Working principle of backflush screen changer

In the plastic extrusion production process, the plastic melt will produce some decomposition products after a long period of plasticization, and the raw material itself also contains some impurities. The presence of these impurities not only affects product quality, but also affects the continuity and stability of production. The screen changer is arranged between the screw head and the extruder head to filter out impurities and foreign matter in the plastic melt to obtain a pure melt.

With the increase in the price of plastic raw materials, extrusion manufacturers have artificially increased the proportion of recycled materials used in order to reduce production costs and increase profits. The proportion of recycled materials added in some agricultural plastic products reaches 80%~90%. Screen changer is one of the important factors that affect the quality of plastic recycled materials. The extensive use of recycled materials has greatly promoted the development of screen changers, brought a broad market to the application of screen changers, and put forward new requirements for screen changers.

In the plastic extrusion production process, the plastic melt will produce some decomposition products after a long period of plasticization, and the raw material itself also contains some impurities. The presence of these impurities not only affects product quality, but also affects the continuity and stability of production. The screen changer is arranged between the screw head and the extruder head to filter out impurities and foreign matter in the plastic melt to obtain a pure melt.

The non-stop screen changer has the characteristics of continuous production and convenient screen change. It is an ideal supporting device for the extrusion granulator. The non-stop screen changer is generally composed of the screen changer body and the filter screen. It is composed of perforated plate, plunger and heater. The plastic melt flows through the filter screen on the plunger, and impurities gradually accumulate in the filter screen. The melt pressure rises with the accumulation of time, and the filter screen should be replaced in time when it reaches the load that the equipment can withstand. When replacing the filter screen, first pull out the upper plunger until the filter screen is exposed to the body, and then replace the filter screen. After the upper plunger returns to its original position, replace the filter screen in the lower plunger in the same way to complete a screen change process. This type of non-stop screen changer has a simple structure and is suitable for extrusion production with relatively clean raw materials. However, it is difficult to thoroughly clean the waste plastics used in the production of recycled materials. During the production of recycled materials, a large amount of melt impurities accumulate on the filter screen in a relatively short period of time. The filter performance of the filter screen decreases and the pressure of the machine head increases. When the melt pressure exceeds, it will squeeze through the filter. If this type of screen changer is used, it will inevitably replace the filter screen frequently, and even cause downtime, which seriously affects the production capacity and yield of the equipment. Therefore, in order to reduce downtime, increase production and economic benefits, and improve the quality of recycled materials, it is urgent to overcome these problems. In view of this, a high-efficiency automatic screen changer with automatic flushing function has appeared abroad, which is very suitable for the recycling and processing of waste plastics.

The automatic flushing screen changer consists of the screen changer body, plunger; metal filter screen, porous plate, filter screen support, backwashing body, backwashing plunger, etc. The driving part is mostly hydraulic cylinder. The screen changer body and the backwash body are designed separately for easy processing.

Its working principle: the plastic melt flows into the screen changer body through the backwash body, and the impurities are filtered out by the metal filter screen. The impurities on the filter gradually accumulate, and the melt pressure rises accordingly. When the pressure of the melt in front of the screen reaches the set value, the backwash plunger moves down under the push of the hydraulic cylinder to switch the state. A small part of the melt flows back to bring out the impurities accumulated on the filter screen. When the melt flows back After the time reaches the preset time, the backwash plunger starts to move upwards under the action of the hydraulic cylinder, and reaches the preset state. A small part of the melt flows back to bring out the impurities accumulated in the filter, and the backflow reaches the preset state. After a period of time, the backwash plunger returns to its original position. In this way, an automatic cleaning process of the filter screen is realized, and the purpose of cleaning the filter screen is realized. The filter screen can be recycled, which greatly extends the time between screen changes and can be continuously produced for a long time.