JP2018079642A - Screw for injection molding and injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw for injection molding that effectively levelling off the molten state of a resin material and an injection molding machine having the same.SOLUTION: An injection molding machine 1 has a heating cylinder 21 and a screw 30 accommodated in the heating cylinder 21. The screw 30 has a flight section 35 in a compression section being a section of a part of a flight 33, the flight section being formed such that an angle β, between an axis line L of a rotational axis 31 and a base end side surface 35a, in the tip end side is larger than that in the base end side.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an injection molding screw used in an injection molding machine and an injection molding machine having the same.

  A conventional screw used in an injection molding machine is disclosed in Patent Document 1. This screw has a rotating shaft and a spiral flight projecting from the outer periphery of the rotating shaft, and is configured to send a resin material from the proximal end side to the distal end side along the axial direction by the rotation of the rotating shaft. Has been.

  In order to stabilize the quality of a molded product in injection molding, it is necessary to make the molten state of the resin material uniform, and the molten state is made uniform by melting and kneading the resin material as a whole at a relatively early stage. It is one of the important elements. In the prior art, in the screw, the shearing force acting on the resin material is changed by adjusting the depth of the screw groove between the flights, and the molten state of the resin material is smoothed (equalized).

Japanese Patent Laid-Open No. 2006-182687

  However, since resin materials have different characteristics depending on the type, advanced technology and experience are required to adjust the depth of the screw groove according to the resin material. And if the screw groove is too shallow due to insufficient adjustment, the shearing force acting on the resin material becomes too strong and burns occur, and if the screw groove is too deep, the shearing force acting on the resin material becomes too weak and unmelted. I will. Therefore, it has been difficult to make the molten state of the resin material uniform.

  Therefore, an object of the present invention is to provide an injection molding screw capable of effectively smoothing the molten state of a resin material and an injection molding machine having the same.

  FIG. 7 schematically shows the melting mechanism of the resin material in the screw groove of the injection molding screw. In the injection molding screw 130, the solid resin material charged from the hopper is conveyed toward the injection nozzle side (left side in FIG. 5) through the screw groove M formed between the flights 133. During this conveyance, the resin material is heated and melted by heat transfer from the heating cylinder 121, and an unmelted layer called the solid bed SB and a melt called MF film MF that overlaps the heating cylinder inner surface 121a side of the solid bed SB. A layer is formed. When the melt film MF is formed, the solid bed SB is melted by the heat generated by the shear energy therein, and the melt film MF grows in the thickness direction. When the thickness of the melt film MF grows beyond the clearance between the tip of the flight 133 and the inner surface 121a of the heating cylinder 121, the melt film MF is scraped off by the advancing flight 133 and collected behind the screw groove M. To become a melt pool MP. The scraped melt film MF circulates in the melt pool MP and is kneaded with each other.

  As a result of intensive studies on such a melting mechanism, the present inventor has found a configuration for effectively melting an unmelted solid bed staying on the tip side in the screw groove, and has reached the present invention.

  In order to achieve the above object, an injection molding screw according to an aspect of the present invention includes a rotating shaft and a spiral flight provided to protrude from an outer peripheral surface of the rotating shaft, and at least of the flight. A part of the section is formed so that an angle formed between the axis of the rotating shaft and the base end side surface of the flight is larger in the tip end portion than in the base end portion.

  In the present invention, there is provided a compression portion formed such that the depth of the screw groove between the flights or the axial length of the screw groove decreases from the proximal end side toward the distal end side, and the flight It is preferable that the section disposed in the compression portion is formed so that the angle continuously increases from the proximal end side toward the distal end side.

  In the present invention, the flight is such that the angle of the section disposed on the distal end side of the compression portion in the flight is larger than the angle of the section disposed on the proximal side of the compression section in the flight. Preferably it is formed.

  In the present invention, the angle is preferably in the range of 20 degrees to 80 degrees.

  In order to achieve the above object, an injection molding machine according to another aspect of the present invention includes the injection molding screw and a heating cylinder that accommodates the injection molding screw.

  According to the present invention, in at least a part of the section of the flight, the angle formed between the axis of the rotary shaft and the base end side surface of the flight is larger at the distal end portion than at the proximal end portion in the section. Is formed. Because of this, in the screw groove formed between the flights, the molten resin material stays near the base end and the unmelted resin material stays near the tip, but the resin material stays near the tip. Can be strengthened at the proximal end portion and weakened at the distal end portion in a partial section or the whole of the flight. Therefore, it is possible to accelerate the melting by applying a strong shearing force to the unmelted resin material at an early stage and to suppress the excessive shearing force from acting on the resin material after melting. The state can be leveled effectively.

