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jpx(at)Qenesis.com
Guest

Posted: Wed Apr 16, 2008 6:57 am Post subject: Grommets

I was surprised to find halves of grommets lying on the floor of my  

hangar the other day.  In January, they were installed in the leading  

edge ribs.  It has been too cold here in Toronto to do much work on my  

plane since then.



As far as I can tell, the holes in the aluminum ribs shrunk from the  

cold and cut the grommets in half.  I am glad I found this out before  

pulling all the wires through !



The holes were drilled a hair smaller than the grommets, which fit  

nicely without bunching up.  The holes were carefully deburred and I  

can rotate my finger in the holes without feeling a sharp edge.



The grommets I purchased from Spaenaur rather than the local hardware  

store.  They are specd as material: SBR, hardness: 60 durometer +/-5.



Are these grommets the wrong material ?



Should there be slack around the grommet when fitted in the hole ?



Some other problem I haven't thought of ?



Thanks,



Jeff Page

Dream Aircraft Tundra #10

echristley(at)nc.rr.com
Guest

Posted: Wed Apr 16, 2008 7:32 am Post subject: Grommets

Jeff Page wrote:

 	  Quote: 	
		   



 I was surprised to find halves of grommets lying on the floor of my 

 hangar the other day.  In January, they were installed in the leading 

 edge ribs.  It has been too cold here in Toronto to do much work on my 

 plane since then.



 As far as I can tell, the holes in the aluminum ribs shrunk from the 

 cold and cut the grommets in half.  I am glad I found this out before 

 pulling all the wires through !



 The holes were drilled a hair smaller than the grommets, which fit 

 nicely without bunching up.  The holes were carefully deburred and I 

 can rotate my finger in the holes without feeling a sharp edge.



 The grommets I purchased from Spaenaur rather than the local hardware 

 store.  They are specd as material: SBR, hardness: 60 durometer +/-5.



 Are these grommets the wrong material ?



That would be my guess.  If it was too cold to work on the plane and you 
	


believe the aluminum shrunk, then the grommet were possibly as brittle 

as glass.  One of the techniques for manufacturing rubber bushings is to 

freeze them and then machine them like metal.  They got nice and brittle 

(but probably didn't shrink much), and then the aluminum closed in on 

them.  Probably happened several times.



Try keeping a 60W lightbulb turned on in the plane.

sportav8r(at)gmail.com
Guest

Posted: Wed Apr 16, 2008 7:57 am Post subject: Grommets

60W light bulb isn't going to help much at altitude.  It gets COLD up there.  I'd suggest a re-do with looser holes or different material.  Just my $.02



-Bill B



On Wed, Apr 16, 2008 at 11:27 AM, Ernest Christley <echristley(at)nc.rr.com (echristley(at)nc.rr.com)> wrote:

 [quote]--> AeroElectric-List message posted by: Ernest Christley <echristley(at)nc.rr.com (echristley(at)nc.rr.com)>

  

 Jeff Page wrote:

  	  Quote: 	
		   --> AeroElectric-List message posted by: Jeff Page <jpx(at)Qenesis.com>

 

 I was surprised to find halves of grommets lying on the floor of my hangar the other day.  In January, they were installed in the leading edge ribs.  It has been too cold here in Toronto to do much work on my plane since then.

  

 As far as I can tell, the holes in the aluminum ribs shrunk from the cold and cut the grommets in half.  I am glad I found this out before pulling all the wires through !

 

 The holes were drilled a hair smaller than the grommets, which fit nicely without bunching up.  The holes were carefully deburred and I can rotate my finger in the holes without feeling a sharp edge.

 

 The grommets I purchased from Spaenaur rather than the local hardware store.  They are specd as material: SBR, hardness: 60 durometer +/-5.

 

 Are these grommets the wrong material ?

 

 	
 That would be my guess.  If it was too cold to work on the plane and you believe the aluminum shrunk, then the grommet were possibly as brittle as glass.  One of the techniques for manufacturing rubber bushings is to freeze them and then machine them like metal.  They got nice and brittle (but probably didn't shrink much), and then the aluminum closed in on them.  Probably happened several times.

  

 Try keeping a 60W lightbulb turned on in the plane.

