Bearings
Types of bearings are mechanical parts that support and constrain the rotation or swing of a shaft. The shaft and the bearing form a dynamic connection to transmit the load and restrict the movement of the shaft.
Bearings The structure of axle bearings has long been recorded in ancient Chinese books. In 1279, Guo Shoujing of China created an astronomical instrument that functions similarly to modern thrust roller bearings. In 1772, C. Wallow of England designed and manufactured ball bearings and installed them on mail trucks for trial use. In 1794, P. Worth of England obtained the patent for ball bearings. In the mid-19th century, with the advancement of bearing materials, lubricants and mechanical manufacturing processes, Europe began to have relatively complete sliding bearings. In 1881, H.R. Hertz of Germany published a paper on the contact stress of ball bearings. On the basis of Hertz's achievements, R. Striebeck of Germany, A. Pamgren of Sweden and others conducted a large number of experiments and contributed to the development of the design theory and fatigue life calculation of rolling bearings. In 1883, N.P. Petrov of Russia applied Newton's law of viscosity to calculate bearing friction. In the same year, B. Toll of the United Kingdom discovered that there was oil film pressure in the bearings of nuclear submarine bearings when measuring the friction coefficient of vehicle bearings, and measured the oil film pressure distribution. curve. In 1886, O. Reynolds of the United Kingdom conducted a mathematical analysis of Thor's discovery and derived the Reynolds equation, which laid the foundation for hydrodynamic lubrication theory. After the 1960s, the theory of elastohydrodynamic lubrication gradually matured, and rolling bearings designed according to this theory greatly increased their service life.
There are many types of bearings. According to the load direction it can bear, it can be divided into: ① Radial bearings, also called radial bearings, bear radial loads. ②Thrust bearing, also called thrust bearing, bears axial load. ③ Radial thrust bearings, also called radial thrust bearings, bear both radial and axial loads. According to the different friction properties of bearing operation, they can be divided into two categories: sliding friction bearings (gliding bearings for short) and rolling friction bearings (rolling bearings for short).
Angular contact bearing: a rolling bearing with a nominal contact angle between the ball and the ring greater than 0° but less than 90°. It can bear both radial load and axial load. Can work at higher speeds. The larger the contact angle, the higher the axial load capacity. High-precision and high-speed bearings usually have a contact angle of 15 degrees. Under the action of axial force, the contact angle will increase. Single row angular contact ball bearings can only bear axial load in one direction. When bearing radial load, additional axial force will be caused. And it can only limit the axial displacement of the shaft or housing in one direction. If they are installed in pairs, make the outer rings of the pair of bearings face each other, that is, the wide end faces the wide end face, and the narrow end faces the narrow end face. This avoids causing additional axial forces and limits the axial play of the shaft or housing in both directions.
Outer spherical bearing: a radial rolling bearing with an outer spherical surface and a wide inner ring with a locking piece. Mainly intended for simple shell use.
Linear motion bearing: a rolling bearing in which the two raceways have relative linear motion in the rolling direction.
Ball bearing: A rolling bearing in which the rolling element is a ball.
Deep groove ball bearings: radial ball bearings with each ring having a continuous groove raceway with a cross-section approximately one-third of the circumference of the ball, suitable for precision instruments, low-noise motors, Cars, motorcycles and general machinery are the most widely used bearings in the machinery industry. It has a simple structure and is easy to use and maintain. It is mainly used to bear radial load and can also bear certain axial load. When the radial clearance of the bearing increases, it has the performance of angular contact ball bearing and can bear larger axial load. This type of bearing has small friction coefficient, high limit speed, and various size ranges and forms. Solid and durable, highly versatile and low-noise, can operate at high speeds and is easy to install. Single row deep groove ball bearings also have a sealed design that requires no relubrication and maintenance. Single row ball bearings with ball gap and double row ball bearings are suitable for heavy load conditions.
Thrust ball bearings: Thrust rolling bearings in which the rolling elements are balls.
Roller bearing: Rolling element is a rolling bearing.
Cylindrical roller bearing: The rolling element is a radial rolling bearing with cylindrical rollers. It is a separable bearing and is very convenient to install and disassemble. Cylindrical roller bearings are divided into single row, double row and four row.
According to the number of rows of rolling elements installed in the bearing, cylindrical roller bearings can be divided into single-row, double-row and multi-row cylindrical roller bearings. Among them, the single row cylindrical roller bearing with cage is the most widely used.
In addition, there are cylindrical roller bearings with single row or double row full complement rollers and other structures.
