1 . C concept and structure of b all screw
Ball screw
The ball screw is composed of several components, including screw, nut, steel balls, pre-compression part, reverser and dust-proof device. Its main function is to convert rotary movement into linear movement, transforming sliding movement into rolling movement.
In 1898, the concept of using steel balls between the nut and screw to convert the sliding contact of a traditional screw into rotating contact was first introduced. This change in friction from sliding to rolling allowed the rotary motion of the steel balls in the nut to be transformed into linear motion, resulting in better torque conversion and reduced positioning issues and damage compared to traditional screws.
The invention of the ball screw is credited to Rudolph G. Boehm of Texas, who received a U.S. patent in 1929. When used as the active component, the nut is converted into linear motion with the screw's rotation angle, guided by specifications. specific. The passive part can be connected to the nut via a nut carrier.
The ball screw assembly is typically made of steel and consists of a female nut and a screw with a helical groove that matches the screw groove.
The groove inside the nut contains many small chrome steel balls. As these balls circulate inside the nut, they provide smooth movement along the bolt, while a baffle or return system traps the balls and allows them to circulate through the nut.
When combined with a motor, the efficiency of a ball screw can reach 90%. They are highly accurate, accurate to within a few thousandths of an inch per foot.
Ball screws are used by various industries for precise control, including aerospace, computer, electronics, automotive and medical industries.
Ball screws are often employed in manufacturing processes such as robots, automated assembly lines, material handling equipment, conveyors, machine tools, wire control, and precision assembly equipment.
two . How does a ball screw work?
The ball screw assembly consists of a screw and nut, each with a complementary spiral groove. The balls roll within these grooves, serving as the only point of contact between the nut and bolt.
When the screw or nut rotates, the balls are directed through the deflector into the ball return system inside the nut. They move continuously through the return system to the opposite end of the ball nut and then exit to the threaded raceway of the ball screw and nut for repeated circulation in a closed loop.
The ball nut plays a crucial role in determining the load and service life of the ball screw assembly. The relationship between the number of threads in the ball nut circuit and the number of threads in the ball screw determines which component will experience fatigue (wear) failure first.
There are two types of ball return methods used in ball nuts: external circulation and internal circulation.
In external circulation, the balls return to the opposite end of the circuit through a return tube, which extends beyond the outer diameter of the ball nut.
ball nut with external circulation
Internal circulation involves the balls passing or returning along the inner wall of the nut, which has a smaller diameter than the outer diameter of the ball nut.
ball nut with internal circulation
In the case of internal circulation, the ball follows a rotating circuit and is forced to travel over the top of the screw thread through the return system. This is known as a cross-baffle internal return system.
In a cross-baffled ball nut, the balls rotate the shaft only once and the circuit is closed by a spherical deflector (B) inside the nut (C), allowing the balls to cross between adjacent grooves at points (A) and ( D).
ball nut with internal circulation
When a long ball screw rotates at high speed, if its slenderness ratio reaches the natural harmonic of the shaft size, it may begin to vibrate. This is known as critical speed and can significantly reduce the life of the ball screw. It is recommended not to operate the screw at a speed exceeding 80% of its critical speed for safety reasons.
Rotation Ball Nut Component
In some applications, longer shaft lengths and higher speeds are required, and in these cases the use of a rotating ball nut assembly is required.
3 . B all screw manufacturers
- South Korea: SBC.
- Japan: NSK, THK, IKO.
- Sweden: SKF, Schneeberger Schneeberg.
- Germany: IF, Rexroth.
