[roc-chat] Re: best way to ....
- From: "Tom Hanan" <Tom.Hanan@xxxxxxxxxxxxxxx>
- To: <roc-chat@xxxxxxxxxxxxx>
- Date: Mon, 21 Nov 2011 16:01:18 -0800
Mix consistency problems (pun intended) are why they developed multi part
processes using a single rounded cup with a rounded mix stick and then
improved them again by replacing cups and sticks all together with multipart
mixing tips.
A lot has changed / improved since they "vetted" the composite processes and
materials for the B2. For one thing better materials and multipart mixing
tips are now available over the counter.
A master builder will always be able to do miracles with a blob of this,
mixed with a blob of that, based upon experience and skill. If you are not a
master builder, train under one, listen to one, and or take advantage of
newer process technologies designed to take the "magic" out of achieving
reliable & repeatable results.
"The tools to those who can use them"
The best part of the discussion for a newbie has been the "magic" of priming
and after coating filled adhesives! That part of the "magic" typically will
not change no matter how you do your multipart mixing!
I don't recommend relying on any joint you can't visually inspect in a hobby
environment!
P.S. I personally do not fly anything "BIG" > multi "D" at the Lake because
I am there with kids and kid built rockets. I want them to safely learn from
their mistakes and or lack of attention to detail. So for the big stuff take
my comments with a grain of salt knowing that they are not hobby related. I
am always drawn to the simplest way to do things. Less hassle mixing means
more time and attention spent on priming and over coating the joint to
maximize reliability.
Best Regards,
Tom Hanan
President & CTO
Model-T-UAV
Tom.Hanan@xxxxxxxxxxxxxxx
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From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx]
On Behalf Of Rick Maschek
Sent: Sunday, November 20, 2011 6:46 PM
To: ROC-Chat
Subject: [roc-chat] Re: best way to ....
Ditto on the double cup use. I once had an area on a fin that never set up
because of unmixed. A B-2 worker told me about double cupping and never had
the problem again.
Rick
_____
Date: Sun, 20 Nov 2011 16:54:20 -0800
From: kramer@xxxxxxxxxxxx
To: roc-chat@xxxxxxxxxxxxx
Subject: [roc-chat] Re: best way to ....
Clarification on the clarification on the..... well you know
I didn't mean to say you weigh out each component in a separate cup and then
mix them (bad idea), double cup equals,
Weigh all the parts into the first cup, weigh part a, tare the scale part b,
tare, part C, etc
mix all the components in the first cup, THEN transfer ALL of the mixed
adhesive to the second cup, throw away the mixing stick and with a new
mixing stick mix it some more.
Here is the reason, when you mix, even if you scrape the container REALLY
well, the bottom corners are usually not mixed well. By pouring it into the
second cup you keep this unmixed adhesive out of the part. When you need
that last little bit of adhesive out of the cup is when the problem shows
up, scraping the bottom of the mix cup sometimes some of the unmixed stuff
can come out.
I did a FMEA (failure analysis) on an aerospace part that failed. A
critical failure was linked back to improper mix (BTW, they put the test
coupons together first then bonded the part), when we looked at the retain
in the cup, two things became apparent, there was almost no resin in the
retain cup, and the adhesive in the cup didn't cure properly due to
incomplete mix. The adhesive was hard but not fully cured. The test
coupons tested out fine so one one suspected there was a problem until a
part failed during fist article testing. This was a REALLY expensive
failure.
Just my professional opinion. At the day job I always insist on ether
double cup or static mixer on a mix gun.
Mike Kramer
On 11/20/2011 1:13 PM, Tom Hanan wrote:
Single cup mixing is the fastest, easiest and most accurate especially when
adding additional parts to the cup using an included syringe or plunger
applicator.
Pour the first part into the cup, while still on the scale add and mix
whatever weights, of the 2nd, 3rd or 4th parts of fillers, stabilizers and
or catalysts needed to achieve the best ratios for the specific application.
Simply follow the manufacturer's instructions on the order and or timing of
the multiple parts need to be added. The technique is so fast, simple and
accurate that we rarely have the problems typical with multi cup mix ups.
Pun intended!
Hope this helps.
P.S. We store the 2nd, 3rd and 4th parts in the applicators between mix-ups
w/o any problem since there is minimal exposure to air. Since we are running
well below Mach we tend to favor joint flexibility and durability over
rigidity.
