Method and Equipment for Electromagnetic Dynamic Plasticating Extrusion of Polymer Materials

A. Field of the Invention

The present invention relates to a method for electromagnetic dynamic plasticating extrusion to be used in the sphere of processing polymer materials, and the equipment designed for realizing the method.

B. Description of Related Art

Prior to the present invention, the chief equipment used in the processing of polymers was various types of screw extruder. The screw extruder is required to work in a required steady state and the solid material is conveyed entirely by friction. Compaction of material proceeds slowly while the pressure that is established is fairly low and venting of gases inefficient, resulting in low conveying efficiency. Plasticating and melting relies chiefly on exterior heating and heat caused by shearing. The melting rate is low and plastication uneven. Mixing which depends entirely on the process of shearing is not very efficient. Melt pumping depends mainly on the shearing of the melt, and since the material being processed has a high viscosity and elasticity, resistance to melt pumping is fairly high, leading to low pumping rates. Due to the above-mentioned drawbacks in extrusion methods there are limits to increasing output and improving the quality of the extrusion. Due to the high temperatures of extrusion, increase in output is also limited by the slow cooling rate of the attached auxiliary equipment. Besides, it is also difficult to overcome the random disturbances caused by different variables, thus limiting improvement in the quality of extrusion products.

The conventional screw extruder consists of the following systems: power transmission, extruding, heating and cooling and control. The extruding system comprises the screw, which is also the heart of the screw extruder. For a long time, attention has generally been focussed on research in the screw's structure and its mechanisms; therefore its structure has been improved continuously, with the result that there are now many different new types of screw extruder. But, the new screw extruders, whatever their improvements, all have to be fitted with an independent drive motor and power transmission, thus increasing the size of the screw extruder. It also leads to such drawbacks as energy loss during power transmission, leakage of lubricants and pollution, friction and wear of machine parts and noise caused by contact of machine parts and finally poor stress bearing condition. Again, because the screw has a large length to diameter L/D ratio (normally greater than 20) and with increasing requirments on increasing output and improving product quality, the usual method of solving the contradiction between output and quality, using conventional technology, is to increase the L/D ratio of the screw. But increase in L/D ratio is always accompanied by a corresponding increase in the difficulty of screw and barrel manufacture, increased cost of machining and an overall increase in size and weight of the machine. At the same time, the friction and wear between screw and barrel is worsened, which not only directly affects the life of the extruder but also greatly increases energy consumption.

The object of the present invention is to avoid the drawbacks inherent in prior art screw extruder technology, to provide a new method of extrusion which utilizes electromagnetic energy which is applied through a moving magnetic body to provide the various types of energy required for the dynamic plastication of the polymer material and also a new extrusion equipment which does away with the single drive motor and power transmission system of the screw extruder and the conventional screw with large L/D ratio.

Until now there has been no mention in the literature, either Chinese or foreign, of an electromagnetic dynamic method of plasticating extrusion and the relevant equipment for realizing the method. A run-through of the relevant literature by the International Centre For Information of the Guangdong Scientific and Techololgical Information Research Institute has also shown that there is no mention of such a method in the literature.

The above-mentioned objectives of the present invention can be realized through the following measures:

The present method utilizes the rotational and pulsed magnetic-field which result respectively from an electromagnetic winding device and axial electromagnetic bearing and the electromagnetic energy which is applied through a metal moving body which revolves and vibrates in the magnetic-field to provide the various types of energy required for the dynamic plastication and extrusion of the polymer material. The extrusion process of material includes, dynamic solids conveying, plasticating mixing and melt pumping. The entire process takes place in a state of periodic oscillation. The frequency and amplitude of oscillation can be adjusted and controlled respectively.

The above-mentioned process works as follows:

1. Dynamic solids conveying

The material is periodically compressed and released, instantaneous pressure causes the material to be compacted rapidly and conveyed. At the same time the entrapped air in the bulk material and volatile matter are rapidly expelled in the process of compaction.

