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Thread: Name plate and mystery sand lift!

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    Senior Member evlwht-guy's Avatar
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    Name plate and mystery sand lift!

    As promised I have a few new projects. My daughter bought a Hyundai automobile. So I decided to make her a name plate for the front with her name in Korean script. The name plate was a lost foam casting. I hit the internet to find out what her name looked like spelled in the Korean Hangul text and I found that it wasn't easy to spell it exactly but it was possible to get it close. Her name is Haeley and it was only possible to spell Halley. Anyway, I zoomed up the text to the size I wanted and printed out 2 copies. One I spray contact cemented to a piece of blue foam and used it to saw out the letters. The second I glued to the licence plate back so that I could accurately glue on the sawn out letters. I didn't make the second pattern the full width of the plate but only the width of the letters...I was worried that the paper would crinkle when I painted on the plaster. as it turned out this was not a problem, I should have made it full size as on the final casting you can see the edge of the paper.....but this will be painted black and will not really be noticeable. See below some photos. The first is the image on the computer and the second is the finished pattern. I went to a lot of effort to put "Cheap Caulk" around the inside of the frame. Unfortunately the caulk was not cheap enough and the fillet didn't come out. The 3rd picture shows the back side of the pattern where I glued cut in half straws to provide venting. These straws connected to a long passage inside the lumps on the ends. these passages were then connected to the sprues and vents....which as you can see are hollow. The pattern is made tilted to fill from one side to the other. I did this because I wanted to make sure I didn't get a cold short from the metal spreading out thin.


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    Senior Member Bull's Avatar
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    Nice work!
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    Senior Member evlwht-guy's Avatar
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    So here is the pattern being buried...unfortunately I didn't get a picture of the coated pattern. that pattern in the sand prior to pouring. [just ignore the wooden pattern box in the background, it is another project.] and the sand and bucket after pouring.


    When I poured the aluminum just went in and in. til the crucible an A20 was almost empty. All the time I am pouring I am thinking...."where the hell is all this aluminum going???" I had on top of the sand 2 cast iron molds, which you can see in the background with the pile of ingots from the second pour. I intended to pour both patters at the same time but ran out of metal on the plate. I had a case of the dreaded "mystery sand lift" It actually lifted the sand in the bucket and tilted the 2 cast iron cornbread molds that were on top. You can actually see the difference in the sand level in picture ##3 Anyway, when I got the piece out it looked like this.

    But fortunately the front was good and with a little...[a lot] of work I was able to make use of the part. The whole part was much thicker than it was supposed to be. like 2 inches on the high side when it was supposed to be 1/2 inch. Another problem I had was cooling the sand. An enourmous amount of heat went in to the sand and since many of my scoops and buckets are plastic it was difficult to handle the sand until it had cooled. I really need to get a metal cement mixing bucket instead of plastic ones to dump my casting sand in to.

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    Senior Member evlwht-guy's Avatar
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    Here is what I had to do to saw the back off....fortunately I have a power band saw...but don't think the job was easy. The blade drifts when sawing something like this. It would almost have been easier to make a new pattern than go to all this hassle......but I might end up with the same problem....so I worked on this one.


    It is good to have a lot of tools! Note the bucket used to power the saw downwards. Note also that these photos are cutting the last third off. I had to cut from each end as far as i could than saw those t pieces off and saw off the middle. Took several evenings.

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    Senior Member evlwht-guy's Avatar
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    Here are some pictures of the almost finished plate and the 3 biggest pieces I cut off it. We have here also a picture of the back...showing some of the porosity in the cast. I do flux with lite salt and degass with pool-shock but I always get some porosity.

  6. #6
    Great save.
    I figure about 15 lbs of uplift. It seemed to be pretty equal pressure from the thickness of the cutoffs. I recall reading the method is better for verticle rather than horizontal casting because the uplift is based on horizontal area and height of the sprue.
    Guys from the factory told me that when the large foam engine patterns are placed in the flask and if they still had their hand in the bedding when the air float or vibration stopped it was difficult to pull out.
    If you think you can't do it, you're right!

