23/05/2022 – Cold rolling
Doubling the capacity of strip mills
The German machine making company Fuhr is well known for its competence in the field of cold rolling machines. The portfolio covers everything from pay-offs via rolling stands to inline measuring systems and take-ups. Fuhr’s specific strength are customized turnkey machines build from standardized approved modules.
There is only a handful of machine builders for cold rolling machines worldwide and amongst them Fuhr is covering the widest range. Cross sections start from 0.1mm² and end at 1,000mm². Materials are ferrous, non-ferrous and precious metals such as low carbon, high carbon and stainless steels, copper, aluminum and their alloys, gold, silver and titanium.
A specialty of Fuhr is rolling mills for complex shaped wires, but also narrow strips from 2mm to 30mm width and 0,1mm to 1,5mm thickness are an important field. Traditionally there are two different methods to produce narrow metal strips.
Slitting wide strip coils
Cold rolled strip coils in typical widths between 500mm and 2,000mm are fed to longitudinal slitting lines. The slitter uses two sets of sharp rotary blades where the width of the blades equals the width of the strips. At the slitting line’s exit the single strips are wound to tape style coils. The length of each coil is identic to the length of the initial wide strip coil. The precision of slitted strip is good, but the shearing process creates burrs even if the rotary blades are kept in good condition. Costly single strip edge trimming processes are required to smoothen the edges or create defined edge forms.
Rolling from wire
Hot rolled rod or drawn wires are the feedstock for the rolling process. Typically, a combination of 2Hi horizontal flattening stands and vertical edge rollers is used. The strip’s edge form is defined by the edge rolls’ groove design. The edges are smooth and free of burrs. The strips are layer wound on reels. Alternatively coreless layer wound coils can be produced. Compared to the tape style coils of slitting lines the length of strips rolled from wire is virtually endless and only limited by the take-up’s capacity. This advantage has been motivation for many strip rolling mill installations because the consumers of strip are enabled to run their machines for many hours without interruption for coil change.
Combined rolling and slitting
The great advantage of rolling huge production lengths with defined burr-free edges opposed by the higher productivity of slitting lines was Fuhr’s inspiration to develop a concept which combines the best of both processes where wire is rolled to strip and finally slit into multiple strips. The development of this innovative process was supported by the German Federal Ministry for Economic Affairs and Energy. The most challenging part was the design of the shearing rolls and the selection of their material because the lifetime of the shears should be much higher than in classical slitting lines.
End of 2021 the first combined rolling and slitting line was installed by Fuhr. It produces two aluminum strips of 3/8” width at thicknesses of 0.015” to 0.030” which are used for cable armoring. The line is fed with 3/8” diameter hot rolled aluminum wire rod of the 5000-series. Compared to a single strip rolling mill, the duo strip mill doubles the production capacity while labor costs are constant, and the machine price and its space requirements are only 30% higher. Moreover, the energy costs per ton of produced strip are drastically reduced.
Future enhancements of the combined process
The first installation was a proof of concept which will now be deployed to applications for different materials and end uses. Aluminum and Copper strips are used for example in the production of finned tubes for heat exchangers and for cable shielding. Copper strip is used for bus bars in photovoltaic modules. Strips from steels and stainless steels are widely used in many industries. The number of strips is not limited to two and can be enhanced. Fuhr is encouraging strip makers and end users to get in touch and discuss the feasibility of combined rolling and slitting for their product.
wire 2022, hall 11 booth A 50