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What Is Shrink-Fitting?

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  • Written By: Malcolm Tatum
  • Edited By: Bronwyn Harris
  • Last Modified Date: 15 November 2014
  • Copyright Protected:
    2003-2014
    Conjecture Corporation
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Shrink-fitting is a process that is often used in order to create a firm hold at the joint of two different materials. This approach normally calls for heating one of the components so that it expands enough to fit around the other. As the heated component cools, it begins to retract, creating a snug fit and seal at the joint. This process can be used in a number of applications, ranging from plumbing jobs to the creation of a number of different products.

The general idea of shrink-fitting focuses on what is known as thermal expansion. This is simply the understanding that certain types of metals and other materials will expand when subjected to a certain amount of heat for a specified period of time. While the material is still in an expanded state, it is possible to fit it around a different material that is at room temperature. Once the heated material begins to cool, it slowly contracts around the cooler material. The end result is a tight fit that makes the joint between the two components very secure.

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One of the easiest ways to understand how shrink-fitting works is to consider the need to join two sections of a drainpipe. One of the sections is heated to cause the end to expand. As the end expands, it is fitted over the end of the other section of drainpipe. At this point, whatever agent was used to introduce the heat is removed, allowing the heated section to gradually cool down. As it does so, the small space between the overlapping ends of the two sections also shrinks, creating a tight seal.

This same general concept of shrink-fitting can be employed in other applications. Wagon wheels are often rimmed with metal sections around the diameter of the wheels. In order to create a secure fit, the metal is heated until it expands enough to slip over the diameter of the wheel and then is allowed to cool. As the cooling takes place, the expansion reverses and the rim contracts to hug the wheel closely. The end result is a tight fit that is sometimes further secured with the aid of a few screws, ensuring that the wheel will remain functional for much longer than a wheel unprotected by the metal rim.

At times, the method for shrink-fitting will involve not only heating the external component but also applying some sort of cold to the inner component. This means that even as one component is being expanded with the use of heat, the other is contracting as the result of the introduction to cold. Using this dual approach can often expedite the joining of the two materials and also aid in creating a secure fit that is likely to last for a long time. While shrink-fitting was once done manually, the process today is often managed using technologically advanced equipment that is capable of achieving the ideal amount of exposure to heat and cold necessary to allow for the successful joining of components under optimum conditions.

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