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 ''tight'' fitting mating parts that produces a joint which is held together by friction after the parts are pushed together.
Depending on the am ...
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 change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
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 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag Inclusion (mineral), inclusions (up to 2% by weight), which give it a ...
tyre around the rim of a wooden cart wheel by a
wheelwright
A wheelwright is a 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 or shaper of wood) as in shipwright and arkw ...
, or of a steel tyre to the
wheel
A wheel is a circular component that is intended to rotate 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 machines. Wheels, in conjunction wi ...
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 center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
, and is fitted around it. After cooling, the tyre contracts, binding tightly in place. 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 induction coil that creates an electromagnetic field within th ...
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 Shape-memory coupling is a system for connecting pipes using shape-memory alloys. In its typical form the technique uses an internally ribbed sleeve of alloy such as Tinel that is slightly smaller in diameter than the pipes it is to connect. The sl ...
, which is achieved by means of a phase transition.
External links
Overview of interference fits
Industrial processes
Materials science
{{Mech-engineering-stub