What Each Rod Material Actually Contains
Tin-phosphor bronze rod is a copper alloy containing tin and phosphorus, with copper as the base metal, 3 - 10 % tin and 0.03 - 0.35 % phosphorus. Tellurium copper rod is a copper alloy containing a small controlled addition of tellurium, usually between 0.4 % and 0.7 %, with the balance copper. Both are wrought rod products, both machine well compared with pure copper, and both are supplied in the round, hexagonal and square sections used on automatic lathes, but their property profiles are almost opposite.
Designation systems separate them clearly. Tellurium copper falls in the free-cutting copper group covered by ASTM B301 for free-cutting copper rod, bar, wire and shapes and by EN 12164 for rod for free machining purposes, in which the material is designated CuTe with the number CW118C. Tin-phosphor bronze rod and bar are covered by ASTM B139/B139M, with plate, sheet, strip and rolled bar covered by ASTM B103/B103M, by EN 12167 for copper alloy bars and profiles, and by JIS H3250 for copper and copper alloy rods and bars. The GB/T 5231 designation system lists both the tellurium-bearing copper grades and the tin-phosphor bronze grades, so an order written in any of these systems can be matched across.
Property Comparison
| Property | Tellurium copper rod | Tin-phosphor bronze rod |
|---|---|---|
| Main addition | 0.4 - 0.7 % tellurium | 3 - 10 % tin, 0.03 - 0.35 % phosphorus |
| Colour | Close to red copper, slightly darker | Bronze or brown |
| Electrical conductivity | About 93 % IACS | About 15 - 20 % IACS |
| Thermal conductivity | High, slightly below pure copper | Clearly lower than tellurium copper |
| Machinability | Excellent, suited to high precision and automatic lathes | Good casting and machining behaviour |
| Strength and wear | Moderate strength, good conductivity retained | High strength, high wear resistance, good fatigue performance |
| Corrosion resistance | Good; tellurium does not reduce copper corrosion resistance | Excellent in atmosphere and seawater |
The conductivity gap is the key number. Tellurium copper keeps conductivity near 93 % IACS because the addition is small and does not disturb the copper lattice appreciably; it exists to break chips during machining. Tin-phosphor bronze derives its strength, wear resistance and fatigue performance from the tin and phosphorus in solid solution and in hard phases, and those additions are exactly what reduce conductivity to 15 - 20 % IACS.
Applications of Each Material
Tellurium copper rod is used in the electrical and electronic industry for contacts and connectors that work under high current and mechanical stress, in mechanical manufacturing for high precision screws, nuts and connectors because of its cutting performance, and in mould making where a wear resistant, thermally conductive mould material is needed, particularly for plastics moulding. It is often selected where a lead-free free-machining copper is preferred to a leaded grade.
Tin-phosphor bronze rod is used for parts where mechanical duty dominates: gears, bearings, bushings, wear plates, springs and spring contacts, pump and valve components, and marine or chemical equipment where corrosion resistance in aggressive media is essential. It also machines and casts well enough to be used in complex shapes that would be difficult to form from a high conductivity copper.
How to Choose Between Them
The decision usually follows one question: does the part have to carry current or conduct heat, or does it have to resist load, wear and corrosion? Where high electrical and thermal conductivity is required, such as electrical contacts and high precision mechanical parts that also dissipate heat, tellurium copper rod is the better choice. Where high strength, wear resistance and good fatigue performance are required, such as gears, bearings and springs, tin-phosphor bronze rod is more suitable. Where corrosion resistance is the dominant requirement, especially in marine engineering and chemical equipment, tin-phosphor bronze rod is again the stronger option. When both conductivity and wear resistance are demanded, the usual solution is to use tellurium copper for the conducting body and a phosphor bronze or bronze insert for the wear surface.
Both materials are supplied as round, square, hexagonal and flat rod in a range of diameters, in the drawn, straightened and cut lengths suited to automatic machining, with chemical and mechanical certification for each heat and export packing for sea, air and courier transport.
Frequently Asked Questions
Q: What is the conductivity difference between the two rods?
A: Tellurium copper reaches about 93 % IACS, while tin-phosphor bronze is in the range of 15 - 20 % IACS. Tellurium copper is therefore the conductor grade and phosphor bronze the mechanical grade.
Q: Why is tellurium added to copper?
A: The 0.4 - 0.7 % tellurium addition breaks chips and lubricates the cutting edge, so the alloy machines far better than pure copper while retaining nearly the conductivity of a high purity copper.
Q: Which rod is better for seawater service?
A: Tin-phosphor bronze. Its tin content gives excellent corrosion resistance in atmospheric and marine environments, which is why it is used for marine and chemical equipment components.
Q: What standards cover these rods?
A: Tellurium copper rod is covered by ASTM B301 and EN 12164 as CuTe / CW118C, while tin-phosphor bronze rod and bar are covered by ASTM B139/B139M, EN 12167 and JIS H3250, with GB/T 5231 designations for both families.
Q: Can the two be used in the same assembly?
A: Yes. A common solution is a tellurium copper conductor body combined with a wear resistant phosphor bronze insert, which delivers conductivity and mechanical durability in one component.
Q: What forms are supplied?
A: Both materials are produced as round, square, hexagonal and flat rod in multiple diameters, drawn and straightened to length, with chemical and mechanical certificates for each heat.
