What are Hopper dryers? Ultimate Guide 2022￼
2022/05/11 By LZ
Concept and general information
Hopper dryers are installation, which usually locates above the loading opening of the equipment. It designs to dry polymeric raw materials. Such drying is usually common for polymers of low hygro-scopicity.
It is in order to reduce the number of problems with the possible moisture content of raw materials during processing and improve the quality of finished plastic products.
Polymeric materials having a low hygroscopic index do not require drying. In particular, this applies to the most common polyolefin – polyethylene and polypropylene.
However, for one reason or another, for example, if raw materials do not store correctly in the warehouses of raw material sellers, the material may still contain moisture in sufficiently large quantities.
In these cases, the polymer needs to dry and heat for a short time right before load into the material cylinder of the equipment. It is in order to increase the productivity of processing processes, such as injection molding or extrusion.
It is for this purpose that hopper dryers are common in the modern plastics processing industry.
The design and principle of operation of hopper dryers
The standard design of a modern hopper dryer, hot air passes through the polymer material in the hopper from bottom to top. Relatively dry air lowers the moisture content of the plastic and exits the drying zone, mixing with the surrounding air.
In the most advanced polymer dryers, common for materials that require the best drying. Such as polyethylene terephthalate (PET, PET), air circulates in the system, and the dryer comes with a moisture absorption unit.
This unit allows you to radically reduce the humidity of the air with the help of special absorbers and direct it to the drying area for the most effective dehumidification.
Hopper dryers functions
The dried material is taken from the bottom zone of the hopper dryers. In this case, in parallel, undried raw materials enter the upper zone of the bunker with the help of a vacuum loader. This leads to a countercurrent of heated air and wet polymer moving from top to bottom. It has a positive effect on the quality of dehumidification.
It should note that with all the advantages of the above-describes hot air drying, and we are talking primarily about the relative simplicity and cheapness of the equipment common. This process is the most inefficient among those common.
The Process of Drying of Hopper Dryers
The heated air leaving the hopper dryers is not re common. It is important that it enters the same room where the air is taken from for drying, thus increasing the humidity of the source air.
In addition, the exhaust air is quite hot, which consumes additional electricity and makes the temperature in the workshop higher. It is usually not required. All these factors lead to relatively high costs for the drying process.
More technically advanced and efficient is a dryer that runs on not only hot, but also compressed air. The essence of the process is that the more air compresses, the less water it can contain. Thus, compressed air is, by definition, relatively drier without much additional preparation such as dehumidification.
Drying process of the polymer material
The drying process of the polymer material consists in the absorption of moisture by expanding hot air. With an increase in gas volume, moisture from the polymer raw material partially, but in a larger volume than with hot air drying technology, passes into the former compressed air.
In this case, the humidified air leaving the hopper dryers is usually also thrown into the workshop. without any purification and dehumidification. In certain models of bunker-dryers with hot compressed air, its zoned supply, coupled with heating of the polymer, provides.
How hopper dryers work?
Hot compressed air and compressed air in general, absorbs water from the polymeric material more efficiently than air at atmospheric pressure. During recent years, leading manufacturers of peripheral equipment and. In particular, dryers have begun to use this fact, offering fresh solutions for drying polymer raw materials.
Generally, the development of hopper dryers with a working agent in the form of sharply cools compresses air is of interest. It is also successfully shows itself instead of a hot analogue.
Due to their high cost and technical complexity, vacuum hopper drying systems have somewhat fade into the shadows. They design to remove water from plastics as deep as possible.
The essence of the operation of such a dryer for polymers comes from the physical fact that at low pressure. For example, 0.4 bar the boiling point of water drops to about 45 degrees C
Application of hopper dryers
Polymer hopper dryers are good for getting rid of surface moisture found on plastic pellets. These devices have a number of significant advantages:
- Low price,
- A wide range of manufacturers around the world,
Ease of operation and maintenance
The vast majority of hopper dryers are common for plastic injection molding. A much smaller amount is common for various types of blow molding and other plastics processing methods. For extrusion, due to its high productivity, dryers for polymers with a large hopper volume are common.
The bunker-dryer mounts directly on the injection molding machine or extruder, and designs for drying wet polymer raw materials with hot air.
The polymer hopper drying, into which the original wet material enters before being sent to the injection molding machine, during the drying process quickly removes excess moisture from it with a stream of hot air.
Advantages of our drying bins
- Stainless steel working parts
- Demountable design
- Easy cleaning
- Temperature control system, with automatic power off of heating elements
- Possibility of installing a magnetic catcher
Why Drying bins is very important during production?
The drying bin is an important piece of equipment for the production of plastic products. The moisture content of the polymer granule negatively affects the quality of finish products and leads to a high level of defects:
Hopper dryers Surface defects are easy to observe on finish products and tiny voids appear inside them during casting, the color changes and the mechanical properties of the product deteriorate.
Thus, the moisture inevitably present in the recycle polymer granulates causes a lot of problems if the raw material has not been properly prepare before casting.
This can be both residual moistures after polymer processing, and moisture that hygroscopic polymers absorb during storage or transportation. As a result, not only the appearance of products suffers, but also their technical characteristics, strength and durability.
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