Wow, just figured out the hard way that PETG-HF is apparently not everything I thought it was.
I’ve ordered several rolls of it and was generally happier with it than regular PETG. It prints easier and it looks better. I didn’t consider the fact that the trade off for it printing fast means it has to melt easier. I knew it, I just didn’t consider all the implications of it.
I have a lot of re-usable spools for PLA that I’ve made myself - out of PLA. Obviously I knew those wouldn’t work for PETG-HF refills, so I decided to make me some spools out of PETG-HF to put some of those on. Little did I know that wouldn’t work either, until I pulled one out of the dryer this morning. Bambu says dry PETG-HF at 65, just like you would expect. What you don’t expect or find until you dig into the TDS is that the glass transition temp for PETG-HF is 66 - literally 1 degree more than the drying temp - not the 80 to 85 of normal PETG.
Well, obviously my dryer isn’t accurate enough to maintain 65 without ever hitting 66.
For my general needs this fact would seem to make PETG-HF almost useless for me because if it goes outside or into the car it will fare only slightly better than PLA. I live in Atlanta, and in the parked car 60 and 66 might as well be the same thing. That said, my Sunlu PETG holds up fine in the car - it just doesn’t look anywhere near as good as Bambu PETG-HF.
But I’m absolutely floored at the fact that the glass transition temp is so much lower on PETG-HF. It almost makes it seem like it shouldn’t even be called a variant of PETG.
PETG in dryers isn’t perfect from my experience, I’ve transitioned to ABS as its more reliable. Dryers often blow hotpspots and by the looks this is whats hit this with a constant blasting of heat. As for the car, they may be less intense as its not so concentrated but ymmv.
Most of the consumer-grade filament dyers are notoriously inaccurate. I have a dual FixDry, super happy with it generally, but the temp/humidity sensor is low down on the main panel, near the heat source - accuracy also impacted as there is a plastic flow deflector fitted right over the fan. I have to set the machine about 10Deg C higher than indicated to get the drying temperature required in the majority of the box, which for PETG means its ~75-80Deg local to the heat source to achieve a real drying target of 65Deg C. Even ABS printed spools are deforming!! So for drying its either cooler for longer or require the PP reuseable spools from BBL. When dry it prints great, but the properties of PETG-HF are slightly disappointing, strength & durability etc, but to be fair to BBL look to be very close to the TDS.
Oh, I hold no illusions as to the (in)accuracy of filament dryers. In my case I have a Sunlu S4, so considering its size and the way it opens and everything else about it there’s really no way it could have a consistent temperature at all. No doubt it has to get quite a bit hotter at the bottom to stand any chance of heating the top. And then of course it has to cycle on and off and let the temp swing as it does so.
The part that really perplexes me is simply the fact that Bambu says to dry this stuff at 65 yet its glass transition is only 1 degree higher at 66. I honestly don’t think any filament dryer of any calibre could pull that one off.
Of course I can just dry it for longer at a lower temp (which is what I would have expected Bambu to call for, all things considered) or get more durable spools for it. I have an A1 so I can’t print ABS or anything more durable myself due to the toxic fumes (well, I guess I could make them out of Polymaker PA6, but then each spool would take more than $20 worth of filament).
And the info that would have made it clear to me that I can’t dry PETG-HF on a spool made of PETG-HF is in the data, I just failed to piece it all together before I made several spools. I can always use the spools for PLA though, so the one that got melted is the only one that’s actually a loss. And since PLA and PETG-HF are the same price, that’s a non-issue.
My big disappointment only comes from the fact that I thought I had found a good alternative for standard PETG, as this stuff looks so much better. The reality for me, though, since that glass transition of 66 degrees makes it unsuitable for use outdoors or in the car where I live, is that I can only use PETG-HF in the same situations where I can already use PLA. And that just returns me back to my Sunlu brand PETG, which works fine but just looks bad.
