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Oil Canning

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ron.mcgann(at)baesystems.
Guest

Posted: Mon Sep 17, 2007 3:09 am Post subject: Oil Canning

Hey all,

 

 Getting to the final assembly stage.  I pulled out the VS that was completed over 3 years ago.  Did not know any better at the time and thought my first airplane part was just fine.  But there is significant oil canning on both of the large aft-lower panels.  The only other oil canning I have is very minor on one or two of the lower wing skin panels, so the VS is really giving me the irrits.  Any clues on how to tighten the skins?

 

 cheers,

 Ron

 187 finishing     [quote][b]

ron.mcgann(at)baesystems.
Guest

Posted: Tue Sep 18, 2007 3:00 pm Post subject: Oil Canning

Zero responses. Searched the RV-10 archives and there is  very little there.  I guess I can only assume that no other RV-10  builder has any oil canning.  The general RV archives are only a little  more enlightening.  

  

 What happened to the  good old days - when a basic building query met with half a dozen or more  immediate useful suggestions?    I hope the list has not not  exhausted itself as a resource for builder  assistance.

  

 I know oil canning is common on all metal aircraft, but  I am interested in solutions that the -10 crowd may have deployed  to reduce or eliminate the problem - unless of course I am the ONLY  crappy builder with oil canning.

  

 cheers,

 Ron

 187  finishing 



 [quote]         From: owner-rv10-list-server(at)matronics.com    [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of McGANN,    Ron

Sent: Monday, 17 September 2007 8:38 PM

To:    rv10-list(at)matronics.com

Subject: Oil    Canning

   



   

Hey all,



Getting to the final assembly stage.  I    pulled out the VS that was completed over 3 years ago.  Did not know any    better at the time and thought my first airplane part was just fine.  But    there is significant oil canning on both of the large aft-lower panels.     The only other oil canning I have is very minor on one or two of the lower    wing skin panels, so the VS is really giving me the irrits.  Any clues on    how to tighten the skins?



cheers,

Ron

187 finishing  	  Quote: 	
		  



href="http://www.matronics.com/Navigator?RV10-List">http://www.matronics.com/Navigator?RV10-List

href="http://forums.matronics.com">http://forums.matronics.com



	
[b]

Jack.Phillips(at)cardinal
Guest

Posted: Tue Sep 18, 2007 3:09 pm Post subject: Oil Canning

No, you're not the only one.  When I mounted my  horizontal stabilizer on the tail cone I found a couple of areas that weren't as  tight as the rest.  I've been watching to see what response you  get.

  

 Jack Phillips

 #40610



   From: owner-rv10-list-server(at)matronics.com  [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of McGANN,  Ron

Sent: Tuesday, September 18, 2007 7:00 PM

To:  rv10-list(at)matronics.com

Subject: RE: Oil  Canning

 

 Zero responses. Searched the RV-10 archives and there is  very little there.  I guess I can only assume that no other RV-10  builder has any oil canning.  The general RV archives are only a little  more enlightening.  

  

 What happened to the  good old days - when a basic building query met with half a dozen or more  immediate useful suggestions?    I hope the list has not not  exhausted itself as a resource for builder  assistance.

  

 I know oil canning is common on all metal aircraft, but  I am interested in solutions that the -10 crowd may have deployed  to reduce or eliminate the problem - unless of course I am the ONLY  crappy builder with oil canning.

  

 cheers,

 Ron

 187  finishing 



 [quote]         From: owner-rv10-list-server(at)matronics Ecom    [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of McGANN,    Ron

Sent: Monday, 17 September 2007 8:38 PM

To:    rv10-list(at)matronics.com

Subject: Oil    Canning

   



   

Hey all,



Getting to the final assembly stage.  I    pulled out the VS that was completed over 3 years ago.  Did not know any    better at the time and thought my first airplane part was just fine.  But    there is significant oil canning on both of the large aft-lower panels.     The only other oil canning I have is very minor on one or two of the lower    wing skin panels, so the VS is really giving me the irrits.  Any clues on    how to tighten the skins?



cheers,

Ron

187 finishing  	  Quote: 	
		  



href="http://www.matronics.com/Navigator?RV10-List">http://www.matronics.com/Navigator?RV10-List

href="http://forums.matronics.com">http://forums.matronics.com



	




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[b]

DAVELEIKAM(at)wi.rr.com
Guest

Posted: Tue Sep 18, 2007 3:52 pm Post subject: Oil Canning

I have an area on one elevator with a lose  skin.  I went to see my tech counselors RV-6 and he had a few of the same  in different sections.  He said it happens and if it is not dramatic,  not to worry.  Sorry, I can't offer more info.

