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Q: We build communications equipment for the military. Most of this equipment is used in sheltered applications, and thus is not exposed to the weather. We paint to meet MIL-DTL-14072 Finishes for Ground Based Electrnic Equipment. We currently use one part alkyd enamel paints, and two part epoxy paints. We are interested in adding powder coat paints, but this MIL Spec doesn't reference its use. I have found one MIL Spec on powder coat paint, MIL-PRF-24712. However, I'm unable to find a paper trail that will allow us to use this paint on our products. I've read that the military is interested in the use of powder coat paints, and that companies are using powder coat paint for military applications. However, it sounds like you have to get special permision to use it. Can you point me in the right direction?

This is a very good and seemingly timely question. Powder coatings are one of, if not the best, coating technology to protect a vast array of military products. They are tough, extremely durable, can be formulated in all colors and glosses, and are the most regulatory compliant of all industrial coating technologies. The specification you cite, MIL-PRF-24712 was originated in 1989 and revised in 1995. Surprisingly there are no qualified products recognized by the military agency responsible for this specification.

The specification covers a cornucopia of powder coating chemistries ranging from epoxy, to polyester, acrylic and polyurethane. It also describes three different classes related to service environment and performance requirements. The military has recognized that MIL-PRF-24712A has become obsolete and they are diligently working on a major revision. Part of this revision involves separating the immersion service class from MIL-PRF 24712 and embodying it in MIL-PRF-23236. NAVSEA initiated this change to cover powder coatings used primarily as corrosion-control materials. The new version of MIL-PRF 24712 is expected to be published before the end of the year (2009).

As for whether powder coating technology exists to meet MIL-PRF-24712 and MIL-PRF-23236, the answer is yes. It is just a matter of an interested powder coating manufacturer submitting appropriate products to the governing military agency for qualification. I can provide contact information of individuals who may be willing to work with you in qualifying powder coating for these specifications.

Date asked: 27 October 2009

Q: I am a cost estimator for a manufacturing company in Northern Illinois. I am looking for a formula that I might use to calculate how much powder to allot when quoting items that require powder coating. Right now, I have a formula that I use but it seems like my powder coating pricing may be somewhat high. Can you help?

Here’s how to make the calculation:

(192.4/powder-specific gravity)/thickness in mils = coverage of 1 lb of powder at 100% efficiency

For example:

(192.4/1.6)/2.5 mils = 48.10 ft²/lb

Using 70% efficiency, then one pound of powder covers 33.7 ft² (48.10 · 0.70).

If the powder costs $2.75/lb, then it costs $0.082/ft². Therefore, a part having 3.0 ft² = $0.246 per part.

The 192.4 number is derived by taking into account the relationship of pounds and inches to the grams and milliliters used in quoting specific gravity. Choosing an efficiency factor is critical to the validity of the calculation. Part geometry and whether you the powder is reclaimed heavily influence this number. Simple two-dimensional parts will provide higher efficiency, as will reclaiming and reusing the oversprayed powder. Spraying to waste (no reclaim) may result in efficiency in the 40–50% range. Reclaiming your powder can provide efficiency as high as 96%. The minor loss can be attributed to powder deposits on hooks and racking and 1–2% loss of material upon baking.

Also, it is important to note that this cost per part captures only the material cost. You still need to account for cleaning and pretreatment, as well as the cost to bake the parts and, of course, labor associated with the process. You won’t have to worry about waste disposal or volatile organic emissions, and your insurance costs should be lower than running a solvent-borne coating operation.

Date asked: 06 October 2009

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