Despite the careful design and manufacture of moulds, and constantly improve the level of technology, even using CAD/CAM system, strive to design and produce as much as possible perfect work mould, but as a result of extrusion section shape is various and complex, the dimensional precision demand is higher and higher, and the influence of extrusion production of various technological factors and changes, etc., makes the design and manufacture of mold production profile, still can appear this or that defects.

    Hollow aluminum is a common decorative materials and industrial profiles. For the hollow profile, weld quality directly affects the quality of the aluminum itself. If the weld quality closes nevertheless, aluminum after surface treatment appear black belt or serious color, will lead to product scrap, cause irreparable damage. So analysis based on the weld formation mechanism of hollow aluminum extrusions, to ensure that the hollow aluminum weld quality.

    First, the mechanism of formation of the weld

    Metal through the tap hole into several shares regrouped in the welding chamber, as a result of the existence of shunt bridge, a bridge is inevitable to form metal flow of rigid zone, the diffusion of metal atoms in the combined with slower, the organization of the metal density decreased. So use shunt combination die extrusion profiles will inevitably exist weld; But can make a good weld of profile after surface treatment to avoid or mitigate such phenomena as black belt. To guarantee the quality of weld, we must make room welded seam metal can fully spread, otherwise, will form a loose, particle bulky and uneven and other parts of the organization, as a result, the deformation degree to a few bigger, especially metal deformation, weld chamber to form a larger water hydrostatic pressure.

    Extrusion, the uneven flow of metal can lead to result in a lot of additional stress profile products, to produce all kinds of defects. Such as welding wire, size is not stable, more root profile different length, etc. In order to overcome the defects due to uneven metal flow, must study how to make the section on metal flow velocity. Factors that can affect the metal flow speed of die hole can be summarized as the following two basic factors:

    1 supply section of each part on the metal allocation amount. The profile area ratio of each part and the corresponding supply ratio of the amount of metal parts are equal.

    2 metal flow influenced by the size of the frictional resistance, when the supply of material, the more the amount of metal part smaller frictional resistance is, this part profile die out the faster speed, conversely the more slowly.

    2.1 metal supply distribution ratio, mold design and manufacturing. After the mould making out, the distribution of the metal is basic fixed proportion.

    2.2 most of the mold, metal allocation amount clearly have determined that the frictional resistance between metal and die is capable of improvement. So as to achieve the purpose of the metal flow velocity adjustment.

    3 the friction between metal and die consists of three parts:

    3.1 contact friction between metal and die F1

    F1 = mu? Rho? s.

    Type: mu: the coefficient of friction

    Rho: MPa unit pressure

    S: metal and die surface contact friction area was

    Conclusion by the type: rho and S is a fixed value, have an effect on friction F1 is mu. Therefore, to improve on the surface of the metal and mould friction conditions, will be able to adjust the metal flow velocity.

    3.2 contact friction between metal and die working with F2

    F2 = mu? Rho? ∑ S = mu? Rho? ∑ L1H1

    Type: ∑ S: metal and section parts die work in contact with the area of the part was

    L1: mm contact part of the work with circumference

    H1: the contact part of the work with mm wide

    Can be seen from the type of rho and L1 is a fixed value affect the friction coefficient of friction is mu and work belt width H1, as long as the adjustment of mu and H1, can achieve the purpose of adjusting the metal flow velocity

    3.3 relative motion of the friction between metal and metal F3

    F3 = f? Rho/ц

    Type: f: the coefficient of friction of metals and metal

    Rho: MPa unit pressure

    ц: metal flow rate in mm/min

    From the type, the f is a variable values, with the temperature changes, in the unit under the condition of invariable pressure metal flow speed faster, the smaller values of F3, when F1 and F2's role is more obvious.

    During extrusion, therefore, reasonably control the extrusion temperature and extrusion speed can significantly alter the flow rate of the metal.

    Second, the sunshine cause of serious

    1 extrusion pressure is too low, the welding force is low. Factors of the low extrusion is comprehensive, there are also factors on the mold process. Has the following several ways:

    1.1 a relatively low extrusion, can improve the mold welding together, increase the thickness of upper die, appropriate reduce the tap hole.

    1.2 according to the profile shape size and shape of the cross-section, appropriate adjustments extrusion temperature 10 ~ 20 ℃.

    1.3 choose appropriate extrusion machine, will arrange the profile extrusion on the larger models.

    1.4 deepen welded room (can) by using the method of bridge will bypass "sink". But must pay attention to the heavy bridge will also reduce the extrusion pressure, so using this method according to the specific circumstances. In the process of production, as the mould wear and tear, wall thickness also increases as the material, extrusion ratio is decreased, the wear to a certain extent, severe weld will affect the surface quality of the material.

    2 tap hole design is too large (especially for extrusion ratio, low profile), the extrusion pressure is reduced, thus reducing welding together.

    2.1 welding is too small, the room is too shallow or volume form the hydrostatic pressure is not enough. Is reasonable on the premise of ensure the mold core rigidity, strength and increase the volume of solder. Can be increase the sectional area of welded room, also can be increase the height of the weld chamber.

    2.2 tap hole layout is not reasonable, unreasonable shunt bridge design and processing. Should try to make the weld Angle or the decorative surface on, and USES the drop shape shunt bridge and the reasonable weld Angle, make the solder in solder room plane (i.e., preforming zone).

    3 the influence of the production process

    3.1 internal defects of casting rod easily appear on the hollow profile of the weld (difficult deformation area). High amount of Mg, Si and Fe content will add solder too bad, suggested that the Mg and Si ratio around 1.2 ~ 1.4 range, Fe content lower than 0.20% can get good weld quality.

    3.2 extrusion temperature and extrusion speed

    High temperature of aluminum rod is conducive to the spread of the metal, but metal bonding mold phenomenon, at the same time, high temperature, the organization of the metal grain growth and growth speed, the weld microstructure of bulky. The extrusion speed too fast, the metal deformation work increases, metal temperature is larger. In addition, the extrusion temperature, extrusion pressure will reduce, thus lowers the welded together. Accordingly, when extrusion temperature should be controlled is great and mold to reduce the influence of other factors on the profile.

    3.3 extruded ingot tube

    Reasonable selection of spindle drum temperature, Suggestions for thick wall profile extrusion cylinder temperature slightly increased 5 ℃ or so, but for thin wall profiles and diversion hole is too big, can be appropriately reduced 5 ℃ or so, on the other hand, need to clear the container regularly, yu product scale, or container has deformation, such as drum and extrusion cylinder and the pressure pad clearance is too large, these all affect the quality of weld.

    3.4 quenching

    Uneven cooling will also affect the quality of the weld. Discharge slide on using graphite products, contact with graphite, heat dissipation is not timely, local temperature rise, thus accelerate the side seam grain grew up, after oxidation profile is easy to appear the phenomenon of black belt. But equipment cooling capacity is enough, also can avoid this phenomenon. So, slide had better use heat blanket, and not easy to wipe profiles.

    3.5 the influence of alkali corrosion oxide

    To reduce the surface quality of the weld, can also be relative adjustment alkali corrosion time, temperature.

    conclusion

    To solve the quality problem of the hollow profile of the weld, first to "diagnosis" mold, then select a reasonable process or adjusted to mould of extrusion process. Serious as a result of the profile or bad or welding at after anodic oxidation surface treatment such as black belt, ribbon phenomenon such as color, affect the quality to use.