JPS6247702B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the manufacturing method of plastic pipe fittings.

Manufacturing methods for plastic pipe fittings with sockets equipped with grooves for attaching rubber rings include injection molding,
There is also a secondary processing method (a method in which the end of the plastic tube is press-fitted into the socket molding mold).In either method, when the core mold escapes, the core is removed from the undercut of the socket. Forcibly pull out the mold,
The present inventors have already proposed a so-called forced removal method.

1A to 1D show forced punching in the case of injection molding.

In FIG. 1A, 1' is an outer mold, which is divided into a high-temperature member 11' and a low-temperature member 12' at a position corresponding to a rubber ring mounting groove. 2'
is a core mold, which is divided into a high-temperature member 21' and a low-temperature member 22' at a position corresponding to a groove for attaching a rubber ring. Therefore, in the injection molded plastic joint P′, there is a groove for attaching the rubber ring.
A′ and its vicinity are the high-temperature member 1 of the outer mold 1′.
1' and the high-temperature member 21' of the core mold 2', it is in an appropriately thermally softened state with elasticity.

After injection molding, as shown in FIG. 1B, both members 11' and 12' of the outer mold are demolded, and then, as shown in FIG. 1C, the high temperature member 2 of the core mold 2' is removed.
1' is moved out. In this case, since the rubber ring mounting groove A' and its vicinity are in an elastic state as described above, the high-temperature member 2 of the core mold 2'
1', it elastically returns to its original shape.

After the high-temperature member 21' of the core mold 2' is removed, the entire core mold 2' is removed, as shown in FIG. 1D.

In the initial stage of forced punching in the case of injection molding, the high-temperature member 21' of the core mold 2' is replaced with the low-temperature member 21'.
must be moved independently with respect to 2′,
In addition to different temperature controls for the high-temperature member 21' and the low-temperature member 22', there is a two-step process in which a time difference must be provided for the escape movement of the high-temperature member 21' of the core mold 2' and the entire core mold 2'. Since an evacuation operation is required, it is inevitable that the structure of the core mold 2' and the evacuation operation become complicated.

FIGS. 2A to 2D show forced punching in the case of secondary processing.

In FIG. 2A, 1'' is an outer mold, which is divided into a high-temperature member 11'' and a low-temperature member 12''.
2'' is a core mold, which is composed of a high temperature zone 21'' and a low temperature zone 22''.P'' is a plastic tube whose heating end is connected to the outer mold 1'' and the core mold 2. '' and is molded into the socket. In this case, the groove part A′ for attaching the rubber ring is
The high-temperature member 11'' of the outer mold 1'' and the high-temperature zone 21'' of the core mold 2'' are placed in a moderate thermally softened state with elasticity.

After socket molding, as shown in FIG. 2B, the high temperature member 11'' of the outer mold is moved out and the core mold 2'' is moved out. In this case, since the rubber ring mounting groove A' and its vicinity are in an elastic state as described above, despite the forcible removal of the core mold 2'', as shown in FIG. Restores to the original shape immediately after next processing.

In Fig. 2C, the socket tip B' is the core mold 2''
In this case, the diameter of the socket tip B' is larger than the diameter R' of the original pipe P'', and tensile hoop stress remains at the socket tip B'. Therefore, the socket tip B' comes into contact with the low temperature zone 22'' of the core mold 2'' with sufficient surface pressure, and the rubber ring mounting groove A' and its vicinity can be efficiently cooled.

After cooling the tip of the socket, as shown in Figure 2D,
The tip of the socket is shaped using the auxiliary mold 3''.

In the case of forced punching in the case of the above-mentioned secondary processing, the core mold 2'' has a high temperature zone 21'' and a low temperature zone 22''.
The high-temperature member 2 may be
Since there is no need to separate the core mold into the low-temperature member 22' and the low-temperature member 22', and there is no need to separate these separate members at different times, it is possible to simplify the structure and operation of the core mold, which is advantageous.

Therefore, it would be advantageous if the forced punching shown in FIGS. 2A to 2D could be applied to injection molding.

