Shrink-fitting is a technique in which an
interference fit
An interference fit, also known as a pressed fit or friction fit, is a form of fastening between two tightfitting mating parts that produces a joint which is held together by friction after the parts are pushed together.
Depending on the amoun ...
is achieved by a relative size change after assembly. This is usually achieved by heating or cooling one component before assembly and allowing it to return to the ambient temperature after assembly, employing the phenomenon of
thermal expansion
Thermal expansion is the tendency of matter to increase in length, area, or volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions).
Substances usually contract with decreasing temp ...
to make a joint. For example, the thermal expansion of a piece of a metallic drainpipe allows a builder to fit the cooler piece to it. As the adjoined pieces reach the same temperature, the joint becomes strained and stronger.
Other examples are the fitting of a
wrought iron
Wrought iron is an iron alloy with a very low carbon content (less than 0.05%) in contrast to that of cast iron (2.1% to 4.5%), or 0.25 for low carbon "mild" steel. Wrought iron is manufactured by heating and melting high carbon cast iron in an ...
tyre around the rim of a wooden cart wheel by a
wheelwright
A wheelwright is a Artisan, craftsman who builds or repairs wooden wheels. The word is the combination of "wheel" and the word "wright" (which comes from the Old English word "''wryhta''", meaning a worker - as also in shipbuilding, shipwright ...
, or of a steel tyre to the
wheel
A wheel is a rotating component (typically circular in shape) that is intended to turn on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machin ...
of a railway engine or rolling stock. In both cases the tyre will be heated and expands to slightly greater than the wheel's
diameter
In geometry, a diameter of a circle is any straight line segment that passes through the centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...
, and is fitted around it. After cooling, the tyre contracts, binding tightly in place. The bombard
Mons Meg was assembled from longitudinal staves of iron held in place by shrink-fitted iron hoops.
A common method used in industry is the use of
induction shrink fitting which refers to the use of
induction heating
Induction heating is the process of heating electrically conductive materials, namely metals or semi-conductors, by electromagnetic induction, through heat transfer passing through an inductor that creates an electromagnetic field within the coi ...
technology to pre-heat metal components between 150˚C and 300˚C thereby causing them to expand and allow for the insertion or removal of another component. Other methods of shrink-fitting include compression shrink fitting, which uses a cryogen such as liquid nitrogen to cool the insert, and
shape memory coupling, which is achieved by means of a
phase transition
In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic Sta ...
.
References
External links
Overview of interference fits
Industrial processes
Materials science
{{Mech-engineering-stub