Section Four The Basics of Bonding

Numerous factors affect a joint in operation, and joints created with adhesive bonds are no exception. This section provides an overview of critical factors to consider when designing bonded joints. Adhesive experts, either in-house or at an adhesive manufacturer or distributor, can provide valuable insights into choosing the best adhesive for a robust, reliable and cost-effective bo nded joint.

A good adhesive application depends on both the properties of the adhesive and the application itself. ‘Application’ in this sense is the job the adhesive is required to do, although the term is also used to describe how an adhesive is physically handled, applied and cured. The adhesive’s properties, such as shear strength, fixture time, depth of cure and resistance to environmental conditions, are strongly dependent on the substrates bonded, surface preparation, how the adhesive was applied and cured, the bond geometry and the resulting distribution of stress. Process factors to consider include cycle time, required industry approvals or certifications, adhesive costs, training and equipment for dispensing and curing the adhesive.

Theories related to the adhesion phenomenon include mechanical interlocking, electrostatic adhesion, diffusion and wetting. Surface preparation methods capitalise on these theories to increase bond strength.