Designing a new engine for a big(ger) boat...

[barts]

I believe that I used some of that PEEK or something close to it on what is called a 'ruling machine' for making diffraction gratings. Sort of a flat version of a prism to sort out light into its various wavelengths. The PEEK, of whatever it was had at least PTFE and graphite in it. It's virtue in that application was that the static friction was extremely low. No vibration from stickiness at the start of motion.

Please tell us what PEEK stands for so that I can look into it.

Mike

https://en.wikipedia.org/wiki/PEEK

"A disadvantage is the high price, which limits its application to high value items."

1" rod x 12" == $133.97 at MSC

- Bart

[Jack Innes]

Mike,
There is quite a bit of information on PEEK here;

http://www.victrex.com/en/products/vict ... lymers.php?

Jack

[Lopez Mike]

Jack,
Got a blank page with that URL.

PEEK isn't what I was using. The material I used was relatively soft. Mostly really slippery.

I'll bet that Delrin would do for the external stuff on an engine like those rollers and various rod ends.

Mike

[Albert]

Fred, this engine takes care of propulsion of SL "Antonia" which is owned by a gentleman living in this area. The engine is his own design and was built in his precision-engineering workshop. Also the very unusual boiler (steam generator) was designed and built there.

I rather stick to more modest, lower-tech solutions. Min Deern is an Elliot Bay hull driven by a twin Pearl engine and a VFT boiler. Operation is most easy and pleasant.

Albert

[Jack Innes]

Jack,
Got a blank page with that URL.

PEEK isn't what I was using. The material I used was relatively soft. Mostly really slippery.

I'll bet that Delrin would do for the external stuff on an engine like those rollers and various rod ends.

Mike

Mike,

Another try at the link. PEEK is derived from its actual name - polyaryletherketones

http://www.victrex.com/en/products/vict ... MgodXiQAUw

If that fails again Google Victrex PEEK polymers

I would agree that Derlin would perform well & is likely easier to find.

Jack

Jack

[DetroiTug]

The material I used was relatively soft. Mostly really slippery.

That sounds like UHMW. Widely used in automation.

"I'll bet that Delrin would do for the external stuff on an engine like those rollers and various rod ends."

I wouldn't bet a whole lot on that. I've used Delrin extensively over the years, it's ok for small bearings in mechanisms where side loadings are low etc. Delrin cuts extremely easy, machinists love it. Its relegated to very clean non abrasive applications. It's also brittle and will not tolerate any sort of impact or overloading in lightly designed cross sections. And it's pricey, with no real benefit - Use bronze.

-Ron

[Albert]

Small correction regarding the engine on SL "Antonia": Not the pistons but the cylinder liners are made of PEEK. On the other side, the pistons have no piston rings. Sealing is a question of proper material selection and tight tolerances. No lubrication needed.

No poppet valves but transversally located piston valves, the liners of which are also made of PEEK. There are two different channels for steam inlet and discharge, top and bottom of each cylinder.

Albert

[marinesteam]

PEEK is one of the few thermoplastics that is suited to high temperature service. It will take temperatures that turn Delrin into a pile of goo. It's available in modified form with the addition of fillers & performance modifiers like kevlar, graphite and PTFE (Teflon). It's not inexpensive but sometimes it's the best material for a job and it's viable alternative to metals on some applications. Most materials require that heat be removed from a mold when injection molding, PEEK usually requires that the molds be heated!

Ken

[DetroiTug]

Discussing Uniflows. Here is my buddy Gary's Uniflow powered steam car. 3 x 4 twin double acting. Stainless steel cylinder liners, aluminum pistons and bronze piston rings. No steam oiling. Briggs and stratton poppet valves. Single rotating chain driven cam shaft that slides linearly to opposite lobes for reverse.

He's ran it quite a bit and it appears to be holding up quite well. He also has an alternate base casting that will convert the engine for marine use. He will be selling kits of this engine sometime in the future.




-Ron

[barts]

After deciding we're going to use the Kitchen rudder, I switched back to a large single cylinder uniflow. I did some simulations of this engine to see what the torque might look like as the engine rotates. Here's an engine based on a Detroit Diseasel 149 cylinder, 5.75" x 5.75" bore & stroke, 15" con-rod, 215 psia steam, exhausting into a 26" Hg vacuum, with 1% clearance. Cut-off is at 5, 10 and 15% travel; @400 rpm 8.5, 15 and 21 ihp respectively. Steam consumption is 13-14 lbs/ihp for all three cut-offs. Thermal losses are not modeled; adiabatic expansion and compression are assumed.

One can clearly see the reverse torque spikes due to cylinder compression. In this design, I've added a relief valve into the cylinder head that relieves any pressure over the inlet pressure back into the steam chest; alternatively I could increase the clearance a couple of percent. Note that a good vacuum is absolutely needed on one of these engines; even w/ the relief valves I'm inclined to make the extra clearance chambers use vacuum operated valves to close; if the vacuum fails the engine suddenly gets a lot more clearance. The better the vacuum, the smoother these engines run.

There's a noticeable asymmetry due to both the finite con rod length and, more important, the 1" diameter piston rod reducing the area on the bottom of the piston. Next step is to add a torsional vibration estimate, since this has a long prop shaft and a heavy 28" prop that acts as a very effective flywheel.

Program written in python using the Freesteam steam table approximations, plotted w/ gnuplot and converted to jpg w/ gimp.

- Bart