fastener has been a boon to engineering, allowing the application
of axial loads to join a wide variety of components. Inventors
have struggled to come up with analogous devices to apply a
uniform radial load to fasten and seal cylindrical components.
This has brought us press fits, thermal shrink fits, shaft collars,
hose clamps, crimp rings, magnetic pulse forming, etc.
UniLok rings offer new ways to
join and seal cylindrical components. These metal rings
are supplied in the expanded condition and shrink 4.5% in diameter
when heated. Once shrunk, UniLok rings apply a uniform
gripping pressure that is seamless, powerful and consistent.
The gripping force can be set between 220 N (50 lb) and 130
kN (30,000 lb) by choice of the ring dimensions. UniLok
rings can clamp a holder to a delicate optical lens or swage
a fitting onto a pipe to seal 400 bar (6000 psi). No other
fastener system provides seamless radial pressure over these
force levels with comparable radial close-up.
UniLok rings are made
with nickel-titanium shape memory alloys, sometimes called
memory metal or Nitinol. See the Technology
page for a discussion of the shape memory effect.
We produce UniLok rings
from several different alloys, each formulated and processed
to achieve specific functionality. However, we will restrict
discussion here to our most commonly used material, Alloy H.
This alloy has a Heat-To-Recover characteristic that makes it
suitable for most fastening and sealing applications.
If you find this alloy does not produce the behavior you need,
consult the Alloy Selection
page to see if any of our other materials are better suited.
H-T-R rings begin to shrink when
heated above 45°C(113°F). Full clamping force
is achieved by heating to 165°C(330°F). To insure
full heating, H-T-R rings are marked with temperature indicating
paint that changes color at 165°C. HTR rings maintain
their tight grip over an operating range of -65°C (-85°F)
to +300°C (+572°F). If the rings are cooled
with liquid nitrogen they will relax their grip on cooling below
-120°C, allowing disassembly or repositioning.
UniLok rings produce highly reliable joints because the shrinkage
and clamping pressure generated are intrinsic properties of
the ring material. Benefits over conventional techniques
such as crimping, welding, adhesives, elastic assembly and threaded
-low installation temperature
-joins and seals dissimilar materials
-simple verification of correct installation
-seamless 360° clamping pressure
-immunity to vibration, shock, and thermal cycling
-a unique product that enables efficient designs
Follow these simple steps
to select the proper ring.
1) Select the
UniLok product drawing for the desired ring geometry.
Locate rings of the nominal diameter required.
2) Based on the
ring cross-section dimensions, and the nominal clamping forces
tabulated, choose a ring that meets your space constraints and
force requirement. See PD-009
Clamping Force Calculation for the relationship between
clamping force, pressure, and ring stress.
3) The outside
diameter of your assembly where the ring will be installed is
termed the substrate diameter. Adjust the substrate diameter
and its tolerance such that:
substrate diameter is smaller than the "Minimum As Supplied"
ring ID to insure installation clearance.
minimum substrate diameter, when compressed by the ring, is
larger then the "Minimum Substrate Diameter" to insure clamping
some UniLok rings and try them out! The clamping force
varies somewhat with the heating method, the substrate materials
and geometry, and the operating temperatures. Functional
testing is required to confirm system performance. Odds
are, the ring you have selected will do the job.
UniLok H-T-R rings are easy to install.
Position the ring on your assembly and heat until the thermochromic
paint changes color. Heat may be applied by oven, hot
air gun, infrared, direct electric resistance heating, etc.
H-T-R Ring Removal
Rings may be removed by cutting with abrasive or carbide tools.
Alternately, HTR rings will relax their grip if cooled below
-120°C (-185°F) using liquid nitrogen. Rings will
re-grip on warming to room temperature. However, the gripping
force is sensitive to changes in the substrate diameter.
Please consult Intrinsic if your application requires multiple
mate / de-mate cycles.
See the UniLok
HTR Installation Guide for more detailed information regarding
installation and removal.
Once installed, Alloy H behaves like a conventional material,
except at low temperatures where the clamping force is reduced.
Normally, minimum operating temperatures can be specified at
-55°C to -65°C. Qualification testing should always
include functional testing at the minimum operating temperature
of the assembly.
Standard Alloy H UniLok rings are available in a variety of
rectangular and circular cross-sections with inside diameters
ranging from 1.4 mm (0.054") to 150 mm (6.0"). New
rings of virtually any size can be produced for specific applications.