David
Were the 100+ failures due to a failure of the conformal coating
material, or are they attributable to another issue - contamination
under the coating, poor application, bad design? The best coating in
the world is only a band-aid on a poorly designed or built product.
And on a less serious note, to the other Graham: OK, one should not
drink Skydrol, but what aviation hydraulic fluids would you normally
imbibe??? I'm sticking with the G&T.
regards,
Graham Collins
Process Engineer,
Northrop Grumman Canada Corporation
Halifax
(902) 873-2000 ext 6215
>>> [log in to unmask] 03/10/04 08:45AM >>>
Graham,
For the record, acrylic coatings have been in use in the aerospace
industry,
on flight systems of all types and locations, for over 30 years now. We
have
even seen circuits running with water as they pass the dew point, no
failure
recorded.
I take exception to that!
I have personally documented over 100 failures due to moisture in
aircraft systems!!
David A. Douthit
Manager
LoCan LLC
Graham Naisbitt wrote:
>Folks
>
>For the record, acrylic coatings have been in use in the aerospace
industry,
>on flight systems of all types and locations, for over 30 years now.
We have
>even seen circuits running with water as they pass the dew point, no
failure
>recorded.
>
>Their chemical resistance is excellent (MIL Spec term) but they do
have
>selective solvent resistance including moisture (remember that water
is a
>solvent) but can easily be removed using most chlorinated or
fluorinated
>solvents.
>
>Urethanes will provide better solvent resistance hence they are more
>difficult to rework / repair.
>
>I was once asked: "does you coating survive exposure to "Skydrol", an
>aviation hydraulic fluid that should NEVER be drunk!!! (Worse than
Mountain
>Dew I am told!)
>
>I asked why, and was informed that it was: "in case the circuit gets
sprayed
>by this stuff whilst in flight."
>
>My reaction: "This is a circuit in the cockpit of the aircraft, and
you are
>worried about the effects of a hydraulic leak of Skydrol spraying onto
a
>circuit in a sealed housing - why? There ain't no pilot still in
there...."
>
>"Er, good point. Hadn't really thought that one through...."
>
>They used an acrylic!
>
>--
>Regards Graham Naisbitt
>
>[log in to unmask]
>
>Cell: 079 6858 2121
>Office: +44 (0)1252 813706
>
>Concoat Limited - Engineering Reliability in Electronics
>
>NEW Additional Web address: www.conformalcoating.com
>
>www.concoat.co.uk www.concoatsystems.com
>
>
>
>
>>Hans, All,
>>
>>We use both AR and UR in different applications on Class 3. It
really
>>depends on your end use and fitness for use, and in particular the
unit or
>>requirement specification you are trying to meet. AR is easier to
rework
>>etc, bit that also means it can be less effective when it comes to
>>protection... tougher coating = generally harder to remove.
>>
>>If you have a requirement to protect against aircraft fluids etc,
then AR
>>will be a poorer choice. If you want to use it in a telephone box, AR
will
>>do a great job. AR does however have better moisture properties than
UR.
>>None of course are truly hermetic, but they will do well in a
>>condensation/evaporation scenario.
>>
>>AR may be good for rework (if/when it is needed), but it also needs
to be
>>good for service, which may be decades.
>>
>>Clive ff.
>>
>>
>>
>>-----Original Message-----
>>From: Hinners Hans M Civ WRALC/LUGE
[mailto:[log in to unmask]]
>>Sent: 09 March 2004 15:00
>>To: [log in to unmask]
>>Subject: Re: [TN] Pros and Cons on Type UR vice Type AR Conformal
>>Coating
>>
>>
>> *** WARNING ***
>>
>>This mail has originated outside your organization,
>>either from an external partner or the Global Internet.
>> Keep this in mind if you answer this message.
>>
>>I've approved switching from UR to AR at the request of the repair
line. The
>>assemblies are IPC-A-610 Class 3, on aircraft,crew accessible cargo
area.
>>
>>Hans
>>
>>~~~~~~~~~~~~~~~
>>Hans M Hinners
>>AC-130 Systems Engineer
>>
>>WR-ALC/LUGE
>>Special Operations Forces / Combat Search & Rescue
>>System Program Office
>>226 Cochran St
>>Robins AFB, GA 31098
>>DSN Prefix: 468
>>Com: (478) 926 - 5847
>>Fax: (478) 926 - 4911
>>mailto:[log in to unmask]
>>
>>
>>-----Original Message-----
>>From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
>>Sent: Tuesday, March 09, 2004 8:15 AM
>>To: [log in to unmask]
>>Subject: Re: [TN] Pros and Cons on Type UR vice Type AR Conformal
Coating
>>
>> One thing to know is that AR can be coated to patch UR but not
the
>>other way around. Patching AR with UR creates a mix that takes too
long to
>>dry, stays soft. So to switch from UR to AR is recommended.
>> Regards,
>> Ramon
>>
>>
>>
>>>-----Original Message-----
>>>From: - Bogert [SMTP:[log in to unmask]]
>>>Sent: Monday, March 08, 2004 4:55 PM
>>>To: [log in to unmask]
>>>Subject: [TN] Pros and Cons on Type UR vice Type AR Conformal
Coating
>>>
>>>As a Class 3 customer we are considering mandating transition from
>>>Type UR
>>>
>>>
>>to Type AR conformal coating, to make it easier to replace failed
>>components. Are there any Class 3 users of Type AR coating? What is
track
>>record for using Type AR? Are there any compatibility issues with
certain
>>types of solder masks? Any input you have would help. Another
advantage
>>with AR would be for returned equipment. The OEM could remove all
the
>>coating from an assembly using alcohol, then perform
>>
>>
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