Let’s talk about something that it is not controversial!

And then, there are those things that are not controversial (confused with this beginning? Please check my previous post).

Those things that everyone agrees upon. Those topics that generate a broad consensus.

In a glass container plant, one of those – rare… - subject’s, concerns Critical Defects.

The definition of critical defect does not leave any doubt: “defects that could or are likely to result in hazardous or unsafe conditions for individuals using the glass container or be injurious to their health, under normal conditions of use as defined between the glass manufacturer and the filler.”

Or in other words: “A defective condition on the bottle (or jar) which can/may cause physical injury or even death to the consumer or our direct customer during normal use/operating conditions. Based on judgment and experience indicates that it could likely result in a substantial Customer or Consumer complaint.”

Bottom line: when they are detected every effort must be made to avoid that the defective units reach the pallet and are shipped to the customer- at all costs!

The examples of defects that are considered to be critical are not even arguable:

-Bird swing, spike (any plunger pull on the container inside surface), over press/wire edge finish, flanged finish (horizontal glass projection at guide ring and neck ring match area), chipped finish, internal stuck glass; internal loose glass; internal soft blister, sharp external stuck glass, sharp (or could be broken to become sharp) seam, etc...etc.

Basically we are referring to any defect that could result in a substantial Customer or Consumer complaint.

Off course there are some less obvious.

Here I would include for instance defects that can affect the sealing surface of the glass container and therefore cause the loss of vacuum and ultimately spoil the filled product (being that the case).

Upon detection, or even the suspicion of occurrence, actions must be undertaken immediately both in the Hot End and the Cold End.

The secret about any defect is to make sure we are in control, not the defect.

As long as we know when it happened and then can TRACE/TRACK it effectively, we will never have problems.

The most important is to immediately eliminate risk (reject at Hot End) and make decisions in CUSTOMERS’ favor.

A detailed report, as per procedure, should be required for each and every CRITICAL DEFECT we identify during production.

Independently if the defect is detected in the Hot End or in the Cold End the procedures usually establish redundant mechanisms.

These mechanisms usually imply that some final product is rejected – just to be safe – even though it is reasonably admitted that no critical defected was packed.

We find small variations in these procedures between glass manufacturers but we can safely say that the final goal in all is to make absolutely sure that no critical defect is packed and unintentionally sent to customers.

From my experience there are two situations of great concern in what regards the management of critical defects:

• ON and OFF situations (the defect occurs intermittently);

• The critical defect runs in the production (more of what is in the Lehr at time of detection).

Now this is a REAL issue when the defect is of difficult visual detection and the inspection machines struggle to reject it…

Let me give you the following analogy (with the courtesy of a very good friend of mine).

Let’s imagine that the plant floor is a football pitch (soccer pitch if you are in the US).

The operator that is the Hot End in the IS machine is the striker and the operator that is the Cold End (the Quality Inspector so to speak) is the goalkeeper.

The goalkeeper has the objective of stopping all the balls (defects) that the striker shoots at him preventing that they reach the goal (the final pack) - preventing a goal of being scored.

I have to say that off course the objective of the Hot End operator it is not to produce defects. It does not want to score a goal. This is just an image to illustrate a specific situation.

If the striker does not shoot too many balls at the goal keeper at the same time the goalkeeper can defend its goal and prevent the score.

But if the striker starts shooting various balls simultaneously in different goal directions the goalkeeper just it is not able to stop them all. Some will relentlessly go into the goal.

The best way to break down a system is to overload it!

Basically this means that while the Hot End works on the critical defect, it must be simultaneously rejected at Hot End.

And that rejection only must be stopped when we have absolutely sure that the critical defect root cause was found and corrected!

In the Hot End it is better to not jump to conclusions too early and allow sometime for confirmation.

Follow-up in the Cold End – after the defect was declared fixed - is critical!

Let’s talk about something controversial!

You know…

There are those subjects that when come up during a conversation between friends are bound to give much discussion.

I would say that: politics, religion and sports are perhaps among those subjects that frequently have the effect of stir up the spirits.

In a glass container plant there is one particular matter that has a similar effect (OK! Among others…)

And that concerns visual or cosmetic defects. Or more precisely the actions or procedures to take when there is the detection of such type of defects.

