Temperature Variations Cause Inconsistent Liner Placement

    Posted by Mike Bonner

    Oct 17, 2016 10:02:00 AM

    In this segment of our continuing examination of the can end liner process, we are going to get into some basic process mathematics. But before you run screaming from your computer (or reach for your mouse), let me just say that it’s pretty basic and pretty straightforward – and I think you’ll find it interesting, too!

    First, Some Background

    In our recent blog post, Variation in Liner Placement Impacts Delivery, Quality, and Cost, too!, we noted that compound viscosity affects placement:

    “Though the compound is rubber-like when cured, when dispensed, it is in a liquid form and, like all liquids, viscosity determines how it flows. The flow behavior is important in the end result because the “rubber” seal formed in the groove must be smooth and even if it is going to do its job."

    And then, in our post, Improving Weight Control on Older Liners, we showed the relationship between viscosity and temperature by referencing the compound supplier’s own data. I’ve included the chart from their lab here for convenience.

    The Transitive Property

    Remember sitting in High School Algebra Class thinking, “When would I ever have to use this stuff?”

    I do. And that was a long…long…long time ago!

    But then I got out into the real world and started analyzing processes – and all that math suddenly became useful – like the transitive property – which, in case you’ve forgotten, states:

    If a = b, and b = c, then a = c

    So what has that got to do with liner placement?compound-viscosity-vs-temp-chart.jpg

    Actually, everything. Let’s follow the logic in our process…

    First, we’ll let a = “temperature."
    Next, we’ll let b = “viscosity."
    Finally, we’ll let c = “placement."

    Now it gets fun…

    The graph in Figure 1 clearly shows that “temperature equals viscosity”, or a = b. (Well, to be more accurate, temperature directly affects viscosity, but now we’re splitting hairs…)

    Next, in the blog post, Variation in Liner Placement Impacts Delivery, Quality, and Cost, too!,  we pretty clearly demonstrated how compound viscosity affects placement. Therefore, b = c.

    So, it’s pretty easy to see that, if temperature affects viscosity (a = b), and viscosity affects placement (b = c), then temperature must affect placement (a = c).

    Wouldn’t your high school math teacher be proud?

    Mine would. Probably surprised, too!

    But Which Temperature is Important?

    So, if temperature affects placement, then all we have to do is control temperature and we can solve our placement problems, right?

    Actually, in many ways, yes!

    But that is where it starts to get a little complicated…

    To directly answer the question, the important temperature is that of the compound as it is being applied.

    Not the ambient temperature.

    Not the temperature at the bulk supply.

    Not the temperature in the hose.

    So if we can control the temperature of the compound as it exits the nozzle, it will be at a predictable viscosity and we can go a long way toward controlling the liner process.

    Stacking the Deck Against Us

    In reality, all those temperatures are not separate. In fact, some of them join forces to work against us, messing up our best efforts to control temperature and thereby, our process. For instance, the ambient temperature affects the temperature of the bulk supply, and of the compound in the hose on its way to the nozzle.

    To make matters worse, the ambient temperature is constantly changing – from day-to-night and season-to-season. And, the factories we are talking about are way too large to attempt to control the ambient year-round. Besides, the best temperature for the compound is usually NOT the best temperature for the operators. Moreover, many of the devices that control the compound generate heat from shear and friction. It presents a real control nightmare.

    Still, we need a solution that will control the temperature of the compound in such a way as to overcome these factors and assure that it will always be at the desired temperature when it reaches the nozzle. A tall order, to be sure, but doable.

    But that’s a topic for another post…

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    Topics: Manufacturing

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