Wax piston sprue extruder?

Discussion in 'Lost wax casting' started by Zapins, May 21, 2018.

  1. Jason

    Jason Gold

    What is the effective distance of one turn on your screw? That will decide your RPM. No different than a propeller. I think you are going to find 100 rpm is way too fast. I see more like 20 in my mind with that fat bastard.
     
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    I think that the place that makes the machinable wax filament for 3d printing uses a screw based machine to produce their filament. Might be some good people to talk to although I'm not sure how they would feel about giving up too much information..
     
  3. Zapins

    Zapins Gold

    See this is why I didn't want a piston type extruder.

    Check near the end of the video. See how lumpy it is?

     
  4. Jason

    Jason Gold

    Meh, that guys rig is shit.... I think a screw PUSHING a piston is a better route. Speed is not your friend with this.;)

     
  5. Zapins

    Zapins Gold

    Seems more stable than the first guy's. But its so close to a proper extruder why not just go the last step and have infinite capacity if the hopper is full?

    What I want to find out is how important and why do people use a breaker plate? How important is it at the hobbyist level for evening out flow. No mention of this on the forums that I've seen. I guess I'll find out soon enough haha.
     
  6. Jammer

    Jammer Silver Banner Member

    That thing should make sprues, a caramel macchiato, and kill Batman. A simple idea snowballs into a way too complicated machine.
     
  7. DavidF

    DavidF Administrator Staff Member Banner Member

    Thats likely because the nozzle diameter is so large that there is very little back pressure to form up the plastic....
     
  8. Jason

    Jason Gold

    Yeah, but I could watch that sprue maker poop out wax all day long. It's pretty damn cool in a rube goldberg sorta way.
     
  9. Peedee

    Peedee Silver

    Augers tend to spit out the incoming material back into the hopper, think about the interaction of the screw as it leads in to the front edge of the hopper feed (front wall/tube edge opening) at this transition the pressures roll the material up and out, counter to what you may expect to happen. I am of course talking sh*t, literally, I worked for a long time on 10-12" chicken manure augers and got a good feel for the dynamics and how pressures change in the transition.
     
  10. Jason

    Jason Gold

    Hilarious! Peedee, the chicken poop commander!
     
  11. joe yard

    joe yard Silver

    Just doing some eye ball math with the gear box / motor turning the screw you have cast. The extruder will have an output of between 1 and 2 Lb of paraffin a minute at full speed.
    You are planning on machining the tolerances rather tight. This is something that might have to be adjusted to allow for slip. In an extruder slip is a major consideration as it will directly effect the temperature and consistency of the plastic. While the final temperature will be fine controlled by the heater on the nozzle. The material should be close to the extruded temperature by the time it makes it to the dye. With the arrangement of the heaters you have. You will not have to worry about the wax freezing and locking up the screw. You can just turn up the heaters to get a liquid state along the screw.
    Where the wall / screw clearance will mater is. If you do not have enough clearance to allow the wax to churn during compression. Any trapped air will be forced out the front of the screw and through the dye. Sufficient space around the screw should be allowed for air to pass back along the length of the screw and out the back. The churning action will ensure consistent thermal mixing while forcing the air to take the path of least resistance out the back.
    It is looking like a nice design Zapins. It will serve you well and have a very high output capacity.

    Joe
     
  12. Zapins

    Zapins Gold

    1 to 2 lbs a minute. Wow that's a monster. That's like 3 feet of hollow 1 inch rod a minute or 1.5 solid 1 inch rod. If I make smaller diameter rod then I might have trouble keeping up with production. Lol. That sounds like a good problem to have.

    The folks on the extruder forum are saying that for plastic a large gap is good. They said 0.3mm is ideal. 0.4 or 0.5 made it harder to crank the screw as too much plastic got into the gap. But since wax isn't plastic, I have no idea what the ideal gap is. And 0.3 mm is a huge gap. What do you think?

