GB2178997A

GB2178997A - Screw for a molding machine

Info

Publication number: GB2178997A
Application number: GB08616826A
Authority: GB
Inventors: Mitsuaki Eshima; Takashi Kamiyama; Osamu Segawa
Original assignee: Toshiba Machine Co Ltd
Current assignee: Shibaura Machine Co Ltd
Priority date: 1985-07-10
Filing date: 1986-07-10
Publication date: 1987-02-25
Also published as: JPH0576408B2; GB8616826D0; DE3622974A1; JPS6211612A

Abstract

A screw S adapted for a molding machine, preferably an injection molding machine comprises a feed zone F, a compression zone C and a metering zone M disposed in this order from a material resin inlet 51. The metering zone M is provided with a mixing portion 53 of plunger type, the mixing portion 53 being provided with a plurality of grooves 54, 55 consisting of two groups arranged alternately around the mixing portion 53, each groove having two ends, one open and the other closed, adjacent grooves being unable to communicate with each other. The screw S is also provided on the outer peripheral surface with a main flight 52 arranged spirally throughout the three zones F, C, M and a sub-flight 56 arranged spirally along a portion of the compression zone C and/or the metering zone M, the sub-flight 56 having a height lower than that of the main flight 52 by 0.2-1.0 mm. A slightly modified screw is shown in Figure 7, (not shown). <IMAGE>

Description

SPECIFICATION Screw adapted for molding machine This invention relates to a screw adapted for a molding machine and particularly to a screw for an injection molding machine for attaining high kneading effect of a material resin.

An injection molding machine usually comprises a heating cylinder, a screw located in the heating cylinder to be rotatable and movable therein and a drive means for operating the screw. Various constructions of the screws are proposed in this field of art for attaining adequate kneading and color dispersion effects of a material to be plasticized such as resin.

Figure 1 shows a front portion of a screw of an injection molding machine for attaining the improved resin kneading and dispersion effects disclosed, for example, in Japanese Patent Publication No. 24493/1968. The screw 1 of Figure 1 is provided with a screw head 2 at the front portion thereof with a small clearance between the same and the inner surface of the heating cylinder and the screw head 2 is provided with a plurality of grooves 3 and 4 each of which has one end opened at the outer periphery of the screw head 2 and the other end closed. The grooves 3 and 4 are arranged alternately around the screw head so as to have reverse end configurations to prevent them from communicating with each other.Figure 2 shows a screw member 11 of the type disclosed in the Japanese Utility Model Laid-Open (KOKAI) Publication No. 138613/1983, which generally consists of a feed zone F at the rear portion of the screw, a compression zone C at the middle portion thereof and a metering zone M at the front end thereof. A mixing flight 12 is provided for the outer surface of the compression zone C and/or the metering zone M of the screw 11 along a predetermined length of the screw and the mixing flight 12 consists of one or more spirals and is provided with a plurality of grooves arranged in parallel with the axis of the screw and having varied depths.Figure 3 shows a part of a screw for an injection molding machine of the type disclosed in the Japanese Utility Model Publication No. 18180/1980, which is provided with a main flight 21 and a sub-flight 22 having both ends connected to the main flight 21.

In the usual molding operation, with these conventional screws, it is found that in use of the screws of the types shown in Figures 1 and 2, a color agent such as a pigment added to the material resin can be sufficiently dispersed, but when the screw has to be rotated at a high speed, a product includes flushes and silver streaks caused by the presence of the unmelted material, the introduction of a gas and the like. In use of the screw of the type shown in Figure 3, although the defects or problems caused by the presence of the unmelted material and the introduction of the gas into the material can be eliminated, the plasticizing ability of the screw for the material becomes low and it is required to increase the back pressure of the screw to attain the adequate dispersion of the coloring agent such as pigment.

Generally, in a usual molding operation carried out by a high-cycled operation of the screw, when a material to be melted such as polyethylene (PE), polypropylene (PP) and polyamide (PA) is used, formation of fish eye, inadequate color dispersion of master-batch and dry color, and inadequate kneading of the material will be observed, and in order to obviate these defects, a high back pressure will have to be applied to the screw.

Application of the high back pressure, however, will reduce the resin plasticizing ability, which results in lower productivity.

In order to eliminate the defects or problems described above, a prior art further provides screws having various kinds of barrier sub-flights. In use of these screws, however, the problems regarding the adequate color dispersion have not yet been solved when the material resin such as PE, PP and PA is utilized though the problem regarding the unmelted resin is somewhat improved.

