Bearing failures

The main causes of premature end of life of the bearings are: improper lubrication, contamination, excessive overload, improper use and/or mishandling or improper installation.

Statistics concerning the causes of premature end of life of these elements are the following:

Chart on the causes of premature degradation of bearings

A premature end of life of the bearings means an additional expense for the customer, since they are expected to last as long as the vehicle, although for the reasons above this is not always the case.

  

CONTAMINATION:

Bearing contaminated by foreign particles

Contamination by foreign particles can cause problems with the correct operation of the bearings.

Dust, dirt or any kind of foreign particles can affect the lubrication of the bearings.

Water is a particular contaminating agent; an amount of 1% water in grease or oil can mean reduced lubricant life. Humidity and water contamination produce a chemical attack and corrosion in the bearings. 

IMPROPER LUBRICATION:

Bearing damage due to improper lubrication

Improper lubrication is the main reason for bearing fatigue. Improper lubrication can be caused by: overfilling, underfilling, incorrect specification, mixture of various lubricants, incompatibility, incorrect lubrication and irregularities in the replacement intervals (needle bearings, crankshaft semi-bearings), deterioration of grease or oil, water and contaminating particles.

The manufacturer should select the type of lubricant according to the bearing and its use.

Damage caused by poor lubrication may have the following symptoms:

a)   Discoloration or darkening: this appearance of the bearing is due to the contact of metal with metal at high temperatures. In mild cases, discolouration in the tracks and the rollers is common, as these surfaces have contact with each other. In extreme cases, heat discolours the metal itself.

Bearing discolouration due to lack of lubrication

b)  Scratches: this is the start of a serious lubrication problem, due either to lack of lubrication or to an excessive temperature at which the lubricant is unable to keep the lubricating film. Both cases require immediate attention. These scratches have the appearance of cuts in the metal.

Degradation of the bearing with material detachment

The heat caused by high temperatures located at a particular point, may also cause deformation of the bearing geometry, which results in asymmetrical rollers, destruction of the cage, a transfer of metal, loss of torque and power and an inadequate contact of the bearing.

c)  Overload: An overload of the bearings can be caused by excessive load, excessive turning speed, high temperature, malfunction or misadjustment. The higher the overhead, the shorter the durability of the bearing. 

Bearing damage due to overload

Overload symptoms are: noise, vibration, abnormally high temperatures, swarf and decreased performance.

 The bearing must be replaced whenever any overload symptoms are detected, so as to avoid serious subsequent damages (cracks in the bearings themselves or their guides, deformation and scratches).

INCORRECT HANDLING AND INSTALLATION:

Technicians must have knowledge about the proper methods for installing bearings, as well as having available the necessary tools.

Another premature bearing damage can be caused by improper storage. Before installing, the technician should make sure that the bearing is supplied in an anti-corrosive packaging and in good condition.

During installation, the technician's tool must all be clean. The lubricant layer the bearing is supplied with should be maintained and not removed. 

Damage due to improper installation

Poor handling or using improper tools can cause burrs which result in an incorrect seat, which can increase contact stress at a certain point, exponentially shortening the durability of the bearing, as it is subject to irregular loads, torque increase and even excessive temperature.

It should not be forgotten that many bearings are made of steel, bronze or brass, so that they can be easily damaged if not handled properly.

ADVICE

Currently, damage to bearings is less frequent due to improvements in their design, training of technicians and sellers, but it is always good to know what the most common causes of damage are and how to prevent them.

Good lubrication and adequate insulation from contaminating agents, prevention of overloading and proper handling are essential to extend their durability and prevent further damage.

The following are two practical tips to reduce contamination:

a) When inspecting a bearing, it is advisable to clean the surrounding area to avoid contaminants.

b) When replacing a bearing, the surrounding area should also be kept clean, as well as the location where it is to be installed. It is advisable to coat the bearing with a thin layer of oil before installation.