C360 C36000 Brass

This paper is intended as a brief primer on Free Cutting Brass, UNS C36000. Free-Cutting Brass, which many people know by it's traditional name, CDA Alloy 360, is the most important commercial copper alloy, surpassing all but copper itself in terms of annual consumption. Exact quantities are difficult to calculate, but over 600 million pounds of Free Cutting Brass are consumed in the U.S. each year.

Despite this large usage, brass is underutilized as an automatic screw machine feedstock. Perhaps ten times more leaded steel is used than Free Cutting Brass. In general industrial products, and brass screw machine parts are scarce enough today in automotive vehicles to be listed as an endangered species.

Are the properties of leaded steel uniquely needed when making screw-machine parts? Is leaded steel so cheap that brass can only be justified for a small number of specialty products? Or, as some suspect, is steel specified more out of tradition than actual need... or simply in error based on off-the-shelf cost considerations that neglect actual net cost?

CDA surveyed engineers, designers, purchasing agents and automatic screw machine operators to find the answers.

In short, CDA found that while most automotive designers and engineers know a little bit about Free Cutting Brass, few individuals surveyed know enough about the material to consider specifying it for automotive products. Clearly, the brass industry is facing an information gap. Here, then, is some basic information about Free-Cutting Brass: how it is made, what it's properties are and what advantages it offers to automotive designers.

C36000 Brass Seamless Tubes Standard Specification:

C360 Free Cutting Brass Most common brass, excellent high speed machining operations and superior thread rolling and knurling characteristics. Easily soldered and brazed and has very good resistance to corrosion.

Fair to excellent corrosion resistance. Excellent machinability. Fabricated by machining, roll threading and knurling.

Applications: gears, pinions, automatic high-speed screw machine parts.

C36000 Free Machining Brass / Free Cutting Brass is ideally suited for high speed machining operations with its superior machinability, thread rolling and knurling characteristics. Its machinability rating of 100 is standard against which all other copper alloys are rated. It is easily soldered or brazed and has good resistance to corrosion.

Typical Application of C36000 CDA 360 / CuZn36Pb3 - Free Machining Brass

• ARCHITECTURE: Terrazzo Strip
• AUTOMOTIVE: Sensor Bodies, Threaded Inserts for Plastic, Fluid Connectors, Thermostat Parts
• BUILDERS HARDWARE: Lock Bodies, Hardware, Fittings
• CONSUMER: Hot Combs (to Straighten Hair)
• FASTENERS: Bolts, Nuts, Screws
• INDUSTRIAL: Faucet Components, Pneumatic Fittings, Fluid Connectors, Automatic Screw Machine Parts, Unions, Adapters, Screw Machine Products, Gauges, Valve Seats, Valve Trim, Valve Stems, Nozzles, Pinions, Gears
• PLUMBING: Plumbers' Brass Goods, Faucet Stems, Faucet Seats, Plumbing Fittings

Figure 5
Figure 6

Free-Cutting Brass is almost always supplied in the half-hard (HO2) temper for screw machine applications, although soft annealed (060) and Hard (HO4) tempers are also available for special-purpose applications. Most screw machine feedstock is sold in round and hexagonal rod in sizes ranging from 12 to 38 mm (to 1 1/2 in). Smaller and larger-diameter rods, as well as octagonal rod, square and rectangular bar, flats and a wide variety of standard and custom shapes are also available,Figure 6. Domestically produced products must conform with the requirements of ASTM B 16.

Many designers are surprised to learn that in the half-hard condition, C36000's properties are roughly comparable with steel. Actually, brass's strength falls in a range between hot rolled and hot-rolled and cold reduced AISI 12L14 leaded steel. The properties data in Table 1 show that specifying hard C36000 in place of cold-drawn leaded steel entails a sacrifice of only about 10% in yield strength. Notice the two sets of mechanical properties for brass: the lower values represent the specification minimums as given in ASTM B 16; the higher set represents typical or nominal values.

On the basis of strength alone, brass can safely be substituted for leaded steel in the majority of common screw machine products. Such products have modest to intermediate strength requirements (AISI 12L14 is not heat-treatable, for example).

