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Your Position:Home > News> The company dynamic > The influence of the filter screen on the filter molding.
The influence of the filter screen on the filter molding.
Source: http://www.huazongsj.com Release time: 2017-12-22


Plastic extruder is also one of the types of plastic machinery.
The extruder can be divided into right Angle head and bevel head, according to the flow direction of the head and the Angle of the center line of the screw.
In the extrusion process of the extruder, the molten material is transmitted to the mold through the filter screen.
The screen filters the material and improves the mixing effect of the material.
However, the filter can also cause the process to fluctuate, resulting in back pressure and melting material temperature rise, and sometimes decrease.

The filter will affect the temperature of the melt material.

When a blocked filter is replaced, the pressure drops suddenly and the temperature of the molten material may decrease, resulting in a change in the size of the product.
In order to maintain the same size of the product, the screw speed of the extruder can be adjusted, and the linear speed of the extruder can be adjusted.
When extrusion round products, these changes may not cause serious problems, but in the extrusion flat or irregular shape of the products, plastic melt temperature changes may affect the appearance of product size.
For example, in a flat mold, the cooler melt material may make the center of the sheet thin, and the periphery thick.
This can be corrected by automatic or manual adjustment of the mold.

Behind the screen converter, a gear pump that guarantees the steady flow of molten material into the mold can prevent the problem from occurring.
However, the temperature change of the melt material after the filter is changed still needs to be solved through the adjustment of the mold.
At the same time, because the gear pump is easily damaged by hard impurities, the gear pump also needs to be protected by fine mesh.

Some hard PVC processors do not wish to use the reason of the filter, filter can make PVC plastic melt temperature and prone to degradation, so you need to thermal stability and better materials, thus increasing the cost of materials.
The use of PVC - specific filter converter will also increase the cost.
So most rigid PVC processors either avoid using a filter, or use a coarse filter that does not carry a converter, and only filter the impurities of larger particles.

So how do you choose a filter?

Steel wire is the most commonly used metal filter material.
Although stainless steel is expensive, it can be used in some PVC production lines or other occasions to avoid rust.
The nickel alloy filter is applied to avoid the corrosion of fluoropolymer or PVDC.

In general, the screen mesh (or the number of wires per inch) is 20 ~ 150 or more.
The filter screen of 20 mesh is thicker;
The screen mesh of 40 ~ 60 mesh is thinner.
The screen mesh of 80 ~ 150 mesh is very fine.

The mesh of most screen mesh is square, with the same number of wires in each direction.
The Dutch way of weaving is to use coarse wire in horizontal direction, and it is specified as double digits, for example, 32x120 square root /in(1in=25.4mm).
The filter net which is made by Dutch weaving method does not need to set up parallel screen in the filter device to play fine filtration.

The size of the mesh is determined according to the diameter of the wire, and there is no need to be completely consistent.
For example, a screen of 20 mesh with a diameter of 24in and a diameter of 0.02in, with a hole of 0.01in each side;
A 20 mesh filter made of 30in and 0.01in diameter of wire is slightly larger in each side, 0.04in.
This is because the filaments are not thin enough to filter and are more likely to block (1in=25.4mm).

In general, the filter device is installed in the most coarse screen to protect the plate, while the smallest filter is faced with the extruder.
, for example, from the protective plate to the extruder filter arrangement may be 20 40 sieve sieve / / 60 sieve, because this kind of arrangement structure can prevent mesh blocked, and impurities can be "into" protection board inside the hole.

If the fine mesh sieve of 80 or more, to prevent the rotary motion of the mesh is molten material or big impurities block, you can put a coarse mesh in front (such as 20/100/60/20 of the sieve).
Since this type of device is identical from both sides, in order to ensure that they are not turned upside down, symmetrical arrangement is sometimes used (20 mesh /60 mesh /100 mesh /60 mesh /20 mesh).

Some processors deliberately reverse the filter, allowing the coarse screen to filter the larger particles on the upstream surface.
In their view, this method allows for more lateral melt material to be passed, and to make the material on the upper surface of the protection plate less decomposed.

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