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IN FOCUS

Standard closures are simple while sports caps are complex?

Big variety: Challenges in closure quality inspection

Dr Gerd Fuhrmann

It’s not that easy, but it’s safe to say that all kinds of closures need attention in quality inspection as there are numerous defects that can occur during production. While quality inspection is a necessity for standard one piece closures, it’s especially true for sports caps which have gained popularity in recent years. The diversity and complexity of these plastic closures have rapidly evolved to support a wide variety of functions. Due to this, these more complicated closures demand high quality in order to perform their essential duties.

The rise in sports caps can be attributed to a growing population engaging in fitness activities as well as anyone that can benefit from one handed opening and closing of their favorite drink. In most industrialized nations in the last few years, this desire for convenient consumables has increased the demand of sports caps. To put it simple: The more active people are, the more they need the “on the go” ease of plastic bottles topped with sports caps.

While “classic” standard closures like one-piece caps for water and soda need an exhaustive inspection just as ever, technology has advanced to allow for sports caps to be thoroughly inspected as well. First off, for all closures, its best to inspect as quickly as possible after production. The simple reason: Upon detection of defective parts, the operator needs to be alerted to correct the specific defect by adjusting their production parameters to return produced parts to within tolerance and prevent further scrap. Secondly, an inspection must be detailed and precise. While this is a very obvious demand, it can be a challenging task - especially when a multi-piece specialty closure has to be inspected. Due to their complex structure, inspection must be performed from multiple angles with special lighting to detect defects. Meanwhile, production lines are continuously increasing output. That’s why there has to be a reliable and fast quality inspection to support a constant production speed without interruptions. 

Fig. 1: Hard to inspect: complex multi-piece closures

Vision Inspection Systems

Due to the many requirements and the wide variety of plastic closures, it is impractical to look for an “all-in-one” inspection system. Closure manufacturers must choose carefully in which way their parts are inspected and which specific quality criteria must be ensured. For instance, there is no benefit in having an inspection system for the head plate decoration if your client’s crucial need is to ensure seal cone quality.

For complete quality inspection, a vision system has proven to be a worthwhile option. The CapWatcher III by Intravis is a vision system for inline inspection of 100% of caps in a standard closure production line. It can also be used offline as a re-sorting inspection of suspect batches in combination with a bunker, sorter and octabin filler. It inspects one piece closures with single or multi threads with tamper bands. The CapWatcher III is the third generation of its kind, being developed for modern production rates up to 252.000 closures per hour. It is equipped with up to seven high resolution cameras to inspect even the most lightweight and translucent closures with thin walls and smaller tamper evident bands. 

The criteria of the inner inspection on a cap include diameter and ovality of the tamper evident band and the seal cone as well as color deviations, flaw lines, short and longshots. The outer inspection includes open and closed as well as vertical shortshots, contamination on the side walls, poorly folded flaps and closure height.

Additionally, one camera captures the cavity number on every closure, which is read by the system. A special object separation with integrated microhole inspection enables the correlation of detected microholes to the specific cavities. Also, all other detected defects can be assigned to their corresponding cavity. In the case of a defective cavity, the operator can enable the removal of all caps with the specific cavity number.

Fig. 2: The inner inspection reveals about defects and deviations like flow lines, liner inconsistencies and seal cone damage

Inspection of Specialty Closures

The CapWatcher SC is, in comparison to the CapWatcher III, not a predefined system off the shelf but a system strongly aligned to the according requirements. That’s why it does not have a specific form or equipment. The CapWatcher SC system inspects specialty closures like sports caps with flip-top and push-pull features as well as multiple tamper bands and assembled caps. The system builds upon the proven inspection of the CapWatcher III by adding inspections specifically designed for specialty closures. They detect a wide variety of material and manufacturing defects inspecting for a contamination-free appearance. The system inspects specialty closures on criteria like assembly faults, missing components, flawless tamper bands and damage to joints and hinges. Dosing inserts, liners and child protection mechanisms can be inspected as well. When necessary, an exact rotational positioning of the closure is automated, making inspection precise and safe. 

Integrated Inspection Systems

When space is a premium, an inspection system completely integrated into the production machine is also an option. The advantages are obvious: no extra foot print and the inspection system is reduced to cameras, lighting, software and an HMI. Even with this minimal configuration, inspection capabilities of an integrated inline system are just as robust as with stand alone systems. This is especially advantageous for assembly cap manufacturers. Deploying a vision system strategically inside the assembly machine can ensure the quality of the multiple parts before and the final assembled piece after.

Systems like these are individually manufactured alongside close development exclusively for a customer’s needs. Vision systems have proven to be an effective form of quality inspection. As you can see, closure inspections, just as the closures themselves, offer an endless variety.

Fig. 3: The CapWatcher III: With speeds up to 2.52.000 objects per hour, it inspects closures like one-piece caps for water and soda