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    Senior Member evlwht-guy's Avatar
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    Soooo. Why the mystery lift phenomena. the aluminum is not heavier than the sand like Iron is so what is going on. In my case I think the boiling action of the foam burning up, caused a crack around the perimeter of this plate and it sort of "ratcheted" its way up. The pulsing of the bubbling gas being momentarily strong enough to overcome the weight of the sand above it. Note in my pattern the high end is more pushed upwards than the low end as there was less sand there. I believe that every pulse raised the mold shell above it and sand flows in and then supports the new height of the top of the pattern. I believe that this phenomena is worse the wider and flatter the pattern is. I saw recently a report that someone else had seen this but with un-coated patterns in "Stinky" sand....IE sand that had been used with un-coated patterns a lot and had much plastic residue in it. What I think may be happening here is that the sand does not let the gas out well and acts as an impermeable layer. I really believe that this phenomena is aided by low head pressure and not enough weight on top. The lifting occurs well before the sprue fills and causes head pressure.

    Another solution is to place a board in the sand just above the pattern. This will provide solid pressure above the pattern and hopefully stop the "Ratcheting" action of the boiling and sand filling in. This will also prevent the sand from crushing down as the mold fills and the pattern is consumed and no longer supports the weight of the sand above it. I had this problem in casting the bumper step project for my truck several years ago. It was buried very deeply and was in the mold horizontally rather than tilted so the metal flowed in and took away all the support for the shell and it partially collapsed....fortunately leaving me with a usable part.

    Another solution is to wrap the pattern in fiberglass drywall tape. I used this on my Towel drying hanger years ago. If I was to do another one of these I would do all these things to insure a good outcome.

    When I get the part painted and installed I will post another picture.

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    Senior Member cactusdreams's Avatar
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    Nice project and cool looking pattern! The dynamics of loose sand can still befuddle me. I think sandcrab is on to it with the verticle positioning and that's how metalbynevin does it too.
    http://www.alloyavenue.com/vb/showth...155#post162155
    Do you think the weights on top had anything to do with it? I once had a crazy idea to make a petrobond riser as my bucket wasn't very deep for a pattern. Didn't think about how the loose sand would react with that weight on top. The pour was going OK till it started filling the riser, then it started to float and the whole thing tilted over. The pic tells the dynamic story.
    Attachment 15149Attachment 15150
    People who say it cannot be done should not interrupt those who are doing it.

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    Senior Member evlwht-guy's Avatar
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    Hey cactus dreams. I think your pouring cup thing basically fell in to the mold cavity.

  10. #10
    Senior Member evlwht-guy's Avatar
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    Quote Originally Posted by sandcrab View Post
    Great save.
    I figure about 15 lbs of uplift. It seemed to be pretty equal pressure from the thickness of the cutoffs. I recall reading the method is better for verticle rather than horizontal casting because the uplift is based on horizontal area and height of the sprue.
    Guys from the factory told me that when the large foam engine patterns are placed in the flask and if they still had their hand in the bedding when the air float or vibration stopped it was difficult to pull out.
    I bleieve that the height of the sprue is not part of the problem...but rather the sand not being packed well and the bubbling action as the metal hits the foam. These sprues never really did fill. I think the wide horizontal area acts like a hydraulic jack...the larger capacity hydraulic jacks have a larger piston...I think this is what is at work here the large flat horizontal area giving it more power. I also failed to vibrate the sand to compact it as well. I really need to create a checklist to help me remember all the details. I think rapping or Vibrating the container of sand will help mitigate this issue as well. Tubho Mott reports that he has had this with his sand when it gets "saturated to the point where the dreaded sand float is now happening to me"

    Anyway, I think you are correct when you suggest that wide things should be placed in the sand sideways....it is just that a plaque needs to be face down to make sure the lettering comes out good.

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