Shrink fitting is a procedure in which heat is used to produce a very strong joint between two pieces of metal, one of which is inserted into the other. Heating causes one piece of metal to contract or expand on to the other, producing interference and pressure which holds the two pieces together mechanically.
Most applications involve a shaft with a given outside diameter and another part such as a gear, steering knuckle, rollers or washer which has a bore hole. There are several forms of this type of joint, characterized by the amount of tolerance (space) between the two parts. The shrink fitting process is used for the interference fit type joint.
By heating the mass around the bore hole uniformly, it is possible to significantly expand the size of the hole. The shaft is then easily inserted into the expanded hole. Upon cooling, the mass around the hole shrinks back to its original size and frictional forces create a highly effective joint.
Industries and applications
- Railway - gearboxes, wheels, transmissions
- Machine tools - lathe gearboxes, mills
- Steel works - roll bearings, roll neck rings
- Power generation - various generator components
- Cement Industries rollers
- Rerolling mill rollers
Due to the need to insert a core and also that to be effective, the core has to be in relatively close proximity to the bore of the part to be heated, there are many application in which the above bearing heater type approach is not feasible.
There are a huge number of industries and applications which benefit from shrink fitting or removal. In practice, the methodology employed can vary from a simple manual approach where an operator assembles or disassembles the parts to fully automatic pneumatic or hydraulic press arrangements.
- Automotive starter rings onto flywheels
- Timing gears to crankshafts
- Motor stators into motor bodies
- Motor shafts into stators
- Removal and re-fitting of a gas turbine impeller
- Removal and re-fitting of hollow bolts in electrical generators
- Assembly of high precision roller bearings
- Shrinkfitting of 2-stroke crankshafts for ship engines
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