Why do aluminum extrusion profiles have particles

We can see that the intuitive defects include twisting, slag inclusion, deformation, bending and so on. In the process of aluminum extrusion profiles, it is difficult for us to observe the defects of the adsorbed particles, and it is difficult to find out if we do not observe carefully or touch them by hand. Why are particles produced, and if measures are taken, what are the hazards?

Main factors of "adsorbed particles"

Mold, casting rod, extrusion process.

The operating level of the operator is also reflected in these three elements. On the basis of production practice, it is necessary to continuously analyze the problems and sum up experience to reduce or avoid "adsorbed particles", aluminum sticking, rough surface, scratches, and profiles. Defects such as tearing greatly improve the yield and production efficiency of the profile.

Mould

In extrusion production, the mold is working under high temperature and high pressure, and the mold is elastically deformed under the influence of pressure and temperature. The working belt of the mold starts to be parallel to the extrusion direction. After being pressed, the working belt deforms into a horn shape. Only the cutting edge of the working belt touches the sticky aluminum formed by the profile, which is similar to the cutting edge of a turning tool. During the formation process of sticky aluminum, particles are continuously carried out by the profile and adhere to the surface of the profile, resulting in "adsorbed particles". With the continuous increase of the sticky aluminum, the mold rebounds instantaneously, which will form bite marks. If the sticky aluminum accumulates too much and cannot be pulled out by the profile, the sticky aluminum will not fall off when the mold rebounds instantly, which will cause problems such as rough surface of the profile, bright strips, tearing of the profile, and mold blockage.

The extrusion die we are currently using is basically a flat die. When the cast rod is not peeled, the surface of the cast rod and internal impurities accumulate in the dead zone of the metal flow in the mold. With the advancement of the extrusion cast rod and the number of extrusions The impurities in the dead zone are constantly changing, and some of them are taken out by the normal flowing metal and accumulated in the space after the deformation of the working belt. Some are pulled off by the profile, forming "adsorbed particles". Therefore, the mold is the key factor that causes the "adsorbed particles".

Extrusion process

The correct selection of extrusion process parameters is also an important factor affecting "adsorbed particles". Through field observation, if the extrusion temperature and extrusion speed are too high, there will be more "adsorbed particles". The reason is that due to high temperature and high speed, the flow rate of the profile increases, the degree of mold deformation increases, the flow of metal is accelerated, and the deformation of the metal is increased. The resistance is relatively weakened, and the phenomenon of aluminum adhesion is more likely to form; for a large extrusion coefficient, the deformation resistance of the metal is relatively increased, and the dead zone is relatively increased, which improves the conditions for the formation of aluminum adhesion, and the probability of forming "adsorbed particles" increases; If the difference between the heating temperature of the casting rod and the mold temperature is too large, it is easy to cause aluminum sticking problems and even mold blockage; the roughness of the mold surface and the hardness of the working belt surface are also the reasons for the aluminum sticking and the formation of "adsorbed particles". 

Casting quality

The quality of the cast rod is an important factor affecting the aluminum profile surface and extrusion molding.

The cause of "adsorbed particles" has a lot to do with the quality of the cast rod. The common structural defects of cast rods include slag inclusion, porosity, coarse grains, segregation, and bright grains. Slag inclusion is molten slag, oxide scale or other impurities mixed into the cast rod, also called inclusion. The low-power test piece generally presents irregularly shaped black holes, which are recessed in the matrix, and are amorphous soft tissues of different colors, which destroy the continuity of the cast rod. During the extrusion process, the slag is easily separated from the matrix. When passing through the working belt of the mold, it adheres to the entrance end to form sticky aluminum, which is continuously pulled out by the flowing metal to form "adsorbed particles"; looseness is There are macroscopic and microscopic dispersive shrinkage cavities in the grain boundary and dendrite network, irregular black pinhole-like small dots on the low-power test piece, triangular holes between the dendrites, the fracture structure is not dense, and the serious looseness is often Accompanied by pores, slag inclusions, etc., it is difficult to weld with metal in extrusion production, thereby forming a phenomenon of aluminum adhesion; coarse crystal grains are when the melt metal is overheated or the casting temperature is too high. The coarse grain structure that is easy to appear in the cast rod, accompanied by intergranular cracks, makes the metal discontinuous, and the problem of aluminum sticking is also easy to occur in the extrusion production; segregation is the easy-to-melt precipitate that condenses on the surface of the cast rod. Also called segregation tumor, it is formed by the exudation of the fusible composition and condensed on the surface of the cast rod. In the extrusion production, it gathers in the dead zone of the die metal flow. As the number of extrusion cast rods increases, they are extruded. Or pulled out by the flowing profile to form "adsorbed particles". All these cast rod defects have one thing in common, that is, poor welding with the cast rod matrix, resulting in discontinuity of matrix flow, which is an important factor in the formation of "adsorbed particles".

The hazards of "adsorbed particles"

Performance of "adsorbed particles" and its impact on product quality

There are more and more ways of surface treatment of aluminium profile, in addition to general oxidation profiles, there are spray profiles, electrophoresis profiles, wood grain paint profiles, fluorocarbon spray profiles, etc.

The defect of "adsorbed particles" has little effect on general oxidized materials, but has a greater impact on other processing methods, mainly because it hinders the appearance of the surface of these profiles.

In extrusion production, the "adsorbed particles" of the extruded profile can be found after careful observation or sliding on the surface of the profile by hand. Most of the small particles can be removed by blowing or wiping in the sawing process. However, some of them are still adsorbed on the surface of the profile due to static electricity. After aging treatment, these particles adhere more closely to the surface of the profile. In the pretreatment process of the profile surface, due to the influence of the bath concentration, some can be removed, but small pits are formed on the surface of the profile, and some cannot be removed, which will form a bump (this problem is in the production of electrophoresis and spraying profiles. Often appears).

In the production process of electrophoresis and spraying profiles, it is difficult to remove them, which affects the appearance of the profiles and causes waste products. Therefore, it is necessary to continuously observe and analyze in the extrusion production practice, summarize its causes, and take timely measures to reduce or eliminate the occurrence of such defects. If you want to understand the methods and measures to reduce or eliminate, we will elaborate on the next blog, and continue to pay attention to us.