What are the advantages of the screw nut seat?

What are the advantages of the screw nut seat? 

Screw nut seat (referred to as ball screw pair) is an ideal transmission device for the conversion of rotary motion and linear motion. Its structural feature is that the ball (as an intermediate transmission element) is installed between the nuts of the spiral groove to reduce friction. Its working principle is: the screw and nut are processed into arc-shaped spiral grooves. When the screw nut seats are sleeved together, a spiral raceway can be formed, and the raceway is filled with balls. As the lead screw rotates relative to the nut, axial displacement occurs between the two. The ball may roll along the raceway to reduce frictional drag. After the balls roll on the lead screw for several weeks, they roll one by one between the lead screw and the nut through the return guide device (ball return device) to form a closed loop tube.

In the screw nut seat round rolling process, the ball is called the internal circulation type. The internal circulating ball screw is equipped with a reverser (reverse ball return device). The returning ball enters the reverser from the thread raceway. With the help of the reverser, the ball is forced through the top of the helical teeth into the adjacent raceway to achieve circulation. In this process, when rolling between the reverser and the outer ring of the screw, the balls will not slide out along the raceway. Usually, the nut is equipped2-4Reversers, which are evenly distributed along the circumference of the nut. A circular reverser that has a convex key and cannot float in the hole is called an intermittent reverser; a circular reverser that can float in the hole is called a floating reverser. The advantages of the internal circulation type are compact radial size and good rigidity. Due to its short return raceway stroke, friction loss is small, so the efficiency is high. The ball that is out of contact with the lead screw during the return process is called the external circulation type. The ball screw pair of the external circulation type is different according to the ball return method, and includes a plug type and a spiral groove type. The upper elbow is the oil return pipe. The balls may circulate between the screw and nut pairs. The two ends of the elbow can also play a role in blocking the ball and preventing the ball from sliding out along the raceway. The intubation external circulation has the characteristics of simple structure and convenient manufacture. However, because the return raceway protrudes from the outside of the nut, the radial size is large, and the wear resistance and impact resistance at both ends of the elbow are poor. Spiral groove type, that is, the spiral groove is milled on the outer ring of the nut, and holes are drilled at both ends of the groove and tangent to the thread raceway to form a return raceway. The helical groove type has a smaller radial dimension than the cannula type structure, but is more complicated to manufacture.

In the transmission process, there is basically rolling friction between the ball, screw and nut. Therefore, the screw nut seat has the following advantages:

(1) High transmission efficiency

The transmission efficiency of the ball screw pair is very high, up92%～98%, is an ordinary screw drive2～4Times

(2) High positioning accuracy and high repeated positioning accuracy

The driving torque of the ball screw pair is reduced to about1/3, The heating rate is greatly reduced, and the temperature increase is reduced. In addition, when the ball screw pair is installed, measures such as eliminating axial clearance by preloading are taken, so that the ball screw pair has high positioning accuracy and repeated positioning accuracy.

(3) Long service life

The ball screw pair is made of high-quality alloy steel, and the surface hardness of the raceway after quenching and heat treatment is as high60～HRCTherefore, its actual life is much longer than that of the sliding screw, which makes up for the deficiency that its manufacturing cost is higher than that of the sliding screw.

(42) High stiffness

After pre-tightening, the ball screw pair can eliminate the axial clearance and improve the stiffness of the system.

(5) Reversibility of transmission

The ball screw pair eliminates the crawling phenomenon that may occur in the transmission process, and can realize two transmission modes that convert rotary motion into linear motion or convert linear motion into rotary motion and transmit power.

Because the ball screw pair has the above advantages, the ball screw is widely used in the linear feed system of various small and medium-sized CNC machine tools. However, since the friction coefficient of the ball screw pair is small and cannot be self-locking, it is used in the vertical position. In order to prevent the spindle box from automatically sliding due to sudden power failure, a braking device must be added.