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If you’ve been following my posts in this IPS series; we’ve already discussed what IPS (Inches Per Second) measurement is and how it relates to the bottling industry.
Basically, IPS is the glass industry’s strength rating of any given bottle.

This post will take a more technical ‘deep-dive’ into other methods of measuring IPS and introduce a more dynamic IPS calculation for fillers and glass manufacturers alike.

The many ways of measuring IPS – getting technical:

From Physics, we know that the magnitude of an impact is properly measured by integrating the acceleration waveform to determine the area under that curve, which would result in units of velocity, e.g. IPS

To integrate a waveform requires very high frequency data so a proper result can be calculated. A typical waveform for an impact on a bottle lasts about 1.5 to 2 milliseconds, so you need to have at least 80,000 to 100,000 samples per second (80 to 100 samples per millisecond) to properly capture the waveform.

We also know from Physics that the current speed of the bottle is equal to the total area so-far under the curve. This is illustrated in example below:

Freestanding Impact Acceleration Graph

In this example, the bottle was hit with an impact pendulum and a IPS rating of 47 IPS.

The total area under the curve is 18 in/sec. The bottle’s speed changed by 18 in/sec due to the impact.

Would you have guessed from the above graph that the pendulum was traveling at 47 inches/second (IPS) when it hit the bottle and started transferring its energy to it? Even in this very constrained example, the “area under the curve” does not equal the speed of the impacting pendulum.

The law of conservation of momentum says that we can calculate/predict the pendulum’s speed if we know the bottle’s mass and final speed and the impacting pendulum’s mass.

The difference in speeds (47 IPS in and 18 IPS out) demonstrates that the bottle was of much greater mass than the pendulum weight. If (and only if) they were the same weight, then the area under the curve be the same as the speed of the pendulum.

As we’ve already covered in my last blog post, many companies test bottles using the well-established pendulum method. Others with equipment such as the X-Ray Fluorescent Spectrometer and a Scanning Electron Microscope. And of course, I could go on.

Bottles can be tested using numerous techniques. The example shown above was a theoretical, but not very practical, way to test IPS prior to the introduction of in-line impact sensors.

Though some in-line sensors, including ours, have high enough sampling intervals to calculate the area under the curve; for now at MMAAZZ, we will continue using the pendulum device to calibrate sensors in order to use the same methodology that bottle makers use.


The dynamics of the real world versus lab testing:

Bottles have heels. They have shoulders. And of course, they have necks. On the line, it is as important to know where the impact occurs on the container as it is to know the magnitude. For instance, the middle of the body of a bottle is more forgiving, flexible, if you will, than the shoulder or the heel.


 

“Various strengths exist for different parts of the bottle. Also, strengths for momentary loading, such as for impacts during handling, are significantly different than those for long sustained loads.”

- Kiy L. Yam, The Wiley Encyclopedia of Packaging Technology



Not surprisingly, the real world is a complex environment with diverse variables that affect how a container responds to impact.

In-line sensors detect not just where on the line damaging impact is occurring, but can also detect where on the bottle variables such are pressure are occurring. Sensors are housed in an exact replica of the bottles being processed and travel along the line to collect this information dynamically. 

With real-time feedback from the in-line sensor, the operator can know exact locations on the line where higher pressure is taking place and what impacts the containers are receiving, in-fact here at MMAAZZ we’re also working on determining a rate of degradation from scuffing that a bottle receives on each pass of the line.


What fillers have to say about in-line sensors for IPS:

A significant point was raised by Carlsberg’s Senior Packaging Expert, Jane Tinning when she said, “Where glass breakage occurs is not necessarily the highest or only high-impact area.”

Specifically, in the case of Carlsberg’s first use of in-line sensors, it was determined that impacts received by bottles were causing damage on the bottle surface and weakening the glass, until other impacts downstream (though small) caused breakage. Without our sensors, Carlsberg could not have identified the weak point on its line.

Still have questions about IPS? Let’s talk.