Corrosion Deterrents

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  For general information we want to share a little bit of what happens between the “As received” and “Finished Project.”  A customer was dissatisfied with his previous powder coat job from a local vendor. The frame had rust showing up much sooner than he would have expected and could tell that the metal underneath was being affected. Powder coat is pretty tough stuff and should be a functional finish for many years. Because we were aware of his concerns, we took extra steps to inhibit the formation of rust in the future.

  As received, overall, at first glance, the frame and fork don't appear to have any serious problems. Later photos will show the concerns that Brian had with the durability of the previous powder coating.

  Areas such as this are obvious indications that corrosion has occurred.

  Having been previously powder coated his frame would require chemical stripping. We use the strongest stripper that we can find, preferably a methylene chloride formula. This product is dangerous and generally no longer available to consumers. During use it is recommended to have no bare skin exposed, wear heavy chemical resistant glove, a face shield, and an organic vapor respirator. A well-ventilated space is a must. Access to running water and soap is also a good idea for neutralization should skin contact occur.

These areas were less noticeable prior to the stripping process, but became quite apparent after the first chemical stripping treatment.

 The chemical stripping process typically takes 3 treatments to remove powder coating. Each one takes about an hour to complete. 

Chemical stripping - Second processing, about 90% of the original finish has been removed.

 There are variations in the powder coat composition that determine the difficult of removal. If lucky, the first treatment causes the bulk of the coating to resemble the skin of a Shar Pei puppy, almost falling off the frame in sheets. Others only turn the coating soft, with a massive amount of manual scrapping required. Still others turn the coating into a crystal-like material, scrapping causing it to flake off in tiny chips. To borrow from Forrest Gump, it’s like a box of chocolates, you never know what you’re going to get.  

Chemical stripping - Third processing, about 97% of the original finish has been removed.

  Once the chemical stripping is completed, usually removing about 95% of the coating, the frame is media blasted. We use Coal Slag as our media. This is done in an enclosed cabinet with a dust collection/filtration system. Hearing protection and a dust mask are highly recommended. A typical frame and fork can take from 45 minutes to an hour and a half to process.

  After media blasting the frame is hand sanded to smooth out the patina left by the media blast process. At the same time the frame is inspected for any paint or residual powder coat that was missed in the previous steps. This is removed with emery cloth or a sharp blade. High pressure air blast is used to remove media material that may have found its way into the tubing through the weep holes. At this time the frame is also rigged for the powder coating process, allowing the frame to receive an electrical charge.

  Just prior to powder coating the frame is washed down with a mild solvent to remove any oils and loose dust. It is then gone over lightly with a propane torch which also burns of residual small particles and lint from the cleaning cloths.

One of the most popular and effective forms of pretreatment for a steel frame is iron phosphate. Iron phosphate is a conversion coating that provides a barrier against oxidation. It is most effective on bare, clean steel. Iron phosphate provides increased corrosion resistance. Most powders provide a salt-spray rating of 250 hours on clean metal. A treatment of Iron phosphate adds a second layer of protection and can extend the salt-spray rating to 500-1500 hours, depending on the process.

  As an added bonus, iron phosphate provides increased adhesion. An Iron phosphate pretreatment causes a small amount of surface material to be deposited on the bike frame and fork. This material is slightly textured so the powder can grip it better. This improved adhesion is especially helpful because it helps keep the coating intact should the parts be occasionally bumped during their use.

As an additional corrosion deterrent, we started the powder coating process with a Zinc Rich powder coat primer. Zinc Rich primers are best used for steel substrates and work exceptionally well on sandblasted steel providing inter-coat adhesion to the steel. Being enriched with zinc protects the steel against oxidation and rusting. The reasoning behind this is the zinc in the primer will sacrifice itself by combining with oxygen and moisture forming a zinc oxide layer keeping the steel beneath protected from rust.

  Of course, the powder coating itself is a strong layer of corrosion prevention on its own. Most of the frames that we process rely solely on the coating for both appearance, durability, and protection. This, plus Brian’s election to have the bike clear coated after the decals were applied, give the maximum amount of protection that we have to offer.