A needle bearing is a roller bearing with cylindrical roller that is thin and long relative to its diameter.
This type of roller is called needle roller.
Despite its small cross section, the bearing still has a high load carrying capacity.
Needle roller bearings are equipped with thin and long rollers (roller diameter D ≤ 5mm, L / D ≥ 2.5, L is the roller length), so the radial structure is compact.
Its inner diameter size and load capacity are the same as other types of bearings, the smallest outer diameter, especially suitable for radial support size limited support structure.
Depending on the application, bearings or needle roller and cage assemblies without inner ring are available.
At this time, the journal surface and the shell hole surface matched with the bearing directly serve as the inner and outer rolling surfaces of the bearing.
In order to ensure the same load capacity and running performance as the ferrule bearing, the hardness of the raceway surface of the shaft or casing hole, machining accuracy and surface quality should be similar to the raceway of the bearing ring.
This type of bearing can only withstand radial loads.
The installation of needle roller bearing is usually carried out using an auxiliary sleeve.
At this time, the auxiliary roller or the auxiliary sleeve holds the needle without causing the needle to fall out, and the journal pinch the needle with its own chamfer.
As the needle bearing moves slowly inward on the journal, the auxiliary roller or the auxiliary sleeve slowly withdraws until it is loaded into the working position.
The outer diameter of the auxiliary roller and the auxiliary sleeve should be 0.1-0.3 mm smaller than the shaft diameter.
When installing, first apply the grease to the inner surface of the outer ring of the bearing, and place the needle on the inner surface (there should be a gap when placing the last needle).
Then push the auxiliary roller or auxiliary sleeve instead of the journal or the inner ring of the bearing into the outer ring hole, and align the end surface with the end face of the mounting shaft or the end surface of the bearing inner ring that has been mounted on the shaft.
Then apply pressure with a press or a hammer.
Needle roller bearings can also be installed by applying a thin layer of lubricating oil to the outer diameter of the auxiliary sleeve and inserting the outer ring of the bearing so that the auxiliary sleeve and the outer ring of the bearing form an annular hole, and then the needle is placed in the annular hole.
After loading the needle, push the auxiliary sleeve out with the working shaft.
For needle roller bearings without inner ring or outer ring, when installing, first apply a thin layer of grease to the rolling surface of the shaft or housing hole, and then apply the needle to the grease on the installation site.
A gap should be left when the last needle is placed.
The size of the gap is preferably 0.5 mm on the circumference of the needle bearing.
Do not squeeze the last needle into it, or install a smaller needle.
Because the bearing will be stuck and cannot be rotated during hard extrusion; when the load is small, the clearance is too large, which may cause the needle to twist and break when the bearing is running.
For needle roller bearings with only the outer ring, since the outer ring wall is very thin, do not hit it with a hammer, and press it with a press.
Because the pressure is not uniform when the hammer is struck, it is easy to cause local deformation of the outer ring of the needle bearing.