TechnologyRESISTRON

RESISTRON impulse sealing system for thermoplastic films.

Modern packaging has to meet increasingly high quality and visual requirements. Ever faster cycle rates must be reconciled with the thinner and hence more sensitive film types which are in use today. This makes it even more difficult to guarantee a repeatable sealing process.

The “RESISTRON sealing system” developed by ROPEX is a complete system configuration comprised of several application-specific components. The two most important of these components are the RES temperature controller and the RES sealing tool. The RES sealing tool is a heat sealing bar with a heat sealing band and a matching counter bar which are tailored to your individual sealing application. By combining it with the system components, you obtain a customized system configuration.

Impulse sealing with heat sealing bands

Heat sealing bands are basically thin metal strips or wires made from a special resistance alloy, which must satisfy certain physical requirements. These strips are profiled, formed and coated depending on the application. The heat sealing band performs a dual function in the RESISTRON context. When supplied with power, it serves as a heat source for the sealing process. At the same time, it acts as a temperature sensor which changes its resistance as the temperature rises. The ability of the RES temperature controller to measure this resistance change rapidly during the heating-up and cooling-down phases is crucial for this highly dynamic and sensorless control concept.
This explains the rigorous specifications which are defined for the heat sealing band alloy. The most important characteristics of a heat sealing band are:

  • Temperature coefficient of the resistance
  • Specific resistance
  • Expansion behavior

These characteristics, along with your heat sealing application, have a decisive influence on the specifications of the electrical components and the mechanics of the sealing bar. The overall system is clearly very complex and all system components need to interact optimally with one another.

Our advice to you is to have your heat sealing application calculated by our support team. A complete system can then be put together for you including all essential components and settings.

How the RESISTRON temperature controller works

In order to obtain an optimal application, the value of each parameter must be determined and the sequence of steps adapted to the heat sealing task. Observing these parameters regardless of the conditions in which a production machine operates is the key challenge for the RESISTRON temperature controller.

Extremely precise and fast measurements are essential in order to accurately determine and control the temperature of a heat sealing band. In a heat sealing system with a RESISTRON temperature controller, this is achieved without sensors by measuring the voltage and current at the heat sealing band. The measurements are repeated fifty or sixty times a second. The ACTUAL temperature can then be calculated from the voltage and current values using the heat sealing band’s resistance characteristic. It is subsequently compared with the SET temperature and corrected if the difference is not zero. This is done by altering the transformer voltage until ACT = SET. Even very low thermal loads are instantly detected and can be corrected quickly and precisely. A power controller on the primary side of the transformer works as an actuator.

Since the primary current which is controlled is much lower, the heat losses are also smaller, paving the way for the compact controller design which users value so highly.

Heat sealing bars with a heat sealing band

The heat sealing bar which acts as the substructure for the heat sealing band is generally made from aluminum. It incorporates all of the design elements that are necessary in order for the band to do its job reliably, for example:

 

  • Bar end blocks to compensate expansion
  • Electrical connections for the high-current and measurement cables
  • Fixation for the heat sealing band
  • Holes for coolant (if required)
  • Insulating layers for the heat sealing band

The most popular design is a straight sealing bar with a rectangular section, which comes in lengths ranging from a few centimeters to several meters. Contoured sealing bars can be supplied with both 2D contours (e.g. circular, angular or curved) and 3D contours for sealing tubes or spouts.

Specific design rules apply to this kind of tool, and high precision is vital to achieve a homogeneous temperature distribution. Our developers use advanced CAD systems for this purpose, to create a three-dimensional view of the heat sealing bar. The CAD file can then be sent to the customer, who integrates it into the company’s own CAD environment.

Heat sealing band

As already mentioned elsewhere, the heat sealing band is the main component in the sealing process, which is why particular attention should be paid to an accurate geometry, a profile which is adequate for the process and coppered or silvered passive zones. Of course, the electrical characteristics of the heat sealing band alloy must be complied with, such as the specific resistance and temperature behavior. A heat sealing band which is optimally matched to the substructure is crucial to the success of your impulse sealing system.

We design heat sealing bands which are individually tailored to your requirements as well as a matching substructure on request.

Customized solutions

Is your application unusual? Does it need a customized solution? If so, you’ve come to the right place! ROPEX has longstanding experience in impulse sealing and the development of heat sealing applications, which makes us optimally qualified to provide relevant answers no matter how unique the problem.

We design a heat sealing bar and band that fit your requirements profile and put together exactly the sealing system you’re looking for. We can also perform sealing trials in our test lab using your actual film and quantify the results. We then provide you with a detailed Application Report containing all relevant components, the parameters needed for the sealing process and any necessary technical drawings of the mechanical parts.

System configuration

The RESISTRON sealing system is comprised of several application-specific components, of which the temperature controller, the impulse transformer and the heat sealing bar are the three most important for your heat sealing application. Various other system components such as a current filter, current transformer and counter bar are also required. The combination of all these components adds up to your individual heat sealing system.

Our support team helps you configure your application and integrate it in the machine and the process chain. The Application Report which is prepared for you by ROPEX forms the starting point for all RESISTRON sealing systems in your machine.