Tuesday, 24 August 2010

Freezing your bits off

Since I started cleaning my PET tape with acetone it can be hard to remove the parts from it sometimes. Somebody suggested trying freezer spray a while back, so I gave it a go.

I got this Arctic Spray, which is intended for freezing water pipes so that you can work on them without draining the water. I must admit I wouldn't fancy having a strict time limit if I was plumbing, you would have to be sure you had all the right tools and materials to start with. My occasional forays into plumbing rarely go to plan and usually involve a trip to B & Q in the middle.

I tried it first on an ABS part before the bed had cooled for any length of time, so it would be at about 100°C and the parts still soft. The part curled up at the edges and so came off easily. I thought I had ruined it by making it warp, but to my surprise it became flat again when it cooled. Still that seems a bit risky, and the spray isn't cheap, so now I cool the bed to 50°C with a fan and then spray any stubborn parts that I can't pull off. It works a treat but I don't know how long a can will last. It would have to be a lot of uses to make it worth the cost: £4.49 plus £2.20 on eBay. Hitting them with a block of wood and a hammer is a lot cheaper!


  1. Off-topic, but since you mentioned it:
    I've used these quite a lot for plumbing at home. Particularly useful for adding and moving central heating radiators.
    Complete everything you need to do apart from connecting it to the system, freeze it, cut the pipe, splice in what you're connecting, Bob's your uncle.
    Dead easy, particularly with push-fit - no real need to worry about "time limits"!

  2. A cheaper option in the long run could be to place a few peltiers below the bed to cool it well below room temperature after a print.

    An example - http://cgi.ebay.com/POWER-GENERATION-TEG-HIGH-TEMP-THERMOELECTRIC-PELTIER-/310155795073#ht_2815wt_1137

    Apparently rated for -60 to 225 degrees C.

    In theory you could also use one or more to heat the bed as well, but warm up time and efficiency may be an issue.

    In an ideal world you could have a low thermal expansion coefficient print surface (ceramic?) that also doesn't degrade with time. This surface could then be actively cooled well below room temperature with the peltier after a print leading to the plastic parts popping off on their own accord due to the difference in contraction rates. Then use a servo controlled paddle attached to the Mendel's X-axis to cleanly sweep all the now free parts off the moving Y-axis below into an awaiting collection bin.

    Back in reality though things obviously would never be that simple.

  3. Nice theory but not all parts pop off when you cool them. In general it seems pretty random. For example, I printed a bed that included two z-leadscrew-bases overnight and by morning they had cooled to room temperature. One had popped off and the other needed a good tug. They are the biggest thickest pieces and the hardest to hold down so you would think they might be relied upon to release when cool.

  4. Mind you I suppose they might if cooled to -60C!

  5. I believe that's just a can of R134a. Know any HVAC guys?

  6. @shblythe
    Push-fit!! He said plumbing. Push-fit's not plumbing; it's for girls.

  7. Anon,
    No but I could do with one to service my aircon if we ever get any hot weather in the UK again.

  8. For me works best smash parts with hammer from side, well if you have enough heavy bed, but you do :-) give it a try

  9. @solstice
    Quite right, far better to use something slow and cumbersome.
    Should we develop an IDE in VB.NET next? :-P

  10. You'd need to have an air compressor handy, but a Hilsch-Ranque vortex tube would be a less costly and wasteful source of chilled air in the long run.
    It's a simple passive device with no moving parts or expendables (not counting the compressor). Here are plans online to build one:
    Actually, the central vortex could probably be made on a reprap to make it easier for people to build them, though it'd likely need some secondary machining to get things smooth.