Shrink Fitting

Tight Tolerance Fit

Shrink Fitting, or “compression fitting,” is a process that inserts a pin or bushing into a housing or other assembly requiring an extremely tight tolerance fit.  The shrink fitting process can be used as an alternative to conventional press fitting, or more likely, to permit a mechanical fit that otherwise could not be accomplished via the mechanical force of press fitting.

Components of All Sizes

NitroFreeze has successfully completed numerous shrink fitting projects, including large steel pipes, sized at over 24” diameter, to intricate miniaturized parts. Satisfied customers include large multinational corporations, US Department of Defense contractors, research labs, transportation industry, including trucking, air and railroad companies.

NitroFreeze is capable of shrink fitting applications either in-house or at your facility.
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Process

During the cryogenic shrink fitting process, the insert is cooled via exposure to a cryogen, typically carbon dioxide (solid or liquid) or liquid nitrogen in order to reduce its size through the contraction associated with reduced temperatures. A companion operation of heating the housing (or other part) that receives the insert is conducted to enlarge the opening by taking advantage of the expansion associated with increased temperatures.

While it is not always necessary to use both heating and cooling in combination, the most demanding shrink fitting applications, including those with the tightest tolerances, often require this multi-step approach.

Care should be taken when using any cryogen, and the material and relative masses should be considered carefully. Since steel may be subject to additional transformation when exposed to cryogenic temperatures, additional processing either before or after may be warranted. Heating of metals (for expansion) should also be controlled and not induce unnecessary thermal stress on the component during the shrink-fit process.