Cutting up scrap (in this case a pressure cooker)

Hi. I'm seeking ideas on how to cut up in pieces (say 20mm square) some aluminium scrap I have. I won't be able to use my large shear, because the aluminium is too thick, and sawing it up seems like would be arduous. The scrap is a pressure cooker. I'm looking for suggestions. Thanks. Rich

 

I've always liked using a weed burner torch to heat up large pieces of aluminum. Just heat it to hot short temp and whack it with a hammer. Initial heat takes some time but once it's warmed up it goes quick.

 

The big old pressure cookers for canning were cast. Newer ones, of any size, seem to be drawn. As noted above these are both thin and not the best alloy.
If cast, cut off the bottom with a reciprocating saw (safest) or a carbide blade in a skill saw (not recommended). Once the bottom is removed is is easy to bash the rest apart with a big hammer. #3 to #8.

If it a serviceable 23 quart unit sell* it (fall canning season is best) and use the cash to buy/find some other aluminum.

* or use it to make jelly/jam. We all need yet another hobby.

 

I am thinking of using an hydraulic punch contraption to nibble away at the pressure cooker parts. I'd end up with circular pieces. Although a contraption making use of a hammer might well do. (I'm speculating here, and I might require a big hammer). Of course, the problem is, I'm not faced with perfectly flat workpieces. Unless I can bash the metal more-or-less flat before cutting. I have a sledge hammer, I'll see what I can do. Aluminium is about 3mm thick.

 

I use a table saw with a carbide tipped blade, cuts through aluminum like butter. Caution however if you decide to use a table or circular saw, the chips produced are really nasty, appropriate PPE is an absolute must!

 

I'm assuming you're running a crucible furnace. Something that thin placed partially over the exhaust hole will get to hot short in no time and will easily break apart and probably start to melt through the hole and into the crucible.

Pete

 

as long as chunky aluminium scrap can fit inside crucible then for fuel furnace the aluminium will melt when its reached its eutectic point what ever the alloy. The smaller the size, eg thin plates, UBC, your yield will be lower. If flame is coming up around and over top edge of crucible and exhausting through centre the lid, then metal will be preheated and will reduce melting time by 20-25%
On the pic below we can see 7kg ingot (600mm long) sticking out of A100 crucible in 3000Hz induction furnace. You can see by the colour of side wall of crucible closest to ingot that the power densities are concentrated on crucible wall disproportionately closest to aluminium ingot, this then leads to overheating unless power is controlled more closely

In a fuel, or electric resistance furnace you not going to see these same issues, so dont need to get carried away and cut scrap up to small. Just keep feeding the scrap into crucible to keep the melting process moving
As always best to start with heating crucible empty first
Turn furnace off
charge 90% full of scrap of what ever you can get in there
fire up burner and away you go


Let crucible do the work

 

Kelly
sitting with first cup of coffee prior to tackling the mornings issues

To get the 2nd question out of way first
For what you doing best to leave crucible out of furnace and cool naturally on ceramic fibre and not a cold surface. There is no merit in putting crucible back in furnace. There shouldn't be too much aluminium skim sitting on wall of crucible, if there is need to clean when crucible is hot. As you pointed out aluminium oxide and heat can produce corundum and once generated its difficult to remove

Furnace design:
This is complex question, as typically we are dealing with industrial furnace, and some of the crucibles can:
Melting and hold: up to 1800kg aluminium
Holding only: +3000kg

• For Gas/Oil furnace its best to heat the crucible empty for best practice on first charge of the day, this way crucible is uniform, it should only need 10-15 min if melting aluminium, depending on size of burner and the crucible volume to be melted
• For aluminium crucibles in larger aluminium furnaces application, the crucible is generally made of different materials and has increased density than Salamander crucible along with low temperatures glazes to protect crucible body from oxidation as the specific crucible is made to work within a specific temperature range. As the crucible diameter increases there is more surface area and radiant losses
• In fuel furnace you can make the furnace with dense refractory lined up in 20 litre steel bucket, or you could start to zone refractories to remove the heat loss and large temperature variations that are imposed by just using dense refractories
• If the furnace is small the additional costs wouldn't be that much

