Ball Screw Check and Maintenance Ball screw is the most commonly used transmission element in tool machinery and precision machinery, its main function is to convert rotary motion into linear motion, or to convert torque into axial repeated force, while having the characteristics of high precision, reversibility and high efficiency. Because of its small friction resistance, ball screws are widely used in various industrial equipment and precision instruments. The ball screw is composed of screw, nut, steel ball, prepress sheet, reverser and dust protector. The fault caused by the ball screw is a variety of faults, some faults are gradual faults, need a development process, with the increase of use time more and more serious; there are some sudden failures, generally no obvious signs, but suddenly, this failure is caused by a variety of adverse factors and the outside world. Therefore, through the correct detection to determine the real cause of failure is the premise of fast and accurate maintenance. (1) Check and repair the clearance of ball screw nut pair and support system When the reverse error of the CNC machine tool is large, the positioning accuracy is unstable, and the tool mark appears in the quadrant, it is necessary to first detect whether the screw system has a gap. The method of detection is as follows: place the dial indicator with the steel ball in the center hole of one end of the lead screw, measure the axial runout of the lead screw, and move the other dial indicator measuring table. Rotate the screw forward and backward, observe the value on the two dial gauges, and confirm the fault location according to the change of the value. (a) Detection and repair oflead screw support bearing clearance If the dial indicator measuring the lead screw does not swing when the lead screw is rotated forward and backward, it indicates that the lead screw does not runout. If the dial indicator pointer swings, it indicates that the lead screw has a beating phenomenon. The difference between the maximum and minimum measurements of the dial indicator is the axial runout distance of the lead screw. At this time, we must check whether the back cap of the support bearing is locked, whether the support bearing has been worn and failed, and whether the pre-loaded bearing washer is suitable. If there is no problem with the bearing, just reconfigure the pre-load washer. If the bearing is damaged, it is necessary to replace the bearing, reinstall the preload washer, and then tighten the back cap. The axial runout size of the lead screw mainly depends on the precision of the pre-loaded washer of the supporting bearing. The most ideal state of screw installation accuracy is that there is no positive and negative clearance, and the supporting bearing should have an interference of about 0.02mm. (b) Detection and maintenance of gap generated by double nut pairs of ball screw Through detection , if it is confirmed that the fault is not caused by the lead screw runout. It is necessary to consider whether there is a gap between the screw and the nut pair, and the detection method in this case is basically the same as the detection of the screw runout. Use a dial indicator to measure the work table connected to the nut, turn the lead screw in positive and negative direction, detect the maximum gap between the lead screw and the nut, and then adjust. (c) Testing and maintenance of single nut pair For single-nut ball screw, the clearance between the screw and nut pairs cannot be adjusted. If the gap between the screw and nut pair is detected. First check whether the thread arc of the lead screw and nut has been worn, such as serious wear, must replace a new set of lead screw nuts. If the wear is slight, it can be replaced with a larger diameter ball to repair. First of all, the maximum clearance of the screw nut pair is detected, which is converted to the increase of the ball diameter, and then the appropriate ball is selected and reassembled. (d) The gap between the nut flange and the workbench is not fixed properly This problem is generally easy to be ignored, because of the long-term reciprocating movement of the machine, the screws fixing flange is loose and produces a gap, and the highest fault factor is eliminated when checking the screw nut gap. (e) The ball screw nut pair movement is not smooth, excessive noise and other faults maintenance. The movement of the ball screw nut pair is unstable and the noise is too large, mostly due to poor lubrication, but sometimes it may be caused by the servo motor drive parameters are not adjusted. (2) Bearing, screw nut pair poor lubrication Machine in the work such as noise and vibration, after the detection of mechanical transmission part of the problem, first of all to consider the problem of poor lubrication, many machines after years of operation, screw nut automatic lubrication system is often blocked, can not automatically lubricated. High temperature and high-speed grease can be added to bearings and nuts to solve the problem. Grease can ensure the normal operation of bearings and nuts for several years.
