Self-lubricating Bearing Bushings Designs The various bushing types, its designs and materials are described in the following:
Select your bushing size
PTFE composite bushings
POM composite bushings
Solid bronze bushings
Split bronze bushings
Plugged graphite bronze bushings
Bimetal bearings bushings
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Choose the bushing design material&environment
The most important factors to take into account when choosing the material and the surface finish of the counter surface on which the ring slides are the load conditions such as the load, the angle of oscillation, the type of movement and environmental influences. If there is a risk of corrosion, the counter surface should be sufficiently resistant. Corrosion scars in the counter surface and, for example, abrasive particle contamination as a by-product of corrosion increase the surface roughness and accelerate wear. In these cases, the use of stainless steel or a surface treatment such as hard chrome, nickel plating or electrolytic oxidation should be considered.
Related Self-lubricating Bearings Design PV value bearings
1、Definition Load Pressure P: Load pressure equals to the result gained by making the value of load pressure divide the vertical shade projected by the load-shouldering surface of the bushing (Unit N/mm2). Running Velocity V: Defined running velocity as the relative linear velocity against the mating surface (Unit: N/mm2). PV Value Define PV value as the result gained by multiplying the load value P and the velocity V (Unit N/mm2-m/s). Permissible PV value:Max permissible value shall be smaller than the value gained by multiplying the max permissible pressure and the max permissible velocity(Unit N/mm2-m/s).
2、Max permissible PV value The bushing can run for a short time when achieves its max PV value. It*s the running service ife requirement that decides the requirement for tbe value. In bushing design, we require that the max permissible PV value shall be smaller than the value gained by multiplying the max permissible load pressure and the max permissible running velocity;
The inside diameter of the bushing depends on the diameter of its mating axis.
2、Length of the bushing
The length of the bushing depends on the size of the pressure-shouldering surface.
The longer the bushing, the less pressure at the surface, for the longer bushing, the load on the bushing is relatively lessened- But simultaneously, it may result in deviation contact or lower cooling efficiency and thus shorten the service life of the bushing. On the contrary if the length of the bushing is too short, lubricating grease may quickly flow out of the bushing. Therefore, it hardly forms a grease film and capability of the bushing is accordingly debased.
The main advantage of standard composite self-lubricating bushings rest with their thin wall thickness.
Standard bushings thickness can be 0.5mm, 0.75mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm.
Self-lubricated Bushings Design Design of the Mating Axis
Surface roughness, hardness and plating of the mating axis will have great influence on the capability of the self-lubricating bushing. High-quality surface of the mating axis can prolong the life of the bushing while rough surface will shorten the life of the bushing.
1、Surface roughness of the mating axis When self-lubricating bushings being used in the condition of fluid lubrication and the surface of the mating axis is rough, the convex points on the bushing and its axis will cut the oil film and thus the surface of the axis and the bushing will directly contact with each other therefore, to improve the capability of the bushing, it requires polishing the surface of the mating axis as smooth as a mirror; thus can reduce the clearance of the oil film and make the film work well For most self-lubricating bushings applied in the condition of dry friction or marginal lubrication^ controlled roughness from 0.32 to 1.25 is acceptable and there is no need ta polish the surface of the mating axis as smooth as a mirror.
2、Hardness of the mating axis If there is no hard article in the lubricating condition, good performance can be achieved by using bushing materials and hardness recommended in the following form. If not, it would be better to use the harder material for the mating axis.
With the exception of being burnt, the service life of self-lubricating bushing depends on the abrasion degree of the bushing’s inner diameter. In conditions like dry friction, boundary lubrication and oil lubrication, the abrasion of the same bushing will be different Main factors that may influence the service life are character and direction of the load, lubrication condition, running speed, environment temperature, hardness of the mating axis, roughness of the mating surface material of the mating axis, air quality around etc Therefore, it’s difficult to calculate the actual abrasion quantity. Regardless the factors like influence from the load and speed, difference caused by running direction, kinds of lubricating oil, mating clearance, roughness and impurities penetration degree, the abrasion W can be calculated by the following formula.
Before the bushing is pressed into the housing: as the outside diameter of the bushing is bigger than the inside diameter of the housing, strong pressure can be available in the housing. And also this kind of fixing can assure the roundness of the bushing and make the bushing well fixed avoiding abrasion caused by sliding of the bushing in the housing. The interference can be calculated by the following formula:
Min interference Min OD of the bushing-Max ID of the housing
Max interference Max OD of the bushing-Min ID of the housing
Here are some situations in which self-lubricating and pre-lubricating bearings should be considered by a designer. The need to reduce maintenance or increase reliability is often encountered in practice. Inaccessible bearings in all types of equipment are ready candidates for self-lubrication, as are pieces of equipment in remote locations. By replacing metal bearings with self-lubricating bearings, substantial savings can be achieved. Likewise, self-lubrication can improve the useful life of equipment that should be neglected, such as consumer appliances.