Wednesday, 2 January 2008

If it's not one thing it's another!

The third post in a row about my extruder breaking, not a good start to the year!

Now that I am making solid test shapes rather than hollow ones the extruder is working a lot harder and all it seems to do is break down. The drive cable started to disintegrate this afternoon, I could hear the strands breaking :-



It was still limping on however when this happened :-



The brass nozzle started to come out of the PTFE heat barrier. This was ironic because it was only yesterday that I said I had not had this problem in a forum discussion. Others have had it happen and the collective wisdom is to use a pipe clip round the end of the PTFE to secure it.

And the JB Weld which insulates the heater wire has turned to dust :-




So some rebuilding to do!
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12 comments:

  1. Kyle Corbitt2 January 2008 at 01:01

    Well, it's good to know that JB Weld fails in heat-intensive conditions, even with little mechanical stress. A more robust alternative should probably be found.

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  2. nophead2 January 2008 at 08:47

    I have my eye on Cerastil but I might give induction heating a try first.

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  3. vik-olliver2 January 2008 at 20:53

    I use BBQ paint. It works well but you do have to fire it to 200C.

    I spray down 3 layers, each dried with a hair dryer, wind on the nichrome, spray on and dry another 4 layers, then gently blowtorch it (Santa did not deliver hot air gun). Using a cut-down M6 brass bolt helps line up the nichrome and stops the barrel coming out of the PTFE. I recommend a 5mm starter hole for the tap to keep things tight.

    It's good up to 600C, though I suspect the thermistor I've got isn't...

    Vik :v)

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  4. nophead2 January 2008 at 21:07

    Hi Vik,
    Is that insulated nichrome with the BBQ paint or bare?

    I don't think the PTFE will take 600C!

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  5. Stephen Gutknecht3 January 2008 at 03:51

    so am I wrong to start to suggest that the Darwin 1.0 Extruder (built to specifications on the Wiki) really can't deal with 240c that HDPE requires? Seems like we are burning up a lot of things and putting a lot of stress.

    My point here is... HDPE doesn't seem to be an officially supported material... and we need to start talking if we RepRap officially wants to support this and suggest what design changes are required?

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  6. Stephen Gutknecht3 January 2008 at 03:52

    Vik: I too would love a written up details / photos of your JBWeld alternate (BBQ paint, M6 brass bolt).

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  7. nophead3 January 2008 at 08:59

    Stephen,
    Yes I think it is fair to say it doesn't quite cope with HDPE but then nobody ever claimed it did. I only started using HDPE because I can't get PCL filament here in the UK.

    Forrest Higgs pioneered the use of HDPE but he used his own extruder design.

    I don't think the mk2 needs big changes to be more reliable though. There are meterials like Cetastil (used for potting wire wound resistors) that easily stand these temperatures. And although the JBWeld decomposes, it was still working fine until I touched it.

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  8. David17 January 2008 at 23:10

    JBWeld alternative?

    Thermosteel

    http://www.afcinternational.com.au/myweb/products/thermosteel_tech.htm
    http://people.consolidated.net/cargochemical/prod_thermoSteel.html

    Looks like it could be available for muffler repair at auto parts stores.

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  9. David17 January 2008 at 23:12

    Forgot to add:
    ThermoSteel withstands temperatures to 2400 degrees F/ 1316 degrees C

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  10. nophead18 January 2008 at 00:11

    Thanks David,
    Interesting stuff and available in the UK so I ordered some to play with. If it also an electrical insulator but a good thermal conductor then it could be just the job.

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  11. David18 January 2008 at 01:11

    Sodium Silicate aka Waterglass also looks like an interesting high temperature material.
    http://en.wikipedia.org/wiki/Water_glass

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  12. John Gilmore22 January 2008 at 00:21

    That "waterglass" stuff sounds promising. From the wikipedia article, I think I've seen little cylinders filled with it (a silvery grey substance) for sale in the local auto parts store as a radiator sealant. Sounds easy - Add a bit of water, smear the part, blowtorch.

    Probably not that simple though. May have to bake it in the oven instead, to get an even enough temperature. It sounds like it's quite hard and brittle. The comment about its use for glue paper is a bit worrisome.

    "When used as a paper cement, the tendency is for the sodium silicate joint eventually to crack within a few years, at which point it no longer holds the paper surfaces cemented together."

    Still, it's refered to as a "glass like substance" that breaks down at 1500 C. Might be just what we're looking for. Sounds a lot more promising that JB weld anyway. I wonder if the tensile strength is high enough to use it in place of the PTFE Cylinder? It's certianly not a wonderful heat conductor, as the article on use as a passive fire barrier would indicate. (under "intumescent")

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