User Guide

The following questions will help you narrow adhesive choices to
two or three possibilities for evaluation.
Q1 What surfaces are to be bonded?
This is the first clue to how much strength will be needed and which
products may work best. Be sure to understand the surface conditions.
For example, is the surface painted and with what kind of paint? If
the material is a plastic, what kind ? And is there a mold release on
the surface? For bare metals, will the surface be clean or protected
with a finish oil?
Q2 What are the general characteristics of the structural
adhesive types?
3M structural strength adhesives bond the load-bearing parts of a
product. As a rule of thumb, structural strength adhesives reach a
minimum of 1,000 psi overlap shear strength. 3M formulations
include the following pastes and liquids:
• Epoxy adhesives are available in one and two-part formulations
and provide the highest strength at elevated temperature and
chemical resistance of all 3M adhesives.
• Acrylic adhesives bond the widest variety of substrates including
hard-to-bond plastics and oily metal. The distinction is high
strength bonding without the surface preparation needed for
epoxies and urethanes
• Urethane adhesives are generally lower cost and cure quickly to an
elastic bond in applications requiring flexibility between dissimilar
materials. Impact resistance is a distinctive characteristic.
• Cyanoacrylate adhesives are high strength liquid formulations
known as instant adhesives. On rigid plastic, glass, metal, rubber,
and other low porosity substrates, they harden in seconds
through reaction with surface moisture.
Q3 What is the present bonding or joining method?
When the answer provides likes/dislikes and advantages/disadvantages
of the current method, it is easier to determine if structural adhesive
can improve the end product quality and/or the production process.
Q4 What is the preferred bonding range?
This is often the biggest clue to help understand which product will
work best. Start with open time – the amount of time you have to
apply and reposition – and then ask about time to handling strength
and full cure. This could lead to productivity improvements.
Q5 Can simple surface preparation be included in the
production process?
Maximum bond strength and environmental resistance can be easily
achieved by cleaning with IPA/water (50:50 mix) and abrading with
Scotch-Brite
®
Surface Conditioning Products if the surface is very smooth.
Q6 To what environment will the bonded part be exposed?
Remember that in general, epoxies hold up the best to harsh
environments.
Q7 What is the joint design and how will parts fit together?
For the best adhesive bond, there should be at least a .003"-.005"
gap between the parts for shear and 0.015" - 0.020" for peel . The
gap should be as consistent as possible.
Q8 To what types of stress will the bond be subjected?
Strength can be readily matched to the substrate and stress
characteristics to which the bond will be subjected. Most adhesives
and tapes perform better when the primary stress is tensile or shear.
In most industrial applications, however, a combination of stresses
are involved that may include cleavage and peel.
Q9 What is the preferred method of application?
Depending on formulation, 3M structural adhesives are available in
a variety of cartridge sizes, 5-gallon pails, and 55-gallon drums. You
can apply manually or with automated bulk systems.
For more details...
Please visit www.3M.com/adhesives and consult the structural
adhesives section in the 3M Adhesives and Tapes Design and
Production Guide. You can call 3M tech service for personal
assistance with all the information you need.
Simplifying adhesive decisions for your application
Tensile Shear
Peel
Cleavage
Tensile is pull exerted equally over the entire joint. Pull
direction is straight and away from the adhesive bond.
Shear
is pull directed across the adhesive, forcing the substrates
to slide over each other.
Cleavage
is pull concentrated at one edge of the joint, exerting
a prying force on the bond. The other edge of the joint is
theoretically under zero stress.
Peel
is concentrated along a thin line at the edge of the bond
where one substrate is flexible. The line is the exact point where
an adhesive would separate if the flexible surface were peeled
away from its mating surface. Once peeling has begun, the
stress line stays out in front of the advancing bond separation.
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