It is commonly known that different materials, compounds and surfaces have different cohesion and adhesion properties. Hence, using one type of adhesive is not suitable for all industrial applications. Thankfully, there are different types of adhesives available with different chemical compositions and properties which are suitable for different applications.  Choosing the right adhesive is extremely critical for your project.Thermosetting adhesives are  most commonly used for bonding different surfaces and materials including metals, rubbers, silicone, glass, acrylic, polyester, polyimide (Kapton) and other polymers in aerospace, defence, oil and chemical, electronics and electrical, medical, optical and OEM, among other industries. These adhesives can be further classified into acrylic adhesives, epoxy adhesives, phenolic, melamine, and formaldehyde resins, polyurethane adhesives and rubber and silicone-based adhesives. Out of these, epoxy-based thermosetting adhesives are  most widely used in an array of industrial applications. Epoxy adhesives offer excellent strength while offering resistance to high temperatures, chemicals, moisture and dust, making them a popular choice.

How Various Industries Benefit From Using Adhesives

The modern adhesive manufacturing industry has grown a lot in recent years, both in terms of technology and significance. Traditionally, two or more substrates were fastened together mechanically with the help of welding, rivets, screws, and bolts. In such cases, metal screws and rivets were at risk of rusting, while the holes made to accommodate them decrease the structural integrity of the surface. However now, high-performance adhesives can be applied to any surface and provide additional weather and moisture resistance. Some specially engineered adhesives can provide additional chemical resistance. Using industrial adhesives also has other benefits such as:

• Reduces the equipment’s weight.
• Minimises corrosion.
• Higher bonding strength.
• Bonds at a microscopic level by filling pores.
• Thermal and Electrical conductive properties as desired.

Applications Of Adhesives

As stated above, modern thermosetting adhesives have a lot of advantages and are used in a wide range of industries for various applications. Some of the typical applications of adhesives are as follows:

• In the aerospace industry, adhesives are used for the manufacture of aeroplanes, rotorcrafts,  satellites, helicopters, and unmanned aerial vehicles.
• Adhesives are used in electrical and electronic industries for their excellent thermal and electrical properties.
• The medical sector employs adhesives to manufacture equipment, syringes, prosthetics, etc.
• Adhesives are used in the optical industry for their transparent, non-yellowing property, and excellent electrical, thermal and chemical resistances.
• The oil and chemical industry also takes advantage of adhesives for upstream, midstream and downstream applications.

Selection Criteria Of Adhesive

1. Surface Type

Knowing what type of surface the adhesive is going to be applied to is the most important factor in the Adhesive selection process. There are various types of adhesives, some of which are specially designed for certain surfaces such as metals, plastics, rubbers, glass etc. In order to choose the right adhesives you must consider the type of substrates, surface finish and energy,, surface hardness, cleanliness, porosity, coefficient of thermal expansion and area to be bonded.

• For applying adhesives to metal, composites and other structural surfaces, epoxy and MMA adhesives are highly recommended.
• For bonding, coating and potting small electrical components, epoxy-based one and two component adhesives are a good choice.
• If a surface makes clamping difficult, pressure sensitive adhesives and contact adhesives are the best choices for a removable bond.

2. Surface Finish & Wettability

The surface’s finish i.e its roughness and surface energy are also important factors affecting the adhesive’s strength. Sometimes adhesives may have a difficult time bonding to extremely smooth surfaces, while some adhesives might not work well with porous substrates. Certain plastic and rubber substrates have an extremely low surface energy, making them difficult to adhere to. They require special surface treatment in order to activate the surfaces for good adhesion. Most surfaces can be easily prepared by using a simple three step process i.e.cleaning, roughening and drying before applying adhesives. Surface wettability is another important factor to consider. In order to achieve optimal adhesion, the adhesive must wet out the surface that needs to be bonded.  Wetting out means that adhesive must flow and cover the entire surface area for maximum adhesion. So, while selecting an adhesive, you have to consider the surface energy of the substrate and adhesive. The surface energy of the adhesive should be lower than the surface energy of the substrate that is to be bonded. This will ensure that the adhesive effectively wets out the surface, ensuring long-lasting adhesion.

3. Cleanliness

It is a common requirement for any adhesive that the surface of the substrate should be clean. While all adhesives generally require a cleaning of the surface so that there is no dirt, dust, oil, grease or any other contaminants, some might need surfaces to be sterilised with chemicals and complex processes, including abrasion, chemical etching, or plasma treatment.

