Rubber injection molding device and rubber product manufacturing method

1. A rubber injection molding device comprising:

a mold having a molding cavity therein;

an injecting machine including an injection cylinder having an injection chamber for storing a rubber therein, and an injection plunger for injecting the rubber from the injection chamber into the molding cavity by an advancement of the injection plunger;

a feed machine having a feed cylinder with a feed aperture formed at a tip end thereof and connected with the injection chamber through a feed duct, and being adapted to feed into the injection chamber, through the feed duct the rubber in a mixed state, and

a pushing assembly which has a piston that pushes into the injection chamber the rubber that remains within the feed duct after a feed operation of the rubber by the feed machine, and the piston directly closes a connecting aperture between the feed duct and the injection chamber at a forward travel limit of the piston.

2. A rubber injection molding device according to claim 1 , further comprising:

a reverse flow prevention member for retaining the rubber within the injection chamber and preventing a reverse flow of the rubber into the feed duct from the injection chamber, after the rubber within the feed duct has been pushed into the injection chamber.

3. A rubber injection molding device according to claim 1 , wherein the piston has essentially a same cross-sectional shape as the feed duct, where rubber within the feed duct is pushed into the injection chamber through the piston being moved forward along the feed duct by a driving device.

4. A rubber injection molding device according to claim 3 , wherein the piston is in a shape of a rod.

5. A rubber injection molding device according to claim 3 , wherein the feed duct is equipped in a form of a straight line, and a movement passage is formed in a form of a straight line along with the feed duct for permitting the piston to move forward within the feed duct or to draw backwards within the feed duct.

6. A rubber injection molding device according to claim 1 , further comprising a heating apparatus for heating provided at an outer peripheral portion of the feed duct so as to heat the rubber that is fed from the feed machine.

7. A rubber injection molding device comprising:

a mold having a molding cavity therein;

an injecting machine including an injection cylinder having an injection chamber for storing a rubber therein, and an injection plunger for injecting the rubber from the injection chamber into the molding cavity by an advancement of the injection plunger;

a feed machine having a feed cylinder with a feed aperture formed at a tip end thereof and connected with the injection chamber through a feed duct, and being adapted to feed into the injection chamber, through the feed duct the rubber in a mixed state; and

a pushing assembly which pushes into the injection chamber the rubber that remains within the feed duct after a feed operation of the rubber by the feed machine,

wherein the injection plunger that moves forwards and backwards according to charging of the rubber into the injection chamber by a feed of rubber from the feed machine comprises a detection device for detecting withdrawal to a set withdrawal limit and a control unit for stopping the feed of the rubber by the feed machine based on detection by the detection device, the set withdrawal limit being set so that an amount of rubber charged into the injection chamber added to an amount of remaining rubber pushed in from the feed duct will be a set amount for a single charge.

8. A rubber injection molding device according to claim 1 , wherein the injection chamber has a tapered shape at a tip end part extending to a tip end nozzle of the injection cylinder, and the injection plunger has, at a tip end thereof, a tapered shape that is a same shape as the tip end part of the injection chamber so that the tip end part of the injection plunger mates with the tip end part of the injection chamber to fill the tip end part of the injection chamber at a forward limit thereof.

9. A manufacturing method of a rubber product by using an injection molding device comprising a mold having a molding cavity therein; an injecting machine including an injection cylinder having an injection chamber for storing a rubber therein, and an injection plunger for injecting the rubber from the injection chamber into the molding cavity by an advancement of the injection plunger; a feed machine having a feed cylinder with a feed aperture formed at a tip end thereof and connected with the injection chamber through a feed duct, and being adapted to feed into the injection chamber, through the feed duct the rubber in a mixed state; and a pushing assembly which has a piston that pushes into the injection chamber the rubber that remains within the feed duct after a feed operation of the rubber by the feed machine, the method comprising the steps of:

pushing the rubber that remains within the feed duct, into the injection chamber by the piston of the pushing assembly, after a feed action of the rubber by the feed machine;

closing a connecting aperture between the feed duct and the injection chamber directly by the piston of the pushing assembly at a forward travel limit of the piston; and

injecting the rubber stored in the injection chamber into the molding cavity by a forward motion of the injection plunger so that the rubber is vulcanization molded within the molding cavity.

10. A manufacturing method of a rubber product according to claim 9 , wherein the rubber, when injected into the molding cavity, is heated to a temperature of not less than 85% of a vulcanization temperature of the rubber in the molding cavity.

11. A manufacturing method of a rubber product according to claim 9 , wherein the feed duct is heated by a temperature higher than a highest temperature of the rubber fed from the feed machine.