JPS6018528B2 - Vent device for vent type injection molding machine - Google Patents

Description

[Detailed description of the invention] The present invention relates to a pent device for a pent-type injection molding machine.

Usually, resin materials containing a large amount of moisture and volatile components such as monomers (hereinafter simply referred to as volatile components), such as polycarbonate,
Nylon, methacrylic resin, AS, . For ABS, cellulose resin, etc., drying and prevention of moisture absorption are performed as processing operations before molding. However, since this operation cannot be performed continuously on a large amount of material, a pent hole connected to a vacuum pump, etc. is installed in the heating cylinder to ensure that the material evaporates quickly and reliably during the process from material to molded product. Pent-type injection molding machines, which can remove parts, etc., have come into use. Here, the pent-type injection molding machine will be explained with reference to FIG.
It consists of a second stage 7 having a metering part 6, and the material supplied in a moist state from the supply part 2 of the first stage 4 is gradually sent forward (to the left in the figure) by the rotation of the screw 1. While being heated, it is compressed and heated to melt, and passes through the first metering section 3 to the pen section 5 of the second stage 7.

At this time, the pressure of the molten material compressed in the shallow part of the first metering part 3 suddenly decreases, the volume expands, and the volatile components contained in the material become foamed. It breaks the resin film surrounding the pent hole 8 and pops out into the pent hole 8, where it is sucked into a vacuum pump or the like (not shown).
The molten material from which volatile matters have been removed in this manner is sent to the second metering section 6 of the second stage 7, where it reaches a pressure that is balanced with a predetermined back pressure and is sent forward of the screw 1.
This process continues in this manner until the metering process is completed. The measured resin material is then pushed forward by the screw 1 at its retraction limit (moving to the left in the figure) and injected into a mold (not shown).

As mentioned above, the pent-type injection molding machine does not require operations such as preheating before molding, unlike conventional methods, and can reliably and continuously mold materials containing volatile components in a short time. However, there is a vent-up phenomenon and the material may get stuck in the vent hole, making it difficult to change the color or resin, and in addition, the material comes in contact with air through the vent hole. Vent-up has the disadvantage that it may be oxidized depending on the material.When removing volatile matter etc. from the pent hole 3, the volatile matter etc. are removed from the pent hole 3.
Pent-up is a phenomenon that occurs at any time, such as during metering plasticization, after metering is completed, or when machine operation is temporarily stopped.As a result, the pent hole is blocked and the venting effect is eliminated. Not only that, some of the material is likely to be sucked into the vacuum pump, which may cause the pump to malfunction. As a result of various tests, the inventor found that for pent-up during metered plasticization, the pressure in the pent port section is reduced to 30 to 75 mHg, and at the same time as the screw rotation is stopped, the inside of the vent port is brought to atmospheric pressure, as shown in the experimental example shown below. It was confirmed that pent-up does not occur when using open vents, continuous vacuum degassing, or reduced pressure below 2% Hg. Experimental example Material: PMMA (Delbet 8 sails) (no pre-drying) Screw rotation speed: 18. p. m Back pressure: 1 to 5k9/Water using machine: IS9 Ship V (manufactured by Toshiba Machinery) In the result diagram, zones 1 to 3 are three temperature control regions divided in order from the hopper side to the tip of the barrel.

This means that while the screw is rotating, the material resin inside the screw flight tends to foam, and gases such as volatile matter generated within the material resin break the coating of the material resin and fly out from the resin surface. As a result of the negative pressure inside, the pressure is reduced to the inside of the material resin, but if the inside of the pent port is returned to atmospheric pressure at the same time as the screw rotation stops, the surface of the resin facing the pent hole changes from an expanded state to a contracted state. It is thought that this condition will continue even after the machine is stopped and pent-up will not occur.

In addition, vent-up is likely to occur when the machine is stopped, especially when restarted after stopping molding. This is because the volatile matter and other gases generated by the material resin that has been heated and stagnated inside the cylinder gradually enter the pent hole. As a result, it is pushed up to

Therefore, the inventor used a vacuum pump to reduce the pressure inside the pent port to 30 to 7 Hg during plasticization, and when stopping the machine halfway or restarting the stopped machine, the vent hole should be closed. If you close it with a stopper and prevent pent-up, you can deal with pent-up both while the screw is rotating and under other circumstances. Problems with color changes, resin changes, and prevention of material oxidation can be prevented by supplying the stopper. We have found a solution to this problem by applying an active gas through the air vents, and have arrived at the present invention.

The present invention eliminates the drawbacks mentioned above, namely, pent-up, which can occur at any time during heating of the heating cylinder, including when the screw is rotating, and also makes it easy to change colors and resins, and prevents oxidation of the material. An object of the present invention is to provide a pent device for a pent-type injection molding machine.

Next, one embodiment of the present invention will be described with reference to FIGS. 2 and 3. Reference numeral 11 represents a heating cylinder, and 12 represents a screw.

Reference numeral 13 denotes a pent hole, which opens into a pent chamber 14 which is airtightly surrounded by the pent hole 13.

At the upper part of the pent chamber 14, there is a cypress 19 connected to a piston 18 which is slidably moved back and forth in an air cylinder 17 by air pressure applied from an air source 15 through an air valve 16.
The pent hole 13 is opened when the screw 12 rotates during metering plasticization, and when the screw 12 stops rotating, the pent hole 13 is closed as shown in FIG. 3 to prevent foaming and swelling of the material resin. ing.

The pent chamber 14 is provided with an exhaust port 21 that communicates with a vacuum pump 201 for reducing the pressure inside the pent chamber 14.
The plug 19 is made of a soft and resistant material such as copper, conical metal, or aluminum, and the gap with the vent hole 13 is 0.0.
It is set to about 5 to 0.1 so that volatile components can escape from inside the cylinder 11, but resin cannot pass through.

Further, as shown in FIG. 4, if an air supply port is provided in the plug 22 and the piston 23 by a through hole 24, and an inert gas such as N2 gas is applied from the gas source 25 into the cylinder 11 and into the pent chamber 14. The pressure of the inert gas not only prevents pent-up but also prevents oxidation of the resin material, such as nylon.

26 is a switching air valve, and 27 is a filter.

With the structure and operation effects as explained above, the drawbacks listed at the beginning have been removed, and it is not only possible to prevent venting, but also to change colors,
The problems of resin replacement and material oxidation prevention were also resolved.

[Brief Description of the Drawings] Fig. 1 is an explanatory diagram of a pent injection molding machine. FIG. 2 is a diagram showing one embodiment according to the present invention. Figure 3 is the second
An explanatory diagram showing one state in the figure. FIG. 4 is a diagram showing another embodiment according to the present invention. 13... Pent hole, 14... Pent chamber, 16, 24... Air valve, 19, 22
・・・・・・Bung, 21... ．． ．． exhaust port. Power’ Figure Male Figure Game 3 Kaede O〆Gen

Claims (1)

[Claims] 1. A vent chamber of a vent type injection molding machine, in which a vent hole provided in a heating cylinder has an open vent chamber, can be depressurized by a vacuum pump, etc., is moved forward and backward by an air cylinder while maintaining a small gap from the vent hole. A plug is provided that controls the opening and closing of the vent hole and has an air supply port for acting inert gas on the resin inside the cylinder and inside the vent chamber, and while the screw is rotating, the vent hole is opened and the vent port section is closed. A vent device for a vent type injection molding machine, characterized in that the pressure is reduced to 30 to 75 cmHg and the vent hole is closed during injection operation, color change, and resin change while the screw rotation is stopped.