Metal Melter

[Kram]

New element connections. Last time I crimped copper tube around it to suck some heat out - copper melts at element temperatures! But Im out of scrap tube.

This time I gas brazed the copper with sillicon bronze tig rod and borax. Near enough the melting point and should add enough mass at the hot end to prevent connections melting.

@Onoff I will try to do a pour this week!

SCR giving a range of 180-1900w which is much more usable, decent power factor at 800-1500w which is where it will be used most.

 

[Onoff]

@Onoff I will try to do a pour this week!

Good stuff. No phone / internet here at the mo courtesy of BT. "Tomorrow" allegedly. Having to wander up the garden now and piggyback off a neighbour's.

 

[Pete.]

View attachment 369725
New element connections. Last time I crimped copper tube around it to suck some heat out - copper melts at element temperatures! But Im out of scrap tube.

This time I gas brazed the copper with sillicon bronze tig rod and borax. Near enough the melting point and should add enough mass at the hot end to prevent connections melting.

If you double the crimped end of the element wire by folding it back on itself and twisting the tail around it will double the cross-sectional area and the end will carry twice the current before it gets as hot as the coiled section.

 

[Kram]

Yes thats how many people do it, these cheap coils come in a pre cut length so ohms are a premium, easily work hardens and oxidises so twists and crimps to itself can be poor.

I could have done that by twisting off cuts from the old elements but I prefer this way using copper. The last inche is uncoiled straight which puts the join back from the hot face, it should stay under 700c at the hot end of the join.

I was running out of time but I dipped the next cow print in wax to fill up all the print holes, so now I need to remove the excess, clean out the text, do the plaster tomorrow.

 

[Kram]

Got the big wax melter out. Used 1.5 pillar candles. 500w is very fast! At about 75c I dipped the former.

Quite happy with the result.

Cleaning the pan might be a pain. Wax probably a bad idea to contaminate annodising dye/sealing water.

 

[DAPPH]

Slooking gud !

 

[Onoff]

If I recall correctly you're dipping the former in wax so you can hopefully unscrew it?

 

[Kram]

Yeah, warm it to 75c and should twist out no problems.

Took a while preparing the next cows. Parafin wax is easy to dig out of the text, red wax will bend tungstens! Didnt get a pic but poured the plaster ok, I hope.

It stood 2 hours then I heated the back with propane, it was superglued to a steel sheet. The heat has started to get melty, hoping it hasnt damaged the mold. Probably should have been more patient and stuck it in furnace

Ready for burnout..

 

[Kram]

Alphabet soup

The mould was superglued down to the steel sheet for the plaster, to stop it floating up. Seems I was impatient and didnt use enough propane to melt the glue, even tho the print was melty. Wax may be better next time!

 

[Kram]

Burn out complete for today, only 230c.. Going out soon. I can see lots of 3d print lines. Plaster has absorbed some PLA so it could do with a hotter burn out.
It took an age to get the steam out!

 

[Onoff]

Burn out complete for today, only 230c..

How come so low? Still amazed the PLA burns out at all and doesn't leave a residue/ash.

Would you say it burns out "as well" as wax?

 

[Kram]

The temp is not nessasarily accurate but close enough.
When it was set 160-180c but still damp (plaster measuing 70-90cc on the top), the PLA came out as a clear liquid like in the soup pic. 45 mins later the steaming had finished, it turned into a nasty brown liquid. Poured it out and is brittle/glassy plastic.

An hour at 230c my stainless bowl had burnt clean and back to shiny, but you can see jn places the plaster is grey coloured.

Wax is a lot easier, most of the wax had gone just from propane in the first pic - gone either absorbed or ran out.

 

[Kram]

550g of nuts. Later I added another 210g, the runners and riser of the last melt - all from the clean nuts.

I messed about with sand a while before deciding on this approach. However the sand needed seiving so was a little lumpy, wasnt my best attempt!

The steel sheet was 0.8mm thick, seemed ok to stop the sand getting in while ramming, the plaster wasnt damaged.

As I was getting ready I turned the heat up, then I noticed the element had fallen. However it was still making good electrical contact so i turned it right up 2500w until it got to 886c.