• For electric resistance furnace I would consider 8KW on 10lbs of aluminium to be quite high powered
• If you look at the attached link to the licensee of Morgan electric resistance furnace, Molten Metal Products UK (there is no affiliation with Morgan Crucible other than MMP is the UK distributor for Morgan crucibles and are all ex-employees of Morgan furnace dept, however I'm using this as the information is very transparent) MMP-Electric-Bale-out.pdf (moltenmetalproducts.com)

• Take the small bale out size 1 or 2 which is 46KW melting 119-271 kg. Then look at the surface area of the crucible 520-616 mm OD x 500-700mm H then you start to compare this to 8kg on 10lb (5 kg) you starting to think that the furnace you using might be overpowered. Now the crucible wall can only transfer X-amount of energy efficiently, to melt the alloy (Cu or Al). If you can't transfer energy, then it sits in furnace chamber and juts keeps heating.
• If the electric furnace chamber is 100% sealed like it should be then heat will only go through crucible of heat up external refractory/furnace shell, there this equates to heat losses and $$,
• If chamber is 100% sealed, then you find that temperature will start to increase if crucible can't handle the increase heat transfer
• The crucible likes to run hot, oxidation is the killer, so this is why there are a range of crucibles to handle difference temp, and alloys.
• Furnace design is key, using microporous insulation against out steel shell fabrication, followed by range of insulation fibre products can help reduce heat loss and keep the heat in chamber moving through crucible to the melt...this is what you wanting to melt the metal
• spacing the heater coils in through the height of chamber can help distribute the heat
• sealing chamber reducing heat loss to the melt surface losses only
• make up light weight insulating cover ...further reduce heat loss
• all this speeds up melting process, reduces costs, and waiting time and make for a better control on the temperature of alloy

 

Kelly

Sodium silicate:

• Typically most foundry grades of sod silicate binders are alkaline. and CO2 used to cure the sand system, typical binder ratios can vary by 4% is probably good starting point. These sand binders are made to break down with heat from casting process, easy knock out, good surface finish etc. These binders normally start with letter "A", then a number which is solids content.
• Silicates used in refractory coating, are generally Neutral based and begin with letter "N". These are stronger and used in rigidizes, refractory coatings etc.

Crucible preheat:

• The manufacture generally advisers to preheat crucible on first charge with empty crucible in fuel of burner furnace is that there are low temperatures glazes on the outside of the crucible body which are going to be operating in low temperature environment eg. zinc , aluminium, and therefore the object is to glaze the crucible body to prevent from oxidation as this can only happen with time and temperature, therefore the crucible may need to be heated up to 950 C first to develop the glaze to melt the aluminium with casting temperature of 660-780 C
• Once the glaze has been developed in electric resistance furnace, the charge can be added cold, and furnace turned on to melt the alloy. The charge will act as heat sync, and reduce the temperature on crucible side wall, and then crucible, and metal temperatures stabilise over melting of charge. In your specific case where the crucible has a lot of power then you may have to wait for the chamber temperature to drop 100 C then can go ahead and charge
• Occasional if furnace has been left standing for weeks/months then its good idea to got through and do the preheating to evelevated the crucible temperature and then recondition the glazing system
• Other than that you can charge and melt cold in resistance furnace, as heating is very even through crucible wall as long as chamber is sealed.
• For Fuel furnace, would suggest preheating crucible first from cold empty and then getting crucible to RED HOT, Then charge, or stop furnace and then charge, depending what scrap your melting and whether furnace design has fuel or supercharge preheating (chamber exhausting over tip rim of crucible) ...I think we dwelled on this in previous postings.
• In the case of the Salamander crucible, there is NO low temperature glaze on the crucible, its made to melt all alloys, and therefore its a compromise on performance, price, and availability. Yes you could get a better more sophisticated crucible to melt small amounts of aluminium, the issue are:
  • do suppliers have them on their shelf...most probably not, as no forecasted demand
  • are customers willing to pay additional 2-3X the price of whats being purchased now for hobby foundry...as product needs to be cost effective, and end customer needs to see value.
  • Can suppliers make, and offer the crucible sizes that's required for small hobby foundry, yes they can however need to place special order, etc.
• Industrial applications have larger furnaces, so target customer is also specific to certain crucible range and offering, but easier to forecast demand