Fire Hazard June 28, 2014 10:08PM |
Registered: 10 years ago Posts: 16 |
Anonymous User
Re: Fire Hazard June 28, 2014 10:37PM |
Re: Fire Hazard June 28, 2014 10:52PM |
Registered: 10 years ago Posts: 474 |
I agree try to minimize everything that will burn and they should be in a metal enclosure with thermal fuses because obviously the plastic that your printing with will burn. One of the worst things is when the thermistor becomes unattached to the heat source. Very important to try to minimize that possibility even if it's not ideal for the thermal readout ring terminals and little screwed in standoffs with thermistor glued in seem to be a better choice. When wires short or break firmware can take care of it but there still should be a thermal fuse located somewhere near the source and a fire resistant chamber or guard over whole machineQuote
goldenmongoose
ABS and/or PLA can easily catch fire when you have a runaway hot end. I've said it a million times. 3d printed parts have no business on a 3d printer x carriage. We're exposing a thermoplastic material to high temperature environments for the sake of building a 3d printed 3d printer. We need to have some serious conversations about safety conflicting with ideology. I could not live with myself if someone died using one of my products. It hasn't happened yet to my knowledge, but it will. It's only a matter of time before someone's house gets burnt down.
Anonymous User
Re: Fire Hazard June 28, 2014 11:44PM |
Re: Fire Hazard June 28, 2014 11:51PM |
Registered: 10 years ago Posts: 1,381 |
Re: Fire Hazard June 29, 2014 12:48AM |
Admin Registered: 13 years ago Posts: 7,000 |
Anonymous User
Re: Fire Hazard June 29, 2014 01:18AM |
Re: Fire Hazard June 29, 2014 05:43AM |
Registered: 10 years ago Posts: 474 |
what I was talking about is not glued into the hot end its glued into a 3 mm brass stand off with something that looks like a high temperature adhesive. And then the little 3 mm stud screws into the heater block so it is replaceable. If you look at the ring terminal ones that they sell it has something that looks like the same adhesive not saying it can't fail but I think I trust it more than tapeQuote
goldenmongoose
I'm not so sure about gluing a thermistor onto a hot end. I think rpone did a cheaper hot end with a glue on thermistor, but I think axial components are the safer way to go.
See: [en.wikipedia.org].
There's a body armor called "dragon skin" that can withstand a .50 cal bullet. But when exposed to high heat, the glue holding the plates of ceramic disks together softens and disintegrates; Might be useful information if your in, oh say Iraq, Iran, Ipod? Basically glue and heat don't mix
Re: Fire Hazard June 29, 2014 11:26AM |
Registered: 11 years ago Posts: 973 |
Anonymous User
Re: Fire Hazard June 29, 2014 12:11PM |
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cnc_dick
what I was talking about is not glued into the hot end its glued into a 3 mm brass stand off with something that looks like a high temperature adhesive. And then the little 3 mm stud screws into the heater block so it is replaceable. If you look at the ring terminal ones that they sell it has something that looks like the same adhesive not saying it can't fail but I think I trust it more than tape
Re: Fire Hazard June 29, 2014 11:53PM |
Registered: 10 years ago Posts: 16 |
Re: Fire Hazard June 30, 2014 12:07AM |
Registered: 10 years ago Posts: 16 |
Re: Fire Hazard June 30, 2014 03:53AM |
Registered: 10 years ago Posts: 474 |
Re: Fire Hazard June 30, 2014 06:28AM |
Registered: 11 years ago Posts: 251 |
Anonymous User
Re: Fire Hazard June 30, 2014 07:30AM |
Re: Fire Hazard June 30, 2014 08:48AM |
Registered: 10 years ago Posts: 16 |
Re: Fire Hazard June 30, 2014 09:04AM |
Registered: 12 years ago Posts: 23 |
Anonymous User
Re: Fire Hazard June 30, 2014 09:22AM |
Re: Fire Hazard June 30, 2014 02:55PM |
Registered: 11 years ago Posts: 172 |
Quote
Gonetotx
My plan is to...
