Historical Perspective of Sealing Validation
Despite technological advances the tube industry has not kept up or taken advantage of new technology. And while the European Union has adopted tube sealing standards, the United States has yet to implement modern industry consensus standards.
Weakness in Testing Phase
Tubes received from tube manufacturers have negligible standards for empty tube testing. We know of no company that has adopted a true incoming product evaluation. What testing is done is mostly superficial – they may measure physical dimensions or the wall thickness with a micrometer, weigh it, or look at the number of layers – but those do nothing to determine the tube’s most important features: the ability to seal and the parameters that are required to properly seal the tube. In most cases defective tubes are not found until they are run on the production line… too little, too late.
The industry’s test and evaluation equipment is equally outdated. What little test equipment there is on the market does not fully test the tube and are primitive in design. The rare exceptions are offerings from AnC Precision.
Weakness in Production Phase
The limitations continue with the filling and sealing machines in the production phase. Instead of precise stepper motors, many still use outdated technology like mechanical cranks, chain drives, sprockets, cams, and air cylinders, and few have electronic controls.
Surprisingly, the tube’s ability to seal is not evaluated until it is already filled and sealed on a production line, and even then only by simplistic methods like pressing or stepping on the tube and looking for leaks. This method is not scientific as each test person may exert different pressure. If it is automated (often with the aid of an air cylinder) it still does not accurately evaluate the quality of the seal. In some cases a production run is interrupted in the middle to test new empty tubes, thus throwing off what few production parameters have been established.
Example Scenario
Let’s examine some potential problems that could occur if accurate and appropriate measurements are not available.
Suppose we have a typical plastic tube. Through our testing, AnC Precision has found these tubes are capable of, say, a True burst pressure threshold of 40 psi as measured on the inside of the tube. However, many manufacturers routinely use 25 or 30 psi for their burst testing, are satisfied with that, and consider it acceptable. It is their upper bound value; it is also their lower bound value. We advocate that 40 psi – what the tube can actually handle – be the upper bound, rather than 30 psi that the industry now settles for.
We can still make a production run go / no-go decision at, say, 25 psi, but tubes should still be periodically tested at 40 psi.
Now, suppose during the course of a production run the tubes are holding good at 25 psi, and at some point we do a test at 40 psi and the tube fails. Even though the tube would have passed a test of 25 psi, we now know that something (e.g., temperature, pressure, dwell time, or a small difference in tube thickness) has changed in the process. We should investigate what has changed and fix it before continuing production.
By having an acceptable range, not just one value, we can more easily detect an undesirable trend and be proactively alerted to undesirable process changes before we have a bunch of burst tubes on the production floor.
The purpose of this example is to illustrate the importance of knowing and monitoring the exact values at which the tube will burst. The corresponding test pressure will provide a better understanding of the product that you are producing and provide a more consistent reliable manufacturing process.
As we will see, AnC Precision products are the only instruments on the market which methodically measure and record all of the parameters of the tube’s sealing process.
Tube Industry Ready to Adopt New Model
General Concepts
We envision a future where modern manufacturing process standards are commonplace in the tube industry. AnC Precision is able to meet this challenge today.
Tube manufacturers will be required to provide test data on the tube’s ability to seal (e.g. temperature, pressure, dwell time, etc.), and the values at which the tube will burst (e.g. 30 psi). This can be accomplished using two AnC Precision machines.
- Sealing values (temperature and pressure of the hot air, and dwell time) are determined by the tube manufacturer (TS-100 Tube Sealing Machine).
- The sealed tube is then tested for its burst pressure psi using a true pressure test instrument (PTS-100).
The collected test data is then passed on to the buyer (the tube filling company) along with the tubes. Tubes are only shipped if the test data results are acceptable by the buyer.
- When the empty tubes are received at the tube filling company in the United States they are again subject to incoming test and evaluation using AQL lot sampling[1] and the same methods and instrumentation as used by the tube manufacturer.
- This collected test data is used to set up the production line parameters (temperature, pressure, dwell time, etc.).
- After incoming acceptance testing the tubes are evaluated for maximized performance on the production line, defined as the maximum number of tubes per minute while still meeting the manufacturing criteria.
- The tubes are accepted and ready for filling. Tubes in the production line are randomly tested with the same AnC Precision instrumentation to ensure the production line is set up correctly and is producing reliably-filled tubes that meet their manufacturing criteria.
SUMMARY: In this model the tube is tested along the entire path and there is assurance of no surprise production loss.
Solutions from AnC Precision
AnC Precision machines electronically determine the tube length and automatically self-adjust. They are the only machines that record and report findings using printers, USB memory sticks, and Ethernet interfaces.
Footnotes
[1] Acceptance Quality Limit is defined as the “quality level that is the worst tolerable” (source: ISO 2859-1 standard).