What is Adhesive Bonding?

What is an Adhesive Bonding?

Adhesive Bonding is the process of joining two surfaces together, usually with the creation of a smooth bond. This may involve the use of glue, epoxy, or one of a wide range of plastic agents which bond either through the evaporation of a solvent or through curing via heat, time, or pressure.

With this technique, components are connected with adhesives. The wide range of adhesive types available allows a wide variety of materials to be glued together in products as diverse as vehicles, cell phones, personal care products, buildings, computers, and medical devices.

Adhesives have tended to create relatively weak bonds, but with the use of new self-curing adhesives, these bonds now come close to the strength of the materials themselves. As a result, gluing is now the preferred method of joining for many applications, especially when the joint is no longer exposed to heat or weathering.

Many modern adhesives are carbon-based petrochemical derivatives that can be used for a variety of bonding applications, including bonding metal and various materials. This type of adhesive uses either direct contact or a third surface, such as tape, to make the connection.

Composite applications commonly bonded using adhesives include fiberglass and fiber epoxies such as boron epoxy and carbon epoxy. Modern adhesives can also be used to join building materials due to their shear strength and toughness, of which plywood is a widely used and well-known example.

Pre-treatment of Adhesive Bonding

Pre-treatment can be used to modify surfaces in a targeted way and thus make them more adhesive. In addition to coating the substrates with an adhesion promoter (primer) to enable good adhesion, surfaces can also be modified by various methods to prepare them for gluing. The most common surface pretreatment methods are listed in the adjacent figure.

The selection of the pre-treatment process is application-specific, taking into account

  • The materials to be joined.
  • Their surface condition.
  • The type and amount of surface contamination.
  • The adhesive to be used for bonding the substrates.
  • The stresses on the glued product over its life cycle (e.g., mechanical, thermal, or medial).

The selection should be validated through appropriate testing.

Adhesive Bonding
Adhesive Bonding

Selection of Adhesive Bonding

The selection of a suitable adhesive for a particular application should be based on a specific requirement profile. This requirement profile lists all immediate, verifiable requirements for the component to be bonded and, as a result, for the bond and the adhesive.

It is possible to distinguish between requirements that must be met and those whose fulfillment is advantageous but not necessary. Also, specifications derived from the bonding process, including those from upstream and downstream process steps, must be taken into account.

The diagram above provides a summary of the most important parameters to take into account when choosing adhesives.

Advantages of Adhesive Bonding

One of the main advantages of adhesive bonding is that it allows tension loads to be evenly distributed, thereby reducing the stress on the joint. Because they are applied within the joint, adhesives are also invisible within the assembly.

Due to the properties of adhesives, they can form an adhesive and sealant at the same time and at the same time withstand vibrations and bending loads. The ability to act as a seal allows adhesives to protect a joint from corrosion.

While adhesive bonds can be applied to metal-to-metal, plastic, glass, rubber, ceramic, and many other combinations of materials, this process can be used to bond irregularly shaped surfaces without practically changing the dimensions or geometry of the parts.

Adhesives also add very little to the weight of the materials being joined and can be used to quickly join dissimilar substrates and heat-sensitive materials.

One of the greatest advantages of adhesive bonding is the versatility it offers, enabling the joining of a large number of elements and being easily automated.

Disadvantages of Adhesive Bonding

However, there are several limitations to the use of adhesives. First, they are prone to failure if they are exposed to extreme heat or the elements. It can also take some time for adhesives to fully set and achieve full strength.

They also often require surface preparation treatments, including cleaning the surface of the materials to be joined. Other surface treatments associated with adhesives include abrasion to create a stronger bond.

Adhesives can also cause disassembly-related issues compared to other, less permanent joining techniques.

Uses of Adhesive Bonding

Adhesive bonding is used across many industries including automotive, aerospace, medical, and even textiles. Due to the versatility of this process for a range of material types the only real limitations arise with use, such as for outdoor applications that need to withstand weathering.

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