Metal Pour
50% preparation of the PLA originals, 45% preparation of the investment, and 5% management of the pour. You have seen making the trees with the PLA originals. Today I melted metal, poured, and held my breath. First metal pour. I also made some videos, but the autofocus on the Panasonic LX100-2 is so crap (or maybe it was the operator who was more focussed on the metal pour), that I have scrapped the videos. But some stills are OK, as you will see.
I purchased an ingot of casting aluminium, and bandsawed some pieces to fit into my melting crucible. Then I washed and wirebrushed the pieces in hot detergent. There was minimal dross in the melt, so this step was worthwhile, and the ingots must have been fairly free of contaminants.
Next, was measuring the investment powder and water, using kitchen electronic scales. After mixing there is a 10 minute window for thorough mixing, removal of air bubbles in the vacuum chamber, and pouring into the investment moulds, which had been prepared beforehand. (see last post).
10 minutes sounded like lots of time, but this was a real time and motion study, having everything ready, with no delays. But when I saw the clouds of silica dust I remembered that I should be wearing a mask. So, quick dash, pull on mask, find hearing aids dislodged by the mask, and back to mixing the investment mixture.
Then, 1.5 hours for the moulds to set hard, and remove the rubber caps with the pouring funnels built in. That exposes the bottom of the wax trees. The hose clamps were to assist security of handling the steel cylinders with flask forceps. Next time I will position them closer to the funnel end.
The moulds, after removal of the rubber ends, are placed in the investment oven, for 4 hours at 250ºc, 2 hours at 400c, and 2+hours at 750ºc. The wax and PLA plastic is burnt out and the investment powder sets really hard. The steel cylinder is red hot. The wax and PLA comes out as smoke, with no other remnants seen.
The aluminium ingots are melted at 710ºC, and any dross is scooped off the surface.
Meanwhile, I have placed a sheet of cement sheet on the floor, a tray of dry sand, and moulds for any excess aluminium melt. There is a bucket of cold water ready.
when the mould has been at 750ºc for at least an hour, and the aluminium has melted at 710ºc, the mloten metal is poured into the moulds, which have been removed from the investment oven. Made a video, but not showing because very poor quality. After about 30 minutes, the still very hot mould is plunged into cold water, which blows out much of the investment.
And here is the result……
These are the rear wheel forks. I need 4. 2 were unusable, and will be remelted. 4 are good to OK, and after some filling with JB Weld, and painting, will be fine. The 2 failed forks were those closest to the funnel. Not sure why.
These are the centre columns. I need 2. All 3 are repairable. One is very good. Again, the top one, closest to the funnel, (RHS) will be remelted. I did not vacuum the melt into the moulds, and the weight of melt is lowest at that level. (maybe the cause for the poor result there?)
so, when I had a closer look at home, none of the pieces are perfect, but they are not too bad. For a first run, I am really pleased.
With many thanks to Stuart Tankard for his advice and encouragement.
johnsmachines 