Offshoot of Mark [e57]'s 'welding augers' topic.

I’m trying to cast a bonnet badge in a low melt point tin/copper alloy for my old tractor. The originals, for the Renault’s from ‘56 thru ‘61, were made of crummy Perspex, so being dross to start with, they mostly snapped off, got mangled into the turnips and can’t be got for love nor money! Beats me why manufacturers ruin good products with crappy finishing touches just to save a few centimes.

I was prompted to try making a ‘pastiche’ metal badge [ it’s about 8” wide and 3” high] after a visit with my grandchildren to a Bell Foundry not far from here, where the medieval technology still reigns. When I tell you that the [working] overhead gantry was made entirely of oak, you’ll get the picture! Bell bronze is about 80% tin; 20% copper, and melts at around 1700°F. They were actually quite cagey at the foundry about the exact details, [ in case I was a spy from Bow or Ohio?! ]. They were using a mix of techniques, casting into plaster/clay/goat droppings [!] molds, with the lost wax process for lettering and décor appliqué. 1700°F is a bit hot for me as yet, so I plumped for a low melting point lead-free solder, [ 99.5% tin, 0.5% copper, MP 441°F and close to the eutectic ], as it’s a stock UK plumbers’ item. I’d prefer American Iron & Metal’s [AIM] ‘Castin ®’ solder alloy, quatenary eutectic [ 96.2% tin 2.5% silver, 0.8% copper and 0.5% antimony ] - its MP is lower at 422°F, plus, it’s immune to ‘tin-pest’, a form of rot which can attack pure tin items from below about 55°F. But I can’t find any! I can get Sn/Cu badges plated in chrome, or even gold for her 50th jubilee perhaps.
[ Lead is bad news for plating baths, BTW]

I started out intending to make the badge using the lost-wax process, where a wax pattern is buried in a ceramic jacket, the wax subsequently melted out to leave a mold cavity. I duly built a badge model in lead sheet, epoxy putty etc., using pics from the web to get the size & proportions right; and my existing tractor hood for the contours. From this I made a split mold from clear silicone sealant, glass-fibre etc., in order to cast the wax masters. I'm using pure beeswax BTW. As this part of the project neared completion, I discovered high temperature RTV silicone elastomer! Hurrah! I could now build a proper gravity die-casting mold, go into mass production and lose all that long-winded medieval goats’ droppings goo investment fandango used by the Bell founders. The special RTV [ Rhodia 3255 in France ] is good for 570°F in short bursts. I’m currently at the RTV mold stage- ready to cast the silicone rubber die halves, after taking a delivery of a couple of pounds of RTV from Marseilles. I’m using a wax master here, as I found you can carve and engrave the pattern easily to improve detail and get good draft angles. I’m waiting on two items in the post from England- an electronic scale for accurate catalyst dosing, and a laser infrared thermometer for accurate casting temperature - overheated molten metal shortens rubber mold life dramatically. I’ll post more detail when I have some metal badges to show, but basically I’m going all out now for a full ‘vacuum-cast’ piece!

As to general casting -

Aluminum cast alloys [ easy to get hold of scrap castings, but avoid sheet materials, spec. not suitable ] melt around 1200°F. Sand casting is well within the amateurs’ scope with a little gas furnace and if you can find a friendly foundry, the proper sand is cheap for making up the cope and drag. You need patterns of course. One proviso - molten aluminum readily dissolves iron so you need a proper ceramic/plumbago crucible, but you can transfer crucible to mould box with an iron ladle. Items can be lost-wax cast in 'plaster of paris' but it must be bone, ie in an oven, dry!!
BTW: There is plenty of detail on the net on ‘how to’ 'DON'TS!' and ‘risk avoidance’. Play safe!
Can’t be easily plated, but can be permanently dyed, anodised or acid-etched.

Zinc base alloys, like Mazak, melt around 693°F, and exist a-plenty in old scrapped auto parts etc. This is quite a strong material, and it is very fluid when molten so it will reproduce fine details from the pattern. Plating by pro’s only. Best painted or left as cast. Sacrificial boat parts a possibility?

