metal for steam engine??

[kye]

hi guys, im planning on casting up some parts for a steam engine in particular the steam cylinder, stand ( which will have the slide in it) and the fly wheel. these are going to be cast in one go, but i dont know what metal is going to be the most suitable for these mainly high wear parts. i dont have any bronze or brass alloys but what i do have is a heap of copper, aluminium, some tin and some zinc. so i suppose what im wondering is which out of brass, bronze(tin) and or aluminium bronze would be best?

 

[rkepler]

Out of what you listed bronze is the most common cylinder material. The traditional material is "gunmetal bronze" (aka CDA 905) a high tin bronze, but I've see Everdur (CDA 655, a silicon bronze) used as well. If you're going to run it on steam you'll likely want cast iron rings for the piston, but if you're planning in running on air you can get away with o-rings (viton rings can suffice for steam rings and will server always as seals). I don't know about aluminum bronze for either, it's usually considered a real PITA to work and I think most folks avoid it for that reason.

 

[JorgensenSteam]

Three types of metal can be found at Budget Castings which seem to be good for engines, which are:

360 aluminum
Red brass
White manganese brass

Standard brass is said to be hard to cast due to separation of the copper and zinc.

I look for metal that provides a clean surface finish, will readily pour at a reasonable temperature, and is in the 80% or greater range for machinability.
Cost of the above metal alloys is generally high.

Gray cast iron is a much less expensive material, but also much more difficult to cast since it has such a high melting temperature. Gray cast iron will provide the best wear characteristics of any metal (in my opinion), and gray cast iron running on gray cast iron is the ultimate from what I have read in the old books of when the large engines were made.

 

[kye]

so i did a little looking around on the net as well as taking what you guys said into consideration, ive decided to go with i high leaded bronze that will contain 10% lead and 10%tin. reasons being 1-will be the easiest to make because i can just use unfluxed plumbers solder which is usually 50/50 lead tin to make it. 2- the high lead content means a lower melting point and will improve its casting properties. and 3- its machinability is rated at 80.

this is the wooden model of the steam engine.

 

[Tin Falcon]

nice looking pattern . one thing i noctice thou is lack of risers IIRC the metal has to follow a path in the large fill tube thought the cavty fo rthe part and up a riser that allows for complete fill no air pockets.
I have only done a lot f reading you are ahed of me on the doing end.
Tin

 

[sunworksco]

Silicon bronze is the wisest choice.
Regards,
Giovanni

 

[steamer]

Silicon bronze is the wisest choice.
Regards,
Giovanni

Not a bad choice.....but it's aweful to machine...very stringy....why not 660 bearing bronze...machines "like butta" and holds up to steam just fine...especially in models.

Spent the afternoon making this eyebolt out of silcon bronze for my boat....aweful stuff...even for a 2 HP, 12" lathe.

Dave

 

[sunworksco]

Beautiful work Steamer!
You are right about hardness but the cylinder needs hardness.
Giovanni

 

[hopeless]

I am just resuming a project that has been languishing in dust for about 10 years (due mainly to a lack of skills at that time. Improving now :big Its a Bolton No 5 marine steam engine out of castings. The cylinder and quite a few bits all made of 'gunmetal'. There have been many made and still work quite well which is not that surprising as they don't run for long periods.
Cheers
Pete

 

[sunworksco]

Is this the engine?
Kind regards,
Giovanni

[ame]http://youtu.be/4IhsLmX6HG4[/ame]

 

[kye]

so i decided to do a "proof of concept" casting of the pattern in aluminium today to weed any problems i would face before i cast it up in bronze. dispite a few hikups like not have enough greensand and a mis-alinement of the cope and drag the castings came out lovely.

casting fresh out of the mold.

the stand cleaned up a little.

and again.

this photo shows the mis alinement.

the flywheel.

now for the not so good bit, i was wrried/expecting the steam cylinder to suffer from shrinkage thats why i did it today in the aluminium. as you can see it surtainly did so i need to redesign the riser and gates for it.

mackye

 

[ShedBoy]

I would call that a great first run. Best thing about melting is it can be remelted. Its all a learning curve.