 

 

 

 

 [b]

rob(at)hyperion-ef.com
Guest

Posted: Wed Apr 16, 2008 8:20 am Post subject: Grommets

While not disputing that the grommets failed, I must question your

explanation.  The coefficient of thermal expansion for aluminum alloy 3003

(a common sheet alloy) is 12.9 microinch/inch deg F, so doing the math for a

1 inch diameter hole and a temperature change from a really hot 100 deg F

day for installation and a really cold minus 50 deg F day during the winter

you get a worst case diameter change of slightly less than .002 inch.  A

half inch diameter hole would change less than .001 inch for the same

temperature change.



Installing the grommets into an undersize hole, thus stressing the grommet,

is probably the culprit, not contraction alone.

Best regards,



Rob Housman

Irvine, CA 

Europa XS Tri-Gear

A070

Airframe complete



--

Flagstone(at)cox.net
Guest

Posted: Wed Apr 16, 2008 8:21 am Post subject: Grommets

Jeff:



Your finding has me concerned.  Could you provide the following details:



1 Grommet Dimensions or Spaenaur part #:

    Inside Diameter

    Groove Diameter

    Outside Diameter

    Groove Width

    Overall Thickness



2 Hole Diameter



3 Rib thickness



Were the wires in conduit?  If so what was the outside diameter of the 

conduit.



Do you have a pic of the installed grommet and the split grommet you can 

post?



Thanks



Mark



---

echristley(at)nc.rr.com
Guest

Posted: Wed Apr 16, 2008 8:53 am Post subject: Grommets

Bill Boyd wrote:

 	  Quote: 	
		   60W light bulb isn't going to help much at altitude.  It gets COLD up

 there.  I'd suggest a re-do with looser holes or different material.  Just

 my $.02



   


	


OK.  A 120W bulb.....and a really long drop cord. 8*)

jpx(at)Qenesis.com
Guest

Posted: Thu Apr 17, 2008 5:17 am Post subject: Grommets

Mark,



Here is the link to the grommet info:

http://www.spaenaur.ca/pdf/sectionJ/J69.pdf

The grommets are not all the same size, but most are 315-263.  So the  

groove diameter is 7/16 and I would have drilled 27/64" holes.

I think the ribs are 6061-T6 32 thou.

Unfortunately, I have a bad cold, so I won't be able to visit the  

hangar to take photos.  If you held a grommet in your fingers and  

sliced it vertically with a dull knife, tearing as well as cutting,  

that's what they look like.

I pushed the grommets in when it was about freezing temperature, but  

they were still quite pliable.  They were not difficult to install  

using just my fingers.  It didn't run any wire or conduit in them,  

just left them there.  The frame of the wing is rivetted, but the  

skins are not on it yet.  It is just sitting on the workbench.



As long as the SBR material is considered aviation quality, I expect I  

just need larger holes.



Jeff



 	  Quote: 	
		   Time: 09:21:58 AM PST US

 From: <Flagstone(at)cox.net>

 Subject: Re: Grommets



 Your finding has me concerned.  Could you provide the following details:



 1 Grommet Dimensions or Spaenaur part #:

     Inside Diameter

     Groove Diameter

     Outside Diameter

     Groove Width

     Overall Thickness



 2 Hole Diameter



 3 Rib thickness



 Were the wires in conduit?  If so what was the outside diameter of the

 conduit.



 Do you have a pic of the installed grommet and the split grommet you can

 post?

Bubblehead

Joined: 26 Oct 2007
Posts: 48
Location: N. Richland Hills, TX

Posted: Thu Apr 17, 2008 6:03 am Post subject: Re: Grommets

 	  rob(at)hyperion-ef.com wrote: 	
		  While not disputing that the grommets failed, I must question your

explanation.  The coefficient of thermal expansion for aluminum alloy 3003

(a common sheet alloy) is 12.9 microinch/inch deg F, so doing the math for a

1 inch diameter hole and a temperature change from a really hot 100 deg F

day for installation and a really cold minus 50 deg F day during the winter

you get a worst case diameter change of slightly less than .002 inch.  A

half inch diameter hole would change less than .001 inch for the same

temperature change.



Installing the grommets into an undersize hole, thus stressing the grommet,

is probably the culprit, not contraction alone.

