The forward and backward thread elements are important extruder spare parts.
1. Forward thread element
The forward screw element is mainly used for conveying materials. The shape of the screw groove of the forward screw element can be rectangle or other shape. At present, the screw groove of the twin screw is mostly adopted.
2. Reverse thread elemen
The reverse screw element is also a one of the extruder spare parts. The shape of the double screw reverse screw element is similar to that of the forward screw element, except that the spiral direction of the spiral groove is opposite. Since the reverse thread is conveying material in the opposite direction and the positive thread is conveying material in the extrusion direction, high pressure is generated in front of the inlet of the reverse thread section to overcome the resistance caused by the reverse flow in the reverse thread, so that the material is transported forward through the gap of the reverse thread.In the extruder, the reverse screw element can be used to achieve the purpose of forming different pressure zones (sometimes up to a few mepa) at different positions in the axial direction of the twin screw or over relatively short distances, depending on the extrusion process.For example, to a certain position in the screw shaft to join liquid additives or foaming agent, to join the position must be in the low pressure area, at the moment before joining area set up reverse thread element form high pressure sealing effect, prevent the liquid additives or foaming agent to the reverse flow, and after the extrusion spare parts one of reverse thread element of low pressure area is formed to the addition of additives or foaming agent.
The pressure drop element in the reverse thread has no forward conveyance capacity. In fact, the forward conveyance of materials is at the cost of pressure loss.The size of the pressure drop is an important factor to be considered when designing and selecting the reverse screw element.The twin-screw inverse screw element is the resistance element, so when the pressure increases, it should be set in front of the positive screw conveying element, in order to overcome its resistance, so that the material will be transported to the direction of the mouth mold.If you add one section of the reverse threaded element, you get one pressure peak. If you add two sections of the reverse threaded element, you get two pressure peaks.In the same way, more than one counterscrew element can be set as needed.