Vacuum extract anti-backflow device for screw extruder

The utility model discloses a vacuum extract anti-backflow device for a screw extruder. The vacuum extract anti-backflow device comprises a screw barrel and a vacuum chamber, wherein the vacuum chamber is located above the screw barrel, wherein an air inlet which is communicated with the vacuum chamber is formed in the screw barrel; an extraction opening which is communicated with a vacuum pipe of a vacuum pump is formed in the bottom of the side wall of the vacuum chamber; a boss is fixedly arranged at the bottom of the vacuum chamber and on the periphery of the air inlet; a distance is formed between the side part of the boss and the side wall of the vacuum chamber; a through hole which is in the same center line together with the air inlet is formed in the boss; and the aperture of the through hole is more than or equal to that of the air inlet. The boss disclosed by the utility model is capable of preventing gas and small molecular weight impurities, which flow down along the side wall of the vacuum chamber, from flowing back to the screw barrel, so that the quality of a plastic product is ensured; and the vacuum extract anti-backflow device has the characteristics of being simple in structure and convenient to use, and is suitable for various screw extruders.