Liners and casting tubes.

I see that Loki's LE liner/tube set is $60, and the X phenolic are $72.50. Yikes! Aerocon's phenolic set is $24. Any idea why the price is so different?

AMW has XX convolute for $80, and RCS has them for $87.45, and casting tubes are separate.

Since Aerocon's are half the price, what's the downside?

What are the other options out there?

Bat-mite said:

I see that Loki's LE liner/tube set is $60, and the X phenolic are $72.50. Yikes! Aerocon's phenolic set is $24. Any idea why the price is so different?

AMW has XX convolute for $80, and RCS has them for $87.45, and casting tubes are separate.

Since Aerocon's are half the price, what's the downside?

What are the other options out there?

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aerocons are straight phenolic like the BT's and couplers youd buy at PML. Loki / amw / aerotech are the black liners that are supplied with all of the commercial hot loads you buy . Dont waste your money on the cheap liners unless you plan to run a real low solids (low 70's) or a very low Pc motor . The cheap liners almost always split , burn thru very easily. My experience only.

Eric

Randy at Always Ready Rocketry has the PML type phenolic liners and the Loc type paper casting tubes, I've run some pretty hot stuff, 82% to 85% solids through them without any issues, I do wrap my grain stack and the outside of the liner with pyro flash tape though. ($21.95)

For really hot stuff, slots or long burners, he has long burn casting sets which have a double PML type liner and a Loc type paper casting tube ($34.95)

Besides the high quality and higher thermal insulation that Eric mentioned, the convolute liners which others and myself sell are manufactured in a completely different method than what spiral tubes are. Convolute wound tubes are MUCH more labor intensive and use more expensive materials, so manufacturing differences are the main driving force in the cost difference.

Once the setup is done, spiral tube machines can run continuously, making tube after tube on the same mandrel until the giant rolls of paper run out. Even then, adding a new roll is a fairly easy process. The kraft paper they are made from has been impregnated with phenolic resin. Once the tubes are made, they are baked, and then they are pretty much done.

Convolute wound tubes are made one at a time and each tube is wrapped on its own chrome plated mandrel. The substrate is ran through a bath of resin, ran through a squeegee (more or less) to remove excess resin and then wrapped around an individual chrome plated mandrel. Until the tube is wrapped, baked, cured and centerless ground to its final OD, and then removed from the mandrel, the mandrel can not be used to make another tube. So if you want to make lots of tubes in a short period of time and in many different sizes, you need a BOAT LOAD of expensive mandrels.

From a thermal stand point, convolute tubes have roughly about 50-55% phenolic resin in them vs only around 5~20% in spiral tubes. Phenolic resin is what mainly does most of the insulating. The substrate alone would just burn into ash and float away. Phenolic however chars and remains in place. A higher phenolic resin content is the main reason why they are far superior thermal insulators. The stiffer and more rigid the spiral phenolic tubes are, the more phenolic resin content. The softer and less brittle they are, the less phenolic resin. Convolute paper grades like X, XX, and XXX are slightly more dense (flat paper) than LE or CE grades (woven fabrics) and thus have slightly better insulating properties. In a nut shell, you get what you pay for, but each has its place for use.

Thanks, Scott.

Scott- I've heard of people reusing the convolute liners for several motors. What are your thoughts on this?

I've heard the same thing. Re-use sure would make things more economical.
Tubes and liners make up a substantial portion of the cost of EX reloads.
I'm researching the possibility of rolling my own. Linen, as used in the
most expensive liners, is the costliest part. Canvas, as used in less expensive
tubes, is far cheaper. Kevlar and Nomex are much closer to canvas in cost
than linen. I bet you could get multiple uses out of a Kevlar/phenolic tube.
My lathe is too small to turn long mandrels, but long enough to make mandrels
for liners for a couple of 98 or 75mm grains. I can adapt a grinder to the lathe
carriage to allow me to grind the OD to spec. I have a fabric supplier lined up.
They'll be happy to send samples. I'm still waiting for a phenolic resin manufacturer
to return an email.

OleO said:

I've heard the same thing. Re-use sure would make things more economical.

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Just got one from RCS the other day... will try it in my I413 alumaflame EX motor next weekend at the tripoli wisconsin launch. Will report back to see what it looks like if all goes well.

I've been reusing Aerotech/ CTI liners and phenolic nozzles for years. I've found that "I" can't reuse the long burn motor liners or the medusa nozzles. My "hottest running formula is WR. I have no issue running it in any of the spent liners. I do about 95% of my Ex in Aerotech/CTI case with spent liners/nozzles and other parts. CTI 54mm FC are also very reusable. AT and CTI are all very compatible. I've made 'nozzle holders' to run some phenolic nozzles in snap ring cases. It's called Research/Experimental...but don't limit yourself to just propellant formulas.

Tony