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.