casting small parts

[Rich2502Participant @rich2502]

hi guys, i want to cast in ally two of these plastic ratchet pawls from a chainsaw, i have never cast anything before exept lead bullets, i have no casting equipment, other than a big propane torch,or oxy/propane cutter.But i am an engineer so i can improvise! I do not fancy filing them out of solid.

what can you tell me about this project ?

 

2% shrinkage would probably not matter.

[Rich2502Participant @rich2502]

[JasonBModerator @jasonb]

If you are not worried about shrinkage then take an RTV rubber mould, use this to cast was “patterns” and then use the lost wax casting method. You can always build up any critical surfaces by glueing card to then so you have a machining allowance where it matters.

 

Can’t remember the link to Abby’s site but that has a good description of the method

 

J

 

EDIT this is the site http://www.unionsteam.co.uk/gallery/casting/ you can do it on a smaller scale with a small ladle to heat the metal, Alex Tiranti do all the materials.

 

 

Edited By JasonB on 04/03/2011 07:30:42

[Michael Cox 1Participant @michaelcox1]

It is not difficult to melt and cast aluminium especially for relativly small items such as the ones that you show. If you have a big propane burner you can probably get away with a stainless steel mug or pot as a crucible surrounded by insulating brick as a furnace. Thermalite or Celcon blocks from your local builders merchant make good insulating bricks and are relatively cheap.

 

If you can model the parts in polystyrene foam then it would be very simple to cast these by the lost foam method.

 

For details of simple foundry methods see my website:

http://mikesworkshop.weebly.com/foundry.html

 

If yyou decide to cast the parts give some consideration to sensible safety precautions.

 

Mike

[Engine BuilderParticipant @enginebuilder]

I agree with Mike , you can melt aluminium with a large torch. I
used this on my earlier attempts but have now built a furnace. I would
reccomend using metal that has been cast before and not use extrusions
or drinks cans . That way you know its properties are good for casting.

I have 21 tutorial videos videos on casting on my youtube channel if you have some time to spare.

I can’t get the link to work, you’ll have to type it into your browser

youtube .com/myfordboy

 

Edited By Engine Builder on 04/03/2011 13:01:49

Edited By Engine Builder on 04/03/2011 13:02:48

Edited By Engine Builder on 04/03/2011 13:05:23

[Rich2502Participant @rich2502]

Thanks for your help fellas.

[Gone AwayParticipant @goneaway]

Someone posted this link recently Artful Bodger which looked quite good to me although I haven’t tried anything yet.

 

He’ll show you how to do aluminum casting with some charcoal and a hole in the ground.

[Keith Wardill 1Participant @keithwardill1]

Hi, Richard,

 

I have been making my own small ally castings for years now – much faster than fabricating. As you may have already found out, there is tons of stuff on the Web. For what you need, lost-foam is probably the best. Hardest thing to make is the patterns. Don’t use standard ‘closed cell’ white foam, like the stuff used for packaging or ceiling tiles, etc. It is very hard to shape accurately and smoothly – use the hard foam sold for things like house wall insulation – it is usually coloured some pale pastel colour, and is cheap by the sheet (comes in very thick sheets too). This stuff can be cut easily with a fine saw blade, sharp knife or hot wire, and can be sanded very smooth with fine sandpaper. With care, it can even be turned.

 

When I have made the pattern, I usually give it a coat of (builders) finishing plaster, mixed about as thick as cream, or two or three thick coats of latex paint. This allows you to use almost any fine, dry sand to contain the pattern – simply fill an old bucket with the sand, and bury the pattern in it, tapping the container to help the sand fill all the voids. Almost any sand can be used – I usually get a bag of quartz sand, used for swimming pool filters because its fine and consistant, but I have used builders sand, and even dust swept up from a footpath – just make sure it is dry. The latex coat prevents it collapsing into the pattern when you do the casting, and gives a much smoother finish to the casting.

 

Biggest problem I have had is small voids and inclusions in the casting metal. Inclusions are cause by not skimming the dross from the top of the molten metal (carefully!), but I have never really found an answer to the voids. It doesn’t always happen – I have been told that flux should be added to the molter metal (never been able to find what, or where to get it), or that the melt should be left to stand for a short while, or that it was too hot – you get a different opinion from everyone consulted. I posted on this forum some time ago to see if anything useful was forthcoming, but got no answers, so I carry on my own way – Best way is to to try it and see – Don’t let the H&S crowd put you off too much – of course you need to take care, but then you have to with anything in the modern world.

