Advanced Composite Rocket Component
Construction Other Stuff
The Other Stuff
This page is my "Other Stuff Page" on
Composites. It was my
original page but now
that I'm making a nice page it is now my "Other Stuff Page". This stuff
will slowly work it's way onto my other pages...
Resources
Coker's how to series
Aerocon's cache of
Tom
Cloud's "Creating Fiberglass Tubing" I myself
have cached it here
because sometimes good stuff vaporizes
Vern's Starfire Body Tubes - His page on
glassing
the tubes for his Starfire Rocket. There are other good building
tips and photos on his site.
ROL
Forums
Trailer Trash
Shadow
Composite Videos - I picked up the video set on ROL - A very good
set. The last I checked, however, their website had been down for
weeks. Are they still in business? If not then find somebody to borrow
this video set from.
Quicklinks
- COMPOSITE MATERIALS / FABRICATORS - a great link of links.
From ROL How To Forum:
>>I want to build
a large scrach built rockets 4" to 12" that will take any motor
combination that I can fit and not break. Kevlar? Graphite? weights and
weave? Price is not a big concern. I have used fiberglass but that
seems to add a lot of weight.
>>Mike Sutton
Mike,
Fiberglass shouldn't be
adding that much in weight- certainly less
than a pound on a four inch rocket. Since price is not a concern, why
not try vacuum bagging whatever fabric you choose? You will get to the
optimum fabric/resin ratio, and lightest weight.
If you do bag, Kevlar
becomes an option. 3 oz Kevlar has the bulk
of 9 to 12 oz 'glass, but it's very, very tough. You'll have to cover
it with either a finish coat or glass, or two rolled on coats of resin,
to get an acceptable surface. If you sand through to the kevlar, you
will get the eternal fuzzies.
Carbon fiber is easier to
get a really good surface finish, and
it is much stronger and stiffer than anything else. A layer of 5 oz,
vacuum bagged, is stronger and stiffer than several layers of 6 oz
'glass. John Coker flew his Generic 6 inch rocket on an N2000, with one
layer of 5 oz on the tubes. I've used two layers of 10.1 oz carbon with
good surface finish and incredible stiffness.
If you're just doing
tubes, a plain weave will give you enough
flex. If you're going into a bagged fin can, you may want to go with a
satin weave, which has better formability. Get more info at
fiberglast.com
Another good thread on ROL How To Forum
Fiberglassing,
Fiberglass and Carbon Fiber
Tom
Cloud's
"Creating
Fiberglass Tubing" Looks good too. I'd like to try this and make
some carbon fiber tubing.
Making sheet stock is described in Video #3 of the Shadow Composites
video set (among other things).
Tom Cloud has a great description of tooling and process for rolling
your own tubes from scratch. It's on ROL (I think) and
I have cached it here.
Best gems are making the full length mandrels and also how to work
release using mylar for re-usable mandrels. Nothing on heat tape or
curing. See Dave Triano's videos for that.
Vacuum Bagging
Heat
Shrink Tape
Tube wrapping is best done with heat
shrink tape. Less mess and fewer disposables than vacuum bagging.
Right now I'm using
www.shrinktape.com
-
Dunstone: Hi Shrink Tape; specifically the perforated, release coated,
0.002 film in 100 yard rolls (about $22). It's also available from
Aerocon and others, but Dunstone did have the perforated and others
didn't (I must add that Dunstone told me the perforations were more for
volatiles and less for bleeding, so I may decide to skip the cost of
the perforated for what little advantage they think itwould provide for
epoxy bleeding) They are happy to talk to you and sell you just one
roll so don't let the crispness and formality of the website put you
off. Or order from Bob at Aerocon.
The heat tape curve shows usability in the 200F through 400F range,
with optimal at 300F. Talking with Dunstone, they indicated that 200F
was likely minimal, and that, if possible, spiking to even 220F or 240F
if not 300F would be best. All it takes is the spike as it holds
tension even after cooling. So I may reset my curing oven to have a
very high themp overtemp, a 220F or 240F "tape set limit", and then
lower for propellant curing and post curing.
