Block isolation

[cp4449]

For clubs with signals, how do you isolate the blocks? What do you use for rail joint bars? Between the ends of the rails?

Thx in advance

[makinsmoke]

Watching the signal crew after we finished laying new track on the C&IG.
They removed the joiners and inserted plastic between the rail ends shaped
to the rail contour. Plastic the size and shape of the joiners is then sandwiched
between the rail and joiners. Everything is bolted back up but I did not see if
they used the same steel bolts with insulators or used non ferrous ones.

Take care,
Brian

[optigman]

G-10 Fiberglass / Epoxy is a really good choice for insulated rail joiners and spacers between rails. Extremely durable and strong.

[Steggy]

For clubs with signals, how do you isolate the blocks? What do you use for rail joint bars? Between the ends of the rails?

Thx in advance

Please see attached for an example of a suitable insulated joint. Proper material choices are essential if the joint is expected to last.

ABS Insulated Joint

ABS Insulated Joint Exploded View

[cp4449]

Thank you all, I got great ideas

[southwestern737]

I have used both of those, but I think the easiest is to put a solid pastic tie in where you want the block, screw the rail to it with for screws on each rail run through the foot of the rail, then cut the rail between the screw and fill the gap with silicone. I have never had a problem with a joint I did this way.
Brent

[cp4449]

Great idea. We use aluminum rail on plastic ties already.

[johnpenn74]

Schraeder RR catalog once had the spacers to go between the rails. See picture. About 1/8 thick. I am not sure they make them any more. I have passed a request on to enterprise plastics to make the same but always get a song and dance about about some new half and half product they have in the works. Does anyone else know a place then can inject or just cut these out? Waterjet or laser maybe?

I have also wanted to try what the prototype does and plastic dip the bolts and slice bars in liquid plastic to coat them. Anyone tried it yet?

JP

[johnpenn74]

Jumpers,
You didn't ask for it, but for jumpers I use aluminum electric fence wire (it comes in a few different thicknesses) and screw it into the aluminum track with a stainless self tapping screw. The idea is the similar metal should eliminate any corrosion issues.

Pictured is the yard entry block to protect on a blind curve. This application uses the fiberglass G10 insulated joiners.

JP

[Steggy]

I have also wanted to try what the prototype does and plastic dip the bolts and slice bars in liquid plastic to coat them. Anyone tried it yet?

During the design of the ABS at the Illinois Live Steamers (ILS), I evaluated doing exactly what you describe. I set it aside after realizing how much the rail ends move around due to expansion and contraction with temperature. Full-size practice works because steel's coefficient of expansion with temperature is much less than that of aluminum. In our scale, the aluminum rail we mostly use causes a lot of sliding in the joint, which would quickly scrape away the plastic.

Another method that was tried at the ILS was insulating the rail joiners (splice bars) with heavy grade heat shrink tubing. It didn't take very long for a failure to occur. Again, expansion was the culprit, causing the shrink tubing to tear where it was in contact with the end of the rail.

Aluminum rail expands at a rate of slightly more than 0.015 inches per 10 degrees F increase in temperature (in contrast, steel's expansion rate is around 49 percent of that for aluminum). As there are two rails joined, the gap between rail ends would close at the rate of approximately 0.031 per 10 degrees F increase in temperature. Early on in my research on getting reliable block occupancy detection with 7-1/2 inch gauge track at the ILS, I determined with a pyrometer that aluminum rail temperature on a sunny summer day can reach about 180 degrees F. Going the other way, sub-zero weather is common during winter and, yes, a few brave souls have run their equipment at the ILS on such cold days.

If I use zero degrees F as the baseline, the temperature gradient experienced at the ILS would result in a calculated change of 0.558 inches in a joint's rail gap. In practice, that much movement isn't normally possible, as the mechanics of the rail joint limit how much sliding can occur. In the case of contraction in cold weather, the rail joiner screws are subjected to considerable shear stress and in fact, we have had screws fail under such conditions. Going the other way, total rail abutment on a hot day has led to sun kinks.

The insulated joint I described in an earlier post was the result of considerable research into the track's thermal and mechanical characteristics. Aside from positively insulating the two rails, the joint design has good structural integrity and will tolerate at least 250 pounds loading directly over the gap. That's 500 pounds per wheelset, which is loading that is seldom encountered in 1-1/2 inch scale.

[rkcarguy]

What length of rail was this based upon BDD? From freezing to our hottest temps here, I've figured I need a 1/4" gap at freezing temperature for every joint with 20' or less lengths of the 3/8x1 steel flat bar I'm using for rail.

Another thing to point out, is be very careful with the selection of plastics used for isolating parts. A friend of mine spent a week mounting all these white UHMW strips to his trailer frame so he could slide stuff on and off without scratching the frame. It was sort of translucent white just like the plastic in that rail joint in the picture above. Within 18 months it had gone all chalky white and cracked in several places and at each screw. Most of the projects I bid with plastic parts in them specify a black, UV stabilized UHMW plastic which is supposed to be good for 20+ years.
As I'm going to be dealing with heavier loads on my 12" railroad, I'm planning on using phenolic sheet for my isolators. The open ends on this can absorb water, so its important to seal the cut edges with something to prevent that and it will last a long time.

[Steggy]

What length of rail was this based upon BDD? From freezing to our hottest temps here, I've figured I need a 1/4" gap at freezing temperature for every joint with 20' or less lengths of the 3/8x1 steel flat bar I'm using for rail.<

Oops! Forgot to mention that. Ten foot rail sections were observed.

Another thing to point out, is be very careful with the selection of plastics used for isolating parts.

The joiner insulators we use at the Illinois Live Steamers were in the past fabricated from white Delrin® acetal resin, McMaster-Carr SKU 8739K42, which has held up well. A few years ago, I reevaluated the design and changed this part to black, MDS-filled, cast nylon, McMaster-Carr SKU 2882K21, which is better able to cope with the sliding action it sees as the rails expand and contract. The butt end insulators are fabricated from black Delrin, McMaster-Carr SKU 8662K61. These materials aren't particularly cheap, but are worth the cost when the goals of long-term reliability and joint structural integrity are considered. Insulated joints that were installed in 2003 during early testing are still structurally and electrically sound.

Delrin has somewhat better tensile and impact ratings than MDS-filled nylon. On the other hand, the screws of an insulated joint using nylon for the joiner insulator can be tightened more without binding than with a joint using Delrin. This characteristic should produce a joint with better structural integrity.

As I'm going to be dealing with heavier loads on my 12" railroad, I'm planning on using phenolic sheet for my isolators. The open ends on this can absorb water, so its important to seal the cut edges with something to prevent that and it will last a long time.

Phenolic is not as mechanically strong as Delrin and, as you noted, has hygroscopic tendencies, not something that's desirable with an electrical insulator. Also, phenolic can be hard on cutting tools. I do not recommend its use in this application.