  

 Dave Leikam

 40496  

 Wing guts

  

 [quote]   ---

jeff(at)westcottpress.com
Guest

Posted: Tue Sep 18, 2007 4:02 pm Post subject: Oil Canning

Hi Ron,

I've got quite a bit of oil canning in my elevators.  My tech counselor shrugged and said don't worry about it... but I'm not happy with it and may re do those parts if I've got some time to kill while waiting on panel parts.



I showed it to a cousin of mine who's done repair work on Airforce 1.  He suggested drilling a hole in the middle of it, dimpling and flush riveting the hole.



I've not tried it... can't tell you if it works... but if you do, and it does... please let me know.



Jeff Carpenter

40304

N410CF

On Sep 18, 2007, at 3:59 PM, McGANN, Ron wrote:

[quote]  Zero responses. Searched the RV-10 archives and there is very little there.  I guess I can only assume that no other RV-10 builder has any oil canning.  The general RV archives are only a little more enlightening.  

  

 What happened to the good old days - when a basic building query met with half a dozen or more immediate useful suggestions?    I hope the list has not not exhausted itself as a resource for builder assistance.

  

 I know oil canning is common on all metal aircraft, but I am interested in solutions that the -10 crowd may have deployed to reduce or eliminate the problem - unless of course I am the ONLY crappy builder with oil canning.

  

 cheers,

 Ron

 187 finishing 



  	  Quote: 	
		        From: owner-rv10-list-server(at)matronics.com   [mailto:owner-rv10-list-server(at)matronics.com (owner-rv10-list-server(at)matronics.com)] On Behalf Of McGANN,   Ron

Sent: Monday, 17 September 2007 8:38 PM

To:   rv10-list(at)matronics.com (rv10-list(at)matronics.com)

Subject: Oil   Canning

  

Hey all,



Getting to the final assembly stage.  I   pulled out the VS that was completed over 3 years ago.  Did not know any   better at the time and thought my first airplane part was just fine.  But   there is significant oil canning on both of the large aft-lower panels.    The only other oil canning I have is very minor on one or two of the lower   wing skin panels, so the VS is really giving me the irrits.  Any clues on   how to tighten the skins?



cheers,

Ron

187 finishing  	  Quote: 	
		  

href="http://www.matronics.com/Navigator?RV10-List">http://www.matronics.com/Navigator?RV10-List

href="http://forums.matronics.com">http://forums.matronics.com



	


href="http://www.matronics.com/Navigator?RV10-List">http://www.matronics.com/Navigator?RV10-List

href="http://forums.matronics.com">http://forums.matronics.com



	
[b]

EFDsteve(at)aol.com
Guest

Posted: Tue Sep 18, 2007 4:20 pm Post subject: Oil Canning

Dan Checkoway has something on his RV-7 site about this.  He just used  some RTV to attach some pieces of "J" channel to the inside of the  tailcone, between the ribs to stiffen the skins.  His entry on this is  Sept. 2, 2005.

  

 Steve Weinstock

 40230

  

 In a message dated 9/18/2007 6:12:04 P.M. Central Daylight Time,  Jack.Phillips(at)cardinalhealth.com writes:

  	  Quote: 	
		     No, you're not the only one.  When I mounted my    horizontal stabilizer on the tail cone I found a couple of areas that weren't    as tight as the rest.  I've been watching to see what response you    get.

    

   Jack Phillips

   #40610



         From: owner-rv10-list-server(at)matronics.com    [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of McGANN,    Ron

Sent: Tuesday, September 18, 2007 7:00 PM

To:    rv10-list(at)matronics.com

Subject: RE: Oil    Canning

   

   Zero responses. Searched the RV-10 archives and there is    very little there.  I guess I can only assume that no other RV-10    builder has any oil canning.  The general RV archives are only a little    more enlightening.  

