What materials are you working on?
The strength of any adhesive relies completely on the preparation and condition of the surfaces being bonded. It is usually easier to bond two like materials together as the adhesive only needs to be suited to one material, however, when trying to join different materials together (such as rubber & metal), it will require a specialised adhesive. Additionally, there are many metals that are inactive, and you will need a primer or an activator for the adhesive to work properly.
There are a few different ways to measure the strength of a bond, the first one is shear strength, it is measured in PSI and refers to the amount of force that would need to be made to rip the bond apart. Adhesives with a higher shear strength rating will be able to tolerate larger impacts and forces. The second measure is peel strength, also measured in PSI this refers to the amount of pressure needed to peel apart the two pieces of materiel – imagine the movement of peeling a sticker off a window.
To give you some context, lots of people would assume that super glue is pretty strong, but they are not utilised in furniture manufacturing due to constant joint movement easily breaking apart the bond. In this example, an epoxy glue is well suited as the bond allows for the pressures a piece of furniture is put through.
Just like using force to tear apart a bond (mechanical force), bonds can also be broken down thermally. All adhesives have a temperature range in which they are designed to perform under. In some applications such as plumbing and pipework, adhesives may be subject to temperatures well in excess of 100℃. It could be extremely dangerous if the wrong type of adhesive was used and failed. It is always important to anticipate the severity of temperature fluctuation for bonding applications and use a solution that will cope.
Viscosity and Cure time
Viscosity refers to the thickness of your adhesive substance. Generally, the higher the viscosity value, the thicker the liquid will be. A general rule of thumb is the higher the viscosity the longer it will take to cure. However, there are applications that can be extremely complex to glue things together and it can be messy if the viscosity is low. If the adhesive is too thin, it may spill onto unwanted surfaces before it is cured, in these cases the tackiness of a highly viscous glue will be favourable.
Difficult Surface for bonding
Dirty or inactive metals can increase the difficulty of creating a strong bond. A primer or activator will be able to activate passive surfaces as well as speed up the cure time. Dirty surfaces can be prepped with a surface preparation substance to make a strong and long-lasting bond.