Pre-Powder Coating Treatment

Article From: Products Finishing,

Posted on: 10/1/2002

Question: We have recently purchased a powder coater, and I am responsible to come up with a cleaning, rinsing and treating process for steel boxes.

Question:

We have recently purchased a powder coater, and I am responsible to come up with a cleaning, rinsing and treating process for steel boxes. On the PF site I read about Plaforization. It sounds very convenient with only one dip station. Our largest box will probably be 2 × 2 × 1 ft. Our boxes are mainly for indoors, but we want a good enough seal and corrosion resistance for exterior use also. Could you please e-mail or phone me with your thoughts on whether Plaforization is right for us? Also, could you get me some pricing and a sample of your product? C.C.

Answer:

First, to set the record straight, I do not have anything to do with the company that has developed and sells this commercial process. So I will not be able to get you samples or pricing of a coating system. To be honest, I had never heard the name Plaforization until you submitted this question, but this is a unique one that did pique my interest.

Although I had not heard of the Plaforization process by name in the past, I am familiar with the concept of a single-stage clean and phosphate coating. After investigating further, though, I found that this particular process differentiates itself from others on the market. Traditional single stage cleaner/phophatizers use a phosphoric acid-based solution with phosphates, accelerators and surfactants to clean and convert the surface. The overspray can typically be recirculated for some time and will eventually need to be disposed of and recharged with new chemicals. Another process that may be more similar, although not as widely used, was the Cool Phos system that used methylene chloride along with a small amount of water and phosphoric acid to clean and create a light iron phosphate conversion coating.

This Plaforization process is significantly different from either of these. While none of the information I found gets into specific chemical reactions, it is generally described as an organic solvent that cleans and creates a conversion coating in one step. It states that the oil removed from the metal surface is incorporated into the conversion coating film. That is why they state that the average workpeice should have no more than 14 g of oil per 100 sq ft of treated surface area. Available information states that the organic solvent is responsible for removing the oil, and then a "phosphate polymer" adsorbs it and incorporates it into the coating structure.

The process is operated at room temperature, does not require precleaning (unless the parts exceed the average oil loading of 14 g/100 ft2), can be air dried or used with an oven to speed drying, takes 60-90 sec and has no waste since it is consumed by the coating. It is suggested that the chemical tank be agitated and filtered. The process can be done with either an immersion or spray system and will work with either steel or galvanized steel.

The coating is said to have corrosion resistance similar to iron phosphate, but less than zinc phosphate. It should be noted, though, that iron phosphate is typically used to increase paint adhesion, and zinc phosphate is used when you want to increase corrosion performance of the coating system. The web site indicated that there could be some problems associated with TGIC powders, but it was not specific as to the potential problems. Although this would not effect you, one potential drawback is that it is not compatible with electrocoating systems.

While none of the information I reviewed discussed specific costs, it is implied that the chemicals are more than those used in a standard phosphate system. Obviously, it would be important to determine overall system cost with something like this. Several potential cost advantages that would be available with the Plaforization process would be lower capital equipment investment, significantly lower energy usage, no investment in a water treatment facility and no discharge or disposal.

Since you appear to be a captive shop, you may have some control over the oils used in the manufacturing process. This would seem critical in order to make the system operate effectively. Although, there are no specifics mentioned regarding oils, it makes sense that the success of this coating must be at least partially dependent on the type of lubricant being removed. It does state that water-based oils cannot go into this system, although it does not get further into what types of mineral oils it is compatible with or which additives may create problems. In the case of commercial jobshops where there is no control over incoming oil, this could create problems. Most phosphate systems are very robust and can handle a variety of lubricants and soils effectively.

Since the process probably sounds too good to be true, it should be investigated thoroughly before committing to a system. Given your application, it sounds like the pretreatment may be sufficient for the indoor boxes that you manufacture, although it may not work for the outdoor applications, depending on what they are used for, where they go, and customer expectations and/or specifications. Also, do you coat the inside of these boxes? If so, you may already be aware of the Faraday cage effect that will make coating the inside of these fairly difficult. This will increase the dependence on the pretreatment in those areas where the powder is especially thin.

The information I found on this process can be located at www.pfonline.com/articles/010102.html and the links on that page.

 

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