Vacuum Bagging Carbon Fiber/Resin: Expert Guide

Vacuum bagging is a critical process in manufacturing high-performance parts using carbon fiber and resin. While vacuum bagging in a Ziplock bag might seem like a quick and easy alternative, it is not recommended due to various reasons. Let's delve into why this approach is not ideal and explore better alternatives.

Why Not Use a Ziplock Bag for Vacuum Bagging?

Material Compatibility

Ziplock bags are not designed for the high pressures and temperatures associated with vacuum bagging. The plastic material may not withstand these conditions, leading to potential damage or failure during the process. Additionally, the resin may cause the plastic to degrade over time, compromising the integrity of the bag.

Vacuum Integrity

Creating and maintaining a proper vacuum seal with a Ziplock bag can be challenging. This is critical for achieving optimal compaction of the carbon fiber and resin. Without a consistent vacuum, the final product may not meet the required quality standards.

Mold Release

Applying mold release on the inside of a Ziplock bag might help prevent resin from sticking, but the effectiveness can be compromised due to the material's inherent properties. If the bag leaks or fails, it could result in a mess and waste of materials.

Durability

Commercial vacuum bagging materials like nylon or polyethylene are specifically designed for this purpose. They are more durable and capable of withstanding the rigors of the process, unlike standard Ziplock bags.

Preferred Alternatives for Vacuum Bagging

For a successful outcome, it is best to use materials specifically designed for vacuum bagging. Here are some preferred alternatives:

1. Custom Polyethylene Bags

You can purchase large rolls of 3 mil polyethylene bags with a circumference of 60" or 48". These are essentially floppy plastic tubes that can be used to create a custom-sized bag. Seal one end with sealant tape, insert the part with the wet layup, peelply, separator, and breather. Then seal the other end and hook it up to your vacuum pump. You can achieve a large diameter bag and ensure proper compaction.

2. Ziplock Bags with Careful Considerations

While using a Ziplock bag is possible, it comes with several limitations. The stretching factor of a Ziplock bag is lower compared to vacuum bags made for this purpose. A stretching factor of around 400 is ideal for achieving an optimal vacuum seal. Sharp 3D curves in the part can cause the Ziplock bag to stretch beyond its limits and fail. To mitigate this, you will need a larger bag that can accommodate the part's curves.

Additionally, consider the temperature limit of a Ziplock bag. It may not be suitable for autoclave processes. A Ziplock bag can be easily damaged by sharp edges or other factors, and even a tiny hole can prevent you from achieving a full vacuum. This can lead to wasted resources and a suboptimal product.

Steps for Successful Vacuum Bagging

Here are the steps to follow for a successful vacuum bagging process:

1. Prepare the Materials

Gather all the necessary materials, including the carbon fiber, resin, molds, sealant tape, and breather fabric.

2. Create the Bag

For custom polyethylene bags, seal one end of the tube with sealant tape. Insert the part with the wet layup, peelply, separator, and breather fabric. Seal the other end.

3. Inject the Vacuum

Connect the vacuum hose to the bag, ensuring proper sealing at the connection. Draw a vacuum and check for leaks. If you are using a Ziplock bag, carefully monitor the seal and ensure there are no leaks.

4. Monitor the Process

Keep an eye on the bag's condition throughout the process. Ensure the resin and carbon fiber are properly compacted and that the vacuum seal is maintained.

5. Curing and Finishing

Allow the part to cure according to the resin manufacturer's instructions. Once cured, you can peel off the bag and finish the part as needed.

Conclusion

In conclusion, while using Ziplock bags for vacuum bagging is possible, it is not recommended due to the limitations in material compatibility, vacuum integrity, and durability. Investing in specialized vacuum bagging materials can significantly improve the quality and consistency of your final product. By following the guidelines provided in this guide, you can achieve a successful vacuum bagging process.