Mechanical fasteners vs adhesives in the MRO industry
Joy Dascalu | February 07, 2023Figure 1. Airplane turbine at Riga International Airport.
Historically, the maintenance, repair and operations (MRO) market has been resistant to technological change and advancements. Mechanical fasteners have been relied upon for much of human history to ensure that connections between machine parts continue to operate smoothly, safely and securely. Adhesives also date back to ancient history but they have been the subject of significant improvement.
MRO engineers use a variety of mechanical fasteners across many industries from food production to aerospace manufacturing. Wherever machinery such as hydraulics, motors, turbines, compressors and engines need to be used and maintained, fasteners are used.
As more options become available for joining materials it may be beneficial to rethink mechanical fasteners. While mechanical fasteners will not be replaced completely, there are some use cases where other options may perform better.
Potential issues with mechanical fasteners
MRO engineers are often more comfortable using traditional fasteners when joining materials. However, in some situations, this might not be the most sustainable or practical solution. For instance, using mechanical fasteners may limit material options and lead to material fatigue. Labor, material and processing costs may also increase as a result.
When using mechanical fasteners such as bolts and screws, it is required to create a hole in both parts so the fastener component can be passed through. This method creates a route where contaminants can travel through and damages the structural integrity of the joined parts. In some circumstances, mechanical fasteners may require fixing plates to secure different materials.
Using adhesives for material joining
Adhesives are lighter than mechanical fasteners and they do not damage the surface of the substrate to be effective. However, surface pretreatment methods may be needed to prepare the surface for bonding. Significant alterations are not required when using adhesives unlike when using mechanical fasteners.
Adhesives can also defray costs associated with drilling or tapping. They can be ideal in hazardous locations where mechanical fastening options may not be easily accessible or possible. Their use may help prevent vibrational loosening which is a large contributing factor to mechanical failure.
Adhesives are not the best choice in all situations and often are the optimal choice when they are used to provide an inert barrier between likely corrosive metals or to set up a water-resistant barrier. They may also be designed to resist specific chemicals and can mitigate differential thermal expansion rates. Structural adhesives can distribute force over the entire bond area instead of just at the joining site. Consequently, adhesives work best when applied to large clean areas as stresses are spread out over the bonded surface area and are likely stronger than welding, rivets, or threaded assemblies in these cases.
Figure 2. Silicone adhesive sealant. Source: Cjp24/SS BY-SA 3.0
Potential applications
A variety of MRO applications can benefit from adhesives. Anaerobic engineering adhesives are convenient adhesives that can cure at room temperature. There are many options that are not solvent based, so they are safer for workers and for the environment. Low-volatile organic compound and sustainable adhesives are also being developed to offer increasing environmental benefits.
While typically the longer the cure time the stronger the final bond, many adhesives reach fixture times in a few minutes. There are different curing options for adhesives as well, with some curing faster when exposed to high-intensity UV light. As a result, exposed edges can have a stronger bond while the remainder will cure anaerobically.
Process improvements may also make adhesives easier to use, for example, two-part/no-mix adhesives are available where the activator is sprayed onto a substrate before the adhesive.
Adhesives can be used to mount electrical panels, conduits and I&C equipment. In the oil industry, adhesives can even replace welding commonly used in petrochemical applications. Some other applications include:
- Gasketing - Anaerobic adhesives can replace pre-cut gaskets.
- Pipe sealing - Adhesive solution can be applied to gaps in connections and fittings to prevent leaks of fluids and gases.
- Retaining - Anaerobic adhesives can fill spaces between a variety of components.
- Threadlocking - Adhesives can be applied to mechanical fasteners to prevent loosening and corrosion. This will reduce the occurrences of failure and reduce the need to tighten bolts.
Some adhesives are very difficult to remove, unlike many threaded assemblies. This can be a drawback to using adhesives depending on the application. Adhesives can be removed with service products when they are no longer required. However, removing some adhesives may involve the use of solvents.
Downsides to adhesive use
While the product range of adhesives is growing, adhesives might not bond as well on all surfaces. Mechanical fasteners are trustworthy and there is little mess involved when installing them. Many fasteners are also easy to remove and adjust, with many options requiring minimal training. On the other hand, working with adhesives might not always be a simple process.
Adhesives typically require a cure time that varies between products. Longer cure times can affect efficiency. It is also easy to incorrectly use adhesives due to improper application or mixing. The wrong adhesive may be selected and result in bond failure. A common misapplication is over-applying the adhesive resulting in field failure and increased costs.
Figure 3. Adhesives can be applied to MRO parts as a preventative measure, reducing downtime and maintenance needs.
Sustainability and cost benefits
MRO engineers are facing increasing pressure to incorporate sustainable practices in support of worldwide and national climate-change targets. Accordingly, MRO engineers are now more ready to consider alternative measures to traditional solutions. In an effort to reduce carbon footprints, engineering adhesives are being used to replace mechanical fasteners.
When using adhesives instead of mechanical fasteners, the number of tools and parts that are purchased can be reduced. This offers a reduction in transportation costs and storage. For instance, a single adhesive solution can be used to replace hundreds of washers. This reduces the energy, and fuel consumption in washer manufacturing, and transportation and storage requirements are reduced.
Some adhesive manufacturing companies have tested their products in mechanical fastener replacement. For example, the Loctite team has calculated that 50 mL of their adhesive can replace around 850 of M10 washers.
Adhesives can also be applied to MRO parts as a preventative measure. This can lead to reduced downtime and less need for replacement parts. Reducing downtime results in increased economic efficiency and reduces operating costs. Unsustainable side effects such as increased use of energy and resource can also be reduced with effective preventative maintenance.
[Learn more about industrial adhesives on GlobalSpec.com]
Moving forward
Product ranges for adhesives to replace mechanical fasteners are increasing as adoption increases. Safer and sustainable adhesives are available in the form of solvent-free and non-CLP classified ranges of adhesives.