[China Aluminum Industry Network] In the extrusion production of aluminum profiles, there are some small particles on the surface of the profile that are adsorbed on the surface of the profiles in different degrees. This kind of defect has only a slight touch, and it is difficult to find without careful observation or hand touch. However, it seriously affects the surface appearance of oxidation, electrophoretic painting and sprayed profiles, reduces production efficiency and yield, and is a fatal flaw in high-grade decorative profiles. Therefore, the analysis of its formation mechanism, and the continuous observation and analysis in the extrusion production practice, summarizing its causes and taking timely measures are effective means to reduce or eliminate the occurrence of such defects.
In order to further improve the quality of the company's products and create a high-end brand image, the company's technical staff of the Ministry of Technology and the production of first-line technical workers in-depth study of this defect, has achieved remarkable results in reducing the adsorption of granular burrs.
First, the cause of particle adsorption analysis 1, the appearance of granular burrs on the surface of the extrusion is divided into four types:
1) Air dust adsorption, dust, aluminum swarf, oil stains and moisture generated from coal-fired aluminum rod heating furnaces condense into particles that adhere to the surface of hot profiles.
2) Impurities in aluminum rods, such as metal inclusions and non-metallic inclusions that are not sufficiently refined by refining.
3) The dust in the aging furnace adheres.
4) The defects in the aluminum rod and the β-phase AlFeSi in the composition precipitate at a high temperature, which reduces the plasticity of the metal and lowers the tensile strength, resulting in granular burrs.
Formation of “adsorption particles†2 Causes 1) Effect of aluminum rod quality Due to high-temperature casting, casting speed is fast, and cooling intensity is high, β-phase AlFeSi in the alloy cannot be converted into spherical alpha-phase AlFeSi in time due to β-phase AlFeSi in the alloy. The appearance of needle-like structure, high hardness, poor plasticity, low tensile strength, not only will cause extrusion cracks at high temperature extrusion, but will produce granular burrs, this burr is not easy to clean, feel strong, often accompanied near the particles There are verrucous tails, observed under a metallographic microscope, showing a grayish brown, rich in iron in the composition.
Impurities in aluminum rods, aluminum rods in the casting process, the refining is not sufficient, dirt, refining agents, covering agents and powder coatings and oxide film inclusions mixed into the rod, these substances in the extrusion process, the plasticity of the metal and The tensile strength is significantly reduced and grainy burrs are easily generated.
The structural defects of rods are often loose, coarse grains, segregation, bright grains, etc. All of these cast rod defects have one thing in common, that is, the welding of the matrix of the cast rod is not good, resulting in the discontinuity of the flow of the matrix. During the extrusion process, slag inclusions can be easily separated from the matrix and adhere to the inlet end when passing through the working zone of the mold to form sticky aluminum, which is continuously pulled out by the flowing metal and can easily produce granular burrs.
2) Influence of the mold In the extrusion production, the mold is operated 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 from parallel to the extrusion direction, and after the pressure is applied, the working belt is deformed into a trumpet shape. Only the edge portion of the working belt contacts the aluminum stick formed by the profile and is similar to the cutting edge of the turning tool. In the formation of sticky aluminum, particles are constantly being carried out by the profile and adhere to the surface of the profile, resulting in "adsorbent particles". With the continuous increase of sticky aluminum, the mold will instantly rebound and bite marks will be formed. If the sticky aluminum deposits are too large to be pulled out by the profiles, the sticky aluminum will not fall off when the die instantly rebounds, and problems such as rough surface of the profile, bright strips, tearing of the profiles, and blockage of the profiles will occur. The sticky aluminum phenomenon of the mold is shown in Figure 1. The extrusion die we use today is basically a planar die. In the case where the cast bar is not stripped, the surface and internal impurities of the cast bar deposit in the dead zone of the metal flow in the die, with the advancement of the extrusion die and the number of extrusions With the increase, the impurities in the dead zone are constantly changing. Some of them are carried out by normal flowing metal and accumulate in the deformed space of the working belt.