Prototype three rotor steam impulse turbine

[SandyC]

Hi John,

As always, a superb piece of engineering and I have no doubt it will deliver a fair power output when finalised.

You mentioned your tacho only going to 29K.... is it an optical unit?...i.e. one that uses the prop blades as impulse source. (assuming a 2 blade prop would mean 58K impulses).
If so, then by using a disc (attached to the engine shaft) with only 1 reflector on it you could double the max count, if you see what I mean.

You also mentioned possibly making a new rotor from ALI, to see if it will accelerate faster.... probably true...however, ALI and STEAM are NOT good bed mates.... not quite so bad on air, although even this can be pretty abrasive.

Just thoughts.

Keep up the great build, and hope the BONES don't give you to many more problems....you could sure do with a respite from all that.

Best regards.
SandyC  ;D ;D

 

[Bogstandard]

Thanks for that Sandy,
It is always nice having a steam mentor in the background.
I have a wonderful piece of titanium that could be used, but with so much machining on it I think it would end up in my recycle bin.
The ali rotor was in fact just for an exercise in seeing how much faster the acceleration could be made. If and when the matched pair are made, they will be done in bronze, but skinned down a lot more than the rotor in this one. In fact they might be made hollow with supports inside the ends. I have a massive glut of bronze bar at the moment.

I hadn't thought of using a reflecting strip on a disc. It would definitely be safer than using what I usually do (don't ask). I will try it.

Thanks again for the input.

John

 

[Bogstandard]

Away we go with another bit of this saga.
What I am going to be doing here is planning for the next bit to be made, but before it could be fitted, the casing has to be brought up to a nearly finished state.

What you see here are the makings of the exhaust system, but normally I would make a proper bent up job of it, silver soldered, the works. But this is just going to be a way of getting the gases away, hopefully with no back pressure. Just a big lump of rough cut ali and a couple of bits of 1/2" ali tube. This will not be made yet, if you remember, earlier in this post, I said that most of the mountings will be done by using the solid end plates as the fixing area. So that takes us onto the next pic.

What I have done here, is mark up the block and end plates so they go back into the same position. For this I used a drill point instead of the usual pop mark. A pop mark usually throws up a small crater edge which requires flatting down, by using a drill point a quick wipe over with a scotchbrite will knock off anything that is sticking up.
The next job was to blue up the end caps as shown, and reassemble without the rotor. The top and two sides of the block positions were scribed onto the blued end caps, then taken apart again. That is what is shown here.

The end caps, before being hacked down needed a bit of blingy turning doing. Much easier to do while they are still round. So they were mounted into the same bored soft jaws that were used to put all the precision stuff on them, and the bit of facing was carried out. This not only removed all the old scribe marks but made a nice boss feature on the face. Both ends were done to the same settings.

In this one, I have been to my bandsaw and cut off the excess material on the outside of the lines. Then reassembled the caps on. Notice that I haven't removed the bit off the bottom face.

Because the only flat and square areas now on the assembly are surrounded by rough cut end caps, I just can't tap it down onto parallels. I came up with a small v-block that the casing will sit on, and be tapped down on to. On the jaws of the vice I used a bit of double sided tape to stick two small HSS lathe bits that will sit between the end caps and so keep the block square.

This is how it all sits in position, a bit precarious, but if only small cuts are taken on the top face, quite acceptable.

A flycutter was used to bring the end caps to size, then the final cut just took a minute amount off the rotor casing. The first side done.

V-block got rid of, two bits of lathe tooling taken off the jaws, one piece was put down where the v-block was. The face that had just been machined (and deburred) was put against the fixed jaw, a bit of bar was put between the moveable jaw and the job. Tightened up, tapped down onto the bit bit of lathe tooling and the side face was machined the same as the top face was done. It was flipped over and the second side was machined. This now gives me three sides (top and both sides) to work with.

Now onto a solid milling base. Job tapped down onto a para. The bottom bit of the end cap was flycut down to give a nice flat base.

A radius edged cutter was fitted and the remaining curved bit of the end cap was machined away.

The job was flipped around and the same settings were used to get a nicely formed, solid base, for mounting the engine onto a baseplate.

Now just waiting for the exhaust to be made.

To follow will be the making of the exhaust system, I hope.


John

 

[rake60]

Great stuff here John.

I'm looking forward to every "next post"!

Rick

 

[Bogstandard]

Rick, glad you are enjoying it, I know I am.

What I am mainly showing here, are my way around problems, using just the basics what you have around the workshop. These ways can be used not just on this build, but anywhere a bit of machining of this sort has to be carried out.

Smooth, close fitting and matching parts can make a basic engine into a real looker.


John

 

[CrazySteamer]

Hi John.

Ive been following your progress, and it all looks good. Ive got a three inch scale model road locomotive, and the some orignals have a steam terbine on the side to make electrisity for the headlights.