Lead is toxic, weak & it creeps; apart from fishing weights, best avoided IMHO. MP 621°F

Copper, MP 1980°F. It is castable, but absorbs furnace gasses and distorts, but it can be cold forged and filed to final form. You will need a bit more ooomph than a gas furnace- probably charcoal and a blower, and casting has to be poured out of the crucible. Plateable, but why bother?

Brasses vary enormously in alloying elements, usually copper-zinc, but many commercial items contain lead to ease machining, so be aware. The MP is about 1650°F.
Iron ladles slowly dissolve [check] as per aluminum, you need a ceramic melt crucible.

As a final note, Google “David Reid melting metals in a domestic microwave oven” and make your wife’s day!!!!

Hey, don’t shoot me, I’m only the piano player!

Alan



[This message has been edited by Alan Belson (edited 10-23-2006).]

Great read. sounds like quite a project. I have to ask though Alan, can you explain 'tin-pest'?

I built a Christmas display for a building owner a few years a ago and it required guy wires to hold a frame to a rooftop. I used #14 STR stripped the ends, wrapped them around an eyelet, fluxed and soldered. I used regular plumbing solder, not sure of the %'s though. Now I'm wondering if this was a bad idea because Christmas season is well below 55 F.

Alan,
Is this what folks on my side of the pond would call a hood ornament? Did you consider casting it out of a 2 part epoxy of desired hardness and applying a surface finish?
Joe

jps; 'Tin-pest' is where the pure tin metal literally crumbles to powder. At or below 55F, the metal can very slowly change from a bright metal phase to a dull gray one, and it is reputed that once started, it rots into the rest of the piece like a canker. Remelting removes the problem, for instance if it occurs in ingots- not much help in an art piece! Very small additions [ say 1 or 2%] of other metals like lead, silver or antimony prevent the 'disease', so lead-bearing solders are not at risk. The 0.5% copper in my alloy may be enough- I don't know- but 'Castin' is definitely not affected. Any lead bearing tin solder is a good choice for outside work; it goes grey with age but will last for centuries.

Joe; Yes,this is a hood ornament, it just says 'RENAULT' in a version of the Company 'diamond' logo. The originals were clear plastic, probably perspex; [these tractors were made in the fifties]. They painted part of the inside surface with a block color, and part of it was 'chromed', so that it looked like a metal badge with enamelled relief. They all fell off as the puny 1/16" diameter cast-plastic rivets snapped! The block colors, BTW, yellow/blue/magenta/green denoted the engines fitted, choice of 4 basic models from 16 thru 35hp.
And yes, now that I will have an RTV mould, I can try a casting in clear resin to better mimic the originals.

Alan

Try for information here:
http://www.lindsaybks.com/

These people have all sorts of "interesting" books (EG:Embalming for Fun and Profit ?!)

Backyard foundry is one of their specialties.

TW

I second the emotion for lindsay books, have quite a library of their titles. Get Castain's two casting books and the reprinted US Navy foundry manual.

I have a small foundry setup, can melt bronze and brass and have made belt buckles, 3" long anvil paperweights and brass bobeches for a chandelier I built and other similar sized items. Great fun, you could cast the hotter metals easily now that you understand the complexities of mould and pattern making. I started out with pewter, then moved on to brass & bronxe. My source of metal is scrap valves and other plumbing stuff and I usually throw in a handful of copper wire to deepen the color.
My next project is to whittle some patterns for some double and triple barrell lugs because the local supply houses only carry aluminum units. I still have little experience in making cores and cored patterns and the lug project is a good place to start.
I have a friend who recently cast a bronze 11 foot diameter sphere, fabricated of 24 x 30 inch plates that were welded together. As patterns he used rubber stamp technology to produce a prayer for peace in about 22 languages. The whole unit is assembled as a fountain, the sphere will turn by hand. It is a pretty awesome sight to behold, took tons of silicon bronze and a small crew of smoke crazed metal heads.

[This message has been edited by Almost Fried (edited 10-24-2006).]