 

The following links show what is possible, and give lots of useful advice.

 

http://www.backyardmetalcasting.com/
http://www.metalwebnews.com/fd.html
http://www.nucleus.com/~harlan/castings.html

http://members.optushome.com.au/terrybrown/welcome.html

 

Keith

 

[Les Jones 1Participant @lesjones1]

Hi Keith,

Here’s a place to buy aluminium drossing flux.

Artisan foundry store.

I have not tried using it yes as I have not finished building my furnace.

Les.

[Keith Wardill 1Participant @keithwardill1]

Thanks a lot for the info, Les. There may be still a problem, because I didn’t mention that I live in Romania. I didn’t really go into on the last post as it was a bit off thread, but I have also gone through the internet to find some flux (don’t remember your link though, so maybe I’ll try them) – the problem is one I have moaned about on the forum previously – the postal charges of companies shipping UK – Romania are nothing less than downright theft, or they don’t want to ship here anyway. The postal thing is the companies, not the Post Office (or whatever it is these days). I have been quoted postal charges for small packages of over 40 pounds, then found out that they could be sent privately (also by post) for only a fiver – so who is doing the ripping-off?

 

Shipping prices from Germany are very low in comparison – I got a complete tower PC shipped here from Germany, insured, for 9 Euros – problem is that I can’t find a German company that will ship me only a (relatively) small amount of flux. I guess maybe I will find somewhere here in Romania eventually – there are small foundries around.

 

Thanks again,

Keith

[Ian S CParticipant @iansc]

Had a look on Google last night, and came across a bloke casting parts for motorcycles, sumps, rocker covers etc., he said, don’t stir the mix, just skim the top. Don’t over heat, that causes gas inclusions. He does not use flux. I think the flux contains floride(spelling). I think from memory one should not use iron for a melting container, unless it is coated with clay, or similar. Ian S C

[TerrydParticipant @terryd72465]

Hi,

 

I believe that in emergency, washing soda can be used as a flux. Not tried it yet but saw it in a couple of place on the internet. Oh, and table salt as a cover shield to prevent gas dissolving while melting ,

 

Terry

 

Regards

 

[Gordon WParticipant @gordonw]

I am getting interested in small ally casting, not tried yet. Many years ago I did work in a proper foundry (iron) so have an idea how to go about it..Question:- with lost foam patterns where does all the foam go? I’ve tried burning different sorts and all make a right stink with lots of smoke. Is it possible that this may contribute to voids in finished casting? Any ideas what foam might be best from this point of view, rather than finish of pattern?

[Michael Cox 1Participant @michaelcox1]

Hi Gordon,

Polystyrene foam is used for lost foam casting. The conventional white packaging foam is ok for large parts that will be machined afterwards. This type of foam gives a rather coarse finish. The blue closed cell “styrofoam” is much better for for small parts and give a good surface finish. It is available on ebay.

When the alumimium is poured the foam firstly melts and soaks into the surounding sand. As it gets hotter it depolymerises and changes from polystyrene back to styrene. Some boils and exits the mould and catches fire during the pour.

Most of the changes occur at the surface of the molten aluminium from whence all the vapours can escape into the surrounding sand and they are not then trapped in the casting so there is little or no voidage generated in the metal.

Yes, there is some smell and a little smoke when the vapours burn but not that much. Most of the styrene ends up in the sand and is trapped by it.

Polystyrene foam is the only common foam with the right properties for lost foam casting. Polyurethane foams are unsuitable because they do not depolyimerise but decompose producing a hard black char and some very toxic gases. Polyester foams, such as used to make sponges, are too soft to model accurately.

Mike

[geoffrey ballParticipant @geoffreyball88162]

A suitable flux can be made from washing soda but not washing soda straight from the bag or you will have an emergency – the crystals contain a lot of water which must be first driven off. What I do is place a quantity of soda crystals in a dry bean can and heat it gently on a camping gas stove. Leave it until all the bubbling stops at which point you will have lumps of white anhydrous sodium carbonate. After allowing it to cool crush to a powder, it is then ready for use. I have found that a teaspoonful added to an A4 crucible of aluminium does the trick.

