The importance of steel ball crushing load test
As an important part of ball bearings, steel balls have a great influence on the life, accuracy, vibration and running characteristics of ball bearings. When the bearing works, the contact surface of the steel ball and the raceway is actively small, and the compressive stress per unit area is large, generally up to 150-500 kg/mm2.
The points on the contact trajectory of the steel ball to the raceway are cyclically stressed. Under normal circumstances, the number of cycles per minute is more than tens of thousands of times. Under the repeated action of cyclic stress, the high carbon steel ball is prone to fatigue damage. This phenomenon is called contact fatigue, which is one of the main features of the normal damage of the steel ball in the bearing. When contact fatigue reaches a certain level, it will lose its ability to work.
The crushing load of the carbon steel ball refers to the pressure value of the steel ball when it is broken. It is an important indicator of the comprehensive performance of the steel ball. There are many factors in the processing of the steel ball affecting the crushing load value of the steel ball, such as the original metallographic structure of the steel ball, the microstructure of the heat treatment and different processing methods, the geometric precision of the stainless steel ball surface and the processing time of the steel ball. And test methods for measuring the crushing load of steel balls. The crushing load inspection of steel balls is a very important task in the quality inspection of steel balls, which also plays a significant role in the life and dynamic performance of the bearings.
How are bearing balls made?
Bearing balls are the component of a ball bearing that permit smooth, friction-free rotary motion. They are typically manufactured out of steel, but can also be made from other materials such as silicon nitride ceramic, plastic or even glass.
Steel bearing balls, such as low carbon steel ball, are easily the most common ball material, with tens of millions produced annually. They are near-perfectly round and are polished with a mirror-like finish to provide precision rotary motion in machines, power tools, motors, power transmission and hundreds of other applications.
Have you ever wondered how they are made? The answer is a multi-step process that converts a slug of unhardened steel to a hardened, ground and polished round ball.
Metal bearing balls are manufactured from steel wire or rod. During the first step in the process, the wire or rod is cut into small pieces called slugs. The volume of material for the slug is slightly larger than that of the finished ball. The excess material is removed in subsequent machining steps. At this stage, the material has not been hardened and is somewhat malleable. This is important so that the slug can be formed into a spherical shape in the next manufacturing step.
The slug is then fed to a header machine where the balls are put through a cold-forming process called heading. In cold heading, the slug is placed between two semi-spherically shaped dies and shaped under pressures between 10 and 20 tons. It is a high-speed process and can be very loud, especially for large-diameter balls, requiring ear protection for machine operators. Heading forms the slug into a spherical shape called a raw ball. There is a little excess material that still needs removal.
The excess material, called flash or burrs, needs to be filed away. This is done in the flashing process, also referred to as filing. This removes the flash, but they are not yet perfectly round and the metal is still soft. There are two different machining variations that manufacturers use, but both involve rolling the balls between metal plates.