It is a figure showing a schematic structure of an injection molding machine concerning one embodiment of the present invention. It is a side view of the screw for injection molding which the injection molding machine of FIG. 1 has. It is a fragmentary sectional view of the screw for injection molding of FIG. It is a figure which shows typically the melting mechanism in the screw groove of the screw for injection molding of FIG. It is a figure which shows the shear stress distribution analysis result about the compression part of the screw for injection molding. It is a figure which shows the resin temperature distribution analysis result about the supply part of the screw for injection molding. It is a figure which shows typically the melting mechanism in the screw groove of the conventional screw for injection molding.

  Hereinafter, an injection molding machine according to an embodiment of the present invention and a screw included in the injection molding machine will be described with reference to FIGS.

  FIG. 1 is a diagram showing a schematic configuration of an injection molding machine according to an embodiment of the present invention. FIG. 2 is a side view of an injection molding screw included in the injection molding machine of FIG. FIG. 3 is a partial cross-sectional view of the injection molding screw of FIG. 4 is a diagram schematically showing a melting mechanism in the screw groove of the injection molding screw of FIG. 2, and (a) is a screw groove arranged in a proximal end portion of the compression portion. , (B) is a screw groove disposed in the tip side portion.

  An injection molding machine 1 according to an embodiment of the present invention shown in FIG. 1 is for producing a molded body using a thermoplastic granular resin material as a raw material. The injection molding machine 1 has a mold clamping unit 10 and an injection unit 20 disposed on a machine base 2.

  The mold clamping unit 10 moves the movable die plate 12 forward and backward by bending the toggle link mechanism 11 using a driving force of a motor (not shown) as a drive source, and the movable die 13 fixed to the movable die plate 12 is fixed to the fixed die plate. The mold is closed and opened with respect to the fixed mold 15 fixed to 14.

  The injection unit 20 includes a cylindrical heating cylinder 21, an injection nozzle 22 provided at the tip of the heating cylinder 21, and an injection that is accommodated in the heating cylinder 21 and kneads the resin material supplied into the heating cylinder 21. A molding screw (hereinafter simply referred to as “screw 30”), a support member 23 that rotatably supports the screw 30, a hopper 24 into which a resin material is charged, a hopper block 25 provided with the hopper 24, and a heating And a heater 26 disposed outside the cylinder 21.

  In the injection molding operation of the injection molding machine 1, the screw 30 accommodated in the heating cylinder 21 is rotated and the heating cylinder 21 is heated to a high temperature by the heater 26. Thereby, the resin material supplied from the supply port 24a of the hopper 24 advances while being melted and kneaded from the proximal end side of the heating cylinder 21 to the distal end side (right side to left side in each drawing). Then, the melted and kneaded resin material is weighed by rotating the screw 30 by a rotation driving means such as a metering motor (not shown). After metering, the screw 30 is advanced by an advancing / retreating drive unit including an injection motor and a ball screw mechanism (not shown), whereby a predetermined amount of molten resin material is injected through the injection nozzle 22 into the cavity in the closed mold. Is done.

  Here, the screw 30 accommodated in the heating cylinder 21 will be described in detail.

  As shown in FIGS. 2 and 3, the screw 30 is provided with a supply unit, a compression unit, and a metering unit in order from the proximal end side to the distal end side. The screw 30 includes a cylindrical rotary shaft 31, a check head 32 that functions as a backflow suppression valve provided at the tip of the rotary shaft 31, and a spiral flight provided on the outer peripheral surface of the rotary shaft 31. 33.

  The rotating shaft 31 is formed so that the portion disposed in the supply portion has the same diameter throughout, and the portion disposed in the compression portion continuously increases in diameter from the proximal end side toward the distal end side. The portion arranged in the weighing unit is formed to have a larger diameter than the portion arranged in the supply unit and the same diameter throughout.

  The flight 33 is formed so that the distance from the axis L of the rotating shaft 31 to the tip surface is constant and has a helical shape with an equal pitch throughout. Since the diameter of the rotating shaft 31 continuously increases in the compression portion from the proximal end side toward the distal end side, the screw groove M formed between the flights 33 in the compression portion from the proximal end side toward the distal end side. It is formed so that the depth of is small. Alternatively, the compression portion may be formed such that the flight pitch (that is, the length of the screw groove M in the axis L direction) continuously decreases from the proximal end side toward the distal end side.

  The flight 33 has a supply part flight part 34 arranged in the supply part, a compression part flight part 35 arranged in the compression part, and a weighing part flight part 36 arranged in the measurement part.

