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1. There are seams or poor welding
Hollow aluminum alloy profiles are extruded using a plane shunt combination die. The metal goes through the process of shunting and welding, so there are welding lines in the hollow profiles. If the metal welding is not good and gaps appear, it is a defect. There are two reasons for the gap. One is that the shunt hole and the welding chamber are small, the metal flow is insufficient, and the metal does not form enough hydrostatic pressure in the welding chamber. The product is not welded well and flows out of the die hole, resulting in welding of the product. Gaps; the second is caused by excessive lubrication and poor lubrication causing poor welding of hollow profiles. The former can be solved by grinding or milling to enlarge the shunt hole and the welding chamber area, and increase the metal supply flow, so that the metal can form sufficient hydrostatic pressure in the welding chamber. The latter can be solved by using a non-lubricated extrusion process.
2. The wall of the aluminum alloy profile has a concave or convex arcuate surface.
1）The reason for the concave arcuate surface of the hollow aluminum alloy profile wall: the mold core working belt is lower than the lower mold hole working belt, and the effective length of the mold core working belt is too short. Correction method: Place a spacer ring between the mold core and the lower mold so that the mold core working belt is at the same height as the lower mold hole sizing belt under stress. At the same time, the same thickness is reduced at the outlet of the lower mold.
2）Reasons for the bulging of the hollow aluminum alloy profile wall: the mold has been used for too long, the mold core working belt is severely worn, grooves appear, and the friction resistance is increased. The slow metal flow causes the hollow profile wall to bulge. Correction method: If the profile wall thickness tolerance allows, you can file or polish the surface of the working belt of the mold core to reduce the friction resistance; if the wear of the mold core working belt is serious and the profile wall thickness has reached the upper deviation, the mold can be Preheat to about 300°C, repair weld the mold core shape, then file it to the required size and polish it before use; if the mold core working belt is not worn, file the outer obstruction and the inner stagnation of the mold core working belt. That’s it.
3. Surface stripes on aluminum alloy profiles
Stripes appear on the outer surface of extruded profiles, which are more obvious after anodizing. This defect is mostly seen on the parts with large differences in wall thickness of the profile, the welding parts of the metal under the shunt bridge, and the back side with "branches" and threaded holes on the inside.
cause:
1）The "branches" and threaded holes on the inside of the profile cause surface streaks due to insufficient or excessive metal supply;
2）Stripes on the profile surface caused by the welding area under the mold shunt bridge;
3）Problems in profile cross-section design. Due to the large wall thickness difference of the profile, the parts where the length of the working belt changes suddenly will produce stripe-like color difference after anodization;
4）Due to insufficient cooling capacity of the machine, black streak areas are caused after anodization;
5）The quality of the cast billet itself is not good, which affects the stripe color difference after anodization of the extruded material.
Correction method:
1）Check whether there are any large differences in wall thickness, branches and threaded holes on the decorative surface of the profile in the customer's drawings;
2）The shunt bridge should be designed on the non-decorative surface of the profile. While ensuring the strength of the mold, the welding chamber should be as large as possible so that the metal can form sufficient hydrostatic pressure;
3）For large-diameter pipes or large-size hollow profile molds, an upper welding chamber can be provided on the male mold;
4）For the "branches" or stripes at the threaded holes on the inside of the profile, the mold repair method is to polish the mold hole working belt of these parts, polish them smooth, or modify or reduce the connection transition radius of these parts;
5）Sometimes the stripes are formed by the casting material itself, which requires uniform heating temperature and thorough homogenization annealing;
6)After the extruded material exits the die hole, its grain size depends on the temperature entering the quenching zone and the cooling rate in the quenching zone. If the cooling temperature is too low and the cooling rate is uneven, the grains will be too large or the grain size will be uneven. The color difference will be more obvious after anodization, requiring the operator to adjust the air pressure and cooling water pressure of the cooling system in a timely manner.
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