JPS6410173B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a screw for resin molding.

Plasticization and melting of resin in molding machines such as extrusion molding machines and injection molding machines is an extremely important problem. In other words, this has a large impact on the quality, productivity, defective rate, personnel costs, etc. of the molded product. Therefore, various studies have been conducted and numerous proposals have been made regarding the screws of plasticizing devices.

The present invention relates to a screw for a plasticizing device, and its purpose is to provide a plasticizing screw that has excellent melting efficiency, large plasticizing ability, uniform melting, and excellent kneading properties.

Generally, many of the plasticizing screws used in molding machines are shown in FIG. In Fig. 1, the screw 1 includes, from the material supply side, a supply zone 3 where the screw groove 2 is deep, a compression zone 4 where the screw groove depth gradually becomes shallower as it goes forward in the axial direction, and a compression zone 4 where the screw groove depth is shallow. It consists of a weighing zone 4a.
5 is Skrill Flight. The melt form of the thermoplastic resin for such a normal screw 1 is as follows:
This is illustrated by the melting model shown in Figure 2a. FIG. 2a shows a configuration in which an unmelted solid (solid bed) 6 and a melt (molten body) 7 coexist separately in the screw groove 2. However, even in such a molten state, as the melting progresses and the unmelted ratio X/W, which is expressed as the ratio of the width X of the solid bed 6 in the screw groove 2 to the width W of the screw groove 2, becomes smaller, the solid bed 6 itself will rise. Due to changes in rigidity due to temperature, shear contact of the melt 7, etc., this molten form is distorted, and as shown in FIG. 2b, unmelted solid pieces 8 are suspended in the melt 7.
This form is noticeable during high-speed plasticization when the rotation of the screw 1 is increased, and as unmelted substances are mixed into the molded product, uneven strength of the molded product, changes in color tone, color unevenness in coloring molding, etc. changes in liquidity;
This causes many undesirable consequences such as air bubble inclusion. Moreover, this form restricts the plasticizing ability so that it does not occur in the plasticizing process, that is, it causes restrictions on the cycle and continuous production amount. Note that 9 is a heating cylinder.

There is one shown in FIG. 3 that has improved the melting form. That is, the cross-sectional area of the passage is changed by displacing the screw groove bottom in the radial direction. 4a and 4b show the AA cross section and the BB cross section of FIG. 3, but the cross-sectional shape may be circular as shown in FIG. 3 or polygonal.
In short, by changing the cross-sectional area of the screw groove passage and repeatedly compressing and relaxing the solid bed 6 in the form shown in FIG. The aim is to increase the efficiency of melting by preferentially transporting only the molten metal to the front. This melting form has the effect of promoting melting in the early stage of melting, and in the late stage of melting when the molten solid pieces 8 are floating, the screw gap is made shallower and the unmelted solid pieces 8 are selectively melted. There is.

However, like the conventional conventional screw 1 shown in Fig. 1, the melting mechanism has not been fundamentally improved, and the screw groove 2 is completely filled with solid bed 6 during high-speed rotation, resulting in a decrease in plasticizing ability. Or cause change. That is, the solid bed 6 formed by the screw groove 2
At the contact surface with the inner wall of the heating cylinder 9, it is pressed against the inner wall of the heating cylinder by the internal pressure of the screw groove and receives heat from the inner wall of the heating cylinder, and at the same time, the resin generates heat due to the shearing action between the inner wall of the heating cylinder and the solid bed due to the rotation of the screw. to form a melt film. Therefore, melting is performed sequentially from the contact surface of the solid bed with the inner wall of the heating cylinder. In other words, the temperature of the solid bed can only be expected to increase due to heat conduction from the outer periphery of the solid bed.
Moreover, resin is a poor conductor of heat and has a disadvantage in its melting mechanism, which is not very promising.

In view of this point, the present invention aims to actively destroy the solid bed upstream to increase melting efficiency, and downstream to perform selective melting in which the melt passes through as is and unmelted material is melted.
As shown in FIG. 5, the passage cross-sectional area of the screw groove 2 is changed by displacing the screw groove bottom 2 in the radial direction along the screw flight 5, so that the upstream passage cross-sectional area gradually increases and eventually becomes smaller. A single or plural recesses 10 or grooves are provided at the bottom of the screw groove along the screw flight 5, and the recesses 10 and the like are not provided in the area where selective melting is performed.

FIG. 6 shows its conceptual diagram. In other words, it is a model diagram in which the screw groove 2 is developed along the screw flight 5 and the recess 10 is shown as a cross section along the screw flight 5.

FIG. 6 shows an embodiment in which a recess 10 is provided in a circumferential portion P where the screw groove bottom 2a becomes gradually shallower and then gradually deeper. However, in Fig. 6, it is shown in a considerably shrunken state only in the left and right directions. In this example, the length of P is the length of one circumference of the screw 1, but this means that the portion where the screw groove bottom 2a gradually becomes shallower and then gradually becomes deeper is the length of half the circumference of the screw 1, which is two turns. If the length is longer, the length can be changed accordingly.

