Drawn Cadmium Bronze Rod
Drawn cadmium bronze rod is produced through a cold-drawing process. It contains 98.5%-99% copper and 1%-1.5% cadmium. It exhibits high conductivity, strength, and excellent wear resistance, making it widely used in conductive and wear-resistant components such as motor commutators, switch contacts, and brush holders. Its diameter typically ranges from 5-100mm and its length from 1-6m. Its typical grade is QCd1.0. The addition of cadmium increases the copper’s strength by over 30% while maintaining an IACS conductivity exceeding 80%, making it one of the few copper alloys that offers both strength and conductivity.
The production process for drawn cadmium bronze rods involves key steps, including smelting, ingot casting, hot rolling, drawing, and annealing. First, electrolytic copper (purity ≥99.95%) and cadmium ingots (purity ≥99.9%) are smelted in a medium-frequency induction furnace at 1100-1150°C. Cadmium is added as an intermediate alloy (e.g., Cu-Cd10) to prevent burnout. Electromagnetic stirring ensures uniform composition, with a cadmium content tolerance of ±0.05%. Semi-continuous casting is used to produce round ingots with diameters of 80-150mm. The cooling rate is 80-100°C/min, followed by homogenization annealing (600-650°C for 4-6 hours) to eliminate compositional segregation. The ingots are then hot-rolled to 700-750°C and rolled into rods with diameters of 15-120mm. The reduction ratio per pass is 25%-35% to ensure a dense structure. Cold drawing is the core process for achieving high precision. It utilizes multiple passes, with a total deformation of 60%-80%, and a deformation of 15%-20% per pass. Graphite lubricant is used to reduce friction, resulting in a final diameter tolerance of ±0.05mm and a surface roughness of Ra ≤ 0.8μm. Intermediate annealing is performed under hydrogen protection at 350-400°C for 2-3 hours to eliminate work hardening and maintain a bar hardness of HV100-120, facilitating subsequent drawing. The finished product undergoes low-temperature annealing (200-250°C) as required to stabilize its dimensions and properties.
The performance advantages of drawn cadmium bronze rods make them irreplaceable in the field of electrical conductivity and wear resistance. First, it offers a balance of high strength and high conductivity. QCd1.0 has a tensile strength of ≥450MPa, a yield strength of ≥200MPa, and a conductivity of ≥80% IACS, far superior to brass (conductivity of 25%-35% IACS), making it suitable for components that both bear force and conduct current. Second, it offers excellent wear resistance, with a Brinell hardness of ≥120HB and a friction coefficient of ≤0.3. Under sliding friction conditions (such as contact between commutators and brushes), the wear rate is 60% lower than that of pure copper, extending its service life by 3-5 times. Third, it offers excellent corrosion resistance, with a corrosion rate of ≤0.01mm/year in air and transformer oil, and salt spray resistance of ≥300 hours after passivation. Fourth, it offers excellent machinability, enabling precision machining such as turning, milling, and drilling, with machining efficiency 40% higher than that of stainless steel, allowing the fabrication of complex contacts and terminals. Fifth, it offers excellent weldability, allowing for connections using argon arc welding and brazing, with the weld conductivity maintaining 90% of that of the parent material. The above ensures smooth current conduction.
Across various application scenarios, drawn cadmium bronze rods are a core material for high-end conductive components. In motor manufacturing, the commutator segments of large generators utilize QCd1.0 rods with a diameter of 50-80mm. These rods are machined into commutator segments to ensure stable contact during current switching. In switchgear, the moving contacts of high-voltage circuit breakers utilize cadmium bronze rods with a diameter of 20-30mm to withstand arc wear and mechanical stress during switching. In rail transit, the sliders of subway pantographs utilize drawn cadmium bronze rods with a diameter of 30-50mm to ensure reliable electrical connection and wear resistance to the contact network. In precision instrumentation, the conductive shafts of potentiometers utilize small-gauge rods with a diameter of 5-10mm, balancing conductivity and structural support. In aerospace, the waveguide components of airborne radars utilize cadmium bronze rods with a diameter of 10-20mm to ensure stable operation in high-altitude, low-pressure environments.
Industry trends indicate that drawn cadmium bronze rods are moving toward low-cadmium, high-precision, and multifunctional characteristics. Low-cadmium bronze rods (cadmium content 0.5%-0.8%) achieve this by adding trace amounts of rare earth elements (such as cerium and lanthanum) to reduce cadmium content (reducing toxicity) while maintaining high strength and conductivity, with a tensile strength exceeding 420 MPa. High-precision drawing technology is being promoted, with diameter tolerances controlled within ±0.01mm, meeting the precision requirements of micromotors. Surface coatings (such as silver and gold plating) further enhance conductivity and oxidation resistance, reducing contact resistance by 30%. Intelligent production technology, employing online hardness testing and dimensional monitoring, has increased product performance consistency to 99.5%. Environmentally friendly production processes are being refined, with the adoption of closed melting and cadmium recovery systems to reduce cadmium volatilization pollution and achieve a waste recovery rate exceeding 95%. With the development of new energy motors and high-end equipment, demand for high-performance drawn cadmium bronze rods will continue to grow, driving the industry to achieve greater breakthroughs in material optimization and green production.
