By nature glass is a material which is peculiar. It is very strong if undamaged and very weak if severely scratched. Its strength it is highly dependable of the surface condition and the presence of stress concentrators.
Glass container production is a high speed mass production process.
Some defects may be present for a short time and then disappear, other might pop-up unexpectedly.
Glass container production will never result in “zero defective”. Glass containers are primary packaging and thus the allowable number of defective bottles is low.
Any glass production line therefore needs to have a variety of container inspections (machines, human) to detect and remove non-conforming bottles and jars (refer to post “Quality Control (QC) activities in a glass container plant – Overview.”).
All faults (defects, the stress concentrators) must be eliminated before they reach the palletizer. That is, so to speak, the primary objective of the quality control activities in a container glass plant.
Equally important is the collection and spread of all the data and feedback that outcomes from and concerns to all controls performed along the process. This is crucial for fault correction.
Often the fault is detected downstream (at Cold End) requiring a correction upstream (at Hot End).
The quicker the information reaches the agent that can act on the process – for correction – less defective units will be produced, rejected, scraped …
In this industry, it is easy to understand that for the effectiveness and efficiency of the Quality System is key one communication process: the communication between Hot End and Cold End.
It helps both areas. Improves and makes everyone’s task easier in the plant. Improves efficiency which means that improves Quality.
In a glass plant: high efficiency means low defect rate, which translates in production stability.
Communication must be bidirectional: from the Hot End to the Cold End and vice-versa. In the end communication is all about trust.
If the defects are timely informed, in an accurate and dependable way:
Increases the trust placed by each one on its counterpart;
This trust is returned in the form of better information;
Trust is gained with rigor and accuracy in the information provided;
Accurate and detailed information must be exchanged, reporting:
Mould number with problem;
Inside or outside cavity;
Area of the container with defect: finish, body, bottom, mould seam,…,
Rejection percentage of inspection machines (if detected at the Cold End);
Samples of defective containers must be delivered to the Hot End (if detected at the Cold End);
When reporting defects to the Hot End – from the Cold End - one key aspect of the communication process is to prioritize what to communicate.
Analyzing the different defects of the container;
Order the defects by importance;
Informing immediately the Hot End colleague of the most severe defects detected;
Follow the less severe defects detected (prevent that they became more severe, follow-up trends);
Inform less severe defects when there are no other priorities.
Nowadays is frequent to see glass plants operating some kind of computer based system that manages the data collection, spread and display. Records are performed electronically and messages are exchanged between areas.
Records and messaging comprise:
All production losses;
Information of moulds rejection by mould number reader and inspection machine;
Warning messages (both ways);
Information also when there are no rejections (allow to know production trends, are inputs to decision making);
Mould change (verification and validation at Cold End);
Hot End rejections: for later verification at Cold End (after lehr time);
Of the most importance is to record all occurrences: an inspection which was not recorded does not exist!
Two more aspects of communication in a glass plant should be mentioned:
Communication between (within) shifts prevents surprises and facilitates the anticipation / prevention of problems. It facilitates the work of all and it must be oral and written (for the review of previous shift records).
It is done each with its counterpart. Major shift events must be reported. Also, the most frequent defects detected and mould numbers with more problems. Physically, the samples of the major defects detected must be reviewed together.
Communication between shifts and day-shift team it is done through Supervision and it is an important input for the Production Daily Meeting.
It is very important to leave - for review of the day-shift team – samples of defects whose rejection depends of the shift criteria (more frequently cosmetic defects).
Thus, visual standards of acceptance / rejection can be established and a criterion is standardized. Critical periods can be limited and decisions can be taken regarding the packed production (eg. colour variations, seeds and bubbles,…,).
It is crucial to convey to the Supervision the shift concerns and difficulties. These help to set the work priorities of the day-shift teams.