best material for cylinder and piston

[ryckmans_t]

Hello, just got a lathe and got interested in simple steam engine as a training challenge... I noticed that authors usually recommend to make the piston and cylinder of a steam engine using different metals - apparently using the same metal for both makes them stick together. Is this true? I am planning to use brass for the piston and silver steel for the piston, so I should be okay. Any suggestions?
many thanks
Thomas

[derekwarner_decoy]

Hi PD's .....& welcome to Paddleducks Thomas....possibly brass [LG2] or bronze for the cylinders [INOX] AISI316 for the piston.......the latter being non corrosive....the reason I quote those grades is that they are available in bar stock so are more cost effective to purchase small quantities........keep us posted with your progress .....Derek

[andy]

Hi,

to use different metals is right, otherwise the engine really can stick together!

To use brass for the cylinder and steel for the piston was ok, if you think, it was better to make a new cylinder than a piston, when the engine is worn. Usually the harder material is taken for the cylinder, because a piston is easier to rebuilt.

Steel can rust, think that there will some water into the engine by the steam.

My engine was made with cylinders of inox steel and pistons of brass.

I know, that some machines are made of brass/brass, but this is not so good. But it´s possible to use 2 different kinds of brass, was better than nothing.

Andy

[antopia]

Hi Thomas,

my choice in the modern world, I would use Tufnol(whale brand is what I have used) for the piston that would be my first choice second would be brass using a bronze cylinder gunmetal rather than pb1(a very hard bronze).
brass on bronze is ok as there is plenty of steam oil around.

the piston rod would always be stainless steel as rusting is a problem with steel.

wear in a cylinder  has 2 forms one is the friction, dissimilar metals solves some of this but
most important is the thrust as the piston moves in the chamber, if the piston moves cleanly
without slop and a true fit in the piston guide then it would last many years without wear.

so for the piston guide I would use a hard bronze.

also if using a Tufnol piston the addition of an o-ring with a ptfe overlay then you could quite easily make the piston -.010" clear of the bore and it would still be very efficient and wear would be almost non existant.

Regards
Steven

   

[MikeR C]

I am surprised that nobody voted for cast iron for both cylinder and piston, or at least cylinder. Cast iron is one of the few metals that will run on itself with out galling (sticking) and will run on most other metals without problems. It is cheap, takes little machining power (good for small machine tools), makes a small chip when cut (no long razor sharp ribbons), and will finish to a mirror surface.
It is however, dirty to work with because of the graphite inclusions, though this makes it self lubricating, and the small chips are very abrasive so a vacuum while cutting is a good idea. Alot of auto engines have cast iron cylinders and rings, even though they have aluminium pistons it's the rings that do the rubbing.
Cast iron the miracle metal:)

If anyone has a "wear pair" chart I would very much like to see it. I had one but can no longer find it.

Thx
MikeR C

[mjt60a]

....the piston rod would always be stainless steel as rusting is a problem with steel.....

a quick look at an old 'Mamod' engine I've had (but not used) since I was at school is certainly proof of that! Incidentaly, it has a brass cylinder and piston, no lubricator and no guide (it's a single acting oscillator) and the piston is like a stick in a bucket!

[Stuart Badger]

Nowadays many stam engines use a neoprene O ring for the piston cylinder seal and for the piston rod if needed (double acting). These O rings will stand the high temperatures and require far less lubricant than metal to metal piston/cylinders. You also get a MUCH better seal and can use a very 'thin' piston.

Stuart

[derekwarner_decoy]

Hi PD's....& yes MikeR_C.....acknowledged that spheriodal grey iron [3D] is an excellent building material for cylinder block construction negating porosity.....Derek

[philjoe5]

Although I've built several "steam" engines, I have only run them on compressed air.  I picked up some 7000 series aluminum recently.  I decided to build an engine around it.  I made a cylinder block with it and paired it up with a bronze piston.  This engine runs quite well and I'd like to try running it on steam.  I plan to make a displacement lubricator before attaching a steam line.  The aluminum has an advertised hardness comparable to 1018 CRS.  But there's that coefficient of expansion with aluminum, even this grade, that's about 3x steel.  What are my chances of getting a run out of steam with such a combination?  Any advice or wisdom from experience always appreciated,

Cheers,
Phil