Best regards,



Rob Housman

Irvine, CA 

Europa XS Tri-Gear

A070

Airframe complete



-- 	




Rob - I think you're using the coefficient for the aluminum and then computing the change based on the size of the hole. The change in hole size is because of the change in the aluminum size. 1" or 1/2" hole doesn't matter - only the amount of aluminum around the hole!



Actually, as the aluminum cools wouldn't it contract, making the hole bigger? The temperature would have to rise so the aluminum expands to make the hole smaller. 



My opinion is the bushings got brittle and maybe had flaws or residual stresses that made them break. I doubt change in hole diameter had anything to do with it.



John

_________________
John
Keller, TX
RV-8 N247TD

Flagstone(at)cox.net
Guest

Posted: Thu Apr 17, 2008 6:35 am Post subject: Grommets

Jeff:



That's all I need to work with.  Thanks



Hope you feel better



Mark

---

bob(at)bob-white.com
Guest

Posted: Thu Apr 17, 2008 6:56 am Post subject: Grommets

On Thu, 17 Apr 2008 07:03:17 -0700

"Bubblehead" <jdalman2000(at)yahoo.com> wrote:



<snip>

 	  Quote: 	
		   

 

 Rob - I think you're using the coefficient for the aluminum and then computing the change based on the size of the hole. The change in hole size is because of the change in the aluminum size. 1" or 1/2" hole doesn't matter - only the amount of aluminum around the hole!

 

 Actually, as the aluminum cools wouldn't it contract, making the hole bigger? The temperature would have to rise so the aluminum expands to make the hole smaller. 

 

 My opinion is the bushings got brittle and maybe had flaws or residual stresses that made them break. I doubt change in hole diameter had anything to do with it.

 

 John

 

 --------

 John Dalman

 Elburn, IL

 RV-8 N247TD

 



Hi John,
	




When you're looking at the dimensional change in the material, you have

to look at the overall dimensions of the item.  Say you have a piece of

aluminum 10 inches X 10 inches with a 1 inch dia hole in the center.

If a drop in temperature causes the material to shrink 0.001 inch per

inch (just to pick a number), the new dimensions will be 10 thousandths

less or 9.99 X 9.99 and the inside hole will be .999 inches in dia.

The size of the internal hole will be the same as if the material was

still there.

Bob W. 

-- 

N93BD - Rotary Powered BD-4 - http://www.bob-white.com

3.8 Hours Total Time and holding

Cables for your rotary installation - http://roblinstores.com/cables/

hooverra(at)verizon.net
Guest

Posted: Thu Apr 17, 2008 6:57 am Post subject: Grommets

Jeff,

	Just a guess but exposure to solvents could breakdown SBR. I cannot

imagine that hole size alone is the issue.



http://www.alliedrubber.com/Gasket/SBRRubber.cfm.htm



"When exposed to petroleum derivatives, the performance of this rubber is

inferior to many other synthetics. Red SBR rubber is popular for use as a

gasket in low pressure applications such as washers and gaskets for the

heating and plumbing trades. Black SBR is commonly used for abrasion

conditions such as skirtboard and chute lining."



Ralph & Laura Hoover

RV7A N527LR



--

rob(at)hyperion-ef.com
Guest

Posted: Thu Apr 17, 2008 12:39 pm Post subject: Grommets

I'm glad to hear that I wasn't the only student that did not fall asleep in

freshman physics lecture.

Best regards,



Rob Housman

Irvine, CA 

Europa XS Tri-Gear

A070

Airframe complete



--

bhcishere(at)ca.rr.com
Guest

Posted: Thu Apr 17, 2008 1:00 pm Post subject: Grommets

Heat makes the hole bigger.  Haven't you ever had to remove a stubborn bolt? 

That is done with a torch to make the hole bigger.