2. Dynamic plasticating mixing

In this part of the process the material undergoes forced vibration, heat dissipation occurs within the material and forced orientation of the molecules takes place simultaneously in a state of dynamic vibration. Intermolecular slipping also occurs and all this results in the uniform and rapid melting of the material. Besides, in a state of vibration, instantaneous changes in shearing rates and pressure cause the material to be mixed, thus quickening and intensifying the blending of the various components and the dissipation of the low molecuar fillers.

3. Dynamic melt pumping

Oscillating vibration lowers the viscosity and elasticity of the melt and flow resistance is correspondingly lowered. Extrusion output increases, extrusion temperature is lowered, extrusion swelling is reduced correspondingly and the random disturbances are modulated by periodical vibration, resulting in a significant increase in the quality of extrusion products.

In order to implement the above-mentioned method, the present invention also provides an electromagnetic dynamic plasticating extruding equipment for the processing of polymer materials. This equipment comprises: lower support base; electromagnetic winding device mounted on the lower support base; electromagnetic bearing fixed to the lower support base; metal moving components encased inside the electromagnetic winding device in line with a common axis, forming with it a radial magnetic levitation gap, and an axial magnetic levitation gap with the electromagnetic bearing; stationary components fixed coaxially to the electromagnetic winding device and together with the moving components forming a processing space communicating with the outside, helical channels for conveying the materials being cut on said moving components or stationary components.

An embodiment of the present invention is further illustrate with reference to the accompanying drawings.

FIG. 1 diagrammatically illustrates the principles and structure of the electromagnetic dynamic plasticating extruder for polymer materials.

FIG. 2 represents the vertical view of the outer barrel. It shows the four Archimedes spiral grooves.

In FIG. 1, represents the electromagnetic winding device mounted on a lower support base 10. An outer barrel 2 is radially supported by magnetic levitation inside the electromagnetic winding device and supported axially by magnetic levitation from the electromagnetic bearing 6 which is fixed to the lower support base 10. There is an electromagnetic gap of 0.5 mm-2 mm between the outer barrel 2 and the electromagnetic winding device 1. An upper bearing end wall 7 is fixed to the electromagnetic winding device 1. The outer screw 3 is fixed to an upper end wall 7 and fitted inside the outer barrel 2; there is a small gap of 0.1 mm-1 mm between the outer barrel 2 and outer screw 3. There is an electromagntic gap of 1.5 mm-3 mm between the outer barrel 2 and the electromagntic bearing 6. An inner barrel 4 is encased inside the outer screw 3 and is fixed to it. There is an auxiliary heating element 11 installed between the inner barrel 4 and the outer screw 3. This heating element only operates before the equipment is started, and stops operating once the equipment is in normal operation. An inner screw 5 is fixed to the center of the lower inner headface of the outer barrel 2 and revolves in synchronism with the outer barrel 2. The inner head face of the upper bearing endwall 7 together with the upper headface of the outer barrel 2 form a processing space designated Zone I which is connected to the two feed hoppers 9 that are mounted symmetrically on the upper endwall 7. In Zone I there are 3-9 Archimedes spiral channels cut on the inner surface of the upper endwall 7 and the upper head face of outer barrel 2, with a small gap of 0.05 mm-0.5 mm between the channel tops and preferably with no friction caused by direct machanical contact taking place. The processing space between the inner surface of the outer barrel 2 and the outer surface of the outer screw 3 is Zone II. On the surface of the outer screw 3 in Zone II there are cut single, double, triple or multiple helical channels. These channels are divided into two or several sections by side plasticating balls 12 used for calendering plastication. The side plasticating balls 12 can only roll and vibrate within the arcuate channels on the periphery of the outer screw 3. The number of side plasticating balls 12 can be zero or between 5-12. The circular space between the bottom head face of outer screw 3 and the lower inner headface of the outer barrel 2 forms the processing space designated as Zone III. The two circular head faces in Zone III have 3-9 Archimdeds spiral channels cut on them and these channels are each divided into two sections by head face plasticating balls 13. The head face plasticating balls 13 can only roll and vibrate within circular channels cut on the surfaces of the bottom head face of the outer screw 3 and the lower inner headface of outer barrel 2. The number of headface plasticating balls 13 can be between 3-10 or zero. The processing space formed by the helical channels between the inner barrel 4 and the inner screw 5 is designated as Zone IV. This Zone is connected to the adaptor 8 which is mounted on the inner barrel 4 and through it connected to various types of dies.

