Hot Rubber Moulds

river project, Work in Progress

 

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Whilst working on the burn out moulds that didn’t work I also decided to make a few batches of hot rubber moulds. The process is lengthier, but once the final plaster mould is fired in the kiln the waxes will melt out leaving hollow spaces for the molten metal to be poured into.

To start the rubber needs to be melted in the machine, by being fed into the top, and the press placed on top of it, using gravity to push it down to melt. It then drips out of the bottom into a bucket to be poured. Whilst it is melting I prepared the objects, by applying vegetable oil to each object for easier release from the moulds, then embedding them into clay, creating tunnels with the clay for objects that were going to be solid (although for the brick shown in the photos this was not necessary as I wanted it to be hollow and this required one side to pour in the wax). I then made a tube out of metal or plastic secured with duct tape, and pressed it into the clay bases around the objects. The tube then needed to be waterproofed with extra clay, ready for the melted rubber to be poured in. The next step was to pour the hot rubber into the moulds, and leave it to set. Once it was set I then made a basic plaster mix and poured this into the leftover space in the moulds of the bones (not the brick) to create a flat base for them to rest on.

When the plaster had set I then removed the metal/plastic tube and the clay from the moulds, and flipped them the right way up, using a craft knife as shown to make a few cuts into each mould, to allow me to remove the objects from the moulds. Once this was done they needed to be thoroughly washed to remove clay residue, and then secured with elastic bands or duct tape ready to pour the wax into.

Foundry Work: Burn out

river project, Videos, Work in Progress

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I haven’t updated in a while, as I have been busy physically making work in the foundry this term, which takes up a lot of my physical and mental energy- it is a very hands on, time consuming process, and at the time of writing this I have no finished pieces, as my first mould did not work.

The photos above show the process of making the mould.

  1. The bones were first pressed into clay, which then had plaster poured over the top of it. This photo shows the second stage, where the clay has been removed and cleaned away, to reveal the bones embedded into the plaster
  2. The next stage was to join each of the bones together with soft wax sausages, moulded by hand- this would later become the channels that the metal ran through
  3. The soft wax sausages then needed larger hard wax tubes attached, using hot knives heated over a Bunsen burner to melt and attach them- the top tubes would become channels for the hot metal to run through, and the bottom ones were for ventilation. The wax and bones then needed to be de-greased so that the grog (a special mix of plaster) would stick to it
  4. I then began layering on the grog, carefully over the wax and bones, so as not to damage or dislodge them, extending the wax tubes at the top of the mould as I did so
  5. This photo shows the additional wax tubes added as I applied grog- the joins on the wax tubes were wrapped with the soft wax to strengthen them
  6. Another stage in the grog process
  7. At this point the mould was stood upright, using more grog, onto the board I was working on, and the wax tubes further extended
  8. Once it was upright I then needed to build soft wax around a paper cup, to create the funnel for the top of the mold, which was then attached to the wax tubes. I added more grog as I went along for support, as the wax tubes were very fragile, and the cup was heavy from the added wax
  9. I then made a cylinder out of plastic using plastic sheeting and duct tape, to fit around the mould. To keep it in place I used fabric dipped in plaster to create a band around the middle of the mould, about halfway up (for support) and more of the fabric dipped in plaster around the bottom (to seal the plastic to the board)
  10. The next stage was to make the second coat grog mix (it is made with ludo instead of fine casting plaster) and carefully fill the cylinder to the top with this mix. This had to be done slowly, in stages, to prevent the heavy mixture from damaging the rest of the mould, and also to make sure it was completely filled.
  11. Once it was set Becky (the technician) removed the plastic layer, and covered the outside in fabric dipped in plaster to make a sturdy outer layer, and the mould was then fired in the kiln at a very high temperature to melt the wax and burn out the bone fragments. This photo shows the mould once it had been filled with molten bronze and left to set

The video above shows the pouring process in the foundry, done by Becky and another technician. My mould is the middle one!

12. This photo shows Becky removing the outer layer from my mould
13. We then began to smash my mould open (carefully) to see if it had worked
14. This photo shows the broken mould- you can see the metal has filled the cup and the top of the wax channels, but stops at the bones
15. The fragments of bone in my hand- this mould failed as the kiln did not get hot enough to burn the bones out, meaning the metal had nowhere to go.

I was very disappointed that this mould failed, but it was an experiment, and myself and Becky realised that the kiln was not going to be able to reach the kind of temperature we needed without it breaking my mould. This mould took me nearly two months to complete, as I had to wait between each step to check with Becky that I was doing it right, and to ask what the next stage was, as it was my first time doing this, but I am already halfway on the shell mould. This is because once you know what you are doing it is much easier to just get on and do it, which I will continue to do! Also I have only been in the foundry 3 days a week, as Wednesdays it shuts at 12.30 and I struggle to get in early enough, and Fridays it is shut. Going forwards I plan to finish the shell burn out mould (hopefully it will work) and also continue making wax versions of some of my bigger bones, to make into a mould. My next post will show the process of making a hot rubber mould, and waxes from that!