Curing Ovens; Post
Curing
Dave Muesing of Mr Fiberglass indicates
his epoxy can be post cured up
to 240F. Without post cure the Tg is 164-170F.
Dave Triano of Shadow Composites indicates that Aeropoxy has an
equivalent temperature of 170F for a standard cure. The implication
being that a "normal post cure" isn't necessary with Aeropoxy unless
really high heat tolerance is desired. I don't know what the limit is,
but thought it was 170F (which begs the question). If you know, let me
know. I'll have to re-watch his 3 videos as the info is scattered in
there. The implication from the Novaar article is "about 175F" for the
post cure oven.
I got good hits off
this
Google Query. Here's a Gougeon Brothers one for Pro Set Epoxy
called
Post
Cure Basics, and another called
Building
Post Cure Ovens. Here's
a big one along
my lines thinking.
EAR Chapter 176 article on
building
your own post cure oven in this issue.
The referenced
"Novaar Free Press"
has pictures of the Shadow Aero curing oven as built by Bart Merkley.
John RockDale's
Shadow Composites Curing oven. With pictures and a wattage /
performance graph.
Mike's Propellant & Composite Curing Oven
I've build a propellant curing oven (for PBAN), and find it useful for
many things. It's big enough to post cure perhaps 20" x 22" sheet stock
vacuum bagging, or short tubes. I may make a curing oven extension for
tubing.
This oven works well and heats quickly even with relatively small
bulbs. The interior is about 28" deep by 12" wide, by 23" high.
The walls are 2" thick, originally for pink foam sheet insulation, and
originally lined with luan plywood. It's now insulated with R13
fiberglass and lined with Hardibacker board.
The back 6-7 inches are designated for "heat source dujour", leaving
20-21" available. That size was conveniently chosen to allow jelly roll
pans to fit to allow more of shorter product to be cured. It's
otherwise nicely generous as It will hold the propellant curing rack
(shown) along with a gallon of PBAN and quart of Epoxy with some room
to spare, so I can be warming the PBAN to cast one batch while another
is curing. Or drying AP for the next batch while one batch is curing.
You do need a fan to stir the air. In this oven, I was noting a 20F
differential between the top and bottom when not running a fan. I like
to let the fan run continuously and have the heat source switch.
I was running 2x200w bulbs for heat, but found that a single 200W bulb
provided decent heatup and max heat capabilities. This is partially due
to the nearly airtight sealing and generous insulation.
I'm planning on adding the Eliwell thermal controller back in, but with
a new industrial J type thermocouple, with a new location not subject
to heat/humidity, and with always having a backup high limit overtemp
thermostat. With this controller I can keep the temperature as tight as
1 degree though I usually run it 0-5 F. With my water heater thermostat
the hysteresis is about 20F, which is wider than I'd like.
Safety Recommendations
I had an overtemp excursion and while I was preparing alterations, had
another. The second both overexpanded the pink foam on the bottom,
popping the liner, and melted on the top, and tripped the garage GFCI.
It was being controlled by an Eliwell EWPC902. I think that my
thermocouple might not have been rated for high temps / humidity, and I
think running it with the door cracked to let humidity escape allowed
humidity and heat to affect the controller, located about where you see
the GFCI in the picture. I didn't have a high temp backup limit.
Since the GFCI tripped in the garage, I decided the unit itself should
have it's own GFCI. You see a "no-outlet" GFCI in the picture on the
right. I wanted to ensure that it would always shutdown even if it was
plugged into a non GFCI outlet if a fault occured.
I am also using (curently) a water heater thermostat as the temperature
limit. These are very heavy duty and designed for high temperatures and
some humidity. Most have a working range of 90 or100 F on the low side
to upwards of 170 F on the high side. Some have a separate 190F manual
reset over temp limit. If you want ones for specific temperatures, or
perhaps a higher temperature, then checkout, for example, CanTherm
thermostats such as sourced by DigiKey.
DO have a high overtemp limit thermostat that is bulletproof. DO have a
built in GFCI built into the unit.
Shadow Composites Curing Oven
The above referenced
"Novaar Free Press"
has pictures of the Shadow Aero curing oven as built by Bart Merkley.