Here is my Renault Tractor Badge casting project.

1. This is the original, plastic Renault hood badge. It was made of clear ‘perspex’
with lettering on the inside, so it was impossible to make an exact copy in metal.


2. Hand made lead-sheet masters; badge and hood contour plate, from pics and actual tractor hood.


3. Silicone mold taken off lead-sheet masters. I used clear silicone caulk for the impression.
This is a complex split mold as the part has no flat contours. Mold, parts and assembly.




4. Beeswax pattern from the above mold, carved, re-engraved and in it’s RTV molding box.




[This message has been edited by pauluk (edited 11-10-2006).]

5. Mold halves in RTVfor badge body.


6. Problem: Air-bubbles in RTV moulds. The uncured RTV had such a high viscosity, it needed a 29”mercury vacuum to de-gas it. My hand-pump only made 7”, so the fine detail [‘RÉGIE NATIONALE’] is a separate centrifuged graven plaque, making a 2-part badge assembly.
By careful mold design, mixing and pouring, bubbles can be minimised or kept off important surfaces.
Spincasting mould pattern laid up ready for pouring the RTV. Engraved master in brass.
Note ‘dummy’ casting opposite for balance and the ‘dirt pads’ -this is an old Alfred Herbert trick- dross and air are driven through the impression into a dead-end for a better casting.



7. Spin-casting mold. I hand-cut the runners with a sharp blade, it’s easier than trying to mould them.


8. Spincasting die, assembled and ready for mounting on the machine.
I dusted molds with talc; fine graphite powder is supposed to be superior. I raided the bathroom.
The discs are ‘Duralumin’, 4% copper aluminum-alloy, as strong as steel.


9. Home made spincasting machine. 40 yr. old 230v 1Ø 1480rpm 4-pole motor, set vertical in oak frame.
Die fixes with a set-screw to the motor shaft. Note: motor is open-framed, hence the aluminum slot cover.
Cooling is not a problem; the motor only runs short bursts and has virtually no load.
Gives about 18 psi hydraulic pressure on metal at a 1” radius, equal to about a 4 ft head of metal.


10. Machine fitted with ‘coffee can’ guard and running at speed. Concentricity is vital, so
accurate RTV mold and die parts were turned on the lathe.
Guard needed to be 1” higher than the header: Molten metal can eject up as well as out!




[This message has been edited by pauluk (edited 11-10-2006).]

11. Pouring alloy, main casting. 99.9% tin, 0.5% copper at 511°F. TheRTV,[ ‘Rhodia’ 3255, there are other brands ], has a limit of 572°F.
-Hence the need for accurate temperature control to conserve mold life.


12. Infra red thermometer measures melt temperature.


13. Problem: IR thermometer cannot ‘see’ liquid metal due to it’s low emissivity. My solution was to float some chunks of graphite on the melt and measure their temperature.


14. Die showing hollow sprue. Anything over 32 grams [1.13 oz] was ejected!
-Hence need for higher guard! In future I need to make rotating headers with a smaller hole at top
and with a larger recess under, to allow more metal to be poured and retained as the sprue.


15. Die opened showing castings in impressions. Zero flash, no leaks and pads filled.


16. Plaque / balancer / pads / runners assembly, on hollow sprue. ‘Regie Nationale’.
Reproduction is astounding- it cast my thumbprint left in the release agent!




[This message has been edited by pauluk (edited 11-10-2006).]

17. Badge body castings, with die parts, molds, bolts etc., after a casting session.
Note quick-release method!


18-19. Casting after fettling and polishing.




20-21. Badge body and plaque assembled with epoxy and then fitted to the tractor hood with csk.18-8 screws. I am still debating whether to enamel between the letters.


I am quite pleased with it.

Estimated cost? $250, [ tools & materials purchased ], plus 120 hours labor.

Alan

{ Edited for images }


[This message has been edited by pauluk (edited 11-10-2006).]

[This message has been edited by pauluk (edited 11-10-2006).]

Alan,

Amazing work! Congratulations on your sucess. I assume that the lovely Missus B is happy you are done mucking up her kitchen.