Figure 7

Machinability

The most important feature of C36000 is, of course, its unexcelled machinability. No material of comparable strength machines faster and produces better surface finishes than Free-Cutting Brass. Brass's two-phase structure tends to form broken chips instead of continuous coils, which would interfere with high speed machining. Lead acts synergistically with the alpha-beta structure, causing chips to shatter into tiny fragments. Lead also provides some internal lubrication against the surface of the cutting tool.

Maximum recommended form-tool and single-point cutting speeds for Free-Cutting Brass are between 300 and 1,000 sfm (surface feet per minute) with high speed steel tooling and between 500 and 1,600 sfm with carbide. Corresponding maximum speeds for leaded steel range between 200 and 300 sfm (about 10% higher in proprietary resulfurized, rephosphorized, tellurium- or selenium-treated grades). Screw-machine operators tend not to run their equipment at maximum speed for either brass or steel and therefore don't take full advantage of brass's high-speed capability, but the difference between these "handbook" machinabilities for brass and steel shows what could be accomplished, if pursued. In fact, Free-Cutting Brass's machinability far surpasses the speed capacities of today's fastest commercial machine tools. Major breakthroughs are still a few years into the future, but ultra-high speed machining at up to 18,000 sfm (5,500 meters per minute) has already been demonstrated on a pilot scale in Europe.

Brass's high machinability also means measurably better surface finishes than can be achieved with leaded steel, even at brass's faster cutting speeds and higher feed rates. Dimensional control is simpler with Free-Cutting Brass because of substantially reduced tool wear. Fewer out-of-tolerance parts mean lower rejection rates and lower net production costs.

seamless tube and ferrule stock of copper and various copper

alloys up to 31⁄8 in. [80 mm] inclusive, in diameter, for use in

C71000 . . . 80-20 Copper-Nickel

C71500 . . . 70-30 Copper-Nickel

surface condensers, evaporators, and heat exchangers. The following coppers and copper alloys are specified:3 (Warn- ing—Mercury is a definite health hazard in use and disposal.

C71520

C71640

70-30 Copper-Nickel—

Welding Grade Copper-nickel-iron- manganese

(See 12.1.))

Copper or Copper Alloy UNS No.

Previously Used

Designation Description

C72200 . . . . . .

A Designations listed in Classification B224.

Tubes of Copper Alloy UNS No. C19200 shall be supplied in any one of the following tempers, one of which

Temper

C23000 99.8

C28000 99.7

C44300 99.6

C44400 99.6

C44500 99.6

C68700 99.5

shall be specified: (1) annealed (O61), (2) light-drawn (H55),

(3) hard-drawn (H80), or (4) hard-drawn, and end-annealed (HE80).

TABLE 3 Tensile Requirements—SI Values

NOTE 1—See Table 2 for tensile requirements—inch-pound values.

C60800, C61300, C61400, and C68700 be subjected to a stress-relieving thermal treatment subsequent to straightening. If required, this must be specified on the purchase order or contract. Tolerances for roundness and length, and the condi- tion of straightness, for tube so ordered, shall be to the requirements agreed upon between the manufacturer and the purchaser.

Mechanical Properties

Material specified to meet the requirements of the ASME Boiler and Pressure Vessel Code shall have tensile properties as prescribed in Table 2 or Table 3.

Grain Size for Annealed Tempers

Grain size shall be a standard requirement for all product in the annealed (O61) temper.

Samples of annealed-temper tubes selected for test shall be subjected to microscopical examination per Test Methods E112 at a magnification of 75 diameters and shall show uniform and complete recrystallization.

Products other than of Copper Alloy UNS Nos. C19200 and C28000 shall have an average grain size within the limits of 0.010 to 0.045 mm. These requirements do not apply to tubes of light-drawn (H55), hard-drawn (H80), hard-drawn and end-annealed (HE80), or drawn and stress-relieved tem- pers (HR50).

Expansion Test

Tube specimens selected for test shall withstand the expansion shown in Table 4 when expanded in accordance with

Test Method B153. The expanded tube shall show no cracking or rupture visible to the unaided eye.