Bryan



---

mrspudandcompany(at)veriz
Guest

Posted: Fri Apr 18, 2008 4:17 am Post subject: Grommets

[quote]Jeff, Unless you live on the South Pole in the middle of winter, there is no way that normal grommets, as you described them, will just split apart and fall off!!  The expansion/contraction of the aluminum is so small as to not be a factor. Are you sure someone didn’t cut them off, just to play a mind game with you?? Roger   [b]--

jpx(at)Qenesis.com
Guest

Posted: Fri Apr 18, 2008 6:36 am Post subject: Grommets

AeroElectric-List Digest Server <aeroelectric-list(at)matronics.com> wrote:



[quote] *



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                      Total Messages Posted Thu 04/17/08: 22

            ----------------------------------------------------------

 Today's Message Index:

 ----------------------



      1. 04:49 AM - Re: Ground Power - Z31A  (Robert L. Nuckolls, III)

      2. 04:56 AM - Re: Re: Rear Mounted Batteries - more questions    

 (Robert L. Nuckolls, III)

      3. 05:49 AM - "Chubby" wires and fuseblocks  (Robert L. Nuckolls, III)

      4. 06:13 AM - Switch ratings   (Robert L. Nuckolls, III)

      5. 06:17 AM - Re: Grommets  (Jeff Page)

      6. 07:06 AM - Re: Grommets  (Bubblehead)

      7. 07:35 AM - Re: Re: Grommets  ()

      8. 07:56 AM - Re: Re: Grommets  (Bob White)

      9. 07:57 AM - Re: Grommets  (RALPH HOOVER)

     10. 01:39 PM - Re: Re: Grommets  (Rob Housman)

     11. 02:00 PM - Re: Re: Grommets  (Bryan)

     12. 02:14 PM - Thermal expansion (was Grommets)  (raymondj)

     13. 03:12 PM - Re: Rear Mounted Batteries - more questions  (n277dl)

     14. 05:44 PM - A Bit of Help, Please  (Speedy11(at)aol.com)

     15. 06:44 PM - Re: A Bit of Help, Please  (Joemotis(at)aol.com)

     16. 06:55 PM - Questions on avionics  ()

     17. 07:13 PM - pinout for Softcom ATC-P intercom??  (Charlie England)

     18. 07:22 PM - Re: A Bit of Help, Please  (Robert L. Nuckolls, III)

     19. 07:42 PM - Re: Re: Transponder for sale (mode S)  (Charlie England)

     20. 07:48 PM - Re: Questions on avionics  (Ernest Christley)

     21. 08:28 PM - Re: Questions on avionics  (Mike)

     22. 08:34 PM - Re: Questions on avionics  (Mike)



 ________________________________  Message 1    

 _____________________________________

 Time: 04:49:12 AM PST US

 From: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>

 Subject: Re: Ground Power - Z31A

 At 11:38 PM 4/16/2008 +0200, you wrote:



>

> Bob

>

> Please can you confirm the correct procedure for using the ground power on

> Z31a architecture.

>

> Is it imperative to first switch on the "ground power" switch, before

> switching on the master switch?



    No. The ground power may be turned on at any time in the

    starting sequence without regard to damage to the system.

    The ground power circuits as depicted are reverse polarity

    and ov protected . . .



> Would I just switch ground power off, once the aircraft has started?



    Yes.

> What would happen if ground power switch was inadvertantly left on for an

> indefinite period, or turned on whilst the aircraft engine was running?



    No big deal. IF the ground power source voltage was set

    higher than your ship's regulator, your alternator

    would not come on line and pick up system loads as long

    as the ground power was connected. If you're getting a

    start from a battery cart - as ship's systems came

    alive, your ship's alternator would begin to charge/

    re-charge ALL batteries in the system . . . including those

    in a still connected ground power cart.



    If you're using external power from an engine driven or

    AC mains powered cart, then would would expect the external

    voltage source to be set at "battery charging" voltage

    levels (14.2 or 28.5). In this case, you could turn on

    ground power long before closing the master switch and

    let ground power replenish you ship's battery. After

    15 minutes or so, your ship's battery may well contain

    sufficient snort to start your engine and ground power

    could be disconnected for the start an subsequent

    pre-flight. If the ground power is a battery cart,

    then no charging of the ship's battery can take place

    and you're obligated to use ground power to get the

    engine started. After starting, you'd want to turn

    ground power off so that ALL of your ship's alternator

    output was being used to replenish stored energy in

    the ship's battery.



    In cold weather, you may wish to use ground power

    as a routine assist for getting the engine

    started even if your battery is in good shape.



