Non-Chemical Torch considerations

[element47]

This is about selecting a torch for melting several ounces of silver in a boraxed melting dish.

In Steves' videos I see him melt silver using a Bernz-0-Matic (what we used to call) regulator torch with MAPP gas. The melting time appears to be in the ten minute range for a half-charge in the melting dish.

Of course...if you heat up silver to its melting point, it's not like it has a choice. It melts. But I myself have never been that impressed with MAPP gas. I am aware of the BTU ratings well above propane and all that, but it doesn't exactly move me.

I am sure there are folks on this forum who have used oxy-acetylene torches to melt PMs. Obviously, the addition of oxygen (and assuming the use of the correct torch and regulator) permits massively higher temps.

Thus I would assume:

1: Melt temps can be reached quite a bit quicker; indeed....maybe TOO quick = danger of vaporized silver. Or a shattered melting dish. Care would definitely be required.
2: Your fuel expense could go down a fair amount (plus you would have a welding rig that could be used for normal gas welding) Because you are buying your fuel (acetylene) in presumably larger tanks, it's a lot cheaper than MAPP in those small hand-held tanks. Yes, you would be adding in the cost of oxygen, but oxygen is pretty cheap, and it last a long time if you are not cutting lots of steel w/oxy-acetylene. You are also using the torch for 20% of the time as you would having to keep the MAPP torch on it for so long. I used to have this gear (an ordinary oxy-acet rig) but had to get rid of it when I moved to an apartment.
3: Seems to me that one could adjust to a mildly reducing flame, especially in the after-pour "pull-away" phase of an ingot pouring operation and this would have a favorable effect upon the finished ingot.

Anyone with experience-based comments in this regard?

 

[Harold_V]

It borders on the impossible to get a better setup than a natural gas torch with oxygen. That's especially true if you consider the high cost of acetylene. There's more than enough heat to melt platinum (I used that setup for years).

Harold

 

[element47]

Thanks, Harold! I happen to have a never-used National 3A torch http://www.nationaltorch.com/3ab.html

That's a nice alternative and I see it can operate on nominal gas pressure. All I need is the proper oxy-natgas tip.

Many thanks for the tip; no pun intended!

 

[Militoy]

It borders on the impossible to get a better setup than a natural gas torch with oxygen. That's especially true if you consider the high cost of acetylene. There's more than enough heat to melt platinum (I used that setup for years).

Harold

Are there any technical reasons not to use acetylene, other than the expense? I already have 2 oxy-acetylene setups - so that's what I've been using for the few little test melts I've done so far. I'm going to keep filling my tanks and using them for cutting and bending / heating metal anyway - so putting on my little torch, and the little bit of gas I use for PMs doesn't seem too big an issue.

 

[element47]

I have read that acetylene has a propensity to impart carbon to a melt, which makes sense. In a PM melt we would probably like not to have carbon imparted to the melt, and in the case of silver which in its plastic zone has a great affinity for oxygen (both absorbs it and gives it up crossing that zone) we would not like to impart oxygen, either. An oxyacetylene flame has rather precisely defined regions, whereas an alkane (nat gas, propane) flame has a wider, more feathery flame. The bottom line is that while an oxyacetylene flame can focus a heck of a lot more heat into the work, thus getting the task done lots faster than a MAPP flame, it would seem to me that using acetylene would require MUCH more precise hand-control and careful maintenance of distance-from-work to avoid chemically influencing a melt.

 

[refiningisfiner]

so the MAPP torch is the best setup to use? i am at the point where i need the best torch for the job at hand.... will be refining all the PM's :mrgreen:

 

[Militoy]

so the MAPP torch is the best setup to use? i am at the point where i need the best torch for the job at hand.... will be refining all the PM's :mrgreen:

Using MAPP doesn't preclude the use of oxygen in the mix - I have oxy-propane and oxy-MAPP equipment, as well as my oxyacetylene rigs. My question above was strictly based on the fact that I'm already filling the big acetylene tanks on a regular basis. So - what I picked up from this thread is that nat gas is cleanest - and acetylene is considered the dirtiest in the general molecular chain of gas fuels. My first melts were done using an antique pump-type gasoline painter's torch - so anything I do to improve that situation is probably an improvement!

 

[Harold_V]

Militoy,
Unfortunately, for some reason I never got back to this thread.
The use of acetylene for melting ether gold or silver is without issues. In fact, if anything, it's most desirable for silver, where a carbon rich environment can serve to limit, or even eliminate, oxygen that is absorbed.

If you choose to use the oxy/acet torch for the platinum group, simply avoid a reducing flame.

Harold