  The supply portion flight portion 34 is formed such that the angle α formed by the axis L of the rotation shaft 31 and the base end side surface 34a is constant throughout. The supply part flight part 34 is a section arranged in the supply part on the proximal end side with respect to the compression part in the flight 33.

  The compression portion flight portion 35 is connected to the distal end side of the supply portion flight portion 34, and the angle β formed by the axis L of the rotation shaft 31 and the proximal end side surface 35a continuously increases from the proximal end side toward the distal end side. (However, β7> β6> β5> β4> β3> β2> β1 ≧ α). The compression part flight part 35 is a section arranged in the compression part in the flight 33.

  The measuring portion flight portion 36 is connected to the distal end side of the compression portion flight portion 35 and is formed so that the angle γ (where γ ≧ β) formed by the axis L of the rotating shaft 31 and the base end side surface 36a is constant throughout. ing. The weighing part flight part 36 is a section arranged in the weighing part on the tip side of the compression part in the flight 33.

  In the present embodiment, the angle α is 20 degrees, the angle β continuously changes from 20 degrees to 80 degrees, and the angle γ is 80 degrees. Of course, the angle α, the angle β, and the angle γ may have other sizes unless they are contrary to the object of the present invention.

  The flight 33 has a constant angle (for example, 90 degrees) between the axis L of the rotary shaft 31 and the tip side surface (the surface facing the left side in FIG. 3) of the supply part flight part 34, the compression part flight part 35, and the measurement part flight part 36 ).

  Next, the melting mechanism of the resin material in the screw groove M of the compression part of the screw 30 described above will be described. In the screw groove M, a solid bed SB and a melt film MF that overlaps the solid bed SB are formed, and the melt pool MP formed by scraping the melt film MF by the flight 33 is closer to the rear of the screw groove M (that is, the base end). Formed).

  And in the screw groove M of the part of the base end side in a compression part, as shown to Fig.4 (a), the axial line L of the rotating shaft 31, and the base end side surface of the flight 33 (specifically compression part flight part 35). Since the angle formed by 35a is small, the distance between the base end side surface 35a and the inner surface 21a of the heating cylinder 21 is narrow, and therefore a relatively strong shearing force acts on the solid bed SB. Therefore, the melting of the solid bed SB is promoted.

  Further, in the screw groove M at the distal end side in the compression portion, as shown in FIG. 4B, the axis L of the rotary shaft 31 and the proximal end side surface 35a of the flight 33 (specifically, the compression portion flight portion 35). Since the angle between the base end side surface 35a and the inner surface 21a of the heating cylinder 21 is large, it is possible to prevent excessive shearing force from acting on the resin material after melting.

  As described above, according to the injection molding machine 1 of the present embodiment, since the above-described screw 30 is provided, the compression portion flight portion 35 that is a partial section of the flight 33 is more distal than the proximal end portion. Is formed such that the angle β formed by the axis L of the rotating shaft 31 and the base end side surface 35a is larger. Thus, in the screw groove M formed between the flights 33, the molten resin material stays near the base end and the unmelted resin material stays near the tip, but stays near the tip. The shearing force acting on the resin material can be strengthened on the proximal end side of the compressed portion flight portion 35 and weakened on the distal end side. Therefore, it is possible to accelerate the melting by applying a strong shearing force to the unmelted resin material at an early stage and to suppress the excessive shearing force from acting on the resin material after melting. The state can be leveled effectively.

  Similarly, when the screw 30 is viewed as a whole, the angle γ of the weighing part flight part 36 is larger than the angle α of the supply part flight part 34, so that a strong shearing force is applied to the unmelted resin material in the supply part. Thus, the melting can be promoted, and the excessive shearing force can be prevented from acting on the molten resin material in the measuring section, so that the molten state of the resin material can be effectively leveled.

  In addition, the compression portion is formed so that the depth of the screw groove M between the compression portion flight portions 35 decreases from the proximal end side toward the distal end side, and the compression portion flight portion 35 extends from the proximal end side to the distal end side. The angle β is formed so as to continuously increase as it goes to. Since it did in this way, the shear force which acts on the resin material which retains near the front-end | tip in the screw groove M can be made comparatively strong at the beginning, and can be gradually weakened as it progresses from the base end side to the front end side. . Therefore, the molten state of the resin material can be made more effective.

  Further, since the angle α, the angle β, and the angle γ are within a range of 20 degrees to 80 degrees, the angle range is relatively large. Therefore, the shearing force can be changed in a wide range.