John RockDale's
Shadow Composites Curing oven. With pictures and a wattage /
performance graph.
I
think their oven specs post
cure at 180F as John's curve was targeting 180F temperature. I noted
somewhere comments on not wanting to hit an overtemp of 190F (on the
utilized thermostat, not for any specific other reason), with a reset
temp of 160F, and this suggests a water heater type thermostat ...
though those usually must be manually reset ... so I don't know what
they specifically specify or use.
Post Curing in General
One Quote from a europa-list digest:
Aeropoxy loves heat.
Once you reach a certain temperature, the TGA will be that temperature. Now if
you post Cure at a lesser temperature for many hours, it will elevate TGA to
~194 degrees F..
Here's a good Tg quote from
http://ozreport.com/pub/Ozv3n130.htm
The temperature at which the
strength of the resin degrades (softens) is called the Tg (T sub g)
(glass
transition temperature). Room temp cure resins like: Aeropoxy has a Tg
of 194°F
(90°C), or Dow Derakane 411-45 vinylester's Tg is 210°F
(98°C), while
polyester is <150°F (65°C). Some of the elevated cure
(>250°F 121°C)
epoxy resin systems have a Tg in excess of 450°F (232°C).
Not only
must the oven used to
cure a pre-preg part be large enough, but the temperature must be
carefully
controlled over the entire part and tool surfaces. The rise time
(°'s per
minute), the plateau (temp vs. time), and the fall time (°'s per
minute) must
be accurately controlled and documented if it is to be a structural
flight part.
Scrap pieces are also cured with each part to document craftsmanship.
Before the
cure cycle is started, the part is put under vacuum bagging to squeeze
the
fabric layers together and start the flow of the room temp resin. Then
the part
and tool are placed in the oven for the proper cure cycle. This costs
time,
materials, and labor.
There are two forms of shrinkage: primary shrinkage and secondary
shrinkage. All thermoplastic resin systems shrink when they cure
due
to internally generated heat (exotherm) during the crosslinking
process. This primary shrinkage can be observed after the casting
has
cooled and been demolded from the pattern. Selecting hardeners
that
are commensurate with the mass of material being cast and the ambient
temperature of the shop can control primary shrinkage.
Secondary
shrinkage is a result of applying external heat (oven) during post
curing. This shrinkage can be observed after the final post
cure.
Using slow ramp-up rates, more dwell temperatures and longer time at
each temperature can minimize secondary shrinkage.
On Epoxy brands for Post curing from
http://www.rcgroups.com/forums/showthread.php?p=2216246#post2216246
Aeropoxy is certainly a lot better than
West Systems or such stuff. Its
a very thin, excellent laminating resin, with excellent curing results
when heated. Because post curing improves the overall strength of the
laminate (from more cross linking) I consider this to be a key aspect
of epoxy choice. Nothing else I have used (West, JeffoCo, Ez-Lam, Poly
Poxy) holds up nearly as well as Aeropoxy does to high temperature
curing. Plus price does significantly influence my buying decisions.
Mold Release
A mold release is needed, particularly
when making flat plate. Dave Triano shows making flat composite plate
on glass using using Vacuum Bagging in his Video #3. He applies a spray
release, but notes that it's HazMat to ship.
Using Hairspray as a mold release
This from a West System Article
Mold Release, PVA & Hair Spray.
It suggests that heavy duty hair spray might be usable in place of the
HazMat spray PVA (and other) products. I don't know if you could brush
epoxy onto it as Dave does in his video (vs laying impregnated fabric
on it). Note they do say PVA works best over wax and not so well on
it's own.
Loctite 770, loki's stuff, ... Mr Fiberglass's stuff, ...
Foam
Polyurethane foam,
syntactic (sp?) foam.
Epoxy Specs
I'm gathering specs, but focusing more
on Tg and post viscosity. Tg as it relates to the "Transition to Glass"
or in other words the temperature at which the epoxy will start to
soften. Viscosity as it relates to ability to we fabrics for
laminations.
