[Ball Screw] Ball Screw Principle Ball Screw Structure Ball screw selection
What is a ball screw
The ball screw is composed of screw, nut, steel ball, preloading piece, reverser and dust protector. Its function is to convert rotational motion into linear motion, which is a further extension and development of the Acme screw. The important significance of this development is to change the bearing from sliding action to rolling action.
Ball screwPrinciple
1. According to the national standard GB/T17587.3-1998 and application examples, the ball screw (has basically replaced the trapezoidal screw, commonly known as screw) is an actuator used to convert rotational motion into linear motion; or convert linear motion into rotational motion, and has high transmission efficiency and accurate positioning.
2. When the ball screw is used as the active body, the nut will follow the rotation angle of the screw and convert it into linear motion according to the lead of the corresponding specification. The passive workpiece can be connected to the nut through the nut seat, thereby achieving corresponding linear motion.
Ball ScrewUses
Ball screw bearings provide a wide range of standardized products to suit various uses. Widely used in machine tools, ball circulation methods include circulating duct type, circulator type, and end cover type. Preloading methods include positioning preloading (double nut method, position preloading method) and constant pressure preloading. The appropriate type can be selected according to the purpose. The screw has a high-precision ground precision ball screw (accuracy is divided into 6 grades from CO-C7) and a cold-rolled ball screw bearing formed by high-precision cold rolling (accuracy is divided into 3 grades from C7-C10) level). In addition, in order to cope with the urgent need of users for delivery, there are also finished products with the shaft end processed, semi-finished products that can be freely processed on the shaft end, and cold-rolled ball screw bearings. As the peripheral parts of this bearing, the screw support unit, nut support, lock nut, etc. necessary for use have also been standardized and are available for users to choose.
Ball screwApplications
Ultra-high DN value ball screw: high-speed machine tools, high-speed comprehensive machining centers.
End cover ball screw: rapid handling system, general industrial machinery, automated machinery.
High-speed ball screw: CNC machinery, precision machine tools, industrial machinery, electronic machinery, high-speed machinery.
Precision grinding grade ballsLead screw: CNC machinery, precision machine tools, industrial machinery, electronic machinery, conveying machinery, aerospace industry, actuators, valve switching devices used in other antennas, etc.
Nut-rotating (R1) series ball screws: semiconductor machinery, industrial robots, woodworking machines, laser processing machines, conveying devices, etc.
Rolling grade ball screw: low friction, smooth operation, fast delivery and low price.
Heavy-duty ball screws: all-electric injection molding machines, stamping machines, semiconductor manufacturing equipment, heavy-duty brakes, industrial machinery, and forging machinery.
Ball screwTypes
There are two commonly used circulation methods: external circulation and internal circulation. The balls that sometimes break out of contact with the screw during the circulation process are called outer circulation; those that always remain in contact with the screw are called inner circulation. Each closed circuit of the ball is called a row, and the number of leads contained in each closed circuit of the ball is called the number of turns. Each nut of the internal circulation ball screw pair has 2 rows, 3 rows, 4 rows, 5 rows, etc., and each row has only one turn; each row of the outer circulation ball screw has 1.5 turns, 2.5 turns, and 3.5 turns.
1) External circulation: External circulation is when the balls return to the space between the screw nut through the spiral groove or cannula on the outer surface of the nut after the circulation process. Re-enter the cycle. As shown in Figure 2-3, the return methods of the external circulation ball screw nut pair during ball circulation mainly include end cap type, cannula type and spiral groove type. Commonly used external circulation methods are end cap type; intubation type; spiral groove type. End cover type, a longitudinal hole is machined on the nut as a return channel for the balls. The cover plates at both ends of the nut are provided with return ports for the balls, through which the balls enter the return pipe to form a circulation. The intubation type uses a bent pipe as the return pipe. This structure has good craftsmanship, but because the pipe protrudes outside the nut, the radial size is larger. Spiral groove type, which mills a spiral groove on the outer circle of the nut. Through holes are drilled at both ends of the groove and are tangent to the threaded raceway to form a return channel. This structure has a smaller radial size than the intubated structure, but has a smaller radial size than the intubated structure. Manufacturing is more complicated. The external circulation ball screw has a simple outer circulation structure and manufacturing process and is widely used. The disadvantage is that it is difficult to make the raceway joints smooth, which affects the stability of the ball raceway.
2) Internal circulation: The internal circulation uses a reverser to realize ball circulation. There are two types of reversers. The cylindrical convex key reverser has a cylindrical part embedded in the nut and a reverse groove 2 at the end. The reverse groove is positioned by the round key 1 on the outer surface of the cylinder and its upper end to ensure alignment with the direction of the threaded raceway. Oblate insert reverser, the reverser is a general round-headed flat key insert, the insert is embedded in the groove of the nut, and has a reverse groove 3 at its end, which is positioned by the outer contour of the insert. Comparing the two reversers, the latter is smaller in size, thereby reducing the radial size of the nut and shortening the axial size. butThe outer contour of this reverser and the dimensional accuracy of the grooves on the nut require relatively high precision. The picture shows the end-cap type circulation, for reference only.
Ball screw screw selection
The nut of the ball screw can be divided into: elbow type, circulator type, according to the circulation method of the steel ball. End cap type. The specialties of these three circulation methods.
Elbow type
(SBN, BNF, BNT, BNFN, BIF and BTK types) these models can be found in the search.
Circulating guide vane type (HBN type)
These models are the most typical nuts, which use elbows to circulate the steel balls. The steel ball is picked up from the groove of the screw shaft and enters the elbow, then returns to the groove and performs an infinite circular motion.
Circulator type
(Types DK, DKN, DIK, JPF and DIR)
These models are the smallest nuts available , change the traveling direction of the steel ball through the circulator, cross the outer diameter of the screw shaft and return to the original position, doing infinite circular motion.
End cap type
(SBK, SDA, SBKH, WHF, BLK, WGF, BLW, WTF, CNF and BLR types)
These models are the most suitable nuts for high-speed feeding. The steel ball is pulled from the groove of the screw shaft into the through hole of the nut using the end cover, and then returns to the groove through the through hole, performing an infinite cycle.
Ball screwFeatures
1, small friction loss, transmission efficiency High
Because there are many balls rolling between the screw shaft and the screw nut of the ball screw pair, high motion efficiency can be obtained. Compared with the previous sliding screw pair, the driving torque is less than 1/3, that is, the power required to achieve the same motion result is 1/3 of using the sliding screw pair. Very helpful in saving power.
2High precision
Ball screw pairs are generally produced continuously using the world’s highest level of mechanical equipment. Especially in the factory environment of grinding, assembly, and inspection processes, temperature and humidity are strictly controlled, and accuracy is fully guaranteed due to a complete quality management system.
3High-speed feed and micro-feed possible
Since the ball screw pair uses ball motion, it starts The torque is extremely small, and there will be no crawling phenomenon like sliding motion, ensuring precise micro-feeding.
4High axial stiffness
The ball screw pair can be preloaded, because the preload can make the axial clearance reach a negative value, thus obtaining High rigidity (by adding pre-pressure to the balls in the ball screw, when it is actually used in mechanical devices, etc., the rigidity of the nut part can be enhanced due to the repulsive force of the balls).
5It cannot self-lock and has transmission reversibility
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