In the extrusion process of the extruder, the molten material is sent to the mold through the screen.
Filters filter materials and improve the mix of materials.
However, the filter can also cause the process to fluctuate, causing the back pressure and molten material to rise, and sometimes decrease.
The extruder's filter is fixed on a protective plate of a porous or groove, which can seal the extruder and the mold.
Clean screen pack produced less pressure, with the increase of pressure, the number of impurities in the intercept of the resin filter net is more, thereby blocking the filter screen.
Filter will affect the temperature of the molten material when to replace the filter on the block, pressure suddenly drops, the temperature of the molten material may also decline, resulting in the size of the products change.
To keep the same size of the product, adjust the screw speed of the extruder and adjust the linear speed of the extruder.
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 strip thin, and the surrounding area is thicker.
This can be corrected by automatic or manual adjustment of the mold.
In the back of the filter converter, a gear pump that ensures that molten material is stabilized into the mold can prevent the problem from occurring.
However, the temperature changes that occur after the melt material is replaced by the filter will still need to be solved by adjusting the mould.
Meanwhile, the gear pump also needs to be protected by a careful filter because the gear pump is easily damaged by hard impurities.
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 for filters can also increase costs.
So most of the hard PVC processors either avoid the use of the filter, or use a crude filter without a converter, which filters only the larger particles.
How to choose the filter wire is the most commonly used metal filter material.
Stainless steel is expensive, but can be used in certain PVC production lines or other occasions to avoid rust.
Nickel-alloy filters are applied to avoid situations where fluoride polymers or PVDC are corrupted.
In general, the screen mesh (or the number of wires per inch) is 20 to 150 or more.
The screen of the screen is thicker;
40 to 60 screen filters are thinner;
The screen of 80 ~ 150 mesh is very delicate.
Most mesh screens are woven, with the same number of wires in each direction.
The Dutch weaving method USES coarse wire in the horizontal direction and is defined as a double number, for example, 32x120 root/in (1in = 25.4 mm).
It is not necessary to set up the mesh screen in the filter device to filter the filter.
The size of the sieve mesh is determined by the diameter of the wire, and there is no need to be completely consistent.
For example, a screen of 20 mesh filters, which is made of 24in and 0.02 in diameter, is 0.01 in each side.
The screen, which is 30in in diameter and 0.01 in diameter, has a slightly larger open hole of 0.04 in each side.
This is because the filaments are not very thin and are more likely to block (1in = 25.4 mm).
In general, the filter is installed in the most crude filter on the protective board, while the thinnest filter is facing 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).
Because the device type from the sides look the same, so in order to ensure that they will not be reversed, sometimes also USES symmetrical arrangement (20 60 sieve sieve / / 100 60 sieve sieve / / 20 sieve).
Some processors are deliberately turning the screen upside down, allowing the thick filter to filter the larger particles of the upper surface.
They argue that this approach allows more lateral melt material to be passed and disintegrate less material on the upper surface of the protection board.
Since a wire filter is prone to rusting, avoid moisture in storage, or rust will appear in the extrude.
More seriously, the rusty screen is easy to break and filter out the impurities, leakage, therefore, to store mesh in plastic bags or anti-rust paper.
When extruding PVC material, do not place the exposed strainer in the extruder.
This is due to the corrosion of hydrochloric acid in the air near the head mold.
Extrusion of PVC best practices is, in die head installed a cabinet of smoke, and you must see to it that the standby screen placed far away from here, even after its use bags can be placed in the freezer.
It is easy to get anti-roll phenomenon when purging and cleaning the board, causing the cover to be broken and the sliding surface not to match, thereby causing leakage.
In this way, not only will cause the cleaning time consuming, and leakage of molten material may affect thermocouple numerical, will also damage the heater, sometimes may even lead to fire.
For single exhaust, two-stage extruding machine, if the back pressure of the filter in the changes, so it will reduce the number of the second paragraph, but the output of the first paragraph will not be affected.
When the back pressure is approximately 2500lb/in2 (1lb = 0.4536 Kg, 1in = 25.4 mm), the molten material from the first segment begins to leak into the vent.
To avoid this phenomenon, change the filter when the pressure is low.
In addition, the gear pump behind the filter also has the effect of inhibiting the leakage of molten material into the vent.
If the filter is filtered through a large piece of junk (such as a piece of paper), it will suddenly fail completely, making the pressure of the extruder to peak quickly.
Therefore, in order to prevent this from happening, there must be safety systems such as the safety diaphragm, safety pin or the alarm that is connected to the pressure gauge
