(1) Fully grill the screws and nuts with a gas welding flame.
(2) Then apply oil or sewing machine oil to the red-hot screw.
(3) The screw is heated and expanded, and the rust between the screw and the nut is squeezed to increase the gap. After the oil drops, the screw shrinks rapidly and cools, and the gap between the screw and the nut is further increased. After the oil flows in, the screw can be unscrewed. Note that this method should be used with caution for screws with plastic parts nearby, and the screws that have been burned should not be reused.