Water content of a wet egg tray reaches up to 65%~75% after molded by an egg tray machine, and it’s hard to make it lower by any mechanical method. Actually, about 3.5~4kg moisture is dehydrated from every kilogram of molded fiber products through drying process.
Therefore, drying is a vital technical process in egg tray production, and manufacturing cost of drying account for a great proportion in molded fiber packaging production. It is a key measure to improve drying efficiency for higher benefits.
Wet molded paper egg carton
Technological Conditions
1. Drying temperature
Temperature increase accelerates drying speed. However, overheat will decreases performance index such as overall rigidity, form temperature gradient, and lead to defects. In addition, overhigh temperature of hot air makes higher energy consumption but lower efficiency.
Hence, when egg trays are in the process of drying, temperature of hot air in contact with egg trays is generally controlled at 110°C approximately, and are required to be the same inside drying equipment every corner.
2. Humidity of hot air
The control of humidity of hot air is so important. At the start of egg tray drying, if evaporation of water is not discharged in time, humidity level in drying equipment will increase continuously. Consequently, drying time is longer and efficiency is lowered.
For hot air circulating drying equipment, it’s necessary to regulate the ratio between circulatory hot air and fresh hot air, so as to avoid excessive humidity.
3. Speed and flow rate of hot air
Regulating speed and flow rate of hot air that enters into drying equipment is an effective method to accelerate drying speed too.
Out diffusion speed of wet egg trays depend, to a great extent, speed and flow capacity of hot air inside the egg tray drying facility. High speed and sufficient hot air is needed to blow surface of wet egg trays, until they are dried evenly. Generally, wet molded egg trays will be dried quickly when speed of hot air reaches 5m/s.
Tips
Apart from above mentioned technological conditions, here are 3 tips you may consider in practice.
1. Reduce wall thickness appropriately
The thicker the thickness becomes, the harder to dry. When design a paper molded egg tray, it’s better to minify wall thickness as much as possible, on the condition of meeting its overall stiffness and packaging performance requirements. In this way, not only improve drying efficiency, but also reduce consumption of fiber material.
2. Enlarge moisture gradient properly between surface and internal
During drying process, difference in water concentration is major engine of formation of water inner diffusion. Moisture gradient is usually improved by regulating of temperature, humidity level, wind speed and amount of wind. However, excessive speed of water external diffusion will result in too much shrinkage of wet egg tray, which will have a negative effect on drying.
3. Improve temperature advisably when drying
Increase of drying temperature is favorable to transfer of moisture from interior to surface of egg tray. But in routine production, increase of temperature is restricted in many aspects. Hence, temperature can be increased advisably.
Conclusion
Drying process has a direct influence on quality and manufacturing cost of egg trays. Therefore, it’s very important to master its drying mechanism and characteristics and then determine logical drying technological conditions. So far, problems such as high energy consumption and low drying efficiency still remained in this industry. Good drying performance can be obtained by reasonable and flexible controlling of temperature, humidity level and flow capacity of hot air.