Ive started making a single rotor terbine of simmilar design to yours, but with 50mm diameter rotor, (This makes it more or less in scale) made from steel with 20 pockets. This gives a similar sized pocket to yours. It will be running on 5mm protected roller bearings (I had a couple lieing around). The covers will also be fixed on in a slightly diffrent manner - just to increace orthentisity.

Ive got a couple of queries for you.
You were saying that when you were running it up, you reached the power band of the rotor, I was wondering what sort of rmp this was at. I have a motor that Im going to use that should make 12 volts, at about 24000 rpm - was hoping this would be within the turbines power band, or do I have to put a gear reduction in - or find a diffrent motor? Obviousely because my rotor is bigger than yours the power band will be slightly less.

Another thing I was wondering about was how much power the turbine would create. You were talking of making some bigger ones and putting them in a boat. This must take quite a bit of power.

I was hoping for about 20 watts from my terbine - this means I can have a couple of 5 watt headlights, a couple of 3 watt lait lights, and still have a bit left to put in the canopy so I can see what im doing. I will be running on steam at 200 psi - which is considerbly higher, than what you were running at - but I was going to throttle it back a lot at the nozel, and hopefully increace the effishancy a bit. Also wondering how much steam you think the turbine will take?

Do you think there will be any isseues with cavitation? I could always throttle it back at a controle valve, and have a bigger nozel on the terbine, this would in affect put a degree of superheat on the steam, at the pressuer drop.

The terbine seems quite noisey, I was hoping for a quite humm from it - any idears for a silencer.

Finaly, Im wondering about the life of the terbine, at that speed it cant be long, after 5 - 6 hours it will have gone round a million times, I was hopeing for the life to run into the hunderads of hours?

Any advice would be greatly aprceated.

Simon

 

[Bogstandard]

Hi Simon,

Welcome to HMEM.

You have asked such a lot, I just don't know where to start.

The first thing, I won't know anything definite about this turbine until it is fully finished.

The second thing, is I am not a turbine designer, but someone who takes an idea to fruition, by using a few known parameters. It might not be super efficient, but it will definitely work. So a lot of your questions I just cannot answer.

I can tell you, you will not be able to silence it to a hum in the space you have available. It is just the way fast turbines have to run. If you throttle the exhaust to quieten it, you will stop the turbine running efficently. Bearing whine is also a hard thing to cover up.

I will be using a gearbox to drop the speed right down to turn model boat propellors.

I honestly think you have gone the wrong way with yours.

On model locos, because like you, they have very high pressure steam. They use very deep pockets but a lot less of them, only five or six, plus a diameter of about an inch, and use pure steam power to turn them at a much lower speed, driving the generator direct or even stepping up the speed by use of a gearbox, to run a faster generator. This would keep the noise down to acceptable levels. Maybe that is the direction you should be looking at. I am sure if you do a search for turbines on a model loco site you will get a lot more useful information on higher pressure turbines for models than I could ever hope to supply you with.

I am running mine at a very low 40PSI, so the speed has to be a lot higher to get it to its power band.

I made my first one last year, and used it to drive a high speed, precision dc motor as a generator. It gave out 17 volts, but I didn't measure amperage. It has a rotor of 60mm diameter, and is running on about 40psi. This vid shows it all.

[ame]http://www.youtube.com/watch?v=KW6V7JWbQwk[/ame]

I am sorry I couldn't help you any more.

John

 

[Bogstandard]

Hacking metal again for this post. I am going to be making the exhaust. It might not seem to be an important item, but if I get it wrong and 'strangle' the gases, I will get back pressure to the engine, and give what little efficiency it might have, a hefty backwards jolt. If that does happen I will just have to redesign.

---------------------------------------------------------------------------------------------

These are the bits I will make the exhaust out of. A lump of rough cut ali and a couple of bits of ali pipe. You might ask, why a longer bit of ali pipe, well I have already spotted a minor problem a few operations away, so that will give me a quick fix. It pays to plan ahead.
I have done a quickie sketch on the block to show what it will eventually look like.
I won't be showing how I get the block all square and parallel because I showed how that was done in an earlier post. So the next pic shows the block all square and ready for the next op.

The block is all square, and I have drawn on it the basic layout of what will be required for the next op. I find that doing this helps to prevent silly mistakes when mounted onto the machine.
If you notice at the back, is my notebook. You can't see the writing on there very well, but it is a total machining order for all the drilling operations. Size of drill, exact position on the block for each hole, depth of holes and the correct order to drill them in. I did all this by holding the block and planning it out by using the sketch drawn on it. So basically, I can mount it in the vice, get the central location and then just merrily drill away, using the coordinates shown in my little book. Once again, it pays to plan ahead.

