Reinforcing a long segmented (weak) core with angle iron.

Discussion in 'Sand Casting' started by Melterskelter, Nov 11, 2022.

  1. Melterskelter

    Melterskelter Gold Banner Member

    I have been casting 26" iron prism-shaped pieces for a couple years now. The cores used to make them are silicate-bound and, because of their large length/cross section ratio plus segmentation by deep indentations are quite weak. To lift them out of the core box without breaking them requires that they be reinforced somehow. Until yesterday I was doing this using mushroom shaped 1" segments of 3/4 diameter steel drilled and tapped on axis and then attaching the core to a 1/8 x 3" flat bar which acted as a "strongback." That system worked pretty well with only a couple failures in maybe 30 to 40 molds. But yesterday one of the mushrooms pulled out and the core fell off the strong back as I was assembling a mold and the furnace was running. Fortunately this happened before the iron had started to melt. So, I just turned off the fuel and headed home to make a new core and make it with an angle-iron reinforcement. There were reasons to believe such a system should be good and a few other reasons to wonder if it might cause expansion problems etc.

    I like the idea of using angle as the wedge shape naturally pushes outward as extraction force is applied and sand seems to naturally resist such force better than say a flat bar on end might or a pipe or round bar, though I suspect each would would also work fine. The angle iron seemed most appropriate.

    Here are pics of the results---which were good (and the casting was "perfect.")

    Here are the molds not long after casting
    2 26's steaming soon after casting..JPG

    Here is a top view of the core still in the casting and just out of the sand. Note the two 1/4-20 studs protruding from the sand.
    The core after casting with .75 inch andgle reinforcement..JPG
    Here is the core partially knocked out of the casting. Note the impression of the underside of the angle in the sand. You can also see that I (unecessarily?) ground down the angle right where it crossed ribs to provide a bit more clearance here.
    Knocking the core out of the casting with angle reinforcement.JPG

    This is a pic of the pattern under construction. It gives a sense of the segmentation of the core. What is actually going on in this photo is I am making epoxy fillets at the intersection of the ribs and sides of the prism.
    Pattern15.jpg
    Here is a pic of the core. The core weighs 6 pounds 4 oz. It is composed of 5% coal added and 5% sodium silicate weakened with sugar and diluted with water. These cores fall right out of the casting and leave a shiny finish. But if you neglect to weaken the care with sugar (I covered this elsewhere) you will not be able to get the core out with a hammer and chisel!
    Sand Chamfer5.JPG

    I am very pleased with this method of reinforcing the core. It felt rock-solid where the mushroom method felt like it was always on the edge of failure. Here is a pic of the “mushrooms.” When I used them, they were embedded head-side down in the sand core.

    image.jpg

    I'll be using angle iron reinforcement from now on in these patterns and in the smaller sister version----my 18" prisms. An, I think this is a method with wider application.

    Denis
     
    Last edited: Nov 11, 2022
    Tobho Mott, Tops and Mantrid like this.
  2. Billy Elmore

    Billy Elmore Silver

    Would it be possible to lighten the back of the core out so it would not be so heavy and would not need that extra support or is it more related to the length of the core? Im not 100% sure Im seeing this right but if I am you could shell the backside of the core and would not only lighten the core making it less likely to break due to its on weight but would also save materials as the core mass could be reduced significantly. Also does it have to be one solid length? Can it be made into just the smaller sections so you just have four small cores? I realize that there is more going on behind the scenes than you can get from the pics so forgive me if I asked a stupid question.LOL
     
  3. Melterskelter

    Melterskelter Gold Banner Member

    What you suggest about making the core in segments could work. On occasion I have cracked a core and had good results just pushing the two halves together if the break was clean and there was no fragmentation. But making them as a single piece is less futzy than three pieces. And trying to handle the one-piece core, even if lighter due to coring, would be chancy at best. The segments are deeply divided from one another.

