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Copper Fabrication

Using metal plastic deformation method, copper ingots are processed into plates, strips, foils, pipes, rods, profiles and wires. The most important metal plastic processing methods are rolling, extrusion and drawing. Forging, deep drawing, copper spinning and other processing techniques can also be used. General specifications of copper and copper alloy processing materials: plate is (0.4~25)×(600~3000) mm; strip width is 600~1000 mm; foil thickness is 0.005~0.05 mm; pipe diameter can be up to 360 mm; capillary diameter As small as 0.5 mm; rod diameter 5~160 mm; wire diameter as small as 0.01 mm. Product supply status can be divided into five types: soft (M), hard (Y) and extra hard (T). The consumption of copper fabrication materials is second only to steel and aluminum, and is mainly used as electrical conductivity, thermal conductivity, corrosion resistance, wear resistance and advanced elastic materials.

There are many varieties of copper alloys, and their plastic processing properties vary greatly. Red copper and most brass, bronze and white copper have good hot workability, with a deformation temperature of 500 to 1050°C. Lead-containing alpha brass and lead-containing bronze, etc., because the low melting point lead is not dissolved in solid copper and is only distributed on the grain boundaries, it is easy to cause hot cracking during hot processing, so it is suitable for cold processing. Except for the aging of bronze alloys containing beryllium, chromium, zirconium, etc., deformed copper alloys are all work-hardened alloys. The hot and cold deformation rates of red copper, low-zinc brass, etc., which have the best plasticity, can reach more than 90%.

In the plastic processing of copper and copper alloys, in addition to ensuring stable and consistent mechanical properties, dimensional tolerances and surface quality of the products, the grain size of copper materials that require deep drawing performance must also be controlled. For example, brass grains are coarse and deep drawing This will cause “orange peel” to appear on the surface of the product. Generally, the deep drawing process requires the grain size of the thin plate to be 0.03 to 0.07 mm. In order to control the grain size of the product, the deformation amount and the intermediate annealing process system should be controlled during cold working; the heating temperature and final rolling temperature should be controlled during hot working. If the final rolling temperature is too high, the grains will continue to grow after coiling. These quality requirements are guaranteed by technology and equipment.

Smelting And Casting

The purpose is to obtain a melt with a certain chemical composition and temperature, remove gases and harmful impurities in the melt, and provide ingots for plastic processing. Alloys such as copper, brass, and bronze are generally smelted with an iron-core power frequency induction furnace with a furnace capacity of more than 12 to 15 tons. Two smelting furnaces and a holding furnace are used as a set to cast two flat ingots at the same time. In recent years, natural gas-fueled shaft furnaces are often used to smelt copper. After melting, the copper is sent to a holding furnace for casting. The launder is equipped with a protective gas nozzle. The furnace output is more than 10 tons per hour. Special alloys are sometimes smelted in high-frequency induction furnaces or medium-frequency induction furnaces. Copper and copper alloys, especially red copper, are highly absorbent during smelting. The gas dissolved in the metal will cause pores in the ingot. Logs and elements such as phosphorus and manganese are often used as deoxidizers; in order to prevent metal and low-melting point alloy elements from Evaporation and oxidation burning losses can be covered with charcoal or borax. Ingots are mainly cast by vertical semi-continuous, continuous or horizontal continuous casting. Horizontal continuous casting slabs have developed rapidly in recent years. The thickness of the cast slab can reach 10 to 20 mm. The thickness of the brass can reach 40 mm and the width can reach 800 mm. Some alloys use micro-stroke reverse thrust. Tin-phosphorus brass, lead brass, etc. that are difficult to hot-roll have been widely used. Horizontal continuous casting strips are milled and homogenized on the machine train and then rolled into coils. As cold-rolled strips, the coil depends on the rolling mill capacity. , can reach more than 5 to 10 tons, and the rapid component analysis of smelting can report the results in 3 minutes. When casting, the casting temperature, casting speed, cooling intensity and crystallizer height should be controlled.

Continuous casting and rolling technology has been applied to copper machining. Continuous casting in the continuous casting and rolling process mainly uses the moving mold forming method. According to the structure, it can be divided into three types: wheel-belt type, double-belt type and two-roller type. There are many types of continuous rolling mills. The strip rolling mill has 3 to 7 stands, and the wire rod rolling mill has as many as 18 to 23 stands. The thickness of the strip rolled out by the continuous rolling mill is 2 to 6 mm, and the diameter of the wire blank is 6 to 12 mm.

