How To Connect A Ball Screw To A Coupling

Ball screws, as core components of precision drive systems, have their connection quality with couplings directly affecting equipment operation accuracy. This blog provides a detailed explanation of the assembly process through images, helping you avoid 90% of installation pitfalls and ensuring smooth and efficient operation of the drive system.

01. Preparation before assembly

Before assembly, prepare an open-end wrench, torque wrench, dial indicator, and other tools. It is recommended to use flexible couplings or membrane couplings. Pay special attention to cleaning the ball screw shaft end and the coupling bore, as residual oil can cause slipping at the mating surfaces. It is suggested to use non-woven fabric soaked in industrial alcohol for wiping, and the wiping direction should be parallel to the axis.

Measure the diameter of the ball screw shaft and the bore size of the coupling, ensuring the tolerance fit is within H7/h6 range. Use an outside micrometer to measure three cross-sections of the screw shaft end, ensuring the diameter deviation does not exceed 0.01mm. The coupling halves need to be pre-installed on the drive motor shaft, paying attention to the installation direction of the fixed end and the free end.

02. Step-by-step installation guide

First, insert half of the coupling onto the end of the screw shaft. If using the thermal fitting method, ensure that the heating temperature does not exceed 120°C. When using a hydraulic puller for assistance, maintain uniform pressure increase. It is recommended to control the installation speed at 5 mm/min. The critical step is the fit between the coupling keyway and the screw key. It is suggested to apply molybdenum disulfide grease to reduce assembly resistance.

Second, when tightening the locking nut, follow the torque value specified in the coupling manual. Locking nuts of M12 specification typically require a torque of 30-45 N·m, which should be applied in three diagonal steps. After installation, check the end face clearance of the coupling with a feeler gauge. A 0.03 mm feeler gauge must not be inserted more than 3 mm deep; otherwise, the concentricity needs to be readjusted.

03. Key techniques for concentricity correction

When using the dual dial method for correction, the dial indicator should simultaneously monitor radial and axial deviations. Radial runout tolerance ≤ 0.02mm, face runout tolerance ≤ 0.01mm. During the correction process, adjust the thickness of the motor base shims to compensate for deviations; each 0.05mm shim can change about 0.03mm of radial deviation. It is recommended to use a laser alignment tool for precise correction, which can improve efficiency by more than three times.

In special operating conditions, thermal expansion compensation must be considered. When the working temperature exceeds 60°C, an axial clearance of 0.1-0.3mm should be reserved. For long-stroke ball screws, it is recommended to use a telescopic diaphragm coupling. After calibration, an unloaded trial run is required, with the speed gradually increasing from 500 rpm to the rated speed, during which the temperature rise should be monitored using an infrared thermometer, ensuring it does not exceed 15°C.

04. Common installation issue solutions

When abnormal vibrations occur, first check if the coupling bolts are tightened in a star pattern. If black metal powder is found, it indicates axial over-constraint, and the preload force needs to be readjusted. For elastic couplings, the compression of the rubber elements should be controlled between 80% and 90% of the nominal value, as excessive compression accelerates aging.

Transmission accuracy often decreases due to excessive concentricity deviation. This can be rechecked using the three-point measurement method. Measure at three positions around the circumference of the coupling: 0°, 120°, and 240°, and calculate the vector sum of radial deviations. If the deviation exceeds the allowable value, loosen the mounting base bolts and recalibrate. It is recommended to use a hydraulic jack for micron-level adjustments.

05. Key points of daily maintenance and upkeep

Check the coupling fastener torque value every 500 hours; if the attenuation exceeds 20%, replace it immediately. Rubber couplings need to have their elastomers replaced every two years, while metal diaphragm couplings require inspection for fatigue cracks. It is recommended to establish an equipment vibration database and trigger maintenance alerts when vibration values exceed the baseline by 30%.

Lubrication maintenance should use NLGI Grade 2 lithium-based grease, with the greasing amount controlled at 60%-70% of the cavity volume. Pay special attention to the protective cover seal to prevent metal debris from entering the mating surfaces. For equipment that has been idle for a long time, manually rotate the lead screw 2-3 turns each month and apply anti-rust oil on the coupling surface to keep the drive system in optimal standby condition.

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