| :::: Tapper Roller Bearings ::::
Single row taper roller bearings have tapered inner and outer ring raceways between which tapered rollers are arranged. The tapered surfaces, if extended, meet at a common apex on the bearing axis. The functional forces of the tapered rollers rest on an integral flange of the inner ring.
This
construction a provides a high capacity for radial loads, axial
loads in one direction and combined loads. Axial load carrying capacity
is dependent on the magnitude of the contact angle. The bearings
with the large contact angle series 313 and 323 - are suitable for
accommodating heavier axial loads.
As
a rule, the single row taper roller bearings are arranged in pairs,
because the taper roller bearing itself can carry axial load in
one direction only.Proper running clearance or preload can be obtained
by adjusting the distance of the two bearings against one another
Being separable, the inner ring with tapered roller and cage assembly
(Cone) and outer ring (Cup) can be mounted individually, which results
lit simplified mounting and dismounting.
Bearing internal clearance is the total displacement of one bearing ring to the other ring under no load conditions. It is called radial internal clearance when the displacement is in the radial direction and axial clearance when the displacement is in the axial direction.
It is essential to select radial internal clearance which is suitable for the operating conditions, because the bearing internal clearance after mounting greatly influences the properties such as bearing life, operating temperature and vibration.
As a general rule, the bearing internal clearance of a Ball Bearing should be close to zero when mounted and running at its operating temperature. For this purpose the following must be considered :
1.
Fitting conditions.
Bearings manufactured with normal internal clearance, will run satisfactorily under ordinary operating conditions and with. shaft and housing limits for light and normal loads.
Bearings with greater oil smaller internal clearance than normal are required where operating and mounting. conditions differ from the normal, requiring interference tits for both rings, unusual operating temperatures etc. Bearings with a clearance other than the normal are identified by the suffixes C1 to C5.
C1
-radial internal clearance less than C2.
Single Row Taper Roller Bearings are ordinarily mounted in pair,,; and the suitable operating clearance and / or preload is adjusted during mounting. The magnitude of axial clearance or of the preload is selected according to the operating conditions, the bearing size and type and according to the required rigidity of the application.
In operation under normal conditions, the working surfaces of a bearing are subjected to very high alternating stresses due to the continuous action of the rolling elements, on the tracks. This will eventually result hi flaking of the raceways or rolling elements, as a result of fatigue of the material and is called the fatigue failure.
LIFE
The bearing life is defined as the number of revolutions achieved by the bearing before the first signs of fatigue failure appear
When a group of identical bearings operate under identical load conditions, the life of the individual bearings show a considerable dispersion. Therefore when selecting a bearing it is more practical to adopt the life that the majority of the bearings will attain or exceed. For this reason the basic rating file, of a group of bearings is defined as Me number of revolutions (or hours a/ some given constant speed) that 90 % of the group of bearings will attain or exceed before the first evidence of fatigue develops. This basic rating life is in line with ISO definition.
BASIC LOAD RATINGS
The basic dynamic load rating "C" is defined as the constant bearing load which will give air ISO basic rating life, as defined above, of' one million revolutions. It refers to pure radial load for radial bearings and to pure axial load for thurst bearings.
Similarly the basic static load rating "Co" is defined as the static load which corresponds to a total permanent deformation of the rolling elements and race ways at the most heavily stressed contact point of 0.0001 times the diameter of the rolling elements. It refers to pure radial load for radial bearings and to pure axial load for thurst bearings.
The relationship between the basic rating life, the basic dynamic load rating and the bearing load can be presented in the ISO equation as
L 10 =( C/ p)p
Where,
Uptil now we have only considered the pure radial load or the pure axial load. In practice however, both radial and axial loads may act on a bearing simultaneously. It is therefore necessary to calculate the equivalent dynamic bearing load.
This is defined us that hypothetical load, constant in magnitude and direction, which when applied would have the same influence on bearing life as the actual loads to which the bearing is subjected.
Rolling bearings have to be adequately lubricated for satisfactory operation. The main purposes of rolling bearing lubrication are
To prevent direct metallic contact between the rolling elements, raceways and cages. To prevent the bearings from corrosion and wear To prevent the ingress of contamination Cooling of the bearing
Rolling bearings may be lubricated with grease or oil, the choice of which depends primarily on the temperature range, operating speeds and loading conditions of the bearings concerned. However in special cases solid lubricant may also be used.
The limiting speeds for both grease and oil lubrication are given in. the bearing tables.
GREASE LUBRICATION
In majority of the applications under normal operating conditions, grease lubrication is generally used. Grease has certain advantages over oil, of being easily retained in housing as well as its sealing effect against the entry of the moisture and other foreign particles.
Excessive grease is detrimental to satisfactory bearing performance and will cause rapid temperature rise, particularly if speeds are high. In general, the quantity of grease necessary to ensure that the bearing operates well should be equal to approximately 25 to 40 % of its free internal volume. However, when bearing is operating at slow speed, it should be filled fully with grease in order to have good protection against corrosion.
OIL LUBRICATION
Oil lubrication is generally used when high speeds / operating temperatures are beyond the range of application of greases, or where oil is also used as coolant, or where bearing.,; are integrated into a mechanism that is already lubricated with oil (Gear Boxes)
Viscosity of the lubricating oil is the main factor to be considered to suit the diverse applications with respect to speed, temperature and loading conditions. Mineral oils are mostly used for lubricating bcuritigs.
The fundamental prerequisite for the correct mounting and dismounting of bearings is cleanliness of working site,tools, all components of bearing arrangement, lubricant and bearings themselves. Any contamination from foreign matter will result in rapid deterioration of the bearings.
MOUNTING OF BEARINGS
Prepare all the equipment, parts and the necessary tools before mounting. Ensure that they are clean. Bearings are supplied in protective packages and should not be taken out earlier than immediately before mounting so that they do not become dirty.
Rolling bearings can be mounted on the shaft either in cold or warm
condition. While large bearings are mounted by heating them in suitable
mineral oil upto a temerpature of 70' to 900 C, small and medium
size bearings can usually be driven. on to the shaft in cold condition
with the use a f suitable mounting tools and a press. The force
applied for pressing must not be transmitted through the rolling
elements, the necessary jig must be placed so that it bears upon
that ring which is being driven on, and/or upon both rings simultaneously.
Dismounting of bearings must be simple and must not damage the bearings or adjacent components. Small and medium size bearings can be dismounted by applying light hammer blows to a suitable drift around the ring face or by using a puller or other suitable withdrawal tools.
Large bearings generally require greater force for dismounting and oil injection method is invariably used in such cases. Induction heaters and thermo withdrawal tools are also used for dismounting of heavy interference inner rings of cylindrical roller bearings.
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