Sheet, Strip And Foil Production

Plate, strip, and foil are generally produced using the belt method, while extra wide plates are produced using the block method. Some still use the block method to produce plates, but the tolerances and shapes of the plates are poor, and the yield is also low. Nowadays, plate and strip production has developed into large-scale ingot rolling to improve quality, yield and production efficiency. The ingots weigh more than 10 to 12 tons. The ingot is heated in a walking furnace without face milling, hot-rolled to 10-14 mm by a two-roller reversing rolling mill, and rolled into a coil by a three-roller coiler. After the strip is milled by a double-sided milling machine, it is cold-rolled to 2 to 4 mm by a four-roller reversible or irreversible rolling mill, or a two-stand four-roller continuous rolling mill or a pendulum rolling mill, and then passed through a four-high rolling mill or an eight-high rolling mill. Three-stand four-high continuous rolling mill, twelve-high rolling mill, and twenty-high rolling mill roll strips or foils to required sizes. The cold rolling mill is equipped with hydraulic pressing, hydraulic roll bending, automatic thickness control system, flat shape controller and electronic computer control and recording storage device to ensure the accuracy and flatness of the rolled strip. The strip tolerance can reach 3~ 5 microns, the smallest can be ±1 micron. Water or emulsion is used as lubricant for hot rolling, emulsion is mostly used for intermediate rolling, and oil is used as lubricant for finishing rolling. It is equipped with a multi-stage cooling system with individually controlled nozzles to control the roll shape. Tin-phosphorus bronze and lead brass are cold rolled using horizontal continuous casting strips. The starting hot rolling temperature varies with the alloy, generally 650 to 1050°C. The total deformation of hot rolling can reach about 95%. The total deformation of alloys such as copper and low zinc brass can reach 60 to 90% after annealing, with low plasticity and complex The alloy is 40 to 60%. Different deformation amounts are selected for finishing rolling according to performance requirements. In order to ensure the flatness of plates and strips, tension and bending is sometimes used. The rolled strip is cut into required sizes by slitting and transverse shearing machines. In addition to being produced by rolling, copper foil can also be produced by electrolysis and is used in the electronics industry to produce printed circuits.

Pipe, Rod And Profile Production

Pipes are mainly made by extrusion or cross-rolling and perforation, and are made by cold rolling and drawing; they can also be directly produced by the extrusion process. Alloys such as lead brass and tin-phosphorus bronze that are difficult to thermally deform can also withstand hot extrusion deformation. Extrusion outflow speed: copper and brass can reach 5000 mm/second, while tin-phosphor bronze is only 30 mm/second. Maximum extrusion ratio: 500:1 for red copper and brass, 40:1 for bronze, and 20:1 for white copper. In addition to extrusion, bars and profiles are also billeted by pass rolling, and the finished products are drawn out. Extrusion and rolling can also be used to directly obtain finished products. The extrusion process is developed with long ingots and large extrusion ratio, water-sealed and oxidation-free extrusion.

The stretching of pipes and bars is mostly performed on a linear chain stretching machine, with an elongation coefficient of less than 2.0. Nowadays, we use ingots weighing 500 kilograms to produce pipe blanks through extrusion or cross-rolling and perforation, cold rolling with rapid three-line or single-line pipe rolling machines, and then using the moving core coil to stretch the pipe to produce pipes. The diameter of the coil can reach 2020 mm. Thin tubes are stretched using small diameter coiled tubing. The characteristics of pipe rolling are good metal deformation conditions, high elongation coefficient (4.5 to 12 for copper, 3 to 8 for brass), uniform wall thickness of the product and high internal and external surface quality, and is suitable for rolling alloys that are difficult to deform. Welded pipes are made of cold-rolled strips and produced by high-frequency welding or argon arc welding. The welded pipe blank is then stretched by a disc to produce pipes. This production process is rarely used.

Wire Production

The billet is supplied by extrusion, rolling or continuous casting and rolling, and the finished product is drawn out. The diameter of the wire blank is 6 to 12 mm. It is first drawn roughly on a single wire drawing machine, and then finely drawn on a multiple wire drawing machine. Thin wires are often finely drawn on a wire drawing machine in 18 to 25 passes. For copper and copper alloy wires, the total deformation rate between two annealings is about 90%. High lead brass, manganese brass, aluminum bronze, beryllium bronze, etc. are only 50 to 70%. Copper wire is mainly used as a conductive material. Generally, it needs to be annealed after cold drawing to improve the conductive properties.

Heat Treatment

Metal heat treatment during processing is divided into intermediate annealing, finished product annealing and solution-aging treatment. After hot rolling, the blank generally does not need intermediate annealing, which is only used when incomplete thermal deformation causes hardening. Intermediate annealing is to recrystallize the structure of the reprocessed material to facilitate continued cold processing. Annealing of finished products can improve the structure and eliminate residual stress, thereby controlling the mechanical properties of the product. The annealing temperature of copper and copper alloys is between 400 and 700°C, and the annealing temperature of the finished product to eliminate residual stress is as low as 75°C. Solid solution-aging treatment is only used for copper alloys that can be strengthened by heat treatment, such as beryllium bronze, aluminum-nickel copper and other alloys, and the quenching temperature is as high as 810°C. For the same alloy, the heat treatment temperature of thick-gauge products should be appropriately higher than that of thin-gauge products. To prevent oxidation, dezincification and discoloration, a protective atmosphere is introduced during annealing. Generally, bell-type furnaces, box-type furnaces or traction-type furnaces with strong circulation ventilation are used. In the past ten years, air cushion annealing furnaces have been widely used for annealing finished products of copper and copper alloy strips, and can obtain high-quality strips. In order to obtain products with good surface quality, vacuum heat treatment can also be used.