  In the embodiment described above, the angle β of the compression portion flight portion 35 is continuously changed from 20 degrees to 80 degrees, but is not limited thereto. For example, the compression portion flight portion 35 is formed such that the angle β is constant (for example, 50 degrees) over the whole, and the relationship between the angle α, the angle β, and the angle γ is expressed as γ> β. It may be changed stepwise as it proceeds to the supply unit, the compression unit, and the metering unit so that> α.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these examples. Those in which those skilled in the art appropriately added, deleted, and changed the design of the above-described embodiments, and combinations of the features of the embodiments as appropriate, also include the present invention as long as they include the gist of the present invention. It is included in the scope of the invention.

  Next, the results of analyzing the shear stress distribution and the resin temperature distribution by simulation using Examples and Comparative Examples of the injection molding screw of the present invention are shown in FIGS.

  FIG. 5 is a diagram showing a shear stress distribution analysis result for the compression portion of the injection molding screw. FIG. 6 is a diagram showing a resin temperature distribution analysis result for the supply part of the injection molding screw. 5 and 6, (a) shows the analysis result for the example, and (b) shows the analysis result for the comparative example. FIG. 5 shows that the darker the color, the higher the shear stress, and FIG. 6 shows that the darker the color, the higher the resin temperature.

  In the example, in the screw 30 of the present embodiment described above, the angle α of the flight 33 is 20 degrees, the angle β is continuously changed from 20 degrees to 80 degrees, and the angle γ is 80 degrees. did. On the other hand, in the comparative example, the same configuration as that of Example 1 was adopted except that the angle α, the angle β, and the angle γ were all 80 degrees.

  According to FIG. 5 (a), the width of the portion where the shear stress is strong near the flight is wide on the base end side, and the width of the portion where the shear stress is strong gradually decreases from the base end side toward the tip side. This width is almost the same as the width of the proximal side surface. On the other hand, according to FIG.5 (b), the width | variety of the location with a strong shear stress near flight is narrow over the whole. From this, it is clear that in the example, a strong shearing force can be applied to the resin material at an earlier stage than the comparative example in the compression portion.

  Moreover, FIG. 6A shows that the temperature of the resin material is higher from a position closer to the base end side than FIG. 6B. In particular, in FIGS. 6A and 6B, the difference is remarkable when the temperatures in the vicinity of the second flight from the base end side are compared. These differences are thought to be due to the difference in shearing force acting on the resin material caused by the difference in the shape of the proximal side surface of the flight. From this, it is clear that in the example, the temperature of the resin material can be increased at an earlier stage in the supply unit than in the comparative example.

  Therefore, the effects of the present invention are clear from the simulation results.

  DESCRIPTION OF SYMBOLS 1 ... Injection molding machine, 2 ... Machine stand, 10 ... Clamping unit, 11 ... Toggle link mechanism, 12 ... Movable die plate, 13 ... Movable die, 14 ... Fixed die plate, 15 ... Fixed die, 20 ... Injection Unit: 21 ... Heating cylinder, 21a ... Inner surface, 22 ... Injection nozzle, 23 ... Support member, 24 ... Hopper, 24a ... Supply port, 25 ... Hopper block, 26 ... Heating heater, 30 ... Screw (screw for injection molding), 31 ... Rotating shaft, 32 ... Check head, 33 ... Flight, 34 ... Supply part flight part, 34a ... Base end side, 35 ... Compression part flight part, 35a ... Base end side, 36 ... Metering part flight part, 36a ... Base End side surface, L ... axis, M ... screw groove, SB ... solid bed, MF ... melt film, MP ... melt pool.

Claims (5)

A rotating shaft, and a spiral flight provided on the outer peripheral surface of the rotating shaft,
At least a part of the flight is formed such that the angle formed between the axis of the rotary shaft and the base end side surface of the flight is larger at the front end than at the base end. Characteristic screw for injection molding. A compression portion formed such that the depth of the screw groove between the flights or the axial length of the screw groove decreases from the proximal side toward the distal side,
2. The injection molding according to claim 1, wherein a section disposed in the compression portion in the flight is formed such that the angle continuously increases from a proximal end side toward a distal end side. Screw.   The flight is formed such that the angle of the section disposed on the distal end side from the compression portion in the flight is larger than the angle of the section disposed on the proximal side from the compression section in the flight. The screw for injection molding according to claim 2.   The said angle | corner exists in the range of 20 to 80 degree | times, The screw for injection molding as described in any one of Claims 1-3 characterized by the above-mentioned.   An injection molding machine comprising: the injection molding screw according to any one of claims 1 to 4; and a heating cylinder that accommodates the injection molding screw.