Stirling Engine : Laura

I think you are clutching at straws here, the external and internal diameters are not going to vary by that much and it is not going to make any real difference to the running of the engine. These engines are not meant to run continuously, they only demonstrate the principle and are meant to look good on a shelf.

When demonstrating the person watching does not matter that it will run for 5 minutes or 20.

Get over it and move on, time is far too precious 

While I am waiting for my new kit to arrive from Bengs, I have decided to use all the left over bits and pieces from this build to make another Stirling engine but this second engine will use a stainless steel D. Cylinder rather than the supplied glass tube. I am still in the process of working out how to fit the stainless steel tube and what thickness is best but I have a few ideas and I am sure that something can be worked out.

But for now I have come across and unexpected problem with a new part that I ordered weeks ago as a spare : the base plate (part #1) is bowed ie.slightly bent across the width. I did try clamping it in the vice but this did no good as it just sprang back into the original shape. What if I were to first heat the brass plate with a blow torch before putting it in the vice : would this help and how hot should it be ?

Any other suggestions (other than to take up knitting) are welcome.

To take out a bend you'll probably need to actually reverse the existing bend slightly not just clamp it flat. Clamping flat might take some of it out but not all. Metal is elastic (springy) in that it will return to it's original shape provided that it hasn't been taken beyond its elastic limit into the plastic region. To put a permanent set (or take one out) you'll have to go beyond that limit so that the metal actually permanently deforms.

I'd probably not heat it as it could start to warp and bend even more. You really need to bend it beyond flat so that it will then spring back to flat. One thing to watch is that now the plate is full of holes it will want to bend where there is least metal.

What did you go for in the end, the beam of the flame licker?

Not sure how it will work out but brass is annealed by getting it red hot and chucking into plenty of cold water. Your local ambient shouldn't make much difference to that but it needs to cool rapidly so plenty of water compared with the part and move it about in it if you can.

Your tube may be blowing off due to the air in the engine expanding when it's heated up. The displacer pushing it off somehow may be another but doubt if it's that. Vibration and or pressure changes might make it work it's way out - much more likely I would have thought. Maybe you can add some sort of end stop that doesn't get in the way of the flame to see if that is causing it.

John

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You don't have to quench brass or copper unless you want to get on with the job a bit quicker.

Ian S C

I remember now what happened the last time I heated a sheet of brass and it was not a good result ; it warped in many different places. So today I put the bent plate in a vice and gave it a few good taps with the hammer ; pushing it by hand was not helping. That seems to have done the job. Because I am not soldering the cylinder holders to the base plate as per the instructions but bolting the parts together using a 1/4'' square brass bar then this also helps to keep everything flat and even.

In engineering terms, what do you call that 1/4'' brass bar with all the M2 bolts passing through it which connects the cylinder holders to the base plate ?

Edited By Brian John on 04/04/2016 13:01:18

Edited By Brian John on 04/04/2016 13:02:50

"Cleat" would probably be the best term to use. On larger steel structures it would be in the form of a piece of angle iron rather than the square that you have used

Hi Brian

I have followed your thread form time to time and I enjoy it very much.

Here is some pic of the hot cap of my Stirling engine.

It is made of stainless steal and was fabricated out of three separated pieces that were Tig-welded together (my father did the welding).

The wall thickness of the tube is 1.5 mm (you can probably decrease it to 1 mm)

The hot cap is then bolted directly to the Displacer cylinder without any gasket but the Stirling engine still works well, it runs for about 18 minutes.

Here is link to a video of the engine runing **LINK**

Anders

Thank you for the photos and link Anders. What you have built for your hot cap is what I have in mind to build for my engine although mine will be longer (same length as the glass tube). It was suggested to me that I use the stainless steel tubing that comes with the solar powered garden lights but I think this is far too thin. I have a piece of stainless steel tubing from Tonkin Steel but it has a 1.6mm thick wall ; I am thinking of reducing the thickness at the end down to about 1mm by putting it in the lathe. I only have to do this for the last 3cm where it makes contact with the flame. I should be able to do this in my lathe if I take it slow and just shave off a bit at a time.

Once that is done, the stainless steel tube will be fitted to a brass collar, similar to yours, using JB WELD. Then a brass cap will be fitted into the flame end, also using JB WELD. Because I am only using a metho burner, the JB WELD should be able to withstand the heat generated.

Anyway, that's the plan but we all know what happens to plans !

Edited By Brian John on 05/04/2016 02:11:00

Brian do a test first by joining some scrap together with the JBWeld and then hold it in the flame I think the temps will be too high for it.

With the right flux you should be able to silver solder it which you are good at.

Edited By JasonB on 05/04/2016 07:42:12

The metho burners I build for my steam engines out of plumbers brass end caps have the pipe work and the burner end joined with JB WELD. You can see the dark grey fillet at the joins. I would think if they can take the temperature of the fire box then it should be okay for the Stirling engine...maybe !

Is there some other way to do it ? I have heard that stainless steel can be silver soldered to brass using an aggressive flux. Any comments on that ?

Edited By Brian John on 05/04/2016 08:06:01

JB Weld is rated by its' manufacturers at 500 degrees F max working temperature. Check their website if you don't believe me.

Since firebox/burner temps may exceed that by a large margin I'd say building burners with it is risky. If a burner comes apart while lit the fuel could spill over a wide area possibly setting fire to anything in its' path.

I'd use silver solder rather than JB Weld. Just my $0.02 worth. JD

Wise words, Jeff

Here, for convenient reference, is the UK page for the 'High Temperature' product.

MichaelG.

Brian as I said in my post above it can be soldered with the right flux. You want Tenacity No5 or HT5 if buying from CuP Alloys.

Your pipe joints are also threaded if I remember rightly so teh JBWeld is not stressed, just a sealant.

JB WELD is rated for 287 degrees C. The link above is not the  product I used. When I first constructed my boilers I put some soft solder whose melting temperature is 180 degrees C on a piece of copper inside the firebox. It did not melt at all so I assumed that the temperature inside the firebox was less than the melting point of the solder hence less than the fail point of the JB WELD. Was my reasoning unsound ?

http://www.jbweld.com/collections/epoxy-adhesives/products/j-b-weld-twin-tube

I will admit that it may not hold up against a direct flame so, like Jason said, it might be worth testing first before using it to construct a hot cap for the Stirling engine.

The flux for soldering stainless steel will have to be purchased here in Cairns. It is unlikely that it can be posted in the mail. I may have to make a few phone calls tomorrow ; I do not fancy my chances.

Edited By Brian John on 05/04/2016 18:00:56

If you use JB Weld for the methylated spirit burner application what is your plan B if it does fail?

Are you OK with the risk of skin burns or a house fire?

Hope nothing bad happens. I wouldn't risk it, silver solder would be far safer and almost as easy, but that's just my opinion.

JB Weld is fine for a lot of repairs and building non critical things. As a fuel containment/ sealant or at high temp or pressure I wouldn't trust it at all. Last posting from me on this. JD

.

Noted

MichaelG.

Yes you have to be a bit careful when talking about JBWeld, its a bit like Araldite people use the name but they make a lot of products. When refering to Model use the usual one is as per Brian's link and is in fact the only one called "J-B Weld" on the packet rather than Marineweld, woodweld, kwikweld, etc

Edited By JasonB on 05/04/2016 19:43:29

.

... and I naively assumed that Brian would have selected the 'High Temperature' product.

MichaelG.