Author Topic: Piston Material .........  (Read 1287 times)

toolznthings

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Piston Material .........
« on: August 18, 2018, 01:53:50 PM »
Seeing where Mikehinz was searching for suitable materials for pistons on his build I though I would mention a plastic I'm trying.
With aluminum cylinders I wanted a cost effective material that would be slippery and have good strength and not absorb moisture. Stays stable in size so far in my test.
McMaster-Carr has Noryl PPO rods that fit the bill, so will see how it goes. Machines nice, both in the lathe and mill, holds tapped threads well,too.

Thought I would mention it. Read the specs from their catalog. 

Offline Ye-Ole Steam Dude

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Re: Piston Material .........
« Reply #1 on: August 18, 2018, 06:26:44 PM »
Hi Brian,

Please keep us informed on your findings using this material. Very interesting to me.

Have a great day,
Thomas
Thomas

Offline Reggleston

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Re: Piston Material .........
« Reply #2 on: August 18, 2018, 08:47:56 PM »
Just finished a vertical engine using a fitted Delrin piston in a honed cast iron cylinder bore. Has a surprising amount of torque for a piston that is completely ring less. Current operating on compressed air. Takes appreciable hand application on the flywheel to stop piston movement. Piston is showing signs of abrasion wear in spite of my best cylinder honing effort, so not sure how long it will last, addition of lubricator should help this issue. Will most likely try an O ring on the piston as a next step. Delrin is also easily machined and relatively inexpensive. Will take a look at the material you are using.
Bob E

toolznthings

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Re: Piston Material .........
« Reply #3 on: August 18, 2018, 09:08:45 PM »
Here's a couple of pictures of the piston from the Norly bar stock with o-ring groove that is cut deeper than spec for a looser to cut down on the friction.
There's a PTFE filled delrin, but have not used that one before. Other types of lubrication filled stock, but most others tend to absorb moisture like nylon.
Some get pretty expensive,too.
If I ever get this thing to run I'll have a better idea. So far no scratches in the aluminum bores. Aluminum not the ideal cylinder material,but..........

Thanks for the replies !

Offline Ye-Ole Steam Dude

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Re: Piston Material .........
« Reply #4 on: August 18, 2018, 09:30:34 PM »
Hey again Brian,

The outside of your piston, is that the natural finish or did you turn that down from an oversize piece of stock? If you did turn it down, what tool and what speed. Sure looks good.

Thanks for this info and have a great day,
Thomas
Thomas

Offline derekwarner

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Re: Piston Material .........
« Reply #5 on: August 18, 2018, 11:22:27 PM »
Guys......manufacturers publish data on their 'plastic' materials such as below. One area they do not differentiate is static to dynamic applications 

DelrinŽ acetal (Polyoxymethylene POM) combines low friction and high wear resistance with the stiffness and strength needed in parts designed to replace metal. It provides a wide operating temperature range (-40°C to 120°C), good colorability and good mating with metal and other polymers, as well as dimensional stability in high precision molding.


A few points for consideration ....abrasion resistance in dynamic applications at elevated temperatures and the physical strength in these [piston] applications at moderate steam pressures

From the steam tables  :happyreader: we see 120 degrees C approximates to just under 1 Bar or 14 PSI.........so forget using any such material for steam applications bordering on these limits

Derek

« Last Edit: August 18, 2018, 11:58:55 PM by derekwarner_decoy »
Derek L Warner - Honorary Secretary [Retired]
Illawarra Live Steamers Co-op - Australia
www.ils.org.au

Offline mikehinz

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Re: Piston Material .........
« Reply #6 on: August 19, 2018, 01:18:37 AM »
All, the info above is very helpful.  Since I'm not intending to run the engine I'm currently building on steam, I'm thinking about trying several materials, with an emphasis on low'ish cost and ease of machining.  So I already have some 12L14 on hand that's big enough to make a 1.25" OD piston, then I think I'll order some cast iron bar (cheapist from Mcmaster or Hobby Metal Kits0,  and some Delrin and some of the Noryl material.   I may also try machining and oring groove on the various materials and getting a few Viton or Silicon orings to try. 

Since my engine has an aluminum cylinder, it's sort of backwards from conventional practice so I think a light weight, low friction material might be best.  I did things this way since I'm trying to learn machining technique(s) and a big chuck of 6061 for the cylinder is way cheaper than a big chunk of cast iron.  Later on in my journey I'll most likely want to try running engines on steam and for sure I want to launch into attempting some IC engines in due course.  In either of those cases, material selection will be extremely important.

Thanks for all the excellent info!

Mike.
MIke
Wichita, KS, USA

toolznthings

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Re: Piston Material .........
« Reply #7 on: August 19, 2018, 01:31:15 AM »
Hey again Brian,

The outside of your piston, is that the natural finish or did you turn that down from an oversize piece of stock? If you did turn it down, what tool and what speed. Sure looks good.

Thanks for this info and have a great day,
Thomas

Hi,
I turned the final 1" diameter from oversized bar. I happen to use standard TPG321/322 inserts for most everything.
I'm sure HSS tool bit would work just as good. Probably ran around 600 RPM and a couple thou feed rate.

Offline galland

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Re: Piston Material .........
« Reply #8 on: August 19, 2018, 03:40:14 PM »
I have used some of the high performance plastics in my air powered engines for many years now. None of mine are ran on steam but I never intended that. I like the idea of never having to oil the pistons since these plastics are self lubricating. One thing I pay attention to is the expansion rate in the specs because they do vary quite a bit. I have built some engines in a cool shop and then down the road had them seize when demonstrating them on a warm day because the plastics expand more the than the metal cylinders. I have never used Noryl but after you mentioned it I checked the specs and they are very good for expansion. If they wear decent then they would be a good choice. Here are just 3 of my engines with plastic pistons.     Gary

   

toolznthings

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Re: Piston Material .........
« Reply #9 on: August 19, 2018, 05:10:51 PM »
Really nice looking engines ! Thanks for sharing.  :ThumbsUp:

Offline Ye-Ole Steam Dude

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Re: Piston Material .........
« Reply #10 on: August 19, 2018, 05:59:18 PM »

Hi,
I turned the final 1" diameter from oversized bar. I happen to use standard TPG321/322 inserts for most everything.
I'm sure HSS tool bit would work just as good. Probably ran around 600 RPM and a couple thou feed rate.
[/quote]

Thanks Brian for the info.

Have a great day,
Thomas
Thomas

Offline mikehinz

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Re: Piston Material .........
« Reply #11 on: August 19, 2018, 06:15:16 PM »
Galland, those are beautiful engines!  Your work is superb!

May I ask exactly which 'high-performance plastic' you used for your pistons?  I'm experimenting now and any input is helpful. 

Thanks in advance.

Mike. 
MIke
Wichita, KS, USA

Offline galland

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Re: Piston Material .........
« Reply #12 on: August 20, 2018, 12:36:01 AM »
Hi Mike,  I have tried various plastics over the years. Way back I used Torlon 4301 and it worked great but then the price went through the roof. I still buy 1/4 inch dia. because it isn't outrageous but on up to 1 inch its very costly. I have had good luck with Delrin 100 for 1/4 inch bores but for larger bores I have been using Ertalyte PET-P with good results. The 2 cylinder horizontal I showed has a .812 bore. I will look at trying some Noryl now that is has been mentioned.

     Gary

 

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