It’s the first sunny day of the week and you’re sitting in your office thinking about heading out a little early to enjoy it when your line supervisor steps into your doorway to deliver the news you were hoping wouldn’t come…
“The Liner’s Down…Again”
“QC put the lot on hold – two skids that may need to be sorted before they can ship, and if those ends aren’t there in the morning, there will be hell-to-pay!”
So much for leaving early…
So What Happened?
And the story comes out…
“Everything’s been running fine all week. Then, right after lunch, the audit showed weights were up, and right after that, the vision system started kicking them out for placement. Rather than continue to make scrap, we shut the liner down. The mechanic is out there trying to get things running again.”
Maybe he will find something…
Answers Don’t Come Easy
So you talk to the mechanic and the results are not as clear as you’d hoped.
“It’s the same batch of compound we’ve been running all week. The gun seems to be operating just fine. The timer is spot on, and so is the pressure. I took the pressure down a little and got the weight back in line. Though the mount wasn’t loose and didn’t look like it had shifted, I moved it toward the inside of the groove a touch and now placement is good again. I have no idea what changed.”
The Answer Was Right Outside Your Window All Along
Unfortunately, you were looking for a problem with the liner – when you should have been looking at the forecast.
The real problem is the sun came out. And when that sun started beating down on the roof, it heated the header running in the trusses overhead and in turn, the compound got warm. As the compound temperature increased, its viscosity dropped, and from there, the issues with weight and placement cascaded until production was stopped altogether!
In our post, How Stabilizing Compound Temperature Improves Liner Weight Consistency, we noted:
“…the flow through a fixed orifice is dependent on the combination of the viscosity of the fluid being dispensed and the pressure behind it.”
Translation: the drop in viscosity allowed more compound to flow through the nozzle, even though the pressure didn’t change.
Then, in our post, Variation in Liner Placement Impacts Delivery, Quality, and Cost, too!, we described how that temperature related reduction in viscosity affects placement:
“When the viscosity is too low, the compound can spread out and become too thin to perform the sealing function properly. Even worse, as it flows it is subject to the centrifugal force from the rotating end. This has a tendency to pull the compound toward the outside of the groove.”
You Can’t Control the Weather
The weather is going to change…
This is so ingrained in our existence that we have designated the annual cycles with names like winter, spring, summer and fall. And we expect changes in our lives as we move through those seasons – all linked to the change in temperature. We have carried this over into our dispensing process expectations as well, with many manufacturers adopting summer and winter blends to compensate.
But do we stop to think about the daily and hourly variations that impact our processes? In our post, The Impact of Temperature and Pressure on Liner Weight Consistency, we related these changes this way:
“On a typical summer day, temperatures can fall to 60°F overnight and reach 90°F during the day…[and as a result] the viscosity of our compound will range from 2800 cps overnight to 2400 cps during the day. That’s a change of roughly 15% over the course of the day!”
And there is no way we can live with a 15% process variation over the course of the day.
So what are we to do?
Control What You Can
Modern temperature control technologies now make it possible to control the temperature of your process fluid all the way to the point where it is being dispensed on the end. This means your process can operate independent of variations in ambient temperature. And eliminating that 15% variation will dramatically reduce quality holds and machine downtime right at the source.
And you may actually get to enjoy that sunny weather after all!
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