Tg - This can be raised through a high temp cure and/or post cure. If
you don't have a curing oven, then it may be even more important to
select an epoxy with a higher Tg from a room temperature cure. This is
more important for motor mount tube layups and fin bondings. It may be
important also if your rocket will be dark in color and flown in hotter
weather, as a black rocket in the sun can get to 160F or higher (which
requires post cure for West System for example).
Visosity is important mostly as it relates to ability to wet fabric for
laminations. Aside from that it's less important, in general, except
for the fact that some hobby & home center epoxies have thickening
agents that might not have been to your choosing for your application.
Mr Fiberglass
Mr Fiberglass specs
are here. The Tg is in
the 164-171F range for a room temperature cure. From the specs you can
cure / post cure up to 250F (which also goes hand in hand with a good
heat shrink tape set).
West Systems
West Systems has a
physical
properties page here The Tg is rather low for a room
temperature cure. It is in the 120-140F range. Heat Deflection
Temperature can be as low as 118F.
Aeropoxy
Aeropoxy. I'm looking ofr links now.
I've read on the net that the Tg is 194F for a room temp cure, but am
not sure. It does seem to be the highest of the lot.
ACP EZ-Lam
ACP has EZ-Lam.
http://www.acp-composites.com/acp-ez.htm.
I don't know the specs, but I did note on that page that they have a
high temp version suitable for making exhaust header laminations, etc.
That might be a good candidate for motor tubes and fin mount fillets in
lieu of the Shadow Aero high temp special epoxy.
Pro Set
CST has Pro Set and West Systems; Post
cure can get Tg to 180F
Suppliers
http://www.mrfiberglass.com
- Dave Muesing is Mr Fiberglass. Dave's a great guy and he's got
attractive prices on his line of Epoxy as well as West System and also
everything else for composite construction from core materials, glass,
carbon fiber, kevlar, vacuum bagging .
http://www.fibreglast.com/showproducts-category-Sandwich+Cores-18.html
- Core matereials, foam core boards, endgrain balsa (seems decent
pricing), etc.
For foam
core (polyurethane), Aircraft spruce seems to have best prices; not
sure about their end grain balsa products.
http://www.solarcomposites.com/
- the least expensive I've seen - and their Sleeve prices make sleeving
vs wrapping nearly a push. The CF, FG, and also CF tape prices are also
great. Good release, etc. Check em out.
Northern Fiberglass
Sales - I found them looking for Frekote 700 products (mould
release).
http://www.acp-composites.com/
- Aerospace Composite Products. A very broad and comprehensive
selection of products for composite construction
John R. Sweet Co - We
are distributors of FRP materials and supplies. We mainly serve the
light-marine industry, primarily canoe and kayak manufacturers ...
Carbcom - Carbon
FIber and Kevlar Fabrics, but only that. No Fiberglass. No resins. From
Hawaii! but responsive, shipping same day, and only (!) 5-6 days UPS
ground. Company oriented, but no minimum order. They often have
specials like 5.7oz x 50" 3kx3k fabric cut on special for $23/yd no
minimum.
http://www.aeroconsystems.com
- Aerocon Sytems. Always good to see what Bob's got now. Heat shrink
tape, fiberglass, and carbon tow, what else? what now?
http://www.cstsales.com - The
Composites Store
www.a-c-m.com
if you do
choose carbon
fiber check out the prices at www.a-c-m.com. $17 per linear yard
(48.5in diameter) for 5.6oz satin weave I think. I've ordered once and
there is a 6 yd minimum but the price is MUCH less than anywhere else
I've seen.
www.fiberglast.com
Aircraft Spruce -
Sport Aircraft supply; good composite selection of supplies and
materials; to some a one stop shop.
www.shrinktape.com -
Dunstone: Hi Shrink Tape - Direct Mfg / Supplier of shink tape;
samples, and no order too small. Look for perforated release coated
tape for wrapping those tubes. Tell them Dave Muesing of Mr Fiberglass
sent you.
http://www.aerosleeves.com
- These guys have very nice glass and carbon fiber woven into
continuous length sleeves with no seams for very easy layup.
Here's a boat
builder's supplier link page - good for resins, fabrics, release
coatings, etc.
the sock guys? aerosock? Loc Sock?
www.shadowaero.com
The ROL Construction Forum.
