There are times in engineering when you have to fit incompatible pieces together. Because it is too large or too little, the attachment component may not fit in the housing.

Shrink fitting is a technique used for an interference fit. This method can be used to integrate incompatible parts easily.

A tight fit between two mating pieces creates a negative geometric clearance. For example, a shaft’s inner diameter exceeds the hole where it will be fastened. You can make use of interference fit here.

An interference fit has two options. One by force, the other via shrink-fit. To shrink-fit means to use a heating or cooling component before placing it in a machine or equipment.

After installation, the component reverts to its original size and temperature. For example, a shrink-fit connects things like bearings and hubs. Cold pressing these parts makes sure they fit together tightly, making the joint stronger.

So, now that the parts have been shrunk, you can put them with their mate. After their placement, the temperature returns to normal owing to thermal expansion.

Shrink Fitting: Procedure

Thermal expansion and contraction are used in various ways in the process. The exterior attachment must be heated for it to expand.

Once heated, the two pieces are now a perfect match. As the outer component cools and returns to room temperature, it shrinks and provides a snug fit.

You can also make things shrink by using cryogenic methods. However, this process is very different from the one that uses heat.

To induce contraction, you cool the interior component using liquid nitrogen. Now that the inside component has shrunk, the exterior section of the item can easily accommodate it. The component will also expand at room temperature, allowing a snug fit with the exterior housing or attachment. Several industries employ this approach nowadays. Here’s why.

Why do Industries Prefer Cryogenic Fitting?

An advanced science, metallurgy is essential to many industries, construction sites, and other places of work. Cryogenics’ technological integration with various mechanical processes has boosted productivity in these fields. The following are the reasons why it is becoming more popular:

  • Melting two metals together does not change their composition.
  • The subzero temperatures chill the inner sections of components to expedite the procedure.
  • By rapidly cooling it to its freezing point, the cryogenic liquid shrinks the metal formed inside the other. After determining and finalising the position, the metal is cooled down to room temperature.
  • The final shape of the component is seamless and clean after the fitting process.
  • Heating a component to shape will cause it to overheat and melt. It degrades the element’s physical and chemical properties. The cryogenic fittings ensure that the components retain their original shape.

Summing Up

Shrink fitting is a critical technique that everybody in engineering must know. Shrink-fit is required when using liquid nitrogen to create a substantial interference between components. However, it is less damaging to the attachments when compared to heating. 

Notably, cryogenic processing is considered to be superior to thermal processing. Besides, cold shrinking uses extremely low nitrogen temperatures to shrink components. The cooling trays can shrink a part to the point where it can be put into an engine block. 

When the part reaches room temperature, it expands and firmly anchors itself in the engine block. This is a shrink fit.

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