Consider Thread Rolling

Rolled threads have many advantages to offer. Economy, strength, accuracy. Fine surface finish. Unusually high rates of production. Less material cost. No chips

Cold forming is perhaps the best description of the thread rolling process. A cylindrical blank having an outside diameter between the major and minor diameters of the finished thread is rotated between hardened steel dies bearing the reverse thread form. The die threads penetrate the blank surface to form the thread roots and displace material radially outward to form the crests. Unlike other threading processes, metal is neither removed nor wasted, but displaced.

The cold forming that threads receive during the rolling process strengthens them in three ways: tension, shear, and fatigue resistance. Static tensile tests have reported increases in the ultimate strength of the parts of approximately 30 percent.

Thread grain structure is not severed, it is instead reformed in continuous unbroken lines following the thread contours. Rolled threads have increased resistance to stripping because such failures are compelled to take place across, rather than with, the grain flow.

Fatigue resistance is realized in several ways. Threads are produced with burnished roots and flanks, free from surface imperfections that might prove to be starting points for fatigue failure. Surface layers of the thread, particularly those in the roots, are stressed in compression. These compressive stresses must be overcome before the tensile stresses that cause fatigue failure can be built up. Fatigue strength is reported to be improved by 50-75 percent. Tests on bolts first heat-treated to a hardness of 35-40 Rockwell C and subsequently rolled, show an increased fatigue strength.

Approximate Percentage of Material Saved by Thread Rolling

Thread Size Savings 1⁄4–20 25% 5⁄16–18 22% 3⁄8–16 21.5% 7⁄16–14 20% 1⁄2–13 19.25% 5⁄8–11 18.75% 3⁄4–10 17% 7⁄8–9 16% 1–8 16% 11⁄4–7 14.5% 11⁄2–6 14% 13⁄4–5 14% 2–41⁄4 14% 21⁄2–4 12.6%

 

Tesker Manufacturing Corporation
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