Seamless Rolled Rings
Seamless rolled rings, unlike roll-formed metal rings, have been forged from a single "donut" shaped block of metal, making forged rings seamless with great tensile strength and structural integrity. For this reason, seamless rolled rings are formed to be used in train car or automobile wheels, bearing housings, gears, engine turbines, jet engine turbines and wind turbines. Seamless rings may be forged into a wide range of dimensions, ranging from small bearing housings weighing only a few pounds to wind turbine slewing rings weighing several hundred pounds.
Beginning as a solid, circular block of metal, seamless rings are heated to low or high forging temperatures and are then pounded into a flatter circular shape which is then punched in the center to form a "donut" shape. This shape is then placed in forging calendars which roll the new ring from the inside and outside, squeezing and kneading the ring's thickness smaller and enlarging its diameter. As the ring is calendared it continues to be pounded, flattened and shaped until it reaches precise dimensions. Rings can be shaped at high forging temperatures for faster forging or, for rings (such as aluminum car wheels) which require high pressure resistance, at low temperatures for longer times. Lower forging temperatures and longer forging times result in greater tensile strength.
The process of squeezing and calendaring during seamless ring forging aligns the grainflow of the metal as it condenses the ring's molecules, removing cracks, pores and defects. Unlike other types of ring forming, such as roll forming, this forging process creates a seamless ring with great integral strength, capable of resisting high degrees of internal or external pressure. This is why wheel hubs, bearing housings and turbine slews - all applications which apply significant force - are made from seamless forged rings. Cost efficiency for forgings can be greater than roll forming, since forged rings are molded instead of stamped out, leaving very little wasted material. Ring forging is, however, more time consuming than roll forming rings, making long runs of roll formed rings less expensive than long runs of seamless forged rings. Due to the precise demands of their applications, forged rings also often require extensive alignment, testing, coating and plate finishing.