First it is necessary to clarify the classification logic of the two: radial bearings are bearing types classified by force direction (primarily bearing radial loads i.e., loads perpendicular to the shaft centerline) while sliding bearings are bearing types classified by friction mode (on a par with rolling bearings and relying on sliding friction for operation). Radial bearings include "radial sliding bearings" and "radial rolling bearings" and the common comparison between "radial bearings and sliding bearings" in daily use is actually a comparison between "radial rolling bearings" and "sliding bearings (including radial sliding bearings)" with details as follows:
I. Core Classification and Definition Differences
1. Radial Bearings
Radial bearings are bearings mainly used to bear radial loads (such as the self-weight of the shaft and radial forces generated by gear transmission) and can be divided into "radial rolling bearings" and "radial sliding bearings" according to the friction mode. In daily engineering if not specifically stated "radial bearings" usually refer to "radial rolling bearings". Taking radial rolling bearings as an example they internally include four main components which are rolling elements (such as balls rollers) inner ring (closely fitted with the shaft) outer ring (fitted with the bearing seat) and cage (separating rolling elements) and rely on the rolling of rolling elements to realize the rotation of the shaft and convert sliding friction into rolling friction.
2. Sliding Bearings
Sliding bearings are bearings that realize rotation through sliding friction between the shaft journal (rotating part of the shaft) and the bearing bushing (fixed part) and can be divided into "radial sliding bearings" (bearing radial loads) and "thrust sliding bearings" (bearing axial loads) according to the force direction which is a friction type classification independent of rolling bearings. They have a simple structure with no rolling elements and usually consist of a bearing seat and a bearing liner (mostly made of materials such as Babbitt metal copper alloy engineering plastic) and the shaft journal and bushing need to be isolated by a lubricating oil film to reduce friction and wear.
II. Structural Design Differences
1. Radial Rolling Bearings (Typical Radial Bearings)
Radial rolling bearings must include rolling elements (balls cylindrical rollers tapered rollers etc. mostly made of high-carbon chromium bearing steel GCr15) inner ring (interference fit between the inner hole and the shaft with a raceway on the surface) outer ring (transition fit between the outer circle and the bearing seat with a raceway on the surface) and cage (mostly made of stamped steel or engineering plastic to prevent collision of rolling elements) and some sealed models also include sealing rings/dust covers. They have a high structural complexity with 4-5 core components and the processing precision of rolling elements and raceways is extremely high (raceway roundness error ≤ 0.001mm surface roughness Ra ≤ 0.1μm) and strict control of radial clearance (usually 0.01-0.05mm) is required. They are mostly standardized products (such as deep groove ball bearings cylindrical roller bearings) and can be directly installed through the fit between the inner ring and the shaft and between the outer ring and the bearing seat without additional adjustment of bushing clearance.
2. Sliding Bearings
The core components of sliding bearings are the bearing seat (cast iron or cast steel material) and the bearing liner (inlaid or cast in the bearing seat with material selected according to working conditions such as Babbitt metal for low-speed heavy-load conditions and copper alloy for high-speed light-load conditions) with no rolling elements and some models include oil grooves/oil holes (for lubricating oil injection) and thrust rings (bearing a small amount of axial load). They have low structural complexity with 2-3 core components but the fit clearance between the bearing liner and the shaft journal needs to be precisely controlled (the clearance is usually 0.001-0.002 times the shaft journal diameter such as 0.05-0.1mm clearance for a 50mm shaft journal diameter) and processes such as scraping are required to ensure fit precision. They are mostly non-standard customized products (especially large sliding bearings) and the coaxiality between the shaft journal and the bushing needs to be adjusted during installation and some models require on-site casting of the bearing liner (such as Babbitt alloy bushing) resulting in a long installation cycle.