Post on 19-Jun-2015
ALLOWABLE SPEEDS
V.GOPI KRISHNA
13MCD1053
TIME
•WE KNOW THAT TIME IS MORE valuable FOR US AND WE RUN FOR IT.•THE ENTIRE WORLD IS AUTOMATED NOW A DAYS•WITH THIS AUTOMATION WE MAKE OUR MACHINES RUN ALONG WITH US.
LIFE TIME
• one of the important characteristic that the life time of any particular machine decides is its speed.
ex. bikes
ALLOWABLE SPEED
• As rotational speed of the bearing increase, the temperature of the bearing also rises due to heat produced inside the bearing by friction.
• The bearing can’t maintain stable operation.• The maximum speed at which it is possible for
the bearing to continuously operate without the generation of excessive heat beyond specified limits, is called the allowable speed (min-1).
category
• The allowable speed of a bearing depends on the type of bearing are:
Bearing dimensions Load Lubricating conditions and Cooling conditions.
• Bearing size - Higher speed will result in higher axial and radial thrust loads. The existing bearings may become inadequate to carry the increase in thrust loads.
• Maximum allowable working pressure (MAWP) - Increasing the RPM will increase differential pressure by the square of the speed ratio. The maximum RPM will be limited to a point where pressure will not exceed the MAWP.
• Bearing lubrication requirement - The bearing lubrication requirement increases with RPM. At higher RPM oil-ring lubrication may no longer be sufficient, and forced-feed lubrication may be required.
• Cooling
A quality lubricant must be used. The lubricant must be replenished and changed when necessary.
calculation
• If rotational speed is to exceed allowable rotational speed given in the dimensions table, it will require special considerations such as using a bearing for which cage specifications, internal clearance and precision have been thoroughly checked.
• It will also require adopting forced circulation, jet oil or mist oil lubrication as the lubrication method.
• when radial bearings are mounted on vertical
shafts, lubricant retentions and cage guidance are not favorable compared to horizontal shaft mounting.
• Therefore, the allowable speed should be reduced to approximately 80% of the listed speed.
• For bearings to be used under heavier than normal load conditions, the allowable speed values listed in the bearing tables must be multiplied by an adjustment factor.
Adjustment factor on bearing load
Adjustment factor on combined bearing load