Shrink Fitting with Induction Heating

Click links below to read one of our many shrink fitting Application Notes; Learn how you can benefit from the advantages of induction heating:

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Overview
Using Induction
Setup
Materials
Problems
Tricks

Most applications involve a shaft with a given outside diameter and another part such as a bearing, gear, steering knuckle 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.

Calculations For Shrink Fitting

Modern induction heating systems provide the speed, accuracy and repeatability necessary to produce quality shrink-fitted joints. With a properly designed work coil, induction heating can uniformly heat the bore hole, producing repeatable expansion. With the remote heat station capability of solid state induction heating power supplies, shrink fitting can be done on the production line.

Induction systems typically used for metal to shrink fitting range from 1 to 20kW, depending on the parts and application requirements.

For induction shrink-fitting applications a pancake or helical-shaped coil is placed inside the metal part that is to be expanded. RF power is applied until the part reaches the appropriate temperature. The induction coil is then quickly removed from the hole and the shaft that is to be inserted is then slid into position. The assembly is then allowed to cool. Pressure develops as the heated component contracts. Depending on the mass of the material to be expanded, a pancake-shaped coil is sometimes employed.

Metal parts: metal housing material (bearing, gear, etc.) with a tight tolerance opening; insert for housing (tight tolerances on the outer diameter are also important)
Alignment fixture (optional)
Power Supply & Induction Coil: Fast, precise heating works best.

If the inner and outer diameters of the bearing or gear are not held at tight tolerances, the shrink fit will not be possible.
There can be no burs on the joining surfaces.
If the two metal parts are not properly aligned, the shaft will not slide into the correct position.

Allow a long soak time for the metal housing (bearing, gear, etc.) to ensure that the whole mass has reached uniform temperature and expanded.
Employ an alignment fixture to smoothly guide the shaft into the housing.

utm_medium	material	docid	title	blurb	regn_link	pre-reg link	pre-link ppc	post-reg link	onClick download	onClick, View
shrink fitting	steel	shrinkfitting_16	Shrink fitting a gear securely on a shaft (automotive)	The customer was using a torch, which can lead to inconsistent part quality. Induction's precise heating means the client can count on consistent results in their process	apps_able.php	shrink-fitting.php		db_shrink.html
shrink fitting	stainless steel	shrinkfitting_13	Heating a stainless steel sleeve for industrial washers	The customer currently uses electric ovens that run 24 hours a day, 5 days per week and their primary concern is to save on the energy cost of heating the parts in the ovens.	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_12	Shrinkfitting a steel mud pump liner	A twenty-turn helical coil is used to heat the chain. The chain is fed through the coil at a rate of 1 meter per minute to reach the desired 1760 ºF (960 ºC) for the tempering process...	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_11	Shrink fit a steel gear onto a steel gear motor shaft	A four-turn helical internal coil is used to heat the gear bore. The coil is inserted into the gear bore and power is applied for 90 seconds to reach the required 400 ºF (204 ºC) and expand the gear bore...	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_10	Shrink fitting a carbide ring into a valve seat	A three turn helical coil is used to heat the steel valve seat. The steel valve seat is placed in the coil and heated for 50 seconds to enlarge the center hole & drop the carbide ring in for the shrink fitting process.	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_9	Shrink fitting auto turbo charger impeller blades onto an aluminum shaft	Induction heating provides repeatable results, reduced cycle time, lower consumables cost and even distribution of heating	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_8	Shrink fitting aluminum pulley to insert inner bearing	A three turn helical coil is used to heat the aluminum pulley. The pulley is heated to 464 ºF (240 ºC) in 20 seconds to expand the inner diameter and then the inner bearing is inserted to form the completed part.	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_6	Shrink fitting an assembled wrist pin into a connecting rod	Induction heating provides more accurate control of heat vs a flame burner, it heats only the knuckle, not the whole part, it prevents discoloring due to lower temperature used and increases productivity due to repeatability & ease of operation. A foot pedal & timer is used.	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_5	Shrink fitting a cast iron rocker arm assemblies	A four-turn helical coil heats the ring at one end of the assembly. The coil is designed to concentrate the field towards the center of the assembly where the thermal mass is greatest.	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_4	Shrink fit a motor shaft and roller	Processing with induction heat saves power and time. The complete tube does not have to reach the desired temperature as it does when heating with an oven. Being able to selectively heat a zone allows for a much quicker transfer of heat.	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_3	Shrink fitting a Camshaft Gear	Heating a camshaft gear with a bore size of 1.630" to shrink fit over a steel shaft that has a diameter of 1.632". A temperature of 500F is required for the gear to expand 0.002" in order to slip over the shaft.	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_2	Shrink fitting a Fuel Pump Housing and Inserts	To heat an aluminum fuel pump housing measuring 8" x 4 1/2" x 3 1/2" to 375F, allowing steel parts to be inserted.	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired
shrink fitting		shrinkfitting_1	Shrink fit a carbon graphite ring insert into an outer steel band	Induction heating provides a highly effective joint, accurate & repeatable heat, precise control of cycle times, uniform and repeatable results and hands-free heating that involves no operator skill for manufacturing	apps_able.php	shrink-fitting.php		db_shrink.html		not needed; hard-wired