In recent years, an increasing number of ball screws have been used in various machinery to meet the demands of high-precision and high-performance equipment, making ball screws one of the widely used transmission components. In CNC machinery, THK ball screws can improve positioning accuracy and extend lifespan. In older machinery, THK ball screws have gradually replaced x-m threads. Ball screws usually incorporate preload to eliminate backlash during mechanical operation; however, if the ball screw is improperly installed, it cannot achieve high precision and long lifespan. Therefore, let's explore the failure analysis of THK ball screws!

　　Causes and Prevention of THK Ball Screw Problems

　　The following describes three main causes of THK ball screw problems and their prevention methods. The maintenance clearance of the ball screw is too large.

　　1. No preload or insufficient preload

　　When a ball screw without preload is placed vertically, the nut will rotate and descend due to its own weight; due to the considerable backlash in a screw without preload, it can only be used for machinery with low operating resistance, but the main concern is that positioning accuracy is not required. Determine the accurate preload in different application scenarios and adjust the preload before leaving the factory; therefore, please provide detailed information on the equipment's operating conditions before ordering the ball screw.

　　2. Excessive torsional displacement

　　1) Improper material selection.

　　2) Improper heat treatment, too thin hardening layer, uneven hardness distribution, or too soft material. The standard hardness of steel balls, nuts, and screws are respectively:

　　HRC 62 to 66, HRC 58 to 62, HRC 56 to 62.

　　3) Improper design/excessive slender ratio, etc. The smaller the slender ratio of the screw, the higher the rigidity. When the slender ratio is too large, the screw will sag due to its own weight. The ball screw shown in the figure on the right is supported only on one side, but this design with weaker rigidity should be avoided as much as possible.

　　3. Improper selection of THK ball screw bearings

　　Generally, THK ball screws need to be combined with angular contact bearings, especially bearings with a high-pressure angle design are the preferred choice; when an axial load is applied to the ball screw,

　　because general deep groove ball bearings will produce a certain amount of axial clearance, deep groove ball bearings are not suitable for this. Ball screw maintenance 4. Incorrect bearing installation

　　1) If the bearing is installed on the ball screw and the fit is unreliable, backlash will occur when subjected to axial load. This may be caused by the screw shoulder being too long or too short.

　　2) If the perpendicularity between the bearing supporting surface and the axis of the V-shaped tooth of the lock nut is poor, or the parallelism between the two corresponding lock nut surfaces is poor, it will cause the bearing to tilt; therefore, the V-shaped tooth of the lock nut on the screw shoulder and the bearing supporting surface are machined simultaneously.

　　Grinding is used for processing to ensure perpendicularity.

　　3) Combine two lock nuts and a spring washer to secure the bearing to prevent it from falling off during operation. Ball screw maintenance

5. Insufficient rigidity of the nut seat or bearing seat

　　When the rigidity of the nut seat and bearing seat is insufficient, deformation will occur due to the equipment's own weight and the mechanical load. This method is used to detect the rigidity of the nut seat; the same test is also used to detect the rigidity of the housing.

　　6. Incorrect assembly of the nut seat or housing

　　1) Due to the lack of vibration and pin reinforcement, the equipment will fall off. Use a solid lock instead of a spring pin for positioning.

　　2) Due to the fixing screw being too long or the threaded hole of the nut seat being too shallow, the nut fixing screw cannot be tightened.

　　3) Due to vibration and insufficient spring washers, the nut fixing screw loosens.

　　7. The surface parallelism or flatness of the support is beyond tolerance

　　Regardless of whether the surface of the coupling component is ground or knurled, as long as its parallelism or flatness exceeds the tolerance range, the reproducibility of the position when the machine moves will deteriorate; therefore, in a machine, thin shims are usually used between the support table and the machine body to achieve adjustment. THK ball screw maintenance 8. Improper combination of motor and ball screw

　　1) If the coupling is not firmly connected, or the original rigidity is poor, a rotational difference will occur between the screw and the motor.

　　2) Not suitable for gear drive, or when the drive structure is not a rigid body, a measuring belt drive can be used to prevent slippage.

　　3) Key looseness, or improper combination between the key, keyway, and hub, resulting in excessive clearance between these devices.

　　Un smooth operation of THK ball screw

　　1. Incorrect bearing installation

　　1) Rough surface of the ball groove of the screw or nut.

　　2) Roundness of steel balls, screws, or nuts exceeds the tolerance range.

　　3) Lead error or pitch circle diameter of the screw or nut exceeds the tolerance range.

　　4) Incorrect assembly of the return pipe.

　　5) Uneven size and hardness of steel balls.

　　These problems should not occur in high-quality products.

　　2. Foreign objects entering the steel ball track

　　Packaging materials obstructing the steel ball track: Ball screws are packaged with many materials and anti-rust bags at the factory. If the packaging or arrangement is not performed according to the proper steps, foreign objects and other objects may obstruct the steel ball track, causing the steel balls to slip, preventing normal rolling or causing blockage.

　　The above is an analysis of the failure of THK ball screws. Please contact us if you need more information!