All drilling finished, now to get it fixed to the engine.

I am a firm believer in keeping things simple, but accurate. To make sure the mounting bolts line up perfectly and the block will sit in the correct position on the engine. I lined up the block against the engine by resting them both on the surface plate, and used a rule to align the block with the casing end caps. Without disturbing them, I put a fillet of superglue along one edge to tack them together.
Aluminium, when cleaned, forms a new oxide layer within seconds. So when you come to remove the glue, you will find it just peels off, bringing the oxide layer with it, it just cleans straight off, and does no damage at all.
Time for a ***, cup of coffee and a quick surf on HMEM, just to allow time for the glue to dry.
When dry I spotted thru with a drill the same size as the hole. The block was given a slight tap to separate them. The spotted holes were drilled and tapped into the engine end plates.

The exhaust block shown here has been blued and the position of the exhausts from the engine were marked on it. This was done by using the height gauge and a vernier to transfer the hole positions. Then a cutting area was marked on. It was then freehand cut on the miller.

I will just explain what I was doing on this pic.
The block was tapped down onto a pair of paras. Because I want the holes to go all the way thru the block, the paras have to be removed before going all the way thru. So what I did was to cut down with the milling cutter (this one is a four flute slot drill, you cannot use an end mill for drilling down into solid material because it hasn't got a full face cut on the end) until there was only about 10 thou before cutting all the way thru.
I roughed out all the material in the hole, all down to the same depth, then cleaned up the edges to the marked lines. The final operation for the hole was to tap out the parallels without disturbing the block, then punch thru the last bit of metal and do a cleaning cut around the hole. The reason for this was that the parallels would have been machined as well if they were left in there, but the main one was that all the heavy machining was done while still supported by the paras, only very light machining was carried out after the paras were removed.
The block was remounted into the chuck with the paras, and the same operation was carried out on the second hole.

This pic shows the finished block with the detected problem showing in the bottom of the big cutout. By planning well ahead, I had detected that this square hole would penetrate into the reverse exhaust passage, but by now using a longer tube, this cutout will be sealed and everything will be as though it had never happened.
Why cut the holes all the way thru the block?
I decided that when this exhaust is fitted and sealed to the engine, I will require access to allow inspection of the rotor without a full stripdown, and to clean out the exhaust itself.
So I will be fitting a nice brass access/cover plate to the exhaust block.

Just a few mounting bolt holes to drill, baseplate to be made, oil passageways to be drilled and the mentioned plate to be made and fitted.
The engine will then be finished. The controller will then be needed, but I will be using a modified one of the type I fitted to my piston valve engine, I already know what mods will be required, so that will be a fairly quick but precision job.

Exhausted John (pun)

 

[Bogstandard]

On the last post I had reached a stage to start finishing off the engine and putting on a few final details.


The first thing you will notice on this shot is that I have fitted the exhaust pipes. If you look at the big square hole, you will see how the tube has effectively sealed the hole that had broken thru. Also a bit of brass plate had been blued up. Not shown, but what I did was mark where I wanted the mounting holes to be, squared up the plate and very accurately drilled the clearance holes. The reason for the accuracy is because I want to flip the plate over when finished to reveal the good side, and the holes will still have to line up, all nine of them.

Normally I would stick the plate to the block with a dab of superglue, but in this case I didn't want to risk damaging the good side, so I used double sided tape instead. The holes were spotted thru with a drill. To get the plate off, I just flashed over it with my blowtorch, to get it warm, and it just peeled apart with no problems, and no damage.

The spotted thru holes were drilled to depth and then using my tapping stand, all nine holes were finished off, plenty of tapping oil, because ali has a bad tendency to grab.
You can also just notice that I have put a bit of tape onto the face sitting down on the surface plate. It only takes a minute bit of swarf to get between the finished face and the plate and it will be scratched very badly. Why make work for yourself, when a little thing like putting on a bit of tape is so easy to do.

On this shot, you can see why I wanted to protect the face. It is in fact a piece of engraving plate, and it comes ready polished, with a protective plastic covering that is removed to show the nice lustre. I am lucky in that there must be an engraving firm in my area, and this is always available at my scrap dealer, for normal scrap price. I don't use a lot of it, but it just gives this side of the engine a bit of a lift in the looks department.

A big leap on this shot, a lot has been done. Very small drain holes were drilled underneath the exhaust, these are to automatically drain any steam condensate that settles in the bottom of the exhaust chambers.
Small holes were drilled from the top of the end plates, down to where the rotor spacers pass thru the end plates. I mentioned in an earlier post that I might have them running with oil in there, to form a barrier to stop the steam reaching the main bearings. These small holes were opened up on the top face with a larger drill to form a small oil cup.
The major bit was to make a baseplate for the engine.
The next few shots show the engine from different angles.