[Keith Wardill 1Participant @keithwardill1]

Apologies to Richard for this going OT, but some interesting stuff (to me) has come up.

 

Michael: – I have used the white packing foam in the early days, but I wouldn’t really use it now – you are right that it seems to produce a very rough casting, and I had some problem with deformation, which seemed to happen during the pour. This took the form of apparent ‘bulges’ in the casting, as though the pattern had collapsed in a certain area. I have no explanation for this, but it has never happened with the ‘hard foam’ – incidentally, it comes in all colours, and I usually get mine at a builders merchant, its very cheap, and can be bought in single sheets up to about 1metre x 60cms, and up to 10cms thick – avoids the postal costs and delay on eBay. (will they send a single sheet through the post?). You can stick it together with a hot glue gun (plastic sticks). The info about the fumes and molten plastic, etc is interesting – I wondered if this was a cause of voids and the inclusions, but I had no way to prove it. Most users seem also to use the latex paint or thin plaster coat technique – I certainly get better castings using it – how would this affect the absorption of the styrene, etc into the sand?

 

Gordon W: This hard foam can be turned and sanded to a very smooth finish. There is usually a fair amount of stink and flames when you pour – really makes your eyes water – don’t lean over it when you do a pour.

 

Ian SC and TerryD. I have heard of using Borax as a flux – is this what you mean by washing soda?. Like you, I haven’t tried it, but its on the books for a try soon – I bought a big box full. I also have tried salt to prevent gas absorption, but results were a bit indifferent. The salt appeared to melt on top of the metal. I tried skimming it off just before pouring, but still got small pinholes and voids. I also tried leaving it on the metal, and just pouring ‘as is’, but again the results where indifferent – still some voids and inclusions.

I was told once that the purification tablets used for swimming pools could be used as a flux – may be this is where the floride (?) idea comes from. The tablets have to be plunged into the melt, so it melts and comes up through the metal (so I was told), so I bashed a piece of aluminium tune flat near the end, filled the last few centimetres with crushed swimming pool tablet, and flattened the end of the tube to keep it in place. This tube was then stuck into the melt. (very carefully!). After a few moments, there was a thick cloud of vile-smelling smoke and some bright white flames as the tube melted. I have to report that once again, no real conclusive results.

 

I have had conflicting advice on (over)heating – some say (as IanSC), that it shouldn’t be overheated (how do you tell without a pyrometer?). I have read that it should be heated until the metal is running freely (like mercury), then removed from the heat, skimmed, and left to stand for some moments until it develops a ‘claret-coloured skin’ on the top. It does develop a sort of coating if you do this, but to me it looks more like oxidation. Then what to do? – skim it again? pour it? – what?. And this makes no sense if a gas exclusion material like salt is used – so lots of confusion here.

 

The annoying thing is that on occasion, I have had the ‘perfect pour’ with no ‘remedies’ except skimming the dross – the casting is great, no holes, no inclusions and turns up a treat. I have tried reproducing the conditions as best I can (can’t control the weather though!), and the next pour is rubbish.

As IanSC comments, I have also read about iron containers, but where I live crucibles don’t exist. However, I tried stainless steel canisters – these seemed to work fine, but very quickly develop holes – the metal doesn’t melt – it sort of erodes away – and it is dangerous getting hot metal around your feet. Nonetheless, some good pours from it. I have also made steel crucibles from a chunk of steel pipe with a thick plate welded onto the end. These last much better than the stainless steel cans (but will still eventually develop holes). Again it is hard to say whether they affect the pour , sometimes the final casting was great, sometimes a dud.

 

Despite these problems, I still use the technique – it is often much quicker to make a casting than to fabricate a part, and quite often, pinhole voids can be ignored. When I started, I was surprised how easy it was to produce parts, providing you remeber that molten aluminium is dangerous if not handled carefully.

 

Regards, Keith.

[Michael Cox 1Participant @michaelcox1]

Hi Keith,

I agree that the fine structured styrofoam is much better than the coarse white packaging foam.