Single row cylindrical roller bearings are divided into N type, NU type, NJ type, NF type and NUP type according to the different ring ribs. Cylindrical roller bearings have a large radial load capacity and can also withstand certain one-way or two-way axial loads depending on the structure of the ring ribs.
NN type and NNU type double row cylindrical roller bearings have compact structure, strong rigidity, large load-bearing capacity, and small deformation after being loaded. They are mostly used to support machine tool spindles.
FC, FCD and FCDP four-row cylindrical roller bearings can withstand large radial loads and are mostly used in heavy machinery such as rolling mills.
Cylindrical roller bearings are mainly used in motors, machine tools, petroleum, rolling mill loading and unloading machinery and various industrial machinery.
Tapered roller bearing: The rolling element is a radial rolling bearing with tapered rollers.
Needle roller bearings: radial rolling bearings whose rolling elements are needle rollers.
Spherical roller bearings: Aligning radial rolling bearings whose rolling elements are convex spherical or concave rollers. Bearings with convex spherical rollers have a spherical raceway on the outer ring; bearings with concave rollers have a spherical raceway on the inner ring.
Thrust roller bearings: Thrust rolling bearings in which the rolling elements are rollers.
Thrust cylindrical roller bearing: The rolling element is a thrust rolling bearing with cylindrical rollers.
Thrust tapered roller bearing: The rolling element is a thrust rolling bearing with tapered rollers.
Thrust needle roller bearing: The rolling element is a thrust rolling bearing with needle rollers.
Thrust spherical roller bearing: The rolling element is an aligning thrust rolling bearing with convex spherical or concave rollers. The raceway of the bearing seat ring with convex spherical rollers is spherical, and the raceway of the bearing shaft ring with concave spherical rollers is spherical.
Bearing with seat: A component that combines a radial bearing and a seat. There is a bottom plate with screws on the support surface parallel to the axis of the bearing.
Spherical plain bearings: The sliding contact surface is spherical and is mainly suitable for spherical sliding bearings for swing motion, tilting motion and rotational motion.
Combined bearing: A rolling bearing that is composed of two or more bearing structures mentioned above in one set of bearings. Such as needle roller and thrust cylindrical roller combined bearings, needle roller and thrust ball combined bearings, needle roller and angular contact ball combined bearings, etc.
Other bearings: rolling bearings with structures other than those mentioned above.
Sliding bearings: Sliding bearings have no inner and outer rings and no rolling elements. They are generally made of wear-resistant materials. It is often used in low-speed, heavy-duty and mechanical rotating parts where lubricating oil and maintenance are difficult.
Rolling mill bearings: Rolling mill bearings are generally only used to bear radial loads. Compared with deep groove ball bearings of the same size, they have greater radial load capacity, and their limit speed is close to that of deep groove ball bearings, but The machining requirements for shafts and shell holes matched with this type of bearing are relatively high, and the inclination of the axis of the inner ring and the axis of the outer ring is allowed to be very small (2°-4°). If the inclination of the two axes exceeds the limit, the roller and the ring will not rotate. The contact condition of the channel will deteriorate, seriously affecting the load capacity of the bearing and reducing the service life of the bearing. Therefore, if this type of bearing needs to be installed in a host component that is subject to axial load, it can only be used if other types of bearings are also used to bear the axial load.
Generally speaking, bearings are mostly rolling bearings (ball and roller bearings). A rolling bearing is a precision mechanical component that changes the sliding friction between the running shaft and the shaft seat into rolling friction, thereby reducing friction losses. Rolling bearings generally consist of outer rings, inner rings, rolling elements and cages. Rolling bearings are easy to use and maintain, work reliably, have good starting performance, and have high load-bearing capacity at medium speeds. Compared with sliding bearings, rolling bearings have larger radial dimensions, poorer vibration damping capabilities, shorter service life at high speeds, and louder noise.
The radial bearing among rolling bearings (mainly bearing radial force) usually consists of 4 parts: inner ring, outer ring, rolling elements and rolling element cage. The inner ring is tightly sleeved on the journal and rotates with the shaft, and the outer ring is installed in the bearing seat hole. There are raceways on the outer circumference of the inner ring and the inner circumference of the outer ring. When the inner and outer rings rotate relative to each other, the rolling elements roll on the raceways of the inner and outer rings. They are separated by cages to avoid mutual friction.
Thrust bearings are divided into two parts: tight rings and loose rings. The tight ring is tight with the shaft sleeve, and the live ring is supported on the bearing seat.
Rings and rolling elements are usually made of rolling bearing steel with high strength and good wear resistance. The surface hardness after quenching should reach HRC60~65. The cage is mostly made of mild steel stamping, or it can also be made of copper alloy, cloth, bakelite or plastic.