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Because cold drawn bars are strengthened by drawing process, they are sometimes used by design engineers to gain strength in parts without expensive heat treating. This, added to their easier machinability, means energy savings.
The close tolerances to which cold finished steel bars are produced permit much smoother working collets. Adjustments need not be made for extreme under - and over-size variations.
These same accuracies, together with the smooth surface finish of a cold finished bar may reduce the need for all-over machining.
A cold finished bar is bright and smooth and has a metallic luster. The surface does not need to be machined for the sake of accuracy or appearance. The finest accuracy and appearance are, of course, found in the ground and polished bars.
A cold finished steel bar is straight. It feeds out easily in machining and works efficiently in the reels. Higher revolutions pre minute are practicable because of less machine vibration with cold finished steel.
Cold drawing is a cold working operation and, as such, increases both the tensile and yield strengths of steel. The yield strength is usually about doubled. Ductility is reduced somewhat while hardness is increased. It should be kept in mind that the center of a cold drawn bar, as a general rule, is cold worked to essentially the same degree as are the zones nearer the surface and consequently, these properties are changed the same amount through the bar.
Newer speciality steels included in this book provide strengths from well over 100,000 psi to above 150,000 psi tensile in-the-bar and require NO HEAT TREATMENT. These steel bars, developed exclusively by Niagara LaSalle, are uniform and machinable.
TRUE TO SHAPE
Cold finished steel bars are true to shape. They are drawn through precision dies which effectively control the shape to be produced, i.e., round, hexagons, flats and squares.
Seams and other defects are more readily discovered in cold finished operations, thus lowering the percentage of parts rejected after machining. With cold finished bars, parts can be machined more accurately, which cuts down on extra operations such as grinding on critical diameters. This, in combination with the higher mechanical properties of cold drawn bar stock, operates to provide higher quality parts.
The size accuracy, finish, straightness and concentricity of cold finished steel bars are important in machining - especially to the operation of automatic screw machines. Cold drawn bars are produced from Special Bar Quality of Alloy Bar Quality hot rolled bars. Internal soundness is thus being checked directly at the producing mill. Cold drawing, then, improves the inherent machinability of some steels by 15 to 25% and makes chips easier to break and dispose of, which can be important to high output NC and CNC equipment. Cold drawn bars cut easier and cleaner.
The number of parts you produce per hour, per machine, along with tool life, will normally increase when you use bars in the cold drawn condition.
LESS SCREW MACHINE MAINTENANCE
Scale, which can collect and work its way into moving segments of the machine and cause premature parts wear, has been removed in cold finishing, there is less out-of-roundness to cause strain on collets, pushers and fingers. Because tolerances are more accurate, fewer machine adjustments have to be made. These and other advantages all add up to less labor, maintenance and cost.