Cleaning and Coating (2)

Moderatore: Moderatore Area Tecnica

Cleaning and Coating (2)

Sostienici

Sponsor
 

Cleaning and Coating (2)

Messaggioda Aldebaran » 02/07/2010, 22:16

Rope Wire
Rope wire is produced primarily for use in the construction of wire rope. The principal grades of rope wire are level 1, 2,
3, and 4 wires, each with its own requirements with respect to tensile and torsional properties. The tensile strength
requirements for these grades are shown in Fig. 2. The torsion testing of rope wire is usually done on a 203 mm (8 in.)
length of the wire held between the jaws of a torsion testing machine. Minimum torsion requirements are based on the
following formulas:
Galvanized rope wire can be galvanized either before or after drawing to finished size. When galvanizing is done at
finished size, the strength requirements are 10% less than those for uncoated rope wire, and the torsion test requirements
are reduced 30 to 50%, depending on size. Rope wire that is galvanized before being drawn to finished size meets the
tensile and torsional properties of uncoated wire except as indicated in the above formulas for level 4 steel wire drawn
after galvanizing. Wire galvanized at finished size can be produced on levels 1, 2, and 3.
Wire for Fasteners
Included in wire for fasteners is wire intended for such applications as bolts and cap screws, rivets, wood and self-tapping
screws, and scrapless nuts. Depending on the application, such wire must be able to be forged, extruded, cold upset, roll
or cut threaded, drilled, and hardened by suitable thermal treatment.
The type and grade of steel used in wire for fasteners depend on the requirements of the finished product and the nature of
the required forming operations. Compositions range from that of 1006 grade steel, which is used for such items as
common rivets, to that of a 0.55 to 0.65% C steel intended for lockwashers or screwdrivers. Low-carbon wire can be
drawn from hot-rolled slow-cooled rod. Medium-carbon and high-carbon wire rod can be either annealed or spheroidized
in-process.
The coating on the wire must provide sufficient lubrication in the header dies and must have the necessary lubricating
qualities to prevent galling or undesirable die wear. Although lime-soap coatings are common, phosphate coatings are
frequently used for more demanding applications. Producing phosphated wire may involve coating the cleaned rod or
process wire with zinc phosphate and then coating with lime or borax to carry the lubricant during subsequent drawing.
It is important that the wire be internally homogeneous and free of seams and other surface imperfections.
Decarburization must be held to a minimum for those products that are to be hardened by thermal treatment.
Mechanical Spring Wire for General Use
The several types of steel wire used for mechanical springs are produced in a variety of chemical compositions, but the
primary consideration is that the wire have the specific properties necessary for the application. The required properties
vary with the intended use of the spring and with the problems involved in its fabrication. The factors governing the
selection of spring wire include:
• The load range through which the spring must operate
• The corresponding stress range for the wire
• Weight and space limitations
• Expected life of the spring
• Temperatures and other environmental conditions to be encountered in service
• Severity of deformation to be encountered during fabrication
As stress on the wire is increased, wire with higher strength is required. Because the surface of the wire is the most highly
stressed part of a spring and because spring motion gives rise to torsion effects, freedom from surface imperfections
becomes increasingly important as maximum stress or required service life is increased. Surface condition is very
important in music spring steel wire and is even more important in valve spring quality wire. The characteristics of
springs are discussed in the article "Steel Springs" in this Volume.
There are three types of spring wire for general use:
• Hard-drawn spring wire (covered in ASTM A 227 and A 679)
• Oil-tempered spring wire (ASTM A 229)
• Spring steel wire for thermal-treated components (ASTM A 713)
Music spring steel wire is used in springs that are subject to high stresses and require good fatigue properties. Final
cold drawing is commonly performed by the wet white liquor method to develop a characteristic smooth bright luster.
Phosphated music wire is also common. Manufacturers employ specialized coiling tests, twist tests, torsion tests, and
bend tests to verify that the exacting requirements of this type of wire are met. Specification ASTM A 228 describes
music spring steel wire in detail. Tensile strength ranges are given in Table 14.
Mechanical Spring Wire for Special ApplicationsMechanical spring wire for such applications as automotive hood hinge springs, sewer augers, torque rods, and valve
springs is specially designed for each application. One such material is oil-tempered valve spring quality carbon steel wire
(ASTM A 230). Steel wire that is oil tempered for mechanical springs is defined in ASTM A 229 and A 679. Another is
over-head door spring steel wire. Depending on design and conditions of service, making springs from the latter material
