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A power screw is a drive used in machinery to convert a rotary motion into a linear motion for power transmission. It produces uniform motion and the design of the power screw may be such that (a) Either the screw or the nut is held at rest and the other member rotates as it moves axially. A typical example of this is a screw clamp. (b) Either the screw or the nut rotates but does not move axially. | Module 6 Power Screws Version 2 ME IIT Kharagpur Lesson 1 Power Screw drives and their efficiency Version 2 ME IIT Kharagpur Instructional Objectives At the end of this lesson the students should be able to understand Power screw mechanism. The thread forms used in power screws. Torque required to raise and lower a load in a power screw Efficiency of a power screw and condition for self locking. 6.1.1 Introduction A power screw is a drive used in machinery to convert a rotary motion into a linear motion for power transmission. It produces uniform motion and the design of the power screw may be such that a Either the screw or the nut is held at rest and the other member rotates as it moves axially. A typical example of this is a screw clamp. b Either the screw or the nut rotates but does not move axially. A typical example for this is a press. Other applications of power screws are jack screws lead screws of a lathe screws for vices presses etc. Power screw normally uses square threads but ACME or Buttress threads may also be used. Power screws should be designed for smooth and noiseless transmission of power with an ability to carry heavy loads with high efficiency. We first consider the different thread forms and their proportions Square threads- The thread form is shown in figure-6.1.1.1. These threads have high efficiency but they are difficult to manufacture and are expensive. The proportions in terms of pitch are h1 0.5 p h2 0.5 p - b H 0.5 p a e 0.5 p a and b are different for different series of threads. Version 2 ME IIT .