To put the question in very candid terms usually the discussion turns around: if detected we should reject or not such type of defects. After all, the glass producer is “tolerated” to produce a certain percentage of those of defects, isn’t it????

Let’s take a step back for a while and see where it all begins.

Unfortunately, producing glass containers it is not an activity free of producing defective units. There will be defective units in virtually every production batch. And this is true even after the producer has checked each individual product (trough automatic inspection machines)!

Is there anyone who can guarantee that automatic inspection is 100% reliable?

When the defect does not result in life or death outcomes, the supplier it is not expected to deliver defect-free goods. I am not saying the glass filler will not always demand that from the glass supplier. And I know that there is not a single glass supplier that will approach its customers saying: “most probably in this batch of bottles that I am sending to you, you will have defective units”.

I am just saying that there is the need in the supplier/customer relationship to set the limit between acceptability and refusal in a way that can be agreed upon and measured.

That limit is called the “AQL” – Acceptance Quality Limit.

Defects are classified in three main groups: Critical Defects, Major Defects (sometimes subdivided in Major A and Major B) and Minor Defects. Each glass defect is then framed accordingly with this classification.

For each one of the former defect categories are established AQL levels (quality level that is the worst tolerable process average when a continuing series of lots is submitted for acceptance sampling). These AQL levels (given in percentage) will ultimately translate in acceptance and rejection numbers for determined sample sizes and type of defect.

Usually there are standard AQL levels that the producer uses for its standard catalogue products and sometimes for exclusive products – sold exclusively to a single customer – are agreed specific AQL levels.

So, in a way, AQL’s seem to respond to the question concerning the percentage of visual/cosmetic defects to reject or accept.

But then there are some curious variations…

Like different sampling plans with different AQL levels for glass containers destined to the local market and the export market…

It makes one wonder if the customers are more or less demanding depending of their geographical location… (Just being ironic!)

AQL levels are a tool for regulating – commercially – the relation between producer and supplier. But operationally – on the glass plant shop floor – it poses a couple of challenges. Most notably in terms of communication of Quality Standards.

Quality Inspectors like any other “inspection equipment” need to be “calibrated”. Their criteria must be in line with the criteria defined by the Quality Manager. So every caution must be taken when communicating the concept of AQL and its implications to the quality inspections.

It cannot transpire the idea that it is allowed to produce a certain quantity of defects. AQL is not a Desired Quality Limit.

Also we cannot allow that it is perceived that some glass containers must have better quality than others depending if they are destined to customer A or B or market Y or Z.

The actions undertaken by the Quality Inspectors must have the ultimate goal of preventing that defective units are packed. Independently of the defects severity or AQL classification.

So this brings us to a hot topic.

Glass manufacturers are very much focused on efficiency. In fact – efficiency – is perhaps the most important KPI (Key Performance Indicator) in a glass plant. Even more important than Quality related KPI’s like a Quality Complaints index.

Now that is a controversial statement!

So everything that hurts efficiency in a glass plant is took very seriously and object of great discussion. So it is not rare to find moments of tension and eyebrows raised when:

• A visual/cosmetic defect is detected in an inspection at the end of the lehr and rejected with the Mould Number Reader;

• A visual/cosmetic defect is detected in a light screen inspection and it is not possible to adjust the appropriate inspection machine (the rejection it is not consistent) to reject the defect. Finally the defect is rejected in the Mould Number Reader.

The argument is: why reject with 100% efficiency a defect that is “allowed” in a certain percentage? We are losing more-or-less-good bottles (or jars)!!!!

Things have – are – changing.

Most of the times because of customers or market demand and pressure.

In fact, ourselves, the final consumers, we are the driving force behind the ever increasing demand in terms of Quality.

Having clear instructions known and understand by all players at the plant floor level it is a great help.

The procedures usually take in consideration the occurrence frequency – if it is continuous or intermittent – and severity of the visual defect, establishing the correspondent action:

• Immediate rejection by MNR and information for correction to the Hot End;

• Information to the Hot End, allow one lehr time for correction and if not corrected rejection by MNR.

If the procedures are clear and people know what they are doing that usually works.

I believe there is also a word for that: training.

