IMHO IPDI is the superior curative for HTPB and other polyols I’ve experimented
with. MDI and PAPI are also popular favourites and will cure HTPB without the
need for a cure rate catalyst but IPDI offers superior mechanical advantages –
much tougher polymer, much stretchier and generally a better bond. You will
however need to utilise a curing catalyst (like an organic tin compound) to
bring down the curing time to something practical.
You might (if you look hard enough) find pure enough MDI in a urethane shop –
sometimes it’s used as the curing agent for 2 part (urethane) expansion foam
packs.
Good Luck,
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Wyatt Harris
Sent: Friday, 31 January 2020 2:43 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Introduction / getting started with APCP
Appreciate all the replies! One follow-up question for now: I can't see what
csrocketry has to offer for curatives since I'm not TRA level 2, but if IPDI
isn't the best curative for HTPB, any advice on good non-isocyanate
alternatives? I don't have the book with me, but I seem to remember ECP just
mentioning various isocyanates as curatives for HTPB? Suppose I'll give the
IPDI I have a try for now.
I'd love to go to that APCP course, and maybe I will one day, but don't have
the time now unfortunately.
Thanks,
Wyatt #2
On Thu, Jan 30, 2020 at 5:18 PM Terry McCreary <tmccreary@xxxxxxxxxxxxxxx
<mailto:tmccreary@xxxxxxxxxxxxxxx> > wrote:
Hello Wyatt, ECP is a pretty good reference IMHO, but the author is ugly and
his wife dresses him funny.;-)
You were wise to go with the HTPB system, mainly because that's what most
amateurs use, so finding a mentor who can stand beside you and provide
direction isn't a major undertaking. And of course, it cures faster...though
I've never had much luck with IPDI alone as a curative. If you haven't done so
already, you might check Chris Short's site, he has curatives for sale.
https://www.csrocketry.com/
I'm a little concerned about isocyanate vapors. Either work outdoors under a
pop-up awning on a calm day, or have active venting -- a good fan blowing out
of an open window, with more open windows in the are, and arranged so the vapor
doesn't go over you as it exits.
In ECP I concentrated on 29mm motors (I'm frugal. Or cheap. Whatever), but 38mm
is significantly easier to pack, if you're packing and not pouring. A
single-grain 38mm has about the same mass as two 29mm grains.
Feel free to holler if you have questions.
Best -- Terry (who is actually handsome. Debonair. Witty. And modest, I
forgot modest.;-))
On 1/30/2020 2:10 PM, Wyatt Harris wrote:
Hi everyone,
I've been subscribed to AROCKET off an on for the last ~20 years, and I believe
this is my first post (I may have sent one when I followed this forum back in
high school, but I can't remember).
To provide a bit of an intro about myself, for those that care, or at least to
show that I'm not coming at this totally out of the blue:
I started building rocket motors in middle school and continued into high
school (early 2000's). They were almost all KNSB motors (thank you for your
website Richard Nakka!), with the exception of a large LOX/hybrid that I built
with a propulsion engineer from Raytheon, and launched at BALLS 2004.
I went on to get a BS in Astronautical Engineering, where as a senior I was
chief engineer for a boosted dart rocket project that was launched at WSMR in
2009. Following college I got a MS in Mechanical Engineering, did some other
stuff for a few years, and am presently 1.5 years into a 3 year PhD program in
Astronautical Engineering (not researching anything propulsion related however;
I'm actually examining a GNC topic for spacecraft RPO).
To the subject of this email: I recently got back into building small rocket
motors as a hobby. I've made a few small KNSB motors, though I'm more
interested now in moving on to APCP. I have the APCP/HTPB kit from Firefox. For
the time being, I intend to build and test motors with <50g of propellant.
I'm reaching out to the forum with the hope that this might be a good place to
get some advice on working with APCP (especially regarding safety, common
pitfalls and best practices). I've got and have read through Experimental
Composite Propellant, Plastic Resin Bonded Fuel Systems (Firefox book), the CP
technologies book (doesn't seem very helpful for APCP though), and I also have
Burnsim. I intend to proceed following the procedures outlined in the first two
books as closely as possible.
If this is the right place to ask, I suspect I'll have plenty of questions
moving forward, but to pose a couple to start:
(1) My main concern right now is proceeding safely, so any practical advice out
there regarding safe production of small APCP (<300g) batches? My initial plan
is to use an open garage with PPE including nitrile gloves, goggles and VOC
respirator. I've taken a look at the SDS's for the chemicals involved, it seems
that IPDI is is the nastiest component? The SDS for this makes it sound very
toxic.. how concerned should I be about this for the small batches I'm making?
Any concerns/things I should know about other chemicals such as
AP/HTPB/EHA/tepanol? I'm not planning to do any crazy propellant formulations
(exotic oxidizers/metals) at this point.
(2) I opened up the teponal (HX-878) from the kit and noted that it is
*extremely* viscous (challenging to remove any with a tongue depressor). Since
it's been a while since I bought the Firefox kit, wondering if this is normal,
or has it gone bad?
Thanks for reading the long email. Thank you in advance for any advice!
-Wyatt
--
Dr. Terry McCreary
Professor Emeritus
Murray State University
Murray KY 42071
