What is a Ball Screw?
A ball screw, like all screws, is a rod with a helical groove that translates rotational motion into linear motion.
Why use a Ball Screw?
Common screws slide on their threads and pull the connecting piece with them. This is how an ACME screw works. This sliding motion is easy to produce but extremely ineffiecient; around 40% of the input power is transferred to the work piece. To improve on this idea the sliding contact must be replaced with rolling elements. Ball Screws use ball bearings in the nuts to roll along the screw. The balls must recirculate or they will fall out of the nut. This leads to the current designs for recirculating ball screws that have efficientcies greater than 90%.
Anaheim Automation's Ball Screw Offering
Anaheim Automation offers a high-quality line of ball screws offering flexibility and high performance. As a distributor of and TBI Motion ball screws, Anaheim Automation is sure to have the right ball screw for your application. Choose from a wide range of stroke lengths, as well as multiple different preload and accuracy ratings.
TBI Ball Screws: TBI provides Anaheim Automation with a low cost ball screw assembly solution that saves up to 50% next to competitors, without compromising quality. Both ground and precision rolled ball screws are available, from 4mm to 80mm in diameter. High precision grades from C0 to C10 are available, delivering up to 7,240kgf of dynamic linear force. Anaheim Automation will cut any ball screw to fit the length requirements of your application.
Physical properties of a Ball Screw:
The four main components of a ball screw include the ball screw shaft, ball nut, ball bearings, and the seal, further explained below.
1. Ball Screw Shaft:
The Screw Shaft is a long bar of chromium steel that has grooves formed into a helical pattern. This is the main body of a Ball Screw.
- Ball Groove design: When forming the groove for a ball screw it is important to think of the points of contact. The most common groove style is the Gothic Arch. This type of groove allows for four points of contact at all times. With four contact points the ball can be loaded in any direction in that plane.
- Pitch circle diameter of balls: The pitch circle (dm) is measured from the center of the bearing to the center of the bearing on the other side of the screw. This measurement is used for the maximum speed calculations.
- Nominal Diameter: The outside diameter of the screw. This measurement is useful for sizing the screw as it is easy to measure.
- Root Diameter: Diameter from the bottom of the groove to the bottom of the adjacent groove. This is the smallest part of the screw and is important for the critical speed calculation.
- Lead: It is the distance the nut travels in one rotation. The larger the lead the faster the nut can travel. The lead also determines the vertical maximum payload and the stopping power of the screw. This is because the load angle is steeper for greater leads; the amount of weight it can hold is less.
- Ball diameter: The diameter of the ball bearing that would fit into the groove with a preload of 0. This is used to calculate the diameter of the ball bearing that would give a certain preload. The bigger the balls compared to the nut and screw gap, the higher the preload.
2. Ball Nut (Nut and Ball Recirculation):
There are 3 main styles of Ball Screw Nuts each with a specialty:
- Profile Ball Groove: This is the most common type of ball nut, it is easy to make and has good consistent performance. Its simplicity makes this nut easy to mass produce and adjust to fit most sizes, leads, and loads. The balls are recirculated by tubes that pick up the bearings then deposit them back into the cycle. The number of rows of balls before they are recirculated is usually between 1.5-3.5 rows to keep the return tube size manageable and re-balling easier.
- Ball Pitch Circle Diameter: This nut has a trimmer profile because it does not use tubes to move the balls. Instead a deflector is used to bump the bearings into the previous track. This means that there must