An object of this invention is to eliminate defects or disadvantages encountered in the prior art and to provide an improved screw adapted for an injection molding machine capable of attaining high kneading effect.

Another object of this invention is to provide an improved screw having a structure capable of attaining high color dispersion effect while maintaining high resin plasticizing power or ability.

A further object of this invention is to provide a screw provided with main and sub-flights having a difference in height suitable for attaining improved kneading and color dispersion effects while maintaining the high resin plasticizing ability.

These and other objects can be achieved, according to this invention, by providing a screw adapted for a plastic material molding machine to be rotatable and movable in a heating cylinder thereof and provided with a feed zone, a compression zone, and a metering zone disposed in this order from a material inlet side towards a material outlet side, wherein the metering zone is provided with a mixing portion at a front end portion thereof so that a clearance exists between the outer peripheral surface of the mixing portion and the inner surface of the heating cylinder, the mixing portion is provided with a plurality of grooves consisting of two groups arranged alternately around the outer surface thereof, each having two ends one opened and the other closed, so that adjacent two grooves have different end shapes so as not to communicate with each other and the screw is also provided on the outer peripheral surface with a main flight spirally arranged throughout the feed, compression and metering zones and a sub-flight spirally arranged throughout the compression zone so that the sub-flight has a height lower than the height of the main flight by 0.2 ~ 1.0 mm.

Brief description of the drawings In the accompanying drawings: Figures 1, 2 and 3 are schematic views showing bodies or parts of conventional screws of various types adapted for a molding machine; Figure 4 is a schematic view of a screw according to this invention adapted for a molding machine; Figure 5 shows a part of a longitudinal section of the screw shown in Figure 1 for explaining the melting or kneading effect thereof; Figure 6 is a perspective view of a model product prepared for the comparison tests of the present invention and the conventional screws; Figure 7 is a schematic view of another embodiment of the screw of this invention; and Figures 8A through BC are diagrams of the conventional screws used for the comparison tests, in which the screw of Figure 8A is provided with a mixing portion and a full flight, the screw of Figure 8B is provided with a full flight and sub-flight having both ends connected to the full flight in a closed manner, and the screw of Figure 8C is also provided with a full flight and a sub-flight opened at both ends.

Description of the preferred embodiment Figure 4 shows a screw S adapted for a plasticized material forming machine, preferably an injection molding machine, and the screw comprises a feed zone F connected to a driving member 50 such as a piston rod at the rear end of the screw, a compression zone C at the middle portion thereof, and a metering zone M at the front end thereof. A screw head 59 is attached to the front end of the screw S. The screw S is disposed in a heating cylinder H and a material to be plasticized is introduced into the feed zone F through a supply port 51 such as a hopper and then guided into the compression zone C and the metering zone M in accordance with the rotation of the screw S as shown by the arrow Y.

A main flight 52 is provided on the outer surface of the screw S through the feed, compression and metering zones continuously and herically with an equal pitch. On the front end portion of the metering zone M is provided a mixing portion 53 of a plunger type with a small clearance between the mixing portion and the inner surface of the heating cylinder H. the mixing portion 53 is provided with a plurality of grooves 54 and 55 on the peripheral surface thereof. Each of the grooves 54 and 55 has one end opened at the outer peripheral surface of the mixing portion 53 and the other end closed, and the grooves 54 and 55 are formed so as to have reverse end configurations respectively so as not to communicate with each other.A sub-flight 56 is herically provided on the outer peripheral surface of the compression zone C of the screw so that the height, i.e. depth, of the sub-flight 56 is less than that of the main flight 52 by 0.2 ~ 1.0 mm, whereby the molten material in the groove 57 formed by the main flight 52 is fed into the groove 58 over the sub-flight 56 while preventing unmelted material from introducing into the groove 58 through the clearance as shown in Figure 5.

Results of test operations of the screws according to this invention shown in Figures 4 and 7 and according to conventional types shown in Figures 8A through 8C incorporated in the injection molding machine are described hereunder with reference to Table 1. The test operations were carried out under the following conditions.

Molded product: Box (shown in Figure 6) 305 grams Material to be molded: Polypropylene Molding Condition: Screw revolution number: 175 r.p.m. (MAX) Back pressure: 0 Operation cycle: Injection - 5 sec., Cooling - 10 sec., One cycle - 22 sec.

Barrel temperature: Nozzle (220 C), Front portion of barrel (220 C), Middle portion (210 C), Rear portion (200 C) Type of molding machine: 1S - 550 (manufactured by TOSHIBA KIKAI KABUSHIKI KAISHA); clamping pressure 550 tonss; screw diameter 75(t).

