How to reduce the radial runout of SFE Precision Ground Ball Screw
The radial runout of SFE Precision Ground Ball Screw directly affects the positioning accuracy and operational stability of the precision equipment, so it is necessary to take targeted measures from the whole process of manufacturing, assembly, use and maintenance, etc., so as to control the deviation within the allowable range (e.g., C3 level ≤3μm, C5 level ≤5μm). It is necessary to take targeted measures in the whole process of manufacturing, assembly, use and maintenance to control the deviation within the permissible range (e.g. C3 level ≤ 3μm, C5 level ≤ 5μm). Specific methods are as follows.
one. Manufacturing: Control the precision error from the source
1.Enhance the processing precision of screw shaft
Adopt ultra-precision grinding process (such as nano-grade wheel grinding), control the roundness error of screw shaft outer circle ≤1μm, cylindricity error ≤2μm/1000mm, ensure the concentricity of the shaft body and the threaded raceway (coaxiality ≤0.002mm). ).
When profile grinding the threaded raceway, real-time correction of the grinding wheel trajectory is carried out through online laser detection, so as to reduce the deviation of the spiral line of the raceway (the error of the guide range is ≤0.003mm/300mm), and to avoid the cyclic deviation of the contact point of the ball.
2.Optimization of material and heat treatment process
Selected homogenized alloy steel (such as SUJ2 bearing steel, non-metallic inclusions grade ≤ 0.5), eliminating internal loosening through forging, reducing the potential danger of deformation after heat treatment.
Adopt "whole quenching + low temperature tempering" technology (hardness HRC58-62) and aging treatment (120℃×24h) to release internal stresses and avoid the increase of radial runout caused by stress relaxation in the process of use.
Second, assembly and installation: reduce additional error superposition
1.Precise positioning of the bearing support system
The bearing housings at both ends of the screw are processed by high-precision boring (roundness of the holes ≤ 0.001mm, coaxiality of the two holes ≤ 0.002mm) and the bearings are fixed by the hot mounting process (overload 0.001-0.003mm) to ensure that The inner ring of the bearing and the screw journal are tightly fitted.
Preloaded angular contact ball bearings (e.g. 7000 series) are used to eliminate bearing clearance through axial preload, avoiding radial runout caused by bearing clearance when the screw is rotating.
2.Optimization of the fit between the nut and the screw
Detect the fit clearance between the inner raceway of the nut and the raceway of the screw before assembly, and achieve a "zero clearance" or "micro-preload" fit by screening the diameter of the balls (tolerance ≤ 0.0005mm), to Reduce the radial shaking of the nut in the transmission process.
For long travel screws (length > 2m), add a guiding support seat in the middle, correct the deflection of the screw through adjustable structure (such as wedge block fine-tuning), and control the full runout increment ≤ 2μm/m.
Use and maintenance: Prevent precision decay
1.Reasonable matching of operating parameters
Avoid over-rated speed operation (e.g. the maximum speed of SFE2020 model ≤3000r/min), and if necessary, carry out dynamic balancing correction (residual unevenness ≤1g・mm/kg) to reduce radial vibration caused by centrifugal force.
Control the temperature fluctuation of the working environment ≤±2℃, and cool down the screw by means of a thermostatic oil tank (oil temperature control accuracy ±0.5℃) to avoid the increase of radial runout caused by thermal deformation (coefficient of thermal expansion ≤11×10-⁶/℃).
2.Regular inspection and correction
After the equipment has been running for 500 hours, it is necessary to inspect the radial full runout with the help of laser interferometer, and once it is found that the deviation exceeds the limiting value (e.g., the accuracy of C3 grade is more than 3 μm), the calibration can be completed by grinding the positioning surface of the bearing or adjusting the position of the support seat.
When replacing the balls, the same batch of products with the same accuracy level should be used (the difference in diameter should be controlled within 0.0003mm), and the preload should be reapplied (the size of which should be 10%-15% of the rated dynamic load), so as to restore the precision of the fit between the components.
Fourth, the strengthening measures of special working conditions
Corrosive environment protection: stainless steel screws (such as 304 material) surface nitriding treatment (nitriding layer depth of 5-10μm), to enhance the surface hardness (HV800 or more), to avoid corrosion caused by abnormal radial runout.
Structural reinforcement for heavy load scenarios: choose large diameter models (such as SFE3232 and above), and add rigid shims (such as hardened steel plate, flatness ≤ 0.001mm) between the nut holder and the equipment bed to reduce the impact of deformation of the base under load on the screw.
Through the above measures, the radial runout of SFE Precision Ground Ball Screw can be stably controlled within the range of the designed accuracy level, ensuring that it realizes micron-level positioning accuracy in precision machine tools, semiconductor equipment and other scenarios. In practical applications, it is necessary to formulate a customized plan based on the working conditions of the equipment (e.g., speed, load, and environment), and to maintain long-term stability through regular calibration.
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