Hot air and stirling engines

[Ian S CParticipant @iansc]

Hello Gordon,with some of my engines I keep the displacer at atmospheric pressure by making the shaft out of tubing,there must be no leaks inside the engine,but if you make it with the tube,you can solder the cold end on easily(if you try to solder a sealed container you’ll have fun,the air inside expands as it heats and blows the solder out).If you want to completely seal the displacer use Arildite,or similar,works ok,if it falls of the motor is too hot anyway.Itis possible to make a moving regenerator type diplacer using steelwool,tryed it once with limited success,I think I know where I went wrong so I might try again.That was the type used in the full size Robinson engines.I assume that your proposed motor is of similar proportion,maybe similar to a Robinson motor with a short fat displacer,for a model quite big,sounds as though you normally work in full size engineering.I’v got one with 2 1/4″ bore concentric with 1 1/4″ power stroke,and its not that much more powerful than another of 1 3/4″ bore x 3/4″ power stroke.

[wheeltapperParticipant @wheeltapper]

Hi

A quick question, would a Stirling engine like mine (see pic from my last post ) work if I made the top and bottom plates from 5mm perspex?

 

I,ve got some smoked perspex doors from an old cabinet that are that thick.

 

then I could put a sealing groove in them.

 

cheers

the curious side of Roy

[Murray TrickerParticipant @murraytricker65189]

Hi to all. Reading with interest your comments re HAE’s. I have built Stirling one and it runs OK. Now building Jan Ridders coffe cup HAE. Can’t source carbon rod at less than $30  (12″) from a New Plymouth firm. A lot to pay for one piston. Have used 6mm al plate for top and base and have cut old innertube up to make seals. Progress is slow as i only get about 1/2 day per week in my shop. Havent made displacer yet but was thinking of using an old CD or two in a sandwich with some sort of seal between them to create a low thermal conductivity barrier. Any comments? Murray T.

[Mark Smith 3Participant @marksmith3]

Another kiwi welcome, Murray. When you say “stirling one” do you mean the Roy darlington engine, or the warblington laminer flow engine?

I think, to answer gordons question the top and bottom plates are best made of high heat conducting material such as aluminium.

[Gordon WParticipant @gordonw]

Thanks for replies, will plan for a leather piston seal, and hollow displacer rod. Was thinking more of fatigue stress in disp. with constant change of pressure. My planned engine has disp. chamber 100mm bore x 100mmstroke, chamber length 300mm, in S/St. Disp. will be 95mm dia. ? x 200mm long. Power piston aprox. 60mm dia. to suit 2CV barrel i’ve just dug up, with stroke to suit! Both axes parallel. Next find big flywheel, and redraw plans. My small LTD motor has leak in displacer gland bearing ,I made this by fitting a plug at each end of bush, bored 1.5mm with brass rod, 1/16 dia polished down to fit.,but it leaks!! Yes was in engineering, mostly as Draffy, now retired

[Ian S CParticipant @iansc]

Roy,no use aluminium or copper if its going free,I used two old fry pans found in a rubbish skip.Murray CDs are too heavy,find some foam,get some nichrome wire from an old heater element,a power supply,battery charger would do.you can use a vertical wire to cut circles,make your center hole first and use a pin through this to cut the dia.Mount the wire horizontal above a board at the right hight to slice to thickness.You need to tension the wire with a spring because when it heats it goes slack.Gordon,I think the hollow shaft for the displacer might be the best bet,the inside of the displacer is at atmospheric pressure,if you seal the displacer the pressure goes up when it heats,so thats one stress got rid of.My flywheels are made of steel plate,or off cuts from steel bar-or stainless-or cast iron,what evers at hand,or old sewing machine handwheel does very well.Some people seem to think you have to have a cast wheel,but scrap metal is much cheaper(free),and doesn’t take very long even with just a drill and files to make one with spokes,do it well and it looks like its cast.Welcome one and all IAN S.C.

[wheeltapperParticipant @wheeltapper]

Thanks for the info Ian, I’ll have to have a wander round a boot sale or two.

I made the displacer piston from thin balsa sheet eventually, seems happier with that.

 

cheers

Roy

[Ian S CParticipant @iansc]

Thats it Roy balsa is good,might have used it myself,but I’v got 40km to go to town and I don’t drive,also I’d have to pay for it,the foams free!I know I’m mean,but why buy if you can do with what you’v got.You might use the CDs for a flywheel,I did that on a tin can one.Think I used 6 of them.IAN S.C.Good nite.

[Ian S CParticipant @iansc]

Mark,just a question about best practice for cup seals,which is best side out?I’v been putting the inside ie furry side out,on the latest made today I rubbed in some graphite powder(its for the LTD),my idea is that this side will bed to the cylinder better.Thereis an artical in ME some where,but I haven’t found it.

