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Key Highlights:
Drying is essential for many materials – in general, even non-hygroscopic materials perform better after passing through the dryer.
When choosing the right dryer for your production requirements, i.e. small batches or long-term production, performance, operating costs, and maintenance costs should be considered.
By maximizing efficiency with the right selection of equipment, production efficiency can be maintained and manufacturing problems caused by wet materials can be eliminated.
Expansion
In plastics processing plants, material dryers are standard equipment, as improper drying of thermoplastics can lead to aesthetic and mechanical defects due to the presence of water.
Moisture may originate from inside the plastic particles of the hygroscopic resin or condense on the surface of the non-hygroscopic resin. If the material is not dried correctly, it can lead to potential problems during machining and post-processing of components.
When cosmetic defects occur in non-hygroscopic resins, such as polyethylene or polypropylene, these defects can often be traced back to excess surface moisture deposited due to rapid changes in temperature and humidity. This problem can be solved by allowing the raw material to equilibrium in the atmosphere around which it is processed so that the surface moisture can evaporate, or it can be traditionally dried using a hot air dryer to remove the surface moisture[Learn more about 'plastics', 'engineering plastics', 'modified plastics' and other industry knowledge, massive material super physical property tables, super material selection cases, cost reduction and efficiency improvement solutions, welcome to enter the "plastic library network" to solve! ！！！This preheating is especially useful when the material is stored outdoors in the cold and is brought into warmer and humid conditions for processing.
Therefore, proper drying techniques must be employed to prevent appearance problems and even chemical reactions, such as hydrolysis, where water molecules can break the chemical bonds within the polymer, affecting the mechanical properties of the material.
It is also important to note that some non-hygroscopic materials may still need to be dried due to the presence of additives. For example, impact modified acetal (POM) usually does not need to be dried, but if an impact modifier is added, it needs to be pre-dried.
All material manufacturers will advise on the upper limit of humidity for optimal material processing, which can be found in their material processing datasheets.
It's also important to keep in mind that over-drying the material for too long or too high a temperature can also cause potential problems. Over-drying and long residence times during the drying process can lead to color changes and subsequent part scrapping.
Drying technology
The desiccant dryer first appeared in the late 50s of the 20th century, when the first generative dryer using silica gel as a desiccant was developed. Further progress has been made with the addition of microprocessor control and the drying unit becoming more compact. The dehumidifying film provided by a compressed air dryer is not a desiccant, but a filter that blocks water molecules, unlike a desiccant dryer, this type of dryer does not require regeneration. Desiccant drying with existing vacuum dryers also presented challenges.
There are a number of drying options available to plastics processors to ensure that their raw materials are in the best condition for today's processing, these are:
Hot air dryer- Designed to remove surface moisture from non-hygroscopic materials[Learn more about 'plastics', 'engineering plastics', 'modified plastics' and other industry knowledge, massive material super physical property tables, super material selection cases, cost reduction and efficiency improvement solutions, welcome to enter the "plastic library network" to solve! ！！！and preheat the material before processing.
Twin tower ** desiccant dryer- There are two towers, evenly filled with hygroscopic material. During operation, one tower is used to actively remove moisture from the compressed air flowing through it, while the other undergoes the opposite process, removing moisture to rejuvenate the desiccant material.
Runner dryer- Designed to solve the energy problems associated with other types of drying. The rotary dryer has a constant **.
Vacuum dryingIt is designed to speed up the drying process of plastic materials by reducing the boiling point of water from 100 °C to 56 °C with a vacuum, which takes 20% less time than a desiccant dryer.
Compressed air dryer- Typically a drying method for smaller throughput machines, the dryer is equipped with two desiccant beds, similar to a dehumidifying dryer.
Silo dehumidifierDesigned for bulk storage systems where a silo dehumidifier is used to remove moisture from the air inside the resin silo. Dehumidifiers work by using desiccant materials to absorb moisture from the air.
Drying process
Proficiency is the key to the drying process, and it involves four key elements: heat, airflow, **, and drying time. All of these play a key role in achieving effective drying of materials to maintain production efficiency and quality.
The first drying parameter is heat, which requires the pellets to be heated to release moisture[Learn more about 'plastics', 'engineering plastics', 'modified plastics' and other industry knowledge, massive material super physical property tables, super material selection cases, cost reduction and efficiency improvement solutions, welcome to enter the "plastic library network" to solve! ！！！The second is **, which is the temperature at which the air condenses and moisture molecules can be released from the outside of the particles. Third, drying parameters need to be known, because it takes time to dry plastic particles to get water molecules off the surface of the particles. Finally, the fourth parameter is the airflow around the pellets, which delivers low**heat or dry heated air to the pellets in the dryer. The volume of this air must be sufficient to maintain the temperature required for the throughput of the material in the dryer.
A good drying procedure should be considered:
The temperature at which the material is dried
** of the air around the material in the dryer
Airflow around the material
The time it takes to reach the desired **
Comply with dryer maintenance requirements
Moisture analysis of the material before and after drying
Proper drying procedures can reduce potential manufacturing delays due to moisture-related defects.
Liaising with equipment vendors when selecting equipment can streamline the process and maintain efficient production. Material consistency is essential for producing quality products, and proper drying ensures that material properties are consistent throughout processing. Moisture-related challenges need to be adequately addressed from the outset to prevent manufacturing process problems.
Materials that are not dried properly can affect the material in a number of ways, these are:
The surface finish is poor, and there are figure-eight marks
Reduced mechanical properties
Effect on electrical performance
Changes in impact strength and elongation at break
The decrease in the viscosity of the material leads to spillage
Short lenses can change color if they are excessively dry.
Increased power consumption The injection molding machine has poor melt performance and increased torque
Technology
When choosing a dryer, it is important to understand what the current cost per ton of dry material is with existing equipment. Understand your requirements and the system around your manufacturing methods that work best for your plant.
Small batch production by desiccant dryer is expensive, on the contrary, high volume production by desiccant dryer significantly reduces the drying cost per ton of material[Learn more about 'plastics', 'engineering plastics', 'modified plastics' and other industry knowledge, massive material super physical property tables, super material selection cases, cost reduction and efficiency improvement solutions, welcome to enter the "plastic library network" to solve! ！！！However, the cost of keeping the desiccant dryer running all the time is expensive.
The cost of traditional desiccant dryers versus the adoption of vacuum drying technology needs to be explored, as generally the use of vacuum offers many revenue advantages such as faster drying, reduced maintenance, etc., and is considered a modern, efficient process and there are several advantages of these technologies that are now being actively used in the industry from generation to generation.
In the digital age, the drying process can now also be intelligent, with the addition of load cells and advanced control systems that allow operators to easily monitor and manage drying parameters. Previously, these drying parameters needed to be checked and monitored manually.
Monetto challenged the design of traditional dryer structures through R&D and developed a more efficient method for drying polymers. Their breakthrough was to redesign the flow of material through the dryer hopper by adding a hollow "rocket-like projectile" to the dryer's core, allowing for a more consistent flow of material and reducing dwell time compared to traditional desiccant dryers.
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