    Link to the other forum with their comments.
    https://davehakkens.nl/community/fo...-extruder-using-lost-wax-casting/#post-139182
     
  13. joe yard

    joe yard Silver

    For all purposes wax acts like plastic in a lot of ways. It will be a question to be answered by trial and error as to the amount of gap that works the best. Start out tight and see how it works. If it is to tight and you have problems. Cut off a few thousandths at a time. The wax will have better lubrication properties than plastic. This will help with the problems associated with the plastic binding when the gap is to large. The friction caused by the wax between the screw and wall will be converted to heat that will be churned back into the mass of wax pulling heat away but not before the temperature difference at the side wall has assisted in lubrication. Further heat will be generated as the wax is sheared during the process.
    All looks very good and I don’t think you will have any problems at all! Some fine tuning of the heat settings and you will hit the ground running.

    Joe
     
  14. Peedee

    Peedee Silver

    Jason, for real, that was my first job on leaving school at 16 (I worked my way up from churning the sh*t off the belts into them to installing and maintaining) they could eat you from the feet up if you slipped into the hopper!

    Zap, do you think the bronze screw will come up to temperature with the rest of the assembly? It may act as a chill and you will get a build up of semi solid wax on it? Be interesting to see the thing in action now -
     
  15. Zapins

    Zapins Gold

    Yeah I'm really unsure. It is hollow so it might be possible to run some kanthal wire up inside it. But I think it might just need an extended period of preheat to warm it all up first. Might shoot for 90F since the wax softens around 146 to 160f and the churning action will probably add more heat.
     
    Last edited: Feb 21, 2019
  16. dtsh

    dtsh Silver

    I'm not very experienced with either wax or plastic, but I have dealt with both in their fluid states occasionally and it seems to me that wax will be much less viscous than most plastics and I suspect you will need tighter tolerances to contain it.
    That said, I too have some experience similar to Peedee's and even a worn out auger that should have been replaced decades before will often still work; albeit with less flow and head available. Were I guessing, I would think around 0.15-0.25mm clearance would probably provide reasonable head/pressure at the nozzle, especially if the nozzle is fairly large.
     
  17. Zapins

    Zapins Gold

    I'm running into problems. I need to get the screw machined and maybe keyed to accept a 7/8" shaft.

    The inside of cylinder is 3.01" and the outside of the screw is 3.11 to 3.08" so there is some room to remove material. The screw is 22 inches long.

    The screw is too big to lathe easily. Especially the key part. So the local machinist that helps me out with projects can't do it. I'm wondering if I should cut the back off the screw and use a slot to turn the screw instead of trying to ket the screw?

    I also bought a thrust bearing that needs to be set into a milled socket on a 1/2" thick steel plate I bought.

    The issue is shipping this stuff is going to cost a fortune and so will local machining shops. I'm unsure how to continue.

    I couldn't get the cylinder to unscrew so I cut the end off it. I will weld it into a frame to support it later.

    20190422_132409.jpg
     
  18. Jason

    Jason Gold

    Send it to AvE at the town pump.. Tell him to put his money where his mouth is.:D
     
  19. You need to find a machinist with a larger lathe. If he can only turn it between centers get him to turn it down to fit inside the cylinder then worry about the drive end. You can manually drill out the hole then when he turns it between centers the hole will wind up in the center of the turned casting.

    How big is the hole? I would suggest tapping the hole and threading the end of the shaft (left hand threads) with a shoulder so it screws in and stops. Another option is to cross drill and put a shear pin through the hole and shaft to pin the shaft in place. It will be a little harder to put a keyway in a blind hole.

    If you put a slot in the end try an X shape so it won't slip sideways. You know how a screwdriver slips versus a Phillips. Or grind and file a big slot in what you have and weld ears on a shaft with the shaft extending farther into the hole to act as a guide.
     
  20. If you haven't welded the support for the thust bearing on, it should be straightforward to chuck it up on a four jaw chuck in the lathe and machine the recess for the thrust bearing. Once the thrust bearing support is carefully welded in place to avoid distortion, you should be able to jig everything in position and use a thick metal filled epoxy to bed the thrust bearing into place against the support to ensure full contact.
     

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