may involve coiling with high initial tension and sharp bending to produce the required end formations, and the springs
may be subjected to repetitive applications of high stress in service. Typical tensile strengths are shown in Table 15.
Upholstery Spring Construction WireUpholstery spring construction wire includes the several types of wire used for upholstery springs, plus the wires
employed for borders and braces, hog rings, links, and frames. Upholstery spring wire is used in the manufacture of
springs for mattresses, bed springs, and related applications. This type of spring wire is not intended for the manufacture
of other types of springs. Upholstery spring wire is drawn from thermally treated or controlled cooled wire rod or wire.
The producer determines manufacturing practice and selects specific carbon and manganese ranges within approximately
0.45 to 0.75% and 0.60 to 1.20%, respectively, to meet end-use requirements.
Upholstery spring wire is commonly produced with a dry-drawn finish and in sizes from 20 to 4 gage (0.89 to 5.72 mm,
or 0.035 to 0.225 in.). Specification ASTM A 407 covers specifications for wire used in producing the various types of
coil springs in common use. Table 16 lists the tensile strength ranges for one such type of wire.
Wire for Upholstery Springs. Zig-zag, square-form, and sinuous-type springs, which are extensively used in
furniture, are made from hard-drawn carbon steel wire produced from controlled cooled rods, patented rods, or patented
wire. These wires are commonly produced in 13 to 8 gage (2.34 to 4.11 mm, or 0.92 to 0.162 in.). Full requirements are
covered in ASTM A 417. Tensile strength ranges for this type of wire are given in Table 17.
Upholstery spring wire is also produced for Marshall spring wire types (open wound, not knotted) and lacing helical
springs (ASTM A 407). Border and brace wires, generally of lower tensile values, are produced as round wire
reinforcements or for cold-rolling purposes.
Wire for Other Specific Applications
Steel wire for miscellaneous specific applications includes wire for such diverse products as brush handles, clothes
hangers, chains, cotter pins, screens, staples, and steel wool. Two products for which substantial quantities of wire are
used are chain link fences and construction wire for automobile tires.
Chain link fence wire is a low-carbon or medium-low-carbon steel wire suitable for the production of chain link fence
fabric. It is produced in diameters of 3.05, 3.76, and 4.88 mm (0.120, 0.148, and 0.192 in.) and is supplied uncoated (for
zinc coating after weaving), zinc coated prior to weaving, or aluminum coated prior to weaving.
Zinc-Coated Fence Wire. Requirements for zinc-coated chain link fence fabric, which is zinc coated either before or
after weaving, are covered in ASTM A 392.
Aluminum-Coated Fence Wire. Requirements for aluminum-coated chain link fence fabric are covered in ASTM A
491. This wire is always aluminum coated before weaving.
Tire bead wire is used for reinforcing the beads of pneumatic tires. Uniformity in chemical and mechanical properties
and a surface finish to which rubber will adhere are essential for satisfactory performance. Tire bead wire is most
commonly produced 0.94 mm (0.037 in.) in diameter and brass plated. Mechanical property tests are conducted on wire
samples that have been heated for 1 h at 150 °C (300 °F). Minimum breaking strength for wire 0.94 mm (0.037 in.) in
diameter is 129 kg (285 lb). In torsion testing, the wire must withstand a minimum of 58 twists in a 203 mm (8 in.) gage
length.
A considerable and growing quantity of wire between 0.18 and 0.38 mm (0.0069 and 0.015 in.) in diameter is used
annually for the purpose of providing cord reinforcement for radial tires. This extremely fine, high-tensile wire is
produced from controlled cooled rods by drawing, followed by drawing, patenting, and a second drawing and patenting.
After the second patenting operation, the wire is brass plated wet drawn and then formed into strands to be embedded into
the tire rubber.
Fine Wire
Fine wire is considered to include all wire less than 0.89 mm (0.035 in.) in diameter, as well as some coarser wire up to
1.57 mm (0.062 in.) in diameter when so designated. Fine wire is commonly produced with bright, liquor, coppered, or
phosphate finishes; with galvanized, tin, or cadmium coatings; and in the hard-drawn, annealed or oil-tempered
conditions. Aircraft cords, broom wire, brushes, fishhooks, florist wire, hose reinforcement, paper clips, insect screens,
and safety pins are examples of items produced entirely or in part from various kinds of fine wire.
Aircraft cord wire is a hard-drawn, high-tensile-strength, high-carbon steel wire designed for the manufacture of
flexible cords and multiple-wire strands for aircraft controls. This type of wire is usually either tin coated or zinc coated.
Common sizes range from 0.18 to 0.81 mm (0.007 to 0.032 in.) in diameter.
Hose-reinforcing wire is a hard-drawn grade commonly furnished in three tensile ranges: 2070 to 2410 MPa (300 to
350 ksi), 2240 to 2590 MPa (325 to 375 ksi), and 2410 to 2760 MPa (350 to 400 ksi). Sizes up to 0.508 mm (0.020 in.) in
diameter are provided in all ranges. Sizes over 0.508 mm (0.020 in.) are furnished in the lower two ranges. The wire
