The extruder is one of the most commonly used plastic processing machinery and equipment, extruder vent-flow natural become a frequently encountered problems, the following is the solution of four kinds of vent-flow extruder reasons Xiaobian finishing and the corresponding.
Screw factor
The exhaust type screw adopts multi - stage design, the advantage of this design is that the exhaust port is under normal pressure, and the material will not flow out. There is an exhaust port of the extruder requires a 2 - order screw, there are 3 exhaust ports need 2 - order screw.
Each 1 order has normal pressure, compression and metering section, the first - order starting stage is the normal pressure feeding, the second - stage is the normal pressure exhaust section, which is the position of the exhaust port.
There are 2 main problems in the design of the screw of the exhaust extruder:
First, when it reaches the exhaust gas, the material must be completely melted in order to discharge the volatile parts;
Second, the second order screw feeding amount must be greater than first order screw, so that the second start of the spiral groove is not full, so that the exhaust port can be maintained at normal pressure. When the feed rate of the first - order screw is larger than that of the second - order screw, the melt in the extruder will flow back.
Resolvent
Reducing the feed rate of the first order or adding the feed rate of the order of second.
Two, process conditions
The easiest and most convenient way to solve the risk is to change the process conditions. Such as cooling, increasing the friction and shear stress along the cylinder or screw and increasing friction or viscosity along the surface of the cylinder to increase the amount of the material.
Resolvent
The first - order feed rate can be reduced by the following ways:
(1) the temperature in the 2 and 3 zones of the steel tube
(2) cooling first order screw
(3) using the method of feeding the hungry
(4) and adjust the feeding bin temperature (repeated experiment)
Adding the second order feed rate can be used as follows:
(1) reducing the temperature of the second - order steel tube
(2) the temperature of the second step screw
(3) increase the head temperature
(4) increase the head clearance or reduce the resistance of the nose
(5) reduce the number of filters
(6) using a large gap in the filter net
If you change the processing conditions still can not solve the problem, you have to use other methods, such as re design of the screw, reduce the resistance of the head, the extension of the screw and steel tube or in the extruder and the head between the installation of a gear pump. The installation of gear pump can solve the problem, but it is higher than the cost of the new screw.
Three, exhaust port
If the exhaust port of the screw is only partially filled, exhaust port is still expected, then the design of the exhaust port there is a certain problem.
The exhaust port should be wider than the rolling material flow to ensure that the exhaust port is not blocked by the melt. At the same time, the opening of the exhaust port should not be too large, so that it can reduce the melt residence time and the expansion time of the material flow.
Under normal operation, the spiral groove is half full, when the exhaust port is normal pressure, in fact, there is still pressure in the rolling molten material, the pressure is about 0.21 ~ 0.35MPa or higher, enough to make the exhaust port of the molten material expansion. This outlet when the design should take into account the viscoelastic material normal expansion, otherwise, rolling stream will be "caught", accumulate in the shunt element at. How much of the melt flow expansion is determined by the time it flows through the exhaust port.
Long residence time, big expansion. The dwell time is controlled by the screw speed and the size of the exhaust port, which can reduce the residence time. This is the reason why the low speed extrusion is worse than the high speed extrusion.
However, the greater the opening of the exhaust port, the longer the residence time. When the melt is in the exhaust port, it will block the exhaust port.
Resolvent
Changing the opening of the exhaust port to meet the normal expansion of the melt at the exhaust port. If the rolling material flow expands 5 to 10mm, the depth of the exhaust port should be at least 5 to 10mm.
Four, the exhaust port of the shunt component
For example, a single screw extruder with an exhaust port, which had just been polished by 150mm, was badly expected to produce a qualified product. The operator to melt in grooves at the case to check the exhaust port, but could not see the screw, which indicates that there is a big problem in the design of the shunt element, the operator had to remove the shunt element to check the full extent of the groove. After inspection found that the spiral slot is full of 40%, that the screw design is reasonable.
So the focus of the fault will focus on the shunt component. When checking the shunt element, the exhaust port is found not only in the upper order, but also the material can be expanded by the bottom cut, and the lower order is also provided with the same. There is no need to order screw design of bottom incision, the incision and setting is extremely unfavorable, because it increases the residence time of molten pool in the outlet and the weld pool expanded more, increasing the melt pressure vent accumulation. The other problem is a flat and rectangular shaped outlet, it's more difficult than straight clean. If the shunt element is designed reasonably, the exhaust port should be perpendicular to the radius of the steel tube.
Resolvent
Can be used in the following two ways to repair:
First, the upper end of the cut to fill the metal;
Second, a rectangular opening into a radial direction, enables the operators to see the screw in the melt.
Through the improvement of the above method, the problem is solved, and the quality of the product is produced.
Conclusion: the exhaust screw whether vent-flow, there is a direct relationship between the design and performance of plastic extrusion process, and the screw and the exhaust port, so the producers in the use of a vented extruder for production and processing, to have a thorough understanding of the machining process, resin characteristics and equipment performance, in order to make the normal vented extruder stable operation.