Negative pressure device for removing gas of metal mold gravity casting water jacket sand core

The invention discloses a negative pressure device for removing gas of a metal mold gravity casting water jacket sand core. The negative pressure device comprises a vacuumizer, a combined gas collecting box, a water jacket core, a pouring mold bottom mold and a bottom frame core. The lower part of the bottom frame core is connected with a bottom die exhaust pipeline of a pouring die; a top groove is connected with a water jacket core claw; the lower portion of the combined gas collecting box is connected with the vacuumizer through a pipeline, the upper portion of the combined gas collecting box is connected with a pouring mold bottom mold exhaust pipeline, and pouring waste gas directionally moves into the combined gas collecting box under the action of the vacuumizer. The bottom frame core is designed between the water jacket core and the negative pressure pipeline, the contact area between a negative pressure system and the water jacket core is increased, a part of pouring waste gas can be stored in the bo