Adhesives can solve many design challenges and improve operation efficiency. However, there are many factors that can lead to the success and failure of the bonding application.
Antala discuss the two main types of bond failures, which are cohesive failures and adhesive failures.
Cohesive failure: A cohesive failure occurs when the intermolecular forces within the adhesive breaks down in the bulk layer of the adhesive or in the bulk layer of the material being bonded.
Adhesive failure: An adhesive failure occurs when the adhesive separates from the interface of the substrates or surfaces being bonded but does not tear or split.
There are many adhesives with different properties, and it is important to select the right adhesive. Some adhesives may be incompatible with the substrate or the application environment and as a result, this can lead to weak bonds and adhesive failure. For example, epoxy adhesives are suitable for bonding metals and composites whereas cyanoacrylate adhesives are suited to bonding glass, rubber and plastics.
Poor surface preparation
Contaminants such as grease, oil, dust and dirt on the surface can prevent the adhesive from bonding properly. Good surface preparation including the use of degreasers or abrading, and primers can help resolve these issues.
Sudden changes in the environment, for example the temperature, the level of moisture, Carbon dioxide, PH and Oxygen, amongst other chemicals can have an adverse effect on the adhesive.
High levels of moisture can be problematic where it can prevent the adhesive from curing in some materials while in other materials, it may speed up the reaction. Some materials when exposed to high temperatures can polymerize incorrectly.
Each adhesive has a set of requirements for curing, for example the temperature range and time needed during the application. If these conditions are not met, this could affect the viscosity, wetting, spread and working time of the adhesive.
Minor changes in the mixing ratios for two component adhesives can also affect the cure where they could cause the material to cure too quickly or slowly and the adhesive does not perform to its optimum capability. If the adhesive is insufficiently mixed or if there are any air gaps in the mixture, this could result in a partial chemical reaction and an insufficient cure in the material. For UV curable adhesives, these require the correct wavelength and energy level to cure.
The type and amount of stress on the joint must be considered when selecting the right adhesive. The adhesive bond is subjected to many forces during the assembly process where shear, tensile or cleavage forces on the bond line can cause adhesive bond failure. Depending on the application, the adhesive may require a degree of flexibility.
Antala says it can provide advice and support on suitable products including testing and trials so you can be confident that the product meets your requirements.
Technical datasheets are available for all our products, documenting performance properties and key specification information.