However, when injection molding is assumed to correspond to the secondary processing of the socket shown in Figure 1A, tensile hoop stress remains in the secondary processing socket due to its forced diameter expansion. However, there is a physical difference in that there is no residual stress in the socket of injection molding. In the case of secondary processing, at the stage immediately after forced punching shown in Fig. 2C, due to the residual tensile hoop stress, the socket tip B'
contact with the low temperature zone 22'' with sufficient surface pressure,
In the case of injection molding, there is no residual tensile hoop stress and therefore there can be no surface pressure between the socket tip and the cold zone of the core mold, rather the The elastic recovery of the diameter expansion is incomplete because the elasticity is not perfect, and there is a concern that a gap may occur between the tip of the socket and the low temperature zone of the core mold, even if it is minute.

Therefore, even if the forced punching in the secondary processing shown in FIGS. 2A to 2D is simply applied to injection molding, the inside of the socket tip B' at the stage shown in FIG. It is difficult to achieve satisfactory cooling by the child mold low temperature zone 22'', and it is not industrially viable.

The plastic pipe joint according to the present invention is a plastic pipe joint having a socket with a groove for installing a rubber ring. The mold for injection molding the pipe fitting is placed in both the core mold and the outer mold, with the molding side of the tip of the socket in the high temperature zone and the rest of the mold, with the position corresponding to the groove for installing the rubber ring as the border. Both sides are kept in the low temperature zone, and after the plastic injection, the outer mold is demolded, and then
In the method of ejecting and moving the core mold, the inner diameter of the front part of the socket between the groove for rubber ring installation and the tip of the socket is the same as the inner diameter of the front part of the socket between the groove for rubber ring installation and the back end of the socket. The mold is constructed so that the inner diameter is smaller than the inner diameter of the rear part of the socket, and the high-temperature zone of the outer mold is composed of a heating mold piece, and the low-temperature zone is composed of a low-temperature mold piece. When the mold is moved to escape, the front part of the socket is forcibly expanded in the low temperature zone of the core mold part which is the molding part at the rear of the socket, and the core mold is moved to escape. The heated mold piece of the mold is cooled to a predetermined temperature after the demolding, and this mold piece is used to shape the front part of the socket together with the rubber ring mounting groove immediately after the core mold is moved out. This method is characterized by

In the present invention, the temperature of the high temperature part of the mold is such that the plastic can be maintained in an elastic region immediately after injection, and in the case of vinyl chloride, it is 80 to 100°C. On the other hand, the temperature of the low-temperature part of the mold is such that the plastic immediately after injection can be cooled and solidified to a hardness that allows it to be removed from the mold, and is usually 40 to 60°C.

The present invention will be explained below with reference to the drawings.

FIG. 3 shows a mold apparatus used in the present invention.

In FIG. 3, P is a vinyl chloride pipe joint manufactured according to the present invention, which has a socket equipped with a groove A for attaching a rubber ring, and has a gap between the tip of the socket and the groove for attaching the rubber ring. The inner diameter of the front part B of the socket is smaller than the inner diameter _R2 of the rear part C of the socket between the back end of the socket and the rubber ring mounting groove. Further, the inner diameter R ₃ of the rear end portion D of the socket is approximately equal to the inner diameter R ₁ of the front portion B of the socket.

Reference numeral 1 designates an outer mold, which is divided into a heating mold piece 11 on the molding side of the tip of the socket and a low-temperature mold piece 12 on the molding side of the remaining part, with the rubber ring mounting groove of the socket as a border. The mold piece 12 is divided into upper and lower parts 121 and 122
has been done. The heating mold piece 11 has a built-in heater,
Heating temperature is 80-100°C. The temperature of the low temperature mold piece 12 is 40 to 60°C. 13 is a cylinder for moving the heating mold piece 11. 14 is an injection runner provided on the upper mold 121 of the low-temperature mold piece 12. 15 is a pin attached to the low temperature mold piece 12, and the heating mold piece 11 is locked to this pin.

Reference numeral 2 denotes a core mold, which is divided into a high temperature zone 21 on the molding side of the tip of the socket and a low temperature zone 22 on the side of molding the remaining portion, with the position of the groove for installing the rubber ring in the socket as a boundary. The high temperature zone 21 has a built-in heater, and its heating temperature is 80 to 100°C. The temperature of the low temperature zone 22 is 40 to 60°C. 23 is a hydraulic cylinder for moving the core mold 2.