TABLE 1 Quality Judgement of Product Types Temperature . method color Plasticiz- Total of Screws Temperature ing Power(Kg/H) melted dispersion color kneading ( C) degree dispersion condition Judgement I 215 177 0 A A A II 213 160 0 x O A Ill 208 180 0 x O A IV 213 153 0 0 0 0 V 215 172 0 0 0 0 (I, II and Ill: Conventional Type; IV and V: Types according to this invention) (0: satisfied condition; x: unsatisfied condition; A: not unsatisfied but not completely satisfied condition) In Table 1, the screws of the conventional types I, II and Ill correspond to those shown in Figures 8A through 8C, respectively. The type I of the screw is provided with a full flight 81 and a mixing portion 82 having grooves of the same type as shown in Figure 7. The type II of the screw is provided with a full flight 83 and a sub-flight 84 closed at both ends by the full flight 83 and with no mixing portion, and the screw of the type Ill is also provided with a full flight and a sub-flight 85 having open ends and with no mixing portion. As represented by Table 1, it was found that a screw provided with no sub-flight attains no good or bad kneading effect and a screw provided with no mixing portion attains no good or bad color dispersion effect. The screw provided with the open ended sub-flight (type Ill) is superior to that of the closed ended sub-flight (type II) in the plasticizing power or ability.

The screw of the type IV is one shown in Figure 1 and the screw of the type V is one shown in Figure 7, both screws representing this invention and being provided with full flights 52, 86, sub-flights 56, 87 and mixing portions 54, 88 having grooves of the type described before, respectively. The screw of Figure 1, however, in provided with the sub-flight 56 longer than that 87 of Figure 7. The screws of Figures 1 and 7 produce a molded product superior to those produced by the screws shown in Figures 8A through 8C in the qualities thereof as shown in Table 1. Table 1 also shows the fact that the length of the sub-flight on the outer peripheral surface hardly influences the judgement of the product quality.

The following Table 2 shows another experimental results for obtaining the same effects as those referred to in Table 1 by varying the difference in heights, i.e. depths between the main flight 52 and sub-flight 56 of the screw S (the former is higher than the latter).

TABLE 2 Quality Judgement of Product Difference in Height between Resin Plasticiz- melted color kneading Total Main Flight Temperature ing Power degree dispersion condition Judgement and Sub-Flight ( C) (Kg/H) (mm) 0.15 227 157 0 A 0 A 0.2 213 153 0 0 0 0 1.0 215 172 0 0 0 0 1.5 209 183 x A O A (0: satisfied condition; x: unsatisfied condition; A: not unsatisfied but not completely satisfied condition) As can be seen from Table 2, desirable results were obtained in the case where the height of the full flight is higher than that of the sub-flight by 0.2-1.0 mm, and in the case where the difference is over 1.5 mm or below 0.2 mm, desirable results were not obtained particularly in the color dispersion effect. Although the results shown in Table 2 were obtained by the experiment in use of the screw of the type shown in Figure 4, substantially the same results were obtained in the experiment in use of the screw of the type shown in Figure 7.

These results show the fact that the length of the sub-flight does not severely influence the kneading effects or operations of the injection molding machine.

Claims

1. A screw adapted for a plastic material molding machine to be rotatable and movable in a heating cylinder thereof and provided with a feed zone, a compression zone, and a metering zone disposed in said order from a material inlet side towards a material outlet side, characterized in that said metering zone is provided with a mixing portion at a front end portion thereof so that a clearance exists between the outer peripheral surface of the mixing portion and the inner surface of the heating cylinder, that the mixing portion is provided with a plurality of grooves consisting of two groups arranged alternately around the outer surface thereof, each having two ends, one opened and the other closed, so that adjacent two grooves have different end shapes so as to prevent the communication with each other and that the screw is also provided on the outer peripheral surface with a main flight spirally arranged throughout the feed, compression and metering zones and a sub-flight spirally along a portion of at least one of the compression zone and the metering zone so that the sub-flight has a height lower than the height of the main flight by 0.2 ~ 1.0 mm.

2. The screw according to claim 1 wherein said sub-flight is opened at both ends thereof on the outer surface of the screw.

3. The screw according to claim 1 wherein said plastic material molding machine is an injection molding machine.

4. A screw adapted for a plastic molding machine to be rotatable and movable in a heating cylinder thereof, the screw being substantially as hereinbefore described with reference to Figures 4 and 5 or Figure 7 of the accompanying drawings.