should be sufficiently ductile to wrap around a mandrel four times the wire diameter without fracture.
Paper clip wire is low-carbon steel wire of relatively high strength. It can be tinned or drawn after galvanizing, or it
can have a liquor or copper finish. Diameters of 1.02, 0.91, and 0.80 mm (0.040, 0.036, and 0.0315 in.) are most common.
In these sizes, tensile strength is about 970 MPa (140 ksi).
Safety pin wire is supplied in two grades. The high-carbon grade has a tensile strength of approximately 2210 MPa
(320 ksi), while the low-carbon grade has approximately 1280 MPa (185 ksi).
Alloy Wire
The chemical compositions, quality descriptions, requirements, and tests applicable to alloy wire are described in the
article "Steel Wire Rod" in this Volume. Many alloy steel wires have been developed for specific applications, which
include wires for bearings, chains, and springs, and for cold-heading and cold-forging applications. Several of these are
described in the following sections.
Alloy steel wire for ball and roller bearings is produced by practices that ensure internal soundness, cleanliness,
uniformity of chemical composition, and a good surface. High-carbon chromium steels, such as E51100 and E52100, are
commonly used for ball bearings. Roller bearings are made from high-carbon wires or from low-carbon case-hardening
steels such as 4620 and 8620.
Alloy steel wire for heading, forging, and roll threading is produced by specially controlled manufacturing
practices and is subjected to mill tests and inspection to ensure internal soundness, uniformity of chemical composition,
and freedom from surface imperfections. These precautions are necessary to provide satisfactory heading and forging
performance and proper response to subsequent thermal treatment.
Alloy steel wire for upsetting or forging is commonly produced in one of the following conditions:
• Wire drawn from spheroidize-annealed hot-rolled coils
• Wire spheroidize annealed in process
• Wire spheroidize annealed at finished size
Generally, alloy steel wire for cold heading and cold forging is spheroidize annealed in-process. This permits a light
finishing draft in which the wire is given a special coating finish to facilitate cold forming. There are cases, however
(especially with high-carbon wire), in which the severity of cold work requires spheroidize annealing to be done at
finished size. Specification ASTM A 547 covers alloy steel wire for trimmed hexagon-head bolts.
Alloy Steel Wire for Welded Chains. Chains made from alloy steel wire are generally used for slinging, hoisting,
and load-binding purposes. The wire for these chains must have high strength and good abrasion resistance. In addition,
the carbon content is generally held to a maximum of 0.25% to facilitate electric welding during fabrication of the chains.
Typical grades of alloy steel that satisfy these requirements are 4615, 4620, 4320, 8620, and 8622. The wire is generally
furnished in the spheroidize-annealed condition so that the amount of springback between the ends of the formed links
does not interfere with welding.
Alloy steel spring wire is used for the manufacture of springs intended for operation at moderately elevated
temperatures. Three grades in common use are 6150 chromium-vanadium steel, SAE 9260 silicon manganese, and 9254
chromium-silicon steel, which are covered in ASTM A 231, A 232, and A 401, respectively. ASTM A 877/A 877M also
covers chromium-silicon grades; ASTM A 878/A 878M covers a grade of modified chromium-vanadium steel valve
spring quality wire.
The wire is commonly produced in one of four conditions: oil tempered, spheroidize annealed, annealed in-process, and
patented in-process. Oil-tempered alloy spring wire, commonly produced in diameters up to 12.7 mm (0.500 in.) to tensile
strength or hardness requirements, is intended for very light forming and is generally used for coiling into common types
of springs. Table 18 lists tensile strength ranges for several oil-tempered wires. Annealed alloy spring wire, produced in
diameters up to 15.9 mm (0.625 in.), is used for severe cold forming or coiling (when annealed in process) or for very
severe cold forming or coiling (when annealed at finished size) before hardening and tempering. Tensile strength is not
commonly specified for annealed wire.
Mechanical Properties: Round Wire Versus Flat WireMost round wire is produced and tested to required tensile ranges. With flat wire, the calculation of tensile strength is
inaccurate because of the difficulty of determining the cross-sectional area as a result of the round edges and corners on
the wire. Flat wire is therefore produced and tested to required hardness ranges.
Hardness and tensile properties are related, but a degree of caution must be exercised in converting one to the other. The
standard conversion charts are not accurate for wire. Wire has very directional properties because its grain structure has
been cold worked in only one direction. Generally, at a given hardness, wire has a higher tensile strength than that listed
in the standard conversion charts.
Avatar utente
Aldebaran
 
Messaggi: 5368
Images: 4810
Iscritto il: 31/03/2010, 19:26
Località: Milano - Chieti

Torna a Iron & Steel

Chi c’è in linea

Visitano il forum: Nessuno e 1 ospite