eeded for high-speed applications or when required.
History of Ball Screws:
There have been attempts to replace sliding friction screws with rolling friction screws since the 19 century. However because of the limited level of manufacturing and technology, the first practical application of ball screws was by General Motors, who used ball screws for their steering columns. Since then the technology surrounding ball screws has advanced rapidly. This rapid advance has led them to be used in CNC machines, automated manufacturing, and medical devices. With superior accuracy, repeatability, and high efficiencies ball screws are the best way to translate rotational motion into linear motion.
Ball Screw Applications
Ball screws are used in motion control but require bearing supports and motor couplings to work effectively. By using ball screws in conjunction with linear stages we are able to produce stable linear translation for many applications. For this reason ball screws are used in a broad range of industries ranging from garage door openers to CNC machines and MRI table sliders. Ball screws are not commonly used in applications requiring oscillating motions less than a ball diameter. This type of motion removes the lubrication layer and leads to increased error. This can be worked around using smaller ball screws and special grease.
Lifetime of a Ball Screws
Ball screws have very low friction coefficients, which is the key to both their accuracy and their longevity. The actual life is determined by load, speed, lead and screw size. Common values are 20,000 hours, and 50,000 km or 5 years.
Required Maintenance for a Ball Screw
Most ball screws require a certain degree of regular maintenance; however some specialty balls screws do not require any maintenance! Make sure that the rails are free of contaminates like water, dirt, dust and debris. The nut should also be lubricated using either oil or grease. Grease offers lower overall performance but is much more convenient, cheaper to use, and easier to maintain than oil (which requires a circulation system).
Required Maintenance for a Ball Screw
Backlash- the “lost motion” that comes from looseness in the drive train.
Ball Bearing- a chromium steel ball set to tight tolerances that support loads.
Ball Nut- the nut that rides a ball screw and uses recirculating ball bearings.
Ball Screw Shaft- a chromium steel shaft with helical grooves that house ball bearings to change rotational motion into linear motion.
Elastic Deformation- a changing in shape that is not permanent and will reverse on its own.
End Cap Nut- a style of nut that recirculates at the end, it is used to accommodate large and multiple start leads.
Grease- a lubricant that is not very viscous.
Lead- the linear distance traveled in one rotation.
Lead Error- the difference in the actual travel and the theoretical travel of the ball nut.
Lubricant- a substance that reduces friction between other objects.
Mounting Error- error caused from inaccuracies in mounting the screw in bearings, motors, ball nuts, etc.
Multiple Starting Threads- a screw that has more than one track, only applicable on large leads due to space restraints. Used to add more balls to large lead ball nuts.
Nominal Diameter- the diameter of the thread “tops;” the maximum diameter of the screw
Oil- a lubricant that is highly viscous
Pitch Circle Nut- a style of nut that recirculates the balls every rotation, good for small leads and small nut profiles
Pitch Diameter of Balls- the diameter created by connecting the centers of the ball bearings
Preload- the tightness of the nut to the shaft, caused from the elastic deformation of the parts involved.
Profile Ball Nut- the most common nut type, it uses tubes to recirculate the balls.
Root Diameter- the diameter made from the bottom of the screw, the thinnest point and used in life calculations
Seals- a device used to keep things in, out or both.