    Aside from the possibility of too much ground power

    voltage and/or reversed polarity, there are no risks to

    your airplane's systems that warrant concern. Making

    ground power managed from the pilot's seat

    puts you in control of this resource for the purpose

    of addressing the task at hand.



    It's an energy management problem with solutions

    determined by equipment available, condition of

    your battery and immediate goals. I recall reading

    a story many moons ago where a pilot used his ground

    power jumper cables to get his car started using

    his airplane's battery after returning from a trip

    and finding the car battery was not up to the task.



> Your assistance as always is appreciated.



    Pleased to be of service sir!



    Bob . . .

 ________________________________  Message 2    

 _____________________________________

 Time: 04:56:17 AM PST US

 From: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>

 Subject: Re: Re: Rear Mounted Batteries - more   questions

 At 02:54 PM 4/16/2008 -0700, you wrote:



>

> Bob and list,

>    Using the previously attached document as reference...

>

> Assumptions... rear mounted batteries.  Main Bat Cntctr, Aux  Bat cntctr

> and Xfeed Cntctr all mounted in rear beside the batteries.



     Hmmmm . . . normally we'd like to see the cross-feed contactor

     mounted on the firewall. This provides nice fat-wire terminals

     from both batteries to serve as distribution points for the

     two batteries in addressing their respective tasks.



>  2awg ground wire to fwd central gnd bus attached to the engine via stud

> through firewall. XFEED cnctr closed for starting.  2AWG wire from the

> same side of XFEED cntctr that the main bat cntctr is connected to

> starter cntctr.



      Okay . . .



> Questions.... Can I then run appropriate sized wire (tbd) from the same

> side of the starter cntctr as the 2awg wire is attached to the main pwr bus?



      Yes. If your cross-feed contactor were up front

      then the battery distribution tie point would be

      on the cross-feed contactor. With the configuration

      you've described, then the starter contactor becomes

      the tie point.

> If so, I also assume I would run appropriate sized wire ~8-10 awg (but not

> the heavy 2awg) from aux bat side of the XFEED to the Aux bus and use same

> wire to from the aux alt (prob 8 amp b&C alternator).



      Oops . . . sounds like you're describing a Z-14

      architecture using an SD-8 on the aux side. Not

      recommended due to aux battery contactor loads being

      such a significant portion of the SD-8's output.

      Suggest a Z-13 architecture is more appropriate to

      maximizing the capabilities of the SD-8.

> Hope this makes sense.  Really just trying to understand if I can only run

> two fat wires from the batteries to the firewall if I want to ground at

> the firewall  or need to pull the extra "hot fat wire".



      Let's talk about your architecture and choices

      of hardware to fill the various slots. What

      shortcomings do you perceive with a Z-13 architecture

      that drives you toward dual batteries?



      Bob . . .

         ----------------------------------------)

         ( . . .  a long habit of not thinking   )

         ( a thing wrong, gives it a superficial )

         ( appearance of being right . . .       )

         (                                       )

         (                  -Thomas Paine 1776-  )

         ----------------------------------------

 ________________________________  Message 3    

 _____________________________________

 Time: 05:49:19 AM PST US

 From: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>

 Subject: "Chubby" wires and fuseblocks



> Comments/Questions: I dont' undestand how to connect large current loads

> to FASTON fuse blocks.

>

> Max wire into FASTON seems to be #10

>

> Fuses up 30A are sold by B&C

>

> Most #10 wire is not rated for 30A.



     I don't know of any #10 wire that is not rated for

     30A in airplanes.

> What am I missing?

>



    I don't recommend any fuses beyond 14AWG/15A be used

    in the fuse blocks. What systems are you wiring

    that demand the use of larger wire/fuses?



         Bob . . .



         ----------------------------------------)

         ( . . .  a long habit of not thinking   )

         ( a thing wrong, gives it a superficial )

         ( appearance of being right . . .       )

         (                                       )

         (                  -Thomas Paine 1776-  )

         ----------------------------------------

 ________________________________  Message 4    

 _____________________________________

 Time: 06:13:51 AM PST US

 From: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>

 Subject: Switch ratings



> Comments/Questions: Hi Bob,

>

> Re: S700-2-10 switch

>

> What is the current rating for this switch?



    The S700 series switches are Carling G-series devices.

