Thin Aluminum Strips

Analysis on the Causes of Deformation Pattern Defects on the Surface of Thin Aluminum Strips and Solutions
Thin aluminum strips used for architectural decoration generally need to go through processes such as stretch-bending straightening and annealing. For the process of first stretching, bending and straightening and then annealing and direct slitting, when the finished product is cut, it will be found that there will be sticking damage and plate on the surface. If the deformation is severe, the deformation pattern will appear. Through long-term production tracking, after one pull and straightening, obvious edge loose phenomenon will be found in the trimming process. For the surface defects with serious deformation, in terms of shape, they can be roughly divided into three imprinting forms of flower shape, continuous section of bending Linear, as well as scattered dots in the form of bulge. Defects are mostly generated at the two ribs, which mostly appear in the middle of the roll and after the middle of the roll. For a continuous section of similar shape, one place appears in a circle, and it is reversed by deformation somewhere, and the shape of a roll is not fixed, with a continuous line. Shape or overall linear defects occur more frequently, so they are collectively referred to as deformed lines.
This article analyzes the various possible causes of this defect from the cold rolling, stretching, bending and annealing processes, and proposes corresponding solutions for your reference.
1 Formation of deformed streaks
1.1 Characteristics of Defects
The cold-rolled plate shape is characterized by tight edges, serious looseness in the middle, and serious oil on the surface of the plate (especially the edges).
In the final product alloy state, the thickness of H22 soft state is mostly below 0.5mm.
When the finished product is produced, the edge of the plate shape is loose, and most of the defects appear after the middle of the whole roll.
The location is mostly rib, and the shape is irregular, and there is no fixed period.
The same batch of the same melt and the same batch of rolling show different degrees of severity.
1.2 Defect occurrence process
No deformation pattern defects were found in production and inspection before cold rolling and annealing, and defects were found during annealing and trimming, and it was judged that the defects occurred in the annealing process.
1.3 Causes of Defects
According to the absence of fixed position and shape of defects, there are individual deformation lines in the same batch of rolled coils in the same heat, eliminating chemical composition and rolling process problems, and no external force is applied during the annealing process, and only part of the deformation occurs under the same annealing process conditions. Therefore, the problem of the annealing process is excluded, so the reason for analyzing the uncertainty of the defect should also be the fluctuation of the uncertainty, because the effect of the uncertainty before the annealing is not manifested, so the analysis of the deformation pattern is caused by the deformation and stress distribution after straightening. After annealing, the extremely uneven stress can produce irregular deformation caused by recovery in a larger space. However, each process is closely linked, especially for the influence of plate shape, it is necessary to control the hot rolling, cold rolling, and stretch-bending leveling within an adjustable and stable range to reduce the accumulation of internal influencing factors and the difficulty of controlling a certain process. Guarantee the stability of production and quality.
2 Analysis of factors for the formation of deformation streaks
According to the production process data of a large number of defective coils, some interference factors (operation level) are excluded, and the possible factors are analyzed by means of comparison and summarization.
 
2.1 Cold-rolled shape
From the comparison of the coils rolled in the same batch and the same batch of tension leveling in the same heat, from the cold-rolled shape chart, the shape fluctuation is not large, and the edge of the non-deformed grain is slightly loose in comparison. Considering the large tension on the line and the accuracy of the shape roll measurement, the difference between the online shape and the offline shape is relatively large, which is only for reference, but it can reflect the difference between the shape of different coils.
2.2 Cold-rolled sheet with oil
There is a lot of oil on the surface of cold rolling. One is that direct annealing will produce annealing oil spots, and the other is that the stretching and bending straightening is not clean, which will cause embossing or micro-slip at the tension roll or straightening roll.
2.3 Processing rate
For this batch, the deformed lines are mainly concentrated in the thickness of 0.25mm ~ 0.5mm, and the distribution of cold rolling passes is as follows:
3.0-1.4-0.75-0.45
3.0-1.3-0.7-0.4
3.0-1.25-0.65-0.34
A large processing rate makes the shape of the plate difficult to control, and the ribs are loose. The actual production shows that the deformation pattern with a small processing rate is lighter, and a suitable processing rate can better ensure the shape of the plate.
2.4 Tension control of tension and bending
The stretch-bending tension is divided into three tensions, uncoiling tension, straightening tension and coiling tension. In actual production, the plate shape is generally adjusted by setting the elongation rate, so the straightening tension is fixed because the elongation rate is fixed. The unwinding tension is generally 8% to 15% of the yield limit, and the coiling tension is generally 1.1 to 1.5 times the unwinding tension. The uncoiling tension range of this batch is 12-14N/mm2, the coiling tension is 9-13N/mm2, and the elongation is 0.05%-0.1%.
2.5 Straightener
There are two sets of roll boxes above the leveler and two sets of roll boxes below. Because of the equipment manufacturer, there is currently only one set of roll boxes above, which weakens the ability to adjust the shape of the plate. And the work roll of the leveler has been used for a long time without grinding and surface treatment.
2.6 Annealing process
Annealing is mainly to eliminate part of the work hardening, so that the mechanical properties of the material reach the range we expect, but the heating generally adopts rapid heating, one is to refine the grains, and the other is to shorten the annealing time, but too fast heating speed will make the material deform faster. . Degreasing and some stress relief can be done at a low temperature first.
2.7 State changes between layers
After the cold rolling is completed, it is directly and quickly transferred to the annealing production, and the thin aluminum strips can be closely connected with each other without rewinding.
3 Deformation pattern key quality point control
3.1 Cold rolling process control points
Ensure the smoothness of the sleeve and the quality of the bottoming, and reduce the stress concentration caused by bulges and wrinkles on the material.
To ensure that the cold rolling tension fluctuation is small, and quickly adjust to a good shape at the beginning of rolling.
Reasonable distribution of the processing rate of the passes, the processing rate of each pass is 40%.
Oil on the control panel.
Cold rolling reduces the degree of rib looseness, and annealing is carried out as soon as possible after rolling is completed.
3.2 Stretch-bending straightening process
Set reasonable uncoiling and coiling tension to ensure that the thin aluminum strips and the tension roller slip little.
The shape of the plate is adjusted at the beginning of each roll, and no adjustment is required in the middle process.
Ensure the surface roughness of the 2S roller and the tension roller to reduce slippage.
 
Guarantee the smooth surface and bottoming quality of the steel sleeve.
Use the appropriate amount of oil injection lubrication.
3.3 Annealing process
The annealing process adopts the suspension method, and after annealing, it is suspended in the air for cooling and then transported.
Set a suitable heating rate.
Slowly air-cooled after annealing.
4 Summary
The deformation pattern is the irregular deformation of the material: one is the release of stress concentration or there is no obvious irregular deformation, and the other is the space for deformation. The key is to control the flatness of the plate shape and reduce the heating unevenness in the annealing process; secondly, do the production details, the surface of the sleeve is smooth and clean, and the bottoming and so on. Then continuously optimize the process parameters matching the upstream and downstream processes. It is best to anneal directly after cold rolling production, and use the finished product drawing and leveling process.