Bonding carbon fiber tubing can be tricky, messy, and time consuming. This article will break down the key steps on how to bond carbon fiber tubes.
There are many variables to consider when bonding carbon fiber tubing: loading scenarios, materials being bonded, adhesive selection, operating temperature, environmental exposure, chemical exposure, and other factors. Typically, most standard two-part epoxies work well. For most applications, we recommend 3M’s Scotch-Weld DP-420 NS (no sag). For special applications, we recommend reaching out to the adhesive manufacturer directly.
PPE: proper ventilation, safety glasses, gloves, and respiratory protection (if needed)
Bond-Prep: Determine tools available and solvent needed.
- Abrasive: Surface prep both surfaces using 120 grit sandpaper, drum sander, rotary tool, flex hone, etc.
- Solvent: Remove all mold release, dust and debris from tube using acetone or isopropyl alcohol.
Tape: Use masking tape to protect surfaces surrounding the bond area
Bonding: Adhesive, mixer/dispenser, and applicator. This can be as simple as a mixing stick and jar.
Finishing: Rags and towels for proper adhesive cleanup.
1) Adhesive Selection: Determine the best adhesive for the job.
Work life: Consider the complexity of the bond and how much time is available for application and fixturing. This may help determine the working life needed for the assembly.
Loading scenario: Ensure a sufficient adhesive is selected for the loading scenario. For example, 3M DP420 has an estimated shear strength of ~2,200 /sq. in. with common materials like aluminum and steel. When bonding to unique materials, such as HDPE, other adhesives may be better suited.
Environment: Most standard 2-part epoxies have an operating temperature of <250°F. Consider temperature and other chemical exposure when choosing an adhesive.
Galvanic Corrosion: Be advised, carbon fiber can cause galvanic corrosion on aluminum. If the aluminum is anodized, this should prevent corrosion since there is a layer of oxide between the carbon fiber and bare aluminum. The epoxy adhesive also can act as a layer to prevent corrosion. Another common way of preventing galvanic corrosion is to use a non-conductive outer (or inner) layer of fiberglass in the carbon fiber part to ensure the aluminum and carbon fiber do not come in contact.
2) Assembly Design: Proper fit and bond area is critical to ensure a strong bond.
Proper fit: When bonding to carbon fiber tubes, it is essential to factor in the proper “bond-gap”. For most 2-part epoxies, a bond-gap of ~0.005”-0.010” (per side) is recommended. This will ensure the proper amount of adhesive is used. Other adhesives may require a thinner, or thicker, bond gap. Consult the adhesive supplier for proper fit recommendations.
Bond Length: There are a lot of factors to consider when designing a bonded assembly. The loading scenario greatly influences the minimum bond length. For ferrule tubing, a good rule of thumb is a minimum bond length of 2-3x the inside diameter. For tubes <1” diameter, we recommend a 3” bond length as a default.
3) Bond-Prep: If not done correctly, the bond will be less strong.
Abrade: Using 120 grit sandpaper, or one of the other methods mentioned above, remove all gloss from the bond areas. This will increase the surface energy, thus increasing the strength of the bond.
Clean Surface: Wipe bond area with solvent. Gloves should be worn during all steps, so oils are not transferred to the bonding area. Allow solvent to evaporate (surface should look dull, gloss should to be removed). Can do a water bead test to verify sanding is adequate.
Bond: Apply adhesive liberally throughout both bond surfaces. 100% coverage will ensure a proper bond. When connecting the parts, adequate adhesive squeeze out should be observed.
Clean-up: After application, wipe away all excess epoxy. Use solvent to clean the non-bonded surface.
Fixture: Fixture or secure the bonded assembly to prevent movement while parts cure. As the epoxy cures, there is a possibility the bonded components will shift, affecting dimensions of the assembly.
Cure: Refer to the adhesive tech data sheet for the correct time, temp, and sometimes humidity cure process. Some epoxies require multiple days at room temp to cure properly. Do not handle the part until fully cured.
If you follow the above instructions, you should achieve a proper and sufficient bond. To summarize, there are many two-part epoxies that work well. It is just as important to selecting a good adhesive, as it is to properly prep the surface. Refer to the adhesive tech data sheet for the correct surface prep. You will want to sand the interior (or exterior) with sandpaper (120-180 grit) and remove all the glossy resin surface. You will visually see when it is removed. Once removed, clean with solvent and refer to the adhesive tech datasheet for proper cure. If you have any questions, do not hesitate to contact us.