    

   What happened to the    good old days - when a basic building query met with half a dozen or more    immediate useful suggestions?    I hope the list has not not    exhausted itself as a resource for builder    assistance.

    

   I know oil canning is common on all metal aircraft,    but I am interested in solutions that the -10 crowd may have deployed    to reduce or eliminate the problem - unless of course I am the ONLY    crappy builder with oil canning.

    

   cheers,

   Ron

   187    finishing 



    	  Quote: 	
		                 From: owner-rv10-list-server(at)matronics.com      [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of McGANN,      Ron

Sent: Monday, 17 September 2007 8:38 PM

To:      rv10-list(at)matronics.com

Subject: Oil      Canning

     



     

Hey all,



Getting to the final assembly stage.  I      pulled out the VS that was completed over 3 years ago.  Did not know      any better at the time and thought my first airplane part was just      fine.  But there is significant oil canning on both of the large      aft-lower panels.  The only other oil canning I have is very minor on      one or two of the lower wing skin panels, so the VS is really giving me the      irrits.  Any clues on how to tighten the      skins?



cheers,

Ron

187 finishing  	  Quote: 	
		  

	
	
	


 

  



See what's new="_blank">Make AOL Your Homepage.

  [quote][b]

DLIUDVINAITIS(at)aol.com
Guest

Posted: Tue Sep 18, 2007 6:08 pm Post subject: Oil Canning

Ron,

 I myself have not had any signs of oil canning. Have done my Hs,  wings, Vs, tailcone 1.5 years ago still have not seen any.  Maybe when  you were assembling Hs, wings, Vs, etc. you started at the ends and worked  riveting inward towards centers.   I myself started in center of  assembles and worked outward this I thought  would help by letting metal  shrink/strech outwards towards the ends of assembles. worked for me I  have no oil canning visible as for solving problem. shrinking  metal/streching I would go with tech recommendations an/or move on and keep  building.

  

 Dave Liudvinaitis

 #40466

 fuselage, side skins 



Make AOL Your Homepage.

ron.mcgann(at)baesystems.
Guest

Posted: Tue Sep 18, 2007 6:43 pm Post subject: Oil Canning

Thanks all for the  responses.  

  

 As mentioned, I am at the  stages of final assembly and the vast majority of panels are tighter than a  drum.  I religiously started riveting from the centre and worked towards  the edges - as you have done Dave.  On perhaps a handful of panels,  the skin is not quite so tight and exhibits a slight 'wobble' when pressed in  just the right spot, but the skin always recovers to the  relaxed condition.  The VS is just way too loose in my mind and needs  to be tightened.   I have heard other descriptions of oil canning  as the skin popping out when pressed in a particular place - and staying there  until pressed again. Am I confusing some flex in the panels with something  more insidious?

  

 cheers,

 Ron

 



 [quote]         From: owner-rv10-list-server(at)matronics.com    [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of    DLIUDVINAITIS(at)aol.com

Sent: Wednesday, 19 September 2007 11:37    AM

To: rv10-list(at)matronics.com

Subject: Re: Oil    Canning

   

   Ron,

   I myself have not had any signs of oil canning. Have done my Hs,    wings, Vs, tailcone 1.5 years ago still have not seen any.  Maybe    when you were assembling Hs, wings, Vs, etc. you started at the ends and    worked riveting inward towards centers.   I myself started in    center of assembles and worked outward this I thought  would help by    letting metal shrink/strech outwards towards the ends of    assembles. worked for me I have no oil canning visible as for    solving problem. shrinking metal/streching I would go with tech    recommendations an/or move on and keep building.

    

   Dave Liudvinaitis

   #40466

   fuselage, side skins 



         Make AOL Your Homepage.

