JPH0716981B2 - Injection mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of an injection molding die used for molding a molded body using a raw material containing a thermoplastic resin.

[Conventional technology]

Conventionally, as a magnet roll used as a magnetic brush forming means in an electrophotographic apparatus, a magnet having a magnetic pole formed on the outer surface of a ferrite magnet obtained by molding in a column shape has been generally used. The demand for plastic magnet rolls has increased due to demands for lighter weight and smaller size. This plastic magnet roll is a mixture (lubricant, dispersant or plasticizer) mainly composed of thermoplastic resin such as polyamide, polyethylene, ethylene / vinyl acetate / copolymer and magnetic powder such as hard ferrite powder and rare earth magnet powder. Injection molding method in which a compound formed into 3-5 mm square granules is supplied to a cylinder of an injection molding machine, heated and melted, and injected and filled into a molding die into which a shaft is inserted. The most common method is to manufacture (usually molded in a magnetic field for anisotropy). The injection molding die used for molding the above-mentioned plastic magnet roll has a structure as shown in FIGS. 3 and 4, for example. That is, in both figures, 1 is a sleeve, which is formed of a non-magnetic material such as stainless steel into a hollow cylindrical shape to form a molding cavity. Next, 2 is a magnetic pole member,
It is composed of a permanent magnet 21 having a rectangular cross section and a yoke 22 having a ladder cross section, and is arranged according to the magnetic pole specifications required for the magnet roll to be molded. Reference numeral 3 denotes a spacer, which is arranged in a gap formed between the sleeve 1 and the magnetic pole member 2 to form, for example, a mold having a circular cross section as a whole. 4 is a shaft.

[Problems to be solved by the invention]

As is clear from FIGS. 3 and 4, the injection molding die as described above is a combination type of the sleeve 1 and the four magnetic pole members 2, so that the distance between the two is 0.1 to 0.5 mm. There may be gaps. In the space formed by the sleeve 1 and the magnetic pole member 2, it is desirable that the spacer 3 is closely contacted with the sleeve 1 and the magnetic pole member 2 so as to be filled and arranged without forming a gap. As is clear from the figure, since it has an extremely complicated shape or contour, it is impossible to fill and dispose the spacers 3 without forming a gap, and the processing is extremely complicated. Therefore, due to the presence of the above-mentioned gap, not only the thermal conductivity is remarkably lowered, the molding cycle is lengthened and the efficiency is lowered, but also the sleeve 1 is deformed without being able to withstand the internal pressure at the time of injection molding and the defective rate. There is a problem such as increasing

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems existing in the prior art and to provide an injection molding die having no gap between members constituting the die.

[Means for solving problems]

In order to solve the above-mentioned problems, in the present invention, a hollow cylindrical cavity member forming the outer peripheral surface of a molded body and a plurality of gold members arranged outside the cavity member and holding the cavity member. In an injection-molding die that is combined with a die member, a hollow cylinder is provided that is inscribed in the outer end of the die member, and the space formed between the hollow cylinder, the cavity member, and the die member is low. The technical means of filling the spacer made of a melting point alloy in the molten state and the solidified filled state was adopted.

[Action]

With the above structure, the space formed by the hollow cylinder, the cavity member, and the mold member can be completely filled with the spacer, no matter how complicated the structure, and there can be no gap. Of.

〔Example〕

FIG. 1 is a cross-sectional view of an essential part showing an embodiment of the present invention, and the same parts are designated by the same reference numerals as those in FIGS. 3 and 4. In the figure, 3a is a spacer, which is made of a low melting point alloy such as Pb-Sn alloy or Bi-Pb-Sb alloy. That is, at a predetermined position around the sleeve 1 which is a hollow cylindrical cavity member forming the outer peripheral surface of the molded body,
After arranging a plurality of magnetic pole members 2 which are mold members, a hollow cylinder having a diameter corresponding to the circumscribed circle of the magnetic pole members 2 is arranged, and when the above alloy in a molten state is injected, solidified first
The spacer 3a shown in the figure can be formed, and the spacer 3a can fill the space formed by the sleeve 1, the magnetic pole member 2 and the hollow cylinder (not shown) without a gap.

As the low melting point alloy, in addition to the above alloys, binary, ternary or multi-component alloys of metals having a low melting point such as Sn, Bi, Pb, Cd and In can be used. Those having a eutectic or a composition close to eutectic exhibit particularly low melting points, and are therefore desirable. Since Bi or Sb expands contrary to a normal metal or alloy when it solidifies, the use of an alloy containing the above elements can further complete the filling of the space.

FIG. 2 is a cross-sectional view of the essential parts showing another embodiment of the present invention. The one shown in the same figure is a magnetic pole yoke 23 made of a magnetic material.
The magnetic pole member 2a is formed by the electromagnetic coil 24 and the electromagnetic coil 24, and the operation is the same as in the above embodiment.

In this embodiment, an example of an injection molding die for molding a magnet roll having an asymmetrical magnetic pole arrangement is shown, but it is naturally applicable to an injection molding die for a magnet roll having a symmetrical magnetic pole arrangement. . Further, it is needless to say that the present invention can be applied to a molding other than the magnet roll, and further to an injection molding die for molding a molding having a cross-sectional shape other than circular.

〔The invention's effect〕

The injection-molding die of the present invention has the following effects because of the structure and operation as described above.

(1) Since the members constituting the mold are in close contact with each other, the heat conduction becomes extremely good, and the time required for solidifying the molten raw material becomes short, so that the molding cycle can be shortened and the efficiency can be greatly improved.

(2) The strength of the mold can be remarkably improved by the close contact of the mold constituent members, defects due to deformation of the mold member can be eliminated, and the life of the mold can be increased.

(3) No matter how complicated the shape or contour of the space formed by the mold components can be easily and reliably filled with the spacer made of the low melting point alloy, the number of man-hours and time for manufacturing the mold Can be significantly reduced and shortened.

[Brief description of drawings]

FIGS. 1 and 2 are horizontal cross-sectional views of a main part showing an embodiment of the present invention, and FIGS. 3 and 4 are a horizontal cross-sectional view of a main part and a vertical cross-sectional view with parts omitted showing a conventional example, respectively. . 1: Sleeve, 2, 2a: Magnetic pole member, 3, 3a: Spacer.

Claims (3)

[Claims] 1. An injection molding comprising a combination of a hollow cylindrical cavity member forming an outer peripheral surface of a molded body and a plurality of mold members arranged outside the cavity member and holding the cavity member. In the molding die, a hollow cylinder that is inscribed in the outer end of the mold member is provided, and a spacer made of a low melting point alloy is melted in the space formed between the hollow cylinder, the cavity member and the mold member. An injection mold, which is filled in a filled and solidified state. 2. The injection molding according to claim 1, wherein the low melting point alloy is a binary, ternary or multi-component alloy of a metal having a low melting point such as Sn, Bi, Pb, Cd and In. Mold. 3. The low melting point alloy is a Pb-Sn alloy or Bi-Pb-
The mold for injection molding according to claim 1, which is a Sn alloy.