A business associate recently posted on my forum on linkedin : https://www.linkedin.com/groups/6966345
Need to know the procedures for conducting the leak test of pouches made of different laminates and of different products.
The baseline for setting the vacuum pressure, hold time, delay, release time etc.
Is there any standards for different laminates or pouch sizes?
Thank you in advance for your kind support.
I answered as follows :
Hello Mr. Karthick.
Thank you for posting your query on this forum.
Hope my answer below is helpful to you and other readers. You all are welcome to share your views. Maybe your views can help enhance my “limited” knowledge on this “vast” subject of packaging.
Firstly lets define Leakage :
“the accidental admission or escape of liquid or gas or light through a hole or crack.”
Or in simpler words relevant to our subject, “an Undesirable Escape of product from its container / packaging” can be termed as leakage.
Surprising though it may sound, there is nothing in the world called as “Bullet-Proof” or “Water-Proof”. A bullet-proof vest is actually a bullet-resistant vest which is resistant only upto a certain calibre of projectile fired from a certain distance. A Water-proof watch is actually a Water-Resistant watch which is resistant only upto a certain depth or certain exposure time.
Similarly, there is nothing like a Leak-Proof container. It is actually a leak-resistant container which is resistant to leakage only upto a certain pressure or condition. Beyond which it will start leaking.
So, any and every container / package will leak. The higher the resistance, the better the container.
There are 2 general types of Leak Tests.
The Vacuum Leak Test which is the most common one and is used for almost any kind of impervious package such as bottle or pouch or sachet, etc.
The Pressure Leak Test which is useful only on Semi-Rigid packaging such as bottles.
The Pressure Leak Test is done by closing the open end with a plug and injecting air into it and holding it under pressure for a second or 2. If the pressure drops, it signifies leakage. This test has its own flaws and is highly dependent on the sealing plug quality and certain other factors.
Variants of this test enable online pre-fill leak detection of 100% samples which is a positive point in its favour. Automatic rejection system can also be added to the filling line to remove faulty containers before they reach the filling station.
Other variants also allow you to test the Filled Containers by pressing the side walls and measuring tightness. Not a fool-proof method but has its own set of advantages.
Coming to our main topic of discussion on Vacuum Leakage Test.
Vacuum Leakage Test (VLT) is done by placing a package in a transparent chamber like a Dessicator, applying Vacuum and holding it there for some time.
VLT is primarly of 2 types. Wet Test and Dry Test.
If your product is solid or in powder form and the package has air inside it, then its better to test it submerged in water. When vacuum is applied, the pressure in the Tank reduces and drops below atmospheric pressure. The air inside the package will start expanding till the pressure inside the package is equal and opposite to the vacuum level. So if you have a 400 mmhg vacuum in the tank, the pressure inside the packaging with be + 400 mm hg. If there is any pinhole or leakage in the pouch / container, you will see a stream of air bubble emanating from the package. We then hold the vacuum at this level for some a few seconds. During this period, weak seals and capillary defects (which were not immediate leakages, but would have failed anyway in the market), will open up and show airbubbles. The vacuum is then released and tank brought back to normal atmospheric pressure. The packages are then removed and cut open to inspect the content. Is it wet ? Sometimes packages may not show air bubbles but you will find that the end of the test the water will have penetrated into the package through the leak points.
If your product is in liquid for, then you can test it in dry condition also. The product will pressurise during the vacuum phase and will ooze out from the leak points, if any.
This test is very easy and versatile. Unfortunately it is unable to detect micro-leakages from packages which contain high viscosity fluids. Eg. Ketchup, Paste, etc., because the product itself blocks the pinhole and prevents escape of air / product.
Another new concept coming up in the market is of Micro-Leak Detection systems which uses a combination of Gas and Gas sensors to detect leakages. We shall be introducing a product of this type in the first quarter of 2016 to the Asian Market.
Coming back again to our main topic and your question of “How much Vacuum” and “How much Hold Time”.
As I said in the beginning, there is nothing as a Leak Proof Packaging.
All packages will leak (or burst) at a certain pressure.
The higher your need for quality, the higher will be your Vacuum and Time setting.
Company A is a local manufacturer of Tea in pouch. His distribution is in a range of 300-400 Kms. His product gets sold in less than 1 month and his brand is not a very famous one. He will suffice with 300 mmhg and 30 second test.
Company B is a Multi-National giant packing Tea in a pouch. His distribution is in a range of 1000-2000 Kms or even export. His product gets sold in about 3-6 months and his brand is a premium one. He cannot allow a leaking package to spoil his brand image. He will need even 500 mmhg and 120-180 second test.
There is no “one size fits all” concept here.
The basic rule of thumb is that start at 300mmhg and check if market complaints are getting reduced. If not, increase the vacuum and / or time. Till the point you reach a scenario where your market complaints are zero or negligible. Then use it as a benchmark for regular testing.
ASTM D 4991 specifies a method wherein the vacuum is gradually increased to about 950mbar to detect the level of vacuum at which the Rigid Containers (Bottles) start leaking.
ASTM D 5094 (Method B) specifies a Vibration Test followed by a vacuum leak test at 250 mmhg for 10 mins.
ASTM D 3078 specifies “Low”, “Medium” and “High Vacuum” Test levels at 30 second for Flexible Packages. Low = 305-330mmhg, Medium = 457-483mmhg, High = 609-635mmhg.
Another scenario is that you need to ensure that your package is worthy of Air-Travel in non-pressurised Aircrafts or fit for use in high-altitude locations. ASTM 6653 gives a table of various flying altitudes and vacuum / pressure levels at those heights. Eg. If you need to ensure that your product is safe at an altitude of 20,000 ft above sea level, set the Vacuum Leakage Test to be greater than 411mmhg.
More data on this is available on http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html
Note—Since we are using vacuum gage, you must subtract the desired mmhg from 760 to achieve the vacuum mmhg. For example, 760 – 349 = 411 vacuum mmhg, equating into 20,000 ft.
Hope I was able to explain the method and values properly. And the information was useful to you and others.
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