2019-05-14 17:15


Continuous heating and pulse sealing

Pulse sealing process is a good substitute for the widely used classical continuous heating sealing tool, which provides very effective solutions and multiple benefits in complex thermal sealing applications.
In most cases where the plastic film must be thermally bonded, use a continuously heated sealing tool. The technology involves electrically heating metal sealing jaws and then maintaining them permanently at a settable temperature. This is usually the easiest way to bond plastic films together. Unfortunately, this technology may be very simple, but it also has shortcomings of sealing joint quality or machine productivity, which are difficult to compensate. In particular, the molten film cannot be directly cooled in a closed tool, so once the two halves are opened, a durable seal can be obtained, which is a major disadvantage. When handling the film (thick film or aluminum composite material) with high elastic force after the sealing process due to the bag or bag geometry or packaging goods, it may be necessary to add additional cooling station or process in the machine to enable the joint to be actively cooled after the sealing tool is opened. This means that the design engineers of packaging machinery manufacturers face more challenges and higher operating costs, such as the compressed air required to cool the joints. The heat emitted by the continuously heated tools is also harmful to the packaged products and the film itself. Once again, appropriate design measures must be integrated into the packaging machine to compensate for the adverse effect of the heat sealing tool on the packaged goods. Problems such as impermissible thermal stress or easy-to-open thermal joints can be avoided through the pulse sealing process. The melting heat of the film is actually only generated when the sealing process is actually required. For this purpose, the current flowing through the resistor causes the temperature there to rise. Once the current is interrupted, the resistance will start to cool because the heat generated will dissipate into the tool or environment. Therefore, the melting heat introduced into the membrane is removed again and the joint is cooled.


Other advantages

Compared with continuous heating, pulse sealing has several other advantages:

Reduce power consumption

Electrical energy is required only during the heating phase of the sealing cycle. During the cooling phase, no current is fed to the heat seal. Whether any heat is actually needed or not, the sealing tool that is continuously heated is heated.

No heating or cooling time

Compared with the alternative of continuous heating, when the machine is started or stopped, the pulse controlled sealing tool only has negligible heating and cooling time. The tool for continuous heating consists of solid metal parts, which must be heated before the machine is ready for use. If the sealing tool is to be maintained, it must be cooled first. A few minutes delay is not uncommon. The heat sealing belt heats up and cools down within hundreds of milliseconds, or in the worst case, for a few seconds.

Pulse sealing - perfect control of sealing process!


Through the classical time control, the current can be delivered to the heat sealing belt within a settable time. During this period, the band continued to heat up; At the end of the heating cycle, turn off the heating and cool the heat seal again by releasing the heat into the environment. This method of only remotely controlling the heating element is similar to the pulse sealing with heat sealing tape, and the sealing process is extremely difficult to control because there is absolutely no way to control the sealing temperature. Although it is theoretically possible to cool the joint under pressure, the sealing temperature cannot be controlled, so it can change from one heating pulse to the next. Even if constant heating power is provided within a constant sealing time, the final temperature will vary according to the initial temperature of the heat sealing belt. This is especially true if the packaging machine is not running continuously or regularly. To avoid this situation, not only the sealing time but also the sealing temperature should be controlled. Only in this way can a real pulse sealing process be described, because in this case, an ideal square wave pulse can be generated, which is more or less significant, depending on the heating and cooling rate of the heat sealing belt, and the temperature curve can be generated to change with time. This rectangular shape ensures repeatable sealing quality and high machine output within a given sealing cycle time, as well as the optimal ratio of sealing time to cooling time. With the RESISTRON temperature controller for heat sealing tape and our CIRUS UPT pulse sealing system, ROPEX provides a perfect solution.

RESISTRON or CIRUS? Two alternative plastic film pulse sealing processes

Each of these technologies is an excellent alternative to sealing thermoplastics using the pulse method. The effective interaction between the RESISTRON temperature controller and the heat sealing belt and the fact that all components in the control circuit are individually designated by ROPEX ensure the optimal ratio of sealing time to cooling time at a given sealing temperature. Because the special design of our CIRUS tool is combined with the UPT temperature controller, the UPT temperature controller can well adapt to this technology, so the heating pulse generated is almost ideal. In particular, CIRUS technology has achieved very fast heating and cooling rates, resulting in extremely short processing time for plastic film thermal bonding. You can find more detailed descriptions of RESISTRON and CIRUS technologies on the RESISTRON and CIRUS pages of our website.





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