oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
|
Post by oldnorton on Apr 24, 2015 8:37:48 GMT
Hi Julian
Yes I fully agree with your comment that the packing must fill the groove and apply pressure to the cylinder walls. When I said that the 3/16 Reeves PTFE packing was accurate, I meant that it worked well in a 3/16 groove. Interestingly, I see from their website that the same part number is now described as 5mm square so they agree with your description!
Does anyone know what the graphite impregnated material is made from? Clearly it is no longer asbestos, so is it a synthetic (plastic) or natural fibre?
Norm
|
|
|
Post by Doug on Apr 26, 2015 7:12:54 GMT
Hi Julian Yes I fully agree with your comment that the packing must fill the groove and apply pressure to the cylinder walls. When I said that the 3/16 Reeves PTFE packing was accurate, I meant that it worked well in a 3/16 groove. Interestingly, I see from their website that the same part number is now described as 5mm square so they agree with your description! Does anyone know what the graphite impregnated material is made from? Clearly it is no longer asbestos, so is it a synthetic (plastic) or natural fibre? Norm The stuff I have just got is glass fibre strands
|
|
|
Post by Deleted on Apr 26, 2015 8:37:18 GMT
|
|
|
Post by chris vine on Apr 27, 2015 19:56:30 GMT
Hi Michael,
That is quite a range of graphite packings they produce. I guess we don't need the inconel reinforced versions! but I wonder which would be best for our piston type applications??
Chris.
|
|
|
Post by Deleted on Apr 27, 2015 20:50:01 GMT
Hi Chris , We're spoilt for choice but this looks definately promising : www.klinger.co.uk/assets/files/k46.pdfI'll read some more of the material specs and see if there is anything better but I don't think there is based on quick run through . The simple cotton graphite type which is nearest to the traditional 'graphited yarn' used by model engineers is actually rather poor in comparison to K46 . Best , MichaelW
|
|
|
Post by chris vine on Apr 27, 2015 21:39:23 GMT
When you have worked out what you think is best, we should all write and ask for a sample. It will last us for years!!
Chris.
|
|
oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
|
Post by oldnorton on Apr 28, 2015 20:44:08 GMT
Michael, thank you for the link to the Klinger site, as the one who raised the question "what is this stuff" it is interesting to browse. They seem to offer graphite impregnated PTFE as a high performance material. The K46 is described as "carbon based…an economic alternative to pure graphite", well that could be charred natural fibres for all we know - not that there is anything wrong with that as it probably 'hangs in there / withstands pressure / and self-lubricates'.
My original thoughts were "what are the model engineering suppliers choosing to supply" when they advertise 'graphite impregnated packing'. And, is this undefined material going to be any better than pure PTFE woven packing, or graphite impregnated PTFE woven packing. Julian has given his opinion which I fully believe and accept.
Never mind piston rings, I am also thinking of piston rod and valve rod glands. There is another thread here this week with someone suffering from PTFE gland packing seizing up when hot and questioning whether it is a lubrication failure. The old asbestos+graphite was probably ideal if its coefficient of expansion was similar to the iron it was packed in to - Julian has the best idea in buying up the old stock!
Norm.
|
|
jma1009
Elder Statesman
Posts: 5,901
|
Post by jma1009 on Apr 28, 2015 21:09:05 GMT
thank you norman!
i am rather concerned that what Doug bought recently is as useless as the stuff i bought off ME suppliers and was consigned to the bin.
Doug, can you give me the gap and depth of the slot on your pistons and i will see if ive enough spare of the 'old stuff' to send to you of correct size. some stuff ive a lot of but other sizes precious little!
cheers, julian
|
|
|
Post by Doug on Apr 29, 2015 8:16:50 GMT
thank you norman! i am rather concerned that what Doug bought recently is as useless as the stuff i bought off ME suppliers and was consigned to the bin. Doug, can you give me the gap and depth of the slot on your pistons and i will see if ive enough spare of the 'old stuff' to send to you of correct size. some stuff ive a lot of but other sizes precious little! cheers, julian Hi Julian i will have a look and get back to you regarding the size of my speedy pistons, the new stuff looks quite good to be fair it is a synthetic fibre (probably glass fibre) with lots of graphite packed into it, it does look far superior to the last lot i used (some very old untwisted gland packing) I will thow some into Butch and report on the result. It's got to be worth a trial to see if its any use going forward or if we are all going to need to find a new solution.
|
|
|
Post by joanlluch on Apr 29, 2015 22:30:56 GMT
I think nobody mentioned standard automotive piston rings. I've been discussing this possibility privately. Has anyone ever thought on them or actually fitted them? Thanks.
|
|
|
Post by chris vine on Apr 30, 2015 1:03:30 GMT
Hi Joan,
I have read about the idea for using automotive piston rings, I think in an article about making piston rings in ME, many years ago. From memory, I think the comment was that the wall pressure would be too high for our uses.
however I am not sure that the wall pressure would matter that much as (from what others have said in this thread I think) most of the wall pressure comes from the gas pressure behind the ring.
One good way to find out of course: Try it and tell us what happens!!
