A Tech Bite from Greener Vice-President & co-owner Matt Wojtech
This Tech Bite topic was recommeded on our Suggest a Topic page by one of our Technical Resource Blog subscribers. In return for using his suggestion, he will receive a collection of Greener Corporation merchandise.
Pressure + Heat + Time
Whether you are running a familiar flexible packaging material or converting to a new traditional or sustainable structure, Pressure + Heat + Time is the foundation for producing quality heat seals.
This Greener Tech Bite compares how the Pressure + Heat + Time sealing equation affects the setup of flow wrappers and vertical baggers and explains how these sealing factors are influenced by your specific packaging material and conditions.
A typical vertical bagger or long dwell flow wrapper might run at 60-80 packages per minute. A typical rotary flow wrapper runs faster, around 200-250 packages per minute, with shorter dwell times that make optimizing pressure and heat levels more crucial.
Pressure
Rotary Sealing Jaws
Sealing pressure applied by rotary sealing jaws is adjusted with springs or compression washers, but it is also affected by the clearance setting, sealing jaw serration design and alignment, and by the knife and anvil adjustment.
Pressure levels must be high enough to initiate a seal and to caulk off leakers by forcing melted sealant layer into gaps at the corners, along the fold of the fin seal or gussets, and at package wrinkles, but not so high that the seal is crushed or split.
Reciprocating Sealing Jaws
The application of pressure by the flat, reciprocating sealing jaws on most vertical baggers is simpler, with fewer variables. Sealing jaw serration design and alignment still have a big effect on pressure, but there is no clearance adjustment to fine tune and the fly-thru style knife does not create impact that alters pressure levels.
Even with the longer dwell times on vertical baggers, problems with leakers often stem from issues in the package formation process. Wrinkles and pleats create varying thicknesses in the package that can be difficult to seal across without damaging the package.
Heat
Heat is important on all machines, and becomes more crucial with the typically shorter dwell times on rotary flow wrappers. The optimum sealing jaw temperature setting depends on your flexible packaging material, the model, condition, setup, and running speed of your wrapper or bagger, and the design of your sealing jaws.
To ensure that your jaws are providing consistent heat across the package, check the temperature at multiple points along the sealing face with a contact pyrometer. (Non-contact pyrometers are less accurate.) You may find temperature variations between the middle and the ends, especially with larger, longer jaws on vertical baggers.
You can make this heat profile more consistent by coating heaters and thermocouples with heat sink compound, which fills in air gaps to improve heat transfer and sensing accuracy; by switching to preferentially wound heaters, which are hotter near the ends to compensate for typical heat loss there; and by utilizing sealing jaws made from a more thermally conductive material.
Temperature Window
It’s important to know the accurate temperature setting window for your flexible packaging material. The temperature window provided by your material supplier is a general guide, typically determined on a lab sealer with flat, non-serrated jaws, that can’t account for your specific conditions such dwell time, setup, and sealing jaw design.
You likely have standard sealing jaw temperature settings for each packaging material you run. But if you are experiencing problems, it’s a good idea to recalibrate this temperature window.
And if you are converting to a new structure, determining the material’s temperature window for your application is a vital step for setting up your wrappers or baggers.
- Start by running packages at production speed and make needed adjustments until seal quality meets your standards.
- Run additional tests, dropping the temperature by increments of 5° F, or 3° C, until seal integrity is unacceptable.
- Then add back 5° F (or 3° C) to this number—this is your minimum temperature setting.
Return to your original temperature setting, and make incremental increases of 5° F, or 3° C, until the package is distorted or damaged.
Subtract 5° F, or 3° C to get your maximum temperature setting.
- The span between seal failure and seal distortion is your seal temperature window.
Time
Thermal Transfer Efficiency
During the sealing process, Thermal Transfer Efficiency affects the dwell time required to transfer heat from the sealing jaws to the sealant layers of the packaging material. Improving levels of pressure and heat applied by the jaws can improve Thermal Transfer Efficiency and reduce the time required to produce a quality seal.
Greener’s XR™ Sealing Jaws utilize unique serration geometry to increase the pressure that can be applied to move sealant into gaps and seal off leaks without crushing or splitting the seal.
And by reducing temperature variation, XR™ and other jaw designs made from Dura-Therm material transfer more heat to the sealant layer without distorting or damaging the package.
By improving Thermal Transfer Efficiency, Greener’s advanced sealing jaw technology reduces dwell times to improve seal quality and allow faster machine speeds.
To learn more about optimizing Pressure + Heat + Time on your packaging application, contact Greener Corporation. We provide integrated parts and technical service solutions worldwide.