FIG. 7 is an example of an axial cross section taken along the screw flight 5 in FIG.

The operation of the screw 1 constructed in this way will be explained in detail with reference to FIGS. 8a to 8d.

In the initial stage of melting, as shown in FIG. 8a, the solid bed 6 formed in the screw groove 2 is displaced in the radial direction in the solid bed fracture zone of the present invention, and the cross-sectional area of the screw groove passage gradually decreases. Since a plurality of concave portions 10 are provided along the screw flight in the range where the curve increases again,
As shown in FIG. 8b, the solid bed 6 sinks into the recess 10 and breaks starting from the periphery of the recess 10. On the other hand, the solid bed 6 moving on the screw groove bottom 2a whose passage area other than the recess 10 gradually decreases is pressed against the inner wall of the heating cylinder 9 and melts from the pressed contact surface, and is piled up on the depressed solid bed 6. During this process, the melt 7 comes into contact with the depressed and fractured surfaces of the solid bed 6, so heat transfer occurs in which the heat of the hot melt 7 is transferred from these multiple fracture surfaces to the cold solid bed 6, which promotes the temperature increase and softening of the solid bed 6. At the same time, Melt 7
The hot melt 7 and the cold solid bed 6 are distinctly separated and coexisted, so that closer thermal contact and homogenization occur between the two, promoting melting and mixing. In this way, once the solid bed 6 is destroyed, the recess 10 is formed in the screw groove bottom 2a while changing the relative position of the solid beds 6.
A new solid bed 6 is again formed as shown in FIG. This formed solid bed 6 again forms a new depressed fracture surface in the next step, as shown in FIG. 8d. Such shearing contact with the melt 7 on the fracture surface enhances the aforementioned effects such as better heating of the solid bed 6, promotion of melting, and improved mixing. Next, the solid bed 6 is repeatedly broken, and the melted memelt 7 is transported to the front of the screw 1, where it is transported to a melt sorting zone 12 which is almost common to the downstream metering zone 4a.
In the narrower screw gap δ, a strong shearing action is selectively applied to the unmelted solid pieces 8 to melt them, mix them, knead them, and homogenize them. In addition, 11
is a relatively large solid bed failure zone in the screw gap.

9 and 10 show other embodiments in which, in the melting and sorting zone 12, instead of displacing the screw groove bottom 2a in the radial direction to form a narrow slit with the inner wall of the heating cylinder, a second flight is formed, respectively. 13. Barrier 1
4 to form a narrow slit with the inner wall of the heating cylinder,
It is designed to perform melt sorting. however,
This slit clearance is at least larger than the flight clearance between the screw flight 5 and the inner wall of the heating cylinder 9, and the clearance is determined mainly by the type of resin. In this way, substantially the same effects as those described above can be obtained.

As described above, according to the present invention, by early breaking of the solid bed and subsequent selective melting, it is possible to perform plastic melting that is thermally and physically homogeneous and has good thermal efficiency. In particular, with crystalline low viscosity resins, the plasticizing ability is significantly improved, and with amorphous high viscosity resins, the screw driving torque is significantly reduced, resulting in energy savings.

[Brief explanation of the drawing]

FIGS. 1 and 3 are front views showing different examples of conventional devices similar to the present invention, FIGS.
b is a melting model diagram showing the melted form of the resin in the screw shown in FIG. 1, FIGS. 6 is a developed cross-sectional view showing the screw shown in FIG. 5 developed along the screw flight; FIG. 7 is a cross-sectional view taken along the - line in FIG. 5; FIG. 9 and 10 are front views showing different embodiments of the present invention, respectively. 1...Scrill, 2...Scrill groove, 5...Scrill flight, 6...Solid bed, 7...
Melt, 9 heating cylinder, 10... recess, 13... second
Flight, 14... Barrier.

Claims (1)

[Claims] 1. A region is provided in which the groove bottom of the screw groove is displaced in the radial direction to change the passage cross-sectional area of the screw groove,
A resin-molded screw in which a single or multiple recesses are provided along the screw flight in an area where the cross-sectional area of the passage gradually decreases and increases upstream within the region. 2. A second flight is derived from the screw flight downstream of the portion where the screw is provided with the concave portion, and the second flight is joined to the screw flight again, and at least the screw flight and the inner wall of the heating cylinder are attached to the second flight portion. Claim 1 has a structure having a clearance larger than the clearance of
Screw for resin molding as described in section. 3 The screw has a structure in which the screw groove has a barrier along the axial direction downstream of the portion where the recess is provided, and the barrier portion has a clearance larger than the clearance between the screw flight and the inner wall of the heating cylinder. A screw for resin molding according to claim 1.