[Mark Smith 3Participant @marksmith3]

Hi, Ian good question but intuition makes me think that grain side or the smooth goes to the outside of the cup that’s how bike pumps are as for as I remember. But you could be right, the flesh side could bed in better. Trial and error that’s what its all about.

[Murray TrickerParticipant @murraytricker65189]

Thanks guys for your help. My Sterling One I think is the one designrd by a ChCh Kiwi cant remember his name but he wrote a great book on “how to make’. Random thought. Has anyone tried graphite impreganated nylon or teflon bushes as piston liners or maybe bore liners? They seem to come in small sizes and close tolerance (.001”) operate at high temps too. Cant have too much massI would think.

[Ian S CParticipant @iansc]

Mark, i’ll go and try one grain side out.Murray,yes i’v tried carbon impregnated teflon,bought a stick of it nearly 20yrs ago,still got a bit about 2″ long by 1″dia,but I keep all the swafe,and use tha in a little mould to make bushes.It is effected quite a bit by heat,and it seems to swell if it gets too much oil on it.On one engine I had to ream out a bush after I had stripped the engine for an over haul,it had worn out the crankshaft,the bush was through the piston to the displacer.I’v never used commetially made plastic bushes on models,but have used oil impregnated nylon on agricultural machinery,with 35mm bore,seems to work ok.

[CirclipParticipant @circlip]

At the risk of being called a HSE nanny Ian, be awfully careful when playing with Teflon (PTFE by any other name) cos if you “Cook” it, it can become a rather good slime capable of eating yer bits away. Int’ trade it’s called Hydroflouric Acid and you don’t need that in ANY sort of quantities.

 

  Regards, Morrisons agent.

[Ian S CParticipant @iansc]

Murray,Ted Warbrook was the Kiwi who wrote the book etc on the stirling one engine,there was an artical in ME about Roy Darlington and his “Whatsit” engine,I’v also built one,it goes ok with a cast iron piston in a steel cylinder.Don’t worry Circlip I know the dangers with Teflon and high temps,ment to mention that when I read Murray’s piece suggesting Teflon bearings would be ok at high temps,its ok to use it at the cold end,as long as you can monitor the temp,ie if your motor over heats,use bronze or cast iron.

[Mark Smith 3Participant @marksmith3]

Hi Ian, Sorry I missed you today but you got to see my messy workshop. Sometimes the tools find their way back to the right place and after a good tidy up it looks a lot better. Funny how you know my wife from bowls umpires, small world isn’t it. If I don’t see you before I will be in Darfield on the 1st Nov.

I was talking to Allan from Avon engineering supplies today, ( he supplies a lot of our equipment at work) I asked him about teflon string that was being discussed in another thread. He said it is available here but couldn’t say where, just that he had seen it recently.

I also got an email from Kevin who lives in pegasus village asking me about supplies of materials. He is from the UK and said he is very restricted for supplies here. I told him about the Little Metals Co.

I suppose you saw my new engine in its rough form at the moment. I want to use the same self pressurising pump that Phillips used in the 1930s engine which will be driven off the opposite side of the piston to the crank; a bit hard to describe here but when I see you I will explain how I think it will work  As you see I have used a crank, bearings and conrod from a line trimmer which should handle more power than the links and pins I have used so far; the engineering has already been done. I am going to use two gas seals inside the bearing set to minimise losses. The only thing I am concerned about is the extra friction from the seals might make starting more difficult. The stroke is 33mm and bore is 37mm.

mark

PS When I said Warblington in an earlier post I meant Warbrook. Combination (ala James Joyce} of  Warbrook and Darlington.

Edited By Mark Smith 3 on 29/09/2009 09:23:09

[Ian S CParticipant @iansc]

Hi Mark,I was in town to pick up some castings from a foundry,promised last thurs,they say they will be ready this thurs-we’ll see’I’ll prob be in town friday.Yes I got a supprise when your wife opened the door,I thought-I know you,this must be the wrong place,but no when I asked about you she said you were working.Had quick look in the workshop,saw the vertical engine,and I think some bits of the new one.And I met the dog.You think your workshops a mess,you ain’t seen nothing yet!I’v been working on my largest motor,put a new burner in,it came out of a Primus stove.I need to make a new hot end for it,the old one is mild steel,its got a bulge in the end so I better get a new one in stainless,Does Little Metals have stainless tube,About 60mm bore?The motor is going ok,started it the other day,hadn’t been run for about 2 yrs,light it up,and of it went.

[CirclipParticipant @circlip]

Question to our Anti-podium bretheren, what happened to this site :- http://www.steamengine.com.au/index.php?start=5  ?????

