Heat exchangers and condensers place conflicting demands on a metal: the tubes must conduct heat well, while the supporting structures must resist vibration, erosion and chloride attack without deforming. C28000 extra hard round bar resolves that conflict by supplying the 60/40 copper-zinc alloy already work hardened, so components such as tube plates, baffle spacers, tie rods and machined fittings reach their required stiffness without post-forming heat treatment.
Where Extra Hard Round Bar Is Used
C28000, widely known as Muntz metal, contains approximately 60 % copper and 40 % zinc. In the extra hard temper the bar carries a high dislocation density from the last cold reduction pass, which raises yield strength and hardness while retaining enough residual ductility for threading, grooving and light bending. Maintenance departments and OEM fabricators use the grade for tube sheets and support plates of shell-and-tube exchangers, condenser water-box fittings, spacer bars, wear strips and studs, and for machined bushes that operate in wet, mildly corrosive service.
Composition and Governing Standards
| Item | Requirement |
|---|---|
| Copper (Cu) | 59.0 – 63.0 % |
| Zinc (Zn) | Balance |
| Lead (Pb) | Low residual, per the applicable product standard |
| Density | 8.39 g/cm³ |
| Seamless tube standard | ASTM B135 |
| Condenser and heat exchanger tube | ASTM B111 |
| Plate, sheet, strip and rolled bar | ASTM B36 |
| Japanese rod and bar designation | JIS H3250, grade C2800 |
Temper is declared using the ASTM B601 system. Round bar in the extra hard condition is ordered as a work-hardened temper line, and the minimum tensile strength and elongation that apply to that line are read directly from the governing standard. Bar is supplied in the drawn, extruded or rolled condition depending on diameter, with straightness, ovality and diameter tolerance agreed at order stage.
Thermal, Electrical and Mechanical Behaviour
| Property | Value |
|---|---|
| Thermal conductivity | about 120 W/(m·K) |
| Electrical conductivity | about 28 % IACS |
| Modulus of elasticity | about 103 GPa |
| Coefficient of thermal expansion | about 20.9 × 10⁻⁶ /K |
| Melting range | approximately 900 – 940 °C |
In an exchanger the bar seldom carries the thermal duty itself; it supports the tubes and machined parts that do. Its electrical and thermal conductivity nevertheless matter for earthing straps, current-carrying fittings and brazed joints, where the 60/40 alloy gives dependable performance without the cost of a high-conductivity grade. Cold work raises strength and reduces conductivity only slightly, so the extra hard temper remains acceptable for these duties.
Machining, Threading and Assembly Practice
Machining: the beta phase gives the alloy a short chip and respectable machinability; positive rake tooling and moderate cutting speeds with flood coolant are standard practice.
Threading: extra hard bar holds thread form well and resists thread stripping, which is useful for tie rods and studs in vibrating service.
Drilling tube sheets: use sharp, correctly ground drills and avoid generating heat, because local overheating can soften the temper around the hole.
Joining: brazing and soldering are straightforward; welding requires controlled heat input and, in most exchanger assemblies, is replaced by rolling or brazing the tubes into the sheet.
Distortion control: keep machining passes balanced on both sides of a plate and finish with a light pass to limit residual stress movement.
Seawater and Condenser Service
C28000 has a long record in marine and condenser environments: it resists salt spray well, tolerates the neutral to slightly alkaline water chemistry of cooling circuits and holds up where mechanical erosion accompanies the flow. Two precautions belong in the specification: keep water velocity inside the range recommended for the tube system so that impingement attack does not start, and remember that high-zinc brasses can dezincify in aggressive chloride waters, which is why water chemistry is reviewed where the alloy faces continuous sea water. When the partial pressure of ammonia or sulphide is high, a copper-nickel grade is specified instead.
FAQ
Q: What does "extra hard" mean for C28000 bar?
It is a work-hardened temper produced by a final cold reduction, giving high strength and hardness while retaining enough ductility for threading and light bending.
Q: What is the difference between C28000 and C26000 bar?
C28000 contains about 60 % copper and is stronger and harder; C26000 contains about 70 % copper and is chosen where ductility and deep forming matter more than strength.
Q: Is C28000 bar suitable for sea water service?
Yes, with a review of water chemistry and flow velocity; where chlorides are aggressive and continuous, dezincification resistance is assessed before the grade is approved.
Q: How are round bar dimensions specified?
By diameter, diameter tolerance, length, straightness, temper and the governing standard, with the temper designation taken from the ASTM B601 system.
Q: Can C28000 bar be welded?
It can be brazed easily and welded with controlled heat input, but exchanger assemblies usually roll or brace tubes into the sheet instead of welding.
Q: Why is brass bar used for tube sheets?
It offers strength, machinability and corrosion resistance at a moderate cost, and it machines cleanly into accurate holes for tube rolling.