 

I am intrigued by your statement that you can buy the fine structured stuff at a builders merchant. All I can get from a builders merchant seems to be the right stuff but aluminium foil coated on both surfaces. On top of that they only sell in 2.4 x 1.2 sheets. Do you have the name of the product and the names of any suppliers?

 

On the question of porosity aluminium dissolve hydrogen when it is hot. The hydrogen comes from water in the furnace gases. Water reacts with aluminium to produce hydrogen and aluminium oxide. On cooling the hydrogen comes out of solution creating porosity. The swimming pool tables contain either chlorine or bromine (not fluoride) and this scavenges and reacts with any dissolved hydrogen eliminating it from the metal.

I have tried using Lo Salt (made for people on low salt diets) as a flux. This melts at a lower temperature than common salt (it is actually a mixture of sodium chloride and potassium chloride). It is very effective in ridding the molten metal of dross. This all floats to the surface as a greyish powder that is very easy to scape of with a drossing spoon. I have also recently tried sodium bicarbonate (baking soda) but this seems to provide little benefit.

 

With regard to crucibles I use stainless steel canisters. Unfortunately many of these are very thin and do not last long. It is better to pay more for something made with thicker guage material. I buy heavy guage stainless steel mugs in Portugal which seem to last for ages, Unfortunately I have not found a supplier in the uk.

I also find that if you heat a new stainless steel vessel for some time to red heat to form a good layer of oxide on it then this insulates the metal from the molten aluminium and the vessel then last a lot longer before perforation.

Mike

[Gordon WParticipant @gordonw]

Thanks for all the info.I remember using styrofoam in road vehicles, both for insulation and structural strength, then the different colours indicated the density of the foam, and hence its properties. Don’t know if this applies to all the makes. Scrap insulated lorries and containers would be a good source, up to about 6″ thick.

[Keith Wardill 1Participant @keithwardill1]

Hi, Michael,

 

I am a little surprised at the difficulty yo have getting the hard foam I described. The difference might be due to the way houses are built in UK. I used to live in Germany, then about 3 years ago moved to Romania. In both countries (in fact, most of Europe),it is commone practise to built new houses with this foam used as a cladding on the outside walls, then covered with a skim coat of waterproof concrete. Certainly in Germany and here in Romania I can walk into any builders or DIY store (we have several large ones near where I live, and buy this stuff in any thickness up to 10cms, either by the sheet or by volume. It comes in different colours, which doesn’t seem to have any significance. When it is cut, it is a consistent smooth finish – no apparent ‘cells’ like you see in the white packing foam. The surface ahs a slightly reflective, almost silky appearance. It is quite hard – it is possible to kneel on it and only leave slight depressions – my missus like to use a piece for kneeling down when weeding.

 

Yo are obviously more knowledgeable abou chemistry than me – I am limited to the ‘try it while standing well back’ school of thought, but it is useful to know that the swimming pool tablets should work – but its a horribly smelly business! Thanks for the tip about LO Salt – I don’t know whether I can get that here, but I’ll take a look – I hadn’t heard about sodium bicarbonate. I can get big bags of the stuff from the local wholesaler, so maybe I”ll try that when I get time.

Like you, I started off with stainless steel canisters, but as you say, quickly found out that there is stainless steel and steel that looks like stainless. I also had the problem of it quickly virtually desintegrating, so that is why I went to the thick steel tube I mentioned earlier. It was a real pain when the canister leaked whilst in the furnace. I have a piece of stainless tube now, about 10 cms diameter, with walls about 4 mm thick, so I intend to weld a stainless plate to the bottom, and see how that lasts. Apropos the use of stainless – I suspect this does ‘pollute’ the melt in some way – it does not melt in the temperatures reached with aluminium, but seems to erode away. Assuming the metal goes somewhere , it must end up either as dross, or in the aluminium – any ideas what this will do?

 

I have read somewhere about allout alloying with copper – I experimented with this by dropping small chunks of copper pipe in the melt – they do ‘disappear’ – they are not left behind in the cannister. I assume the mechanism for this is the same as for stainless (i don’t know for sure). I don’t know how to go about any scientific testing of this, but the resulting castings did seem to be harder – it turned more like Dural than aluminium. On one occasion, I put quite lot of copper in, and the resulting cast had a distinctly gritty feel when I cam to turn it. I thought it was inclusions, but ther was nothing visible, just an odd feel when turning.

