There are circumstances in engineering when you are faced with the problem of fitting incompatible parts. For example, the housing may be too big or small for the attachment component. And shrink fitting is a process that can help with this dilemma.

It is a technique used when employing an interference fit. Through this process, you can easily fit incompatible components together.

What Does It Mean to Shrink-Fit?

In engineering, there is what is known as an interference fit. For example, when fitting different parts of machinery or equipment, you need to attach two parts.

You can use an interference fit when a tight fit between two mating parts create a negative geometrical clearance, for example, where the inner part of a shaft is larger than the hole where it will be fixed.

So, there are two ways to do an interference fit. One is by using force, and the other by using a shrink-fit. Meanwhile, to shrink-fit means to use a heating or cooling component before installing the component in a piece of equipment or machine. After the component is installed, it returns to its original size as it regains its ambient temperature.

A shrink-fit is used for joining bearings, bushings, retainers, and hubs. Cold pressing these components ensures a tight fit for more reinforced strength of the joint created. So, after the components are shrunk, they can now be installed into their partner. They return to their ambient temperature via thermal expansion upon installation.

How Is a Shrink-Fit Done?

The process incorporates various techniques that utilise thermal expansion and contraction. It involves heating the outer attachment so that it expands.

Upon heating, the two portions can now fit together easily. In addition, the outer component will shrink as it cools down and returns to room temperature, creating a tight fit.

You can also achieve shrink fitting using cryogenic techniques. However, this process is the opposite of the procedure using heat.

Here, you cool the inner part using liquid nitrogen to cause contraction. When the internal component shrinks, it can now fit easily into the outer portion. Likewise, the part will expand as it returns to room temperature, creating a perfect fit with the external housing or attachment.

Why Liquid Nitrogen Is Good for Shrink Fits

Shrink-fit is essential for creating a strong interference between components by using liquid nitrogen. However, compared to the heating process, it causes less damage to the attachments.

The cryogenic process is better than the heating process. Meanwhile, it requires precision to create a reliable interference fit for various components like bearings, hubs, shafts, and sockets.

Some applications for shrink-fitted components include:

  • Gear mechanisms
  • Nuclear reactor vessels
  • Crankshafts used in ships

Unlike other applications for cryogenic techniques, shrink fits require only a small amount of liquid nitrogen. Therefore, using liquid nitrogen for shrink-fits doesn’t need the installation of onsite liquid nitrogen tanks. Besides, the use of liquid nitrogen is also known as one of the safest assembly processes. There is no likelihood of damage, unlike using a heating method.

It is useful to know what a shrink-fit is and how it works. It is an essential technique that anyone should use to attach various machinery and equipment components in engineering.

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