MARTINSR and BARRYK - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Body - Exterior
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 12-07-2004, 08:40 PM
outlaw17's Avatar
Member
 
Last photo:
Join Date: Jan 2003
Location: C-eh N-eh D-eh
Posts: 168
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
MARTINSR and BARRYK

I seen something here awhile ago that was from both of you that was about painting temperatures , both shop and vehicle temperatures and the amount that the curing rate changes with dropping temeratures . Can you point me to a site that details this or can you explain in more detail ? The reason I ask is because I paint in a shop that has a regular cross flow booth with no make-up air unit . When we paint we have to make sure a bay door is open at least a foot or so so we dont snuff all the pilot lights . Of course it is time to re -paint the Lamborghini and its getting down to -28 or lower here at night and around the -20 mark during the day , makes for a cold shop when sucking in that cold air but the boss cant get it through his thick scull that temperature makes a HUGH difference.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 12-07-2004, 09:07 PM
MARTINSR's Avatar
Brian Martin,Freelance adviser
 
Last photo:
Join Date: Jun 2004
Location: San francisco bay area
Age: 55
Posts: 12,671
Wiki Edits: 0

Thanks: 614
Thanked 948 Times in 848 Posts
You said it, temperature makes a HUGE difference. I am sure Barry will have more of facts on this but as far as I was taught by S-W in a nutshell NOTHING you would be shooting is going cure below 55 degrees. Ok, let's say there is a "safety net" built into that recommendation by S-W of the 55 degrees, well below 30 sure as heck is too cold.

So, if nothing cures, everything you send out the door is "soluable", the customer gets a pretty crappy product.

I remember being told that if you were to get that car in that was sprayed in sub 55 degrees into 65 or so it would still cure, even days later. I have seen it to some degree (if you'll pardon the pun) but no testing to prove it.

How does he buff something that may need it when it is that cold and it is uncured?
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 12-08-2004, 03:52 AM
Member
 
Join Date: May 2002
Location: Gig Harbor WA
Posts: 107
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I attended a PPG painting seminar a couple of years back and the instructor said that all new paints that use activators are designed to "cross link" when they are cured correctly. He said that below 60 degrees F that the cross linking will not occur and if the system does not cross link with in about one hour it never will. He said what you end up with is paint that may look cured but has no toughness to it. David
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 12-08-2004, 08:08 AM
MARTINSR's Avatar
Brian Martin,Freelance adviser
 
Last photo:
Join Date: Jun 2004
Location: San francisco bay area
Age: 55
Posts: 12,671
Wiki Edits: 0

Thanks: 614
Thanked 948 Times in 848 Posts
Yes David, you are right. I didn't make that clear, the paint may appear to be "dry" and "hard" but that doesn't mean it is "cured" by "crosslinking" of the molecules. Only then will the paint/clear be the product the manufacture designed it to be.

It needs the 55 or 60 degrees to do that. Anything below that temp all you have in reality is a "1K" product.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 12-08-2004, 07:32 PM
Member
 

Last journal entry: Suggestions worth sharing
Last photo:
Join Date: Jun 2004
Location: Kansas City, MO
Posts: 132
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
A general rule of thumb is that most chemical reactions undergo a change in rate of 2X to 3X per 10 degree C. So, a temperature change of, for example, 30 degrees C (or 54 degrees F) would be expected to cause a rate change of between 8 times and 27 times. (It's possible to predict whether one's closer to the two-fold or three fold rate change if one knows the specific type of reaction being considered.)

Some 2K finishes will respond more or less adversely to low temperature cures based on the following considerations. At low temperatures, an epoxy which uses a volatile aliphatic amine curative can potentially lose some amine to volatilization before the amine can crosslink with the epoxy groups. Even more commonly, however, at low temperatures, some amine curatives can react with carbon dioxide in the air to form amine carbonates before the amine can crosslink with the epoxy. In either of these cases, the result will be a film with less than optimum properties, even if the film eventually warms up enough to partially crosslink. The best case situation is probably with higher equivalent weight epoxy combined with a high equivalent weight polyamide curative. However, these systems are less likely to be encountered today because they are not low VOC systems.

A similar situation exists with urethanes, as low temperature cures can cause the isocyanate to react with moisture from the air before they crosslink the resin.

Despite the above considerations, specially formulated products do exist for low temperature cure...both in urethane chemistries and epoxies. Some can cure successfully in below freezing temperatures. To the best of my knowledge, however, these are mostly found in industrial maintenance finishes as opposed to auto refinish products.

Bottom line, as stated in previous posts, better not go much outside manufacturer's recommendations, or you risk sacrificing paint film properties.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 12-08-2004, 07:50 PM
MARTINSR's Avatar
Brian Martin,Freelance adviser
 
Last photo:
Join Date: Jun 2004
Location: San francisco bay area
Age: 55
Posts: 12,671
Wiki Edits: 0

Thanks: 614
Thanked 948 Times in 848 Posts
Great stuff Bill Can you put the "rate change" in bodymans lanquage Does it refer to the "amount of molecules" that link? Like if you had 100 molecules that you would prefer to link four ways, "2X" would mean only 50 linked while "3X" would mean 75 linked?
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 12-09-2004, 04:53 AM
Dutchman's Avatar
Old Salt
 
Last photo:
Join Date: Apr 2003
Location: Portsmouth, Virginia
Age: 56
Posts: 491
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Outlaw,

You don't have a heat system installed in the shop?

