Causes and countermeasures for the formation of 'adsorbed particles' on the surface of extruded aluminum profiles

In the extrusion production of aluminum profiles, common defects are relatively intuitive, such as bending, twisting, deformation, and slag inclusion. The defect of 'adsorbed particles' is difficult to find without careful observation or touching by hand. The harm is: 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. 1 The performance of 'adsorbed particles' and its impact on product quality. There are more and more ways of surface treatment of aluminum profiles. In addition to general oxidation profiles, electrophoresis profiles, spray profiles, fluorocarbon spray profiles, wood grain paint profiles, etc. have appeared one after another. There are many tricks. The defect of 'adsorbed particles' has little effect on general oxidizing 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. In the process of sawing and placing in the basket, blow or wipe with wind, and most of the small particles can be removed. 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.　　2 Reasons for the formation of 'adsorbed particles'　　2.1 Influence of mold 　　 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 die 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 there are too many sticky aluminum accumulations 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. 1. The extrusion die we are now 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 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 causing the 'adsorbed particles'. Schematic diagram of the aluminum-bonded area Figure 1 Schematic diagram of the aluminum-bonded area 　　2.2 Influence of extrusion process 　　The correct selection of extrusion process parameters is also an important factor that affects '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 metal The resistance is relatively weakened, and the phenomenon of aluminum adhesion is more likely to be formed; 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'. One.　　　3 　Measures to reduce 'adsorbed particles'　　3.1 Problems that should be paid attention to in mold design, manufacturing, and use　　(1) The design of the mold must meet the calculation requirements of stiffness and strength in order to reduce the amount of elastic deformation of the mold under pressure. When determining the working belt, the length of the working belt, the form of the empty knife, the form of the die neck and the welding chamber, etc. must be considered to select the best value of the parameters. For the selection of coefficients such as diversion holes and diversion holes of the mold, choose a larger value as much as possible within the allowable range to achieve the purpose of reducing the pressure. 3.2 Choosing the appropriate extrusion parameters According to the extrusion coefficient, profile section conditions, mold conditions, equipment conditions, etc., select the best extrusion temperature, casting rod heating temperature, mold temperature and extrusion speed, and in the production process , Constantly adjust these parameters. These are the main measures to eliminate or reduce 'adsorbed particles'.　
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