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In my last post, I explained that the IPS (Inches Per Second) measurement came about as a strength rating for glass producers.

Today, IPS is fast-becoming a vital measurement tool for fillers trying to design and process a lightweight bottle design without reaching a breaking point (literally) where it cannot withstand the impact it receives on a given line.

When I started out in this industry I asked a lot of questions to better understand IPS. As anyone who has ever Googled ‘IPS Glass’ or an equivalent search string can attest, it’s historically been a term used in glass production and isn’t particularly well documented outside of that industry.

So, let’s dig into what an IPS rating of a bottle really means.

What an IPS rating means:

The glass producers that I contacted to learn about the IPS rating mentioned that they use the industry’s standard testing device, an impact pendulum, to test and verify the rating of their bottles once they are produced.

The pendulum method entails a pendulum striking the bottle using a defined amount of impact in Inches per Second (can also be Centimeters Per Second or CMS) by a known mass, so that bottles can be tested under strict guidelines and standard impacts.

In the simplest terms, the IPS rating of a bottle means that a bottle is certified to have a given percentage of breakage when it is tested on a pendulum. It isn’t an automatic guarantee that breakage will occur simply because a bottle receives an impact greater than its IPS rating, however the probability of breakage will increase.

As an example, let’s assume a particular bottle is designed with an IPS of 20 and a breakage of 1 per 10,000. If that bottle receives an impact measuring 25 IPS, the bottle may not break but its likelihood of breakage will increase considerably. All of this depends greatly on the bottle itself but for the bottle in our example, an impact of 25 IPS may mean that the probability of breakage increased to 5 per 10,000 bottles, or five times greater.

It is also important to know where the impact happens, particularly if the impact happens in the middle of the body of the bottle. The middle of the body of the bottle is more forgiving (flexible if you may) than the shoulder or the heel. But we can talk about this more on another post…

Fact re: Lightweighting


So, why is IPS such a vital tool for the bottling industry? 

Over the last few decades the push has been to reduce the weight of the glass bottles. Fillers want to reduce container costs but at some point, putting less glass in the bottle will cause the bottle to be more fragile and break easily.

In The Wiley Encyclopedia of Packaging Technology, author Kiy L. Yam explains, “Lightweighting is perhaps the most important innovation in keeping glass packaging competitive. The rules for performance of lightweight designs are no different; stresses generated from the applied forces must not exceed the surface strengths. However, as glass is removed from the design, the stresses will increase with decreasing wall thickness and there will be a limit to lightweighting when the surface strengths of the bottle are exceeded.”

We established that when bottles are impacted with forces higher than their IPS rating, the result is higher than expected breakage rates on the filling line.

I’m not breaking news that breakage creates downtime. Reduction of downtime is crucial in the running of efficient plants. Breakage creates mess. Breakage takes product off the line that is already filled, due to possible contamination. Breakage can cause injury.

The bottom line is that breakage costs money.

If there is excessive breakage on a line, who is at fault? Is the line running too fast or is the bottle not up to standards? The development of IPS has helped in many ways to reduce breakage and questions of fault.

Does the industry have the tools it needs to solve the breakage puzzle?

My next blog will look into other ways to calculate IPS and look at the various effects of variables such as spin, tilt, scuffing and shock that containers ‘experience’ and whether these dictate a more dynamic IPS calculation for fillers and glass manufacturers alike.