THE BUSINESS OF VISCOSITY BLOG



    It’s Too Cold for Blisters! Temperature Control in Deep Winter

    Posted by Mike Bonner

    Feb 24, 2015 2:25:00 PM

    To remind us that we are in the dead of winter here in the Midwest and across the Eastern Seaboard, Mother Nature has been delivering sub-zero temperatures and snow by the foot.  winter snow thermometer   iStock 000011070422Small resized 600These are the times that try a coater’s soul!

    The cold brings up issues that those of you in warmer climates may never experience, and sometimes they seem to defy logic.

    Problems from Out of Nowhere

    Dan called me the other day to discuss a problem that he was experiencing on his coating line.  All of a sudden, on a product that they’ve run dozens of times, he is getting blisters.  He’s asked all of the right questions:

    1. Is the paint at the right viscosity?

    2. Is it from the same lot that worked fine just last month?

    3. Is the film within specifications?

    4. Are the oven temperatures set correctly?

    5. Are the parts clean?

    A quick check of the setup sheets confirmed that the answers to all of these questions was a resounding “Yes”.  Dan automatically assumed that something had changed with the paint.  He called his formulator – they even checked samples from the same lot in their lab – but he was assured that everything with the paint was fine from their end.

    So Dan’s question to me was as obvious as his frustration…

    How Can This Be Happening?

    It’s a fair question.  If all of the conditions are the same, how can the result be different?

    Of course, the answer is equally obvious – not all of the conditions are the same!

    Mother Nature has thrown Dan a curveball.

    Make that a snowball…

    The Ever Changing Environment

    All coaters understand the impact of environment on the coating process.  This is the reason that they often spend hundreds of thousands, even millions of dollars, to make sure that the environment in the booth – temperature and humidity – are carefully controlled.  Dan’s company is no exception.  They have advanced controls to make sure that their booth conditions are constant year-round. 

    He knew that I would ask about the environment and, even with the extremes in the weather lately, Dan was proud to report that they have been able to maintain consistency in their coating environment.  This time, he was sure that I wasn’t going to “get him” on the environmental influence over his process!

    Still, there was the issue of blisters…

    The Environment Outside the Booth

    Dan runs a tight ship.  His people and processes are way above average.  They understand the value of maintaining a high velocity through their plant.  Short turns.  Minimum inventory.  They do it all – and well.

    Dan and his team are also smart enough to know that they were looking over the top of something and that a second set of eyes – a pair not as well acquainted with their processes – might be of use in ferreting out the source of the problem.

    So we walked his process from the point of application backwards.  Just as Dan had presented, everything seemed to be in order.  And then we got to the warehouse…

    The heaters were all running full blast, but the high-lo drivers were all bundled-up in their winter coats, and I could see my breath.  As you would expect, there was a steady stream of trucks in and out of the bays.  In spite of their procedures, carefully designed to keep the doors closed as much as possible, the overhead doors were constantly in motion as the material handlers did their carefully choreographed dance.

    In this case, it was more like ice dancing…

    Enter the Law of Unintended Consequences

    Per procedure, Dan’s materials team rotated their stock, staging the partial drum and coating left over from the last run, to be used first on this next one.  This was stored on the floor level for easy access and timely delivery directly to the line.  It’s an impressive process, and like everything else in their plant, extremely well managed.

    In this case, in this time, however, this proved to be the smoking gun we were looking for.  Actually, the “smoke” was more like our condensed breath…

    The bitter cold air mass coming in through the doors was forcing the warmer air from the heaters upward and settling on the floor – right where the staged coating was being stored.  Because of the extended length of this cold snap, all of the staged paint had acclimated to this cold temperature – and this was how it was being delivered to the line.

    Dan nailed it with his first question.  It was all about the viscosity of the coating.

    Like most operations, Dan’s process is to check the viscosity of the coating and then adjust with solvent.  The thought process is that this gets them painting faster and helps them maintain their throughput.  Most of the time it works pretty well, but not this time.  This time, they added a lot of solvent to get the cold paint down to the target viscosity and then applied it.  All of this extra solvent had to come out in the curing oven.  As the paint started to skin over, the excess solvent below the surface, still attempting to escape, lifted the skin and formed the blisters. 

    Worse yet, that drum of paint was functionally ruined.  To save the cost of the drum, it was relegated to use as a “thinner” for the drums to follow.  Dan’s team modified their process to add agitation time to warm the paint to an acceptable temperature and then the “thinning drum” was used to bring the viscosity into range.  Unfortunately, this added a lot of time to the process and totally destroyed Dan’s schedule, leaving him with a lot of calls to make to his customers to explain the situation.

    Dan thanked me for my time, and my help in tracking down their issue, but he clearly wasn’t happy.  His problem was identified, but it wasn’t solved.

    And he wasn’t looking forward to making all those calls…

    Orange peel is one common defect that can appear in your paint or coating finish when temperature control isn’t consistent. Get your free copy of our Controlling Orange Peel eGuide to learn more about identifying and troubleshooting the issues that cause orange peel.

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    Topics: Manufacturing, Temperature control

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