Solutions to the “tail shrinkage” defect of extruded aluminum profiles by extruder

Knowledge 1: Introduction to common problems of tail shrinkage in the extrusion process of the extruder:

In the extrusion production of aluminum profiles, the semi-finished products after cutting and tailing will have defects commonly known as “tail shrinkage” after alkali corrosion inspection. The mechanical properties of aluminum profiles containing this structure cannot meet the requirements, and there are hidden safety hazards. At the same time, when the aluminum alloy profile produced is subjected to surface treatment or turning processing, due to the existence of this defect, the internal continuity of the material will be destroyed, which will affect the subsequent surface and finishing, and will seriously cause obscured scrap or damage to the turning tool. This is a common problem in production. Here, this article briefly analyzes the causes of aluminum tail shrinkage and the method of elimination.

Knowledge 2: The classification of tail shrinkage in extruded aluminum profiles by extruders. Among them, “shrinkage” is divided into two types: hollow shrinkage and ring shrinkage:

• 1) Hollow tail shrinkage: A hollow is formed in the center of the extruded bar and the end of the bar. The cross section shows a hole with an uneven edge or a hole with other impurities on the edge. The longitudinal shape is a funnel (cone) with the tip of the funnel. Toward the direction of metal outflow, it mainly occurs in single-hole flat die extrusion, especially the tail part of the extruded profile with small extrusion coefficient, large product diameter, thick wall or using oily extrusion gasket.
• 2) Ring-shaped tail shrinkage: The two ends of the extruded shunt molded product (especially the head) are in a discontinuous ring or arc shape, and the crescent shape is more obvious on both sides of the welding line. The ring-shaped shrinkage of each hole product The tail is symmetrical. The formation of shrinkage The reason for the formation of shrinkage: The mechanical conditions for the formation of shrinkage are; when the advection phase is over and the extruded gasket gradually approaches the die, the extrusion increases and generates a pressure dN cylinder against the side surface of the extrusion cylinder. This force is combined with the frictional force dT cylinder. When the force balance condition (dN cylinder dT cylinder) ≥ dT pad is broken, the metal located around the squeezed gasket area flows backwards along the edge into the center of the blank, forming a shrinking tail .

Knowledge 3: What are the extrusion conditions that the extruder causes to shrink tail formation:

• Extrusion residue is left too short
• The extruded gasket is oily or dirty
• The surface of the ingot or wool is not clean
• The length of the tail of the product is not in compliance with the regulations
• Extrusion cylinder lining is out of tolerance
• Suddenly increase the extrusion speed at the end of extrusion.

Knowledge 4: Elimination method of aluminum extrusion machine tail shrinkage and measures to reduce and prevent the formation of tail shrinkage:

• Strictly follow the process regulations to cut the excess pressure and saw the head and tail, keep the lining of the extrusion cylinder intact, prohibit the extrusion of the gasket from oiling, reduce the temperature before the aluminum rod extrusion, use a special convex gasket, adopt Reasonable length of residual material.
•  The surface of the extrusion tool and the aluminum rod should be clean
• Frequently check the size of the squeeze cylinder and replace unqualified tools
• Smooth extrusion. In the late extrusion stage, the extrusion speed should be slowed down, the thickness of the excess pressure should be appropriately left, or the extrusion method should be used to increase the residual material.

Knowledge 5: In order to effectively eliminate the phenomenon of tail shrinkage during the production of aluminum extrusion presses, the excess thickness of the extruder is also very heavy. The following is the excess thickness standard we developed for your reference:

Tonnage of Extruder (T) Remaining Thickness (mm)

• <800T ≥15mm
• 800-1000T ≥18mm
• 1200T ≥20mm
• 1600T ≥25mm
• 2500T ≥30mm
• 4000T ≥45mm