Advantages of Structural Epoxy as an Adhesive

Industrial adhesives provide the solutions for structural bonding, cylindrical assembly, threadlocking, flange and thread sealing and a range of other design challenges, Design engineers use adhesives over other joining methods like thermal joining and mechanical fastening because they distribute the stress load over a broad area and at the same time reduce stress at the joints. Once they are applied at the joints, adhesives would be invisible at the assembly. Different types of adhesives include anaerobic adhesives, cyanoacrylates, light cure acrylics, light cure cyanoacrylates, hot melt adhesives, structural epoxy and polyurethanes.

Epoxy as a structural adhesive

Structural epoxy is a type of adhesive that bonds very well to a wide range of substrates and can fill large volumes and gaps. Cured epoxies typically have excellent cohesive strength and good chemical and heat resistance. Operating temperature is a single most important factor that qualifies an adhesive for a certain application. For example, in the electric motor housing, temperatures can exceed the boiling point of water and at these temperatures structural epoxy, acrylic and urethane are very good candidates. Epoxies also show good resistance to water, mild acids, isopropyl alcohol, ethyl/methyl based fluids, hydrocarbons, gasoline and oils.

Major advantages of structural epoxy

The main advantage of structural epoxy as an adhesive system is the production of assemblies mechanically equivalent to or even stronger than conventional metal-fastened parts at lower cost and weight. Additionally, structural epoxy offers outstanding corrosion resistance even with prolonged exposure to aggressive solvents, high temperature and hostile environment. Some of the additional advantages of using structural epoxy are:

-        Uniform stress distribution and larger stress-bearing areas

-        Outstanding resistance to fatigue, mechanical shock and thermal shock

-        Improved load-bearing and sealing properties between substrates

-        Can bond different substrate materials together like metals, plastics, elastomers, ceramics, glass and wood

-        Can bond materials of different coefficients of thermal expansion even when subjected to low or high temperatures

-        Smooth, contour-free surfaces without external projections and gaps

-        Gap-filling capabilities reduce required tolerances

-        Galvanic corrosion between dissimilar metal substrates are minimized

-        Provides thermal and/or electrical insulation or conductivity

-        Wide service temperature range capability

-        Long term durability

Considerations to a successful bonding

Surface preparation – this process is as easy as cleaning the surfaces with solvent to remove oils, greases and other possible contaminants that could hinder bonding strength. Certain forms of oxidation due to loose rust formed on iron can contaminate the adhesive. In some applications, however, surface cleaning may require abrasion, chemical surface etching, heat treatment, plating processes or plasma treatment so as to obtain adequate adhesion.

Joint design – is as important as adhesive selection. It requires the proper selection of style, proper surface preparation and use of careful applications and assembly procedures. Joint design should minimize stress concentrations by ensuring that load distribution is made over the entire bonded area. Joint style should also serve to improve bond strength.

The most frequent causes of adhesive joint failures does not involve the bonding strength of the adhesive but due to poor joint design, inadequate surface preparation and improper choice of the adhesive for the substrate and operating temperature.