Improving Weight Control on Older Liners

    Posted by Mike Bonner

    Jul 22, 2016 1:04:39 PM

    In our post, Getting World Class Performance Out Of Old Liner Equipment, we noted:

    “In many industries, rather than replace the whole machine, it is commonplace to retrofit it with new technologies to bring its performance up to contemporary standards.”

    And then went on to state:

    “The key to a successful upgrade project is to closely examine your process to identify those parameters that are directly related to the defects you’re experiencing, then to focus your efforts specifically in those areas.”

    Know Where to Look

    When one of our customers was experiencing issues with liner weight consistency, they asked us to help evaluate their situation. During our discussions they revealed that they saw variations from day-to- night and season-to- season, which their operators addressed by adjusting pressure – their main approach to controlling liner weight. The result was that they “chased” their target – sometimes under, other times over. This had been going on for years. They had attributed this to temperature variation and had installed a homespun temperature control system many years earlier, but it didn’t help, which drove them to the conclusion that the problem was not temperature related.

    Go Where the Observations Point You

    From prior experience, we knew that, with fixed orifice dispense systems, like the liner application, variation issues often originate in the material delivery system – and they were often temperature related. So, in spite of their assertions, we decided to start by identifying the relationship between temperature and liner weight in their application. The logical place to start was with the relationship between temperature and compound viscosity. The compound supplier’s lab was able to provide the data shown in Figure 1, which is a “classic” sealer curve.

    Figure 1: Compound Viscosity vs. Temperature

    The next step was to establish how this temperature based viscosity variation affected liner weight. We set up a system to closely control pressure and temperature going to the gun, then, holding the other parameters constant, measured liner weight as temperature was varied. Shown in Figure 2, of particular interest was that fact that the slope of the line was comparable to the coefficient of the exponential material curve at just over 1.2 mg/°F

    Compound-weight-versus-temperature.jpgFigure 2: Compound Weight vs. Temperature

    This confirmed the liner behavior as a fixed orifice system and further suggested that the mechanics were stable.

    Good news for the finance department!

    When All Else Fails, Try Real Data

    The logical next step was to analyze the performance of their existing system during normal operation. Logging various points in the system from start- up through the first several hours of production, the issue is predictably clear, as shown in Figure 3.

    Figure 3: Baseline Data

    In this chart we can see that the temperature at the gun inlet varies widely – especially for the first 90 minutes of production – and the liner weight follows accordingly. As the compound cools, weight falls, as it warms, weight increases. This is in keeping with the “controlled test” data shown in Figure 2 above and drives two primary conclusions:

    1. The existing temperature control system is not stabilizing temperature.
    2. It is essential to stabilize temperature at the point-of- application (the gun) if we are to stabilize the liner weight.

    Fix Only What’s Broken

    By combining thermo-electric heating and cooling with a glycol recirculation circuit driving our re-corable coaxial hose and tracing technologies, we were able to concentrate the temperature control function into a small package that could be mounted close to the gun and extend the “temperature control envelope” all the way to the “point-of- application”.

    As shown in Figure 4, this produced a stable, controlled temperature all the way to the gun. The result, a near doubling of the C pk , and a reduction of holds for liner weight by nearly 50%! With temperature stable and controlled, other critical process parameters, like pressure regulation, could be independently examined.

    Figure 4: Controlled Process

    The opportunity for process improvement in this situation is limited only by the time and resources available to be dedicated to its pursuit. But at some point, it becomes a case of diminishing returns…

    Download our free case study to see how temperature control improved operational quality and efficiency for this manufacturer.


    Topics: Manufacturing

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