...install redundant thermistors with software to cut off power if the temperature difference exceeds a nominal value
...install thermal fuses where fire hazards exist
...install thermal shielding if possible between the heater block and the plastic support above it
Re: Fire Hazard June 30, 2014 06:21PM |
Registered: 10 years ago Posts: 469 |
Re: Fire Hazard July 02, 2014 04:24AM |
Registered: 12 years ago Posts: 300 |
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Gonetotx
This discussion about heater spec is really good info for me. I'm using a 12 volt power supply for the hot end and a 24 volt supply for the hotbed. I have no idea what the spec is for my extruder heater. Will a 20 watt heater be enough for the ABS? What is the difference between the 20 watt and the 3 watt flame proof 6.8 ohm resister? By calculation, I would have to tune down the voltage supply to about 4.5 volts to get the 3 watts. Is this correct. What are your thoughts about the safety of running the hotbed on 24 volt power? I did this to speed up the heat up time.
Re: Fire Hazard July 02, 2014 05:47AM |
Admin Registered: 12 years ago Posts: 2,569 |
Re: Fire Hazard July 02, 2014 06:09AM |
Registered: 12 years ago Posts: 300 |
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DeuxVis
One way to avoid the thermistor to detach from the hotend is to wrap the heating block - including thermistor and heating resistor - with a few turns of "self fusing" silicone heat resistant tape :
Quote
Added benefit for both solutions is to lower heat waste through air blowing on the heating block, and diminish radiation transmission of heat to the part being printed.
Re: Fire Hazard July 02, 2014 08:23AM |
Registered: 10 years ago Posts: 553 |
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jaguarking11
Honestly, I cant seem to find a proper thermal fuse for ABS 300c preferably. However this one should work nicely connected in series with the resistor or heated cartridge. It looks to be 240c thermal fuse. Which should work nicely with pla. Just tape it to the hot end and connect it in a series with the resistor. Not a bad price either. IF a thermal runaway happens, it trips and kills the hot end, damaging the print and possibly chewing through the filament, but no fire.
[www.ebay.com]
This brings me to the point of having a proper metal chamber on a 3d printer. I think its beneficial for the print and beneficial to contain any sort of hazard. If done properly you could put a 70c thermal fuse connected to a relay and a heatsink to smooth out the temperature inside a heated build chamber. Ensuring that if any fire does start it kills the print and then the chamber will smother out any fire. Could be an effective means to keep people safe and have a heated chamber as well.
Re: Fire Hazard July 02, 2014 09:28AM |
Admin Registered: 11 years ago Posts: 1,063 |
Re: Fire Hazard July 02, 2014 10:41AM |
Registered: 10 years ago Posts: 553 |
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thejollygrimreaper
i solved this problem many moons ago by using axial thermistors and insulating the leads with ptfe sleeve:
click here
using this method there is nearly no easy way to get it into a thermal runaway mode, as the thermistor cannot physically leave the heater-block,
Re: Fire Hazard July 02, 2014 10:56AM |
Registered: 10 years ago Posts: 790 |
Re: Fire Hazard July 02, 2014 11:52AM |
Registered: 10 years ago Posts: 553 |
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MrDoctorDIV
I've got the E3D v5 and I've hit 380C with the stock thermistor. Maybe it's a hit and miss quality thing. Still works weeks later. Reports samish temp of bed thermistor at cold, so I assume it's temp reporting hasn't changed.
Re: Fire Hazard July 02, 2014 01:28PM |
Admin Registered: 11 years ago Posts: 1,063 |
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tjb1
I don't see power limiting working for many, my J-Head with a 40w cartridge has trouble maintain temp with the blower fan. I have to slow fan down to 180 to maintain 200c, should make a duct so not as much hits the heater block but hard enough to find a place for a fan on a Kossel Mini, let alone hard mount it and make room for a duct that doesn't affect hotend temps.
Re: Fire Hazard July 02, 2014 02:36PM |
Registered: 10 years ago Posts: 790 |