Brock

 

[metalmad]

Nice one Mate
just chuck em back in tomorrow :big:
Well done
Pete

 

[Herbiev]

Apart from the missalignment it looks like a good pour. Remember practice makes perfect :idea:

 

[kye]

over the last couple of days i was able to get some more casting done. i now have two good castings of the flywheel, two of the cylinder and one of the stand.

just out of the sand.

back side still needs cleaning up.

cylinder.

and finally the stand, which im really happy about how its turned out.

cheers, kye.

 

[JorgensenSteam]

Very nice work Kye.

Pat J

 

[bezalel2000]

Hi Kye

Looks like you've sussed out the shrinkage problem you had. Looking good Thm:

Have you given any more thought to the idea of the leaded bronze?

I've decided to go with i high leaded bronze that will contain 10% lead and 10%tin. - the high lead content means a lower melting point and will improve its casting properties. and 3- its machinability is rated at 80

The reason I ask is that one of your reasons for using leaded bronze (lower melting temperature) contradicts my understanding of the metallurgy involved in Lead Copper alloys.

The Binary Phase diagram lead-Copper and the ternary phase diagram Lead-Tin-Copper both show that the melting temperature of the alloy is not going to be reduced by much until the lead exceeds 90%.
It is the Tin that mostly reduces the melting temperature.

Here is the Lead-Copper phase diagram you can see the melt temp doesn't get much below 960 deg C until it is nearly all lead. In fact what your looking at is melting temperatures similar to or slightly less than Eutectic Cast Iron

And here is the Lead - Tin - Copper phase diagram. Same story, the best melting temp you'll get using Copper and Plumbers solder is at the intersection of the Red an Blue lines (about 830 deg C) Where the copper content is about 67% any higher or lower the melting temperature increases.

Below the red line there is a faint doted line that represents what melting temperature you can achieve with electricians solder - 60/40 eutectic solder. By using eutectic solder with even less copper say 64% you can achieve a melting temperature of around 785 deg C.

I'll leave it as an exercise for you to work out what the melting temperature of your proposed alloy is at
(Cu80% - Sn10% - Pb10%)

Any way all the best with it, I just wanted to give you a heads up on what your dealing with and how you can calculate alloy melting temperatures if you didn't already know.

Cheers
Bez

 

[kye]

hi guys, sorry for the lack of replies im back at uni now and that has understandably taken priority.

bez, thankyou for that very informative post regarding bronze compositions :bow:, i was very interested in reading how little the lead percentage effected the melting temperature of bronze. though nothing should surprize me in the world of metalurgy it is such a very large field of science(??? or feild of its own)!!!!

having being thinking about this for what has been probably been close to a month and a half, the concept of me making my own alloy while sounding appealing probably its going to be the best option in the long run. the only reason i was considering it is because of the relatively large amount of copper i have (found 40m worth of old mains wiring that had been dug up from an old clubhouse, equated to roughly 20kg of copper ;D) but i figure i may as well use what bronze scrap i do have laying about.

as for progress ive made the wooden pattern for the base of the engine, im rather happy with how it looks so far considering im designing this guy myself. ive also done small amounts of turning on the other parts after work on my bosses lathe as well as designs for the other parts to come.

i also tried my hand at fabrcating a crank shaft, in the end it was a complete failure BUT in a way i wont it to be ive learnt so very much from it that im sure when i finally get around to making one for this project it will come together and work without any (touch wood) problems.

i spose now all i need to do is buy my self a nice lathe (which i am currently "trying" to save for, uni isnt very understanding in that prospect :-[) and this little project of mine may one day come together :big:.

p.s. if anyone knows of a goodish lathe for a basicly complete noivice around the $1000au price range suggestions would be so so very much apprieciated. ive run into what seems to be something a lot of beginners run into when trying to choose a new machine, doing lots of research but as a result feeling completely overwhelmed and more confused then when you started, the best advise i can figure would deffinently come from some of the stupidly wise and experienced guys here .

cheers kye.

 

[bezalel2000]

Hi Kye

You could always cash in the copper at a scrap merchant.
As clean copper scrap (stripped from the insulation), 20kg should get near $150 that aught to help buy some tooling for your lathe or even the alloy you were after. ;D

Are you planning to mount the engine on the timber plinth or use it as a pattern for a greensand mold?

Bez

 

[kye]

hi all, just a small update.

i was able to cast the base of the engine as im on a week break from uni (really not much of a break given the 7 assignments currently on my plate :- )

it was only a quick pour so the sand mould came out a little rough in the edges, but for the most part im really happy with it.

kye