The big cap made by extrusion mould is generally caused by uneven die surface resulting in unclean shear, and aluminum gradually adheres to the outside. The following are several reasons for extrusion mould that may lead to extrusion big cap:
1. The end face of the extrusion die is uneven or has a defect so that the locking surface has a gap, and the aluminum flows. Mold defects to timely repair welding, die surface must be milling flat.
2. The outer circle of the feeding cavity is too large (the mold distance is too short), the locking area of the mold barrel is small ------ the outer circle of the feeding cavity and the wall distance of the cylinder are normally left unilateral 10mm limit is not less than 5mm, the extrusion ratio of the mold is too high, do not simply use the method of expanding the shunt cavity to relieve pressure. With such extrusion mold production, the top, bottom, left and right center must be aligned to prevent mold distance deviation.
3, the extrusion die has no water milling mouth, the die closed surface is too large, the compression value per unit area is small - less than the outlet pressure, the die surface run aluminum stick aluminum after shearing is not clean, resulting in uneven die surface. This big hat is difficult to clean. Note that the cylinder surface should be properly oiled and no longer stick to aluminum. The aluminum on the die surface can be cut off repeatedly. The indentation of the cylinder on the die surface can be oiled so that the aluminum on the die surface can not stick to the mold and be cut off. Even if there is occasionally a small flying edge, success.
4. If the nozzle size of the extrusion die is smaller than the size of the cylinder working face, the closed area of the cylinder die is small and the cylinder working face is vulnerable. Pay attention to the diameter of the nozzle of the mold and the diameter of the working face of the large barrel when the small machine mold is refitted to the large machine.
5. The thickness of the extrusion mould is not enough, and the pressure of the extrusion cylinder is on the mould sleeve. The thickness of the mould and mould sleeve should conform to the principle of the first 3 and the last 1, that is, the guide surface of the mould should protrude the mould sleeve 1mm. ------ the mold sleeve is never directly affected by extrusion pressure, otherwise, the mold sleeve is vulnerable to deformation.
6. The gap between the mold sleeve and the mold is too large, and the aluminum sticking in the gap leads to the uneven shear surface. This situation is commonly seen in small machine modification over the mold.
7. The extrusion ratio is too high, the export resistance is greater than the extrusion pressure, the locking surface is uneven, and aluminum flows out from the locking surface. Most of this situation will occur stuffy car phenomenon, can appropriately improve the temperature of the rod and mold, tube temperature. If necessary, the mold sleeve or gasket can be heated before machine production. At the same time, the length of the short rod can be appropriately reduced and the fixed length can be reduced. Aluminum bar too short can be stamping production without blindly increasing the bar temperature, high bar temperature is also easy to cap, but also limit the speed of improvement.
