When we go to a factory, engineers usually tell us, Noah, that's the screen changer. It's very simple to filter impurities. But when we really started using or buying, we found it has a lot of models, many many names, looks exactly the same. Do you look Like a deer caught in the headlights? Today, we pick up what is a screen changer, and how does it work? If you have any good suggestions or question, you can e-mail me to share them,
In the process of extrusion, there will produce much impurity what do not useful for us even is harmful, such as the black spots on the surface of plastic particles for PC pelletizer, maybe come from decomposition or denaturation of plastic after a long-time heating and some impurities in original.
The screen changer is usually installed between the screw head and the mould, as shown in the picture.
Okay, I admit this figure is a little big. This is a big corrugated pipe extrusion line structure. Here is a simple picture to see the composition of the structure.
The screen changer is generally composed: the screen changer body (1), the filter screen (2), the fixer of filter screen, may have many holes (3), the plunger and drive unit (4) and the heater.
Let's take the picture above as an example. There are two exactly the same square filter screen on fixer. One is mounted on the melt flow path. When filter screen becomes dirty, it will be replaced by another clean one by the Hydraulic driven piston. The pushed dirt one can be removed and cleaned. Then worker fix a clean one in the hole.
The two sets of filter screen can be mounted on the same steel plate, rotate around an axis, or slide along a straight line of the guide rail. The former is operated manually by lever, while the latter slides back and forth with hydraulic pressure from one side to the other.
Continuous screen changer: Continuous screen changer will gradually move the new screen into the melt flow while removing the old screen. The moving speed of the changing screen can be adjusted automatically according to the impurity quality. The pressure and melt temperature changes caused by intermittent changing operation can be eliminated by using continuous changing device. A set of continuous switchers is designed according to the rotating skateboard. Several nets are arranged around the turntable driven by ratchet mechanism. Rotate the turntable, remove the old group from the melt flow, and replace it with a new group before touching the melt flow.
Here, the melt flow path is called Melting channel, which can have one, two, four...
There are several working groups called working position, which can have one, two, three, four, eight...
The shape of mesh group can be classified into plate, mesh belt, cylindrical, blocking and so on.
Of course, the filter can be square or circular, or fan-shaped.
Detailed categories and images can be viewed by clicking on this page: https://www.kalshine.com/plastic-machinery/screen-changer/continuous-screen-changer-melt-filter.html
Not ending yet. Backflush screen changer? It's often mentioned. What is that? How does it work?
Backflush screen changer is generally used in the case of more impurities. It can achieve the goal of frequent screen changing and fast screen changing. It is very suitable for the recycling of waste plastics.
The main structure is: screen changer body, plunger; metal filter, porous plate, filter support, backwash body, backwash plunger and so on. The driving part mostly uses hydraulic cylinder.
Simply, it is the same as the principle of the interchangeable screen changer. The impurities gather in the net group and reach a certain pressure value. Backwash plunger pushes the net group aside. A small part of the melt flows back with the net group and brings out the impurities on the net. When the pressure value is reduced to a certain value, the net group is pulled back to its original position by the piston. In the process, there is still melt flowing towards the cavity just now. They are wrapped with impurities on the surface of the mesh group and discharged the mesh changer together. Of course, the actual situation is much more complicated. There are many problems with sealing, such as the difficulty of electronic control, and so on.