Ball Screw Assembly
Ball screw assemblies are frequently made of steel; the nut and balls can be made of plastic for lower demand applications. Ball screws are usually powered by a motor, though they require relatively low amounts of energy. Ball screws offer up to 90% efficiency while requiring a third of the power that standard sliding screws use. Important ball screw considerations include desired lifespan, operating environment temperature and humidity, required torque, output force, backlash and contamination. Ball screw assemblies are used by many industries including the aerospace, computer, electronic, automotive, medical and manufacturing industries.
Precision ball screws are used for medical instruments; other applications for ball screw assemblies include material handling equipment, conveyors and machine tools, robotic lines, precision assembly equipment, semiconductor manufacturing and fly by wire aircraft and missile control among many others.
Ball screws can be manufactured using a variety of techniques. Cold rolled steel is cut and machined by machines that remove material to create the threading. The ball screw can then be ground to smooth any rough or sharp edges. It may also be milled or
rolled. Ball screw assemblies consist of a shaft threaded with helical grooves called the screw. Screws used as fasteners taper near the end; these, however, maintain a uniform diameter the length of the screw. The threading of the screw is complimented by the internal threading of the nut. The two parts do not twist together like a nut on a bolt; instead, small ball bearings inside the nut travel along the grooves in the screw. They spiral around and around as the nut moves, providing smooth motion as they rotate. Deflectors inside the assembly keep the balls traveling with the nut. In an external ball return system, the balls are returned to the opposite end of the nut by a return tube that curves around the outside diameter of the nut. The internal ball return system employs the same idea but without using exterior tubes. Various deflectors and return methods are used to recirculate the ball bearings because they enable the ball screw to function.
