Over hauling in power screws

Q.  In power screws, if friction angle Φ is less than lead angle λ, then the screw undergoes _______
- Published on 14 Sep 15

a. over hauling
b. self locking
c. both a. and b.
d. none of the above

ANSWER: over hauling

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    Discussion

  • Sravanthi   -Posted on 04 Nov 15
    1) Over-hauling screws:

    - If Φ ≤ λ in the equation T = (Wdm / 2) x tan ( Φ - λ), then torque required to lower the load is negative or zero.

    - Hence no torque is required for the load to move downwards which rotates the screw. This screw is called as over hauling screw.

    - These screws have friction angle less than or equal to lead angle.

    2) Self locking screws:

    - These types of screws are used in screw jacks and C-clamps

    - Self locking screws have friction angle greater than lead angle and the torque required is positive.

    - tan Φ > tan λ or μ > l / πd

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