A inexpensive source for vacuum pumps would be recycled refrigeration compressors and air compressors.

Larry C

Mighty impressive! Alan, what was your method of melting that down it appears to be a cast iron stove?

Alan, Nice, actually great job.

Thanks for posting the results.

Bravo Alan

..how many can you cast with those molds?

Alan, is the tractor gas or diesel? I am a member of two diesel forums and some of the members have done their own badges as well. Even though the forums are for Mercedes diesels and Navistar diesels, many of the members are diesel addicts and own tractors as well.

Thanks all for your kind comments, much appreciated.

LarryC, a] The lovely Missus B [ I can’t tell you how pleased she was to read that, thankyou ] was out all day Sunday helping run a stall raising money for the ‘old and unwanted doggies’ Home at an exhibition. Cat's away, mice.....b] She has a new kitchen nearly ready at the other end of the house - this one is due for the dumpster next spring- so she only went half-ape. & c] I cleaned up most of the mess, but you never quite get rid of all the evidence, do you? As long as you don’t spill tin alloy on anything porous or organic, this is a very clean operation and the temperature is not much more than for toffee or caramelised sugar. I’m told [www.] that some of the lower m.p. alloys containing bismuth stink awfully, and of course lead-alloys are a no-no in the kitchen.
I have an old compressor somewhere in the queue for renovation- I might turn it into a vac pump.

Mark; It’s a quartz-halogen hob. The top is black glass of some sort, with 4 ‘lamps’ under and it just wipes clean, even after 6 years of spills of everything- burned milk, meat juices, sugar, etc.. It has thermostatic controls, [ lovely for melting metals! ] but a slow response. Gets ruddy hot though, over 600°F. BTW my stainless ladle was $1.50 in the supermart.

Togol, Other users on the www state 25-40 castings from a mould before imperfections begin to occur, this is after all rubber.
The life depends a lot on how hot the metal is, and how detailed the casting needs to be to be acceptable. I spin-cast six plaques and they all look identical. Once a charge has all melted in the pot, [ and thus the braking action of the latent heat of fusion of the un-melted portion is lost], the temperature rockets up fast! If you guess, you’re in trouble IMO - many users complain of ‘gassing’, a sure sign of burning the RTV; my IR thermometer only cost $30, and is a boon to an old fuss-pot like me, wandering round the supermarket checking out the temperatures of the chiller cabinets & checkout staff; [ "This one's still alive, dear!" ]
Rhodia’s technical department reckon it will take a few shots of pure lead at over 620°F
The dusting of the mold in talc or graphite prolongs life too, by reducing scouring and direct contact.
I also bought a little electronic balance [ increments 0.03 oz ] to measure the catalyst, as getting the right RTV mix is also vital, and I wanted quite a few batches.

Big B. It's a direct-injection diesel engine, naturally aspirated, 6 speed box + 1 reverse.
Renault fitted the unbreakable [British!] water-cooled Perkins 3-cylinder engine, the type P3 TA/4924 in this model, 2.365 liter, 30hp at 1700rpm. There was also a choice of 16hp gasoline [ mainly for vinyards ], plus 22hp or 35hp models with air-cooled MWM 3-cylinder diesels.
They built around 13,500 of the 30hp variant between 1956-60. Very few got exported.

Alan


[This message has been edited by Alan Belson (edited 11-11-2006).]

Alan, I enjoy seeing your excellent work,it takes me back since it's been > 36 years when I was in H.S. foundry class.
where I poured Aluminum, Brass, and Iron in silica sand.

I was in the class for three years, and I managed to make a lot of stuff, but sadly
all of it, my plaques, pots and pans, bookends, pier joints, hurricane lamps, door knockers, peace symbols, weather vanes, house signs, crucifix....are all gone.....


Why three years??....well,..... it was easier than Electric Shop, where I regularly burned up almost everything.

oh the irony as an electrician in a foundry
these past few months heh??