 	  Quote: 	
		  



href="http://www.matronics.com/Navigator?RV10-List">http://www.matronics.com/Navigator?RV10-List

href="http://forums.matronics.com">http://forums.matronics.com



	
[b]

Tim Olson

Joined: 25 Jan 2007
Posts: 2881

Posted: Tue Sep 18, 2007 7:13 pm Post subject: Oil Canning

Well, when there's so much stress that it goes "pop pop" as you

press and release, where it makes a concave and then when you

push opposite, it "pops" loudly out, then I'd think it might

be worth doing something about.  The skin will have areas

where it will flex some though, and although I'm not addressing

any known engineering things on this plane or any other, I'm guessing

that you don't want it always stretched super tight, as wings and

surfaces need to flex.  Maybe John can comment a bit.  If you do

have a section oil canning, and it can't be easily fixed by some

riveting, it may be time for taking one of a few measures.  I've heard

of stiffners either being riveted in or prosealed in.  The access area

around my stall warning plate got oil-canning like that.  I added

stiffners in that particular area around the hole...2 of them, one

in each direction.  That took care of it.  But, I'm cautious to offer

that as general advice, because I'm sure there are some areas where

adding stiffners might make things too...well...stiff.



I'm not sure that the list can give a definite answer on it, and it's

something that either might be best referred to a tech counselor

locally, or played by "ear" (with the popping noise).  That's probably

why you didn't get quick answers....most people are just waiting to

hear what someone has to say, because the exact magnitude isn't known

without standing there by it.



Sorry, I know that didn't help, but it was a shot.



Tim Olson - RV-10 N104CD - Flying



McGANN, Ron wrote:

 	  Quote: 	
		   Thanks all for the responses. 

  

 As mentioned, I am at the stages of final assembly and the vast majority 

 of panels are tighter than a drum.  I religiously started riveting from 

 the centre and worked towards the edges - as you have done Dave.  On 

 perhaps a handful of panels, the skin is not quite so tight and exhibits 

 a slight 'wobble' when pressed in just the right spot, but the skin 

 always recovers to the relaxed condition.  The VS is just way too loose 

 in my mind and needs to be tightened.   I have heard other descriptions 

 of oil canning as the skin popping out when pressed in a particular 

 place - and staying there until pressed again. Am I confusing some flex 

 in the panels with something more insidious?

  

 cheers,

 Ron

 

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

     *From:* owner-rv10-list-server(at)matronics.com

     [mailto:owner-rv10-list-server(at)matronics.com] *On Behalf Of

     *DLIUDVINAITIS(at)aol.com

     *Sent:* Wednesday, 19 September 2007 11:37 AM

     *To:* rv10-list(at)matronics.com

     *Subject:* Re: Oil Canning

 

     Ron,

     I myself have not had any signs of oil canning. Have done my Hs,

     wings, Vs, tailcone 1.5 years ago still have not seen any.  Maybe

     when you were assembling Hs, wings, Vs, etc. you started at the ends

     and worked riveting inward towards centers.   I myself started in

     center of assembles and worked outward this I thought  would help by

     letting metal shrink/strech outwards towards the ends of

     assembles. worked for me I have no oil canning visible as for

     solving problem. shrinking metal/streching I would go with tech

     recommendations an/or move on and keep building.

      

     Dave Liudvinaitis

     #40466

     fuselage, side skins 

 

 

 

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

     Make AOL Your Homepage.

 

     *

 

     href="http://www.matronics.com/Navigator?RV10-List">http://www.matronics.com/Navigator?RV10-List

     href="http://forums.matronics.com">http://forums.matronics.com

 

     *

acs(at)acspropeller.com.a
Guest

Posted: Wed Sep 19, 2007 12:10 am Post subject: Oil Canning

Ron, I had a similar problem with the VS but it occurred whilst I was adjusting nose ribs for a better fit (previous well known issue) and I was introducing a twist whilst trying to tighten the skin. Relaxed the shape and allowed the natural form to dictate the lay up without putting too much pressure on the fit. The skin should “suck” into the airflow in any case and unless it drums should not be an issue.  

Otherwise you could always shove in a packet of self-expanding packaging foam!  

John 40315   

Do not archive and I in no way endorse inflatable RV-10’s  

     

   

        

  

From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of McGANN, Ron

 Sent: Wednesday, 19 September 2007 12:41 PM

 To: rv10-list(at)matronics.com

 Subject: RE: Oil Canning  

  

   

Thanks all for the responses.    

