Structural Analysis of Ball Screws
Ball Screws realize high-precision linear motion conversion through rolling friction, and its core structure consists of four key components, each part of which operates in concert to ensure the high efficiency and stability of the transmission.
Screw shaft is the basic component of ball screw, usually made of high strength alloy steel, and after quenching, grinding and other processes, so that its surface hardness is as high as HRC58 - 62, with excellent wear resistance and rigidity. The shaft is precision machined with spiral raceway, and the shape and accuracy of the raceway directly affects the movement trajectory and transmission performance of the ball. There are two common types of raceways, single arc and double arc, double arc raceway contact angle is large, bearing capacity is stronger, suitable for heavy-duty working conditions.
The nut, as a moving part cooperating with the screw shaft, is also made of high quality alloy steel. Inside the nut, there is a spiral raceway matching with the screw shaft, and the processing precision is very high to ensure good contact with the ball. The nuts are divided into integral type and split type. Integral type nuts have compact structure and good rigidity, and are often used in occasions requiring high precision; split type nuts are easy to install and adjust, and are suitable for equipments requiring frequent disassembly. The nut is also equipped with the import and export of the ball, which is used to cooperate with the ball return device to realize the cyclic movement of the ball.
Balls are the key components of Ball Screws to realize low friction transmission, and are generally made of high carbon chrome bearing steel with very high dimensional accuracy and roundness. Balls and screw shaft, nut raceway to form a point contact or a small area of line contact, compared with the surface contact of the sliding screw, significantly reduces the frictional resistance, improve transmission efficiency, its transmission efficiency can reach 90% - 98%. According to the load and precision requirements, the ball can choose different diameters and number of balls, larger diameter ball bearing capacity, a larger number of balls can improve the smoothness of the movement.
The ball return device is responsible for guiding the ball to return to the initial position after completing a period of travel, realizing continuous cyclic motion. There are two types of ball return devices: internal and external. Internal circulation ball return device is installed inside the nut, through the reverser to guide the ball in the nut inside the circulation channel to return, has a compact structure, smooth movement, low noise and other advantages, commonly used in high-speed, high-precision transmission system; external circulation ball return device is set up in the nut outside the conduit or tube, the ball will be guided back to the beginning of the start end of the bearing capacity is larger, easy to maintenance and replacement of the ball for the heavy-duty, Low-speed occasions.
In addition, in order to eliminate axial clearance and improve transmission rigidity, ball screws often use double-nut preload technology, by adjusting the relative position of the two nuts, so that the ball in the raceway to produce preload; lubrication system is also indispensable, the use of grease or oil lubrication, which can effectively reduce the friction between the ball and the raceway, and extend the service life of the ballscrews; in the process of installation, strict control of straightness of the screw shaft and parallelism with the installation base surface, is the most important factor in the installation process. In the installation process, strictly controlling the straightness of the screw shaft and the parallelism with the installation base surface are the key links to ensure the accuracy of the ball screw transmission.