Thanks for the ideas. I’ll maybe post again when I have had time to go and play again.

Best Regards,

Keith

[TerrydParticipant @terryd72465]

Hi All,

 

Re: using steel tools etc. Iron does pollute the melt and cause problems with Aluminium castings. When we used to be provided with small sample packs of foundry chemicals (by Foseco) in school there was a powdered clay supplied which could be made into a liquid ‘slip’ (as in pottery) and used to coat the steel tools used for degassing, dross removal etc. to protect the melt from this contamination.

 

In order to de-gas the tablets are held at the bottom of the crucible with a rod which has a domed cap welded to the end (looks a bit like a metal sink plunger), this was perforated so that it held the tablet down but allowed the gases to pass through. In industry nitrogen is pumped through the melt remove the nitrogen. It is usual to use a nucleating agent after de-gassing to ensure fine grain.

 

Hi Keith,

 

Borax is not the same as washing soda .  Borax can be used as a flux for silver soldering, but I’m not sure about it’s use in aluminium casting. Washing soda is Sodium carbonate available from any supermarket. I’m not sure whether it works or not, I’ve just read about it. I have usually had access to proper chemicals, but no longer unfortunately.

 

Regards

 

Terry

Edited By Terryd on 10/03/2011 17:13:52

[Keith Wardill 1Participant @keithwardill1]

Hi, Terry,

 

I asked about Borax/washing soda, because borax is used as a cleaning agent. I have, as you say, used it for flux with silver solder, but I wasn’t sure if it was the same or a related chemical to sodium carbonate (I’m a total loss at chemistry – sorry)

 

Do you have any idea exactly what iron (and steel) does to aluminium? I know it ‘erodes’ away in contact with molten aluminium, but as I noted earlier, I have had (apparently) perfectly good castings (no voids, no entrapments) that were prepared in either stainless or iron containers. What I am looking for here is to try and isolate the circumstances under which this happens – I know all the books and info says don’t use iron/steel (even stainless), but nonetheless, it does work sometimes. Maybe there is a defect in the casting composition which is not apparent in simple castings with no great stress, but I am still interested in why I can (for example) cast a set of pulleys which are fine, and an hour later, using the same materials, technique and containers, get a casting which is scrap because of the voids and entrapped ‘dirt’.

 

Incidentally, just as an experiment, I experimented with making a near liquid mix from local clay (out of our garden!), painted inside my iron crucible. I let it dry overnight, then did a melt in it. Much to my surprise, the clay stayed relatively intact, except where I bashed it when I was skimming the melt. After I had finished it was baked to a hard, dark orange-brown colour – it seems encouraging enough to follow up to see what happens. (but unfortunately, the casting was not too good – lots of pinholes when I cut it open)

 

 Geoff Ball (thanks) also mentions using washing soda, and its preparation for use earlier in this thread, so thats another avenue to try.

 

Thanks for the input – all good stuff – apologies to Richard chuklbutty who started this thread, for inadvertantly hi-jacking it

 

 

 

Edited By Keith Wardill on 10/03/2011 19:30:34

Edited By Keith Wardill on 10/03/2011 19:32:31

[Anonymous]

Posted by Keith Wardill on 10/03/2011 15:04:27:

 

I have read somewhere about allout alloying with copper – I experimented with this by dropping small chunks of copper pipe in the melt – they do ‘disappear’ – they are not left behind in the cannister. I assume the mechanism for this is the same as for stainless (i don’t know for sure). I don’t know how to go about any scientific testing of this, but the resulting castings did seem to be harder – it turned more like Dural than aluminium.

 

 

Errr, that’s because basically it is duralumin! The main alloying elements of duralumin are aluminium and copper, although it normally also contains maganese and magnesium. More generally the 2xxx series of alloys are based on aluminium and copper. These alloys were widely used in the aircraft industry, and also have the useful property of age hardening. A downside is that the copper makes the alloys prone to exfoliation corrosion. The 2xxx series are generally being replaced by the 7xxx series in the aircraft industry, as they are less prone to corrosion.

 

Regards,

 

Andrew

[Author]

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