Chris.
|
|
|
Post by joanlluch on Apr 30, 2015 6:51:53 GMT
One good way to find out of course: Try it and tell us what happens!! Of course. But my post was more on the aim to start a sub-thread, albeit short lived, covering the use of automotive piston rings in case someone has tried them before. I have been told by not a single person that they should work. Think of this, if they work then this discussion becomes suddenly a matter of the past: (1) Piston rings are something that remain hidden, so there should be no arguments against them by even the most 'traditionalist' MEs. (2) Provided small enough sizes are available in small quantities we can use the "2 Stroke" types which can be pinned to clear the ring gap to reach the valve ports, thus creating what Roger aims for with his design. (3) Automotive piston rings did not (obviously) exist in the steam days, so I must ask myself whether they would be used in full size if the technology would have existed. Same applies to PTFE and some other materials that did not exist at the time. I would be very surprised to learn that nobody has tried automotive rings in a steam engine before, because considering them is a very obvious thing to do IMO. To some extent your reply -encouraging me to try and post the result of my own trials- seems to suggest that nobody else has done it before, but that would be very odd, wound't it?. At least a ME article was published some time ago on this, which is interesting to know, so I suppose somebody may be able to post some pros and cons based on experience or actual facts. Thanks, Joan
|
|
|
Post by Roger on Apr 30, 2015 7:15:25 GMT
I wonder if model IC engines in the larger sizes made by companies such as OS would be a source of rings as spare parts for the smaller ones? I'm not sure what sort of engines are out there for say 40mm cylinder bores but things like chain saws come to mind. I suspect that rings from IC engines are not normally considered because the locomotives are usually constrained by the bore sizes being set in the design ie not freelance. The chances of finding suitable rings is slim. Also, it's not that hard to make them yourself if you have a lathe, and I doubt if there's a Model Engineer in the UK making a steam locomotive who doesn't have one.
|
|
|
Post by miketaylor on Apr 30, 2015 7:53:24 GMT
I had a quick look at ebay and found this straight away
5PCS NEW 40MM PISTON WT RINGS FOR STIHL MS200 MS200T 020T CHAINSAW
40mm and you get the pistons as well!!
Mike
|
|
|
Post by Roger on Apr 30, 2015 8:28:03 GMT
I had a quick look at ebay and found this straight away 5PCS NEW 40MM PISTON WT RINGS FOR STIHL MS200 MS200T 020T CHAINSAW 40mm and you get the pistons as well!! Mike My guess that you'll mostly find metric sizes so they won't suit most scale locomotives. Out of interest, you can buy a piece of 2" CI x 6" long from eBay for £16
|
|
|
Post by miketaylor on Apr 30, 2015 8:38:53 GMT
Hi Roger,
I picked 40mm because that was the size you stated. I agree you may be right about most stuff being metric.
However, as Joan pointe dout the ring size is not exactly in view.
I am working to 1.625 cylinders at present but could happily look at shifting down a couple of mil to 40mm.
Anyway, rings of around the sort of size 5 inch models require are clearly out there and available cheaply which was the point I was making.
Since the rings I quoted seem to be a standard chainsaw size they must be readily available for a few quid a pair off the shelf.
Mike
|
|
oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 693
|
Post by oldnorton on Apr 30, 2015 8:52:32 GMT
"Out of interest, you can buy a piece of 2" CI x 6" long from eBay for £16" - I thought you were worried about rust :-)
CI piston rings on model steam has been extensively reported in the ME publications going back to Trimble 1984, then several by Tubal Cain 1994, and many more authors since then. I am just ploughing my way through all the earlier writings. The reviews have been led by those in the model IC engine world as their need is far more demanding with higher piston speeds and combustion pressures. The model IC piston rings will no doubt work in a model steam engine but ring wall pressure will (most likely) be higher. This will increase drag, but more destructively will likely remove more of the oil film. Since steam engines work well with limp oily packing they really do not need much CI ring wall pressure.
Most people making an engine would/could take on the ring manufacture, but if not then rings are available from the model parts suppliers in imperial sizes, and whoever made them hopefully knew how to do it correctly.
Norm.
|
|
|
Post by Roger on Apr 30, 2015 9:28:53 GMT
"Out of interest, you can buy a piece of 2" CI x 6" long from eBay for £16" - I thought you were worried about rust :-) I didn't say I was using them ;-)
|
|
|
Post by joanlluch on Apr 30, 2015 9:53:28 GMT
To be honest I haven't thought that the lack of imperial sizes could be an issue. In metric sizes you can take 'off the shelf' rings from 28 mm upward. There's no shortage watsoever on them. The smaller ones are apparently used in motor chainsaws or motor grass cutters (whatever you call them :-)).
|
|
jma1009
Elder Statesman
Posts: 5,901
|
Post by jma1009 on Apr 30, 2015 10:16:31 GMT
hi joan,
there is not the slightest difficulty buying piston rings for cast iron cylinders in miniature locos. Stuart Turner and Clupet have been making them for generations. there is no reason why a 1" dia bore should not be turned to 25mm etc.
however both Doug's sets of cylinders are gunmetal.
cheers, julian
|
|