Constructing a Nearly Indestructible Salad Bowl

[Adam]

In our Composite Materials class we created these cool bowls using carbon fiber prepreg pieces, shaped into a metal bowl-shaped mold. There are seven layers. We did a vacuum bag debulk after layer 4. The most difficult part was ensuring that there was no "bridging" of the material and minimizing wrinkles. 

 

 

 

[lo_0l]

On 2/13/2023 at 4:06 PM, Adam said:

In our Composite Materials class we created these cool bowls using carbon fiber prepreg pieces, shaped into a metal bowl-shaped mold. There are seven layers. We did a vacuum bag debulk after layer 4. The most difficult part was ensuring that there was no "bridging" of the material and minimizing wrinkles. 

 

 

 

This looks awesome @Adam! What are you making next? 🙂

[Mongo]

How is a vacuum bag debulk procedure different to the procedure that creates the final part... (different other than simply not introducing the heat to melt the resin)?  Can I reuse the bag for several debulks?  Can I reuse the bag for the final part?

[John Kimball]

On 2/28/2023 at 4:21 PM, Mongo said:

How is a vacuum bag debulk procedure different to the procedure that creates the final part... (different other than simply not introducing the heat to melt the resin)?  Can I reuse the bag for several debulks?  Can I reuse the bag for the final part?

The debulk process is just vacuum bagging the part for a few minutes to consolidate the plies before moving on. the more plies you have, the more loft the part will have. Debulking decreases the loft. On contoured parts it's very a very important step. 

The only difference in debulking and curing is the heat. Debulking can be as short as 15 minutes under vacuum or overnight. Sometimes a pressure debulk is needed in the autoclave, and sometimes a heated debulk is needed to help the resin flow a little bit.

Typically, debulks are used every 4 plies, but depends on the thickness of the part. The bag can be reused for the debulks, but aren't usually used again for the cure.

[Julia]

Cool looking bowl. I'm assuming this isn't food grade though. How would someone make this usable for food service?  Or might it be safe to put fruit or other produce in for decorative purposes?

[John Kimball]

5 minutes ago, Julia said:

Cool looking bowl. I'm assuming this isn't food grade though. How would someone make this usable for food service?  Or might it be safe to put fruit or other produce in for decorative purposes?

Correct. Definitely NOT food grade. There are special resins that are food grade, but epoxy isn't. Dry goods might be okay, but probably best to avoid any consumed items due to leaching.  

[lo_0l]

13 minutes ago, John Kimball said:

Correct. Definitely NOT food grade. There are special resins that are food grade, but epoxy isn't. Dry goods might be okay, but probably best to avoid any consumed items due to leaching.  

Are there food safe epoxies that could be used?

[John Kimball]

15 hours ago, lo_0l said:

Are there food safe epoxies that could be used?

To be more clear, if cured properly, commercial epoxy resin is generally food-safe (at least in most cases). It is therefore not dangerous if a foodstuff comes into contact with an epoxy resin surface for a short time and without heat. However, most epoxy resins use Bisphenol-A (BPA) as an ingredient in epoxy resins because of it's superior curing properties. There are concerns that when plastics that contain BPA are heated (like a water bottle in a hot car), the BPA can leach into the contents. A lot of casting resins are considered food grade and most likely use Bisphenol-F as a curing agent ingredient. But it is always wise to check with a manufacturer if the resin is considered food grade and heat resistant.

I would also add that epoxies formulated for laminating structural composites may contain other ingredients that can leach into foods, so I would advise against using those structural epoxies for anything food related.

This site has some good information regarding food grade epoxy and what to look for if you need a food grade resin. 
https://resin-expert.com/en/guide/food-safe-epoxy