   

As mentioned, I am at the stages of final assembly and the vast majority of panels are tighter than a drum.  I religiously started riveting from the centre and worked towards the edges - as you have done Dave.  On perhaps a handful of panels, the skin is not quite so tight and exhibits a slight 'wobble' when pressed in just the right spot, but the skin always recovers to the relaxed condition.  The VS is just way too loose in my mind and needs to be tightened.   I have heard other descriptions of oil canning as the skin popping out when pressed in a particular place - and staying there until pressed again. Am I confusing some flex in the panels with something more insidious?    

   

    

cheers,  

    

Ron  

  

    	  Quote: 	
		        

  

From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of DLIUDVINAITIS(at)aol.com

 Sent: Wednesday, 19 September 2007 11:37 AM

 To: rv10-list(at)matronics.com

 Subject: Re: Oil Canning    

Ron,  

    

I myself have not had any signs of oil canning. Have done my Hs, wings, Vs, tailcone 1.5 years ago still have not seen any.  Maybe when you were assembling Hs, wings, Vs, etc. you started at the ends and worked riveting inward towards centers.   I myself started in center of assembles and worked outward this I thought  would help by letting metal shrink/strech outwards towards the ends of assembles. worked for me I have no oil canning visible as for solving problem. shrinking metal/streching I would go with tech recommendations an/or move on and keep building.  

    

   

    

Dave Liudvinaitis  

    

#40466  

    

fuselage, side skins   

  

 <![if !supportLineBreakNewLine]> <![endif]>        

  

Make AOL Your Homepage.  

   	  Quote: 	
		    href="http://www.matronics.com/Navigator?RV10-List">http://www.matronics.com/Navigator?RV10-Listhref="http://forums.matronics.com">http://forums.matronics.com 	
            - The RV10-List Email Forum - 	
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AV8ORJWC

Joined: 13 Jul 2006
Posts: 1149
Location: Aurora, Oregon "Home of VANS"

Posted: Thu Sep 20, 2007 6:33 pm Post subject: Oil Canning

Last night at work (2AM local), I asked the former VANS Quality Control Inspector his opinion on your dilemma.  “The kit is so well formed that few compound curves exist.  The exterior skin should lay (naturally and *tight*) against the underlying framing structure - everywhere.”    

   

Yes, you can use Draw Clecos but he says they were rarely needed.  Most often it is the flanges not being bent  or fluted consistently to the correct angle so they cause either a dimple or pimple to act on the skin.  A few of the symmetric parts such as bulkheads have a left and right side which could contribute to a need for modifying the flanges.  Occasionally they would see a hurried rigging and lay-up early on the build process before the manufacturer fully understood the technique.  Most of the Horizontal and Wing are constant rib design to help reduce such a problem.  

   

On the RV-10 several differing competitive teams (A-B-C-D) to build subsections (Empennage – Fuselage – FWF – Canopy) which could occasionally cause fitment dissimilarity.  We builders tend to think if it as one big parts team.  The use of shim stock or tapered shims could correct some miss alignment issues (which I have seen on a few inspections).  Usually the builder accepts the occasional pimple (outty) or dimple (inny) as being a simple rock in the road to completion. There were a series of bad parts (not VANS phrase) on the RV-9 but the RV-10 has been pretty solid in the parts fabrication area.  (Not to take away from what John Hilger and others ran into with cracked parts).  As I understand it, the QC Department is now closed there.  I guess they have reached perfection   

   

We are often using 0.070 or 0.090 skin at work and several layers “webs” (it’s a pressure vessel) and the skin must be in full contact with the underlying semi-monoque framing everywhere before wet riveting.  When replacing panels, we use Lexan for a template and black fine tip markers to get the edges within 0.001 of the original skin.  It often stretches upon removal – hence the pulling of a template.  

   

He said more attention to flange “finish” angle and the consequence of “Springback” when they formed the part originally will help.  Fluting pliers is another tool.  I am attaching  pdf’s of what draw clecos look like.  In a production environment, we use a pneumatic draw cleco tool to speed the process of installation and removal of the clecos.  

   

Again oil canning is rare, is usually seen on assemblies completed early in the RV-10 build – and is rare but you are certainly not alone.  Proper preparation of each framing member will reduce the likelihood.  Some parts needed grinding on the curved flanges because they caused a projecting “hard point”.  

