ALLVAR negative thermal expansion washers and spacers are designed to combat changing preload with temperature. Drastic temperature changes and thermal cycling can cause brutal wear and tear on a variety of fastened assemblies. When tight margins of safety create a near-unobtainable preload requirement, securing these assemblies can be challenging. Negative thermal expansion alloys can help solve your tough thermal fastening issues with constant preload washers, ensuring a safe and reliable system with joints that endure wide temperature ranges.

Constant Preload Washer Features

Negative Thermal Expansion (NTE) ALLVAR Alloy 30:

  • Has an axial Coefficient of Thermal Expansion of -30.0ppm/°C at room temperature.
  • Has a positive CTE in the radial direction (similar in magnitude to Aluminum).
  • Can stabilize the mechanical force on other components. In a fastened assembly, the NTE can compensate for the expansion or contraction mismatch between the bolt and structural components.
  • Exhibits mechanical and material properties similar to other Titanium alloys.
  • Can be machined like many other metals, tolerances of ±0.001” are easily achievable for the most critical applications.
  • Is manufactured into standard size washers and custom thickness spacers.
Constant preload enabled by negative thermal expansion washers utilizing thermal mismatch

Value Propositions for Constant Preload Washers

ALLVAR Alloy constant preload washers:

  • Enable smaller, lower profile, and lighter structures by eliminating the need for long compliant bolts and flexures.
  • Increase structure longevity by reducing thermal cycling fatigue.

The image to the left demonstrates how preload fluctuations stay below ± 200N simply by using an ALLVAR Alloy washer or spacer. Without the ALLVAR Alloy washer or spacer, LAV/Lplate=0, the clamping force is significantly reduced as temperature decreases. With an ALLVAR Alloy washer thickness of 20% of the plate thickness, LAV/Lplate=0.20, there is a near constant load kept across the same temperature range. This is a huge difference from the 50% preload reduction with a 120°C temperature change. 

That is why we call these constant preload washers. When used to combat thermal mismatch, these washers compensate for the thermal mismatch between the bolt and plate material, creating a more reliable joint across wide temperature ranges.

NTE Washer and Spacer Products Available

Negative CTE washers and spacers from ALLVAR compensate for the natural expansion and contraction of other materials with variations in temperature. ALLVAR Alloy washers and spacers combat other materials’ thermal displacement to keep constant preloads – whether it’s 80°C or -150°C. Athermalization of fastened assemblies can be achieved by eliminating the thermal changes in clamping force induced by different materials’ CTEs.

Nominal Washer size Washer Inside Diameter Washer Outside Diameter Thickness Range Washer Standards ASME B18.24 Part Number Item Number
Nominal Washer Size
Washer Inner Diameter
Washer Outer Diameter
Thickness Range
Washer Standard
ASME B18.22.1 Part No.
0.028" - 0.036"
ASME B18.22.1
0.036" - 0.045"
ASME B18.22.1
0.036" - 0.045"
ASME B18.22.1
0.036" - 0.045"
ASME B18.22.1

Design Resources for ALLVAR Thermal Compensation Washers

We have resources to help you design with ALLVAR Constant preload Washers. Explore the following informative articles and guides for more information.

Thermal Compensating Washers for CTE Mismatch

Learn how to use negative thermal expansion ALLVAR washers or spacers to maintain a constant preload.

Design with Athermal Materials in SOLIDWORKS

Ready to get your hands dirty designing with ALLVAR Alloy 30? Request the material definition file on this page and follow the guide to model with ALLVAR Alloy 30.

Cryogenic Solutions for Thermal Expansion

A short article about ALLVAR Alloy 30 washer compensated joints in cryogenic environments

Introductory Guide to Tailored Thermal Expansion

Want to create a zero or tailored CTE Structure? Learn how to tune CTE by compensating positive CTE materials with negative CTE ALLVAR Alloy 30.

CTE Mismatch in Bolted Joints – Negative Thermal Expansion Washers offer a solution! 

Learn how to tackle CTE mismatch – one washer at a time – with this bolted joint simulation case study.

Constant Preload Washer Related Posts

Learn more about negative thermal expansion washers and spacers and the work being done on this application in the ALLVAR blog series.

Knowledge is Power

Our ALLVAR University video series offers a deeper dive into designing with ALLVAR Alloy 30. These specific videos offer more information related to the constant preload washer application.

Contact Us Today to Revolutionize Your Thermal Performance

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