A description of the working process of the machine is given below:

The material from the hoppers enters Zone I and, due to the action of the Archimedes spiral channels is, uniformly spread in a peripheral direction and conveyed to Zone II. In Zone II the material is dynamically conveyed and compacted, resulting in venting of gases, and continuously softened and melted due to the vibration and revolution of the outer barrel caused by electromagnetic action. The side plasticating balls 12 also exert a powerful dynamic calendering force on the material. Because the bottom head face of the outer screw is stationary while the outer barrel revolves, the material is cut, shunted, scraped and mixed when it enters Zone III. In Zone III the material undergoes both dynamic conveying and variable speed mixing by the spiral channels and dynamic calendering caused by the headface plasticating balls 13, becoming as a result thoroughly melted. The melted material then enters Zone IV and is again cut, shunted, scraped and mixed because the inner barrel is stationary while the inner screw revolves synchronously with the outer barrel, and due to the action of the inner screw is then compacted, pumped and metered under a certain temperature through the adaptor to the die.

Compared to prior art extrusion technology, the present invention prossesses the following advantages:

(1) Because of integration of the entire unit, and elimination of the drive motor and power transmission system, a screw with large L/D ratio. The axial dimension of the machine is very small and so is the space that it occupies. Its size and weight is only 1/3 to 1/4 of that of a conventional screw extruder with a corresponding output.

(2) The actual manufacture of the present invention when compared to the conventional screw extruder is much simpler, and the time required to manufacture it is also much shorter. The manufacturing costs of the present invention decrease to about 1/3 to 1/4 of those of the conventional screw extruder with the same output .

(3) Because the structure is symmetric axially, it bears stress well and can therefore implement high-speed extrusion. In addition, because a large diameter screw is used for dynamic solids conveying, conveying efficiency is consequently very high, resulting in high ouput. On the other hand, because there is no energy loss due to a drive system, and due to dynamic plastication and a low extrusion temperature, and also because a special cooling system is unnecessary, the energy consumption is also low, the energy consumption/output ratio being lower than that of the conventional screw extruder by 40%-60%.

(4) Because a large diameter screw is used for conveying solids and a small diameter screw is used for metering the melt, pressure is established rapidly when solids are conveyed in a state of vibration. Since pressure increases instantaneously, it is beneficial for the venting of gases through the hoppers. Also because the material is repeatedly calendered, cut, shunted, scraped and mixed in a dynamic state, good result are obtained in the venting of gases and also in mixing and plastication. The quality of the extruded products is markedly higher than those produced by a conventional screw extruder.

(5) Because orientation of the polymer molecules is forced to take place under a state of vibration, slipping between molecules takes place easily, the melting and plasticating temperatures are relatively low, so the extrusion temperature is consequently about 20 C.-40 C. lower than those of a conventional screw extruder, thus greatly alleviating the contradiction caused by increasing the output of a conventional screw extruder and the slow cooling rate of the auxiliary equipment.

(6) Because of the short resident time of the material in the equipment and the low temperature of dynamic melt extrusion, stagnation and disassociation do not take place easily, so the equipment can be used for processing a wide range of materials, especially for processing various types of heat-sensitive plastics.

(7) Because all the working components of the present invention are axially symmetric and not under any exterior force or moment of force and the moving parts are at the same time in a state of electromagnetic levitation, therefore the present invention has good stress bearing qualities, low friction wear and as a result a long lifetime.

(8) Because there is no drive motor, power transmission system and machanical bearings, noise is low and there is no pollution caused by lubricants.