 

 It used to have an LTD freebie of good proportions on it.

 

    Regards  Ian. (Morrison’s) 

 

 

[Mark Smith 3Participant @marksmith3]

good question I seem  remember seeing that LTD. But that’s Aussies for you no surprises there!

Not sure about stainless that big they’ve got a lot of stuff there. You could get that rolled up somewhere and tiged shut.

Edited By Mark Smith 3 on 29/09/2009 19:10:58

[Mark Smith 3Participant @marksmith3]

Another problem has shown up with my vertical engine. Running on meths it will run happily for hours but if I run  on gas the power and rpm goes up considerably but only for a few minutes then an awful clattering ensues. I think this is due to the tolerances being too close and the piston and displacer growing in length until they hit each other. When it cools the noise goes away. I think I need to shorten the displacer by a mil or two; what think ye?

Edited By Mark Smith 3 on 30/09/2009 09:16:30

[Ian S CParticipant @iansc]

Sound likely.I got problems with my biggest(also vertical)I said the hot end was distorted,took it of(just unscrews)and took the displacer out,the cold end although retained by being peined around was lose,and sliding in and out at that end,yet it had been developing good power,I’ll have to fix that.Then I filled the water tank,and all the water fell out,a cracked coupling in the plumbing system,and a crack in the water jacket.I think I’ll get 30mm of 60mm dia stainless bar,and carve a cup shape piece and braze it on the existing hot end after cutting off the bit on the end that is a repare done the same way but in mild steel.Perhaps I should have left it under the bench,it wasn’t hurting anyone.Just thinking about your displacer,I think that with the extra heat the end is bulging and hitting the end of the hot cap,as temp drops it goes back to normal,2 or 3mm off wouldn’t hurt.I had the same thing a few years back,and it knocked the end out of the hot cap,I brazed it back again and it is still going,it started off as a 3″ length of 2.5″dia 316 stainless steel and cost over $30 in the early 1990s.

[CirclipParticipant @circlip]

If you’re going to have to buy a piece of Stainless sheet to make a hot cap, the grade to go for is 321, Tripetanium stabilized to prevent intergrobular corrosion. 

 

  Regards  Ian.

[Mark Smith 3Participant @marksmith3]

I found the problem with the infernal clattering noise. I locate the displacer rod in the base with a grub screw. The screw came loose and the displacer parted company belting its way independently in the cylinder. I need now to cut a groove in the rod to make sure it stays put. It has good power on gas; it takes quite a lot of grip on the shaft to slow it and even more to bring it to a stop. It seems to have most torque about a third of its full revs.

[Ian S CParticipant @iansc]

Circlip,I’ll get a piece of bar 316 works ok for me,its not the best to machine (304 better),but I’v used 316 for other hot caps.I’ll need 60mm dia,and I’ll just see how long I can get,I’ll use the existing threaded bit 6″ from the end,I need 1 1/4″ min length.I’v fixed the displacer,and the water leaks,and reassembled the motor,and run it,don’t think its got the power it had before the repare!I re-epoxyed the cold end of the displacer after cleaning the oil from inside (not sure how it got there).Peined the end over the disc that holds the rod,then put dents in behind the disc.I might have to take the rod the full length and screw it at the hot end,or make that front disk brass or steel and solder it.The screw in your motor was in the hot end?so it would not be able to be locktited,but it maybe a good idea to lock it some how.

[CirclipParticipant @circlip]

Just as a rough guide Ian SC, 303L and 304L for general SS usage, 316L for Hygenics and 321 for heat apps. unless you want to go into the exotics like Inconels etc.

 

  Used 321 grades exclusively for the zorst systems on the BR Diesel locos, Seemed to work quite well, sorry, Full size systems.

 

  If you can get the “L” designations of those three, they are easier to machine (L for low carbon content), saves any fear of rusting, and oh yes they do. Ask the guys who built the Thames barrier.

 

  Boring a Bar of material seems hard work, Know anyone with TIG welding facilities??

 

  Regards  Ian.

[Ian S CParticipant @iansc]

Hi Ian,its mostly a case of what I can pick up,tried the outfit mentioned by Mark,but they only handle brass,bronze, copperand aluminium,but I got some addresses,but I think I’ll check out the muffler repare shops,should be able to get welding done there also.316 is also used for marine work ie prop shafts.Yes boring thin shelled cups say 3″ deep is a little tedious,and as you near the end of things a little nerve wracking,the first one was not that long after I got my lathe.The hot cap has an internal 32 tpi thread to attach it to the cold end just next to the water jacket,a good fitting fine thread seems to be enough to seal the joint,not needing O ring or gasket.’Frade don’t always use the ideal materials,best is sometimes whats in the junk box.

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