Hard-drawn tubes not end annealed are not subject to this test. When tubes are specified end annealed, this test is required and shall be performed on the annealed ends of the sampled tubes.

Tubes for ferrule stock are not subject to the expansion test.

Test Method—Each test specimen shall be flattened in a press at three (3) places along the length, each new place to be rotated on its axis approximately one third turn from the last flattened area. Each flattened area shall be at least 2 in. in length. A flattened test-specimen shall allow a micrometer caliper set at three (3) times the wall thickness to pass freely over the flattened area. The flattened areas of the test specimen shall be inspected for surface defects.

During inspection, the flattened areas of the test- specimen shall be free of defects, but blemishes of a nature that do not interfere with the intended application are acceptable.

Tubes for ferrule stock are not subject to flattening test.

Residual Stress Test

A residual stress test, when specified in the purchase order, is required only for Copper Alloy UNS Nos. C23000, C28000, C44300, C44400, C44500, C60800, C61300, C61400, and C68700 and when not supplied in an annealed temper.

Unless otherwise specified, the producer shall have the option of testing the product to either the mercurous nitrate test, Test Method B154, or the ammonia vapor test, Test Method B858, as prescribed below.

1. Mercurous Nitrate Test:

   1. Warning—Mercury is a definite health hazard and therefore equipment for the detection and removal of mercury vapor produced in volatilization is recommended. The use of rubber gloves in testing is advisable.

   2. The test specimens, cut 6 in. [150 mm] in length, shall withstand without cracking, an immersion in the standard mercurous nitrate solution prescribed in Test Method B154. The test specimen shall include the finished tube end.

2. Ammonia Vapor Test:

   1. The test specimens, cut 6 in. [150 mm] in length, shall withstand without cracking ,the ammonia vapor test as prescribed in Test Method B858. For the purposes of this specification, unless otherwise agreed between purchaser and supplier, the risk level identified in the Annex of Method B858, shall be specified as risk level (pH value) of 10.

Nondestructive Testing

Each tube shall be subjected to the eddy-current test in

13.1.1. Tubes may be tested in the final drawn, annealed, or heat-treated temper or in the drawn temper before the final anneal or heat treatment unless otherwise agreed upon by the supplier and the purchaser. The purchaser may specify either of the tests in 13.1.2 or 13.1.3 as an alternative to the eddy-current test.

Eddy-Current Test—Each tube shall be passed through an eddy-current testing unit adjusted to provide information on the suitability of the tube for the intended application. Testing shall follow the procedures of Practice E243.

The depth of the round-bottom transverse notches and the diameters of the drilled holes in the calibrating tube used to adjust the sensitivity of the test unit are shown in Tables 5 and 6, and Tables 7 and 8, respectively.

Tubes that do not actuate the signaling device of the eddy-current tester shall be considered to conform to the requirements of this test. Tubes causing irrelevant signals because of moisture, soil, and like effects may be reconditioned and retested. Such tubes, when retested to the original test parameters, shall be considered to conform if they do not cause output signals beyond the acceptable limits. Tubes causing irrelevant signals because of visible and identifiable handling marks may be retested by the hydrostatic test prescribed in 13.1.2, or the pneumatic test prescribed in 13.1.3. Tubes meeting requirements of either test shall be considered to conform if the tube dimensions are within the prescribed limits, unless otherwise agreed upon between the manufacturer and the purchaser.

Hydrostatic Test—Each tube shall stand, without showing evidence of leakage, an internal hydrostatic pressure sufficient to subject the material to a fiber stress of 7000 psi [48 MPa] as determined by the following equation for thin hollow cylinders under tension. The tube need not be tested at a hydrostatic pressure of over 1000 psi [7.0 MPa] unless so specified.

P 5 2St/~D 2 0.8t!

where:

P = hydrostatic pressure, psig [MPa];

t = thickness of tube wall, in. [mm];

D = outside diameter of the tube, in. [mm]; and

S = allowable stress of the material, psi [MPa].

Pneumatic Test—Each tube shall be subjected to an internal air pressure of 60 psig [400 kPa], min, for 5 s without