Fabrication of Copper and Copper Alloy Tubes, Rods and Sections

Table 3-53: Typical data of a facility to roll brass strips

Hot rolling

Type of mill Mainly Duo

Dimensions start 250 - 130 mm thickness, 450 - 1.000 mm width Final dimensions 15 - 12 mm thickness, 450 - 1.000 mm width Temperature 750 - 800 °C

Rolling force Abt. 10 - 12 kN/mm sheet width Surface milling 0,3 - 0,7 mm cutting of both surfaces 1^st Cold rolling

Type of mill Mainly Quarto

Rolling force Abt. 15 - 20 kN/mm sheet width Dimension reduction and

rolling speed

Reduction 15 mm to 4 mm thickness in multiple passes, speed 100-200 m/min

Conversion ratio 70 - 80 % Annealing^*) (recrystallisation)

Temperature 550 - 600 °C 2^nd and final rolling

Type of mill Mainly Quarto, alternatively, depending on sheet thickness, Sexto or stands with 20 rolls are used Rolling force Abt. 2 - 1o kN/mm sheet width, depending of type of

mill used

Rolling speed Reduction 4 to 1 mm: 300 - 500 m/min, multiple passes

Reduction 1 to 0,1 mm: 500 - 1000 m/min, multiple passes

Cutting of sheets to strips

Type of equipment Longitudinal strip cutting machine

*) Annealing required after every conversion ratio of more than 70-80 %.

Annealing temperatures selected depending of material properties to be achieved.

The described concept for sheet and strip fabrication, based on hot and cold rolling corresponds to the conventional concept and is also suitable for high production rates.

However, there are concepts industrially applied or under development for direct casting of sheets or strips followed by cold rolling. Such concepts bypass the hot rolling operation. One method is the horizontal casting used for copper alloy strip production. These concepts are also applied for rod and profile casting. Furthermore, different other systems have been proposed for continuous strip and sheet casting and some are under development.

the start material for the fabrication process are copper and/or copper alloy billets. The production concept of copper tubes (c.f. Figure 3-18) is somewhat different from the production concept required for the fabrication of copper alloy tubes, rods and sections (c.f.

Figure 3-19).

Preheating

Extruding

Breakdown Rolling

Drawing

Annealing

Section Rolling

Sawing to Length Drawing

Annealing Coiling

Cooling Water Systems

Protection Gas Supply

Lubricant Systems

Effluent Treatment

Spent Lubricant Drawing

Straighten

Copper Tubes

Copper Tube Coils Copper Billets

Figure 3-18: Fabrication of copper tubes

Preheating Extruding De-Scaling

Pickling Drawing Annealing Pickling Sawing to

Length

Pickling Drawing Annealing Pickling Straighten

Cooling Water Systems

Protection Gas Supply

Lubricant Systems

Pickling Systems Billets

Effluent Treatment Spent

Lubricant

Sludge CuSO4, NiSo4

Neutralisation Tubes Copper & Alloy Rods Copper Copper & Alloy

Sections Copper Copper & Alloy

Figure 3-19: Fabrication of copper alloy tubes and rod/sections from copper and copper alloys

The billets in a first stage are electrically or indirectly pre-heated by gas-fired units. Starting from pre-heated billets, hydraulically operated extrusion presses are used for pressing unfinished tubes from copper and copper alloy as well as for the production of copper alloy rods and sections. For the fabrication of copper tubes different processes are industrially applied:

- Tube extrusion followed by multi-step drawing to size,

- tube extrusion followed by breakdown rolling followed by several steps of drawing to size, and

- hot piercing mill followed by breakdown rolling and drawing to size.

The process concept applied depends of the type of product to be fabricated. For billets, which are extruded or rolled to tubes with thick walls, breakdown rolling has normally the preference as first size reduction step. For tubes extruded to thin walls, tube drawing machines are applied. For the fabrication of copper alloy rods and sections material extruding in coils or straight length, cleaning and pickling, drawing to size using drawbenches or continuous drawing machines, heat treatment for certain alloys and straightening and sawing are normally the sequences of the fabrication process.

The whole process, started by the extrusion press or the hot piercing mill, is a sequence of (mostly) reducing steps changing shape and size. During these processing steps the tools of the equipment for size and shape changing are cooled and protected by adequate media, using emulsions for the breakdown rolling and lubricants for the drawing units. The emulsions for the breakdown rolling are cleaned up by filtration, thus increasing the life time and reducing the amount of lubricant to be disposed for treatment. However, the lubricants used for the drawing steps are completely lost with the product and no oily materials have to be rejected from the drawing processes.

Annealing may be required as intermediate operation during the stepwise size reduction process in order to enable the fabrication of the different finished products of copper and copper alloys. For annealing a reducing atmosphere has to be maintained exogas or N2/H2

mixtures using as protection gas. Exogas is produced in reactors at site, N2/H2 mixtures are generated by mixing of pure gases which are purchased and stored at site in special tanks.

Annealing furnaces in use have inductive electrical or indirect gas-fired heating. Also pickling or degreasing operations may be required as finishing procedure for the products. As pickling solution, mainly sulphuric acid is used, for some special alloys mixtures of nitric and sulphuric acid are applied.

For degreasing the tubes after the final working down step chlorine/hydrocarbons or aliphatic hydrocarbons are in use. For some special products also alkaline solutions can be applied.

Chlorine hydrocarbons require gas capture and cleaning. Special chemicals are in use to

obtain special high standard surfaces of specific products. The chlorine/hydrocarbons containing vent gases from degreasing of the tubes after the final processing stage are treated in a reactor by passing through active carbon or resin. Loaded carbon is re-generated by treatment with steam, resin by treatment with hot air.

The fabrication scrap produced during the different size reduction steps is reused in the melting and casting shop. Cooling water is required for extrusion and for different other purposes. The cooling water for direct or indirect cooling is provided in once-trough systems or from circuits with re-cooling in cooling towers. Blowdowns are treated; solids as scale and oxides are separated and recycled.