TAI provides on-site testing and analysis services here at our Boulder, CO facility (though we partner with an internationally renowned test facility for shock and vibe testing). From stiffness, to thermal conductance, thermal cycling, shock & vibe, tensile strength measurements and more, we have you covered! While we provide most of our own testing services, our sister company, TAI, Inc., can also provide some strap testing services, and they will be releasing their own thermal strap products and thermal management services in late 2017.
TAI also provides complimentary thermal assessments, providing mass and performance projections, schedule and pricing ROM's, and (when possible/if viable), Preliminary Trade Analysis of alternative aluminum and copper straps.
Which Flexible Thermal Link / Strap is Best for Your Application?
With several strap products to choose from, it is important to understand which material and configuration may make the most sense for your program, given your performance requirements, and the environmental/operating conditions. The list below details some of the most important factors to consider when making your decision:
|Range of Motion
Copper Rope / Cabling Straps (CuTS®)
Depending on who makes your straps, copper rope (cabling / braid) assemblies are either soldered/brazed/welded, or made using proprietary cold press (solderless) processes (by TAI).
When it comes to flexibility, durability, and performance, the OFHC copper rope strap is the preferred, and most frequently used, in all industries/applications. They are the most durable of all thermal strap products available, and are the ideal choice for applications operating at < 60K. They offer flexibility on all axes, and can handle exponentially greater loads and life cycle bending/flexing (TAI's CuTS® assemblies utilizing our OFHC UltraFlex™ Copper Cabling, have been flex tested to 1,000,000 cycles).
TAI's CuTS® are the most affordable copper rope thermal straps on the market, and the lowest priced straps commercially-available. They typically cost just 1/5 - 1/2 the price of any competing metallic foil or rope thermal strap, and just 1/5 - 1/10 the cost of any carbon strap available.
Most customers prefer to use CuTS® for cryocoolers, space applications, electronics cooling, and cold laboratory instruments, because they offer the best combination of high flexibility, durability, thermal performance, vibration damping, and extremely low cost.
- Mass: Copper is heavy, and in extremely mass-sensitive applications, a graphite strap may be your only option, especially in those requiring a high conductance to low mass ratio, or those above 60K.
- Copper rope straps---even those made by TAI---can be stiff if multiple rows are incorporated into the design AND the braid length is below 1". At these shorter lengths, they still offer improved flexibility over stacked metallic foils, but they are not as flexible as single row or longer double row CuTS®.
Graphite straps offer the highest thermal performance of any of the strap products (above cryogenic temperatures); ranging from 800 W/(m-K) - 2,000 W/(m-K). TAI's pyrolytic graphite sheet links / straps (PGL™), offer the highest thermal performance in the industry; with over 2x the material conductance of our graphite fiber straps, and >30% performance over any competing graphite or graphene sheet thermal strap. Graphite straps are also the lightest thermal links commercially-available; weighing in at just 1/4 - 1/10 the mass of all other strap types (making them ideal for many spacecraft / satellite applications).
Whether one uses a stacked film/sheet or rope/woven cloth form, the assembly methods involve epoxying graphite or carbon/mulitlayered graphene composite material, into fittings made of aluminum, other metals (copper, titanium, etc.), or composites. Graphite fiber rope and woven sheet straps (GFTS® - only made by TAI), offer flexibility, have spaceflight heritage, and are fairly durable (spaceflight qualification data is available on our website, and upon request). Stacked non-woven sheet configurations (PGS and graphene composite), while extremely fragile, offer greater flexibility on 2 of 3 axes, and improved thermal performance by roughly 20-40% (depending on the material, and after taking into account resistance losses due to the materials and assembly process). Graphite and carbon-based straps in general, are ideal for thermally conductive vibration damping/isolation. However, there are significant trade-offs...
- Unlike Woven Graphite Fiber Sheets (TAI's GraFlex III), stacked pyrolytic graphite and multilayered graphene composite foils/sheets/films are extremely fragile. These can be damaged easily----something as simple as improperly removing the material or strap assembly from its plastic bag can cause the sheets to tear. Graphite rope/GFTS® assemblies are far more robust, but they too, are not as durable as metallic straps.
- Graphite straps are not ideal at very low temperatures (< 60K). Performance drops quickly and dramatically below 100K, and bottoms out at temperatures typically associated with cryocoolers, cryomodules, dilution refrigerators, and other equipment operating in the mK, or 4K to 40K range (making OFHC copper or 5N aluminum more attractive).
- Graphite straps are expensive. While TAI's GFTS® and PGL™ products now sell for the same price as competing metallic foil straps, they are still more expensive than CuTS®, and can also include NRE/design fees (in a prototype program), that are higher than metallic straps. However, TAI's graphite / carbon straps are the most affordable carbon based straps commercially-available.
Stacked Metallic Foil Straps (Copper and Aluminum)
Volume-restricted applications (requiring high thermal performance), may sometimes benefit from a stacked foil configuration (especially if the operating temp is between 50K - 80K). Cu foil straps---due to the increased density/cross sectional area of the flexible portion of the strap---can offer slightly improved thermal performance over rope straps/CuTS® (depending on the type of cabling/weave). In extremely mass-sensitive applications, a stacked aluminum foil strap may be a better alternative, but you often sacrifice performance. These straps are usually made via welding, or pressing foils, and then brazing the assembly.
- Stiffness: Depending on the thickness and length, foil straps often extremely stiff on each axis. As a result; they are often designed into "S" and "U" shapes, to give them any flexibility at all (on the other x and z axes). However, doing so increases the length of the strap, which often negates the benefits of using foils to begin with. For example: many of our customers are able to substitute a much shorter copper rope or carbon strap (with a gentle L or U shape), resulting in reduced or equivalent mass, while offering equivalent (or improved) performance. Further, substituting a cu rope strap (for an al or cu foil), often saves our customers thousands of dollars per unit (see below).
- The assembly methods (brazing/soldering/welding) cause increased stiffness.
- Foil straps typically cost 2-5x more than our CuTS®. Not only are the materials more expensive, but the assembly process is more complex and involves additional steps and costs (thus the exponentially higher price).
In most cases, foil straps are not the ideal solution. However, there are specific applications and environments in which they may offer benefits over a graphite or copper rope strap.
Copper vs Graphite Thermal Conductivity