So I was casting aluminium today and made a test casting of what will ultimately be a brass part for desktop stained glass lamps. This guy's wife wants brass 4" lamp wheels and is willing to trade some C section purlins I need to make some flasks. The mould has a hand cut runner in the lid that feeds into the outer ring and then across to the center of the casting. It's been fettled and sand blasted and will need further machining including a hole in the center and a "brass thread" hole. Retail this casting and the accompanying ring sells for USD$170 each: https://www.delphiglass.com/bulbs-caps-hardware/odyssey-hardware/4-wheel
Hi Denis, it's resin sand and it was poured hot as the metal texture goes between the sand grains in places, I'm using phenolic urethane resin sand this time round. The pattern ring and hub was hand made out of aluminium on the lathe with 3mm thick extrusion bar for the three arms and sanded to give some draft. The inner hub is held on with a screw and the rest is held on with good quality super glue. The aluminium used is something intended for pressure die casting and gives a beautiful smooth silver finish straight out of the sand but has good machining properties.
So, this is a PUNB process? If I missed it, sorry. But a thread on this process might be of interest including how part looked prior to fettling and blasting. Nice part. Denis
Yes….I hope he does a thread on it as it is not something I’ve done and I don’t recall anyone else reporting on it. Denis
I used to call it polyurethane no bake, but HT1 patiently pointed out that that it's actually phenolic urethane no bake. The stuff has three components with the third seemingly a cross linker that speeds up the cure. It's not practical for home use unless you have a foundry nearby that uses it and is willing to sell the various components due to the short life and the cost ~$400 for 40 litres. Sodium silicate/CO2 is cheaper, commonly available by comparison and lasts a long time on the shelf to give virtually identical performance. I'll take some photos of the other unused moulds next time I'm in the foundry, I think some graphite brushed on will give it that extra smoothness. Edit: I had a trawl though my smartphone and took some photos of the various patterns as constructed: This pattern will cast a brass tube to be machined into the rings to fit the lamp wheel. Lamp wheel pattern before priming and sanding: Lamp wheel pattern sanded smooth before coating with aluminium powder based release agent: The mould in the foreground is the brass tube mould, the lid is a generic slab of resin sand sawn to size roughly with a giant power hacksaw blade and then a hole for the pouring cup and runner drilled in it.
We had to make some emergency bronze castings today and I brushed a coating of graphite onto a wheel mould and cast one in gunmetal bronze. I cut the runner off with a grinder, you can see some shrink as it fed the casting. I've added photos of the casting still in the sand, after hosing off the sand and finally after fettling and sand blasting. I'll machine the remainder of the runner off in the lathe and machine the critical surfaces. Still in the sand mould, the moulds were stacked as they were made so are not perfectly flat leaving a 1.2mm thick bronze flashing. Top side of the casting showing the runner detail: Casting after a hit with water to knock off the loose sand: Runner is cut off and sand blasted:
Ok the bronze wheel is fettled, filed and the rim machined to size, just have to drill the center hole and tap it and mask it up and sand blast the non machined areas. I do love machining gunmetal bronze and the casting is sound and flawless. In future the order of operations would be to fettle, file, sand blast and then machine it last.