    The data sheet for this line of products may be reviewed

    at:



 http://www.aeroelectric.com/Mfgr_Data/Switches/Carling_G-series.pdf



    Note that these are rated at up to 20A in 120VAC systems.

    In the article at:



 http://aeroelectric.com/articles/Switch_Ratings.pdf



    we explore the simple ideas behind current ratings

    and service life of switches as installed in various

    working environments.



> I would like to use this switch to turn on rotating beacons (12 amps) and

> strobe lights (11 amps) using the circuit in figure 11-18 (page 11-19) in

> the 11th edition of your book. The B&C catalog lists the rating as '15VAC

> maximum'. How does this rating apply to a 14 volt system?

> My application would run 23 amps through the switch. Will the switch

> handle this load?



    Yes, you'll probably get a satisfactory service life

    using the S700-2-10 for this application. But I'm curious

    as to where you got these current values. I'm also curious

    as to why you have a combination of strobes and rotating

    beacons on the same airplane.



         Bob . . .



         ----------------------------------------)

         ( . . .  a long habit of not thinking   )

         ( a thing wrong, gives it a superficial )

         ( appearance of being right . . .       )

         (                                       )

         (                  -Thomas Paine 1776-  )

         ----------------------------------------

 ________________________________  Message 5    

 _____________________________________

 Time: 06:17:15 AM PST US

 From: Jeff Page <jpx(at)Qenesis.com>

 Subject: Re: Grommets

 Mark,



 Here is the link to the grommet info:

 http://www.spaenaur.ca/pdf/sectionJ/J69.pdf

 The grommets are not all the same size, but most are 315-263.  So the

 groove diameter is 7/16 and I would have drilled 27/64" holes.

 I think the ribs are 6061-T6 32 thou.

 Unfortunately, I have a bad cold, so I won't be able to visit the

 hangar to take photos.  If you held a grommet in your fingers and

 sliced it vertically with a dull knife, tearing as well as cutting,

 that's what they look like.

 I pushed the grommets in when it was about freezing temperature, but

 they were still quite pliable.  They were not difficult to install

 using just my fingers.  It didn't run any wire or conduit in them,

 just left them there.  The frame of the wing is rivetted, but the

 skins are not on it yet.  It is just sitting on the workbench.



 As long as the SBR material is considered aviation quality, I expect I

 just need larger holes.



 Jeff



> Time: 09:21:58 AM PST US

> From: <Flagstone(at)cox.net>

> Subject: Re: Grommets

>

> Your finding has me concerned.  Could you provide the following details:

>

> 1 Grommet Dimensions or Spaenaur part #:

>     Inside Diameter

>     Groove Diameter

>     Outside Diameter

>     Groove Width

>     Overall Thickness

>

> 2 Hole Diameter

>

> 3 Rib thickness

>

> Were the wires in conduit?  If so what was the outside diameter of the

> conduit.

>

> Do you have a pic of the installed grommet and the split grommet you can

> post?

 ________________________________  Message 6    

 _____________________________________

 Time: 07:06:31 AM PST US

 Subject: Re: Grommets

 From: "Bubblehead" <jdalman2000(at)yahoo.com>



 rob(at)hyperion-ef.com wrote:

> While not disputing that the grommets failed, I must question your

> explanation.  The coefficient of thermal expansion for aluminum alloy 3003

> (a common sheet alloy) is 12.9 microinch/inch deg F, so doing the math for a

> 1 inch diameter hole and a temperature change from a really hot 100 deg F

> day for installation and a really cold minus 50 deg F day during the winter

> you get a worst case diameter change of slightly less than .002 inch.  A

> half inch diameter hole would change less than .001 inch for the same

> temperature change.

>

> Installing the grommets into an undersize hole, thus stressing the grommet,

> is probably the culprit, not contraction alone.

> Best regards,

>

> Rob Housman

> Irvine, CA

> Europa XS Tri-Gear

> A070

> Airframe complete

>

> --

 Rob - I think you're using the coefficient for the aluminum and then  

  computing

 the change based on the size of the hole. The change in hole size is  

  because of

 the change in the aluminum size. 1" or 1/2" hole doesn't matter -   

 only the amount

 of aluminum around the hole!