4. Adhesive Strength

One must also consider the bonding strength of the adhesive in comparison to the requirements for the task. Some strong adhesives might be used to join materials for long-lasting adhesion while others are designed for lighter adhesion so that the surfaces can be separated as the need for the process dictates. One must also remember that just the adhesive’s strength is not the sole factor that determines the strength of the bond. A strong adhesive might not be of use at all if the surface resists the chemical compounds of the adhesive. Hence it is critical to consult our technical team for selecting the best adhesive for your application.

5. Desired Properties From The Adhesives

Thermosetting and structural adhesives are usually used for projects that require strong mechanical adhesion On the other hand, thermoplastic hot melts can be heated and set again and again. It completely depends on what properties you are looking for in an adhesive to select the right adhesive. In addition to bond strength, other properties that are critical to consider are chemical resistance, thermal and electrical conductivity/insulation, optical clarity, flame retardancy, resistance to thermal cycling, temperatures that the bond will be exposed to and industrial certifications the adhesive needs to meet. Adhesive selection can be a more elaborate process depending on your application requirements.

6. Application Method

The application method is another important factor to consider for selecting the right adhesive for your needs. It makes a lot of difference if the adhesive is going to be applied by hand or by special equipment,such as syringes, spray guns, rollers or gun applicators. Alternatively, your manufacturing process could also demand a fully automated metre, mix and dispense system for applying the adhesive. Depending on the method of application suitable for your manufacturing, our adhesives can be packaged in various cans, syringes and cartridges for manual, semi-automatic and automatic dispensing.

7. Environment & Element

Environment, temperature, and elements are factors that can cause serious damage to the adhesive over a long period. Most modern industrial adhesives provide some form of resistance to temperature, humidity and other corrosion elements. However, some adhesives provide additional protection and are meant for use in industries where the pressure of the environment and elements such as heat, moisture, pressure, humidity and chemicals are extreme, such as in aerospace, defence, oil and chemical etc. The life of your bonded components is highly dependent on the choice of the adhesive and the environmental conditions it is designed for withstanding.

Testing Parameters Considered For Adhesive Selection

Adhesive testing is a necessary process and is highly recommended before manufacturing, purchasing and applying adhesive to the entire surface. This is because adhesives can malfunction after being applied to the entire surface.  In this adhesive selection guide, we are sharing questions that you should ask before selecting an adhesive for your business needs.

1. How much temperature can the adhesive withstand?

The temperature tolerance of an adhesive depends on its specific formulation and intended use. So, you have to consider your needs and convey them to the adhesive manufacturer to get the ideal solution. It is important to consult the manufacturer’s specifications for information on the minimum and maximum temperature the adhesive can withstand. Furthermore, it is also important to mention the nature of thermal cycling the adhesive will need to withstand during the life of the bonded parts.

2. How much and what type of force and pressure can the adhesive take?

Certain adhesives are used under extreme mechanical shocks, forces and vibrations for a short amount of time and be fine, however, they might break down rather easily if the force is applied for long periods. Similarly, some adhesives might endure light force and pressure for long periods but are not suitable for high-force and high-pressure environments. Various forces can act on the adhesive, such as tensile, flexural, shear, compressive, bending and peeling. Choose an adhesive based on this information, selecting one that fits your requirements.

3. What additional properties should the adhesive have?

If your industrial process requires certain properties in an adhesive like thermal and electric conductivity, heat resistance, water and moisture resistance, chemical resistance, non-yellowing etc. you should test such properties first-hand before purchasing the adhesive. 

4. How much is the adhesion strength?

You should take an adhesion strength test for the nature of forces acting on the bonded components before selecting the adhesive to find out if the adhesive is as strong as your requirement. This will help you find and appropriately use the right adhesive for your needs You can also look up other testing parameters and selection criteria with our helpful guide on questions to analyse while selecting an adhesive.

Conclusion

To summarise, one type of adhesive is not suitable for different types of materials and surfaces. You have to figure out which adhesives are best suited for your industrial application. The above selection criteria is a good guideline to figure out the right adhesive for your use. Our team of technical experts will assist you with selecting the best adhesive for your application through the design, prototyping and manufacturing processes. . Kohesi Bond is a professional adhesive manufacturer in India that custom formulates adhesives specifically designed and crafted for your unique business needs. If you are looking for a tailor-fitted adhesive, sealant, coating, potting and encapsulation compound, or if you have additional queries about adhesives, feel free to contact us!