JP2000094481A - Gate bush - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and smoothly cut a gate simultaneously with the opening of a mold with good cooling effect even by shortening an injection molding cycle by providing a plurality of protruding bars on an inner wall of a gate bush. SOLUTION: The gate bush comprises a plurality of protruding bars 6 projecting in a section near an end of a gate. The number of the bars 6 is about 2 to 5. Its sectional shape is a V shape, an angular shape, a curve shape or the like. A range of forming the bars 6 is about 10 mm as long as from an end in the longest, and generally about 5 mm. Here, a distance between an inner wall of the bush near an end of the gate and a center of the bush is shortened, and a contact area of a molten plastic with an inner surface of the bush is increased. Thus, a cooling effect is remarkably enhanced. Even when a molding cycle is accelerated, a fault such as stringiness does not occur, the gate can be smoothly cut, and an acceleration of the cycle and a cost reduction can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gate bush which is one of mold parts for plastic injection molding and injection blow molding.

[0002]

2. Description of the Related Art A gate bush which is one of conventional mold parts for plastic molding has a shape shown in a longitudinal sectional view of FIG. 1A and an AA sectional view of FIG. 1B. That is, a conical cavity 2 is provided inside a cylindrical metal 1 and a large circular hole 3 and a small circular hole 4 (gate) are formed from both sides of a circular side surface. It is manufactured in two ways: electroforming and machining.

In injection molding, after being clamped, a high-temperature and high-pressure molten plastic enters through a large circular hole 3 and rapidly flows into a small circular hole 4 (gate) into a space (product part) sandwiched between a cavity and a core. And left to cool. After opening the mold, it is required that the gate part cuts cleanly and the gate does not remain in the product.However, there is a strong demand for faster molding cycles to increase productivity and lower costs. Because of the shortest distance, the center of the gate is insufficiently cooled, often causing the gate to not be cut and threading to occur. It is inevitable to finish the gate by post-processing. For this reason, the cost is increased, the quality of the remaining gates becomes poor due to poor appearance, or the lid is often formed by injection molding using a core gate. There are problems such as occasional occurrence of serious quality complaints.

[0004]

In view of the above, the present invention provides a good cooling effect even if the injection molding cycle is shortened.
It is an object of the present invention to provide a gate bush in which a gate portion can be reliably and neatly cut at the same time when a mold is opened.

[0005]

In order to achieve the above object, in the gate bush of the present invention, the vicinity of the tip of the gate portion is not a conventional circular cross section, but is a B near the gate shown in FIG. As shown in (b) to (d) in the -B cross-sectional view, a configuration in which a plurality of ridges 6 were inserted in the cross section was adopted.

The structure in which the cross section near the tip of the gate includes the plurality of ridges 6 is selected from two or more in the number of ridges, and about 2 to 5 pieces have a cooling effect and workability. Is desirable.

FIG. 4A shows the cross-sectional shape of the ridge 6.
Any of V-shape (a), square (b), curve (c), etc. as shown in (c) may be used, but when manufactured by electroforming, from the viewpoint of uniform electrodeposition, V-shape or curve Shape is desirable.

[0008] The range in which a plurality of ridges 6 are inserted is shown in FIG.
As shown in the figure, it is sufficient that the length is about 10 mm at the longest from the tip end, and it is particularly preferable that the length is about 5 mm, but this range is not particularly limited.

In the method of manufacturing by electric discharge machining and machining,
There are problems such as difficulty in processing and hindrance to polishing the inner surface, and the method by electroforming is suitable because it can be easily manufactured, but is not particularly limited.

[0010]

According to the present invention, FIG. 5A and FIG.
As shown in the figure, the distance D between the inner wall of the gate bush near the tip of the gate and the center of the gate bush is reduced, and the contact area between the molten plastic and the gate bush is increased. Even if the molding cycle is accelerated, the gate can be reliably cut cleanly.

[0011]

EXAMPLE A 12 mm brass rod was prepared and the side was cut vertically. Then, as shown in the EE cross-sectional view of FIG. 6 (b), two V-shaped grooves 7 were cut from two ends to 10 mm from the tip. Provided
Next, the cross hatched portion in FIG. 7 was cut by an NC lathe to produce a mother die 8. Next, after polishing with blue powder etc.
Using the master 8, electroforming is performed in a nickel sulfamate main component solution, nickel is given an average thickness of about 4 mm, and then the master 8 is pulled out and cut with a lathe to form a gate bushing part. Finished products were manufactured. This gate bush had a structure in which two V-shaped ridges were located at 5 mm from the tip end.

The gate bushing component of the present invention manufactured as described above and the conventional gate bushing component having the same dimensions and a circular cross section near the tip of the gate are assembled into an injection molding die for a lid, and the conventional molding is performed. When molded for one day at a speed about 1.5 times faster than the cycle, the product of the present invention was cleanly cut with zero threading of the gate, whereas the conventional gate bush was 20 times shorter from the start of molding. After a minute, stringing occurred frequently and production was stopped immediately.

[0013]

Since the present invention is constructed as described above, the distance between the gate bush inner wall near the tip of the gate bush and the center of the gate bush is shortened, and the molten plastic and the gate bush are reduced. As the contact area with the inner surface increases, the cooling effect becomes remarkably high, so that even if the molding cycle is accelerated, defects such as stringing do not occur and cutting is performed neatly. Therefore, it is possible to solve problems of quality complaints such as speeding up of a molding cycle, cost reduction due to no need for post-processing, and remaining gates or packing drop due to this.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a conventional gate bush.

FIG. 2 is a longitudinal sectional view of a lid in which stringing has occurred in a gate portion.

FIG. 3 is a side view of the gate bush of the present invention and a cross-sectional view near the gate.

FIG. 4 is a sectional view of the vicinity of the gate of the gate bush of the present invention, showing an example of the shape of a ridge 6;

FIG. 5 is a side view comparing the distance between the inner wall surface and the center of the gate bush of the present invention with a conventional product.

FIGS. 6A and 6B are a side view and a cross-sectional view when a groove 7 is machined in a brass bar for a mother die, which is the first step when the gate bush of the present invention is manufactured by electroforming.

FIG. 7 is a side view showing a cut portion in a step of forming a master mold for electroforming of a gate bush by machining according to the present invention.

[Explanation of symbols]

1 cylindrical metal 2 conical cavity 3 large circular hole 4 small circular hole 5 stringing 6 ridge 7 groove 8 matrix

Claims (1)

[Claims] 1. A gate bush which is a mold part for plastic injection molding and injection blow molding, wherein a plurality of ridges 6 are provided on an inner wall of the gate bush.