Sodium silicate

Discussion in 'Sand Casting' started by Martin Thomas, Mar 9, 2021.

  1. Martin Thomas

    Martin Thomas Copper

    Hi Guys.
    I have been a member for a while (but lurk in the shadows trying to learn) and have posted my first effort at casting which was a simple hinge a little while ago, which I was happy with. I am now attempting to cast a kickstart pedal for my vintage motorcycle. I am trying to make the mould from sand and sodium silicate but am having problems with the pattern sticking to the sand/silicate mixture. The pattern has been sprayed with gloss paint and has a nice draft on all parts, I have attached a few photographs.
    I am using a fine sand and adding 5% sodium silicate by weight and using a dusting of talcum powder as a releasing agent and gassing with CO2. When I try and pull the pattern from the mould is seems to be lightly glued in place and is a nightmare to remove.
    I also have green sand to hand and may have to use that but thought sand/sodium silicate would give a smoother finish.
    If anyone can shed any light on where I am going wrong it would be greatly appreciated.

    Regards
    Martin. U.K
    Sticky sand.jpg Pedal 2.jpg Pedal 3.jpg Pedal 3.jpg Pedal 3.jpg
     
  2. Billy Elmore

    Billy Elmore Silver

    A good coat of johnsons wax will help stop sticking
     
    dtsh likes this.
  3. dtsh

    dtsh Silver

    Hard to tell from the pic, but you may need more draft on them. A smooth finish and some talc should be enough otherwise
     
  4. Martin Thomas

    Martin Thomas Copper

    Hi Billy & dtsh.
    Thanks for the replies, I have some mirror glaze mould release wax here as I play about with fiberglass mouldings as well, don't know why I never thought of that. Will have another go in the morning. dtsh the photographs don't really show the draft properly, I was pretty particular with the pattern. Most of it was 3d printed and then painted to a gloss finish, just hope its enough.
    Should I gas it before removing the pattern or after the pattern is removed?
    Thanks guys.
     
  5. Billy Elmore

    Billy Elmore Silver

    I do not know enough about homebrewed core making to tell you. My experience has been in shell cores and oil baked cores. I would just cast in green sand.
     
  6. rocco

    rocco Silver

    Definitely before.
     
  7. DavidF

    DavidF Administrator Staff Member Banner Member

    You should gas it before the pattern is withdrawn.
    The problem with it pulling cleanly from the mold might actually be that the paint is soft still.
    Most rattle can paints will not fully harden for weeks. I would suggest using automotive touch up paints as they are pretty quick drying. I think they are lacquer based vs enamel based paints.
     
    John Gaertner likes this.
  8. Jammer

    Jammer Silver Banner Member

    If those are cores, won't the 44U be backwards in the casting?
     
  9. rocco

    rocco Silver

    If I understood the O.P. correctly, these are to be molds not cores.
     
  10. Peedee

    Peedee Silver

    If you are in the UK look out for Plastikote rattle can paints, they cure up a lot quicker and harder than most. I've used Meguires release wax before on tough patterns and it does help.

    I think David is on the money with soft paint issue just by gut feeling.
     
    John Gaertner likes this.
  11. Melterskelter

    Melterskelter Gold Banner Member

    This is to be cast in Aluminum? The reason I ask is that I am wondering about the strength of the cast aluminum bar I think I see on the pattern that looks like it would support the pedal. Maybe I am making things up and that is not the arrangement.

    Denis
     
  12. Peedee

    Peedee Silver

    What is the bike? We like photos
     
  13. Martin Thomas

    Martin Thomas Copper

    Thanks for the replies, I am overwhelmed with the advise offered. The bike is a 1944 Harley model U sidevalve.
    Jammer- This is not a core, but a copy of what I want to cast.
    Peedee- Yes I am in the U.K. I have heard of Plasticote and may have a can kicking around in the workshop. You may be right as for the paint being soft as it has only been painted a few days and maybe some chemical reaction is taking place between the soft paint and the sodium silicate. I have some Mirror glaze (same as Maguiars) mould release wax which contains carnauba wax so will apply several coats of that before my next attempt.
    Melterskelter-The pedal will be in alluminium (hopefully). The bar you are referring to is for core placement within the mould. The pedal actually slides onto a 1/2" shaft.
    Peedee-As you like photos, here is one of the bike that is causing all my problems !

