THE BUSINESS OF VISCOSITY BLOG



    Where and When You're Consistent Makes All the Difference

    Posted by Mike Bonner

    Nov 28, 2016 10:04:00 AM

    SCS-blog-image-consistency.pngNo, this isn’t a lesson in parenting, though reflecting back on raising our daughter, the thought is certainly applicable! The point is that consistency is just as important in our dispensing processes as it is in our parenting experience!

    Let’s examine why…

    What to Control 

    Seems like a good place to start! What are we really trying to control anyway? Though we, at Saint Clair Systems, are known for temperature control systems for fluid dispensing operations, when we say “fluid temperature," what we really mean is “fluid viscosity."

    What is Control? 

    When we say “control”, what we really mean is “consistency” or “stability” in a given process variable. Minimizing temperature variation (read: viscosity variation) is as important as the actual temperature (viscosity) itself. You can set your other liner parameters, like nozzle diameter, pressure, gun on-time, end rotation speed, line speed, etc., to work with almost any viscosity (within reason). But it is hard to make those changes “on-the- fly” to compensate for changes in viscosity brought about by changes in compound temperature.

    But equally important is “repeatability." Having a stable process variable is almost useless if you can never get back to those conditions again. Setups are expensive, because when you’re setting up, you’re not running product – which means you’re not making money…

    Where to Control

    This is one of the most important components of control – and the one most often glossed over.

    We talk about point-of-application all the time. This means controlling temperature (viscosity) right at the place where it is being used. But point-of-application is not always enough. In a liner operation, for instance, pressure drop in the fluid path between the regulator and the nozzle determines the pressure at the nozzle, which in turn determines the flow rate.

    This is also a function of the viscosity of the compound. Therefore it is essential to control the temperature, and thus the viscosity of the compound, over the entire path between the regulator and the nozzle. This is defined as “the temperature control envelope."

    Do gaps matter?

    Yes. As my grandfather used to say, “Close only counts in horseshoes and hand grenades!”

    The picture above shows what happens when there is a gap in the temperature control envelope – and it is worth a bit of study. Though shown for a common fixed orifice spray nozzle, the end effect is the same with our liner nozzle. In this case, the cooler material in the gun between the nozzle and the control point is at a higher viscosity than the temperature controlled material. And if the control envelope is not contiguous, or does not extend all the way to the nozzle, this happens every time there is a pause in dispensing – and in liner applications, this happens frequently.

    This, too, is often given the short-shrift.

    Let’s say we are running 401 ends at 80mg/end (dry), and the compound is 63% solids, which means dispensing 127mg of compound on each end. This is the equivalent of 0.0067in3/end. Now let’s say we use a 1/4” pipe nipple that is just 1” long to connect between our temperature-controlled components and our gun, and that it is left open to ambient. That fitting holds just 0.1inof compound, but that equates to 15 ends being lined with the wrong viscosity material before the correct viscosity material reaches the gun. And that happens every time we get a pause in liner operation.

    So, yes, it’s important!

    When to Control

    The answer is easy…

    Always! (Isn’t that the answer you expect from the temperature control guys?)

    But is that really necessary?

    The fact is, it is necessary to affect control when the temperature of the compound, ergo the viscosity, deviates from that range over which our system is designed to operate effectively.

    There are those who will profess that you must blend heating and cooling to maintain consistency. But, in reality, if the compound is at the correct viscosity, the best thing to do is…nothing. It is also the most energy efficient and the most cost effective. It doesn’t happen often, but in the daily and seasonal cycles, it does happen.

    The time to control is when the ambient temperature attempts to draw the compound temperature down, raising the viscosity above our desired operating point. Or when the combination of ambient temperature and friction – created by shear and mechanical components within the dispensing path – drive the compound temperature up, pulling the viscosity below our desired operating point.

    So, yes, knowing where and when to be consistent is critically important – and not just in parenting!

    Get your free copy of our Process Temperature Control Case Study to see how one manufacturer was able to improve production and reduce issues via temperature control solutions.

    free_process_temperature_control_case_study

    Topics: Temperature control

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