Former injection molding engineer here - this is a dirty secret in the molding industry too: high flow variants of polymers is just marketing speak for shorter molecular chains. This enables them to melt at a lower temp to enable lower viscosity at a given process temp. Unfortunately, nearly every desirable performance attribute of thermoplastics is a function of hydrocarbon chain length, so this will reduce strength and toughness along with temperature resistance
Totally I bought tonnes of the stuff very very unhappy with it,mine melted too in the dryer, I’m that angry about it I will never buy bambu filament again, no now I’m using something at over half the price and prints better for me anyway bambu filament is pants
Yeah, I hear you. However, defining Tg is not an exact science, and is also very expensive. In an attempt to define an industry standard fixed temperatures for TDS, the DSC testing for example compiles variables of material & testing methods to reduce a range of results and then calculates the formally stated Tg and Tm temperatures, so each manufacturers budget can interpret things slightly differently - DSC testing is not based on physical deflections. I always look at the Heat Deflection Temperature (HDT) or Vicat Softening, as those values are obtained using (much cheaper) physical tests of the material under load. They are usually lower values than Tg, but according to the BBL TDS for PETG-HF not in this case!! There is also an American standard called UL 746 that is sometimes given in TDS and is a continuous-use temperature (so would be the most relevant here) and of course would always be much lower than Tg. I’m hoping to replace some ASA prints with this PETG-HF for larger outside parts to save cost and ease printing difficulty, so am also trying to justify being able to use it.
Just as a heads up for those that said they just dry longer at a lower temp.
I was having issues with some filament a while ago and talking to the support team for the brand found out that extending the drying time does not exactly compensate for using a lower temperature/the necessary drying temperature for filament. Extended drying at lower temperatures may have some effect BUT that is based on the idea that filament could dry out like a sponge left to air dry. In reality filament must reach a specific temperature to release the absorbed moisture and without reaching that temperature the drying process remains incomplete and the filament will still retain moisture
Not saying it’s going to or is happening
but I wanted to give that heads up to avoid a possible issue in the future to those drying longer to compensate.
I dry at slightly lower temperatures but I use a dry air purge in my filament dryer. It lets me knock a couple of degrees off to increase margins but doesn’t seem to really affect drying times.
Your point is a good one, though. It’s heat that provides the energy to get water unstuck from the filament and it really affects how much water can be swept away from the filament.
Yep, completely agree; it’s physics,… lower air temp is just not as efficient in getting the moisture out, and will also likely not get the RH down low enough to ever completely dry it out. That’s why the manufacturers publish a recommended temp & time.
Regretfully the weight losses you mention include loss from the plastic spool and the cardboard center. The cardboard can hold massive amounts of moisture compared to PLA or PETG.
Oops. Would like to clarify my previous reply. I did not wish to imply that the lower dry temperature might be insufficient to dry the filament, but rather that amounts of weight loss is unclear using the method pictured. I do agree that there is a range of dry temperature that is effective, and extra time is also effective. However there will be a temperature that is too low, unsure if Bambu publishes a range of dry temperatures.
Filament dryer box stays closed. I have dry air plumbed into the bottom of a Sunlu S2. The bottom plate gets silicone sealed to plug the gap from that bottom plate to the S2 body. That’s the only mods to the S2.
The dry air flow comes from a medium sized aquarium pump pushing room air through a column of silica gel beads. I use indicating beads. As the air travels through the desiccant it loses the ambient air moisture and to the accuracy of the cheap hygrometer I use to measure it, the RH is 2% with a half used up column of beads. In my setup, 800g of beads is enough to dry about 30 spools of filament before they need regeneration.
I built a base to hold the pump, hygrometers, and silica gel reservoir but you can do the same thing with an aquarium pump, a long and short straw to get the air in and out of a container of desiccant, and some tubing. This is what I built, though. Probably overkill for many but this is what I use now.
I just added that because it proves your point. PETG HF in my experience will lose more moisture drying than PLA, but at the lower temps, it didn’t push as much out as it would in 12 hours as it could at higher temps.
