Ball screw nuts change torque into thrust without rotating themselves. The ball bearings rotate instead and the nut housing remains radially static as it slides on the shaft. Ball screw nuts can be made from plastic or metal; the shaft of the ball screw is machined from steel. Frequently used with linear slides and linear actuators, ball screws provide smooth linear motion that can be precisely controlled.
They use low amounts of energy when motorized and can be up to 90% efficient in their use of power. Important ball screw considerations include desired lifespan, operating environments temperature and humidity, required torque, output force, backlash and contamination. Ball screws and nuts 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 screws 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 screw assemblies are constructed from milled, rolled or ground parts. Milling requires machines and tools that cut and remove material; rolling applies a series of dies to a metal blank to punch out the right shape. Ground ball screws are machined, hardened then ground for very accurate dimensions. Custom ball screws that require high levels of precision are ground.
After the nut is fabricated, ball bearings are placed in the grooves between the nut and screw shaft. External ball return parts are added on the outside of the nut to circulate the balls through the nut. They are short curved tubes that provide a path for the balls that have reached the top of the nut to travel to the bottom and start the process again.
Internal ball return systems or deflectors are also used. Ball screw nuts found in lead screws or acme screws are different because the nuts found in those screws do not actually house ball bearings. Instead, the threading of the nut and of the shaft directly interact and the two parts rotate together. Lubrication allows for smooth turning despite the high friction that occurs. Lead screws are simple to design and manufacture while offering high precision.