Particularly in automotive construction and in the aerospace industry, aluminum plates and sheets is used to an increasing extent due to its little weight with but high strengths. Without these innovative aluminum materials for structural parts or exposed applications it would be very hard to satisfy the condition of low weight. Many of these applications demand for the cold-rolled aluminum strip to be treated in a process of annealing combined with fast cooling to achieve formability and the necessary material strengths.
For the production of such grades, SMS group supplies suitable heat and chemical treatment lines. In addition to material heat treatment, the strip surfaces undergo an extra chemical treatment. The lines cover a vast range of materials. Material thicknesses are between 0.2 and 4.5 millimeters, while the strip width may be more than 2.5 meters.
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Heat and chemical treatment lines (HCTL)
From cold rolled to automotive and aeroplane strip products
The use of aluminum as a lightweight construction material in automobiles and also in the aviation industry continues to be on the rise. Subsequent to the cold rolling process, the aluminum sheets have to undergo a heat treatment to regain formability as well as the required material strengths. Especially the heat treatment and the cooling of the strip play a major role. To increase flatness the strip has the possibility to run through a tension leveler. The strip surfaces must be cleaned before they are coated. The chemical treatment prepares the strip for transportation and further processing. These processes can take place separately in different facilities or combined in a heat and chemical treatment line, which can provide financial benefits.
Main process steps:
- Annealing and cooling
- Tension leveling
- Cleaning
- Chemical treatment
- Aging
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Water cooling with pre-defined cross-bow
Floatation annealing furnace and cooling equipment
The furnace and cooling technology is the heart of the process. The strip enters a floatation furnace where it is guided sinusoidal in a contactless floating mode. It is heated up and kept at the required strip temperatures in time, so the aluminum-alloy obtains their structure. Especially 2xxx and 7xxx aerospace alloys require highcooling rates of some 400 kelvin per second. For 6xxx automotive alloys mostly moderate but flexible cooling rates between 25 and 100 kelvin per second are necessary. The cooling process is executed as a combination of water and air cooling. A mathematical model calculates the necessary settings for the annealing and cooling process under consideration of the mechanical properties.
After the furnace, some alloys pass through a tension leveler to improve the required strip flatness. Depending on the material requirements the machine is able to operate without switching the leveling cartridge in either stretch bending or pure stretch mode. The settings are specified by a physical process model. In the following spray cleaning process the remaining surface impurities will be removed and the strip surface will be activated. Here special nozzles are used to avoid clogging and the nozzle bars are switchable for higher process flexibility.
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High-performance floatation furnace for aluminum automotive qualities. -
Chemical treatment
Coating technologies geared to your requirements
After annealing and cooling, a chemical coating is precisely applied onto the strip surface by a vertical or horizontal roll coater. The strip is coated evenly on each side with predefined surface thicknesses. Alternatively, a spray passivation can be used instead of roll coating. Passivation creates a uniform and dense layer of aluminum oxide on the surface (sealing layer). This layer serves several purposes: It improves the corrosion protection of the strips and thus protects them from undesirable corrosion.
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ChemCoater for heat treatment of aluminum strip -
Cleaning technology
Cleaning and de-oxidation
We design all our cleaning components to ensure excellent surface quality at minimum media consumption. You'll find a wealth of experience in our cleaning sections, so we can supply sophisticated components with a high level of automation. Normally, in our systems, the strip passes through spraying tanks made of stainless steel. Several nozzle tubes with clog-free, spoon-type nozzles in the closed tanks spray the cleaning medium onto both strip surfaces. It's easy to adjust the spray angle of the nozzles from the outside during the ongoing process.
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Cleaning technology for aluminum strip
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