Using UHMW polyethylene to line inside rails for a launch tower

I am just looking at the idea of using Using UHMW polyethylene to line inside rails for a launch tower.

Below are some typical values for the material. In looking at the values below would this product make a good lining, or is this just a bad idea?

Heat Deflection Temp (°F / °C)
at 66 psi 203 / 95
at 264 psi 180 / 82

Approx. Melting Temperature (°F / °C) 275 / 136

Max Operating Temp (°F / °C) 180 / 82

Thermal Conductivity
(BTU-in/ft²-hr-°F) 2.84
(x 10-4 cal/cm-sec-°C) 10.0

Flammability Rating HB

I work with this material, it tends to flex or extend when it changes temperature. And the elongation is surprising. From morning to afternoon, this "lining" might do some warp inside the rail.

Just my advice...
Steeve

Crumb fire said:

I work with this material, it tends to flex or extend when it changes temperature. And the elongation is surprising. From morning to afternoon, this "lining" might do some warp inside the rail.

Just my advice...
Steeve

Click to expand...

I was thinking soley about it becomming damaged from the heat and only being good for so many launches before it had to be replaced. However I did not think of it from that perspective, but you have brought up a good point.

Thank you Steeve.

UHMW also doesnt react well to some chemicals used as cleaners, why not use self adhesive teflon tape?

Materials such as this are slick so there are problems bonding to it. One industry trick is to hit it briefly with a flame, nowhere near enough to melt it. Then for perhaps 15 minutes afterwards stuff sticks to it permanently. That's used for printing cycling water bottles for instance.

Sounds a lot like what a rocket motor will do to it.

I'd leave it as an option for the rail buttons but not the rail.

Gerald

I would say, make sure you can replace the rail and try it. The naysayers all had issues with powder coat paint, but it worked alright for one.

If you go find that thread you will realize that the bottom end gets hit with WAY more heat. So if your rocket is long enough, maybe leave the last few inches unlined.

I wouild avoid teflon. It has been used as an ingredient in igniter formulas.

Sparky Ti + Teflon = Thermite.

Gerald

Any coating degradation will depend on whether the flame impinges on the plastic for an extended period of time.

Quite frankly, the anodized aluminum has a very hard and thus low friction surface. You are unlikely to get a significantly lower friction surface with either Teflon or polyethylene. In fact, Kapton tape would be a better choice because it is extremely smooth and does not melt.

If you want a plastic surface, use a self-adhesive tape over the rail. If it's damaged, simply peel of the damaged tape and replace. Neither Teflon or polyethylene will react with hot titanium or any other metals on incidental contact unless they are powdered and well mixed. Both will melt/char first, and that will be the source of any degradation.

Bob

As a long time user of aluminum-rail competition towers, I can confirm that they do not stay adequately smooth without considerable cleaning and maintenance...I clean 'em with steel wool and use Blaster teflon spray or similar. Teflon or Kapton tape is an interesting idea. They tend to have very good adhesives so changing the tape would probably take a solvent like Goof-off. Anodizing would probably help too, though I doubt it would last forever.

I've used towers extensively for competition and actually tested various materials at one time based upon their slickness. I forget the engineering term for that property, but was working on modifying a tower design that a guy out of California had designed (darn, can't remember his name, but he was another engineering guy that most people know). I found no appreciable difference in performance among the less draggy materials. We were doing all sorts of testing with aerospace grade brass tubing and Teflon. I guess part of it depends on how closely your rails are to your rocket. If they aren't smashing against it, then part of the flight might occur with only one side of your rocket touching it at one time.

Pat_B said:

I've used towers extensively for competition and actually tested various materials at one time based upon their slickness. I forget the engineering term for that property, but was working on modifying a tower design that a guy out of California had designed (darn, can't remember his name, but he was another engineering guy that most people know). I found no appreciable difference in performance among the less draggy materials. We were doing all sorts of testing with aerospace grade brass tubing and Teflon. I guess part of it depends on how closely your rails are to your rocket. If they aren't smashing against it, then part of the flight might occur with only one side of your rocket touching it at one time.

Click to expand...

Coefficient of Friction might be the term you were looking for.

Yes, that's it!

I painted the rails on my steel launch rail with TechLine Dry Film Lubricant. It's meant for coating the stationary rubbing surfaces inside a car engine like bearings, piston skirts, thing like that. It lowers the friction so that a motor makes more power from less friction loss. 3/8ths of an inch on both sides of the slot is more than good for even the rail shoes I machine for my larger rockets. I then rub a candle up and down the slot, the wax makes a great lube.