To produce plastic pipe fittings according to the invention, plastic is injection molded at a temperature of about 180°C. In this molded body P, the groove A for attaching the rubber ring of the socket and the front part B of the socket are approximately 80 to 100 degrees thick due to the heating mold piece 11 of the outer mold 1 and the high temperature zone 21 of the core mold 2. ℃ and has considerable elasticity.

After injection molding, as shown in FIG. 4A, the cold mold piece 12 of the outer mold is demolded, and then the heated mold piece 11 of the outer mold is moved out by operating the hydraulic cylinder 13. At the same time, the power supply to the heater of the heating mold piece 11 is cut off, and this mold piece 11 is cooled.

After the mold pieces have been moved to escape, the core mold 2 is moved to escape by operating the hydraulic cylinder 23, as shown in FIG. 4B. Due to this evacuation movement of the core mold 2, the core mold 2 goes through a stage of forced removal from the elastic rubber ring mounting groove A as shown in FIG. 4B, and then as shown in FIG. 4C. , low temperature zone 2
2 and the front part B of the socket, it escapes from the joint molded body P.

In the state shown in FIG. 4B above, the diameter of the socket front part B is expanded, and in this case, since the socket front part B is not perfectly elastic, it undergoes some degree of permanent deformation, but in the state shown in FIG. 4C, , since the outer diameter R ₂ of the low temperature zone 22 of the core mold 2 is larger than the original inner diameter of the socket front part B (R ₁ in FIG. 3), the socket front part B is forcibly closed. While in the expanded state, the low temperature zone 22 of the core mold 2 moves within the front part B of the socket.

Therefore, sufficient surface pressure is generated between the socket front part B and the low temperature zone 22 of the core mold 2, and the core mold 2 moves while maintaining a strong close contact between them. During this movement of the core mold 2, the socket front part B and the adjacent rubber ring mounting groove A can be efficiently cooled.

When the escape movement of the core mold progresses and the back end of the core mold reaches the front part of the socket, the core mold 2 is stopped as shown in FIG. 4D, and the mold of the outer mold is removed. The piece 11 is moved back by operating the hydraulic cylinder 13, and the front part B of the socket and the groove A for attaching the rubber ring are shaped. In this case, the outer diameter of the inner end 20 of the core mold 2
R ₃ and the inner diameter of the front part B of the socket are approximately equal, the temperature of this rear end part 20 is 40 to 60°C, and the mold piece 11 is also sufficiently cooled by cutting off the power to the heater as described above. Therefore, the above-mentioned shaping can be performed well.

In the present invention, as described above, while the low temperature zone 22 of the core mold passes through the small diameter part B of the socket tip in an expanded state, heat is removed from the inner surface of the small diameter part B, and the socket tip The part (the part consisting of A and B) is being cooled. In this case, it is advantageous to improve the cooling effect by slowing down the withdrawal speed of the core mold, but
It is necessary to set the speed to 2 cm/sec or more as this will reduce the working speed, and therefore, it is necessary to increase the heat removal efficiency on the inner surface of the small diameter part under such high-speed drawing of the core mold. It is.

Factors that contribute to this improvement in heat removal efficiency are the close contact between the low-temperature zone of the core mold and the inner surface of the small-diameter portion when the two pass through the inner surface of the small-diameter portion, and the length L of the inner surface of the small-diameter portion.

To ensure close contact, the inner diameter _R1 of the small diameter portion at the tip of the socket is made smaller than the outer diameter _R2 of the low temperature zone of the core mold, and _R1 / _R2 is usually 0.85 to 0.95. . When the low-temperature zone of the core mold passes through the small diameter part B, the small diameter part B shows plastic elongation in the circumferential direction, although it is slight, and at 0.95 or more, the above-mentioned close state under sufficient contact pressure On the other hand, it becomes difficult to secure
If it is less than 0.85, the thinning of the small diameter part B and the elongation in the longitudinal direction become noticeable, making it difficult to shape the socket tip part 3 after drawing out the core mold, and as shown in FIG. 4C, Frictional force F acting on the inner surface of the small diameter part B
becomes large, and the bending moment M acting on the rubber ring mounting groove during the core mold withdrawal becomes large.
The deformation of the rubber ring mounting groove becomes noticeable, and it becomes difficult to restore the rubber ring mounting groove to its normal shape even with the above-mentioned shaping.

