Powdercoated wrought iron furniture
10-01-2005, 04:03 AM
#1
I miss my 03 CL-S :(
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Powdercoated wrought iron furniture
I'm thinking of getting this set or something like it soon for my balcony:
http://www.overstock.com/cgi-bin/d2....od_id=1030558#
Does powdercoated wrought iron furniture rust? I'll be leaving it outside year-round, so it'll be exposed to plenty of rain, snow and sun. I'd hate to buy this and have it rust or leave rust stains in the balcony.
http://www.overstock.com/cgi-bin/d2....od_id=1030558#
Does powdercoated wrought iron furniture rust? I'll be leaving it outside year-round, so it'll be exposed to plenty of rain, snow and sun. I'd hate to buy this and have it rust or leave rust stains in the balcony.
10-01-2005, 12:17 PM
#2
Burning Brakes
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I powdercoat for a living...
And have been doing so for 15 years now, but I do more than powdercoat.
There are two basic items to consider here: weatherability and corrosion resistance. They are not the same thing. One at a time.
Weatherability is the coatings resistance to fade (color changeing, generally turning lighter) and the elements, rain snow, ice and dew. As an overall average in the United States, any object left outdoors, be it a car, furniture or plants will be wet fifty percent of the time. I have cabinets at work that simulate concentrated sunlight in a controlled environment, and the light emitted by the ultraviolet lamps by themselves generally cause very little damage on their own. However, elevate the temperature to 50 C during the four hour light cycle and add a four hour condensation cycle at 50 C, your poorer coatings fall apart quickly.
Powder coatings are very robust, but it is very important that the correct chemistry and system are used. I'll explain.
As far a corrosion is concerned, epoxy powder coatings are very cost effective and is considered to be the king of corrosion control over all powder coatings. However, epoxy absolutely sucks at chalking and fading, so weather to use it or not depends upon the outdoor application. I have a business unit that powder coats fasteners for building construction for metal industrial buildings. For the sides of the buildings, we use screws powder coated with a polyester TGIC which has excellent corrosion resistance and color retention properties. However, the TGIC is almost twice the cost of an epoxy. For screws on the roof, that almost no one ever sees, we use an epoxy for its excellent corrosion resistance. Who gives a rats ass about a chalking black screw on a flat indudtrial roof? Not me.
Corrosion resistance:
As in all painting, liquid or powder, surface preperation is the key. The substrate must be free of organic soils (dirt, oil, grease) and inorganic soils (rust, oxides of metals). Generally, after the part is fabricated it is run through a 3, 5 or 7 stage washing system, and in one of the last steps, a light coating of iron phosphate is applied, and it is very important. Essentially, you can consider powder coating a two step system...pretreat followed by powder coating.
The iron phosphate etches the surface of the metal, but more importantly leaves a microscopic but none the less rough surface. This helps anchor the powder coating, sprayed on as solid plastic particles that are positively charged and thus are attracted to a negatively charged (grounded) target. This is one of the advantages of powder coating; it relies very little on operator technique to insure adequate coverage. It goes virtually everywhere, and is generally uniformly applied as powder coatings are a self limiting system it terms of film thickness. Think of it this way: With a negatively charged target (after all, it hangs from a metal hook), positively charged particle are attracted to the target. But as the positive particles adhere, the outside layer of the powder coating becomes positive, and sooner or later, the positive particles that are charged in the gun begin to repel. This is called "back ionization", and depending on part geometry and complexity usuall results in a film thickness of 2 to 3 thousands of an inch. Doesn't sound like much, but a properly selected powder coating will do the job.
If I test a bare metal part coated only with iron phosphate, it will corrode quickly in my salt spray cabinets. 24 hours or so. And if I powder coat a bare metal part with powder coating only, and scribe the surface, it will fail in about 240 hours or so. So, when I put the two together, does that mean I will get 264 hours of performance out of the coated object?
No. More like 2,500 to 3,000 hours. And remember, this is a 5% salt solution that goes on 24 hours a day. The two systems compliment each other.
What you do when you powdercoat an object is to essentially encase it in plastic, and plastic doesn't rust. Your plastic car battery holds concentrated sulfuric acid, and if your car has aluminum wheels they have an acrylic powder coating on them and exist in one of the nastiest environments you can find on a car. The view of the automakers is that a finish on a car, with proper care and no damage is that it should last for ten years. After that, they're off the hook.
Now in the case of an outdoor furniture manufacturer who powder coats, I can't imagine them not being educated as to how to specify the correct powder coating system for outdoor use. I doubt the retail outlet will know this, but what you want is a polyester, polyester TGIC, or polyurethane system for outdoor use.
