Screw linkage structure for use in an injection molding machine

Details Screw linkage structure for use in an injection molding machine Screw linkage structure for use in an injection molding machine

1993-06-16

1994-09-06

Heitbrink, Tim

Plastic article or earthenware shaping or treating: apparatus

With apparatus assembly or dismantling means or with idle part

For extrusion or injection type shaping means

425192R, B29C 4517

Patent

active

053443039

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to a structure for linking a screw, in an injection molding machine, with a sleeve, transmitting an axial injection force and a rotational force, for measurement to the screw.
2. Background Art
An injection molding cycle in an injection molding machine comprises a clamping process for clamping a mold; an injection process for injecting a molding material (or a molten resin) into a cavity of the clamped mold; a dwell process for keeping the molding material filled into the mold cavity, at a predetermined pressure for a given period of time after injection of the molded material; an opening process for opening the mold to remove the molded product; and measurement and melting process for measuring and melting the molding material by applying heat and applying screw rotation.
During the injection process, a screw is driven toward a nozzle without rotating the screw. During the measurement process, the screw is forced to rotate out from the dwell position.
Use of the screw of the injection molding cycle creates a transmission of both axial and rotational forces. To this end, a conventional injection molding machine of in-line screw type (the melting and injection of the molding material are effected in a coaxial manner), includes a screw linkage structure as shown in FIG. 4.
The in-line screw injection molding machine depicted in FIG. 4 comprises a pusher plate 1 receiving a tie bar 2, of an injection section. The tie bar 2 is slidably displaceable to-and-fro. The pusher plate 1 includes at its center a housing 3 secured thereto, and at its front a screw sleeve 4 (hereinafter referred to simply as a sleeve 4). The sleeve 4 is supported by a bearing 5, so as to be rotatable with respect to the housing 3. On the rear side of the pusher plate 1 there is arranged an injection mechanism 6 whose fore-end is supported on the pusher plate 1. The sleeve 4 is provided with a pulley 7, rotationally driven by a servo-motor for measurement (not shown). A screw 8 is loaded onto the front surface of the sleeve 4 with the aid of a linkage structure. The linkage structures includes a spline bush 9 and a retainer 10, to transfer movement in the axial direction, (or to-and-fro direction) arising from the injection mechanism 6, and to transfer rotational movement caused by the servomotor, to the screw 8.
FIG. 5 depicts, in more detail, a structure for linking the screw 8 to the sleeve 4, which corresponds to the structure disclosed in Japanese Patent Laid-open Publication No. 1-115615. The structure includes a splined portion 11, formed on the rear end of the screw 8, fitted into a spline bush 9. The spline bush 9 is fitted into an insertion hole 12, provided in the front surface of the sleeve 4. The portion of the screw 8, immediately in front of the splined portion 11, is tapered into a small diameter portion 13 to define, at the fore-end of the splined portion 11, a shoulder. The shoulder is brought into contact with the rear surface of the retainer 10. The spline bush 9 and the retainer 10 are externally fastened to the sleeve 4 using common bolts 14. This allows the base of the screw 8 can be driven in both axial and rotational directions by the sleeve 4.
Inconveniently, this structure involves a drawback that the small diameter portion 13, which must be arranged immediately in front of the splined portion 11 for attachment of the retainer 10 to the screw 8, presents less strength against torsion or bending moment applied thereto, when the screw 8 is rotated by the sleeve 4. Furthermore, the shoulder at the foreend of the splined portion 11 serves substantially as a fore-end surface of spline teeth which is allowed to abut against the rear surface of the retainer 10. Due to its smaller contact area, however, a plastic deformation may arise in the spline teeth or the retainer 10. In addition, the retainer 10 requires a diameter large enough to cover the spline bush 9 for attachment to the sleeve 4.
In another conventional structure for linking the screw 8 with the

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