In the present invention, while the core mold is being pulled out, the rubber ring mounting groove of the socket is cooled as the heat is removed from the inner surface of the small tip diameter portion B, and the amount of heat absorbed by the inner surface of the small diameter portion B is large. Therefore, the longer the length L of the inner surface of the small diameter opening B, the more effectively the rubber ring mounting groove can be cooled. It is desirable that the ratio L/L' be 0.5 or more; if it is less than 0.5, it will be difficult to sufficiently cool the rubber ring mounting groove. On the other hand, if the inner length L of the small diameter opening is too long, when the low temperature zone of the core mold passes through the small diameter opening, frictional force will be applied to the inner surface of the small diameter opening, as in the case described above. As F increases, the bending moment M acting on the rubber ring mounting groove due to this frictional force increases, and the deformation of the rubber ring mounting groove becomes significant.
It is desirable that L' be 0.8 or less.

As mentioned above, according to the injection molding manufacturing method of the plastic joint according to the present invention, when the core mold is moved out, the front part of the socket is placed in the low temperature zone of the core mold with sufficient surface pressure. The front part of the socket and the groove for attaching the rubber ring adjacent thereto can be efficiently cooled during the escape movement of the core mold. Thus, the core mold can be escaped at once, and the structure of the core mold and the evacuation operation can be simplified compared to the two-stage evacuation of the core mold in the case of injection molding described above.

Furthermore, since the front part of the socket and the groove for installing the rubber ring can be shaped by returning the mold piece for molding the front end of the socket in the outer mold, there is no need for a separate mold for shaping. From this point of view, the structure and operation of the entire mold can be simplified.

[Brief explanation of the drawing]

Figure 1A, Figure 1B, Figure 1C, and Figure 1D
2 is an explanatory diagram showing conventional forced punching when plastic pipe fittings are injection molded, and Fig. 2A, Fig. 2B, Fig. 2C, and Fig. 2D are explanatory diagrams showing plastic pipe fittings made by secondary processing. FIG. 3 is an explanatory diagram showing the conventional forced punching in the case of molding, FIG. 3 is an explanatory diagram showing the mold device used in the present invention, FIG. 4A, FIG. 4B, FIG. FIG. 3 is an explanatory diagram showing a method of manufacturing a plastic pipe joint according to the present invention. In the figure, P is a plastic pipe joint, A is a groove for installing a rubber ring, B is a front part of the socket, C is a rear part of a socket, 1 is an outer mold, 11 is a heating mold piece of the outer mold, 12 2 is the low temperature mold piece of the outer mold, 2 is the core mold,
21 is a high temperature zone of the core mold, and 22 is a low temperature zone of the core mold.

Claims (1)

[Claims] 1. A mold for injection molding a plastic pipe joint having a socket with a groove for installing a rubber ring, both the core mold and the outer mold, are placed at the position corresponding to the groove for installing the rubber ring. The molding side of the tip of the socket is kept in a high temperature zone, and the remaining side is kept in a low temperature zone. After injection of plastic, the outer mold is demolded, and then the core mold is removed and moved. The inner diameter of the front part of the socket between the rubber ring mounting groove and the socket tip is made smaller than the inner diameter of the rear part of the socket between the rubber ring mounting groove and the back end of the socket. The high temperature zone of the outer mold is formed by a heating mold piece, and the low temperature zone is formed by a low temperature mold piece, and when the core mold moves out, the rear part of the socket In the low temperature zone of the core mold part, which is the molding part, the front part of the socket is forcibly expanded and the core mold is moved to escape,
The heated mold piece of the outer mold is cooled to a predetermined temperature after the demolding, and the front part of the socket is shaped with the rubber ring mounting groove immediately after the core mold is moved out. A method of manufacturing a plastic pipe joint, characterized in that: