JPS6157163B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mold for molding thermosetting materials such as rubber or synthetic resin, particularly rubber.

Conventionally, for example, in transfer molding of rubber, a split mold is usually used, but the material rubber often wraps around the split surface, and it is inevitable that so-called burrs will adhere to the molded product. Ta. In particular, when molding thermosetting materials such as rubber, the low-temperature plastic material is press-fitted into the cavity and then the mold is heated to harden and mold. I don't like that the material protrudes into the slight gap in the cracked surface.
For this reason, attempts have been made to prevent the occurrence of burrs as much as possible by increasing the surface precision of the joint surfaces of the molds or by increasing the clamping pressure during molding. However, even if surface precision or mold clamping pressure was to be increased, there were technical, equipment, and economic difficulties, such as the upper limits of metal processing and the need for unnecessarily large equipment. .

This invention was developed in view of the above-mentioned points, and aims to provide a molding die that can prevent the occurrence of burrs by making some improvements to the die. . Therefore, according to the present invention, not only can the work of deburring the molded product be omitted at once, but also the work of removing the burr remaining in the mold, which was conventionally performed for each molding, is no longer necessary, and the molding cycle can be shortened. It is possible to increase this significantly.

That is, in this invention, one or both of the upper mold and the lower mold constituting the cavity is made relatively thin, and the outer surface of the thin mold has a convex portion smaller than the cavity surface. By interposing the fulcrum, the fulcrum of the pressure applied to the outer surface of the mold and the fulcrum of the mold joint surface during mold clamping are made different, so that the cut-off portion of the mold joint surface is tightly and tightly attached. This is what I did. Embodiments of the present invention will be described below with reference to FIGS. 1 to 6 of the accompanying drawings.

FIG. 1 is an exploded sectional view of a transfer molding apparatus showing an embodiment of the present invention, in which 10 is a lower mold;
11 is an upper mold, 20 is a pot mold, and 25 is a plunger to be fitted into the pot 21 of the pot mold 20. The lower mold 10 has a molding cavity 12,
12 are provided as appropriate. The upper mold 11 is a relatively thin mold, and the cavity 1 of the lower mold 10 is
Gate holes 13, 13 are provided at positions corresponding to holes 2, 12, and the outer surface side 1 of the upper mold 11 is
A convex portion 15 smaller than the cavity surface is protruded around the opening of the gate hole 13 of 1a (that is, the side other than the cavity 12 side). In other words, the convex portion 15 is formed slightly inward from the cut-off portion 14 formed by the lower mold 10, upper mold 10, and upper mold 11 that partition the cavity surface, when viewed from the main material input direction. It will be done. The thickness of this convex portion 15 is approximately 0.05 mm in the embodiment.
FIG. 2 is an enlarged sectional view of the main parts of the molding die shown in FIG. 1 when the mold is clamped. Since the structure is smaller than the upper mold 1,
A shift in the fulcrum (i.e., the point of force) occurs between the fulcrums A, A of the pressure applied to the outer surface 11a of the mold and the fulcrums B, B of the mold joint surface, which is the cavity surface side, as shown by the chain line in the figure. Then, the upper mold 11 is bent slightly inward of the cavity 12, and the supporting points B and B of the mold joint surfaces, that is, the cut-out portion 14, are tightly and closely attached, and the cavity 12 is sealed.
FIG. 2a is an explanatory diagram showing the difference in the above-mentioned fulcrums. Therefore, even when the material in the pot 21 is press-fitted into the cavity 12 through the sprue 22 of the pot mold 20 and the gate 13 of the upper mold 11 and is pressurized, the material flows from the cut-off portion 14 onto the joint surface of the mold. This prevents burrs from flowing out and prevents the formation of burrs.

As mentioned above, the thickness (height) of the convex portion 15 formed on the upper mold 11 is preferably about 0.05 mm; making it too large increases the amount of deformation of the mold, resulting in damage to the cavity and There is a risk of deforming the molded product. In addition, in the embodiment, the upper mold 11 provided with the convex portion 15 needs to be slightly warped by the mold clamping pressure as described above, so it is constructed relatively thinly, but it should be made extremely thin as described above. Since this will cause permanent deformation of the mold, it is natural to design the thickness so that the above-mentioned bending deformation is within the elastic limit. Therefore, the thickness of this mold depends on the size of the molded product and mold clamping pressure, etc., but to give an example, when molding a small molded product with a thickness of about 10 mm, the thinner mold The wall thickness of the upper mold 11 (in the embodiment shown in FIG. 1) is about 5 to 15 mm.

As mentioned above, in the mold according to the present invention, the cavity is sealed and the gap for material to flow out to the joint surface of the mold is almost closed, but the material is forced out by press-fitting. Since the molecular size and viscosity of air are negligibly small compared to plastic materials, air can freely flow out even when the mold is sealed.
If necessary, a necessary number of scribed grooves of about 1/1000 to 2 mm may be provided on the joint surface of the mold surrounding the cavity and communicated with the cavity to serve as air outflow grooves. If the gap is of this size, there is almost no possibility that a material such as rubber will be press-fitted into the groove.

FIG. 3 is an exploded sectional view of the transfer molding apparatus similar to FIG. 1, and in this embodiment, the above-mentioned convex portion 15 is provided on the lower surface of the pot mold 20 above the upper mold 11. Incidentally, instead of the pot mold 20, a pressing plate 26 provided with a convex portion 15 may be used to inject the material into the cavity 12, and then the press plate 27 may be used to clamp the mold. In this case, the pot mold 20 and the plunger 25 are removed to the side and placed on standby. In the above embodiment, the convex portion 1 formed on the pot mold 20 or the presser plate 26
5 is formed smaller than the cavity surface, and the upper mold 11 is thin, as shown in FIG.
This embodiment is completely similar to the embodiments of FIGS. 1 and 2.

FIG. 5 is a sectional view of a main part of a mold showing another embodiment, for example, when molding an annular object such as a tire. In this embodiment, the convex portion 15 is formed into a substantially annular shape so as to correspond to the molded cavity 12. One or an appropriate number of material injection gates 13 are provided.

FIG. 6 shows a sectional view of an embodiment in which a middle mold 16 is provided, and in this case, both the upper mold 11 and the lower mold 10 are provided with convex portions 15, 15.

As described above, in the present invention, one or both of the upper mold 11 and the lower mold 10 of the split mold is made relatively thin, and the outer surface of the thin mold is lower than the cavity surface. It is sufficient if a small convex portion is also provided. In the above-described embodiments, the convex portion is formed integrally with the upper mold or the lower mold itself or with the mold, plate, etc. that comes into contact with the outer surface of these, but there are some considerations in the design of the mold, economic efficiency, etc. In consideration, a thin plate having a predetermined shape may be inserted into a predetermined position to form a convex portion.

Further, in the above embodiments, transfer molding was mainly described, but it goes without saying that the present invention can also be used in injection molding.

As described above, in this invention, by bending a part of the mold constituting the cavity very slightly, the cut-out portions on the joint surfaces of the mold are brought into tight contact and the cavity is sealed. Therefore, even when molding a thermosetting material such as rubber, the material does not flow out onto the joint surface of the mold, and the generation of burrs is prevented. Therefore, not only can the deburring work of the molded product after molding be omitted at once, but also a beautiful finish of the molded product can be expected. Furthermore, this invention eliminates the need to remove burrs remaining in the mold, which was conventionally done after each molding, and enables continuous molding, greatly improving the molding cycle. It offers many advantages in terms of gender, etc.

[Brief explanation of the drawing]

Fig. 1 is an exploded cross-sectional view of a transfer molding apparatus showing an embodiment of the present invention, Fig. 2 is an enlarged cross-sectional view of the main parts during mold clamping, and Fig. 2a is an explanatory diagram showing the difference in the supporting points. , FIG. 3 is an exploded cross-sectional view of a transfer molding apparatus showing another embodiment, FIG. 4 is a cross-sectional view of the main parts of the same when the mold is clamped, and FIG. 5 shows an embodiment having an annular cavity. FIG. 6 is a cross-sectional view of the main part of the mold, showing an embodiment in which the mold has a medium mold. 10...Lower mold, 11...Upper mold, 12...Cavity, 14...Cutting part, 15...Convex part, 16
... Medium size, 20 ... Pot type, 25 ... Plunger, 26 ... Holder plate, A ... Support point for pressure applied to the outside surface of the mold, B ... Support point for pressure applied to the mold joint surface.

Claims (1)

[Claims] 1. In a mold divided into two or more parts, either one or both of the upper mold and the lower mold is made relatively thin, and a convex portion smaller than the cavity surface is interposed on the outer surface of the thin mold. By making the fulcrums A, A of the pressure applied to the outer surface of the mold different from the fulcrums B, B of the mold joint surface during mold clamping, the cut-off portions of the mold joint surface are tightly and tightly attached. A molding die that does not produce burrs.