JPS5941239A - Mold for injection molding - Google Patents

Abstract

PURPOSE:To obtain the titled mold that can provide an item with a low injection molding pressure without any short shot, burn mark, sink mark, etc., by supporting a gate tip in a floated manner by a spring thereby allowing the size of the gate to be varied in accordance with the injection pressure of the resin. CONSTITUTION:A melted resin is injection molded into cavities 1, 2 through a sprue 3, runners 4 and thin film gates 5. In the mold for said injection molding, the thin film gate 5 comprises a stationary gate 9 and the gate tip 6 housed slidably in a retaining chamber 8 through a spring 7.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to the design of a mold used in molding plastics. In particular, it relates to the design of molds, especially gates, when injection molding thermoplastics.

(b) Background Art Conventionally, short shots, cracks, sink marks, insufficient pressure, etc. have been cited as defects in molded products due to gate shape and dimensions. Furthermore, the current trend in the design of injection molding machines seems to be toward increasing the injection pressure.

This is considered to be a request for high-cycle molding, but in this case, it goes without saying that the design should take into account the balance between injection pressure and the shape and dimensions of the gate and cavity. be. In short, the gate must match the injection pressure and the molded product, but in practice it is difficult to determine the gate dimensions. In other words, the injection pressure actually varies greatly even during the shot period during molding.

Until now, no one with adjustable functions was known.

(c) Purpose of the Invention As stated above, when injection molding is performed, various defects occur in molded products. In order to eliminate defects caused by gate dimensions among these causes, it is an object of the present invention to provide a mold in which the gate dimensions of the mold can be adjusted during molding. It should be noted that a gate with a dimension adjustment function has not been known until now. To provide an injection mold characterized in that a formed gate is held floating by springs so as to be freely widened or narrowed according to changes in injection pressure. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1, which will be explained below based on drawings shown as examples, is a schematic diagram of an example of an injection molding die according to the present invention. In this figure, 1.2 is the cavity, 3 is the sprue, 4 is the runner, and 5 is the gate.
is a thin layer gate.

FIG. 2 is a sectional view taken along the line AA' in FIG. 1, showing the main parts of the structure of the present invention. In this figure, 6 is the gate chip,
Reference numeral 7 denotes a spring, which is set so that the gate chip 6 moves in response to changes in the resin pressure flowing through the gate 5, and the gate interval changes. 8 is a gate chip holding chamber, and 9 is a fixed gate, which is designed to be sufficiently wide so that changes in the gate chip 6 do not become meaningless. In short, this portion only needs to have at least the function of movably holding the gate chip 6. FIG. 3 is a view showing the plane AA' of FIG. 1, and shows the state of the thin layer gate 5. In FIG. FIG. 4 is a graph showing changes over time in the injection pressure applied to the cylinder during injection molding. First, in the stage, resin flows through the sprue 3 and the runner 4, and the injection pressure P1 is small. However, B
The stage is a state in which the resin flows through the gate 5, and a considerably high pressure is required as indicated by P2. One of the reasons why an injection molding machine requires a large injection pressure is thought to be that the injection pressure is transferred to the C stage. The reason why the molding material moves from the B stage to the C stage is considered to be that the viscosity of the molding material decreases due to frictional heat generation at the gate 5, resulting in a decrease in the injection pressure.

Next, the D stage shows the pressure at the time of completion of filling, the E stage shows the holding pressure state, and the F stage shows the mold opening state.

As explained above, in the present invention, the need for large injection pressure in the B stage is alleviated by automatically widening the gate, thereby suppressing the generation of excessive frictional heat generation. In other words, in stage B,
Gate 5 opens due to high injection pressure, gate 5 narrows in C stage, and cavity l in D stage.
, 2 has a mechanism for opening the gate 5 so that sufficient pressure is applied to the inside.

(F) Effect This invention makes the gate part independent from a part of the runner and the cavity part to form a gate chip, and the gate formed by this gate chip can be made wide or narrow according to changes in injection pressure. It is characterized in that it is held floating with springs so as to change the shape, so it has the following effects.

(1) Filling is possible even at low injection pressure.

(2) Gate heat generation can be suppressed to an appropriate level.

<3> Sufficient pressure can be applied to the m-shaped product (4) It is possible to fill the cavity with equal pressure.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a mold as an embodiment of this invention, Figure 2
The figure is a sectional view taken along line A-A' in figure 1, and figure 3 is a cross-sectional view taken along line A-A' in figure 1.
Figure 4, which shows the A' side, is a graph showing changes over time in the injection molding pressure applied to the cylinder during injection molding. ■, 2 is the cavity 3 is the sprue 4 is the runner 5 is the gate 6 is the gate chip 7 is the spring 8 is the gate chip holding chamber 9 is a fixed gate Patent applicant Toshikuro Takemoto (other 2 Figure 1 Figure 2 Figure 6 °l Figure 3 Figure 4 Injection distance t

Claims (1)

[Claims] (1) In an injection mold, the gate part is made independent from a part of the runner and the cavity part to form a gate chip, and the gate formed by this gate chip can be widened or narrowed according to changes in injection pressure. An injection mold characterized by being held floating by a spring so as to change the shape of the mold.