Basic knowledge of ball screw nut pair

Ball screw nut pair in nc machine tool is rotary motion into linear motion transmission device in common use. It with ball rolling instead of lead screw nut pair of sliding, the friction force is small, has a good performance. 1, the composition of the ball screw nut pair: screw, nut, ball and raceway ( Back to the bead) And nut. 2, the working principle of ball screw nut pair on the screw and nut has a circular spiral groove, will they involution form the spiral groove. In a ball in the race, when a single relative movement between screw and nut, along the spiral groove ball rolling, rolling on the screw by return after several laps boot device and one roll back to the screw and nut, form a closed loop. 3, ball screw pair of advantages: (1) small friction coefficient, high transmission efficiency, the transmission torque is small. (2) the high sensitivity, stable transmission, is not easy to produce, with precision and high positioning precision. (3) wear small, long service life, good accuracy stable. (4) can be eliminated by preloaded and clearance measures to improve the axial stiffness and reverse accuracy. (5) motion is reversible. Ball screw pair of faults: manufacturing complex, high cost, in the vertical installation cannot be self-locking, so need additional braking mechanism. 4, the circulation of the ball screw nut pair way ball circulation way have outer loop and the inner loop. 1) Outer loop ball and screw in the process of return out of contact for external loop. Outer loop ball screw pair according to the main return way ball loop are intubation type and spiral groove type two kinds. Characteristics of type external loop intubation: good molding process, but due to pipe is prominent in the nut body, radial size larger. Intubation type circular spiral groove external loop: the characteristics of this kind of structure than intubation structure radial size small, but made more complex. Spiral groove outside loop 2) Inner loop ball contact with screw is always in the process of circulation for the inner loop. Circulate in the characteristics of the ball screw vice: advantage: radial compact size, good rigidity, return of raceway is shorter, small friction loss. Weakness: the reverser processing difficult. 5, ball screw nut pair of axial clearance adjustment of the ball screw transmission clearance refers to axial clearance, but also eliminate the screw to install the clearance between the part and driving part. Eliminate clearance method often USES the double nut structure: using the relative axial displacement of the two nut made of two ball nut ball against respectively in the spiral groove on the two opposite sides. Note: pre-tightening force shoulds not be too large, otherwise it will make racing torque increases, reduce the transmission efficiency, shorten service life. Double nut screw eliminate clearance method: low shim gap type low double nut adjustable gap type low tooth difference adjustable gap type 1) Gasket type adjustable gap as shown, adjusting shim thickness around the two nut produce axial displacement, can eliminate the gap and pre-tightening force. Advantages: simple structure, good rigidity. Disadvantages: adjust the inconvenience, raceway wear, cannot eliminate smell sensitive to preload at any time. Gasket adjustable gap type 2) Double nut adjustable gap type left nut outer end without flange with screw thread, fixed with two round nut, with a flat key limit nut in nut inside the transmission, flange nut right outside. Adjust, as long as the twisted inside round nut can eliminate the gap and generate pre-tightening force. Features: simple structure, good rigidity, preloaded, reliable and adjusting shown in use, but can't be accurate quantitative adjustment. 3) Tooth difference adjustable seam type, as shown in the system of two nuts on the flange of the cylindrical gear, respectively and fastening on opposite sides of the sleeve ring gear meshing, the teeth are respectively a and b and are a tooth, adjustment, first remove the inner gear ring, let the two nut relative to the sleeve rotation - the same direction A tooth, and then insert the inner gear ring, the two nut to produce relative angular displacement, the axial displacement X = 1 / a 1 / b, the adjustment method can accurate preload volume, easy to adjust, but the structure of the internal gear size is big. 6, ball screw support ways of nc machine tool feed system to obtain higher transmission stiffness, besides strengthening the stiffness of the ball screw pair itself, correct installation of ball screw and the rigidity of the supporting structure is also cannot be ignored. After such as to reduce the stress, the deformation of the bearing should be reinforced rib, should increase the surface contact between the bearing and the machine tool, and USES the high stiffness of thrust bearing. Low end thrust bearing, the installation method is suitable for the short trip small screw, its carrying capacity is small, low axial stiffness. Low end thrust bearing, the other end of the centripetal ball bearings, which is used for screw longer, when the thermal deformation caused by screw elongation, its one end fixed and the other end of the trace of the axial float. Low on both ends of the thrust bearing, thrust bearing is put on the ends of the ball screw and pre-tightening force, can increase the axial stiffness, and screw only sustain tension at work, but this way sensitive to the thermal deformation of a ball screw. Low on both ends of the thrust bearing and centripetal ball bearings, its both ends have larger rigidity, this approach also applies to withstand the axial and radial load.