So yes, this should be a good purchase for you. But will it last 50 years? Maybe, maybe not. It depends how severe the sunlight and corrosiveness of the atmosphere in your are is.
Powder coatings, as a rule, are more corrosion resistant compared to liquid coatings by a minimum of ten to one, and in the case of particurarly cheap liquid coatings, I have seen a 100:1 advantage.
So, open that wallet and support the economy. Hope this explains this for you.
There are two basic items to consider here: weatherability and corrosion resistance. They are not the same thing. One at a time.
Weatherability is the coatings resistance to fade (color changeing, generally turning lighter) and the elements, rain snow, ice and dew. As an overall average in the United States, any object left outdoors, be it a car, furniture or plants will be wet fifty percent of the time. I have cabinets at work that simulate concentrated sunlight in a controlled environment, and the light emitted by the ultraviolet lamps by themselves generally cause very little damage on their own. However, elevate the temperature to 50 C during the four hour light cycle and add a four hour condensation cycle at 50 C, your poorer coatings fall apart quickly.
Powder coatings are very robust, but it is very important that the correct chemistry and system are used. I'll explain.
As far a corrosion is concerned, epoxy powder coatings are very cost effective and is considered to be the king of corrosion control over all powder coatings. However, epoxy absolutely sucks at chalking and fading, so weather to use it or not depends upon the outdoor application. I have a business unit that powder coats fasteners for building construction for metal industrial buildings. For the sides of the buildings, we use screws powder coated with a polyester TGIC which has excellent corrosion resistance and color retention properties. However, the TGIC is almost twice the cost of an epoxy. For screws on the roof, that almost no one ever sees, we use an epoxy for its excellent corrosion resistance. Who gives a rats ass about a chalking black screw on a flat indudtrial roof? Not me.
Corrosion resistance:
As in all painting, liquid or powder, surface preperation is the key. The substrate must be free of organic soils (dirt, oil, grease) and inorganic soils (rust, oxides of metals). Generally, after the part is fabricated it is run through a 3, 5 or 7 stage washing system, and in one of the last steps, a light coating of iron phosphate is applied, and it is very important. Essentially, you can consider powder coating a two step system...pretreat followed by powder coating.
The iron phosphate etches the surface of the metal, but more importantly leaves a microscopic but none the less rough surface. This helps anchor the powder coating, sprayed on as solid plastic particles that are positively charged and thus are attracted to a negatively charged (grounded) target. This is one of the advantages of powder coating; it relies very little on operator technique to insure adequate coverage. It goes virtually everywhere, and is generally uniformly applied as powder coatings are a self limiting system it terms of film thickness. Think of it this way: With a negatively charged target (after all, it hangs from a metal hook), positively charged particle are attracted to the target. But as the positive particles adhere, the outside layer of the powder coating becomes positive, and sooner or later, the positive particles that are charged in the gun begin to repel. This is called "back ionization", and depending on part geometry and complexity usuall results in a film thickness of 2 to 3 thousands of an inch. Doesn't sound like much, but a properly selected powder coating will do the job.
If I test a bare metal part coated only with iron phosphate, it will corrode quickly in my salt spray cabinets. 24 hours or so. And if I powder coat a bare metal part with powder coating only, and scribe the surface, it will fail in about 240 hours or so. So, when I put the two together, does that mean I will get 264 hours of performance out of the coated object?
No. More like 2,500 to 3,000 hours. And remember, this is a 5% salt solution that goes on 24 hours a day. The two systems compliment each other.
What you do when you powdercoat an object is to essentially encase it in plastic, and plastic doesn't rust. Your plastic car battery holds concentrated sulfuric acid, and if your car has aluminum wheels they have an acrylic powder coating on them and exist in one of the nastiest environments you can find on a car. The view of the automakers is that a finish on a car, with proper care and no damage is that it should last for ten years. After that, they're off the hook.
Now in the case of an outdoor furniture manufacturer who powder coats, I can't imagine them not being educated as to how to specify the correct powder coating system for outdoor use. I doubt the retail outlet will know this, but what you want is a polyester, polyester TGIC, or polyurethane system for outdoor use.
So yes, this should be a good purchase for you. But will it last 50 years? Maybe, maybe not. It depends how severe the sunlight and corrosiveness of the atmosphere in your are is.
Powder coatings, as a rule, are more corrosion resistant compared to liquid coatings by a minimum of ten to one, and in the case of particurarly cheap liquid coatings, I have seen a 100:1 advantage.
So, open that wallet and support the economy. Hope this explains this for you.
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