I have got the engine sitting in my claws for this shot, it gives some relativity of size.

The main part of the engine is now finished. On final assembly it will have all the screws replaced with stainless ones. I only usually use these black ones for engine assembly during build, they will be used again, for the next build.
I ran the engine up again with the new exhaust on, it ran about 50% quieter, the expansion chamber and change of direction worked really well, with no sign of back pressure or performance loss. In fact it sounded as though the speed had increased, but that might be because I could actually hear things this time.

I am now about two weeks over on this project, mainly because I am dragging my a**e at times. So this project has to be finished this week.
Tomorrow I might do a little build showing the adapter for regreasing bearings, then carry on with the control valve build. Just depends how I feel.

John

 

[Powder keg]

This is coming along nicely John! I'm really enjoying your post's)

Thanks, Wes

 

[zeusrekning]

Looks great John. I really like the way the exhaust looks.
Tim

 

[Bogstandard]

Thanks Lads,

I would call it the 'brutal' look.

John

 

[Divided He ad]

John,

I want it!!

That looks FANTASTIC! :bow:


Ralph.

I'm going to have to steal ( I mean ask your permission!) the plans etc on this one ;D

 

[wareagle]

Bog,

As usual, you are doing supurb work there. Thank you very much for taking the time to do the write ups and take the pictures as you go along. That is a huge time commitment in itself. Each new post is eargerly awaited.

It won't be long until you have it up and running, and no doubt it will be a performer!

 

[Bogstandard]

I'm going to have to steal ( I mean ask your permission!) the plans etc on this one

What you see is what you get. In the post, all major or critical dimensions are given.
Everything after that is make to fit. If I did plans for everything it would take forever.

If it helps, use it. I don't charge for anything.

The bit to come for the control valve will have dimensions all over it.

Got to go out soon, I have to buy some grease nipples for the regreaser project.

John

 

[zig 2007]

i have been following this project very closely and am amazed at the quality of this engine :bow:all hail Mr standard

 

[Bogstandard]

Zig,

Many thanks for the praise, but it isn't really needed.
There are a lot more gifted people than myself on here, it is just that I show every little step on the way to make an engine.
Just enjoy what you read and see, and hope it helps you to become a maker of model engines.

John

 

[CrazySteamer]

Hi John.

Turbines looking good.

Mine although has the same sort of rotor - has turned out quite diffrent to yours - of course because im fitting mine to a model traction engine it has to look authenric. I have a 55mm diameter rotor with 12 steps. I have been experementing with nozel angle, and design.

I have found that mounting the nozzel slightly lower than you have is benafishel, but the main thing I have found is that making the diverging section of the nozzel taper outwards is much benerfit. My nozzel starts at 4mm and then goes down to 1.2mm (Of course the drill puts about a 45 deg taper here). Then the nozzel opens out to about 2.5mm at a 12 deg taper. I made this using a silver steel d shaped taper reamer that I knocked up.

I think its well worth the extra 10 mins to make a taper reamer, as I found the pick up speed was greatly improved after Id done this.

I found that using this consideration I managed to get 3 watts running at 6 volts, and 12,000 rpm (Its blody noisey thou). This was running at about 80 psi air pressure.

I also found that air consumprion wasnt too bad.

I think id be able to get about 6 watts at a little more pressure - but I ran out of 6 volt bulbs. However I think under steam pressure the performance will be greatly improved. I think im going to fiddle with the nozzel a bit more when I get it under steam power. Im going to try reducing the throat to 1mm (Thats my smallest drill), and putting a longer opening taper on the diverging section (Mabey takingit out to 3mm at 12 deg).

When I get the turbine under steam pressure ill take a few photos, and put them on here (when Ive worked out how).

I was very interested in yr exhaust, and I think I might fit somthing simerler. (Mabey with some rock wool packing in ther somwhere to help with the noise).

Hope you dont mind me steeling yr idears
When you get it finished let us know what sort of power yr getting?

Simon

 

[Bogstandard]

Simon,
I wouldn't try putting anything in the way of the exhaust gasses, all it will do is strangle the engine.
The way to silence a turbine is to expand the gases and make them change direction. That is why I mentioned in my previous post to you, where you need space to silence a turbine. On jet turbine test beds, the silencers used are the size of large houses, with very complex baffles inside.
You could put an outer casing on the engine and fill the gap with rockwool, that would help to silence bearing whine, but not exhaust.
Yours is actually fairly slow running, I am hoping to have my one between 25 to 30K RPM on 40 psi. I don't want it any faster because it will be going to a gearbox, and I don't know how the gears will stand up to that sort of speed.

John

 

[Bogstandard]

I mentioned earlier that I would show how to make a bearing re-greaser.
It is here.

http://www.homemodelenginemachinist.com/index.php?topic=1681.0

John