   

Drilling it and pulling it “in” might be a USAF Air Force One thing cause they are not Certificated aircraft or OBAM built aircraft (they are Bureau built).  Naval aviators would just slap Okum on it – like the expanding foam idea. I don’t know what Army Air Corp guys would do, they started in balloons didn’t they?   

   

Questions and Responses are what make this build so great.  

   

John  

600  

Do not Archive  

         

  

From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of McGANN, Ron

 Sent: Tuesday, September 18, 2007 4:00 PM

 To: rv10-list(at)matronics.com

 Subject: RE: Oil Canning  

  

   

Zero responses. Searched the RV-10 archives and there is very little there.  I guess I can only assume that no other RV-10 builder has any oil canning.  The general RV archives are only a little more enlightening.      

   

    

What happened to the good old days - when a basic building query met with half a dozen or more immediate useful suggestions?    I hope the list has not not exhausted itself as a resource for builder assistance.  

    

   

    

I know oil canning is common on all metal aircraft, but I am interested in solutions that the -10 crowd may have deployed to reduce or eliminate the problem - unless of course I am the ONLY crappy builder with oil canning.  

    

   

    

cheers,  

    

Ron  

    

187 finishing   

   	  Quote: 	
		        

  

From: owner-rv10-list-server(at)matronics.com [mailto:owner-rv10-list-server(at)matronics.com] On Behalf Of McGANN, Ron

 Sent: Monday, 17 September 2007 8:38 PM

 To: rv10-list(at)matronics.com

 Subject: Oil Canning  

     

Hey all,

 

 Getting to the final assembly stage.  I pulled out the VS that was completed over 3 years ago.  Did not know any better at the time and thought my first airplane part was just fine.  But there is significant oil canning on both of the large aft-lower panels.  The only other oil canning I have is very minor on one or two of the lower wing skin panels, so the VS is really giving me the irrits.  Any clues on how to tighten the skins?

 

 cheers,

 Ron

 187 finishing    	  Quote: 	
		    href="http://www.matronics.com/Navigator?RV10-List">http://www.matronics.com/Navigator?RV10-Listhref="http://forums.matronics.com">http://forums.matronics.com

Hexnut_Draw_Cleco.pdf

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Hexnut_Draw_Cleco.pdf

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46.64 KB

Downloaded:

301 Time(s)

Draw_Cleco.pdf

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Draw_Cleco.pdf

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AV8ORJWC

Joined: 13 Jul 2006
Posts: 1149
Location: Aurora, Oregon "Home of VANS"

Posted: Sat Sep 22, 2007 8:17 am Post subject: Oil Canning

Oil Canning  

A moderate deformation or buckling of sheet material, particularly common with flat sheet metal surfaces. Typically caused by uneven stresses at the fastening points. This terminology also refers to the popping sound made when pressure is applied to the deformed sheet forcing the deformation in the opposite direction.   

  

  

Oil canning can be defined as the actual waviness in the flat areas of roofing and siding panels. Generally the period and amplitude of the wave depend on the continuous width of the flat.  

   

Oil canning is an inherent part of light gauge cold formed metal products, particularly those with broad flat areas. Profiles having wide flat surfaces are often referred to as "architectural" roofing and siding panels. Such panels are distinguished from corrugated shapes as the latter are more fluted in design, have much narrower flats, and are less likely to exhibit oil canning.  

   

Background  

Oil canning has a number of causes:  

1. Metal coil  

Residual stresses induced during coil production can contribute. Examples of other contributing features are:  

a. Full center - the coil is longer in the middle of the strip; this is the most common example. (The gradation manifests as ripples or buckles near mid-coil.)  

b. Wavy edge - the coil is longer on the edge of the strip.  

c. Camber - the deviation of a side edge from a straight line. (This is not always a problem.)  

These conditions exist to some extent in all metal and tend to become more exaggerated as the strength level of the rolled sheet product increases and also for thinner and wider sheet product. When excessive, each circumstance may cause oil canning after roll forming by the manufacturer.  

