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Composite adhesive bonding

Although reaction injection molding (RIM) and long fiber injection molding (LFI) allow for the production of larger, more complex parts than ever, there still comes a time when you need to join two separate parts together. At those times, applying an adhesive is a cost-effective, long-term solution.

Adhesives work well with Romeo RIM’s reaction injection molded polyurethane products. They can be used to assemble composite components, such as inserts to assemblies or secondary brackets, and join structural ones. They are strong, long-lasting, durable, and bond well with our thermoset polymers. They are also extremely affordable and help to simplify the production process as well as lessen time and labor requirements.

There are a wide variety of adhesives available, each with their own unique benefits. This guide will help you pick the right adhesive for your project as well as teach you more about the adhesive application process and how to best prepare your products.

Types of Adhesives

Anything capable of sticking two other things together can be considered an adhesive – from humble Scotch tape to powerful industrial-strength glues. Some common adhesives used in manufacturing include silicone, hot melt, rubber, polyvinylacetate, polyimide, anaerobic and water-based. However, three of the most common types used to bond composites are epoxies, acrylics, and urethanes, each of which present their own unique advantages.

Epoxies are among the strongest adhesives as well as the most resistant to temperature and weather. They work especially well when bonding composites that are also epoxy-based, and can last for long periods of time with minimal wear and tear. Epoxies come in a number of forms, from low-viscosity liquids to solid pastes and films. However, they can occasionally become brittle when bonded to certain materials, so they may not be ideal in every situation.

Acrylics are slightly less strong than epoxies but still quite tough and durable. They also boast the fastest cure times of any of the common composite adhesives. Adhesives come in both one- and two-component varieties, and as a result bond well with a wide variety of different materials.

Urethanes are neither as strong as epoxies nor as quickly curing as acrylics, but have decent overall performance and are a well-balanced choice. They stand out when compared to other adhesives in regards to their flexibility, impact resistance and their ability to stay bonded at both very high and very low temperatures. Like acrylics, urethanes are a solid choice for a wide number of products.

Choosing the Right Adhesive

When selecting the right adhesive to join your parts together, there are a number of questions you can ask yourself to aid in the selection process. Some example questions include:

  • What materials or composites will be bonded?
  • What sort of atmosphere or environment will the parts be used in? (Consider factors such as temperature variations, extreme weather, moisture and humidity levels, and potential exposure to UV and other types of radiation)
  • Does the adhesive need resist water, oil, acids, bases or other chemicals?
  • Will the parts regularly be subjected to impacts, vibration or stress?
  • Does the adhesive need to serve as a thermal or electric insulator?

Questions such as the above will help you choose the ideal adhesive for every situation. If you have further questions, Romeo RIM is also happy to help you with the selection process.

Preparing for Composite Adhesive Bonding

In order to prepare a surface properly for the application of adhesive, there are a number of things that you must do.

First, you must make sure that the surface is clean. Dust, dirt and debris as well as grease or oil can weaken the bond between the surface and the adhesive. You can use a brush or blasts of clean, dry air to remove dust. Alternately, wipe or spray the surface with a solvent such as non-ionic detergent, alkaline or isopropyl alcohol.

Make sure to dry the surface properly before applying the adhesive! Avoid using tissues or fibrous cloths, as they can leave behind debris and residue of their own.

After cleaning, the surface is usually abraded to prepare for the application of the adhesive. Popular methods of abrasion include blasting with sand or grit, using a wire brush, or machining and scoring with cutting tools. Certain specially prepared chemicals may also be used for surface abrasion.

During the process, be careful to avoid damaging the composite surface fibers, as this can also weaken the adhesive bond. Make sure to brush or wipe off the surface to remove any debris potentially caused by abrasion. As with the cleaning step, dry the surface thoroughly before beginning to apply adhesive.

In some cases, the composite may be coated with a primer before applying the adhesive. Primers can be a cost- and time-effective alternative to some of the more complex preparation processes and can also further protect the surface from wear, tear and damage.

Health and Safety Considerations

Fumes from certain adhesives may cause irritation to the eyes or respiration system in cases of prolonged exposure. When working with adhesives, make sure to wear goggles and a mask or other mouth covering at all times.

Many adhesives are environmentally friendly, but it is always important to research. Consider the volatile organic compound (VOC) emissions of each adhesive when making your selection.

Always store adhesives in sealed containers in a well ventilated area with a temperature of no lower than 40 degrees Fahrenheit (5 degrees Celsius) and no higher than 85 degrees Fahrenheit (30 degrees Celsius). Do not store adhesives near reactive or flammable chemicals.

If adhesive spills at any time, clean up the spill immediately while wearing appropriate protective gear.

Contact Romeo RIM today for more information about using adhesives in concert with our reaction injection polyurethane products.

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