Shortening
At the tail end of some extruded products, after low magnification inspection, there is a horn-like phenomenon in the middle part of the cross section, which is called shrinking tail.
Generally, the tail of the forward extrusion product is longer than that of the reverse extrusion, and the soft alloy is longer than the hard alloy. The shrinkage of the forward extruded product is mostly in the form of an annular disjoint layer, and the shrinkage of the reverse extruded product is mostly in the shape of a central funnel.
The metal is extruded to the rear end, and the ingot skin and foreign inclusions accumulated on the dead corner of the extrusion cylinder or the gasket flow into the product to form a secondary shrinkage; when the residual material is too short and the center of the product is insufficiently fed, the form a type of abbreviation. From the end of the tail to the front, the tail gradually becomes lighter and disappears completely.
The main cause of shrinkage
1. The residual material is too short or the length of the cut end of the product does not meet the regulations;
2. The extrusion pad is not clean and has oil stains;
3. In the later stage of extrusion, the extrusion speed is too fast or suddenly increases;
4. Use a deformed squeeze pad (a raised pad in the middle);
5. The temperature of the extrusion cylinder is too high;
6. The extrusion cylinder and the extrusion shaft are not aligned;
7. The surface of the ingot is not clean, there are oil stains, segregation tumors and folding and other defects are not removed;
8. The inner sleeve of the extrusion cylinder is not clean or deformed, and the inner lining is not cleaned with a cleaning pad in time.
Prevention method
1. Leave residue and cut tails as required;
2. Keep the molds clean;
3. Improve the surface quality of the ingot;
4. Reasonably control the extrusion temperature and speed to ensure smooth extrusion;
5. Except for special circumstances, it is strictly forbidden to apply oil on the surface of the tool and mold;
6. The gasket is properly cooled.
