Trapezoidal screw: Pure sliding friction - brass (good self-lubrication) has a very low efficiency of 60%, a simple structure, low cost and no precision, large surface contact load, large starting resistance, resulting in creeping and creeping during ultra-low speed operation. Trapezoidal screws can be selected when there is no precision requirement, a large axial load is required, the budget is low and the cost needs to be reduced, the speed is low, and the occasion is not important.
Ball screw: It realizes high-efficiency and low-friction transmission through rolling media, with an efficiency of more than 90%. Compared with surface contact, ball is point contact, with smaller load, higher precision and higher cost.
The speed of the screw is limited, and it is best to control it within 1500rpm. If the screw is too long, it needs to be pressed down to within 1000rpm.
Unit movement of the screw: lead (pitch, Pb)
[Fixed seat]: Angular contact bearings are used in pairs to constrain the axial direction of the screw and are mainly used to bear the axial force of the screw
[Support seat]: Deep groove ball bearings are used alone, purely to support the tail of the screw, so that it does not run around and can slide axially
[Fixed + Support]: The most classic structure
[Fixed + Free]: There is no way to put it, there is no place to install the support seat (short stroke, structural requirements), the speed cannot be too high, and the load should not be too large
[Fixed + Fixed]: Not suitable for high-speed operation, heating will cause the screw to deform and get stuck, very good rigidity, high precision
[Support + Support]: No precision, loose mechanism, small load, almost no requirements for motion performance---hand-cranked adjustment mechanism
Nut structure of ball screw
[External circulation]: Better high-speed performance, complex structure, higher cost
[Internal circulation]: Slightly lower cost, more compact structure, easy to install
Ball Screw precision
C0 C1 .......C7 C10 ...
The larger the number, the worse the accuracy and the lower the cost
The screw rods of C7 and later are processed by extrusion molding --- rolled screw rods: high production efficiency----cheap, short delivery time
The screw rods of C5 and earlier are processed by whirlwind milling + grinding --- ground screw rods: low production efficiency---very expensive, high accuracy
The most used: C7
Ball Screw Preload
Effectively prevent the nut seat from offsetting due to clearance when the load is large (improve the dynamic accuracy of large loads)
Increases internal stress, greater resistance, and increased heat generation