Mould Number Reader (MNR) = Basic Tool for Quality Control

Personally I am not a fan of DIY jobs.

In fact I try to avoid them at all costs. I prefer to pay to professionals who – for sure – can do the task much better than I will ever be able to. It is a question of personal taste and also much clumsiness.

But from time to time there comes the occasional emergency where I have to get my hands dirty.

In those rare occasions one thing that I have found at my own cost is that there is always the right tool for the task at hand.

If you try to use the not-so-OK- but- I- think-it-will-work-tool usually things won’t work.

Or perhaps they do, but it will cost you double of the effort and the final result will not be perfect.

Unless you are Portuguese…We proud ourselves to be very good at improvising.

In my opinion just an excuse for bad planning…but that it’s a different story…

Coming back to our analogy.

For the Quality Inspector in a glass container plant, the tool that cannot be missing is the Mould Number Reader (MNR).

It would be like that if your job was to hammer nails.

But...without having a hammer.

You can do it…but it will take you more effort (and time) and the final result will probably be a crooked nail.

The MNR is an equipment installed in the line inspection machines which reads a code engraved in the glass containers. This allows the recognition by the inspection machine of the mould number that is being inspected.

The code is usually engraved in the body of the container – dot code, placed in the heel area – or in the bottom – as an alphanumeric code. What determines if a dot code or alphanumeric code is used is the type of MNR reader that is installed on the inspection machines. The type of reader used will determine the engraving area and type of code.

The fact that the inspection machine “knows” what is the container mould number that is being inspected at all times has two important advantages.

First, it allows that the machine can be programed to reject systematically specific mould numbers.

When a defect is detected at the Cold Inspections or informed by the Hot End – from its inspections as well - it is the Quality Inspector responsibility to guarantee that the defective containers do not contaminate the packed product.

If in the “old days” it was admissible to have the Quality Inspector rejecting by hand at the annealing lehr exit the defective containers, nowadays with bigger and faster IS production machines that task is simply impossible and in fact not reliable. Simply put, there is no time to do it!

In our days, the Quality Inspector programs the MNR to reject specific mould numbers accordingly with the outcome of the inspections performed in the Cold End or Hot End.

This rejection is automatic and systematic regardless if the container actually has a defect or not. Remember that the occurrence rate of a defect in a specific mould is not always 100% (on the contrary!).

A second outcome is that it allows the collection of valuable information that associates defects to the mould number of the inspected containers.

Most of common process defects are mould/cavity related.

When an inspection machine inspects a container and detects a defect and rejects it, “knows” the container mould number. That number is collected, treated statistically and displayed on screen. This is key information for process correction.

But it is not all rosy!

The MNR must always be effective!

We have to have absolute sure that upon programing a mould number for rejection ALL containers with that very same mould number – from that point on - are rejected and are not packed in the palletizer.

That is when the reading efficiency comes into play.

Reading efficiency is the percentage of good readings: the ones which the machine identifies correctly the mould number of the container.

We are aiming for a 99% of reading efficiency. The standard that we see in many glass plants is 97% and above.

The reading efficiency of the MNR is a parameter that must be regularly monitored and actioned if the efficiency is not satisfying.

It is always possible to make absolutely sure that defects are not packed even though the reading efficiency is not at 99%.

We can program the inspection machine to reject the remaining percentage of mould numbers in which the machine cannot identify the mould number, regardless if they have defects or not.

Although guaranteeing the rejection we are prejudicing plant efficiency since some of the rejected containers are free from defects.

The reading efficiency is strongly hampered if the code engraving it is not clear and prominent. If the code starts to fade the Quality Inspector must report and ask for the necessary correction to its Hot End counterpart.

This is one of those occasions where we can test if there is real team workbetween Hot End and Cold End. They must work together for the greater good of always having a high mould number reading percentage.

For example, upon detection of a critical defect – always an unexpected situation - all procedures to undertake must guarantee without any reasonable doubt that the critical defect was rejected and did not reach the pallet.

It is easily understandable that in this situation it is of special importance rejecting the critical defect using the highest mould number reading efficiency.

In parallel – before using the MNR - the best practice advises to always test for repeatability: program mould number, test rejection X times, check total number of rejections; thus confirming that the MNR can be trustingly used.