Views: 12 Author: Site Editor Publish Time: 2022-12-07 Origin: Site
1. Screw elements
This design's advantage depends on the exhaust port's natural pressure so that the raw material is not discharged. There is an exhaust port for the extruder provisions of the 2-stage screw. There are two exhaust ports must be a 3-stage screw. Each stage has a natural pressure section, a reduction section, and a metering section. The first stage starts with a natural pressure feeding section, and the second is a natural pressure exhaust section, the part to which the exhaust port belongs. There are two key issues in the design of the exhaust extruder screw.
First, the raw material must all be melted when it reaches the exhaust section to discharge the volatile components.
Second, the feed of the second-stage screw must exceed that of the first-stage screw so that the groove is not filled at the beginning of the second stage and the natural pressure at the exhaust port is maintained. When the feed volume of the 1st stage screw is more significant than that of the 2nd stage screw, the melt in the extruder will have a backflow. To solve this problem, it is necessary to reduce the first stage's feed volume or increase the second stage's feed volume.
2. Process standards
The easiest and quickest way to deal with the backflow is to change the process standard. For example, reduce the temperature, increase the friction and shear stress along the barrel or screw, and increase the friction or viscosity along the surface of the barrel to increase the feed rate.
The feed volume of the first stage can be reduced in various ways, as follows.
(1) Increasing the temperature of the barrel zone 2 and zone 3.
(2) Cooling the first stage screw.
(3) Use the starvation method of feeding.
(4) Adjust the feed hopper's temperature (constant testing is required).
Upgrading the feeding volume of the 2nd stage can be chosen as follows:
(1)Reduce the temperature of the 2nd stage steel bucket.
(2) Increase the temperature of the 2nd stage screw.
(3) Increase the engine temperature.
(4)Enlarge the engine clearance or reduce the engine friction resistance.
(5) Decrease the total number of screens.
(6) Apply a screen with a more significant gap.
If changing the production and processing standards still cannot solve the difficulties, you have to choose another way, such as designing the scheme screw again, reducing the engine friction resistance, extending the screw and steel barrel, or installing a gear oil pump in the middle of the extruder and engine. Installing a gear oil pump can solve the bubbling material problem, but it is a little more expensive than a new screw.
3. Exhaust port
If the screw at the exhaust port is only partially filled and the exhaust port is still bubbling material, then the design of the exhaust port has some problems. The exhaust port should be wider than the overturned material flow to ensure that the melt does not block the exhaust port. At the same time, the opening degree of the exhaust port should not be considered to reduce the melt residence time and the expansion time of the material flow. In normal operating conditions, the screw groove is semi-filled, and the exhaust port is at natural pressure at this time. However, there is still working pressure in the flip wear-resistant material, which is about 0.21~0.35MPa or higher, which is enough to expand the wear-resistant material at the exhaust port. In that case, the exhaust port should consider all the normal viscoelastic expansion of the raw material when designing the plan. Otherwise, part of the overturned material flow will be "hooked" and deposited at the various components. The amount of swelling of the melt stream is determined by the period of the vent. Longer retention time results in more significant swelling. The dwell time is manipulated by the screw speed ratio and the number of exhaust ports, and the dwell time can be reduced by increasing the screw speed ratio. This is why the low-speed gear extrusion is more severe than the fast extrusion material bubble. However, the larger the value of the exhaust port opening, the longer the dwell time. When the melt is deposited in the exhaust port, it will block the exhaust port, and the way to deal with it is to change the opening degree of the exhaust port to achieve all normal expansion of the melt at the exhaust port. If the overturned material flow swelling is 5 ~ 10mm, the height of the exhaust port should be at least 5 ~ 10mm.
4. Exhaust port of the shunt components
Cite a real-life example. With 150mm just polished with the exhaust port of the single-screw extruder, the plastic extrusion sheet is a more severe bubble material and can not produce excellent goods. The operator wanted to check the condition of the wear-resistant material in the screw groove at the exhaust port, but there was no way to see the screw, which indicated that there was a big problem with the design of the shunt components, and the operator had no choice but to remove the shunt components to check the level of filling of the screw groove. After the inspection, it was found that the screw slot was only 40% full, indicating that the screw design was effective.
The focus of the common problem was then on the shunt component. Although this is a well-known extruder manufacturer, the design of the shunts had significant shortcomings. When examining the various components, it was found that the exhaust port was not only equipped with a bottom opening in the upper stage, which allowed the raw material to expand usually, but also in the lower stage. It is not necessary to design the bottom opening for the upper stage screw, and it is awful to set this opening because it increases the time that the melt stays at the exhaust port and makes the melt expand a lot, which increases the melt working pressure accumulation at the exhaust port. Another problem is the flat and square exhaust ports, which are more challenging to clean than the straight ones. If the manifold design is effective, the exhaust port should be vertical to the radius of the barrel. Based on the above analysis, the shunt component can be repaired in the following two forms.
First, the upper step bottom incision will be covered with metal.
Second, the square opening is changed to tangential, which allows the operator to see the condition of the wear-resistant material in the screw. After improving the above methods, the problem of bubbling material is solved, and high-quality goods are produced and manufactured.