Casting in Rubber

[philmarks]

For the PBO log so to speak, I now have some experience casting in rubber (NO, NOT the willie casting kits that are available!).

I needed to make up a rubber end cap/bend for my heat exchanger, which was obsolete. To avoid having to replace the heat exchanger (£1,400) I cast a part myself in rubber. Cost about £50, and I've got 2 spare as well.

So, if anyone needs help with rubber casting, I can give some pointers.

Rgds
Phil



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[david_bagshaw]

go on tell us how it is done, with pictures as well


<hr width=100% size=1>David
<A target="_blank" HREF=http://www.euroboating.net>http://www.euroboating.net</A>

 

[Johnjo]

Yes, please tell all, very interested !

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[Blue_Blazes]

Soooooooo disappointed. Thought this was going to be tips for fetishist anglers)

<hr width=100% size=1>One of these days I'll have a boat that WORKS

 

[burgundyben]

Trust you!

you've no time for messing around with rubber fetishes, get on with those boats.

Rubber casting stuff is available through the classic car suppliers, think Frost Auto Restoration Techniques (FART - no joke) do it.

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[Avocet]

Re: Trust you!

I used a cold-cast polyurethane called "Flexane" a few years ago - made by a company called ITW Devcon. Don't know if they're till around but it seemed straightforward and worked well.

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[richardandtracy]

Very interested.

I can cast aluminium (cost £2 for all the gear), but not rubber. What's the process etc.? £50 start-up cost seems a bit dear for me, but knowing how it's done may enable a significant price reduction.

Regards

Richard.


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[claudio]

What do you need to cast aluminium ?

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[penfold]

Re: Trust you!

Devcon is (I think) part of Dow Corning, so no danger of them vanishing over night. Their stuff is available from a variety of sources; I use <A target="_blank" HREF=http://rswww.com>Radio Spares</A>. The £50 is approximately what is charged for the smallest set of gummy mix.

cheers,
david

<hr width=100% size=1>This candidate works well when cornered and watched like a rat in a trap.

 

[richardandtracy]

Casting in Aluminium

The things you need for sand casting in aluminium are:-

A furnace
A crucible
Some fuel
An air blower
Tongs
A mould
Aluminium

For the ultimate cheapskate:-
The furnace is fairly easy to make. Find a large metal bucket or some old ducting and line it with at least 2" of concrete (the more the better) but do leave room for your crucible and fuel inside. There must be an air hole at the bottom to blow air in (approx 2" dia).
Make the furnace lid from a disc of re-inforced concrete with a hole in the middle - cast it in a ring formed from a section of the same stuff as used for the body of the furnace. Make sure there are 2 steel loops sticking up out of the lid as it will be HOT when you want to take it off.

The crucible can be a bit of steel box section. Weld a base on it and 2 lugs at the top corners (diagonally opposite) and a loop opposite the corner you're going to use as a spout. Make sure the base weld is watertight, as molten aluminium is very runny.

Make some tongs to lift the crucible by its lugs (to remove from the furnace) and another to tip the crucible to pour. A third set of tongs will be needed to lift the furnace lid.

Fuel to go into the furnace can be charcoal, but it rapidly absorbs water from an opened bag. That way the second burn from a bag a week after the first won't get hot enough. So I use coal - which burns much hotter and can spall the concrete of the furnace, but the furnace only costs pennies and I'm not bothered.

The blower can be a cheap hot air paint stripper with a heat shield from a Fray Bentos pie tin to stop the plastic melting.

The mould is made with vegetable cooking oil poured into dry building sand until it clumps nicely. Then pack this into a wooden box without a base (made from any old timber) and tamp it down around a pattern of the shape you want to cast. Remove the pattern, arrange a couple of vent holes and a pouring hole. Note, this stage can take time to get right, and it's important.

The aluminium to melt can be almost anything. Try to go for stuff that was originally cast - like crankcases, old pistons, electric motor housings etc. If you use foil or aluminium cans, do a first melt and make ingots, this will allow all the sludge and dross to float to the surface before an important melt. Cut this into chunks small enough to go in the crucible and put in a moderate excess for the item you're casting (to allow for feeder holes etc).

Finally, fire up the furnace and put the blower on full. Lower in the crucible with the aluminium and stand back for 5 minutes. The inside of the furnace should now be a bright yellow-red and there will be a translucent plume of flame up out of the hole in the lid (if it's yellow & flickering, there's not enough air). Look through this flame to see if the aluminium in the crucible is molten. When completely molten (and glowing a very dull red inside the furnace - hard to see because the rest is very bright), remove the crucible and pour. If you see stuff floating on the aluminium, try to skim it off with a metal spoon on a poker, but don't take too long about it!

After an hour or two, break open the mould (wearing leather gloves to be on the safe side). The sand nearest the casting will have a burnt/ charcoal grey colour, and the aluminium will be all bright and shiny. The outside surface of the furnace will boil water drops on contact for 4 to 5 hours after removing the blower - it's HOT, keep kids away!

Remember, aluminium melts at 660C, a drop of molten metal on paper or cloth will start a fire. Don't burn yourself. Also, when making the furnace, allow plenty of time for the concrete to dry out. If you don't, you could get a steam explosion when you fire it up the first time.

For pictures & somebody else's write up, look at www.backyardmetalcasting.com . I have no connection with this site, it's just that seeing what was there gave me the confidence to have a go.

Happy casting!

Regards

Richard.


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[seaesta]

Re: Casting in Aluminium

WOW!! I thought I was adventurous casting a lead angel in an old tea pot! I ve just got to have a go at this just to finally convince the neighbours I am completely barmy!

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[vyv_cox]

Re: Casting in Aluminium

Did you ever see a TV programme about a guy doing VSO on an island in South Pacific? He got all the locals collecting aluminium drinks cans, then built a furnace similar to this one and started a casting industry, making a whole variety of useful objects. One of the few money-making schemes owned by the island. By the time he left after 1 year the income of the island had increased enormously. Seems a lot more useful than some of the projects on offer for VSO people.

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[richardandtracy]

Re: Casting in Aluminium

I do all my casting on the patio. The neighbours have known I'm barmy for years though.

The advantage of using coal as the fuel is that, while it pours smoke, at least it smells like a steam train!

Regards

Richard.


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[richardandtracy]

Re: Casting in Aluminium

I must admit I didn't see that. Wish I had.

I tend not to use aluminium cans or anything like that myself, because I have about 2cwt of LM6 scrounged from scrap containers at work. Makes for better castings than general unknown scrap, but it's a pig to machine dry - very gummy on the tool tips, and needs lots of paraffin lubrication. LM6 is also the best non-heat treatable alloy for marine work (which is why I was so keen to grab it!).

Something like teaching small scale casting and that sort of thing is the perfect type of job for VSO. Minimal scavenged materials and local labour. There's a set of 7 books available about making a metalworking machine shop from scratch (see http://www.lindsaybks.com/dgjp/djgbk/series/index.html ), which starts with a little foundry similar to the one I described earlier. Each machine built uses the equipment made in the previous books + hand tools - a fantastic way to bootstrap a third world economy into a semi industrial state. Perfect VSO fodder - I don't know if it's been done, but I'm certain it would be possible.

Regards

Richard.


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