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Mechanical Rod Packing
http://www.rypn.org/forums/viewtopic.php?f=1&t=40466		 Page 1 of 3
Author:  Rick Rowlands [ Wed Mar 08, 2017 11:19 pm ]
Post subject:  Mechanical Rod Packing
I'm trying to learn about mechanical rod packing, as its getting to be time to refurbish or replace the packing on the J&L 58. The attached photos show what I have. I am not sure who made this packing. The individual segments are made of babbitt. Four segments fit into a steel ring with flat springs providing tension when installed. I am probably going to need new segments made for one of the rods since it had to be turned down some to eliminate pitting and wear marks.

Who makes this style packing nowadays?

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Author:  mikefrommontana [ Wed Mar 08, 2017 11:53 pm ]
Post subject:  Re: Mechanical Rod Packing
A cursory look on Google reveals people who make mechanical packing--but I have the nagging suspicion that the price point won't be pleasant. It may be easier to cast and machine new babbit segments, along with any other components requiring renewal. The main spring and housing components appears to be usable.

Just my two cents.

Michael Seitz
Missoula MT
Author:  NYCRRson [ Thu Mar 09, 2017 12:31 am ]
Post subject:  Re: Mechanical Rod Packing
I do not believe that anyone makes a rod packing like that anymore. I do not remember the trade name for it, but you can find it in an old loco cyclopedia from the 40's.

I did recast some of the segments for a segmented cylinder rod packing on a fireless loco using babbit.

I created a wood pattern that was shaped like an unworn packing segment with about a 15% shrinkage allowance. Then I made a high temperature silicone rubber (two part liquid) mold around that pattern.

I made a mold box and filled the bottom half with clay, embedded the wood pattern and some marbles "half way" into the clay (marbles are there to align the mold halves). Then poured half of the silicone mold. Once it setup I removed the alignment marbles and poured the second half (be sure to use some release agent).

Remove the mold box and wood pattern, cut a "runner" for the metal to enter the mold (and a few vent holes), slap the two mold halves back together with some strong rubber bands, melt some babbit and pour away.

I was able to pour about a dozen packing segments from babbit with that mold with no problems.

Then you need to scrape the internal diameter of the segments for a "coarse" fit to the rod and install them. They will quickly wear into a "close" fit.

Not too difficult, I still have the rubber mold, but it may not be for the same rod diameter.

Cheers, Kevin.
Author:  Rick Rowlands [ Thu Mar 09, 2017 12:54 am ]
Post subject:  Re: Mechanical Rod Packing
Kevin,

That is an excellent idea. Thanks.

Rick
Author:  TrainDetainer [ Thu Mar 09, 2017 1:05 am ]
Post subject:  Re: Mechanical Rod Packing
The segment packing you have in the top pic looks like Paxton-Mitchell. P-M was out of the metallic packing business many years ago. Last info I have is they sold/gave the patterns/line/remaining stock to Midwest Central. I don't know if MC still has the stuff or not. The packing I have (3-3/4" piston rods) is not of babbitt or babbitted - they are cast red brass (very red/high copper content). They did have the feel and look of babbitt when first removed, but a good cleaning with brake cleaner removed the steam oil and grunge and revealed the real material.
Author:  CCDW [ Thu Mar 09, 2017 1:42 am ]
Post subject:  Re: Mechanical Rod Packing
Regardless of all the information you may receive I strongly recommend that you speak directly to Kelly Anderson. He helped me and his experience is exemplary and very accurate.

CCdW
Author:  Rick Rowlands [ Thu Mar 09, 2017 2:10 am ]
Post subject:  Re: Mechanical Rod Packing
TrainDetainer,

Your mention about Midwest Central sparked a thought in my brain. I have one of their old catalogs so I pulled it out and found a section on the Paxton Mitchell packing and yes that is exactly what I have.

So in the interest of spreading knowledge here are the pages out of Shop Services catalog. Pretty good pricing too!

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Author:  Rick Rowlands [ Thu Mar 09, 2017 2:11 am ]
Post subject:  Re: Mechanical Rod Packing
Three more pages.

