JPH0310487B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high kneading screw that can be applied to injection molding machines and extrusion molding machines.

Generally, in an injection molding machine, the screw moves backward during plasticization and moves forward during injection, so the effective length of the screw changes, the mechanical energy and heat transfer energy applied to the resin change, and the direction of the stroke changes. Differences in resin temperature (uneven kneading) were unavoidable.

The conventional screws shown in FIGS. 1 and 2 had a problem in that, especially when molding vinyl chloride, the difference in resin temperature in the stroke direction was large, making it difficult to achieve a wide range of molding conditions.

In order to eliminate the above-mentioned conventional drawbacks, the present inventors conducted intensive research and found that if the melting is promoted by rapidly applying shearing force at the tip of the screw without causing much melting in the screw groove, The present invention was achieved by discovering that the difference in resin temperature becomes smaller.

That is, the present invention provides at the tip of the screw a row of polyhedral mixing portions whose cross section perpendicular to the axis is composed of a flat or large curved surface, and the tip has a depth h'=1/
By providing a weir with a throttle groove of 2H to 1/5H (H is the maximum depth from the outer diameter of the polyhedron) and width w = 1/2W to 1/5W (W is the width of one side of the polyhedron),
During plasticization, the unmolten resin is captured and a strong shearing force is applied to provide effective kneading and cleaning effects. During injection, the aperture at the tip of the mixing section backs up the injection pressure.
It is an object of the present invention to provide a high-kneading screw that reduces backflow.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows a high-kneading screw according to an embodiment of the present invention. It's Skrill. The length L of the mixing section 2 is 1 to
It has a length of 3D (D is the screw diameter), and the mixing section cross section A to A is a large curved surface 3 (for example, R = 3h to 10h, where h is the groove depth of the metering part a), as shown in Figure 4. It is a polyhedron composed of planes 3' and 3', and has a slight twist in the direction of the screw axis. Note that W is the width of the curved surface 3 or plane 3' of the polyhedron.

Also, at the tip of the mixing section 2, l = 0.2L ~
A weir 4 is installed in a section of 0.5L, and the weir 4 has a depth h′=1/
A throttle groove 5 having a width of 2H to 1/5H (H is the maximum depth from the outer diameter of the screw of the polyhedron) and a width w of 1/2W to 1/5W is provided. Further, the portions where the mixing spaces b are adjacent to each other are divided by outer peripheral portions (flights) 7 having a width of 1 to 5 mm and circumscribing the inner wall surface 6 of the cylinder. Further, the throttle groove 5 is located on the opposite side of the mixing section 2.

Next, to explain the operation, in the mixing section 2,
A resin flow occurs in the direction of arrow d shown in FIG.
Further, the resin passage section b, which is composed of the cylinder inner wall surface 6 and the mixing section curved surface 3 or flat surface 3', has a wedge-shaped structure that is tapered in the flow direction of the resin.

Therefore, even vinyl chloride, which is difficult to gel, moves along the flow shown by arrow d, and as the screw 1 rotates, it is strongly pressed against the cylinder inner wall surface 6 by the wedge action of the mixing part curved surface 3 or flat surface 3', and as a result of the rotation. The mechanical energy becomes strong shearing energy, which acts on the unmelted resin and rapidly accelerates melting.

Furthermore, the weir 4 has the effect of preventing unmelted resin trapped in the corner portion 7 from overflowing to the tip of the screw. Therefore, the unmelted resin c is captured at the corner portion 7 and the weir 4, receives strong shearing energy, and rapidly melts. The molten resin passes through the weir 4 and the throttle groove 5, and is pooled in a certain amount in a space (not shown) at the tip of the screw chip 8.

Further, the molten resin pooled in a certain amount as described above is injected into a mold (not shown) in the next cycle, but at this time, the tip of the screw tip is under high pressure, so the resin tends to flow back toward the screw. At this time, the weir 4 and the throttle groove 5 act as resistance during injection to prevent backflow due to injection pressure.

Now, here, the shear rate γ of the wall surface is the screw diameter D,
When the screw rotation speed is N and the groove depth is H, γ=πDN/H... Also, the Newtonian fluid flow equation is, if the viscosity is μ and the shear stress is τ, then τ=μγ... ∴τ=πμDN/H... Therefore, as mentioned above, Due to the wedge action, the resin is strongly pressed against the cylinder inner wall surface 6, and as is clear from equation (3), the smaller the groove depth H becomes, the greater the shearing force τ becomes. In other words, the kneading effect increases. Furthermore, as the shearing force τ increases, the cleaning action on the mixing surface increases. Furthermore, in the throttle groove 5 at the tip of the mixing section, the groove depth h' is h'<<H, and the kneading effect and cleaning effect in this part are further increased.

As explained in detail above, the present invention provides a mixing section having a row of polyhedrons whose cross section perpendicular to the axis is a flat surface or a large curved surface at the tip of the screw, and has a depth h'=1/2H to 1 at the tip. /5H (H is the maximum depth from the outer diameter of the polyhedron), width w = 1/2W ~ 1/5
By providing a weir with a throttle groove of W (W is the width of one side of the polyhedron), it has a kneading effect and a cleaning effect even when molding vinyl chloride resin, etc., which is difficult to gel and prone to retention burns. Since no burning occurs and there is extremely little unevenness in resin temperature, a wide range of molding conditions can be used and cycle-up is possible. Further, the degree of kneading can be changed by changing the twist angle of the mixing part or by changing the outer diameter of the mixing part.

A high-kneading molding machine, which is an earlier application of the present invention, has been proposed in Japanese Patent Application Laid-Open No. 58-207936, but this machine is equipped with multiple rows of mixing sections, so that the pressure is reduced at the boundary between each mixing section. PVC resin, which has high viscosity and poor thermal stability, causes retention burns and has many retention areas, making it difficult to clean. Since the mixing section of the present invention is in one row, there is no sudden change in pressure, no residual burns, self-cleaning properties, less variation in resin temperature, and at the same time, the plasticizing ability is higher than that of conventional machines. Improve further. Furthermore, if the throttle groove at the tip is finely regulated, backflow during injection can be prevented even without a backflow prevention valve, which is highly effective for use with vinyl chloride resin.

[Brief explanation of the drawing]

Fig. 1 is a side view schematically showing a conventional screw for PVC, Fig. 2 is a side view of a conventional Dalmage screw, and Fig. 3 shows the tip of the screw in an injection molding machine showing an embodiment of the present invention. A side view, FIG. 4 is a sectional view taken along line A to A in FIG. 3, and FIG. 5 is an enlarged view of section B in FIG. 4. Explanation of the main parts of the diagram, 1...Skrill, 2...
Mixing section, 3...large curved surface, 3'...plane,
4...Weir.

Claims (1)

[Claims] 1 At the tip of the screw, a single row of polyhedral mixing parts whose cross section perpendicular to the axis is composed of a flat surface or a large curved surface is provided, and the depth h' = 1/2H to 1/5H is provided at the tip.
(H is the maximum depth from the outer diameter of the screw of the polyhedron), and by providing a weir with a throttle groove of width w = 1/2W to 1/5W (W is the width of one side of the polyhedron), it is possible to mix during plasticization. This high-kneading screw is characterized by having an action and a cleaning action, and is designed to prevent backflow during injection.