    The new strong back was dead simple to make and should prevent breaking. Coring out the core also would be an ideal solution. But for my low run volume, it’s more trouble to me than it’s worth. I use the core sand to replenish my green sand as there is invariably some sand lost due to contamination with pine needles, dirt, and general sloppiness. I just put the core pieces in the muller and and let it render them back to sand while I shovel the mold sand on the floor and trample it to prepare it for mulling.

    I was mulling today while light snow fell. The temps will barely break freezing if they do so at all the next ten days. So buckets of green sand a are stored in the barns heated bathroom to prevent freeze up. Tomorrow I pack a 48” camel back straight edge to pour Thurs morning with temps around 26F. Iron is already in the pot.

    This morning I printed this blind riser using an .8mm nozzle—-finished in 1 hr 40 mins. Then sanded for 2 minutes with 120 paper and the epoxied. Oh ya, it is two-toned as my grey spool ran empty midway through printing.

    D354578F-6D40-443E-A865-2C1C6746D20C.jpeg
    Here is a short video of it after epoxy. I don’t think it need any more finishing prior to use.
    https://youtube.com/shorts/XHFR5A-RG8Q?feature=share

    Denis
     
    Chazza, Billy Elmore and Tops like this.
  4. Tops

    Tops Silver Banner Member

    Denis, getting a message on YouTube:

    "If the owner of this video has granted you access, please sign in."

    Print looks Nice. Does the depressed top of the riser help initiate a collapse?
     
  5. Melterskelter

    Melterskelter Gold Banner Member

    Oh, yikes! I see I accidentlally listed it as "Private" rather than the intended "Unlisted" I fixed it and it should now be accessible if you click the link.

    And, yes, the central depression helps it collapse more easily in that area. I try to do everything I can to make the iron feed from the central collapse of the riser rather than some other random place that might be a part of or border on the casting.

    Denis
     
    Last edited: Nov 29, 2022
    Tops and Chazza like this.
  6. Billy Elmore

    Billy Elmore Silver

    What infill level are you using Denis? I have to go above 50% on gating parts or the machine will crush them. That slows down my print time a little but this Stacker is nearly twice as fast as standard printers so it makes up for it. I use a .6 nozzle and depending on detail will print between .2 and .35 layer height. I have printed at .4 and had decent results but required too much sanding. At .2 I dont have to do anything but mount them. I have recently added all of our fillets with the printer and have had to do nothing but glue them on and pin them in place. No more tuffill!
     
  7. Chazza

    Chazza Silver

    Nice work on the printer Denis.
    Inspired by your posts, I have been doing similar things to my risers on the wood lathe,
    Cheers Charlie
     
  8. Tops

    Tops Silver Banner Member

    Thanks Denis. I still cannot see the video, tried on 2 devices.
     
  9. rocco

    rocco Silver

    Same here, this is what I get when I click on the link.

    private video.jpg
     
  10. Melterskelter

    Melterskelter Gold Banner Member

    Jeepers! I thought I had fixed it and must not have clicked the final "save" button. Please try it again. I can not test it here as it has always (naturally) worked for me and sorry for the trouble!

    Denis
     
    Tops likes this.
  11. Tops

    Tops Silver Banner Member

    All is good now, thanks.
     
    Melterskelter likes this.
  12. Melterskelter

    Melterskelter Gold Banner Member

    Billy, I do not know which Stacker model your company bought. But they appear to be industrial-grade machines with price tags to match. And, for your workaday use that makes absolute good sense.

    I am using a .8mm nozzle for general printing and that cuts down print times dramatically. Surface finish is just a bit coarser than .4mm. With the option to just clear coat the part with epoxy, I am fine with print quality except for fine detail work like nameplate and logos. Resin does the trick there.

    I have had no trouble with damage to patterns for parts or risers. But, I am not using a hydraulic compression machine to form molds. I do use a Jet pneumatic ramming tool in addition to my hand ram. I use a 20% infill but also specify "Gyroid" pattern infill which I think is stronger than a simple criss-cross default pattern.