Tom Hanan
President & CTO
Model-T-UAV
Tom.Hanan@xxxxxxxxxxxxxxx
CONFIDENTIALITY NOTICE: This email message and any accompanying data or
files is confidential and may contain privileged information intended only
for the named recipient(s). If you are not the intended recipient(s), you
are hereby notified that the dissemination, distribution, and or copying of
this message is strictly prohibited. If you receive this message in error,
or are not the named recipient(s), please notify the sender at the email
address above, delete this email from your computer, and destroy any copies
in any form immediately. Receipt by anyone other than the named
recipient(s) is not a waiver of any attorney-client, work product, or other
applicable privilege.
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx]
On Behalf Of Jim - TFJ
Sent: Sunday, November 20, 2011 9:34 AM
To: roc-chat@xxxxxxxxxxxxx
Cc: 'Gregory Lyzenga'
Subject: [roc-chat] Re: best way to ....
Just some points of clarification on West System & DP-460
The West System epoxies do not come with fillers added, the DP-460 does.
There's a great cost disparity between the 3M DP products and bulk epoxies
like West and others.
West System (and others) have numerous additivies to alter the
characteristics of the base resin.
They include adhesive fillers like the high density (404) or colloidal
silica (406) to fairing filler (407) and microlight (410).
Like I said before, if a rocket can go subteranean and fly again (at least
the fin can section was flyable), then it must be pretty good stuff.
Here's a selection chart on the fillers.
http://www.westsystem.com/ss/filler-selection-guide/
I use the adhesive filler for stuff like centering rings, and the fairing
filler for fins other areas.
If you only bought one though, I'd go with the fairing filler because it's
much easier to sand.
The 406 is brutal to try and sand.
Jim G.
_____
From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx]
On Behalf Of Mike & Nancy Kramer
Sent: Sunday, November 20, 2011 8:17 AM
To: roc-chat@xxxxxxxxxxxxx
Cc: Gregory Lyzenga
Subject: [roc-chat] Re: best way to ....
Not smart enough not to weigh in on this one,
Laminating resins like west or proset are really not designed to be
adhesives but are designed to laminate. The viscosity of West system is
about 1,000 cPs (centipoise), as compared to 20,000 cPs for 3M DP-460 or
70,000 cPs for DP-190G. Peel strength is another measure of how tough a
adhesive is. Just comparing West System has a "T-Peel" of around 5 lb-in,
DP -460 has a T-Peel of greater then 60 lb-in. It is a VERY tough adhesive,
plus the higher viscosity will keep it in place during bonding. JB weld has
high shear strength but isn't the toughest stuff.
Adding fillers like cabosil or micro balloons, helps the viscosity but
doesn't help the peel strength a lot.
On JB weld, it is great stuff for the right application. Bonding a retainer
on a motor mount, great application need high temp capability, high shear
strength, relatively high viscosity, not worried about peel.
For fin fillets, not as concerned about temperature, needs high viscosity,
high peel strength, not as worried about shear strength (fins fail in peel
not shear), a better candidate would be DP-460. MUCH tougher, will keep the
fin on during a hit that would snap it off with JB weld or west mixed with
silica.
Couple of other comments,
Mix, always weigh (or use duo pac) if it is a critical joint. harbor
freight sells small scales really cheep. 1 to 1 by volume doesn't equal 1
to 1 for weight on all systems.
Double Cup, weigh in one cup, mix the adhesive, then pour (scrape) all of it
into another cup, using a new mixing stick mix it again, don't use any of
the 'leftovers' in the first cup. Smart and final sells 'french fry boats'
the cardboard boats that resturants serves fries in, works great as a place
to mix resin. A sleeve of them last a LONG time, coffee stir sticks from
S&F are good for mixing and rally cheep.
Temperature - Time - Adhesives. Hard doesn't equal strong. Most room
temperature adhesives need a long time to get to full strength (think days
at room temp, weeks at 50 degrees F), heating them to even 120 F for a few
hours significantly speeds things up.
Surface prep, wipe - sand - wipe. Wipe them with solvent then sand, then
wipe again. Careful some cleaners leave a residue. I use Acetone or MEK.
Bond to PVC - DP-460 will give 500 lb shear strength when bonding to PVC
MUCH higher than most adhesives.
Mike Kramer
On 11/19/2011 10:51 PM, Gregory Lyzenga wrote:
On Nov 19, 2011, at 6:17 PM, Mike Ostby wrote:
Thanks Greg. Sounds like beefing up the couplers is in order. So how is
that best done?
To be honest, since after that experience, I've sort of sworn off cardboard
couplers. I tend to use phenolic most often. But when I do use cardboard,
I stiffen it by laminating it on the inside with fiberglass or carbon/kevlar
cloth, using an inflated balloon inside the coupler to compress it.
- Greg
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