Sealing Machine Issues
When a company buys several machines of the same type for different locations, it might be forgiven for expecting the same parameter settings would be needed in each location. Sometimes the company will ask, "All our machines are the same. Can we just validate a sample?"
Sealing temperature is set by controlling the temperature of a sealing platen. However, the temperature we really need to control is at the interface between the tray and the lid. At this point, the actual temperature will be influenced not only by the sealing platen temperature, but also by the thermal conductivity and thickness of any platen coating, lidding material, tray material, and tray support.
The potential impact of replacing platen coatings and tray support gaskets should not be overlooked, not only because of thickness and conductivity rates but also because a change in textured surface may trap more or less air and thus impact heat transfer. The temperature and humidity of the clean room and packaging material storage areas may need be taken into account.
Pressure is applied by a piston or pistons driven by pneumatic forces, and the applied force is determined by measuring the air pressure. In some units, the force is measured with a load cell. The length and bore of the pipework supplying compressed air to each machine can impact the rate of sealing pressure. When we measure the force applied to a sealing platen and convert this into contact pressure, this gives only the average contact pressure. Variations in flange thickness, flange width, wear on platen coating, and the hardness of the tray support gasket all affect the actual sealing pressure around a tray flange.
Dwell time may be measured in several ways. For example, the dwell timing may be started by:
- Initiation of the sealing cycle
- Sensing the position of the actuating piston
- The cylinder air pressure reaching a predetermined level
Because several different methods of dwell time control may be used, achieving the same result will require different machine settings for machines from different manufacturers and even for new and old versions of the same sealing machine model.
Returning to the question "Can we just validate a sample?," the answer is an emphatic "No." Each machine must be validated, and you should expect to need different sealing recipes to achieve a common seal quality.
Rolande Hall, FIMMM Pkg Prof