Controlling WAX shrink.

Discussion in 'Lost wax casting' started by Jason, May 4, 2019.

  1. Jason

    Jason Silver Banner Member

    Here's the situation. I'm trying to pour solid wax rod inside a closed off 3/4" copper pipe. After it hardens, I've been hitting the copper pipe with a weed burner. Then I just poop the wax outta the tube. Trouble is, most of the time I find voids inside the wax cylinder. This is obviously being caused by the wax shrinking. I tried preheating the copper pipe with a flame and pouring in the wax. Pretty much same result. We had a similar thread at AA, but hell I can't find it.

    Any of you got any suggestions??? I tried heat, maybe I should submerge the copper pipe in ice water and fill it with hot wax?? A small void inside is fine, but much more than that is becoming a problem.
     
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    Working on the same thing right now. Taking a mold off a piece of pipe then using the mold to produce a hollow sprue. Ill let you know how it works out.
    Ive run into issues with wax and air bubbles (assuming air bubbles is your problem) before and one thing that does help is to heat the wax up "hot" and hold it "hot" over night, then cool it off to a more normal temperature before pouring. This has been a pretty repeatable issue for me and a repeatable cure.
    Side though.... I just picked up a vacuum wax injector that I though would be a hail Mary for my wax patterns but what im running into is that the flow rate is pretty low on it (same as my injection pots) even at 15 psi and unfortunately the internal valving is quite small and im not sure how much larger I can drill it out. Might have to machine my own valve block to get this thing to do what I want it to, but I bought it right so im still happy.
    But that brings me to another Idea ;);) In a video I posted on one of Kellys threads the guy poured a perfect void free wax inside a chamber where the wax and the mold were both under vacuum. Im beginning to think this may be the direction I need to move in, but it seems like it might be a too slow a process for production work. Especially if I heat the vacuum chamber....
     
  3. Jason

    Jason Silver Banner Member

    umm... no air bubbles... Pouring hot wax down a hot pipe... As the wax hardens, it shrinks inside the pipe and leaves the center with voids. I've tried adding more wax after a few minutes and keep topping up the pipe. Remember this dumb ass move I made? After this hardens, I'm getting big gaping holes inside the wax tube.
     
  4. DavidF

    DavidF Administrator Staff Member Banner Member

    Does it have to be solid?? Your problem is more the nature of the beast. A different wax might help out some, like a filled pattern wax, but you need to come up with a way to make a riser and keep the wax in it molten so the lower rod can draw from it as it cools and you need a very gradual cool down cycle (over the course of several hours)
     
  5. Jason

    Jason Silver Banner Member

    Sounds like casting metal.. :rolleyes: Sure helps if it's mostly solid in this case. I'm using for forming into a shape I need. Hollow parts causes it to break and becomes a big issue when shelling. PM sent.
     
  6. DavidF

    DavidF Administrator Staff Member Banner Member

    Yep just like metal cooling, just more severe. You have a programmable temp controller on your kiln. Use it!! Set it up for a 24 hour cool down and add the riser to your pipe.
    I thought a filled pattern wax might help you, but not if your going to try and bent the part later it wont. Stuff can be pretty brittle...
     
  7. Jason

    Jason Silver Banner Member

    Good idea.. If only I could fit a 24inch long piece in my tiny jewelry kiln. I built the pid for 110 and didn't wire it up with big stuff for the 220 kiln. :(
    I know.. you told me so.:oops:
     
  8. DavidF

    DavidF Administrator Staff Member Banner Member

    So do it in sections and join them??? or break out a sheet of aluminum and drop it on the stove and start rolling out a rod?? That poo your working with softens up pretty easily....
     
  9. Jason

    Jason Silver Banner Member

    lol.... good idea. When I sober up tomorrow, I'll try it. Tonight I'm killing a bottle of midori.:D
     
  10. Zapins

    Zapins Silver

    I just keep filling it over and over as it shrinks. It takes forever and it's very annoying that's one of the reasons I'm making the extruder. I should be able to bypass that irritation.
     