There was nowhere near enough brass. The pour basin and sprue went dry, almost none in the riser, quite a bit of unplanned leakage. The result is a lot of shrinkage all over. Cows face is worse than last time.

I did attempt to video but again cocked that up with the camera pointing at me for most of the pour.

 

[Onoff]

here was nowhere near enough brass. The pour basin and sprue went dry, almost none in the riser, quite a bit of unplanned leakage. The result is a lot of shrinkage all over. Cows face is worse than last time.

Still progress though! Learning all the time etc. Cheers.

 

[DAPPH]

550g of nuts. Later I added another 210g, the runners and riser of the last melt - all from the clean nuts.

View attachment 370409
I messed about with sand a while before deciding on this approach. However the sand needed seiving so was a little lumpy, wasnt my best attempt!

The steel sheet was 0.8mm thick, seemed ok to stop the sand getting in while ramming, the plaster wasnt damaged.
View attachment 370410
View attachment 370411
As I was getting ready I turned the heat up, then I noticed the element had fallen. However it was still making good electrical contact so i turned it right up 2500w until it got to 886c.
View attachment 370412

View attachment 370417

View attachment 370418

View attachment 370419
There was nowhere near enough brass. The pour basin and sprue went dry, almost none in the riser, quite a bit of unplanned leakage. The result is a lot of shrinkage all over. Cows face is worse than last time.

I did attempt to video but again cocked that up with the camera pointing at me for most of the pour.

Do you recall being taught about " Eureeka , Eureeka , I've found it! Shouted out to his wife when he was in the bath
Archemeedes used the volumes & weights to prove what was gold and what was brass /copper alloys .

Use that principle to find the amount of brass needed .

Re the brass .... get hold of a graduated Pyrex flask / jug that the wax form will fit in to , pop the form in and top up to a known water level carefully fish out the form and note the new water level , subtract the lowest from the highest and you have the volume in CC of the form , then add 20% more to find the required amount of brass. ( aka casting volume plus a bit spare )
IIRC Brass contracts up to 13% after casting ?

Don't add any more water just add brass till you get the casting volume figure
Then start melting confident you have enough . If you poke a few spare unvented 1/2 to 1" holes in the sand any excess a can be poured ithe holes for casting into turning blanks
What sort of flux are you adding to the melt just before you pour it ? Borax or Sif weld ?

 

[DAPPH]

Make your venting sprues at least 1/4 inch in diameter perhaps add six or more to let the molten brass rush in and the air out quickly , you ought to be able to cut the unwantd sprue metal off & polish the roughnees off

When thinking of the venting sprues think of an upside-down spider where the legs are joined to the outer edge of the body shape .

 

[Onoff]

I did suggest borax as a flux... @Kram , any thoughts? Happy to get some posted down to you.

I, as an aside, have been diligent in my research. Just back from the pub. 2 pints of British Bulldog followed by two of Grasshopper...as the Bulldog was finished.

 

[Onoff]

Did you use the printed former in the end (and unscrew from the clay)?

 

[Kram]

Plan to try the former either today or this week.

@DAPPH How much of that is from experience?

I have some borax but it would eat the cuicibles quicker, so I dont use it. I might try citric cleaning the nuts and graphite powder or a carbon source as a cover. However with a huge surface area of nuts, losing 10% is acceptae I think, should be much less when remelting solid bits.

The 3d print will need under 170g of brass. The problem was my carved sand runners leaked and used more than I expected. A previous one was 350g.. A traditional plaster pouring tree would use less brass, but double the plaster - dont have all that much left! 2 or 3 more attemps.

to let the molten brass rush in and the air out quickly

Turbulence is not desired. Slow is much better. With the correct excess of brass there will be plenty of head to get the air out when a porus medium is used. Its not an extreme detailed object like a grasshopper*


Sprues are for filling, there is only one and it should be a very specific size.
Vents, yes they can be many, shouldnt be needed with porus plaster. 1/4" is way too big.

I may change things and try using the vacuum chamber for the next pour.


*

 

[Onoff]

However with a huge surface area of nuts

Boasting again?