    Once again thanks for your help.
    Martin

    44U.jpg
     
  14. Billy Elmore

    Billy Elmore Silver

    Nice bike! I would cast in green sand and maybe not use a core and maybe drill or make with shaft in it. It is possible to cast the part with the shaft already in it instead of using a core but the casting would not swivel around the shaft. I have done this a lot in the past. Im not sure how that would affect the strength of the out lying material but I know I would find out before I made a core.LOL
     
  15. Peedee

    Peedee Silver

    You may have some issues with paints reacting, I think the plasticote is acrylic based so relatively benign. I would do that in petro-bond or greensand but hey potatoes potatoes......
     
  16. Martin Thomas

    Martin Thomas Copper

    Hi Billy, yeah I can see where you are coming from but I have made a few test cores from sand/sodium silicate and they are the only things that have come out exactly as I intended. If only it was all that easy. I lined a length of copper pipe inside with acetate paper, rammed it up gassed it and pushed it out, worked a breeze.

    Peedee-I have some greensand to hand, I will be ramming up the mould with both types and see what looks the best, when I tried greensand last time I had small edges breaking away, not really sure how damp it should be or how hard to ram it up. I have a hydraulic press I could use, would more pressure help with greensand. Seems to be a big learning curve, haha. I did consider petrobond as I have seen a few castings on youtube with it and it seems to hold together better. How do they make it look so easy. Guess there is no replacement for experience.
    Martin
     
  17. Peedee

    Peedee Silver

    Squeeze test for regular greensand. Take a clump and squeeze it in your hand into a 'sausage' if it sticks to your hand it may be a little wet. Try to break it in half and see how clean it breaks (I'm doing a poor job of explaining this!) There are lots of threads on this scattered around

    Be careful using greensand with a hydraulic press in a mould, too compact and you'll need to vent the hell out of.

    I found oil bonded sands a dream to work with, that's not to say that's needed for this project.
     
    dennis likes this.
  18. Martin Thomas

    Martin Thomas Copper

    Thanks Peedee, I didn’t want to have to purchase any more sand (petrobond) just for one casting, but I can see my fascination with casting growing. Will stick with the normal ramming up process then.
    Martin.
     
  19. Billy Elmore

    Billy Elmore Silver

    Yes...the press is a good idea...there is a learning curve with that as well. I use a press and have even built a pneumatic press for a vertical molding machine. Unless there is an overhead sand system to feed the molds and you are making multiple molds it can be more of a pain in the ass to use than just regular hand ramming. I have never used oil bonded sand but know that there are lots more vents needed.
     
  20. Melterskelter

    Melterskelter Gold Banner Member

    My take:

    Green sand should work fine and surely what would have been used on the original part. There is no need for use of a hydraulic press! Just ram it up in the standard fashion and it will cast fine, Using a core is added complexity with very little gain. It would take a minute or two to bore out the uncored part. But fiddling with getting a core to work may spoil several castings that would have otherwise worked out.

    Sodium silicate will also work fine. Ordinary paste wax is the key to good release as already mentioned. Nothing fancy needed. Silicone spray seems to not work well as a release agent. I would have thought it should work, but I’ve not had good experience with it.

    Making a cylindrical core (not recommended for this part) is easier if the core box is a tube slit lengthwise. When it is slit on one side it will spring open slightly. Squeeze it together and tape it to hold it closed. Pack it with sand and gas it or use a kicker. Once solid, remove the tape. The tube springs open and the the core falls out.

    Keep it simple is good advice, especially when on the early part of the learning curve. There are so many pitfalls inherent in casting that minimizing steps and variables reduces frustration.

    Denis
     

Share This Page