JPS5913336B2 - Screw for extruder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a screw used in an extruder for plasticizing and extruding a thermoplastic resin.

The extruder conventionally used to extrude thermoplastic resin has a screw installed in the barrel, which rotates to plasticize the thermoplastic resin, which is then extruded through a die installed at the tip of the barrel. As shown in Fig. 3, the part where the thermoplastic resin inside the barrel is plasticized is provided with a flight 2' for resin feeding on the core body 1' of the screw, and a helix 0 groove 3 of the screw consisting of this flight z. The thermoplastic resin fed from a hopper (not shown) is transferred in the axial direction first, i.e. in a relatively deep manner in the feeding section, and then in the compression section in the helical groove g sequentially in the extrusion direction. Here, the resin is heated and kneaded and the extrusion pressure of the resin 5 is increased.Finally, in the measuring section, the spiral groove 3 is made into a uniform shallow groove, and the resin flows along this narrow flow path. The resin is uniformly kneaded and melted, the resin pressure is maintained at a desired pressure, the resin is measured, and the resin is extruded from a die (not shown) provided at the tip. Therefore, the extrusion rate of this type of extruder is determined by the shallow part of the helical groove 3, and if the depth of the groove in this area is made deeper, the extrusion rate can be increased even with the same size screw, but then The following problems arise. The bulk specific gravity of the resin is different between the solid state and the molten state, and the latter is larger, so if the depth of the groove at the screw tip is deepened, the resin will be extruded from the screw tip faster. , a part where the resin is not clogged occurs in the middle of the screw, causing unstable extrusion. Furthermore, when trying to extrude a large amount of resin using a screw having such a shallow groove portion, a large amount of frictional heat is generated due to shearing of the resin, making it difficult to control the resin temperature. Therefore, should I use a larger extruder to increase the amount of extrusion? 5. A forced cooling device is added, but the equipment cost increases, and in the latter case in particular, the low thermal conductivity of the resin causes local heating, which adversely affects extrusion performance. In view of this, the present invention has a supply section that is supplied with thermoplastic resin, a compression section that increases the pressure of the resin transferred from the supply section, and a metering section that measures the amount of resin to be extruded. In the screw unit installed in the barrel of the extruder with On the contrary, the core of the screw is made to have a uniform thickness in the supply section, compression section, and metering section.

That is, in the present invention, the supply section and the compression section of the screw have the same shape. This will be explained in detail based on the embodiment shown in the drawings. In FIG.
The thermoplastic resin is transferred through the spiral groove 3 made up of flights 2 and heated and kneaded, but the measuring section of such a screw is provided with flights 4 facing in the opposite direction.
This becomes a resistance part to the transfer of the resin, and it is possible to increase the amount of resin extruded while suppressing the heat generation of the resin. For example, P = 65 mmφ, L/D = 25 (here, D is the diameter of the screw, and L is the length. ) The depth of the spiral groove at the base is 10m7! L. Measuring section groove depth 3.5m1
L's conventional extruder rotated about 50 times per minute, and the resin temperature was 15 to 20°C higher than the limiting temperature. In contrast, the depth of the grooves in the screws of the present invention having the same dimensions is all 10 m.
m1 has a flight in the opposite direction for 5 turns at the tip, and at a rotation rate of about 50 times per minute (approximately the same extrusion amount), 5 to 1
The temperature rise is about 0℃, and even if the rotation speed is increased to 70 times per minute, the temperature rise is only about 10 to 20℃.If the temperature rise is the same, the screw according to the present invention has a higher extrusion rate. It turns out that it can be increased. In the above-mentioned embodiments, the depth of the spiral groove is constant, that is, the diameter of the core body is uniform, and the flight in the opposite direction is also a one-threaded spiral. If it is made more effective, the effect as a resistor part will be further improved. In addition, the length of the flight in the opposite direction is appropriately selected depending on the pressure and flow rate of the resin. Furthermore, Fig. 2 shows a case where the screw is applied to a screw of a vent type extruder, and the diameter of the core 1 of the screw is uniform and the depth of the groove 3 is uniform from the resin supply side to the vent part 5. In front of the vent part 5, that is, in the measuring part on the resin supply side, a flight 4 facing in the opposite direction is provided. The screw of such a vented extruder is provided with a supply section, a compression section, and a metering section on the upstream side (=resin supply side) and downstream side, respectively. The resin is supplied, compressed, and measured in a supply section, a compression section, and a metering section on the upstream side of the vent section 5, and then reaches the vent section 5, and then in the vent section 5 as a supply section on the downstream side. After a new injection agent such as a foaming agent is injected, the injection agent and resin are compressed and measured in a compression section and a metering section on the downstream side, respectively. The compression section and metering section on the downstream side have shallow grooves, as in the conventional case. In this embodiment, the amount of resin extruded into the vent portion 5 can be increased. As explained above, according to the present invention, a flight in the opposite direction is provided near the tip of the screw provided in the barrel, and this acts as a resistance to the transfer of resin by the screw, so that the groove depth of the measuring portion of the screw is increased. It is possible to make the screw depth deeper than that of a conventional screw, and therefore, compared to a conventional screw, it is possible to increase the extrusion amount while suppressing heat generation of the resin even if the L/D is the same.

Further, in the present invention, the core of the screw has a uniform thickness in the supply section, compression section, and metering section, so that the depth of the groove in the metering section becomes deep and design and manufacturing are facilitated.

[Brief explanation of drawings]

1 and 2 are side views showing different embodiments of a screw for an extruder according to the present invention, and FIG. 3 is a side view of a conventional screw for an extruder. 1... Screw one-core body, 2... Flight, 3...
Spiral groove, 4...Reverse flight.

Claims (1)

[Scope of Claims] 1. A supply section that is supplied with thermoplastic resin, a compression section that increases the pressure of the resin transferred from this supply section, and a measurement section that measures the amount of resin to be extruded, in order in the axial direction. In the screw installed in the barrel of the extruder, the direction of the resin feeding flight in the metering section is opposite to the direction of the resin feeding flight in the feeding section and the compression section, and the core of the screw is set in the feeding section, A screw for an extruder characterized by having a uniform thickness in a compression section and a metering section. 2. The screw for an extruder according to claim 1, characterized in that a plurality of flights in opposite directions are provided in the measuring section of the screw.