rings offer over 10 times the motion of conventional thermal shrink fits. This allows looser tolerances on mating parts and results in the large interference strains needed to achieve consistent clamping pressure. Installation time for shrink fits can be quite limited, while heat-to-recover UniLok rings allow unlimited time for positioning components prior to shrinkage.

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metal shrink ring binds cluster of magnet segments or peizoelectric crystals

Accelerometer Assembly
Clamp mass elements and piezoelectric material against the center post of shear type accelerometers.  UniLok shrink rings provide easy assembly, consistent performance, and insensitivity to temperature extremes.

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NiTiNb SMA ring fastens piezoelectric accelerometer crystals and mass elements

Shaft Clamps
Reliable clamping in a lightweight, compact, balanced package.  No threaded fasteners to vibrate loose. Much smaller size than mechanical shaft collars of equivalent holding strength. Precise axial and angular positioning can be achieved since heat is used to set the clamp, rather than applying an external torque which can cause unwanted movement. Use for rotary power transmission, instrument assembly and torsion bars. We make UniLok shrink collars for small diameter shafts where other collar styles are unavailable.

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nitinol shape memory shaft collar attaches components such as gears and flexible couplings

Axial Preload
Allows a precise preload force to be applied and then locked in.  Avoids the fines generation which occurs when press fitting.  Use for bearings, disk mounting, and other axially preloaded assemblies.

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NiTi memory metal fastener ring disk mount locks in axial preload

Preload of Threaded Fasteners
UniLok memory metal rings installed as washers expand in length as they shrink in diameter, applying controlled preload.

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shape memory alloy bolt preload expanding washer

Locking Nuts
Heat shrink rings provide positive locking of critical threaded joints.  No interference with torque/tension relationship during tightening.

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free running nut locked by nitinol shrink ring for vibration resistance

Hermetic Seal
UniLok rings swage thin-walled metal cups and tubes onto headers to seal hermetic assemblies.  The ring drives the can onto the teeth and holds it there for the life of the joint. Use in the packaging of gyroscopes, sensors, fuses, and other electro/optical/mechanical packages.

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NiTiNb shrink collar seals cap on hermetic cannister

Tube Joints
UniLok heat shrinkable rings offer the controlled strength and uniformity of clamping pressure to terminate anything from thin elastomeric tubing to heavy wall steel pipe.

In the joint pictured, UniLok rings swage the tubes onto a fitting with circumferential sealing lands, teeth, on its outside surface.  This geometry is used for deformable composite tubing and thin wall metallic tubing such as aluminum conduit and ducting.
Generally, the fitting is a harder material than the tube.  The teeth bite into the tube, locally flowing the tube material to create the seal and providing a mechanical interlock for burst, tensile and bending strength.

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cryogenic NiTiFe shape memory tube coupling

Swaged Fitting Tube Joint
The UniLok ring compresses a fitting onto the outside of a tube.  Teeth on the inside of the fitting barrel are driven into the surface of the tube.  This design is applicable to most metallic pipe and tube except for very thin wall (small t/d).  It is also used for attaching metal fittings to rigid composite tube and polymeric fittings to thin wall metal tube.
Typically the fitting material is chosen to be of similar hardness to the tube.  However, polymeric fittings are generally of lower hardness than the tubing.  In this case sealing is achieved by flattening of the teeth against the tube.

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nitinol shrink ring swages fitting onto tube

Hose Termination
The UniLok ring compresses elastomeric or plastic tubing onto a fitting with closely spaced sealing lands.  Potential applications include sonar towed arrays, geophysical streamers, high temperature Viton® sleeving, Teflon® tubing, and wiring harness boots for high temperature applications.  Generally UniLok rings are advantageous for high strength or thin walled tubing where crimp rings and hose clamps fail due to insufficient retained clamping force or non-uniform clamping pressure. Thin UniLok bands can be used where the closure mechanism on other bands creates problems with snagging, space constraints or, in towed arrays, noise generation.

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heat-shrinkable metal hose clamp seals tube to fitting

Rod and Cylinder Mechanical Joints
Many designs are possible depending on the requirements and materials involved.  One cylinder may overlap the other with a UniLok ring compressing the outer cylinder onto the inner cylinder.  In other cases, each end of a coupling sleeve is compressed onto a cylinder end by a ring. The joint may hold by simple friction of smooth surfaces pressed together, or teeth can be machined on one surface to dig into the other.  The outer cylinder or sleeve is normally slotted to reduce the ring clamping force required.  Slots offer the additional benefit in toothed designs by introducing circumferential interruptions in the teeth that increase torque strength.  Use for telescoping structures, metal to ceramic joints, etc.

Large tubular structures can be joined with simple marmon clamps locked in place by shape memory alloy rings.


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High strength coupling with zero axial and angular play. 


rod coupling with SMA shrinking fastener rings


Interlocking crenellated cylinders, high torque strength

crenellated cylinder joint with shape memory lock ring

Tamperproof Fastening
UniLok nitinol rings are ideal for security and general tamper proofing applications, offering no conventional means of dis-assembly.  Removal generally requires cutting with powered abrasive tools or cooling with liquid nitrogen.  Use for field assembly of security hardware, tamperproof closures for instruments, etc..

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tamperproof closure locked by ntitinol shrink rings

Blind Assembly
Since UniLok rings are actuated by temperature, they can be installed in remote or inaccessible locations. Heating can be accomplished by placing the assembly in an oven, ducting hot air or oil to the ring, induction heating or by conduction from an electric heater element.


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blind assembly with SMA clamp ring
alloy selection
active fasteners
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AHE drawing
BHE drawing
part numbering
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AHM drawing
BHM drawing
material properties

Copyright 2003 Intrinsic Devices, Inc. All rights reserved.
UniLok® is a registered trademark of Intrinsic Devices, Inc.
Viton®, Teflon®, Kevlar® and Tyvek®are registered trademarks of DuPont