  11. Jason

    Jason Silver Banner Member

    Do you think reheating the pipe during refilling helps? Just keeps overflowing on me.:mad:
     
  12. Zapins

    Zapins Silver

    I don't think it helps. Preheating or cooling the mold shouldn't have an affect on the wax shrinkage. Wax will shrink a specific amount between two specific temperatures. You can only reduce shrinkage by pouring wax at the lowest possible liquid temperature. Then the wax will have a smaller difference in temperature and shrink less.

    An extruder works differently by using pressure and a little bit of heat to crush wax through a die avoiding the shrinkage issue entirely because the wax isn't really molten at all so it shrinks a very small amount which isn't noticeable.
     
    Last edited: May 5, 2019
    Jason likes this.
  13. crazybillybob

    crazybillybob Silver Banner Member

    What if you cool the outside of the copper pipe (ice bucket for 5 mins) pour wax in, dump it out? Basically slush cast the tube. That's how I would do it with silicone or resin if temps were an issue.
     
  14. Jason

    Jason Silver Banner Member

    Bruce that would work good if I wanted to keep it hollow. I need to bend these rods into an 'S' curve. I know a tube is less flimsy than a solid cylinder, so I might just give that a try and slush the walls a little thicker. My current method sucks. I'll pickup some 1" stuff and give it a whirl. I can always carve it back.
     
  15. oldironfarmer

    oldironfarmer Silver Banner Member

    I know everyone is in a hurry, and I don't know as much about wax as I do glass :rolleyes: but, chill the pipe, and only pour in a pipe diameter or so at a time, give it time to suck the middle down to feed the shrinkage, then add a little more. Hot wax should weld to the stiff stuff already in the pipe and give you another flat top to shrink down. Oh, and support the pipe so it doesn't fall off the bench.:p

    Your kiln may be different but I found out my 220v kiln has only 110v coils. Low is both coils in series on 110v, medium is one coil on 110v, and high is each coil on a separate leg (still 110v per coil). I about never figured it out because the rotary switch is hard to follow. You should be able to hook your PID to one coil only and do what you want, including firing up the other coil manually if you need more heat. Cold inrush was blowing my relay so I separated circuits and found they were 110v. Yours may be different but maybe not. Mine is a Paragon.
     
  16. Jason

    Jason Silver Banner Member

    Good idea Andy... My cat piss kiln is also an old paragon. I know exactly what you mean by the rotary switch is a mind bender. I like your idea of filling the pipe 3/4" at a time.
    I see you saw me screaming like a little girl when I sent wax a flyin'.... If ya can't laugh at yourself, wtf good are you.:D
     
  17. crazybillybob

    crazybillybob Silver Banner Member

    Jason,
    Just keep slush molding till it's solid. The thin layers cool faster and the shrinkage will be on the inside. Last pour would fill the center. It will take longer but no shrink.
     
  18. Rasper

    Rasper Copper

    I pour my square sprue stock in an open face mold, so the shrinkage is on the open face. To pour a round wax rod, I would take the section of 3/4 inch pipe and, using a grinder with a cut-off wheel, make two parallel cut down the length of the pipe, opening a gap of say 3/8 of an inch wide the length of the pipe, and then use some clay to make s kind of funnel and pour it open faced. After it's cold I would trim off the 3/8 inch ridge.

    Richard
     
  19. Jason

    Jason Silver Banner Member

    Thanks Richard.. Another fine idea too.
     
  20. Jason

    Jason Silver Banner Member

    Walking around the homelessshithole tonight, I hit the plumbing department... In copper, the largest stuff they carry is 3/4":rolleyes:.... I decided I wanted to go up to around an inch. I ended up with a top rail off a chainlink fence.:oops: At least it's cheaper than copper. I sliced a 3/8" slot out of that sucker and leveled it on the bench in some clay. Even after cleaning with acetone, my clay was still not interested in sticking to it.:rolleyes: So I whipped out the metal tape and taped up some walls in the slot. After dumping in the wax, I almost had a huge crisis as the stupid clay melted. She sprung a few leaks, but all is under control as this animal is slowly cooling on the bench. We'll see what it looks like tomorrow. This thing took half of my pot in wax... So yeah if the dam let go, this would have been a big mess.:( If this fails, looks like I'll be stuck slushing. Impatience is my trademark.:D

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    Last edited: May 9, 2019

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