welding seam line problem in extrusion

First of all we should clear is the aluminum extrusion die would have been the basic of welding seam line, depending on the aluminum extrusion process, but in actual production, we can as much as possible to reduce or avoid the aluminum extrusion mold welding seam line, following a brief introduction about first aluminum extrusion mold welding seam line of some of the basic problems.
What is a die closing line (weld line)? Aluminum extrusion profile welding line, also known as the die line. Die term, refers to the convex, concave die (or upper, lower die) compressed together this is called die closing. After compression molding will appear in the clamping area of the interface line, known as the clamping line. It is the aluminum material through the mold shunt, divided into many strands of aluminum flow, and then in the mold welding chamber after re-welding out of the mold forming, a combination line formed on the profile. Generally by some split die (bridge die) extrusion formed hollow profile is more common, a few flat die, due to the design of the guide groove, processing improper, will also appear welding line. It is a defect in the surface and internal processing properties of aluminum. Some profiles, with the naked eye can be seen, one or more white or gray color lines, some although we do not see with the naked eye, but after the amplification of the instrument, or profile after finishing, welding line can be clearly seen. In the production process of aluminum tube, there are two kinds of production processes: seamless and slit. In the extrusion process of slit tube, the blank material is extruded by 3~4 holes on the mold, and the welding line is naturally formed at the joint site, and an obvious welding line will appear at the position of the welding line after anodizing.
How is the closing line (welding line) formed for aluminum extrusion die? 1, the problem of the mold itself leads to: the mold structure is unreasonable, the mold closing is itself misaligned, the mold exhaust is not good 2, the aluminum rod after the split mold, the metal is cut in the bridge position in the middle line of the aluminum profile just below the obvious boundary, this is the so-called welding line. However, the aluminum metal directly below the bridge has the largest degree of deformation and low hydrostatic pressure. If it enters the working belt of the extrusion die immediately, it will cause obvious black line defects on the surface of the aluminum profile after oxidation. There are many reasons for the welding line of extrusion die. Oil pollution, too fast speed and low rod temperature may cause the welding line. If the flow of the split hole is not uniform, the gap between the hydrostatic pressure on both sides of the bridge is large, resulting in the welding line position offset under the bridge chamfering position, resulting in serious welding defects, the guide Angle under the bridge but seriously obstructs the aluminum flow, the metal on both sides because of the large deformation difference, leading to the serious color separation of the aluminum profile. Can the die closing line in aluminum extruded profile be removed in chemical casting? Part of the mold closing line is different from other parts of the structure, and contact with acid and alkaline bath will form bright or black lines which are different from other parts. Should try to avoid contact with acid, alkali, chemical polishing is the use of strong acid so can not be removed. The only way to eliminate it is to change the mold guide structure, try to move the die closing line to the non-decorative surface or corner position, and try to increase the guide plate. Of course, you can also change the surface treatment, in short, to avoid contact with acid, alkali as far as possible.