 Actually, as the aluminum cools wouldn't it contract, making the   

 hole bigger? The

 temperature would have to rise so the aluminum expands to make the   

 hole smaller.

 My opinion is the bushings got brittle and maybe had flaws or   

 residual stresses

 that made them break. I doubt change in hole diameter had anything to do with

 it.



 John



 --------

 John Dalman

 Elburn, IL

 RV-8 N247TD

 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=177406#177406

 ________________________________  Message 7    

 _____________________________________

 Time: 07:35:53 AM PST US

 From: <Flagstone(at)cox.net>

 Subject: Re: Re: Grommets

 Jeff:



 That's all I need to work with.  Thanks



 Hope you feel better



 Mark

 ---

jpx(at)Qenesis.com
Guest

Posted: Fri Apr 18, 2008 6:46 am Post subject: Grommets

In this case, the grommets were not exposed to anything other than  

temperature change.  I took them out of the box, installed them in the  

ribs and let them wait in the cold until things warmed up and I could  

continue my work.



The rubber is soft enough that I think the holes would have to become  

dramatically smaller to cut the grommets.



Since 15 or 20 of them were halved, I don't think it is just a  

defective grommet.  I will be inspecting all the rest when I get back  

to the hangar.



Assuming I started cuts in the grooves during installation, I still  

wouldn't expect to find them in half on the floor 



Jeff

 	  Quote: 	
		   Jeff,

 	Just a guess but exposure to solvents could breakdown SBR. I cannot

 imagine that hole size alone is the issue.



 http://www.alliedrubber.com/Gasket/SBRRubber.cfm.htm



 "When exposed to petroleum derivatives, the performance of this rubber is

 inferior to many other synthetics. Red SBR rubber is popular for use as a

 gasket in low pressure applications such as washers and gaskets for the

 heating and plumbing trades. Black SBR is commonly used for abrasion

 conditions such as skirtboard and chute lining."



 Ralph & Laura Hoover

 RV7A N527LR

n801bh(at)NetZero.com
Guest

Posted: Fri Apr 18, 2008 1:54 pm Post subject: Grommets

I will chime in and comment.... This is really hard to believe they split all by themselves. Are you sure someone didn't remove them and split them with a razor and them drop them on the floor as a joke/ prank etc...

Ben Haas

N801BH

www.haaspowerair.com



-- Jeff Page <jpx(at)Qenesis.com> wrote:

--> AeroElectric-List message posted by: Jeff Page <jpx(at)Qenesis.com>



In this case, the grommets were not exposed to anything other than  

temperature change.  I took them out of the box, installed them in the  

ribs and let them wait in the cold until things warmed up and I could  

continue my work.



The rubber is soft enough that I think the holes would have to become  

dramatically smaller to cut the grommets.



Since 15 or 20 of them were halved, I don't think it is just a  

defective grommet.  I will be inspecting all the rest when I get back  

to the hangar.



Assuming I started cuts in the grooves during installation, I still  

wouldn't expect to find them in half on the floor 



Jeff

 	  Quote: 	
		   Jeff,

 Just a guess but exposure to solvents could breakdown SBR. I cannot

 imagine that hole size alone is the issue.



 http://www.alliedrubber.com/Gasket/SBRRubber.cfm.htm



 "When exposed to petroleum derivatives, the performance of this rubber is

 inferior to many other synthetics. Red SBR rubber is popular for use as a

 gasket in low pressure applications such as washers and gaskets for the

 heating and plumbing trades. Black SBR is commonly used for abrasion

 conditions such as skirtboard and chute lining."



 Ralph & Laura Hoover

 RV7A N527L========================;        - The AeroElectric-List===============================================================================================


	


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   [quote][b]

jpx(at)Qenesis.com
Guest

Posted: Sat Apr 19, 2008 7:10 pm Post subject: Grommets

Two of you both thought my grommet problem so absurd that it must be a prank.

I wish that were true, but my T hangar is locked.

They were exposed only to cold air, darkness, time and my installation.

When I get to the hangar next, i will be taking a close look at all of  

them, to see if the ones remaining are partly torn, or if some of them  

are perfectly intact.

I will also try to do some tests with some still in the box to see if  

I can tear them like that.

