The invention provides an automatic reducing device of a seam welder, relating to a reducing mechanism of a
cement tube reinforcement cage
welding device, which can adapt a continuous vertical rib
feeding mode. The automatic reducing device comprises a reducing cylinder and a reducing cylinder control mechanism, wherein the reducing cylinder is arranged on a main disk and used for driving a
welding head to move radically, and the reducing cylinder control mechanism is arranged on a tie bar trolley and used for controlling the reducing cylinder to move axially. The main disk is provided with a central hole; the reducing cylinder comprises a reducing screw rod, a rear disk, a front disk, a chain 1, a
steering wheel group 1, a chain 2, a
steering wheel group 2 and a connection link. The reducing cylinder control mechanism comprises a reducing
control rod the cross section of which is a hexagon, a
clutch and a driving mechanism; the driving mechanism is fixedly connected to the trolley; and the reducing
control rod is connected with the driving mechanism through the
clutch. After the reducing
control rod of the invention is meshed with the reducing screw rod,, the reducing control rod can drive the reducing screw rod to rotate when rotating; the rotation of the reducing screw rod drives the front disk and the rear disk to move axially; and the axial movement of the front disk and the rear disk can drive the
welding head to move radically via the chain 1 and the chain 2, thereby realizing reducing.