Heat Seals… the good, the bad, and the ugly!
Chances are if you’re reading this article you likely have some type of vacuum packaging machine. Dating back to the 1940s, vacuum packaging continues to be the best solution for extending the shelf life of most perishable goods. Without the need for freezing or adding unwanted preservatives, fresh meats and countless other products can benefit from vacuum packaging. However, the positive results associated with vacuum sealing are greatly diminished when your packaging equipment is not properly maintained.
In this article we’re going to review a common problem with vacuum sealed products and a few potential solutions that may save you a lot of time and money. Commonly referred to as “leakers”, you may find that a percentage of your vacuum packaged items will loosen up over time thus exposing your product to oxygen and microorganisms that contribute to spoilage. Since a slow “leaker” is often not immediately identified they can easily be overlooked and sent out to customers. Many times, defects in the packaging materials are thought to be the cause of a slow “leaker” but more often it is actually the heat seal applied by the machine that is compromised. So, let’s assume no changes have been made to your process, what should you look for to reduce the risk of “leakers”?
Answer – check the heat seal applied by your vacuum packaging machine. Is the seal too hot, too cold, not enough pressure, too many creases, or simply no seal at all? Knowing how to identify a good heat seal from a poor one is critical when determining the cause of a “leaker”.
A good seal requires three things; pressure, temperature, and a flat bag.
Hold your vacuum sealed bag up to a light so you can really see what’s going on. Poor seal pressure will result in a seal that looks spotty or broken. If this is your problem, then you might be tempted to correct it by turning up the seal time, but this won’t provide results you’re looking for. The most likely cause would be a leak in your machines seal bellow or piston. Depending on the manufacturer, your machine will either have bellows or pistons located up in the lid or on the deck. Both systems require either atmospheric pressure or compressed air to be introduced in order to pinch off and seal the bags inside the vacuum chamber. Over time these bellows or pistons will likely develop leaks and loose their ability to provide adequate pressure during the seal process, thus resulting in a spotty seal and dreaded “leakers”.
What if the seal pulls apart too easily and won’t hold up during normal handling? You may simply need to adjust your seal time so the wire heats up more. Or maybe the seal wire you’re using isn’t correct. Every machine is designed to use a specific width, shape, and thickness of seal wire. When replacing you must verify that the Teflon tape and seal wire being installed is in compliance with the manufacturer’s specifications. Another cause for a weak seal might be that your seal wire isn’t properly isolated from the bar itself. Many machines are equipped with metal sealing bars typically made out of aluminum. These bars provide significant advantages over fiber bars because they can last forever if cared for properly. However, electricity will find the path of least resistance so it’s possible that a weak seal may result from a seal wire not receiving the power it needs so check to make sure your wire is isolated properly.
A Flat Bag
Oftentimes the most likely cause for a heat seal “leaker” is also the most obvious. Pay close attention when laying bags across the bar prior to closing the lid. The opening of the pouch should be laid flat across the bar and needs to be long enough that the mouth is able to close. When is comes to using the correct vacuum pouch, size does matter! Don’t settle for using vacuum bags that are too short or too long just because your supplier doesn’t carry them. JVR carries over 100 sizes of 3 and 4mil vacuum pouches to fit every product. Improperly sized bags will be difficult to lay flat and you’ll likely discover unwanted creases in the seal area. Every crease doubles up the amount of plastic being sealed, and most machines are not designed to seal through four or more layers of material. So next time your running your vacuum sealer check to see how the bags are being laid across the bar because it might be the reason for your “leakers”.
This article is one of a series of troubleshooting articles meant to assist customers in addressing concerns with their vacuum packaging equipment. If you’re currently vacuum packaging but aren’t satisfied with the results you’re receiving, then please consider contacting tech support at JVR Industries. Based just outside of Buffalo, NY JVR has specialized in vacuum packaging equipment for over 45 years and offer free over the phone technical support for all brands of equipment.