Sure is weird though.  We install grommets to protect the wires, so  

they should be tougher than the insulation.



Jeff



 	  Quote: 	
		   Are you sure someone didn't cut them off, just to play a mind game with

 you??



 Roger


	


 	  Quote: 	
		  > 	Just a guess but exposure to solvents could breakdown SBR. I cannot

> imagine that hole size alone is the issue.

 I will chime in and comment.... This is really hard to believe they spli

 t all by themselves. Are you sure someone didn't remove them and split t

 hem with a razor and them drop them on the floor as a joke/ prank etc...



 Ben Haas

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sun Apr 20, 2008 4:59 am Post subject: Re: Grommets

Holes and temperature had nothing to do with it. Extract from:

http://www.alliedrubber.com/Gasket/SBRRubber.cfm.htm



Neoprene is known for its resistance to oil, gasoline, sunlight, ozone and oxidation; however, there are other polymers that have better resistance to these same elements. Neoprene's most important advantage is its ability to combine these properties moderately into one all-purpose polymer. 

Resistance to corrosive actions of chemicals is good. Neoprene exhibits resilience, tensile strength, tear resistance and dynamic properties; abrasion resistance and compression set properties.



COLOR Black

DURO 40,50,60,70,80

TENSILE900

ELONGATION300%

TEMP-20°F to 170°F

OIL RESIST Good



Nitrile's (Buna-N) resistance to the more aromatic distillates of petroleum is better than neoprene, and it exhibits excellent resistance to mineral and vegetable oils, but relatively poor resistance to the swelling action of oxygenated solvents such as acetone and the ketones. Resistance to heat aging is good. 

Nitrile exhibits good resilience, low permanent set, good abrasion resistance and some ozone resistance. Tear resistance is inferior to natural rubber.

Nitrile accommodates applications where oils and heat are prevalent.



COLOR Black/ White

DURO 60

TENSILE300

ELONGATION900%

TEMP-20°F to 170°F

OIL RESIST. Good



SBR: Certain types of SBR offer improved wear resistance in tire treads while others provide better low temperature flexibility. SBR has similar resistance to solvents and chemicals as natural rubber and it can be successfully bonded to a wide range of materials. 

When exposed to petroleum derivatives, the performance of this rubber is inferior to many other synthetics. Red SBR rubber is popular for use as a gasket in low pressure applications such as washers and gaskets for the heating and plumbing trades. 



COLOR Red/Black

DURO 75

TENSILE400

ELONGATION150%

TEMP-29°F to 170°F

OIL RESIST. None  [This should be a clue]



Summary. SBR should NEVER be used for grommets near petroleum vapors, oils  or solvents.



General advice: It is always a surprise when modern materials fail. Companies spend a lot of money to prevent problems like this, and even materials "not recommended" for an application usually don't fail quickly. But beware inexpensive materials made for specific applications not-your-own. Surprises happen. Things break.



"In times of rapid change, experience could be your worst enemy."

---Jean Paul Getty

_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

klehman(at)albedo.net
Guest

Posted: Sun Apr 20, 2008 5:50 am Post subject: Grommets

Another product that may be suitable is the plastic snap bushings such 

as Spruce 04-05730. I never liked putting soft grommets from any source 

in very thin metal.

Ken

Jeff Page wrote:

 	  Quote: 	

 Two of you both thought my grommet problem so absurd that it must be a 

 prank.

 I wish that were true, but my T hangar is locked.

 They were exposed only to cold air, darkness, time and my installation.

 When I get to the hangar next, i will be taking a close look at all of 

 them, to see if the ones remaining are partly torn, or if some of them 

 are perfectly intact.

 I will also try to do some tests with some still in the box to see if I 

 can tear them like that.

 Sure is weird though.  We install grommets to protect the wires, so they 

 should be tougher than the insulation.

 Jeff

> Are you sure someone didn't cut them off, just to play a mind game with

> you??

>

> Roger

>>     Just a guess but exposure to solvents could breakdown SBR. I cannot

>> imagine that hole size alone is the issue.

> I will chime in and comment.... This is really hard to believe they spli

> t all by themselves. Are you sure someone didn't remove them and split t

> hem with a razor and them drop them on the floor as a joke/ prank etc...

>

> Ben Haas

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