In the linear module series of screw systems, the proper installation and maintenance of ball screws are crucial. Below, we will discuss the factors contributing to excessive clearance in ball screw assemblies and the corresponding solutions.
1.Inappropriate Ball Screw Bearings:
Ball screws must be paired with angular contact bearings, especially those designed for high thrust angles. When a ball screw bears axial loads, standard deep groove ball bearings tend to produce some axial play. Therefore, deep groove ball bearings are not suitable for this application.
2.Improper Installation of Ball Screw Bearings:
If the bearing is improperly installed on the ball screw, and they do not fit together securely, this can result in axial play, especially when subjected to axial loads. This situation may occur due to the shoulder of the screw being either too long or too short. Proper perpendicularity between the bearing contact surface and the V-shaped shaft center of the locking nut, or optimal parallelism of the locking nut faces in two corresponding directions, ensures that the bearing remains properly aligned. To achieve this, machining both the V-shaped thread on the screw shoulder and the bearing contact surface is necessary, preferably through grinding.
3.Insufficient Parallelism or Flatness of Ball Screw Support Mounts:
Regardless of whether the mating component surfaces are ground or milled, if their parallelism or flatness exceeds tolerance limits, it will result in poor reproducibility accuracy during table movement. To compensate for this, thin shims are often used between the ball screw support mount and the machine body.
4.Excessive Torsional Displacement:
This may occur due to inappropriate material selection, improper heat treatment, insufficient hardening depth, uneven hardness distribution, or overly soft materials. The standard hardness values for steel balls, nuts, and screws are typically HRC6266, HRC5862, and HRC56~62, respectively.
5.Lack of Preload or Insufficient Preload:
When a ball screw is vertically oriented without any preload, the nut may rotate and slide due to its weight. Ball screws without preload can only be used in machines with relatively low operating resistance, and positioning precision is generally not a primary concern. The correct preload amount varies depending on the application and should be adjusted and set before shipping. Therefore, it's important to provide detailed information about your equipment's operating conditions when ordering a ball screw.
6.Inadequate Rigidity of Nut Housing or Bearing Housing:
If the nut housing or bearing housing lacks rigidity, the weight of the components or machine loads can cause deflection.
7.Improper Assembly of Nut Housing or Bearing Housing:
Vibration or the absence of retaining pins can lead to component loosening. Solid locks can replace spring pins for better positioning. Additionally, using excessively long fixing screws or having shallow screw holes in the nut housing can prevent the nut from securely locking. Vibrations or the absence of spring washers can also result in loosening of the nut housing screws.
8.Incorrect Connection Between Ball Screw and Motor:
An improper coupling or insufficient rigidity can lead to backlash between the screw and the motor. If gear-driven or if the drive structure is not rigid, timing belts can be used to prevent slippage.
9.Loose Key Joints:
Any improper pairing or gaps between keys, keyways, and pulleys can lead to clearance between these components."
Please note that this translation provides an overview of the factors and solutions related to excessive clearance in ball screw assemblies, and the original text appears to be technical and may require further clarification for specific applications.
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