Semi-finished Copper and Copper Alloy Products

Semi-finished Products

The semi-finished good's production sequence can roughly be summed up by the following steps:  smelting and casting, hot forming, cold forming often in combination with heat treatment and final cutting.

Smelting and Casting

The production of semi-finished goods begins with the smelting of copper materials and the casting of certain forms (such as billets, extrusion billets, etc.). Smelting and casting follow a strict production programme.  The metallic charge as well as the alloy composition are also strictly controlled before casting.  The subsequent analysis of the alloy composition and control for impurities are made within two minutes of smelting through spectral analysis and a pneumonic dispatch system test.  In this way, the smelting process can be corrected if necessary before casting occurs.  Smelting takes place in electric induction furnaces and the forms are cast in continuous casting lines.  Billets are made primarily in a semi-continuous casting strand, while extrusion billets are produced in a continuous casting strand.

Hot Shaping

The hot shaping of copper materials occurs above the recrystallization temperature of copper and copper alloy which is between 750 °C und 950 °C, depending on the material's composition.  Solidification cannot occur as a result of recrystallization while hot shaping.  Strain hardening (soft annealing) is however possible by slowly decreasing the temperature. Metal's resistance to reshaping generally decreases as temperature increases.

Different copper materials have different hot forming properties.  With homogeneous, single-phase copper alloys, deformation resistance increases as the percentage of copper in the alloy increases.  The heterogeneous alloys CuZn and CuAl, however, have a lower deformation resistance, because the emerging β-solid solution has better hot forming properties than that of the α-solid solution.  Heterogeneous brass with at least 37% Zn Content, unalloyed copper, and CuAl alloys exhibit the best hot shaping properties (listed in order of suitability).  Here, brass is characterized in the β-phase by a very low deformation resistance.  CuSn, CuSnPb-, CuNiZn- and CuNi alloys are not particularily well suited for hot shaping. 

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Cold Forming

Cold forming, which takes place below the recrystallization temperature, increases the yield strength as the material is formed (strain hardening).  Because α-Solution has the best cold forming properties, the homogeneous copper alloys are best suited to cold forming.  With the exception of copper-nickel alloys, the general rule of thumb is that the hardening ability of the material through the high level of resistance is determined by the soft state.  The more a material is cold formed, the stronger and more elongated it will become, and thus will have a better capacity for forming. 

Both pure copper and copper-zinc alloys have excellent cold forming properties.  Copper-nickel alloys, low alloyed copper, and copper-tin alloys work relatively well with cold forming.  Less successful with cold forming are copper-aluminum alloys, copper-lead-tin alloys with a high tin or lead content, copper-zinc alloys with a high zinc content, and the β- and (α-β)-varieties.

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Production of Sheets and Strips

Raw materials used to produce sheets and strips are placed on wrought casting plates and processed in semi-continous casting plants.  The plates have a length of about 5 m, a width from 600 to 800 mm and a thickness of approximately 120 mm.  For materials that do not hot shape easily, such as copper-tin wrought alloys, or in situations where the production volume is small and makes more economical sense, the sheets are strips are continuously cast on a horizontal band system with dimensions of 600 mm wide and 25 mm thick.  In this scenario, the otherwise necessary production steps of "warming" and "hot rolling" are not needed.  For hot rolling, the slabs are heated to a temperature above the recrystallization temperature and are then rolled down to 1/10 of its initial thickness on a dual reversing roller. Afterwards, a few tenths of a millimeter are milled on each side to remove the casting skin and scales. 

The approximately 10 mm thick pre-rolled strips are then cold rolled down over several passes to the desired thickness, 2 to 3 mm. Single or multiple annealing steps with the corresponding pickling and drying processes are required when the material is difficult to shape and is particularily thick.  Thinner dimensions are annealed in a continuous oven under protective gasses without having to undergo the pickling process.  With intermediate annealing (recrystallization), the resulting material regains its good formability.  Lastly, the materials goes through the final cold rolling pass, those with narrow strips or difficult to shape materials undergo reverse multi-rolling

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Production of Wire

Wire rod is very important in today's market.  Using either the SOUTHWIRE- or Hazelett process, copper cathodes are melted down and cast.  Using the same heat, the wires are then rolled down to eg ∅ 12 mm.  Energy is saved by having to only heat the material one time.  The resulting coil weighs approximately 5 to 8 t. 

In both larger and finer casting machines, the wire is typically initially produced without regard to the final dimensions.  The casting machines operate by pulling the wire through in several passes.  Because the diameter of the wire is reduced with each pass, the final passes through the casting machine, where the wire is thinner, can go very quickly.  The machines coil the wire at a speed between 40 to 60 m/s.  The wire will often be delivered in a harden state, since it must be annealed anyway when being enameled.  If it is later annealed, the heat treatment is carried out under protective gas so that a pickling process will not be necessary.

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Production of Rods and Profiles

In the production of rods and profiles it is assumed that continuously cast billets and extrusion billets are made with a diameter of approximately ∅ 150 to 300 mm, 200 to 800 mm long respectively.  They are heated in induction or gas furnaces to an extrusion temperature, which is above the recystallization temperature.  Next, the heated pins are pressed onto an extruder with the desired width.  The opening of the die tool determines the shape of the rod as it leaves the press.  For particularily wide diameters the rods and profiles are left in straight lengths, whereas those with a smaller diameter are coiled.

The surface of the rods and profiles are oxidized due to the high temperatures in the press.  This oxidized layer is removed by pickling.  Straight length rods are submerged in a pickling bath and coiled rods are continuously run through the pickling bath.  All further processing of the rods is made by cold forming. 

Ring materials rods are continually run through combined machines.  In these machines the finishing processes are made.  These, in order of operation are cut and drawing/extraction, quality control, cutting into lengths, and straightening.  Straight rods and profiles are placed on long drawing benches.  In many cases larger diameter rods and profiles are delivered "as is" after undergoing quality control, cutting, and straightening.  Other extrusion rods and profiles are placed in straightening machines or formed to a desired shape.

Rod and profile materials are checked for imperfections as well as shape tolerance.

Production of Tubes and Pipes

Copper pipes can be produced by various manufacturing methods. In the two most common methods, the continuously casted blocks are either heated and then pressed into tubes or are reduced in a pilger mill. Afterwards, the material undergoes a series of processes, predominantly performed by drawing the copper through a series of dies.  Following this, materials can be moved to a cold pilger.  Pipes are then tested  for imperfections by eddy currents and cut to the desired size. Pipes made of soft materials are typically formed into coils, whereas those out of harder materials are left as straight lengths.

Copper alloys, such as copper-nickel, are pressed into relatively thin pipes, which are then pulled to the desired length.  The creation of copper pipes by welding is not a common process in Germany.

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