I did some experiments a while back with annealing PLA in a water bath

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discussion
(James Kao) #1

I did some experiments a while back with annealing PLA in a water bath (using a sous vide device from my kitchen). I made 4 test pieces and held 3 of them for 60 minutes at 70C, 80C, and 90C. Then I put all four pieces in a 210F oven with 85g tungsten weights on them. The unannealed piece deformed and the weight fell off after less than 10 minutes. The rest were pretty much stable for the next hour.

I used this technique to then anneal a garage door opener holder (printed in the same red PLA) for my car, which has survived for 1.5 years with 2 summers of hot sun parking.

(Paul Gross) #2

Excellent result!

Can you tell us the theory behind water-bath annealing of PLA? How is the almost-boiling water supposed to affect the bending strength of PLA?

(Carlton Dodd) #3

@Paul_Gross
I was unfamiliar with annealing as well, so I looked it up:
anneal: heat (metal or glass) and allow it to cool slowly, in order to remove internal stresses and toughen it.

(hon po) #4

@James_Kao Thanks for the post. Learn something new.

@Paul_Gross Just a guess, may be it remove the weaker point inside the structure.
http://www.annealingplastics.com/

(James Kao) #5

There were a couple of papers that I found when searching for plastic and PLA annealing. A few that got me in the temperature range (and got me thinking that I should do it in water instead of air) were:
http://onlinelibrary.wiley.com/doi/10.1002/pen.23304/abstract
http://www.4spepro.org/view.php?article=005392-2014-03-28&category=Bioplastics

(hon po) #6

@James_Kao No time to digest, but a casual search didn’t find water/air in the article. I could only think of water as brillant way to control the cooling rate.

This give more incentive to add higher temp heated chamber to the arsenal.

(James Kao) #7

Yeah, the paper covers temperature. I decided to use water because I can’t regulate my oven that precisely in those ranges.

(Mark Fuller) #8

Did you keep the bag interior dry ?

(James Kao) #9

I didn’t use a bag, I just threw the parts into water. Using a sous vide bag would put compression on the parts while annealing, and leaving air in the bag would cause it to float since the parts are light.

(Paul Gross) #10

Regarding the water… can I ask, did you measure the parts for dimensional variation, possibly caused by the pla absorbing water?

This will only matter for parts that have been designed with close tolerances, for example when they have to fit snugly into each other.

(James Kao) #11

No, my main purpose was to find a way to put my garage door opener holder back on service after it sagged and lost its grip on my car’s sun visor. Interestingly, while most types of plastics have easily findable water absorption rates (in terms of % increase after 24 hours of immersion), I couldn’t find any for PLA.

(Michael Scholtz) #12

Brilliant observations, and thank you for sharing. After a discussion I had last week about pla disforming in boiling water I have jsed this to soften parts for push fits Eg onto a stepper shaft. This would definitely be usefull to add to that knowledge. Did you play with fill % and how did that affect it if not what fill did you print at.

(James Kao) #13

I’ve used a heat gun to soften PLA and ABS to fine tune fitting parts. In this case, my only goal was to increase the heat resistance of the part. The garage door opener holder is a thin walled part similar to the test pieces and have no infill.

(Peter Hertel) #14

Very interesting indeed! Thanks for sharing, this is something I must keep in mind.

(Dani Epstein) #15

This is absolutely fascinating, I never would have guessed. I am quite familiar with annealing different metals (mainly silver and gold alloys), but who would have thought that plastics could be annealed?

I recently created a mandala out of PLA and softened it in boiling water in order to drape it over a plate, and after a few moment it handled like freshly boiled pasta. So annealing it in hottish water seems bizzarre and counter-intuitive. Oh well.

(Brad Hopper) #16

Nice result and nice use for the seldom used sous vide :slight_smile:

(Peter Hertel) #17

Just an idea, but would it work to drop the part in a pot of almost-boiling water and let it sit until its cooled down? That would be very simple.

(shubham bane) #18

what is mean by annealing pla

(Dani Epstein) #19

@Peter_Hertel it seems that an integral part of the process is the duration of the annealing, which in James’s case was an hour. You would presumably need to sustain the temperature between 70C and 90C for that time.

@shubham_bane Annealing is essentially heat-treating a meal or plastic in this case well below its melting point in order to alter its crystalline structure. With PLA, the benefits appear to be greater heat tolerance.

(shubham bane) #20

thanks