Q&A: Gap Size Specifications

By: Jose Tirado 20. May 2013

 

Q. I cannot find a standard or a design rule that specifies the minimum gap necessary for complete coating during electrocoating. We design complex, geometrical metal fabrications, and many times we have to leave small gaps between components of the assemblies. R.D.

 

A. There is no formal standard or design rule that I know of for determining minimum gap sizes. Whether or not your electrocoat would properly deposit in gaps will depend on your specific electrocoat technology, application and operating conditions of voltage; percent solids; temperature; agitation; and dwell time. Whether or not your machine is a square transfer or continuous monorail could also have an impact on the outcome of coating inside minimum gaps.

The ability of electrocoat paint to deposit in tight spaces is called throwpower. Most electrocoats will build inside gaps of 8-10 mm to a depth of 1-3 inches, with a decreasing film thickness pattern from the outside to the inside. As the gap size increases, the thickness profile will equalize between the outside and inside. For gaps around 25 mm, typical electrocoats could deposit more than 400 mm.

Testing several gap sizes in probe assemblies would indicate the minimum distance or gap for your specific geometry and conditions in regards to not only film deposition, but also for adequate cleaning and phosphating. In my experience, open gaps of 7-8 mm or smaller are acceptable if they are open in both ends, but could be too small for liquids to freely enter and exit if the gap is closed on one end. In many cases with small gaps of less than 1 mm, liquids enter via capillary action and get trapped deep inside. These conditions create unacceptable quality defects due to kick-outs and boil-outs. 

To read more of Jose Tirado's answers to reader's e-coat questions, click HERE

ECOAT Q&A: Quoting E-Coat Costs

By: Jose Tirado 5. September 2012

 

Q. I have a customer who wants me to quote his product line based on an average square-foot price without analysis of the parts. How can I accomplish this, since my selling price is basically based on the number of parts we can hang per carrier and number of carriers processed per hour? Also, what is the best way to calculate amount of e-coat applied per square foot of part? A.I.

 

A. To a certain extent, asking you to quote based on an average price per square foot without seeing the parts is not fair, since not all square feet coated cost the same. For example, a 1-sq-ft piece of 18-gauge galvanized is cheaper to electrocoat than a 1-sq-ft piece of ½-inch steel plate. 

 

If you currently price based on pieces per carrier or load, you must have a dollar value you want to generate per carrier/load. In order for you to obtain that value, you must have obtained some numbers from your profit/loss statement (P&L) that included all costs plus profit, divided by the number of loads you ran during the time frame you used the P&L. If you also had the square-foot number from all those loads, then you could calculate your actual cost per square foot equivalent to your value per carrier/load and provide that number to your customer. I have seen some job shops use this technique. It is easy, and quickly generates quote numbers, but it is not good enough to determine efficiency and competitiveness of the coater.

 

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