Focus on the Bearing Industry for 20 Years!
The accuracy (spherical error) of the ball for rolling bearing has reached the field of an ultra micron, and the requirements for ball material and manufacturing technology are also improving. The ball is made of high carbon chromium bearing steel (vacuum degassing); Stainless steel (g95cr18, g102cr18mo); Engineering ceramics (silicon nitride, silicon carbide, alumina); Of course, there are also balls of other materials, such as cemented carbide, glass, plastic, carbon steel balls, etc. More special balls include porous balls, hollow balls, balls for ball mills, balls for polishing devices, etc. porous balls are used in push rods, ball valves, etc; Hollow spheres are used in aircraft engines; Ball for ball mill is used for crushing pigments, ferrite and food; Polishing ball is used for surface polishing of aluminum die castings and deburring of castings and stamping parts.
1) Ball diameter variation Δ Dws
Place a steel ball between the plane and the probe perpendicular to the plane, change the direction of the steel ball for measurement, and calculate the difference between the large value and the small value of the steel ball diameter at this time (two-point contact method). The probe adopts a pointer micrometre or electronic micrometre. The accuracy of the measuring instrument is divided into 0.1 ~ 0.02 microns according to the grade of the ball.
2) Spherical error Δ RSw
The roundness meter or profilometer shall be used for measurement, and the measured section must not be less than 3 sections.
3) Batch diameter variation VDwL
The diameter of the ball is not exactly the same as that of the ball. Place a ball between the plane and the probe perpendicular to the plane and change the direction of the ball for measurement. At this time, the arithmetic mean of the measured large and small values is called the average diameter of the ball. Take the ball with the average diameter measured in advance as the standard ball, and compare it with the standard ball after measurement by pointer micrometer or electronic micrometer. The batch diameter difference is the difference between the average diameter of the large ball and the average diameter of the small ball in the batch. It represents the change in the average diameter of the ball in the batch.
4) Surface roughness Ra
The surface roughness measurement instrument or double barrel microscope is used for measurement, and the qualification can be determined according to the relevant contents of CSBTS tc98.63-1999 technical conditions for surface roughness of rolling bearing steel ball or according to the internal control standard.
The spindle bearing for the computer HDD spindle motor and VTR drum requires high rotation accuracy and minimal vibration. If the high-speed rotating bearing vibrates, the HDD will produce the reading error, which will also affect the image and sound quality of VTR. In addition to the requirements for dimensional accuracy (ball diameter variation, spherical error and batch diameter variation) specified in GB / T 308.1-2013, there are also requirements for waviness. If the roundness measuring instrument is used to amplify the ball 200000 times to measure its shape, there are various waveforms in the circumferential direction.
Waviness is the amplitude of each point on the surface of the ball. There are various high and low alternating waves from fine to long. The waviness is measured with a ball waviness meter. Let the ball rotate at a certain speed, the stylus contacts the spherical surface, turn the movement of the stylus into an electrical signal, and measure the amplitude of each circumference of the ball and the speed of amplitude change. The number of concave-convex waves on each circumference of the ball is divided into several regions from fine to long.
The fatigue life test of the ball is carried out by the vibration life test machine. Life is related to the purity of the material and the structure of the ball (strength of the matrix).
The ball for the rolling bearing is required to have high dimensional accuracy and will not change for a long time. The decomposition of residual austenite will cause the change of size with time, so its content must be strictly controlled.
In order to prolong the service life of steel balls, the purity of materials is continuously improved with the development of refining technology. At present, it has almost reached the limit. In the future, it is necessary to constantly explore the development of new steel grades and heat treatment processes. In addition, more and more attention is paid to the dynamic vibration performance of the bearing. The reasons for the vibration of the bearing include the shape error of the channel and the shape error of the ball. Among them, the shape error of the ball has a great impact. Therefore, most of the used balls require a roundness below 0.05 micron.