I've done some crazy things like heating the metal with heat lamps, mix the paint in the shop and then quickly paint the area needed. Now, this was on Navy aircraft and the only thing to worry about was the peeling off during a flight.
Anytime the temp went below 55 things got complicated.

Wouldn't think about doing a whole car without proper temp control.

Dutch

Last edited by Dutchman; 12-10-2004 at 07:18 AM.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 12-09-2004, 07:09 PM
Member
 

Last journal entry: Suggestions worth sharing
Last photo:
Join Date: Jun 2004
Location: Kansas City, MO
Posts: 132
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Martin, you have the right idea. When we say "50% reaction", we mean that half of the reactive functional (or crosslinkable) groups have been reacted, and half remain un-reacted.

Footnote: "Percentage reaction" is subtly but significantly different from considering the fraction of molecules that have been reacted at one or more sites, for the case of a multi-functional resin and crosslinker. I'm not sure if there was any confusion regarding this distinction or not. If I need to claify further, feel free to let me know, but I think you have the gist of the idea.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 12-11-2004, 04:42 AM
Member
 
Last photo:
Join Date: Apr 2004
Location: Georgia
Posts: 3,573
Wiki Edits: 0

Thanks: 10
Thanked 57 Times in 36 Posts
Quote:
Originally posted by Dbodily
I attended a PPG painting seminar a couple of years back and the instructor said that all new paints that use activators are designed to "cross link" when they are cured correctly. He said that below 60 degrees F that the cross linking will not occur and if the system does not cross link with in about one hour it never will. He said what you end up with is paint that may look cured but has no toughness to it. David
*******************************************
Tell the PPG instructor he is all wet!
In automotive refinish all isocyanate's products go dormant at 48-49 degrees and there is good reason for this.
As P-B pointed out epoxy and architectural coats can be made to cure in colder temps. Example, a few years back I made a clear to cure in the area of 40 degrees for a specific situation (non automotive) If it was used for automotive it would be unbuffable.
Urethane and ploy urethane clears will skim below 48 degrees but even with accelerator all cross-linking stops at about 48 -50 degrees.
The reason some tech sheets say 55 degrees is them metal temp
is usually around 8 degrees cooler than the outside air. So if metal temp is 48 degrees and its 55 air temp the undercoat is going to Flash than go dormant and than act as an insulator
and the second coat will now slowly cure out. Bad news.

Most important thing in cold is get the metal to in the 70 degree mark before you paint, than when done painting put heat source back on and keep outside air at least 55 or higher for as long as you can.

Back to the PG guy. 2K urethane clears and primers will fully cure out after going dormant with proper heat.
Epoxies will but CAN take six months a little different deal.

Last edited by BarryK; 12-11-2004 at 06:24 AM.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 12-11-2004, 06:54 AM
Member
 
Join Date: May 2002
Location: Gig Harbor WA
Posts: 107
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Barry,
Now I am really confused. In your last paragraph you mention (at least that is how I interpeted your last paragraph) that if the temperature gets up to some acceptable level the paints will finally cross link. But if what Powderbill says is true and that at low temperatures some of the amines may volatize before they can cross link or react with CO2 to form amine carbonates and that in urethanes the isocyanates may react with moisture before they can all cross link how can all of the epoxy groups and urethanes cross link. Am I missing something here. I thought that for a proper cross link all of the molecules must be effected. If some of the amines or isocyanates have reacted in some other form what do the "extra" molecules of the paint cross link with. In this case won't there be some degree of lack of cure that is permanent? I am trying to understand this. Thanks David Bodily
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 12-11-2004, 07:30 AM
Member
 
Last photo:
Join Date: Apr 2004
Location: Georgia
Posts: 3,573
Wiki Edits: 0

Thanks: 10
Thanked 57 Times in 36 Posts
True statement but if you noticed I made the reference to "Automotive Refinishing"
No blanket statement can cover all the different coatings out there.
The clear I made was a test deal for FAA and had to be activated with a three part deal to make it work.

About 10 years ago BF Goodrich who at the time owned Tremco
(now Transtar)
in coordination with about four other companies one was American who PPG owns did extensive test on all the automotive finishes with relationship to cold.
What they found with the Urethanes in this business-(not the crossed linked-Cheaper systems) was when exposed to normal heat for the next 72 hours the products cured out to with in 10% of ideal conditions.

Now for ease of understanding, yes P-B is right BUT the average
plastic mixing cup can be off ratio of 3-5 % anyways and I have seen ones off 8-9%. Paint measuring sticks? where you stop at the line and angle your looking at can be 3%.
Most products in this industry just hope its mixed with- in 10% range for proper working.

Edit,
I would like to add these tests were done by freezing at 24 hours right after painting and the way the test was was done can make a big difference. Solvent evaporation will depend on temp and humidity of course and when I say freezing we did the test from 32 degrees to 50 degrees--all make a difference in net result.

Last edited by BarryK; 12-11-2004 at 07:59 AM.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 12-11-2004, 07:34 AM
Member
 
Join Date: May 2002
Location: Gig Harbor WA
Posts: 107
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Barry that certainly make sense. thanks David Bodily
Reply With Quote Quick reply to this message

Recent Body - Exterior posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -6. The time now is 04:49 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.