You mentioned your thumprint , and IRC
Styrofoam being used as a pattern experimentally at that time. you can imagine what the rough casting looked like from foam that "looked" smooth

I did get to use it to make some truly heavy Brass apple paperweights for the teachers.....sort of a brown nose idea at the time... anything for a better grade huh?

anyway my magnum opus was a Brass cup, saucer, & spoon .... with the spoon inside the cup....., in one pour.
I had to make (3) three part molds.. two were total wrecks, because the cores that I had baked gave way and ruined them.

The last casting was near perfect, but I still had to sandblast, deburr, file, and buff to a high polish... and lacquer coat it. This took a very long time ....but......

I was not allowed to keep it !

..... I was "asked" to leave it for the display case outside the offices of the principal. My "final" grade was dependent on my thoughtful consideration

needless to say, I was really ticked off in 1970, and since mentioning it here, am furious all over again.



[This message has been edited by togol (edited 11-12-2006).]

Beautiful work Alan! Please post pics of any additional finishing that you do. I've just been glancing over what you've done and need to reread to get a better handle on it. I can tell that you love a challenge.
Joe

If I wanted to cast my own silver or copper ingots, what would be the best type of fuel? I've heard charcoal is pretty good, but do they mean the same kind you cook burgers on a grill? How suitable is MAPP gas?
Thanks
-Josh

Copper melts at 1984°F, silver at 1763°F. Mapp gas torches reach that temperature, but when melting up at these temperatures, the power of the furnace is important if you are to succeed- long drawn out heating times with an undersized heat source introduces problems of gas absorption and oxide [or dross] formation. That loss of metal costs money!
I melted [and cast in DRY sand] copper in an iron ladle using charcoal as a boy in the fireplace with our vacuum cleaner on ‘blow’ providing the air blast. Don’t do this as it stinks out the house!

Any BBQ charcoal is fine, but I’d go for a good hardwood natural charcoal brand and not ‘briquettes’ or domestic coals, as you are then assured there is no sulphur in the fuel. This element, if absorbed into either Ag or Cu, will create havoc with any forging or other later work, making the metal brittle [ ‘hot’ or ‘cold-shortness’- as in cookies or pastry].

To get the temperatures required you need to blow air into the furnace with a blower and a tuyau [ let’s use the right words!] or pipe. Iron pipe or conduit is fine, stainless steel is better, as there is less likely-hood of melting the end off! A BBQ charcoal furnace with a blower will easily hit 3500°F, so take care or you can melt the firebricks. And believe me, a plastic vacuum cleaner pipe WILL catch fire!

‘The Furnace’ could be just some firebricks arranged to form a suitable hearth.
Both copper and silver absorb lots of oxygen and other gasses while molten, and these cause the metal to distort or ‘blister’ as the gasses come out of solution upon solidification. You need to melt quickly and then cast. [ Drag any dross or crud floating on the top of the melt off first]. Small amounts of blistering can be cold-forged out by hammering. If extensively cold-working these metals, an occasional anneal with a gas torch up to dull red-hot will make the piece more malleable and less prone to cracking. Let the piece air cool, or walk it with tongs to your water bucket for a quench- but see later paragraph.

Iron from melting-crucibles [ including stainless steel ] will be dissolved a little into the metals, probably not enough to bother you, but the electrical conductivity will be ruined by a very small amount of iron. Similarly, oxides of copper or silver in the cast piece will lower the conductivity and can also lower strength and other properties of the metals, hence the need for fast melt and cast.

If you are serious, there are www. sites which sell proper ceramic crucibles and tongs. Wear proper protective gear against burns [ cotton or leather, not man made ] and most important of all, as Norm says , wear Safety Glasses, because if you encounter ‘blister conditions’, the metals can spit. Do NOT cast into wet sand or damp plaster molds- that risks a steam explosion- in fact don’t have water anywhere near, except perhaps in a fire extinguisher. Working outside is the best plan. For ingots, 'chill casting' into a welded-up mild steel box-mold, with suitably tapered sides for release, would be ideal. Dust with talc or powdered graphite to aid knocking out.

Best of luck, and play safe!

Alan


[This message has been edited by Alan Belson (edited 11-18-2006).]