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Coil Processing
Monday | 30 September, 2013 | 9:36 am

Successful slitting

By Lauren Duensing

Above: To guarantee precise cuts on aluminum, it’s important to pay attention to the band tension so the strip will not be damaged. It’s also important to ensure material does not build up on the knives.

Aluminum slitting line provides quality products that meet close manufacturing tolerances

September 2013 - According to numbers released at the end of July from The Aluminum Association, Arlington, Va., aluminum demand has been affected by weakening global market sentiment. However, the light metal’s prospects are forecast to improve in the long-term as a result of activity in the automotive sector and an improvement in housing. The Aluminum Association forecasts a “slight improvement in Europe as well, at least year over year, as the German economy shows signs of resilience.”

Continued expansion of the market means a growing need for processing equipment. Remchingen, Germany-based Burghardt + Schmidt has “built lines for aluminum for more than 60 years,” says Thomas Baral, managing director. “The lines operate at high cutting speeds and with great precision to enable high productivity. In recent years, the market for aluminum products has grown considerably. The market for aluminum, automotive, aviation, lithography, beverage cans, etc. is enjoying a sustained boom, so B+S has decided to pursue this path actively.”

When designing slitting lines for aluminum, B+S takes into account that the material is soft, which affects both the cutting quality and the recoiling. “It’s pretty important that the tension of the band is accurately compensated in the system so that the strips will not be damaged or even cracked,” Baral says. “During the cutting of aluminum, attention must also be paid to the knives so that the material does not build up on these. Only when emphasis is placed on all these points, a precise final product can be expected.”

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Customers demand quality

AMAG Austria Metall AG, Ranshofen, Austria, is a manufacturer of aluminum semis and cast-house products for the processing industry. The company has its casting and rolling operations in Ranshofen and a smelter in Sept-Iles, Quebec, Canada. It manufactures products for a diverse customer base, including markets such as aircraft, automotive, bike/motorbike, consumer electronics, decoration, packaging, heat exchanger, lighting and sporting equipment. 

The company has worked with B+S on several projects, including a recently installed aluminum slitting line, which was purchased as part of an overall quality initiative. AMAG wanted to increase its line capacity; improve cutting edges and surface quality, especially on soft strips; improve coiling quality and tension; and increase flexibility to meet customer requirements, in particular with respect to special sizes. 

 “Ever-closer manufacturing tolerances and quality demands are becoming increasingly important,” says Georg Weger, managing director, AMAG rolling. “Accuracy and precision are very important to our customers, and these requirements will play an even bigger role in the future. The experience of B+S and the high standard of precision in the slitting lines, especially for thin and delicate metal strips, prompted us to decide to buy the line from B+S.”

“The line is a combined wide-strip slitting unit for aluminum material with or without delicate surfaces,” Baral says. “The maximum width of the incoming material is 1,900 millimeters, the thickness range is 0.2 millimeters to 2.0 millimeters, the line speed runs up to 800 meters per minute for edge trimming and up to 400 meters per minute for slitting.”

The line features a double eccentric flying cut-to-length shear on the entry end to ensure that the scrap at the beginning of the rolled aluminum can be removed quickly, an integrated ink jet printer system that can label the strip both on the top and bottom, a vacuum brake roll for sensitive surfaces, an electrostatic oiling device on the brake, a semiautomatic strip clamping device to feed the strips from the slitter to the recoiler mandrel, a fully automatic strapping device to strap rings at the turnstile and a directly connected packaging line with weigh station that arranges fully automatic tilting, packing and transportation of the coils.

“The combination of edge trimming and slitting shear with two shear changing devices allows the alternation of both methods (trimming and slitting) in a pretty short time,” Baral says. “The preparation of the second knife parallel to the production increases the line capacity and the flexibility in meeting customer requirements.”

During roll-shear cutting of aluminum strips, the material is cut by two cutting edges, which are offset by the distance of the cutting gap and penetrate the material from opposite directions. The cutting process follows three stages: the deformation zone, clean-cut zone and fracture zone, with the goal of a minimum burr in the fracture zone. AMAG’s line can achieve cutting burrs ranging from a maximum of 0.03 millimeters to 0.07 millimeters, depending on the strip thickness. In addition, the line is adjusted carefully within the range of several microns to ensure it produces precise cutting edges.

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Taking care with sensitive surfaces

“AMAG has increased the line capacity, the cutting edge and the surface quality, especially for soft strips,” says Weger, in addition to improving the coiling quality and the coiling tension. Capacity can be increased because two shear housings slit the strips into different widths so the knife blocks can be prepared for the next strip in parallel during production. 

The electrostatic oiling machine applies dry-film lubricants and conventional oils, allowing the strip to be finished at the shear, which eliminates a separate downstream processing step. Reducing the amount of handling decreases opportunities for error and helps AMAG ensure the same high-quality surfaces on fast-hardening alloys as well as conventional T4 tempers.

“Soft and thinner material, especially with delicate surfaces can be processed [on the line],” Weger says. “The looping pit combined with the vacuum brake roll allows us to coil the strips constantly over its entire length, even if the material is thin, resulting in large differences in strip length. This type of retaining device is extremely surface friendly and therefore can also be used for sensitive surfaces without any problems. Furthermore, this device can be tailored to individual product requirements.”

“The vacuum roll tensioning system is a special, extremely surface-friendly braking system,” Baral adds. “There are more and more materials where it is important not to damage the surface. Sensitive surfaces demand systems that do not impact these. Our vacuum brake roll leaves neither scratches nor pressure marks on the strips. Not only the technics of our high-precision slitting and stretch-bend leveling lines but also a special transportation system for the sensitive material is important for our clients. This development shows that the trend toward ever-thinner and sensitive material grows on the world market. This will have an impact on the United States.” MM

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