   

2. Fabrication  

a. Slitting - The slitting of a master coil can release and redistribute residual forces. The coil's esponse can create or increase oil canning. The economics of rolling and coating wider coils makes slitting almost mandatory.  

b.Forming - New residual stresses can be created during some forming operations. Architectural panel profiles typically require more forming along sides than in the middle, and often require more forming along one side than the other. This dictates that forming commences along the sides. This sequential "working" of the sheet will have a tendency to "trap" uneven metal contained within the coil in the panel central areas (corrugated ribbed profiles are most often worked from the center out, thereby "pushing" the uneven metal to the edges).  

   

3. Installation  

a. Misalignment of the support system - Structural supports that are produced, fabricated and installed within allowable tolerances can create a "non-planar" or contoured bearing surface. Stresses induced while panels conform to this surface can contribute to oil canning.  

b. Over engagement of panels - Most panels accommodate transverse thermal expansion by flexing of webs and by "take up" at side joints. When panels are over engaged, these relief features are hindered or eliminated. In the extreme the "over engagement" process itself can generate waviness. Either cause can contribute to oil canning.  

c. Over driving of fasteners - This operation creates stresses in the panel and provides a "reading line" at the fasteners.  

d. Longitudinal Expansion - The surface temperature of exposed panels cycles throughout the year and even fluctuates daily. The temperature and the cycle depend on many variables, e.g. project location and orientation, cloud cover, panel inclination, surface finish or color, system thermal insulation characteristics. The panels' physical response is to expand or contract. If panels are restrained by "thru-fasteners", clips, or perimeter details, they try to accommodate or relieve thermal forces through several mechanisms, i.e. "slotting" around fasteners, out-of plane "bowing", local distortion of flat areas - "waviness". The magnitude of thermal force depends on the restraint provided (hence the panel stiffness and support stiffness), on the base materials' physical properties, and on the temperature differential between the support structure and the external skin. Waviness can be amplified when there is uneven fastener restraint along the panel. Such restraint is common on "concealed fastener" systems having fasteners along one edge and an interlock along the other. Waviness caused by thermal forces differs from other forms of oil canning in that waves can appear and disappear as the sun rises and moves around the building.  

e. Movement of the primary structure - Excessive differential deflection, racking, drift, or settlement within the primary structure can cause noticeable waviness within panel flats. This distortion can be temporary or sustained.  

f. Handling - Carrying of panels in the flat or twisting of panels can induce a wavy appearance to a previously flat panel. Twisting can occur if one corner of a panel is used to lift a panel or to remove the panel from a bundle.  

   

Coil producers and panel manufacturers attempt to minimize these conditions and produce quality products. On going research seeks improved production methods. All of the above factors can and do occur and can cause oil canning in architectural roofing or siding products. While a number of factors dictate the panel design, the following are items that the designer, panel manufacturer, and erector may consider in reducing the occurrence of oil canning:  

   

1. Coil:  

Tension or stretcher leveling, a process whereby the metal is "stretched" in coil form beyond its yield point, will provide a flatter surface less prone to oil canning. In general the heavier the gauge the less likely a product is to oil can. The possibility of oil canning can be reduced by ordering tension leveled and re-squared material.  

   

2. Design:  

The addition of stiffening beads "breaks-up" the flat surface and makes oil canning less apparent. Embossing will also help hide surface waviness in the metal. The selection of lower gloss coatings and lighter colors tend to minimize the visual effect of oil canning.  

   

3. Installation:  

More stringent specifications regarding the alignment of the supporting structure will focus attention on this critical aspect. Instructions to the erection forces regarding proper handling, spacing, and fastening should be a part of the manufacturers' delivery packet.  

   

Conclusion  

Oil canning is an aesthetic problem. Normally structural integrity is not affected. However, structural integrity must be reviewed if the distortion results from an extreme external influence. Since many uncontrollable factors are involved, no manufacturer can realistically assure the total elimination of oil canning. With careful attention to the production and selection of material, to the panel design, and to installation practice, oil canning can be effectively minimized.  

   

Unless specified tolerances have been accepted by the panel provider and panel manufacturer and are incorporated into the contract documents prior to fabrication, and if reasonable precautions have been taken, oil canning is not grounds for panel rejection.  

  

John Cox  

#600  

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