Attempt 10: 10mm socket, oversized, with a head of extra material

[jes]

This is another try at #2, but instead of just using another socket for a head of material, I'm going to use a large solid cylinder.

Socket printed 10% oversize in x/y and 6% in z.

[jes]

Socket mass: 6.7g Filler mass: 61g (lol, possibly overdid this)

Socket height: 21mm Outside diameter: 15.5mm Across flats of hexagon: 11.6mm

[jes]

[jes]

Need to flip flask upside down when putting it in the furnace.

[jes]

Sintered part:

Socket mass: 11.2g (+67%) Filler mass: 39.7g (-65%)

Socket height: 19.7mm (-6%) Outside diameter: 14.0 (-10%) to 14.7 (-5%) Across flats of hexagon: 10.3 (-11%) to 11.0 (-5%)

The socket was warped slightly at the hexagon end, hence the disparate measurements. Since taking the measurements I squashed it in the vice to square it up a bit.

At the square end, there is some solid material in what should be the hole. This is almost certainly due to bubbles in the plaster.

[jes]

[jes]

There are some clear holes in the surface of the bronze.

[jes]

I sanded the outside of the socket a bit to see what it would look like. It comes up shiny, although the pinholes are still obvious.

I also cut the block of filler material in half and sanded one surface to see what it looks like. This too has pores inside, but otherwise looks good.

I then cut away the unwanted material inside the square hole using a carbide burr in a cordless drill, and attached a 1/4-inch ratchet to the socket. I was able to put a moderate amount of torque through it, against the head of a bolt, but eventually the socket tore open, as pictured.

I'm not sure if the weakness comes from not being sintered for long enough, or from pores inside.

[jes]

If the part is not sintered well enough, we presumably solve that by holding it at 865 degrees for longer (maybe 8 hours instead of 4).

If the problem is the porosity, then we need to work out why the powder is leaving holes when the plastic is burnt off. Perhaps the plastic is being evicted too quickly? If we were to hold the plastic in a liquid state for longer, it would have longer to sink down and fill the space, which might improve the porosity.

So for the next part I probably want to hold it at 865 for 8 hours, and ramp from 150 to 400 more slowly.

[jes]

Interestingly the surface quality was much better in #1, not sure what has changed from that.

[jes]

The bronze is very hard to file, seems much harder than aluminium.

[jes]

Here's what the sanded surface of the filler material looks like under the microscope:

[jes]

Maybe the difference is that in #1 there was plenty of empty space for the gases to escape through, but this time the entire part was solid, so escaping gases had to burst holes through the liquidish bronzey plastic material.

[jes]

Total mass changed from 67.7g to 50.9g, a loss of 25%.