Friday, 28 December 2007

Wear and tear

My extruder's heater went open circuit so I removed the heat shield to have a look at it. I have actually run it for many hours now and have extruded quite a lot of HDPE. I have about 200g of extruded test objects and scrap which represents about 13 hours operation. I only recently started saving my scrap so I must have extruded a lot more. The 2.5Kg reel of HDPE is noticeably smaller.

The heater has also run for a lot longer than the extruder has been extruding. I got fed up of waiting for it to warm up at the start of each run so my host software leaves it on. I keep meaning to put a timeout in the firmware to turn it off when there hasn't been any Ethernet messages for a while as I have left it on for long periods a few times.

The extruder is starting to show some signs of aging. The plastic shield which keeps the fan draft away from the nozzle looked like this when I made it :-



But now it looks like this :-



The nozzle itself now looks like this :-



The JBWeld that surrounds the heater wire has gone very dark and has several cracks in it. One of the heater connections broke off in a previous accident so I dug it out and joined a piece of copper wire by squeezing it tight and soldering it. There is now no sign of the solder which is why it has gone open circuit.

The black stuff which looks like bitumen must be slow cooked HDPE. I am surprised that long term heating to 240°C causes it to decompose. I don't know if the white surface on the shield is just due to its surface melting a bit or whether something boiled off the nozzle and condensed onto it or reacted with it.

Even the high temp insulation over the thermistor wires is starting to look a bit sad!

I also noticed that the steel wire that forms the flexible drive coupling is starting to break up. A couple of strands have snapped and there is a pile of black dust on top of the pump shell.



The heater connection should be easy to fix. I have a few planned improvements to make to the extruder but I will wait till parts wear out before replacing them with better ones to get the most use of it.
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3 comments:

  1. Forrest Higgs29 December 2007 at 12:55

    This is magnificent work, Nop! You've got miles ahead of where I was with HDPE. There may be hope for that stuff yet. :-)

    I'm building an ABS extruder over the holidays. Wish me luck.

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  2. nophead29 December 2007 at 17:34

    Yes good luck with the ABS, it looks like the most promising as far as accuracy is concerned. I might end up following in that direction.

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  3. Stephen Gutknecht3 January 2008 at 03:41

    Your information is great, and I think this is the true area that the RepRap project has to focus on. At least in person, I get so many people focused on the 3 axis movement (electronics, motors, etc) and not on actually melting and printing things ;)

    Thanks for the great detail in your posting.

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