solution to the "tail shrinkage" defect of extruded aluminum profile extruded by extruder

Knowledge 1: Introduction to the common problems of tail shrinkage in the extrusion process of extruder:
　　In the extrusion production of aluminum profiles, there will be defects commonly known as "tail shrinkage" after alkali etching inspection of the semi-finished parts after cutting heads and tails, and the mechanical properties of aluminum profiles containing this organization cannot meet the requirements, and there are potential safety hazards. At the same time, when the aluminum alloy profile is produced for surface treatment or turning, the existence of the defect destroys the internal continuity of the material, which will affect the subsequent surface and finishing, and seriously cause the harm such as dark grain scrapping or damage to the turning tool, which is a common problem in production.

Knowledge 2: Classification of shrinkage of extruder extruded aluminum profiles Among them, "shrinking tail" is divided into two types: hollow shrinking tail and annular tailing:
　　1) hollow tail shrinkage: in the extrusion type, the center of the bar tail end forms a hollow, the cross-section is presented as a hole with a non-smooth edge or a hole with other impurities at the edge, longitudinally a funnel-shaped (conical), the tip of the funnel is towards the direction of metal outflow, mainly appears in the single-hole plane die extrusion, especially the extrusion coefficient is small, the diameter of the product is large, the tail of the thick-walled or the extrusion gasket with oil stain is more obvious.
　　2) Annular tail shrinkage: the two ends of the extrusion shunt mold (especially the head) are discontinuous annular or arc-shaped, and the crescent-shaped shape is more obvious on both sides of the weld line, and the annular tail shrinkage of each hole product is symmetrical. Formation of tail shrinkage Causes of tail shrinkage: The mechanical conditions for tail shrinkage are; When the advection phase is over, the extrusion gasket gradually approaches the mold, and the extrusion increases and generates a pressure on the surface of the extruded cylinder side dN cylinder. This force, together with the frictional dT-cylinder, forms a tail reduction when the balance condition of the force (dN cylinder dT-cylinder) ≥ the dT pad, the metal around the extruded pad area flows backwards along the edge into the center of the blank.

　Knowledge 3: What are the extrusion conditions for the formation of tail shrinkage caused by the extruder:
　　1. The extrusion residue is left too short
　　2. The squeezing gasket is oily or not clean
　　3. The surface of the ingot or wool is not clean
　　4. The length of the finished cut of the product is not in accordance with the regulations
　　5. The lining of the extrusion cylinder is out of tolerance
　　6. Suddenly increase the extrusion speed at the end of the extrusion.

Knowledge 4: Elimination method of tail shrinkage formed by aluminum extruder and measures to reduce and prevent tail shrinkage:
　　1. In strict accordance with the process regulations, shear the pressure margin and sawing the head and tail, keep the lining of the extrusion cylinder intact, prohibit the extrusion of the gasket to extract oil, reduce the temperature before the extrusion of the aluminum rod, use a special convex gasket, and adopt a reasonable length of residual material.
　　2. The surface of the extrusion tool and aluminum rod should be clean
　　3. Frequently check the size of the extrusion cylinder and replace the unqualified tools
　　4. Smooth extrusion. In the later stage of extrusion, the extrusion speed should be slowed down, and the thickness of the pressure allowance should be appropriately retained, or the method of increasing the residue should be used.