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Author:  Mike Tillger [ Thu Mar 09, 2017 5:35 am ]
Post subject:  Re: Mechanical Rod Packing
These people make a similar product:
http://www.c-p-i.com/en/wear-products/packing-wiper-rings/
http://www.c-p-i.com/media/cms_page_media/11/cpi%20mech%20pck%20bklt%20US-updte6%2011-.pdf

Mike Tillger
Author:  Dave [ Thu Mar 09, 2017 8:45 am ]
Post subject:  Re: Mechanical Rod Packing
The CPI products resemble the France Compressor packings I retrofit to a Shay when the Paxton Mitchell rings disintegrated a couple decades ago. I think we used a stack of 4 instead of two...... very pleased with the results. If you decide to cast your own, Jack Anderson used to cast his with a product called "diesel babbit" and had good service with them. There was a Paxton Mitchell hand cranked lathe that was sold for custom boring the packings for fast refitting while in the roundhouse that i wish I had one of today.
Author:  Rick Rowlands [ Thu Mar 09, 2017 8:58 am ]
Post subject:  Re: Mechanical Rod Packing
I was thinking about how to make a mold for casting my own. I came up with drawing up a segment in CAD, enlarging it slightly to compensate for shrinkage then having that shape cut out of a piece of steel plate with a waterjet. Pour the babbitt and after it cools strip it out of the mold and it should be quite near net shape. Assemble two segments, bore them out to size and install.

I do not see any reason why that would not work.
Author:  Dave [ Thu Mar 09, 2017 11:10 am ]
Post subject:  Re: Mechanical Rod Packing
It's about how it was done back when it was done daily with the exception of the computer stuff. Of course it will work.
Author:  NYCRRson [ Thu Mar 09, 2017 11:11 am ]
Post subject:  Re: Mechanical Rod Packing
Waterjetting an opening in a plate and then pouring metal into it should work. I did not have access to a waterjet.

You may need to scrape/sand them to get them flat.

The ones I replaced where definitely babbit, I melted the originals as part of the replacements.

I would imagine they where made of different soft metal compositions. Probably some kind of brass composition for superheated units ?

Kevin.
Author:  crij [ Thu Mar 09, 2017 2:14 pm ]
Post subject:  Re: Mechanical Rod Packing
Might be a crazy idea, but by the looks of the wear parts in the diagram, I would assume there was some thickness tolerance to keep everything working correctly.

To make it slightly easier with less to machine and the need to make holding fixtures, how about pouring a sheet of Babbitt? Once cool pass it through a thickness roller and then waterjet the half moons out of the plate? Once that is done all you would have to do is final boring, no worries about shrink allowances or how to fixture the parts. Heck the waterjets are accurate enough, you might be able to run in the fit directly off the as cut parts.

Just idea out of left field...
Rich C.
Author:  OldColony [ Thu Mar 09, 2017 3:07 pm ]
Post subject:  Re: Mechanical Rod Packing
Number 9 at the WW&F had similar packing glands on the piston rods.
The silicon rubber molds worked well to make new rings. The two part silicon was obtained from MicroMark, but probably available other places. The babbitt was bought from McMaster. We opted for a high tin content thinking it would wear better. After one season we are pretty happy with the results. It certainly was easier than expected.
A pattern was turned out of plastic to the size of the old pieces plus shrinkage, as mentioned. A practice piece was cast to estimate the shrinkage.
Flat head machine screws were used to support the pattern while pouring the first half of the mold and when removed they formed nice funnel shaped pour holes. The molds were poured into and supported by a 4 sided box bent from a strip of aluminum sheet.
There are two rings, one ring is rectangular in cross section and one with a taper one the outside so that it presses against the piston rod. They are half rings, so total of four pieces.
A nice thing about the silicon is that it doesn't cool the melt too fast, so you don't have to heat the babbitt up very far beyond the melting point. Fresh babbitt seemed to work better than remelt.
There will be some roughness to the finish after pouring but the soft metal seems to squish enough to make it steam tight.
One more thing: they need plenty of lubrication. We found that without a steady supply of oil the packings will start to leak. and probably wear faster. An oil cup that feeds a felt ring around the rod makes sure it's got plenty of oil.
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