Working Principle of Plastic Electrostatic Separators

Plastic electrostatic separators play a crucial role in the recycling and sorting industries. With the increasing production and consumption of plastics, the need for effective separation methods has become more urgent. These separators utilize the differences in electrical properties of plastics to achieve efficient separation. This article will delve into the working principle of plastic electrostatic separators, including the charging process, separation mechanism, and influencing factors.

Charging Process

Triboelectric Charging

One of the common charging methods in plastic electrostatic separators is triboelectric charging. When different plastics come into contact or rub against each other, electrons are transferred between them, resulting in the plastics acquiring positive or negative charges. The specific charge acquired by a plastic depends on its triboelectric properties. For example, in the Hamos EKS electrostatic plastic/plastic separators, the plastic mixture is fed via a vibrating conveyor into a tribo – electric charging unit. Different plastics are charged here according to the specific properties of the material, taking on either a positive or negative charge. The charging occurs due to the difference in the ability of plastics to gain or lose electrons during friction. Plastics with a higher tendency to lose electrons will become positively charged, while those with a greater ability to gain electrons will become negatively charged.

Corona Discharge Charging

Another charging method is corona discharge charging. In this process, a high – voltage electrode is used to ionize the surrounding air. The ionized air then charges the plastic particles as they pass through the ionized region. This method is often used when more precise and uniform charging is required. The high – voltage electrode creates a strong electric field, which causes the air molecules to ionize. The charged ions then attach to the plastic particles, giving them an electrical charge.

Separation Mechanism

Electrostatic Field Separation

After the plastic particles are charged, they enter a high – tension field. In this field, the charged particles are separated based on their charges. Positive particles are attracted by a negative electrode, while negative particles are attracted by a positive electrode. For instance, in the Hamos EKS separators, after charging, the mixture enters a high – tension field where the components are separated electrostatically into pure sorted fractions, determined by their different charges. The separation is based on Coulomb’s law, which states that the force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. In the high – tension field, the charged plastic particles experience an electrostatic force that causes them to move towards the electrode with the opposite charge.

Trajectory Separation

In some electrostatic separators, the separation is also achieved by changing the trajectory of the falling particles. When a mixture of charged particles falls past a charged object, the particles with the correct charge are repelled or attracted, causing them to fall into different collection areas. For example, in a simple electrostatic separator design, the negatively charged plastic particles may be repelled by a negatively charged plate and fall into one collection bin, while the positively charged particles are attracted to a positively charged plate and fall into another bin.

Factors Affecting Separation Efficiency

Material Properties

The electrical conductivity and triboelectric properties of plastics are key factors. Plastics with significantly different electrical conductivities or triboelectric behaviors are easier to separate. For example, separating PVC from PET is relatively easier because they have distinct electrical properties. PVC can acquire a negative charge more easily during triboelectric charging compared to PET. Additionally, the presence of additives and fillers in plastics can also affect their charging and separation. Additives and fillers can change the surface properties of plastics, influencing the electron transfer during charging.

Particle Size

The size of the plastic particles also affects the separation efficiency. Smaller particles generally have a larger surface – to – volume ratio, which means they can be charged more easily. However, very small particles may also be more difficult to separate due to their higher susceptibility to air currents and electrostatic forces between particles. In general, for optimal separation, the particle size should be within a certain range. For many electrostatic separators, a particle size of around 10 mm is considered suitable.

Humidity

Humidity can have a significant impact on the charging and separation process. High humidity can cause the plastic particles to absorb moisture, which can reduce their electrical resistance and affect the charging ability. Moisture on the surface of the particles can also lead to the dissipation of charges, making it more difficult to achieve effective separation. Therefore, it is often necessary to ensure that the plastic particles are dry before entering the electrostatic separator.

Applications of Plastic Electrostatic Separators

Recycling of Plastic Waste

Plastic electrostatic separators are widely used in the recycling of plastic waste. They can separate different types of plastics from mixed plastic waste, such as separating ABS from PS in electronic scrap, or separating PET from PVC in beverage bottles. This allows the recycled plastics to be used as high – quality raw materials in the production of new plastic products. For example, in the recycling of PVC windows, the electrostatic separator can remove the plastic impurities from the PVC window regrind fully automatically, ensuring that the recycled PVC meets the high – quality standards for new PVC plastic windows.

Plastic Production Waste Separation

In the plastic production process, there is often a certain amount of production waste. Electrostatic separators can be used to separate different types of plastics in this waste, enabling the reuse of valuable plastic materials. For instance, in the production of plastic packaging materials, the separator can separate PP from PE waste, reducing waste and saving resources.

Conclusion

Plastic electrostatic separators are important equipment for plastic recycling and sorting. By understanding the working principle, including the charging process, separation mechanism, and the factors affecting separation efficiency, we can optimize the operation of these separators and improve the separation quality. With the continuous development of technology, plastic electrostatic separators are expected to play a more important role in the field of plastic recycling, contributing to environmental protection and resource conservation.