Boosting the scope of shrink fits with engineering adhesives

01 April 2019

Bonded shrink fit assemblies not only enhance the service life of an assembly but pave the way for new design concepts and cost savings.

Higher load transmission can be obtained from existing designs and geometries and there’s the potential for equal performance with relaxed tolerances and the reduction in size and weight of the assembly.

Traditional interference fits generate strength solely from metal-to-metal contact of surface peaks, an area that represents a relatively small percentage of the overall joint surface. Small micro-movements at the joint interface can produce particles which abrade and reduce the contact surface even more. This leads to fretting corrosion, accelerated wear and ultimately, failure.

In a bonded assembly, anaerobic retaining adhesives fill the surface irregularities and clearance gaps between the metal parts, then cure to create a very dense and high strength bond that increases joint strength and achieves maximum load transmission. The cured resin increases the area of surface contact to 100 percent so the distribution of stress and joint reliability are improved and part life increased.

It’s easy to see why designers are increasingly favouring retaining adhesives to replace, or complement, conventional assembly methods. When employed without structural bonding, pins or key/keyway assemblies, for example, have uneven distribution of mass and imbalance that can lead to vibration at high speeds. Splines and serrations cause high stresses due to the ‘notch effect’ that occurs around the key that will, during the service life of the assembly, require costly remedial machining.

Welding or soldering are limited to compatible metals and the parts can be distorted by the high temperatures required. Heating of the material can lead to residual stresses and structural degradation and additionally make disassembly for subsequent maintenance difficult or even impossible.

Read the full article in the April issue of DPA