Ball screws are force and motion-transfer devices in the family of power-transmission screws. They operate like conventional power shaft screw but the rolling friction of bearing balls replaces sliding friction. Ball screws consist of a screw, steel nuts, and balls that operate similarly to bearing components.
The screw has a precision ground or rolled helical groove acting as the inner race. The nut has internal grooves that act as the outer race. Circuits of precision steel balls recirculate in the grooves between the screw and nut. Either the screw or nut turns while the other moves in a linear direction.
Adequate lubrication must be provided when ball screw is used,insufficient lubrication will result in contact of metal, which in turn leads to increase of friction and friction loss, thus cause failure or shortening of service life. Lubricants applied to ball screws can be divided into 2 types, namely lubricating oil and consistent grease. In general speaking, in respect of maintenance, consistent grease will lead to increase of dynamic friction torque linearly along with increase of rotating speed, hence oil lubrication is deemed the better way when speed exceeds 3-5m/min; however, don't forget the fact that there have been examples that using grease has been capable of achieving speed of 10m/min,with respect to the equipment.
Any foreign matter or water,if allowed to enter the ball screw,may increase friction and cause damage. For example,the entry of chips or cutting oil may be expected with machine tools depending on the work environment. Where entry of foreign matter is anticipated,use a bellows or telescopic cover, to cover the screw shaft completely.
When offset load phenomenon occurs, screw life and noise tend to be directly affected,which would usually be accompanied with hand feel of rough running.In the event unload running and running right after assembling demonstrate different degree of cases, this should be ascribed to the poor assembly accuracy which will produce offset load phenomenon.
