CN2334574Y - A four-stage reactive extrusion screw - Google Patents

Abstract

The utility model relates to a four-section reactive extrusion screw, which relates to a screw used for a single screw extruder. The screw is divided into a feeding section, a melting section, a homogenizing section and a reaction section. The length of the reaction section is 20%-45% of the total length of the screw; the groove depth of the reaction section is 10%-50% deeper than that of the homogenization section, and there are mixing elements in the melting section. The screw is used for extrusion processing of silane cross-linked polyethylene, which can obviously increase the efficiency of grafting reaction, increase output and improve processing quality. It can not only be used for extrusion processing of silane cross-linked polyethylene pipes, cables, plates and profiles, but also for other polyolefin reactive extrusion or foam extrusion.

Description

A four-stage reactive extrusion screw

The utility model relates to a screw used for a single-screw extruder, which is suitable for plastic reaction extrusion processing, in particular to silane crosslinked polyethylene graft reaction extrusion processing.

Generally, the traditional single-screw extruders used in plastic processing are mostly three-sections, and the screw is divided into a feeding section, a melting section and a homogenizing section. Granular or powdery plastics are continuously extruded through plasticization and homogenization in the extruder. During the extrusion process, the plastics undergo different physical states, but their chemical structures do not change. In plastic reaction extrusion processing, for example, in the extrusion process of silane cross-linked polyethylene, in addition to undergoing physical processes in the extruder, raw materials also need to complete silane grafting reaction, which is more complicated than the general plastic extrusion process . The residence time distribution of the ordinary three-stage screw extruder is too wide, and the complete melting zone of the material is relatively short, which obviously cannot fully meet the requirements of reaction extrusion, and the reaction efficiency cannot be effectively improved only by increasing the screw length. For ordinary equal-distance variable-depth screws, plastic particles can be completely melted at about four-fifths of the total length of the screw. Although the mixing type screw and the separation type screw can increase the relative length of the complete melting zone of the material, there is still melt retention. The problem of too wide time distribution is very unfavorable to improve the efficiency of grafting reaction, so ordinary single-screw extruders are not suitable for reaction extrusion processing.

The purpose of this utility model is to provide a screw rod which can be used for plastic reaction extrusion processing. This screw rod can be used for extrusion processing of silane cross-linked polyethylene, which can obviously improve grafting reaction efficiency, increase output and improve processing quality.

The utility model is a four-section reaction extrusion screw, which is provided with a reaction section after the homogenization section of the common three-section screw, and the screw groove depth of the reaction section is greater than the screw groove depth of the homogenization section; There are mixing elements. The length of the reaction section is 20%-45% of the total length of the screw; the groove depth is 10%-50% deeper than that of the homogenization section. The mixing elements are separated or barrier structures.

Fig. 1 is a structural schematic diagram of a four-stage reactive extrusion screw of the present invention.

As shown in Figure 1 of the utility model, the screw rod is divided into a feeding section 1, a melting section 2, a homogenizing section 3 and a reaction section 4. The structure of the first three sections is similar to the traditional three-section screw, and the well-known structural forms such as equidistant gradient depth and equidistant abrupt depth can be used. The reaction section 4 is located after the homogenization section 3, and its length is 20% of the total length of the screw. %-45%. The screw groove of the reaction section 4 is 10%-50% deeper than the screw groove of the homogenization section 3, and the compression ratio of the screw rod is 1.4-4.5. This can make the melt depressurize in the reaction section 4 and increase the residence time of the melt. The melting section 2 is provided with a mixing element. The mixing element adopts a known structure, and its structure adopts the separation as shown in Figure 1 Barrier-type mixing elements can also be used in addition to the mixing elements, which can accelerate the melting of materials. According to the conventional screw design principle, the depth of the screw groove changes from deep to shallow, and the screw groove in the homogenization section is not allowed to change from shallow to deep, so as to prevent the extrusion from being unstable. However, for reactive extrusion, the viscosity and density of the material will change with the progress of the chemical reaction, and the factors affecting stable extrusion will also change. For reactive extrusion processes such as grafting, crosslinking, and foaming, it is entirely possible After the homogenization section, the spiral groove is deepened for decompression treatment, and the requirements of reactive extrusion can be realized under the condition of ensuring stable extrusion. After the melt passes through the homogenization section, it is decompressed in the reaction section and completes the reaction and is uniformly transported forward. When the utility model is used for extrusion processing of silane cross-linked polyethylene, the viscosity of the melt of the polyethylene-silane system increases significantly with the increase of the grafting rate, and the decompression in the reaction section helps to reduce the melt viscosity. The shear rate can prevent excessive shearing of the melt and cause thermal degradation.

In the extrusion processing of silane cross-linked polyethylene pipes, the four-stage screw extruder of the present invention is adopted, and the size of screw 1# used is: diameter 65mm, length-to-diameter ratio 30:1, compression ratio 2.0, feeding section The groove depth is 9.6mm, the melting section uses separate mixing elements, the homogenization section has a groove depth of 4.46mm, and the reaction section is an equidistant and equal-depth screw with a groove depth of 5.8mm. This extruder is the same as the common three-stage single-screw extruder with equidistant gradual change (the size of screw 2# used: diameter 65mm, length-to-diameter ratio 30:1, compression ratio 1.88, feeding section groove depth 7.5mm) and equidistant Comparative test of common three-stage single-screw extruder with variable depth and barrier-type mixing elements (size of screw 3# used: diameter 65mm, length-to-diameter ratio 30:1, compression ratio 3.5, feeding section groove depth 9.1) The result shows that when the residence time of molten material is 1 minute, the output of screw 3# is 28kg/h, the output of screw 2# is 37.5kg/h, and the output of screw 1# is 46.5kg/h; When it is 2 minutes, the output of screw 3# is 18.5kg/h, the output of screw 2# is 25.5kg/h, and the output of screw 1# is 31.8kg/h. It can be seen from the experimental results that the utility model can significantly prolong the residence time of the molten material. Under the same formula and reaction conditions, the extrusion output of the reactive extruder of the utility model is higher than that of the two common three-stage single-screw extruders. The output of the machine is increased by about 60% and 25% respectively. The four-stage single-screw reaction extruder also has the characteristics of narrow material residence time distribution, which is very beneficial for improving the efficiency of grafting reaction. Under the condition of constant formula and cross-linking degree, it can greatly improve extrusion Yield, product uniformity and appearance quality are all improved.

The four-stage reaction extrusion screw of the utility model can not only be used for the extrusion processing of silane crosslinked polyethylene pipes, cables, plates and profiled materials, but also can be used for other polyolefin graft crosslinking reaction extrusion, foaming extrusion Extrusion and other reactive extrusion processing.

Claims (3)

1. A four-section reactive extrusion screw includes a feeding section, a melting section, and a homogenizing section, and is characterized in that: a reaction section is arranged after the homogenizing section, and the screw groove depth of the reaction section is greater than that of the homogenizing section Depth; kneading elements are provided in the melting section. 2. The four-stage reactive extrusion screw according to claim 1, characterized in that: the length of the reaction section is 20%-45% of the total length of the screw; the depth of the screw groove is 10% deeper than that of the homogenization section -50%. 3. The four-stage reactive extrusion screw according to claim 1, characterized in that the mixing elements are separated or barrier.