Plastics usually go through five stages of recycling and processing. The purity of plastics after the first stage of separation plays a decisive role in the quality of re granulation in the thermoplastic stage. The importance of separation can not be ignored. But at present, most of China's recycling enterprises are still relatively backward in sorting technology, and most of them adopt manual selection. However, with the expansion of production and the increase of labor cost, the automatic sorting system will gradually replace the manual sorting.

There are three major sorting requirements in the recycled plastics market: removing metals from plastics, classifying plastics of different colors and different types of plastics. As the leader of plastic recycling and sorting technology, S + s (Shuangshi Sorting Technology Co., Ltd.) has corresponding detection technology for these three applications

1、 Sorting metal

The S + s sorting system adopts electromagnetic induction metal detector. Its working principle is that the electrified coil will form a magnetic field, and once metal enters, the magnetic field will change. The electromagnetic induction metal detector based on this principle can confirm whether there is metal passing through by monitoring the change of magnetic field. Compared with the widely used iron remover, this technology is not only effective for ferromagnetic metals, but also can detect non magnetizable metals such as stainless steel and copper.

At present, the color sorter on the market mainly uses two kinds of optical color separation sensors combined with effective digital analysis software to achieve color separation function, one is CMOS sensor, the other is CCD sensor.

CMOS is widely used in grain color separation applications, and then introduced into the plastic color selection industry. However, in the design of CMOS sensor, each pixel needs to be converted into digital signal after amplifier, so the image quality of CMOS is slightly poor, and it is suitable for the application with less mottled plastic content or material color difference.

Compared with CMOS, true color CCD sensor can ensure that the pixel signal is not distorted during transmission, so the imaging effect is better. The recognition of true color CCD sensor is close to that of human eye, so it is very suitable for the application with complex color mixing or high purity requirements. CCD sensor system is used in S + s recycling system, and even light blue and light green bottle pieces can be separated in PET bottle piece recycling.

3、 Sorting different plastic materials

In plastic recycling, manual sorting will also encounter some difficulties. Some polymers are difficult to be identified by human eyes in the case of the same color, such as pet and PVC of the same color. In the thermoplastic stage, different plastics will have different thermal melting points (for example, pet is about 260 ℃, PVC is about 170 ℃), if different polymers are not completely separated, the products will have great defects. S+S The separation system adopts near-infrared detection technology. The plastic passes through the near-infrared detector head, and the light is reflected through the plastic. Different plastics have different light wavelengths. High performance computers can identify different plastics by different wavelengths (as shown in the figure below). This technology is not limited by the specific gravity and external color of materials, and is being used more and more widely in the recycling industry 。

In addition to the core detection sensor, a set of automatic separation system also needs to be equipped with a suitable material conveying system to evenly spread the materials, so as to avoid the error elimination caused by the overlapping of materials. The rapid and accurate removal device can accurately locate the impurity position and remove it in time. Only when these three links are closely combined can the effective separation of the first stage of plastic recovery be realized.

S + s, which is specialized in the production and development of recovery and separation system, has developed many series of recovery and separation systems based on the above technologies. In this year's petpoint, according to the demand of PET bottle recycling industry, S + S's newly launched separation system, flake purifier, can realize more functions of one machine Purifier adopts a modular design, which can be equipped with metal detection, CCD camera and near-infrared sensor module on a sorting equipment, which can synchronously realize the three functions of separating metal, variegated plastics and heterogeneous plastics. It can greatly improve the efficiency of plastic recycling, which is helpful to pet purification.