    The silver and blue pattern above I spent 2 measured minutes knocking off the high spots with 120 paper and then coated with one coat of epoxy and it drew perfectly today. That is a big time saving over manually making a similar riser in my amatuer shop.

    I did print the flasks I will use to make silicate-bound molds for the half-scale angle plate. Here is the link in Onshape if you care to look.

    https://cad.onshape.com/documents/1...renderMode=0&uiState=63883d71b7dceb4302b38e0a

    upload_2022-11-30_21-48-21.png

    upload_2022-11-30_21-50-1.png

    The total print time was about 4.5 hours which is pretty fast for my little Prusa MK3s

    The resulting prints are about as strong as if they were made from Baltic birch, I think.

    Since these flask parts are made to be screwed together, I will simply wax them as they will not need to draw in the usual fashion of mold making. I'll just split them off the sand mold.

    I'd love to see a few close-up views of what the Stacker can do.

    Denis
     
    Last edited: Dec 1, 2022
    Billy Elmore likes this.
  13. Billy Elmore

    Billy Elmore Silver

    I didnt have anything in the shop that has not ran in the foundry yet except for some failed prints on pour cups which were some of the first ones and the quality isnt that great. I was learning the new filaments as well. We use specialty filaments for our applications and there was a learning curve with each filament. These didnt make the cut mainly due to warpage but do show some print lines. I think I am about to print a few more small pieces today and will get some better pics with comparison to same parts printed on ender 3 pro. The Stacker can produce high quality but leaving it at factory settings will print decent quality at a much faster rate but the ender will print better quality in about 2.5 the time. The Stackers are huge at 16.5 W x 19.5L and I think 22H. They are way over priced but still much cheaper than some competitors in the same range. I got a quote for a similar sized printer at 140K and we got the Stacker for 15K. The little enders are like 189$ right now.LOL
     

    Attached Files:

  14. Melterskelter

    Melterskelter Gold Banner Member

    Thanks for the pictures Billy. It looks like the print surface quality is about the same on the Stacker as it is on my Prusa. And that makes sense since they’re both using the same technology with the apparent main difference being the build volume capability and the multihead capability of the stacker versus the smaller build volume and a single head of the process.It could be fun if I sent you a STL (or STEP or almost any other format) file that I have sliced and printed here and you run it through your slicer there just to see how the print times compare. It would not be necessary to actually cut the part but just to see what the prep time says in the slicer output.

    When you buy an industrial machine like that, is product support also comparable to the price differential?

    Denis
     
  15. Billy Elmore

    Billy Elmore Silver

    Not for that price...but they do have exceptional tech support. Not sure how big the company is or how many employees they have but the guy I deal with on tech support has actually contacted me when we ordered the wrong part and got us the right part before they processed the order. He has helped me many times as I was struggling with learning all the new features and the slicing software. Not going to say I would personally ever consider buying one that expensive but for industrial uses it has been great. Send me the file and I will run it through both slicing programs and see what it comes up with. I am printing with all three at the moment and using the same part with same layer heights. The Stacker is a 40 minute print and the crealitys are an hour and 57 minutes. I can run the Stacker much higher layer height and get it even faster but wanted to see the comparison at same settings except speed. I think I actually slowed the Stacker down a little on a file a while back and left it there so it could run even faster.
     
  16. Billy Elmore

    Billy Elmore Silver

    Couple of videos running dual head. One at 30% speed to compare and the other at 100% on slicing controller...I can edit the default speed of the machine to go even faster if I wanted to.

     
  17. Billy Elmore

    Billy Elmore Silver

    Printed these on .16 layer height on both machines. Using PACF on Ender 3 Pro and ColorFabb HT black on Stacker. Print time Ender 1 hour 57 minutes and 46 minutes Stacker.
     

    Attached Files:

Share This Page